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53,540 | https://en.wikipedia.org/wiki/Terminal%20emulator | A terminal emulator, or terminal application, is a computer program that emulates a video terminal within some other display architecture. Though typically synonymous with a shell or text terminal, the term terminal covers all remote terminals, including graphical interfaces. A terminal emulator inside a graphical user interface is often called a terminal window.
A terminal window allows the user access to a text terminal and all its applications such as command-line interfaces (CLI) and text user interface (TUI) applications. These may be running either on the same machine or on a different one via telnet, ssh, dial-up, or over a direct serial connection. On Unix-like operating systems, it is common to have one or more terminal windows connected to the local machine.
Terminals usually support a set of escape sequences for controlling color, cursor position, etc. Examples include the family of terminal control sequence standards that includes ECMA-48, ANSI X3.64, and ISO/IEC 6429.
Background
In the early days of computing, with the advent of interactive computing, the prevailing model involved a central computer connected to multiple terminals. This configuration, known as the centralized or mainframe model, featured a powerful central computer that performed all the processing tasks, while terminals served as input/output devices for users to interact with the system. These systems were initially character based.
Character-oriented terminals
Emulators
When personal computers became ubiquitous in the 1980s, they offered the option of running software on the user's personal computer, providing an opportunity to replace the expensive and space consuming hardware terminals with something that had additional functions. Immediately software became available, that could emulate the functions of the hardware terminals on a PC. Examples of such software for DOS were Telix or Telemate, which was published in 1988 and could emulate a DEC VT102 terminal.
Workstations, usually running versions of Unix, also became common in the 1980s. Unix systems usually provided access to the command line with locally-attached or dial-up terminals. Unix workstations were designed to be used primarily through a graphical user interface (GUI); to provide access to the command line, the GUI included terminal emulator applications that behaved like locally-attached terminals.
During the 1990s, new operating systems like Windows and OS/2 arrived, providing the technical background for more terminal emulators like Telix for Windows, ZOC for OS/2, or PuTTY, which was initially released for Windows in 1998 and which (together with its derivates) is still one a very popular choice to this day.
Through the success of Linux, especially running on data centers and cloud servers, the necessity of accessing remote computers through character based terminals remains. This is evident in the fact, that today lists of terminal emulators that could serve as alternative to the aforementioned PuTTY offers over 100 alternatives.
Examples of terminals emulated
Many terminal emulators have been developed for physical hardware terminals such as VT52, VT100, VT220, VT320, IBM 3270/8/9/E, IBM 5250, IBM 3179G, Data General D211, Hewlett-Packard HP700/92, Sperry/Unisys 2000-series UTS60, Burroughs/Unisys A-series T27/TD830/ET1100, ADDS ViewPoint, AT386, Siemens Nixdorf (SNI) 97801, Televideo 925, and Wyse 50/60.
Some terminal emulators, such as xterm, implement additional features not present in the emulated terminal.
Additionally, programs have been developed to emulate assorted system console "terminals" such as the Sun workstation console and the Linux console.
Finally, some emulators simply refer to a set of standards, such as the standards for ANSI escape codes.
Such programs are available on many platforms, including DOS, Unix-like systems including Linux and macOS, Windows, and embedded operating systems found in cellphones and industrial hardware.
Implementation details
Unix-like systems
In the past, Unix and Unix-like systems used serial port devices such as RS-232 ports, and provided device files for them.
With terminal emulators these device files are themselves emulated by a pair of pseudoterminal devices. These in turn emulate a physical port/connection to the host computing endpoint – hardware provided by operating system APIs, or software such as rlogin, telnet or SSH, among others. In Linux systems, example, these would be (for the master side) and (for the slave side) pseudoterminal devices respectively.
There are also special virtual console files like /dev/console. In text mode, writing to the file displays text on the virtual console and reading from the file returns text the user writes to the virtual console. As with other text terminals, there are also special escape sequences, control characters and functions that a program can use, most easily via a library such as ncurses. For more complex operations, the programs can use console and terminal special ioctl system calls. One can compare devices using the patterns vcs ("virtual console screen") and vcsa ("virtual console screen with attributes") such as /dev/vcs1 and /dev/vcsa1.
Some terminal emulators also include escape sequences for configuring the behavior of the terminal to facilitate good interoperation between the terminal and programs running inside of it, for example to configure paste bracketing.
The virtual consoles can be configured in the file /etc/inittab read by init—typically it starts the text mode login process getty for several virtual consoles. X Window System can be configured in /etc/inittab or by an X display manager. A number of Linux distributions use systemd instead of init, which also allows virtual console configuration.
CLI tools
Typical Linux system programs used to access the virtual consoles include:
to switch the current virtual console
to run a program on a new virtual console
to close a currently unused virtual console
Local echo
Terminal emulators may implement a local echo function, which may erroneously be named "half-duplex", or still slightly incorrectly "echoplex" (which is formally an error detection mechanism rather than an input display option).
Line-at-a-time mode/Local editing
Terminal emulators may implement local editing, also known as "line-at-a-time mode". This is also mistakenly referred to as "half-duplex". In this mode, the terminal emulator only sends complete lines of input to the host system. The user enters and edits a line, but it is held locally within the terminal emulator as it is being edited. It is not transmitted until the user signals its completion, usually with the key on the keyboard or a "send" button of some sort in the user interface. At that point, the entire line is transmitted. Line-at-a-time mode implies local echo, since otherwise the user will not be able to see the line as it is being edited and constructed. However, line-at-a-time mode is independent of echo mode and does not require local echo. When entering a password, for example, line-at-a-time entry with local editing is possible, but local echo is turned off (otherwise the password would be displayed).
The complexities of line-at-a-time mode are exemplified by the line-at-a-time mode option in the telnet protocol. To implement it correctly, the Network Virtual Terminal implementation provided by the terminal emulator program must be capable of recognizing and properly dealing with "interrupt" and "abort" events that arrive in the middle of locally editing a line.
Synchronous terminals
In asynchronous terminals data can flow in any direction at any time. In synchronous terminals a protocol controls who may send data when. IBM 3270-based terminals used with IBM mainframe computers are an example of synchronous terminals. They operate in an essentially "screen-at-a-time" mode (also known as block mode). Users can make numerous changes to a page, before submitting the updated screen to the remote machine as a single action.
Terminal emulators that simulate the 3270 protocol are available for most operating systems, for use both by those administering systems such as the z9, as well as those using the corresponding applications such as CICS.
Other examples of synchronous terminals include the IBM 5250, ICL 7561, Honeywell Bull VIP7800 and Hewlett-Packard 700/92.
Virtual consoles
Virtual consoles, also called virtual terminals, are emulated text terminals, using the keyboard and monitor of a personal computer or workstation. The word "text" is key since virtual consoles are not GUI terminals and they do not run inside a graphical interface. Virtual consoles are found on most Unix-like systems. They are primarily used to access and interact with servers, without using a graphical desktop environment.
See also
Binary Synchronous Communications
List of terminal emulators
Online service provider
Serial interface
Terminal multiplexer
Notes
References
External links
Terminal Window Definition by The Linux Information Project (LINFO)
VTTEST – VT100/VT220/XTerm test utility A terminal test utility by Thomas E. Dickey
User interfaces
Technical communication tools
Bulletin board systems | Terminal emulator | [
"Technology"
] | 1,941 | [
"User interfaces",
"Interfaces"
] |
53,601 | https://en.wikipedia.org/wiki/Metal%20casting | In metalworking and jewelry making, casting is a process in which a liquid metal is delivered into a mold (usually by a crucible) that contains a negative impression (i.e., a three-dimensional negative image) of the intended shape. The metal is poured into the mold through a hollow channel called a sprue. The metal and mold are then cooled, and the metal part (the casting) is extracted. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods.
Casting processes have been known for thousands of years, and have been widely used for sculpture (especially in bronze), jewelry in precious metals, and weapons and tools. Highly engineered castings are found in 90 percent of durable goods, including cars, trucks, aerospace, trains, mining and construction equipment, oil wells, appliances, pipes, hydrants, wind turbines, nuclear plants, medical devices, defense products, toys, and more.
Traditional techniques include lost-wax casting (which may be further divided into centrifugal casting, and vacuum assist direct pour casting), plaster mold casting and sand casting.
The modern casting process is subdivided into two main categories: expendable and non-expendable casting. It is further broken down by the mold material, such as sand or metal, and pouring method, such as gravity, vacuum, or low pressure.
Expendable mold casting
Expendable mold casting is a generic classification that includes sand, plastic, shell, plaster, and investment (lost-wax technique) moldings. This method of mold casting involves the use of temporary, non-reusable molds.
Sand casting
Sand casting is one of the most popular and simplest types of casting, and has been used for centuries. Sand casting allows for smaller batches than permanent mold casting and at a very reasonable cost. Not only does this method allow manufacturers to create products at a low cost, but there are other benefits to sand casting, such as very small-size operations. The process allows for castings small enough fit in the palm of one's hand to those large enough for a train car bed (one casting can create the entire bed for one rail car). Sand casting also allows most metals to be cast depending on the type of sand used for the molds.
Sand casting requires a lead time of days, or even weeks sometimes, for production at high output rates (1–20 pieces/hr-mold) and is unsurpassed for large-part production. Green (moist) sand, which is black in color, has almost no part weight limit, whereas dry sand has a practical part mass limit of . Minimum part weight ranges from . The sand is bonded using clays, chemical binders, or polymerized oils (such as motor oil). Sand can be recycled many times in most operations and requires little maintenance.
Loam molding
Loam molding has been used to produce large symmetrical objects such as cannon and church bells. Loam is a mixture of clay and sand with straw or dung. A model of the produced is formed in a friable material (the chemise). The mold is formed around this chemise by covering it with loam. This is then baked (fired) and the chemise removed. The mold is then stood upright in a pit in front of the furnace for the molten metal to be poured. Afterwards the mold is broken off. Molds can thus only be used once, so that other methods are preferred for most purposes.
Plaster mold casting
Plaster casting is similar to sand casting except that plaster of paris is used instead of sand as a mold material. Generally, the form takes less than a week to prepare, after which a production rate of 1–10 units/hr-mold is achieved, with items as massive as and as small as with very good surface finish and close tolerances. Plaster casting is an inexpensive alternative to other molding processes for complex parts due to the low cost of the plaster and its ability to produce near net shape castings. The biggest disadvantage is that it can only be used with low melting point non-ferrous materials, such as aluminium, copper, magnesium, and zinc.
Shell molding
Shell molding is similar to sand casting, but the molding cavity is formed by a hardened "shell" of sand instead of a flask filled with sand. The sand used is finer than sand casting sand and is mixed with a resin so that it can be heated by the pattern and hardened into a shell around the pattern. Because of the resin and finer sand, it gives a much finer surface finish. The process is easily automated and more precise than sand casting. Common metals that are cast include cast iron, aluminium, magnesium, and copper alloys. This process is ideal for complex items that are small to medium-sized.
Investment casting
Investment casting (known as lost-wax casting in art) is a process that has been practiced for thousands of years, with the lost-wax process being one of the oldest known metal forming techniques. From 5000 years ago, when beeswax formed the pattern, to today's high technology waxes, refractory materials, and specialist alloys, the castings ensure high-quality components are produced with the key benefits of accuracy, repeatability, versatility, and integrity.
Investment casting derives its name from the fact that the pattern is invested, or surrounded, with a refractory material. The wax patterns require extreme care for they are not strong enough to withstand forces encountered during the mold making. One advantage of investment casting is that the wax can be reused.
The process is suitable for repeatable production of net shape components from a variety of different metals and high performance alloys. Although generally used for small castings, this process has been used to produce complete aircraft door frames, with steel castings of up to 300 kg and aluminium castings of up to 30 kg. Compared to other casting processes such as die casting or sand casting, it can be an expensive process. However, the components that can be produced using investment casting can incorporate intricate contours, and in most cases the components are cast near net shape, so require little or no rework once cast.
Waste molding of plaster
A durable plaster intermediate is often used as a stage toward the production of a bronze sculpture or as a pointing guide for the creation of a carved stone. With the completion of a plaster, the work is more durable (if stored indoors) than a clay original which must be kept moist to avoid cracking. With the low cost plaster at hand, the expensive work of bronze casting or stone carving may be deferred until a patron is found, and as such work is considered to be a technical, rather than artistic process, it may even be deferred beyond the lifetime of the artist.
In waste molding a simple and thin plaster mold, reinforced by sisal or burlap, is cast over the original clay mixture. When cured, it is then removed from the damp clay, incidentally destroying the fine details in undercuts present in the clay, but which are now captured in the mold. The mold may then at any later time (but only once) be used to cast a plaster positive image, identical to the original clay. The surface of this plaster may be further refined and may be painted and waxed to resemble a finished bronze casting.
Evaporative-pattern casting
This is a class of casting processes that use pattern materials that evaporate during the pour, which means there is no need to remove the pattern material from the mold before casting. The two main processes are lost-foam casting and full-mold casting.
Lost-foam casting
Lost-foam casting is a type of evaporative-pattern casting process that is similar to investment casting except foam is used for the pattern instead of wax. This process takes advantage of the low boiling point of foam to simplify the investment casting process by removing the need to melt the wax out of the mold.
Full-mold casting
Full-mold casting is an evaporative-pattern casting process which is a combination of sand casting and lost-foam casting. It uses an expanded polystyrene foam pattern which is then surrounded by sand, much like sand casting. The metal is then poured directly into the mold, which vaporizes the foam upon contact.
Non-expendable mold casting
Non-expendable mold casting differs from expendable processes in that the mold need not be reformed after each production cycle. This technique includes at least four different methods: permanent, die, centrifugal, and continuous casting. This form of casting also results in improved repeatability in parts produced and delivers near net shape results.
Permanent mold casting
Permanent mold casting is a metal casting process that employs reusable molds ("permanent molds"), usually made from metal. The most common process uses gravity to fill the mold. However, gas pressure or a vacuum are also used. A variation on the typical gravity casting process, called slush casting, produces hollow castings. Common casting metals are aluminum, magnesium, and copper alloys. Other materials include tin, zinc, and lead alloys and iron and steel are also cast in graphite molds. Permanent molds, while lasting more than one casting still have a limited life before wearing out.
Die casting
The die casting process forces molten metal under high pressure into mold cavities (which are machined into dies). Most die castings are made from nonferrous metals, specifically zinc, copper, and aluminium-based alloys, but ferrous metal die castings are possible. The die casting method is especially suited for applications where many small to medium-sized parts are needed with good detail, a fine surface quality and dimensional consistency.
Semi-solid metal casting
Semi-solid metal (SSM) casting is a modified die casting process that reduces or eliminates the residual porosity present in most die castings. Rather than using liquid metal as the feed material, SSM casting uses a higher viscosity feed material that is partially solid and partially liquid. A modified die casting machine is used to inject the semi-solid slurry into reusable hardened steel dies. The high viscosity of the semi-solid metal, along with the use of controlled die filling conditions, ensures that the semi-solid metal fills the die in a non-turbulent manner so that harmful porosity can be essentially eliminated.
Used commercially mainly for aluminium and magnesium alloys, SSM castings can be heat treated to the T4, T5 or T6 tempers. The combination of heat treatment, fast cooling rates (from using uncoated steel dies) and minimal porosity provides excellent combinations of strength and ductility. Other advantages of SSM casting include the ability to produce complex shaped parts net shape, pressure tightness, tight dimensional tolerances and the ability to cast thin walls.
Centrifugal casting
In this process molten metal is poured in the mold and allowed to solidify while the mold is rotating. Metal is poured into the center of the mold at its axis of rotation. Due to inertial force, the liquid metal is thrown out toward the periphery.
Centrifugal casting is both gravity and pressure independent since it creates its own force feed using a temporary sand mold held in a spinning chamber. Lead time varies with the application. Semi- and true-centrifugal processing permit 30–50 pieces/hr-mold to be produced, with a practical limit for batch processing of approximately 9000 kg total mass with a typical per-item limit of 2.3–4.5 kg.
Industrially, the centrifugal casting of railway wheels was an early application of the method developed by the German industrial company Krupp and this capability enabled the rapid growth of the enterprise.
Small art pieces such as jewelry are often cast by this method using the lost wax process, as the forces enable the rather viscous liquid metals to flow through very small passages and into fine details such as leaves and petals. This effect is similar to the benefits from vacuum casting, also applied to jewelry casting.
Continuous casting
Continuous casting is a refinement of the casting process for the continuous, high-volume production of metal sections with a constant cross-section. It's primarily used to produce a semi-finished products for further processing. Molten metal is poured into an open-ended, water-cooled mold, which allows a 'skin' of solid metal to form over the still-liquid center, gradually solidifying the metal from the outside in. After solidification, the strand, as it is sometimes called, is continuously withdrawn from the mold. Predetermined lengths of the strand can be cut off by either mechanical shears or traveling oxyacetylene torches and transferred to further forming processes, or to a stockpile. Cast sizes can range from strip (a few millimeters thick by about five meters wide) to billets (90 to 160 mm square) to slabs (1.25 m wide by 230 mm thick). Sometimes, the strand may undergo an initial hot rolling process before being cut.
Continuous casting is used due to the lower costs associated with continuous production of a standard product, and also increased quality of the final product. Metals such as steel, copper, aluminum and lead are continuously cast, with steel being the metal with the greatest tonnages cast using this method.
Upcasting
The upcasting (up-casting, upstream, or upward casting) is a method of either vertical or horizontal continuous casting of rods and pipes of various profiles (cylindrical, square, hexagonal, slabs etc.) of 8-30mm in diameter. Copper (Cu), bronze (Cu·Sn alloy), nickel alloys are usually used because of greater casting speed (in case of vertical upcasting) and because of better physical features obtained. The advantage of this method is that metals are almost oxygen-free and that the rate of product crystallization (solidification) may be adjusted in a crystallizer - a high-temperature resistant device that cools a growing metal rod or pipe by using water.
The method is comparable to Czochralski method of growing silicon (Si) crystals, which is a metalloid.
Terminology
Metal casting processes uses the following terminology:
Pattern: An approximate duplicate of the final casting used to form the mold cavity.
Molding material: The material that is packed around the pattern and then the pattern is removed to leave the cavity where the casting material will be poured.
Flask: The rigid wood or metal frame that holds the molding material.
Cope: The top half of the pattern, flask, mold, or core.
Drag: The bottom half of the pattern, flask, mold, or core.
Core: An insert in the mold that produces internal features in the casting, such as holes.
Core print: The region added to the pattern, core, or mold used to locate and support the core.
Mold cavity: The combined open area of the molding material and core, where the metal is poured to produce the casting.
Riser: An extra void in the mold that fills with molten material to compensate for shrinkage during solidification.
Gating system: The network of connected channels that deliver the molten material to the mold cavities.
Pouring cup or pouring basin: The part of the gating system that receives the molten material from the pouring vessel.
Sprue: The pouring cup attaches to the sprue, which is the vertical part of the gating system. The other end of the sprue attaches to the runners.
Runners: The horizontal portion of the gating system that connects the sprues to the gates.
Gates: The controlled entrances from the runners into the mold cavities.
Vents: Additional channels that provide an escape for gases generated during the pour.
Parting line or parting surface: The interface between the cope and drag halves of the mold, flask, or pattern.
Draft: The taper on the casting or pattern that allow it to be withdrawn from the mold
Core box: The mold or die used to produce the cores.
Chaplet: Long vertical holding rod for core that after casting it become the integral part of casting, provide the support to the core.
Some specialized processes, such as die casting, use additional terminology.
Theory
Casting is a solidification process, which means the solidification phenomenon controls most of the properties of the casting. Moreover, most of the casting defects occur during solidification, such as gas porosity and solidification shrinkage.
Solidification occurs in two steps: nucleation and crystal growth. In the nucleation stage, solid particles form within the liquid. When these particles form, their internal energy is lower than the surrounded liquid, which creates an energy interface between the two. The formation of the surface at this interface requires energy, so as nucleation occurs, the material actually undercools (i.e. cools below its solidification temperature) because of the extra energy required to form the interface surfaces. It then recalescences, or heats back up to its solidification temperature, for the crystal growth stage. Nucleation occurs on a pre-existing solid surface because not as much energy is required for a partial interface surface as for a complete spherical interface surface. This can be advantageous because fine-grained castings possess better properties than coarse-grained castings. A fine grain structure can be induced by grain refinement or inoculation, which is the process of adding impurities to induce nucleation.
All of the nucleations represent a crystal, which grows as the heat of fusion is extracted from the liquid until there is no liquid left. The direction, rate, and type of growth can be controlled to maximize the properties of the casting. Directional solidification is when the material solidifies at one end and proceeds to solidify to the other end; this is the most ideal type of grain growth because it allows liquid material to compensate for shrinkage.
Cooling curves
Cooling curves are important in controlling the quality of a casting. The most important part of the cooling curve is the cooling rate which affects the microstructure and properties. Generally speaking, an area of the casting which is cooled quickly will have a fine grain structure and an area which cools slowly will have a coarse grain structure. Below is an example cooling curve of a pure metal or eutectic alloy, with defining terminology.
Note that before the thermal arrest the material is a liquid and after it the material is a solid; during the thermal arrest the material is converting from a liquid to a solid. Also, note that the greater the superheat the more time there is for the liquid material to flow into intricate details.
The above cooling curve depicts a basic situation with a pure metal, however, most castings are of alloys, which have a cooling curve shaped as shown below.
Note that there is no longer a thermal arrest, instead there is a freezing range. The freezing range corresponds directly to the liquidus and solidus found on the phase diagram for the specific alloy.
Chvorinov's rule
The local solidification time can be calculated using Chvorinov's rule, which is:
Where t is the solidification time, V is the volume of the casting, A is the surface area of the casting that contacts the mold, n is a constant, and B is the mold constant. It is most useful in determining if a riser will solidify before the casting, because if the riser does solidify first then it is worthless.
The gating system
The gating system serves many purposes, the most important being conveying the liquid material to the mold, but also controlling shrinkage, the speed of the liquid, turbulence, and trapping dross. The gates are usually attached to the thickest part of the casting to assist in controlling shrinkage. In especially large castings multiple gates or runners may be required to introduce metal to more than one point in the mold cavity. The speed of the material is important because if the material is traveling too slowly it can cool before completely filling, leading to misruns and cold shuts. If the material is moving too fast then the liquid material can erode the mold and contaminate the final casting. The shape and length of the gating system can also control how quickly the material cools; short round or square channels minimize heat loss.
The gating system may be designed to minimize turbulence, depending on the material being cast. For example, steel, cast iron, and most copper alloys are turbulent insensitive, but aluminium and magnesium alloys are turbulent sensitive. The turbulent insensitive materials usually have a short and open gating system to fill the mold as quickly as possible. However, for turbulent sensitive materials short sprues are used to minimize the distance the material must fall when entering the mold. Rectangular pouring cups and tapered sprues are used to prevent the formation of a vortex as the material flows into the mold; these vortices tend to suck gas and oxides into the mold. A large sprue well is used to dissipate the kinetic energy of the liquid material as it falls down the sprue, decreasing turbulence. The choke, which is the smallest cross-sectional area in the gating system used to control flow, can be placed near the sprue well to slow down and smooth out the flow. Note that on some molds the choke is still placed on the gates to make separation of the part easier, but induces extreme turbulence. The gates are usually attached to the bottom of the casting to minimize turbulence and splashing.
The gating system may also be designed to trap dross. One method is to take advantage of the fact that some dross has a lower density than the base material so it floats to the top of the gating system. Therefore, long flat runners with gates that exit from the bottom of the runners can trap dross in the runners; note that long flat runners will cool the material more rapidly than round or square runners. For materials where the dross is a similar density to the base material, such as aluminium, runner extensions and runner wells can be advantageous. These take advantage of the fact that the dross is usually located at the beginning of the pour, therefore the runner is extended past the last gate(s) and the contaminates are contained in the wells. Screens or filters may also be used to trap contaminates.
It is important to keep the size of the gating system small, because it all must be cut from the casting and remelted to be reused. The efficiency, or , of a casting system can be calculated by dividing the weight of the casting by the weight of the metal poured. Therefore, the higher the number the more efficient the gating system/risers.
Shrinkage
There are three types of shrinkage: shrinkage of the liquid, solidification shrinkage and patternmaker's shrinkage. The shrinkage of the liquid is rarely a problem because more material is flowing into the mold behind it. Solidification shrinkage occurs because metals are less dense as a liquid than a solid, so during solidification the metal density dramatically increases. Patternmaker's shrinkage refers to the shrinkage that occurs when the material is cooled from the solidification temperature to room temperature, which occurs due to thermal contraction.
Solidification shrinkage
Most materials shrink as they solidify, but, as the adjacent table shows, a few materials do not, such as gray cast iron. For the materials that do shrink upon solidification the type of shrinkage depends on how wide the freezing range is for the material. For materials with a narrow freezing range, less than , a cavity, known as a pipe, forms in the center of the casting, because the outer shell freezes first and progressively solidifies to the center. Pure and eutectic metals usually have narrow solidification ranges. These materials tend to form a skin in open air molds, therefore they are known as skin forming alloys. For materials with a wide freezing range, greater than , much more of the casting occupies the mushy or slushy zone (the temperature range between the solidus and the liquidus), which leads to small pockets of liquid trapped throughout and ultimately porosity. These castings tend to have poor ductility, toughness, and fatigue resistance. Moreover, for these types of materials to be fluid-tight, a secondary operation is required to impregnate the casting with a lower melting point metal or resin.
For the materials that have narrow solidification ranges, pipes can be overcome by designing the casting to promote directional solidification, which means the casting freezes first at the point farthest from the gate, then progressively solidifies toward the gate. This allows a continuous feed of liquid material to be present at the point of solidification to compensate for the shrinkage. Note that there is still a shrinkage void where the final material solidifies, but if designed properly, this will be in the gating system or riser.
Risers and riser aids
Risers, also known as feeders, are the most common way of providing directional solidification. It supplies liquid metal to the solidifying casting to compensate for solidification shrinkage. For a riser to work properly the riser must solidify after the casting, otherwise it cannot supply liquid metal to shrinkage within the casting. Risers add cost to the casting because it lowers the yield of each casting; i.e. more metal is lost as scrap for each casting. Another way to promote directional solidification is by adding chills to the mold. A chill is any material which will conduct heat away from the casting more rapidly than the material used for molding.
Risers are classified by three criteria. The first is if the riser is open to the atmosphere, if it is then it is called an open riser, otherwise it is known as a blind type. The second criterion is where the riser is located; if it is located on the casting then it is known as a top riser and if it is located next to the casting it is known as a side riser. Finally, if the riser is located on the gating system so that it fills after the molding cavity, it is known as a live riser or hot riser, but if the riser fills with materials that have already flowed through the molding cavity it is known as a dead riser or cold riser.
Riser aids are items used to assist risers in creating directional solidification or reducing the number of risers required. One of these items are chills which accelerate cooling in a certain part of the mold. There are two types: external and internal chills. External chills are masses of high-heat-capacity and high-thermal-conductivity material that are placed on an edge of the molding cavity. Internal chills are pieces of the same metal that is being poured, which are placed inside the mold cavity and become part of the casting. Insulating sleeves and toppings may also be installed around the riser cavity to slow the solidification of the riser. Heater coils may also be installed around or above the riser cavity to slow solidification.
Patternmaker's shrink
Shrinkage after solidification can be dealt with by using an oversized pattern designed specifically for the alloy used. s, or s, are used to make the patterns oversized to compensate for this type of shrinkage. These rulers are up to 2.5% oversize, depending on the material being cast. These rulers are mainly referred to by their percentage change. A pattern made to match an existing part would be made as follows: First, the existing part would be measured using a standard ruler, then when constructing the pattern, the pattern maker would use a contraction rule, ensuring that the casting would contract to the correct size.
Note that patternmaker's shrinkage does not take phase change transformations into account. For example, eutectic reactions, martensitic reactions, and graphitization can cause expansions or contractions.
Mold cavity
The mold cavity of a casting does not reflect the exact dimensions of the finished part due to a number of reasons. These modifications to the mold cavity are known as allowances and account for patternmaker's shrinkage, draft, machining, and distortion. In non-expendable processes, these allowances are imparted directly into the permanent mold, but in expendable mold processes they are imparted into the patterns, which later form the mold cavity. Note that for non-expendable molds an allowance is required for the dimensional change of the mold due to heating to operating temperatures.
For surfaces of the casting that are perpendicular to the parting line of the mold a draft must be included. This is so that the casting can be released in non-expendable processes or the pattern can be released from the mold without destroying the mold in expendable processes. The required draft angle depends on the size and shape of the feature, the depth of the mold cavity, how the part or pattern is being removed from the mold, the pattern or part material, the mold material, and the process type. Usually the draft is not less than 1%.
The machining allowance varies drastically from one process to another. Sand castings generally have a rough surface finish, therefore need a greater machining allowance, whereas die casting has a very fine surface finish, which may not need any machining tolerance. Also, the draft may provide enough of a machining allowance to begin with.
The distortion allowance is only necessary for certain geometries. For instance, U-shaped castings will tend to distort with the legs splaying outward, because the base of the shape can contract while the legs are constrained by the mold. This can be overcome by designing the mold cavity to slope the leg inward to begin with. Also, long horizontal sections tend to sag in the middle if ribs are not incorporated, so a distortion allowance may be required.
Cores may be used in expendable mold processes to produce internal features. The core can be of metal but it is usually done in sand.
Filling
There are a few common methods for filling the mold cavity: gravity, low-pressure, high-pressure, and vacuum.
Vacuum filling, also known as counter-gravity filling, is more metal efficient than gravity pouring because less material solidifies in the gating system. Gravity pouring only has a 15 to 50% metal yield as compared to 60 to 95% for vacuum pouring. There is also less turbulence, so the gating system can be simplified since it does not have to control turbulence. Plus, because the metal is drawn from below the top of the pool the metal is free from dross and slag, as these are lower density (lighter) and float to the top of the pool. The pressure differential helps the metal flow into every intricacy of the mold. Finally, lower temperatures can be used, which improves the grain structure. The first patented vacuum casting machine and process dates to 1879.
Low-pressure filling uses 5 to 15 psig (35 to 100 kPag) of air pressure to force liquid metal up a feed tube into the mold cavity. This eliminates turbulence found in gravity casting and increases density, repeatability, tolerances, and grain uniformity. After the casting has solidified the pressure is released and any remaining liquid returns to the crucible, which increases yield.
Tilt filling
Tilt filling, also known as tilt casting, is an uncommon filling technique where the crucible is attached to the gating system and both are slowly rotated so that the metal enters the mold cavity with little turbulence. The goal is to reduce porosity and inclusions by limiting turbulence. For most uses tilt filling is not feasible because the following inherent problem: if the system is rotated slow enough to not induce turbulence, the front of the metal stream begins to solidify, which results in mis-runs. If the system is rotated faster it induces turbulence, which defeats the purpose. Durville of France was the first to try tilt casting, in the 1800s. He tried to use it to reduce surface defects when casting coinage from aluminium bronze.
Macrostructure
The grain macrostructure in ingots and most castings have three distinct regions or zones: the chill zone, columnar zone, and equiaxed zone. The image below depicts these zones.
The chill zone is named so because it occurs at the walls of the mold where the wall chills the material. Here is where the nucleation phase of the solidification process takes place. As more heat is removed the grains grow towards the center of the casting. These are thin, long columns that are perpendicular to the casting surface, which are undesirable because they have anisotropic properties. Finally, in the center the equiaxed zone contains spherical, randomly oriented crystals. These are desirable because they have isotropic properties. The creation of this zone can be promoted by using a low pouring temperature, alloy inclusions, or inoculants.
Inspection
Common inspection methods for steel castings are magnetic particle testing and liquid penetrant testing. Common inspection methods for aluminum castings are radiography, ultrasonic testing, and liquid penetrant testing.
Defects
There are a number of problems that can be encountered during the casting process. The main types are: gas porosity, shrinkage defects, mold material defects, pouring metal defects, and metallurgical defects.
Casting process simulation
Casting processes simulation uses numerical methods to calculate cast component quality considering mold filling, solidification and cooling, and provides a quantitative prediction of casting mechanical properties, thermal stresses and distortion. Simulation accurately describes a cast component's quality up-front before production starts. The casting rigging can be designed with respect to the required component properties. This has benefits beyond a reduction in pre-production sampling, as the precise layout of the complete casting system also leads to energy, material, and tooling savings.
The software supports the user in component design, the determination of melting practice and casting methoding through to pattern and mold making, heat treatment, and finishing. This saves costs along the entire casting manufacturing route.
Casting process simulation was initially developed at universities starting from the early 1970s, mainly in Europe and in the U.S., and is regarded as the most important innovation in casting technology over the last 50 years. Since the late 1980s, commercial programs are available which make it possible for foundries to gain new insight into what is happening inside the mold or die during the casting process.
See also
Bronze and brass ornamental work
Bronze sculpture
Forging
Foundry
Porosity sealing
Spin casting
Spray forming
Stone mould
References
Notes
Bibliography
.
.
.
.
.
External links
Interactive casting design/manufacturing examples
Castings or Forgings? A look at the advantages of each manufacturing process
Video clip of a 50 gram arc cast alloy solidifying
Metalworking
Jewellery making
History of metallurgy
Metallurgy
Sculpture techniques
es:Fundición
hr:Lijevanje
pt:Fundição | Metal casting | [
"Chemistry",
"Materials_science",
"Engineering"
] | 7,172 | [
"Metallurgy",
"History of metallurgy",
"Materials science",
"nan"
] |
53,603 | https://en.wikipedia.org/wiki/Double%20star | In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes.
This occurs because the pair either forms a binary star (i.e. a binary system of stars in mutual orbit, gravitationally bound to each other) or is an optical double, a chance line-of-sight alignment of two stars at different distances from the observer. Binary stars are important to stellar astronomers as knowledge of their motions allows direct calculation of stellar mass and other stellar parameters. The only (possible) case of "binary star" whose two components are separately visible to the naked eye is the case of Mizar and Alcor (though actually a multiple-star system), but it is not known for certain whether Mizar and Alcor are gravitationally bound.
Since the beginning of the 1780s, both professional and amateur double star observers have telescopically measured the distances and angles between double stars to determine the relative motions of the pairs. If the relative motion of a pair determines a curved arc of an orbit, or if the relative motion is small compared to the common proper motion of both stars, it may be concluded that the pair is in mutual orbit as a binary star. Otherwise, the pair is optical. Multiple stars are also studied in this way, although the dynamics of multiple stellar systems are more complex than those of binary stars.
The following are three types of paired stars:
Optical doubles are unrelated stars that appear close together through chance alignment with Earth.
Visual binaries are gravitationally bound stars that are separately visible with a telescope.
Non-visual binaries are stars whose binary status was deduced through more esoteric means, such as occultation (eclipsing binaries), spectroscopy (spectroscopic binaries), or anomalies in proper motion (astrometric binaries).
Improvements in telescopes can shift previously non-visual binaries into visual binaries, as happened with Polaris A in 2006. It is only the inability to telescopically observe two separate stars that distinguishes non-visual and visual binaries.
History
Mizar, in Ursa Major, was observed to be double by Benedetto Castelli and Galileo. The identification of other doubles soon followed: Robert Hooke discovered one of the first double-star systems, Gamma Arietis, in 1664, while the bright southern star Acrux, in the Southern Cross, was discovered to be double by Fontenay in 1685. Since that time, the search has been carried out thoroughly and the entire sky has been examined for double stars down to a limiting apparent magnitude of about 9.0. At least 1 in 18 stars brighter than 9.0 magnitude in the northern half of the sky are known to be double stars visible with a telescope.
The unrelated categories of optical doubles and true binaries are lumped together for historical and practical reasons. When Mizar was found to be a binary, it was quite difficult to determine whether a double star was a binary system or only an optical double. Improved telescopes, spectroscopy, and photography are the basic tools used to make the distinction. After it was determined to be a visual binary, Mizar's components were found to be spectroscopic binaries themselves.
Observation of double stars
Observation of visual double stars by visual measurement will yield the separation, or angular distance, between the two component stars in the sky and the position angle. The position angle specifies the direction in which the stars are separated and is defined as the bearing from the brighter component to the fainter, where north is 0°. These measurements are called measures. In the measures of a visual binary, the position angle will change progressively and the separation between the two stars will oscillate between maximum and minimum values. Plotting the measures in the plane will produce an ellipse. This is the apparent orbit, the projection of the orbit of the two stars onto the celestial sphere; the true orbit can be computed from it. Although it is expected that the majority of catalogued visual doubles are visual binaries, orbits have been computed for only a few thousand of the over 100,000 known visual double stars.
Distinction between binary stars and other double stars
Confirmation of a visual double star as a binary star can be achieved by observing the relative motion of the components. If the motion is part of an orbit, or if the stars have similar radial velocities or the difference in their proper motions is small compared to their common proper motion, the pair is probably physical. When observed over a short period of time, the components of both optical doubles and long-period visual binaries will appear to be moving in straight lines; for this reason, it can be difficult to distinguish between these two possibilities.
Designations
Some bright visual double stars have a Bayer designation. In this case, the components may be denoted by superscripts. An example of this is α Crucis (Acrux), whose components are α1 Crucis and α2 Crucis. Since α1 Crucis is a spectroscopic binary, this is actually a multiple star. Superscripts are also used to distinguish more distant, physically unrelated, pairs of stars with the same Bayer designation, such as α1,2 Capricorni, ξ1,2 Centauri, and ξ1,2 Sagittarii. These optical pairs are resolvable by the naked eye.
Apart from these pairs, the components of a double star are generally denoted by the letters A (for the brighter, primary, star) and B (for the fainter, secondary, star) appended to the designation, of whatever sort, of the double star. For example, the components of α Canis Majoris (Sirius) are α Canis Majoris A and α Canis Majoris B (Sirius A and Sirius B); the components of 44 Boötis are 44 Boötis A and 44 Boötis B; the components of ADS 16402 are ADS 16402A and ADS 16402B; and so on. The letters AB may be used together to designate the pair. In the case of multiple stars, the letters C, D, and so on may be used to denote additional components, often in order of increasing separation from the brightest star, A.
Visual doubles are also designated by an abbreviation for the name of their discoverer followed by a catalogue number unique to that observer. For example, the pair α Centauri AB was discovered by Father Richaud in 1689, and so is designated RHD 1. Other examples include Δ65, the 65th double discovered by James Dunlop, and Σ2451, discovered by F. G. W. Struve.
The Washington Double Star Catalog, a large database of double and multiple stars, contains over 100,000 entries, each of which gives measures for the separation of two components. Each double star forms one entry in the catalog; multiple stars with n components will be represented by entries in the catalog for n−1 pairs, each giving the separation of one component of the multiple star from another. Codes such as AC are used to denote which components are being measured—in this case, component C relative to component A. This may be altered to a form such as AB-D to indicate the separation of a component from a close pair of components (in this case, component D relative to the pair AB.) Codes such as Aa may also be used to denote a component which is being measured relative to another component, A in this case. Discoverer designations are also listed; however, traditional discoverer abbreviations such as Δ and Σ have been encoded into a string of uppercase Roman letters, so that, for example, Δ65 has become DUN 65 and Σ2451 has become STF 2451. Further examples of this are shown in the adjacent table.
Examples
Visual binaries
Acrux
Capella
p Eridani
Gamma Leonis
Gamma Andromedae
Polaris
Procyon
Sirius
Alpha Centauri system (AB) and Proxima Centauri (thus α Cen C): Actually a three-star system
Optical doubles
Alpha1 and Alpha2 Capricorni
Theta Muscae and Theta Muscae B
Zeta1 and Zeta2 Scorpii
Eta1 and Eta2 Coronae Australis
Winnecke 4 (Messier 40)
Uncertain
Albireo A and Albireo B
Kappa1 and Kappa2 Coronae Australis
Omicron1 and Omicron2 Centauri
Mizar system (Aa/Ab/Ba/Bb) and Alcor system (thus Mizar Ca/Cb), generally considered a physical system.
References
Star types | Double star | [
"Astronomy"
] | 1,770 | [
"Star types",
"Astronomical classification systems"
] |
53,664 | https://en.wikipedia.org/wiki/Kingdom%20%28biology%29 | In biology, a kingdom is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla (singular phylum).
Traditionally, textbooks from Canada and the United States have used a system of six kingdoms (Animalia, Plantae, Fungi, Protista, Archaea/Archaebacteria, and Bacteria or Eubacteria), while textbooks in other parts of the world, such as Bangladesh, Brazil, Greece, India, Pakistan, Spain, and the United Kingdom have used five kingdoms (Animalia, Plantae, Fungi, Protista and Monera).
Some recent classifications based on modern cladistics have explicitly abandoned the term kingdom, noting that some traditional kingdoms are not monophyletic, meaning that they do not consist of all the descendants of a common ancestor. The terms flora (for plants), fauna (for animals), and, in the 21st century, funga (for fungi) are also used for life present in a particular region or time.
Definition and associated terms
When Carl Linnaeus introduced the rank-based system of nomenclature into biology in 1735, the highest rank was given the name "kingdom" and was followed by four other main or principal ranks: class, order, genus and species. Later two further main ranks were introduced, making the sequence kingdom, phylum or division, class, order, family, genus and species. In 1990, the rank of domain was introduced above kingdom.
Prefixes can be added so subkingdom (subregnum) and infrakingdom (also known as infraregnum) are the two ranks immediately below kingdom. Superkingdom may be considered as an equivalent of domain or empire or as an independent rank between kingdom and domain or subdomain. In some classification systems the additional rank branch (Latin: ramus) can be inserted between subkingdom and infrakingdom, e.g., Protostomia and Deuterostomia in the classification of Cavalier-Smith.
History
Two kingdoms of life
The classification of living things into animals and plants is an ancient one. Aristotle (384–322 BC) classified animal species in his History of Animals, while his pupil Theophrastus (–) wrote a parallel work, the Historia Plantarum, on plants.
Carl Linnaeus (1707–1778) laid the foundations for modern biological nomenclature, now regulated by the Nomenclature Codes, in 1735. He distinguished two kingdoms of living things: Regnum Animale ('animal kingdom') and Regnum Vegetabile ('vegetable kingdom', for plants). Linnaeus also included minerals in his classification system, placing them in a third kingdom, Regnum Lapideum.
Three kingdoms of life
In 1674, Antonie van Leeuwenhoek, often called the "father of microscopy", sent the Royal Society of London a copy of his first observations of microscopic single-celled organisms. Until then, the existence of such microscopic organisms was entirely unknown. Despite this, Linnaeus did not include any microscopic creatures in his original taxonomy.
At first, microscopic organisms were classified within the animal and plant kingdoms. However, by the mid–19th century, it had become clear to many that "the existing dichotomy of the plant and animal kingdoms [had become] rapidly blurred at its boundaries and outmoded".
In 1860 John Hogg proposed the Protoctista, a third kingdom of life composed of "all the lower creatures, or the primary organic beings"; he retained Regnum Lapideum as a fourth kingdom of minerals. In 1866, Ernst Haeckel also proposed a third kingdom of life, the Protista, for "neutral organisms" or "the kingdom of primitive forms", which were neither animal nor plant; he did not include the Regnum Lapideum in his scheme. Haeckel revised the content of this kingdom a number of times before settling on a division based on whether organisms were unicellular (Protista) or multicellular (animals and plants).
Four kingdoms
The development of microscopy revealed important distinctions between those organisms whose cells do not have a distinct nucleus (prokaryotes) and organisms whose cells do have a distinct nucleus (eukaryotes). In 1937 Édouard Chatton introduced the terms "prokaryote" and "eukaryote" to differentiate these organisms.
In 1938, Herbert F. Copeland proposed a four-kingdom classification by creating the novel Kingdom Monera of prokaryotic organisms; as a revised phylum Monera of the Protista, it included organisms now classified as Bacteria and Archaea. Ernst Haeckel, in his 1904 book The Wonders of Life, had placed the blue-green algae (or Phycochromacea) in Monera; this would gradually gain acceptance, and the blue-green algae would become classified as bacteria in the phylum Cyanobacteria.
In the 1960s, Roger Stanier and C. B. van Niel promoted and popularized Édouard Chatton's earlier work, particularly in their paper of 1962, "The Concept of a Bacterium"; this created, for the first time, a rank above kingdom—a superkingdom or empire—with the two-empire system of prokaryotes and eukaryotes. The two-empire system would later be expanded to the three-domain system of Archaea, Bacteria, and Eukaryota.
Five kingdoms
The differences between fungi and other organisms regarded as plants had long been recognised by some; Haeckel had moved the fungi out of Plantae into Protista after his original classification, but was largely ignored in this separation by scientists of his time. Robert Whittaker recognized an additional kingdom for the Fungi. The resulting five-kingdom system, proposed in 1969 by Whittaker, has become a popular standard and with some refinement is still used in many works and forms the basis for new multi-kingdom systems. It is based mainly upon differences in nutrition; his Plantae were mostly multicellular autotrophs, his Animalia multicellular heterotrophs, and his Fungi multicellular saprotrophs.
The remaining two kingdoms, Protista and Monera, included unicellular and simple cellular colonies. The five kingdom system may be combined with the two empire system. In the Whittaker system, Plantae included some algae. In other systems, such as Lynn Margulis's system of five kingdoms, the plants included just the land plants (Embryophyta), and Protoctista has a broader definition.
Following publication of Whittaker's system, the five-kingdom model began to be commonly used in high school biology textbooks. But despite the development from two kingdoms to five among most scientists, some authors as late as 1975 continued to employ a traditional two-kingdom system of animals and plants, dividing the plant kingdom into subkingdoms Prokaryota (bacteria and cyanobacteria), Mycota (fungi and supposed relatives), and Chlorota (algae and land plants).
Six kingdoms
In 1977, Carl Woese and colleagues proposed the fundamental subdivision of the prokaryotes into the Eubacteria (later called the Bacteria) and Archaebacteria (later called the Archaea), based on ribosomal RNA structure; this would later lead to the proposal of three "domains" of life, of Bacteria, Archaea, and Eukaryota. Combined with the five-kingdom model, this created a six-kingdom model, where the kingdom Monera is replaced by the kingdoms Bacteria and Archaea. This six-kingdom model is commonly used in recent US high school biology textbooks, but has received criticism for compromising the current scientific consensus. But the division of prokaryotes into two kingdoms remains in use with the recent seven kingdoms scheme of Thomas Cavalier-Smith, although it primarily differs in that Protista is replaced by Protozoa and Chromista.
Eight kingdoms
Thomas Cavalier-Smith supported the consensus at that time, that the difference between Eubacteria and Archaebacteria was so great (particularly considering the genetic distance of ribosomal genes) that the prokaryotes needed to be separated into two different kingdoms. He then divided Eubacteria into two subkingdoms: Negibacteria (Gram-negative bacteria) and Posibacteria (Gram-positive bacteria). Technological advances in electron microscopy allowed the separation of the Chromista from the Plantae kingdom. Indeed, the chloroplast of the chromists is located in the lumen of the endoplasmic reticulum instead of in the cytosol. Moreover, only chromists contain chlorophyll c. Since then, many non-photosynthetic phyla of protists, thought to have secondarily lost their chloroplasts, were integrated into the kingdom Chromista.
Finally, some protists lacking mitochondria were discovered. As mitochondria were known to be the result of the endosymbiosis of a proteobacterium, it was thought that these amitochondriate eukaryotes were primitively so, marking an important step in eukaryogenesis. As a result, these amitochondriate protists were separated from the protist kingdom, giving rise to the, at the same time, superkingdom and kingdom Archezoa. This superkingdom was opposed to the Metakaryota superkingdom, grouping together the five other eukaryotic kingdoms (Animalia, Protozoa, Fungi, Plantae and Chromista). This was known as the Archezoa hypothesis, which has since been abandoned; later schemes did not include the Archezoa–Metakaryota divide.
‡ No longer recognized by taxonomists.
Six kingdoms (1998)
In 1998, Cavalier-Smith published a six-kingdom model, which has been revised in subsequent papers. The version published in 2009 is shown below. Cavalier-Smith no longer accepted the importance of the fundamental Eubacteria–Archaebacteria divide put forward by Woese and others and supported by recent research. The kingdom Bacteria (sole kingdom of empire Prokaryota) was subdivided into two sub-kingdoms according to their membrane topologies: Unibacteria and Negibacteria. Unibacteria was divided into phyla Archaebacteria and Posibacteria; the bimembranous-unimembranous transition was thought to be far more fundamental than the long branch of genetic distance of Archaebacteria, viewed as having no particular biological significance.
Cavalier-Smith does not accept the requirement for taxa to be monophyletic ("holophyletic" in his terminology) to be valid. He defines Prokaryota, Bacteria, Negibacteria, Unibacteria, and Posibacteria as valid paraphyla (therefore "monophyletic" in the sense he uses this term) taxa, marking important innovations of biological significance (in regard of the concept of biological niche).
In the same way, his paraphyletic kingdom Protozoa includes the ancestors of Animalia, Fungi, Plantae, and Chromista. The advances of phylogenetic studies allowed Cavalier-Smith to realize that all the phyla thought to be archezoans (i.e. primitively amitochondriate eukaryotes) had in fact secondarily lost their mitochondria, typically by transforming them into new organelles: Hydrogenosomes. This means that all living eukaryotes are in fact metakaryotes, according to the significance of the term given by Cavalier-Smith. Some of the members of the defunct kingdom Archezoa, like the phylum Microsporidia, were reclassified into kingdom Fungi. Others were reclassified in kingdom Protozoa, like Metamonada which is now part of infrakingdom Excavata.
Because Cavalier-Smith allows paraphyly, the diagram below is an 'organization chart', not an 'ancestor chart', and does not represent an evolutionary tree.
Seven kingdoms
Cavalier-Smith and his collaborators revised their classification in 2015. In this scheme they introduced two superkingdoms of Prokaryota and Eukaryota and seven kingdoms. Prokaryota have two kingdoms: Bacteria and Archaea. (This was based on the consensus in the Taxonomic Outline of Bacteria and Archaea, and the Catalogue of Life). The Eukaryota have five kingdoms: Protozoa, Chromista, Plantae, Fungi, and Animalia. In this classification a protist is any of the eukaryotic unicellular organisms.
Summary
The kingdom-level classification of life is still widely employed as a useful way of grouping organisms, notwithstanding some problems with this approach:
Kingdoms such as Protozoa represent grades rather than clades, and so are rejected by phylogenetic classification systems.
The most recent research does not support the classification of the eukaryotes into any of the standard systems. In 2009, Andrew Roger and Alastair Simpson emphasized the need for diligence in analyzing new discoveries: "With the current pace of change in our understanding of the eukaryote tree of life, we should proceed with caution." Kingdoms are rarely used in academic phylogeny and are more common in introductory education, where 5-6 kingdom models are preferred.
Beyond traditional kingdoms
While the concept of kingdoms continues to be used by some taxonomists, there has been a movement away from traditional kingdoms, as they are no longer seen as providing a cladistic classification, where there is emphasis in arranging organisms into natural groups.
Three domains of life
Based on RNA studies, Carl Woese thought life could be divided into three large divisions and referred to them as the "three primary kingdom" model or "urkingdom" model.
In 1990, the name "domain" was proposed for the highest rank. This term represents a synonym for the category of dominion (lat. dominium), introduced by Moore in 1974. Unlike Moore, Woese et al. (1990) did not suggest a Latin term for this category, which represents a further argument supporting the accurately introduced term dominion.
Woese divided the prokaryotes (previously classified as the Kingdom Monera) into two groups, called Eubacteria and Archaebacteria, stressing that there was as much genetic difference between these two groups as between either of them and all eukaryotes.
According to genetic data, although eukaryote groups such as plants, fungi, and animals may look different, they are more closely related to each other than they are to either the Eubacteria or Archaea. It was also found that the eukaryotes are more closely related to the Archaea than they are to the Eubacteria. Although the primacy of the Eubacteria-Archaea divide has been questioned, it has been upheld by subsequent research. There is no consensus on how many kingdoms exist in the classification scheme proposed by Woese.
Eukaryotic supergroups
In 2004, a review article by Simpson and Roger noted that the Protista were "a grab-bag for all eukaryotes that are not animals, plants or fungi". They held that only monophyletic groups should be accepted as formal ranks in a classification and that – while this approach had been impractical previously (necessitating "literally dozens of eukaryotic 'kingdoms) – it had now become possible to divide the eukaryotes into "just a few major groups that are probably all monophyletic".
On this basis, the diagram opposite (redrawn from their article) showed the real "kingdoms" (their quotation marks) of the eukaryotes. A classification which followed this approach was produced in 2005 for the International Society of Protistologists, by a committee which "worked in collaboration with specialists from many societies". It divided the eukaryotes into the same six "supergroups". The published classification deliberately did not use formal taxonomic ranks, including that of "kingdom".
In this system the multicellular animals (Metazoa) are descended from the same ancestor as both the unicellular choanoflagellates and the fungi which form the Opisthokonta. Plants are thought to be more distantly related to animals and fungi.
However, in the same year as the International Society of Protistologists' classification was published (2005), doubts were being expressed as to whether some of these supergroups were monophyletic, particularly the Chromalveolata, and a review in 2006 noted the lack of evidence for several of the six proposed supergroups.
, there is widespread agreement that the Rhizaria belong with the Stramenopiles and the Alveolata, in a clade dubbed the SAR supergroup, so that Rhizaria is not one of the main eukaryote groups.
Comparison of top level classification
Some authors have added non-cellular life to their classifications. This can create a "superdomain" called "Acytota", also called "Aphanobionta", of non-cellular life; with the other superdomain being "cytota" or cellular life. The eocyte hypothesis proposes that the eukaryotes emerged from a phylum within the archaea called the Thermoproteota (formerly known as eocytes or Crenarchaeota).
Viruses
The International Committee on Taxonomy of Viruses uses the taxonomic rank "kingdom" in the classification of viruses (with the suffix -virae); but this is beneath the top level classifications of realm and subrealm.
There is ongoing debate as to whether viruses can be included in the tree of life. The arguments against include the fact that they are obligate intracellular parasites that lack metabolism and are not capable of replication outside of a host cell. Another argument is that their placement in the tree would be problematic, since it is suspected that viruses have various evolutionary origins, and they have a penchant for harvesting nucleotide sequences from their hosts.
On the other hand, there are arguments in favor of their inclusion.
One of these comes from the discovery of unusually large and complex viruses, such as Mimivirus, that possess typical cellular genes.
See also
Cladistics
Phylogenetics
Systematics
Taxonomy
Notes
References
Further reading
Pelentier, B. (2007-2015). Empire Biota: a comprehensive taxonomy, . [Historical overview.]
Peter H. Raven and Helena Curtis (1970), Biology of Plants, New York: Worth Publishers. [Early presentation of five-kingdom system.]
External links
A Brief History of the Kingdoms of Life at Earthling Nature
The five kingdom concept
Whittaker's classification
Kingdom | Kingdom (biology) | [
"Biology"
] | 3,918 | [
"nan"
] |
53,683 | https://en.wikipedia.org/wiki/Nuclear%20fallout | Nuclear fallout is residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave has passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes. The amount and spread of fallout is a product of the size of the weapon and the altitude at which it is detonated. Fallout may get entrained with the products of a pyrocumulus cloud and when combined with precipitation falls as black rain (rain darkened by soot and other particulates), which occurred within 30–40 minutes of the atomic bombings of Hiroshima and Nagasaki. This radioactive dust, usually consisting of fission products mixed with bystanding atoms that are neutron-activated by exposure, is a form of radioactive contamination.
Types of fallout
Fallout comes in two varieties. The first is a small amount of carcinogenic material with a long half-life. The second, depending on the height of detonation, is a large quantity of radioactive dust and sand with a short half-life.
All nuclear explosions produce fission products, un-fissioned nuclear material, and weapon residues vaporized by the heat of the fireball. These materials are limited to the original mass of the device, but include radioisotopes with long lives. When the nuclear fireball does not reach the ground, this is the only fallout produced. Its amount can be estimated from the fission-fusion design and yield of the weapon.
Global fallout
After the detonation of a weapon at or above the fallout-free altitude (an air burst), fission products, un-fissioned nuclear material, and weapon residues vaporized by the heat of the fireball condense into a suspension of particles 10 nm to 20 μm in diameter. This size of particulate matter, lifted to the stratosphere, may take months or years to settle, and may do so anywhere in the world. Its radioactive characteristics increase the statistical cancer risk, with up to 2.4 million people having died by 2020 from the measurable elevated atmospheric radioactivity after the widespread nuclear weapons testing of the 1950s, peaking in 1963 (the Bomb pulse). Levels reached about 0.15 mSv per year worldwide, or about 7% of average background radiation dose from all sources, and has slowly decreased since, with natural background radiation levels being around 1 mSv.
Radioactive fallout has occurred around the world; for example, people have been exposed to iodine-131 from atmospheric nuclear testing. Fallout accumulates on vegetation, including fruits and vegetables. Starting from 1951 people may have gotten exposure, depending on whether they were outside, the weather, and whether they consumed contaminated milk, vegetables or fruit. Exposure can be on an intermediate time scale or long term. The intermediate time scale results from fallout that has been put into the troposphere and ejected by precipitation during the first month. Long-term fallout can sometimes occur from deposition of tiny particles carried in the stratosphere. By the time that stratospheric fallout has begun to reach the earth, the radioactivity is very much decreased. Also, after a year it is estimated that a sizable quantity of fission products move from the northern to the southern stratosphere. The intermediate time scale is between 1 and 30 days, with long term fallout occurring after that.
Examples of both intermediate and long term fallout occurred after the 1986 Chernobyl accident, which contaminated over of land in Ukraine and Belarus. The main fuel of the reactor was uranium, and surrounding this was graphite, both of which were vaporized by the hydrogen explosion that destroyed the reactor and breached its containment. An estimated 31 people died within a few weeks after this happened, including two plant workers killed at the scene. Although residents were evacuated within 36 hours, people started to complain of vomiting, migraines and other major signs of radiation sickness. The officials of Ukraine had to close off an area with an radius. Long term effects included at least 6,000 cases of thyroid cancer, mainly among children. Fallout spread throughout Europe, with Northern Scandinavia receiving a heavy dose, contaminating reindeer herds in Lapland, and salad greens becoming almost unavailable in France. Some sheep farms in North Wales and the North Of England were required to monitor radioactivity levels in their flocks until the control was lifted in 2012.
Local fallout
During detonations of devices at ground level (surface burst), below the fallout-free altitude, or in shallow water, heat vaporizes large amounts of earth or water, which is drawn up into the radioactive cloud. This material becomes radioactive when it combines with fission products or other radio-contaminants, or when it is neutron-activated.
The table below summarizes the abilities of common isotopes to form fallout. Some radiation taints large amounts of land and drinking water causing formal mutations throughout animal and human life.
A surface burst generates large amounts of particulate matter, composed of particles from less than 100 nm to several millimeters in diameter—in addition to very fine particles that contribute to worldwide fallout. The larger particles spill out of the stem and cascade down the outside of the fireball in a downdraft even as the cloud rises, so fallout begins to arrive near ground zero within an hour. More than half the total bomb debris lands on the ground within about 24 hours as local fallout. Chemical properties of the elements in the fallout control the rate at which they are deposited on the ground. Less volatile elements deposit first.
Severe local fallout contamination can extend far beyond the blast and thermal effects, particularly in the case of high yield surface detonations. The ground track of fallout from an explosion depends on the weather from the time of detonation onward. In stronger winds, fallout travels faster but takes the same time to descend, so although it covers a larger path, it is more spread out or diluted. Thus, the width of the fallout pattern for any given dose rate is reduced where the downwind distance is increased by higher winds. The total amount of activity deposited up to any given time is the same irrespective of the wind pattern, so overall casualty figures from fallout are generally independent of winds. But thunderstorms can bring down activity as rain allows fallout to drop more rapidly, particularly if the mushroom cloud is low enough to be below ("washout"), or mixed with ("rainout"), the thunderstorm.
Whenever individuals remain in a radiologically contaminated area, such contamination leads to an immediate external radiation exposure as well as a possible later internal hazard from inhalation and ingestion of radiocontaminants, such as the rather short-lived iodine-131, which is accumulated in the thyroid.
Factors affecting fallout
Location
There are two main considerations for the location of an explosion: height and surface composition. A nuclear weapon detonated in the air, called an air burst, produces less fallout than a comparable explosion near the ground. A nuclear explosion in which the fireball touches the ground pulls soil and other materials into the cloud and neutron activates it before it falls back to the ground. An air burst produces a relatively small amount of the highly radioactive heavy metal components of the device itself.
In case of water surface bursts, the particles tend to be rather lighter and smaller, producing less local fallout but extending over a greater area. The particles contain mostly sea salts with some water; these can have a cloud seeding effect causing local rainout and areas of high local fallout. Fallout from a seawater burst is difficult to remove once it has soaked into porous surfaces because the fission products are present as metallic ions that chemically bond to many surfaces. Water and detergent washing effectively removes less than 50% of this chemically bonded activity from concrete or steel. Complete decontamination requires aggressive treatment like sandblasting, or acidic treatment. After the Crossroads underwater test, it was found that wet fallout must be immediately removed from ships by continuous water washdown (such as from the fire sprinkler system on the decks).
Parts of the sea bottom may become fallout. After the Castle Bravo test, white dust—contaminated calcium oxide particles originating from pulverized and calcined corals—fell for several hours, causing beta burns and radiation exposure to the inhabitants of the nearby atolls and the crew of the Daigo Fukuryū Maru fishing boat. The scientists called the fallout Bikini snow.
For subsurface bursts, there is an additional phenomenon present called "base surge". The base surge is a cloud that rolls outward from the bottom of the subsiding column, which is caused by an excessive density of dust or water droplets in the air. For underwater bursts, the visible surge is, in effect, a cloud of liquid (usually water) droplets with the property of flowing almost as if it were a homogeneous fluid. After the water evaporates, an invisible base surge of small radioactive particles may persist.
For subsurface land bursts, the surge is made up of small solid particles, but it still behaves like a fluid. A soil earth medium favors base surge formation in an underground burst. Although the base surge typically contains only about 10% of the total bomb debris in a subsurface burst, it can create larger radiation doses than fallout near the detonation, because it arrives sooner than fallout, before much radioactive decay has occurred.
Meteorological
Meteorological conditions greatly influence fallout, particularly local fallout. Atmospheric winds are able to bring fallout over large areas. For example, as a result of a Castle Bravo surface burst of a 15 Mt thermonuclear device at Bikini Atoll on 1 March 1954, a roughly cigar-shaped area of the Pacific extending over 500 km downwind and varying in width to a maximum of 100 km was severely contaminated. There are three very different versions of the fallout pattern from this test, because the fallout was measured only on a small number of widely spaced Pacific Atolls. The two alternative versions both ascribe the high radiation levels at north Rongelap to a downwind hot spot caused by the large amount of radioactivity carried on fallout particles of about 50–100 micrometres size.
After Bravo, it was discovered that fallout landing on the ocean disperses in the top water layer (above the thermocline at 100 m depth), and the land equivalent dose rate can be calculated by multiplying the ocean dose rate at two days after burst by a factor of about 530. In other 1954 tests, including Yankee and Nectar, hot spots were mapped out by ships with submersible probes, and similar hot spots occurred in 1956 tests such as Zuni and Tewa.
However, the major U.S. "DELFIC" (Defence Land Fallout Interpretive Code) computer calculations use the natural size distributions of particles in soil instead of the afterwind sweep-up spectrum, and this results in more straightforward fallout patterns lacking the downwind hot spot.
Snow and rain, especially if they come from considerable heights, accelerate local fallout. Under special meteorological conditions, such as a local rain shower that originates above the radioactive cloud, limited areas of heavy contamination just downwind of a nuclear blast may be formed.
Effects
A wide range of biological changes may follow the irradiation of animals. These vary from rapid death following high doses of penetrating whole-body radiation, to essentially normal lives for a variable period of time until the development of delayed radiation effects, in a portion of the exposed population, following low dose exposures.
The unit of actual exposure is the röntgen, defined in ionisations per unit volume of air. All ionisation based instruments (including geiger counters and ionisation chambers) measure exposure. However, effects depend on the energy per unit mass, not the exposure measured in air. A deposit of 1 joule per kilogram has the unit of 1 gray (Gy). For 1 MeV energy gamma rays, an exposure of 1 röntgen in air produces a dose of about 0.01 gray (1 centigray, cGy) in water or surface tissue. Because of shielding by the tissue surrounding the bones, the bone marrow only receives about 0.67 cGy when the air exposure is 1 röntgen and the surface skin dose is 1 cGy. Some lower values reported for the amount of radiation that would kill 50% of personnel (the ) refer to bone marrow dose, which is only 67% of the air dose.
Short term
The dose that would be lethal to 50% of a population is a common parameter used to compare the effects of various fallout types or circumstances. Usually, the term is defined for a specific time, and limited to studies of acute lethality. The common time periods used are 30 days or less for most small laboratory animals and to 60 days for large animals and humans. The LD50 figure assumes that the individuals did not receive other injuries or medical treatment.
In the 1950s, the LD50 for gamma rays was set at 3.5 Gy, while under more dire conditions of war (a bad diet, little medical care, poor nursing) the LD50 was 2.5 Gy (250 rad). There have been few documented cases of survival beyond 6 Gy. One person at Chernobyl survived a dose of more than 10 Gy, but many of the persons exposed there were not uniformly exposed over their entire body. If a person is exposed in a non-homogeneous manner then a given dose (averaged over the entire body) is less likely to be lethal. For instance, if a person gets a hand/low arm dose of 100 Gy, which gives them an overall dose of 4 Gy, they are more likely to survive than a person who gets a 4 Gy dose over their entire body. A hand dose of 10 Gy or more would likely result in loss of the hand. A British industrial radiographer who was estimated to have received a hand dose of 100 Gy over the course of his lifetime lost his hand because of radiation dermatitis. Most people become ill after an exposure to 1 Gy or more. Fetuses are often more vulnerable to radiation and may miscarry, especially in the first trimester.
Because of the large amount of short-lived fission products, the activity and radiation levels of nuclear fallout decrease very quickly after being released; it is reduced by 50% in the first hour after a detonation, then by 80% during the first day. As a result, early gross decontamination, such as removing contaminated articles of outer clothing, is more effective than delayed but more thorough cleaning. Most areas become fairly safe for travel and decontamination after three to five weeks.
One hour after a surface burst, the radiation from fallout in the crater region is 30 grays per hour (Gy/h). Civilian dose rates in peacetime range from 30 to 100 μGy per year.
For yields of up to 10 kt, prompt radiation is the dominant producer of casualties on the battlefield. Humans receiving an acute incapacitating dose (30 Gy) have their performance degraded almost immediately and become ineffective within several hours. However, they do not die until five to six days after exposure, assuming they do not receive any other injuries. Individuals receiving less than a total of 1.5 Gy are not incapacitated. People receiving doses greater than 1.5 Gy become disabled, and some eventually die.
A dose of 5.3 Gy to 8.3 Gy is considered lethal but not immediately incapacitating. Personnel exposed to this amount of radiation have their cognitive performance degraded in two to three hours, depending on how physically demanding the tasks they must perform are, and remain in this disabled state at least two days. However, at that point they experience a recovery period and can perform non-demanding tasks for about six days, after which they relapse for about four weeks. At this time they begin exhibiting symptoms of radiation poisoning of sufficient severity to render them totally ineffective. Death follows at approximately six weeks after exposure, although outcomes may vary.
Long term
Late or delayed effects of radiation occur following a wide range of doses and dose rates. Delayed effects may appear months to years after irradiation and include a wide variety of effects involving almost all tissues or organs. Some of the possible delayed consequences of radiation injury, with the rates above the background prevalence, depending on the absorbed dose, include carcinogenesis, cataract formation, chronic radiodermatitis, decreased fertility, and genetic mutations.
Presently, the only teratological effect observed in humans following nuclear attacks on highly populated areas is microcephaly which is the only proven malformation, or congenital abnormality, found in the in utero developing human fetuses present during the Hiroshima and Nagasaki bombings. Of all the pregnant women who were close enough to be exposed to the prompt burst of intense neutron and gamma doses in the two cities, the total number of children born with microcephaly was below 50. No statistically demonstrable increase of congenital malformations was found among the later conceived children born to survivors of the nuclear detonations at Hiroshima and Nagasaki. The surviving women of Hiroshima and Nagasaki who could conceive and were exposed to substantial amounts of radiation went on and had children with no higher incidence of abnormalities than the Japanese average.
The Baby Tooth Survey founded by the husband and wife team of physicians Eric Reiss and Louise Reiss, was a research effort focused on detecting the presence of strontium-90, a cancer-causing radioactive isotope created by the more than 400 atomic tests conducted above ground that is absorbed from water and dairy products into the bones and teeth given its chemical similarity to calcium. The team sent collection forms to schools in the St. Louis, Missouri area, hoping to gather 50,000 teeth each year. Ultimately, the project collected over 300,000 teeth from children of various ages before the project was ended in 1970.
Preliminary results of the Baby Tooth Survey were published in the 24 November 1961, edition of the journal Science, and showed that levels of strontium-90 had risen steadily in children born in the 1950s, with those born later showing the most pronounced increases. The results of a more comprehensive study of the elements found in the teeth collected showed that children born after 1963 had levels of strontium-90 in their baby teeth that was 50 times higher than that found in children born before large-scale atomic testing began. The findings helped convince U.S. President John F. Kennedy to sign the Partial Nuclear Test Ban Treaty with the United Kingdom and Soviet Union, which ended the above-ground nuclear weapons testing that created the greatest amounts of atmospheric nuclear fallout.
Some considered the baby tooth survey a "campaign [that] effectively employed a variety of media advocacy strategies" to alarm the public and "galvanized" support against atmospheric nuclear testing,, and putting an end to such testing was commonly viewed as a positive outcome for a myriad of reasons. The survey could not show at the time, nor in the decades that have elapsed, that the levels of global strontium-90 or fallout in general, were life-threatening, primarily because "50 times the strontium-90 from before nuclear testing" is a minuscule number, and multiplication of minuscule numbers results in only a slightly larger minuscule number. Moreover, the Radiation and Public Health Project that currently retains the teeth has had their stance and publications criticized: a 2003 article in The New York Times states that many scientists consider the group's work controversial, with little credibility with the scientific establishment, while some scientists consider it "good, careful work". In an April 2014 article in Popular Science, Sarah Fecht argues that the group's work, specifically the widely discussed case of cherry-picking data to suggest that fallout from the 2011 Fukushima accident caused infant deaths in America, is "junk science", as despite their papers being peer-reviewed, independent attempts to corroborate their results return findings that are not in agreement with what the organization suggests. The organization had earlier suggested the same thing occurred after the 1979 Three Mile Island accident, though the Atomic Energy Commission argued this was unfounded. The tooth survey, and the organization's new target of pushing for test bans with US nuclear electric power stations, is detailed and critically labelled as the "Tooth Fairy issue" by the Nuclear Regulatory Commission.
Effects on the environment
In the event of a large-scale nuclear exchange, the effects would be drastic on the environment as well as directly to the human population. Within direct blast zones everything would be vaporized and destroyed. Cities damaged but not completely destroyed would lose their water system due to the loss of power and supply lines rupturing. Within the local nuclear fallout pattern suburban areas' water supplies would become extremely contaminated. At this point stored water would be the only safe water to use. All surface water within the fallout would be contaminated by falling fission products.
Within the first few months of the nuclear exchange the nuclear fallout will continue to develop and detriment the environment. Dust, smoke, and radioactive particles will fall hundreds of kilometers downwind of the explosion point and pollute surface water supplies. Iodine-131 would be the dominant fission product within the first few weeks, and in the months following the dominant fission product would be strontium-90. These fission products would remain in the fallout dust, resulting in rivers, lakes, sediments, and soils being contaminated with the fallout.
Rural areas' water supplies would be slightly less polluted by fission particles in intermediate and long-term fallout than cities and suburban areas. Without additional contamination, the lakes, reservoirs, rivers, and runoff would be gradually less contaminated as water continued to flow through its system.
Groundwater supplies such as aquifers would however remain unpolluted initially in the event of a nuclear fallout. Over time the groundwater could become contaminated with fallout particles, and would remain contaminated for over 10 years after a nuclear engagement. It would take hundreds or thousands of years for an aquifer to become completely pure. Groundwater would still be safer than surface water supplies and would need to be consumed in smaller doses. Long term, cesium-137 and strontium-90 would be the major radionuclides affecting the fresh water supplies.
The dangers of nuclear fallout do not stop at increased risks of cancer and radiation sickness, but also include the presence of radionuclides in human organs from food. A fallout event would leave fission particles in the soil for animals to consume, followed by humans. Radioactively contaminated milk, meat, fish, vegetables, grains and other food would all be dangerous because of fallout.
From 1945 to 1967 the U.S. conducted hundreds of nuclear weapon tests. Atmospheric testing took place over the US mainland during this time and as a consequence scientists have been able to study the effect of nuclear fallout on the environment. Detonations conducted near the surface of the earth irradiated thousands of tons of soil. Of the material drawn into the atmosphere, portions of radioactive material will be carried by low altitude winds and deposited in surrounding areas as radioactive dust. The material intercepted by high altitude winds will continue to travel. When a radiation cloud at high altitude is exposed to rainfall, the radioactive fallout will contaminate the downwind area below.
Agricultural fields and plants will absorb the contaminated material and animals will consume the radioactive material. As a result, the nuclear fallout may cause livestock to become ill or die, and if consumed the radioactive material will be passed on to humans.
The damage to other living organism as a result to nuclear fallout depends on the species. Mammals particularly are extremely sensitive to nuclear radiation, followed by birds, plants, fish, reptiles, crustaceans, insects, moss, lichen, algae, bacteria, mollusks, and viruses.
Climatologist Alan Robock and atmospheric and oceanic sciences professor Brian Toon created a model of a hypothetical small-scale nuclear war that would have approximately 100 weapons used. In this scenario, the fires would create enough soot into the atmosphere to block sunlight, lowering global temperatures by more than one degree Celsius. The result would have the potential of creating widespread food insecurity (nuclear famine). Precipitation across the globe would be disrupted as a result. If enough soot was introduced in the upper atmosphere the planet's ozone layer could potentially be depleted, affecting plant growth and human health.
Radiation from the fallout would linger in soil, plants, and food chains for years. Marine food chains are more vulnerable to the nuclear fallout and the effects of soot in the atmosphere.
Fallout radionuclides' detriment in the human food chain is apparent in the lichen-caribou-eskimo studies in Alaska. The primary effect on humans observed was thyroid dysfunction. The result of a nuclear fallout is incredibly detrimental to human survival and the biosphere. Fallout alters the quality of our atmosphere, soil, and water and causes species to go extinct.
Fallout protection
During the Cold War, the governments of the U.S., the USSR, Great Britain, and China attempted to educate their citizens about surviving a nuclear attack by providing procedures on minimizing short-term exposure to fallout. This effort commonly became known as Civil Defense.
Fallout protection is almost exclusively concerned with protection from radiation. Radiation from a fallout is encountered in the forms of alpha, beta, and gamma radiation, and as ordinary clothing affords protection from alpha and beta radiation, most fallout protection measures deal with reducing exposure to gamma radiation. For the purposes of radiation shielding, many materials have a characteristic halving thickness: the thickness of a layer of a material sufficient to reduce gamma radiation exposure by 50%. Halving thicknesses of common materials include: 1 cm (0.4 inch) of lead, 6 cm (2.4 inches) of concrete, 9 cm (3.6 inches) of packed earth or 150 m (500 ft) of air. When multiple thicknesses are built, the shielding multiplies. A practical fallout shield is ten halving-thicknesses of a given material, such as 90 cm (36 inches) of packed earth, which reduces gamma ray exposure by approximately 1024 times (210). A shelter built with these materials for the purposes of fallout protection is known as a fallout shelter.
Personal protective equipment
As the nuclear energy sector continues to grow, the international rhetoric surrounding nuclear warfare intensifies, and the ever-present threat of radioactive materials falling into the hands of dangerous people persists, many scientists are working hard to find the best way to protect human organs from the harmful effects of high energy radiation. Acute radiation syndrome (ARS) is the most immediate risk to humans when exposed to ionizing radiation in dosages greater than around 0.1 Gy/hr. Radiation in the low energy spectrum (alpha and beta radiation) with minimal penetrating power is unlikely to cause significant damage to internal organs (although if contamination is ingested, inhaled or on the skin, and thus in close proximity to tissues and organs, the effect of these 'massive' particles may be catastrophic). The high penetrating power of gamma and neutron radiation, however, easily penetrates the skin and many thin shielding mechanisms to cause cellular degeneration in the stem cells found in bone marrow. While full body shielding in a secure fallout shelter as described above is the most optimal form of radiation protection, it requires being locked in a very thick bunker for a significant amount of time. In the event of a nuclear catastrophe of any kind, it is imperative to have mobile protection equipment for medical and security personnel to perform necessary containment, evacuation, and any number of other important public safety objectives. The mass of the shielding material required to properly protect the entire body from high energy radiation would make functional movement essentially impossible. This has led scientists to begin researching the idea of partial body protection: a strategy inspired by hematopoietic stem cell transplantation (HSCT). The idea is to use enough shielding material to sufficiently protect the high concentration of bone marrow in the pelvic region, which contains enough regenerative stem cells to repopulate the body with unaffected bone marrow. More information on bone marrow shielding can be found in the Health Physics Radiation Safety Journal article Selective Shielding of Bone Marrow: An Approach to Protecting Humans from External Gamma Radiation, or in the Organisation for Economic Co-operation and Development (OECD) and the Nuclear Energy Agency (NEA)'s 2015 report: Occupational Radiation Protection in Severe Accident Management.
The seven-ten rule
The danger of radiation from fallout also decreases rapidly with time due in large part to the exponential decay of the individual radionuclides. A book by Cresson H. Kearny presents data showing that for the first few days after the explosion, the radiation dose rate is reduced by a factor of ten for every seven-fold increase in the number of hours since the explosion. He presents data showing that "it takes about seven times as long for the dose rate to decay from 1000 roentgens per hour (1000 R/hr) to 10 R/hr (48 hours) as to decay from 1000 R/hr to 100 R/hr (7 hours)." This is a rule of thumb based on observed data, not a precise relation.
United States government guides for fallout protection
The United States government, often the Office of Civil Defense in the Department of Defense, provided guides to fallout protection in the 1960s, frequently in the form of booklets. These booklets provided information on how to best survive nuclear fallout. They also included instructions for various fallout shelters, whether for a family, a hospital, or a school shelter were provided. There were also instructions for how to create an improvised fallout shelter, and what to do to best increase a person's chances for survival if they were unprepared.
The central idea in these guides is that materials like concrete, soil, and sand are necessary to shield a person from fallout particles and radiation. A significant amount of materials of this type are necessary to protect a person from fallout radiation, so safety clothing cannot protect a person from fallout radiation. However, protective clothing can keep fallout particles off a person's body, but the radiation from these particles will still permeate through the clothing. For safety clothing to be able to block the fallout radiation, it would have to be so thick and heavy that a person could not function.
These guides indicated that fallout shelters should contain enough resources to keep its occupants alive for up to two weeks. Community shelters were preferred over single-family shelters. The more people in a shelter, the greater quantity and variety of resources that shelter would be equipped with. These communities’ shelters would also help facilitate efforts to recuperate the community in the future. Single family shelters should be built below ground if possible. Many different types of fallout shelters could be made for a relatively small amount of money. A common format for fallout shelters was to build the shelter underground, with solid concrete blocks to act as the roof. If a shelter could only be partially underground, it was recommended to mound over that shelter with as much soil as possible. If a house had a basement, it is best for a fallout shelter to be constructed in a corner of the basement. The center of a basement is where the most radiation will be because the easiest way for radiation to enter a basement is from the floor above. The two of the walls of the shelter in a basement corner will be the basement walls that are surrounded by soil outside. Cinder blocks filled with sand or soil were highly recommended for the other two walls. Concrete blocks, or some other dense material, should be used as a roof for a basement fallout shelter because the floor of a house is not an adequate roof for a fallout shelter. These shelters should contain water, food, tools, and a method for dealing with human waste.
If a person did not have a shelter previously built, these guides recommended trying to get underground. If a person had a basement but no shelter, they should put food, water, and a waste container in the corner of the basement. Then items such as furniture should be piled up to create walls around the person in the corner. If the underground cannot be reached, a tall apartment building at least ten miles from the blast was recommended as a good fallout shelter. People in these buildings should get as close to the center of the building as possible and avoid the top and ground floors.
Schools were the preferred fallout shelters according to the Office of Civil Defense. Schools, not including universities, contained around one-quarter of the population of the United States when they were in session at that time. The distribution of schools across the nation reflected the population density, and they were often the most suitable building in a community to act as a fallout shelter. Schools also already had organization with leaders in place. The Office of Civil Defense recommended altering current schools and the construction of future schools to include thicker walls and roofs, better-protected electrical systems, a purifying ventilation system, and a protected water pump. The Office of Civil Defense determined that around 10 square feet of net area per person were necessary in schools that were to function as a fallout shelter. A normal classroom could provide 180 people with area to sleep. If an attack were to happen, all the unnecessary furniture was to be moved out of the classrooms to make more room for people. It was recommended to keep one or two tables in the room if possible to use as a food-serving station.
The Office of Civil Defense conducted four case studies to find the cost of turning four standing schools into fallout shelters and what their capacity would be. The cost of the schools per occupant in the 1960s were $66.00, $127.00, $50.00, and $180.00. The capacity of people these schools could house as shelters were 735, 511, 484, and 460 respectively.
The US Department of Homeland Security and the Federal Emergency Management Agency in coordination with other agencies concerned with public protection in the aftermath of a nuclear detonation have developed more recent guidance documents that build on the older Civil Defense frameworks. Planning Guidance for Response to a Nuclear Detonation was published in 2022 and provided in-depth analysis and response planning for local government jurisdictions.
Nuclear reactor accident
Fallout can also refer to nuclear accidents, although a nuclear reactor does not explode like a nuclear weapon. The isotopic signature of bomb fallout is very different from the fallout from a serious power reactor accident (such as Chernobyl or Fukushima).
The key differences are in volatility and half-life.
Volatility
The boiling point of an element (or its compounds) determines the percentage of that element that a power reactor accident releases. The ability of an element to form a solid determines the rate it is deposited on the ground after having been injected into the atmosphere by a nuclear detonation or accident.
Half-life
A half life is the time it takes the radiation emitted by a specific substance to decay to half the initial value. A large amount of short-lived isotopes such as 97Zr are present in bomb fallout. This isotope and other short-lived isotopes are constantly generated in a power reactor, but because the criticality occurs over a long length of time, the majority of these short lived isotopes decay before they can be released.
Preventive measures
Nuclear fallout can occur due to a number of different sources. One of the most common potential sources of nuclear fallout is that of nuclear reactors. Because of this, steps must be taken to ensure the risk of nuclear fallout at nuclear reactors is controlled.
In the 1950s and 60's, the United States Atomic Energy Commission (AEC) began developing safety regulations against nuclear fallout for civilian nuclear reactors. Because the effects of nuclear fallout are more widespread and longer lasting than other forms of energy production accidents, the AEC desired a more proactive response towards potential accidents than ever before. One step to prevent nuclear reactor accidents was the Price-Anderson Act. Passed by Congress in 1957, the Price-Anderson Act ensured government assistance above the $60 million covered by private insurance companies in the case of a nuclear reactor accident. The main goal of the Price-Anderson Act was to protect the multi-billion-dollar companies overseeing the production of nuclear reactors. Without this protection, the nuclear reactor industry could potentially come to a halt, and the protective measures against nuclear fallout would be reduced. However, because of the limited experience in nuclear reactor technology, engineers had a difficult time calculating the potential risk of released radiation. Engineers were forced to imagine every unlikely accident, and the potential fallout associated with each accident. The AEC's regulations against potential nuclear reactor fallout were centered on the ability of the power plant to the Maximum Credible Accident (MCA). The MCA involved a "large release of radioactive isotopes after a substantial meltdown of the reactor fuel when the reactor coolant system failed through a Loss-of-Coolant Accident". The prevention of the MCA enabled a number of new nuclear fallout preventive measures. Static safety systems, or systems without power sources or user input, were enabled to prevent potential human error. Containment buildings, for example, were reliably effective at containing a release of radiation and did not need to be powered or turned on to operate. Active protective systems, although far less dependable, can do many things that static systems cannot. For example, a system to replace the escaping steam of a cooling system with cooling water could prevent reactor fuel from melting. However, this system would need a sensor to detect the presence of releasing steam. Sensors can fail, and the results of a lack of preventive measures would result in a local nuclear fallout. The AEC had to choose, then, between active and static systems to protect the public from nuclear fallout. With a lack of set standards and probabilistic calculations, the AEC and the industry became divided on the best safety precautions to use.
This division gave rise to the Nuclear Regulatory Commission (NRC). The NRC was committed to 'regulations through research', which gave the regulatory committee a knowledge bank of research on which to draw their regulations. Much of the research done by the NRC sought to move safety systems from a deterministic viewpoint into a new probabilistic approach. The deterministic approach sought to foresee all problems before they arose. The probabilistic approach uses a more mathematical approach to weigh the risks of potential radiation leaks. Much of the probabilistic safety approach can be drawn from the radiative transfer theory in Physics, which describes how radiation travels in free space and through barriers. Today, the NRC is still the leading regulatory committee on nuclear reactor power plants.
Determining extent of nuclear fallout
The International Nuclear and Radiological Event Scale (INES) is the primary form of categorizing the potential health and environmental effects of a nuclear or radiological event and communicating it to the public. The scale, which was developed in 1990 by the International Atomic Energy Agency and the Nuclear Energy Agency of the Organization for Economic Co-operation and Development, classifies these nuclear accidents based on the potential impact of the fallout:
Defence-in-Depth: This is the lowest form of nuclear accidents and refers to events that have no direct impact on people or the environment but must be taken note of to improve future safety measures.
Radiological Barriers and Control: This category refers to events that have no direct impact on people or the environment and only refer to the damage caused within major facilities.
People and the Environment: This section of the scale consists of more serious nuclear accidents. Events in this category could potentially cause radiation to spread to people close to the location of the accident. This also includes an unplanned, widespread release of the radioactive material.
The INES scale is composed of seven steps that categorize the nuclear events, ranging from anomalies that must be recorded to improve upon safety measures to serious accidents that require immediate action.
Chernobyl
The 1986 nuclear reactor explosion at Chernobyl was categorized as a Level 7 accident, which is the highest possible ranking on the INES scale, due to widespread environmental and health effects and "external release of a significant fraction of reactor core inventory". The nuclear accident still stands as the only accident in commercial nuclear power that led to radiation-related deaths. The steam explosion and fires released approximately 5200 PBq, or at least 5 percent of the reactor core, into the atmosphere. The explosion itself resulted in the deaths of two plant workers, while 28 people died over the weeks that followed of severe radiation poisoning. Furthermore, young children and adolescents in the areas most contaminated by the radiation exposure showed an increase in the risk for thyroid cancer, although the United Nations Scientific Committee on the Effects of Atomic Radiation stated that "there is no evidence of a major public health impact" apart from that. The nuclear accident also took a heavy toll on the environment, including contamination in urban environments caused by the deposition of radionuclides and the contamination of "different crop types, in particular, green leafy vegetables ... depending on the deposition levels, and time of the growing season".
Three Mile Island
The nuclear meltdown at Three Mile Island in 1979 was categorized as a Level 5 accident on the INES scale because of the "severe damage to the reactor core" and the radiation leak caused by the incident. Three Mile Island was the most serious accident in the history of American commercial nuclear power plants, yet the effects were different from those of the Chernobyl accident. A study done by the Nuclear Regulatory Commission following the incident reveals that the nearly 2 million people surrounding the Three Mile Island plant "are estimated to have received an average radiation dose of only 1 millirem above the usual background dose". Furthermore, unlike those affected by radiation in the Chernobyl accident, the development of thyroid cancer in the people around Three Mile Island was "less aggressive and less advanced".
Fukushima
Like the Three Mile Island incident, the incident at Fukushima was initially categorized as a Level 5 accident on the INES scale after a tsunami disabled the power supply and cooling of three reactors, which then suffered significant melting in the days that followed. However, after combining the events at the three reactors rather than assessing them individually, the accident was upgraded to an INES Level 7. The radiation exposure from the incident caused a recommended evacuation for inhabitants up to 30 km away from the plant. However, it was also hard to track such exposure because 23 out of the 24 radioactive monitoring stations were also disabled by the tsunami. Removing contaminated water, both in the plant itself and run-off water that spread into the sea and nearby areas, became a huge challenge for the Japanese government and plant workers. During the containment period following the accident, thousands of cubic meters of slightly contaminated water were released in the sea to free up storage for more contaminated water in the reactor and turbine buildings. However, the fallout from the Fukushima accident had a minimal impact on the surrounding population. According to the Institut de Radioprotection et de Sûreté Nucléaire, over 62 percent of assessed residents within the Fukushima prefecture received external doses of less than 1 mSv in the four months following the accident. In addition, comparing screening campaigns for children inside the Fukushima prefecture and in the rest of the country revealed no significant difference in the risk of thyroid cancer.
International nuclear safety standards
Founded in 1974, the International Atomic Energy Agency (IAEA) was created to set forth international standards for nuclear reactor safety. However, without a proper policing force, the guidelines set forth by the IAEA were often treated lightly or ignored completely. In 1986, the disaster at Chernobyl was evidence that international nuclear reactor safety was not to be taken lightly. Even in the midst of the Cold War, the Nuclear Regulatory Commission sought to improve the safety of Soviet nuclear reactors. As noted by IAEA Director General Hans Blix, "A radiation cloud doesn't know international boundaries." The NRC showed the Soviets the safety guidelines used in the US: capable regulation, safety-minded operations, and effective plant designs. The Soviets, however, had their own priority: keeping the plant running at all costs. In the end, the same shift between deterministic safety designs to probabilistic safety designs prevailed. In 1989, the World Association of Nuclear Operators (WANO) was formed to cooperate with the IAEA to ensure the same three pillars of reactor safety across international borders. In 1991, WANO concluded (using a probabilistic safety approach) that all former communist-controlled nuclear reactors could not be trusted, and should be closed. Compared to a "Nuclear Marshall Plan", efforts were taken throughout the 1990s and 2000s to ensure international standards of safety for all nuclear reactors.
See also
Debris fallout
Dirty bomb
Fallout: An American Nuclear Tragedy
Fallout Protection—U.S. government booklet
Effects of nuclear explosions
Fallout (RTÉ drama)—Irish drama exploring scenarios following a nuclear accident at Sellafield.
Fallout (series)
Fallout shelter
Fission product
Hot particle
Human radiation experiments
List of nuclear accidents
Lists of nuclear disasters and radioactive incidents
Neutron bomb
Mutation breeding#Radiation breeding
Nuclear fallout effects on an ecosystem
Nuclear terrorism
Nuclear War Survival Skills by Cresson Kearny
Nuclear weapon design
Potassium iodide
Project GABRIEL
Protect and Survive, a series of booklets and a public information film series produced for the British government in the 1970s and 1980s.
Radioactive contamination
Radiation poisoning
Radiation biology
Radioactive waste
Radiological weapon
Joseph Rotblat
Salted bomb
Survival Under Atomic Attack, an official U.S. government booklet regarding the effects of a nuclear attack.
References
Further reading
Glasstone, Samuel and Dolan, Philip J., The Effects of Nuclear Weapons (third edition), U.S. Government Printing Office, 1977. (Available Online)
NATO Handbook on the Medical Aspects of NBC Defensive Operations (Part I – Nuclear), Departments of the Army, Navy, and Air Force, Washington, D.C., 1996, (Available Online)
Smyth, H. DeW., Atomic Energy for Military Purposes, Princeton University Press, 1945. (Smyth Report)
The Effects of Nuclear War, Office of Technology Assessment (May 1979), (Available Online )
T. Imanaka, S. Fukutani, M. Yamamoto, A. Sakaguchi and M. Hoshi, J. Radiation Research, 2006, 47, Suppl A121–A127.
Sheldon Novick, The Careless Atom (Boston MA: Houghton Mifflin Co., 1969), p. 98
External links
NUKEMAP3D – a 3D nuclear weapons effects simulator powered by Google Maps. It simulates the effects of nuclear weapons upon geographic areas.
Aftermath of war
Fallout
Radiation health effects
Environmental impact of nuclear power
Radiobiology
Radioactive contamination
Fallout
+
Radiological weapons | Nuclear fallout | [
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"nan",
"Nuclear physics",
"Radiation effects",
"Radioactivity"
] |
53,686 | https://en.wikipedia.org/wiki/Archimedes%27%20screw | The Archimedes' screw, also known as the Archimedean screw, hydrodynamic screw, water screw or Egyptian screw, is one of the earliest hydraulic machines named after Greek mathematician Archimedes who first described it around 234 BC, although the device had been used in Ancient Egypt. It is a reversible hydraulic machine, and there are several examples of Archimedes screw installations where the screw can operate at different times as either pump or generator, depending on needs for power and watercourse flow.
As a machine used for lifting water from a low-lying body of water into irrigation ditches, water is lifted by turning a screw-shaped surface inside a pipe. In the modern world, Archimedes screw pumps are widely used in wastewater treatment plants and for dewatering low-lying regions. Run in reverse, Archimedes screw turbines act as a new form of small hydroelectric powerplant that can be applied even in low head sites. Such generators operate in a wide range of flows (0.01 to 14.5 ) and heads (0.1 m to 10 m), including low heads and moderate flow rates that is not ideal for traditional turbines and not occupied by high performance technologies.
History
Earliest records
The screw pump is the oldest positive displacement pump. The first records of a water screw, or screw pump, date back to Hellenistic Egypt before the 3rd century BC. The Egyptian screw, used to lift water from the Nile, was composed of tubes wound round a cylinder; as the entire unit rotates, water is lifted within the spiral tube to the higher elevation. A later screw pump design from Egypt had a spiral groove cut on the outside of a solid wooden cylinder and then the cylinder was covered by boards or sheets of metal closely covering the surfaces between the grooves.
Some researchers have proposed this device was used to irrigate the Hanging Gardens of Babylon, one of the Seven Wonders of the Ancient World. A cuneiform inscription of Assyrian King Sennacherib (704–681 BC) has been interpreted by Stephanie Dalley to describe casting water screws in bronze some 350 years earlier. This is consistent with Greek historian Strabo, who describes the Hanging Gardens as irrigated by screws.
Archimedes' role
The screw pump was later introduced from Hellenistic Egypt to Greece. It was described by Archimedes, on the occasion of his visit to Egypt, circa 234 BC. This tradition may reflect only that the apparatus was unknown to the Greeks before Hellenistic times. Athenaeus of Naucratis quotes a certain Moschion in a description on how Hiero II of Syracuse commissioned the design of the Syracusia, a luxury ship which would be a display of naval power. It is said to have been the largest ship built in classical antiquity and was launched by Archimedes who designed device with a revolving screw-shaped blade inside a cylinder to remove any potential water leaking through the hull. Archimedes' screw was turned by hand, and could also be used to transfer water from a low-lying body of water into irrigation canals.
Archimedes never claimed credit for its invention, but it was attributed to him 200 years later by Diodorus, who believed that Archimedes invented the screw pump in Egypt. Depictions of Greek and Roman water screws show them being powered by a human treading on the outer casing to turn the entire apparatus as one piece, which would require that the casing be rigidly attached to the screw.
Development and modern use
German engineer Konrad Kyeser equipped the Archimedes screw with a crank mechanism in his Bellifortis (1405). This mechanism quickly replaced the ancient practice of working the pipe by treading. The world's first seagoing steamship driven by a screw propeller was the SS Archimedes, which was launched in 1839 and named in honor of Archimedes and his work on the screw. Developments in maritime transport occurred over the next 180 years from the Fawcett, Preston and Company double blade design and patents by Sharrow Marine to address rotary propulsion and flow control on boating vessels through loop propellers. Electricity generation through hydropower pumps such as the Meriden project operated by New England Hydropower also uses Archimedes screw to direct water into the top, rather than the bottom, of the screw which forces it to rotate.
Archimedes screws are used in sewage treatment plants because they cope well with varying rates of flow and with suspended solids. Screw turbines (ASTs) are a new form of generator for small hydroelectric powerplants that could be applied even in low-head sites. The low rotation speed of ASTs reduces negative impacts on aquatic life and fish. This technology is used primarily at fish hatcheries to lift fish safely from ponds and transport them to another location. An Archimedes screw was used in the successful 2001 stabilization of the Leaning Tower of Pisa. Small amounts of subsoil saturated by groundwater were removed from far below the north side of the tower, and the weight of the tower itself corrected the lean.
Other inventions using Archimedes screws include the auger conveyor in a snow blower, grain elevator, concrete mixer and chocolate fountain.
Design
The Archimedes screw consists of a screw (a helical surface surrounding a central cylindrical shaft) inside a hollow pipe. The screw is usually turned by windmill, manual labor, cattle, or by modern means, such as a motor. As the shaft turns, the bottom end scoops up a volume of water. This water is then pushed up the tube by the rotating helicoid until it pours out from the top of the tube.
The contact surface between the screw and the pipe does not need to be perfectly watertight, as long as the amount of water being scooped with each turn is large compared to the amount of water leaking out of each section of the screw per turn. If water from one section leaks into the next lower one, it will be transferred upwards by the next segment of the screw.
In some designs, the screw is fused to the casing and they both rotate together, instead of the screw turning within a stationary casing. The screw could be sealed to the casing with pitch resin or other adhesive, or the screw and casing could be cast together as a single piece in bronze.
The design of the everyday Greek and Roman water screw, in contrast to the heavy bronze device of Sennacherib, with its problematic drive chains, has a powerful simplicity. A double or triple helix was built of wood strips (or occasionally bronze sheeting) around a heavy wooden pole. A cylinder was built around the helices using long, narrow boards fastened to their periphery and waterproofed with pitch.
Studies show that the volume of flow passes through Archimedes screws is a function of inlet depth, diameter and rotation speed of the screw. Therefore, the following analytical equation could be used to design Archimedes screws:
where is in and:
: Rotation speed of the Archimedes screw (rad/s)
: Volumetric flow rate
Based on the common standards that the Archimedes screw designers use this analytical equation could be simplified as:
The value of η could simply determinate using the graph or graph. By determination of , other design parameters of Archimedes screws can be calculated using a step-by-step analytical method.
Variants
A screw conveyor is a similar device which transports bulk materials such as powders and cereal grains. It is contained within a tube and turned by a motor to deliver material from one end of the conveyor to the other and particularly suitable for transport of granular materials such as plastic granules used in injection moulding. It may also be used to transport liquids. In industrial control applications, the conveyor may be used as a rotary feeder or variable rate feeder to deliver a measured rate or quantity of material into a process.
A variant of the Archimedes screw can also be found in some injection moulding machines, die casting machines and extrusion of plastics, which employ a screw of decreasing pitch to compress and melt the material. It is also used in a rotary-screw air compressor. On a much larger scale, Archimedes's screws of decreasing pitch are used for the compaction of waste material.
Reverse action
If water is fed into the top of an Archimedes screw, it will force the screw to rotate. The rotating shaft can then be used to drive an electric generator. Such an installation has the same benefits as using the screw for pumping: the ability to handle very dirty water and widely varying rates of flow at high efficiency. Settle Hydro and Torrs Hydro are two reverse screw micro hydro schemes operating in England. The screw works well as a generator at low heads, commonly found in English rivers, including the Thames, powering Windsor Castle.
See also
Archimedean spiral
Screw-propelled vehicle
Screw (simple machine)
Spiral pump
Toroidal propeller
Vitruvius
Notes
Sources
P. J. Kantert: "Manual for Archimedean Screw Pump", Hirthammer Verlag 2008, .
P. J. Kantert: "Praxishandbuch Schneckenpumpe", Hirthammer Verlag 2008, .
P. J. Kantert: "Praxishandbuch Schneckenpumpe" - 2nd edition 2020, DWA, .
Nuernbergk, D. and Rorres C.: „An Analytical Model for the Water Inflow of an Archimedes Screw Used in Hydropower Generation", ASCE Journal of Hydraulic Engineering, Published: 23 July 2012
Nuernbergk D. M.: "Wasserkraftschnecken – Berechnung und optimaler Entwurf von archimedischen Schnecken als Wasserkraftmaschine", Verlag Moritz Schäfer, Detmold, 1. Edition. 2012, 272 papes,
Rorres C.: "The turn of the Screw: Optimum design of an Archimedes Screw", ASCE Journal of Hydraulic Engineering, Volume 126, Number 1, Jan.2000, pp. 72–80
Nagel, G.; Radlik, K.: Wasserförderschnecken – Planung, Bau und Betrieb von Wasserhebeanlagen; Udo Pfriemer Buchverlag in der Bauverlag GmbH, Wiesbaden, Berlin (1988)
External links
The Turn of the Screw: Optimal Design of an Archimedes Screw, by Chris Rorres, PhD.
"Archimedean Screw" by Sándor Kabai, Wolfram Demonstrations Project, 2007.
"Archimedes Screw Examples Various sources, 2021
Pumps
Screws
Screw, Archimedes
History of mining
Rotating machines
Egyptian inventions
Ancient inventions
Hanging Gardens of Babylon
Ptolemaic Kingdom
Sennacherib | Archimedes' screw | [
"Physics",
"Chemistry",
"Technology"
] | 2,227 | [
"Pumps",
"Machines",
"Turbomachinery",
"Physical systems",
"Rotating machines",
"Hydraulics"
] |
53,694 | https://en.wikipedia.org/wiki/Pig%20iron | Pig iron, also known as crude iron, is an intermediate good used by the iron industry in the production of steel. It is developed by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with silica and other dross, which makes it brittle and not useful directly as a material except for limited applications.
Etymology
The traditional shape of the molds used for pig iron ingots is a branching structure formed in sand, with many individual ingots at right angles to a central channel or "runner", resembling a litter of piglets being nursed by a sow. When the metal had cooled and hardened, the smaller ingots (the "pigs") were simply broken from the runner (the "sow"), hence the name "pig iron". As pig iron is intended for remelting, the uneven size of the ingots and the inclusion of small amounts of sand are insignificant issues when compared to the ease of casting and handling.
History
The Chinese were already making pig iron during the later Zhou dynasty (which ended in 256 BC). Furnaces such as Lapphyttan in Sweden may date back as far back as the 12th century; and some in the County of Mark dating back to the 13th century, which is now part of Westphalia, Germany. It remains to be established whether these northern European developments were derived from the Chinese ones. Wagner has postulated a possible link via Persian contacts with China along the Silk Road and Viking contacts with Persia, but there is a chronological gap between the Viking period and Lapphyttan.
Smelting and producing wrought iron were known in ancient Europe and the Middle East, but it was produced in bloomeries by direct reduction. Small prills of pig iron dispersed in slag are produced in all iron furnaces, but the operator of a bloomery had to avoid conditions causing the phase transition of the iron into liquid in the furnace, as the prill globules or any resulting pig iron are not malleable so can't be hammered in a single piece. Alternatively, decarburizing the pig iron into steel was an extremely tedious process using medieval technology, so in Europe before the Middle Ages the prills were discarded with the slag.
Uses
Traditionally, pig iron was worked into wrought iron in finery forges, later puddling furnaces, and more recently, into steel. In these processes, pig iron is melted and a strong current of air is directed over it while it is stirred or agitated. This causes the dissolved impurities (such as silicon) to be thoroughly oxidized. An intermediate product of puddling is known as refined pig iron, finers metal, or refined iron.
Pig iron can also be used to produce gray iron. This is achieved by remelting pig iron, often along with substantial quantities of steel and scrap iron, removing undesirable contaminants, adding alloys, and adjusting the carbon content. Ductile iron can also be produced using certain high purity grades of pig iron; depending on the grade of ductile iron being produced, the pig irons chosen may be low in the elements silicon, manganese, sulfur and phosphorus. High purity pig iron is used to dilute any elements in a ductile iron charge which may be harmful to the ductile iron process (except carbon).
Modern uses
Pig iron was historically poured directly out of the bottom of the blast furnace through a trough into a ladle car for transfer to the steel mill in mostly liquid form; in this state, the pig iron was referred to as hot metal. The hot metal was then poured into a steelmaking vessel to produce steel, typically an electric arc furnace, induction furnace or basic oxygen furnace, where the excess carbon is burned off and the alloy composition controlled. Earlier processes for this included the finery forge, the puddling furnace, the Bessemer process, and the open hearth furnace.
Modern steel mills and direct-reduction iron plants transfer the molten iron to a ladle for immediate use in the steel making furnaces or cast it into pigs on a pig-casting machine for reuse or resale. Modern pig casting machines produce stick pigs, which break into smaller piglets at discharge.
References
Ancient Egyptian technology
Ancient Roman technology
Chinese inventions
Ferrous alloys
Iron
Metalworking
Smelting
Steelmaking | Pig iron | [
"Chemistry"
] | 894 | [
"Ferrous alloys",
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53,696 | https://en.wikipedia.org/wiki/Division%20%28mathematics%29 | Division is one of the four basic operations of arithmetic. The other operations are addition, subtraction, and multiplication. What is being divided is called the dividend, which is divided by the divisor, and the result is called the quotient.
At an elementary level the division of two natural numbers is, among other possible interpretations, the process of calculating the number of times one number is contained within another. For example, if 20 apples are divided evenly between 4 people, everyone receives 5 apples (see picture). However, this number of times or the number contained (divisor) need not be integers.
The division with remainder or Euclidean division of two natural numbers provides an integer quotient, which is the number of times the second number is completely contained in the first number, and a remainder, which is the part of the first number that remains, when in the course of computing the quotient, no further full chunk of the size of the second number can be allocated. For example, if 21 apples are divided between 4 people, everyone receives 5 apples again, and 1 apple remains.
For division to always yield one number rather than an integer quotient plus a remainder, the natural numbers must be extended to rational numbers or real numbers. In these enlarged number systems, division is the inverse operation to multiplication, that is means , as long as is not zero. If , then this is a division by zero, which is not defined. In the 21-apples example, everyone would receive 5 apple and a quarter of an apple, thus avoiding any leftover.
Both forms of division appear in various algebraic structures, different ways of defining mathematical structure. Those in which a Euclidean division (with remainder) is defined are called Euclidean domains and include polynomial rings in one indeterminate (which define multiplication and addition over single-variabled formulas). Those in which a division (with a single result) by all nonzero elements is defined are called fields and division rings. In a ring the elements by which division is always possible are called the units (for example, 1 and −1 in the ring of integers). Another generalization of division to algebraic structures is the quotient group, in which the result of "division" is a group rather than a number.
Introduction
The simplest way of viewing division is in terms of quotition and partition: from the quotition perspective, means the number of 5s that must be added to get 20. In terms of partition, means the size of each of 5 parts into which a set of size 20 is divided. For example, 20 apples divide into five groups of four apples, meaning that "twenty divided by five is equal to four". This is denoted as , or . In the example, 20 is the dividend, 5 is the divisor, and 4 is the quotient.
Unlike the other basic operations, when dividing natural numbers there is sometimes a remainder that will not go evenly into the dividend; for example, leaves a remainder of 1, as 10 is not a multiple of 3. Sometimes this remainder is added to the quotient as a fractional part, so is equal to or , but in the context of integer division, where numbers have no fractional part, the remainder is kept separately (or exceptionally, discarded or rounded). When the remainder is kept as a fraction, it leads to a rational number. The set of all rational numbers is created by extending the integers with all possible results of divisions of integers.
Unlike multiplication and addition, division is not commutative, meaning that is not always equal to . Division is also not, in general, associative, meaning that when dividing multiple times, the order of division can change the result. For example, , but (where the use of parentheses indicates that the operations inside parentheses are performed before the operations outside parentheses).
Division is traditionally considered as left-associative. That is, if there are multiple divisions in a row, the order of calculation goes from left to right:
Division is right-distributive over addition and subtraction, in the sense that
This is the same for multiplication, as . However, division is not left-distributive, as
For example but
This is unlike the case in multiplication, which is both left-distributive and right-distributive, and thus distributive.
Notation
Division is often shown in algebra and science by placing the dividend over the divisor with a horizontal line, also called a fraction bar, between them. For example, "a divided by b" can be written as:
which can also be read out loud as "divide a by b" or "a over b". A way to express division all on one line is to write the dividend (or numerator), then a slash, then the divisor (or denominator), as follows:
This is the usual way of specifying division in most computer programming languages, since it can easily be typed as a simple sequence of ASCII characters. (It is also the only notation used for quotient objects in abstract algebra.) Some mathematical software, such as MATLAB and GNU Octave, allows the operands to be written in the reverse order by using the backslash as the division operator:
A typographical variation halfway between these two forms uses a solidus (fraction slash), but elevates the dividend and lowers the divisor:
Any of these forms can be used to display a fraction. A fraction is a division expression where both dividend and divisor are integers (typically called the numerator and denominator), and there is no implication that the division must be evaluated further. A second way to show division is to use the division sign (÷, also known as obelus though the term has additional meanings), common in arithmetic, in this manner:
This form is infrequent except in elementary arithmetic. ISO 80000-2-9.6 states it should not be used. This division sign is also used alone to represent the division operation itself, as for instance as a label on a key of a calculator. The obelus was introduced by Swiss mathematician Johann Rahn in 1659 in Teutsche Algebra. The ÷ symbol is used to indicate subtraction in some European countries, so its use may be misunderstood.
In some non-English-speaking countries, a colon is used to denote division:
This notation was introduced by Gottfried Wilhelm Leibniz in his 1684 Acta eruditorum. Leibniz disliked having separate symbols for ratio and division. However, in English usage the colon is restricted to expressing the related concept of ratios.
Since the 19th century, US textbooks have used or to denote a divided by b, especially when discussing long division. The history of this notation is not entirely clear because it evolved over time.
Computing
Manual methods
Division is often introduced through the notion of "sharing out" a set of objects, for example a pile of lollies, into a number of equal portions. Distributing the objects several at a time in each round of sharing to each portion leads to the idea of 'chunking' a form of division where one repeatedly subtracts multiples of the divisor from the dividend itself.
By allowing one to subtract more multiples than what the partial remainder allows at a given stage, more flexible methods, such as the bidirectional variant of chunking, can be developed as well.
More systematically and more efficiently, two integers can be divided with pencil and paper with the method of short division, if the divisor is small, or long division, if the divisor is larger. If the dividend has a fractional part (expressed as a decimal fraction), one can continue the procedure past the ones place as far as desired. If the divisor has a fractional part, one can restate the problem by moving the decimal to the right in both numbers until the divisor has no fraction, which can make the problem easier to solve (e.g., 10/2.5 = 100/25 = 4).
Division can be calculated with an abacus.
Logarithm tables can be used to divide two numbers, by subtracting the two numbers' logarithms, then looking up the antilogarithm of the result.
Division can be calculated with a slide rule by aligning the divisor on the C scale with the dividend on the D scale. The quotient can be found on the D scale where it is aligned with the left index on the C scale. The user is responsible, however, for mentally keeping track of the decimal point.
By computer
Modern calculators and computers compute division either by methods similar to long division, or by faster methods; see Division algorithm.
In modular arithmetic (modulo a prime number) and for real numbers, nonzero numbers have a multiplicative inverse. In these cases, a division by may be computed as the product by the multiplicative inverse of . This approach is often associated with the faster methods in computer arithmetic.
Division in different contexts
Euclidean division
Euclidean division is the mathematical formulation of the outcome of the usual process of division of integers. It asserts that, given two integers, a, the dividend, and b, the divisor, such that b ≠ 0, there are unique integers q, the quotient, and r, the remainder, such that a = bq + r and 0 ≤ r < , where denotes the absolute value of b.
Of integers
Integers are not closed under division. Apart from division by zero being undefined, the quotient is not an integer unless the dividend is an integer multiple of the divisor. For example, 26 cannot be divided by 11 to give an integer. Such a case uses one of five approaches:
Say that 26 cannot be divided by 11; division becomes a partial function.
Give an approximate answer as a floating-point number. This is the approach usually taken in numerical computation.
Give the answer as a fraction representing a rational number, so the result of the division of 26 by 11 is (or as a mixed number, so ) Usually the resulting fraction should be simplified: the result of the division of 52 by 22 is also . This simplification may be done by factoring out the greatest common divisor.
Give the answer as an integer quotient and a remainder, so To make the distinction with the previous case, this division, with two integers as result, is sometimes called Euclidean division, because it is the basis of the Euclidean algorithm.
Give the integer quotient as the answer, so This is the floor function applied to case 2 or 3. It is sometimes called integer division, and denoted by "//".
Dividing integers in a computer program requires special care. Some programming languages treat integer division as in case 5 above, so the answer is an integer. Other languages, such as MATLAB and every computer algebra system return a rational number as the answer, as in case 3 above. These languages also provide functions to get the results of the other cases, either directly or from the result of case 3.
Names and symbols used for integer division include div, /, \, and %. Definitions vary regarding integer division when the dividend or the divisor is negative: rounding may be toward zero (so called T-division) or toward −∞ (F-division); rarer styles can occur – see modulo operation for the details.
Divisibility rules can sometimes be used to quickly determine whether one integer divides exactly into another.
Of rational numbers
The result of dividing two rational numbers is another rational number when the divisor is not 0. The division of two rational numbers p/q and r/s can be computed as
All four quantities are integers, and only p may be 0. This definition ensures that division is the inverse operation of multiplication.
Of real numbers
Division of two real numbers results in another real number (when the divisor is nonzero). It is defined such that a/b = c if and only if a = cb and b ≠ 0.
Of complex numbers
Dividing two complex numbers (when the divisor is nonzero) results in another complex number, which is found using the conjugate of the denominator:
This process of multiplying and dividing by is called 'realisation' or (by analogy) rationalisation. All four quantities p, q, r, s are real numbers, and r and s may not both be 0.
Division for complex numbers expressed in polar form is simpler than the definition above:
Again all four quantities p, q, r, s are real numbers, and r may not be 0.
Of polynomials
One can define the division operation for polynomials in one variable over a field. Then, as in the case of integers, one has a remainder. See Euclidean division of polynomials, and, for hand-written computation, polynomial long division or synthetic division.
Of matrices
One can define a division operation for matrices. The usual way to do this is to define , where denotes the inverse of B, but it is far more common to write out explicitly to avoid confusion. An elementwise division can also be defined in terms of the Hadamard product.
Left and right division
Because matrix multiplication is not commutative, one can also define a left division or so-called backslash-division as . For this to be well defined, need not exist, however does need to exist. To avoid confusion, division as defined by is sometimes called right division or slash-division in this context.
With left and right division defined this way, is in general not the same as , nor is the same as . However, it holds that and .
Pseudoinverse
To avoid problems when and/or do not exist, division can also be defined as multiplication by the pseudoinverse. That is, and , where and denote the pseudoinverses of and .
Abstract algebra
In abstract algebra, given a magma with binary operation ∗ (which could nominally be termed multiplication), left division of b by a (written ) is typically defined as the solution x to the equation , if this exists and is unique. Similarly, right division of b by a (written ) is the solution y to the equation . Division in this sense does not require ∗ to have any particular properties (such as commutativity, associativity, or an identity element). A magma for which both and exist and are unique for all a and all b (the Latin square property) is a quasigroup. In a quasigroup, division in this sense is always possible, even without an identity element and hence without inverses.
"Division" in the sense of "cancellation" can be done in any magma by an element with the cancellation property. Examples include matrix algebras, quaternion algebras, and quasigroups. In an integral domain, where not every element need have an inverse, division by a cancellative element a can still be performed on elements of the form ab or ca by left or right cancellation, respectively. If a ring is finite and every nonzero element is cancellative, then by an application of the pigeonhole principle, every nonzero element of the ring is invertible, and division by any nonzero element is possible. To learn about when algebras (in the technical sense) have a division operation, refer to the page on division algebras. In particular Bott periodicity can be used to show that any real normed division algebra must be isomorphic to either the real numbers R, the complex numbers C, the quaternions H, or the octonions O.
Calculus
The derivative of the quotient of two functions is given by the quotient rule:
Division by zero
Division of any number by zero in most mathematical systems is undefined, because zero multiplied by any finite number always results in a product of zero. Entry of such an expression into most calculators produces an error message. However, in certain higher level mathematics division by zero is possible by the zero ring and algebras such as wheels. In these algebras, the meaning of division is different from traditional definitions.
Calculator
Enter two numbers to find their quotient:
/ =
See also
400AD Sunzi division algorithm
Division by two
Galley division
Inverse element
Order of operations
Repeating decimal
Rule of division (combinatorics)
Notes
References
External links
Planetmath division
Division on a Japanese abacus selected from Abacus: Mystery of the Bead
Chinese Short Division Techniques on a Suan Pan
Elementary arithmetic | Division (mathematics) | [
"Mathematics"
] | 3,432 | [
"Elementary mathematics",
"Arithmetic",
"Elementary arithmetic"
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53,702 | https://en.wikipedia.org/wiki/Boltzmann%20constant | The Boltzmann constant ( or ) is the proportionality factor that relates the average relative thermal energy of particles in a gas with the thermodynamic temperature of the gas. It occurs in the definitions of the kelvin (K) and the gas constant, in Planck's law of black-body radiation and Boltzmann's entropy formula, and is used in calculating thermal noise in resistors. The Boltzmann constant has dimensions of energy divided by temperature, the same as entropy and heat capacity. It is named after the Austrian scientist Ludwig Boltzmann.
As part of the 2019 revision of the SI, the Boltzmann constant is one of the seven "defining constants" that have been defined so as to have exact finite decimal values in SI units. They are used in various combinations to define the seven SI base units. The Boltzmann constant is defined to be exactly joules per kelvin. Correspondingly, the SI units for temperature and energy are calibrated to one another so that kelvin = joules.
Roles of the Boltzmann constant
Macroscopically, the ideal gas law states that, for an ideal gas, the product of pressure and volume is proportional to the product of amount of substance and absolute temperature :
where is the molar gas constant (). Introducing the Boltzmann constant as the gas constant per molecule (NA being the Avogadro constant) transforms the ideal gas law into an alternative form:
where is the number of molecules of gas.
Role in the equipartition of energy
Given a thermodynamic system at an absolute temperature , the average thermal energy carried by each microscopic degree of freedom in the system is (i.e., about , or , at room temperature). This is generally true only for classical systems with a large number of particles, and in which quantum effects are negligible.
In classical statistical mechanics, this average is predicted to hold exactly for homogeneous ideal gases. Monatomic ideal gases (the six noble gases) possess three degrees of freedom per atom, corresponding to the three spatial directions. According to the equipartition of energy this means that there is a thermal energy of per atom. This corresponds very well with experimental data. The thermal energy can be used to calculate the root-mean-square speed of the atoms, which turns out to be inversely proportional to the square root of the atomic mass. The root mean square speeds found at room temperature accurately reflect this, ranging from for helium, down to for xenon.
Kinetic theory gives the average pressure for an ideal gas as
Combination with the ideal gas law
shows that the average translational kinetic energy is
Considering that the translational motion velocity vector has three degrees of freedom (one for each dimension) gives the average energy per degree of freedom equal to one third of that, i.e. .
The ideal gas equation is also obeyed closely by molecular gases; but the form for the heat capacity is more complicated, because the molecules possess additional internal degrees of freedom, as well as the three degrees of freedom for movement of the molecule as a whole. Diatomic gases, for example, possess a total of six degrees of simple freedom per molecule that are related to atomic motion (three translational, two rotational, and one vibrational). At lower temperatures, not all these degrees of freedom may fully participate in the gas heat capacity, due to quantum mechanical limits on the availability of excited states at the relevant thermal energy per molecule.
Role in Boltzmann factors
More generally, systems in equilibrium at temperature have probability of occupying a state with energy weighted by the corresponding Boltzmann factor:
where is the partition function. Again, it is the energy-like quantity that takes central importance.
Consequences of this include (in addition to the results for ideal gases above) the Arrhenius equation in chemical kinetics.
Role in the statistical definition of entropy
In statistical mechanics, the entropy of an isolated system at thermodynamic equilibrium is defined as the natural logarithm of , the number of distinct microscopic states available to the system given the macroscopic constraints (such as a fixed total energy ):
This equation, which relates the microscopic details, or microstates, of the system (via ) to its macroscopic state (via the entropy ), is the central idea of statistical mechanics. Such is its importance that it is inscribed on Boltzmann's tombstone.
The constant of proportionality serves to make the statistical mechanical entropy equal to the classical thermodynamic entropy of Clausius:
One could choose instead a rescaled dimensionless entropy in microscopic terms such that
This is a more natural form and this rescaled entropy exactly corresponds to Shannon's subsequent information entropy.
The characteristic energy is thus the energy required to increase the rescaled entropy by one nat.
Thermal voltage
In semiconductors, the Shockley diode equation—the relationship between the flow of electric current and the electrostatic potential across a p–n junction—depends on a characteristic voltage called the thermal voltage, denoted by . The thermal voltage depends on absolute temperature as
where is the magnitude of the electrical charge on the electron with a value Equivalently,
At room temperature , is approximately which can be derived by plugging in the values as follows:
At the standard state temperature of , it is approximately . The thermal voltage is also important in plasmas and electrolyte solutions (e.g. the Nernst equation); in both cases it provides a measure of how much the spatial distribution of electrons or ions is affected by a boundary held at a fixed voltage.
History
The Boltzmann constant is named after its 19th century Austrian discoverer, Ludwig Boltzmann. Although Boltzmann first linked entropy and probability in 1877, the relation was never expressed with a specific constant until Max Planck first introduced , and gave a more precise value for it (, about 2.5% lower than today's figure), in his derivation of the law of black-body radiation in 1900–1901. Before 1900, equations involving Boltzmann factors were not written using the energies per molecule and the Boltzmann constant, but rather using a form of the gas constant , and macroscopic energies for macroscopic quantities of the substance. The iconic terse form of the equation on Boltzmann's tombstone is in fact due to Planck, not Boltzmann. Planck actually introduced it in the same work as his eponymous .
In 1920, Planck wrote in his Nobel Prize lecture:
This "peculiar state of affairs" is illustrated by reference to one of the great scientific debates of the time. There was considerable disagreement in the second half of the nineteenth century as to whether atoms and molecules were real or whether they were simply a heuristic tool for solving problems. There was no agreement whether chemical molecules, as measured by atomic weights, were the same as physical molecules, as measured by kinetic theory. Planck's 1920 lecture continued:
In versions of SI prior to the 2019 revision of the SI, the Boltzmann constant was a measured quantity rather than having a fixed numerical value. Its exact definition also varied over the years due to redefinitions of the kelvin (see ) and other SI base units (see ).
In 2017, the most accurate measures of the Boltzmann constant were obtained by acoustic gas thermometry, which determines the speed of sound of a monatomic gas in a triaxial ellipsoid chamber using microwave and acoustic resonances. This decade-long effort was undertaken with different techniques by several laboratories; it is one of the cornerstones of the 2019 revision of the SI. Based on these measurements, the CODATA recommended to be the final fixed value of the Boltzmann constant to be used for the International System of Units.
As a precondition for redefining the Boltzmann constant, there must be one experimental value with a relative uncertainty below 1 ppm, and at least one measurement from a second technique with a relative uncertainty below 3 ppm. The acoustic gas thermometry reached 0.2 ppm, and Johnson noise thermometry reached 2.8 ppm.
Value in different units
Since is a proportionality factor between temperature and energy, its numerical value depends on the choice of units for energy and temperature. The small numerical value of the Boltzmann constant in SI units means a change in temperature by 1 K only changes a particle's energy by a small amount. A change of is defined to be the same as a change of . The characteristic energy is a term encountered in many physical relationships.
The Boltzmann constant sets up a relationship between wavelength and temperature (dividing hc/k by a wavelength gives a temperature) with one micrometer being related to , and also a relationship between voltage and temperature (kT in units of eV corresponds to a voltage) with one volt being related to . The ratio of these two temperatures, / ≈ 1.239842, is the numerical value of hc in units of eV⋅μm.
Natural units
The Boltzmann constant provides a mapping from the characteristic microscopic energy to the macroscopic temperature scale . In fundamental physics, this mapping is often simplified by using the natural units of setting to unity. This convention means that temperature and energy quantities have the same dimensions. In particular, the SI unit kelvin becomes superfluous, being defined in terms of joules as . With this convention, temperature is always given in units of energy, and the Boltzmann constant is not explicitly needed in formulas.
This convention simplifies many physical relationships and formulas. For example, the equipartition formula for the energy associated with each classical degree of freedom ( above) becomes
As another example, the definition of thermodynamic entropy coincides with the form of information entropy:
where is the probability of each microstate.
See also
Committee on Data of the International Science Council
Thermodynamic beta
List of scientists whose names are used in physical constants
Notes
References
External links
Draft Chapter 2 for SI Brochure, following redefinitions of the base units (prepared by the Consultative Committee for Units)
Big step towards redefining the kelvin: Scientists find new way to determine Boltzmann constant
Constant
Fundamental constants
Statistical mechanics
Thermodynamics | Boltzmann constant | [
"Physics",
"Chemistry",
"Mathematics"
] | 2,091 | [
"Physical quantities",
"Physical constants",
"Thermodynamics",
"Statistical mechanics",
"Fundamental constants",
"Dynamical systems"
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53,711 | https://en.wikipedia.org/wiki/Henri%20Becquerel | Antoine Henri Becquerel (; ; 15 December 1852 – 25 August 1908) was a French physicist who shared the 1903 Nobel Prize in Physics with Pierre and Marie Curie for his discovery of radioactivity. The SI unit of radioactivity, the becquerel (Bq), is named after him.
Biography
Family and education
Becquerel was born in Paris, France, into a wealthy family which produced four generations of notable physicists, including Becquerel's grandfather (Antoine César Becquerel), father (Alexandre-Edmond Becquerel), and son (Jean Becquerel). Henri started off his education by attending the Lycée Louis-le-Grand school, a prep school in Paris. He studied engineering at the École Polytechnique and the École des Ponts et Chaussées.
Career
In Becquerel's early career, he became the third in his family to occupy the physics chair at the Muséum National d'Histoire Naturelle in 1892. Later on in 1894, Becquerel became chief engineer in the Department of Bridges and Highways before he started with his early experiments. Becquerel's earliest works centered on the subject of his doctoral thesis: the plane polarization of light, with the phenomenon of phosphorescence and absorption of light by crystals. Early in his career, Becquerel also studied the Earth's magnetic fields. In 1895, he was appointed as a professor at the École Polytechnique.
Becquerel's discovery of spontaneous radioactivity is a famous example of serendipity, of how chance favors the prepared mind. Becquerel had long been interested in phosphorescence, the emission of light of one color following the object's exposure to light of another color. In early 1896, there was a wave of excitement following Wilhelm Conrad Röntgen's discovery of X-rays on 5 January. During the experiment, Röntgen "found that the Crookes tubes he had been using to study cathode rays emitted a new kind of invisible ray that was capable of penetrating through black paper". Becquerel learned of Röntgen's discovery during a meeting of the French Academy of Sciences on 20 January where his colleague Henri Poincaré read out Röntgen's preprint paper. Becquerel "began looking for a connection between the phosphorescence he had already been investigating and the newly discovered x-rays" of Röntgen, and thought that phosphorescent materials might emit penetrating X-ray-like radiation when illuminated by bright sunlight; he had various phosphorescent materials including some uranium salts for his experiments.
Throughout the first weeks of February, Becquerel layered photographic plates with coins or other objects then wrapped this in thick black paper, placed phosphorescent materials on top, placed these in bright sun light for several hours. The developed plate showed shadows of the objects. Already on 24 February he reported his first results. However, the 26 and 27 February were dark and overcast during the day, so Becquerel left his layered plates in a dark cabinet for these days. He nevertheless proceeded to develop the plates on 1 March and then made his astonishing discovery: the object shadows were just as distinct when left in the dark as when exposed to sunlight. Both William Crookes and Becquerel's 18 year old son Jean witnessed the discovery.
By May 1896, after other experiments involving non-phosphorescent uranium salts, he arrived at the correct explanation, namely that the penetrating radiation came from the uranium itself, without any need for excitation by an external energy source. There followed a period of intense research into radioactivity, including the determination that the element thorium is also radioactive and the discovery of additional radioactive elements polonium and radium by Marie Skłodowska-Curie and her husband Pierre Curie. The intensive research of radioactivity led to Becquerel publishing seven papers on the subject in 1896. Becquerel's other experiments allowed him to research more into radioactivity and figure out different aspects of the magnetic field when radiation is introduced into the magnetic field. "When different radioactive substances were put in the magnetic field, they deflected in different directions or not at all, showing that there were three classes of radioactivity: negative, positive, and electrically neutral."
As often happens in science, radioactivity came close to being discovered nearly four decades earlier in 1857, when Abel Niépce de Saint-Victor, who was investigating photography under Michel Eugène Chevreul, observed that uranium salts emitted radiation that could darken photographic emulsions. By 1861, Niepce de Saint-Victor realized that uranium salts produce "a radiation that is invisible to our eyes". Niepce de Saint-Victor knew Edmond Becquerel, Henri Becquerel's father. In 1868, Edmond Becquerel published a book, La lumière: ses causes et ses effets (Light: Its causes and its effects). On page 50 of volume 2, Edmond noted that Niepce de Saint-Victor had observed that some objects that had been exposed to sunlight could expose photographic plates even in the dark. Niepce further noted that on the one hand, the effect was diminished if an obstruction were placed between a photographic plate and the object that had been exposed to the sun, but " … d'un autre côté, l'augmentation d'effet quand la surface insolée est couverte de substances facilement altérables à la lumière, comme le nitrate d'urane … " ( ... on the other hand, the increase in the effect when the surface exposed to the sun is covered with substances that are easily altered by light, such as uranium nitrate ... ).
Experiments
Describing them to the French Academy of Sciences on 27 February 1896, he said:
One wraps a Lumière photographic plate with a bromide emulsion in two sheets of very thick black paper, such that the plate does not become clouded upon being exposed to the sun for a day. One places on the sheet of paper, on the outside, a slab of the phosphorescent substance, and one exposes the whole to the sun for several hours. When one then develops the photographic plate, one recognizes that the silhouette of the phosphorescent substance appears in black on the negative. If one places between the phosphorescent substance and the paper a piece of money or a metal screen pierced with a cut-out design, one sees the image of these objects appear on the negative ... One must conclude from these experiments that the phosphorescent substance in question emits rays which pass through the opaque paper and reduce silver salts.Comptes Rendus 122: 420 (1896), translated by Carmen Giunta. Accessed 02 March 2019.
But further experiments led him to doubt and then abandon this hypothesis. On 2 March 1896 he reported:
I will insist particularly upon the following fact, which seems to me quite important and beyond the phenomena which one could expect to observe: The same crystalline crusts [of potassium uranyl sulfate], arranged the same way with respect to the photographic plates, in the same conditions and through the same screens, but sheltered from the excitation of incident rays and kept in darkness, still produce the same photographic images. Here is how I was led to make this observation: among the preceding experiments, some had been prepared on Wednesday the 26th and Thursday the 27th of February, and since the sun was out only intermittently on these days, I kept the apparatuses prepared and returned the cases to the darkness of a bureau drawer, leaving in place the crusts of the uranium salt. Since the sun did not come out in the following days, I developed the photographic plates on the 1st of March, expecting to find the images very weak. Instead the silhouettes appeared with great intensity ... One hypothesis which presents itself to the mind naturally enough would be to suppose that these rays, whose effects have a great similarity to the effects produced by the rays studied by M. Lenard and M. Röntgen, are invisible rays emitted by phosphorescence and persisting infinitely longer than the duration of the luminous rays emitted by these bodies. However, the present experiments, without being contrary to this hypothesis, do not warrant this conclusion. I hope that the experiments which I am pursuing at the moment will be able to bring some clarification to this new class of phenomena.Comptes Rendus 122: 501–503 (1896), translated by Carmen Giunta. Accessed 02 March 2019.
Late career
Later in his life in 1900, Becquerel measured the properties of beta particles, and he realized that they had the same measurements as high speed electrons leaving the nucleus. In 1901 Becquerel made the discovery that radioactivity could be used for medicine. Henri made this discovery when he left a piece of radium in his vest pocket and noticed that he had been burnt by it. This discovery led to the development of radiotherapy, which is now used to treat cancer. In 1908 Becquerel was elected president of Académie des Sciences, but he died on 25 August 1908, at the age of 55, in Le Croisic, France. He died of a heart attack, but it was reported that "he had developed serious burns on his skin, likely from the handling of radioactive materials."
Honors and awards
In 1889, Becquerel became a member of the Académie des Sciences. In 1900, Becquerel won the Rumford Medal for his discovery of the radioactivity of uranium and he awarded the title of an Officer of the Legion of Honour. The Berlin-Brandenburg Academy of Sciences and Humanities awarded him the Helmholtz Medal in 1901. In 1902, he was elected as a member of the American Philosophical Society. In 1903, Henri shared a Nobel Prize in Physics with Pierre Curie and Marie Curie for the discovery of spontaneous radioactivity. In 1905, he was awarded the Barnard Medal by the U.S. National Academy of Sciences. In 1906, Henri was elected Vice Chairman of the academy, and in 1908, the year of his death, Becquerel was elected Permanent Secretary of the Académie des Sciences. During his lifetime, Becquerel was honored with membership into the and the Royal Academy of Berlin. Becquerel was elected a Foreign Member of the Royal Society (ForMemRS) in 1908. Becquerel has been honored with being the namesake of many different scientific discoveries. The SI unit for radioactivity, the becquerel (Bq), is named after him.
There is a crater named Becquerel on the Moon and also a crater named Becquerel on Mars. The uranium-based mineral becquerelite was named after Henri. Minor planet 6914 Becquerel is named in his honor.
See also
A. E. Becquerel (his father)
Antoine César Becquerel (his grandfather)
Jean Becquerel (his son)
References
External links
including the Nobel Lecture, "On Radioactivity, a New Property of Matter", 11 December 1903
Becquerel short biography and the use of his name as a unit of measure in the SI
Annotated bibliography for Henri Becquerel from the Alsos Digital Library for Nuclear Issues
Henri Becquerel, SI-derived unit of radioactivity
"Henri Becquerel: The Discovery of Radioactivity", Becquerel's 1896 articles online and analyzed on BibNum [click 'à télécharger' for English version].
1852 births
1908 deaths
20th-century French physicists
Corps des ponts
École des Ponts ParisTech alumni
École Polytechnique alumni
Experimental physicists
Foreign associates of the National Academy of Sciences
Foreign members of the Royal Society
French Nobel laureates
French nuclear physicists
Members of the American Philosophical Society
Members of the French Academy of Sciences
Nobel laureates in Physics
Nuclear history of France
Presidents of the Société Française de Physique
Radioactivity
Scientists from Paris
Becquerel family | Henri Becquerel | [
"Physics",
"Chemistry"
] | 2,536 | [
"Radioactivity",
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53,716 | https://en.wikipedia.org/wiki/DV%20%28video%20format%29 | DV (from Digital Video) is a family of codecs and tape formats used for storing digital video, launched in 1995 by a consortium of video camera manufacturers led by Sony and Panasonic. It includes the recording or cassette formats DV, MiniDV, HDV, DVCAM, DVCPro, DVCPro50, DVCProHD, Digital8, and Digital-S. DV has been used primarily for video recording with camcorders in the amateur and professional sectors.
DV was designed to be a standard for home video using digital data instead of analog. Compared to the analog Video8/Hi8, VHS-C and VHS formats, DV features a higher video resolution (on par with professional-grade Digital Betacam) and also records audio digitally at 16-bit like CD. The most popular tape format using a DV codec was MiniDV; these cassettes measured just 6.35 mm/¼ inch, making it ideal for video cameras and rendering older analog formats obsolete. In the late 1990s and early 2000s, DV was strongly associated with the transition from analog to digital desktop video production, and also with several enduring "prosumer" camera designs such as the Sony VX-1000.
In 2003, DV was joined by a successor format called HDV, which used the same tapes but with an updated video codec with high-definition video; HDV cameras could typically switch between DV and HDV recording modes. In the 2010s, DV rapidly grew obsolete as cameras using memory cards and solid-state drives became the norm, recording at higher bitrates and resolutions that were impractical for mechanical tape formats. Additionally, as manufacturers switched from interlaced to superior progressive recording methods, they broke the interoperability that had previously been maintained across multiple generations of DV and HDV equipment.
Development
DV was developed by the HD Digital VCR Association: in April 1994, 55 companies worldwide took part, which developed the standards and specifications of the format.
The original DV specification, known as Blue Book, was standardized within the IEC 61834 family of standards. These standards define common features such as physical videocassettes, recording modulation method, magnetization, and basic system data in part 1. Part 2 describes the specifics of video systems supporting 525-60 for NTSC and 625-50 for PAL. The IEC standards are available as publications sold by IEC and ANSI.
DV compression
DV uses lossy compression of video while audio is stored uncompressed. An intraframe video compression scheme is used to compress video on a frame-by-frame basis with the discrete cosine transform (DCT).
Closely following the ITU-R Rec. 601 standard, DV video employs interlaced scanning with the luminance sampling frequency of 13.5 MHz. This results in 480 scanlines per complete frame for the 60 Hz system, and 576 scanlines per complete frame for the 50 Hz system. In both systems the active area contains 720 pixels per scanline, with 704 pixels used for content and 16 pixels on the sides left for digital blanking. The same frame size is used for 4:3 and 16:9 frame aspect ratios, resulting in different pixel aspect ratios for fullscreen and widescreen video.
Prior to the DCT compression stage, chroma subsampling is applied to the source video in order to reduce the amount of data to be compressed. Baseline DV uses 4:1:1 subsampling in its 60 Hz variant and 4:2:0 subsampling in the 50 Hz variant. Low chroma resolution of DV (compared to higher-end digital video formats) is a reason this format is sometimes avoided in chroma keying applications, though advances in chroma keying techniques and software have made producing quality keys from DV material possible.
Audio can be stored in either of two forms: 16-bit Linear PCM stereo at 48 kHz sampling rate (768 kbit/s per channel, 1.5 Mbit/s stereo), or four nonlinear 12-bit PCM channels at 32 kHz sampling rate (384 kbit/s per channel, 1.5 Mbit/s for four channels). In addition, the DV specification also supports 16-bit audio at 44.1 kHz (706 kbit/s per channel, 1.4 Mbit/s stereo), the same sampling rate used for CD audio. In practice, the 48 kHz stereo mode is used almost exclusively.
Digital Interface Format
The audio, video, and metadata are packaged into 80-byte Digital Interface Format (DIF) blocks which are multiplexed into a 150-block sequence. DIF blocks are the basic units of DV streams and can be stored as computer files in raw form or wrapped in such file formats as Audio Video Interleave (AVI), QuickTime (QT) and Material Exchange Format (MXF). One video frame is formed from either 10 or 12 such sequences, depending on scanning rate, which results in a data rate of about 25 Mbit/s for video, and an additional 1.5 Mbit/s for audio. When written to tape, each sequence corresponds to one complete track.
Baseline DV employs unlocked audio. This means that the sound may be +/- ⅓ frame out of sync with the video. However, this is the maximum drift of the audio/video synchronization; it is not compounded throughout the recording.
Variants
Sony and Panasonic created their proprietary versions of DV aimed toward professional & broadcast users, which use the same compression scheme, but improve on robustness, linear editing capabilities, color rendition and raster size.
All DV variants except for DVCPRO Progressive are recorded to tape within interlaced video stream. Film-like frame rates are possible by using pulldown. DVCPRO HD supports native progressive format when recorded to P2 memory cards.
DVCPRO
DVCPRO, also known as DVCPRO25 and D-7, is a variation of DV developed by Panasonic and introduced in 1995, originally intended for use in electronic news gathering (ENG) equipment.
Unlike baseline DV, DVCPRO uses locked audio, meaning the audio sample clock runs in sync with the video sample clock. Audio is available in 16-bit/48 kHz precision.
When recorded to tape, DVCPRO uses wider track pitch—18 μm vs. 10 μm of baseline DV—which reduces the chance of dropout errors during recording. Two extra longitudinal tracks provide support for audio cue and for timecode control. Tape is transported 80% faster compared to baseline DV, resulting in shorter recording time. Long Play mode is not available.
DVCPRO50
DVCPRO50 was introduced by Panasonic in 1997 and is often described as two DV codecs working in parallel.
The DVCPRO50 doubles the coded video data rate to 50 Mbit/s. This has the effect of cutting total record time of any given storage medium in half. Chroma resolution is improved by using 4:2:2 chroma subsampling.
Following the introduction of the AJ-SDX900 camcorder in 2003, DVCPRO50 was used in many productions where high definition video was not required. For example, BBC used DVCPRO50 to record high-budget TV series, such as Space Race (2005) and Ancient Rome: The Rise and Fall of an Empire (2006).
A similar format, D-9 (or Digital-S), offered by JVC, uses videocassettes with the same form-factor as VHS.
Comparable high quality standard definition digital tape formats include Sony's Digital Betacam, introduced in 1993, and MPEG IMX, introduced in 2000.
DVCPRO Progressive
DVCPRO Progressive was introduced by Panasonic alongside DVCPRO50. It offered 480 or 576 lines of progressive scan recording with 4:2:0 chroma subsampling and four 16-bit 48 kHz PCM audio channels. Like HDV-SD, it was meant as an intermediate format during the transition time from standard definition to high definition video.
The format offered six modes for recording and playback: 16:9 progressive (50 Mbit/s), 4:3 progressive (50 Mbit/s), 16:9 interlaced (50 Mbit/s), 4:3 interlaced (50 Mbit/s), 16:9 interlaced (25 Mbit/s), 4:3 interlaced (25 Mbit/s).
The format was superseded by DVCPRO HD.
DVCPRO HD
DVCPRO HD, also known as DVCPRO100 and D-12, is a high-definition video format that can be thought of as four DV codecs that work in parallel. Video data rate depends on frame rate and can be as low as 40 Mbit/s for 24 frame/s mode and as high as 100 Mbit/s for 50/60 frame/s modes. Like DVCPRO50, DVCPRO HD employs 4:2:2 color sampling. It was introduced in 2000.
DVCPRO HD uses smaller raster size than broadcast high definition television: 960x720 pixels for 720p, 1280x1080 for 1080/59.94i and 1440x1080 for 1080/50i. Similar horizontal downsampling (using rectangular pixels) is used in many other magnetic tape-based HD formats such as HDCAM. To maintain compatibility with HD-SDI, DVCPRO100 equipment upsamples video during playback.
Variable framerates (from 4 to 60 frame/s) are available on Varicam camcorders. DVCPRO HD equipment offers backward compatibility with older DV/DVCPRO formats.
When recorded to tape in standard-play mode, DVCPRO HD uses the same 18 μm track pitch as other DVCPRO flavors. A long play variant, DVCPRO HD-LP, doubles the recording density by using 9 μm track pitch.
DVCPRO HD is codified as SMPTE 370M; the DVCPRO HD tape format is SMPTE 371M, and the MXF Op-Atom format used for DVCPRO HD on P2 cards is SMPTE 390M.
While technically DVCPRO HD is a direct descendant of DV, it is used almost exclusively by professionals. Tape-based DVCPRO HD cameras exist only in shoulder mount variant.
A similar format, Digital-S (D-9 HD), was offered by JVC and used videocassettes with the same form-factor as VHS.
The main competitor to DVCPRO HD was HDCAM, offered by Sony. It uses a similar compression scheme but at higher bitrate.
DVCAM
In 1996, Sony responded with its own professional version of DV called DVCAM.
Like DVCPRO, DVCAM uses locked audio, which prevents audio synchronization drift that may happen on DV if several generations of copies are made.
When recorded to tape, DVCAM uses 15 μm track pitch, which is 50% wider compared to baseline. Accordingly, tape is transported 50% faster, which reduces recording time by one third compared to regular DV. Because of the wider track and track pitch, DVCAM has the ability to do a frame-accurate insert edit, while regular DV may vary by a few frames on each edit compared to the preview.
Digital8
Digital8 is a combination of the tape transport originally designed for analog Video8 and Hi8 formats with the DV codec. Digital8 equipment records in DV format only, but usually can play back Video8 and Hi8 tapes as well.
Comparison of DV implementations
Recording media
Magnetic tape
The table below show the physical DV cassette formats at a glance:
DV was originally designed for recording onto magnetic tape. Tape is enclosed into videocassette of four different sizes: small, medium, large and extra-large. All DV cassettes use wide tape. DV on magnetic tape uses helical scan, which wraps the tape around a tilted, rotating head drum with video heads mounted to it. As the drum rotates, the heads read the tape diagonally. DV, DVCAM and DVCPRO use a 21.7 mm diameter head drum at 9000 rpm. The diagonal video tracks read by the heads are 10 microns wide in DV tapes.
Technically, any DV cassette can record any variant of DV video. Nevertheless, manufacturers often label cassettes with DV, DVCAM, DVCPRO, DVCPRO50 or DVCPRO HD and indicate recording time with regards to the label posted. Cassettes labeled as DV indicate recording time of baseline DV; another number can indicate recording time of Long Play DV. Cassettes labeled as DVCPRO have a yellow tape door and indicate recording time when DVCPRO25 is used; with DVCPRO50 the recording time is half, with DVCPRO HD it is a quarter. Cassettes labeled as DVCPRO50 have a blue tape door and indicate recording time when DVCPRO50 is used. Cassettes labeled as DVCPRO HD have a red tape door and indicate recording time when DVCPRO HD-LP format is used; a second number may be used for DVCPRO HD recording, which will be half as long.
Panasonic stipulated use of a particular magnetic-tape formulation—metal particle (MP)—as an inherent part of its DVCPRO family of formats. Regular DV tape uses Metal Evaporate (ME) formulation (which, as the name suggests, uses physical vapor deposition to deposit metal onto the tape), which was pioneered for use in Hi8 camcorders. Early Hi8 ME tapes were plagued with excessive dropouts, which forced many shooters to switch to more expensive MP tapes. After the technology improved, the dropout rate was greatly reduced, nevertheless Panasonic deemed ME formulation not robust enough for professional use. Tape-based professional Panasonic DVCPRO camcorders and decks only record onto DVCPRO-branded cassettes, effectively preventing use of ME tape.
Small size (MiniDV)
Small cassettes (66 x 48 x 12.2 mm), also known as S-size or MiniDV cassettes, had been intended for amateur use, but have become accepted in professional productions as well. MiniDV cassettes are used for recording baseline DV, DVCAM, and HDV. These cassettes come in lengths up to about 14~20.8GB for 63 or 90 minutes of DV or HDV video. When recording in DVCAM, these cassettes hold up to 41 minutes of video. There are some 83-minute versions but these use thinner tape than the 63-minute ones and Panasonic advised against playing these cassettes in DVCPRO decks.
Medium size
Medium or M-size cassettes (97.5 × 64.5 × 14.6 mm), which are about the size of eight-millimeter cassettes, are used in professional Panasonic equipment and are often called DVCPRO tapes. Panasonic video recorders that accept medium cassette can play back from and record to medium cassette in different flavors of DVCPRO format; they will also play small cassettes containing DV or DVCAM recording via an adapter. These cassettes come in lengths up to 66 minutes for DVCPRO, 33 minutes for DVCPRO50 and DVCPRO HD-LP, and 16.5 minutes for the original DVCPRO HD.
Large size
Large or L-size cassettes (125.1 x 78 x 14.6 mm) are close in size to small MII cassettes and are accepted by most standalone DV tape recorders and are used in many shoulder-mount camcorders. The L-size cassette can be used in both Sony and Panasonic equipment; nevertheless, they are often called DVCAM tapes. Older Sony decks would not play large cassettes with DVCPRO recordings, but newer models can play these and M-size DVCPRO cassettes. These cassettes come in lengths up to 276 minutes of DV or HDV video (or 184 minutes for DVCAM). Unlike the VHS and Digital8 formats that use thinner tape for their longest-length variants, the 276-minute DV cassette employs the same tape as its shorter-length variants. On the DVCPRO side, these cassettes have nearly double the tape capacity of their M-size counterparts, with duration up to 126 minutes for DVCPRO, 63 minutes for DVCPRO50 and DVCPRO HD-LP, and 31.5 minutes for the original DVCPRO HD. A thin-tape 184/92/46-minute version was also released.
Extra-large size
Extra-large cassettes or XL-size (172 x 102 x 14.6 mm) are close in size to VHS cassettes and have been designed for use in Panasonic equipment and are sometimes called DVCPRO XL. These cassettes are not widespread, only a few models of Panasonic tape recorders can accept them. Each XL-size cassette holds nearly double the amount of tape as the full-length L-size cassettes with a capacity of 252 minutes of DVCPRO video or 126 minutes of DVCPRO50 or DVCPRO HD-LP video.
File-based media
With proliferation of tapeless camcorder video recording, DV video can be recorded on optical discs, solid state flash memory cards and hard disk drives and used as computer files. In particular:
Sony XDCAM family of cameras can record DV onto either Professional Disc or SxS memory cards.
Panasonic DVCPRO HD and AVC-Intra camcorders can record DV (as well as DVCPRO) onto P2 cards.
Some Panasonic AVCHD camcorders (AG-HMC80, AG-AC130, AG-AC160) record DV video onto Secure Digital memory cards.
JVC GY-HM750 can be set to standard definition mode and in this case will record '.AVI or .MOV SD legacy format' video onto SDHC cards. For clarity - and contrary to what has previously been written, the camera does not natively support SxS memory cards, has no slots for them and requires an optional add-on recorder (or 'adapter' as JVC call it) to achieve this - basically this camera is an 'XDCAM EX' High definition unit and the add-on SxS recorder was only made available to achieve better compatibility in facilities which were Sony based.
Most DV and HDV camcorders can feed live DV stream over IEEE 1394 interface to an external file-based recorder.
Video is stored either as native DIF bitstream or wrapped into an audio/video container such as AVI, QuickTime or MXF.
DV-DIF is the raw form of DV video. The files usually have extensions *.dv or *.dif.
DV-AVI is Microsoft's implementation of DV video file, which is wrapped into an AVI container. Two variants of wrapping are available: with Type 1 the multiplexed audio and video is saved into the video section of a single AVI file, with Type 2 video and audio are saved as separate streams in an AVI file (one video stream and one to four audio streams). This container is used primarily on Windows-based computers, though Sony offers two tapeless recorders, the HDD-based HVR-DR60 and the CompactFlash-based HVR-MRC1K, for use with DV/HDV camcorders that can record in DV-AVI format either making a file-based copy of the tape or bypassing tape recording altogether. Panasonic AVCHD camcorders use Type 2 DV-AVI for recording DV video onto Secure Digital memory card.
QuickTime-DV is DV video wrapped into QuickTime container. This container is used primarily on Apple computers.
MXF-DV wraps DV video into MXF container, which is presently used on P2-based camcorders (Panasonic) and on XDCAM/XDCAM EX camcorders (Sony).
Connectivity
Nearly all DV camcorders and decks have IEEE 1394 (FireWire, i.LINK) ports for digital video transfer. This is usually a two-way port, so that DV video data can be output to a computer (DV-out), or input from either a computer or another camcorder (DV-in). The DV-in capability makes it possible to copy edited DV video from a computer back onto tape, or make a lossless copy between two mutually connected DV camcorders. However, models made for sale in the European Union usually had the DV-in capability disabled in the firmware by the manufacturer because the camcorder would be classified by the EU as a video recorder and would therefore attract higher duty; a model which only had DV-out could be sold at a lower price in the EU.
When video is captured onto a computer it is stored in a container file, which can be either raw DV stream, AVI, WMV or QuickTime. Whichever container is used, the video itself is not re-encoded and represents a complete digital copy of what has been recorded onto tape. If needed, the video can be recorded back to tape to create a full and lossless copy of the original footage.
Some camcorders also feature a USB 2.0 port for computer connection. This port is usually used for transferring still images, but not for video transfer. Camcorders that offer video transfer over USB usually do not deliver full DV quality; usually it is 320x240 video, except for the Sony DCR-PC1000 camcorder and some Panasonic camcorders that provide transfer of a full-quality DV stream via USB by using the UVC protocol. Full-quality DV can also be captured via USB or Thunderbolt by using separate hardware that receives DV data from the camcorder over a FireWire cable and forwards it without any transcoding to the computer via a USB cable or a Firewire to Thunderbolt adapter - this can be particularly useful for capturing on modern laptop computers which usually do not have a FireWire port or expansion slot but always have USB or Thunderbolt ports.
High end cameras and VTRs may have additional professional outputs such as SDI, SDTI or analog component video. All DV variants have a time code, but some older or consumer computer applications fail to take advantage of it.
Usage
The high quality of DV images, especially when compared to Video8 and Hi8 which were vulnerable to an unacceptable number of video dropouts and "hits", prompted the acceptance by mainstream broadcasters of material shot on DV. The low costs of DV equipment and their ease of use put such cameras in the hands of a new breed of videojournalists.
DVCPRO HD was the preferred high definition standard of BBC Factual.
Films
Notable films that were shot on the DV format include:
The Cruise (Bennett Miller—1998)
The Gleaners and I (Agnès Varda—2000)
Chuck and Buck (Miguel Arteta—2000)
The Gleaners and I: Two Years Later (Agnès Varda—2002)
28 Days Later (Danny Boyle—2002)
Inland Empire (David Lynch—2006)
Iraq in Fragments (James Longley—2006)
My First Kiss and the People Involved (Luigi Campi & Giacomo Belletti—2016)
Application software support
Most DV players, editors and encoders only support the basic DV format, but not its professional versions. The exception to this being that most (not all) consumer Sony miniDV equipment will play mini-DVCAM tapes. DV Audio/Video data can be stored as raw DV data stream file (data is written to a file as the data is received over FireWire, file extensions are .dv and .dif) or the DV data can be packed into container files (ex: Microsoft AVI, Apple MOV). The DV meta-information is preserved in both file types being Sub-timecode and Start/Stop date times which can be muxed to Quicktime SMPTE standard timecode.
Most Windows video software only supports DV in AVI containers, as they use Microsoft's avifile.dll, which only supports reading avi files. Mac OS X video software support both AVI and MOV containers.
Tape formulation compatibility
There was considerable controversy solely based on hearsay over whether or not using tapes from different manufacturers could lead to dropouts. Initially this was suggested around the conception of mostly MiniDV tapes in the mid to late 90s as the only two manufacturers of MiniDV tapes (Sony, who produce their tapes solely under the Sony brand; and Panasonic, who produce their own tapes under their Panasonic brand and outsources for TDK, Canon, etc.) used two different lubrication types for their cameras.
A research undertaken by Sony claimed that there was no hard evidence of the above statement. The only evidence claimed was that using ME tapes in equipment designed for MP tapes can cause tape damage and hence dropouts. Sony has done a significant amount of internal testing to simulate head clogs as a result of mixing tape lubricants, and has been unable to recreate the problem. Sony recommends using cleaning cassettes once every 50 hours of recording or playback. For those who are still skeptical, Sony recommends cleaning video heads with a cleaning cassette before trying another brand of tape.
In 1999, Steve Epstein, technical editor of Broadcast Engineering magazine, received the following response from a Sony representative regarding tape stock compatibility:
Sony developed DVCAM based on the DV consumer format. The DV format was designed for use with metal evaporated tape, which offers approximately 5 dB better carrier-to-noise figures than metal particle tape. Customers have requested VTRs that can play additional DV-based 6 mm formats such as the consumer DV LP and DVCPRO. Sony will be offering new VTRs that can play back both of these additional formats without headclog and tape path issues.
It was realized early on that the VTR transport needed to be optimized to play various tape formulations and thicknesses. In addition, there is no need to dub DV LP or DVCPRO footage to another format for use as source material. This new VTR is the DSR 2000 DVCAM Studio recorder, and it is expected to be available later this year.
Robert Ott, Vice President for storage products and marketing, Sony Electronics, Park Ridge, New Jersey
See also
Common Intermediate Format (CIF)
Source Input Format (SIF)
Video CD
References
Television technology
Television terminology
Video storage
Videocassette formats | DV (video format) | [
"Technology"
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"Information and communications technology",
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53,723 | https://en.wikipedia.org/wiki/Digital%20media | In mass communication, digital media is any communication media that operates in conjunction with various encoded machine-readable data formats. Digital content can be created, viewed, distributed, modified, listened to, and preserved on a digital electronic device, including digital data storage media (in contrast to analog electronic media) and digital broadcasting. Digital is defined as any data represented by a series of digits, and media refers to methods of broadcasting or communicating this information. Together, digital media refers to mediums of digitized information broadcast through a screen and/or a speaker. This also includes text, audio, video, and graphics that are transmitted over the internet for viewing or listening to on the internet.
Digital media platforms, such as YouTube, Kick, and Twitch, accounted for viewership rates of 27.9 billion hours in 2020. A contributing factor to its part in what is commonly referred to as the digital revolution can be attributed to the use of interconnectivity.
Examples
Examples of digital media include software, digital images, digital video, video games, web pages and websites, social media, digital data and databases, digital audio such as MP3, electronic documents and electronic books. Digital media often contrasts with print media, such as printed books, newspapers and magazines, and other traditional or analog media, such as photographic film, audio tapes or video tapes.
Digital media has had a significantly broad and complex impact on society and culture. Combined with the Internet and personal computing, digital media has caused disruptive innovation in publishing, journalism, public relations, entertainment, education, commerce and politics. Digital media has also posed new challenges to copyright and intellectual property laws, fostering an open content movement in which content creators voluntarily give up some or all of their legal rights to their work. The ubiquity of digital media and its effects on society suggest that we are at the start of a new era in industrial history, called the Information Age, perhaps leading to a paperless society in which all media are produced and consumed on computers. However, challenges to a digital transition remain, including outdated copyright laws, censorship, the digital divide, and the spectre of a digital dark age, in which older media becomes inaccessible to new or upgraded information systems. Digital media has a significant, wide-ranging and complex impact on society and culture.
Business model
Digital media platforms like YouTube work through a triple-product business model in which platforms provide information and entertainment (infotainment) to the public often at no cost, while simultaneously capturing their attention, and also collecting user data to sell to advertisers. This business model aims to maximize consumer engagement on the platform.
Paid Media
Paid media refers to promotional channels that marketers pay to use, including traditional media (e.g., television, radio, print, or outdoor advertising), online and digital media (e.g., paid search ads, web and social media display ads, mobile ads, or email marketing). This model compels businesses to develop sponsored media then pay social media platforms like Instagram for the right to show such media to customers in the platforms' newsfeeds. These customers become exposed to paid media, sometimes referred to as promoted or sponsored posts.
Owned Media
Owned media refers to digital assets and channels that a company or individual controls and manages. This includes websites, social media profiles for example Facebook etc., blogs, and any other content platforms own and operated by the entity. Entity means the owner or controller of the channel such as business or person managing their online presence
Earned Media
Earned media denotes public relations media channels like television, newspapers, blogs, or video sites that do not require direct payment or control by marketers but are included because viewers, readers, or users are interested in them. Free media is essentially online word of mouth, typically in "viral" trends, mentions, shares, retweets, reviews, recommendations, or content from third-party websites. When one's product or service is so good that users cannot help but post it on their social media, they get a lot of "earned media". They win the credibility of the media compared to other forms of credibility, becoming more transparent.
History
Codes and information by machines were first conceptualized by Charles Babbage in the early 1800s. Babbage imagined that these codes would give him instructions for his Motor of Difference and Analytical Engine, machines that Babbage had designed to solve the problem of error in calculations. Between 1822 and 1823, the mathematician Ada Lovelace wrote the first instructions for calculating numbers on Babbage engines. Lovelace's instructions are now believed to be the first computer program. Although the machines were designed to perform analysis tasks, Lovelace anticipated the possible social impact of computers and program writing. "For in the distribution and combination of truths and formulas of analysis, which may become easier and more quickly subjected to the mechanical combinations of the engine, the relationships and the nature of many subjects in which science necessarily relates in new subjects, and more deeply researched […] there are in all extensions of human power or additions to human knowledge, various collateral influences, in addition to the primary and primary object reached." Other old machine readable media include instructions for pianolas and weaving machines.
It is estimated that in the year 1986 less than 1% of the world's media storage capacity was digital and in 2007 it was already 94%. The year 2002 is assumed to be the year when human kind was able to store more information in digital than in analog media (the "beginning of the digital age").
Digital computers
Though they used machine-readable media, Babbage's engines, player pianos, jacquard looms and many other early calculating machines were themselves analog computers, with physical, mechanical parts. The first truly digital media came into existence with the rise of digital computers. Digital computers use binary code and Boolean logic to store and process information, allowing one machine in one configuration to perform many different tasks. The first modern, programmable, digital computers, the Manchester Mark 1 and the EDSAC, were independently invented between 1948 and 1949. Though different in many ways from modern computers, these machines had digital software controlling their logical operations. They were encoded in binary, a system of ones and zeroes that are combined to make hundreds of characters. The 1s and 0s of binary are the "digits" of digital media.
"As We May Think"
While digital media did not come into common use until the late 20th century, the conceptual foundation of digital media is traced to the work of scientist and engineer Vannevar Bush and his celebrated essay "As We May Think", published in The Atlantic Monthly in 1945. Bush envisioned a system of devices that could be used to help scientists, doctors, and historians, among others, to store, analyze and communicate information. Calling this then-imaginary device a "memex", Bush wrote:
The owner of the memex, let us say, is interested in the origin and properties of the bow and arrow. Specifically, he is studying why the short Turkish bow was apparently superior to the English long bow in the skirmishes of the Crusades. He has dozens of possibly pertinent books and articles in his memex. First, he runs through an encyclopedia, finds an interesting but sketchy article, and leaves it projected. Next, in history, he finds another pertinent item and ties the two together. Thus he goes, building a trail of many items. Occasionally he inserts a comment of his own, either linking it into the main trail or joining it by a side trail to a particular item. When it becomes evident that the elastic properties of available materials had a great deal to do with the bow, he branches off on a side trail which takes him through textbooks on elasticity and tables of physical constants. He inserts a page of longhand analysis of his own. Thus he builds a trail of his interest through the maze of materials available to him.
Bush hoped that the creation of this memex would be the work of scientists after World War II. Though the essay predated digital computers by several years, "As We May Think" anticipated the potential social and intellectual benefits of digital media and provided the conceptual framework for digital scholarship, the World Wide Web, wikis and even social media. It was recognized as a significant work even at the time of its publication.
Impact
The digital revolution
Since the 1960s, computing power and storage capacity have increased exponentially, largely as a result of MOSFET scaling which enables MOS transistor counts to increase at a rapid pace predicted by Moore's law. Personal computers and smartphones put the ability to access, modify, store and share digital media in the hands of billions of people. Many electronic devices, from digital cameras to drones have the ability to create, transmit and view digital media. Combined with the World Wide Web and the Internet, digital media has transformed 21st century society in a way that is frequently compared to the cultural, economic and social impact of the printing press. The change has been so rapid and so widespread that it has launched an economic transition from an industrial economy to an information-based economy, creating a new period in human history known as the Information Age or the digital revolution.
The transition has created some uncertainty about definitions. Digital media, new media, multimedia, and similar terms all have a relationship to both the engineering innovations and cultural impact of digital media. The blending of digital media with other media, and with cultural and social factors, is sometimes known as new media or "the new media." Similarly, digital media seems to demand a new set of communications skills, called transliteracy, media literacy, or digital literacy. These skills include not only the ability to read and write—traditional literacy—but the ability to navigate the Internet, evaluate sources, and create digital content. The idea that we are moving toward a fully digital, paperless society is accompanied by the fear that we may soon—or currently—be facing a digital dark age, in which older media are no longer accessible on modern devices or using modern methods of scholarship. Digital media has a significant, wide-ranging and complex effect on society and culture.
A senior engineer at Motorola named Martin Cooper was the first person to make a phone call on April 3, 1973. He decided the first phone call should be to a rival telecommunications company saying "I'm speaking via a mobile phone". Ten years later, Motorola released the Motorola DynaTAC, the first commercially available mobile phone. In the early 1990s Nokia released the Nokia 1011, the first mass-produced mobile phone. The number of smartphone users has increased dramatically, as has the commercial landscape. While Android and iOS both dominate the smartphone market. A study By Gartner found that in 2016 about 88% of the worldwide smartphones were Android while iOS had a market share of about 12%. About 85% of the mobile market revenue came from mobile games.
The impact of the digital revolution can also be assessed by exploring the amount of worldwide mobile smart device users there are. This can be split into 2 categories; smart phone users and smart tablet users. Worldwide there are currently 2.32 billion smartphone users across the world. This figure is to exceed 2.87 billion by 2020. Smart tablet users reached a total of 1 billion in 2015, 15% of the world's population.
The statistics evidence the impact of digital media communications today. What is also of relevance is the fact that the number of smart device users is rising rapidly yet the amount of functional uses increase daily. A smartphone or tablet can be used for hundreds of daily needs. There are currently over 1 million apps on the Apple App store. These are all opportunities for digital marketing efforts. A smartphone user is impacted with digital advertising every second they open their Apple or Android device. This further evidences the digital revolution and the impact of revolution. This has resulted in a total of 13 billion dollars being paid out to the various app developers over the years. This growth has fueled the development of millions of software applications. Most of these apps are able to generate income via in app advertising. Gross revenue for 2020 is projected to be about $189 million.
Disruption in industry
Compared with print media, the mass media, and other analog technologies, digital media are easy to copy, store, share and modify. This quality of digital media has led to significant changes in many industries, especially journalism, publishing, education, entertainment, and the music business. The overall effect of these changes is so far-reaching that it is difficult to quantify. For example, in movie-making, the transition from analog film cameras to digital cameras is nearly complete. The transition has economic benefits to Hollywood, making distribution easier and making it possible to add high-quality digital effects to films. At the same time, it has affected the analog special effects, stunt, and animation industries in Hollywood. It has imposed painful costs on small movie theaters, some of which did not or will not survive the transition to digital. The effect of digital media on other media industries is similarly sweeping and complex.
Between 2000 and 2015, the print newspaper advertising revenue has fallen from $60 billion to a nearly $20 billion. Even one of the most popular days for papers, Sunday, has seen a 9% circulation decrease the lowest since 1945.
In journalism, digital media and citizen journalism have led to the loss of thousands of jobs in print media and the bankruptcy of many major newspapers. But the rise of digital journalism has also created thousands of new jobs and specializations. E-books and self-publishing are changing the book industry, and digital textbooks and other media-inclusive curricula are changing primary and secondary education.
In academia, digital media has led to a new form of scholarship, also called digital scholarship, making open access and open science possible thanks to the low cost of distribution. New fields of study have grown, such as digital humanities and digital history. It has changed the way libraries are used and their role in society. Every major media, communications and academic endeavor is facing a period of transition and uncertainty related to digital media.
Often time the magazine or publisher have a Digital edition which can be referred to an electronic formatted version identical to the print version. There is a huge benefit to the publisher and cost, as half of traditional publishers' costs come from production, including raw materials, technical processing, and distribution.
Since 2004, there has been a decrease in newspaper industry employment, with only about 40,000 people working in the workforce currently. Alliance of Audited Media & Publishers information during the 2008 recession, over 10% of print sales are diminished for certain magazines, with a hardship coming from only 75% of the sales advertisements as before. However, in 2018, major newspapers advertising revenue was 35% from digital ads.
In contrast, mobile versions of newspapers and magazines came in second with a huge growth of 135%. The New York Times has noted a 47% year of year rise in their digital subscriptions. 43% of adults get news often from news websites or social media, compared with 49% for television. Pew Research also asked respondents if they got news from a streaming device on their TV – 9% of U.S. adults said that they do so often.
Individual as content creator
Digital media has also allowed individuals to be much more active in content creation. Anyone with access to computers and the Internet can participate in social media and contribute their own writing, art, videos, photography and commentary to the Internet, as well as conduct business online. The dramatic reduction in the costs required to create and share content have led to a democratization of content creation as well as the creation of new types of content, like blogs, memes, and video essays. Some of these activities have also been labelled citizen journalism. This spike in user-created content is due to the development of the internet as well as the way in which users interact with media today. As more users join and use social media sites, the relevance of content creation increases. The release of technologies such mobile devices allow for easier and quicker access to all things media. Many media creation tools that were once available to only a few are now free and easy to use. The cost of devices that can access the Internet is steadily falling, and personal ownership of multiple digital devices is now becoming the standard. These elements have significantly affected political participation. Digital media is seen by many scholars as having a role in Arab Spring, and crackdowns on the use of digital and social media by embattled governments are increasingly common. Many governments restrict access to digital media in some way, either to prevent obscenity or in a broader form of political censorship.
Over the years YouTube has grown to become a website with user generated media. This content is oftentimes not mediated by any company or agency, leading to a wide array of personalities and opinions online. Over the years, YouTube and other platforms have also shown their monetary gains. In 2020, the top 10 highest earning YouTube content creators each generated over 15 million dollars. Many of these YouTube profiles over the years have a multi camera set up as we would see on TV. Many of these creators also creating their own digital companies as their personalities grow. Personal devices have also seen an increase over the years. Over 1.5 billion users of tablets exist in this world right now and that is expected to slowly grow About 20% of people in the world regularly watch their content using tablets in 2018
User-generated content raises issues of privacy, credibility, civility and compensation for cultural, intellectual and artistic contributions. The spread of digital media, and the wide range of literacy and communications skills necessary to use it effectively, have deepened the digital divide between those who have access to digital media and those who do not.
The rising of digital media has made the consumer's audio collection more precise and personalized. It is no longer necessary to purchase an entire album if the consumer is ultimately interested in only a few audio files.
Web-only news
The rise of streaming services has led to a decrease of cable TV services to about 59%, while streaming services are growing at around 29%, and 9% are still users of the digital antenna. TV Controllers now incorporate designated buttons for streaming platforms. Users are spending an average of 1:55 with digital video each day, and only 1:44 on social networks. 6 out of 10 people report viewing their television shows and news via a streaming service. Platforms such as Netflix have gained attraction due to their adorability, accessibility, and for its original content. Companies such as Netflix have even bought previously cancelled shows such as Designated Survivor, Lucifer, and Arrested Development. As the internet becomes more and more prevalent, more companies are beginning to distribute content through internet only means. Indeed, young people today are increasingly likely to use TikTok over Google, television or newspapers for their news. With the loss of viewers, there is a loss of revenue but not as bad as what would be expected.
As of 2024 there has also been a wave of those considered too controversial by main-stream media moving over to online platforms such as X (formerly Twitter) to keep spreading their messages. One instance is Tucker Carlson leaving Fox News due to his controversial opinions and moving over to X. This has sparked debate surrounding topics such as free speech and hate speech.
Copyright challenges
Digital media encompasses numerical networks of interactive systems that link databases, allowing users to navigate from one bit of content or webpage to another. Because of this ease, digital media poses several challenges to the current copyright and intellectual property laws. The ease of creating, modifying, and sharing digital media can influence copyright enforcement challenging and many copyright laws are widely seen as outdated. Under current copyright law, common Internet memes are generally illegal to share in many countries. Legal rights can be unclear for many common Internet activities. These include posting pictures from someone else's social media account, writing fanfiction, or covering and/or using popular songs in content such as YouTube videos. During the last decade, the concepts of fair use and copyright have been applied to different types of online media.
Copyright challenges are spreading to all parts of digital media. Content creators on platforms such as YouTube follow guidelines set by copyright, IP laws, and the platform's copyright requirements. If these guidelines are not followed, the content may get demonetized, deleted, or sued. The situation can also occur when creators accidentally use audio tracks or background scenes that are under copyright. To avoid or resolve some of these issues, content creators can voluntarily adopt open, or copyleft licenses or they can release their work to the public domain. By doing this, creators are giving up certain legal rights regarding their content. Fair use is a doctrine of the US Copyright Law that allows limited use of copyrighted materials without the need to obtain permission. There are four factors that make up fair use. The first, Purpose, refers to what the content is being used for. The second factor is what copyrighted content is being used. If the content is non-fiction, it is more likely to fall under fair use than if the content is fiction. The third factor is how much of the copyrighted content is in use. Small amounts of copyrighted content are more likely to be considered fair. The last factor is, whether the use of copyrighted content earns money or affect the value of the content.
Wikipedia uses some of the most common open licenses, Creative Commons licenses, and the GNU Free Documentation License. Open licenses are one aspect of a broad open content movement that advocates for the reduction or removal of copyright restrictions from software, data, and other digital media. To facilitate the collection and consumption of such licensing information and availability status, tools like the Creative Commons Search engine are used mostly for web images, and Unpaywall, or used for scholarly communication.
Additional software has been developed to restrict access to digital media. Digital rights management (DRM) is used to lock material. This allows users to apply the media content to specific cases. DRM allows movie producers to rent at a lower price. This restricts the movie rental license length, rather than only selling the movie at full price. Additionally, DRM can prevent unauthorized modification or sharing of media.
Digital media copyright protection technologies fall under intellectual property protection technology. This is because a series of computer technologies protect the digital content being created and transmitted. The Digital Millennium Copyright Act (DMCA) provides safety to intermediaries that host user content, such as YouTube, from being held liable for copyright infringement so long as they meet all required conditions. The most notable of which is the "notice and take down" policy. The policy requires online intermediaries to remove and/or disable access to the content in question when there are court orders and/or allegations of illegal use of the content on their site. As a result, YouTube has and continues to develop more policies and standards that go far past what the DMCA requires. YouTube has also created an algorithm which continuously scans their cite to make sure all content follows all policies.
One digital media platform known to have copyright concerns is the short video-sharing app TikTok. TikTok is a social media app that allows users to share short videos up to one minute in length, using a variety of visual effects and audio. According to Loyola University's Chicago School of Law, around 50% of the music used on TikTok is unlicensed. TikTok has several music licensing agreements with various artists and labels, creating a library of fair and legal use of music. However, this does not cover all content for its users. A user could still commit a copyright violation on TikTok. One example is, accidentally having music playing on a stereo in the background or recording a laptop screen playing a song.
Online magazines or digital magazines are one of the largest targets for copyright issues. According to the Audit Bureau of Circulations report from March 2011, the definition of this medium is when a digital magazine involves the distribution of magazine content by electronic means; it may be a replica. This definition can be considered outdated now that PDF replicas of print magazines are no longer common practice. These days digital magazines refer to magazines specifically created to be interactive digital platforms such as the internet, mobile phones, private networks, iPad, or other devices. The barriers to digital magazine distribution are thus decreasing. However, these platforms are also broadening the scope of where digital magazines can be published; smartphones are an example. Thanks to the improvements in tablets and other personal electronic devices, digital magazines have become much more readable and enticing through the use of graphic art. The evolution of online magazines began to focus on becoming more of a social media and entertainment platform.
Online piracy has become one of the larger issues that have occurred concerning digital media copyright. The piracy of digital media, such as film and television, directly impacts the copyright party (the owner of the copyright). This action can impact the "health" of the digital media industry. Piracy directly breaks the laws and morals of copyright. Along with piracy, digital media has contributed to the ability to spread false information or fake news. Due to the widespread use of digital media, fake news can receive more notoriety. This notoriety enhances the negative effects fake news creates. As a result, people's health and well-being can directly be affected.
See also
Digital media use and mental health
Electronic media
Media psychology
Virtual artifact
Digital preservation
Digital continuity
Content creation
Digital rhetoric
References
Further reading
Ramón Reichert, Annika Richterich, Pablo Abend, Mathias Fuchs, Karin Wenz (eds.), Digital Culture & Society.
Schiffrin, Anya. Media Capture: How Money, Digital Platforms, and Governments Control the News. Edited by Anya Schiffrin. New York, New York State: Columbia University Press, 2021.
Hyperreality
Information science
Library science
Mass media technology
Articles containing video clips | Digital media | [
"Technology"
] | 5,268 | [
"Information and communications technology",
"Mass media technology",
"Science and technology studies",
"Digital media",
"Multimedia",
"Hyperreality"
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53,734 | https://en.wikipedia.org/wiki/Double-precision%20floating-point%20format | Double-precision floating-point format (sometimes called FP64 or float64) is a floating-point number format, usually occupying 64 bits in computer memory; it represents a wide range of numeric values by using a floating radix point.
Double precision may be chosen when the range or precision of single precision would be insufficient.
In the IEEE 754 standard, the 64-bit base-2 format is officially referred to as binary64; it was called double in IEEE 754-1985. IEEE 754 specifies additional floating-point formats, including 32-bit base-2 single precision and, more recently, base-10 representations (decimal floating point).
One of the first programming languages to provide floating-point data types was Fortran. Before the widespread adoption of IEEE 754-1985, the representation and properties of floating-point data types depended on the computer manufacturer and computer model, and upon decisions made by programming-language implementers. E.g., GW-BASIC's double-precision data type was the 64-bit MBF floating-point format.
IEEE 754 double-precision binary floating-point format: binary64
Double-precision binary floating-point is a commonly used format on PCs, due to its wider range over single-precision floating point, in spite of its performance and bandwidth cost. It is commonly known simply as double. The IEEE 754 standard specifies a binary64 as having:
Sign bit: 1 bit
Exponent: 11 bits
Significand precision: 53 bits (52 explicitly stored)
The sign bit determines the sign of the number (including when this number is zero, which is signed).
The exponent field is an 11-bit unsigned integer from 0 to 2047, in biased form: an exponent value of 1023 represents the actual zero. Exponents range from −1022 to +1023 because exponents of −1023 (all 0s) and +1024 (all 1s) are reserved for special numbers.
The 53-bit significand precision gives from 15 to 17 significant decimal digits precision (2−53 ≈ 1.11 × 10−16). If a decimal string with at most 15 significant digits is converted to the IEEE 754 double-precision format, giving a normal number, and then converted back to a decimal string with the same number of digits, the final result should match the original string. If an IEEE 754 double-precision number is converted to a decimal string with at least 17 significant digits, and then converted back to double-precision representation, the final result must match the original number.
The format is written with the significand having an implicit integer bit of value 1 (except for special data, see the exponent encoding below). With the 52 bits of the fraction (F) significand appearing in the memory format, the total precision is therefore 53 bits (approximately 16 decimal digits, 53 log10(2) ≈ 15.955). The bits are laid out as follows:
The real value assumed by a given 64-bit double-precision datum with a given biased exponent
and a 52-bit fraction is
or
Between 252=4,503,599,627,370,496 and 253=9,007,199,254,740,992 the representable numbers are exactly the integers. For the next range, from 253 to 254, everything is multiplied by 2, so the representable numbers are the even ones, etc. Conversely, for the previous range from 251 to 252, the spacing is 0.5, etc.
The spacing as a fraction of the numbers in the range from 2n to 2n+1 is 2n−52.
The maximum relative rounding error when rounding a number to the nearest representable one (the machine epsilon) is therefore 2−53.
The 11 bit width of the exponent allows the representation of numbers between 10−308 and 10308, with full 15–17 decimal digits precision. By compromising precision, the subnormal representation allows even smaller values up to about 5 × 10−324.
Exponent encoding
The double-precision binary floating-point exponent is encoded using an offset-binary representation, with the zero offset being 1023; also known as exponent bias in the IEEE 754 standard. Examples of such representations would be:
The exponents 00016 and 7ff16 have a special meaning:
000000000002=00016 is used to represent a signed zero (if F = 0) and subnormal numbers (if F ≠ 0); and
111111111112=7ff16 is used to represent ∞ (if F = 0) and NaNs (if F ≠ 0),
where F is the fractional part of the significand. All bit patterns are valid encoding.
Except for the above exceptions, the entire double-precision number is described by:
In the case of subnormal numbers (e = 0) the double-precision number is described by:
Endianness
Double-precision examples
Encodings of qNaN and sNaN are not completely specified in IEEE 754 and depend on the processor. Most processors, such as the x86 family and the ARM family processors, use the most significant bit of the significand field to indicate a quiet NaN; this is what is recommended by IEEE 754. The PA-RISC processors use the bit to indicate a signaling NaN.
By default, 1/3 rounds down, instead of up like single precision, because of the odd number of bits in the significand.
In more detail:
Given the hexadecimal representation 3FD5 5555 5555 555516,
Sign = 0
Exponent = 3FD16 = 1021
Exponent Bias = 1023 (constant value; see above)
Fraction = 5 5555 5555 555516
Value = 2(Exponent − Exponent Bias) × 1.Fraction – Note that Fraction must not be converted to decimal here
= 2−2 × (15 5555 5555 555516 × 2−52)
= 2−54 × 15 5555 5555 555516
= 0.333333333333333314829616256247390992939472198486328125
≈ 1/3
Execution speed with double-precision arithmetic
Using double-precision floating-point variables is usually slower than working with their single precision counterparts. One area of computing where this is a particular issue is parallel code running on GPUs. For example, when using NVIDIA's CUDA platform, calculations with double precision can take, depending on hardware, from 2 to 32 times as long to complete compared to those done using single precision.
Additionally, many mathematical functions (e.g., sin, cos, atan2, log, exp and sqrt) need more computations to give accurate double-precision results, and are therefore slower.
Precision limitations on integer values
Integers from −253 to 253 (−9,007,199,254,740,992 to 9,007,199,254,740,992) can be exactly represented.
Integers between 253 and 254 = 18,014,398,509,481,984 round to a multiple of 2 (even number).
Integers between 254 and 255 = 36,028,797,018,963,968 round to a multiple of 4.
Integers between 2n and 2n+1 round to a multiple of 2n−52.
Implementations
Doubles are implemented in many programming languages in different ways such as the following. On processors with only dynamic precision, such as x86 without SSE2 (or when SSE2 is not used, for compatibility purpose) and with extended precision used by default, software may have difficulties to fulfill some requirements.
C and C++
C and C++ offer a wide variety of arithmetic types. Double precision is not required by the standards (except by the optional annex F of C99, covering IEEE 754 arithmetic), but on most systems, the double type corresponds to double precision. However, on 32-bit x86 with extended precision by default, some compilers may not conform to the C standard or the arithmetic may suffer from double rounding.
Fortran
Fortran provides several integer and real types, and the 64-bit type real64, accessible via Fortran's intrinsic module iso_fortran_env, corresponds to double precision.
Common Lisp
Common Lisp provides the types SHORT-FLOAT, SINGLE-FLOAT, DOUBLE-FLOAT and LONG-FLOAT. Most implementations provide SINGLE-FLOATs and DOUBLE-FLOATs with the other types appropriate synonyms. Common Lisp provides exceptions for catching floating-point underflows and overflows, and the inexact floating-point exception, as per IEEE 754. No infinities and NaNs are described in the ANSI standard, however, several implementations do provide these as extensions.
Java
On Java before version 1.2, every implementation had to be IEEE 754 compliant. Version 1.2 allowed implementations to bring extra precision in intermediate computations for platforms like x87. Thus a modifier strictfp was introduced to enforce strict IEEE 754 computations. Strict floating point has been restored in Java 17.
JavaScript
As specified by the ECMAScript standard, all arithmetic in JavaScript shall be done using double-precision floating-point arithmetic.
JSON
The JSON data encoding format supports numeric values, and the grammar to which numeric expressions must conform has no limits on the precision or range of the numbers so encoded. However, RFC 8259 advises that, since IEEE 754 binary64 numbers are widely implemented, good interoperability can be achieved by implementations processing JSON if they expect no more precision or range than binary64 offers.
Rust and Zig
Rust and Zig have the f64 data type.
See also
Notes and references
Binary arithmetic
Computer arithmetic
Floating point types | Double-precision floating-point format | [
"Mathematics"
] | 2,066 | [
"Computer arithmetic",
"Arithmetic",
"Binary arithmetic"
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53,741 | https://en.wikipedia.org/wiki/Symmetry | Symmetry () in everyday life refers to a sense of harmonious and beautiful proportion and balance. In mathematics, the term has a more precise definition and is usually used to refer to an object that is invariant under some transformations, such as translation, reflection, rotation, or scaling. Although these two meanings of the word can sometimes be told apart, they are intricately related, and hence are discussed together in this article.
Mathematical symmetry may be observed with respect to the passage of time; as a spatial relationship; through geometric transformations; through other kinds of functional transformations; and as an aspect of abstract objects, including theoretic models, language, and music.
This article describes symmetry from three perspectives: in mathematics, including geometry, the most familiar type of symmetry for many people; in science and nature; and in the arts, covering architecture, art, and music.
The opposite of symmetry is asymmetry, which refers to the absence of symmetry.
In mathematics
In geometry
A geometric shape or object is symmetric if it can be divided into two or more identical pieces that are arranged in an organized fashion. This means that an object is symmetric if there is a transformation that moves individual pieces of the object, but doesn't change the overall shape. The type of symmetry is determined by the way the pieces are organized, or by the type of transformation:
An object has reflectional symmetry (line or mirror symmetry) if there is a line (or in 3D a plane) going through it which divides it into two pieces that are mirror images of each other.
An object has rotational symmetry if the object can be rotated about a fixed point (or in 3D about a line) without changing the overall shape.
An object has translational symmetry if it can be translated (moving every point of the object by the same distance) without changing its overall shape.
An object has helical symmetry if it can be simultaneously translated and rotated in three-dimensional space along a line known as a screw axis.
An object has scale symmetry if it does not change shape when it is expanded or contracted. Fractals also exhibit a form of scale symmetry, where smaller portions of the fractal are similar in shape to larger portions.
Other symmetries include glide reflection symmetry (a reflection followed by a translation) and rotoreflection symmetry (a combination of a rotation and a reflection).
In logic
A dyadic relation R = S × S is symmetric if for all elements a, b in S, whenever it is true that Rab, it is also true that Rba. Thus, the relation "is the same age as" is symmetric, for if Paul is the same age as Mary, then Mary is the same age as Paul.
In propositional logic, symmetric binary logical connectives include and (∧, or &), or (∨, or |) and if and only if (↔), while the connective if (→) is not symmetric. Other symmetric logical connectives include nand (not-and, or ⊼), xor (not-biconditional, or ⊻), and nor (not-or, or ⊽).
Other areas of mathematics
Generalizing from geometrical symmetry in the previous section, one can say that a mathematical object is symmetric with respect to a given mathematical operation, if, when applied to the object, this operation preserves some property of the object. The set of operations that preserve a given property of the object form a group.
In general, every kind of structure in mathematics will have its own kind of symmetry. Examples include even and odd functions in calculus, symmetric groups in abstract algebra, symmetric matrices in linear algebra, and Galois groups in Galois theory. In statistics, symmetry also manifests as symmetric probability distributions, and as skewness—the asymmetry of distributions.
In science and nature
In physics
Symmetry in physics has been generalized to mean invariance—that is, lack of change—under any kind of transformation, for example arbitrary coordinate transformations. This concept has become one of the most powerful tools of theoretical physics, as it has become evident that practically all laws of nature originate in symmetries. In fact, this role inspired the Nobel laureate PW Anderson to write in his widely read 1972 article More is Different that "it is only slightly overstating the case to say that physics is the study of symmetry." See Noether's theorem (which, in greatly simplified form, states that for every continuous mathematical symmetry, there is a corresponding conserved quantity such as energy or momentum; a conserved current, in Noether's original language); and also, Wigner's classification, which says that the symmetries of the laws of physics determine the properties of the particles found in nature.
Important symmetries in physics include continuous symmetries and discrete symmetries of spacetime; internal symmetries of particles; and supersymmetry of physical theories.
In biology
In biology, the notion of symmetry is mostly used explicitly to describe body shapes. Bilateral animals, including humans, are more or less symmetric with respect to the sagittal plane which divides the body into left and right halves. Animals that move in one direction necessarily have upper and lower sides, head and tail ends, and therefore a left and a right. The head becomes specialized with a mouth and sense organs, and the body becomes bilaterally symmetric for the purpose of movement, with symmetrical pairs of muscles and skeletal elements, though internal organs often remain asymmetric.
Plants and sessile (attached) animals such as sea anemones often have radial or rotational symmetry, which suits them because food or threats may arrive from any direction. Fivefold symmetry is found in the echinoderms, the group that includes starfish, sea urchins, and sea lilies.
In biology, the notion of symmetry is also used as in physics, that is to say to describe the properties of the objects studied, including their interactions. A remarkable property of biological evolution is the changes of symmetry corresponding to the appearance of new parts and dynamics.
In chemistry
Symmetry is important to chemistry because it undergirds essentially all specific interactions between molecules in nature (i.e., via the interaction of natural and human-made chiral molecules with inherently chiral biological systems). The control of the symmetry of molecules produced in modern chemical synthesis contributes to the ability of scientists to offer therapeutic interventions with minimal side effects. A rigorous understanding of symmetry explains fundamental observations in quantum chemistry, and in the applied areas of spectroscopy and crystallography. The theory and application of symmetry to these areas of physical science draws heavily on the mathematical area of group theory.
In psychology and neuroscience
For a human observer, some symmetry types are more salient than others, in particular the most salient is a reflection with a vertical axis, like that present in the human face. Ernst Mach made this observation in his book "The analysis of sensations" (1897), and this implies that perception of symmetry is not a general response to all types of regularities. Both behavioural and neurophysiological studies have confirmed the special sensitivity to reflection symmetry in humans and also in other animals. Early studies within the Gestalt tradition suggested that bilateral symmetry was one of the key factors in perceptual grouping. This is known as the Law of Symmetry. The role of symmetry in grouping and figure/ground organization has been confirmed in many studies. For instance, detection of reflectional symmetry is faster when this is a property of a single object. Studies of human perception and psychophysics have shown that detection of symmetry is fast, efficient and robust to perturbations. For example, symmetry can be detected with presentations between 100 and 150 milliseconds.
More recent neuroimaging studies have documented which brain regions are active during perception of symmetry. Sasaki et al. used functional magnetic resonance imaging (fMRI) to compare responses for patterns with symmetrical or random dots. A strong activity was present in extrastriate regions of the occipital cortex but not in the primary visual cortex. The extrastriate regions included V3A, V4, V7, and the lateral occipital complex (LOC). Electrophysiological studies have found a late posterior negativity that originates from the same areas. In general, a large part of the visual system seems to be involved in processing visual symmetry, and these areas involve similar networks to those responsible for detecting and recognising objects.
In social interactions
People observe the symmetrical nature, often including asymmetrical balance, of social interactions in a variety of contexts. These include assessments of reciprocity, empathy, sympathy, apology, dialogue, respect, justice, and revenge.
Reflective equilibrium is the balance that may be attained through deliberative mutual adjustment among general principles and specific judgments.
Symmetrical interactions send the moral message "we are all the same" while asymmetrical interactions may send the message "I am special; better than you." Peer relationships, such as can be governed by the Golden Rule, are based on symmetry, whereas power relationships are based on asymmetry. Symmetrical relationships can to some degree be maintained by simple (game theory) strategies seen in symmetric games such as tit for tat.
In the arts
There exists a list of journals and newsletters known to deal, at least in part, with symmetry and the arts.
In architecture
Symmetry finds its ways into architecture at every scale, from the overall external views of buildings such as Gothic cathedrals and The White House, through the layout of the individual floor plans, and down to the design of individual building elements such as tile mosaics. Islamic buildings such as the Taj Mahal and the Lotfollah mosque make elaborate use of symmetry both in their structure and in their ornamentation. Moorish buildings like the Alhambra are ornamented with complex patterns made using translational and reflection symmetries as well as rotations.
It has been said that only bad architects rely on a "symmetrical layout of blocks, masses and structures"; Modernist architecture, starting with International style, relies instead on "wings and balance of masses".
In pottery and metal vessels
Since the earliest uses of pottery wheels to help shape clay vessels, pottery has had a strong relationship to symmetry. Pottery created using a wheel acquires full rotational symmetry in its cross-section, while allowing substantial freedom of shape in the vertical direction. Upon this inherently symmetrical starting point, potters from ancient times onwards have added patterns that modify the rotational symmetry to achieve visual objectives.
Cast metal vessels lacked the inherent rotational symmetry of wheel-made pottery, but otherwise provided a similar opportunity to decorate their surfaces with patterns pleasing to those who used them. The ancient Chinese, for example, used symmetrical patterns in their bronze castings as early as the 17th century BC. Bronze vessels exhibited both a bilateral main motif and a repetitive translated border design.
In carpets and rugs
A long tradition of the use of symmetry in carpet and rug patterns spans a variety of cultures. American Navajo Indians used bold diagonals and rectangular motifs. Many Oriental rugs have intricate reflected centers and borders that translate a pattern. Not surprisingly, rectangular rugs have typically the symmetries of a rectangle—that is, motifs that are reflected across both the horizontal and vertical axes (see ).
In quilts
As quilts are made from square blocks (usually 9, 16, or 25 pieces to a block) with each smaller piece usually consisting of fabric triangles, the craft lends itself readily to the application of symmetry.
In other arts and crafts
Symmetries appear in the design of objects of all kinds. Examples include beadwork, furniture, sand paintings, knotwork, masks, and musical instruments. Symmetries are central to the art of M.C. Escher and the many applications of tessellation in art and craft forms such as wallpaper, ceramic tilework such as in Islamic geometric decoration, batik, ikat, carpet-making, and many kinds of textile and embroidery patterns.
Symmetry is also used in designing logos. By creating a logo on a grid and using the theory of symmetry, designers can organize their work, create a symmetric or asymmetrical design, determine the space between letters, determine how much negative space is required in the design, and how to accentuate parts of the logo to make it stand out.
In music
Symmetry is not restricted to the visual arts. Its role in the history of music touches many aspects of the creation and perception of music.
Musical form
Symmetry has been used as a formal constraint by many composers, such as the arch (swell) form (ABCBA) used by Steve Reich, Béla Bartók, and James Tenney. In classical music, Johann Sebastian Bach used the symmetry concepts of permutation and invariance.
Pitch structures
Symmetry is also an important consideration in the formation of scales and chords, traditional or tonal music being made up of non-symmetrical groups of pitches, such as the diatonic scale or the major chord. Symmetrical scales or chords, such as the whole tone scale, augmented chord, or diminished seventh chord (diminished-diminished seventh), are said to lack direction or a sense of forward motion, are ambiguous as to the key or tonal center, and have a less specific diatonic functionality. However, composers such as Alban Berg, Béla Bartók, and George Perle have used axes of symmetry and/or interval cycles in an analogous way to keys or non-tonal tonal centers. George Perle explains that "C–E, D–F♯, [and] Eb–G, are different instances of the same interval … the other kind of identity. … has to do with axes of symmetry. C–E belongs to a family of symmetrically related dyads as follows:"
Thus in addition to being part of the interval-4 family, C–E is also a part of the sum-4 family (with C equal to 0).
Interval cycles are symmetrical and thus non-diatonic. However, a seven pitch segment of C5 (the cycle of fifths, which are enharmonic with the cycle of fourths) will produce the diatonic major scale. Cyclic tonal progressions in the works of Romantic composers such as Gustav Mahler and Richard Wagner form a link with the cyclic pitch successions in the atonal music of Modernists such as Bartók, Alexander Scriabin, Edgard Varèse, and the Vienna school. At the same time, these progressions signal the end of tonality.
The first extended composition consistently based on symmetrical pitch relations was probably Alban Berg's Quartet, Op. 3 (1910).
Equivalency
Tone rows or pitch class sets which are invariant under retrograde are horizontally symmetrical, under inversion vertically. See also Asymmetric rhythm.
In aesthetics
The relationship of symmetry to aesthetics is complex. Humans find bilateral symmetry in faces physically attractive; it indicates health and genetic fitness. Opposed to this is the tendency for excessive symmetry to be perceived as boring or uninteresting. Rudolf Arnheim suggested that people prefer shapes that have some symmetry, and enough complexity to make them interesting.
In literature
Symmetry can be found in various forms in literature, a simple example being the palindrome where a brief text reads the same forwards or backwards. Stories may have a symmetrical structure, such as the rise and fall pattern of Beowulf.
See also
Automorphism
Burnside's lemma
Chirality
Even and odd functions
Fixed points of isometry groups in Euclidean space – center of symmetry
Isotropy
Palindrome
Spacetime symmetries
Spontaneous symmetry breaking
Symmetry-breaking constraints
Symmetric relation
Symmetries of polyiamonds
Symmetries of polyominoes
Symmetry group
Wallpaper group
Explanatory notes
References
Further reading
The Equation That Couldn't Be Solved: How Mathematical Genius Discovered the Language of Symmetry, Mario Livio, Souvenir Press, 2006, .
External links
International Symmetry Association (ISA)
Dutch: Symmetry Around a Point in the Plane
Chapman: Aesthetics of Symmetry
ISIS Symmetry
Symmetry, BBC Radio 4 discussion with Fay Dowker, Marcus du Sautoy & Ian Stewart (In Our Time, Apr. 19, 2007)
Aesthetics
Artistic techniques
Geometry
Theoretical physics | Symmetry | [
"Physics",
"Mathematics"
] | 3,318 | [
"Theoretical physics",
"Geometry",
"Symmetry"
] |
53,759 | https://en.wikipedia.org/wiki/Category%20%28mathematics%29 | In mathematics, a category (sometimes called an abstract category to distinguish it from a concrete category) is a collection of "objects" that are linked by "arrows". A category has two basic properties: the ability to compose the arrows associatively and the existence of an identity arrow for each object. A simple example is the category of sets, whose objects are sets and whose arrows are functions.
Category theory is a branch of mathematics that seeks to generalize all of mathematics in terms of categories, independent of what their objects and arrows represent. Virtually every branch of modern mathematics can be described in terms of categories, and doing so often reveals deep insights and similarities between seemingly different areas of mathematics. As such, category theory provides an alternative foundation for mathematics to set theory and other proposed axiomatic foundations. In general, the objects and arrows may be abstract entities of any kind, and the notion of category provides a fundamental and abstract way to describe mathematical entities and their relationships.
In addition to formalizing mathematics, category theory is also used to formalize many other systems in computer science, such as the semantics of programming languages.
Two categories are the same if they have the same collection of objects, the same collection of arrows, and the same associative method of composing any pair of arrows. Two different categories may also be considered "equivalent" for purposes of category theory, even if they do not have precisely the same structure.
Well-known categories are denoted by a short capitalized word or abbreviation in bold or italics: examples include Set, the category of sets and set functions; Ring, the category of rings and ring homomorphisms; and Top, the category of topological spaces and continuous maps. All of the preceding categories have the identity map as identity arrows and composition as the associative operation on arrows.
The classic and still much used text on category theory is Categories for the Working Mathematician by Saunders Mac Lane. Other references are given in the References below. The basic definitions in this article are contained within the first few chapters of any of these books.
Any monoid can be understood as a special sort of category (with a single object whose self-morphisms are represented by the elements of the monoid), and so can any preorder.
Definition
There are many equivalent definitions of a category. One commonly used definition is as follows. A category C consists of
a class ob(C) of objects,
a class mor(C) of morphisms or arrows,
a domain or source class function dom: mor(C) → ob(C),
a codomain or target class function cod: mor(C) → ob(C),
for every three objects a, b and c, a binary operation hom(a, b) × hom(b, c) → hom(a, c) called composition of morphisms. Here hom(a, b) denotes the subclass of morphisms f in mor(C) such that dom(f) = a and cod(f) = b. Morphisms in this subclass are written f : a → b, and the composite of f : a → b and g : b → c is often written as g ∘ f or gf.
such that the following axioms hold:
the associative law: if f : a → b, g : b → c and h : c → d then h ∘ (g ∘ f) = (h ∘ g) ∘ f, and
the (left and right unit laws): for every object x, there exists a morphism 1x : x → x (some authors write idx) called the identity morphism for x, such that every morphism f : a → x satisfies 1x ∘ f = f, and every morphism g : x → b satisfies g ∘ 1x = g.
We write f: a → b, and we say "f is a morphism from a to b". We write hom(a, b) (or homC(a, b) when there may be confusion about to which category hom(a, b) refers) to denote the hom-class of all morphisms from a to b.
Some authors write the composite of morphisms in "diagrammatic order", writing f;g or fg instead of g ∘ f.
From these axioms, one can prove that there is exactly one identity morphism for every object. Often the map assigning each object its identity morphism is treated as an extra part of the structure of a category, namely a class function i: ob(C) → mor(C).
Some authors use a slight variant of the definition in which each object is identified with the corresponding identity morphism. This stems from the idea that the fundamental data of categories are morphisms and not objects. In fact, categories can be defined without reference to objects at all using a partial binary operation with additional properties.
Small and large categories
A category C is called small if both ob(C) and hom(C) are actually sets and not proper classes, and large otherwise. A locally small category is a category such that for all objects a and b, the hom-class hom(a, b) is a set, called a homset. Many important categories in mathematics (such as the category of sets), although not small, are at least locally small. Since, in small categories, the objects form a set, a small category can be viewed as an algebraic structure similar to a monoid but without requiring closure properties. Large categories on the other hand can be used to create "structures" of algebraic structures.
Examples
The class of all sets (as objects) together with all functions between them (as morphisms), where the composition of morphisms is the usual function composition, forms a large category, Set. It is the most basic and the most commonly used category in mathematics. The category Rel consists of all sets (as objects) with binary relations between them (as morphisms). Abstracting from relations instead of functions yields allegories, a special class of categories.
Any class can be viewed as a category whose only morphisms are the identity morphisms. Such categories are called discrete. For any given set I, the discrete category on I is the small category that has the elements of I as objects and only the identity morphisms as morphisms. Discrete categories are the simplest kind of category.
Any preordered set (P, ≤) forms a small category, where the objects are the members of P, the morphisms are arrows pointing from x to y when x ≤ y. Furthermore, if ≤ is antisymmetric, there can be at most one morphism between any two objects. The existence of identity morphisms and the composability of the morphisms are guaranteed by the reflexivity and the transitivity of the preorder. By the same argument, any partially ordered set and any equivalence relation can be seen as a small category. Any ordinal number can be seen as a category when viewed as an ordered set.
Any monoid (any algebraic structure with a single associative binary operation and an identity element) forms a small category with a single object x. (Here, x is any fixed set.) The morphisms from x to x are precisely the elements of the monoid, the identity morphism of x is the identity of the monoid, and the categorical composition of morphisms is given by the monoid operation. Several definitions and theorems about monoids may be generalized for categories.
Similarly any group can be seen as a category with a single object in which every morphism is invertible, that is, for every morphism f there is a morphism g that is both left and right inverse to f under composition. A morphism that is invertible in this sense is called an isomorphism.
A groupoid is a category in which every morphism is an isomorphism. Groupoids are generalizations of groups, group actions and equivalence relations. Actually, in the view of category the only difference between groupoid and group is that a groupoid may have more than one object but the group must have only one. Consider a topological space X and fix a base point of X, then is the fundamental group of the topological space X and the base point , and as a set it has the structure of group; if then let the base point runs over all points of X, and take the union of all , then the set we get has only the structure of groupoid (which is called as the fundamental groupoid of X): two loops (under equivalence relation of homotopy) may not have the same base point so they cannot multiply with each other. In the language of category, this means here two morphisms may not have the same source object (or target object, because in this case for any morphism the source object and the target object are same: the base point) so they can not compose with each other.
Any directed graph generates a small category: the objects are the vertices of the graph, and the morphisms are the paths in the graph (augmented with loops as needed) where composition of morphisms is concatenation of paths. Such a category is called the free category generated by the graph.
The class of all preordered sets with order-preserving functions (i.e., monotone-increasing functions) as morphisms forms a category, Ord. It is a concrete category, i.e. a category obtained by adding some type of structure onto Set, and requiring that morphisms are functions that respect this added structure.
The class of all groups with group homomorphisms as morphisms and function composition as the composition operation forms a large category, Grp. Like Ord, Grp is a concrete category. The category Ab, consisting of all abelian groups and their group homomorphisms, is a full subcategory of Grp, and the prototype of an abelian category.
The class of all graphs forms another concrete category, where morphisms are graph homomorphisms (i.e., mappings between graphs which send vertices to vertices and edges to edges in a way that preserves all adjacency and incidence relations).
Other examples of concrete categories are given by the following table.
Fiber bundles with bundle maps between them form a concrete category.
The category Cat consists of all small categories, with functors between them as morphisms.
Construction of new categories
Dual category
Any category C can itself be considered as a new category in a different way: the objects are the same as those in the original category but the arrows are those of the original category reversed. This is called the dual or opposite category and is denoted Cop.
Product categories
If C and D are categories, one can form the product category C × D: the objects are pairs consisting of one object from C and one from D, and the morphisms are also pairs, consisting of one morphism in C and one in D. Such pairs can be composed componentwise.
Types of morphisms
A morphism f : a → b is called
a monomorphism (or monic) if it is left-cancellable, i.e. fg1 = fg2 implies g1 = g2 for all morphisms g1, g2 : x → a.
an epimorphism (or epic) if it is right-cancellable, i.e. g1f = g2f implies g1 = g2 for all morphisms g1, g2 : b → x.
a bimorphism if it is both a monomorphism and an epimorphism.
a retraction if it has a right inverse, i.e. if there exists a morphism g : b → a with fg = 1b.
a section if it has a left inverse, i.e. if there exists a morphism g : b → a with gf = 1a.
an isomorphism if it has an inverse, i.e. if there exists a morphism g : b → a with fg = 1b and gf = 1a.
an endomorphism if a = b. The class of endomorphisms of a is denoted end(a). For locally small categories, end(a) is a set and forms a monoid under morphism composition.
an automorphism if f is both an endomorphism and an isomorphism. The class of automorphisms of a is denoted aut(a). For locally small categories, it forms a group under morphism composition called the automorphism group of a.
Every retraction is an epimorphism. Every section is a monomorphism. The following three statements are equivalent:
f is a monomorphism and a retraction;
f is an epimorphism and a section;
f is an isomorphism.
Relations among morphisms (such as fg = h) can most conveniently be represented with commutative diagrams, where the objects are represented as points and the morphisms as arrows.
Types of categories
In many categories, e.g. Ab or VectK, the hom-sets hom(a, b) are not just sets but actually abelian groups, and the composition of morphisms is compatible with these group structures; i.e. is bilinear. Such a category is called preadditive. If, furthermore, the category has all finite products and coproducts, it is called an additive category. If all morphisms have a kernel and a cokernel, and all epimorphisms are cokernels and all monomorphisms are kernels, then we speak of an abelian category. A typical example of an abelian category is the category of abelian groups.
A category is called complete if all small limits exist in it. The categories of sets, abelian groups and topological spaces are complete.
A category is called cartesian closed if it has finite direct products and a morphism defined on a finite product can always be represented by a morphism defined on just one of the factors. Examples include Set and CPO, the category of complete partial orders with Scott-continuous functions.
A topos is a certain type of cartesian closed category in which all of mathematics can be formulated (just like classically all of mathematics is formulated in the category of sets). A topos can also be used to represent a logical theory.
See also
Enriched category
Higher category theory
Quantaloid
Table of mathematical symbols
Space (mathematics)
Structure (mathematics)
Notes
References
(now free on-line edition, GNU FDL).
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Algebraic structures | Category (mathematics) | [
"Mathematics"
] | 3,087 | [
"Functions and mappings",
"Mathematical structures",
"Mathematical objects",
"Fields of abstract algebra",
"Mathematical relations",
"Category theory",
"Algebraic structures"
] |
53,776 | https://en.wikipedia.org/wiki/Kruskal%27s%20algorithm | Kruskal's algorithm finds a minimum spanning forest of an undirected edge-weighted graph. If the graph is connected, it finds a minimum spanning tree. It is a greedy algorithm that in each step adds to the forest the lowest-weight edge that will not form a cycle. The key steps of the algorithm are sorting and the use of a disjoint-set data structure to detect cycles. Its running time is dominated by the time to sort all of the graph edges by their weight.
A minimum spanning tree of a connected weighted graph is a connected subgraph, without cycles, for which the sum of the weights of all the edges in the subgraph is minimal. For a disconnected graph, a minimum spanning forest is composed of a minimum spanning tree for each connected component.
This algorithm was first published by Joseph Kruskal in 1956, and was rediscovered soon afterward by . Other algorithms for this problem include Prim's algorithm, Borůvka's algorithm, and the reverse-delete algorithm.
Algorithm
The algorithm performs the following steps:
Create a forest (a set of trees) initially consisting of a separate single-vertex tree for each vertex in the input graph.
Sort the graph edges by weight.
Loop through the edges of the graph, in ascending sorted order by their weight. For each edge:
Test whether adding the edge to the current forest would create a cycle.
If not, add the edge to the forest, combining two trees into a single tree.
At the termination of the algorithm, the forest forms a minimum spanning forest of the graph. If the graph is connected, the forest has a single component and forms a minimum spanning tree.
Pseudocode
The following code is implemented with a disjoint-set data structure. It represents the forest F as a set of undirected edges, and uses the disjoint-set data structure to efficiently determine whether two vertices are part of the same tree.
algorithm Kruskal(G) is
F:= ∅
for each v in G.V do
MAKE-SET(v)
for each {u, v} in G.E ordered by weight({u, v}), increasing do
if FIND-SET(u) ≠ FIND-SET(v) then
F := F ∪ { {u, v} }
UNION(FIND-SET(u), FIND-SET(v))
return F
Complexity
For a graph with edges and vertices, Kruskal's algorithm can be shown to run in time time, with simple data structures. Here, expresses the time in big O notation, and is a logarithm to any base (since inside -notation logarithms to all bases are equivalent, because they are the same up to a constant factor). This time bound is often written instead as , which is equivalent for graphs with no isolated vertices, because for these graphs and the logarithms of and are again within a constant factor of each other.
To achieve this bound, first sort the edges by weight using a comparison sort in time. Once sorted, it is possible to loop through the edges in sorted order in constant time per edge. Next, use a disjoint-set data structure, with a set of vertices for each component, to keep track of which vertices are in which components. Creating this structure, with a separate set for each vertex, takes operations and time. The final iteration through all edges performs two find operations and possibly one union operation per edge. These operations take amortized time time per operation, giving worst-case total time for this loop, where is the extremely slowly growing inverse Ackermann function. This part of the time bound is much smaller than the time for the sorting step, so the total time for the algorithm can be simplified to the time for the sorting step.
In cases where the edges are already sorted, or where they have small enough integer weight to allow integer sorting algorithms such as counting sort or radix sort to sort them in linear time, the disjoint set operations are the slowest remaining part of the algorithm and the total time is {{math|O(E α(V))}}.
Example
Proof of correctness
The proof consists of two parts. First, it is proved that the algorithm produces a spanning tree. Second, it is proved that the constructed spanning tree is of minimal weight.
Spanning tree
Let be a connected, weighted graph and let be the subgraph of produced by the algorithm. cannot have a cycle, as by definition an edge is not added if it results in a cycle. cannot be disconnected, since the first encountered edge that joins two components of would have been added by the algorithm. Thus, is a spanning tree of .
Minimality
We show that the following proposition P is true by induction: If F is the set of edges chosen at any stage of the algorithm, then there is some minimum spanning tree that contains F and none of the edges rejected by the algorithm.
Clearly P is true at the beginning, when F is empty: any minimum spanning tree will do, and there exists one because a weighted connected graph always has a minimum spanning tree.
Now assume P is true for some non-final edge set F and let T be a minimum spanning tree that contains F.
If the next chosen edge e is also in T, then P is true for F + e.
Otherwise, if e is not in T then T + e has a cycle C. The cycle C contains edges which do not belong to F + e, since e does not form a cycle when added to F but does in T. Let f be an edge which is in C but not in F + e. Note that f also belongs to T, since f belongs to T + e but not F + e. By P, f has not been considered by the algorithm. f must therefore have a weight at least as large as e. Then T − f + e is a tree, and it has the same or less weight as T. However since T is a minimum spanning tree then T − f + e has the same weight as T, otherwise we get a contradiction and T would not be a minimum spanning tree. So T − f + e is a minimum spanning tree containing F + e and again P holds.
Therefore, by the principle of induction, P holds when F has become a spanning tree, which is only possible if F is a minimum spanning tree itself.
Parallel algorithm
Kruskal's algorithm is inherently sequential and hard to parallelize. It is, however, possible to perform the initial sorting of the edges in parallel or, alternatively, to use a parallel implementation of a binary heap to extract the minimum-weight edge in every iteration.
As parallel sorting is possible in time on processors, the runtime of Kruskal's algorithm can be reduced to O(E α(V)), where α again is the inverse of the single-valued Ackermann function.
A variant of Kruskal's algorithm, named Filter-Kruskal, has been described by Osipov et al. and is better suited for parallelization. The basic idea behind Filter-Kruskal is to partition the edges in a similar way to quicksort and filter out edges that connect vertices of the same tree to reduce the cost of sorting. The following pseudocode demonstrates this.
function filter_kruskal(G) is
if |G.E| < kruskal_threshold:
return kruskal(G)
pivot = choose_random(G.E)
E, E = partition(G.E, pivot)
A = filter_kruskal(E)
E = filter(E)
A = A ∪ filter_kruskal(E)
return A
function partition(E, pivot) is
E = ∅, E = ∅
foreach (u, v) in E do
if weight(u, v) ≤ pivot then
E = E ∪ {(u, v)}
else
E = E ∪ {(u, v)}
return E, E
function filter(E) is
E = ∅
foreach (u, v) in E do
if find_set(u) ≠ find_set(v) then
E = E ∪ {(u, v)}
return E
Filter-Kruskal lends itself better to parallelization as sorting, filtering, and partitioning can easily be performed in parallel by distributing the edges between the processors.
Finally, other variants of a parallel implementation of Kruskal's algorithm have been explored. Examples include a scheme that uses helper threads to remove edges that are definitely not part of the MST in the background, and a variant which runs the sequential algorithm on p subgraphs, then merges those subgraphs until only one, the final MST, remains.
See also
Prim's algorithm
Dijkstra's algorithm
Borůvka's algorithm
Reverse-delete algorithm
Single-linkage clustering
Greedy geometric spanner
References
Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest, and Clifford Stein. Introduction to Algorithms, Second Edition. MIT Press and McGraw-Hill, 2001. . Section 23.2: The algorithms of Kruskal and Prim, pp. 567–574.
Michael T. Goodrich and Roberto Tamassia. Data Structures and Algorithms in Java'', Fourth Edition. John Wiley & Sons, Inc., 2006. . Section 13.7.1: Kruskal's Algorithm, pp. 632..
External links
Data for the article's example.
Gephi Plugin For Calculating a Minimum Spanning Tree source code.
Kruskal's Algorithm with example and program in c++
Kruskal's Algorithm code in C++ as applied to random numbers
Kruskal's Algorithm code in Python with explanation
Graph algorithms
Spanning tree
Articles with example pseudocode
Articles containing proofs
Greedy algorithms | Kruskal's algorithm | [
"Mathematics"
] | 2,038 | [
"Articles containing proofs"
] |
53,781 | https://en.wikipedia.org/wiki/Relative%20permittivity | The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulator measures the ability of the insulator to store electric energy in an electrical field.
Permittivity is a material's property that affects the Coulomb force between two point charges in the material. Relative permittivity is the factor by which the electric field between the charges is decreased relative to vacuum.
Likewise, relative permittivity is the ratio of the capacitance of a capacitor using that material as a dielectric, compared with a similar capacitor that has vacuum as its dielectric. Relative permittivity is also commonly known as the dielectric constant, a term still used but deprecated by standards organizations in engineering as well as in chemistry.
Definition
Relative permittivity is typically denoted as (sometimes , lowercase kappa) and is defined as
where ε(ω) is the complex frequency-dependent permittivity of the material, and ε0 is the vacuum permittivity.
Relative permittivity is a dimensionless number that is in general complex-valued; its real and imaginary parts are denoted as:
The relative permittivity of a medium is related to its electric susceptibility, , as .
In anisotropic media (such as non cubic crystals) the relative permittivity is a second rank tensor.
The relative permittivity of a material for a frequency of zero is known as its static relative permittivity.
Terminology
The historical term for the relative permittivity is dielectric constant. It is still commonly used, but has been deprecated by standards organizations, because of its ambiguity, as some older reports used it for the absolute permittivity ε. The permittivity may be quoted either as a static property or as a frequency-dependent variant, in which case it is also known as the dielectric function. It has also been used to refer to only the real component ε′r of the complex-valued relative permittivity.
Physics
In the causal theory of waves, permittivity is a complex quantity. The imaginary part corresponds to a phase shift of the polarization relative to and leads to the attenuation of electromagnetic waves passing through the medium. By definition, the linear relative permittivity of vacuum is equal to 1, that is , although there are theoretical nonlinear quantum effects in vacuum that become non-negligible at high field strengths.
The following table gives some typical values.
The relative low frequency permittivity of ice is ~96 at −10.8 °C, falling to 3.15 at high frequency, which is independent of temperature. It remains in the range 3.12–3.19 for frequencies between about 1 MHz and the far infrared region.
Measurement
The relative static permittivity, εr, can be measured for static electric fields as follows: first the capacitance of a test capacitor, C0, is measured with vacuum between its plates. Then, using the same capacitor and distance between its plates, the capacitance C with a dielectric between the plates is measured. The relative permittivity can be then calculated as
For time-variant electromagnetic fields, this quantity becomes frequency-dependent. An indirect technique to calculate εr is conversion of radio frequency S-parameter measurement results. A description of frequently used S-parameter conversions for determination of the frequency-dependent εr of dielectrics can be found in this bibliographic source. Alternatively, resonance based effects may be employed at fixed frequencies.
Applications
Energy
The relative permittivity is an essential piece of information when designing capacitors, and in other circumstances where a material might be expected to introduce capacitance into a circuit. If a material with a high relative permittivity is placed in an electric field, the magnitude of that field will be measurably reduced within the volume of the dielectric. This fact is commonly used to increase the capacitance of a particular capacitor design. The layers beneath etched conductors in printed circuit boards (PCBs) also act as dielectrics.
Communication
Dielectrics are used in radio frequency (RF) transmission lines. In a coaxial cable, polyethylene can be used between the center conductor and outside shield. It can also be placed inside waveguides to form filters. Optical fibers are examples of dielectric waveguides. They consist of dielectric materials that are purposely doped with impurities so as to control the precise value of εr within the cross-section. This controls the refractive index of the material and therefore also the optical modes of transmission. However, in these cases it is technically the relative permittivity that matters, as they are not operated in the electrostatic limit.
Environment
The relative permittivity of air changes with temperature, humidity, and barometric pressure. Sensors can be constructed to detect changes in capacitance caused by changes in the relative permittivity. Most of this change is due to effects of temperature and humidity as the barometric pressure is fairly stable. Using the capacitance change, along with the measured temperature, the relative humidity can be obtained using engineering formulas.
Chemistry
The relative static permittivity of a solvent is a relative measure of its chemical polarity. For example, water is very polar, and has a relative static permittivity of 80.10 at 20 °C while n-hexane is non-polar, and has a relative static permittivity of 1.89 at 20 °C. This information is important when designing separation, sample preparation and chromatography techniques in analytical chemistry.
The correlation should, however, be treated with caution. For instance, dichloromethane has a value of εr of 9.08 (20 °C) and is rather poorly soluble in water (13g/L or 9.8mL/L at 20 °C); at the same time, tetrahydrofuran has its εr = 7.52 at 22 °C, but it is completely miscible with water. In the case of tetrahydrofuran, the oxygen atom can act as a hydrogen bond acceptor; whereas dichloromethane cannot form hydrogen bonds with water.
This is even more remarkable when comparing the εr values of acetic acid (6.2528) and that of iodoethane (7.6177). The large numerical value of εr is not surprising in the second case, as the iodine atom is easily polarizable; nevertheless, this does not imply that it is polar, too (electronic polarizability prevails over the orientational one in this case).
Lossy medium
Again, similar as for absolute permittivity, relative permittivity for lossy materials can be formulated as:
in terms of a "dielectric conductivity" σ (units S/m, siemens per meter), which "sums over all the dissipative effects of the material; it may represent an actual [electrical] conductivity caused by migrating charge carriers and it may also refer to an energy loss associated with the dispersion of ε′ [the real-valued permittivity]" ( p. 8). Expanding the angular frequency and the electric constant , which reduces to:
where λ is the wavelength, c is the speed of light in vacuum and = 59.95849 Ω ≈ 60.0 Ω is a newly introduced constant (units ohms, or reciprocal siemens, such that σλκ = εr remains unitless).
Metals
Permittivity is typically associated with dielectric materials, however metals are described as having an effective permittivity, with real relative permittivity equal to one. In the high-frequency region, which extends from radio frequencies to the far infrared and terahertz region, the plasma frequency of the electron gas is much greater than the electromagnetic propagation frequency, so the refractive index n of a metal is very nearly a purely imaginary number. In the low frequency regime, the effective relative permittivity is also almost purely imaginary: It has a very large imaginary value related to the conductivity and a comparatively insignificant real-value.
See also
Curie temperature
Dielectric spectroscopy
Dielectric strength
Electret
Ferroelectricity
Green–Kubo relations
High-κ dielectric
Kramers–Kronig relation
Linear response function
Low-κ dielectric
Loss tangent
Permittivity
Refractive index
Permeability (electromagnetism)
References
Electricity
Electric and magnetic fields in matter
Colloidal chemistry | Relative permittivity | [
"Physics",
"Chemistry",
"Materials_science",
"Engineering"
] | 1,804 | [
"Colloidal chemistry",
"Electric and magnetic fields in matter",
"Colloids",
"Surface science",
"Materials science",
"Condensed matter physics"
] |
53,783 | https://en.wikipedia.org/wiki/Prim%27s%20algorithm | In computer science, Prim's algorithm is a greedy algorithm that finds a minimum spanning tree for a weighted undirected graph. This means it finds a subset of the edges that forms a tree that includes every vertex, where the total weight of all the edges in the tree is minimized. The algorithm operates by building this tree one vertex at a time, from an arbitrary starting vertex, at each step adding the cheapest possible connection from the tree to another vertex.
The algorithm was developed in 1930 by Czech mathematician Vojtěch Jarník and later rediscovered and republished by computer scientists Robert C. Prim in 1957 and Edsger W. Dijkstra in 1959. Therefore, it is also sometimes called the Jarník's algorithm, Prim–Jarník algorithm, Prim–Dijkstra algorithm
or the DJP algorithm.
Other well-known algorithms for this problem include Kruskal's algorithm and Borůvka's algorithm. These algorithms find the minimum spanning forest in a possibly disconnected graph; in contrast, the most basic form of Prim's algorithm only finds minimum spanning trees in connected graphs. However, running Prim's algorithm separately for each connected component of the graph, it can also be used to find the minimum spanning forest. In terms of their asymptotic time complexity, these three algorithms are equally fast for sparse graphs, but slower than other more sophisticated algorithms.
However, for graphs that are sufficiently dense, Prim's algorithm can be made to run in linear time, meeting or improving the time bounds for other algorithms.
Description
The algorithm may informally be described as performing the following steps:
In more detail, it may be implemented following the pseudocode below.
As described above, the starting vertex for the algorithm will be chosen arbitrarily, because the first iteration of the main loop of the algorithm will have a set of vertices in Q that all have equal weights, and the algorithm will automatically start a new tree in F when it completes a spanning tree of each connected component of the input graph. The algorithm may be modified to start with any particular vertex s by setting C[s] to be a number smaller than the other values of C (for instance, zero), and it may be modified to only find a single spanning tree rather than an entire spanning forest (matching more closely the informal description) by stopping whenever it encounters another vertex flagged as having no associated edge.
Different variations of the algorithm differ from each other in how the set Q is implemented: as a simple linked list or array of vertices, or as a more complicated priority queue data structure. This choice leads to differences in the time complexity of the algorithm. In general, a priority queue will be quicker at finding the vertex v with minimum cost, but will entail more expensive updates when the value of C[w] changes.
Time complexity
The time complexity of Prim's algorithm depends on the data structures used for the graph and for ordering the edges by weight, which can be done using a priority queue. The following table shows the typical choices:
A simple implementation of Prim's, using an adjacency matrix or an adjacency list graph representation and linearly searching an array of weights to find the minimum weight edge to add, requires O(|V|2) running time. However, this running time can be greatly improved by using heaps to implement finding minimum weight edges in the algorithm's inner loop.
A first improved version uses a heap to store all edges of the input graph, ordered by their weight. This leads to an O(|E| log |E|) worst-case running time. But storing vertices instead of edges can improve it still further. The heap should order the vertices by the smallest edge-weight that connects them to any vertex in the partially constructed minimum spanning tree (MST) (or infinity if no such edge exists). Every time a vertex v is chosen and added to the MST, a decrease-key operation is performed on all vertices w outside the partial MST such that v is connected to w, setting the key to the minimum of its previous value and the edge cost of (v,w).
Using a simple binary heap data structure, Prim's algorithm can now be shown to run in time O(|E| log |V|) where |E| is the number of edges and |V| is the number of vertices. Using a more sophisticated Fibonacci heap, this can be brought down to O(|E| + |V| log |V|), which is asymptotically faster when the graph is dense enough that |E| is ω(|V|), and linear time when |E| is at least |V| log |V|. For graphs of even greater density (having at least |V|c edges for some c > 1), Prim's algorithm can be made to run in linear time even more simply, by using a d-ary heap in place of a Fibonacci heap.
Proof of correctness
Let P be a connected, weighted graph. At every iteration of Prim's algorithm, an edge must be found that connects a vertex in a subgraph to a vertex outside the subgraph. Since P is connected, there will always be a path to every vertex. The output Y of Prim's algorithm is a tree, because the edge and vertex added to tree Y are connected. Let Y1 be a minimum spanning tree of graph P. If Y1=Y then Y is a minimum spanning tree. Otherwise, let e be the first edge added during the construction of tree Y that is not in tree Y1, and V be the set of vertices connected by the edges added before edge e. Then one endpoint of edge e is in set V and the other is not. Since tree Y1 is a spanning tree of graph P, there is a path in tree Y1 joining the two endpoints. As one travels along the path, one must encounter an edge f joining a vertex in set V to one that is not in set V. Now, at the iteration when edge e was added to tree Y, edge f could also have been added and it would be added instead of edge e if its weight was less than e, and since edge f was not added, we conclude that
Let tree Y2 be the graph obtained by removing edge f from and adding edge e to tree Y1. It is easy to show that tree Y2 is connected, has the same number of edges as tree Y1, and the total weights of its edges is not larger than that of tree Y1, therefore it is also a minimum spanning tree of graph P and it contains edge e and all the edges added before it during the construction of set V. Repeat the steps above and we will eventually obtain a minimum spanning tree of graph P that is identical to tree Y. This shows Y is a minimum spanning tree. The minimum spanning tree allows for the first subset of the sub-region to be expanded into a larger subset X, which we assume to be the minimum.
Parallel algorithm
The main loop of Prim's algorithm is inherently sequential and thus not parallelizable. However, the inner loop, which determines the next edge of minimum weight that does not form a cycle, can be parallelized by dividing the vertices and edges between the available processors. The following pseudocode demonstrates this.
This algorithm can generally be implemented on distributed machines as well as on shared memory machines. The running time is , assuming that the reduce and broadcast operations can be performed in . A variant of Prim's algorithm for shared memory machines, in which Prim's sequential algorithm is being run in parallel, starting from different vertices, has also been explored. It should, however, be noted that more sophisticated algorithms exist to solve the distributed minimum spanning tree problem in a more efficient manner.
See also
Dijkstra's algorithm, a very similar algorithm for the shortest path problem
Greedoids offer a general way to understand the correctness of Prim's algorithm
References
External links
Prim's Algorithm progress on randomly distributed points
Graph algorithms
Spanning tree
Articles containing proofs
Articles containing video clips
Greedy algorithms
Articles with example pseudocode | Prim's algorithm | [
"Mathematics"
] | 1,688 | [
"Articles containing proofs"
] |
53,784 | https://en.wikipedia.org/wiki/Brute-force%20attack | In cryptography, a brute-force attack consists of an attacker submitting many passwords or passphrases with the hope of eventually guessing correctly. The attacker systematically checks all possible passwords and passphrases until the correct one is found. Alternatively, the attacker can attempt to guess the key which is typically created from the password using a key derivation function. This is known as an exhaustive key search. This approach doesn't depend on intellectual tactics; rather, it relies on making several attempts.
A brute-force attack is a cryptanalytic attack that can, in theory, be used to attempt to decrypt any encrypted data (except for data encrypted in an information-theoretically secure manner). Such an attack might be used when it is not possible to take advantage of other weaknesses in an encryption system (if any exist) that would make the task easier.
When password-guessing, this method is very fast when used to check all short passwords, but for longer passwords other methods such as the dictionary attack are used because a brute-force search takes too long. Longer passwords, passphrases and keys have more possible values, making them exponentially more difficult to crack than shorter ones due to diversity of characters.
Brute-force attacks can be made less effective by obfuscating the data to be encoded making it more difficult for an attacker to recognize when the code has been cracked or by making the attacker do more work to test each guess. One of the measures of the strength of an encryption system is how long it would theoretically take an attacker to mount a successful brute-force attack against it.
Brute-force attacks are an application of brute-force search, the general problem-solving technique of enumerating all candidates and checking each one. The word 'hammering' is sometimes used to describe a brute-force attack, with 'anti-hammering' for countermeasures.
Basic concept
Brute-force attacks work by calculating every possible combination that could make up a password and testing it to see if it is the correct password. As the password's length increases, the amount of time, on average, to find the correct password increases exponentially.
Theoretical limits
The resources required for a brute-force attack grow exponentially with increasing key size, not linearly. Although U.S. export regulations historically restricted key lengths to 56-bit symmetric keys (e.g. Data Encryption Standard), these restrictions are no longer in place, so modern symmetric algorithms typically use computationally stronger 128- to 256-bit keys.
There is a physical argument that a 128-bit symmetric key is computationally secure against brute-force attack. The Landauer limit implied by the laws of physics sets a lower limit on the energy required to perform a computation of per bit erased in a computation, where T is the temperature of the computing device in kelvins, k is the Boltzmann constant, and the natural logarithm of 2 is about 0.693 (0.6931471805599453). No irreversible computing device can use less energy than this, even in principle. Thus, in order to simply flip through the possible values for a 128-bit symmetric key (ignoring doing the actual computing to check it) would, theoretically, require 2128 − 1 bit flips on a conventional processor. If it is assumed that the calculation occurs near room temperature (≈300 K), the Von Neumann-Landauer Limit can be applied to estimate the energy required as ≈1018 joules, which is equivalent to consuming 30 gigawatts of power for one year. This is equal to 30×109 W×365×24×3600 s = 9.46×1017 J or 262.7 TWh (about 0.1% of the yearly world energy production). The full actual computation – checking each key to see if a solution has been found – would consume many times this amount. Furthermore, this is simply the energy requirement for cycling through the key space; the actual time it takes to flip each bit is not considered, which is certainly greater than 0 (see Bremermann's limit).
However, this argument assumes that the register values are changed using conventional set and clear operations, which inevitably generate entropy. It has been shown that computational hardware can be designed not to encounter this theoretical obstruction (see reversible computing), though no such computers are known to have been constructed.
As commercial successors of governmental ASIC solutions have become available, also known as custom hardware attacks, two emerging technologies have proven their capability in the brute-force attack of certain ciphers. One is modern graphics processing unit (GPU) technology, the other is the field-programmable gate array (FPGA) technology. GPUs benefit from their wide availability and price-performance benefit, FPGAs from their energy efficiency per cryptographic operation. Both technologies try to transport the benefits of parallel processing to brute-force attacks. In case of GPUs some hundreds, in the case of FPGA some thousand processing units making them much better suited to cracking passwords than conventional processors. For instance in 2022, 8 Nvidia RTX 4090 GPU were linked together to test password strength by using the software Hashcat with results that showed 200 billion eight-character NTLM password combinations could be cycled through in 48 minutes.
Various publications in the fields of cryptographic analysis have proved the energy efficiency of today's FPGA technology, for example, the COPACOBANA FPGA Cluster computer consumes the same energy as a single PC (600 W), but performs like 2,500 PCs for certain algorithms. A number of firms provide hardware-based FPGA cryptographic analysis solutions from a single FPGA PCI Express card up to dedicated FPGA computers. WPA and WPA2 encryption have successfully been brute-force attacked by reducing the workload by a factor of 50 in comparison to conventional CPUs and some hundred in case of FPGAs.
Advanced Encryption Standard (AES) permits the use of 256-bit keys. Breaking a symmetric 256-bit key by brute-force requires 2128 times more computational power than a 128-bit key. One of the fastest supercomputers in 2019 has a speed of 100 petaFLOPS which could theoretically check 100 trillion (1014) AES keys per second (assuming 1000 operations per check), but would still require 3.67×1055 years to exhaust the 256-bit key space.
An underlying assumption of a brute-force attack is that the complete key space was used to generate keys, something that relies on an effective random number generator, and that there are no defects in the algorithm or its implementation. For example, a number of systems that were originally thought to be impossible to crack by brute-force have nevertheless been cracked because the key space to search through was found to be much smaller than originally thought, because of a lack of entropy in their pseudorandom number generators. These include Netscape's implementation of Secure Sockets Layer (SSL) (cracked by Ian Goldberg and David Wagner in 1995) and a Debian/Ubuntu edition of OpenSSL discovered in 2008 to be flawed. A similar lack of implemented entropy led to the breaking of Enigma's code.
Credential recycling
Credential recycling is the hacking practice of re-using username and password combinations gathered in previous brute-force attacks. A special form of credential recycling is pass the hash, where unsalted hashed credentials are stolen and re-used without first being brute-forced.
Unbreakable codes
Certain types of encryption, by their mathematical properties, cannot be defeated by brute-force. An example of this is one-time pad cryptography, where every cleartext bit has a corresponding key from a truly random sequence of key bits. A 140 character one-time-pad-encoded string subjected to a brute-force attack would eventually reveal every 140 character string possible, including the correct answer – but of all the answers given, there would be no way of knowing which was the correct one. Defeating such a system, as was done by the Venona project, generally relies not on pure cryptography, but upon mistakes in its implementation, such as the key pads not being truly random, intercepted keypads, or operators making mistakes.
Countermeasures
In case of an offline attack where the attacker has gained access to the encrypted material, one can try key combinations without the risk of discovery or interference. In case of online attacks, database and directory administrators can deploy countermeasures such as limiting the number of attempts that a password can be tried, introducing time delays between successive attempts, increasing the answer's complexity (e.g., requiring a CAPTCHA answer or employing multi-factor authentication), and/or locking accounts out after unsuccessful login attempts. Website administrators may prevent a particular IP address from trying more than a predetermined number of password attempts against any account on the site. Additionally, the MITRE D3FEND framework provides structured recommendations for defending against brute-force attacks by implementing strategies such as network traffic filtering, deploying decoy credentials, and invalidating authentication caches.
Reverse brute-force attack
In a reverse brute-force attack, a single (usually common) password is tested against multiple usernames or encrypted files. The process may be repeated for a select few passwords. In such a strategy, the attacker is not targeting a specific user.
See also
Bitcoin mining
Cryptographic key length
Distributed.net
Hail Mary Cloud
Key derivation function
MD5CRK
Metasploit Express
Side-channel attack
TWINKLE and TWIRL
Unicity distance
RSA Factoring Challenge
Secure Shell
Notes
References
External links
RSA-sponsored DES-III cracking contest
Demonstration of a brute-force device designed to guess the passcode of locked iPhones running iOS 10.3.3
How We Cracked the Code Book Ciphers – Essay by the winning team of the challenge in The Code Book
Cryptographic attacks | Brute-force attack | [
"Technology"
] | 2,076 | [
"Cryptographic attacks",
"Computer security exploits"
] |
53,785 | https://en.wikipedia.org/wiki/Dictionary%20attack | In cryptanalysis and computer security, a dictionary attack is an attack using a restricted subset of a keyspace to defeat a cipher or authentication mechanism by trying to determine its decryption key or passphrase, sometimes trying thousands or millions of likely possibilities often obtained from lists of past security breaches.
Technique
A dictionary attack is based on trying all the strings in a pre-arranged listing. Such attacks originally used words found in a dictionary (hence the phrase dictionary attack); however, now there are much larger lists available on the open Internet containing hundreds of millions of passwords recovered from past data breaches. There is also cracking software that can use such lists and produce common variations, such as substituting numbers for similar-looking letters. A dictionary attack tries only those possibilities which are deemed most likely to succeed. Dictionary attacks often succeed because many people have a tendency to choose short passwords that are ordinary words or common passwords; or variants obtained, for example, by appending a digit or punctuation character. Dictionary attacks are often successful, since many commonly used password creation techniques are covered by the available lists, combined with cracking software pattern generation. A safer approach is to randomly generate a long password (15 letters or more) or a multiword passphrase, using a password manager program or manually typing a password.
Pre-computed dictionary attack/Rainbow table attack
It is possible to achieve a time–space tradeoff by pre-computing a list of hashes of dictionary words and storing these in a database using the hash as the key. This requires a considerable amount of preparation time, but this allows the actual attack to be executed faster. The storage requirements for the pre-computed tables were once a major cost, but now they are less of an issue because of the low cost of disk storage. Pre-computed dictionary attacks are particularly effective when a large number of passwords are to be cracked. The pre-computed dictionary needs be generated only once, and when it is completed, password hashes can be looked up almost instantly at any time to find the corresponding password. A more refined approach involves the use of rainbow tables, which reduce storage requirements at the cost of slightly longer lookup-times. See LM hash for an example of an authentication system compromised by such an attack.
Pre-computed dictionary attacks, or "rainbow table attacks", can be thwarted by the use of salt, a technique that forces the hash dictionary to be recomputed for each password sought, making precomputation infeasible, provided that the number of possible salt values is large enough.
Dictionary attack software
Cain and Abel
Crack
Aircrack-ng
John the Ripper
L0phtCrack
Metasploit Project
Ophcrack
Cryptool
See also
Brute-force attack
E-mail address harvesting
Intercontinental Dictionary Series, an online linguistic database
Key derivation function
Key stretching
Password cracking
Password strength
References
External links
– Internet Security Glossary
– Internet Security Glossary, Version 2
US Secret Service use a distributed dictionary attack on suspect's password protecting encryption keys
Testing for Brute Force (OWASP-AT-004)
Cryptographic attacks | Dictionary attack | [
"Technology"
] | 635 | [
"Cryptographic attacks",
"Computer security exploits"
] |
53,788 | https://en.wikipedia.org/wiki/Feed%20horn | A feed horn (or feedhorn) is a small horn antenna used to couple a waveguide to e.g. a parabolic dish antenna or offset dish antenna for reception or transmission of microwaves. A typical application is the use for satellite television reception with a satellite dish. In that case the feed horn can either be a separate part used together with e.g. a "low-noise block downconverter" (LNB), or more typically today is integrated into a "low-noise block feedhorn" (LNBF).
Principle of operation
The feed horn minimizes the mismatch loss between the antenna and the waveguide. If a simple open-ended waveguide would be used, without the horn, the sudden end of the conductive walls causes an abrupt impedance change at the aperture, between the wave impedance in the waveguide and the impedance of free space (see horn antenna for more details).
When used with a offset, parabolic or lens antenna, the phase center of the horn is placed at the focal point of the reflector. The characteristic of the feed horn is usually selected with the of the horn's radiation pattern falling on the edge of the reflector (the beamwidth of the horn matching the F/D ratio of the dish). When the shape of the antenna deviates from a circular dish, the feedhorn needs to be shaped accordingly to illuminate the antenna properly.
Applications
For satellite TV reception the feedhorn is mounted at the feed arm of the satellite dish. The feedhorn then connects via a short waveguide to the "low-noise block downconverter" (LNB), a small housing containing a part of the reception electronics (also called the "RF front end"). This LNB converts the high satellite microwave downlink frequencies to lower frequencies, so the TV signals can be more easily transmitted through coaxial cables to receivers located anywhere inside a building. For DTH TV typically the LNB and the feedhorn are integrated into one unit called "low-noise block feedhorn" (LNBF), but separate feedhorns and LNBs are used for more specialized applications.
For satellite uplink (e.g. for transmission of "Direct-To-Home" DTH TV programs, satellite news gathering SNG, satellite internet access or VSAT applications) a block upconverter (BUC) connects via a waveguide to the feedhorn, in order to transmit via the satellite dish to the communications satellite.
Feedhorns are also used in applications like radar, line-of-sight microwave transmission or radio astronomy.
See also
Focal cloud
Horn antenna
Radio frequency antenna types
Satellite broadcasting
Antennas (radio)
pl:Konwerter satelitarny | Feed horn | [
"Engineering"
] | 570 | [
"Telecommunications engineering",
"Satellite broadcasting"
] |
53,800 | https://en.wikipedia.org/wiki/TacTix | TacTix is a two-player strategy game invented by Piet Hein, a poet well known for dabbling in math and science, best known for his game Hex.
TacTix is essentially a two-dimension version of Nim; players alternate moves, removing one or more tokens in a single row or column until the last one is removed. At the time of its founding, TacTix was played on a 6x6 board, but is now usually played on a 4x4 board.
The game can be played in both its misere and non-misere forms. The strategies outlined here make the non-misere variant of the game straightforward. The game is often used as a programming exercise, and many versions are available on the web as Java applets.
Game play
TacTix is played on a NxN grid of squares, where N was initially 6, but has more commonly been played as 4.
Players alternate removing pieces a selected row or column, as many contiguous pieces as desired. For instance, in a 6x6 game, a player might remove pieces one through four on the first row. They cannot remove only the first and third pieces, these are not contiguous.
Players alternate doing this until the last piece is removed. The player who takes the last piece loses in the misère play convention, or wins in the non-misère version.
Strategy
First Player If N Is Odd (non-misere): The player takes the center piece and symmetrically imitates every one of the opponent's moves.
Second Player If N Is Even (non-misere): Player copies opponent's moves symmetrically. You will eventually take the last piece and win.
Variations
The hexagonal variation of the game, played on a six by six by six board, is called TacTex. TacTix can also be played on any size NxN board. A Non Misere version of TacTix, where the player who makes the last move is the winner, is also playable.
Analysis
On the 4×4 grid originally proposed by Hein, the second player will always win with correct play (HAKMEM item #74).
If the game is instead played with the normal play convention (player who takes the last piece wins), the second player can always win by symmetrically mirroring the first player's moves. (Or on an odd × odd size grid, the first player can win by choosing the center piece and subsequently mirroring.)
Tac Tix has 65,536 reachable positions. Out of the reachable positions, 57,156 are winning, and 8,380 are losing
References
External links
TacTix applet from thinks.net
TacTix at Four.com
TacTix iPhone an jPhone game available at the App Store
JavaScript TacTix
Mathematical games | TacTix | [
"Mathematics"
] | 586 | [
"Recreational mathematics",
"Mathematical games"
] |
53,831 | https://en.wikipedia.org/wiki/Missionary | A missionary is a member of a religious group who is sent into an area in order to promote its faith or provide services to people, such as education, literacy, social justice, health care, and economic development.
In the Latin translation of the Bible, Jesus Christ says the word when he sends the disciples into areas and commands them to preach the gospel in his name. The term is most commonly used in reference to Christian missions, but it can also be used in reference to any creed or ideology.
The word mission originated in 1598 when Jesuits, the members of the Society of Jesus sent members abroad, derived from the Latin (nom. ), meaning 'act of sending' or , meaning 'to send'.
By religion
Buddhist missions
The first Buddhist missionaries were called "Dharma Bhanaks", and some see a missionary charge in the symbolism behind the Buddhist wheel, which is said to travel all over the earth bringing Buddhism with it. The Emperor Ashoka was a significant early Buddhist missioner. In the 3rd century BCE, Dharmaraksita—among others—was sent out by emperor Ashoka to proselytize and initially the Buddhist tradition through the Indian Maurya Empire, but later into the Mediterranean as far as Greece. Gradually, all India and the neighboring island of Ceylon were converted. Then, in later periods, Buddhism spread eastward and southeastward to the present lands of Burma, Thailand, Laos, Cambodia, Vietnam, and Indonesia.
Buddhism was spread among the Turkic people during the 2nd and 3rd centuries BCE into modern-day Pakistan, Kashmir, Afghanistan, eastern and coastal Iran, Uzbekistan, Turkmenistan, and Tajikistan. It was also taken into China brought by Kasyapa Matanga in the 2nd century CE, Lokaksema and An Shigao translated Buddhist sutras into Chinese. Dharmarakṣa was one of the greatest translators of Mahayana Buddhist scriptures into Chinese. Dharmaraksa came to the Chinese capital of Luoyang in 266 CE, where he made the first known translations of the Lotus Sutra and the Dasabhumika Sutra, which were to become some of the classic texts of Chinese Mahayana Buddhism. Altogether, Dharmaraksa translated around 154 Hīnayāna and Mahāyāna sutras, representing most of the important texts of Buddhism available in the Western Regions. His proselytizing is said to have converted many to Buddhism in China, and made Chang'an, present-day Xi'an, a major center of Buddhism. Buddhism expanded rapidly, especially among the common people, and by 381 most of the people of northwest China were Buddhist. Winning converts also among the rulers and scholars, by the end of the Tang dynasty Buddhism was found everywhere in China.
Marananta brought Buddhism to the Korean Peninsula in the 4th century. Seong of Baekje, known as a great patron of Buddhism in Korea, built many temples and welcomed priests bringing Buddhist texts directly from India. In 528, Baekje officially adopted Buddhism as its state religion. He sent tribute missions to Liang in 534 and 541, on the second occasion requesting artisans as well as various Buddhist works and a teacher. According to Chinese records, all these requests were granted. A subsequent mission was sent in 549, only to find the Liang capital in the hands of the rebel Hou Jing, who threw them in prison for lamenting the fall of the capital. He is credited with having sent a mission in 538 to Japan that brought an image of Shakyamuni and several sutras to the Japanese court. This has traditionally been considered the official introduction of Buddhism to Japan. An account of this is given in Gangōji Garan Engi. First supported by the Soga clan, Buddhism rose over the objections of the pro-Shinto Mononobe and Buddhism entrenched itself in Japan with the conversion of Prince Shotoku Taishi. When in 710 Emperor Shomu established a new capital at Nara with urban grid plan modeled after the capital of China, Buddhism received official support and began to flourish.
Padmasambhava, The Lotus Born, was a sage guru from Oḍḍiyāna who is said to have transmitted Vajrayana Buddhism to Bhutan and Tibet and neighbouring countries in the 8th century.
The use of missions, councils, and monastic institutions influenced the emergence of Christian missions and organizations, which developed similar structures in places that were formerly Buddhist missions.
During the 19th and 20th centuries, Western intellectuals such as Schopenhauer, Henry David Thoreau, Max Müller, and esoteric societies such as the Theosophical Society of H.P. Blavatsky, The Buddhist Society of Great Britain and Ireland and the Buddhist Society, London spread interest in Buddhism. Writers such as Hermann Hesse and Jack Kerouac, in the West, and the hippie generation of the late 1960s and early 1970s led to a re-discovery of Buddhism. During the 20th and 21st centuries Buddhism has again been propagated by missionaries into the West such as Ananda Metteyya (Theravada Buddhism), Suzuki Daisetsu Teitarō (Zen Buddhism), the Dalai Lama and monks including Lama Surya Das (Tibetan Buddhism). Tibetan Buddhism has been significantly active and successful in the West since the Chinese takeover of Tibet in 1959. Today Buddhists make a decent proportion of several countries in the West such as New Zealand, Australia, Canada, the Netherlands, France, and the United States.
In Canada, the immense popularity and goodwill ushered in by Tibet's Dalai Lama (who has been made honorary Canadian citizen) put Buddhism in a favourable light in the country. Many non-Asian Canadians embraced Buddhism in various traditions and some have become leaders in their respective sanghas.
In the early 1990s, the French Buddhist Union (UBF, founded in 1986) estimated that there are 600,000 to 650,000 Buddhists in France, with 150,000 French converts among them. In 1999, sociologist Frédéric Lenoir estimated there are 10,000 converts and up to five million "sympathizers", although other researchers have questioned these numbers.
Taisen Deshimaru was a Japanese Zen Buddhist who founded numerous zendos in France. Thich Nhat Hanh, a Nobel Peace Prize-nominated, Vietnamese-born Zen Buddhist, founded the Unified Buddhist Church (Eglise Bouddhique Unifiée) in France in 1969. The Plum Village Monastery in the Dordogne in southern France was his residence and the headquarters of his international sangha.
In 1968 Leo Boer and Wener van de Wetering founded a Zen group, and through two books made Zen popular in the Netherlands. The guidance of the group was taken over by Erik Bruijn, who is still in charge of a flourishing community. The largest Zen group now is the Kanzeon Sangha, led by Nico Tydeman under the supervision of the American Zen master Dennis Genpo Merzel, Roshi, a former student of Maezumi Roshi in Los Angeles. This group has a relatively large centre where a teacher and some students live permanently. Many other groups are also represented in the Netherlands, like the Order of Buddhist Contemplatives in Apeldoorn, the Thich Nhat Hanh Order of Interbeing and the International Zen Institute Noorderpoort monastery/retreat centre in Drenthe, led by Jiun Hogen Roshi.
Perhaps the most widely visible Buddhist leader in the world is Tenzin Gyatso, the current Dalai Lama, who first visited the United States in 1979. As the exiled political leader of Tibet, he has become a popular cause célèbre. His early life was depicted in Hollywood films such as Kundun and Seven Years in Tibet. He has attracted celebrity religious followers such as Richard Gere and Adam Yauch. The first Western-born Tibetan Buddhist monk was Robert A. F. Thurman, now an academic supporter of the Dalai Lama. The Dalai Lama maintains a North American headquarters at Namgyal Monastery in Ithaca, New York.
Lewis M. Hopfe in his "Religions of the World" suggested that "Buddhism is perhaps on the verge of another great missionary outreach" (1987:170).
Christian missions
A Christian missionary can be defined as "one who is to witness across cultures". The Lausanne Congress of 1974, defined the term, related to Christian mission as, "to form a viable indigenous church-planting movement". Missionaries can be found in many countries around the world.
In the Bible, Jesus Christ is recorded as instructing the apostles to make disciples of all nations (, ). This verse is referred to by Christian missionaries as the Great Commission and inspires missionary work.
Historic
The Christian Church expanded throughout the Roman Empire already in New Testament times and is said by tradition to have reached even further, to Persia (Church of the East) and to India (Saint Thomas Christians). During the Middle Ages, the Christian monasteries and missionaries such as Saint Patrick (5th century), and Adalbert of Prague (c. 956–997) propagated learning and religion beyond the European boundaries of the old Roman Empire. In 596, Pope Gregory the Great (in office 590–604) sent the Gregorian Mission (including Augustine of Canterbury) into England. In their turn, Christians from Ireland (the Hiberno-Scottish mission) and from Britain (Saint Boniface (c. 675–754), and the Anglo-Saxon mission, for example) became prominent in converting the inhabitants of central Europe.
During the Age of Discovery, the Catholic Church established a number of missions in the Americas and in other Western colonies through the Augustinians, Franciscans, and Dominicans to spread Christianity in the New World and to convert the Native Americans and other indigenous people. About the same time, missionaries such as Francis Xavier (1506–1552) as well as other Jesuits, Augustinians, Franciscans, and Dominicans reached Asia and the Far East, and the Portuguese sent missions into Africa. Emblematic in many respects is Matteo Ricci's Jesuit mission to China from 1582, which was totally peaceful and non-violent. These missionary movements should be distinguished from others, such as the Baltic Crusades of the 12th and 13th centuries, which were arguably compromised in their motivation by designs of military conquest.
Much contemporary Catholic missionary work has undergone profound change since the Second Vatican Council of 1962–1965, with an increased push for indigenization and inculturation, along with social justice issues as a constitutive part of preaching the Gospel.
As the Catholic Church normally organizes itself along territorial lines and had the human and material resources, religious orders, some even specializing in it, undertook most missionary work, especially in the era after the collapse of the Roman Empire in the West. Over time, the Holy See gradually established a normalized Church structure in the mission areas, often starting with special jurisdictions known as apostolic prefectures and apostolic vicariates. At a later stage of development these foundations are raised to regular diocesan status with a local bishops appointed. On a global front, these processes were often accelerated in the later 1960s, in part accompanying political decolonization. In some regions, however, they are still in course.
Just as the Bishop of Rome had jurisdiction also in territories later considered to be in the Eastern sphere, so the missionary efforts of the two 9th-century saints Cyril and Methodius were largely conducted in relation to the West rather than the East, though the field of activity was central Europe.
The Eastern Orthodox Church, under the Orthodox Church of Constantinople undertook vigorous missionary work under the Roman Empire and its successor the Byzantine Empire. This had lasting effects and in some sense is at the origin of the present relations of Constantinople with some sixteen Orthodox national churches including the Romanian Orthodox Church, the Georgian Orthodox and Apostolic Church, and the Ukrainian Orthodox Church (both traditionally said to have been founded by the missionary Apostle Andrew), the Bulgarian Orthodox Church (said to have been founded by the missionary Apostle Paul). The Byzantines expanded their missionary work in Ukraine after the mass baptism in Kiev in 988. The Serbian Orthodox Church had its origins in the conversion by Byzantine missionaries of the Serb tribes when they arrived in the Balkans in the 7th century. Orthodox missionaries also worked successfully among the Estonians from the 10th to the 12th centuries, founding the Estonian Orthodox Church.
Under the Russian Empire of the 19th century, missionaries such as Nicholas Ilminsky (1822–1891) moved into the subject lands and propagated Orthodoxy, including through Belarus, Latvia, Moldova, Finland, Estonia, Ukraine, and China. The Russian St. Nicholas of Japan (1836–1912) took Eastern Orthodoxy to Japan in the 19th century. The Russian Orthodox Church also sent missionaries to Alaska beginning in the 18th century, including Saint Herman of Alaska (died 1836), to minister to the Natives. The Russian Orthodox Church Outside Russia continued missionary work outside Russia after the 1917 Russian Revolution, resulting in the establishment of many new dioceses in the diaspora, from which numerous converts have been made in Eastern Europe, North America, and Oceania.
Early Protestant missionaries included John Eliot and contemporary ministers including John Cotton and Richard Bourne, who ministered to the Algonquin natives who lived in lands claimed by representatives of the Massachusetts Bay Colony in the early 17th century. Quaker "publishers of truth" visited Boston and other mid-17th century colonies, but were not always well received.
The Danish government began the first organized Protestant mission work through its College of Missions, established in 1714. This funded and directed Lutheran missionaries such as Bartholomaeus Ziegenbalg in Tranquebar, India, and Hans Egede in Greenland. In 1732, while on a visit in 1732 to Copenhagen for the coronation of his cousin King Christian VI, the Moravian Church's patron Nicolas Ludwig, Count von Zinzendorf, was very struck by its effects, and particularly by two visiting Inuit children converted by Hans Egede. He also got to know a slave from the Danish colony in the West Indies. When he returned to Herrnhut in Saxony, he inspired the inhabitants of the villageit had fewer than thirty houses thento send out "messengers" to the slaves in the West Indies and to the Moravian missions in Greenland. Within thirty years, Moravian missionaries had become active on every continent, and this at a time when there were fewer than three hundred people in Herrnhut. They are famous for their selfless work, living as slaves among the slaves and together with Native Americans, including the Lenape and Cherokee Indian tribes. Today, the work in the former mission provinces of the worldwide Moravian Church is carried on by native workers. The fastest-growing area of the work is in Tanzania in Eastern Africa. The Moravian work in South Africa inspired William Carey and the founders of the British Baptist missions. , seven of every ten Moravians live in a former mission field and belong to a race other than Caucasian.
Much Anglican mission work came about under the auspices of the Society for the Propagation of the Gospel in Foreign Parts (SPG, founded in 1701), the Church Missionary Society (CMS, founded 1799) and of the Intercontinental Church Society (formerly the Commonwealth and Continental Church Society, originating in 1823).
Modern
With a dramatic increase in efforts since the 20th century, and a strong push since the Lausanne I: The International Congress on World Evangelization in Switzerland in 1974, modern evangelical groups have focused efforts on sending missionaries to every ethnic group in the world. While this effort has not been completed, increased attention has brought larger numbers of people distributing Bibles, Jesus videos, and establishing evangelical churches in more remote areas.
Internationally, the focus for many years in the later 20th century was on reaching every "people group" with Christianity by 2000. Bill Bright's leadership with Campus Crusade, the Southern Baptist International Mission Board, The Joshua Project, and others brought about the need to know who these "unreached people groups" are and how those wanting to tell about the Christian God and share a Christian Bible could reach them. The focus for these organizations transitioned from a "country focus" to a "people group focus". (From "What is a People Group?" by Dr. Orville Boyd Jenkins: A "people group" is an ethnolinguistic group with a common self-identity that is shared by the various members. There are two parts to that word: ethno and linguistic. Language is a primary and dominant identifying factor of a people group. But there are other factors that determine or are associated with ethnicity.)
What can be viewed as a success by those inside and outside the church from this focus is a higher level of cooperation and friendliness among churches and denominations. It is very common for those working on international fields to not only cooperate in efforts to share their gospel message, but view the work of their groups in a similar light. Also, with the increased study and awareness of different people groups, western mission efforts have become far more sensitive to the cultural nuances of those they are going to and those they are working with in the effort.
Over the years, as indigenous churches have matured, the church of the Global South (Africa, Asia, and Latin America) has become the driving force in missions. Korean and African missionaries can now be found all over the world. These missionaries represent a major shift in church history where the nations they came from were not historically Christian. Another major shift in the form of modern missionary work takes shape in the conflation of spiritual with contemporary military metaphors and practices. Missionary work as spiritual warfare (Ephesians, Chapter 6) weapons of a spiritual sense, is the primary concept in a long-standing relationship between Christian missions and militarization. Though when the Church establishes a governance, usually this results in a formation of a national or regional military. (Romans, Chapter 13) Despite the seeming opposition between the submissive and morally upstanding associations with prayer and violence associated with militarism, these two spheres interact in a dialectical way. Yet they when properly implemented they are entangled to support one another in the upholding of a civilizations morality and the prosecution and punishment of criminals. In some cases a nations military may fail to operate according to Godly principles and is not supported by the Church or missionaries, in other cases the military is made up of the Church congregants. The results of spiritual conflict are then present in different ways as prayer can be strategically used, for or against a military.
Nigeria, and other countries have had large numbers of their Christian adherents go to other countries and start churches. These non-western missionaries often have unparalleled success; because, they need few western resources and comforts to sustain their livelihood while doing the work they have chosen among a new culture and people.
One of the first large-scale missionary endeavors of the British colonial age was the Baptist Missionary Society, founded in 1792 as the Particular Baptist Society for the Propagation of the Gospel Amongst the Heathen.
The London Missionary Society was an evangelical organisation, bringing together from its inception both Anglicans and Nonconformists; it was founded in England in 1795 with missions in Africa and the islands of the South Pacific. The Colonial Missionary Society was created in 1836, and directed its efforts towards promoting Congregationalist forms of Christianity among "British or other European settlers" rather than indigenous peoples.
Both of these merged in 1966, and the resultant organisation is now known as the Council for World Mission.
The Church Mission Society, first known as the Society for Missions to Africa and the East, was founded in 1799 by evangelical Anglicans centred around the anti-slavery activist William Wilberforce. It bent its efforts to the Coptic Church, the Ethiopian Church, and India, especially Kerala; it continues to this day. Many of the network of churches they established became the Anglican Communion.
In 1809, the London Society for Promoting Christianity Amongst the Jews was founded, which pioneered mission amongst the Jewish people; it continues today as the Church's Ministry Among Jewish People. In 1865, the China Inland Mission was founded, going well beyond British controlled areas; it continues as the OMF, working throughout East Asia.
The Church of Jesus Christ of Latter-day Saints (LDS Church) has an active missionary program. Young men between the ages of eighteen and twenty-five are encouraged to prepare themselves to serve a two-year, self-funded, full-time proselytizing mission. Young women who desire to serve as missionaries can serve starting at the age of nineteen, for one and a half years. Retired couples also have the option of serving a mission. Missionaries typically spend two weeks in a Missionary Training Center (or two to three months for those learning a new language) where they study the scriptures along with the Book of Mormon, learn new languages when applicable, prepare themselves to teach the Gospel of Jesus Christ, and learn more about the culture and the people they live among. As of December 2019, the LDS Church had over 67,000 full-time missionaries worldwide and over 31,000 Service Missionaries.
Maryknoll
In Montreal in 1910, Father James Anthony Walsh, a priest from Boston, met Father Thomas Frederick Price, from North Carolina. They agreed on the need to build a seminary for the training of young American men for the foreign Missions. Countering arguments that the Church needed workers here, Fathers Walsh and Price insisted the Church would not flourish until it sent missioners overseas. Independently, the men had written extensively about the concept, Father Price in his magazine Truth, and Father Walsh in the pages of A Field Afar, an early incarnation of Maryknoll Magazine. Winning the approval of the American hierarchy, the two priests traveled to Rome in June 1911 to receive final approval from Pope Pius X for the formation of the Catholic Foreign Mission Society of America, now better known as the Maryknoll Fathers and Brothers.
Hindu missions
Hinduism was introduced into Java by travellers from India in ancient times. Several centuries ago, many Hindus left Java for Bali rather than convert to Islam. Hinduism has survived in Bali ever since. Dang Hyang Nirartha was responsible for facilitating a refashioning of Balinese Hinduism. He was an important promoter of the idea of moksha in Indonesia. He founded the Shaivite priesthood that is now ubiquitous in Bali, and is now regarded as the ancestor of all Shaivite pandits.
Shantidas Adhikari was a Hindu preacher from Sylhet who converted King Pamheiba of Manipur to Hinduism in 1717.
Historically, Hinduism has only recently had a large influence in western countries such as the United Kingdom, New Zealand, and Canada. Since the 1960s, many westerners attracted by the world view presented in Asian religious systems have converted to Hinduism. Many native-born Canadians of various ethnicities have converted during the last 50 years through the actions of the Ramakrishna Mission, ISKCON, Arya Samaj and other missionary organizations as well as due to the visits and guidance of Indian gurus such as Guru Maharaj, Sai Baba, and Rajneesh. The International Society for Krishna Consciousness has a presence in New Zealand, running temples in Auckland, Hamilton, Wellington and Christchurch.
Paramahansa Yogananda, an Indian yogi and guru, introduced many westerners to the teachings of meditation and Kriya Yoga through his book, Autobiography of a Yogi.
Swami Vivekananda, the founder of the Ramakrishna Mission is one of the greatest Hindu missionaries to the West.
Ananda Marga missions
Ānanda Mārga, organizationally known as Ānanda Mārga Pracaraka Samgha (AMPS), meaning the samgha (organization) for the propagation of the marga (path) of ananda (bliss), is a social and spiritual movement founded in Jamalpur, Bihar, India, in 1955 by Prabhat Ranjan Sarkar (1921–1990), also known by his spiritual name, Shrii Shrii Ánandamúrti. Ananda Marga counts hundreds of missions around the world through which its members carry out various forms of selfless service on Relief. (The social welfare and development organization under AMPS is Ananda Marga Universal Relief Team, or AMURT.) Education and women's welfare The service activities of this section founded in 1963 are focused on:
Education: creating and managing primary, post-primary, and higher schools, research institutes
Relief: creating and managing children's and students' homes for destitute children and for poor students, cheap hostels, retiring homes, academies of light for deaf dumb and crippled, invalid homes, refugee rehabilitation
Tribal: tribal welfare units, medical camps
Women's welfare: women welfare units, women's homes, nursing homes
Islamic missions
Dawah means to "invite" (in Arabic, literally "calling") to Islam, which is the second largest religion with 2.0 billion members. From the 7th century, it spread rapidly from the Arabian Peninsula to the rest of the world through the initial Muslim conquests and subsequently with traders and explorers after the death of Muhammad.
Initially, the spread of Islam came through the Dawah efforts of Muhammad and his followers. After his death in 632 CE, much of the expansion of the empire came through conquest such as that of North Africa and later Iberia (Al-Andalus). The Islamic conquest of Persia put an end to the Sassanid Empire and spread the reach of Islam to as far east as Khorasan, which would later become the cradle of Islamic civilization during the Islamic Golden Age (622–1258 CE) and a stepping-stone towards the introduction of Islam to the Turkic tribes living in and bordering the area.
The missionary movement peaked during the Islamic Golden Age, with the expansion of foreign trade routes, primarily into the Indo-Pacific and as far south as the isle of Zanzibar as well as the Southeastern shores of Africa.
With the coming of the Sufism tradition, Islamic missionary activities increased. Later, the Seljuk Turks' conquest of Anatolia made it easier for missionaries to go lands that formerly belonged to the Byzantine Empire. In the earlier stages of the Ottoman Empire, a Turkic form of Shamanism was still widely practiced in Anatolia, but soon lost ground to Sufism.
During the Ottoman presence in the Balkans, missionary movements were taken up by people from aristocratic families hailing from the region, who had been educated in Constantinople or other major city within the Empire such as the famed madrassahs and kulliyes. Primarily, individuals were sent back to the place of their origin and were appointed important positions in the local governing body. This approach often resulted in the building of mosques and local kulliyes for future generations to benefit from, as well as spreading the teachings of Islam.
The spread of Islam towards Central and West Africa had until the early 19th century has been consistent but slow. Previously, the only connection was through Trans-Saharan trade routes. The Mali Empire, consisting predominantly of African and Berber tribes, stands as a strong example of the early Islamic conversion of the Sub-Saharan region. The gateways prominently expanded to include the aforementioned trade routes through the Eastern shores of the African continent. With the European colonization of Africa, missionaries were almost in competition with the European Christian missionaries operating in the colonies.
There is evidence of Arab Muslim traders entering Indonesia as early as the 8th century. Indonesia's early people were animists, Hindus, and Buddhists. However it was not until the end of the 13th century that the process of Islamization began to spread throughout the areas local communities and port towns. The spread, although at first introduced through Arab Muslim traders, continued to saturate through the Indonesian people as local rulers and royalty began to adopt the religion subsequently leading their subjects to mirror their conversion.
Recently, Muslim groups have engaged in missionary work in Malawi. Much of this is performed by the African Muslim Agency based in Angola. The Kuwait-sponsored AMA has translated the Qur'an into Chichewa (Cinyanja), one of the official languages of Malawi, and has engaged in other missionary work in the country. All of the major cities in the country have mosques and there are several Islamic schools.
Several South African, Kuwaiti, and other Muslim agencies are active in Mozambique, with one important one being the African Muslim Agency. The spread of Islam into West Africa, beginning with ancient Ghana in the 9th century, was mainly the result of the commercial activities of North African Muslims. The empires of both Mali and Songhai that followed ancient Ghana in the Western Sudan adopted the religion. Islam made its entry into the northern territories of modern Ghana around the 15th century. Mande speakers (who in Ghana are known as Wangara) traders and clerics carried the religion into the area. The northeastern sector of the country was also influenced by an influx of Hausa Muslim traders from the 16th century onwards
Islamic influence first occurred in India in the early 7th century with the advent of Arab traders. Trade relations have existed between Arabia and the Indian subcontinent from ancient times. Even in the pre-Islamic era, Arab traders used to visit the Malabar region, which linked them with the ports of Southeast Asia. According to Historians Elliot and Dowson in their book The History of India as told by its own Historians, the first ship bearing Muslim travelers was seen on the Indian coast as early as 630 CE H. G. Rawlinson, in his book: Ancient and Medieval History of India claims the first Arab Muslims settled on the Indian coast in the last part of the 7th century. Shaykh Zainuddin Makhdum's "Tuhfat al-Mujahidin" also is a reliable work. This fact is corroborated, by J. Sturrock in his South Kanara and Madras Districts Manuals, and also by Haridas Bhattacharya in Cultural Heritage of India Vol. IV. It was with the advent of Islam that the Arabs became a prominent cultural force in the world. The Arab merchants and traders became the carriers of the new religion, and they propagated it wherever they went.
Islam in Bulgaria can be traced back to the mid-ninth century when there were Islamic missionaries in Bulgaria, evidenced by a letter from Pope Nicholas to Boris of Bulgaria calling for the extirpation of Saracens.
Pioneer Muslim missionaries to the Kenyan interior were largely Tanganyikan, who coupled their missionary work with trade, along the centres began along the railway line such as Kibwezi, Makindu, and Nairobi.
Outstanding among them was Maalim Mtondo Islam in Kenya, a Tanganyikan credited with being the first Muslim missionary to Nairobi. Reaching Nairobi at the close of the 19th century, he led a group of other Muslims, and enthusiastic missionaries from the coast to establish a "Swahili village" in present-day Pumwani. A small mosque was built to serve as a starting point and he began preaching Islam in earnest. He soon attracted several Kikuyus and Wakambas, who became his disciples.
In 1380, Karim ul' Makhdum the first Arabian Islamic missionary reached the Sulu Archipelago and Jolo in the Philippines and established Islam in the country. In 1390, the Minangkabau's Prince Rajah Baguinda and his followers preached Islam on the islands. The Sheik Karimal Makdum Mosque was the first mosque established in the Philippines on Simunul in Mindanao in the 14th century. Subsequent settlements by Arab missionaries traveling to Malaysia and Indonesia helped strengthen Islam in the Philippines and each settlement was governed by a Datu, Rajah, and a Sultan. Islamic provinces founded in the Philippines included the Sultanate of Maguindanao, Sultanate of Sulu, and other parts of the southern Philippines.
Modern missionary work in the United States has increased greatly in the last one hundred years, with much of the recent demographic growth driven by conversion. Up to one-third of American Muslims are African Americans who have converted to Islam during the last seventy years. Conversion to Islam in prisons, and in large urban areas has also contributed to Islam's growth over the years.
An estimated US$45 billion has been spent by the Saudi Arabian government financing mosques and Islamic schools in foreign countries. Ain al-Yaqeen, a Saudi newspaper, reported in 2002 that Saudi funds may have contributed to building as many as 1,500 mosques and 2,000 other Islamic centers.
Early Islamic missionaries during Muhammad's era
During the Expedition of Al Raji in 625, the Islamic Prophet Muhammad sent some men as missionaries to various different tribes. Some men came to Muhammad and requested that Muhammad send instructors to teach them Islam, but the men were bribed by the two tribes of Khuzaymah who wanted revenge for the assassination of Khalid bin Sufyan (Chief of the Banu Lahyan tribe) by Muhammad's followers 8 Muslim Missionaires were killed in this expedition., another version says 10 Muslims were killed
Then during the Expedition of Bir Maona in July 625 Muhammad sent some Missionaries at request of some men from the Banu Amir tribe, but the Muslims were again killed as revenge for the assassination of Khalid bin Sufyan by Muhammad's followers 70 Muslims were killed during this expedition
During the Expedition of Khalid ibn al-Walid (Banu Jadhimah) in January 630, Muhammad sent Khalid ibn Walid to invite the Banu Jadhimah tribe to Islam. This is mentioned in the Sunni Hadith .
Ahmadiyya Islam missions
Missionaries belonging to the Ahmadiyya thought of Islam often study at International Islamic seminaries and educational institutions, known as Jamia Ahmadiyya. Upon completion of their degrees, they are sent to various parts of the world including South America, Africa, North America, Europe, and the Far East as appointed by Mirza Masroor Ahmad, present head and Caliph of the worldwide Ahmadiyya Muslim community. Jamia students may be appointed by the Caliph either as Missionaries of the community (often called Murrabi, Imam, or Mawlana) or as Qadis or Muftis of the Ahmadiyya Muslim community with a specialisation in matters of fiqh (Islamic Jurisprudence). Some Jamia alumni have also become Islamic historians such as the late Dost Muhammad Shahid, former Official Historian of the Ahmadiyya Muslim community, with a specialisation in tarikh (Islamic historiography). Missionaries stay with their careers as appointed by the Caliph for the rest of their lives, as per their commitment to the community.
Jain missions
According to Jaina tradition, Mahavira's following had swelled to 14,000 monks and 36,000 nuns by the time of his death in 527 BCE
For some two centuries the Jains remained a small community of monks and followers. However, in the 4th century BCE, they gained strength and spread from Bihar to Orissa, then so South India and westwards to Gujarat and the Punjab, where Jain communities became firmly established, particularly among the mercantile classes. The period of the Mauryan dynasty to the 12th century was the period of Jainism's greatest growth and influence. Thereafter, the Jainas in the South and Central regions lost ground in face of rising Hindu devotional movements. Jainism retreated to the West and Northwest, which have remained its stronghold to the present.
Emperor Samprati is regarded as the "Jain Ashoka" for his patronage and efforts to spreading Jainism in east India. Samprati, according to Jain historians, is considered more powerful and famous than Ashoka himself. Samprati built thousands of Jain Temples in India, many of which remain in use, such as the Jain temples at Viramgam and Palitana (Gujarat), Agar Malwa (Ujjain). Within three and a half years, he got one hundred and twenty-five thousand new temples built, thirty-six thousand repaired, twelve and a half million murtis, holy statues, consecrated and ninety-five thousand metal murtis prepared. Samprati is said to have erected Jain temples throughout his empire. He founded Jain monasteries even in non-Aryan territory, and almost all ancient Jain temples or monuments of unknown origin are popularly attributed to him. It may be noted that all the Jain monuments of Rajasthan and Gujarat, with unknown builders are also attributed to Emperor Samprati.
Virachand Gandhi (1864–1901) from Mahuva represented Jains at the first Parliament of the World's Religions in Chicago in 1893 and won a silver medal. Gandhi was most likely the first Jain and the first Gujarati to travel to the United States, and his statue still stands at the Jain temple in Chicago. In his time he was a world-famous personality. Gandhi represented Jains in Chicago because the Great Jain Saint Param Pujya Acharya Vijayanandsuri, also known as Acharya Atmaram, was invited to represent the Jain religion at the first World Parliament of Religions. As Jain monks do not travel overseas, he recommended the bright young scholar Virchand Gandhi to be the emissary for the religion. Today there are 100,000 Jains in the United States.
There are also tens of thousands of Jains located in the UK and Canada.
Judaism
Historically, various Jewish sects and movements have been consistent in avoiding or even forbidding proselytization (religion-to-religion conversion propaganda) to convert gentiles (non-Jews). They believe that gentiles do not need to convert to Judaism, due to Abrahamic religions being already under the Seven Laws of Noah.
Chabad Lubavitch has a sub-sect that has engaged in an effort to spread Noahidism (Seven Laws of Noah) among non-Jews who follow none of the existing Abrahamic religions.
Orthodox Judaism outreach (kiruv) encourages non-practicing Jews to become more knowledgeable and observant of halakha (Jewish law). Outreach is done worldwide, by organizations such as Chabad Lubavitch, Aish HaTorah, Ohr Somayach, and Partners In Torah.
Members of Reform Judaism began a program to convert to their brand of Judaism the non-Jewish spouses of its intermarried members and non-Jews who have an interest in Reform Judaism. Their rationale is that so many Jews were lost during the Holocaust that newcomers must be sought out and welcomed. This approach has been rejected by both Orthodox Judaism and Conservative Judaism as unrealistic and posing a danger on the entire Jewish faith.
Sikh missions
According to Sikhs, when he was twenty-eight, Guru Nanak went as usual down to the river to bathe and meditate. It was said that he was gone for three days. When he reappeared, it is said he was "filled with the spirit of God". His first words after his re-emergence were: "there is no Hindu, there is no Muslim". With this secular principle he began his missionary work. He made four distinct major journeys, in the four different directions, which are called Udasis, spanning many thousands of kilometres, preaching the message of God.
Currently there are gurdwaras in over 50 countries.
Of missionary organizations, the most famous is probably The Sikh Missionary Society UK. The aim of the Sikh Missionary Society is the Advancement of the Sikh faith in the U.K. and abroad, engages in various activities:
Produce and distribute books on the Sikh faith in English and Panjabi, and other languages to enlighten the younger generation of Sikhs as well as non-Sikhs.
Advise and support young students in schools, colleges, and universities on Sikh issues and Sikh traditions.
Arrange classes, lectures, seminars, conferences, Gurmat camps and the celebration of holy Sikh events, the basis of their achievement and interest in the field of the Sikh faith and the Panjabi language.
Make available all Sikh artifacts, posters, literature, music, educational videos, DVDs, and multimedia CD-ROMs.
There have been several Sikh missionaries:
Bhai Gurdas (1551–1636), Punjabi Sikh writer, historian, missionary, and religious figure; the original scribe of the Guru Granth Sahib and a companion of four of the Sikh Gurus
Giani Pritam Singh Dhillon, Indian freedom fighter
Bhai Amrik Singh, devoted much of his life to Sikh missionary activities; one of the Sikh community's most prominent leaders along with Sant Jarnail Singh Bhindranwale
Jathedar Sadhu Singh Bhaura (1905–1984), Sikh missionary who rose to be the Jathedar or high priest of Sri Akal Takhat, Amritsar
Sikhs have emigrated to many countries of the world since Indian independence in 1947. Sikh communities exist in Britain, East Africa, Canada, the United States, Malaysia, and most European countries.
Tenrikyo missions
Tenrikyo conducts missionary work in approximately forty countries. Its first missionary was a woman named Kokan who worked on the streets of Osaka. In 2003, it operated approximately twenty thousand mission stations worldwide.
Criticism
Contact of Christian missionaries with isolated tribes is asserted as a cause of the extinction of some tribes, such as extinction from infections and even simple diseases such as flu, to which many tribes have no immunity. Documented cases of European contact with isolated tribes show rapid health deterioration, such as the Nambikwara tribe.
Christian missionary work is criticized as a form of colonialism. Some Christian missionary thinkers have recognized complicity between colonialism and missions with roots in 'colonial paternalism'.
Aspects of Christian missionary activity have come under criticism, including concerns about a lack of respect for other cultures. The potential destruction of social structure among the converts is also a concern. The Huaorani people of Amazonian Ecuador have had a well-documented mixed relation with Evangelical Christian missionaries and the contacts they brought to their communities, which some have argued led to the dissolving of unique Huaorani tribes and cultural practices.
Impact of missions
A 2020 study by Elena Nikolova and Jakub Polansky replicates Woodberry's analysis using twenty-six alternative democracy measures and extends the time period over which the democracy measures are averaged. These two simple modifications lead to the breakdown of Woodberry's results. Overall, no significant relationship between Protestant missions and the development of democracy can be established.
A 2017 study found that areas of colonial Mexico that had Mendicant missions have higher rates of literacy and educational attainment today than regions that did not have missions. Areas that had Jesuit missions are today indistinct from the areas that had no missions. The study also found that "the share of Catholics is higher in regions where Catholic missions of any kind were a historical present."
A 2016 study found that regions in Sub-Saharan Africa that Protestant missionaries brought printing presses to are today "associated with higher newspaper readership, trust, education, and political participation."
Missionaries have also made significant contributions to linguistics and the description and documentation of many languages. "Many languages today exist only in missionary records. More than anywhere else, our knowledge of the native languages in South America has been the product of missionary activity… Without missionary documentation the reclamation [of several languages] would have been completely impossible" "A satisfactory history of linguistics cannot be written before the impressive contribution of missionaries is recognised."
Lists of prominent missionaries
American missionaries
Gerónimo Boscana, (Roman Catholic Franciscan) missionary
Isabel Crawford, (Baptist) missionary
Antonio de Olivares, (Roman Catholic Franciscan) missionary
Anton Docher, (Roman Catholic) missionary
Elisabeth Elliot, American Protestant missionary in Ecuador, author and speaker, widow of Jim Elliot of Operation Auca
Mary H. Fulton, female medical missionary to China, founder of Hackett Medical College for Women (夏葛女子醫學院) in Guangzhou, China
Adoniram Judson, first significant missionary in Burma
Eusebio Kino, (Roman Catholic Jesuit) missionary
Zenas Sanford Loftis, medical missionary to Tibet
Ajahn Sumedho, Theravada monk and established Thai Forest Tradition in UK
Robert E. Longacre, Christian linguist missionary to Mexico
Dada Maheshvarananda, Ananda Marga yoga missionary
Fred Prosper Manget, medical missionary to China, founder of Houzhou General Hospital, Houzhou, China, also a doctor with the Flying Tigers and U.S. Army in Kunming, China, during World War II
Lottie Moon, Baptist missionary to China
Arthur Lewis Piper, medical missionary to the Belgian Congo
Dada Pranakrsnananda, Ananda Marga yoga missionary
Darlene Rose, missionary in Papua New Guinea
John Stewart, (Methodist) missionary
José de Anchieta, (Roman Catholic Jesuit) missionary
Peter of Saint Joseph de Betancur, (Roman Catholic Franciscan) missionary
John Allen Chau, (evangelical Christian) missionary killed while attempting to convert the uncontacted Sentinelese
British Christian missionaries
John Hobbis Harris, with his wife Alice Seeley, he used photography to expose colonial abuses
Benjamin Hobson, medical missionary to China, set up a highly successful Wai Ai Clinic (惠愛醫館) in Guangzhou, China.
Teresa Kearney, Sister in Uganda
Olive Hilda Miller, missionary to Jamaica and the Cayman Islands
William Milne, Bible translator to China
Robert Morrison, Bible translator to China
George Piercy, Methodist missionary to China
Sam Pollard, Bible translator to China
James Hudson Taylor, missionary to China, insist on going into the inland of China.
John Wesley
Thomas Henry Sparshott, missionary to East Africa.
See also
John McKendree Springer – Pioneer missionary in Africa
List of Protestant missionaries in China
List of Protestant missionaries in India
List of Roman Catholic missionaries
List of Roman Catholic missionaries in China
List of Roman Catholic missionaries in India
List of Eastern Orthodox missionaries
List of missionaries to Hawaii
List of missionaries to the South Pacific
List of Slovenian missionaries
List of Russian Orthodox missionaries
List of Protestant missionaries to Southeast Asia
List of Roman Catholic missions in Africa
Christian missionaries in New Zealand
Christian missionaries in Oceania
Timeline of Christian missions
Catholic missions
Christianity and colonialism
Christian missionaries
Christianisation
Evangelism
History of Christian missions
Indigenous church mission theory
Mission (Christianity)
Missiology
Missionary kid
Missionary religious institutes and societies
Portuguese Inquisition in Goa and Bombay-Bassein
Religious conversion
Short-term mission
Timeline of Christian missions
References
Further reading
Dunch, Ryan. "Beyond cultural imperialism: Cultural theory, Christian missions, and global modernity." History and Theory 41.3 (2002): 301–325. online
Dwight, Henry Otis et al. eds., The Encyclopedia of Missions (2nd ed. 1904) Online, Global coverage Of Protestant and Catholic missions.
Robinson, David Muslim Societies in African History (The Press Syndicate of the University of Cambridge Cambridge, UK 2004)
Sharma, Arvind (2014). Hinduism as a missionary religion. New Delhi: Dev Publishers & Distributors.
Shourie, Arun. (2006). Missionaries in India: Continuities, changes, dilemmas. New Delhi: Rupa.
Madhya Pradesh (India)., & Niyogi, M. B. (1956). Vindicated by time: The Niyogi Committee report on Christian missionary activities. Nagpur: Government Printing, Madhya Pradesh.
External links
Missionary eTexts
Project on Religion and Economic Change, Protestant Mission Stations
LFM. Social sciences & Missions
Henry Martyn Centre for the study of mission & world Christianity
William Carey Library, Mission Resources
Hiney, Thomas: On the Missionary Trail, New York: Atlantic Monthly Press (2000), pp. 5–22.
EtymologyOnLine (word history)
Christian terminology
Religious practices
Religious occupations | Missionary | [
"Biology"
] | 9,680 | [
"Behavior",
"Religious practices",
"Human behavior"
] |
53,847 | https://en.wikipedia.org/wiki/Resource%20Description%20Framework | The Resource Description Framework (RDF) is a method to describe and exchange graph data. It was originally designed as a data model for metadata by the World Wide Web Consortium (W3C). It provides a variety of syntax notations and formats, of which the most widely used is Turtle (Terse RDF Triple Language).
RDF is a directed graph composed of triple statements. An RDF graph statement is represented by: (1) a node for the subject, (2) an arc from subject to object, representing a predicate, and (3) a node for the object. Each of these parts can be identified by a Uniform Resource Identifier (URI). An object can also be a literal value. This simple, flexible data model has a lot of expressive power to represent complex situations, relationships, and other things of interest, while also being appropriately abstract.
RDF was adopted as a W3C recommendation in 1999. The RDF 1.0 specification was published in 2004, and the RDF 1.1 specification in 2014. SPARQL is a standard query language for RDF graphs. RDF Schema (RDFS), Web Ontology Language (OWL) and SHACL (Shapes Constraint Language) are ontology languages that are used to describe RDF data.
Overview
The RDF data model is similar to classical conceptual modeling approaches (such as entity–relationship or class diagrams). It is based on the idea of making statements about resources (in particular web resources) in expressions of the form subject–predicate–object, known as triples. The subject denotes the resource; the predicate denotes traits or aspects of the resource, and expresses a relationship between the subject and the object.
For example, one way to represent the notion "The sky has the color blue" in RDF is as the triple: a subject denoting "the sky", a predicate denoting "has the color", and an object denoting "blue". Therefore, RDF uses subject instead of object (or entity) in contrast to the typical approach of an entity–attribute–value model in object-oriented design: entity (sky), attribute (color), and value (blue).
RDF is an abstract model with several serialization formats (being essentially specialized file formats). In addition the particular encoding for resources or triples can vary from format to format.
This mechanism for describing resources is a major component in the W3C's Semantic Web activity: an evolutionary stage of the World Wide Web in which automated software can store, exchange, and use machine-readable information distributed throughout the Web, in turn enabling users to deal with the information with greater efficiency and certainty. RDF's simple data model and ability to model disparate, abstract concepts has also led to its increasing use in knowledge management applications unrelated to Semantic Web activity.
A collection of RDF statements intrinsically represents a labeled, directed multigraph. This makes an RDF data model better suited to certain kinds of knowledge representation than other relational or ontological models.
As RDFS, OWL and SHACL demonstrate, one can build additional ontology languages upon RDF.
History
The initial RDF design, intended to "build a vendor-neutral and operating system- independent system of metadata", derived from the W3C's Platform for Internet Content Selection (PICS), an early web content labelling system, but the project was also shaped by ideas from Dublin Core, and from the Meta Content Framework (MCF), which had been developed during 1995 to 1997 by Ramanathan V. Guha at Apple and Tim Bray at Netscape.
A first public draft of RDF appeared in October 1997, issued by a W3C working group that included representatives from IBM, Microsoft, Netscape, Nokia, Reuters, SoftQuad, and the University of Michigan.
In 1999, the W3C published the first recommended RDF specification, the Model and Syntax Specification ("RDF M&S"). This described RDF's data model and an XML serialization.
Two persistent misunderstandings about RDF developed at this time: firstly, due to the MCF influence and the RDF "Resource Description" initialism, the idea that RDF was specifically for use in representing metadata; secondly that RDF was an XML format rather than a data model, and only the RDF/XML serialisation being XML-based. RDF saw little take-up in this period, but there was significant work done in Bristol, around ILRT at Bristol University and HP Labs, and in Boston at MIT. RSS 1.0 and FOAF became exemplar applications for RDF in this period.
The recommendation of 1999 was replaced in 2004 by a set of six specifications: "The RDF Primer", "RDF Concepts and Abstract", "RDF/XML Syntax Specification (revised)", "RDF Semantics", "RDF Vocabulary Description Language 1.0", and "The RDF Test Cases".
This series was superseded in 2014 by the following six "RDF 1.1" documents: "RDF 1.1 Primer", "RDF 1.1 Concepts and Abstract Syntax", "RDF 1.1 XML Syntax", "RDF 1.1 Semantics", "RDF Schema 1.1", and "RDF 1.1 Test Cases".
RDF topics
Vocabulary
The vocabulary defined by the RDF specification is as follows:
Classes
rdf
the class of XML literal values
the class of properties
the class of RDF statements
, , containers of alternatives, unordered containers, and ordered containers (rdfs:Container is a super-class of the three)
the class of RDF Lists
an instance of rdf:List representing the empty list
rdfs
the class resource, everything
the class of literal values, e.g. strings and integers
the class of classes
the class of RDF datatypes
the class of RDF containers
the class of container membership properties, rdf:_1, rdf:_2, ..., all of which are sub-properties of rdfs:member
Properties
rdf
an instance of rdf:Property used to state that a resource is an instance of a class
the first item in the subject RDF list
the rest of the subject RDF list after rdf:first
idiomatic property used for structured values
the subject of the RDF statement
the predicate of the RDF statement
the object of the RDF statement
rdf:Statement, rdf:subject, rdf:predicate, rdf:object are used for reification (see below).
rdfs
the subject is a subclass of a class
the subject is a subproperty of a property
a domain of the subject property
a range of the subject property
a human-readable name for the subject
a description of the subject resource
a member of the subject resource
further information about the subject resource
the definition of the subject resource
This vocabulary is used as a foundation for RDF Schema, where it is extended.
Serialization formats
Several common serialization formats are in use, including:
Turtle, a compact, human-friendly format.
TriG, an extension of Turtle to datasets.
N-Triples, a very simple, easy-to-parse, line-based format that is not as compact as Turtle.
N-Quads, a superset of N-Triples, for serializing multiple RDF graphs.
JSON-LD, a JSON-based serialization.
N3 or Notation3, a non-standard serialization that is very similar to Turtle, but has some additional features, such as the ability to define inference rules.
RDF/XML, an XML-based syntax that was the first standard format for serializing RDF.
RDF/JSON, an alternative syntax for expressing RDF triples using a simple JSON notation.
RDF/XML is sometimes misleadingly called simply RDF because it was introduced among the other W3C specifications defining RDF and it was historically the first W3C standard RDF serialization format. However, it is important to distinguish the RDF/XML format from the abstract RDF model itself. Although the RDF/XML format is still in use, other RDF serializations are now preferred by many RDF users, both because they are more human-friendly, and because some RDF graphs are not representable in RDF/XML due to restrictions on the syntax of XML QNames.
With a little effort, virtually any arbitrary XML may also be interpreted as RDF using GRDDL (pronounced 'griddle'), Gleaning Resource Descriptions from Dialects of Languages.
RDF triples may be stored in a type of database called a triplestore.
Resource identification
The subject of an RDF statement is either a uniform resource identifier (URI) or a blank node, both of which denote resources. Resources indicated by blank nodes are called anonymous resources. They are not directly identifiable from the RDF statement. The predicate is a URI which also indicates a resource, representing a relationship. The object is a URI, blank node or a Unicode string literal.
As of RDF 1.1 resources are identified by Internationalized Resource Identifiers (IRIs); IRI are a generalization of URI.
In Semantic Web applications, and in relatively popular applications of RDF like RSS and FOAF (Friend of a Friend), resources tend to be represented by URIs that intentionally denote, and can be used to access, actual data on the World Wide Web. But RDF, in general, is not limited to the description of Internet-based resources. In fact, the URI that names a resource does not have to be dereferenceable at all. For example, a URI that begins with "http:" and is used as the subject of an RDF statement does not necessarily have to represent a resource that is accessible via HTTP, nor does it need to represent a tangible, network-accessible resource — such a URI could represent absolutely anything. However, there is broad agreement that a bare URI (without a # symbol) which returns a 300-level coded response when used in an HTTP GET request should be treated as denoting the internet resource that it succeeds in accessing.
Therefore, producers and consumers of RDF statements must agree on the semantics of resource identifiers. Such agreement is not inherent to RDF itself, although there are some controlled vocabularies in common use, such as Dublin Core Metadata, which is partially mapped to a URI space for use in RDF. The intent of publishing RDF-based ontologies on the Web is often to establish, or circumscribe, the intended meanings of the resource identifiers used to express data in RDF. For example, the URI:
http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#Merlot
is intended by its owners to refer to the class of all Merlot red wines by vintner (i.e., instances of the above URI each represent the class of all wine produced by a single vintner), a definition which is expressed by the OWL ontology — itself an RDF document — in which it occurs. Without careful analysis of the definition, one might erroneously conclude that an instance of the above URI was something physical, instead of a type of wine.
Note that this is not a 'bare' resource identifier, but is rather a URI reference, containing the '#' character and ending with a fragment identifier.
Statement reification and context
The body of knowledge modeled by a collection of statements may be subjected to reification, in which each statement (that is each triple subject-predicate-object altogether) is assigned a URI and treated as a resource about which additional statements can be made, as in "Jane says that John is the author of document X". Reification is sometimes important in order to deduce a level of confidence or degree of usefulness for each statement.
In a reified RDF database, each original statement, being a resource, itself, most likely has at least three additional statements made about it: one to assert that its subject is some resource, one to assert that its predicate is some resource, and one to assert that its object is some resource or literal. More statements about the original statement may also exist, depending on the application's needs.
Borrowing from concepts available in logic (and as illustrated in graphical notations such as conceptual graphs and topic maps), some RDF model implementations acknowledge that it is sometimes useful to group statements according to different criteria, called situations, contexts, or scopes, as discussed in articles by RDF specification co-editor Graham Klyne. For example, a statement can be associated with a context, named by a URI, in order to assert an "is true in" relationship. As another example, it is sometimes convenient to group statements by their source, which can be identified by a URI, such as the URI of a particular RDF/XML document. Then, when updates are made to the source, corresponding statements can be changed in the model, as well.
Implementation of scopes does not necessarily require fully reified statements. Some implementations allow a single scope identifier to be associated with a statement that has not been assigned a URI, itself. Likewise named graphs in which a set of triples is named by a URI can represent context without the need to reify the triples.
Query and inference languages
The predominant query language for RDF graphs is SPARQL. SPARQL is an SQL-like language, and a recommendation of the W3C as of January 15, 2008.
The following is an example of a SPARQL query to show country capitals in Africa, using a fictional ontology:
PREFIX ex: <http://example.com/exampleOntology#>
SELECT ?capital ?country
WHERE {
?x ex:cityname ?capital ;
ex:isCapitalOf ?y .
?y ex:countryname ?country ;
ex:isInContinent ex:Africa .
}
Other non-standard ways to query RDF graphs include:
RDQL, precursor to SPARQL, SQL-like
Versa, compact syntax (non–SQL-like), solely implemented in 4Suite (Python).
RQL, one of the first declarative languages for uniformly querying RDF schemas and resource descriptions, implemented in RDFSuite.
SeRQL, part of Sesame
XUL has a template element in which to declare rules for matching data in RDF. XUL uses RDF extensively for data binding.
SHACL Advanced Features specification (W3C Working Group Note), the most recent version of which is maintained by the SHACL Community Group defines support for SHACL Rules, used for data transformations, inferences and mappings of RDF based on SHACL shapes.
Validation and description
The predominant language for describing and validating RDF graphs is SHACL (Shapes Constraint Language). SHACL specification is divided in two parts: SHACL Core and SHACL-SPARQL. SHACL Core consists of a list of built-in constraints such as cardinality, range of values and many others. SHACL-SPARQL describes SPARQL-based constraints and an extension mechanism to declare new constraint components.
Other non-standard ways to describe and validate RDF graphs include:
SPARQL Inferencing Notation (SPIN) was based on SPARQL queries. It has been effectively deprecated in favor of SHACL.
ShEx (Shape Expressions) is a concise language for RDF validation and description.
Examples
Example 1: Description of a person named Eric Miller
The following example is taken from the W3C website describing a resource with statements "there is a Person identified by http://www.w3.org/People/EM/contact#me, whose name is Eric Miller, whose email address is e.miller123(at)example (changed for security purposes), and whose title is Dr."
The resource "http://www.w3.org/People/EM/contact#me" is the subject.
The objects are:
"Eric Miller" (with a predicate "whose name is"),
mailto:e.miller123(at)example (with a predicate "whose email address is"), and
"Dr." (with a predicate "whose title is").
The subject is a URI.
The predicates also have URIs. For example, the URI for each predicate:
"whose name is" is http://www.w3.org/2000/10/swap/pim/contact#fullName,
"whose email address is" is http://www.w3.org/2000/10/swap/pim/contact#mailbox,
"whose title is" is http://www.w3.org/2000/10/swap/pim/contact#personalTitle.
In addition, the subject has a type (with URI http://www.w3.org/1999/02/22-rdf-syntax-ns#type), which is person (with URI http://www.w3.org/2000/10/swap/pim/contact#Person).
Therefore, the following "subject, predicate, object" RDF triples can be expressed:
http://www.w3.org/People/EM/contact#me, http://www.w3.org/2000/10/swap/pim/contact#fullName, "Eric Miller"
http://www.w3.org/People/EM/contact#me, http://www.w3.org/2000/10/swap/pim/contact#mailbox, mailto:e.miller123(at)example
http://www.w3.org/People/EM/contact#me, http://www.w3.org/2000/10/swap/pim/contact#personalTitle, "Dr."
http://www.w3.org/People/EM/contact#me, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2000/10/swap/pim/contact#Person
In standard N-Triples format, this RDF can be written as:
<http://www.w3.org/People/EM/contact#me> <http://www.w3.org/2000/10/swap/pim/contact#fullName> "Eric Miller" .
<http://www.w3.org/People/EM/contact#me> <http://www.w3.org/2000/10/swap/pim/contact#mailbox> <mailto:e.miller123(at)example> .
<http://www.w3.org/People/EM/contact#me> <http://www.w3.org/2000/10/swap/pim/contact#personalTitle> "Dr." .
<http://www.w3.org/People/EM/contact#me> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2000/10/swap/pim/contact#Person> .
Equivalently, it can be written in standard Turtle (syntax) format as:
@prefix eric: <http://www.w3.org/People/EM/contact#> .
@prefix contact: <http://www.w3.org/2000/10/swap/pim/contact#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
eric:me contact:fullName "Eric Miller" .
eric:me contact:mailbox <mailto:e.miller123(at)example> .
eric:me contact:personalTitle "Dr." .
eric:me rdf:type contact:Person .
Or, it can be written in RDF/XML format as:
<?xml version="1.0" encoding="utf-8"?>
<rdf:RDF xmlns:contact="http://www.w3.org/2000/10/swap/pim/contact#" xmlns:eric="http://www.w3.org/People/EM/contact#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about="http://www.w3.org/People/EM/contact#me">
<contact:fullName>Eric Miller</contact:fullName>
</rdf:Description>
<rdf:Description rdf:about="http://www.w3.org/People/EM/contact#me">
<contact:mailbox rdf:resource="mailto:e.miller123(at)example"/>
</rdf:Description>
<rdf:Description rdf:about="http://www.w3.org/People/EM/contact#me">
<contact:personalTitle>Dr.</contact:personalTitle>
</rdf:Description>
<rdf:Description rdf:about="http://www.w3.org/People/EM/contact#me">
<rdf:type rdf:resource="http://www.w3.org/2000/10/swap/pim/contact#Person"/>
</rdf:Description>
</rdf:RDF>
Example 2: The postal abbreviation for New York
Certain concepts in RDF are taken from logic and linguistics, where subject-predicate and subject-predicate-object structures have meanings similar to, yet distinct from, the uses of those terms in RDF. This example demonstrates:
In the English language statement 'New York has the postal abbreviation NY' , 'New York' would be the subject, 'has the postal abbreviation' the predicate and 'NY' the object.
Encoded as an RDF triple, the subject and predicate would have to be resources named by URIs. The object could be a resource or literal element. For example, in the N-Triples form of RDF, the statement might look like:
<urn:x-states:New%20York> <http://purl.org/dc/terms/alternative> "NY" .
In this example, "urn:x-states:New%20York" is the URI for a resource that denotes the US state New York, "http://purl.org/dc/terms/alternative" is the URI for a predicate (whose human-readable definition can be found here ), and "NY" is a literal string. Note that the URIs chosen here are not standard, and do not need to be, as long as their meaning is known to whatever is reading them.
Example 3: A Wikipedia article about Tony Benn
In a like manner, given that "https://en.wikipedia.org/wiki/Tony_Benn" identifies a particular resource (regardless of whether that URI could be traversed as a hyperlink, or whether the resource is actually the Wikipedia article about Tony Benn), to say that the title of this resource is "Tony Benn" and its publisher is "Wikipedia" would be two assertions that could be expressed as valid RDF statements. In the N-Triples form of RDF, these statements might look like the following:
<https://en.wikipedia.org/wiki/Tony_Benn> <http://purl.org/dc/elements/1.1/title> "Tony Benn" .
<https://en.wikipedia.org/wiki/Tony_Benn> <http://purl.org/dc/elements/1.1/publisher> "Wikipedia" .
To an English-speaking person, the same information could be represented simply as:
The title of this resource, which is published by Wikipedia, is 'Tony Benn'
However, RDF puts the information in a formal way that a machine can understand. The purpose of RDF is to provide an encoding and interpretation mechanism so that resources can be described in a way that particular software can understand it; in other words, so that software can access and use information that it otherwise could not use.
Both versions of the statements above are wordy because one requirement for an RDF resource (as a subject or a predicate) is that it be unique. The subject resource must be unique in an attempt to pinpoint the exact resource being described. The predicate needs to be unique in order to reduce the chance that the idea of Title or Publisher will be ambiguous to software working with the description. If the software recognizes http://purl.org/dc/elements/1.1/title (a specific definition for the concept of a title established by the Dublin Core Metadata Initiative), it will also know that this title is different from a land title or an honorary title or just the letters t-i-t-l-e put together.
The following example, written in Turtle, shows how such simple claims can be elaborated on, by combining multiple RDF vocabularies. Here, we note that the primary topic of the Wikipedia page is a "Person" whose name is "Tony Benn":
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
@prefix dc: <http://purl.org/dc/elements/1.1/> .
<https://en.wikipedia.org/wiki/Tony_Benn>
dc:publisher "Wikipedia" ;
dc:title "Tony Benn" ;
foaf:primaryTopic [
a foaf:Person ;
foaf:name "Tony Benn"
] .
Applications
DBpedia – Extracts facts from Wikipedia articles and publishes them as RDF data.
YAGO – Similar to DBpedia extracts facts from Wikipedia articles and publishes them as RDF data.
Wikidata – Collaboratively edited knowledge base hosted by the Wikimedia Foundation.
Creative Commons – Uses RDF to embed license information in web pages and mp3 files.
FOAF (Friend of a Friend) – designed to describe people, their interests and interconnections.
Haystack client – Semantic web browser from MIT CS & AI lab.
IDEAS Group – developing a formal 4D ontology for Enterprise Architecture using RDF as the encoding.
Microsoft shipped a product, Connected Services Framework, which provides RDF-based Profile Management capabilities.
MusicBrainz – Publishes information about Music Albums.
NEPOMUK, an open-source software specification for a Social Semantic desktop uses RDF as a storage format for collected metadata. NEPOMUK is mostly known because of its integration into the KDE SC 4 desktop environment.
Cochrane is a global publisher of clinical study meta-analyses in evidence based healthcare. They use an ontology driven data architecture to semantically annotate their published reviews with RDF based structured data.
RDF Site Summary – one of several "RSS" languages for publishing information about updates made to a web page; it is often used for disseminating news article summaries and sharing weblog content.
Simple Knowledge Organization System (SKOS) – a KR representation intended to support vocabulary/thesaurus applications
SIOC (Semantically-Interlinked Online Communities) – designed to describe online communities and to create connections between Internet-based discussions from message boards, weblogs and mailing lists.
Smart-M3 – provides an infrastructure for using RDF and specifically uses the ontology agnostic nature of RDF to enable heterogeneous mashing-up of information
LV2 - a libre plugin format using Turtle to describe API/ABI capabilities and properties
Some uses of RDF include research into social networking. It will also help people in business fields understand better their relationships with members of industries that could be of use for product placement. It will also help scientists understand how people are connected to one another.
RDF is being used to gain a better understanding of road traffic patterns. This is because the information regarding traffic patterns is on different websites, and RDF is used to integrate information from different sources on the web. Before, the common methodology was using keyword searching, but this method is problematic because it does not consider synonyms. This is why ontologies are useful in this situation. But one of the issues that comes up when trying to efficiently study traffic is that to fully understand traffic, concepts related to people, streets, and roads must be well understood. Since these are human concepts, they require the addition of fuzzy logic. This is because values that are useful when describing roads, like slipperiness, are not precise concepts and cannot be measured. This would imply that the best solution would incorporate both fuzzy logic and ontology.
See also
Notations for RDF
TRiG
TRiX
RDF/XML
RDFa
JSON-LD
Notation3
Similar concepts
Entity–attribute–value model
Graph theory – an RDF model is a labeled, directed multi-graph.
Tag (metadata)
SciCrunch
Semantic network
Other (unsorted)
Semantic technology
Business Intelligence 2.0 (BI 2.0)
Data portability
EU Open Data Portal
RDF Schema
Folksonomy
LSID - Life Science Identifier
Swoogle
Universal Networking Language (UNL)
VoID
References
Citations
Sources
Further reading
W3C's RDF at W3C: specifications, guides, and resources
RDF Semantics: specification of semantics, and complete systems of inference rules for both RDF and RDFS
External links
Knowledge representation
World Wide Web Consortium standards
XML-based standards
Metadata
Semantic Web
Bibliography file formats
Modeling languages | Resource Description Framework | [
"Technology"
] | 6,442 | [
"Computer standards",
"Metadata",
"Data",
"XML-based standards"
] |
53,878 | https://en.wikipedia.org/wiki/Betelgeuse | Betelgeuse is a red supergiant star in the constellation of Orion. It is usually the tenth-brightest star in the night sky and, after Rigel, the second-brightest in its constellation. It is a distinctly reddish, semiregular variable star whose apparent magnitude, varying between +0.0 and +1.6, has the widest range displayed by any first-magnitude star. Betelgeuse is the brightest star in the night sky at near-infrared wavelengths. Its Bayer designation is α Orionis, Latinised to Alpha Orionis and abbreviated Alpha Ori or α Ori.
With a radius between 640 and 764 times that of the Sun, if it were at the center of our Solar System, its surface would lie beyond the asteroid belt and it would engulf the orbits of Mercury, Venus, Earth, and Mars. Calculations of Betelgeuse's mass range from slightly under ten to a little over twenty times that of the Sun. For various reasons, its distance has been quite difficult to measure; current best estimates are of the order of 400–600 light-years from the Suna comparatively wide uncertainty for a relatively nearby star. Its absolute magnitude is about −6. With an age of less than 10 million years, Betelgeuse has evolved rapidly because of its large mass, and is expected to end its evolution with a supernova explosion, most likely within 100,000 years. When Betelgeuse explodes, it will shine as bright as the half-Moon for more than three months; life on Earth will be unharmed. Having been ejected from its birthplace in the Orion OB1 associationwhich includes the stars in Orion's Beltthis runaway star has been observed to be moving through the interstellar medium at a speed of , creating a bow shock over four light-years wide.
Betelgeuse became the first extrasolar star whose photosphere's angular size was measured in 1920, and subsequent studies have reported an angular diameter (i.e., apparent size) ranging from 0.042 to 0.056 arcseconds; that range of determinations is ascribed to non-sphericity, limb darkening, pulsations and varying appearance at different wavelengths. It is also surrounded by a complex, asymmetric envelope, roughly 250 times the size of the star, caused by mass loss from the star itself. The Earth-observed angular diameter of Betelgeuse is exceeded only by those of R Doradus and the Sun.
Starting in October 2019, Betelgeuse began to dim noticeably, and by mid-February 2020 its brightness had dropped by a factor of approximately 3, from magnitude 0.5 to 1.7. It then returned to a more normal brightness range, reaching a peak of 0.0 visual and 0.1 V-band magnitude in April 2023. Infrared observations found no significant change in luminosity over the last 50 years, suggesting that the dimming was due to a change in extinction around the star rather than a more fundamental change. A study using the Hubble Space Telescope suggests that occluding dust was created by a surface mass ejection; this material was cast millions of miles from the star, and then cooled to form the dust that caused the dimming.
Nomenclature
The star's designation is α Orionis (Latinised to Alpha Orionis), given by Johann Bayer in 1603.
The traditional name Betelgeuse was derived from the Arabic "the hand of al-Jawzā’ [i.e. Orion]". An error in the 13th-century reading of the Arabic initial yā’ () as bā’ (—a difference in i‘jām) led to the European name. In English, there are four common pronunciations of this name, depending on whether the first e is pronounced short or long and whether the s is pronounced or :
;
;
;
, popularized for sounding like "beetle juice".
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin, issued July 2016, included a table of the first two batches of names approved by the WGSN, which included Betelgeuse for this star. It is now so entered in the IAU Catalog of Star Names.
Observational history
Betelgeuse and its red coloration have been noted since antiquity; the classical astronomer Ptolemy described its color as (hypókirrhos = more or less orange-tawny), a term later described by a translator of Ulugh Beg's Zij-i Sultani as rubedo, Latin for "ruddiness". In the 19th century, before modern systems of stellar classification, Angelo Secchi included Betelgeuse as one of the prototypes for his Class III (orange to red) stars. Three centuries before Ptolemy, in contrast, Chinese astronomers observed Betelgeuse as yellow; Such an observation, if accurate, could suggest the star was in a yellow supergiant phase around this time, a credible possibility, given current research into these stars' complex circumstellar environment.
Nascent discoveries
Aboriginal groups in South Australia have shared oral tales of the variable brightness of Betelgeuse for an unknown period.
The variation in Betelgeuse's brightness was described in 1836 by Sir John Herschel in Outlines of Astronomy. From 1836 to 1840, he noticed significant changes in magnitude when Betelgeuse outshone Rigel in October 1837 and again in November 1839. A 10-year quiescent period followed; then in 1849, Herschel noted another short cycle of variability, which peaked in 1852. Later observers recorded unusually high maxima with an interval of years, but only small variations from 1957 to 1967. The records of the American Association of Variable Star Observers (AAVSO) show a maximum brightness of 0.2 in 1933 and 1942, and a minimum of 1.2, observed in 1927 and 1941. This variability in brightness may explain why Johann Bayer, with the publication of his Uranometria in 1603, designated the star alpha, as it probably rivaled the usually brighter Rigel (beta). From Arctic latitudes, Betelgeuse's red colour and higher location in the sky than Rigel meant the Inuit regarded it as brighter, and one local name was Ulluriajjuaq ("large star").
In 1920, Albert A. Michelson and Francis G. Pease mounted a six-meter interferometer on the front of the 2.5-meter telescope at Mount Wilson Observatory, helped by John August Anderson. The trio measured the angular diameter of Betelgeuse at 0.047″, a figure that resulted in a diameter of () based on the parallax value of . But limb darkening and measurement errors resulted in uncertainty about the accuracy of these measurements.
The 1950s and 1960s saw two developments that affected stellar convection theory in red supergiants: the Stratoscope projects and the 1958 publication of Structure and Evolution of the Stars, principally the work of Martin Schwarzschild and his colleague at Princeton University, Richard Härm.
This book disseminated ideas on how to apply computer technologies to create stellar models, while the Stratoscope projects, by taking balloon-borne telescopes above the Earth's turbulence, produced some of the finest images of solar granules and sunspots ever seen, thus confirming the existence of convection in the solar atmosphere.
Imaging breakthroughs
Astronomers saw some major advances in astronomical imaging technology in the 1970s, beginning with Antoine Labeyrie's invention of speckle interferometry, a process that significantly reduced the blurring effect caused by astronomical seeing. It increased the optical resolution of ground-based telescopes, allowing for more precise measurements of Betelgeuse's photosphere. With improvements in infrared telescopy atop Mount Wilson, Mount Locke, and Mauna Kea in Hawaii, astrophysicists began peering into the complex circumstellar shells surrounding the supergiant, causing them to suspect the presence of huge gas bubbles resulting from convection. However, it was not until the late 1980s and early 1990s, when Betelgeuse became a regular target for aperture masking interferometry, that breakthroughs occurred in visible-light and infrared imaging. Pioneered by J.E. Baldwin and colleagues of the Cavendish Astrophysics Group, the new technique employed a small mask with several holes in the telescope pupil plane, converting the aperture into an ad hoc interferometric array. The technique contributed some of the most accurate measurements of Betelgeuse while revealing bright spots on the star's photosphere. These were the first optical and infrared images of a stellar disk other than the Sun, taken first from ground-based interferometers and later from higher-resolution observations of the COAST telescope. The "bright patches" or "hotspots" observed with these instruments appeared to corroborate a theory put forth by Schwarzschild decades earlier of massive convection cells dominating the stellar surface.
In 1995, the Hubble Space Telescope's Faint Object Camera captured an ultraviolet image with a resolution superior to that obtained by ground-based interferometers—the first conventional-telescope image (or "direct-image" in NASA terminology) of the disk of another star.
Because ultraviolet light is absorbed by the Earth's atmosphere, observations at these wavelengths are best performed by space telescopes.
This image, like earlier pictures, contained a bright patch indicating a region in the southwestern quadrant hotter than the stellar surface.
Subsequent ultraviolet spectra taken with the Goddard High Resolution Spectrograph suggested that the hot spot was one of Betelgeuse's poles of rotation. This would give the rotational axis an inclination of about 20° to the direction of Earth, and a position angle from celestial North of about 55°.
2000s studies
In a study published in December 2000, the star's diameter was measured with the Infrared Spatial Interferometer (ISI) at mid-infrared wavelengths producing a limb-darkened estimate of – a figure entirely consistent with Michelson's findings eighty years earlier.
At the time of its publication, the estimated parallax from the Hipparcos mission was , yielding an estimated radius for Betelgeuse of . However, an infrared interferometric study published in 2009 announced that the star had shrunk by 15% since 1993 at an increasing rate without a significant diminution in magnitude.
Subsequent observations suggest that the apparent contraction may be due to shell activity in the star's extended atmosphere.
In addition to the star's diameter, questions have arisen about the complex dynamics of Betelgeuse's extended atmosphere. The mass that makes up galaxies is recycled as stars are formed and destroyed, and red supergiants are major contributors, yet the process by which mass is lost remains a mystery.
With advances in interferometric methodologies, astronomers may be close to resolving this conundrum. Images released by the European Southern Observatory in July 2009, taken by the ground-based Very Large Telescope Interferometer (VLTI), showed a vast plume of gas extending from the star into the surrounding atmosphere.
This mass ejection was equal to the distance between the Sun and Neptune and is one of multiple events occurring in Betelgeuse's surrounding atmosphere. Astronomers have identified at least six shells surrounding Betelgeuse. Solving the mystery of mass loss in the late stages of a star's evolution may reveal those factors that precipitate the explosive deaths of these stellar giants.
2019–2020 fading
A pulsating semiregular variable star, Betelgeuse is subject to multiple cycles of increasing and decreasing brightness due to changes in its size and temperature. The astronomers who first noted the dimming of Betelgeuse, Villanova University astronomers Richard Wasatonic and Edward Guinan, and amateur Thomas Calderwood, theorize that a coincidence of a normal 5.9 year light-cycle minimum and a deeper-than-normal 425 day period are the driving factors.
Other possible causes hypothesized by late 2019 were an eruption of gas or dust or fluctuations in the star's surface brightness.
By August 2020, long-term and extensive studies of Betelgeuse, primarily using ultraviolet observations by the Hubble Space Telescope, had suggested that the unexpected dimming was probably caused by an immense amount of superhot material ejected into space. The material cooled and formed a dust cloud that blocked the starlight coming from about a quarter of Betelgeuse's surface. Hubble captured signs of dense, heated material moving through the star's atmosphere in September, October and November before several telescopes observed the more marked dimming in December and the first few months of 2020.
By January 2020, Betelgeuse had dimmed by a factor of approximately 2.5 from magnitude 0.5 to 1.5 and was reported still fainter in February in The Astronomer's Telegram at a record minimum of +1.614, noting that the star is currently the "least luminous and coolest" in the 25 years of their studies and also calculating a decrease in radius.
Astronomy magazine described it as a "bizarre dimming",
and popular speculation inferred that this might indicate an imminent supernova.
This dropped Betelgeuse from one of the top 10 brightest stars in the sky to outside the top 20, noticeably dimmer than its near neighbor Aldebaran. Mainstream media reports discussed speculation that Betelgeuse might be about to explode as a supernova,
but astronomers note that the supernova is expected to occur within approximately the next 100,000 years and is thus unlikely to be imminent.
By 17 February 2020, Betelgeuse's brightness had remained constant for about 10 days, and the star showed signs of rebrightening.
On 22 February 2020, Betelgeuse may have stopped dimming altogether, all but ending the dimming episode.
On 24 February 2020, no significant change in the infrared over the last 50 years was detected; this seemed unrelated to the recent visual fading and suggested that an impending core collapse may be unlikely.
Also on 24 February 2020, further studies suggested that occluding "large-grain circumstellar dust" may be the most likely explanation for the dimming of the star.
A study that uses observations at submillimetre wavelengths rules out significant contributions from dust absorption. Instead, large starspots appear to be the cause for the dimming.
Followup studies, reported on 31 March 2020 in The Astronomer's Telegram, found a rapid rise in the brightness of Betelgeuse.
Betelgeuse is almost unobservable from the ground between May and August because it is too close to the Sun. Before entering its 2020 conjunction with the Sun, Betelgeuse had reached a brightness of +0.4 . Observations with the STEREO-A spacecraft made in June and July 2020 showed that the star had dimmed by 0.5 since the last ground-based observation in April. This is surprising, because a maximum was expected for August/September 2020, and the next minimum should occur around April 2021. However Betelgeuse's brightness is known to vary irregularly, making predictions difficult. The fading could indicate that another dimming event might occur much earlier than expected.
On 30 August 2020, astronomers reported the detection of a second dust cloud emitted from Betelgeuse, and associated with recent substantial dimming (a secondary minimum on 3 August) in luminosity of the star.
In June 2021, the dust was explained as possibly caused by a cool patch on its photosphere
and in August a second independent group confirmed these results. The dust is thought to have resulted from the cooling of gas ejected from the star. An August 2022
study using the Hubble Space Telescope confirmed previous research and suggested the dust could have been created by a surface mass ejection. It conjectured as well that the dimming could have come from a short-term minimum coinciding with a long-term minimum producing a grand minimum, a 416-day cycle and 2010 day cycle respectively, a mechanism first suggested by astronomer L. Goldberg.
In April 2023, astronomers reported the star reached a peak of 0.0 visual and 0.1 V-band magnitude.
Observation
As a result of its distinctive orange-red color and position within Orion, Betelgeuse is easy to find with the naked eye. It is one of three stars that make up the Winter Triangle asterism, and it marks the center of the Winter Hexagon. It can be seen rising in the east at the beginning of January of each year, just after sunset. Between mid-September and mid-March (best in mid-December), it is visible to virtually every inhabited region of the globe, except in Antarctica at latitudes south of 82°. In May (moderate northern latitudes) or June (southern latitudes), the red supergiant can be seen briefly on the western horizon after sunset, reappearing again a few months later on the eastern horizon before sunrise. In the intermediate period (June–July, centered around mid June), it is invisible to the naked eye (visible only with a telescope in daylight), except around midday low in the north in Antarctic regions between 70° and 80° south latitude (during midday twilight in polar night, when the Sun is below the horizon).
Betelgeuse is a variable star whose visual magnitude ranges between 0.0 and +1.6 . There are periods during which it surpasses Rigel to become the sixth brightest star, and occasionally it will become even brighter than Capella. At its faintest, Betelgeuse can fall behind Deneb and Beta Crucis, themselves both slightly variable, to be the twentieth-brightest star.
Betelgeuse has a B–V color index of 1.85 – a figure which points to its pronounced "redness". The photosphere has an extended atmosphere, which displays strong lines of emission rather than absorption, a phenomenon that occurs when a star is surrounded by a thick gaseous envelope (rather than ionized). This extended gaseous atmosphere has been observed moving toward and away from Betelgeuse, depending on fluctuations in the photosphere. Betelgeuse is the brightest near-infrared source in the sky with a J band magnitude of −2.99; only about 13% of the star's radiant energy is emitted as visible light. If human eyes were sensitive to radiation at all wavelengths, Betelgeuse would appear as the brightest star in the night sky.
Catalogues list up to nine faint visual companions to Betelgeuse. They are at distances of about one to four arc-minutes and all are fainter than 10th magnitude.
Star system
Betelgeuse generally has been considered to be a single isolated star and a runaway star, not currently associated with any cluster or star-forming region, although its birthplace is unclear. However, starting in 1985, three studies have proposed companion stars to Betelgeuse. In 1985, analysis of polarization data from 1968 through 1983 indicated a close companion with a periodic orbit of about 2.1 years, and by using speckle interferometry, the team concluded that the closer of the two companions was located at (≈9 AU) from the main star with a position angle of 273°, an orbit that would potentially place it within the star's chromosphere. The more distant companion was at (≈77 AU) with a position angle of 278°. Other studies have found no evidence for these companions or have actively refuted their existence, but the possibility of a close companion contributing to the overall flux has never been fully ruled out. High-resolution interferometry of Betelgeuse and its vicinity, far beyond the technology of the 1980s and 1990s, has not detected any companions.
More recently, in 2024, two studies found evidence for a companion star.
One study found that a not yet directly-observed, dust-modulating star or white dwarf of at a distance of AU would be the most likely solution for Betelgeuse's 2170-day secondary periodicity, fluctuating radial velocity, moderate radius and low variation in effective temperature, as of 2024. A second study produced by a different group of researchers showed similar findings.
Distance measurements
Parallax is the apparent change of the position of an object, measured in seconds of arc, caused by the change of position of the observer of that object. Parallax is used in astronomy to estimate distances to the nearest stars. As the Earth orbits the Sun, every star is seen to shift by a fraction of an arc second, which measure, combined with the baseline provided by the Earth's orbit gives the distance to that star. Since the first successful parallax measurement by Friedrich Bessel in 1838, astronomers have been puzzled by Betelgeuse's apparent distance. Knowledge of the star's distance improves the accuracy of other stellar parameters, such as luminosity that, when combined with an angular diameter, can be used to calculate the physical radius and effective temperature; luminosity and isotopic abundances can also be used to estimate the stellar age and mass.
When the first interferometric studies were performed on the star's diameter in 1920, the assumed parallax was . This equated to a distance of or roughly , producing not only an inaccurate radius for the star but every other stellar characteristic. Since then, there has been ongoing work to measure the distance of Betelgeuse, with proposed distances as high as or about .
Before the publication of the Hipparcos Catalogue (1997), there were two slightly conflicting parallax measurements for Betelgeuse. The first, in 1991, gave a parallax of , yielding a distance of roughly or . The second was the Hipparcos Input Catalogue (1993) with a trigonometric parallax of , a distance of or . Given this uncertainty, researchers were adopting a wide range of distance estimates, leading to significant variances in the calculation of the star's attributes.
The results from the Hipparcos mission were released in 1997. The measured parallax of Betelgeuse was , which equated to a distance of roughly or , and had a smaller reported error than previous measurements. However, later evaluation of the Hipparcos parallax measurements for variable stars like Betelgeuse found that the uncertainty of these measurements had been underestimated. In 2007, an improved figure of was calculated, hence a much tighter error factor yielding a distance of roughly or .
In 2008, measurements using the Very Large Array (VLA) produced a radio solution of , equaling a distance of or . As the researcher, Harper, points out: "The revised Hipparcos parallax leads to a larger distance () than the original; however, the astrometric solution still requires a significant cosmic noise of 2.4 mas. Given these results it is clear that the Hipparcos data still contain systematic errors of unknown origin." Although the radio data also have systematic errors, the Harper solution combines the datasets in the hope of mitigating such errors. An updated result from further observations with ALMA and e-Merlin gives a parallax of mas and a distance of pc or ly.
In 2020, new observational data from the space-based Solar Mass Ejection Imager aboard the Coriolis satellite and three different modeling techniques produced a refined parallax of mas, a radius of , and a distance of pc or ly, which, if accurate, would mean Betelgeuse is nearly 25% smaller and 25% closer to Earth than previously thought.
The European Space Agency's current Gaia mission is unable to produce good parallax results for stars like Betelgeuse which are brighter than the approximately V=6 saturation limit of the mission's instruments. Because of this limitation, there was no data on Betelgeuse in Gaia Data Release 2, from 2018 or Data Release 3 from 2022.
Variability
Betelgeuse is classified as a semiregular variable star, indicating that some periodicity is noticeable in the brightness changes, but amplitudes may vary, cycles may have different lengths, and there may be standstills or periods of irregularity. It is placed in subgroup SRc; these are pulsating red supergiants with amplitudes around one magnitude and periods from tens to hundreds of days.
Betelgeuse typically shows only small brightness changes near to magnitude +0.5, although at its extremes it can become as bright as magnitude 0.0 or as faint as magnitude +1.6. Betelgeuse is listed in the General Catalogue of Variable Stars with a possible period of 2,335 days. More detailed analyses have shown a main period near 400 days, a short period of 185 days, and a longer secondary period around 2,100 days. The lowest reliably-recorded V-band magnitude of +1.614 was reported in February 2020.
Radial pulsations of red supergiants are well-modelled and show that periods of a few hundred days are typically due to fundamental and first overtone pulsation. Lines in the spectrum of Betelgeuse show doppler shifts indicating radial velocity changes corresponding, very roughly, to the brightness changes. This demonstrates the nature of the pulsations in size, although corresponding temperature and spectral variations are not clearly seen. Variations in the diameter of Betelgeuse have also been measured directly. First overtone pulsations of 185 days have been observed, and the ratio of the fundamental to overtone periods gives valuable information about the internal structure of the star and its age.
The source of the long secondary periods is unknown, but they cannot be explained by radial pulsations. Interferometric observations of Betelgeuse have shown hotspots that are thought to be created by massive convection cells, a significant fraction of the diameter of the star and each emitting 5–10% of the total light of the star. One theory to explain long secondary periods is that they are caused by the evolution of such cells combined with the rotation of the star. Other theories include close binary interactions, chromospheric magnetic activity influencing mass loss, or non-radial pulsations such as g-modes.
In addition to the discrete dominant periods, small-amplitude stochastic variations are seen. It is proposed that this is due to granulation, similar to the same effect on the sun but on a much larger scale.
Diameter
On 13 December 1920, Betelgeuse became the first star outside the Solar System to have the angular size of its photosphere measured. Although interferometry was still in its infancy, the experiment proved a success. The researchers, using a uniform disk model, determined that Betelgeuse had a diameter of , although the stellar disk was likely 17% larger due to the limb darkening, resulting in an estimate for its angular diameter of about 0.055". Since then, other studies have produced angular diameters that range from 0.042 to . Combining these data with historical distance estimates of 180 to yields a projected radius of the stellar disk of anywhere from 1.2 to . Using the Solar System for comparison, the orbit of Mars is about , Ceres in the asteroid belt , Jupiter —so, assuming Betelgeuse occupying the place of the Sun, its photosphere might extend beyond the Jovian orbit, not quite reaching Saturn at .
The precise diameter has been hard to define for several reasons:
Betelgeuse is a pulsating star, so its diameter changes with time;
The star has no definable "edge" as limb darkening causes the optical emissions to vary in color and decrease the farther one extends out from the center;
Betelgeuse is surrounded by a circumstellar envelope composed of matter ejected from the star—matter which absorbs and emits light—making it difficult to define the photosphere of the star;
Measurements can be taken at varying wavelengths within the electromagnetic spectrum and the difference in reported diameters can be as much as 30–35%, yet comparing one finding with another is difficult as the star's apparent size differs depending on the wavelength used. Studies have shown that the measured angular diameter is considerably larger at ultraviolet wavelengths, decreases through the visible to a minimum in the near-infrared, and increase again in the mid-infrared spectrum;
Atmospheric twinkling limits the resolution obtainable from ground-based telescopes since turbulence degrades angular resolution.
The generally reported radii of large cool stars are Rosseland radii, defined as the radius of the photosphere at a specific optical depth of two-thirds. This corresponds to the radius calculated from the effective temperature and bolometric luminosity. The Rosseland radius differs from directly measured radii, with corrections for limb darkening and the observation wavelength. For example, a measured angular diameter of 55.6 mas would correspond to a Rosseland mean diameter of 56.2 mas, while further corrections for the existence of surrounding dust and gas shells would give a diameter of .
To overcome these challenges, researchers have employed various solutions. Astronomical interferometry, first conceived by Hippolyte Fizeau in 1868, was the seminal concept that has enabled major improvements in modern telescopy and led to the creation of the Michelson interferometer in the 1880s, and the first successful measurement of Betelgeuse. Just as human depth perception increases when two eyes instead of one perceive an object, Fizeau proposed the observation of stars through two apertures instead of one to obtain interferences that would furnish information on the star's spatial intensity distribution. The science evolved quickly and multiple-aperture interferometers are now used to capture speckled images, which are synthesized using Fourier analysis to produce a portrait of high resolution. It was this methodology that identified the hotspots on Betelgeuse in the 1990s. Other technological breakthroughs include adaptive optics, space observatories like Hipparcos, Hubble and Spitzer, and the Astronomical Multi-BEam Recombiner (AMBER), which combines the beams of three telescopes simultaneously, allowing researchers to achieve milliarcsecond spatial resolution.
Observations in different regions of the electromagnetic spectrum—the visible, near-infrared (NIR), mid-infrared (MIR), or radio—produce very different angular measurements. In 1996, Betelgeuse was shown to have a uniform disk of . In 2000, a Space Sciences Laboratory team measured a diameter of , ignoring any possible contribution from hotspots, which are less noticeable in the mid-infrared. Also included was a theoretical allowance for limb darkening, yielding a diameter of . The earlier estimate equates to a radius of roughly or , assuming the 2008 Harper distance of , a figure roughly the size of the Jovian orbit of .
In 2004, a team of astronomers working in the near-infrared announced that the more accurate photospheric measurement was . The study also put forth an explanation as to why varying wavelengths from the visible to mid-infrared produce different diameters: the star is seen through a thick, warm extended atmosphere. At short wavelengths (the visible spectrum) the atmosphere scatters light, thus slightly increasing the star's diameter. At near-infrared wavelengths (K and L bands), the scattering is negligible, so the classical photosphere can be directly seen; in the mid-infrared the scattering increases once more, causing the thermal emission of the warm atmosphere to increase the apparent diameter.
Studies with the IOTA and VLTI published in 2009 brought strong support to the idea of dust shells and a molecular shell (MOLsphere) around Betelgeuse, and yielded diameters ranging from 42.57 to with comparatively insignificant margins of error. In 2011, a third estimate in the near-infrared corroborating the 2009 numbers, this time showing a limb-darkened disk diameter of . The near-infrared photospheric diameter of at the Hipparcos distance of equates to about or . A 2014 paper derives an angular diameter of (equivalent to a uniform disc) using H and K band observations made with the VLTI AMBER instrument.
In 2009 it was announced that the radius of Betelgeuse had shrunk from 1993 to 2009 by 15%, with the 2008 angular measurement equal to . Unlike most earlier papers, this study used measurements at one specific wavelength over 15 years. The diminution in Betelgeuse's apparent size equates to a range of values between seen in 1993 to seen in 2008—a contraction of almost in . The observed contraction is generally believed to be a variation in just a portion of the extended atmosphere around Betelgeuse, and observations at other wavelengths have shown an increase in diameter over a similar period.
The latest models of Betelgeuse adopt a photospheric angular diameter of around , with multiple shells out to 50–. Assuming a distance of , this means a stellar diameter of .
Once considered as having the largest angular diameter of any star in the sky after the Sun, Betelgeuse lost that distinction in 1997 when a group of astronomers measured R Doradus with a diameter of , although R Doradus, being much closer to Earth at about , has a linear diameter roughly one-third that of Betelgeuse.
Occultations
Betelgeuse is too far from the ecliptic to be occulted by the major planets, but those by some asteroids (which are more wide-ranging and much more numerous) occur frequently. A partial occultation by the 19th magnitude asteroid occurred on 2 January 2012. It was partial because the angular diameter of the star was larger than that of the asteroid; the brightness of Betelgeuse dropped by only about 0.01 magnitudes.
The 14th magnitude asteroid 319 Leona was predicted to occult on 12 December 2023, 01:12 UTC. Totality was at first uncertain, and the occulation was projected to only last approximately twelve seconds (visible on a narrow path on Earth's surface, the exact width and location of which was initially uncertain due to lack of precise knowledge of the size and path of the asteroid). Projections were later refined as more data were analyzed for a totality ("ring of fire") of approximately five seconds and a 60 km wide path stretching from Tajikistan, Armenia, Turkey, Greece, Italy, Spain, the Atlantic Ocean, Miami, Florida and the Florida Keys to parts of Mexico. (The serendiptous event would also afford detailed observations of 319 Leona itself.) Among other programmes 80 amateur astronomers in Europe alone have been coordinated by astrophysicist Miguel Montargès, et al. of the Paris Observatory for the event.
Physical characteristics
Betelgeuse is a very large, luminous but cool star classified as an M1-2 Ia-ab red supergiant. The letter "M" in this designation means that it is a red star belonging to the M spectral class and therefore has a relatively low photospheric temperature; the "Ia-ab" suffix luminosity class indicates that it is an intermediate-luminosity supergiant, with properties partway between a normal supergiant and a luminous supergiant. Since 1943, the spectrum of Betelgeuse has served as one of the stable anchor points by which other stars are classified.
Uncertainty in the star's surface temperature, diameter, and distance make it difficult to achieve a precise measurement of Betelgeuse's luminosity, but research from 2012 quotes a luminosity of around , assuming a distance of . Studies since 2001 report effective temperatures ranging from 3,250 to 3,690 K. Values outside this range have previously been reported, and much of the variation is believed to be real, due to pulsations in the atmosphere. The star is also a slow rotator and the most recent velocity recorded was —much slower than Antares which has a rotational velocity of . The rotation period depends on Betelgeuse's size and orientation to Earth, but it has been calculated to take to turn on its axis, inclined at an angle of around to Earth.
In 2004, astronomers using computer simulations speculated that even if Betelgeuse is not rotating it might exhibit large-scale magnetic activity in its extended atmosphere, a factor where even moderately strong fields could have a meaningful influence over the star's dust, wind and mass-loss properties. A series of spectropolarimetric observations obtained in 2010 with the Bernard Lyot Telescope at Pic du Midi Observatory revealed the presence of a weak magnetic field at the surface of Betelgeuse, suggesting that the giant convective motions of supergiant stars are able to trigger the onset of a small-scale dynamo effect.
Mass
Betelgeuse has no known orbital companions, so its mass cannot be calculated by that direct method. Modern mass estimates from theoretical modelling have produced values of , with values of – from older studies. It has been calculated that Betelgeuse began its life as a star of , based on a solar luminosity of 90,000–150,000. A novel method of determining the supergiant's mass was proposed in 2011, arguing for a current stellar mass of with an upper limit of 16.6 and lower of , based on observations of the star's intensity profile from narrow H-band interferometry and using a photospheric measurement of roughly or . A probabilistic age prior analysis give a current mass of and an initial mass of .
Betelgeuse's mass can also be estimated based on its position on the colormagnitudediagram (CMD). Betelgeuse's color may have changed from yellow (or possibly orange; i.e. a yellow supergiant) to red in the last few thousand years, based on a 2022 review of historical records. This color change combined with the CMD suggest a mass of and age of 14 Myr, and a distance from 125 to 150 parsecs (~400 to 500 light years).
Motion
The kinematics of Betelgeuse are complex. The age of Class M supergiants with an initial mass of is roughly 10 million years. Starting from its present position and motion, a projection back in time would place Betelgeuse around farther from the galactic plane—an implausible location, as there is no star formation region there. Moreover, Betelgeuse's projected pathway does not appear to intersect with the 25 Ori subassociation or the far younger Orion Nebula Cluster (ONC, also known as Ori OB1d), particularly since Very Long Baseline Array astrometry yields a distance from Betelgeuse to the ONC of between 389 and . Consequently, it is likely that Betelgeuse has not always had its current motion through space but has changed course at one time or another, possibly the result of a nearby stellar explosion. An observation by the Herschel Space Observatory in January 2013 revealed that the star's winds are crashing against the surrounding interstellar medium.
The most likely star-formation scenario for Betelgeuse is that it is a runaway star from the Orion OB1 association. Originally a member of a high-mass multiple system within Ori OB1a, Betelgeuse was probably formed about 10–12 million years ago, but has evolved rapidly due to its high mass. H. Bouy and J. Alves suggested in 2015 that Betelgeuse may instead be a member of the newly discovered Taurion OB association.
Circumstellar dynamics
In the late phase of stellar evolution, massive stars like Betelgeuse exhibit high rates of mass loss, possibly as much as every , resulting in a complex circumstellar environment that is constantly in flux. In a 2009 paper, stellar mass loss was cited as the "key to understanding the evolution of the universe from the earliest cosmological times to the current epoch, and of planet formation and the formation of life itself". However, the physical mechanism is not well understood. When Martin Schwarzschild first proposed his theory of huge convection cells, he argued it was the likely cause of mass loss in evolved supergiants like Betelgeuse. Recent work has corroborated this hypothesis, yet there are still uncertainties about the structure of their convection, the mechanism of their mass loss, the way dust forms in their extended atmosphere, and the conditions which precipitate their dramatic finale as a type II supernova. In 2001, Graham Harper estimated a stellar wind at every , but research since 2009 has provided evidence of episodic mass loss making any total figure for Betelgeuse uncertain. Current observations suggest that a star like Betelgeuse may spend a portion of its lifetime as a red supergiant, but then cross back across the H–R diagram, pass once again through a brief yellow supergiant phase and then explode as a blue supergiant or Wolf–Rayet star.
Astronomers may be close to solving this mystery. They noticed a large plume of gas extending at least six times its stellar radius indicating that Betelgeuse is not shedding matter evenly in all directions. The plume's presence implies that the spherical symmetry of the star's photosphere, often observed in the infrared, is not preserved in its close environment. Asymmetries on the stellar disk had been reported at different wavelengths. However, due to the refined capabilities of the NACO adaptive optics on the VLT, these asymmetries have come into focus. The two mechanisms that could cause such asymmetrical mass loss, were large-scale convection cells or polar mass loss, possibly due to rotation. Probing deeper with ESO's AMBER, gas in the supergiant's extended atmosphere has been observed vigorously moving up and down, creating bubbles as large as the supergiant itself, leading his team to conclude that such stellar upheaval is behind the massive plume ejection observed by Kervella.
Asymmetric shells
In addition to the photosphere, six other components of Betelgeuse's atmosphere have now been identified. They are a molecular environment otherwise known as the MOLsphere, a gaseous envelope, a chromosphere, a dust environment and two outer shells (S1 and S2) composed of carbon monoxide (CO). Some of these elements are known to be asymmetric while others overlap.
At about 0.45 stellar radii (~2–) above the photosphere, there may lie a molecular layer known as the MOLsphere or molecular environment. Studies show it to be composed of water vapor and carbon monoxide with an effective temperature of about . Water vapor had been originally detected in the supergiant's spectrum in the 1960s with the two Stratoscope projects but had been ignored for decades. The MOLsphere may also contain SiO and Al2O3—molecules which could explain the formation of dust particles.
Another cooler region, the asymmetric gaseous envelope, extends for several radii (~10–) from the photosphere. It is enriched in oxygen and especially in nitrogen relative to carbon. These composition anomalies are likely caused by contamination by CNO-processed material from the inside of Betelgeuse.
Radio-telescope images taken in 1998 confirm that Betelgeuse has a highly complex atmosphere, with a temperature of , similar to that recorded on the star's surface but much lower than surrounding gas in the same region. The VLA images also show this lower-temperature gas progressively cools as it extends outward. Although unexpected, it turns out to be the most abundant constituent of Betelgeuse's atmosphere. "This alters our basic understanding of red-supergiant star atmospheres", explained Jeremy Lim, the team's leader. "Instead of the star's atmosphere expanding uniformly due to gas heated to high temperatures near its surface, it now appears that several giant convection cells propel gas from the star's surface into its atmosphere." This is the same region in which Kervella's 2009 finding of a bright plume, possibly containing carbon and nitrogen and extending at least six photospheric radii in the southwest direction of the star, is believed to exist.
The chromosphere was directly imaged by the Faint Object Camera on board the Hubble Space Telescope in ultraviolet wavelengths. The images also revealed a bright area in the southwest quadrant of the disk. The average radius of the chromosphere in 1996 was about 2.2 times the optical disk (~) and was reported to have a temperature no higher than . However, in 2004 observations with the STIS, Hubble's high-precision spectrometer, pointed to the existence of warm chromospheric plasma at least one arcsecond away from the star. At a distance of , the size of the chromosphere could be up to . The observations have conclusively demonstrated that the warm chromospheric plasma spatially overlaps and co-exists with cool gas in Betelgeuse's gaseous envelope as well as with the dust in its circumstellar dust shells.
The first claim of a dust shell surrounding Betelgeuse was put forth in 1977 when it was noted that dust shells around mature stars often emit large amounts of radiation in excess of the photospheric contribution. Using heterodyne interferometry, it was concluded that the red supergiant emits most of its excess radiation from positions beyond 12 stellar radii or roughly the distance of the Kuiper belt at 50 to 60 AU, which depends on the assumed stellar radius. Since then, there have been studies done of this dust envelope at varying wavelengths yielding decidedly different results. Studies from the 1990s have estimated the inner radius of the dust shell anywhere from 0.5 to , or 100 to . These studies point out that the dust environment surrounding Betelgeuse is not static. In 1994, it was reported that Betelgeuse undergoes sporadic decades-long dust production, followed by inactivity. In 1997, significant changes in the dust shell's morphology in one year were noted, suggesting that the shell is asymmetrically illuminated by a stellar radiation field strongly affected by the existence of photospheric hotspots. The 1984 report of a giant asymmetric dust shell () has not been corroborated by recent studies, although another published the same year said that three dust shells were found extending four light-years from one side of the decaying star, suggesting that Betelgeuse sheds its outer layers as it moves.
Although the exact size of the two outer CO shells remains elusive, preliminary estimates suggest that one shell extends from about 1.5 to 4.0 arcseconds and the other expands as far as 7.0 arcseconds. Assuming the Jovian orbit of as the star radius, the inner shell would extend roughly 50 to 150 stellar radii (~300 to ) with the outer one as far as 250 stellar radii (~). The Sun's heliopause is estimated at 100 AU, so the size of this outer shell would be almost fourteen times the size of the Solar System.
Supersonic bow shock
Betelgeuse is travelling through the interstellar medium at a speed of (i.e. ~) creating a bow shock. The shock is not created by the star, but by its powerful stellar wind as it ejects vast amounts of gas into the interstellar medium at a speed of , heating the material surrounding the star, thereby making it visible in infrared light. Because Betelgeuse is so bright, it was only in 1997 that the bow shock was first imaged. The cometary structure is estimated to be at least one parsec wide, assuming a distance of 643 light-years.
Hydrodynamic simulations of the bow shock made in 2012 indicate that it is very young—less than 30,000 years old—suggesting two possibilities: that Betelgeuse moved into a region of the interstellar medium with different properties only recently or that Betelgeuse has undergone a significant transformation producing a changed stellar wind. A 2012 paper, proposed that this phenomenon was caused by Betelgeuse transitioning from a blue supergiant (BSG) to a red supergiant (RSG). There is evidence that in the late evolutionary stage of a star like Betelgeuse, such stars "may undergo rapid transitions from red to blue and vice versa on the Hertzsprung–Russell diagram, with accompanying rapid changes to their stellar winds and bow shocks." Moreover, if future research bears out this hypothesis, Betelgeuse may prove to have traveled close to 200,000 AU as a red supergiant scattering as much as along its trajectory.
Life phases
Betelgeuse is a red supergiant that has evolved from an O-type main-sequence star. After core hydrogen exhaustion, Betelgeuse evolved into a blue supergiant before evolving into its current red supergiant form. Its core will eventually collapse, producing a supernova explosion and leaving behind a compact remnant. The details depend on the exact initial mass and other physical properties of that main sequence star.
Main sequence
The initial mass of Betelgeuse can only be estimated by testing different stellar evolutionary models to match its current observed properties. The unknowns of both the models and the current properties mean that there is considerable uncertainty in Betelgeuse's initial appearance, but its mass is usually estimated to have been in the range of , with modern models finding values of . Its chemical makeup can be reasonably assumed to have been around 70% hydrogen, 28% helium, and 2.4% heavy elements, slightly more metal-rich than the Sun but otherwise similar. The initial rotation rate is more uncertain, but models with slow to moderate initial rotation rates produce the best matches to Betelgeuse's current properties. That main sequence version of Betelgeuse would have been a hot luminous star with a spectral type such as O9V.
A star would take between 11.5 and 15 million years to reach the red supergiant stage, with more rapidly-rotating stars taking the longest. Rapidly-rotating stars take 9.3 million years to reach the red supergiant stage, while stars with slow rotation take only 8.1 million years. These are the best estimates of Betelgeuse's current age, as the time since its zero age main sequence stage is estimated to be 8.0–8.5 million years as a star with no rotation.
After core hydrogen exhaustion
Betelgeuse's time spent as a red supergiant can be estimated by comparing mass loss rates to the observed circumstellar material, as well as the abundances of heavy elements at the surface. Estimates range from 10,000 years to a maximum of 140,000 years. Betelgeuse appears to undergo short periods of heavy mass loss and is a runaway star moving rapidly through space, so comparisons of its current mass loss to the total lost mass are difficult.
The surface of Betelgeuse shows enhancement of nitrogen, relatively low levels of carbon, and a high proportion of 13C relative to 12C, all indicative of a star that has experienced the first dredge-up. However, the first dredge-up occurs soon after a star reaches the red supergiant phase and so this only means that Betelgeuse has been a red supergiant for at least a few thousand years. The best prediction is that Betelgeuse has already spent around 40,000 years as a red supergiant, having left the main sequence perhaps one million years ago.
The current mass can be estimated from evolutionary models from the initial mass and the expected mass lost so far. For Betelgeuse, the total mass lost is predicted to be no more than about , giving a current mass of , considerably higher than estimated by other means such as pulsational properties or limb-darkening models.
All stars more massive than about are expected to end their lives when their cores collapse, typically producing a supernova explosion. Up to about , a type II-P supernova is always produced from the red supergiant stage.
More massive stars can lose mass quickly enough that they evolve towards higher temperatures before their cores can collapse, particularly for rotating stars and models with especially high mass loss rates. These stars can produce type II-L or type IIb supernovae from yellow or blue supergiants, or type I b/c supernovae from Wolf–Rayet stars. Models of rotating stars predict a peculiar type II supernova similar to SN 1987A from a blue supergiant progenitor. On the other hand, non-rotating models predict a type II-P supernova from a red supergiant progenitor.
The time until Betelgeuse explodes depends on the predicted initial conditions and on the estimate of the time already spent as a red supergiant. The total lifetime from the start of the red supergiant phase to core collapse varies from about 300,000 years for a rotating star, 550,000 years for a rotating star, and up to a million years for a non-rotating star. Given the estimated time since Betelgeuse became a red supergiant, estimates of its remaining lifetime range from a "best guess" of under 100,000 years for a non-rotating model to far longer for rotating models or lower-mass stars. Betelgeuse's suspected birthplace in the Orion OB1 association is the location of several previous supernovae. It is believed that runaway stars may be caused by supernovae, and there is strong evidence that OB stars μ Columbae, AE Aurigae, and 53 Arietis all originated from such explosions in Ori OB1 2.2, 2.7, and 4.9 million years ago.
A typical type II-P supernova emits of neutrinos and produces an explosion with a kinetic energy of . As seen from Earth, Betelgeuse as a type II-P supernova would have a peak apparent magnitude somewhere in the range −8 to −12. This would be easily visible in daylight, with a possible brightness up to a significant fraction of the full moon, though likely not exceeding it. This type of supernova would remain at roughly constant brightness for 2–3 months before rapidly dimming. The visible light is produced mainly by the radioactive decay of cobalt, and sustains its brightness due to the increasing transparency of the cooling hydrogen ejected by the supernova.
Media reporting
Due to misunderstandings caused by the 2009 publication of the star's 15% contraction, apparently of its outer atmosphere, Betelgeuse has frequently been the subject of scare stories and rumors suggesting that it will explode within a year, and leading to exaggerated claims about the consequences of such an event. The timing and prevalence of these rumors have been linked to broader misconceptions of astronomy, particularly to doomsday predictions relating to the Mayan calendrical apocalypse. Betelgeuse is not likely to produce a gamma-ray burst and is not close enough for its X-rays, ultraviolet radiation, or ejected material to cause significant effects on Earth.
Following the dimming of Betelgeuse in December 2019, reports appeared in the science and mainstream media that again included speculation that the star might be about to explode as a supernova – even in the face of scientific research that a supernova is not expected for perhaps 100,000 years. Some outlets reported the magnitude as faint as +1.3 as an unusual and interesting phenomenon, like Astronomy magazine, the National Geographic, and the Smithsonian.
Some mainstream media, like The Washington Post, ABC News in Australia, and Popular Science, reported that a supernova was possible but unlikely, whilst other outlets falsely portrayed a supernova as an imminent realistic possibility. CNN, for example, chose the headline "A giant red star is acting weird and scientists think it may be about to explode", while the New York Post declared Betelgeuse as "due for explosive supernova".
Phil Plait, in his Bad Astronomy blog, noting that Betelgeuse's recent behaviour, "[w]hile unusual . . . isn't unprecedented," argued that the star is not likely to explode "for a long, long time." Dennis Overbye of The New York Times agreed that an explosion was not imminent but added that "astronomers are having fun thinking about it."
Following the eventual supernova, a small dense remnant will be left behind, either a neutron star or black hole. Betelgeuse does not seem to have a core massive enough for a black hole, so the remnant will probably be a neutron star of approximately .
Ethnological attributes
Spelling and pronunciation
Betelgeuse has also been spelled Betelgeux and, in German, Beteigeuze (according to Bode). Betelgeux and Betelgeuze were used until the early 20th century, when the spelling Betelgeuse became universal.
Consensus on its pronunciation is weak and is as varied as its spellings:
Oxford English Dictionary and Royal Astronomical Society of Canada
Oxford English Dictionary
Canadian Oxford Dictionary and Webster's Collegiate Dictionary
Martha Evans Martin, The Friendly Stars
The -urz pronunciations are attempts to render the French eu sound; they only work in r-dropping accents.
Etymology
[[File:Al-Sufi's Orion, 1125 Baghdad copy, Doha Museum of Islamic Art Ms 2. 1998. SO.jpg|thumb|An illustration of Orion (horizontally reversed) in al-Sufi's Book of Fixed Stars. Betelgeuze is annotated as Yad al-Jauzā ("Hand of Orion"), one of the proposed etymological origins of its modern name, and also as Mankib al Jauzā ("Shoulder of Orion").]]
Betelgeuse is often mistranslated as "armpit of the central one". In his 1899 work Star-Names and Their Meanings, American amateur naturalist Richard Hinckley Allen stated the derivation was from the , which he claimed degenerated into a number of forms, including Bed Elgueze, Beit Algueze, Bet El-gueze, and Beteigeuze, to the forms Betelgeuse, Betelguese, Betelgueze and Betelgeux. The star was named Beldengeuze in the Alfonsine Tables, and Italian Jesuit priest and astronomer Giovanni Battista Riccioli had called it Bectelgeuze or Bedalgeuze.
Paul Kunitzsch, Professor of Arabic Studies at the University of Munich, refuted Allen's derivation and instead proposed that the full name is a corruption of the Arabic , meaning "the Hand of al-Jauzā'"; i.e., Orion. European mistransliteration into medieval Latin led to the first character y (ﻴ, with two dots underneath) being misread as a b (ﺒ''', with only one dot underneath). During the Renaissance, the star's name was written as ("house of Orion") or , incorrectly thought to mean "armpit of Orion" (a true translation of "armpit" would be , transliterated as ). This led to the modern rendering as Betelgeuse. Other writers have since accepted Kunitzsch's explanation.
The last part of the name, "-elgeuse", comes from the Arabic , a historical Arabic name of the constellation Orion, a feminine name in old Arabian legend, and of uncertain meaning. Because , the root of , means "middle", roughly means "the Central One". The modern Arabic name for Orion is ("the Giant"), although the use of in the star's name has continued. The 17th-century English translator Edmund Chilmead gave it the name Ied Algeuze ("Orion's Hand"), from Christmannus. Other Arabic names recorded include ("the Right Hand"), ("the Arm"), and ("the Shoulder"), all of al-Jauzā, Orion, as .
Other names
Other names for Betelgeuse included the Persian "the Arm", and Coptic "an Armlet". was its Sanskrit name, as part of a Hindu understanding of the constellation as a running antelope or stag. In traditional Chinese astronomy, the name for Betelgeuse is (, the Fourth Star of the constellation of Three Stars) as the Chinese constellation originally referred to the three stars in Orion's Belt. This constellation was ultimately expanded to ten stars, but the earlier name stuck. In Japan, the Taira, or Heike, clan adopted Betelgeuse and its red color as its symbol, calling the star Heike-boshi, (), while the Minamoto, or Genji, clan chose Rigel and its white color. The two powerful families fought a legendary war in Japanese history, the stars seen as facing each other off and only kept apart by the Belt.Hōei Nojiri"Shin seiza jyunrei"p.19
In Tahitian lore, Betelgeuse was one of the pillars propping up the sky, known as Anâ-varu, the pillar to sit by. It was also called Ta'urua-nui-o-Mere "Great festivity in parental yearnings". A Hawaiian term for it was Kaulua-koko ("brilliant red star"). The Lacandon people of Central America knew it as chäk tulix ("red butterfly").
Astronomy writer Robert Burnham Jr. proposed the term padparadaschah, which denotes a rare orange sapphire in India, for the star.
Mythology
With the history of astronomy intimately associated with mythology and astrology before the scientific revolution, the red star, like the planet Mars that derives its name from a Roman war god, has been closely associated with the martial archetype of conquest for millennia, and by extension, the motif of death and rebirth. Other cultures have produced different myths. Stephen R. Wilk has proposed the constellation of Orion could have represented the Greek mythological figure Pelops, who had an artificial shoulder of ivory made for him, with Betelgeuse as the shoulder, its color reminiscent of the reddish yellow sheen of ivory.
Aboriginal people from the Great Victoria Desert of South Australia incorporated Betelgeuse into their oral traditions as the club of Nyeeruna (Orion), which fills with fire-magic and dissipates before returning. This has been interpreted as showing that early Aboriginal observers were aware of the brightness variations of Betelgeuse. The Wardaman people of northern Australia knew the star as Ya-jungin ("Owl Eyes Flicking"), its variable light signifying its intermittent watching of ceremonies led by the Red Kangaroo Leader Rigel. In South African mythology, Betelgeuse was perceived as a lion casting a predatory gaze toward the three zebras represented by Orion's Belt.
In the Americas, Betelgeuse signifies a severed limb of a man-figure (Orion)—the Taulipang of Brazil know the constellation as Zililkawai, a hero whose leg was cut off by his wife, with the variable light of Betelgeuse linked to the severing of the limb. Similarly, the Lakota people of North America see it as a chief whose arm has been severed.
A Sanskrit name for Betelgeuse is ārdrā ("the moist one"), eponymous of the Ardra lunar mansion in Hindu astrology. The Rigvedic God of storms Rudra presided over the star; this association was linked by 19th-century star enthusiast Richard Hinckley Allen to Orion's stormy nature. The constellations in Macedonian folklore represented agricultural items and animals, reflecting their way of life. To them, Betelgeuse was Orach ("the ploughman"), alongside the rest of Orion, which depicted a plough with oxen. The rising of Betelgeuse at around 3 a.m. in late summer and autumn signified the time for village men to go to the fields and plough. To the Inuit, the appearance of Betelgeuse and Bellatrix high in the southern sky after sunset marked the beginning of spring and lengthening days in late February and early March. The two stars were known as Akuttujuuk ("those [two] placed far apart"), referring to the distance between them, mainly to people from North Baffin Island and Melville Peninsula.
The opposed locations of Orion and Scorpius, with their corresponding bright red variable stars Betelgeuse and Antares, were noted by ancient cultures around the world. The setting of Orion and rising of Scorpius signify the death of Orion by the scorpion. In China they signify brothers and rivals Shen and Shang. The Batak of Sumatra marked their New Year with the first new moon after the sinking of Orion's Belt below the horizon, at which point Betelgeuse remained "like the tail of a rooster". The positions of Betelgeuse and Antares at opposite ends of the celestial sky were considered significant, and their constellations were seen as a pair of scorpions. Scorpion days marked as nights that both constellations could be seen.
In popular culture
As one of the brightest and best-known stars, Betelgeuse has featured in many works of fiction. The star's unusual name inspired the title of the 1988 film Beetlejuice, referring to its titular antagonist, and script writer Michael McDowell was impressed by how many people made the connection. In the popular science fiction series The Hitchhiker's Guide to the Galaxy by Douglas Adams, Ford Prefect was from "a small planet somewhere in the vicinity of Betelgeuse."
Two American navy ships were named after the star, both of them World War II vessels, the launched in 1939 and launched in 1944. In 1979, the French supertanker Betelgeuse was moored off Whiddy Island, discharging oil when it exploded, killing 50 people in one of the worst disasters in Ireland's history.
The Dave Matthews Band song "Black and Blue Bird" references the star. The Blur song "Far Out" from their 1994 album Parklife mentions Betelgeuse in its lyrics.
The Philip Larkin poem "The North Ship", found in the collection of the same name, references the star in the section "Above 80° N", which reads:" 'A woman has ten claws,' /
Sang the drunken boatswain; /
Farther than Betelgeuse, /
More brilliant than Orion /
Or the planets Venus and Mars, /
The star flames on the ocean; /
'A woman has ten claws,' /
Sang the drunken boatswain."Humbert Wolfe wrote a poem about Betelgeuse, which was set to music by Gustav Holst.
Table of angular diameter estimates
This table provides a non-exhaustive list of angular measurements conducted since 1920. Also included is a column providing a current range of radii for each study based on Betelgeuse's most recent distance estimate (Harper et al.'') of .
See also
List of stars in Orion
List of stars that have unusual dimming periods
Stellar evolution
List of semiregular variable stars
List of supernova candidates
Notes
References
External links
Surface imaging of Betelgeuse with COAST and the WHT – interferometric images taken at different wavelengths
Near, mid and far infrared – Infrared Processing and Analysis Center (IPAC) webpage showing pictures at various wavelengths
APOD Pictures:
Mars and Orion over Monument Valley skyscape showing the relative brightness of Betelgeuse and Rigel
Orion: head to toe breathtaking vista the Orion molecular cloud complex from Rogelio Bernal Andreo
The spotty surface of Betelgeuse – a reconstructed image showing two hotspots, possibly convection cells
Simulated Supergiant Star – Freytag's "Star in a Box" illustrating the nature of Betelgeuse's "monster granules"
Why stars twinkle – image of Betelgeuse showing the effect of atmospheric twinkling in a telescope
Red supergiant movie – numerical simulation of a red supergiant star like Betelgeuse
M-type supergiants
Semiregular variable stars
Runaway stars
Population I stars
Orion (constellation)
Orionis, Alpha
2061
Durchmusterung objects
Orionis, 58
039801
027989
TIC objects
Stars with proper names | Betelgeuse | [
"Astronomy"
] | 14,190 | [
"Constellations",
"Orion (constellation)"
] |
10,938,074 | https://en.wikipedia.org/wiki/Sch%C3%B6nberg%E2%80%93Chandrasekhar%20limit | In stellar astrophysics, the Schönberg–Chandrasekhar limit is the maximum mass of a non-fusing, isothermal core that can support an enclosing envelope. It is expressed as the ratio of the core mass to the total mass of the core and envelope. Estimates of the limit depend on the models used and the assumed chemical compositions of the core and envelope; typical values given are from 0.10 to 0.15 (10% to 15% of the total stellar mass). This is the maximum to which a helium-filled core can grow, and if this limit is exceeded, as can only happen in massive stars, the core collapses, releasing energy that causes the outer layers of the star to expand to become a red giant. It is named after the astrophysicists Subrahmanyan Chandrasekhar and Mario Schönberg, who estimated its value in a 1942 paper. They estimated it to be:
where is the mass, is the mean molecular weight, index c denotes the core, and index e is the envelope.
The Schönberg–Chandrasekhar limit comes into play when fusion in a main-sequence star exhausts the hydrogen at the center of the star. The star then contracts until hydrogen fuses in a shell surrounding a helium-rich core, both of which are surrounded by an envelope consisting primarily of hydrogen. The core increases in mass as the shell burns its way outwards through the star. If the star's mass is less than approximately 1.5 solar masses, the core will become degenerate before the Schönberg–Chandrasekhar limit is reached, and, on the other hand, if the mass is greater than approximately 6 solar masses, the star leaves the main sequence with a core mass already greater than the Schönberg–Chandrasekhar limit so its core is never isothermal before helium fusion. In the remaining case, where the mass is between 1.5 and 6 solar masses, the core will grow until the limit is reached, at which point it will contract rapidly until helium starts to fuse in the core.
References
Astrophysics
Stellar astronomy
Stellar dynamics | Schönberg–Chandrasekhar limit | [
"Physics",
"Astronomy"
] | 433 | [
"Stellar astronomy",
"Astronomical sub-disciplines",
"Astrophysics",
"Stellar dynamics"
] |
10,938,230 | https://en.wikipedia.org/wiki/Boron%20suboxide | Boron suboxide (chemical formula B6O) is a solid compound with a structure built of eight icosahedra at the apexes of the rhombohedral unit cell. Each icosahedron is composed of twelve boron atoms. Two oxygen atoms are located in the interstices along the [111] rhombohedral direction. Due to its short interatomic bond lengths and strongly covalent character, B6O displays a range of outstanding physical and chemical properties such as great hardness (close to that of rhenium diboride and boron nitride), low mass density, high thermal conductivity, high chemical inertness, and excellent wear resistance.
B6O can be synthesized by reducing B2O3 with boron or by oxidation of boron with zinc oxide or other oxidants. These boron suboxide materials formed at or near ambient pressure are generally oxygen deficient and non-stoichiometric (B6Ox, x<0.9) and have poor crystallinity and very small grain size (less than 5 μm). High pressure applied during the synthesis of B6O can significantly increase the crystallinity, oxygen stoichiometry, and crystal size of the products. Mixtures of boron and B2O3 powders were usually used as starting materials in the reported methods for B6O synthesis.
Oxygen-deficient boron suboxide (B6Ox, x<0.9) might form icosahedral particles, which are neither single crystals nor quasicrystals, but twinned groups of twenty tetrahedral crystals.
B6O of the α-rhombohedral boron type has been investigated because of its ceramic nature (hardness, high melting point, chemical stability, and low density) as a new structural material. In addition to this, these borides have unique bonding not easily accessible by the usual valence theory. Although an X-ray emission spectroscopic method indicated a probable parameter range for the oxygen site of B6O, the correct oxygen position remained open to question until Rietveld analysis of X-ray diffraction profiles on B6O powders were first carried out successfully, even though these were preliminary investigations.
Preparation
B6O can be prepared by three methods:
solid state reaction between B and B2O3,
reduction of B2O3 and
oxidation of B. The high vapor pressure of B2O3 at elevated temperatures would cause the B excess composition in the process of the solid state reaction between B and B2O3.
In the reduction of B2O3, reductants that can be used include, but not limited to, Si and Mg which remain in B6O as an impurity in the process. While in the oxidation process of B, oxidants such as ZnO would contaminate B6O in the process.
Physical properties
B6O has a strong covalent nature and is easy to compose at temperatures greater than 1,973 K. Boron suboxide has also been reported to exhibit a wide range of superior properties such as high hardness with low density, high mechanical strength, oxidation resistance up to high temperatures as well as its high chemical inertness.
Preliminary first-principle ab initio density functional calculations of the structural properties boron suboxide (B6O) suggest that the strength of bonding in B6O may be enhanced by the presence of a high electronegativity interstitial in the structure. The computational calculations confirm the shortening of covalent bonds, which is believed to favor higher elastic constants and hardness values.
Applications
The potential applications of B6O as a wear-reduction coating for high-speed cutting tools, abrasives, or other high-wear applications, for example, have been an object of intense interest in recent years. However, despite intensive research efforts commercial applications have yet to be realized. This is partly because of the low fracture toughness of the hot-pressed material and the considerable practical challenges associated with densifying stoichiometric B6O material with good crystallinity. Furthermore, numerous mechanical properties of the material were until recently rather poorly understood.
Boron suboxide is also a promising body armor material, but its testing is still in the early stages and no commercial deployment is known as of November 2023. This seems to be due to the expense of synthesizing high-quality B6O powder via the reaction of B2O3 with B and further difficulties in densifying B6O parts via standard industrial sintering and hot-pressing techniques.
See also
Suboxide
Boron trioxide
Boron monoxide
Heterodiamond
Beta carbon nitride
References
Boron compounds
Oxides | Boron suboxide | [
"Chemistry"
] | 972 | [
"Oxides",
"Salts"
] |
10,938,277 | https://en.wikipedia.org/wiki/Robert%20Forester%20Mushet | Robert Forester Mushet (8 April 1811 – 29 January 1891) was a British metallurgist and businessman, born on 8 April 1811, in Coleford, in the Forest of Dean, Gloucestershire, England. He was the youngest son of Scottish parents, Agnes Wilson and David Mushet; an ironmaster, formerly of the Clyde, Alfreton and Whitecliff Ironworks.
In 1818/1819, David Mushet built a foundry named Darkhill Ironworks in the Forest of Dean. Robert spent his formative years studying metallurgy with his father and took over the management of Darkhill in 1845. In 1848, he moved to the newly constructed Forest Steel Works on the edge of the Darkhill site where he carried out over ten thousand experiments in ten years before moving to the Titanic Steelworks in 1862.
It seems that Mushet only began using his middle name 'Forester' in 1845, and only occasionally at first. In his later years he said he had been given the name from the Forest of Dean, although he variously spelled it both 'Forester' and 'Forrester'.
In 1876, he was awarded the Bessemer Gold Medal by the Iron and Steel Institute, their highest award.
Robert Mushet died on 29 January 1891 in Cheltenham. He is buried with his wife and daughter, Mary, in Cheltenham Cemetery.
High quality steel
In the summer of 1848, Henry Burgess, editor of The Bankers' Circular, brought to Mushet a lump of white crystallised metal which he said was found in Rhenish Prussia.
... "Being familiar with alloys of iron and manganese," says Mr. Mushet, "I at once recognized this lump of metal as an alloy of these two metals and, as such, of great value in the making of steel. Later, I found that the white metallic alloy was the product of steel ore, called also spathose iron ore, being, in fact, a double carbonate of iron and manganese found in the Rhenish mountains, and that it was most carefully selected and smelted in small blast furnaces, charcoal fuel alone being employed and the only flux used being lime. The metal was run from the furnace into shallow iron troughs similar to the old refiners' boxes, and the cakes thus formed, when cold and broken up, showed large and beautifully bright facets and crystals specked with minute spots of uncombined carbon. It was called, from its brightness, 'spiegel glanz' or spiegel eisen, i.e., looking-glass iron. Practically its analysis was: Iron, 86…25; manganese, 8…50; and carbon, 5…25; making a total of 100…00."
Mushet carried out many experiments with the metal, discovering that a small amount added during the manufacture of steel rendered it more workable when heated. It was not until 1856, however, that he realised the true potential of this property when his friend Thomas Brown brought him a piece of steel, made using the Bessemer Process, asking if he could improve its poor quality. Mushet carried out experiments on the sample, based on those he had previously carried out with spiegeleisen.
Henry Bessemer himself had realised that the problem of quality was due to impurities in the iron and concluded that the solution lay in knowing when to turn off the flow of air in his process; so that the impurities had been burned off, but just the right quantity of carbon remained. Despite spending tens of thousands of pounds on experiments, however, he could not find the answer.
Mushet's solution was simple, but elegant; he first burnt off, as far as possible, all the impurities and carbon, then reintroduced carbon and manganese by adding an exact amount of spiegeleisen. This had the effect of improving the quality of the finished product, increasing its malleability – its ability to withstand rolling and forging at high temperatures.
I saw then that the Bessemer process was perfected and that, with fair play, untold wealth would reward Mr. Bessemer and myself..."
Mushet's dream was never to be fulfilled. While others made fortunes from his discoveries, he failed to capitalise on his successes and by 1866 was destitute and in ill health. In that year his 16-year-old daughter, Mary, travelled to London alone, to confront Bessemer at his offices, arguing that his success was based on the results of her father's work.
Bessemer, whose own process for producing steel was not economically viable without Mushet's method for improving quality, decided to pay Mushet an annual pension of £300, a very considerable sum, which he paid for over 20 years; possibly with a view to keeping the Mushets from legal action.
Steel rails
In 1857, Mushet was the first to make durable rails of steel rather than cast iron, providing the basis for the development of rail transportation throughout the world in the late 19th century. The first of Mushet's steel rails was sent to Derby Midland railway station, where it was laid at a heavily used part of the station approach where the iron rails had to be renewed at least every six months, and occasionally every three. Six years later, in 1863, the rail seemed as perfect as ever, although some 700 trains had passed over it daily. During its 16 years "life" 1,252,000 detached engines and tenders at the least, apart from trains, had passed over that rail.
Dozzles
When steel solidifies in a mould, uneven cooling causes a central cavity or 'pipe' to form in the casting. In 1861, Mushet invented the 'Dozzle'; a clay cone or sleeve, heated white hot and inserted into the top of the ingot mould near the end of the pour, and then filled with molten steel. Its purpose was to maintain a reservoir of molten steel, which drained down and filled the pipe as the casting cooled. Mushet claimed this, and other small inventions of his, saved the steelmakers of Sheffield 'many millions of pounds' (in 19th century money), yet he received neither payment nor recognition for these inventions. Dozzles, now called hot tops or feeder heads, are still in use today.
Steel alloys
In a second key advance in metallurgy Mushet invented 'R Mushet's Special Steel' (RMS) in 1868. It was both the first true tool steel and the first air-hardening steel. Previously, the only way to make steel hard enough for machine tools had been to quench it, by rapid cooling in water. With self-hardening (or tungsten) steel, machine tools could run much faster and were able to cut harder metals than had been possible previously. RMS revolutionised the design of machine tools and the progress of industrial metalworking, and was the forerunner of high speed steel.
See also
Crucible steel
Spathic iron ore
References
Bibliography
Further reading
Fred M. Osborn, The Story of the Mushets, London, Thomas Nelson & Sons (1952)
1811 births
1891 deaths
Businesspeople in steel
English inventors
History of Sheffield
British metallurgists
People from Coleford, Gloucestershire
People of the Industrial Revolution
Bessemer Gold Medal | Robert Forester Mushet | [
"Chemistry"
] | 1,514 | [
"Bessemer Gold Medal",
"Chemical engineering awards"
] |
10,939,045 | https://en.wikipedia.org/wiki/Carboxypeptidase%20E | Carboxypeptidase E (CPE), also known as carboxypeptidase H (CPH) and enkephalin convertase, is an enzyme that in humans is encoded by the CPE gene. This enzyme catalyzes the release of C-terminal arginine or lysine residues from polypeptides.
CPE is involved in the biosynthesis of most neuropeptides and peptide hormones. The production of neuropeptides and peptide hormones typically requires two sets of enzymes that cleave the peptide precursors, which are small proteins. First, proprotein convertases cut the precursor at specific sites to generate intermediates containing C-terminal basic residues (lysine and/or arginine). These intermediates are then cleaved by CPE to remove the basic residues. For some peptides, additional processing steps, such as C-terminal amidation, are subsequently required to generate the bioactive peptide, although for many peptides the action of the proprotein convertases and CPE is sufficient to produce the bioactive peptide.
Tissue distribution
Carboxypeptidase E is found in brain and throughout the neuroendocrine system, including the endocrine pancreas, pituitary, and adrenal gland chromaffin cells. Within cells, carboxypeptidase E is present in the secretory granules along with its peptide substrates and products. Carboxypeptidase E is a glycoprotein that exists in both membrane-associated and soluble forms. The membrane-binding is due to an amphiphilic α-helix within the C-terminal region of the protein.
Species distribution
Carboxypeptidase E is found in all species of vertebrates that have been examined, and is also present in many other organisms that have been studied (nematode, sea slug). Carboxypeptidase E is not found in the fruit fly (Drosophila), and another enzyme (presumably carboxypeptidase D) fills in for carboxypeptidase E in this organism. In humans, CPE is encoded by the CPE gene.
Function
Carboxypeptidase E functions in the production of nearly all neuropeptides and peptide hormones. The enzyme acts as an exopeptidase to activate neuropeptides. It does that by cleaving off basic C-terminal amino acids, producing the active form of the peptide. Products of carboxypeptidase E include insulin, the enkephalins, vasopressin, oxytocin, and most other neuroendocrine peptide hormones and neuropeptides.
It has been proposed that membrane-associated carboxypeptidase E acts as a sorting signal for regulated secretory proteins in the trans-Golgi network of the pituitary and in secretory granules; regulated secretory proteins are mostly hormones and neuropeptides. However, this role for carboxypeptidase E remains controversial, and evidence shows that this enzyme is not necessary for the sorting of regulated secretory proteins.
Clinical significance
Mice with mutant carboxypeptidase E, Cpefat, display endocrine disorders like obesity and infertility. In some strains of mice, the fat mutation also causes hyperproinsulinemia in adult male mice, but this is not found in all strains of mice. The obesity and infertility in the Cpefat mice develop with age; young mice (<8 weeks of age) are fertile and have normal body weight. Peptide processing in Cpefat mice is impaired, with a large accumulation of peptides with C-terminal lysine and/or arginine extensions. Levels of the mature forms of peptides are generally reduced in these mice, but not eliminated. It is thought that a related enzyme (carboxypeptidase D) also contributes to neuropeptide processing and gives rise to the mature peptides in the Cpefat mice.
Mutations in the CPE gene are not common within the human population, but have been identified. One patient with extreme obesity (Body Mass Index >50) was found to have a mutation that deleted nearly the entire CPE gene. This patient had intellectual disability (inability to read or write) and had abnormal glucose homeostasis, similar to mice lacking CPE activity.
In obesity, high levels of circulating free fatty acids have been reported to cause a decrease in the amount of carboxypeptidase E protein in pancreatic beta-cells, leading to beta-cell dysfunction (hyperproinsulinemia) and increased beta-cell apoptosis (via an increase in ER stress). However, because CPE is not a rate-limiting enzyme for the production of most neuropeptides and peptide hormones, it is not clear how relatively modest decreases in CPE activity can cause physiological effects.
See also
Carboxypeptidase
Carboxypeptidase A
References
Further reading
External links
The MEROPS online database for peptidases and their inhibitors: M14.005
Proteins
EC 3.4.17
Metabolism | Carboxypeptidase E | [
"Chemistry",
"Biology"
] | 1,079 | [
"Biomolecules by chemical classification",
"Cellular processes",
"Molecular biology",
"Biochemistry",
"Proteins",
"Metabolism"
] |
10,939,047 | https://en.wikipedia.org/wiki/Problem%20property | Problem property is terminology used by city governments seeking to apply pressure to the owners and managers of buildings where crime has occurred. "Problem property" is also used to describe any land or building that has negative issues associated with it, such as difficulty to sell, uncertain ownership, flooding, etc.
In the rental-property industry, the theory is that landlords have a duty to ensure tenants will not engage in criminal behavior that affects the quality of life of neighbors. And that the failure of some landlords to screen applicants appropriately for their units can lead to greater criminality and lower quality of life in some neighborhoods.
Critics claim that it is in the political interest of local-government officials and police to shift the blame for crime from the criminals and the responsibility for fighting crime themselves to nearby property owners. This is a common strategy in community policing.
See also
Stigmatized property
References
Urban planning | Problem property | [
"Engineering"
] | 178 | [
"Urban planning",
"Architecture"
] |
10,939,530 | https://en.wikipedia.org/wiki/Evil%20twin%20%28wireless%20networks%29 | An evil twin is a fraudulent Wi-Fi access point that appears to be legitimate but is set up to eavesdrop on wireless communications.
The evil twin is the wireless LAN equivalent of the phishing scam.
This type of attack may be used to steal the passwords of unsuspecting users, either by monitoring their connections or by phishing, which involves setting up a fraudulent web site and luring people there.
Method
The attacker snoops on Internet traffic using a bogus wireless access point. Unwitting web users may be invited to log into the attacker's server, prompting them to enter sensitive information such as usernames and passwords. Often, users are unaware they have been duped until well after the incident has occurred.
When users log into unsecured (non-HTTPS) bank or e-mail accounts, the attacker intercepts the transaction, since it is sent through their equipment. The attacker is also able to connect to other networks associated with the users' credentials.
Fake access points are set up by configuring a wireless card to act as an access point (known as HostAP). They are hard to trace since they can be shut off instantly. The counterfeit access point may be given the same SSID and BSSID as a nearby Wi-Fi network. The evil twin can be configured to pass Internet traffic through to the legitimate access point while monitoring the victim's connection, or it can simply say the system is temporarily unavailable after obtaining a username and password.
Using captive portals
One of the most commonly used attacks under evil twins is a captive portal. At first, the attacker would create a fake wireless access point that has a similar ESSID to the legitimate access point. The attacker then might execute a denial-of-service attack on the legitimate access point which will cause it to go offline. From then on, clients would connect to the fake access point automatically. The clients would then be led to a web portal that will be requesting them to enter their password, which can then be misused by the attackers.
Example
In July 2024 a man was charged by Australian Federal Police with running a fake WiFi network to steal credentials of passengers on at least one commercial flight. An airline had reported that employees had concerns about a suspicious WiFi network identified during a domestic flight.
See also
KARMA attack, a variant on the evil twin attack
Snarfing
Wireless LAN Security
References
External links
Rogue AP software.
Web security exploits | Evil twin (wireless networks) | [
"Technology"
] | 505 | [
"Computer security exploits",
"Web security exploits"
] |
10,939,959 | https://en.wikipedia.org/wiki/Tyler%20poison%20gas%20plot | The Tyler poison gas plot was an American domestic terrorism plan in Tyler, Texas, thwarted in April 2003 with the arrest of three individuals and the seizure of a cyanide gas bomb along with a large arsenal. Authorities had been investigating the white supremacist conspirators for several years and the case received little media coverage and limited attention in public from the government.
Conspirators
The three individuals were linked to white supremacist and anti-government groups. They were:
William Joseph Krar, born 1940, originally from Connecticut then Goffstown New Hampshire
Judith L. Bruey, Krar's common-law wife
Edward S. Feltus of Old Bridge, New Jersey, an employee of Monmouth County Department of Human Services Feltus was a member of the New Jersey Militia.
Krar was alleged to have made his living travelling across the country selling bomb components and other weapons to violent underground anti-government groups. After leaving community college, he moved to New Hampshire and first opened a restaurant and then in 1984 began selling weapons without a license under the name International Development Corporation (IDC). His father was a gunsmith. He was convicted and fined for impersonating a police officer in 1985. He worked for a building supply company and often traveled to Central America - though not on company business - until the company closed in 1988, when he stopped filing tax returns for IDC. He met Bruey in 1989.
Investigation
Federal authorities had been observing Krar since at least 1995, when ATF agents investigated a possible plot to bomb government buildings, but Krar was not charged. In June 2001, police investigating a fire at Krar's Goffstown storage facility found guns and ammunition, but were persuaded this was legitimate as part of his business.
Since the September 11 attacks, their attention was focused on Middle Eastern terrorist activities. They were only alerted to Krar's recent activities by accident when he mailed Feltus a package of counterfeit birth certificates from North Dakota, Vermont, and West Virginia, and United Nations Multinational Force and Observers and Defense Intelligence Agency IDs in January 2002. The package was mistakenly delivered to a Staten Island man who alerted police. In August 2002, FBI investigators spoke to Feltus, who admitted to being in a militia and to be storing weapons.
In January 2003, a Nashville state trooper stopped Krar in a routine traffic stop and found drugs, chemicals, false IDs and weapons in the car. Krar was arrested and the FBI were alerted. Krar was bailed and one month later an FBI lab reported that white powder found in the car was sodium cyanide; an arrest warrant was issued for Krar.
In April 2003, investigators found weapons, pure sodium cyanide and white supremacist material in a storage facility in Noonday, Texas rented by Krar and Bruey. More weapons were found at their Tyler, Texas home. The weapons included at least 100 other conventional bombs (including briefcase bombs and pipe bombs), machine guns, an assault rifle, an unregistered silencer, and 500,000 rounds of ammunition. The chemical stockpile seized included sodium cyanide, hydrochloric acid, nitric acid and acetic acid. The cyanide was in a device with acid that would trigger its release as a gas bomb.
Sentencing
On May 4, 2004, Krar was sentenced to 135 months in prison after he pleaded guilty to building and possessing chemical weapons. Bruey was sentenced to 57 months after pleading to "conspiracy to possess illegal weapons."
As per a lookup at the Bureau of Prisons prisoner database on September 18, 2012, Krar (09751-078) was listed as deceased on May 7, 2009, Bruey (10601-078) was released on May 30, 2008, and no information is available for Edward Feltus.
Reactions
Paul Krugman writing in the New York Times noted how John Ashcroft and the US Justice Department gave no comment or press release about the case, in contrast to other foiled plots of international terrorism. Krugman's piece was noted in Congress by John Conyers. The Christian Science Monitor noted in December 2003 "there have been two government press releases and a handful of local stories, but no press conference and no coverage in the national newspapers."
References
External links
April 2003 crimes in the United States
Terrorist incidents in the United States in 2003
Tyler, Texas
Failed terrorist attempts in the United States
2003 in Texas
Chemical weapons attacks
Terrorist incidents in Texas
Deaths by cyanide poisoning
White nationalist terrorism | Tyler poison gas plot | [
"Chemistry"
] | 934 | [
"Chemical weapons attacks",
"Chemical weapons"
] |
10,940,032 | https://en.wikipedia.org/wiki/Hydrogen%20anion | The hydrogen anion, H−, is a negative ion of hydrogen, that is, a hydrogen atom that has captured an extra electron. The hydrogen anion is an important constituent of the atmosphere of stars, such as the Sun. In chemistry, this ion is called hydride. The ion has two electrons bound by the electromagnetic force to a nucleus containing one proton.
The binding energy of H− equals the binding energy of an extra electron to a hydrogen atom, called electron affinity of hydrogen. It is measured to be or (see Electron affinity (data page)). The total ground state energy thus becomes .
Occurrence
The hydrogen anion is the dominant bound-free opacity source at visible and near-infrared wavelengths in the atmospheres of stars like the Sun and cooler; its importance was first noted in the 1930s. The ion absorbs photons with energies in the range 0.75–4.0 eV, which ranges from the infrared into the visible spectrum. Most of the electrons in these negative ions come from the ionization of metals with low first ionization potentials, including the alkali metals and alkaline earths. The process which ejects the electron from the ion is properly called photodetachment rather than photoionization because the result is a neutral atom (rather than an ion) and a free electron.
H− also occurs in the Earth's ionosphere and can be produced in particle accelerators.
Its existence was first proven theoretically by Hans Bethe in 1929. H− is unusual because, in its free form, it has no bound excited states, as was finally proven in 1977.
In chemistry, hydrogen has the formal oxidation state −1 in the hydride anion.
The term hydride is probably most often used to describe compounds of hydrogen with other elements in which the hydrogen is in the formal −1 oxidation state. In most such compounds the bonding between the hydrogen and its nearest neighbor is covalent. An example of a hydride is the borohydride anion ().
See also
Hydron (hydrogen cation)
Electride, another very simple anion
Hydrogen ion
References
Hydrogen physics
Astrophysics
Anions | Hydrogen anion | [
"Physics",
"Chemistry",
"Astronomy"
] | 445 | [
"Matter",
"Anions",
"Astrophysics",
"Ions",
"Astronomical sub-disciplines"
] |
10,940,038 | https://en.wikipedia.org/wiki/Thiolase | Thiolases, also known as acetyl-coenzyme A acetyltransferases (ACAT), are enzymes which convert two units of acetyl-CoA to acetoacetyl CoA in the mevalonate pathway.
Thiolases are ubiquitous enzymes that have key roles in many vital biochemical pathways, including the beta oxidation pathway of fatty acid degradation and various biosynthetic pathways. Members of the thiolase family can be divided into two broad categories: degradative thiolases (EC 2.3.1.16) and biosynthetic thiolases (EC 2.3.1.9). These two different types of thiolase are found both in eukaryotes and in prokaryotes: acetoacetyl-CoA thiolase (EC:2.3.1.9) and 3-ketoacyl-CoA thiolase (EC:2.3.1.16). 3-ketoacyl-CoA thiolase (also called thiolase I) has a broad chain-length specificity for its substrates and is involved in degradative pathways such as fatty acid beta-oxidation. Acetoacetyl-CoA thiolase (also called thiolase II) is specific for the thiolysis of acetoacetyl-CoA and involved in biosynthetic pathways such as beta-hydroxybutyric acid synthesis or steroid biogenesis.
The formation of a carbon–carbon bond is a key step in the biosynthetic pathways by which fatty acids and polyketide are made. The thiolase superfamily enzymes catalyse the carbon–carbon-bond formation via a thioester-dependent Claisen condensation reaction mechanism.
Function
Thiolases are a family of evolutionarily related enzymes. Two different types of thiolase are found both in eukaryotes and in prokaryotes: acetoacetyl-CoA thiolase () and 3-ketoacyl-CoA thiolase (). 3-ketoacyl-CoA thiolase (also called thiolase I) has a broad chain-length specificity for its substrates and is involved in degradative pathways such as fatty acid beta-oxidation. Acetoacetyl-CoA thiolase (also called thiolase II) is specific for the thiolysis of acetoacetyl-CoA and involved in biosynthetic pathways such as poly beta-hydroxybutyrate synthesis or steroid biogenesis.
In eukaryotes, there are two forms of 3-ketoacyl-CoA thiolase: one located in the mitochondrion and the other in peroxisomes.
There are two conserved cysteine residues important for thiolase activity. The first located in the N-terminal section of the enzymes are involved in the formation of an acyl-enzyme intermediate; the second located at the C-terminal extremity is the active site base involved in deprotonation in the condensation reaction.
Isozymes
Mammalian nonspecific lipid-transfer protein (nsL-TP) (also known as sterol carrier protein 2) is a protein which seems to exist in two different forms: a 14 Kd protein (SCP-2) and a larger 58 Kd protein (SCP-x). The former is found in the cytoplasm or the mitochondria and is involved in lipid transport; the latter is found in peroxisomes. The C-terminal part of SCP-x is identical to SCP-2 while the N-terminal portion is evolutionary related to thiolases.
Mechanism
Thioesters are more reactive than oxygen esters and are common intermediates in fatty-acid metabolism. These thioesters are made by conjugating the fatty acid with the free SH group of the pantetheine moiety of either coenzyme A (CoA) or acyl carrier protein (ACP).
All thiolases, whether they are biosynthetic or degradative in vivo, preferentially catalyze the degradation of 3-ketoacyl-CoA to form acetyl-CoA and a shortened acyl-CoA species, but are also capable of catalyzing the reverse Claisen condensation reaction (reflecting the negative Gibbs energy change of the degradation, which is independent of the thiolase catalyzing the reaction). It is well established from studies on the biosynthetic thiolase from Z. ramigera that the thiolase reaction occurs in two steps and follows ping-pong kinetics. In the first step of both the degradative and biosynthetic reactions, the nucleophilic Cys89 (or its equivalent) attacks the acyl-CoA (or 3-ketoacyl-CoA) substrate, leading to the formation of a covalent acyl-enzyme intermediate. In the second step, the addition of CoA (in the degradative reaction) or acetyl-CoA (in the biosynthetic reaction) to the acyl–enzyme intermediate triggers the release of the product from the enzyme. Each of the tetrahedral reaction intermediates that occur during transfer of an acetyl group to and from the nucleophilic cysteine, respectively, have been observed in X-ray crystal structures of biosynthetic thiolase from A. fumigatus.
Structure
Most enzymes of the thiolase superfamily are dimers. However, monomers have not been observed. Tetramers are observed only in the thiolase subfamily and, in these cases, the dimers have dimerized to become tetramers. The crystal structure of the tetrameric biosynthetic thiolase from Zoogloea ramigera has been determined at 2.0 Å resolution. The structure contains a striking and novel ‘cage-like’ tetramerization motif, which allows for some hinge motion of the two tight dimers with respect to each other. The enzyme tetramer is acetylated at Cys89 and has a CoA molecule bound in each of its
active-site pockets.
Biological function
In eukaryotic cells, especially in mammalian cells, thiolases exhibit diversity in intracellular localization related to their metabolic functions as well as in substrate specificity. For example, they contribute to fatty-acid β-oxidation in peroxisomes and mitochondria, ketone body metabolism in mitochondria, and the early steps of mevalonate pathway in peroxisomes and cytoplasm. In addition to biochemical investigations, analyses of genetic disorders have made clear the basis of their functions. Genetic studies have identified a three-thiolase system in the yeast Candida tropicalis, which has thiolase activity in peroxisomes, where it may participate in beta oxidation, and in the cytosol, where it participates in the mevalonate pathway. Thiolase is of central importance in key enzymatic pathways such as fatty-acid, steroid and polyketide synthesis. The detailed understanding of its structural biology is of great medical relevance, for example, for a better understanding of the diseases caused by genetic deficiencies of these enzymes and for the development of new antibiotics. Harnessing the complicated catalytic versatility of the polyketide synthases for the synthesis of biologically and medically relevant natural products is also an important future perspective of the studies of the enzymes of this superfamily.
Disease relevance
Mitochondrial acetoacetyl-CoA thiolase deficiency, known earlier as β-ketothiolase deficiency, is an inborn error of metabolism involving isoleucine catabolism and ketone body metabolism. The major clinical manifestations of this disorder are intermittent ketoacidosis but the long-term clinical consequences, apparently benign, are not well documented. Mitochondrial acetoacetyl-CoA thiolase deficiency is easily diagnosed by urinary organic acid analysis and can be confirmed by enzymatic analysis of cultured skin fibroblasts or blood leukocytes.
β-Ketothiolase Deficiency has a variable presentation. Most affected patients present between 5 and 24 months of age with symptoms of severe ketoacidosis. Symptoms can be initiated by a dietary protein load, infection or fever. Symptoms progress from vomiting to dehydration and ketoacidosis. Neutropenia and thrombocytopenia may be present, as can moderate hyperammonemia. Blood glucose is typically normal, but can be low or high in acute episodes. Developmental delay may occur, even before the first acute episode, and bilateral striatal necrosis of the basal ganglia has been seen on brain MRI.
References
External links
Protein domains | Thiolase | [
"Biology"
] | 1,859 | [
"Protein domains",
"Protein classification"
] |
10,940,607 | https://en.wikipedia.org/wiki/Imidazolidine%20%28data%20page%29 |
References
Chemical data pages
Chemical data pages cleanup | Imidazolidine (data page) | [
"Chemistry"
] | 10 | [
"Chemical data pages",
"nan"
] |
10,940,802 | https://en.wikipedia.org/wiki/Precursor%20%28chemistry%29 | In chemistry, a precursor is a compound that participates in a chemical reaction that produces another compound.
In biochemistry, the term "precursor" often refers more specifically to a chemical compound preceding another in a metabolic pathway, such as a protein precursor.
Illicit drug precursors
In 1988, the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances introduced detailed provisions and requirements relating the control of precursors used to produce drugs of abuse.
In Europe the Regulation (EC) No. 273/2004 of the European Parliament and of the Council on drug precursors was adopted on 11 February 2004. (European law on drug precursors)
Illicit explosives precursors
On January 15, 2013, the Regulation (EU) No. 98/2013 of the European Parliament and of the Council on the marketing and use of explosives precursors was adopted.
The Regulation harmonises rules across Europe on the making available, introduction, possession and use, of certain substances or mixtures that could be misused for the illicit manufacture of explosives.
Detection
A portable, advanced sensor based on infrared spectroscopy in a hollow fiber matched to a silicon-micromachined fast gas chromatography column can analyze illegal stimulants and precursors with nanogram-level sensitivity.
Raman spectroscopy has been successfully tested to detect explosives and their precursors.
Technologies able to detect precursors in the environment could contribute to an early location of sites where illegal substances (both explosives and drugs of abuse) are produced.
See also
Binary chemical weapon
Chemical synthesis
DEA list of chemicals
Derivative (chemistry)
Educt, a reagent or reactant
Metabolism#Anabolism
Monoamine precursor
Prodrug
Protein precursor
References
Biochemical reactions
Chemical synthesis
Metabolism | Precursor (chemistry) | [
"Chemistry",
"Biology"
] | 346 | [
"Biochemical reactions",
"Cellular processes",
"nan",
"Chemical synthesis",
"Biochemistry",
"Metabolism"
] |
10,940,823 | https://en.wikipedia.org/wiki/Phosphomevalonic%20acid | Phosphomevalonic acid is an intermediate in the Mevalonate pathway.
References
Metabolism | Phosphomevalonic acid | [
"Chemistry",
"Biology"
] | 21 | [
"Biotechnology stubs",
"Biochemistry stubs",
"Cellular processes",
"Biochemistry",
"Metabolism"
] |
10,941,307 | https://en.wikipedia.org/wiki/Phosphomevalonate%20kinase | Phosphomevalonate kinase is an enzyme () in the mevalonate pathway that in humans is encoded by the PMVK gene.
References
External links
EC 2.7.4 | Phosphomevalonate kinase | [
"Chemistry",
"Biology"
] | 41 | [
"Biochemistry stubs",
"Biotechnology stubs",
"Biochemistry"
] |
10,941,726 | https://en.wikipedia.org/wiki/Fructose-bisphosphate%20aldolase | Fructose-bisphosphate aldolase (), often just aldolase, is an enzyme catalyzing a reversible reaction that splits the aldol, fructose 1,6-bisphosphate, into the triose phosphates dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P). Aldolase can also produce DHAP from other (3S,4R)-ketose 1-phosphates such as fructose 1-phosphate and sedoheptulose 1,7-bisphosphate. Gluconeogenesis and the Calvin cycle, which are anabolic pathways, use the reverse reaction. Glycolysis, a catabolic pathway, uses the forward reaction. Aldolase is divided into two classes by mechanism.
The word aldolase also refers, more generally, to an enzyme that performs an aldol reaction (creating an aldol) or its reverse (cleaving an aldol), such as Sialic acid aldolase, which forms sialic acid. See the list of aldolases.
Mechanism and structure
Class I proteins form a protonated Schiff base intermediate linking a highly conserved active site lysine with the DHAP carbonyl carbon. Additionally, tyrosine residues are crucial to this mechanism in acting as stabilizing hydrogen acceptors. Class II proteins use a different mechanism which polarizes the carbonyl group with a divalent cation like Zn2+. The Escherichia coli galactitol operon protein, gatY, and N-acetyl galactosamine operon protein, agaY, which are tagatose-bisphosphate aldolase, are homologs of class II fructose-bisphosphate aldolase. Two histidine residues in the first half of the sequence of these homologs have been shown to be involved in binding zinc.
The protein subunits of both classes each have an α/β domain folded into a TIM barrel containing the active site. Several subunits are assembled into the complete protein. The two classes share little sequence identity.
With few exceptions only class I proteins have been found in animals, plants, and green algae. With few exceptions only class II proteins have been found in fungi. Both classes have been found widely in other eukaryotes and in bacteria. The two classes are often present together in the same organism. Plants and algae have plastidal aldolase, sometimes a relic of endosymbiosis, in addition to the usual cytosolic aldolase. A bifunctional fructose-bisphosphate aldolase/phosphatase, with class I mechanism, has been found widely in archaea and in some bacteria. The active site of this archaeal aldolase is also in a TIM barrel.
In gluconeogenesis and glycolysis
Gluconeogenesis and glycolysis share a series of six reversible reactions. In gluconeogenesis glyceraldehyde-3-phosphate is reduced to fructose 1,6-bisphosphate with aldolase. In glycolysis fructose 1,6-bisphosphate is made into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate through the use of aldolase. The aldolase used in gluconeogenesis and glycolysis is a cytoplasmic protein.
Three forms of class I protein are found in vertebrates.
Aldolase A is preferentially expressed in muscle and brain; aldolase B in liver, kidney, and in enterocytes; and aldolase C in brain. Aldolases A and C are mainly involved in glycolysis, while aldolase B is involved in both glycolysis and gluconeogenesis. Some defects in aldolase B cause hereditary fructose intolerance. The metabolism of free fructose in liver exploits the ability of aldolase B to use fructose 1-phosphate as a substrate. Archaeal fructose-bisphosphate aldolase/phosphatase is presumably involved in gluconeogenesis because its product is fructose 6-phosphate.
In the Calvin cycle
The Calvin cycle is a carbon fixation pathway; it is part of photosynthesis, which convert carbon dioxide and other compounds into glucose. It and gluconeogenesis share a series of four reversible reactions. In both pathways 3-phosphoglycerate (3-PGA or 3-PG) is reduced to fructose 1,6-bisphosphate with aldolase catalyzing the last reaction. A fifth reaction, catalyzed in both pathways by fructose 1,6-bisphosphatase, hydrolyzes the fructose 1-6-bisphosphate to fructose 6-phosphate and inorganic phosphate. The large decrease in free energy makes this reaction irreversible. In the Calvin cycle aldolase also catalyzes the production of sedoheptulose 1,7-bisphosphate from DHAP and erythrose 4-phosphate. The chief products of the Calvin cycle are triose phosphate (TP), which is a mixture of DHAP and G3P, and fructose 6-phosphate. Both are also needed to regenerate RuBP. The aldolase used by plants and algae in the Calvin cycle is usually a plastid-targeted protein encoded by a nuclear gene.
Reactions
Aldolase catalyzes
fructose 1,6-bisphosphate DHAP + G3P
and also
sedoheptulose 1,7-bisphosphate DHAP + erythrose 4-phosphate
fructose 1-phosphate DHAP + glyceraldehyde
Aldolase is used in the reversible trunk of gluconeogenesis/glycolysis
2(PEP + NADH + H+ + ATP + H2O) fructose 1,6-bisphosphate + 2(NAD+ + ADP + Pi)
Aldolase is also used in the part of the Calvin cycle shared with gluconeogenesis, with the irreversible phosphate hydrolysis at the end catalyzed by fructose 1,6-bisphosphatase
2(3-PG + NADPH + H+ + ATP + H2O) fructose 1,6-bisphosphate + 2(NADP+ + ADP + Pi)
fructose 1,6-bisphosphate + H2O → fructose 6-phosphate + Pi
In gluconeogenesis 3-PG is produced by enolase and phosphoglycerate mutase acting in series
PEP + H2O 2-PG 3-PG
In the Calvin cycle 3-PG is produced by RuBisCO
RuBP + CO2 + H2O → 2(3-PG)
G3P is produced by phosphoglycerate kinase acting in series with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in gluconeogenesis, and in series with glyceraldehyde-3-phosphate dehydrogenase (NADP+) (phosphorylating) in the Calvin cycle
3-PG + ATP 1,3-bisphosphoglycerate + ADP
1,3-bisphosphoglycerate + NAD(P)H + H+ G3P + Pi + NAD(P)+
Triose-phosphate isomerase maintains DHAP and G3P in near equilibrium, producing the mixture called triose phosphate (TP)
G3P DHAP
Thus both DHAP and G3P are available to aldolase.
Moonlighting properties
Aldolase has also been implicated in many "moonlighting" or non-catalytic functions, based upon its binding affinity for many other proteins including F-actin, α-tubulin, light chain dynein, WASP, Band 3 anion exchanger, phospholipase D (PLD2), glucose transporter GLUT4, inositol trisphosphate, V-ATPase and ARNO (a guanine nucleotide exchange factor of ARF6). These associations are thought to be predominantly involved in cellular structure, however, involvement in endocytosis, parasite invasion, cytoskeleton rearrangement, cell motility, membrane protein trafficking and recycling, signal transduction and tissue compartmentalization have been explored.
References
Further reading
External links
Tolan Laboratory at Boston University
Protein domains
Lyases
Moonlighting proteins
Glycolysis enzymes
Glycolysis | Fructose-bisphosphate aldolase | [
"Chemistry",
"Biology"
] | 1,830 | [
"Carbohydrate metabolism",
"Glycolysis",
"Protein domains",
"Protein classification"
] |
10,941,831 | https://en.wikipedia.org/wiki/Agent-based%20computational%20economics | Agent-based computational economics (ACE) is the area of computational economics that studies economic processes, including whole economies, as dynamic systems of interacting agents. As such, it falls in the paradigm of complex adaptive systems. In corresponding agent-based models, the "agents" are "computational objects modeled as interacting according to rules" over space and time, not real people. The rules are formulated to model behavior and social interactions based on incentives and information. Such rules could also be the result of optimization, realized through use of AI methods (such as Q-learning and other reinforcement learning techniques).
As part of non-equilibrium economics, the theoretical assumption of mathematical optimization by agents in equilibrium is replaced by the less restrictive postulate of agents with bounded rationality adapting to market forces. ACE models apply numerical methods of analysis to computer-based simulations of complex dynamic problems for which more conventional methods, such as theorem formulation, may not find ready use. Starting from initial conditions specified by the modeler, the computational economy evolves over time as its constituent agents repeatedly interact with each other, including learning from interactions. In these respects, ACE has been characterized as a bottom-up culture-dish approach to the study of economic systems.
ACE has a similarity to, and overlap with, game theory as an agent-based method for modeling social interactions. But practitioners have also noted differences from standard methods, for example in ACE events modeled being driven solely by initial conditions, whether or not equilibria exist or are computationally tractable, and in the modeling facilitation of agent autonomy and learning.
The method has benefited from continuing improvements in modeling techniques of computer science and increased computer capabilities. The ultimate scientific objective of the method is to "test theoretical findings against real-world data in ways that permit empirically supported theories to cumulate over time, with each researcher’s work building appropriately on the work that has gone before." The subject has been applied to research areas like asset pricing, energy systems, competition and collaboration, transaction costs, market structure and industrial organization and dynamics, welfare economics, and mechanism design, information and uncertainty, macroeconomics, and Marxist economics.
Overview
The "agents" in ACE models can represent individuals (e.g. people), social groupings (e.g. firms), biological entities (e.g. growing crops), and/or physical systems (e.g. transport systems). The ACE modeler provides the initial configuration of a computational economic system comprising multiple interacting agents. The modeler then steps back to observe the development of the system over time without further intervention. In particular, system events should be driven by agent interactions without external imposition of equilibrium conditions. Issues include those common to experimental economics in general and development of a common framework for empirical validation and resolving open questions in agent-based modeling.
ACE is an officially designated special interest group (SIG) of the Society for Computational Economics. Researchers at the Santa Fe Institute have contributed to the development of ACE.
Example: finance
One area where ACE methodology has frequently been applied is asset pricing. W. Brian Arthur, Eric Baum, William Brock, Cars Hommes, and Blake LeBaron, among others, have developed computational models in which many agents choose from a set of possible forecasting strategies in order to predict stock prices, which affects their asset demands and thus affects stock prices. These models assume that agents are more likely to choose forecasting strategies which have recently been successful. The success of any strategy will depend on market conditions and also on the set of strategies that are currently being used. These models frequently find that large booms and busts in asset prices may occur as agents switch across forecasting strategies. More recently, Brock, Hommes, and Wagener (2009) have used a model of this type to argue that the introduction of new hedging instruments may destabilize the market, and some papers have suggested that ACE might be a useful methodology for understanding the 2008 financial crisis.
See also discussion under and § Departures from rationality.
See also
Agent-based social simulation
Artificial financial market
Computational economics
Econophysics
Macroeconomic model
Multi-agent system
Statistical finance
References
Computational economics
Monte Carlo methods in finance
Computational fields of study
Agent-based model | Agent-based computational economics | [
"Technology"
] | 863 | [
"Computational fields of study",
"Computing and society"
] |
10,942,146 | https://en.wikipedia.org/wiki/5-Diphosphomevalonic%20acid | 5-Diphosphomevalonic acid (or mevalonate-5-pyrophosphate, or 5-pyrophosphomevalonate) is an intermediate in the mevalonate pathway.
See also
Mevalonic acid
Phosphomevalonate kinase
Pyrophosphomevalonate decarboxylase
External links
Pyrophosphate esters
Carboxylic acids | 5-Diphosphomevalonic acid | [
"Chemistry",
"Biology"
] | 87 | [
"Biotechnology stubs",
"Carboxylic acids",
"Functional groups",
"Biochemistry stubs",
"Biochemistry"
] |
10,942,398 | https://en.wikipedia.org/wiki/Sling%20%28firearms%29 | In the context of firearms, a sling is a type of strap or harness designed to allow a shooter to conveniently carry a firearm (usually a long gun such as a rifle, carbine, shotgun, submachine gun or GPMG) on their body, and/or to aid in greater hit probability by allowing the firearm to be better braced and stabilized during aiming. Various types of slings offer their own advantages and disadvantages, and can generally be divided into several categories.
Types of setup
Simple/traditional sling (two-point) The oldest and most familiar design, this sling design has two connection points that attach to the front and rear of the weapon, and allows the shooter to carry the weapon over their back, with the sling draped across the torso, around the neck or over one shoulder. Some two-point slings, if properly made, can act as a shooting aid.
Ching/CW sling This type of sling is a component of the Scout Rifle concept, and serves not just as a carrying strap, but as an aid to greater hit probability by helping the shooter aim steadily.
Two-point quick-adjust sling Similar to a two-point simple sling, but with the capability to quickly adjust the length of the sling with a pull-tab.
Three-point sling The advantages of the three-point sling are that it functions more like a harness and is therefore strapped to the shooter. This allows the shooter to release the weapon to use their hands for other tasks (such as transitioning to a sidearm) without fear of dropping it on the ground since it will remain hanging from the shooter and easily accessible when needed again. The design of the three-point sling consists of a loop of material (usually cordura or similar) that loops around the torso, and two straps that go to the front and rear of the weapon. The shooter's body and the front and rear of the weapon are the three points that give this design its name.
Single-point sling A specialized sling design that permits the shooter to transition to firing from the opposite shoulder. Like the three-point sling, the single-point sling permits the shooter to drop the weapon and let it hang downward while still attached to their body. This sling design is best suited for short-term tactical use. A single-point sling is only worn in one way, and cannot provide the same degree of long-term anti-fatigue weight support as other slings. The one great advantage of the single point design is that it is very easy to switch from shoulder to shoulder for weak side barricade shooting. Negative attributes of the single-point sling include a tendency to make the rifle dangle and hang off the shooter in an inconvenient fashion; it can interfere with the shooter's movement and hang up on the shooter's gear.
Mounting standards
There are several mounting standards for attaching a sling to a rifle, of which some well known are sling swivel studs, QD/ Flush Cup or snap hooks (i.e. HK-type snap hook or Magpul Paraclip).
Sling mounts also come in different widths for different webbings. The webbing on American slings are typically 1, 1 or 1 inch (25.4, 31.75 or 38.1 mm) wide, while European slings typically are wide.
Sling swivel stud
A sling swivel stud, sometimes called an "Uncle Mike type swivel" after one of the manufacturers, is one type of sling mounting interface. Sling swivels can be mounted to a long gun in various ways, for instance with wood or machine screws attached to the stock, a barrel band, or by using adapters to other mounting standards such as Picatinny or M-LOK.
Sling swivel studs can vary in dimensions. The widest round part of the stud typically measures around 8.9 mm (0.350 inches), the spacing between the flats measure around 7.6 mm (0.3 inches) and the hole for mounting a sling adapter measures around 3.7 mm (0.145 inches).
Quick detach sling mount
Quick detach sling mounts (QD), also called flush cup sling mounts, is another type of sling mounting interface. "QD sling swivel" usually refers to the part attached to the sling, while "flush cup" refer to the corresponding socket on the firearm.
The system consists of a push button swivel attached to the sling (approximate diameter 9.4 mm, a little under inches) which is placed into a mounting socket on the firearm (approximate diameter 9.6 mm, a little over inches). The swivel is kept in place by a four ball detents connected to the push button, which presses against the walls of the socket. The sling swivel can quickly be taken on and off by pushing the QD button, which retracts the ball detents. The flush cup sockets can be either rotating or non rotating.
Flush cups can be mounted to a long gun in various ways, for instance by drilling a hole in the stock and screwing in flush cup socket, or by using an adapter to other mounting standards such as Picatinny or M-LOK.
As a shooting aid
A variation of the single point sling is used in precision target rifle shooting from the prone position. The sling is not intended as a carrying aid, but is used to steady the rifle. For a right-handed shooter, the sling attaches to the top of the left arm, and clips onto the forend of the rifle. The left arm is wrapped under the sling. The sling with upper and lower arm form three sides of a triangle that provide a steady support for the rifle.
Carrying harness
A carrying harness usually refers to a type of sling made primarily for carrying the rifle, and not doubling as a shooting support. For example in biathlon, the carrying harness is often a separate item from the shooting sling, with both being attached to the biathlon rifle. The carrying harness is designed to let the biathlete carry the rifle with minimal hindrance, and in such a way increase performance in the ski track. Special carrying harnesses have also been designed for anti-tank rifles, since such rifles often are too heavy for carrying with a normal rifle sling.
Other examples
Various other forms of weapon slings and harnesses have existed, or experimented with for military trials. An example is the affusto d'assalto (assault carriage) that was devised by the 139° e 140° Reggimento Fanteria Brigata "Bari" in 1917 and used on the Villar Perosa aircraft submachine gun. The same concept was later used on the Brixia M1923 machine gun but using the sling in conjunction with a bipod.
See also
Third Arm Weapon Interface System
Walking fire
Weapon mount
References
External links
Article on AR Slings by TopGunSafes.org
Article on Tactical Slings
Reaper Weapon Support System
Army’s Steadicam Third Arm – An Independent Study
Army Research Lab Show Off Latest Prototype of the ‘Third Arm’
Steadicam Gun Revisited – Spade Gripped Firearm
Firearm components | Sling (firearms) | [
"Technology"
] | 1,464 | [
"Firearm components",
"Components"
] |
10,942,453 | https://en.wikipedia.org/wiki/Health%20services%20research | Health services research (HSR) became a burgeoning field in North America in the 1960s, when scientific information and policy deliberation began to coalesce. Sometimes also referred to as health systems research or health policy and systems research (HPSR), HSR is a multidisciplinary scientific field that examines how people get access to health care practitioners and health care services, how much care costs, and what happens to patients as a result of this care. HSR utilizes all qualitative and quantitative methods across the board to ask questions of the healthcare system. It focuses on performance, quality, effectiveness and efficiency of health care services as they relate to health problems of individuals and populations, as well as health care systems and addresses wide-ranging topics of structure, processes, and organization of health care services; their use and people's access to services; efficiency and effectiveness of health care services; the quality of healthcare services and its relationship to health status, and; the uses of medical knowledge.
Studies in HSR investigate how social factors, health policy, financing systems, organizational structures and processes, medical technology, and personal behaviors affect access to health care, the quality and cost of health care, and quantity and quality of life. Compared with medical research, HSR is a relatively young science that developed through the bringing together of social science perspectives with the contributions of individuals and institutions engaged in delivering health services.
Goals
The primary goals of health services research are to identify the most effective ways to organize, manage, finance, and deliver high quality care; reduce medical errors; and improve patient safety. HSR is more concerned with delivery and high quality access to care, in contrast to medical research, which focuses on the development and evaluation of clinical treatments.
Health services researchers come from a variety of specializations, including geography, nursing, economics, political science, epidemiology, public health, medicine, biostatistics, operations, management, engineering, pharmacy, psychology, usability and user experience design. While health services research is grounded in theory, its underlying aim is to perform research that can be applied by physicians, nurses, health managers and administrators, and other people who make decisions or deliver care in the health care system. For example, the application of epidemiological methods to the study of health services by managers is a type of health services research that can be described as Managerial epidemiology.
Approaches
A common distinction of approaches to HSR is between levels of analysis:
Macro (architecture and oversight of systems)
Meso (functioning of organizations and interventions)
Micro (the individual in the system)
Another distinction can be made between the intent of the research question as either normative/evaluative or exploratory/explanatory.
Collective leadership
Leadership that includes all members of staff and patients in a healthcare setting is referred to as "collective leadership". The idea is that all people involved in healthcare, including those at the receiving end such as patients and caregivers/families, share responsibility for decision making, performance of the healthcare system, and successes. Collective leadership is based on the concept that all stakeholders share viewpoints and knowledge in order to keep up with rapid technological changes, patient-centered outcomes, and the increasing need for specialization in healthcare. The effectiveness of this approach is still being understood and there is no strong evidence to suggest that this approach improves clinical performance, mortality of inpatients, or other outcomes such as staff absences.
Education
Medical conferences and educational meetings are a common approach to help healthcare professionals at an institution learn new skills, keep up with ever-changing clinical practice guidelines, have opportunities for advancing their skills, and create opportunities to connect with peers. Various formats are used including workshops, audits, educational outreach, feedback sessions, lunch-and-learn seminars, and courses. There is a large variety in the inclusion criteria, number of people participating in these sessions, type of interactions (for example, passive seminar or hands-on learning experience), frequency of these opportunities, costs, and learning goals. Research into the effectiveness of these approaches is not strong. Educational meetings may slightly improve professional practice and may have a very small improvement on patient outcomes. In addition, there is weak evidence to suggest that educational meetings may help healthcare staff change their practices to comply with changes or desired practices more than other approaches to encourage change including emails, text messages, or fees.
Low and middle income countries
Research looking into the quality of healthcare in low and middle income countries and different approaches to improving performance of healthcare delivery in countries with resource constraints is growing. The main goal is to improve performance of healthcare. Performance-based payment (P4P) is one approach that has been studied. Performance-based payment is a broad approach that includes the concept of offering financial incentives if specific targets are met.
Data sources
Many data and information sources are used to conduct health services research, such as population and health surveys, clinical administrative records, health care program and financial administrative records, vital statistics records (births and deaths), and other special studies.
Research in different countries
Canada
Several government, academic and non-government agencies conduct or sponsor health services research, notably the Canadian Institute for Health Information and the Canadian Institutes of Health Research (i.e. the third pillar: "research respecting health systems and services"). Others include the Institute for Clinical Evaluative Sciences (ICES) for the province of Ontario, and the Canadian Collaborative Study of Hip Fractures.
Denmark
Data availability
Several registries are available for research use, such as Danish Twin Register or Danish Cancer Register.
France
Public Health Research Laboratory.
HeSPeR (Health Services and Performance Research), Université Claude Bernard Lyon 1
Sweden
Data Availability
Sweden has a substantial number of national-level registries available to researchers. Many of these are administered by the National Board of Health and Welfare, including comprehensive administrative datasets regarding specialist in-patient and out-patient care, municipal social services, as well as cause of death and drug prescription registries. Over 100 clinically oriented quality registries exist oriented towards an array of specific patient populations and sub-domains.
Centers
A number of Swedish universities host research groups focusing on the Health Services Research, including the Karolinska institute, Lund University, and Uppsala University.
United Kingdom of Great Britain and Northern Ireland (UK)
Several governmental agencies exist that sponsor or support HSR, with their remits set by central and devolved governments. These include the National Institute for Health and Care Research (NIHR) and its constituent infrastructure (including the CLAHRC programme); Healthcare Improvement Scotland; Health and Care Research Wales; and Health and Social Care Research and Development. Many universities have HSR units, a web search can find these with relative ease.
United States
Data availability
Claims data on US Medicare and Medicaid beneficiaries are available for analysis. Data is divided into public data available to any entity and research data available only to qualified researchers. The US's Centers for Medicare and Medicaid Services (CMS) delegates some data export functions to a Research Data Assistance Center.
23 Claims data from various states that are not limited to any particular insurer are also available for analysis via AHRQ's HCUP project.
Centers
Colloquially, health services research departments are often referred to as "shops"; in contrast to basic science research "labs". Broadly, these shops are hosted by three general types of institutions—government, academic, or non-governmental think tanks or professional societies.
Government Sponsored
U.S. Department of Veterans Affairs Award in Health Services Research
Institute of Medicine, U.S.-based policy research organization
University Sponsored
Center for Surgery and Public Health, U.S. -based research institute at the Brigham and Women's Hospital (Harvard University Affiliate)
Regenstrief Institute
Institute for Healthcare Policy and Innovation, U.S. -based research institute at the University of Michigan (Founded in 2011, IHPI includes smaller centers focused on specific healthcare topics)
Leonard Davis Institute of Health Economics, U.S.-based center for HSR at the University of Pennsylvania
Think Tank or Professional Society Sponsored
Society of General Internal Medicine, U.S.-based professional organization in internal medicine research
Commonwealth Fund, U.S.-based center for HSR
Rand Corporation Health Division, U.S.-based center for HSR
See also
Health economics
Health workforce research
Health insurance
Health policy
Managed care
Nursing
Pharmacy Practice Research
Priority-setting in global health
Public health
BMC Health Services Research, scientific journal
Health Affairs, scientific journal
Health Services Research, scientific journal
Medical Care, scientific journal
Medical Care Research and Review, scientific journal
World Health Report 2013: Research for universal health coverage, publication of the World Health Organization
References
External links
Alliance for Health Systems and Policy Research, global partnership for health systems research
Health Systems Global, a membership society which aims to convene researchers, policy-makers and implementers from around the world to develop the field of health systems research
Health-EU, portal on public health research of the European Union
Canadian Association for Health Services & Policy Research
Canadian Foundation for Healthcare Improvement
Canadian Knowledge Transfer and Exchange Community of Practice
United States Veterans Affairs: Health Services Research & Development
AcademyHealth, a U.S.-based professional development center for health services research
Cedar Associates LLC, a U.S.-based center for clinical effectiveness decision analytical research
Biostatistics
Epidemiology
Clinical research
Health care quality
Health economics | Health services research | [
"Environmental_science"
] | 1,913 | [
"Epidemiology",
"Environmental social science"
] |
10,942,747 | https://en.wikipedia.org/wiki/Pentosuria | Pentosuria is a condition where the sugar xylitol, a pentose, presents in the urine in unusually high concentrations. It was characterized as an inborn error of carbohydrate metabolism in 1908. It is associated with a deficiency of L-xylulose reductase, necessary for xylitol metabolism. L-Xylulose is a reducing sugar, so it may give false diagnosis of diabetes, as it is found in high concentrations in urine. However glucose metabolism is normal in people with pentosuria, and they are not diabetic. Patients of pentosuria have a low concentration of the sugar d-xyloketose. Using phenyl pentosazone crystals, phloroglucin reaction, and absorption spectrum, pentose can be traced back as the reducing substance in urine, with those that have pentosuria.
Research has shown that pentosuria appears in 3 forms. The most widely studied is essential pentosuria, where a couple of grams of L-xylusol are released into a person's system daily. L-xylulose reductase, contained in red blood cells, is composed of both a major and minor isozyme. For those diagnosed with essential pentosuria, the major isozyme appears to be the same as the minor one. Alimentary pentosuria can be acquired through fruits high in pentose. Finally, drug-induced pentosuria can be developed by those exposed to morphine, fevers, allergies, and some hormones.
Those diagnosed with Pentosuria are predominantly of Jewish root. However, it is a harmless defect, and no cure is needed.
References
External links
Urine
Inborn errors of carbohydrate metabolism | Pentosuria | [
"Chemistry",
"Biology"
] | 363 | [
"Carbohydrate metabolism",
"Urine",
"Excretion",
"Animal waste products",
"Inborn errors of carbohydrate metabolism"
] |
10,942,957 | https://en.wikipedia.org/wiki/Motexafin%20gadolinium | Motexafin gadolinium (proposed tradename Xcytrin) is an inhibitor of thioredoxin reductase and ribonucleotide reductase. It has been proposed as a possible chemotherapeutic agent in the treatment of brain metastases.
History
On May 9, 2006, a New Drug Application was submitted to the United States Food and Drug Administration (FDA) by Pharmacyclics, Inc.
In December 2007, the FDA issued a not approvable letter for motexafin gadolinium.
References
Organogadolinium compounds | Motexafin gadolinium | [
"Chemistry",
"Biology"
] | 124 | [
"Biochemistry stubs",
"Biotechnology stubs",
"Biochemistry"
] |
10,943,640 | https://en.wikipedia.org/wiki/Haploscope | A haploscope is an optical device for presenting one image to one eye and another image to the other eye. The word derives from two Greek roots: haploieides, single and skopeo, to view. The word is often used interchangeably with stereoscope, but it is more general than that. A stereoscope is a type of haploscope, but not vice versa. The word has more currency in the medical field than elsewhere, where it refers to instruments designed to test binocular vision. These instruments include Worth's amblyoscope and the synoptophore.
Commonly haploscopes employ front-surfaced mirrors placed at different angles close to the eyes to reflect the images into the eyes. Reputedly the largest haploscope, with images of over a meter (in fact, 4 feet) square and a viewing distance for each eye of nearly five meters (16 feet), was constructed by Vaegan in about 1975 to research stereoacuity. The large images allowed very small retinal disparities to be presented.
See also
Cheiroscope
Diplopia
Amblyopia
Orthoptist
References
External links
International Orthoptics Association
Orthoptics Association of Australia
Optical devices | Haploscope | [
"Materials_science",
"Engineering"
] | 257 | [
"Glass engineering and science",
"Optical devices"
] |
10,945,580 | https://en.wikipedia.org/wiki/Schwarz%20integral%20formula | In complex analysis, a branch of mathematics, the Schwarz integral formula, named after Hermann Schwarz, allows one to recover a holomorphic function, up to an imaginary constant, from the boundary values of its real part.
Unit disc
Let f be a function holomorphic on the closed unit disc {z ∈ C | |z| ≤ 1}. Then
for all |z| < 1.
Upper half-plane
Let f be a function holomorphic on the closed upper half-plane {z ∈ C | Im(z) ≥ 0} such that, for some α > 0, |zα f(z)| is bounded on the closed upper half-plane. Then
for all Im(z) > 0.
Note that, as compared to the version on the unit disc, this formula does not have an arbitrary constant added to the integral; this is because the additional decay condition makes the conditions for this formula more stringent.
Corollary of Poisson integral formula
The formula follows from Poisson integral formula applied to u:
By means of conformal maps, the formula can be generalized to any simply connected open set.
Notes and references
Ahlfors, Lars V. (1979), Complex Analysis, Third Edition, McGraw-Hill,
Remmert, Reinhold (1990), Theory of Complex Functions, Second Edition, Springer,
Saff, E. B., and A. D. Snider (1993), Fundamentals of Complex Analysis for Mathematics, Science, and Engineering, Second Edition, Prentice Hall,
Theorems in complex analysis | Schwarz integral formula | [
"Mathematics"
] | 323 | [
"Theorems in mathematical analysis",
"Theorems in complex analysis"
] |
10,945,642 | https://en.wikipedia.org/wiki/Wildlife%20of%20Algeria | The wildlife of Algeria is composed of its flora and fauna. Mountains, chotts, wetlands, and grassy desert-like regions all support a wide range of wildlife. The most commonly seen animals include the wild boars, jackals, and gazelles, although it is not uncommon to spot fennecs and jerboas. Leopards and cheetahs are seldom seen.
A variety of bird species make the country an attraction for bird watchers. Barbary macaques are the sole native monkey.
Flora
In the north, the native flora includes the Algerian oak, Atlas cedar, and other conifers. The grape vine is indigenous to the coast. In the Sahara region, some oases have date palms. Acacia with wild olives are the predominant flora in the remainder of the Sahara.
In Algeria forest cover is around 1% of the total land area, equivalent to 1,949,000 hectares (ha) of forest in 2020, up from 1,667,000 hectares (ha) in 1990. In 2020, naturally regenerating forest covered 1,439,000 hectares (ha) and planted forest covered 510,000 hectares (ha). Of the naturally regenerating forest 0% was reported to be primary forest (consisting of native tree species with no clearly visible indications of human activity) and around 6% of the forest area was found within protected areas. For the year 2015, 80% of the forest area was reported to be under public ownership, 18% private ownership and 2% with ownership listed as other or unknown.
Fauna
Mammals
There are 104 mammal species in Algeria, of which three are critically endangered, two are endangered, ten are vulnerable, and three are near-threatened. One of the species listed for Algeria is extinct and one can no longer be found in the wild.
Atlantic spotted dolphin
Caracal
Common dolphin
Rough-toothed dolphin
Orca
Pilot whale
Pygmy killer whale
Birds
North African ostrich
Guinea fowl
Egyptian vulture
Golden eagle
Bonelli's eagle
Griffon vulture
Loons
Grebes
Great crested grebe
Little grebe
European turtle dove
Shearwaters
Black stork
White stork
Petrels
Storm-petrels
Pelicans
Gannets
Cormorant
Bitterns
Herons
Egrets
Storks
Ibises
Spoonbills
Flamingos
Ducks
Geese
Swans
Osprey
Hawks
Kites
Eagles
Caracaras
Falcon
Pheasant
Partridge
Buttonquail
Crane
Rails
Crakes
Coots
Arabian bustard
Oystercatchers
Avocet
Stilt
Thick-knee
Pratincole
Courser
Plover
Lapwing
Sandpiper
Skuas
Jaegers
Gulls
Terns
Auks
Murres
Puffins
Sandgrouse
Pigeons
Doves
Cuckoos
Great spotted woodpecker
Eurasian wryneck
Ani
Barn owls
Typical owls
Nightjars
Swifts
Kingfishers
Bee-eaters
Starling
Reptiles
Algerian sand racer
Bedriaga's fringe-fingered lizard
Boomslang
Desert monitor
Egyptian cobra
Egyptian sand boa
Erycinae
European pond terrapin
False smooth snake
Greek tortoise
Horned desert viper
Iberian wall lizard
Lataste's viper
Leatherback turtle (in the Mediterranean Sea)
Loggerhead sea turtle (in the Mediterranean Sea)
Mediterranean chameleon
Mediterranean house gecko
Moorish gecko
Müller’s sand boa
Red-tailed spiny-footed lizard
Sahara sand viper
Saharan spiny-tailed lizard
Saw-scaled viper
Small-spotted lizard
Small three-toed skink
Southern smooth snake
Two-fingered skink
Viperine water snake
Amphibians
Brongersma's toad
Common toad
European green toad
Mediterranean tree frog
Perez's frog
Sahara frog
Algerian ribbed newt
Edough ribbed newt
North African fire salamander
Fish
Atlantic bluefin tuna
Atlantic blue marlin
Atlantic white marlin
European eel
Angular roughshark
Basking shark
Bignose shark
Blacktip shark
Blacktip reef shark
Bluntnose sixgill shark
Bramble shark
Dusky shark
Great hammerhead
Great white shark
Grey nurse shark
Gulper shark
Kitefin shark
Porbeagle
Sandbar shark
Scalloped hammerhead
Sharpnose sevengill shark
Shortfin mako
Spinner shark
Velvet belly lantern shark
Insects
Acilius duvergeri
Calopteryx exul
Chalepoxenus brunneus
Desert locust
Epimyrma africana
Epimyrma algeriana
Honey bee
Monomorium noualhieri
Onychogomphus costae
Pharaoh ant
Red locust
Strongylognathus afer
Strongylognathus foreli
Other invertebrates
Brine shrimp
Common octopus
Fat-tailed scorpion
See also
Algeria
Réghaïa forest
References
Biota of Algeria
Algeria | Wildlife of Algeria | [
"Biology"
] | 945 | [
"Biota by country",
"Wildlife by country",
"Biota of Algeria"
] |
10,945,768 | https://en.wikipedia.org/wiki/Wildlife%20of%20Angola | The wildlife of Angola is composed of its flora and fauna.
An atlas of the amphibians and reptiles of Angola was published in 2018, and reported 117 species of amphibians and 278 of reptiles.
A major book on the biodiversity of Angola was published in 2019, and reported more than 2,000 species of organisms (plants, invertebrates and vertebrate animals), and 1,313 fossil species.
Fauna
Mammals
Birds
The avifauna of Angola includes a total of 983 species, of which 14 are endemic, 1 has been introduced by humans, and 4 are rare or accidental. 20 species are globally threatened.
The western Angola Endemic Bird Area has 14 range-restricted species. Little is known about the conservation status of the region's birds due to the Angolan Civil War from 1975 until 2002. The greatest diversity of restricted-range species is found in Cuanza Sul Province, and given the uncertainty about their current status, many of these species are listed as threatened. Gabela bushshrikes (Laniarius amboimensis) are common and Monteiro's bushshrikes (Malaconotus monteiri) are fairly common in degraded secondary forest, old coffee plantations and primary forest at Kumbira. Pulitzer's longbills (Macrosphenus pulitzeri) are fairly common at higher elevations at Kumbira as well as in the dense understorey of secondary forest west of Seles. Angola cave chats ((Xenocopsychus ansorgei) are found on the rocky slopes above the forest at Kumbira.
Insects
Fish
Reptiles
There are currently 278 species of reptiles recorded in the country.
Amphibians
There are currently 117 species of amphibians recorded in Angola.
Flora
Angola had a 2018 Forest Landscape Integrity Index mean score of 8.35/10, ranking it 23rd globally out of 172 countries. In Angola forest cover is around 53% of the total land area, equivalent to 66,607,380 hectares (ha) of forest in 2020, down from 79,262,780 hectares (ha) in 1990. In 2020, naturally regenerating forest covered 65,800,190 hectares (ha) and planted forest covered 807,200 hectares (ha). Of the naturally regenerating forest 40% was reported to be primary forest (consisting of native tree species with no clearly visible indications of human activity) and around 3% of the forest area was found within protected areas. For the year 2015, 100% of the forest area was reported to be under public ownership.
The southern and central coasts include the welwitschia, a primitive conifer. The grassy savanna around Lobito includes baobab and euphorbia trees.
The Huambo, Benguela and Huíla provinces are home to montane forest with rare flora.
The grassy savanna in the north includes miombo woodland and some evergreen forest.
Notes
References
Biota of Angola
Angola | Wildlife of Angola | [
"Biology"
] | 600 | [
"Biota by country",
"Biota of Angola",
"Wildlife by country"
] |
10,945,900 | https://en.wikipedia.org/wiki/Wildlife%20of%20Botswana | The wildlife of Botswana refers to the flora and fauna of this country. Botswana is around 90% covered in savanna, varying from shrub savanna in the southwest in the dry areas to tree savanna consisting of trees and grass in the wetter areas. Even under the hot conditions of the Kalahari Desert, many species survive; in fact the country has more than 2500 species of plants and 650 species of trees. Vegetation and its wild fruits are also extremely important to rural populations living in the desert and are the principal source of food, fuel and medicine for many inhabitants.
Three national parks and seven game reserves stretch over 17% of Botswana's land area. The three national parks are the Chobe National Park, the Nxai Pan and Makgadikgadi National Park and the Kgalagadi Transfrontier Park. The seven game reserves are the Central Kalahari Game Reserve, Gaborone Game Reserve, Khutse Game Reserve, Mannyelanong Game Reserve, Maun Game Reserve and Moremi Game Reserve. In addition, a number of small privately owned reserves are maintained.
Geography
The Kalahari Desert, which extends on its western borders into South Africa, Namibia and Angola, is a flat terrain, which covers about 84% of Botswana, known by the epithet "thirstland". It is in fact covered by shrubland vegetation of trees, grasslands, scrub and thorny bushes. Apart from scattered hills and valleys, the dunes system of the southern part contains pans that fill with water during the rains, sustaining the wildlife with its nutrients and grasses.
National parks and wildlife reserves
Chobe National Park
Chobe National Park, with its four ecosystems, is known for its largest wildlife concentration in Africa and extends over an area of . Initially established as a reserve area in 1960 became the first gazetted national park in 1967. Chobe River valley forms the northeast part of the park and has thick forests and lush green plains. The marshland of Savuti forms the western zone. The hinterland is hemmed between the marshland of Savuti on the west and the Linyanti Swamps on its northwest. San people or the Basarwa were the original inhabitants of this land who were hunter gatherers. The park's elephant population is the largest in Botswana, and the animals' seasonal migratory route covers between the Chobe and Linyanti rivers. The body size of the elephants here is the largest. However, their ivory is brittle and their tusks are generally short. Some of the other faunal species seen here are sable, wildebeest, kudu, buffalo and waterbuck, apart from lion, hyena, jackal, bat-eared fox, cheetah and wild dogs. Also more than 500 bird species have been recorded in Chobe National Park.
Kgalagadi Transfrontier Park
Kgalagadi Transfrontier Park (KTP), a transboundary park between Botswana and South Africa, was the first conservation area to be set in the southern Kalahari Desert in May 2000. Out of a total area of , Botswana has control over while the balance is with South Africa. Two ecological zones of savannahs and grasslands of Africa in semi-arid environment, with least anthropological pressure, are represented here by ungulates and large carnivores mammals. The rich faunal and floral diversity has involved several research projects. Its approach from Goborone involves road travel over a distance of .
Makgadikgadi and Nxai National Park
The Makgadikgadi and Nxai National Park, which cover a large area of were established in the 1970s. They have complementarity in wild life migrations, which necessitated merging the two parks into a single entity. It has the pans of Ntwetwe, Makgadikgadi, Nxai, Baines' Baobabs and Kudiakam.
Moremi Game Reserve
Moremi Game Reserve is situated on the eastern side of the Okavango Delta and was named after Chief Moremi of the BaTawana tribe. Moremi was designated as a game reserve, rather than a national park, when it was created. This designation meant that the BaSarwa or Bushmen that lived there were allowed to stay in the reserve.
Khutse Game Reserve
Khutse Game Reserve established in 1971, covering an area of in Bakwena tribal land, has undulating topography of the bush savanna vegetation. It is sparsely populated due to poor water sources and wild life in the mineralised pan system within Khutse has been their major source of sustenance. The wild life of herbivore thrived on grass growing in the pans which in turn has attracted predators.
Central Kalahari Game Reserve
The Central Kalahari Game Reserve, the second largest reserve in Botswana covering an area of , is a habitat of open plains, salt pans and riverbeds. It has wooded mopane forests in the south and east. The indigenous people residing here since ancient times are known as bushmen or the Basarwa or San. Its fame is also due to its Deception Valley where the study of brown hyena (Parahyaena brunnea) has been carried out. Deception was the name given to the salt pans of the valley, which gave deceptive sight (mirage) of a water body from a distance. Tree Island used to be the main camping ground here. Cry of the Kalahari, a famous book made this a popular place. Wild animals such as giraffe, brown hyena, warthog, wild dog, cheetah, leopard, lion, blue wildebeest, eland, gemsbok, kudu, red hartebeest and springbok are seen in the pans and valleys, particularly during the period from December to April.
Communal and private game reserves
Khama Rhino Sanctuary
Khama Rhino Sanctuary was established in 1992, covering of Kalahari sandveld with Serwe Pan, primarily to protect the rhinos which at that time was listed subject to poaching causing fears of extinction. A community trust was established to protect the black and white rhino species left in the area. There are also 30 other animal species found in this area as well as over 250 bird species. There are many activities that can be taken place while at Khama Rhino Sanctuary these include, game drives, nature walks and rhino tracking. The sanctuary is a community trust governed by a board of trustees who are elected from the local communities of Serowe, Paje and . The President of Botswana, Seretse Khama Ian Khama, Paramount Chief of the Bamangwato, is patron of the trust.
Mokolodi Park
Mokolodi Park spreads over a area, is a park maintained by the Mokolodi Wildlife Foundation, a private organization, near Gaborone. Its ecosystem has, as result of restocking efforts, witnessed proliferation of many species of wildlife like white rhino, cheetah, mountain reedbuck, giraffe, zebra, red hartebeest, sable, gemsbok, which coexists along with the indigenous fauna such as kudu, impala, hyena, leopard and water buck. The park is developed as nature reserve with extensive network of jeepable (4x4) paths, which permits viewing the wild life at close quarters. The park administration is planning to expand its limits of conservation area up to the Lion Park opposite to Crocodile Pools.
Northern Tuli Game Reserve
The Northern Tuli Game Reserve is a private reserve covering an area of made up of savannah plains, riverine forests, open marshland and rugged outcrops of sandstone. It is the largest private reserve in Southern Africa. It has the largest elephant population in the world. In addition, more than 350 species of birds have been reported here. Other fauna of Botswana are also commonly found here.
Wildlife management areas
Wildlife management areas (WMAs) are areas where wildlife utilization is controlled by law. The WMAs often function as buffer areas around wildlife reserves, since most wildlife populations spend extended periods outside of the sanctuaries. The concept was developed in the 1980s. Its purpose is to prevent transformation of land, where wildlife is used commercially, into agricultural land, where wild animals are persecuted or even eradicated. Proposals have been made for 12 WMAs, one of them was rejected by district authorities.
Flora
In Botswana forest cover is around 27% of the total land area, equivalent to 15,254,700 hectares (ha) of forest in 2020, down from 18,803,700 hectares (ha) in 1990. In 2020, naturally regenerating forest covered 15,254,700 hectares, of the naturally regenerating forest 0% was reported to be primary forest (consisting of native tree species with no clearly visible indications of human activity) and around 11% of the forest area was found within protected areas. For the year 2015, 24% of the forest area was reported to be under public ownership and 76% private ownership.
Floral diversity of vegetation in Botswana, which receives only an average annual rainfall of about only, is generally defined under three broad heads namely, hardveld, sandveld and Okavango deltaveld which show seasonal difference in its nutrition value, with woody plants recording higher values compared to the grasses; Panicum has recorded more nutritional content during the rainy season.
Hardveld vegetation consists of woody plants and grasses. The woody plants are; Acacia karroo, Albizia anthelmintica, Balanites aegyptiaca, Mopane (Colophospermum mopane), Combretum apiculatum, Grewia bicolor, Grewia flavecens, Grewia monticola, Lonchocarpus capassa and Terminalia.
Sandveld of the Kalahari desert's vegetation expanse consists of grasses, namely Kragrostis pallens, Striagostis uniplumis, Anthephora pubescens, Schmidtia pappophoreides and Megaloprotachne albescens. Woody plants recorded are the Grewia avellana, Grewia retinervis, Lonchocarpus nelsii and Terminalia sericia.
Okavango deltaveld has both grasses and woody plants. The woody plants are the Ficus verruculosa and the Hyphaene crinata. The grasses reported are the Phragmites communis, Dichanthium papillusum, Panicum repens, Andropogon encomus, Echinochloa pyramidalis and Imperata cylindrica.
Ninety percent of Botswana is savanna. Small areas of forest exist, but only in the far north along the Chobe River. Gruff shrubland tends to grow in the dryer desert areas, whilst trees tend to grow in the swamps, particularly in the Okavango delta which have access to more water to thrive. Botswana is home to over 2500 species of plants and over 650 species of trees.
Trees
Common trees are the mopane, baobab, marula, acacia, camel thorn, motopi (shepherd's tree), wild date palm, papyrus, sycamore fig tree, real fan palm, African mangosteen and the sausage tree. The trees tend to grow in areas with a plentiful supply of water, such as in the Okavango Delta swamps.
The baobab tree, known as mowana in the Setswana language are some of the long living trees in Botswana and may grow older than 2000 years. The bark is characteristically pinkish-grey in color, with a shiny tint. Large white flowers, averaging about 12 cm across and appear between October and December, whilst the greyish-brown fruits which average about 24 cm in length appear in April–May.
The marula or morula tree, belonging to the mango family Anacardiaceae, grows to an average of 15 meters (and up to 20 meters) in the Okavango Delta in bushveld and woodland, and has a greyish bark and is deciduous. From January to July, the leaves are grey-green but eventually turn pale yellow and fall off in the latter part of the year during the winter. During the summer months the trees exhibit round to oval fruit, rich in Vitamin C, with a thick peel covering white slippery pulp, which like the leaves turns increasingly yellow at the end of the blooming season. It also bears flowers, pinkish with male and red-purple and white with female.; the male tends to be larger and borne on sparse drooping racemes.
Wild date palm is one of only two species of palm tree which occur on the Okavango Delta, the other being the real fan palm. The palm, an evergreen, tends to reach a height of around and grows in abundance in the swamps in Botswana, along with the papyrus. It exhibits feather-shaped leaves, as compared to the fan-shaped leaves of the real fan palm. The leaves typically grow to about in length with some soft basal leaflets and others which are dark green and rough in appearance. Male florets of the tree are pale dirty-yellow and caduceus and male florets are smaller, globose and have a greener bluer coloring.
The sycamore fig tree is one of the largest trees growing in Botswana, typically found in the Okavango delta growing up to 20 metres. A semi-deciduous tree, it has a deeply fluted stem with bright orange bark and grows figs up to 3 cm in diameter which eventually turn pale red to red when mature from green and peak between July and December.
The deciduous water-thriving African mangosteen in Botswana can grow up to in height, identifiable by its bare, evenly sectioned yellowish-grey stem which stands out against its dense, very dark crown. The bark is grey in color and the tree sports dark green, shiny leathery leaves averaging by , with a yellow veining are diagnostic. The fruit which the tree bears is oval and of a pinky-orange color, about in diameter on average and appears from November to February.
The mmilo tree, the species Vangueria infausta of the family Rubiaceae grows is a small deciduous shrub occurring in wooded grassland and bushveld, particular in rocky areas. It exhibits a yellowish-brown drupe, subglobose edible fruit, up to in diameter of which the seed is often obtained to create a dish called nchwachwa during the dry winter season.
The species Kigelia africana of sausage tree grows in the Okavango Delta, especially in the Xakanaxa, Third Bridge and Mboma Island areas, and can reach heights of up to , making it amongst the tallest trees in Botswana. It is noted for its fruits which resemble oversized sausages and can weigh up to 4–5 kg and up to long and in diameter. The bark is grey and smooth in younger trees and may exhibit leaves up to long and dark red to maroon cup-shaped flowers measuring 15 by 15 cm, which bloom in August to October.
Fauna
Eight bird species, out of the 593 reported, are considered globally threatened. The eastern cattle egret (Bubulcus coromandus, syn. Bubulcus ibis coromandus) is the national bird of Botswana.
Mammals
Mammals found in Botswana include aardwolf, African bush elephant, African civet, African golden cat, African striped weasel, banded mongoose, bat-eared fox, black-footed cat, blue duiker, bongo (antelope), brown hyena, Burchell's zebra, bushbuck, African buffalo, Cape fox, Cape hyrax, Cape wild dog, caracal, South African cheetah, common duiker, common eland, gemsbok, giant sable antelope, Angolan giraffe, greater kudu, ground pangolin, hartebeest, hippopotamus, impala, Kirk's dik-dik, klipspringer, lechwe, African leopard, lion, mountain zebra, oribi, roan antelope, sable antelope, serval, Sharpe's grysbok, sitatunga, southern reedbuck, south-central black rhinoceros, spotted hyena, springbok antelope, steenbok, topi, common warthog, waterbuck, wildebeest, yellow-backed duiker, yellow mongoose, marsh mongoose and meerkat.
Birds
The twelve important ornithological sites selected in Botswana of which seven are wetlands and which are recognized and supported by the BirdLife International known for their bird life cover more than 25% of the land surface of the country. These parks are: The Chobe National Park; the Linyanti Swamp along the Chobe River; the Okavango Delta, the Lake Ngami; the Makgadikgadi Pans; the Central Kalahari; the Manyelanong Hill; the Tswapong Hills; the Boka Dam; the Phakalane Sewage Lagoons; the Southeast Botswana; and the Gemsbok National Park. An initiative started by the IBA is of setting up 'Site Support Groups' (SSGs), an organised group of local people with the objective to "sustain biodiversity to sustain livelihoods in rural Botswana"; there are 150 SSGs in important bird areas reported to be functioning throughout Africa. Red-footed falcon (Falco vespertinus), amur falcon (Falco amurensis) and barn swallow (Hirundo rustica) and Cape vulture (Gyps coprotheres) are some of the birds reported by IBA from the grasslands, wetlands, hills, in areas of Kalahari Highveld, deltas and around lakes created by dams.
The Botswana Bird Club (BBC) established in 1980, now renamed as BirdLife Botswana promotes ornithological knowledge and interest and also publishes a biannual journal called The Babbler and a quarterly newsletter known as The Familiar Chat dealing with all issues of bird conservation, research and training in Botswana.
Manyelanong Game Reserve's small cliffs protect a breeding colony of Cape vultures, the largest such colony in Botswana and hence called the "Otse Vulture Colony" as its vultures are an endangered species protected by law. Protection has enabled the species to proliferate; its numbers in recent years are 70 breeding pairs seen in the colony.
Nata Bird Sanctuary
Nata Bird Sanctuary, established in the early 1990s, is situated to the far northeastern edge of Sowa Pan. It encompasses an area of and maintained as a community project to preserve its 165 bird species. Some of the species reported are the kingfishers, bee-eaters, eagles, bustards and ostriches. Water birds of Africa flock to this place during winter; the bird species reported are teals, ducks, geese, pelicans, spoonbills, greater flamingo and lesser flamingo. The flamingos and pelicans also breed here.
Molluscs
From 1854 to 2023, 63 native species of molluscs (13 bivalves, 24 freshwater snails, 24 land snails and two slugs) have been recorded in 43 genera and 21 families. There are also four introduced species: Cornu aspersum, Lissachatina fulica, Physella acuta and Radix auricularia, which are potentially invasive and of economic concern. The majority of species occur in the regions of the Okavango Delta and the Chobe–Linyanti–Kwando river system along East Caprivi
Butterflies and moths
There are some 370 species of Lepidoptera recorded in Botswana, with over 250 species of butterflies and 115 species of moths.
Gaborone Game Reserve
Gaborone Game Reserve, near the city of Gaborone, has a small area of but provides for popular viewing along roads. It has plenty of birds and wild life in its precincts The reserve is habitat of thorn scrub and woodland to riverine forest and marshland which attracts a wide variety of birds such as raptors a snake eagle, crimson boubou (a genus of brightly coloured, carnivorous passerine bird) and gallinule. Faunal species seen here are the rhino, impala, kudu, ostriches, wildebeest, zebra, gemsbok, bushbuck, springbok, duiker the giant eland (Taurotragus derbianus also known as the Lord Derby eland), which is Africa's largest antelope.
Moremi Game Reserve
Moremi Game Reserve, established in 1965 and expanded over the years and now covering an area of , it is the habitat of mopane woodland and acacia forests, floodplains and lagoons. It is said to be one of the most beautiful reserves in Africa maintained by the Department of Wildlife and National Parks. Birdlife in the park is wide and of varied species; water birds to shy forest dwellers are commonly seen. Other wild life fauna such as elephants, hippos (found in large number in the Hippo Pool), a few rhino and the red lechwe. Moremi is also particularly well known for its African wild dog sightings.
References
External links
Biota of Botswana
Botswana | Wildlife of Botswana | [
"Biology"
] | 4,405 | [
"Biota by country",
"Biota of Botswana",
"Wildlife by country"
] |
10,945,926 | https://en.wikipedia.org/wiki/Wildlife%20of%20Burkina%20Faso | Burkina Faso is largely wild bush country with a mixture of grass and small trees in varying proportions. The savanna region is mainly grassland in the rainy season and semi desert during the harmattan period (defined as the period when stormy and dusty Sahara winds blow dry and hot). Fauna, one of the most diverse in West Africa, includes the elephant, hippopotamus, buffalo, monkey, lions, crocodile, giraffe, various types of antelope, and a vast variety of bird and insect life. The country has 147 mammal species, 330 aquatic species including 121 species of fish and 2067 different plant species. Of the plant species, the dominant endemic species are shea tree (Butyrospermum parkii) and the baobab, the former plant species has immense economic value to the country.
To ensure conservation and preservation of the wildlife of Burkina Faso, four national parks have been established. These are the Po National Park in the south-centre of the country, Arli National Park established in 1954 in the southeast, W of the Niger National Park, a trans frontier park existing since 1957 in the east bordering Benin and Niger and the Deux Balés National Park. The forests, fauna and fish have been declared part of the national estate of Burkina Faso. In addition, the List of national parks of Burkina Faso consist of one UNESCO Biosphere reserve, three complete reserves, six partial reserves and ten protected forests. However, according to conservation classification conducted between 1936 and 1957, the country has 78 protected areas that cover , which accounts to about 14% of the area of the country.
Geography
Wildlife area in the landlocked Burkina Faso in western Africa is spread over a plateau area of . The dominant habitat types are the grassy savanna in the north with transition to the varying thin forests in the south. In Burkina Faso forest cover is around 23% of the total land area, equivalent to 6,216,400 hectares (ha) of forest in 2020, down from 7,716,600 hectares (ha) in 1990. In 2020, naturally regenerating forest covered 6,039,300 hectares (ha) and planted forest covered 177,100 hectares (ha). Of the naturally regenerating forest 0% was reported to be primary forest (consisting of native tree species with no clearly visible indications of human activity) and around 16% of the forest area was found within protected areas. For the year 2015, 100% of the forest area was reported to be under public ownership.
Based on ecological characteristics and climatic conditions, the country is divided under three bio-climatic zones namely, the Sahelian Zone, the Sudanian Zone and the Sudano-Guinean Zone. The Sahelian Zone covers 25% of the area of the northern part of the country, which is further subdivided under the Sahelian and sub-Sahelian sectors. In the Sahelian sector, where the rainfall is only of the order of , the vegetation is mostly of shrubs and wooded grassland or steppe. The sub-Sahelian sector represents the transition zone, receives an average annual rainfall of and represents the transition between the Sahelian and Sudanian bioclimatic zones. The vegetation in this sector has moist Sudan savanna vegetation in the river valleys, while the western half is largely inhabited by humans; most of the large trees in the northern half of the sector are reported to have vanished due to climate change. The Sudan Zone receives higher rainfall in the range of and is further subdivided into three sectors namely, the central plateau sector, the Mouhoun sector and the Pendjari–Mékrou sector and has widely varying vegetation depending on human occupation for agriculture and mostly savanna vegetation, predominantly wooded savanna. the Pendjari–Mékrou sector with its floodplains and many ephemeral rivers, is less populated by humans but has the largest population of mammals in the country; vultures and raptors are also reported. The Sudano-Guinean Zone in the southwest corner of the country is a humid zone with an annual rainfall in the range of . It is heavily wooded with wooded savannas and gallery forests; it has the ambience of a park with its widespread vegetation of Khaya senegalensis, Daniellia oliveri and Isoberlinia forests, tall grasses and savanna vegetation is also a dominant feature. Its human population distribution is low but the wildlife population is the second largest in the country.
The area is drained by many rivers, the most important of them being the Black Volta (Mouhoun), the Red Volta (Nazinon), and the White Volta (Nakambé), which flow into Ghana on the south and form the Volta River.
Climate
Rainy season (June to September) is one of the four seasons in Burkina Faso; the other three being, an intermediate season from September to mid November, the summer of harmattan season of the Sahara hot and stormy winds (mid February to mid June) and the dry and winter cool season from mid November to mid February. During the rainy season is when the shrubs and stunted trees flourish in the savanna in the northern region where rainfall incidence is about 10 inches and the rivers flow full with dense vegetation growing in the southern region of the country when the rainfall incidence is as high as .
National Parks
There are four important national parks in Burkina Faso namely, the Arli National Park existing since 1954, the Deux Balés National Park, Kaboré Tambi National Park and the W of the Niger National Park which is a trans-boundary park existing since 1957.
Arli National Park
The Arli National Park, covering an area of , lies to the southwest of Arli–W–Singou complex. It borders with Benin (the Pendjari River forms the boundary) and Singou Game Ranch on its northwest direction and has large network of drainage system which has vast flood plains. Within the park boundary, the Falaise de Gobnangou is a prominent hill feature with cliffs that extends over from the southwest to the northeast. The park also has many inselbergs. Shrub and tree-savanna (extensive growth of Isoberlinia doka) in the non-flooded areas, Mitragyna inermis with gallery forests in seasonally flooded areas, baobab Adansonia digitata trees near old village sites are some of the vegetation types found in the park.
Deux Balés National Park
The Deux Balés National Park, is located in central eastern Burkina Faso, within Mouhoun Province. It is situated to the west of the Black Volta River. It has an elevation range of . The park was first established in 1937 as the forêts classées des Deux Balés ('the Deux Balés Classified Forests') with an area of . In 2001, the largest number of elephants in West Africa were found in Deux Balés (together with Baporo Forest), estimated at four hundred of them.
Kaboré Tambi National Park
The Kaboré Tambi National Park is situated between Ouagadougou and the border with Ghana. It follows the course of the Nazinon River. It was founded in 1976 as Pô National Park or known as Parc National Kaboré Tambi (PNKT). The park has an area of in the alluvial floodplain on both banks of the ephemeral Volta Rouge River; the river results to small water holes during the summer season. A number of small marshes and lakes also dominate the scene. It maintains contiguity with the Nazinga Game Ranch of area, the Sissili Hunting Concession of ha and the village hunting zones around Nazinga and Sissili villages. The park has varied topography with geological formations of granite outcrops, lateritic plateaus and several isolated high mountains. The vegetation types found here are northern Sudan savanna, shrub savanna, tree-savanna and gallery forests. The park is home to lion, elephant, buffalo and a number of antelope species. Poaching and deforestation activities are an issue in the park. The main road from Ouagadougou to Bolgatanga in northern Ghana runs across the park.
W of the Niger National Park
The W of the Niger National Park was created in August 1954. It is a major national park of the three countries of Niger, Benin and Burkina Faso, and is governed by the three governments. It is around a meander in the River Niger shaped like a "W". Until 2008, the implementation of a regional management was supported by the EU-funded Project ECOPAS (French: Ecosystèmes Protégés en Afrique Soudano-Sahélienne). The three national parks operate under the name W Transborder Park. In the three nations, the park covers about , largely uninhabited by humans, having been until the 1970s a malarial zone of wetlands formed by the delta of the Mékrou River with the Niger, broken by rocky hills. It was declared a Ramsar site in 1990. A cattle route from Mail and Niger to Tago passes through the park creating conservation problems which are proposed to be tackled through many conservation and biodiversity support programmes.
Fauna
As of 2006, Burkina Faso is considered to be one of the West African countries with the largest faunal population.
Mammals
Mammals in Burkina Faso include aardvark, African bush elephant, African civet, African clawless otter, African golden cat, African ground squirrel, West African wild dog, western dwarf buffalo, bushbuck, Cape hare, Cape hyrax, caracal, Northwest African cheetah, common chimpanzee, common genet, Dorcas gazelle, fennec fox, four-toed hedgehog, giant pangolin, West African giraffe, Egyptian wolf, Hausa genet, hippopotamus, African leopard, West African lion, olive baboon, oribi, pale fox, patas monkey, honey badger, red-fronted gazelle, reedbuck, roan antelope, rusty-spotted genet, Senegal bushbaby, serval, side-striped jackal, slender mongoose, speckle-throated otter, spotted hyena, striped hyena, striped polecat, sun squirrel, tree pangolin, warthog, water chevrotain, western hartebeest, white-tailed mongoose and African wildcat.
The common chimpanzee is considered locally extinct in Burkina Faso, but may be migrating back into the country during the rainy season. Hyena are widespread but at low densities.
Reptiles
Three crocodile species are found in the wild, slender-snouted crocodile, Nile crocodile, and dwarf crocodile. According to BirdLife International, there are 119 migrant birds which visit the country out of which 81 belong to Palaearctic species including two species namely Falco naumanni (vulnerable) and Gallinago media (near threatened) of global conservation concern. There are also 10 Important Bird Areas (IBAs) identified which cover 20260 km2 accounting for 7.4% area of the country.
Birds
In Burkina Faso, as of 2005, 497 bird species of various families, including 35 rare or accidental species, 12 near threatened species, three vulnerable species (lesser kestrel Falco naumanni, white-headed vulture Trigonoceps occipitalis and Beaudouin's snake-eagle Circaetus beaudouini) and one endangered species (Egyptian vulture Neophron percnopterus) have been reported. These cover species under several families such as: thirteen of Anatidae, one of Numididae (helmeted guineafowl Numida meleagris), six of Phasianidae, one of Podicipedidae, two of Ciconiidae, one of Anhingidae (African darter Anhinga rufa), one of Pelecanidae (great white pelican Pelecanus onocrotalus), one of Scopidae (hamerkop Scopus umbretta), seventeen of Ardeidae, five of Threskiornithidae, one of family Pandionidae (osprey Pandion haliaetus), thirty-nine of Accipitridae (mostly eagles, vultures and hawks), one of Sagittariidae (secretary-bird Sagittarius serpentarius), eleven of Falconidae, nine of Rallidae, one of Rallidae (African finfoot Podica senegalensis), six of Otididae, one of Gruidae (black crowned-crane Balearica pavonina), three of Burhinidae, eleven of Charadriidae, two of Recurvirostridae, two of Jacanidae, eighteen of Scolopacidae, two of Turnicidae, five of Glareolidae, one of Rostratulidae (Greater painted-snipe Rostratula benghalensis), eight of Laridae, two of Pteroclidae, thirteen of Columbidae, two of Psittacidae, two of Musophagidae, twelve of Cuculidae (cuckoos), one of Tytonidae (barn owl Tyto alba), eight of Strigidae, eight of Apodidae, one of Coliidae (blue-naped mousebird Urocolius macrourus), one of Trogonidae (Narina trogon Apaloderma narina), nine of Alcedinidae, eight of Meropidae, five of Coraciidae, one of Upupidae (Eurasian hoopoe Upupa epops, two of Phoeniculidae, four of Bucerotidae, four of Lybiidae, two of Indicatoridae, two of Indicatoridae, nine of Picidae, three of Platysteiridae, two of Prionopidae, nine of Malaconotidae, two of Campephagidae, nine of Laniidae, two of Oriolidae, three of Dicruridae, two of Monarchidae, three of Corvidae, one of Nicatoridae (western nicator Nicator chloris, nine of Alaudidae, seventeen of Hirundinidae, one of Stenostiridae (African blue-flycatcher Elminia longicauda), one of Paridae (white-shouldered black-tit Parus guineensis), two of Remizidae, one of Certhiidae (spotted creeper Salpornis salvadori), two of Pycnonotidae, four of Phylloscopidae, six of Acrocephalidae, twenty of Cisticolidae, one of Hyliotidae (yellow-bellied hyliota Hyliota flavigaster), twenty-seven species of Muscicapidae, three of Turdidae, three of Timaliidae, one of Zosteropidae (northern yellow white-eye Zosterops senegalensis), nine of Sturnidae, one of Buphagidae (yellow-billed oxpecker Buphagus africanus), eight of Motacillidae, four of Emberizidae, three of Fringillidae, three of Passeridae, nineteen of Ploceidae, nineteen of Estrildidae and six of Viduidae.
Ten Important Bird Areas (IBAs) which cover about (7.4% of the area of the country). These have Sudan–Guinea Savanna biome (A04) (with 30 of the 32 species of this biome), Sahel biome (A03) (with six of eight biome species) and with breeding colony of Gyps rueppellii in the Arli–W–Singou Park complex (accounting for more than 1% of the global population of the species). The number of resident bird species is reported by BirdLife International as 318, out of which 119 are migratory birds. Of the migratory birds, 81 belong to Palaearctic family and two species are of global conservation concern, namely Falco naumanni (vulnerable) and Gallinago media (near threatened).
Insects
Lepidoptera
Flora
The flora of Burkina Faso is composed of 2067 plant species. The most important families in terms of species richness and abundance are the grasses (Poaceae) and legumes (Fabaceae). Many species are distributed widely in the savannas regions of Africa. There are however two endemic plants, Pandanus brevifrugalis and Isoetes jaegeri.
Approximately 15% of the country has forest cover while wooded land constitutes approximately 34% of the area. Very little closed forest can be found and this is mainly of the gallery forest type along waterways. The open forests include savanna of four types, namely Sahelian, Sahelian-Sudanian, Sudanian, and Sudanian-Guinean. Though much of the country is dry and sparse, vegetation can vary considerably. Northern Burkina Faso consists mainly of savanna, acacia woodland, and during the wet season, prickly shrubs and stunted trees flourish. Herbaceous plants include broadleaf deciduous, shrub, desert shrub, semi-desert savanna and thorny scrub. Crops include banana, cassava, bougainvillea, cotton, guava, maize, spinach, Malabar spinach, millet, onions, papaya, sorghum, tomatoes, and yams. Most of the country consists of sparse savanna grasslands, with the occasional shrub or acacia. Although the country only has about 15% forest cover overall, there are many forests in the south, growing denser along the banks of the perennial rivers. These include Diéfoula Forest, Logoniégué Forest, Laba Forest, Dida Forest, Koulbi National Forest, Bontioli Reserve Forest, Nabere Partial Reserve Forest, Koflandé Forest, Maro Forest, Tui Forest, Deux Balés Forest, Kalio Forest, Tisse Forest, Dibon Forest, Pâ Forest, Mou Forest, Boulon Forest, Tigo Forest, Nakambe Forest and Niangoloko Forest, of which about 16% have official protection.
Poverty means that deforestation is a problem in the country and each year the country loses approximately 32,000 hectares of forests, to make way for agriculture and for fuelwood, which around 90% of the national population are dependent upon. Numerous NGOs are active in the country, educating farmers and encouraging them to minimize land clearing and plant trees as well as cultivate the land.
Trees of note include the shea tree (known as karité in the local Dioula language and the baobab. Although the shea tree is indigenous to the semi-arid Sahel region of West Africa, Burkina Faso contains the largest number of them. The shea tree is extremely important to the Burkinabe people and is termed as "women's gold" by the villagers, because the nuts of shea tree can be collected and then processed by crushing and grinding to yield shea butter, important in cuisine and in exports, for use in the manufacture of chocolate and cosmetics such as soap. Shea nuts are the country's third most important export, after cotton and livestock; in 1997, an average tonne of unprocessed shea nuts sold domestically for CFA70,000 (US$980) and overseas for CFA1,00,000 (US$1400). The most important centres of shea butter production are in Sissili Province and Ziro Province. The bark of the tree is also used as an ingredient in traditional medicines and the shell of nut is said to be able to repel mosquitoes and is also said to protect existing trees. The Bambara groundnut (Vigna subterranea) is also grown in abundance; Burkina Faso produced some 20,000 tonnes in 1989, after peanuts (160,000 tonnes) and cowpeas (74,000 tonnes). Between 1982 and 1985, an attempt was made to improve the Bambara groundnut, an initiative which involved the participation of plant breeders in the Grain Legumes Programme.
The country contains populations of Vitellaria paradoxa trees, which often have problems with parasites of the family Loranthaceae.
Four species of Tapinanthus (Tapinanthus dodoneifolius, Tapinanthus globiferus, Tapinanthus ophiodes and Tapinanthus pentagonia) are widespread all across Burkina Faso and Mali and are also subject to being affected by pests. Other trees include Acacia, flamboyant tree, Delonix regia, and neem tree.
Conservation
Fauna conservation areas were first established in 1926, which included five 'parcs de refuge' that covered 536,700 ha.
Global Environment Facility (GEF) in its report to the World Bank to promote conservation of natural habitat in Burkina Faso reported that the biodiversity species profile of Burkina Faso contains "655 wildlife species (mammals and birds); 330 aquatic species (includes 121 fish species), and 1054 plant species (751 grass, 304 tree and brush species)", based on meagre data. It was also noted that the natural habitats were found now only in parks, reserves and gazetted forests as agricultural operations dominated the scene in 70% area of the country. The oryx, cheetah, and giraffe are reported to be totally extinct, probably includes Burkina redneck ostrich. The nearing extinction species were reported to be black and white colobus, dama gazelle, leopard and topi. This alarming situation of loss of biodiversity resulted in creation of national operational strategies not only for rural development in 2001 but also for reforms in the wildlife and protected area sector in 1995 (a Forestry Code was introduced defining the National Forestry Policy and establishing 12 Wildlife Conservation Units covering the entire country in followed in 1996) and Biodiversity Strategy and Action Plan in 2000 with the objective stated as to "ensure responsible management of biological diversity by the populations by 2025".
In conservation and sustainable resources management efforts, the IBA Local Conservation Group with help from BirdLife Partners around the world have set up "site support groups" in Burkina Faso, which was initially begun in 1959 to count birds. This resulted in the training of local volunteers as ornithologists. In 2009, Vogelwacht Utrecht, a Dutch regional volunteer birding group, supported efforts conserve migratory birds. Cambridgeshire Bird Club in the UK has also pitched in with support. However, all these efforts are concentrated at Lake Oursi (included in the List of Ramsar wetlands of international importance) and are yet to permeate to a national scale.
References
External links
United Nations Environment Programme World Conservation Monitoring Centre
Further information
Biota of Burkina Faso
Burkina Faso | Wildlife of Burkina Faso | [
"Biology"
] | 4,671 | [
"Biota by country",
"Biota of Burkina Faso",
"Wildlife by country"
] |
10,946,048 | https://en.wikipedia.org/wiki/Wildlife%20of%20Burundi | The wildlife of Burundi is composed of its flora and fauna. The small, landlocked country is home to 2,950 species of plants, 596 birds, 163 species of mammals, 52 species of reptiles, 56 species of amphibians, and 215 fish species. The wildlife has been drastically reduced in recent years, mainly on account of intense population pressure, conversion of large areas of forest into agricultural land, and extensive livestock farming. The protected area encompasses little more than 5% of the total area of the country.
Legal status
With one exception, there were no national laws on conservation of wildlife during the colonial rule of Belgium nor any national parks established. The exception was a forest reserve, established in 1933. Before 1980, little action was taken to protect wildlife. The first Act issued was Decree No. 1/6, dated 3 March 1980, under which national parks (parc nationaux) and reserves were proposed to preserve and conserve wildlife. Under this decree, forest boundaries were to be defined. The Forest Code of 25 March 1985 was an enabling law under which protected forest areas were decreed, and reserve areas were specified. A national institute for conservation was established, the National Institute for the Conservation of Nature, under the decree of March 1980; now renamed as the National Institute for Environment and Conservation of Nature. It has the responsibility to establish national parks and reserves. It also undertakes scientific research in flora and fauna as well as promoting ecotourism.
Habitat
The wildlife habitat of Burundi, spread over its 15 provinces, is effected by the moderate tropical climate, dominated by variation in elevation. An average annual temperature of is recorded in the plateau region while the Rift Valley records a temperature of . Dry season lasts from June to August and again from December to January. The rainy season is from October to December with annual rainfall varying from ; Bujumbura, the largest city and former capital, has an average rainfall of . The western mountain region receives an average rainfall of ; the eastern plateaus, however, receive an annual rainfall in the range of . The country is dominated by hilly plateaus. The elevation in the plateau varies from with the decreasing trend recorded towards the east and southeast of the country. Its biodiversity is broadly categorized under the terrestrial ecosystems, and the aquatic and semi-aquatic ecosystems. The western area of the country is narrow and borders Lake Tanganyika, formed by the trough of the Rift Valley and the Rusizi River (formed by the border with DR Congo). The western region of the country is formed by the hilly terrain of the Congo-Nile Divide, with many hills lying above elevation; the highest mountains are Mount Teza at and Mount Heha at . The central plateau (about in elevation) forms the middle part of the country. In the southeast, the Malagarasi River flows through the Kumoso depression and borders Tanzania. The northern part of the country is formed of lowland in the Bweru Bugesera region and has two lakes, Cohoha and Rweru; this region is distinct for its Cyperus papyrus vegetation. The forest area is limited to , and the wetlands account for (about 5% of the total area of the country). The montane forest, which occupied nearly 33 to 50% of the country in the past, is mostly denuded and only a patch of of closed forest is recorded on the banks of Lake Tanganyika. Lake Tanganyika, the second-deepest lake in the world, has a water spread of only 8% in Burundi. Other rivers are the Malagarisi and the Ruvuvu. Ruviyaronza, an upper branch of the Kagera River, is the head stream of the Nile which rises in Burundi. The river systems of the country fall under the two main hydrographical basins of the Nile and the Congo Basin. The dominant vegetation that encompasses most of the habitats is of savanna. Acacia, eucalyptus, and oil palm trees are common.
Protected areas
There are three national parks in Burundi:
Kibira National Park is in size and contains the country's largest rainforest and borders Rwanda's Nyungwe National Park.
Ruvubu National Park covers , making it the largest park in the country. It is known for its hiking trails and has expansive views.
Rusizi National Park covers , from Bujumbura (the former capital of Burundi). It is wetland, with hippos, sitatunga (aquatic antelopes) and many species of birds. Declared a national park in 1990, it is situated in the flood plains of the Rusizi River in the outer limits of Bujumbura.
Apart from the national parks, there are four reserves:
Lac Rwihinda Nature Reserve –
Bururi Forest Nature Reserve – (which has the last vestiges of montane forest in the country)
Rumonge Nature Reserve –
Kigwena Forest Nature Reserve –
In addition, there are two natural monuments: Chutes de la Kagera and Nyakazu Gorge.
Flora
The flora is characterized by East African evergreen bushland and secondary grassland, as well as Afromontane vegetation including transitional rainforests in the western mountain region. Hyphaene–Acacia and Brachystegia trees are noted in the lake shores. The Brachystegia–Julbernardia (miombo) trees are seen in south-eastern border area. The Bugesera region in the north and the Kumoso depression on the east have profuse vegetation of Acacia–Combretum trees, and Brachystegia trees. The vascular flora reported is of 2,950 species under 195 families. In the high altitude in particular many species of wild flora are reported to be endemic; 70 species of plants are reported in this category.
Fauna
There are 163 species of mammals, 52 species of reptiles, 56 species of amphibians and 215 species of fish. It is also reported that at high altitudes, endemicity is distinct in 17 species of mammals and 22 species of birds. Lake Tanganyika has 200 species of fish and an equal number of molluscs. A scientific exploration team of the University of Texas at El Paso found the Bururi long-fingered frog (Cardioglossa cyaneospila) (considered extinct for decades), in December 2011 in the Bururi Forest Nature Reserve, after it was last seen in 1949. Seven important species of fauna reported are Genetta piscivora (aquatic genet), Serinus mozambicus (yellow-fronted canary), Cercopithecus lhoesti (L'hoest's monkey), Agapornis fischeri (Fischer's lovebird), Galago moholi (South African galago), Hyperolius viridiflavus, and Hippopotamus amphibius (hippopotamus).
The species reported under endangered and vulnerable categories (as per the IUCN's 2004 Red List) are the following: chimpanzee (Pan troglodytes) (EN), African wild dog (Lycaon pictus) (EN), African golden cat (Profelis aurata) (VU), Carruther's mountain squirrel (Funisciurus carruthersi) (VU), cheetah (Acinonyx jubatus) (VU), lion (Panthera leo) (VU), Ruwenzori shrew (Ruwenzorisorex suncoides) (VU), and spotted-necked otter (Lutra maculicollis) (VU).
Mammals
There are four subspecies of the African buffalo (Syncerus caffer), of which the West African savanna subspecies S. c. caffer found in Burundi number only about 500 now. Sitatunga (Tragelaphus speldi) were once found in many swamps in Burundi, but by the 1980s their numbers had dwindled, and the species' present conservation status is unknown. Waterbuck (Kobus ellipsiprymnus), also called the defassa waterbuck, was found throughout Burundi in the savanna grass land, then became restricted to the Ruvibu National Park. Only were reported in the 1980s and its present status is unknown. Lichtenstein's hartebeest (Alcelaphus Lichtensteinii) occurred in the southeast. Korrigum (also tsessebe, topi or tiang), Damaliscus lunatus, which were found in the eastern flood plains and savanna grasslands, is now extirpated. Impala (Aepyeros melampus), which once inhabited the eastern savannas, is also extirpated. Oribi (Ourebia ourebi), which occurred in the eastern and southern savanna and flood plains, is probably extirpated. Klipspringer (Oreotragus oreotragus), found in rocky outcrops in the south and east, is now extirpated. Grey duiker (Sylvicapra grimmia) is found in large numbers in spite of extensive hunting in the eastern and southern savannas. It is found in Ruvubu National Park.
Birds
Reported avifauna include 596 species (439 resident and 109 seasonal migrants) of which 13 species of global conservation concern and three are introduced species; more species have been found but their details are not recorded (thus UNEP reports 716 species). There are no endemic bird species. There are five Important Bird Areas (IBAs) declared by BirdLife International in the country, which cover an area of and which account for 3.7% of the total area of the country. These coalesce with the national parks and two forest (or nature) reserves. According to BirdLife International, there are 13 species of global conservation concern (six of non-breeding migrants, and balance of breeding type from Albertine Rift and papyrus swamps). These include Phoenicopterus minor (NT), Circus macrourus (NT), Falco naumanni (VU), Gallinago media (NT), Glareola nordmanni (NT), Ardeola idea (NT), Lybius rubrifacies (NT), Kupeornis rufocinctus (NT), Laniarius mufumbiri (NT), Balaeniceps rex (NT), Apalis argentea (VU), Bradypterus graueri (VU), Cryptospiza shelleyi (VU), Calamonastides gracilirostris (VU), and Bugeranus carunculatus (VU).
Environment
Deforestation is a major problem in Burundi, with trees being cut down for fuel or for agricultural clearing; as a result, there is very little natural forest vegetation remaining. Government conservation efforts are minimal, and only 5.4 percent of Burundi's land mass is officially protected. In 2005, the government announced a ban on natural Christmas trees, claiming that around 80,000 conifers per year were lost to the Christmas trade. Much of Burundi's wildlife is threatened with extinction, due to poaching and habitat loss. Gorillas and elephants are already completely extinct in the region.
References
Bibliography
Biota of Burundi
Burundi | Wildlife of Burundi | [
"Biology"
] | 2,319 | [
"Biota by country",
"Wildlife by country",
"Biota of Burundi"
] |
10,946,060 | https://en.wikipedia.org/wiki/Jun%20dimerization%20protein | Jun dimerization protein 2 (JUNDM2) is a protein that in humans is encoded by the JDP2 gene. The Jun dimerization protein is a member of the AP-1 family of transcription factors.
JDP 2 was found by a Sos-recruitment system, to dimerize with c-Jun to repress AP-1-mediated activation. It was later identified by the yeast-two hybrid system to bind to activating transcription factor 2 (ATF2) to repress ATF-mediated transcriptional activation. JDP2 regulates 12-O-tetradecanoylphorbol-13-acetate (TPA) response element (TRE)- and cAMP-responsive element (CRE)-dependent transcription.
The JDP2 gene is located on human chromosome 14q24.3 (46.4 kb, 75,427,715 bp to 75,474,111 bp) and mouse chromosome 12 (39 kb, 85,599,105 bp to 85,639,878 bp), which is located at about 250 kbp in the Fos-JDP2-BATF locus. Alternative splicing of JDP2 generates at least two isoforms. The protein JDP2 has 163 amino acids, belongs to the family of basic leucine zipper (bZIP), and shows high homology with the ATF3 bZIP domain. The bZIP domain includes the amino acids from position 72 to 135, the basic motif from position 74 to 96, and the leucine zipper from 100 to 128. The molecular weight of the canonical JDP2 is 18,704 Da. The histone-binding region is located from position 35 to 72 and the inhibition of the histone acetyltransferase (INHAT) region is from position 35 to 135, which is located before the DNA-binding domain.
JDP2 is expressed ubiquitously but is detected mainly in the cerebellum, brain, lung, and testis. A JDP2 single nucleotide polymorphism (SNP) was detected in Japanese, Korean, and Dutch cohorts, and is associated with an increased risk of intracranial aneurysms.
Posttranscriptional and post translational modifications
Phosphorylation of the threonine (Thr) residue at position 148 is mediated by c-Jun N-terminal kinase (MAPK8; JNK1) and p38 MAPK. Phosphorylated ATF2 inhibits the formation with JDP2 in vitro while phosphorylated JDP2 undergoes proteosomal degradation. It contains putative SUMO modification of lysine (Lys) residue at position 65, and recruits interferon regulatory factor 2 binding protein 1 (IRF2BP1), which acts as an E3 ligase. Phosphorylation of Thr at position 148 is detected in response to various stress conditions such as UV irradiation, oxidative stress, and anisomycin treatment or JDP2 is also regulated by other kinases such as p38 MAPK and doublecortin like protein kinase. Polyubiquitination of JDP2 protein is induced by IRF2BP1. JDP2 displays histone-binding and histone-chaperone activity. and inhibition of p300/CBP induced histone acetylation (INHAT). JDP2 recruits histone deacetylases HDAC1 and HDAC2, HDAC6 and HDAC3. JDP2 has INHAT activity and inhibits histone methylation in vitro.
Function
Phenotypes of gene knockout and transgenic mice
Gene knockout mice have a shorter tail, are smaller, have low neutrophil count. and cell proliferation, and commit to cell cycle arrest because of AP-1 repression. TransgenicJDP2 mice display atrial dilation and myocardial hypertrophy.
Dimer formation and interacting molecules
JDP2 functions as a transcription activator or repressor depending on the leucine zipper protein member it is associated with. JDP2 forms a homodimer or heterodimer with c-Jun, JUNB, JUND, Fra2, ATF2. and acts as a general repressor. On the other hand, JDP2 form a stable heterodimer with CHOP10 to enhance TRE- but not CRE-dependent transcription. In addition, JDP2 has been shown to directly associate with the progesterone receptor (PR) and functionally acts as a coactivator of progesterone-dependent PR-mediated gene transcription. Other proteins such as interferon regulatory factor-2-binding protein-1 (IRF2BP1). CCAAT/enhancer-binding protein gamma (C/EBPγ), HDAC3 and HDAC6 have also been demonstrated to associate with JDP2.
Cell differentiation
JDP2 plays a role in cell differentiation in several systems. Ectopic expression of JDP2 inhibits the retinoic acid-induced differentiation of F9 cells and adipocyte differentiation. By contrast, JDP2 induces terminal muscle cell differentiation in C2 myoblasts and reduces the tumorigenicity of rhabdomyosarcoma cells and restored their ability to differentiate into myotubes. It is also reported that JDP2 plays an important role in the RANK-mediated osteoclast differentiation. Further, JDP2 is involved in neutrophil differentiation and transcription factor Tbx3-mediated osteoclastogenesis for host defense and bone homeostasis. Methylome mapping suggests that JDP2 plays a role in cell progenitor differentiation of megakaryocytes.
Regulation of cell cycle and p53 signaling
JDP2 induces cell cycle arrest through cyclin D, p53, and cyclin A transcription, by increasing JUNB, JUND, and Fra2, and by decreasing c-JUN through the loss of p27kip1. JDP2 downregulates p53 transcription, which promotes leukemogenesis. Mouse p53 protein negatively regulates the JDP2 promoter in F9 cells as part of the JDP2˗p53 autoregulatory circuit. By contrast, JDP2-knockout mice exhibit in downregulation of p53 and p21 proteins.
Apoptosis and senescence
JDP2 appears to be involved in the inhibition of apoptosis. Depletion of JDP2 induces cell death similar to apoptosis. A study also demonstrated that UV irradiation induces JDP2 expression, which in turn down-regulates expression of p53 and thereby protects cells from UV-mediated programmed cell death. Heart-specific JDP2 overexpression protects cardiomyocytes against hypertrophic growth and TGFβ–induced apoptosis. In other settings, JDP2 has been shown to play an important role in the regulation of cellular senescence. JDP2-deficient mouse embryonic fibroblasts are resistant to replicative senescence by recruiting polycomb-repressive complexes (PRC1 and PRC2) to the promoters at the p16Ink4a locus.
Oxidative stress and antioxidative response
The increased accumulation of intracellular reactive oxygen species (ROS) and 8-oxo-dGuo, one of the major products of DNA oxidation, and the reduced expression of several transcripts involved in ROS metabolism in Jdp2-deficient MEFs argue that JDP2 is required to hold ROS levels in check. Furthermore, JDP2 binds directly to the antioxidant responsive element (ARE) core sequence, associates with Nrf2 and MafK (Nrf2–MafK) via basic leucine zipper domains, and increases DNA-binding activity of the Nrf2–MafK complex to the ARE and the transcription of ARE-dependent genes such as HO1 and NQO1. Therefore, JDP2 functions as an integral component of the Nrf2–MafK complex to modulate antioxidant and detoxification programs.
Nuclear reprogramming
JDP2, which has been shown to regulate Wnt signaling pathway and prevent ROS production, may play roles in cell reprogramming. Indeed, a study demonstrated that DAOY medulloblastoma cells can be reprogrammed successfully by JDP2 and the defined factor OCT4 to become induced pluripotent stem cells (iPSC)-like cells. This iPSC-like cells expressed stem cell-like characteristics including alkaline phosphatase activity and some stem cell markers, including SSEA3, SSEA4 and Tra-1-60. Later, another study also showed that JDP2 can substitute Oct4 to generate iPSCs with Klf4, Sox2 and Myc (KSM) or KS from somatic cells. Moreover, they showed that JDP2 anchors five non-Yamanaka factors (ID1, JHDM1B, LRH1, SALL4, and GLIS1) to reprogram mouse embryonic fibroblasts into iPSCs.
Oncogene or tumor suppressor gene
JDP2 may act as a double-edge sword in tumorigenesis. It is reported that JDP2 inhibits Ras-dependent cell transformation in NIH3T3 cells and tumor development in xenografts transplanted into SCID mice. Constitutive expression of JDP2 in rhabdomyosarcoma cells reduced their tumorigenic characteristics. On the other hand, JDP2 induces partial oncogenic transformation of chicken embryonic fibroblasts. Studies using high throughput viral insertional mutagenesis analysis also revealed that JDP2 functions as an oncogene. JDP2-transgenic mice display potentiation of liver cancer, higher mortality and increase number and size of tumors, especially when JDP2 expression is at the promotion stage.
Cancer and disease markers
JDP2 shows the gene amplification of head and neck squamous-cell carcinoma. In pancreatic carcinoma, downregulation of JDP2 is correlated with lymph node metastasis and distant metastasis and strongly associated with the post-surgery survival time, indicating that JDP2 may serve as a biomarker to predict the prognosis of patients with pancreatic cancer. In addition, JDP2 overexpression reverses the epithelial-to-mesenchymal transition (EMT) induced by co-treatment with TGF-β1 and EGF in human pancreatic BxPC-3 cells, suggesting that JDP2 may be a molecular target for pancreatic carcinoma intervention. Furthermore, it has been shown that the expression level of JDP2 gene upon acute myocardial infarction (AMI) is highly specific and a sensitive biomarker for predicting heart failure. In T cell acute lymphoblastic leukaemia, JDP2 regulates pro-survival signalling through direct transcriptional regulation of MCL1 and leads to steroid resistance in vivo.
JDP2 targets and JDP2-regulated genes
JDP2 is involved in the modulation of gene expression. For example, JDP2 regulates MyoD gene expression with c-Jun and gene for galectin-7. JDP2 functionally associated with HDAC3 and acts as a repressor to inhibit the amino acid regulation of CHOP transcription. JDP2 and ATF3 are involved in recruiting HDACs to the ATF3 promoter region resulting in transcriptional repression of ATF3. JDP2 inhibits the promoter of the Epstein–Barr virus (EBV) immediate early gene BZLF1 for the regulation of the latent-lytic switch in EBV infection.
Interactions
JDP2 (gene) has been shown to interact with Activating transcription factor 2.
Notes
References
Further reading
External links
Transcription factors | Jun dimerization protein | [
"Chemistry",
"Biology"
] | 2,525 | [
"Induced stem cells",
"Gene expression",
"Transcription factors",
"Signal transduction"
] |
10,946,073 | https://en.wikipedia.org/wiki/Wildlife%20of%20Cameroon | The wildlife of Cameroon is composed of its flora and fauna. Bordering Nigeria, it is considered one of the wettest parts of Africa and records Africa's second highest concentration of biodiversity. To preserve its wildlife, Cameroon has more than 20 protected reserves comprising national parks, zoos, forest reserves and sanctuaries. The protected areas were first created in the northern region under the colonial administration in 1932; the first two reserves established were Mozogo Gokoro Reserve and the Bénoué Reserve, which was followed by the Waza Reserve on 24 March 1934. The coverage of reserves was initially about 4 percent of the country's area, rising to 12 percent; the administration proposes to cover 30 percent of the land area.
The rich wildlife consists of 8,260 recorded plant species including 156 endemic species, 409 species of mammals of which 14 are endemic, 690 species of birds which includes 8 endemic species, 250 species of reptiles, and 200 species of amphibians. The habitats of these species include the southern region comprising tropical lowland, coastline on the Gulf of Guinea. Mangrove forests, in size, are along the coast line. Montane forests and savannas are in the northern region of the country. Important protected areas for these species are the Mbam Djerem National Park, Benoue National Park, Korup National Park, Takamanda National Park, and the Kagwene Gorilla Sanctuary. Cameroon is an important breeding area for marine and freshwater species such as crustaceans, mollusks, fish, and birds.
Geography
The topography of the country extends from the coastline to hill regions with elevations of up to . The habitat consists of three regions. These are: The dense rainforests in the southern region in the hot and humid climatic conditions; the central region of semi-deciduous forests; and the northern region consisting of semi-deciduous forests of wooded savanna with scattered trees. The climatic conditions are of low to highland with equatorial to tropical climate. Initial coverage of protected areas was in savanna region but it now covers all the ten provinces of the country with all the diversity of its topographic, climatic, hydrological biological features.
The highest mountain in the country is the Mount Cameroon with an elevation of . It is located in southwestern Cameroon in the coastal zone close to the Nigerian border.
The total forest area coverage is reported to be of which of closed forest and is fragmented forest or degraded forests accounting for 27 percent of the total forest area. The forests are also categorized as part of the "Congolian Coastal Forests, Western Congo Basin Forests, Sudanian Savannas, Sahelian Flooded Savannas, Gulf of Guinea Rivers and Crater Lakes, Guinean-Congolian Coast Mangroves, and Gulf of Guinea Marine Ecosystems." One of the important regions is the Cameroonian Highlands forests which extends across the Cameroon Highlands, covering an area of in western Cameroon and eastern Nigeria. The ecoregion lies above elevation, and is surrounded at lower elevations by the Cross-Sanaga-Bioko coastal forests at the southern end of the range, and by forest-savanna mosaic along the central and northern ends of the range; the Cameroon Highlands form the boundary between the Guinean and Northern Congolian forest-savanna mosaic ecoregions, consisting of sub-montane to montane forests and finally sub alpine grasslands. The region is categorized as critical/endangered, but the area under full protection is not great. The area is subject to intense population pressure and conversion of forest lands into agricultural areas.
As part of the Congo Basin, the Sangha River, drained by the tributaries rising in the northern humid region, and flowing into the southern region of the country, is the main water catchment. At the swampy estuary it forms several branches, and is also joined by the Likouala-aux-Herbes, Likouala-Mossaka, and Ubangi (Oubangui) rivers. Another major river, which joins the Sangha River, is the Dja River, which rises in west-central Africa and flows forming the border between Cameroon and the Republic of the Congo, and through the Dja Faunal Reserve, a UNESCO World Heritage Site. The major river drainage is the Chari subbasin of the Congo Basin, which covers Cameroon and the Central African Republic. It drains into the Atlantic Ocean.
Protected areas
Many protected areas are still in "pristine" condition, mostly because there is less tourism in Cameroon than other regions of Africa. According to reported statistics, there were ten protected areas from 1932 to 1960. Six protected areas were added between 1960 and 1980, five more were added between 1980 and 2004, and eight protected areas are under consideration within a final approval process.
The protected areas cover of which (81 percent) is part of the border protected area. The distribution of this protected area within Cameroon covers: The Lowland forest zones of Dja () with corridors connecting to the Nki and Minkébé protected areas, the Nki National Park covering with ecological corridors to Dja and Boumba–Bek, the Boumba Bek National Park covering , and the Lobéké National Park covering (integrated with the Trinational Park of Cameroon, the Central African Republic, and the Republic of Congo and linked with an Eco-corridor to Boumba–Bek Reserve; the Campo Ma'an National Park of , which borders with the Rio de Campo of Equatorial Guinea; and the Savanna Zone comprising the Waza National Park of near Chad border, Faro National Park of area with common boundary with Nigeria, and the Kalamaloué National Park of on the Chad border.
Cameroon's first protected area in the northern part of the country was established in 1932 under the French colonial administration of the black francophone Africa. The first forest reserve created was the Mozogo Gokoro Reserve 12 June 1932 and the second in the same year was the Benue Reserve on 19 November 1932. The third reserve, the Waza Reserve was established on 24 March 1934, initially covering an area of which was extended in 1935 to cover ; this is one of the most popular reserves in the country. Until 1975, there were 9 protected areas with greater focus on the north than the south. Following the Earth Summit of Rio de Janeiro in Brazil in 1992, the number of protected areas increased substantially and were well distributed covering all the ten provinces of the country in widely differing topographic, climatic, hydrological and biological conditions. There are 20 protected reserves which include national parks, zoos, forest reserves and sanctuaries.
Flora
The vegetation varies with elevation. Submontane forests extend from 900 to 1800 meters (3000 to 6000 ft) elevation. Above 1800 meters (6000 ft) elevation are distinct montane forests and patches of montane grassland, bamboo forest, and subalpine grasslands and shrub lands. The ecoregion is characterized by the presence of afromontane species, which have an archipelago-like distribution across the highlands of Africa. Typical afromontane species are Nuxia congesta, Podocarpus milanjianus, Prunus africana, Rapanea melanophloeos, and Syzygium guineense bamendae.
In Cameroon forest cover is around 43% of the total land area, equivalent to 20,340,480 hectares (ha) of forest in 2020, down from 22,500,000 hectares (ha) in 1990. In 2020, naturally regenerating forest covered 20,279,380 hectares (ha) and planted forest covered 61,100 hectares (ha). Around 15% of the forest area was found within protected areas, for the year 2015, 100% of the forest area was reported to be under public ownership.
The evergreen trees found in the rainforests are mahogany, ebony, obeche, dibetu, and sapelli; the trees grow to heights of 200 feet. The trees are also covered with mosses, lichens, and other epiphytes. In the drier woodlands above the rain forests are the tall grasslands and also some areas covered with mountain bamboo. In elevations between 2,400 m and 3,000 m, short grasses are the dominant species, particularly in the region of Mount Cameroon.
Fauna
The most endangered species is the Cross River gorilla, a great ape, whose last reported count was 300, spread over 11 scattered sites both in Cameroon and Nigeria. For preservation of this species of ape, the Kagwene Gorilla Sanctuary and the Takamanda National Park have been specifically established in Cameroon. Elephants migrate between the Lake Chad region in Chad and Cameroon; 300 to 400 elephants are reported to live here. In the dense forest areas of the rainforest ecoregion the fauna commonly reported are; red and green monkeys, chimpanzees, mandrills, rodents, bats, and large number of birds like the small sunbirds, giant hawks and eagles. Elephants are also reported in small numbers. The grassy woodlands have baboons and many species of antelope.
Reptiles
Prominent reptiles reported include the African rock python (Python sebae), the green bush viper (Atheris squamigera) and the African slender-snouted crocodile (Mecistops cataphractus).
Marine turtles reported near the coasts of Cameroon in the Atlantic Ocean are the loggerhead (Caretta caretta), Atlantic green (Chelonias mydas), leatherback (Dermochelys coriacea), hawksbill (Eretmochelys imbricata), and the olive ridley (Lepidochelys olivacea). Cameroon has enacted legislation to protect all these species of turtles. Olive ridley, leatherback, and green turtles are reported to nest on the sandy shoreline between Equatorial Guinea and the Wouri Estuary in Cameroon during November to January.
Mammals
Primates reported are: De Brazza's monkey (Cercopithecus neglectus), the black colobus (Colobus satanas); the patas monkey (Erythrocebus patas); the western gorilla (Gorilla gorilla); the Angolan colobus (Colobus angolensis); the moustached monkey (Cercopithecus cephus); the Gabon bushbaby (Galago gabonensis); the mona monkey (Cercopithecus mona); and the western needle-clawed galago (Euoticus elegantulus). The Cross River gorilla is the most endangered African ape subspecies.
Eleven small mammal species are endemic to the ecoregion: Eisentraut's striped mouse (Hybomys eisentrauti), the African wood mouse (Hylomyscus grandis), the Mount Oku rat (Lamottemys okuensis), Mittendorf's striped grass mouse (Lemniscomys mittendorfi), two brush-furred mouse species (Lophuromys dieterleni) and (Lophuromys eisentrauti), the Oku mouse shrew (Myosorex okuensis), the Rumpi mouse shrew (M. rumpii), the western vlei rat (Otomys occidentalis), Hartwig's soft-furred mouse (Praomys hartwigi), and Isabella's shrew (Sylvisorex isabellae).
Other small mammals present include Stuhlmann's golden mole (Chrysochloris stuhlmanni); the long-tailed pangolin (Manis tetradactyla) and the African clawless otter (Aonyx capensis). Rodents include the lesser cane rat (Thryonomys gregorianus); Dendromurinae (African climbing mice, fat mice, tree mice, and relatives), and Otomyinae (vlei rats and whistling rats). Bats include the lesser woolly bat (Kerivoula lanosa) and Franquet's epauletted bat (Epomops franqueti).
In Cameroon, a range of cetacean species such as humpback whale, right whale, sperm whale, fin whale, sei whale, killer whale, and dolphins are reported on the coast of the Atlantic Ocean. The African manatee (Trichechus senegalensis) is also present.
The Central African cheetah (Acinonyx jubatus soemmeringii) and West African wild dog (Lycaon pictus manguensis) were declared extinct from Cameroon in 2010.
Avifauna
Cameroon has more than 900 bird species which belong to 76 families. Of these 7 are endemic and 20 are specialty species. With this rich reporting of birds, they are categorized as resident birds (found throughout the year), breeding birds (which breed during the season), and migrants birds found only during specific the seasons and wintering birds which resided here during winter away from the colder regions of the north.
Though the ecoregion is rich in bird species, birdwatching is a very limited activity here. The nearby Mount Cameroon and Bioko montane forests ecoregion is also known for the endemic species. The seven endemic species are: the Bamenda apalis (Apalis bamendae), Bangwa forest warbler (Bradypterus bangwaensis), white-throated mountain-babbler (Kupeornis gilberti), banded wattle-eye (Platysteira laticincta), Bannerman's weaver (Ploceus bannermani), Bannerman's turaco (Tauraco bannermani), and Mt. Kupe bushshrike (Telophorus kupeensis). Fourteen species are endemic to the Cameroon Highlands forests and Mt. Cameroon: Andropadus montanus, Phyllastrephus poliocephalus, Laniarius atroflavus, Malaconotus gladiator, Cossypha isabellae and the subspecies Cisticola chubbi discolor (sometimes considered a separate species C. discolor). Nine more montane endemic species are shared with Mt. Cameroon and Bioko: Psalidoprocne fuliginosa, Andropadus tephrolaemus, Phyllastrephus poensis, Phylloscopus herberti, Urolais epichlora, Poliolais lopezi, Nectarinia oritis, Nectarinia ursulae and Nesocharis shelleyi.
Molluscs
Some of the non-marine molluscs species found in the wild in Cameroon are: Bulinus camerunensis, an endangered species found in western Cameroon from Barombi Koto and Debundsha, both crater lakes; Lymnaea natalensis, a species of least concern; and Sinistrexcisa, a new genus of land snail with four new species.
Endangered species
The ecoregion is home to several critically endangered, endangered and vulnerable species of animals. These are the following.
The critically endangered species are: Eisentraut's shrew (Crocidura eisentrauti) also endemic, pitch shrew (Crocidura picea) also endemic, and Rumpi mouse shrew (Myosorex rumpii) also endemic. Gabon dwarf shrew (Suncus remyi) which was earlier rated by IUCN in 2004 as critically endangered is now rated as of least concern.
The endangered species are: arrogant shrew (Sylvisorex morio) also endemic, chimpanzee (Pan troglodytes), crested genet (Genetta cristata), drill (Mandrillus leucophaeus), Eisentraut's mouse shrew (Myosorex eisentrauti). Eisentraut's striped mouse (Hybomys eisentrauti) also endemic, giant African water shrew (Potamogale velox), gorilla (Gorilla gorilla), Hartwig's soft-furred mouse (Praomys hartwigi), Mittendorf's striped grass mouse (Lemniscomys mittendorfi) also endemic, Mt. Oku rat (Lamottemys okuensis) also endemic, Preuss's monkey (or Preuss's guenon) (Cercopithecus preussi), western vlei rat (Otomys occidentalis), wild dog (Lycaon pictus), and Wimmer's shrew (Crocidura wimmeri).
The vulnerable species are: African elephant (Loxodonta africana), African golden cat (Profelis aurata), African pygmy squirrel (Myosciurus pumilio), Allen's striped bat (Chalinolobus alboguttatus), black colobus (Colobus satanas), Cameroon climbing mouse (Dendromus oreas) also endemic, Cameroon soft-furred mouse (Praomys morio) also endemic, cheetah (Acinonyx jubatus), Cooper's mountain squirrel (Paraxerus cooperi) also endemic, Hun shrew (Crocidura attila), Isabella shrew (Sylvisorex isabellae), Ja slit-faced bat (Nycteris major), lion (Panthera leo), mandrill (Mandrillus sphinx), Oku mouse shrew (Myosorex okuensis) also endemic, red-eared guenon (Cercopithecus erythrotis), red-fronted gazelle (Gazella rufifrons), spotted-necked otter (Lutra maculicollis) and West African manatee (Trichechus senegalensis).
Threats
The wildlife is under threat due to many factors. These are: conversion of forest land for agricultural use on account of their rich soil derived from volcanic rocks; pressure to meet firewood requirements; forest fires, particularly in grass land areas; the development of industrial complexes hydro-electric power plants and bauxite mining and forest land slotted for the purpose; as well as hunting. Forest loss in the Bamenda-Banso Highlands and also to certain degree in the Obudu Plateau is reported as more than 50% since the 1960s because of conversion to agricultural lands and good rainfall conditions. Hunting is recorded in the cross border regions of Cameroon. Trading in bush meat is common in the Sangha River Region; bush meat trade is reported to be concurrent with the logging operations. Hunting for ivory, skins and other animal parts is also reported in many national park areas in Cameroon, from within the country and also from cross border poachers.
Conservation
Many NGOs are working in Cameroon for the conservation and preservation of wild life.
Conservation efforts in the Sangha River Tri-national Protected Area are in place in a trans-boundary program sponsored by the World Wide Fund for Nature (WWF) with participation by the Central African Republic, the Congo and the Cameroon. This covers a total area of 2,800,000 ha (6,918,951 acres) encompassing the Dzanga Sangha Special Reserve (the second largest area in the world) in the Central African Republic, which incorporates within its ambit the Nouabalé-Ndoki National Park in the Republic of Congo (Brazzaville) and the Lobéké National Park in Cameroon. Appropriate actions are under implementation in respect of anti-poaching, research and the promotion of tourism to the rain forests (the mammal species of particular interest are elephants, apes, ranging from western lowland gorilla to chimpanzees and bongo). The three park-administrations and the prefects of the three countries meet often to ensure proper monitoring of the conservation activities. Patrolling of the parks is a regular joint effort to prevent poaching, smuggling of ivory and unauthorized fishing and carriage of fire arms in the reserve park
The German Cooperation of Technical Collaboration (GTC) in Central African Republic and Cameroon, and the World Wildlife Fund for Nature (WWF) and Wildlife Conservation Society (WCS - New York) in the Congo are providing large funds for conservation of the parks.
A particular success story of the enabled protection, particularly in the Nouabalé-Ndoki National Park is of the special group of 'eco-guards', who operate under the MFEE (Ministry of Forestry Economy and the Environment), unlike the past practice of deploying rangers, which is reported to have stopped illegal human activities taking place in the park such as poaching.
Ape Action Africa is one such non-profit NGO which was established in 1996 with the primary objective of conservation of endangered gorillas and chimpanzees, which are threatened by the bushmeat trade in Central and West Africa. The NGO not only helps in the rescue and rehabilitation of great apes but also helps in management of a large sanctuary in the Mefou forest.
See also
Natural areas of Cameroon
References
External links
Biota of Cameroon
Cameroon | Wildlife of Cameroon | [
"Biology"
] | 4,299 | [
"Biota by country",
"Biota of Cameroon",
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10,946,157 | https://en.wikipedia.org/wiki/Wildlife%20of%20Cape%20Verde | The wildlife of Cape Verde is found across its archipelago of ten islands and three islets, albeit in smaller numbers of species than mainland Africa. Each volcanic island within the archipelago is unique, and each of them have parks under their jurisdiction, by decree promulgated by the Cape Verde government. Located just off the west coast of Africa, the total land area of the island nation is .
With the exception of bats, there are no truly endemic species of mammal on Cabo Verde; historically, the archipelago was only accessible to creatures with the ability to fly or swim, or (in later years) to be brought by humans. The islands were first explored in 1456, but not actually settled until 1462; humans brought their livestock with them, including donkeys, pigs, cattle and goats—many of the latter are now so wild, they resemble mainland ibex, and are (more or less) considered endemic “by default”.
In the centuries since settlement began, more mainland species (such as the green vervet monkey, cats, dogs, mice, rats and rabbits) would make their way with waves of settlers. There are no snakes present on the archipelago, which has allowed for the proliferation of many other species of other herpetiles, such as geckos, frogs and lizards. The main predators of these reptiles and amphibians would be (besides each other) the various birds of prey and raptors present, including the Egyptian vulture, Eurasian buzzard, kestrel, osprey, peregrine falcon, and the rare Cape Verde kite. This kite species is currently threatened by extinction but may yet be observed on Boa Vista and Maio.
The flora consists of tropical dry forests, scrub land, Mediterranean-climate mountains, and rich coral reefs with abundant marine life. The islands are key migration points and breeding locations for numerous birds, plus the 20 different species of cetaceans—including pilot whales, bottlenose dolphins, and humpback whales—which come to feed and mate in the rich waters. Female green sea turtles come to lay their eggs on secluded beaches, likely the same ones they themselves hatched on.
Some of the wildlife species of Cape Verde are considered as endemic, evolving over millions of years of isolation; the grey-headed kingfisher (Halcyon leucocephala) survived here on insects in the absence of water in the lands of the islands.
In the process of development, many lands in the islands were converted to agricultural fields and several hundred varieties of herbaceous plant and tree species were introduced, resulting in depletion of the original vegetation. However, efforts are now underway at reforestation to improve the wildlife of Cape Verde, with reported planting of three million new trees every year (about 7000 per day), with pine, oak, sweet chestnut and acacia as the prominent varieties being planted. Cape Verde is also one of the world's top ten coral reef biodiversity hotspots.
Geography
The Cape Verde archipelago, a cluster of 10 islands and three islets located in the eastern Atlantic Ocean at a distance of off the coast of Senegal in West Africa, are volcanic in origin. Cape Verde is divided into two areas: the southern leeward islands known as the Sotavento Islands and the windward islands known as the Barlavento Islands in the north; Santo Antão, São Vicente, Santa Luzia, São Nicolau, Sal, and Boa Vista, and the Sotavento Islands of Maio, Santiago (the largest with an area of 991 km2), Fogo (with the only active volcano), and Brava. Nine of these islands which are inhabited have mountainous areas whereas the other islands have flat topography with sandy beaches. There are trees typical of both temperate and tropical climates, depending on elevation, which have created different types of flora and fauna. Given its geographical isolation, it exhibits a unique ecoregion with endemic plant and vertebrate species, particularly birds and reptiles. It is also inferred that arid climate with no sources of surface fresh water and geographic remoteness are the reasons for the islands limited wildlife diversity. As of 2003, there were 48 protected areas covering 0.3% of the islands land mass.
The Cape Verde islands are a very degraded area.
Due to proximity to the Sahara, most of the Cape Verde islands are dry, but on islands with high mountains and farther away from the coast, the humidity is much higher, giving a rainforest habitat that is very degraded by the strong human presence.
Northeastern slopes of high mountains often receive a lot of rain while Southwest slopes are much drier. This umbria areas are identified with cool and moisture.
Some islands, as Santiago with steep mountains, are covered with vegetation where the dense moisture condenses and soaks the plants, rocks, soil, logs, moss etc.
The laurel forest is a type of cloud forest that has developed on mountains, where the dense moisture from the sea or ocean, is precipitated by the action of the relief. The terrain forces up wet and warm air masses, which cool and decreases the dew point, causing moisture to condense and fall as rain or fog. This creates a habitat that is cool, saturating air and soil with moisture.
Protected areas
The protected areas declared under the Official Gazette of Cape Verde, in February 2003 are:
In Santo Antão Island the protected areas are Moroços – Natural Park, Cova/Ribeira Paúl/Torre – Natural Park, Cruzinha – Natural Reserve, Pombas – Protected Landscape and Tope de Coroa – Natural Park.
São Vicente Island has the Monte Verde – Natural Park.
Branco and Raso Islets – Integrated Reserve is the natural reserve in Santa Luzia Island.
São Nicolau Island has Monte Gordo Natural Park and Monte do Alto das Cabaças Natural Reserve.
Sal Island has 11 protected areas namely, the Salinas de Pedra Lume and Cagarral – Protected Landscape, the Monte Grande – Protected Landscape, the Rabo de Junco – Natural Reserve, the Baía da Murdeira – Natural (Marine) Reserve, the Costa da Fragata – Natural Reserve, the Serra Negra – Natural Reserve, the Buracona-Ragona – Protected Landscape, the Salinas de Santa Maria – Protected Landscape, the Morrinho do Filho –Natural Monument, the Ponta do Sino – Natural Reserve, the Morrinho do Açucar – Natural Monument.
In Maio Island protected are the Terras Salgadas – Natural Reserve, Casas Velhas – Natural Reserve, Barareiro e Figueira – Natural Park, Lagoa Cimidor – Natural Reserve, Praia do Morro – Natural Reserve, Salinas de Porto Inglês – Protected Landscape, Monte Penoso e Monte Branco – Protected Landscape and Monte Santo António – Protected Landscape.
Boa Vista Island has the largest number of parks and natural monuments. These are: The Boa Esperança – Natural Reserve; the Ilhéu de Baluarte – Integrated Natural Reserve, the Ilhéu dos Pássaros – Integrated Natural Reserve, the Ilhéu de Curral Velho – Integrated Natural Reserve, the Ponta do Sol – Natural Reserve, the Tartaruga – Natural Reserve, the Natural Park do Norte – Natural Park, the Monte Caçador e Pico Forçado – Protected Landscape; the Morro de Areia – Natural Reserve; the Curral Velho – Protected Landscape; the Monte Santo António –Natural Monument; the Ilhéu de Sal-Rei – Natural Monument; the Monte Estância – Natural Monument; and the Rocha Estância – Natural Monument.
The Santiago Island has two preserved areas in the Serra da Malagueta – Natural Park and the Serra Pico de Antónia – Natural Park.
The Fogo Island has Bordeira, Chã das Caldeiras e Pico Novo Natural Park.
The Rombo Islets have an Integrated Reserve.
With a view to preserve the marine ecosystems and develop fisheries pragmatically, the action initiated included creation of Marine reserves: Santa Luzia Island, and the Islets Raso and Branco, Boavista, Sal and Maio Islands; and Conservation of Cape Verde Endangered Marine Species Project.
Flora
Historically, Cape Verde was probably not rich with greenery, although the evidence of the situation in earlier times is severely lacking. When Cape Verde was first discovered and colonized by the Portuguese in the 15th century, the wildlife consisted mainly of dry forests and scrub habitat, which underwent a sea change under the influence of the inhabitants of this then isolated and uninhabited group of islands. The endemic flora and fauna of the islands were disturbed and have now remained confined mostly in the mountain peaks, steep slopes and other inaccessible areas.
Vegetation in the islands is basically of the savannah or steppe type. There are trees typical of both temperate and tropical climates, depending on elevation. The flatter parts of the islands sustain semi-desert plants while the higher lands have arid shrubland. The leeward slopes tend to contain desert, with a very sparse shrub cover, mostly thorny or toxic. A number of xerophilous plants grow in the brackish subsoil of Maio, Sal, and Boa Vista.
There are 664 listed plant species, which include two threatened species. Over 80 vascular plant taxa are reported to be endemic to Cape Verde; these include Tornabenea, Aeonium gorgoneum, Campanula bravensis (bellflower), Nauplius smithii, Artemisia gorgonum (sagebrush), Sideroxylon marginatum, Lotus jacobaeus, Lavandula rotundifolia, Cynanchum daltonii, Euphorbia tuckeyana, Polycarpaea gayi and Erysimum caboverdeanum (wallflower). Several trees are indigenous such as the blue-green flat-topped dragon tree Dracaena draco, Tamarix senegalensis, Phoenix atlantica (tamareira), in the lagoons and deserts of Boavista, the ironwood tree and a species of fig tree and Faidherbia albida (formerly known as Acacia albida and locally called simply "acácia"). As a result of extensive tree planting since 1975, there are pine trees, oaks and sweet chestnuts on the cool peaks of Santo Antao, eucalyptus on the heights of Fogo, and forests of acacia on Maio.
Fauna
The island has five mammals out of which three are threatened, 75 species of birds including 2 threatened species, 19 reptiles, 132 varieties of fish species including one threatened species. However, the islands do not have snakes and large mammals.
Mammals
The only indigenous mammal found in the island is the grey long-eared bat (Plecotus austriacus). Bat species on the islands account for about 20% of all mammals. Of particular note are those of the family Vespertilionidae: Savi's pipistrelle (Hypsugo savii) and Kuhl's pipistrelle (Pipistrellus kuhlii) in addition to the grey long-eared bat. Feral goats are found on Fogo, the descendants of domestic goats introduced by the Portuguese. Rodent populations were introduced by the Portuguese from early ships which visited the islands. Monkeys are also present in Cape Verde, hailing from the African continent. The slender mongoose (Galerella sanguinea) has also been introduced.
Birds
Cape Verde has many species of endemic birds, which are observed by keen ornithologists and bird watchers on the islands. 130 migrant birds are reported to visit the islands, out of which over 40 nest there. The seabirds which breed on the island are: Fea's petrel, magnificent frigatebird and red-billed tropicbird. Four species of birds, (Alexander's swift, the Raso lark, the Cape Verde swamp-warbler and the Iago sparrow) are also endemic here, while the Cape Verde shearwater is a breeding endemic. The endemic and endangered Bourne's heron is sometimes considered a full species. Also common are the greater flamingo and the Egyptian vulture. There is also an extinct species of quail Coturnix centensis from the Holocene of São Vicente Island.
Terrestrial reptiles
Lizards reported on the islands are 15 species including 12 endemic species, such as the now extinct Cape Verde giant skink (Macroscincus coctei) on Ilhéu Raso, giant gecko (Tarentola gigas) on Raso and Branco islands, Mabuya skinks (6 species), Hemidactylus (3 species) and Tarentola geckos (11 species).
An extinct undescribed species of small Centrochelys tortoise was reportedly present on São Vicente before human settlement.
Invertebrates
Cape Verde has a reported 58 endemic species of spider, including Wesolowskana lymphatica (jumping spider), and Hottentotta caboverdensis, a parthenogenetic scorpion. It has a reported 15 endemic genera and 369 endemic species of insects. Of note are Ceylalictus capverdensis (bee), Thyreus denolii (cuckoo bee), Thyreus batelkai (cuckoo bee), Thyreus schwarzi (cuckoo bee), Thyreus aistleitneri (cuckoo bee), Chiasmognathus batelkai (cuckoo bee), Monomorium boltoni (ant), Scopula paneliusi (geometrid moth) and Serranegra petrophila, a true bug in the family Lygaeidae There also are endemic marine species, including molluscs such as Favartia burnayi, Nassarius caboverdensis, Prunum sauliae, the cone shell Conus josephinae and the Cape Verde spiny lobster (Palinurus charlestoni).
Marine life
The tropical marine environment of the Cape Verde islands of Boavista, Sal and Maio is reported to have a high diversity of sea life. Boavista is part of the Macaronesia Wetlands. Coral reefs are also found extensively in Cape Verde, considered as one of the "world's ten most important coral reefs". There is a large number of endemic marine gastropods (sea snails and sea slugs) on the coasts of Cape Verde.
Marine species reported are bridled dolphin, Atlantic spotted dolphin, long-beaked common dolphin, blue whale, humpback whale, Blainville's beaked whale, common porpoise, barracuda's, moray eels and marine turtles (5 species). Turtles migrate across the Atlantic to breed from May to October. The most prominent species is the endangered loggerhead sea turtle (Caretta caretta). Other species of turtle are the hawksbill sea turtle (Eretmochelys imbricate) which is critically endangered; the green sea turtle (Chelonia mydas), endangered; leatherback sea turtle (Dermochelys coriacea) and olive ridley sea turtle (Lepidochelys olivacea). Hunting of sea turtles remains prevalent per an UNEP report, however turtle conservation measures began in 2008.
Eighteen species of whales and dolphins have been recorded in the waters of the Cape Verde archipelago. The area is cited as one of two known breeding grounds for the humpback whale (Megaptera novaeangliae) of the Northern Hemisphere. Humpback whales migrate annually from the North Sea to winter around Cape Verde from January to mid-May. The humpback whale population became limited due to severe overfishing during the 19th century and, although the total North Atlantic population of humpbacks had rebounded to more than 10,000 individuals by 1993, the Cape Verde population remained uncertain as of 2009.
Threats and legal redress
The status of biological resources of Cape Verde, in the process of degradation, was recognized in 1996 which prompted action in 2005 with several legal instruments that were introduced by the government of Cape Verde. In spite of all the legislation, the level of degradation reported in the Red List of Threatened Species was "26% for angiosperms, over 40% of bryophytes, over 65% of pteridophytes and over 29% of lichens are threatened; furthermore, over 47% of birds, 25% of terrestrial reptiles, 64% of coleopterous, over 57% of arachnids and over 59% of terrestrial mollusks." The number of Alauda razae (calhandra-do-Ilhéu-Raso) and Himantopus himantopus (perna-longa) has still shown a declining trend.
Further, with a view to preserve the marine ecosystems and develop fisheries pragmatically the action initiated included creation of Marine reserves: Santa Luzia Island, and the Islets Raso and Branco, Boavista, Sal and Maio Islands; and Conservation of Cape Verde Endangered Marine Species Project.
Organizations
Institutions and organizations involved with the preservation and conservation of the biodiversity of Cape Verde are: The Directorate General of Agriculture, Forest and Livestock Production, the Institute for the Development of Fisheries (INDP), the University of Cape Verde's National Institute of Agricultural Research and Development (INIDA) and Project Biodiversity.
Noting that the exclusive biological species of Cape Verde are not represented in any germplasm banks across the world and that its fauna and flora of Cape Verde are extremely vulnerable to climate adversities with the natural regenerative conditions considered as poor, INIDA has established "a collection of biological resources for ex situ conservation as a means of backing in-situ conservation of species threatened in some way, as they may be introduced in the wild as needs be, in sites where they are best adapted, through a finely tuned reintroduction program."
See also
Overfishing in West Africa
References
External links
"Aves de Cabo Verde"
Biota of Cape Verde
Cape Verde | Wildlife of Cape Verde | [
"Biology"
] | 3,702 | [
"Biota by country",
"Biota of Cape Verde",
"Wildlife by country"
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10,946,262 | https://en.wikipedia.org/wiki/Wildlife%20of%20Zimbabwe | The wildlife of Zimbabwe occurs foremost in remote or rugged terrain, in national parks and private wildlife ranches, in miombo woodlands and thorny acacia or kopje. The prominent wild fauna includes African buffalo, African bush elephant, black rhinoceros, southern giraffe, African leopard, lion, plains zebra, and several antelope species.
The Wildlife Conservation Act of 1960 decreased the loss of wildlife in Zimbabwe. In the 1990s, Zimbabwe became a leader in Africa of wildlife conservation and management. In 2006 the country reported generating US$300 million yearly from its wildlife in protected areas, rural and community run wildlife management areas, and in private game ranches and reserves. The 12-member Parks and Wildlife Board is responsible for this activity and deciding on policy issues under the Ministry of Environment and Natural Resources Management.
The Zimbabwe Parks and Wildlife Management Authority under the board has the onerous task of overseeing the activities related to ten national parks, nine recreational parks, four botanical gardens, four safari areas, and three sanctuaries. These areas are collectively called the Wildlife Estate which covers an area about , which is equivalent to 12.5% of the total land area of the country.
However, reports by National Geographic News indicate a disturbing trend of decimation of wildlife as a result of a "national economic meltdown" leading to overexploitation of the wildlife resources to meet the finances of the nation.
Legal codes
The Wildlife Conservation Authority initially protected and preserved wildlife in Zimbabwe as "king's game", which was subsequently changed to total state control. However, this created difficulties to the local population who were entirely dependent on the forests for their survival, as they were excluded from using indigenous wildlife resources and also gradually excluded from almost one-half of the country's land base. This seriously affected the sustainable exploitation of the wildlife resources as local people resorted to illegal poaching. However, in the 1960s the economic awareness created a policy shift in managing the wildlife in the country when the Wildlife Conservation Act was introduced. This was followed by the Parks and Wildlife Act of 1975, which enabled the land owners "the right to manage wildlife for their own benefit, thus providing an economic rationale to reinforce the scientific, aesthetic and moral justifications for wildlife conservation". The Parks and Wildlife Act of 1975 has been amended and consolidated in 1982 in which certain animals to be protected have been listed. Hunting of animals has been prohibited except under special permit issued by the minister for scientific or educational purposes or for captive breeding of falcons, live export, and re-stocking, wildlife management or defence of property. Provision also includes taking of indigenous plants, hunting of animals and regulation of fishing. Detailed regulations have been issued to the act.
Wildlife estate
The Wildlife Estate includes eleven national parks: the Chimanimani National Park (including the Eland Sanctuary), Chizarira National Park, the Gonarezhou National Park, the Hwange National Park, the Kazuma Pan National Park, the Mana Pools National Park, the Matusadona National Park, the Matobo National Park, the Nyanga National Park, and Victoria Falls National Park and Zambezi National Parks.
Chimanimani National Park
Chimanimani National Park borders Mozambique in the southernmost area of the Eastern Highlands. It is a mountainous terrain with peak heights of and is the source of many streams and springs enriching the environment of the park with natural falls such as in the Bridal Veil Falls in the Eland Sanctuary. There are also views of the Pork Pie mountain range and the Bridal Veil Falls, which plunges down into a base about 10 m wide. The virgin forest cover is of the dense moist evergreen type. It is approachable only by trekking along hill tracks. It is from the town of Mutare. It has fauna such as eland, sable, bushbuck, blue duiker, klipspringer and also spotted leopard, apart from butterflies, birds, snakes and shy cats.
Chizarira National Park
Chizarira National Park located in northwestern Zimbabwe covers a virgin forest land of area of ; Chizarira means "great barrier". Though it is one of the largest parks, its location is in the remote Zambezi Escarpment and has extensive vistas of its valleys, gorges, plateaus and flood plains. Its large game includes elephant, lion, leopard and buffalo. Its bird species include the African broadbill, Livingstone's flycatcher, western nicator, emerald cuckoo, Angolan pitta and the Taita falcon.
Gonarezhou National Park
Gonarezhou National Park, encompassing an area of about , in southeastern Zimbabwe is in a remote region along the Mozambique border and is the second largest such park in the country; the first largest park is the Hwange National Park. Gonarezhou in Shona means "elephant's tusk" (which the herbalists used to store their medicines) and it also means "place of many elephants". The park's habitat consists of baobabs, scrub lands and sandstone cliffs in the lowveld region. The park is very large, in rugged terrain, and hence remains unaffected by human interference. The park is within the ambit of the transboundary part of the Great Limpopo Transfrontier Park, a peace park that links Gonarezhou with the Kruger National Park in South Africa and the Limpopo National Park in Mozambique. Animals move freely between the three sanctuaries. The park's rich wildlife consists of 500 species of birds, 147 species of mammals, more than 116 species of reptiles, 34 species of frogs and 49 species of fish. The park's rivers and pools have some unique species of aqua fauna such as the Zambezi shark, freshwater goby, black bream and the turquoise killifish.
Hwange National Park
The Hwange National Park (formerly Wankie National Park) established in 1929 with an area of is the largest park and game reserve in Zimbabwe in the south-west corner of the country. The park lies on the main road between Bulawayo and the widely noted Victoria Falls. In the 19th century it was the hunting ground of the Ndebele warrior-king Mzilikazi and it is named after the local Nhanzwa chief. The park is close to the edge of the Kalahari desert, a region with little water and very sparse, xerophile vegetation. While the park abounds in elephant population (one of the largest in the world), it also hosts 100 mammal species, including 19 large herbivores and 8 large carnivores and 400 bird species; Zimbabwe's specially protected animals are all found here. Gemsbok, brown hyena and African wild dogs occur in fairly large numbers (the population of African wild dogs is stated to be of one of the largest surviving groups in Africa now). The very large elephant population has been a matter of concern since, during drought years, they are a burden on the ecological balance of the region. Elephant culling has been done to restrict the population of elephants to 13,000 (less than 1 per km2); against the recommended population of 35,000 – 40,000 animals (0.6 per km2) for the country as a whole. Apart from culling the other suggested option to keep the elephant population under check is sterilization. Conservationists covering this area have also expressed concern at the large "deforestation, poaching and unsustainable resource exploitation" that is occurring in this national park attributed to political and economic instability.
Kazuma Pan National Park
Kazuma Pan National Park covers and is located in the northwest corner of Zimbabwe, between Kazungula and Hwange national parks, and south-west of Victoria Falls. Basically, it was developed as a safe haven for the animals during the hunting season, as it formed an extension of the Matetsi Safari Area. It has a series of depressions, which enriches the ground water which is then pumped during the dry season. It has the largest concentration of about 2,000 buffaloes and also elephants and rhinos. Other species of wildlife seen here are: lion, leopard, giraffe, zebra, gemsbok, roan antelope, sable, tsessebe, eland and reedbuck. The oribi, a small antelope, an endemic species, is rarely sighted in the depressions where a large variety of water birds such as storks, crowned cranes, stilts, cormorants, ducks and kingfishers are also seen making it an attractive bird-watching site.
Mana Pools National Park
The Mana Pools National Park, a UNESCO Natural World Heritage Site, extending over an area of (as part of the Parks and Wildlife Estate that stretches the Kariba Dam in the west to the Mozambique border in the east) is in the region of the lower Zambezi River in Zimbabwe where the flood plain turns into a broad expanse of lakes after each rainy season. As the lakes gradually dry up and recede, the region attracts many large animals in search of water, making it one of Africa's most renowned game-viewing regions. In Shona language, Mana means "four" referring to the four large permanent pools formed by the meandering ox-bow lakes of the middle Zambezi River. Dande Safari Area () established in 1968, and the Urungwe Safari Area () established in 1976 are contiguous to this park. The park's habitat consists of islands, sandbanks and pools, flanked by forests of mahogany, wild figs, ebonies and baobabs. Alluvial deposits along the Zambezi have winterthorn with more diverse woodlands with species of Kigelia africana and Trichelia emetica on the top alluvial layers. The park has the country's biggest concentration of hippopotamuses and crocodiles as well as large dry season mammal populations of elephant and Cape buffalo. Spotted hyena, honey badger, warthog, bushpig, plains zebra and many species of antelope are found here. Bird life consists of 380 species which includes Nyasa lovebird, western nicator, rock pratincole, banded snake-eagle and Livingstone's flycatcher.
Matusadona National Park
Matusadona National Park, a game reserve in 1963, was declared a national park in 1975 covering an area of . It is bounded on the south by the Omay communal, on the north by Lake Kariba, on the east by the Sanyati River and its gorge, and on the west by the Ume River. It has three ecological zones namely, the lake and shoreline grassland forming the first zone, the Zambezi Valley floor made up of a mass of thick jesse and mopane woodland (with sparse grass cover) as the second zone and; the Escarpment area of Julbernadia and Brachystegia woodlands constituting the third zone.
Black rhino, elephants and buffalo inhabit the park. Other species include night ape, honey badger, civet, small spotted genet, slender mongoose, banded mongoose, spotted hyena, serval, lion, leopard, yellow-spotted rock hyrax, black rhinoceros, zebra, warthog, common duiker, grysbok, klipspringer, waterbuck, bushbuck, scrub hare, porcupine, vervet monkey, chacma baboon, side-striped jackal, hippopotamus, roan antelope, kudu and bush squirrel, African clawless otter, white-tailed mongoose, reedbuck, sable antelope, eland, civet, rusty spotted genet, caracal and bush pig; sighted on rarely are Cape wild dog, cheetah, roan and pangolin.
Matobo National Park
The Matobo National Park is part of the UNESCO Matubo Hills, became a national park covering an area of which was established in 1953. It has an exclusive "Intensive Protection Zone" to protect the large population of black and white rhinoceros. The name Matobo means "bald heads" and was selected by the Matabeleland king Mzilikazi whose grave lies in the Matobo Hills close to the park.
Matobo Hills includes a range of domes, spires and balancing rock formations created erosion and weathering within a granite plateau. It has diverse species of vegetation, including examples of mopane, Acacia, Brachystegia, Ficus, Azanza, Ziziphus, Strychnos and Terminalia. Along with rhinoceros, the park supports also a large number of animal species, including zebra, wildebeest, giraffe, kudu, eland, sable antelope, klipspringer, leopard, hyena, cheetah, hippo, warthog, rock dassies, waterbuck, African wildcat, springhare, common duiker, crocodiles, baboons and monkeys. The park is also rich in bird life, including black eagle, African fish eagle, martial eagle, secretarybird, pied crow, Egyptian goose, francolin, and weavers. Fish species in the park include bass, bottle fish, bream, catfish and Melanochromis robustus. The park has a number of dams such as the Maleme Dam, the Mthselele Dam, the Toghwana Dam, the Mesilume Dam, which are all communal camp sites.
Nyanga National Park
The Nyanga National Park in the Eastern Highlands of Zimbabwe located at about from Harare (connected by a black topped road) is made up of rolling green hills terrain with perennial rivers which spread through the park. The park lies between and elevation and has salubrious mountain climate. It is rich in flora and fauna. The faunal species seen in the park are the waterbuck, wildebeest, kudu, zebra, impala, sables and eland. The rivers in the park have fresh water fish such as the Nyanga trout. The visitor attractions in the park are: The Mount Nyangani (2593 m), the Nyangombe Falls, Mutarazi Falls, Pungwe Gorge & Falls, Nyamuziwa Falls, Nyangwe & Chawomera Forts and the Trout Hatchery near Purdon Dam.
Victoria Falls and Zambezi National Park
The Victoria Falls and Zambezi National Parks, a UNESCO Natural World Heritage Site, are located on the western edge of Zimbabwe; the two together cover an area of bounded by the Zambezi River, which borders with Zambia. The Falls and the Pa National Park are on the southern bank of the Zambezi River. The Victoria Falls, one of seven natural wonders of the world, is wide, cascades into the gorge and is formed by five different "falls", out of which four are in Zimbabwe. The catchment area of the falls is made up of rainforests with rich and unique species of flora and fauna. The flora consists of species of fig, mahogany and date palm. An attraction is the large baobab tree near the Falls which is 16 m in diameter and tall. The notable wildlife in the parks consists of elephants, lions, buffalos, leopards and white rhinoceros apart from herds of sable antelope, eland, zebra, giraffe, kudu, waterbuck and impala. The Zambezi River is rich in fish fauna such as bream and fighting tigerfish.
Vegetation
The vegetation or flora type is generally uniform in Zimbabwe. Bushveld or thorny acacia savanna and miombo or dry open woodland dominate the central and western plateau. In the south and southeast, which are dry lowlands, thorny scrub and baobabs are extensive. Cactus-like euphorbias (similar to pipe organs), 30 species of aloes, wildflowers, profusion of jacarandas, and succulent tropical flowers and palms are some of the plant species commonly seen in the country.
The dominant woody species noted in the Northwest Matebeleland, the Sebungwe region, in the Zambezi River Valley and in Gonarezhou National Park are: C. mopane, B. plurijuga, Guibourtia coleosperma, Pterocarpus angolensis and Acacia species, Julbernadia globiflora, Brachystegia boehmii, Erythrophleum africanum, P. angolensis, B. africana, Kirkia acuminata, Adansonia digitata, Screrocarya birrea, B. massaiensis, D. condylocarpon, T. sericea and Combretum species. Brachystegia allenii, J. globiflora, C. apiculatum, Terminali stuhlmannii, and Acacia tortlis, Grewia spp., Terminalia prunioides, S. birrea, Commiphora spp., A. nigrescence, A. digitata, and T. sericea.
Flora
Some of the floral; species of Zimbabwe are: Conyza sumatrensis, Hesperantha coccinea (river lily) and Strychnos spinosa. Flame lily (genus Gloriosa) grows profusely throughout the country and hence is designated as the national flower of Zimbabwe. It is a climbing lily which reaches heights of 8 ft and has bright red and yellow petals.
Fauna
Mammals
There are 199 mammal species in Zimbabwe. The black rhino is listed as critically endangered. The African wild dog is endangered. Among others, vulnerable species include Arends's golden mole, black-footed cat, and ground pangolin.
Amphibians and reptiles
Of the many amphibians and reptiles in Zimbabwe, a few deserve mention due to their status on the IUCN Red List:
Critically endangered
Cave squeaker
Endangered
Forest rain frog
Nyanga river frog
Zambezi flapshell turtle
Zygaspis ferox
Vulnerable
Chimanimani stream frog
Gaboon viper
Inyanga toad
Marshall's pygmy chameleon
Nyanga long reed frog
Fish
The kurper bream is considered critically endangered. Three other species of the Oreochromis genus found in Zimbabwe are listed as vulnerable.
Tourist companies tout catching tigerfish and bream in Mana Pools National Park, and vundu and chessa in the Zambezi. The cornish jack is an unusual fish that uses electricity to locate prey. Another interesting fish is the lungfish. These eel-like fish can survive months out of water by burrowing into hardened mud.
Birds
BirdLife International reported 629 species of bird sighted in Zimbabwe as of 2024. Avibase - Bird Checklists of the World reported 708 species as of 2024. Avibase reports five introduced species.
Four birds in Zimbabwe are listed as critically endangered: the hooded vulture, white-backed vulture, white-headed vulture, and white-winged flufftail. Another eight are listed as endangered and eleven as vulnerable.
References
External links
Biota of Zimbabwe
Zimbabwe | Wildlife of Zimbabwe | [
"Biology"
] | 3,965 | [
"Biota by country",
"Biota of Zimbabwe",
"Wildlife by country"
] |
10,946,320 | https://en.wikipedia.org/wiki/Wildlife%20of%20Chad | The wildlife of Chad is composed of its flora and fauna. West African lions, buffalo, hippopotamuses, Kordofan giraffes, antelopes, African leopards, cheetahs, hyenas, Bush elephants, and many species of snakes are found there, although most large carnivore populations have been drastically reduced since the early 20th century. Elephant poaching, particularly in the south of the country in areas such as Zakouma National Park, is a severe problem.
Vegetation
As of 2011, there were 2,288 species of plants in the country, 55 of which are endemic. Precipitation varies widely from south to the north. The country is also subject to hot, dry, dusty conditions. Harmattan winds are a feature in the northern part of the country. Droughts and locust plagues are also common. The vegetation in the country is broadly categorized under the three regions of the northern Sahara zone, the central Sahel zone, and the southern Sudan zone; all three zones are of equal proportion.
In Chad forest cover is around 3% of the total land area, equivalent to 4,313,000 hectares (ha) of forest in 2020, down from 6,730,000 hectares (ha) in 1990. In 2020, naturally regenerating forest covered 4,293,000 hectares (ha) and planted forest covered 19,800 hectares (ha). For the year 2015, 100% of the forest area was reported to be under public ownership.
The northern part of the country which has the Sahara desert and which borders Libya and the volcanic massif of Tibesti () forms part of the northern zone. Vegetation is dominantly tropical in the tropical zone of the country with deserts having least vegetative growth. However, a large area of desert dunes lie between Lake Chad and the Ouaddai massif, where fringes of xerophytic scrubland is noted.
The montane vegetation on the massif is rich, unlike the vegetation that is in the lowlands. Woody vegetation occurs in some deep gorges of the Ennedi massif, which rises to . A flat terrain supports Sahelian grasslands. The transition zone that lies between the southern Sahel and northern Sudan–Guinea is also a seasonal wetland. The Sudan Savanna zone mostly consists of Sudanian woodland with intermittent vegetation of edaphic grassland and Acacia.
The well-drained soils of the area once supported areas of dense woodlands with ebony and kapok trees (species of the Malvaceae family), but this has declined due to soil erosion and degradation. Vegetation found in the area includes acacias, baobab, desert date, palms, African myrrh, and Indian jujube. Found within the lake itself are aquatic plants such as reeds, papyrus, ambatch, and water lilies.
Fauna
As of 2002, there were at least 134 species of mammals and 532 species of birds (354 species of residents and 155 migrants) in Chad. Before the 20th century, Chad reportedly had a rich fauna of large carnivores in the Lake Chad region, but due to deforestation, hunting and competition from livestock most of the population of lions, leopards, rhinoceros, and hippopotamus have disappeared from the region.
The Zakouma National Park is an important habitat with the highest number of large mammals. Scimitar horned oryx are seen in the reserves of Chad in significant numbers, mostly in the Ouadi Rime Ouadi Achin Faunal Reserve. Also reported to survive in this reserve are the large population of addax (Addax nasomaculatus) and dama gazelle (Nanger dama).
Other species reported are; red-fronted gazelle, dorcas gazelle (Gazella rufifrons, Gazella dama, Gazella dorcas), patas monkey (Erythrocebus patas), striped hyena (Hyaena hyaena), Sudan cheetah (Acinonyx jubatus soemmeringii), caracal (Felis caracal), and Chadian wild dog (Lycaon pictus sharicus), African elephant (Loxodonta africana), otter (Lutra maculicollis), Aonyx capensis, sitatunga (Tragelaphus spekei) and kob (Kobus kob). Rodent species reported are Mastomys verheyeni and gerbil (Taterillus lacustris). African rock pythons and spitting cobras are the reptile species also reported.
Aquafauna
Lake Chad has 179 species of fish which feed on vegetation, phytoplankton and zooplankton. Some of the species reported are catfish (Clarias gariepensis), tilapia, cichlids, characin (Alestes baremoze) and Nile perch (Lates niloticus). Lungfish and sailfin are the two other unique species in the lake. Crocodile and hippopotamus also inhabit the lake as do birds, and it is an important destination for many migratory species of birds.
Avifauna
BirdLife International has reported 532 species of birds of which 354 residents and 155 are migrants, the Avibase - Bird Checklists of the World reports 587 species including 6 globally threatened species. Of these the species under critically endangered, endangered, near-threatened, and vulnerable categories are:
Critically endangered
Slender-billed curlew (Numenius tenuirostris)
Endangered
Egyptian vulture (Neophron percnopterus)
Hooded vulture (Necrosyrtes monachus)
White-backed vulture (Gyps africanus)
Rueppell's griffon (Gyps rueppellii)
Saker falcon (Falco cherrug)
Vulnerable
Marbled teal (Marmaronetta angustirostris)
Secretary-bird (Sagittarius serpentarius)
White-headed vulture (Trigonoceps occipitalis)
Beaudouin's snake-eagle (Circaetus beaudouini)
Greater spotted eagle (Clanga clanga)
Black crowned crane (Balearica pavonina)
Near-threatened
Ferruginous duck (Aythya nyroca)
Bateleur (Terathopius ecaudatus)
Lesser flamingo (Phoenicopterus minor)
Martial eagle (Polemaetus bellicosus)
Pallid harrier (Circus macrourus}
Arabian bustard (Ardeotis arabs)
Stanley bustard {Neotis denhami)
Nubian bustard (Neotis nuba)
Eurasian curlew (Numenius arquata)
Black-tailed godwit (Limosa limosa)
Great snipe (Gallinago media)
Black-winged pratincole (Glareola nordmanni)
African skimmer (Rynchops flavirostris)
European roller (Coracias garrulus)
Red-footed falcon (Falco vespertinus)
Sooty falcon (Falco concolor)
The violet turaco (Musophaga violacea) is a species of least concern, which is found in large numbers in a range of less than covering many African countries including Chad.
Protection
The protected parks, reserves, protection forests, reforestation areas, and Ramsar Wetlands of international importance in the country include the IUCN Level II categorized Aouk (), Goz Beïda, Manda (), and Zakouma () national parks. The country has a number of faunal reserves which are loosely protected including:
Abou Telfane
Bahr Salamat
Beinamar
Binder-Léré
Fada Archei
Larmanaye
Mandelia
Ouadi Rimé-Ouadi Achim
Siniala-Minia
Aside from the numerous protected forests, Tibesti Massif is also a protected area. The wetlands of international importance—under the Ramsar Convention–are the Ramsar Sites at Lake Fitri (; ), Binder-Léré Faunal Reserve (; ) and the Chadian section of Lake Chad (; ).
In addition to parks and reserves, eight Important Bird Areas (IBAs) have been identified and supported by BirdLife International. These cover 11.2percent of the country, an area of , some overlapping with parks and reserves. Of these, the Ouadi Rimé–Ouadi Achim IBA is the largest, covering an area of more than 6 percent of the area of the country.
Conservation
Efforts have been made by the Food and Agriculture Organization to improve relations between farmers, agro-pastoralists and pastoralists in the Zakouma National Park (ZNP), Siniaka-Minia, and Aouk reserve in southeastern Chad to promote sustainable development. As part of the national conservation effort, more than 1.2 million trees have been replanted to check the advancement of the desert, which helps the local economy by way of financial return from acacia trees, which produce gum arabic, and also from fruit trees.
Poaching
Poaching is a serious problem in the country, particularly of elephants for the profitable ivory industry and a threat to lives of rangers even in the national parks such as Zakouma. Elephants have been massacred in herds in and around the parks by organized poaching. The problem is exacerbated by understaffing. A number of wardens have been murdered by poachers.
References
Bibliography
External links
USAID detailed study on "Considerations of Wildlife Resources and Land Use in Chad"
Biota of Chad
Chad | Wildlife of Chad | [
"Biology"
] | 1,985 | [
"Biota by country",
"Wildlife by country",
"Biota of Chad"
] |
10,946,504 | https://en.wikipedia.org/wiki/Wildlife%20of%20Ivory%20Coast | The wildlife of Ivory Coast consists of the flora and fauna of this nation in West Africa. The country has a long Atlantic coastline on the Gulf of Guinea and a range of habitat types. Once covered in tropical rainforest, much of this habitat has been cleared, the remaining terrain being gallery forests and savanna with scattered groups of trees, resulting in a decrease in biodiversity. As of 2016, 252 species of mammal had been recorded in Ivory Coast, 666 species of bird, 153 species of reptile, 80 species of amphibian, 671 species of fish and 3660 species of vascular plant.
Geography
Ivory Coast is a country in western sub-Saharan Africa just north of the equator, bordered by Liberia and Guinea to the west, Mali and Burkina Faso to the north and Ghana to the east. To the south lies the Gulf of Guinea with a coastline where there is a network of lagoons. The land rises from south to north, the terrain being mostly flat to undulating plain, with mountains in the west and northwest. The highest point is Mount Richard-Molard on the border with Guinea, reaching . The main rivers flow from north to south. A dam on the Bandama River, the longest waterway in the country, has created the artificial Lake Kossou, while another on the Sassandra River has created the rather smaller Lake Buyo.
The forests on mountains in the west of the country near the border with Guinea and Liberia, are classified as Guinean montane forests. The Guinean forest-savanna mosaic belt extends across the middle of the country from east to west, and is the transition zone between the coastal forests and the interior savannas. The forest-savanna mosaic interlaces forest, savanna and grassland habitats. Northern Ivory Coast is part of the Sudanian Savanna ecoregion of the Tropical and subtropical grasslands, savannas, and shrublands biome. It is a zone of lateritic or sandy soils, with vegetation decreasing from south to north. Temperatures average between . The main rainy season is between May and September, with the remaining part of the year being dry in the north of the country, as the Harmattan wind blows. In the south the rainfall is higher ( annually and twice as much as the north) and some rain falls in most months.
Flora
As of 2016, 3660 species of vascular plant had been recorded in Ivory Coast. The Ébrié Lagoon is dominated by mangroves and herbaceous vegetation including both rooted and floating aquatic plants. Further inland are extensive swamps with larger herbaceous plants and small trees.
In the southwest of the country, the Taï National Park protects the largest area of forest remaining in the Upper Guinean rainforest belt of West Africa. The vegetation is predominantly dense evergreen ombrophilous forest with emergent trees up to tall, with massive trunks and large buttresses or stilt roots. This mature tropical forest includes some 1,300 species of higher plants and has been designated as a World Heritage Site and a UNESCO Biosphere Reserve. Another area that has been protected is the Comoé National Park, near the border with Burkina Faso. This has a variety of habitats, including gallery forests, woodland, open savannas and wetland.
Fauna
As of 2016, some 252 species of mammal had been recorded in Ivory Coast, 666 species of bird, 153 species of reptile, 80 species of amphibian and 671 species of fish. In the shallow parts of the Ébrié Lagoon there are a range of invertebrates including polychaete worms, nemertean worms, oligochaetes, isopods, amphipods and prawns. Over a hundred species of fish have been recorded here, and the lagoon and surrounding swamps are home to the pygmy hippopotamus, the West African crocodile, the West African slender-snouted crocodile, the dwarf crocodile and the African manatee.
Population growth and civil wars, together with deforestation, the increase area of plantations, hunting for bushmeat and other factors have led to a reduction in diversity among the animals in Ivory Coast, such that many are now restricted to protected areas. Among the 135 species of mammal recorded in Comoé National Park are 11 species of primates including the olive baboon, green monkey, lesser spot-nosed monkey, Mona monkey, black and white colobus, olive colobus, white collared mangabey and western chimpanzee. A total of 17 carnivore species have been observed here, but cheetahs, African wild dogs and lions no longer seem to be present. There are also 21 species of artiodactyl present including hippopotamus, bushpig, bongo, warthog, buffalo, kob, red-flanked duiker, bushbuck, waterbuck, roan antelope and oribi. Mammals recorded in the Taï National Park include the pygmy hippopotamus and 11 species of monkey, as well as African forest elephants, buffaloes, pangolins, bushbuck, leopards, chimpanzees and zebras. Reptiles include crocodiles, lizards and chameleons, as well as snakes such as horned vipers, mambas, and pythons.
Among the 670 species of bird that have been recorded in the country are 10 species of seabird and 119 species of water bird, with the remaining birds being terrestrial. There are no species endemic to the country, but it is visited by 197 species of migratory bird. Some notable birds include 6 species of vulture, raptors, owls, 8 species of stork, African jacana, Ibises, herons, plovers, parrots, 11 species of hornbill, pigeons, and many smaller passerines.
References
Biota of Ivory Coast
Ivory Coast | Wildlife of Ivory Coast | [
"Biology"
] | 1,175 | [
"Biota by country",
"Wildlife by country",
"Biota of Ivory Coast"
] |
10,946,528 | https://en.wikipedia.org/wiki/Activating%20transcription%20factor | Activating transcription factor, ATF, is a group of bZIP transcription factors, which act as homodimers or heterodimers with a range of other bZIP factors. First, they have been described as members of the CREB/ATF family, whereas it turned out later that some of them might be more similar to AP-1-like factors such as c-Jun or c-Fos. In general, ATFs are known to respond to extracellular signals and this suggests an important role that they have in maintaining homeostasis. Some of these ATFs, such as ATF3, ATF4, and ATF6 are known to play a role in stress responses. Another example of ATFs function would be ATFx that can suppress apoptosis.
Genes include ATF1, ATF2, ATF3, ATF4, ATF5, ATF6, ATF7, ATFx.
References
External links
Transcription factors | Activating transcription factor | [
"Chemistry",
"Biology"
] | 204 | [
"Protein stubs",
"Gene expression",
"Signal transduction",
"Biochemistry stubs",
"Induced stem cells",
"Transcription factors"
] |
10,946,579 | https://en.wikipedia.org/wiki/Wildlife%20of%20Sierra%20Leone | The wildlife of Sierra Leone is very diverse due to the variety of different habitats within the country. Sierra Leone is home to approximately 2090 known higher plant species, 147 known species of mammals, 172 known breeding bird species, 67 known reptile species, 35 known amphibian species and 99 known species of fish.
Mammals
There are approximately 147 known species of wild mammals within Sierra Leone. Members of fourteen orders of placental mammals inhabit Sierra Leone. The endangered pygmy hippopotamus has territories around the islands on the Moa River and is widespread in the Gola Forest area. There are three species of wild pig that occur across Sierra Leone: the wart hog, the giant forest hog and the red river hog.
Sierra Leone has 15 identified species of primates that include bushbaby, monkeys and a great ape, the common chimpanzee which is Sierra Leone's largest primate. Chimpanzees are found across the country with the 2010 chimpanzee census estimated a wild population in excess of 5500 more than double the number previously thought to live in the country. This is the second largest population of the endangered subspecies of western chimpanzee, after Guinea,
with the largest density in the Loma area, 2.69 individuals per km2, and the Outamba, with 1.21 individuals per km2.
There are several species of whales and the African manatee in the waters of Sierra Leone. The manatee is an endangered species and lives in the rivers and estuaries of Sierra Leone especially around Bonthe.
Mammals found in Sierra Leone include:
Hippopotamus
African forest elephant
Bongo
Duiker
African forest buffalo
Diana monkey
African leopard
Olive baboon
Guinea baboon
Western chimpanzee
Waterbuck
Western red colobus
Red colobus
Green monkey
Red river hog
Warthog
Lesser spot-nosed monkey
Black-and-white colobus
Pygmy hippopotamus
Serval
African wild dog
Birds
Sierra Leone has over 630 known species of bird ten of which are considered endangered including rufous fishing-owl and Gola malimbe. On the coastal area there are several important sites for migratory ducks and wading birds from the Palearctic realm.
African harrier-hawk
Black-collared lovebird
Blue-headed wood-dove
Iris glossy-starling
White-breasted guineafowl
White-necked rockfowl
North African ostrich
Savanna sparrow
Reptiles
There are 67 known species of reptiles, three of which are endangered, in Sierra Leone including several large reptiles. There are three species of crocodiles, the West African crocodile, the slender-snouted crocodile which lives in forest streams, dwarf crocodile found in mangrove swamps. All the species of sea turtles live in the waters of Sierra Leone with the green turtle and leatherback turtle laying eggs on the shores including on Sherbro Island and Turtle Island. Common species of lizard include the large Nile monitor, the agama seen around settlements, the Brook's house gecko often lives inside houses, and chamaeleos.
Amphibians
As of 2009, the critically endangered Tai toad was discovered in the Gola Forest, which was thought to be endemic to Taï National Park in Ivory Coast.
Fish
A snake eel is a marine fish only known from a single specimen found in the gut of another fish off the coast of Sierra Leone. The country also hosts a number of killifish in the genus Scriptaphyosemion as well as a number of freshwater catfish, including a species of electric catfish.
Invertebrates
Sierra Leone has around 750 species of butterflies. Including one of the largest butterflies the giant African swallowtail the wingspan of which can be up to 25 cm.
In a study in 2011, 140 species of dragonflies and damselflies were found. It is estimated that this represents 80% of the species found in Sierra Leone.
Flora
Wild plant types include the lowland moist and semi-deciduous forests, part of the Western Guinean lowland forests, inland valley
swamps, wooded savannah, bolilands and mangrove swamps. There are about 2,000 known species of plants with 74 species only occurring only in Sierra Leone. Primary rainforest used to cover around 70% of Sierra Leone in the mid-2000s this had reduced to around 6%. Common species include:
Red mangrove which grows in swamp areas along the western coast
Oil palm used for palm oil and palm wine
Cotton tree one of which is a historical symbol of Freetown
Red ironwood tree
See also
Cotton Tree, a kapok tree that was a historic symbol of Freetown
References
External links
Biota of Sierra Leone
Sierra Leone | Wildlife of Sierra Leone | [
"Biology"
] | 936 | [
"Biota by country",
"Wildlife by country",
"Biota of Sierra Leone"
] |
10,946,605 | https://en.wikipedia.org/wiki/Wildlife%20of%20Benin | Benin has varied resources of wildlife comprising flora and fauna, which are primarily protected in its two contiguous protected areas of the Pendjari National Park and W National Park. The former is known for many species of avifauna and the latter park is rich in mammals and predators. In addition, many other forest reserves are noted in the country but are not easily accessible, well protected or adequately surveyed for its wildlife resources. The protected area of Benin which is defined as a National Protected Area System is in northern Benin, mostly with a woody savanna ecosystem. It covers 10.3% of the nation and is part of the three-nation W-Arly-Pendjari Complex (WAP) (of which 43%, 36% and 21% is in Benin, Burkina Faso and Niger respectively).
Forests of particular note are the riparian forests which form a dominant ecosystem, accounting for one-third of the estimated flora of 3,000 species in Benin. These forests are found along river banks consisting of semi-deciduous, dry, and open forest and woodland savanna. However, these systems have been subject to severe misuse by way of deforestation, which necessitated the enforcement of a law, which imposes restrictions on cutting of these forests.
In south Benin, where malaria is a common disease as in the rest of Africa, medicinal plants are used for treatment as a form of traditional or alternative medicine.
National parks
W National Park
W National Park, IUCN Management Category II, a transboundary park among Niger, Benin and Burkina Faso, as a part of the Niger River, encompasses an area of in Benin. The "W" is after the W-shaped bends in the Niger River that borders the park and which is fed by the Tapoa River in the north, and the Mékrou River in the south. Its elevation is between . In addition, the buffer zones are the hunting zones of Mékrou, , Djona, and Kompa, , apart from transition areas in a zone. This area in the West African savanna belt covers terrestrial, semi-aquatic and aquatic ecosystems. Primarily of semi-arid to semi-humid Sudanese wooded savanna, 500 plant species have been identified. Sudanian savanna fauna consists of 70 diurnal mammals and more than 112 species of fish including the monkfish and sawback angelshark. The park has about 200,000 people living within it and on its periphery, which creates conflicts between park managers, herders and farmers.
Pendjari National Park
The Pendjari National Park covers entirely in the far north-west of Benin. It has buffer zones namely, the Pendjari (348,000 ha) that incorporates the hunting zones of Pendjari-Porga (76,000 ha), Batia (75,500 ha) and Konkombri (25,900 ha). Initially known as a forest reserve, it was declared a national park on May 6, 1961, after the independence of Benin. In June 1986, it was classified as a MAB Biosphere Reserve (including the adjoining hunting zones of Pendjari and Atacora). The Pendjari River Valley was recognized as a wetland of international importance and designated as a Ramsar site in February 2007. The park is part of the W-Arli-Pendjari complex (WAP), which is a vast protected area in Benin, Burkina Faso and Niger. The hills and cliffs of the Atakora range make the northwest one of the most scenic areas of Benin. They provide a wonderful backdrop to the Pendjari National Park, which, in its isolation, remains one of the most interesting in West Africa.
Riparian forests
Riparian forests in Benin are important conservation sites that need more care than is currently available. These forests, which are flood-dependent and the flora that is dependent on this source of water, are seen in many parts of Benin. In addition, forest and savanna species are also part of this ecosystem as they have a combination of plants from various forest and savanna types. Hence, riparian forests are more diverse than those of the single one-ecosystem-based vegetation. They also provide food for many animals and other forest species for survival.
The riparian forests ecosystem is in a limited area and spread in a linear shape. The forests account for at least one-third of the estimated 3,000 species of flora of Benin, with several valuable, rare or even endemic species. These forests are woodlands of semi-deciduous, dry, and open forest, and woodland savanna that occur along riverbanks or streams. The physiognomy of this type of forest is highly variable with trees of average height of and some places as high as with dense understorey (undergrowth). Adjacent ecosystems also affect the vegetation in these forests.
However, this ecosystem of hydrophilic and edaphic freshwater forest is of general structural complexity and extent. It was in a state of extinction due to "shifting cultivation, grazing, selective cutting of valuable or rare tree species, roads and dams construction, and over-exploitation of non-timber forest products" to meet the basic needs of rural communities. These practices resulted in the degradation of the ecosystem of rare plants and animals. It reached a critical stage where indigenous multilayered plant communities became extinct in several areas with the resultant creation of open fields, shrubs or savannas of least value. Thus, the degradation of the ecologically rich system necessitated intervention at the Government level through enabling legislation to stop further damage to the ecosystem. The government of the Republic of Benin enacted a forest law (no. 93-009) in July 1993, under which the uniqueness of riparian forests as refuge ecosystem for plants and wildlife of many kinds was duly recognized. The enacted law stated that "clearance of wood and shrubs is not allowed within at both sides of any waterway (article 28). Moreover, in the management plans of most forest reserves in Benin, gallery forests are to be left uncut..." Rare species (e.g. mahogany family species of the Khaya genus; the Moraceae species, Milicia excelsa) outside the gallery forests will not be cut either." Despite such legislation, enforcement is not effective. It is reported that uncontrolled illegal utilisation of forest resources continue, particularly in non-protected areas.
Fauna
Mammals
Predators include lion (Panthera leo), leopard (Panthera pardus), cheetah (Acinonyx jubatus), caracal (Caracal caracal), African wild cat (Felis lybica), African hunting dog (Lycaon pictus), side-striped jackal (Canis adustus), black-backed jackal (Canis mesomelas), spotted hyena (Crocuta crocuta).
Nocturnal predators include African civet (civettictis civetta), small-spotted genet (Genetta genetta), Cape genet (Genetta tigrina), spotted-necked otter (Lutra maculicollis), honey badger (Mellivora capensis), marsh mongoose (Atilax paludinosus), Egyptian mongoose (Herpestes ichneumon), cusimanse (Crossarchus obscurus), white-tailed mongoose (Ichneumia albicauda), slender or pygmy mongoose (Galerella sanguinea), Gambian mongoose (mungos gambianus).
The parks and other areas are home to African bush elephant, rhinoceros and African buffalo and antelopes. Seventeen species have been identified, such as sitatunga (Tragelaphus spekii), bongo (Tragelaphus eurycerus) and korrigum (Damaliscus korrigum korrigum).
Other species of various status are grey duiker (Sylvicapra grimmia), bushbuck, Maxwell's duiker (Philantomba maxwellii), red-flanked duiker (Cephalophus rufilatus), black duiker (Cephalophus niger), yellow-backed duiker (Cephalophus silvicultor), grey duiker (Sylvicapra grimmia)
bohor reedbuck (Redunca redunca), waterbuck (Kobus ellipsiprymnus), Buffon's kob (Kobus kob), roan antelope (Hippotragus equinus), western hartebeest (Alcelaphus buselaphus major), red-fronted gazelle (Eudorcas rufifrons) and oribi (Ourebia ourebi).
Primates reported include olive baboon (Papio anubis), green monkey (Cercopithecus sabaeus) and common patas monkey (Erythrocebus patas).
Reptiles
Reptiles present include Nile crocodile (Crocodylus niloticus), dwarf caiman and chameleons in 100 colour variations.
Tortoises include leopard tortoise (Stigmochelys pardalis), several species of terrapin and turtles – out of eight species of marine turtles four occur in Benin coast, namely, the green sea turtle (Chelonia mydas), olive ridley sea turtle (Lepidochelys olivacea) and leatherback sea turtle (Dermochelys coriacea). The indigenous hawksbill sea turtle (Eretmochelys imbricata) is the source of traditional tortoiseshell.
Lizards are of two types which are both harmless; house geckos and skinks. Both are predatory species.
Birds
Birds are a special feature in all types of habitats ranging from rainforest to deserts in Benin, which have two main climatic zones, namely the thick tropical vegetation in the south and the dry savannas and light woodlands in the north. The birding sites for coastal waders are the coastal lagoons of Les Bouches du Roi and the backwaters of Ouidha beach. Water and forest birds occur in Lake Nokoué and Lake Ahémé. Feathered birds are found in granite rock hills near Dassa-Zoume. The national parks are full of savanna specific birds.
The weaver species reported are: twelve species of weavers of family Ploceidae are found in Benin, out of the overall 111 of the genus Ploceus (true weavers) identified; they are larger than a sparrow, males are more colourful than female species.
Other reported species are Holub's golden-weaver, southern masked weaver (Ploceus velatus), Vieillot's black weaver (Ploceus nigerrimus), black-billed weaver (Ploceus melanogaster), grosbeak weaver (Amblyospiza albifrons), sparrow, buffalo weavers, dideric cuckoo (Chrysococcyx caprius), white-breasted cuckooshrike (Coracina pectoralis) and African fish eagle (Haliaeetus vocifer).
Molluscs
Insects
Insect species found in Benin include the tsetse fly and many vectors of epidemic diseases.
Flora
Dense forests are not recorded in Benin. Along the coastal areas coconut, palmyra palms, oil palms are seen up to Abomey, where after vegetation is savanna merged with that of Guinea and Sudan. Other tree species noted are West African ebony, shea tree, Bombax costatum, called the kapok or tree, and Khaya senegalensis, the Senegal mahogany.
The W National Park constitutes the southern limit of tiger bush plateau distribution. Riverine and gallery forests are noted on the banks of the Mekrou River (with seasonal flows), and other tributaries of the Niger River. The plains have an extensive coverage of grasses. The following are some of the plant species found in the savanna woodlands and grassland:
Adansonia digitata, one of the baobabs
Anogeissus leiocarpus
Celtis spp., the 'hackberry'
Clematis integrifolia
Boscia senegalensis
Balanites aegyptiaca
Bombax costatum, the 'kapok' or
Parkia biglobosa, the 'African locust tree'
Bauhinia variegata, the 'camel's foot tree'
Senna reticulata
Tamarindus indica, the tamarind
Terminalia avicennioides
Prosopis africana
Piliostigma reticulatum
In the evergreen gallery forests, the 'sausage tree' or Kigelia africana and Afzelia africana (the 'lenke' or 'African mahogany') are found. Orchid species are also found here, which are Eulophia cucculata and Eulophia guineensis.
The Pendjari Park consists of grasslands which have no trees or shrubs, shrubs, savanna woodlands, forests along rivers, and shrubs The rocky cliffs of the Pendjari National Park are sparsely wooded. The Volta depression has savanna ecosystem with woodlands and rare species such as Burkea africana, Anogeissus leiocarpus, Pterocarpus erinaceus, Detarium microcarpum, Lannea acida, Sterculia setigera, Combretum ghasalense (syn. Combretum adenogonium) and Acacia spp. On the deep soils of some of the summits and the Atakora escarpment, one finds a greater variety of plant species with Isoberlinia doka and Afzelia africana. The park includes both Guinea savanna woodland and Sudanian savanna, with areas of grassland dominated by Acacia sieberiana and Terminalia macroptera.
The most common species found in the riparian forests are: Pterocarpus santalinoides (Papilionaceae), Cola laurifolia (Sterculiaceae) and Syzygium guineense (Myrtaceae), out of which a few species are endemic and valuable.
Traditional medicine
Malaria, which is a parasite-born disease, is treated by herbal medicines in Benin. The treatment is based on plant species that are extracted and administered orally or through bathing. There are 85 plant species which are used to make 35 mixtures for treatment.
Botanical garden
The diversity of plants in Western Africa is preserved at the Papatia Botanical Garden in northern Benin. This garden, which is spread over 12 ha, is a species-rich savanna area where a hundreds of plant species are taken care of. A tree-nursery is part of this garden created to increase rare species.
Organizations
According to the Strategic Plan for the Conservation and Management of Protected Areas approved in 1994, organizations such as the National Centre for Wildlife Management (or in – CENAGREF) were created in 1996 for the sole purpose of the conservation and management of national parks including the buffer zones and the transition areas. The set up of the direction Pendjari National Park and direction of W National Park in 1996 and 1999 respectively are the administrative organizations under the CENAGREF that are responsible for the management of the parks. The Association of Civil Communities in the Protected Areas of the W National Park and the Séri Zone (Association des Communes Riveraines aux Aires Protégées du Parc W et de la Zone de Séri – ACRAP/WS) and Village Associations for the Management of Wildlife Reserves (or Associations Villageoise de Gestion des Reserves de Faune -AVIGREF) were also set up with the responsibility of community training and promoting multi-level communication between farmers and other stakeholders, capacity building and the development of effective governance following decentralized resource management. IUCN has associated with these organizations to address all aspects of management of the natural resources of the W National Park.
Notes
References
External links
Biota of Benin
Benin | Wildlife of Benin | [
"Biology"
] | 3,292 | [
"Biota by country",
"Biota of Benin",
"Wildlife by country"
] |
10,946,648 | https://en.wikipedia.org/wiki/Wildlife%20of%20Namibia | The wildlife of Namibia is composed of its flora and fauna. Namibia's endangered species include the wild dog, black rhino, oribi and puku.
Endangered species
Namibia has many endangered species within its national parks and wildlife resorts. The puku antelope is limited to about 100 individuals along the Chobe River in Botswana and the Linyati marshes in Namibia. The black rhino and white rhino have suffered the most from poaching and are on the verge of extinction. If there had been no effort to save them in the last 20 years they most likely would have disappeared. While both species occur naturally in Namibia, in many of the reserves they have been reintroduced. The country also has the largest population in southern Africa of cheetahs not contained within national parks. There are over twenty species of antelope ranging from the largest, the eland, to the smallest, the Damara dik-dik. The gemsbok, a striking antelope with long symmetrical horns and distinctive black and white markings, is featured on the Namibian coat of arms. Namibia also harbours a wealth of small mammals including mongoose, jackal as well as the less common antbear and honey badger, both solitary and nocturnal.
National parks and nature reserves
Namibia's parks and reserves range from the open bush of the centre and the north where wildlife is relatively plentiful, to the barren and inhospitable coastal strip with its huge sand dunes. The three main tourist attractions for wildlife in Namibia are Etosha National Park, Waterberg National Park and Cape Cross Seal Reserve.
National parks
Ai-Ais/Richtersveld Transfrontier Park (see also Fish River Canyon and Ai-Ais Hot Springs)
Bwabwata National Park
Etosha National Park
Khaudum National Park
Mudumu National Park
Namib-Naukluft National Park
Nkasa Rupara National Park
Skeleton Coast National Park
Waterberg National Park
Nature reserves
Kaokoland Nature Reserve
Khaudum Nature Reserve
Mamili Nature Reserve
Mudumu Nature Reserve
Fauna
Namibia has 115 species of fish (five endemic). There are about 50 species of frogs (six endemic) but neither caecilians nor salamanders. Namibia is home to 250 species of reptiles with 59 endemic. There were 1331 recorded species of arachnids with 164 endemic but there are potentially 5650 species. Records show 6331 species of insects (1541 of them are endemic). but there are expected to be 35,000 species of insects.
Freshwater insects
19 species of Ephemeroptera
2 species of Plecoptera
35 species of Trichoptera
77 species of Odonata
179 species of Diptera
1 species of Neuroptera
200 species of Coleoptera
45 species of Hemiptera
7 species of Orthoptera
Freshwater invertebrates
3 species of Porifera
2 species of Cnidaria
9 species of Platyhelminthes
5 species of Ectoprocta
10 species of Nematoda
13 species of Oligochaeta
16 species of Hirudinea
52 species of Ostracoda
19 species of Copepoda
Branchiopoda
19 species of Anostraca
19 species of Cladocera
2 species of Notostraca
15 species of Conchostraca
Malacostraca
6 species of Amphipoda
4 species of Isopoda
6 species of Decapoda
Terrestrial invertebrates
25 species of Diplopoda
Mammals
200 species of terrestrial mammals (14 of them are endemic) and 40 species of marine mammals are native to Namibia.
Birds
There are 645 species of birds (14 of them are endemic).
Mollusks
There were 26 species of freshwater snails recorded and 13 species of freshwater bivalves. A number of land gastropods are also found in Namibia.
Flora
There are 4334 species of plants recorded (683 of them are endemic).
Senecio haworthii - woolly senecio
Aloidendron dichotomum - quiver tree
Welwitschia mirabilis
References
Biota of Namibia
Namibia | Wildlife of Namibia | [
"Biology"
] | 829 | [
"Biota by country",
"Biota of Namibia",
"Wildlife by country"
] |
10,947,728 | https://en.wikipedia.org/wiki/George%20E.%20Davis | George Edward Davis (1850–1907) is regarded as the founding father of the discipline of chemical engineering.
Life
Davis was born at Eton on 27 July 1850, the eldest son of George Davis, a bookseller. At the age of fourteen he was apprenticed to a local bookbinder but he abandoned this trade after two years to pursue his interest in chemistry. Davis studied at the Slough Mechanics Institute while working at the local gas works, and then spent a year studying at the Royal School of Mines in London (now part of Imperial College, London) before leaving to work in the chemical industry around Manchester, which at the time was the main centre of the chemical industry in the UK.
Davis worked as a chemist at Brearley and Sons for three years. He also worked as an inspector for the Alkali Act of 1863, a very early piece of environmental legislation that required soda manufacturers to reduce the amount of gaseous hydrochloric acid released to the atmosphere from their factories. In 1872 he was engaged as manager at the Lichfield Chemical Company in Staffordshire. In this job his capacity for innovation flourished. His works included what was at the time the tallest chimney in the UK, with a height of more than .
He married Laura Frances Miller on 10 December 1878, and they had at least two sons, Eric (1881- ) and Kerville (1881 - 1934). He worked as a consultant to the chemical industry jointly with his brother Alfred, founded the Chemical Trade Journal and had 67 patents granted, as well as publishing scientific papers.
Davis was also instrumental in the formation of the Society of Chemical Industry (1881), which he had wanted to name the Society of Chemical Engineering, and was its first Secretary.
He was also interested in microscopy, founding the journal Northern Microscopist in 1881, and publishing a textbook on the subject, Practical Microscopy (1882).
He died in West Dulwich, on 20 April 1907.
Contribution to chemical engineering
Davis identified broad features in common to all chemical factories and wrote the influential A Handbook of Chemical Engineering. He also published a famous lecture series of 12 lectures, given in 1888 at Manchester Technical School (which became University of Manchester Institute of Science and Technology (UMIST)). These lectures defined chemical engineering as a discipline.
His lectures were criticized for being common place know-how since it was designed around operating practices used by British chemical industries. At this time, however, in the United States, this information helped initiate new thinking in the chemical industry, as well as spark chemical engineering degree programmes at several universities in the US.
Recognition
In the 1st floor foyer of Jackson's Mill, the building that houses the School of Chemical Engineering and Analytical Science, University of Manchester, there is a display and memorial to Davis. The George E. Davis Medal of the Institution of Chemical Engineers is named in his honour.
Publications
Volumes I and II
Further reading
TCE March 2012 52–4 "Meet the Daddy"
References
1850 births
1907 deaths
Academics of the University of Manchester Institute of Science and Technology
Alumni of Imperial College London
British chemical engineers
History of the chemical industry
People from Eton, Berkshire | George E. Davis | [
"Chemistry"
] | 632 | [
"History of the chemical industry"
] |
10,947,950 | https://en.wikipedia.org/wiki/Suboxide | Suboxides are a class of oxides wherein the electropositive element is in excess relative to the “normal” oxides. When the electropositive element is a metal, the compounds are sometimes referred to as “metal-rich”. Thus the normal oxide of caesium is Cs2O, which is described as a Cs+ salt of O2−. A suboxide of caesium is Cs11O3, where the charge on Cs is clearly less than 1+, but the oxide is still described as O2−. Suboxides typically feature extensive bonding between the electropositive element, often leading to clusters.
Examples of suboxides other than alkali metal derivatives:
Carbon suboxide, C3O2;
Boron suboxide, B6O;
Phosphorus suboxide, PO;
Titanium suboxides, TiO, Ti2O3, Ti3O5, Ti4O7, and Ti5O9.
Metal-containing suboxides
Suboxides are intermediates along the pathway that forms the normal oxide. Suboxides are sometimes visible when certain metals are exposed to small amounts of O2:
22 Cs + 3 O2 → 2 Cs11O3
4 Cs11O3 + 5 O2 → 22 Cs2O
Several suboxides of caesium and rubidium have been characterized by X-ray crystallography. As of 1997, the inventory includes the following Rb9O2, Rb6O, Cs11O3, Cs4O, Cs7O, Cs11O3Rb, Cs11O3Rb2, and Cs11O3Rb3.
Suboxides are generally colored compounds indicating a degree of electron delocalisation. Cs7O has a unit cell containing a Cs11O3 cluster and 10 Cs atoms. The cluster can be visualised as being composed of three face-sharing octahedra. In the picture below the caesium atoms are purple and the oxygen atoms are red. The Cs-Cs distance in the cluster is 376 pm, which is less than the Cs-Cs distance in the metal of 576 pm. Rb9O2 and Rb6O both contain the Rb9O2 cluster, which can be visualised as two face-sharing octahedra. Rb6O can be formulated as (Rb9O2)Rb3. The Rb-Rb distance in the cluster is 352 pm which is shorter than the Rb-Rb in the metal of 485 pm. It is suggested that caesium suboxides play a role in the Ag-O-Cs (S1) and multialkali Na-K-Sb-Cs photocathodes.
Carbon suboxide
The suboxide of carbon adopts an unremarkable structure. As for related organic cumulenes (e.g. ketene), C3O2 obeys the octet rule.
Related compounds
Subnitrides are also known. For example, Na16Ba6N features a nitride-centered octahedral cluster of six barium atoms embedded in a matrix of sodium.
References | Suboxide | [
"Chemistry"
] | 646 | [
"Oxides",
"Salts"
] |
10,948,234 | https://en.wikipedia.org/wiki/Microthermoforming | Microthermoforming is the abbreviation for microscopic or microscale thermoforming, or, more precisely, for thermoforming of microproducts or microstructure products. Microstructure products means products that have structures in the micrometre range and have their technical function provided by the shape of the microstructure [1]. Thermoforming [2] in turn means shaping of heated and therefore softened semi finished products in the form of thermoplastic polymer films or plates with their edges fixed by three-dimensional stretching. Shaping is carried out mainly by forming the films or plates into female moulds (negative forming) or over male moulds (positive forming). While the other polymer microreplication processes such as micro injection moulding or (vacuum) hot embossing are primary forming processes where forming occurs already in a molten, liquid phase of the heated polymer material, microthermoforming is a secondary forming process where forming occurs in a strongly softened, but still solid phase of the heated polymer.
Moulds for polymer microreplication in general and in particular for microthermoforming can be fabricated by various methods such as mechanical micromachining, lithographic based methods in combination with electroplating (see also the so-called 'LIGA' process) and wet or dry etching. And they can be fabricated of various materials such as metal, silicon and glass.
State of the art
For several years now, at Karlsruhe Institute of Technology (KIT), a pressure or high pressure (thermo)forming process is used to fabricate film microchips for capillary electrophoresis (CE) [3–5] and for three-dimensional cell cultivation [6–8]. The process is derived from the macroscopic trapped sheet forming process [2]. This is a simple variation of vacuum or pressure forming without prestretching, i.e. a single stage forming, into a female mould with heating of the plastic sheet using a contact heating plate inside the forming station. The forming air is supplied via through holes in the heating plate. Still in a laboratory scale process, diverse thermoplastic films also from biodegradable polymers such as polycaprolactone (PCL) with thicknesses typically between 20 and 100 μm are thermoformed. This is performed with gas pressures up to 5 MPa into mechanically micromachined cavities of plate shaped micromoulds from brass.
First examples of processes coming near to something that could be called 'microthermoforming' originate from the second half of the nineties. So, in 1993, dome shaped polymer microstructures for use in electrical membrane switches were fabricated [9]. This was done between a mating upper and lower metal emboss die with a concave and a convex detail, respectively, first in a hot, then in a second cold press. And in 1999, corrugated sheet like polymer microstructures for use e.g. in electrostatic actuators were fabricated [10]. This was also done between heated tools and counter tools, namely in discontinuous processes between stamps or in continuous processes between rollers. Partly, the counter tool was a soft one in the form of a thicker, unpatterned film or plate made from an easily deformable, e.g. elastomeric material which is able to assume the shape of the hard, metallic tool. In 2006, at the School of Polymer, Textile and Fiber Engineering (PTFE) of the Georgia Institute of Technology (GIT), the same technology approach was used to fabricate similar corrugated sheet like structures in a so-called 'rubber-assisted hot embossing process' [11].
Features and applications
The microthermoforming process including its products can have all the advantageous properties of the powerful macroscopic production process. Moreover, the thermoformed microparts have additional, specific properties appearing only in microscale dimensions and resulting from their unusual morphology. Thermoformed e.g. microfluidic structures have free standing microcavities such as channels and reservoirs and they are thin walled partly in the range of a few micrometers. Specific properties of thermoformed microparts are, amongst others, their high flexibility, their small volume and mass, their low thermal resistance and heat capacity, and their low light absorbance and background fluorescence. Morphology and properties of these microparts now can result in improved or even new, so far unthought of applications.
Compared to the other microreplication processes, in microthermoforming, modifications of the film to be formed remain preserved beyond the forming step due to the already mentioned material coherence during this secondary forming process. This enables surface and bulk modification and functionalisation of the three-dimensionally formed films or membranes, namely as highly resolved micro- and nanopatterns, and all side, i.e. on hardly accessible side walls and even behind undercuts. Thus, e.g. thermoformed chips for three-dimensional cell cultivation can be provided with pores, cell adhesion patterns [6–8], surface topologies and electrodes [12].
Future application fields for microthermoforming are expected to be
generally life sciences, e.g. flexible film microchips such as μTAS (Micro Total Analysis Systems) and LOC (Lab-on-a-chip) devices, possibly in continuous format and combined with polytronic circuits, also as human implants
especially tissue engineering, e.g. film substrates or scaffolds for three-dimensional cell cultivation in fundamental research, medical diagnosis, pharmaceutical active substance research, and clinical research and therapy, particularly if integrated in standard laboratory platforms such as petri dishes and microtitre plates
micropackaging, e.g. micro sensor and actuator housings or caps
smart textiles etc.
References
An interim report from the NEXUS Task Force 1998 Market Analysis for Microsystems
Throne JL 1996 Technology of Thermoforming (Munich: Hanser)
Truckenmüller R, Rummler Z, Schaller T and Schomburg WK 2001 Low-cost production of single-use polymer capillary electrophoresis structures by microthermoforming Proc. 12th Micromechanics Europe Workshop (MME) (Cork, Ireland) pp 39–42
Truckenmüller R, Rummler Z, Schaller T and Schomburg WK 2002 Low-cost thermoforming of micro fluidic analysis chips J. Micromech. Microeng. 12 375–9
Truckenmüller R, Giselbrecht S 2004 Microthermoforming of flexible, not buried hollow microstructures for chip-based life sciences applications IEE Proc. Nanobiotechnology 151 163–6
Giselbrecht S, Gietzelt T, Gottwald E, Guber AE, Trautmann C, Truckenmüller R and Weibezahn K F 2004 Microthermoforming as a novel technique for manufacturing scaffolds in tissue engineering (CellChips) IEE Proc. Nanobiotechnology 151 151–7
Giselbrecht S, Gottwald E, Schlingloff G, Schober A, Truckenmüller R, Weibezahn K-F and Welle A 2005 Highly adaptable microstructured 3D cell culture platform in the 96 well format for stem cell differentiation and characterization Proc. 9th Int. Conf. on Miniaturized Systems for Chemistry and Life Sciences (Micro Total Analysis Systems, μTAS) (Boston, MA) pp 376–8
Giselbrecht S, Gietzelt T, Gottwald E, Trautmann C, Truckenmüller R, Weibezahn K-F and Welle A 2006 3D tissue culture substrates produced by microthermoforming of pre-processed polymer films Biomed. Microdevices 8 191–9
Kurosawa M, Haga S, Yamasato H, Kobayashi I and Suzuki S 1995 PET emboss membrane switch Fujikura Technical Review 24 97–100
Dreuth H and Heiden C 1999 Thermoplastic structuring of thin polymer films Sens. Actuators A-Physical 78 198–204
Nagarajan P and Yao D 2006 Rubber-assisted hot embossing for structuring thin film polymeric films Proc. ASME International Mechanical Engineering Congress and Exposition (IMECE) (Chicago, IL)
Gottwald E, Giselbrecht S, Augspurger C, Lahni B, Dambrowsky N, Truckenmüller R, Piotter V, Gietzelt T, Wendt O, Pfleging W, Welle A, Rolletschek A, Wobus AM and Weibezahn K-F 2007 A chip-based platform for the in vitro generation of tissues in three-dimensional organization Lab Chip 7 777-85
Plastics industry
Microtechnology
Forming processes | Microthermoforming | [
"Materials_science",
"Engineering"
] | 1,896 | [
"Materials science",
"Microtechnology"
] |
10,948,483 | https://en.wikipedia.org/wiki/Wildlife%20of%20the%20Democratic%20Republic%20of%20the%20Congo | The wildlife of the Democratic Republic of the Congo includes its flora and fauna, comprising a large biodiversity in rainforests, seasonally flooded forests and grasslands.
The country is considered one of the 17 megadiverse nations, and is one of the most flora rich countries on the African continent. Its rainforests harbour many rare and endemic species, such as the chimpanzee and the bonobo. It is home for more than 10,000 types of plants, 600 timber species, as well as 1,000 bird species, 280 reptile species, and 400 mammal species, including the forest elephant, gorilla, forest buffalo, bongo, and okapi. Many of these wildlife species are threatened animals such as large lowland gorillas and chimpanzees.
Five of the country's national parks are listed as World Heritage Sites: the Garumba, Kahuzi-Biega, Salonga and Virunga National Parks, and Okapi Wildlife Reserve. All five sites are listed by UNESCO as World Heritage In Danger.
Several environmental issues in the DRC threaten wildlife, including overhunting for bushmeat, deforestation, mining and armed conflict. The civil war and resultant poor economic conditions have endangered much of the country's biodiversity. Many park wardens were either killed or could not afford to continue their work.
Fauna
The ecoregion is home to the endangered western lowland gorilla (Gorilla gorilla gorilla), the endangered eastern lowland gorilla (Gorilla berengei graueri), the endangered mountain gorilla (gorilla beringei beringei), African forest elephant (Loxodonta cyclotis), and okapi (Okapia johnstoni).
Animals native to the Democratic Republic of the Congo:
Aardvark
African brush-tailed porcupine
African buffalo
African bullfrog
African civet
African clawed frog
African dwarf frog
African golden cat
African helmeted turtle
African leopard
African manatee
African palm civet
African rock python
African soft-furred rat
African softshell turtle
African striped weasel
African tree toad
Allen's swamp monkey
Angola colobus
Aubry's flapshell turtle
Ball python
Banded mongoose
Banded water cobra
Bili ape
Black-and-white colobus
Black-collared lovebird
Black mamba
Black-necked spitting cobra
Blue duiker
Blue-headed wood dove
Blue monkey
Bohor reedbuck
Bongo
Bonobo
Bushpig
Cape bushbuck
Cape hyrax
Central African oyan
Chameleon
Chimpanzee
Common agama
Common duiker
Common egg eater
Common eland
Congo peafowl
Congo water cobra
Crocodile
Dwarf crocodile
Nile crocodile
Central African slender-snouted crocodile
De Brazza's monkey
Egyptian fruit bat
African forest elephant
Western gorilla
Gaboon viper
Gallagher's free-tailed bat
Giant eland
Giant forest hog
Giant otter shrew
Goliath beetle
Grant's zebra
Greater cane rat
Greater kudu
Great Lakes bush viper
Green bush viper
Green mamba
Grey parrot
Handsome spurfowl
Hartebeest
Hedgehog leaf-toed gecko
Hippopotamus
Honey badger
Jameson's mamba
Johnston's chameleon
Katanga Mountain bush viper
Kob
Kordofan giraffe
Leopard tortoise
Lesser flamingo
Lichtenstein's hartebeest
Lion
Many-banded snake
Marsh mongoose
Monitor lizard
Angolan white-throated monitor
Nile monitor
Savannah monitor
Moustached monkey
Northern white rhinoceros
Okapi
Olive baboon
Oribi
Pangolin
Giant pangolin
Long-tailed pangolin
Tree pangolin
Patas monkey
Puff adder
Puku
Red river hog
Roan antelope
Rock hyrax
Rough-scaled bush viper
Sable antelope
Serval
Side-striped jackal
Sitatunga
Southern reedbuck
Spectral pygmy chameleon
Spotted hyena
Strange-horned chameleon
Stuhlmann's golden mole
Topi
Tropical spiny agama
Trumpeter hornbill
Upemba lechwe
Upemba mud turtle
Warthog
Waterbuck
Yellow-backed duiker
Birds
Butterflies
Ants
There are 803 species of ant confirmed in the DRC, including the highly invasive ant Pheidole megacephala which originates from the country.
See also
Centre National d'Appui au Développement et à la Participation populaire
Acapoeta tanganicae
Labeo simpsoni
References
External links
A blog on bonobo research in Congo
The Digitised Flora of Central Africa
Biota of the Democratic Republic of the Congo
Congo | Wildlife of the Democratic Republic of the Congo | [
"Biology"
] | 914 | [
"Biota by country",
"Biota of the Democratic Republic of the Congo",
"Wildlife by country"
] |
10,948,495 | https://en.wikipedia.org/wiki/Homayoun%20Seraji | Homâyun Serâji ( 1947 – 16 April 2007) was an Iranian scientist, engineer, a JPL senior researcher and former professor of Sharif University of Technology who published extensively in the field of multivariable control systems, focusing on optimal control, pole placement, multivariable PID controllers, and output regulation. Also he has significant publications in the field of Robotics, and space exploration.
Education
Seraji was born and grew up in Tehran. He ranked first in the Iranian national high-school diploma examinations in 1965. He then moved to the United Kingdom and studied at Sussex University and majored in Electrical Engineering. Seraji earned his Ph.D. in Control Systems at the University of Cambridge in 1972.
Career
In 1974, he joined Aryamehr University of Technology (now Sharif University of Technology), as a Professor of Electrical Engineering and was involved in teaching and research in control systems for ten years. He was also selected as a United Nations Distinguished Scientist in 1984.
In 1985, Seraji joined NASA's Jet Propulsion Laboratory (JPL) and Caltech. During his tenure at JPL, he conducted extensive research that has led to major contributions in the field of robot control systems, particularly in: adaptive robot control, control of dexterous robots, contact control, real-time collision avoidance, rule-based robot navigation, and safe spacecraft landing.
The outcome of his research in controls and robotics has been published in 98 peer-reviewed journal papers, 119 refereed conference publications, 5 contributed chapters, and has led to 10 patents.
In 2003, he was recognized as the most-published author in the 20-year history of the Journal of Robotic Systems.
Awards
JPL Edward Stone Award for Outstanding Research Publication in 2003
NASA Group Achievement Award in 1991 and 2002
Fellow of IEEE in 1997
NASA Exceptional Engineering Achievement Award in 1992
NASA Major Space Act Award
See also
Science and technology in Iran
Notes
External links
Homayoun Seraji at JPL
Iranian electrical engineers
Iranian engineers
American people of Iranian descent
American electrical engineers
NASA people
Engineers from Tehran
Academic staff of Sharif University of Technology
1947 births
2007 deaths
Control theorists
Iranian roboticists
Alumni of the University of Sussex
Iranian expatriate academics
American roboticists
Iranian expatriates in the United Kingdom
20th-century American engineers | Homayoun Seraji | [
"Engineering"
] | 456 | [
"Control engineering",
"Control theorists"
] |
10,948,785 | https://en.wikipedia.org/wiki/Wildlife%20of%20Guinea | The wildlife of Guinea is very diverse due to its wide variety of habitats. The southern part of the country lies within the Guinean Forests of West Africa biodiversity hotspot, while the north-east is characterized by dry savanna woodlands. Ecoregions of Guinea are the Western Guinean lowland forests, Guinean montane forests, Guinean forest–savanna mosaic, West Sudanian savanna, and Guinean mangroves.
Populations of large mammals are restricted to uninhabited distant parts of parks and reserves, and those populations are declining. Strongholds of Guinean wildlife are Pinselly Classified Forest, National Park of Upper Niger, Badiar National Park, Mount Nimba Strict Nature Reserve, Ziama Massif, Bossou Hills Reserve, and Diécké Classified Forest.
Fauna
Mammals
Birds
Blue-headed wood-dove
Iris glossy-starling
White-necked rockfowl
White-breasted guineafowl
Reptiles
Amphibians
Insects
Butterflies and moths
Flora
References
Biota of Guinea
Guinea
Nature conservation in Guinea | Wildlife of Guinea | [
"Biology"
] | 201 | [
"Biota by country",
"Biota of Guinea",
"Wildlife by country"
] |
10,948,856 | https://en.wikipedia.org/wiki/Wildlife%20of%20Gabon | The wildlife of Gabon is composed of its flora and fauna. Gabon is a largely low-lying country with a warm, humid climate. Much of the country is still covered by tropical rainforest and there are also grasslands, savannas, large rivers and coastal lagoons.
Overview
Wildlife includes forest elephants, forest buffalos, various antelope and monkey species, sitatungas, leopards, three species of crocodiles, chimpanzees and gorillas, and several marine turtle species which nest along the coast. As of 2002, there were at least 190 species of mammals.
Fauna
Mammals
Gabon has important populations of many mammals including about 35,000 gorillas, 50,000 forest elephants and 64,000 chimpanzees. About a quarter of Africa's gorillas live in Gabon. Other large mammals include the hippopotamus, forest buffalo, bongo and red river hog. A variety of monkeys occur, including the endemic sun-tailed monkey, and the near-endemic mandrill and white-collared mangabey (here near-endemic meaning most of the individuals of these species are in Gabon, but that they also occur in the neighbouring countries as well). Carnivorous mammals include the leopard, golden cat, and various jackals, mongooses, genets and civets. The last lion was killed in 1996 in the savannahs of the east of the country. The West African manatee is found along coasts and large rivers while the humpback whale breeds offshore.
Birds
There are 604 species of birds throughout the country. None of these are endemic but some such as the Dja River warbler, Verreaux's batis, African river martin and black-chinned weaver are restricted to Central Africa and have only small ranges. The grey-necked picathartes and Loango weaver are classed as vulnerable species by the IUCN.
Reptiles
A variety of snakes are found including the Gaboon viper. Sea turtles breed along the coast, particularly the leatherback turtle.
Flora
There are over 7000 species of native vascular plants in Gabon. About 22% of these are endemic. New species are still being discovered such as the tree Cola lizae which was first described in 1987.
Conservation
Wildlife in Gabon faces a number of threats including logging and poaching. However 11% of the country's area is now protected in a network of 13 national parks established in 2002.
References
Sources
African Bird Club (2008) Birds and Birding in Gabon. Accessed 18 June 2008.
Warne, Sophie (2003) Gabon, São Tomé and Príncipe: The Bradt Travel Guide, Bradt.
External links
"Gabon to Create Huge Park System for Wildlife", National Geographic.
Biota of Gabon
Fauna of Gabon
Flora of Gabon
Gabon | Wildlife of Gabon | [
"Biology"
] | 567 | [
"Biota by country",
"Wildlife by country",
"Biota of Gabon"
] |
10,948,885 | https://en.wikipedia.org/wiki/Wildlife%20of%20Equatorial%20Guinea | The wildlife of Equatorial Guinea is composed of its flora and fauna.
Overview
There are approximately 3,250 species of plants. Africa has high animal diversity. There are at least 194 mammal species; 418 species of birds, and 91 reptile species.
Fauna
Mammals are found throughout Equatorial Guinea. Within Equatorial Guinea there are gorillas, leopards, chimpanzees, a small population of African elephants, hippopotamuses, Cape buffalo, crocodiles, pythons, various monkeys among other animals.
The gorillas of Equatorial Guinea are the western lowland gorilla subspecies. The elephants are African forest elephants. Despite poaching, the leopards are widespread and are found even in the suburbs of some major cities. For a full list of mammals, see List of mammals of Equatorial Guinea.
References
External links
Flora de Guinea, Spanish-language database about flora of Equatorial Guinea. Handled by the Royal Botanic Garden of Madrid.
Biota of Equatorial Guinea
Equatorial Guinea
Rainforests of Africa | Wildlife of Equatorial Guinea | [
"Biology"
] | 199 | [
"Biota by country",
"Wildlife by country",
"Biota of Equatorial Guinea"
] |
10,948,968 | https://en.wikipedia.org/wiki/Biodiversity%20of%20Ghana | The wildlife of Ghana is composed of its biodiversity of fungi, flora and fauna.
Biodiversity
Fungi
Ghana is home to a significant number of fungi species including: Aspergillus flavus; Athelia rolfsii; Auricularia auricula-judae; Curvularia; Fusarium oxysporum; Fusarium solani f.sp. pisi; Gibberella intricans; Gibberella stilboides; and Macrophomina phaseolina. The true total number of fungal species occurring in Ghana is in the thousands and given the generally accepted estimate that only about 7 percent of all fungi worldwide have so far been discovered and that the amount of available information is still very small.
Flora
The flora of Ghana is diverse with both indigenous and introduced floral species considered in Ghana's floral diversity. A total of some 3,600 species of the major regional centres of endemism represent the three major taxonomic groups. Floral diversity is more pronounced among the angiosperms represented with well over 2,974 indigenous and 253 introduced species in Ghana. Among the various vegetation types of the tropical rain forest, it is the wet evergreen forest type in the southwestern Ashanti-Kwahu Plain that exhibits the highest level of endemism and species richness in Ghana.
Flora species diversity and endemism in the savanna biomes in Ghana is very sparse and biological diversity of species in the Ghanaian savanna woodlands and gallery forests of the savannas show greater species richness than the dry savannas. Within Ghana, there are areas of high biological diversity, referred to as prime biological locations; such as the Ankasa and Nini-Suhien Conservation Area in the southwestern Ashanti-Kwahu erea terrestrial plain of Ghana, in where the climatic diversity is greater. There are also Encephalartos barteri, and gymnosperm indigenous to Ghana; others growing in various Ghanaian ecological zones are introduced species for purposes including aesthetics and economic. The third taxonomic group; pteridophytes, is well represented in Ghana with 124 known species.
Fauna
Ghana has a vast array of fauna and they are of great significance, as some of Ghana's fauna have attained conservation status because of the current rate of decline in their number and distribution. The fauna of the Ghanaian terrestrial ecosystem, comprise a diverse array of species including several of conservation concern. Ghanaian records show that there is as many as 221 species of amphibians and reptiles, 724 species of birds, 225 mammalian species inhabiting Ghana; with 93 recorded to be inhabiting the Ghanaian savanna ecological zone. As with floral diversity, prime locations for faunal diversity is located in the Ghanaian high forest uplands; accounting for 83% of the total number of butterfly species recorded in Ghana, where canopy stratification and micro-climatic differentiation have provided habitats and niches for specific faunal organisms.
Endemism among Ghanaian terrestrial fauna has been observed in three species of frogs; Hyperolius baumanni; Hyperolius fusciventris; and Hyperolius sylvaticus; and the lizards; and Agama sylvanus found in the Ghanaian Bia Forest Reserve and the Atwema Range Forest Reserve. Ghana has a high degree of butterfly endemism where more than 20 species are classified endemic or near-endemic. Ghana is home to 84 known amphibian species: 78 frogs, 5 toads and caecilians. Threatened species recorded in Ghana include four species of marine turtles and three species of crocodiles. Bird species of conservation concern include seven threatened species, including four species endemic to the Upper Guinea forest block and seven near-threatened species.
Keystone species such as hornbills, parrots and birds of prey (eagles) are well represented in Ghana. Of the 728 birds species confirmed to be occurring in Ghana; 408 are non-passerines and 320 passerines, of which 498 are known or thought to be resident and 176 are regular seasonal bird migrants, including 100 from the Palearctic realm. Of the total number of species occurring; 180 restricted to the Guinea-Congo forests biome and 37 restricted to the Sudan-Guinea savanna biome have been recorded in Ghana. Eleven of the 15 endemic bird species within the Upper Guinea forest occur in Ghana. Six of the total species are considered threatened and 12 are near-threatened.
Ghana is an important country for dozens of vulnerable, threatened, endangered, critically endangered or near-extinct mammalian species including the primates common chimpanzee (Pan troglodytes) and western red colobus (Piliocolobus badius), the big cats lion (Panthera leo) and leopard (Panthera pardus), African bush elephant (Loxodonta africana), and water-birds, being located on the boundary of the east Atlantic Ocean Flyway and Mediterranean Flyway. There are also several rare terrestrial birds, such as the white-necked rockfowl (Picathartes gymnocephalus).
Mammals
Guinea baboon
Red river hog
Birds
Blue-headed wood-dove
Iris glossy-starling
Reptiles
Bitis rhinoceros
Amphibians
Gallery
References and notes
Biota of Ghana | Biodiversity of Ghana | [
"Biology"
] | 1,065 | [
"Biota by country",
"Biota of Ghana"
] |
10,949,013 | https://en.wikipedia.org/wiki/Wildlife%20of%20Guinea-Bissau | Guinea-Bissau is a West-African country rich in biodiversity.
Fauna
Mammals
Predators
There still is much debate about the status of many predator species in Guinea-Bissau. This is, in part, because much of the country remains unstudied, and because of the cryptic nature of many predator species. The lion, for instance, was listed as possibly extinct in Guinea-Bissau during the 2014 assessment of the lion by the IUCN Red List of Threatened Species. However, a picture of a lion was still recorded by a camera trap in 2016 the southeastern Boé region.
Lion (Panthera leo)
Leopard (Panthera pardus)
African wild dog (Lycaon pictus)
African golden cat (Caracal aurata)
Caracal (Caracal caracal)
Serval (Leptailurus serval)
Spotted hyena (Crocuta crocuta)
African wildcat (Felis lybica)
Primates
Western chimpanzee (Pan troglodytes verus)
Herbivores
Red river hog
Warthog
Birds
Blue-headed wood-dove
Iris glossy-starling
Reptiles
Bitis rhinoceros
Marine life
The tropical marine environment of Guinea-Bissau has a high diversity of sea life, notably in and around the Bijagós Archipelago. Fishes include the African butter catfish, Malapterurus occidentalis, Parablennius sierraensis (combtooth blenny), five Synodontis catfish species including annectens, ansorgii, nigrita, schall and waterloti, the three-banded butterflyfish and Trachinus pellegrini. Turtles are also dominant especially the West African mud turtle.
Flora
Flora of Guinea-Bissau
See also
João Vieira and Poilão Marine National Park
References
External links
Biota of Guinea-Bissau
Guinea-Bissau | Wildlife of Guinea-Bissau | [
"Biology"
] | 382 | [
"Biota by country",
"Wildlife by country",
"Biota of Guinea-Bissau"
] |
10,949,072 | https://en.wikipedia.org/wiki/Wildlife%20of%20Liberia | The wildlife of Liberia consists of the flora and fauna of the Republic of Liberia. This West African nation has a long Atlantic coastline and a range of habitat types, with a corresponding diversity of plants and animals. Liberia is considered a biodiversity hotspot and has more intact forests characteristic of the Upper Guinea Massif than do neighbouring countries. There are 2000 species of vascular plants (including 225 tree species), approximately 140 species of mammals, and over 600 species of birds.
Geography
The country lies close to the equator with a long coastline on the Atlantic Ocean. The terrain consists of flat or undulating coastal plains, which rise to a rolling plateau and low mountains in the northeast. A number of short rivers flow from northeast to southwest. The coastal area is characterised by swamps and mangrove forests, while inland the tropical forests give way to grassland on the drier plateau area. The climate is equatorial with some rain all year round but the main rainy season falling between May and October. Most of the coastal area receives about of rain per year but this decreases inland, with the northern part of the country being the driest, with just half the coastal rainfall.
The coastal area west of Monrovia is forested and has coastal swamps and lagoons, and there are swamps around the lagoon of Bassa Bwa, but there are no substantial wetlands inland.
Biodiversity
Liberia can be considered a biodiversity hotspot and has the highest remaining portion of the forests of the Upper Guinea Massif, containing many species endemic to the region. This humid coastal forest ecosystem extends from Liberia through Cote d‘Ivoire, Ghana and Sierra Leone to Togo, and is under threat from deforestation and coastal development. Liberia has more than 2000 species of vascular plant including 225 timber tree species, 140 species of mammal, over 600 species of bird and 75 species of reptile and amphibian.
Flora
Two main types of forest are found in Liberia. Evergreen forests in the south east of the country, which has very high rainfall, are characterised by dense vegetation with trees of varying heights. Sapo National Park exemplifies this forest type, and contains many endemic species. Moist semi-deciduous forest is found in the central and northwestern parts of the country with slightly lower rainfall. This has a more even height and a more open aspect. In 2009 it was estimated that forest cover amounted to about 32% of the country's area. There are eleven partially protected national forests.
Patches of mangrove occur along the coast and near the mouth of many rivers, often lining the banks of the rivers' lower reaches. Mangrove ecosystems are important for biodiversity, as a habitat for crustaceans and young fish, for flood control and erosion control. However, mangroves are threatened by overharvesting for charcoal and firewood, and already there are few remaining areas of primary forest.
Fauna
Mammals
The pygmy hippopotamus occurs in riverine forests inland, for example those beside the Lofa, Cestos and Cavalla Rivers. Liberia is its main habitat, with smaller populations in neighbouring countries. The African manatee also occurs along the coast and in many of the river systems. Other mammals found in the forests are leopards, monkeys, chimpanzees, antelopes, elephants and anteaters. The Liberian mongoose is probably the rarest mammal, none having been seen for years until one was captured in 1989; it is hunted for bushmeat and classified as vulnerable by the IUCN. The red river hog is much more common.
Sapo National Park hosts around 125 species of mammal. These include the African golden cat, the drill, seven species of monkey, Gola malimbe and the Liberian mongoose. The park is also home to the African civet, giant forest hog, speckle-throated otter, seven species of duiker, the water chevrotain and three species of pangolins.
Birds
As of 2016, the number of bird species recorded in Liberia is 695, some resident and some migratory, with 21 of them being globally threatened. These rare species include the white-backed vulture, the hooded vulture and the Balearic shearwater. Lake Piso, a coastal lagoon, is one of five wetland sites in the country which have been designated as Ramsar sites.
Some of the larger birds found in the rainforest are parrots, woodpeckers and hornbills. Flamingoes are found in the coastal swamps and lagoons. Other resident species are the black-collared lovebird, the blue-headed wood-dove, the white-breasted guineafowl and the white-necked rockfowl. The pepper bird (Pycnonotus barbatus) is the national bird.
Around 590 species of bird have been recorded in Sapo National Park. These include the white-breasted guineafowl and white-necked rockfowl, the African fish eagle, the African grey parrot, the great blue turaco, the woodland kingfisher, egrets, hornbills, bee-eaters, rollers and sunbirds.
Reptiles and amphibians
The Nile crocodile and the dwarf crocodile occur in the coastal mangrove swamps but are rare, while the West African crocodile occurs further inland and is relatively common. There are a wide variety of lizards, chameleons, geckos and snakes, including Bitis rhinoceros, a venomous viper endemic to West Africa, slender tree snakes that feed on birds and their eggs, and blind snakes in the genus Typhlops. Six species of turtle are found in Liberia, three marine and three freshwater, although one of the latter, the forest hinge-back tortoise is largely terrestrial.
With the high rainfall, amphibians are plentiful in the country, and include several genera endemic to the region including Silurana, Hymenochirus and Pseudhymenochirus. Other frogs native to Liberia include the African common toad, the western clawed frog, and the crowned bullfrog. A number of species of tree frog live in the foliage of trees, and the worm-like caecilian Geotrypetes seraphini inhabits ants' nests.
Fish
Freshwater fish found in the lakes, rivers, streams and brackish swamps of Liberia include the African brown knifefish, the Guinean killifish, the Jeanpol's killi, the Norman's lampeye, the Rancurel's lampeye and the banded lampeye. The rough-head sea catfish occurs in brackish and marine habitats and is of interest to fisheries. Other commercially-fished species are the Madeiran and round sardinellas, the Spanish mackerel, the bonga, and the European anchovy, and large quantities of shrimps and lobsters are brought ashore.
Butterflies and moths
About 530 species of butterfly are known to be from Liberia, one of which is endemic.
Conservation
Like other West African nations, Liberia is experiencing destruction of its native forests and a resulting decrease in biodiversity. The main conservation threats are the replacement of forests by rubber plantations, and more recently by oil palm plantations, mining, lumbering, unsustainable firewood collection, charcoal production, the introduction of alien species, slash-and-burn cultivation practices and the uncontrolled hunting and harvesting of wild animals and plants. An action plan, running from 2017 to 2027, has been put in place which is designed to educate the populace in order to "promote the conservation and sustenance of Liberia‘s rich biological diversity, resources and culture".
References
See also
Flora of Liberia
Environmental issues in Liberia
Biota of Liberia
Liberia | Wildlife of Liberia | [
"Biology"
] | 1,559 | [
"Biota by country",
"Wildlife by country",
"Biota of Liberia"
] |
10,949,176 | https://en.wikipedia.org/wiki/Wildlife%20of%20the%20Gambia | The wildlife of the Gambia is dictated by several habitat zones over the Gambia's land area of about 10,000 km2. It is bound in the south by the savanna and on the north by the Sudanian woodlands. The habitats host abundant indigenous plants and animals, in addition to migrant species and newly planted species. They vary widely and consist of the marine system, coastal zone, estuary with mangrove vegetation coupled with Banto Faros (barren hypersaline flats), river banks with brackish and fresh water zones, swamps covered with forests and many wetlands.
According to the government of the Gambia, about 3.7% of the land area of the country has been brought under national parks or reserves, and the present wildlife policy is to extend this coverage to 5%. The seven areas included in the protected list are the Niumi National Park, Kiang West National Park, River Gambia National Park, Bao Bolong Wetland Reserve, Abuko Nature Reserve, Tanbi Wetland Complex and the Tanji Karinti River Bird Reserve. These are managed by the Department of Parks and Wildlife Management. The area covered by these parks is 38,000 ha.
The birdlife in the Gambia is colourful and rich, with 560 species inhabiting coastal saltwater, freshwater wetlands, Guinea and Sudan savanna, woodlands and forests, agricultural lands, towns and villages. It is thus a biodiversity hot spot for ornithologists.
Geography
The flat terrain of the Gambia, drained by the Gambia River is categorised under several habitat types. The habitat types are the coast, mangroves and Banto Faros, wetlands, farmlands, savanna and the Sahel habitats, gallery forests and urban habitats.
The coast extends to into the sea with extensive sea green grass meadows where aqua fauna dominate; the long stretch of beach here, with occasional hills or cliffs, is topped with plants which are salt tolerant and bind the terrain. Above these are the very old beaches at an elevation where the rich vegetation consists of baobab (Adansonia digitata) and ron palm (Borassus aethiopum) species interspersed with shrubs and grassland. The sea grass meadows of the coastal areas are rich in green sea turtles (Chelonia mydas), dolphins, common minke whales (Balaenoptera acutorostrata) and Mediterranean monk seals (Monachus monachus), which feed on the fish.
Mangroves and Banto Faros are the mangrove swamp forests seen at the mouth of the Gambia River and extending along the river inland up to Kaur, into the brackish river stretch. It is a transitional zone between aquatic and terrestrial habitats. Two types of mangrove forests, namely the white mangrove colonies and the red mangroves, are of short height near the coast but raise to 15–20 m upstream. Banto Faros are found, after the mangroves, in flat lands which are barren and salt encrusted; however, succulent plants grow in some of the less saline thick mats. Fishes spawn in the mangroves before they move offshore into the sea. Mangrove oysters, (Crassostrea gasar and Crassostrea tulipa) are also extensively found on mangrove trees in this habitat. The trees are used as firewood and as building material.
Wetlands consist of salt pans, lagoons, marshes, mangrove swamps, mudflats, saltwater rivers, fresh water reaches of rivers such as the Gambia River, flooded sand mines, watering holes for animals, paddy fields and ephemeral marshes with reed vegetation in flooded areas. Crustaceans, annelid worms and molluscs are the fauna in the wetlands where migrant birds and wading birds find their feed.
Farmlands, including savanna and woodland, form now a dominant habitat in the Gambia where crops were grown initially on a rotation system of 20 years with a fallow period. This practice has since changed to two or three years rotation. While the agricultural crops grown are sorghum, millet and ground nuts, the tree species retained, within the lands cleared for agricultural use, are the Acacia albida, baobab, ficus species, winterthorn and African locust bean (Parkia biglobosa).
Savanna and the Sahel habitats are of two types. One is the southern Guinea savanna which has rich and dense vegetation of over 50 tree species. The other is the Sudanian savanna which is contiguous to the Guinea savanna on the north bank of the Gambia River. These areas are dry woodlands with soils of laterite formations. The local tree species include silk cotton (Bombax costatum), dry-zone mahogany (Khaya senegalensis) in deeper soil areas and African rosewood (Guibourtia coleosperma). Short grasses and shrubs are seen thinly spread in the Sahelian habitats.
The gallery forests (moisture forests), unlike the rainforest, thrive on groundwater and are integral to savannas. It is a rare habitat found only in Abuko Nature Reserve, Pirang Forest Park and in some stretches of the Gambia River with different set of species with some degree of overlap with rainforests.
Urban habitats consist of numerous villages. The open areas in between have large green stretches with a profusion of tree species, particularly mango (Mangifera indica) trees.
Law of the land
Some parts of the land area of the Gambia, under the protection of the Banjul Declaration of 1977, which is the law on wild life, includes seven protected zones. The law prohibits all types of hunting, except of animals harmful to the environment, such as warthogs, giant pouched rats and francolins. Also, as a signatory to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), the Gambia enforces laws prohibiting export or even possession within the country of any animal skins, horns or turtle shells.
Fauna
Mammals
More than 100 species of mammals have been reported.
Bats
There are 30–40 species of bats. They are of two types, fruit-eating and insect-eating bats. Straw-coloured fruit bats (Eidolon helvum) and epaulated fruit bats (Epomophorus gambianus) are the most common species. Bats help in eating the malarial insects, with each bat consuming about 3000 mosquitoes per night. Eidolon helvum is a commonly seen bat during the rainy season when flowers and fruits (mangoes) are in full bloom.
Rodents
Rodents include the Gambian sun squirrel (Heliosciurus gambianus), striped ground squirrels (Xerus erythropus)s, nocturnal crested porcupines (Hystrix cristata), mongooses, brush-tailed porcupine, civets and genets.
Aquatic mammals
Aquatic mammals include two species of dolphin, the Atlantic bottlenose dolphin (Tursiops truncatus) and the Atlantic humpback dolphin (Sousa teuszii) and the West African manatee (Trichechus senegalensis).
Carnivores
Leopards and hyenas are still occasionally thought to cross into the more remote areas of East Gambia.
Herbivores
Bushbuck, Maxwell's duiker, warthog and hippopotamus.
Primates
Bijilo forests have endangered western red colobus monkey, the callithrix monkey (Chlorocebus sabaeus). King West National Park has baboons, and patas monkeys (Erythrocebus patas). The Senegal bushbaby (Galago senegalensis), Campbell's mona monkey (Cercopithecus campbelli). The River Gambia National park has chimpanzee (Pan troglodytes). The western red colobus (Procolobus badius) are a common sight in the Kiang West National Park, Bijilo Forest Park and Abuko Nature Reserve. Guinea baboon (Papio papio), which is large in size and fierce in appearance, is found in the northern region and also in small numbers in the coastal Makasutu Culture Forest.
The aardvark is also still reported, although very rarely seen.
Reptiles and amphibians
There are 40 snake species, 9 of which are venomous, such as cobras, puff adders and mambas, genus Dendroaspis; the first two are common. The non-venomous reptiles are pythons, bush snakes, lizards agamas and skinks (with brown and orange flanks); Bosc's monitor, Nile monitors (Varanus niloticus), which are voracious predators; tree geckos; and chameleon.
Three species of crocodiles reported are: slender-snouted crocodile (Mecistpos cataphractus), West African dwarf crocodile (Osteolaemus tetraspis) and West African crocodile; the first two are on the endangered list.
Amphibians consist of 33 species, toads, tree frogs, crowned bullfrogs, edible bullfrogs and reed frogs.
Birds
More than 500 species of birds live in the Gambia. The Bijilo Forest Park and the Abuko are important bird habitats. Birds seen here are the pelicans, spoonbills, yellow-billed stork (Mycteria ibis), Goliath heron (Ardea goliath), blue-cheeked bee-eater (Merops persicus), mouse-brown sunbird (Anthreptes gabonicus), African fish eagle (Hieraaetus spilogaster) (in the river valleys). Wetland bird species are Dendrocygna viduata, sacred ibis (Threskiornis aethiopicus), palm-nut vulture (Gypohierax angolensis), crakes, greater painted snipe (Rostratula benghalensis) and African jacana (Actophilornis africanus).
Butterfly distribution in the Gambia is dictated by the boundary of two major biomes of Sahelian and Guinean Savanna species; it is distinctly different between the rainy season and dry season.
Flora
The vegetation of the Gambia is mostly savanna in the upland areas, inland swamp in the low-lying areas, and mangrove swamp along the banks of the lower Gambia River. The country is almost devoid of true forest cover, the most forested area being the Bijo Forest. Nonetheless it is biologically rich, with an estimated 11,600 plant species many of which are used for medicinal purposes. Many plants are grown for food. The cassava (Manihot esculenta) was brought to the Gambia by the Portuguese between the 17th and 18th centuries. It grows up to 4 metres high and is a staple of the national diet, with each person consuming an average of 100 kg per annum in 2002 according to the Food and Agriculture Organization. Coastal inland forest comprises part of Bijilo Forest Park, Abuko Nature Reserve, Pirang Forest Park, and the River Gambia National Park.
The gummy Combretum glutinosum, Combretum micranthum, Combretum paniculatum and Combretum racemosum are common shrubs in the savanna areas of the country. Combretum paniculatum may be found on the edges of the forests in the north of the country. These plants usually have red petals and the Combretum racemosum has red 4-part flowers, but with inflorescence rimmed by white bracts.
References
Bibliography
Further reading
Penney, D. 2009. Common Spiders and Other Arachnids of The Gambia, West Africa. Siri Scientific Press, Manchester. .
Gambia
Biota of the Gambia | Wildlife of the Gambia | [
"Biology"
] | 2,398 | [
"Biota by country",
"Wildlife by country",
"Biota of the Gambia"
] |
10,949,251 | https://en.wikipedia.org/wiki/Sample%20%28material%29 | In general, a sample is a limited quantity of something which is intended to be similar to and represent a larger amount of that thing(s). The things could be countable objects such as individual items available as units for sale, or an uncountable material. Even though the word "sample" implies a smaller quantity taken from a larger amount, sometimes full biological or mineralogical specimens are called samples if they are taken for analysis, testing, or investigation like other samples. They are also considered samples in the sense that even whole specimens are "samples" of the full population of many individual organisms. The act of obtaining a sample is called "sampling" and can be performed manually by a person or by automatic process. Samples of material can be taken or provided for testing, analysis, investigation, quality control, demonstration, or trial use. Sometimes, sampling may be performed continuously.
Aliquot part
In science, a representative liquid sample taken from a larger amount of liquid is sometimes called an aliquot or aliquot part where the sample is an exact divisor of the whole. For example, 10mL would be an aliquot part of a 100mL sample.
Sample characteristics
The material may be solid, liquid, gas, a material of some intermediate characteristics such as gel or sputum, tissue, organism, or a combination of these. Even if a material sample is not countable as individual items, the quantity of the sample may still be describable in terms of its volume, mass, size, or other such dimensions. A solid sample can come in one or a few discrete pieces, or it can be fragmented, granular, or powdered. A section of a rod, wire, cord, sheeting, or tubing may be considered a sample. Samples which are not a solid piece are commonly kept in a container of some sort.
Where goods are sold or supplied by reference to a sample, relevant sale of goods legislation may dictate the supplier's legal obligations in ensuring that the bulk of the goods corresponds with the goods comprising the sample, for example in the UK, the Sale of Goods Act 1979, section 15, the Supply of Goods and Services Act 1982, section 5, and the Consumer Rights Act 2015, section 13.
See also
Core sample
Ice core
Specimen (disambiguation)
References
Analytical chemistry
Clinical pathology
Laboratories | Sample (material) | [
"Chemistry"
] | 483 | [
"nan"
] |
10,949,578 | https://en.wikipedia.org/wiki/4-Maleylacetoacetic%20acid | 4-Maleylacetoacetate (4-maleylacetoacetatic acid) is an intermediate in the metabolism of tyrosine. It is converted to fumarylacetoacetate by the enzyme 4-maleylacetoacetate cis-trans-isomerase. Gluthathione coenzymatically helps in conversion to fumarylacetoacetic acid.
See also
Homogentisate 1,2-dioxygenase
Beta-keto acids
Enones
Diketones | 4-Maleylacetoacetic acid | [
"Chemistry",
"Biology"
] | 110 | [
"Biochemistry stubs",
"Biotechnology stubs",
"Biochemistry"
] |
1,566,231 | https://en.wikipedia.org/wiki/Tar | Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat.
Mineral products resembling tar can be produced from fossil hydrocarbons, such as petroleum. Coal tar is produced from coal as a byproduct of coke production.
Terminology
"Tar" and "pitch" can be used interchangeably. Asphalt (naturally occurring pitch) may also be called either "mineral tar" or "mineral pitch". There is a tendency to use "tar" for more liquid substances and "pitch" for more solid (viscoelastic) substances. Both "tar" and "pitch" are applied to viscous forms of asphalt, such as the asphalt found in naturally occurring tar pits (e.g., the La Brea Tar Pits in Los Angeles). "Rangoon tar", also known as "Burmese oil" or "Burmese naphtha", is also a form of petroleum. Oil sands, found extensively in Alberta, Canada, and composed of asphalt, are colloquially referred to as "tar sands".
Wood tar
Since prehistoric times wood tar has been used as a water repellent coating for boats, ships, sails, and roofs. In Scandinavia, it was produced as a cash crop. "Peasant Tar" might be named for the district of its production.
Wood tar is still used as an additive in the flavoring of candy, alcohol, and other foods. Wood tar is microbicidal. Producing tar from wood was known in ancient Greece and has probably been used in Scandinavia since the Iron Age. Production and trade in pine-derived tar was a major contributor in the economies of Northern Europe and Colonial America. Its main use was in preserving wooden sailing vessels against rot. For centuries, dating back at least to the 14th century, tar was among Sweden's most important exports. Sweden exported 13,000 barrels of tar in 1615 and 227,000 barrels in the peak year of 1863. The largest user was the Royal Navy of the United Kingdom. Demand for tar declined with the advent of iron and steel ships. Production nearly stopped in the early 20th century. Traditional wooden boats are still sometimes tarred.
The heating (dry distilling) of pine wood causes tar and pitch to drip away from the wood and leave behind charcoal. Birch bark is used to make particularly fine tar, known as "Russian oil", used in Russian leather protection. The by-products of wood tar are turpentine and charcoal. When deciduous tree woods are subjected to destructive distillation, the products are methanol (wood alcohol) and charcoal.
Tar kilns (, , , ) are dry distillation ovens, historically used in Scandinavia for producing tar from wood. They were built close to the forest, from limestone or from more primitive holes in the ground. The bottom is sloped into an outlet hole to allow the tar to pour out. The wood is split into dimensions of a finger, stacked densely, and finally covered tight with earth and moss. If oxygen can enter, the wood might catch fire, and the production would be ruined. On top of this, a fire is stacked and lit. After a few hours, the tar starts to pour out and continues to do so for a few days.
Uses
Tar was used as seal for roofing shingles and tar paper and to seal the hulls of ships and boats. For millennia, wood tar was used to waterproof sails and boats, but today, sails made from inherently waterproof synthetic substances have reduced the demand for tar. Wood tar is still used to seal traditional wooden boats and the roofs of historic, shingle-roofed churches, as well as painting exterior walls of log buildings. Tar is also a general disinfectant. Pine tar oil, or wood tar oil, is used for the surface treatment of wooden shingle roofs, boats, buckets, and tubs and in the medicine, soap, and rubber industries. Pine tar has good penetration on the rough wood. An old wood tar oil recipe for the treatment of wood is one-third each genuine wood tar, balsam turpentine, and boiled or raw linseed oil or Chinese tung oil.
In Finland, wood tar was once considered a panacea reputed to heal "even those cut in twain through their midriff". A Finnish proverb states that "if sauna, vodka and tar won't help, the disease is fatal." Wood tar is used in traditional Finnish medicine because of its microbicidal properties.
Wood tar is also available diluted as tar water, which has numerous uses:
As a flavoring for candies (e.g., Terva Leijona) and alcohol (Terva Viina).
As a spice for food, like meat.
As a scent for saunas. Tar water is mixed into water, which is turned into steam in the sauna.
As an anti-dandruff agent in shampoo.
As a component of cosmetics.
Mixing tar with linseed oil varnish produces tar paint. Tar paint has a translucent brownish hue and can be used to saturate and tone wood and protect it from weather. Tar paint can also be toned with various pigments, producing translucent colors and preserving the wood texture.
Tar was once used for public humiliation, known as tarring and feathering. By pouring hot wood tar onto somebody's bare skin and waiting for it to cool, they would remain stuck in one position. From there, people would attach feathers to the tar, which would remain stuck on the tarred person for the duration of the punishment. That person would then become a public example for the rest of the day.
Pitch was familiar in 9th-century Iraq, derived from petroleum that became accessible from natural fields in the region. It was sometimes used in the construction of baths or in shipbuilding.
Coal tar
Coal tar was formerly one of the products of gasworks. Tar made from coal or petroleum is considered toxic and carcinogenic because of its high benzene content, though coal tar in low concentrations is used as a topical medicine for conditions such as psoriasis. Coal and petroleum tar has a pungent odor.
Coal tar is listed at number 1999 in the United Nations list of dangerous goods.
See also
Bitumen
Creosote
Pitch (resin)
Resin
Rollins Tars
Tar Heels
Tar pit
Tarmac
Tar (tobacco residue)
References
External links
Details history and uses of "Rangoon Tar"
Materials
Polymers
Chemical mixtures
Arab inventions | Tar | [
"Physics",
"Chemistry",
"Materials_science"
] | 1,346 | [
"Materials",
"Chemical mixtures",
"Polymer chemistry",
"nan",
"Polymers",
"Matter"
] |
1,566,242 | https://en.wikipedia.org/wiki/Treehouse%20of%20Horror%20VI | "Treehouse of Horror VI" (titled onscreen as "The Simpsons Halloween Special VI") is the sixth episode of the seventh season of the American animated television series The Simpsons, and the sixth episode in the Treehouse of Horror series. It first aired on Fox in the United States on October 29, 1995, and contains three self-contained segments. In "Attack of the 50-Foot Eyesores", an ionic storm brings Springfield's oversized advertisements and billboards to life and they begin attacking the town. The second segment, "Nightmare on Evergreen Terrace", is a parody of the A Nightmare on Elm Street film series, in which Groundskeeper Willie (à la Freddy Krueger) attacks schoolchildren in their sleep. In the third and final segment, "Homer3", Homer finds himself trapped in a three-dimensional world, Earth. It was inspired by the 1962 The Twilight Zone episode "Little Girl Lost". The episode was written by John Swartzwelder, Steve Tompkins, and David X. Cohen and was directed by Bob Anderson.
The first version of the episode was very long, so it featured a very short opening sequence and did not include several trademarks established in previous Treehouse of Horror episodes. "Homer3", pitched by executive producer Bill Oakley, features three dimensional computer animation provided by Pacific Data Images (PDI). In the final scene of the episode, Homer is sent to the real world in the first ever live-action scene in The Simpsons. "Attack of the 50-Foot Eyesores" includes a cameo appearance from Paul Anka, who sings the song "Just Don't Look". Lard Lad Donuts, a fictional Big Boy-inspired donut chain created for the first segment, would ultimately be incorporated into the main continuity of The Simpsons.
In its original broadcast, the episode was watched by 22.9 million viewers, acquired a Nielsen rating of 12.9, finishing 21st in the weekly ratings, and was the highest-rated show on the Fox network the week it aired. In 1996, the "Homer3" segment was awarded the Ottawa International Animation Festival grand prize in Ottawa, Ontario, Canada, and the episode was nominated for the Primetime Emmy Award for Outstanding Animated Program (for Programming Less Than One Hour).
Plot
Opening
Krusty, as the Headless Horseman from The Legend of Sleepy Hollow, holds his laughing head and hurls it at the camera, causing the title, "The Simpsons Halloween Special VI", to appear on-screen in blood.
"Attack of the 50-Foot Eyesores"
Homer goes to Lard Lad Donuts to get a "colossal doughnut". Upon realizing that the colossal doughnut is the name of the doughnut that Lard Lad holds and actual doughnuts that size do not exist, he denounces the store and vows to get a colossal doughnut. He returns that night and steals the giant doughnut from the Lard Lad statue in front of the store. In the midst of a freak storm, Lard Lad and the other giant advertising statues come to life to terrorize Springfield. At Marge's insistence, Homer eventually returns the doughnut to Lard Lad, but that does not stop Lard Lad and his friends from causing destruction.
Lisa goes to the ad agency that created those advertising characters, and an executive suggests the citizens stop paying attention to the monsters as they are advertising gimmicks, and attention is what keeps them motivated. He suggests a jingle will help distract people from watching the monsters. Lisa and Paul Anka later perform a catchy song and the citizens of Springfield stop looking at the monsters, who lose their powers and become lifeless (although Homer has to be dragged away from the Lard Lad statue, holding a sign reading "Now With Sprinkles"). Homer is distracted and Lard Lad drops the doughnut, which rolls past Kang and Kodos, who are trying to hitchhike to Earth's capital. Kent Brockman signs off by warning of the dangers of advertising and Homer says "We'll be right back."
"Nightmare on Evergreen Terrace"
Bart has a nightmare that Groundskeeper Willie is out to kill him. He is slashed with a rake, and the scratches are still on his body after he wakes up. Many other students at Springfield Elementary School also say they were terrorized by Willie in their nightmares. When the students take a test, Martin—having finished his test first—falls asleep and is strangled to death by Willie in his dream, before waking up and dying in the real world. After Bart and Lisa tell Marge about the incident, she explains Willie burned to death after the thermostat was turned too high, his suffering drawn out by the spendthrift disrepair of the school and the parents of the students looking on and doing nothing; Willie swore that he would take his revenge out on their children in their dreams where their parents could not protect them.
Bart, Lisa, and Maggie try not to fall asleep for several days, but eventually, Bart decides that he is going to have to go to sleep and fight Willie in his dream. Bart falls asleep and attempts to find Willie, who appears as a lawn mower. Bart manages to trick Willie into mowing a sandbox containing quicksand, and Willie sinks. Willie recovers and turns into a giant bagpipe spider and is about to kill Bart as well as Lisa, who has entered the dream after also falling asleep. Suddenly, Maggie appears and uses her pacifier to seal the vent on Willie's spider body, resulting in Willie exploding. The Simpsons children awaken and despite being pleased to be alive, Lisa fears that Willie might still be around "out there, and could back, any time, in any form." As it turns out, a very much alive and well Willie exits a bus and tries to scare the children, but loses a shoe as he chases the bus to retrieve a gun he left aboard.
"Homer3" ("Homer Cubed")
Patty and Selma visit the Simpsons, driving Bart, Lisa, and even the pets to evade them and consequently leave almost no place for Homer to hide. Desperate to avoid his wife's sisters, he looks behind a bookcase and enters a mysterious new world in which everything is in 3D. Homer explores the peculiar area, and finds that he is trapped within (the rest of the family can only hear his voice). He seeks help from them, but their attempts to rescue him are fruitless.
After a cone hits Homer, he throws it point first into the floor and accidentally pierces the fabric of the space-time continuum, creating a blackhole that threatens to pull Homer and the rest of the dimension into it. Bart takes command and enters the third dimension to save Homer. Bart is unable to help, however, and the universe implodes on itself. Bart is pulled back into the house and Marge is sad that her husband is gone; Reverend Lovejoy attempts to console her by saying he has gone to "a better place". Homer is sent into the real world, landing in a dumpster in a live-action Sherman Oaks, Los Angeles. He walks around, frightened as people stare at him, but then is pleased to find an erotic cake store.
Production
"Treehouse of Horror VI" was the first of two Treehouse of Horror episodes to be executive produced by Bill Oakley and Josh Weinstein. The episode was "so long" because, according to Oakley, "all three of these segments are very complex stories [...] and it's hard to fit three complete stories into 21 minutes". Because of the length, the episode featured a very short opening sequence and did not include several trademarks established in previous Treehouse of Horror episodes, such as Marge's warning or wraparounds. The first segment, "Attack of the 50-Foot Eyesores", was written by John Swartzwelder, who had previously worked at an advertising agency. "Nightmare on Evergreen Terrace" was written by Steve Tompkins and has been described by David X. Cohen as "one of the scariest [segments]". "Homer3" was written by Cohen, although the idea was pitched by Oakley. The original idea was that Homer would visit several dimensions where he change through different animation art styles, including one where everything was made out of paper cut-outs, but they decided that it would be too complicated.
The episode includes a cameo appearance from Paul Anka, who sings the song "Just Don't Look". In response, he sent a letter to the producers in which he thanked them for the mention. After receiving the letter, they decided to ask him to guest star. According to David Mirkin, he tried to get Al Gore to host the episode, but the producers got no response to their request. "There was an eerie silence," Mirkin said. He added that "if the VP decides now to pursue this showbiz offer, it's just too late [...] He missed his chance."
In the final scene of the episode, Homer is sent to the real world in the first ever live-action scene in The Simpsons. It was filmed on Ventura Boulevard in Studio City and directed by David Mirkin, who later said that Fox "couldn't have been less supportive" because they thought it would be too expensive. The scene involves a crane shot which pulls back as the credits are shown. Fox "begrudgingly" allowed Mirkin to use a crane for the ending. The scene was filmed on a sidewalk with the crane on the street and Mirkin was not able to fully stop traffic for the shot. Because of this, when the camera swings around, a line of cars can be seen backed up on the street. Mirkin was also disappointed in the quality of the camera pan, again blaming the lack of support from Fox and the inability to halt the traffic.
Animation
A large portion of "Homer3" was three dimensional and computer-animated. Supervising director David Silverman was aiming for something better than the computer animation. The animation was provided by Pacific Data Images (PDI) and overseen by Tim Johnson. The animators at PDI worked closely with the 2D animators on The Simpsons and worked hard not to "reinvent the character[s]". The animators storyboarded the segments and showed the PDI animators how they would have handled the scenes. While designing the 3D model of Bart, the animators did not know how they would show Bart's hair. However, they realized that there were vinyl Bart dolls in production and purchased one to use as a model. One of the most difficult parts for the PDI animators was to make Homer and Bart move properly without making them look robotic.
One of the key shots in the segment was where Homer steps into the 3D world and his design transitions into 3D. Executive producer Bill Oakley considers the shot to be the "money shot" and had a difficult time communicating his idea to the animators.
An edited version of Homer3 appeared alongside several other shorts in the 2000 American 3-D animated anthology film, CyberWorld, shown in IMAX and IMAX 3D.
Background jokes
Several background jokes were inserted into "Homer3". The PDI animators inserted a Utah teapot, which was the first object to be rendered in 3D, and the numbers 734 (which on a phone pad correspond to PDI). Several math equations were also inserted in the background. One of the equations that appears is 178212 + 184112=192212. Although a false statement, it appears to be true when evaluated on a typical calculator with 10 digits of precision. The answer is incorrect by approximately 7 x 1029. If it were true, it would disprove Fermat's Last Theorem, which had just been proven when this episode first aired. Cohen generated this "Fermat near-miss" with a computer program. Other equations that appear are Euler's identity and P = NP which is a reference to the famous P vs NP problem, and similarly contradicts the general belief that in fact P ≠ NP. The code 46 72 69 6E 6B 20 72 75 6C 65 73 21 is a string of hexadecimal numbers that, when interpreted as ASCII codes, decodes to "Frink rules!". There is a signpost with x, y, and z, and many basic shapes littered across the screen. While wandering around, Homer walks past a building that is identical to the library from the 1993 computer game Myst, complete with a musical homage to the game's soundtrack. In The Simpsons and Their Mathematical Secrets, Simon Singh notes "we glimpse a cosmological equation (ρm0 > 3H02 /8πG) that describes the density of Homer's universe. Provided by one of Cohen's oldest friends, the astronomer David Schiminovich, the equation implies a high density, which means that the resulting gravitational attraction will ultimately force Homer's universe to collapse. Indeed, this is exactly what happens toward the end of the segment." Cohen told Entertainment Weekly that the equation predicts "the universe is going to one day collapse in on itself, and that was to represent the fact that the 3-D world collapses in on itself at the end." The fate of the universe was an unsolved problem at the time, though Cohen noted in 2018 that “astronomers now believe that our universe will not collapse back in on itself." Cohen would later include references to Fermat's Last Theorem in "The Wizard of Evergreen Terrace", where solutions to it appear on a chalkboard.
Cultural references
The title of "Attack of the 50-Foot Eyesores" is a reference to the film Attack of the 50 Foot Woman.
Lard Lad performs Godzilla’s roar after awakening and the segment includes several references to the film series.
Some of the mascots are parodies of real life mascots. The giant walking mascots of Prof. Peanut, The Giant Exterminator and the Zip Boys named Maury, Mel and Mack are parodies of Mr. Peanut, Mr. Little of the Western Exterminator company, And Manny, Moe and Jack.
"Nightmare on Evergreen Terrace" is a parody of the film A Nightmare on Elm Street and its sequels, and Bart's dream at the opening of the segment features many elements similar to the cartoons of Tex Avery.
Groundskeeper Willie shapeshifting after falling into a sandpit is a reference to the death of the shapeshifting T-1000 in the film Terminator 2: Judgment Day.
The segment "Homer3" is a parody of The Twilight Zone episode "Little Girl Lost", in which a girl travels through a portal to the 4th dimension. At one point, Homer compares the situation to "that twilighty show about that zone".
Homer passes by the library from Myst, a reference to the famed computer game of the era. Series creator Rand Miller later reflected on a call he received from the studio, when asked for permission to use the exact game graphics on the show.
The film Tron is also mentioned by Homer as a means of describing his surroundings.
The three-dimensional rotation shot of the dimensional vortex is a reference to the green glowing grid in the opening credits of the Disney film The Black Hole.
As he is about to fall in the black hole, Homer says, "There's so much I don't know about astrophysics. I wish I'd read that book by that wheelchair guy." This is a reference to the bestseller A Brief History of Time by theoretical physicist Stephen Hawking, who was quadraplegic, and who would make several guest appearances on the series.
The title of the album Erotic Cakes by guitarist Guthrie Govan is a reference to the name of the bakery shop Homer enters in this episode.
The Simpsons-themed doom-metal band Dr Colossus based their song "Lard Lad" on "Attack of the Fifty Foot Eyesores"
Reception
In its original broadcast, "Treehouse of Horror VI" finished 21st in the ratings for the week of October 23 to October 29, 1995, with a Nielsen rating of 12.9. It was watched in approximately 12.4 million households. The episode was the highest-rated show on the Fox network that week.
The authors of the book I Can't Believe It's a Bigger and Better Updated Unofficial Simpsons Guide, Warren Martyn and Adrian Wood, described it as "Complex, very assured and very clever, [...] The computer graphics are outstanding, and the final scene – as Homer enters our dimension – is one of the highlights of the entire series." Colin Jacobson of DVD Movie Guide said, "'Attack of the 50-Ft. Eyesores' stands as the strongest of the three segments. It doesn’t blast off the screen but it seems imaginative and fun. The Nightmare on Elm Street parody has its moments and comes across as generally entertaining. However, it lacks the bite the best pieces offer. Unfortunately, 'Homer3' gives us the weakest of the bunch. It tosses out a few funny bits, but it mostly feels like an excuse to feature some 3-D animation." Ryan Budke of TV Squad listed "Homer3" as the fourth best Treehouse of Horror segment and gave honorable mention to "Nightmare on Evergreen Terrace". Will Pfeifer of the Rockford Register Star called the episode "the best of the annual Halloween episodes". Mike Reiss considers the episode one of his favorites, and his favorite Treehouse installment.
In a retrospective review for The A.V. Club, Erik Adams praises the episode's visual inventiveness: "On a deeper level, 'Treehouse of Horror' endures because it's the one time a year the Simpsons staff can fully embrace the fact they make a cartoon. Various fantasy episodes and trips down the non-canonical timeline also afford this chance, but 'Treehouse of Horror' is a dependable, perennial opportunity to go whole hog with the animated wackiness. Any given episode of The Simpsons might find Homer surviving blunt trauma (and trauma and trauma and trauma, etc.), but only in 'Treehouse of Horror VI' can he trip through an interdimensional rift and drool in state-of-the-art for-1995 computer animation." He also notes that "Nightmare on Evergreen Terrace" is "packed with adventurous character designs and fantastical digressions."
In the July 26, 2007 issue of Nature, the scientific journal's editorial staff listed the "Homer3" segment among "The Top Ten science moments in The Simpsons", highlighting Cohen's "178212 + 184112=192212" equation.
In 1996, the "Homer3" segment was awarded the Ottawa International Animation Festival grand prize. The episode was also submitted for the Primetime Emmy Award in the "Outstanding Animated Program (For Programming less than One Hour)" category because it had a 3D animation sequence, which the staff felt would have given it the edge. The episode did not win the award, which went to A Pinky and the Brain Christmas. Bill Oakley, speaking in 2005 on the DVD commentary for the episode, expressed regret about not submitting "Mother Simpson," an episode with a more emotionally driven plot and felt that it would have easily won had it been submitted.
Notes
References
External links
Pacific Data Images on Homer³
The Simpsons season 7 episodes
1995 American television episodes
Fiction about child murder
Parodies of films
Parody television episodes
Treehouse of Horror
Television episodes about advertising
Television episodes about nightmares
Television episodes about curses
Television episodes written by John Swartzwelder
Television episodes about parallel universes
Television episodes with live action and animation
Fiction about black holes
Fiction about father–son relationships
Television episodes written by David X. Cohen
Halloween television episodes
Television episodes directed by Bob Anderson (director)
it:La paura fa novanta I-X#La paura fa novanta VI
fi:Simpsonit (7. tuotantokausi)#Kauhujen talo, osa 6 (Treehouse of Horror VI) | Treehouse of Horror VI | [
"Physics"
] | 4,132 | [
"Black holes",
"Unsolved problems in physics",
"Fiction about black holes"
] |
1,566,335 | https://en.wikipedia.org/wiki/OGLE-TR-122 | OGLE-TR-122 is a binary stellar system containing one of the smallest main-sequence stars whose radius has been measured. It was discovered when the Optical Gravitational Lensing Experiment (OGLE) survey observed the smaller star eclipsing the larger primary. The orbital period is approximately 7.3 days. The system's primary is thought to resemble the Sun.
OGLE-TR-122B
The smaller star, OGLE-TR-122B, is estimated to have a radius around 0.12 solar radii, or around 20% larger than Jupiter's, and a mass of around 0.1 solar masses, or approximately 100 times Jupiter's. This makes its average density approximately 50 times the Sun's or over 80 times the density of water. OGLE-TR-122b's mass is close to the lowest possible mass for a hydrogen-fusing star, estimated to be around 0.07 or 0.08 solar masses. The observed transit provides the first direct evidence for a star with a radius comparable to Jupiter's.
See also
OGLE-TR-123
EBLM J0555-57
References
Carina (constellation)
Eclipsing binaries
Carinae, V817 | OGLE-TR-122 | [
"Astronomy"
] | 252 | [
"Carina (constellation)",
"Constellations"
] |
1,566,437 | https://en.wikipedia.org/wiki/Physiologically%20based%20pharmacokinetic%20modelling | Physiologically based pharmacokinetic (PBPK) modeling is a mathematical modeling technique for predicting the absorption, distribution, metabolism and excretion (ADME) of synthetic or natural chemical substances in humans and other animal species. PBPK modeling is used in pharmaceutical research and drug development, and in health risk assessment for cosmetics or general chemicals.
PBPK models strive to be mechanistic by mathematically transcribing anatomical, physiological, physical, and chemical descriptions of the phenomena involved in the complex ADME processes. A large degree of residual simplification and empiricism is still present in those models, but they have an extended domain of applicability compared to that of classical, empirical function based, pharmacokinetic models. PBPK models may have purely predictive uses, but other uses, such as statistical inference, have been made possible by the development of Bayesian statistical tools able to deal with complex models. That is true for both toxicity risk assessment and therapeutic drug development.
PBPK models try to rely a priori on the anatomical and physiological structure of the body, and to a certain extent, on biochemistry. They are usually multi-compartment models, with compartments corresponding to predefined organs or tissues, with interconnections corresponding to blood or lymph flows (more rarely to diffusions). A system of differential equations for concentration or quantity of substance on each compartment can be written, and its parameters represent blood flows, pulmonary ventilation rate, organ volumes etc., for which information is available in scientific publications. Indeed, the description they make of the body is simplified and a balance needs to be struck between complexity and simplicity. Besides the advantage of allowing the recruitment of a priori information about parameter values, these models also facilitate inter-species transpositions or extrapolation from one mode of administration to another (e.g., inhalation to oral). An example of a 7-compartment PBPK model, suitable to describe the fate of many solvents in the mammalian body, is given in the Figure on the right.
History
The first pharmacokinetic model described in the scientific literature
was in fact a PBPK model. It led, however, to computations intractable at that time. The focus shifted then to simpler models,
for which analytical solutions could be obtained (such solutions were sums of exponential terms, which led to further simplifications.) The availability of computers and numerical integration algorithms marked a renewed interest in physiological models in the early 1970s.
For substances with complex kinetics, or when inter-species extrapolations were required, simple models were insufficient and research continued on physiological models.
By 2010, hundreds of scientific publications had described and used PBPK models, and at least two private companies have based their business on their expertise in this area.
Building a PBPK model
The model equations follow the principles of mass transport, fluid dynamics, and biochemistry in order to simulate the fate of a substance in the body.
Compartments are usually defined by grouping organs or tissues with similar blood perfusion rate and lipid content (i.e. organs for which chemicals' concentration vs. time profiles will be similar). Ports of entry (lung, skin, intestinal tract...), ports of exit (kidney, liver...) and target organs for therapeutic effect or toxicity are often left separate. Bone can be excluded from the model if the substance of interest does not distribute to it. Connections between compartment follow physiology (e.g., blood flow in exit of the gut goes to liver, etc.)
Basic transport equations
Drug distribution into a tissue can be rate-limited by either perfusion or permeability. Perfusion-rate-limited kinetics apply when the tissue membranes present no barrier to diffusion. Blood flow, assuming that the drug is transported mainly by blood, as is often the case, is then the limiting factor to distribution in the various cells of the body. That is usually true for small lipophilic drugs. Under perfusion limitation, the instantaneous rate of entry for the quantity of drug in a compartment is simply equal to (blood) volumetric flow rate through the organ times the incoming blood concentration. In that case; for a generic compartment i, the differential equation for the quantity Qi of substance, which defines the rate of change in this quantity, is:
where Fi is blood flow (noted Q in the Figure above), Cart incoming arterial blood concentration, Pi the tissue over blood partition coefficient and Vi the volume of compartment i.
A complete set of differential equations for the 7-compartment model shown above could therefore be given by the following table:
The above equations include only transport terms and do not account for inputs or outputs.
Those can be modeled with specific terms, as in the following.
Modeling inputs
Modeling inputs is necessary to come up with a meaningful description of a chemical's pharmacokinetics. The following examples show how to write the corresponding equations.
Ingestion
When dealing with an oral bolus dose (e.g. ingestion of a tablet), first order absorption is a very common assumption. In that case the gut equation is augmented with an input term, with an absorption rate constant Ka:
That requires defining an equation for the quantity ingested and present in the gut lumen:
In the absence of a gut compartment, input can be made directly in the liver. However, in that case local metabolism in the gut may not be correctly described. The case of approximately continuous absorption (e.g. via drinking water) can be modeled by a zero-order absorption rate (here Ring in units of mass over time):
More sophisticated gut absorption model can be used. In those models, additional compartments describe the various sections of the gut lumen and tissue. Intestinal pH, transit times and presence of active transporters can be taken into account
.
Skin depot
The absorption of a chemical deposited on skin can also be modeled using first order terms. It is best in that case to separate the skin from the other tissues, to further differentiate exposed skin and non-exposed skin, and differentiate viable skin (dermis and epidermis) from the stratum corneum (the actual skin upper layer exposed). This is the approach taken in [Bois F., Diaz Ochoa J.G. Gajewska M., Kovarich S., Mauch K., Paini A., Péry A., Sala Benito J.V., Teng S., Worth A., in press, Multiscale modelling approaches for assessing cosmetic ingredients safety, Toxicology. doi: 10.1016/j.tox.2016.05.026]
Unexposed stratum corneum simply exchanges with the underlying viable skin by diffusion:
where is the partition coefficient, is the total skin surface area, the fraction of skin surface area exposed, ...
For the viable skin unexposed:
For the skin stratum corneum exposed:
for the viable skin exposed:
dt(QSkin_u) and dt(QSkin_e) feed from arterial blood and back to venous blood.
More complex diffusion models have been published [reference to add].
Intra-venous injection
Intravenous injection is a common clinical route of administration. (to be completed)
Inhalation
Inhalation occurs through the lung and is hardly dissociable from exhalation (to be completed)
Modelling metabolism
There are several ways metabolism can be modeled. For some models, a linear excretion rate is preferred. This can be accomplished with a simple differential equation. Otherwise a Michaelis-Menten equation, as follows, is generally appropriate for a more accurate result.
.
Uses of PBPK modeling
PBPK models are compartmental models like many others, but they have a few advantages over so-called "classical" pharmacokinetic models, which are less grounded in physiology. PBPK models can first be used to abstract and eventually reconcile disparate data (from physicochemical or biochemical experiments, in vitro or in vivo pharmacological or toxicological experiments, etc.) They give also access to internal body concentrations of chemicals or their metabolites, and in particular at the site of their effects, be it therapeutic or toxic. Finally they also help interpolation and extrapolation of knowledge between:
Doses: e.g., from the high concentrations typically used in laboratory experiments to those found in the environment
Exposure duration: e.g., from continuous to discontinuous, or single to multiple exposures
Routes of administration: e.g., from inhalation exposures to ingestion
Species: e.g., transpositions from rodents to human, prior to giving a drug for the first time to subjects of a clinical trial, or when experiments on humans are deemed unethical, such as when the compound is toxic without therapeutic benefit
Individuals: e.g., from males to females, from adults to children, from non-pregnant women to pregnant
From in vitro to in vivo.
Some of these extrapolations are "parametric" : only changes in input or parameter values are needed to achieve the extrapolation (this is usually the case for dose and time extrapolations). Others are "nonparametric" in the sense that a change in the model structure itself is needed (e.g., when extrapolating to a pregnant female, equations for the foetus should be added).
Owing to the mechanistic basis of PBPK models, another potential use of PBPK modeling is hypothesis testing. For example, if a drug compound showed lower-than-expected oral bioavailability, various model structures (i.e., hypotheses) and parameter values can be evaluated to determine which models and/or parameters provide the best fit to the observed data. If the hypothesis that metabolism in the intestines was responsibility for the low bioavailability yielded the best fit, then the PBPK modeling results support this hypothesis over the other hypotheses evaluated.
As such, PBPK modeling can be used, inter alia, to evaluate the involvement of carrier-mediated transport, clearance saturation, enterohepatic recirculation of the parent compound, extra-hepatic/extra-gut elimination; higher in vivo solubility than predicted in vitro; drug-induced gastric emptying delays; gut loss and regional variation in gut absorption.
Limits and extensions of PBPK modeling
Each type of modeling technique has its strengths and limitations. PBPK modeling is no exception. One limitation is the potential for a large number of parameters, some of which may be correlated. This can lead to the issues of parameter identifiability and redundancy. However, it is possible (and commonly done) to model explicitly the correlations between parameters (for example, the non-linear relationships between age, body-mass, organ volumes and blood flows).
After numerical values are assigned to each PBPK model parameter, specialized or general computer software is typically used to numerically integrate a set of ordinary differential equations like those described above, in order to calculate the numerical value of each compartment at specified values of time (see Software). However, if such equations involve only linear functions of each compartmental value, or under limiting conditions (e.g., when input values remain very small) that guarantee such linearity is closely approximated, such equations may be solved analytically to yield explicit equations (or, under those limiting conditions, very accurate approximations) for the time-weighted average (TWA) value of each compartment as a function of the TWA value of each specified input (see, e.g.,).
PBPK models can rely on chemical property prediction models (QSAR models or predictive chemistry models) on one hand. For example, QSAR models can be used to estimate partition coefficients. They also extend into, but are not destined to supplant, systems biology models of metabolic pathways. They are also parallel to physiome models, but do not aim at modelling physiological functions beyond fluid circulation in detail. In fact the above four types of models can reinforce each other when integrated.
References
Further references:
Reddy M. et al. (2005) Physiologically Based Pharmacokinetic Modeling : Science and Applications, Wiley-Interscience.
Peters S.A (2012) Physiologically-Based Pharmacokinetic (PBPK) Modeling and Simulations, Wiley.
Forums
Ecotoxmodels is a website on mathematical models in ecotoxicology.
Software
Dedicated software:
BioDMET
GastroPlus
Maxsim2
PK-Sim
PKQuest
PSE: gCOAS
Simcyp Simulator
ADME Workbench
General software:
ADAPT 5
Berkeley Madonna
COPASI: Biochemical System Simulator
Ecolego
Free simulation software: GNU MCSIM
GNU Octave
Matlab PottersWheel
ModelMaker
PhysioLab
R deSolve package
SAAM II
Phoenix WinNonlin/NLME/IVIVC/Trial Simulator
Toxicology
Pharmacokinetics
Pharmaceutics | Physiologically based pharmacokinetic modelling | [
"Chemistry",
"Environmental_science"
] | 2,736 | [
"Pharmacology",
"Toxicology",
"Pharmacokinetics"
] |
1,566,591 | https://en.wikipedia.org/wiki/Grandmaster%20Ratte%27 | Grandmaster Ratte' (born Kevin Wheeler in April 1970 and formerly known as Swamp Rat and Swamp Ratte') is one of the founders of the Cult of the Dead Cow hacker group, along with Franken Gibe and Sid Vicious. His official title in the cDc was "Imperial Wizard of ExXxtasy."
References
External links
Phrack magazine profile of Grandmaster Ratte'
Damage, Inc. magazine interview
1970 births
Living people
American bloggers
People from Lubbock, Texas
Lubbock High School alumni
Cult of the Dead Cow members
Texas Tech University alumni | Grandmaster Ratte' | [
"Technology"
] | 116 | [
"Computer security stubs",
"Computing stubs"
] |
1,566,646 | https://en.wikipedia.org/wiki/Sunnyvale%20ESL%20shooting | On February 16, 1988, a mass shooting occurred at the headquarters of ESL Incorporated in Sunnyvale, California, United States. 39-year-old Richard Farley shot and killed seven people and wounded four others. A former employee of the company, he stalked his co-worker Laura Black for four years beginning in 1984. Farley was convicted of seven counts of first degree murder and is currently serving a death sentence at California Health Care Facility.
Background
Perpetrator
Richard Wade Farley was born in Texas on July 25, 1948. He was the oldest of six children. His father was in the military, therefore the family frequently relocated, and eventually settled in California. He graduated from high school in 1966 and attended Santa Rosa Junior College. Farley then joined the United States Navy in 1967 where he stayed for ten years. After his discharge in 1977, Farley began working as a software technician at ESL Inc., a defense contractor in Sunnyvale, California.
Stalking
In April 1984, 35-year-old Richard Farley met 22-year-old Laura Black, who also worked at ESL Inc. Farley described himself as immediately smitten and later said that he instantly "fell in love" with Black. Farley began leaving gifts, including letters and homemade baked goods, on Laura Black's desk and asked her out numerous times. Black repeatedly refused the invitations and later said in an interview that she "tried really to ignore him but to be cordial". Despite her refusals, Farley persisted; he began calling her desk every few hours as well as showing up at Black's aerobics class. By providing false information to the ESL HR department through pretexting, Farley was able to obtain Black's home address and home phone number. Farley was also known to have befriended the custodial department in an attempt to copy keys to Black's desk so he could rifle through her files to gain an insight into her life. He was also known to have pried through confidential personnel files of Black through false pretenses.
During this time, Farley was sending one or two letters to Black a week. Though there were periods of time during which the letters would cease, in total Farley sent about two hundred letters over a period of four years, with the final letter sent from his prison cell after his rampage at ESL. Black moved four times during those four years, but Farley was able to obtain her address every time. Farley doctored photos of him and Black being together and mailed them to her.
In fall of 1985, Black asked the Human Resources Department at ESL for help. ESL ordered Farley to attend psychological counseling sessions, and despite attending these sessions, his harassment of Black continued. By spring of 1986, Farley was threatening fellow ESL employees. Because of his poor performance, his employment with ESL was terminated in May 1986. He had been working for ESL for nine years and spent several months stalking Black full-time, then found work at a rival company, Covalent Systems Corporation in Sunnyvale.
Shooting at ESL and Standoff
Black filed for a temporary restraining order against Farley on February 2, 1988, and it was granted by a family court judge. A court date was set for February 17, 1988 to see if the restraining order should be made permanent.
Farley bought a shotgun and various other weapons and equipment. The restraining order did not prevent him from buying weapons during that time. He also owned a variety of other weapons which were not present during the shooting at ESL, including a Mossberg shotgun barrel and a Ruger .22 LR carbine and over 3,000 rounds of ammunition. On February 9, 1988, he left a package with Black's attorney, claiming to have evidence that he and Black had a longstanding relationship. The package included items such as photographs purportedly showing Black and Farley on dates, a garage door opener to Black's house, and hotel and credit card receipts. Farley claimed that Black kept a stash of cocaine that they shared once. Black's attorney dismissed the package as utter fabrications.
On the day before the court date, February 16, 1988, Farley drove his motorhome to the ESL parking lot in Sunnyvale, California. He later claimed he waited for Black to leave work so he could convince her to rescind the restraining order. If she refused, he would kill himself. At about 2:50 P.M., Farley loaded up his guns, describing his weaponry in his court testimony as a ".380 in front, the ammo pouch in front, .357 magnum to my right side, the .22 magnum behind it, a large buck knife behind that, numerous clips around the other side, and my vest, my nine millimeter, my two shotguns, and I tied a cord around the .22-250 and just draped it over me.” When police searched the building after the shooting they found a Benelli Riot semi-automatic shotgun, a rifle with a scope, a pump-action shotgun, a Sentinel revolver, a Smith & Wesson .357 magnum revolver, a Browning semiautomatic pistol, a Smith & Wesson pistol, a smoke bomb, a leather glove, a belt with pouches filled with ammunition, other bags containing more than 200 rounds of ammunition, and a vest containing more than 800 rounds of ammunition, wooden matches, a foot-long buck knife and sheath, and ear protectors.
Carrying over 1,000 rounds of ammunition with him, he approached ESL's M-5 Building, intending to make his way to Black’s second floor office. First, he fatally shot Lawrence J. Kane, 46, in the parking lot as he left the building. Farley then turned and fired at Randell Hemingway, who ducked behind his car door.
He entered a side door by shooting through the glass of the Mardex Security Door. After entering, Farley killed Wayne “Buddy” Williams Jr. behind his desk near the lobby. He then entered a stairwell where another victim was killed. On the second floor, two men and two women were killed in a hallway as Farley approached Black’s office.
Upon arriving at Black's office, he opened her door which she slammed in his face. He fired a shotgun round through the door, hitting her in the left shoulder and collapsing a lung. The injury sent her unconscious to the floor while Farley moved on.
At 3:15 p.m., Farley called emergency services and stated "I'm the one who's been wasting people." He claimed he was doing it because of Black and the restraining order against him. He also requested that people be kept 300 yards from the M-5 Building.
Farley then held a police SWAT team at bay for five hours by moving from room to room so the SWAT snipers could not target him. During the five-hour standoff, Farley spoke to negotiator Ruben Grivalja. He expressed remorse for his actions and repeatedly threatened to commit suicide. He also claimed to have had severe financial difficulties after losing his home, car, and computer and falling $20,000 behind in his taxes. Farley also fired upon computer equipment within the building.
At 3:35 P.M., Farley stated, in response to being asked if he would surrender, that he wanted to "Gloat a little bit." He also stated that he had enough ammunition to "last two hours" if he fired continuously.
At some point in the siege, he allowed longtime friend and former landlady Linda Walden to leave the building. During this exchange, fellow employee Christine Hansen left her hiding spot and also asked to leave, which Farley allowed. At several points, he told Grijalva that he did not plan to leave ESL alive and, at one period, claimed that he had changed the beneficiary of his life insurance policy from Black to his girlfriend, Mei Chang.
At 4:30 P.M,. Farley agreed to allow officers to rescue wounded individuals on the first floor. Negotiators also obtained audio recording of the conversations, where Farley stated: "There's no more reason to harm anybody; I've run out of enthusiasm for things."
He also expressed regret for shooting Black, and asked about her well-being. He claimed that he wanted Black to live so she could regret what happened. Despite this, Farley never expressed remorse for the seven victims he killed, and claimed he shot them because they were a threat.
Meanwhile, Black regained consciousness and managed to prevent her wound from bleeding further while she and other survivors hid from Farley. Black and other survivors eventually escaped.
At approximately 8:30 p.m., Farley surrendered to police after requesting a sandwich and a soft drink. Seven people were killed by Farley with four more wounded, including Black. Ninety-eight rounds were fired.
Victims
Dead
Lawrence J. Kane, 46, from San Jose
Wayne "Buddy" Williams Jr., 23, from San Jose
Ronald G. Doney, 36, from Manteca
Joseph Lawrence Silva, 43
Glenda Moritz, 27
Ronald Steven Reed, 26
Helen Lamparter, 49, from Sunnyvale
Injured
Laura Black; Shot in the Shoulder
Gregory Scott; Shot in the Forehead
Richard Townsley; Shot in the Chest
Patty Marcott; Broken Arm while fleeing
Aftermath
The next day, court commissioner Lois Kittle made the restraining order against Farley permanent and commented, "Pieces of paper do not stop bullets."
Black survived, but was hospitalized for nineteen days. She continued to work for the same company. Farley wrote to her again from his prison cell, claiming that she had finally won.
During trial, Farley admitted to the killings, but pled not guilty, claiming that he never planned to kill but only wished to get Black's attention or commit suicide in front of her for rejecting him. His attorney claimed that Farley was never a violent man and only had his judgement temporarily clouded by his obsession with Black, and that he would likely never kill again. Prior to the shooting, Farley did not have a criminal record.
The prosecution documented every step of the stalking, produced all the letters he sent, and documented his shotgun and ammunition purchases a week before his rampage at ESL, as well as his other weapons. All this amounted to extensive planning, which was evidence of premeditation.
On October 21, 1991, Farley was found guilty of all seven counts of first degree murder. On January 17, 1992, Superior Court Judge Joseph Biafore Jr. sentenced Farley to death. Because of California law, there were several automatic appeals. On January 22, 1992, Farley was admitted to San Quentin State Prison. On July 2, 2009, the California Supreme Court upheld Farley's death sentence (People v Richard Farley (2009) 46 Cal.4th 1053). , Farley was still on death row at San Quentin State Prison, as CDCR Number H23501. By April 2024, however, he was moved to California Health Care Facility, having been moved out of San Quentin as part of a larger transfer of former death row inmates.
On August 9, 2024, district attorney Jeff Rosen sought to reduce Farley's sentence to life without parole. On December 6, 2024 a Santa Clara County Judge delayed the Ruling in the Resentencing case to March 2025 to allow more victims to speak out.
This massacre helped prompt California's 1990 passage of the first anti-stalking laws in the U.S.
In media
A movie, I Can Make You Love Me (also known as Stalking Laura in the United Kingdom) was made in 1993. Brooke Shields played Black and Richard Thomas played Farley.
The shooting incident is also the subject of a chapter of the book Chinese Playground: A Memoir by Bill Lee, as well as a chapter in Obsession by John Douglas and Mark Olshaker.
The shooting is also the subject of a chapter of the book The Gift of Fear: Survival Signals That Protect Us From Violence by Gavin de Becker.
See also
List of death row inmates in the United States
List of homicides in California
List of rampage killers (workplace killings)
References
External links
Bill Lee's book, "Chinese Playground"
Associated Press news report (Page one and page two) via Newspapers.com
1988 in California
1988 mass shootings in the United States
1988 murders in the United States
Attacks on buildings and structures in 1988
Attacks on buildings and structures in California
Attacks on office buildings in the United States
Crimes adapted into films
Crimes in the San Francisco Bay Area
February 1988 events in the United States
Mass murder in 1988
Mass murder in California
Mass murder in the United States in the 1980s
Mass shootings in California
Mass shootings involving shotguns
Stalking
Workplace shootings in the United States | Sunnyvale ESL shooting | [
"Biology"
] | 2,636 | [
"Behavior",
"Aggression",
"Stalking"
] |
1,566,682 | https://en.wikipedia.org/wiki/Treehouse%20of%20Horror%20VII | "Treehouse of Horror VII" is the first episode of the eighth season of the American animated television series The Simpsons. It originally aired on the Fox network in the United States on October 27, 1996. In the seventh annual Treehouse of Horror episode, Bart discovers his long-lost twin Hugo, Lisa grows a colony of small beings, and Kang and Kodos impersonate Bill Clinton and Bob Dole in order to win the 1996 presidential election. It was written by Ken Keeler, Dan Greaney, and David X. Cohen, and directed by Mike B. Anderson. Phil Hartman provided the voice of Bill Clinton. This is the first Treehouse of Horror episode to be a season premiere.
Plot
Opening
In the kitchen, Homer Simpson lights a jack-o'-lantern but ends up lighting his arm on fire. He runs off screaming while the title, "The Simpsons Halloween Special VII" is shown on screen.
"The Thing and I"
Bart and Lisa hear strange noises coming from the attic. They investigate and discover that there is a monster. Homer and Marge realize that the creature has escaped, prompting Marge to call Dr. Hibbert. He explains that Bart has an evil twin named Hugo. The two were originally conjoined but were separated at birth.
Hugo was deemed too evil to live in society, so they chained him in the attic, where they feed him fish-heads. Bart stays behind as the others leave to search for Hugo, but Bart realizes that Hugo never left the house. Hugo takes Bart to the attic and ties him up, so that he can reattach himself, but Hibbert returns and knocks out Hugo. He then realizes that Hugo's scar is on the wrong side, therefore Bart is technically the evil twin. To make amends for their error, Hibbert and the Simpson family sit down to a turkey dinner with Hugo, leaving Bart locked in the attic with only Hugo's fish-heads to eat.
"The Genesis Tub"
In preparation for the school science fair, Lisa performs an experiment in a petri dish to see if cola will dissolve her baby tooth. Bart gives Lisa a static electric shock, claiming it is part of his project to prove that "nerds conduct electricity". The electric charge is then passed on to the tooth when Lisa tries to touch it, causing it to undergo an unusual reaction which creates a race of miniature beings. Lisa discovers this when inspecting the contents of the tub with a microscope, noting that their rate of evolution is accelerated. Bart destroys some of the ecosystem in Lisa's tub universe with his finger, and the tub people retaliate by sending a squadron of spaceships to attack him. The inhabitants of the tub then shrink Lisa to their size with a miniaturization ray and beam her down into the tub, where they explain that they regard her as God, and Bart as the Devil.
She says she can protect them from Bart if they return her to normal size, but they lack the necessary technology. Suddenly, Bart takes the tub to the science fair to the tub people's horror and submits the tiny universe as his own project, and now Lisa is forced to watch from within as Bart wins first prize. Now stuck in the tub for the rest of her life, Lisa starts to order around the tub people.
"Citizen Kang"
While out fishing, Homer is abducted by Kang and Kodos. They demand that Homer take them to Earth's leader, but Homer informs them of the 1996 United States presidential election and says the winner could be either Bill Clinton or Bob Dole. Kang and Kodos kidnap both Dole and Clinton and place them in suspended animation, assuming their forms through "bio-duplication" to ensure that one of them will become the next leader. Before returning Homer to Earth, the aliens soak him in rum, so nobody will believe him.
Most voters seem to be oblivious to the strange behaviors of Kang and Kodos in disguise, much to Homer's vexation. On the day before the election, Homer stumbles upon the badly hidden spaceship, hijacks it and releases Dole and Clinton from suspended animation. Both candidates agree they should put aside their differences and join forces to defeat the aliens and bring about a new age of bipartisanship, but Homer accidentally ejects them into space. Homer crashes the spaceship into the Capitol and unmasks the aliens, revealing the candidates' true identities to the public. However, despite being exposed, Kang and Kodos declare to the people that the two-party system means they still have to choose one of them, mocking a bystander's suggestion of voting for a third-party candidate instead. Kang is subsequently elected President of the United States, ruling as a monarchical tyrant and enslaving the American population in order to build a giant death ray. Marge complains about the work, but Homer remarks, "Don't blame me, I voted for Kodos!"
Production
Like the previous two Treehouse of Horror episodes, "Treehouse of Horror VII" does not feature any wraparound segments. "The Thing and I" was written by Ken Keeler, "The Genesis Tub" was written by Dan Greaney, and "Citizen Kang" was written by David X. Cohen. Despite the similarities, "The Thing and I" was not based on the plot of the 1982 film Basket Case. "The Genesis Tub" was originally pitched by Cohen, and it was later referenced in the South Park episode "Simpsons Already Did It", when they pointed out that The Simpsons had gotten the idea from the 1962 Twilight Zone episode called "The Little People". The sequence where tiny spaceships attack Bart in "The Genesis Tub" marks one of the first uses of computers in The Simpsons animation. The computer was used to build models for reference and the animators later retraced it. The 1996 Presidential election occurred a few days after the airing of this episode. According to Cohen, the "Citizen Kang" short violated every rule of The Simpsons as it locked the episode in one time and named specific candidates.
Cultural references
Homer sings "Fish Heads", a 1978 novelty song by Barnes & Barnes. In "The Genesis Tub", the glowing rings that "debigulate" Lisa were inspired by Metropolis. Homer crashing the flying saucer into the Capitol dome in the "Citizen Kang" segment is a reference to Earth vs. the Flying Saucers.
Reception
In its original broadcast, "Treehouse of Horror VII" finished 31st in ratings for the week of October 21–27, 1996, with a Nielsen rating of 10.5, equivalent to approximately 10.2 million viewing households. It was the third highest-rated show on the Fox network that week, following Millennium and The X-Files.
In 2017, IGN called "Citizen Kang" the best segment of the entire anthology, and placed the episode itself as number one in its ranking of all "Treehouse of Horror" episodes. The A.V. Club named Kang/Bob Dole's line, "Abortions for some, miniature American flags for others!", one of the best lines in the history of the show.
The ska punk band named I Voted for Kodos takes its name from Homer's line, "Don't blame me, I voted for Kodos", at the end of "Citizen Kang". In a 2000 Entertainment Weekly article, Matt Groening ranked this episode as his seventh favorite in the history of the show.
Kamala Harris quoted a line from "Citizen Kang" ("We must move forward, not backward; upward, not forward; and always twirling, twirling, twirling towards freedom") for a University of Chicago student scavenger hunt in 2013. A filmed clip of this moment was shown at the Simpsons panel during the 2024 San Diego Comic-Con, at a time when Harris was both the sitting vice president and the presumed Democratic presidential nominee.
References
External links
1996 American television episodes
Television episodes about alien invasion
Cultural depictions of Bill Clinton
Television episodes about curses
Fiction about size change
Television episodes about elections
The Simpsons season 8 episodes
Television episodes written by David X. Cohen
Television episodes written by Ken Keeler
Treehouse of Horror
Halloween television episodes
Television episodes written by Dan Greaney
Television episodes directed by Mike B. Anderson | Treehouse of Horror VII | [
"Physics",
"Mathematics"
] | 1,698 | [
"Fiction about size change",
"Quantity",
"Physical quantities",
"Size"
] |
1,566,768 | https://en.wikipedia.org/wiki/Material%20properties%20of%20diamond | Diamond is the allotrope of carbon in which the carbon atoms are arranged in the specific type of cubic lattice called diamond cubic. It is a crystal that is transparent to opaque and which is generally isotropic (no or very weak birefringence). Diamond is the hardest naturally occurring material known. Yet, due to important structural brittleness, bulk diamond's toughness is only fair to good. The precise tensile strength of bulk diamond is little known; however, compressive strength up to has been observed, and it could be as high as in the form of micro/nanometer-sized wires or needles (~ in diameter, micrometers long), with a corresponding maximum tensile elastic strain in excess of 9%. The anisotropy of diamond hardness is carefully considered during diamond cutting. Diamond has a high refractive index (2.417) and moderate dispersion (0.044) properties that give cut diamonds their brilliance. Scientists classify diamonds into four main types according to the nature of crystallographic defects present. Trace impurities substitutionally replacing carbon atoms in a diamond's crystal structure, and in some cases structural defects, are responsible for the wide range of colors seen in diamond. Most diamonds are electrical insulators and extremely efficient thermal conductors. Unlike many other minerals, the specific gravity of diamond crystals (3.52) has rather small variation from diamond to diamond.
Hardness and crystal structure
Known to the ancient Greeks as (, 'proper, unalterable, unbreakable') and sometimes called adamant, diamond is the hardest known naturally occurring material, and serves as the definition of 10 on the Mohs scale of mineral hardness. Diamond is extremely strong owing to its crystal structure, known as diamond cubic, in which each carbon atom has four neighbors covalently bonded to it. Bulk cubic boron nitride (c-BN) is nearly as hard as diamond. Diamond reacts with some materials, such as steel, and c-BN wears less when cutting or abrading such material. (Its zincblende structure is like the diamond cubic structure, but with alternating types of atoms.) A currently hypothetical material, beta carbon nitride (β-), may also be as hard or harder in one form. It has been shown that some diamond aggregates having nanometer grain size are harder and tougher than conventional large diamond crystals, thus they perform better as abrasive material. Owing to the use of those new ultra-hard materials for diamond testing, more accurate values are now known for diamond hardness. A surface perpendicular to the [111] crystallographic direction (that is the longest diagonal of a cube) of a pure (i.e., type IIa) diamond has a hardness value of when scratched with a nanodiamond tip, while the nanodiamond sample itself has a value of when tested with another nanodiamond tip. Because the test only works properly with a tip made of harder material than the sample being tested, the true value for nanodiamond is likely somewhat lower than .
The precise tensile strength of diamond is unknown, though strength up to has been observed, and theoretically it could be as high as depending on the sample volume/size, the perfection of diamond lattice and on its orientation: Tensile strength is the highest for the [100] crystal direction (normal to the cubic face), smaller for the [110] and the smallest for the [111] axis (along the longest cube diagonal). Diamond also has one of the smallest compressibilities of any material.
Cubic diamonds have a perfect and easy octahedral cleavage, which means that they only have four planes—weak directions following the faces of the octahedron where there are fewer bonds—along which diamond can easily split upon blunt impact to leave a smooth surface. Similarly, diamond's hardness is markedly directional: the hardest direction is the diagonal on the cube face, 100 times harder than the softest direction, which is the dodecahedral plane. The octahedral plane is intermediate between the two extremes. The diamond cutting process relies heavily on this directional hardness, as without it a diamond would be nearly impossible to fashion. Cleavage also plays a helpful role, especially in large stones where the cutter wishes to remove flawed material or to produce more than one stone from the same piece of rough (e.g. Cullinan Diamond).
Diamonds crystallize in the diamond cubic crystal system (space group Fdm) and consist of tetrahedrally, covalently bonded carbon atoms. A second form called lonsdaleite, with hexagonal symmetry, has also been found, but it is extremely rare and forms only in meteorites or in laboratory synthesis. The local environment of each atom is identical in the two structures. From theoretical considerations, lonsdaleite is expected to be harder than diamond, but the size and quality of the available stones are insufficient to test this hypothesis. In terms of crystal habit, diamonds occur most often as euhedral (well-formed) or rounded octahedra and twinned, flattened octahedra with a triangular outline. Other forms include dodecahedra and (rarely) cubes. There is evidence that nitrogen impurities play an important role in the formation of well-shaped euhedral crystals. The largest diamonds found, such as the Cullinan Diamond, were shapeless. These diamonds are pure (i.e. type II) and therefore contain little if any nitrogen.
The faces of diamond octahedrons are highly lustrous owing to their hardness; triangular shaped growth defects (trigons) or etch pits are often present on the faces. A diamond's fracture is irregular. Diamonds which are nearly round, due to the formation of multiple steps on octahedral faces, are commonly coated in a gum-like skin (nyf). The combination of stepped faces, growth defects, and nyf produces a "scaly" or corrugated appearance. Many diamonds are so distorted that few crystal faces are discernible. Some diamonds found in Brazil and the Democratic Republic of the Congo are polycrystalline and occur as opaque, darkly colored, spherical, radial masses of tiny crystals; these are known as ballas and are important to industry as they lack the cleavage planes of single-crystal diamond. Carbonado is a similar opaque microcrystalline form which occurs in shapeless masses. Like ballas diamond, carbonado lacks cleavage planes and its specific gravity varies widely from 2.9 to 3.5. Bort diamonds, found in Brazil, Venezuela, and Guyana, are the most common type of industrial-grade diamond. They are also polycrystalline and often poorly crystallized; they are translucent and cleave easily.
Hydrophobia and lipophilia
Due to great hardness and strong molecular bonding, a cut diamond's facets and facet edges appear the flattest and sharpest. A curious side effect of a natural diamond's surface perfection is hydrophobia combined with lipophilia. The former property means a drop of water placed on a diamond forms a coherent droplet, whereas in most other minerals the water would spread out to cover the surface. Additionally, diamond is unusually lipophilic, meaning grease and oil readily collect and spread on a diamond's surface, whereas in other minerals oil would form coherent drops. This property is exploited in the use of grease pencils, which apply a line of grease to the surface of a suspect diamond simulant. Diamond surfaces are hydrophobic when the surface carbon atoms terminate with a hydrogen atom and hydrophilic when the surface atoms terminate with an oxygen atom or hydroxyl radical. Treatment with gases or plasmas containing the appropriate gas, at temperatures of or higher, can change the surface property completely. Naturally occurring diamonds have a surface with less than a half monolayer coverage of oxygen, the balance being hydrogen and the behavior is moderately hydrophobic. This allows for separation from other minerals at the mine using the so-called "grease-belt".
Toughness
Unlike hardness, which denotes only resistance to scratching, diamond's toughness or tenacity is only fair to good. Toughness relates to the ability to resist breakage from falls or impacts. Because of diamond's perfect and easy cleavage, it is vulnerable to breakage. A diamond will shatter if hit with an ordinary hammer. The toughness of natural diamond has been measured as , which is good compared to other gemstones like aquamarine (blue colored), but poor compared to most engineering materials. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamond has a cleavage plane and is therefore more fragile in some orientations than others. Diamond cutters use this attribute to cleave some stones, prior to faceting.
Ballas and carbonado diamond are exceptional, as they are polycrystalline and therefore much tougher than single-crystal diamond; they are used for deep-drilling bits and other demanding industrial applications. Particular faceting shapes of diamonds are more prone to breakage and thus may be uninsurable by reputable insurance companies. The brilliant cut of gemstones is designed specifically to reduce the likelihood of breakage or splintering.
Solid foreign crystals are commonly present in diamond. They are mostly minerals, such as olivine, garnets, ruby, and many others. These and other inclusions, such as internal fractures or "feathers", can compromise the structural integrity of a diamond. Cut diamonds that have been enhanced to improve their clarity via glass infilling of fractures or cavities are especially fragile, as the glass will not stand up to ultrasonic cleaning or the rigors of the jeweler's torch. Fracture-filled diamonds may shatter if treated improperly.
Pressure resistance
Used in so-called diamond anvil experiments to create high-pressure environments, diamonds withstand crushing pressures in excess of 600 gigapascals (6 million atmospheres).
Optical properties
Color and its causes
Diamonds occur in various colors: black, brown, yellow, gray, white, blue, orange, purple to pink, and red. Colored diamonds contain crystallographic defects, including substitutional impurities and structural defects, that cause the coloration. Theoretically, pure diamonds would be transparent and colorless. Diamonds are scientifically classed into two main types and several subtypes, according to the nature of defects present and how they affect light absorption:
Type I diamond has nitrogen (N) atoms as the main impurity, at a concentration of up to 1%. If the N atoms are in pairs or larger aggregates, they do not affect the diamond's color; these are Type Ia. About 98% of gem diamonds are type Ia: these diamonds belong to the Cape series, named after the diamond-rich region formerly known as Cape Province in South Africa, whose deposits are largely Type Ia. If the nitrogen atoms are dispersed throughout the crystal in isolated sites (not paired or grouped), they give the stone an intense yellow or occasionally brown tint (type Ib); the rare canary diamonds belong to this type, which represents only ~0.1% of known natural diamonds. Synthetic diamond containing nitrogen is usually of type Ib. Type Ia and Ib diamonds absorb in both the infrared and ultraviolet region of the electromagnetic spectrum, from . They also have a characteristic fluorescence and visible absorption spectrum.
Type II diamonds have very few if any nitrogen impurities. Pure (type IIa) diamond can be colored pink, red, or, brown owing to structural anomalies arising through plastic deformation during crystal growth; these diamonds are rare (1.8% of gem diamonds), but constitute a large percentage of Australian diamonds. Type IIb diamonds, which account for ~0.1% of gem diamonds, are usually a steely blue or gray due to boron atoms scattered within the crystal matrix. These diamonds are also semiconductors, unlike other diamond types (see Electrical properties). Most blue-gray diamonds coming from the Argyle mine of Australia are not of type IIb, but of Ia type. Those diamonds contain large concentrations of defects and impurities (especially hydrogen and nitrogen) and the origin of their color is yet uncertain. Type II diamonds weakly absorb in a different region of the infrared (the absorption is due to the diamond lattice rather than impurities), and transmit in the ultraviolet below 225 nm, unlike type I diamonds. They also have differing fluorescence characteristics, but no discernible visible absorption spectrum.
Certain diamond enhancement techniques are commonly used to artificially produce an array of colors, including blue, green, yellow, red, and black. Color enhancement techniques usually involve irradiation, including proton bombardment via cyclotrons; neutron bombardment in the piles of nuclear reactors; and electron bombardment by Van de Graaff generators. These high-energy particles physically alter the diamond's crystal lattice, knocking carbon atoms out of place and producing color centers. The depth of color penetration depends on the technique and its duration, and in some cases the diamond may be left radioactive to some degree.
Some irradiated diamonds are completely natural; one famous example is the Dresden Green Diamond. In these natural stones the color is imparted by "radiation burns" (natural irradiation by alpha particles originating from uranium ore) in the form of small patches, usually only micrometers deep. Additionally, Type IIa diamonds can have their structural deformations "repaired" via a high-pressure high-temperature (HPHT) process, removing much or all of the diamond's color.
Luster
The luster of a diamond is described as "adamantine", which simply means diamond-like. Reflections on a properly cut diamond's facets are undistorted, due to their flatness. The refractive index of diamond (as measured via sodium light, ) is 2.417. Because it is cubic in structure, diamond is also isotropic. Its high dispersion of 0.044 (variation of refractive index across the visible spectrum) manifests in the perceptible fire of cut diamonds. This fire—flashes of prismatic colors seen in transparent stones—is perhaps diamond's most important optical property from a jewelry perspective. The prominence or amount of fire seen in a stone is heavily influenced by the choice of diamond cut and its associated proportions (particularly crown height), although the body color of fancy (i.e., unusual) diamonds may hide their fire to some degree.
More than 20 other minerals have higher dispersion (that is difference in refractive index for blue and red light) than diamond, such as titanite 0.051, andradite 0.057, cassiterite 0.071, strontium titanate 0.109, sphalerite 0.156, synthetic rutile 0.330, cinnabar 0.4, etc. (see Dispersion (optics)). However, the combination of dispersion with extreme hardness, wear and chemical resistivity, as well as clever marketing, determines the exceptional value of diamond as a gemstone.
Fluorescence
Diamonds exhibit fluorescence, that is, they emit light of various colors and intensities under long-wave ultraviolet light (365 nm): Cape series stones (type Ia) usually fluoresce blue, and these stones may also phosphoresce yellow, a unique property among gemstones. Other possible long-wave fluorescence colors are green (usually in brown stones), yellow, mauve, or red (in type IIb diamonds). In natural diamonds, there is typically little if any response to short-wave ultraviolet, but the reverse is true of synthetic diamonds. Some natural type IIb diamonds phosphoresce blue after exposure to short-wave ultraviolet. In natural diamonds, fluorescence under X-rays is generally bluish-white, yellowish or greenish. Some diamonds, particularly Canadian diamonds, show no fluorescence.
The origin of the luminescence colors is often unclear and not unique. Blue emission from type IIa and IIb diamonds is reliably identified with dislocations by directly correlating the emission with dislocations in an electron microscope. However, blue emission in type Ia diamond could be either due to dislocations or the N3 defects (three nitrogen atoms bordering a vacancy). Green emission in natural diamond is usually due to the H3 center (two substitutional nitrogen atoms separated by a vacancy), whereas in synthetic diamond it usually originates from nickel used as a catalyst (see figure). Orange or red emission could be due to various reasons, one being the nitrogen-vacancy center which is present in sufficient quantities in all types of diamond, even type IIb.
Optical absorption
Cape series (Ia) diamonds have a visible absorption spectrum (as seen through a direct-vision spectroscope) consisting of a fine line in the violet at ; however, this line is often invisible until the diamond has been cooled to very low temperatures. Associated with this are weaker lines at , , , , and .
All those lines are labeled as N3 and N2 optical centers and associated with a defect consisting of three nitrogen atoms bordering a vacancy. Other stones show additional bands: brown, green, or yellow diamonds show a band in the green at (H3 center, see above), sometimes accompanied by two additional weak bands at and (H4 center, a large complex presumably involving 4 substitutional nitrogen atoms and 2 lattice vacancies). Type IIb diamonds may absorb in the far red due to the substitutional boron, but otherwise show no observable visible absorption spectrum.
Gemological laboratories make use of spectrophotometer machines that can distinguish natural, artificial, and color-enhanced diamonds. The spectrophotometers analyze the infrared, visible, and ultraviolet absorption and luminescence spectra of diamonds cooled with liquid nitrogen to detect tell-tale absorption lines that are not normally discernible.
Electrical properties
Diamond is a good electrical insulator, having a resistivity of to ( – ), and is famous for its wide bandgap of 5.47 eV. High carrier mobilities and high electric breakdown field at room temperature are also important characteristics of diamond. Those characteristics allow single crystalline diamond to be one of the promising materials for semiconductors. A wide bandgap is advantageous in semiconductors because it allows them to maintain high resistivity even at high temperature, important for high power applications. Semiconductors whose carrier mobilities are high such as diamond are easier to utilize in industry because they do not need high input voltage. High breakdown voltage avoids a huge current suddenly occurring at typical input voltages.
Most natural blue diamonds are an exception and are semiconductors due to substitutional boron impurities replacing carbon atoms. Natural blue or blue-gray diamonds, common for the Argyle diamond mine in Australia, are rich in hydrogen; these diamonds are not semiconductors and it is unclear whether hydrogen is actually responsible for their blue-gray color. Natural blue diamonds containing boron and synthetic diamonds doped with boron are p-type semiconductors. N-type diamond films are reproducibly synthesized by phosphorus doping during chemical vapor deposition. Diode p-n junctions and UV light emitting diodes (LEDs, at ) have been produced by sequential deposition of p-type (boron-doped) and n-type (phosphorus-doped) layers.
Diamond's electronic properties can be also modulated by strain engineering.
Diamond transistors have been produced (for research purposes). In January 2024, a Japanese research team fabricated a MOSFET using phosphorus-doped n-type diamond, which would have superior characteristics to silicon-based technology in high-temperature, high-frequency or high-electron mobility applications. FETs with SiN dielectric layers, and SC-FETs have been made.
In April 2004, research published in the journal Nature reported that below , synthetic boron-doped diamond is a bulk superconductor. Superconductivity was later observed in heavily boron-doped films grown by various chemical vapor deposition techniques, and the highest reported transition temperature (by 2009) is . (See also Covalent superconductor#Diamond)
Uncommon magnetic properties (spin glass state) were observed in diamond nanocrystals intercalated with potassium. Unlike paramagnetic host material, magnetic susceptibility measurements of intercalated nanodiamond revealed distinct ferromagnetic behavior at . This is essentially different from results of potassium intercalation in graphite or C60 fullerene, and shows that sp3 bonding promotes magnetic ordering in carbon. The measurements presented first experimental evidence of intercalation-induced spin-glass state in a nanocrystalline diamond system.
Thermal conductivity
Unlike most electrical insulators, diamond is a good conductor of heat because of the strong covalent bonding and low phonon scattering. Thermal conductivity of natural diamond was measured to be about 2,200 W/(m·K), which is five times more than silver, the most thermally conductive metal. Monocrystalline synthetic diamond enriched to 99.9% the isotope 12C had the highest thermal conductivity of any known solid at room temperature: 3,320 W/(m·K), though reports exist of superior thermal conductivity in both carbon nanotubes and graphene. Because diamond has such high thermal conductance it is already used in semiconductor manufacture to prevent silicon and other semiconducting materials from overheating. At lower temperatures conductivity becomes even better, and reaches 41,000 W/(m·K) at (12C-enriched diamond).
Diamond's high thermal conductivity is used by jewelers and gemologists who may employ an electronic thermal probe to distinguish diamonds from their imitations. These probes consist of a pair of battery-powered thermistors mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. This test takes about 2–3 seconds. However, older probes will be fooled by moissanite, a crystalline mineral form of silicon carbide introduced in 1998 as an alternative to diamonds, which has a similar thermal conductivity.
Technologically, the high thermal conductivity of diamond is used for the efficient heat removal in high-end power electronics. Diamond is especially appealing in situations where electrical conductivity of the heat sinking material cannot be tolerated e.g. for the thermal management of high-power radio-frequency () microcoils that are used to produce strong and local RF fields.
Thermal stability
If heated over in air, diamond, being a form of carbon, oxidizes and its surface blackens, but the surface can be restored by re-polishing. In absence of oxygen, e.g. in a flow of high-purity argon gas, diamond can be heated up to about . At high pressure (~) diamond can be heated up to , and a report published in 2009 suggests that diamond can withstand temperatures of and above.
Diamonds are carbon crystals that form under high temperatures and extreme pressures such as deep within the Earth. At surface air pressure (one atmosphere), diamonds are not as stable as graphite, and so the decay of diamond is thermodynamically favorable (δH = ). However, owing to a very large kinetic energy barrier, diamonds are metastable; they will not decay into graphite under normal conditions.
See also
Chemical vapor deposition of diamond
Crystallographic defects in diamond
Nitrogen-vacancy center
Synthetic diamond
References
Further reading
Pagel-Theisen, Verena. (2001). Diamond grading ABC: The manual (9th ed.), pp. 84–85. Rubin & Son n.v.; Antwerp, Belgium.
Webster, Robert, and Jobbins, E. Allan (Ed.). (1998). Gemmologist's compendium, p. 21, 25, 31. St Edmundsbury Press Ltd, Bury St Edwards.
External links
Properties of diamond
Properties of diamond (S. Sque, PhD thesis, 2005, University of Exeter, UK)
Material properties of diamond
Allotropes of carbon
Native element minerals
Superhard materials | Material properties of diamond | [
"Physics",
"Chemistry"
] | 5,014 | [
"Allotropes of carbon",
"Allotropes",
"Materials",
"Superhard materials",
"Matter"
] |
1,567,176 | https://en.wikipedia.org/wiki/Pallet%20fork | The pallet fork is a component of the lever escapement of a mechanical watch. The pallet fork and the lever form one component that sits between the escape wheel and the balance wheel. Its purpose is to lock the escape wheel, and release it one tooth at a time at each swing of the balance wheel, and also give the balance wheel small pushes to keep it going.
In early watches the pallet fork and the lever were made as separate components and joined together. In later watches they were made as a single component as shown in the picture. The combined component is often referred to simply as the "lever". In a straight line Swiss lever type escapement, the lever is shaped like a 'T' or an anchor, which gives this escapement its alternative name of anchor escapement. The lever is pivoted in the center; in operation it rocks back and forth. On the arms of the 'T' are angled surfaces called pallets which alternately engage the teeth of the escapement's escape wheel. The central shaft of the lever ends in a fork, which gives pushes to the balance wheel's impulse pin, which is set off center in a disk on the balance wheel's shaft. To reduce friction, the pallets are made of precisely shaped pieces of ruby jewel. The pallet which the teeth first contact is called the entry pallet, while the other one is called the exit pallet.
Under the fork there is a projecting guard pin which passes through a notch in a separate safety roller disk on the balance shaft. In normal operation it doesn't have a function. Its purpose is to make sure the fork is in the right position to receive the impulse pin if a jar to the watch prematurely 'unlocks' the lever from the escape wheel.
Mechanical alarm clocks and kitchen timers use a less accurate form of the lever in which vertical metal pins are substituted for the pallet jewels. This is called a Roskopf or pin-pallet escapement, and was previously used in cheap pin-lever watches.
Notes and references
Timekeeping components | Pallet fork | [
"Technology"
] | 423 | [
"Timekeeping components",
"Components"
] |
1,567,335 | https://en.wikipedia.org/wiki/Derived%20set%20%28mathematics%29 | In mathematics, more specifically in point-set topology, the derived set of a subset of a topological space is the set of all limit points of It is usually denoted by
The concept was first introduced by Georg Cantor in 1872 and he developed set theory in large part to study derived sets on the real line.
Definition
The derived set of a subset of a topological space denoted by is the set of all points that are limit points of that is, points such that every neighbourhood of contains a point of other than itself.
Examples
If is endowed with its usual Euclidean topology then the derived set of the half-open interval is the closed interval
Consider with the topology (open sets) consisting of the empty set and any subset of that contains 1. The derived set of is
Properties
If and are subsets of the topological space then the derived set has the following properties:
implies
implies
A subset of a topological space is closed precisely when that is, when contains all its limit points. For any subset the set is closed and is the closure of (that is, the set ).
The derived set of a subset of a space need not be closed in general. For example, if with the trivial topology, the set has derived set which is not closed in But the derived set of a closed set is always closed.
In addition, if is a T1 space, the derived set of every subset of is closed in
Two subsets and are separated precisely when they are disjoint and each is disjoint from the other's derived set
A bijection between two topological spaces is a homeomorphism if and only if the derived set of the image (in the second space) of any subset of the first space is the image of the derived set of that subset.
A space is a T1 space if every subset consisting of a single point is closed. In a T1 space, the derived set of a set consisting of a single element is empty (Example 2 above is not a T1 space). It follows that in T1 spaces, the derived set of any finite set is empty and furthermore,
for any subset and any point of the space. In other words, the derived set is not changed by adding to or removing from the given set a finite number of points. It can also be shown that in a T1 space, for any subset
A set with (that is, contains no isolated points) is called dense-in-itself. A set with is called a perfect set. Equivalently, a perfect set is a closed dense-in-itself set, or, put another way, a closed set with no isolated points. Perfect sets are particularly important in applications of the Baire category theorem.
The Cantor–Bendixson theorem states that any Polish space can be written as the union of a countable set and a perfect set. Because any Gδ subset of a Polish space is again a Polish space, the theorem also shows that any Gδ subset of a Polish space is the union of a countable set and a set that is perfect with respect to the induced topology.
Topology in terms of derived sets
Because homeomorphisms can be described entirely in terms of derived sets, derived sets have been used as the primitive notion in topology. A set of points can be equipped with an operator mapping subsets of to subsets of such that for any set and any point :
implies
implies
Calling a set if will define a topology on the space in which is the derived set operator, that is,
Cantor–Bendixson rank
For ordinal numbers the -th Cantor–Bendixson derivative of a topological space is defined by repeatedly applying the derived set operation using transfinite recursion as follows:
for limit ordinals
The transfinite sequence of Cantor–Bendixson derivatives of is decreasing and must eventually be constant. The smallest ordinal such that is called the of
This investigation into the derivation process was one of the motivations for introducing ordinal numbers by Georg Cantor.
See also
Notes
Proofs
References
Further reading
Sierpiński, Wacław F.; translated by Krieger, C. Cecilia (1952). General Topology. University of Toronto Press.
External links
PlanetMath's article on the Cantor–Bendixson derivative
General topology | Derived set (mathematics) | [
"Mathematics"
] | 871 | [
"General topology",
"Topology"
] |
1,567,386 | https://en.wikipedia.org/wiki/Elementary%20arithmetic | Elementary arithmetic is a branch of mathematics involving addition, subtraction, multiplication, and division. Due to its low level of abstraction, broad range of application, and position as the foundation of all mathematics, elementary arithmetic is generally the first branch of mathematics taught in schools.
Numeral systems
In numeral systems, digits are characters used to represent the value of numbers. An example of a numeral system is the predominantly used Indo-Arabic numeral system (0 to 9), which uses a decimal positional notation. Other numeral systems include the Kaktovik system (often used in the Eskimo-Aleut languages of Alaska, Canada, and Greenland), and is a vigesimal positional notation system. Regardless of the numeral system used, the results of arithmetic operations are unaffected.
Successor function and ordering
In elementary arithmetic, the successor of a natural number (including zero) is the next natural number and is the result of adding one to that number. The predecessor of a natural number (excluding zero) is the previous natural number and is the result of subtracting one from that number. For example, the successor of zero is one, and the predecessor of eleven is ten ( and ). Every natural number has a successor, and every natural number except 0 has a predecessor.
The natural numbers have a total ordering. If one number is greater than () another number, then the latter is less than () the former. For example, three is less than eight (), thus eight is greater than three (). The natural numbers are also well-ordered, meaning that any subset of the natural numbers has a least element.
Counting
Counting assigns a natural number to each object in a set, starting with 1 for the first object and increasing by 1 for each subsequent object. The number of objects in the set is the count. This is also known as the cardinality of the set.
Counting can also be the process of tallying, the process of drawing a mark for each object in a set.
Addition
Addition is a mathematical operation that combines two or more numbers (called addends or summands) to produce a combined number (called the sum). The addition of two numbers is expressed with the plus sign (). It is performed according to these rules:
The order in which the addends are added does not affect the sum. This is known as the commutative property of addition. (a + b) and (b + a) produce the same output.
The sum of two numbers is unique; there is only one correct answer for a sums.
When the sum of a pair of digits results in a two-digit number, the "tens" digit is referred to as the "carry digit". In elementary arithmetic, students typically learn to add whole numbers and may also learn about topics such as negative numbers and fractions.
Subtraction
Subtraction evaluates the difference between two numbers, where the minuend is the number being subtracted from, and the subtrahend is the number being subtracted. It is represented using the minus sign (). The minus sign is also used to notate negative numbers.
Subtraction is not commutative, which means that the order of the numbers can change the final value; is not the same as . In elementary arithmetic, the minuend is always larger than the subtrahend to produce a positive result.
Subtraction is also used to separate, combine (e.g., find the size of a subset of a specific set), and find quantities in other contexts.
There are several methods to accomplish subtraction. The traditional mathematics method subtracts using methods suitable for hand calculation. Reform mathematics is distinguished generally by the lack of preference for any specific technique, replaced by guiding students to invent their own methods of computation.
American schools teach a method of subtraction using borrowing. A subtraction problem such as is solved by borrowing a 10 from the tens place to add to the ones place in order to facilitate the subtraction. Subtracting 9 from 6 involves borrowing a 10 from the tens place, making the problem into . This is indicated by crossing out the 8, writing a 7 above it, and writing a 1 above the 6. These markings are called "crutches", which were invented by William A. Brownell, who used them in a study, in November 1937.
The Austrian method, also known as the additions method, is taught in certain European countries. In contrast to the previous method, no borrowing is used, although there are crutches that vary according to certain countries. The method of addition involves augmenting the subtrahend. This transforms the previous problem into . A small 1 is marked below the subtrahend digit as a reminder.
Example
Subtracting the numbers 792 and 308, starting with the ones column, 2 is smaller than 8. Using the borrowing method, 10 is borrowed from 90, reducing 90 to 80. This changes the problem to .
In the tens column, the difference between 80 and 0 is 80.
In the hundreds column, the difference between 700 and 300 is 400.
The result:
Multiplication
Multiplication is a mathematical operation of repeated addition. When two numbers are multiplied, the resulting value is a product. The numbers being multiplied are multiplicands, multipliers, or factors. Multiplication can be expressed as "five times three equals fifteen," "five times three is fifteen," or "fifteen is the product of five and three."
Multiplication is represented using the multiplication sign (×), the asterisk (*), parentheses (), or a dot (⋅). The statement "five times three equals fifteen" can be written as "", "", "", or "".
In elementary arithmetic, multiplication satisfies the following properties:
Commutativity. Switching the order in a product does not change the result: .
Associativity. Rearranging the order of parentheses in a product does not change the result: .
Distributivity. Multiplication distributes over addition: .
Identity. Any number multiplied by 1 is itself: .
Zero. Any number multiplied by 0 is 0: .
In the multiplication algorithm, the "tens" digit of the product of a pair of digits is referred to as the "carry digit".
Example of multiplication for a single-digit factor
Multiplying 729 and 3, starting on the ones column, the product of 9 and 3 is 27. 7 is written under the ones column and 2 is written above the tens column as a carry digit.
The product of 2 and 3 is 6, and the carry digit adds 2 to 6, so 8 is written under the tens column.
The product of 7 and 3 is 21, and since this is the last digit, 2 will not be written as a carry digit, but instead beside 1.
The result:
Example of multiplication for multiple-digit factors
Multiplying 789 and 345, starting with the ones column, the product of 789 and 5 is 3945.
4 is in the tens digit. The multiplier is 40, not 4. The product of 789 and 40 is 31560.
3 is in the hundreds digits. The multiplier is 300. The product of 789 and 300 is 236700.
Adding all the products,
The result:
Division
Division is an arithmetic operation, and the inverse of multiplication. Given that , ,
Division can be written as , , or . This can be read verbally as "a divided by b" or "a over b".
In some non-English-speaking cultures, "a divided by b" is written . In English usage, the colon is restricted to the concept of ratios ("a is to b").
In an equation , a is the dividend, b the divisor, and c the quotient. Division by zero is considered impossible at an elementary arithmetic level.
Two numbers can be divided on paper using long division. An abbreviated version of long division, short division, can be used for smaller divisors.
A less systematic method involves the concept of chunking, involving subtracting more multiples from the partial remainder at each stage.
Example
Dividing 272 and 8, starting with the hundreds digit, 2 is not divisible by 8. Add 20 and 7 to get 27. The largest number that the divisor of 8 can be multiplied by without exceeding 27 is 3, so it is written under the tens column. Subtracting 24 (the product of 3 and 8) from 27 gives 3 as the remainder.
Going to the ones digit, the number is 2. Adding 30 (the remainder, 3, times 10) and 2 gets 32. The quotient of 32 and 8 is 4, which is written under the ones column.
The result:
Bus stop method
Another method of dividing taught in some schools is the bus stop method, sometimes notated as
result
(divisor) dividend
The steps here are shown below, using the same example as above:
034
8|272
0 ( 8 × 0 = 0)
27 ( 2 - 0 = 2)
24 ( 8 × 3 = 24)
32 (27 - 24 = 3)
32 ( 8 × 4 = 32)
0 (32 - 32 = 0)
The result:
Educational standards
Elementary arithmetic is typically taught at the primary or secondary school levels and is governed by local educational standards. There has been debate about the content and methods used to teach elementary arithmetic in the United States and Canada.
See also
Early numeracy
Elementary mathematics
Chunking (division)
Plus and minus signs
Peano axioms
Division by zero
Real number
Imaginary number
Number sentence
Notes
References
Mathematics education
Addition
Subtraction
Multiplication | Elementary arithmetic | [
"Mathematics"
] | 1,997 | [
"Elementary arithmetic",
"Subtraction",
"Sign (mathematics)",
"Elementary mathematics",
"Arithmetic"
] |
1,567,410 | https://en.wikipedia.org/wiki/Sigma-ideal | In mathematics, particularly measure theory, a -ideal, or sigma ideal, of a σ-algebra (, read "sigma") is a subset with certain desirable closure properties. It is a special type of ideal. Its most frequent application is in probability theory.
Let be a measurable space (meaning is a -algebra of subsets of ). A subset of is a -ideal if the following properties are satisfied:
;
When and then implies ;
If then
Briefly, a sigma-ideal must contain the empty set and contain subsets and countable unions of its elements. The concept of -ideal is dual to that of a countably complete (-) filter.
If a measure is given on the set of -negligible sets ( such that ) is a -ideal.
The notion can be generalized to preorders with a bottom element as follows: is a -ideal of just when
(i')
(ii') implies and
(iii') given a sequence there exists some such that for each
Thus contains the bottom element, is downward closed, and satisfies a countable analogue of the property of being upwards directed.
A -ideal of a set is a -ideal of the power set of That is, when no -algebra is specified, then one simply takes the full power set of the underlying set. For example, the meager subsets of a topological space are those in the -ideal generated by the collection of closed subsets with empty interior.
See also
References
Bauer, Heinz (2001): Measure and Integration Theory. Walter de Gruyter GmbH & Co. KG, 10785 Berlin, Germany.
Measure theory
Families of sets | Sigma-ideal | [
"Mathematics"
] | 338 | [
"Families of sets",
"Basic concepts in set theory",
"Combinatorics"
] |
1,567,506 | https://en.wikipedia.org/wiki/Thiourea | Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), except that the oxygen atom is replaced by a sulfur atom (as implied by the thio- prefix); however, the properties of urea and thiourea differ significantly. Thiourea is a reagent in organic synthesis. Thioureas are a broad class of compounds with the general structure .
Structure and bonding
Thiourea is a planar molecule. The C=S bond distance is 1.71 Å. The C-N distances average 1.33 Å. The weakening of the C-S bond by C-N pi-bonding is indicated by the short C=S bond in thiobenzophenone, which is 1.63 Å.
Thiourea occurs in two tautomeric forms, of which the thione form predominates in aqueous solutions. The equilibrium constant has been calculated as Keq is . The thiol form, which is also known as an isothiourea, can be encountered in substituted compounds such as isothiouronium salts.
Production
The global annual production of thiourea is around 10,000 tonnes. About 40% is produced in Germany, another 40% in China, and 20% in Japan. Thiourea can be produced from ammonium thiocyanate, but more commonly it is manufactured by the reaction of hydrogen sulfide with calcium cyanamide in the presence of carbon dioxide.
Applications
Thiox precursor
Thiourea per se has few applications. It is mainly consumed as a precursor to thiourea dioxide, which is a common reducing agent in textile processing.
Fertilizers
Recently thiourea has been investigated for its multiple desirable properties as a fertilizer especially under conditions of environmental stress. It may be applied in various capacities, such as a seed pretreatment (for priming), foliar spray or medium supplementation.
Other uses
Other industrial uses of thiourea include production of flame retardant resins, and vulcanization accelerators.
Thiourea is building blocks to pyrimidine derivatives. Thus, thioureas condense with β-dicarbonyl compounds. The amino group on the thiourea initially condenses with a carbonyl, followed by cyclization and tautomerization. Desulfurization delivers the pyrimidine. The pharmaceuticals thiobarbituric acid and sulfathiazole are prepared using thiourea. 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea and hydrazine.
Thiourea is used as an auxiliary agent in diazo paper, light-sensitive photocopy paper and almost all other types of copy paper.
It is also used to tone silver-gelatin photographic prints (see Sepia Toning).
Thiourea is used in the Clifton-Phillips and Beaver bright and semi-bright electroplating processes. It is also used in a solution with tin(II) chloride as an electroless tin plating solution for copper printed circuit boards.
Thioureas are used (usually as hydrogen-bond donor catalysts) in a research theme called thiourea organocatalysis. Thioureas are often found to be stronger hydrogen-bond donors (i.e., more acidic) than ureas.
Reactions
The material has the unusual property of changing to ammonium thiocyanate upon heating above . Upon cooling, the ammonium salt converts back to thiourea.
Reductant
Thiourea reduces peroxides to the corresponding diols. The intermediate of the reaction is an unstable endoperoxide.
Thiourea is also used in the reductive workup of ozonolysis to give carbonyl compounds. Dimethyl sulfide is also an effective reagent for this reaction, but it is highly volatile (boiling point ) and has an obnoxious odor whereas thiourea is odorless and conveniently non-volatile (reflecting its polarity).
Source of sulfide
Thiourea is employed as a source of sulfide, such as for converting alkyl halides to thiols. The reaction capitalizes on the high nucleophilicity of the sulfur center and easy hydrolysis of the intermediate isothiouronium salt:
In this example, ethane-1,2-dithiol is prepared from 1,2-dibromoethane:
Like other thioamides, thiourea can serve as a source of sulfide upon reaction with metal ions. For example, mercury sulfide forms when mercuric salts in aqueous solution are treated with thiourea:
These sulfiding reactions, which have been applied to the synthesis of many metal sulfides, require water and typically some heating.
Precursor to heterocycles
Thioureas are building blocks to pyrimidine derivatives. Thus thioureas condense with β-dicarbonyl compounds. The amino group on the thiourea initially condenses with a carbonyl, followed by cyclization and tautomerization. Desulfurization delivers the pyrimidine.
Similarly, aminothiazoles can be synthesized by the reaction of α-haloketones and thiourea.
The pharmaceuticals thiobarbituric acid and sulfathiazole are prepared using thiourea. 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea and hydrazine.
Silver polishing
According to the label on consumer products TarnX and Silver Dip, the liquid silver cleaning products contain thiourea along with a warning that thiourea is a chemical on California's list of carcinogens. A lixiviant for gold and silver leaching can be created by selectively oxidizing thiourea, bypassing the steps of cyanide use and smelting.
Kurnakov reaction
Thiourea is an essential reagent in the Kurnakov test used to differentiate cis- and trans- isomers of certain square planar platinum complexes. The reaction was discovered in 1893 by Russian chemist Nikolai Kurnakov and is still performed as an assay for compounds of this type.
Safety
The for thiourea is for rats (oral).
A goitrogenic effect (enlargement of the thyroid gland) has been reported for chronic exposure, reflecting the ability of thiourea to interfere with iodide uptake.
A cyclic derivative of thiourea called Thiamazole is used to treat overactive thyroid
See also
Thioureas
References
Further reading
External links
INCHEM assessment of thiourea
International Chemical Safety Card 0680
Functional groups | Thiourea | [
"Chemistry"
] | 1,457 | [
"Functional groups"
] |
1,567,537 | https://en.wikipedia.org/wiki/GCRT%20J1745%E2%88%923009 | GCRT J1745−3009 is a Galactic Center radio transient (GCRT), or bursting low-frequency radio source which lies in the direction of the Galactic Center.
Discovery
A group of astronomers from Sweet Briar College and the Naval Research Laboratory detected transient emission from two sources in 1998 while studying the Galactic Center. They then began monitoring the region specifically looking for transient sources and detected five bursts of radio waves about 1 meter in wavelength (frequency 330 MHz) during a seven-hour period from September 30 to October 1, 2002.
The five bursts were of equal brightness, with each lasting about 10 minutes, and occurring every 77 minutes. Like an earlier low-frequency transient discovered by the same group, it was given the designation GCRT, an abbreviation for Galactic Center Radio Transient. The source was also nicknamed a burper. The group found no X-ray or γ-ray counterpart to the object.
Another burst from the source was later found in data recorded September 28, 2003, and a weaker burst was found in data recorded March 20, 2004. As of January 2007, no other bursts have been found.
Structure
The discoverers argue that if the source is further than 70 parsecs away, its high brightness temperature would require it to be powered by a coherent emission process. (If within 70 parsecs, the source could be either coherent or incoherent.) They also claim that most known coherent emission processes are unlikely explanations for the source. Models proposed by others include a nulling pulsar, a pair of orbiting neutron stars, a radio-emitting white dwarf, and a pulsar precessing with a period of 77 minutes.
See also
GLEAM-X J162759.5−523504.3
Rotating radio transients
References
External links
BBC Radio interview with Scott Hyman (MPEG)
Science Daily
Mysterious Radio Bursts
Pulsars
Scorpius | GCRT J1745−3009 | [
"Astronomy"
] | 394 | [
"Scorpius",
"Constellations"
] |
1,567,681 | https://en.wikipedia.org/wiki/Froth%20flotation | Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in mineral processing, paper recycling and waste-water treatment industries. Historically this was first used in the mining industry, where it was one of the great enabling technologies of the 20th century. It has been described as "the single most important operation used for the recovery and upgrading of sulfide ores". The development of froth flotation has improved the recovery of valuable minerals, such as copper- and lead-bearing minerals. Along with mechanized mining, it has allowed the economic recovery of valuable metals from much lower-grade ore than previously possible.
Industries
Froth flotation is applied to a wide range of separations. An estimated one billion tons of materials are processed in this manner annually.
Mineral processing
Froth flotation is a process for separating minerals from gangue by exploiting differences in their hydrophobicity. Hydrophobicity differences between valuable minerals and waste gangue are increased through the use of surfactants and wetting agents. The flotation process is used for the separation of a large range of sulfides, carbonates and oxides prior to further refinement. Phosphates and coal are also upgraded (purified) by flotation technology. "Grade-recovery curves" are tools for weighing the trade-off of producing a high grade of concentrate vs cost. These curves only compare the grade-recovery relations of a specific feed grade and feed rate.
Waste water treatment
The flotation process is also widely used in industrial waste water treatment plants, where it removes fats, oil, grease and suspended solids from waste water. These units are called dissolved air flotation (DAF) units. In particular, dissolved air flotation units are used in removing oil from the wastewater effluents of oil refineries, petrochemical and chemical plants, natural gas processing plants and similar industrial facilities.
Principle of operation
The ore to be treated is ground into particles (comminution). In the idealized case, the individual minerals are physically separated, a process known as full liberation. The particle sizes are typically in the range 2–500 micrometers in diameter. For froth flotation, an aqueous slurry of the ground ore is treated with the frothing agent. An example is sodium ethyl xanthate as a collector in the flotation of galena (lead sulfide) to separate it from sphalerite (zinc sulfide). The polar part of xanthate anion attaches to the ore particles and the non-polar hydrocarbon part forms a hydrophobic layer. The particles are brought to the water surface by air bubbles. About 300 g/t of ore is required for efficient separation. With increasing length of the hydrocarbon chain in xanthates, the efficiency of the hydrophobic action increases, but the selectivity to ore type decreases. The chain is shortest in sodium ethyl xanthate that makes it highly selective to copper, nickel, lead, gold, and zinc ores. Aqueous solutions (10%) with pH = 7–11 are normally used in the process. This slurry (more properly called the pulp) of hydrophobic particles and hydrophilic particles is then introduced to tanks known as flotation cells that are aerated to produce bubbles. The hydrophobic particles attach to the air bubbles, which rise to the surface, forming a froth. The froth is skimmed from the cell, producing a concentrate ("conc") of the target mineral.
The minerals that do not float into the froth are referred to as the flotation tailings or flotation tails. These tailings may also be subjected to further stages of flotation to recover the valuable particles that did not float the first time. This is known as scavenging. The final tailings after scavenging are normally pumped for disposal as mine fill or to tailings disposal facilities for long-term storage.
Flotation is normally undertaken in several stages to maximize the recovery of the target mineral or minerals and the concentration of those minerals in the concentrate, while minimizing the energy input.
Flotation stages
The first stage is called roughing, which produces a rougher concentrate. The objective is to remove the maximum amount of the valuable mineral at as coarse a particle size as practical. Grinding costs energy. The goal is to release enough gangue from the valuable mineral to get a high recovery. Some concentrators use a preflotation step to remove low density impurities such as carbonaceous dust. The rougher concentrate is normally subjected to further stages of flotation to reject more of the undesirable minerals that also reported to the froth, in a process known as cleaning. The resulting material is often subject to further grinding (usually called regrinding). Regrinding is often undertaken in specialized regrind mills, such as the IsaMill. The rougher flotation step is often followed by a scavenger flotation step that is applied to the rougher tailings to further recover any of the target minerals.
Science of flotation
To be effective on a given ore slurry, the collectors are chosen based upon their selective wetting of the types of particles to be separated. A good collector will adsorb, physically or chemically, with one of the types of particles. The wetting activity of a surfactant on a particle can in principle be quantified by measuring the contact angles of the liquid/bubble interface. Another important measure for attachment of bubbles to particles is induction time, the time required for the particle and bubble to rupture the thin film separating the particle and bubble. This rupturing is achieved by the surface forces between the particle and bubble.
The mechanisms for the bubble-particle attachment is complex but is viewed as consisting of three steps: collision, attachment, and detachment. The collision is achieved by particles being within the collision tube of a bubble and this is affected by the velocity of the bubble and radius of the bubble. The collision tube corresponds to the region in which a particle will collide with the bubble, with the perimeter of the collision tube corresponding to the grazing trajectory.
The attachment of the particle to the bubble is controlled by the induction time of the particle and bubble. The particle and bubble need to bind and this occurs if the time in which the particle and bubble are in contact with each other is larger than the required induction time. This induction time is affected by the fluid viscosity, particle and bubble size and the forces between the particle and bubbles.
The detachment of a particle and bubble occurs when the force exerted by the surface tension is exceeded by shear forces and gravitational forces. These forces are complex and vary within the cell. High shear will be experienced close to the impeller of a mechanical flotation cell and mostly gravitational force in the collection and cleaning zone of a flotation column.
Significant issues of entrainment of fine particles occurs as these particles experience low collision efficiencies as well as sliming and degradation of the particle surfaces. Coarse particles show a low recovery of the valuable mineral due to the low liberation and high detachment efficiencies.
Flotation equipment
Flotation can be performed in rectangular or cylindrical mechanically agitated cells or tanks, flotation columns, Jameson Cells or deinking flotation machines. Classified by the method of air absorption manner, it is fair to state that two distinct groups of flotation equipment have arisen:pneumatic and mechanical machines. Generally pneumatic machines give a low-grade concentrate and little operating troubles.
Mechanical cells use a large mixer and diffuser mechanism at the bottom of the mixing tank to introduce air and provide mixing action. Flotation columns use air spargers to introduce air at the bottom of a tall column while introducing slurry above. The countercurrent motion of the slurry flowing down and the air flowing up provides mixing action. Mechanical cells generally have a higher throughput rate, but produce material that is of lower quality, while flotation columns generally have a low throughput rate but produce higher quality material.
The Jameson cell uses neither impellers nor spargers, instead combining the slurry with air in a downcomer where high shear creates the turbulent conditions required for bubble particle contacting.
Chemicals of flotation
Collectors
For many ores (e.g. those of Cu, Mo, W, Ni), the collectors are anionic sulfur ligands. Particularly popular for sulfide minerals are xanthate salts, including potassium amyl xanthate (PAX), potassium isobutyl xanthate (PIBX), potassium ethyl xanthate (KEX), sodium isobutyl xanthate (SIBX), sodium isopropyl xanthate (SIPX), sodium ethyl xanthate (SEX). Related collectors include related sulfur-based ligands: dithiophosphates, dithiocarbamates. Still other classes of collectors include the thiourea thiocarbanilide. Fatty acid carboxylates, alkyl sulfates, and alkyl sulfonates have also been used for oxide minerals.
For some minerals (e.g., sylvinite for KCl), fatty amines are used as collectors.
Frothers
A variety of compounds are added to stabilize the foams. These additives include pine oil and various alcohols: methyl isobutyl carbinol (MIBC), polyglycols, xylenol (cresylic acid).
Depressants
According to one vendor, depressants "increase the efficiency of the flotation process by selectively inhibiting the interaction of one mineral with the collector." Thus a typical pulverized ore sample consists of many components, of which only one or a few are targets for the collector. Depressants bind to these other components, lest the collector be wasted by doing so. Depressants are selected for particular ores. Typical depressants are starch, polyphenols, lye, and lime. They are cheap, and oxygen-rich typically.
Modifiers
A variety of other compounds are added to optimize the separation process, these additives are called modifiers. Modifying reagents react either with the mineral surfaces or with collectors and other ions in the flotation pulp, resulting in a modified and controlled flotation response.
pH modifiers include lime (used as quicklime CaO, or more commonly as slaked lime, a slurry of Ca(OH)2), soda ash (Na2CO3), caustic soda (NaOH), sulfuric and hydrochloric acid (H2SO4, HCl).
Anionic modifiers include phosphates, silicates, and carbonates.
Organic modifiers include the thickeners dextrin, starch, glue, and carboxymethyl cellulose (CMC).
Specific applications
Sulfide ores
Prior to 1907, nearly all the copper mined in the US came from underground vein deposits, averaging 2.5 percent copper. By 1991, the average grade of copper ore mined in the US had fallen to only 0.6 percent.
Nonsulfide ores
Flotation is used for the purification of potassium chloride from sodium chloride and clay minerals. The crushed mineral is suspended in brine in the presence of fatty ammonium salts. Because the ammonium head group and K+ have very similar ionic radii (ca. 0.135, 0.143 nm respectively), the ammonium centers exchange for the surface potassium sites on the particles of KCl, but not on the NaCl particles. The long alkyl chains then confer hydrophobicity to the particles, which enable them to form foams.
Chemical compounds for deinking of recycled paper
Froth flotation is one of the processes used to recover recycled paper. In the paper industry this step is called deinking or just flotation. The target is to release and remove the hydrophobic contaminants from the recycled paper. The contaminants are mostly printing ink and stickies. Normally the setup is a two-stage system with 3,4 or 5 flotation cells in series.
pH control: sodium silicate and sodium hydroxide
Calcium ion source: hard water, lime or calcium chloride
Collector: fatty acid, fatty acid emulsion, fatty acid soap and/or organo-modified siloxane
Environmental considerations
As in any technology that has long been conducted on the multi-million ton per year scale, flotation technologies have the potential to threaten the environment beyond the disruption caused by mining. Froth flotation employs a host of organic chemicals and relies upon elaborate machinery. Some of the chemicals (cyanide) are acutely toxic but hydrolyze to innocuous products. Naturally occurring fatty acids are widely used. Tailings and effluents are contained in lined ponds. Froth flotation is "poised for increased activity due to their potential usefulness in environmental site cleanup operations" including recycling of plastics and metals, not to mention water treatment.
History
Flotation processes are described in ancient Greek and Persian literature. During the late 19th century, the process basics were discovered through a slow evolutionary phase. During the first decade of the 20th century, a more rapid investigation of oils, froths, and agitation led to proven workplace applications, especially in Broken Hill, Australia, that brought the technological innovation known as “froth flotation.” During the early 20th century, froth flotation revolutionized mineral processing.
Initially, naturally occurring chemicals such as fatty acids and oils were used as flotation reagents in large quantities to increase the hydrophobicity of the valuable minerals. Since then, the process has been adapted and applied to a wide variety of materials to be separated, and additional collector agents, including surfactants and synthetic compounds have been adopted for various applications.
19th century
Englishman William Haynes patented a process in 1860 for separating sulfide and gangue minerals using oil. Later writers have pointed to Haynes's as the first "bulk oil flotation" patent, though there is no evidence of its being field tested, or used commercially. In 1877 the brothers Bessel (Adolph and August) of Dresden, Germany, introduced their commercially successful oil and froth flotation process for extracting graphite, considered by some the root of froth flotation. However, the Bessel process became uneconomical after the discovery of high-grade graphite in Sri Lanka and was largely forgotten.
Inventor Hezekiah Bradford of Philadelphia invented a "method of saving floating material in ore-separation” and received US patent No. 345951 on July 20, 1886. He would later go on to patent the Bradford Breaker, currently in use by the coal industry, in 1893. His "Bradford washer," patented 1870, was used to concentrate iron, copper and lead-zinc ores by specific gravity, but lost some of the metal as float off the concentration process. The 1886 patent was to capture this "float" using surface tension, the first of the skin-flotation process patents that were eclipsed by oil froth flotation.
On August 24, 1886, Carrie Everson received a patent for her process calling for oil[s] but also an acid or a salt, a significant step in the evolution of the process history. By 1890, tests of the Everson process had been made at Georgetown and Silver Cliff, Colorado, and Baker, Oregon. She abandoned the work upon the death of her husband, and before perfecting a commercially successful process. Later, during the height of legal disputes over the validity of various patents during the 1910s, Everson's was often pointed to as the initial flotation patent - which would have meant that the process was not patentable again by later contestants. Much confusion has been clarified recently by historian Dawn Bunyak.
First commercial flotation process
The generally recognized first successful commercial flotation process for mineral sulphides was invented by Frank Elmore who worked on the development with his brother, Stanley. The Glasdir copper mine at Llanelltyd, near Dolgellau in North Wales was bought in 1896 by the Elmore brothers in conjunction with their father, William. In 1897, the Elmore brothers installed the world's first industrial-size commercial flotation process for mineral beneficiation at the Glasdir mine. The process was not froth flotation but used oil to agglomerate (make balls of) pulverised sulphides and buoy them to the surface, and was patented in 1898 (revised 1901). The operation and process was described in the April 25, 1900 Transactions of the Institution of Mining and Metallurgy of England, which was reprinted with comment, June 23, 1900, in the Engineering and Mining Journal, New York City. By this time they had recognized the importance of air bubbles in assisting the oil to carry away the mineral particles. As modifications were made to improve the process, it became a success with base metal ores from Norway to Australia.
The Elmores had formed a company known as the Ore Concentration Syndicate Ltd to promote the commercial use of the process worldwide. In 1900, Charles Butters of Berkeley, California, acquired American rights to the Elmore process after seeing a demonstration at Llanelltyd, Wales. Butters, an expert on the cyanide process, built an Elmore process plant in the basement of the Dooley Building, Salt Lake City, and tested the oil process on gold ores throughout the region and tested the tailings of the Mammoth gold mill, Tintic district, Utah, but without success. Because of Butters' reputation and the news of his failure, as well as the unsuccessful attempt at the LeRoi gold mine at Rossland, B. C., the Elmore process was all but ignored in North America.
Developments elsewhere, particularly in Broken Hill, Australia by Minerals Separation, Limited, led to decades of hard-fought legal battles and litigations (e. g. Minerals Separation, Ltd. v. Hyde) for the Elmores who, ultimately, lost as the Elmore process was superseded by more advanced techniques. Another flotation process was independently invented in 1901 in Australia by Charles Vincent Potter and by Guillaume Daniel Delprat around the same time. Potter was a brewer of beer, as well as a chemist, and was likely inspired by the way beer froth lifted up sediment in the beer. This process did not use oil, but relied upon flotation by the generation of gas formed by the introduction of acid into the pulp. In 1903, Potter sued Delprat, then general manager of BHP, for patent infringement. He lost the case for reasons of utility, with Delpat arguing that while Delprat's process, which used sulphuric acid to generate the bubbles in the process, was not as useful as Delprat's process, which used salt cake. Despite this, after the case was over BHP began using sulphuric acid for its flotation process.
In 1902, Froment combined oil and gaseous flotation using a modification of the Potter-Delprat process. During the first decade of the twentieth century, Broken Hill became the center of innovation leading to the perfection of the froth flotation process by many technologists there borrowing from each other and building on these first successes.
Yet another process was developed in 1902 by Arthur C. Cattermole, who emulsified the pulp with a small quantity of oil, subjected it to violent agitation, and then slow stirring which coagulated the target minerals into nodules which were separated from the pulp by gravity. The Minerals Separation Ltd., formed in Britain in 1903 to acquire the Cattermole patent, found that it proved unsuccessful. Metallurgists on the staff continued to test and combine other discoveries to patent in 1905 their process, called the Sulman-Picard-Ballot process after company officers and patentees. The process proved successful at their Central Block plant, Broken Hill that year. Significant in their "agitation froth flotation" process was the use of less than 1% oil and an agitation step that created small bubbles, which provided more surface to capture the metal and float into a froth at the surface. Useful work was done by Leslie Bradford at Port Pirie and by William Piper, Sir Herbert Gepp and Auguste de Bavay.
Mineral Separation also bought other patents to consolidate ownership of any potential conflicting rights to the flotation process - except for the Elmore patents. In 1910, when the Zinc Corporation replaced its Elmore process with the Minerals Separation (Sulman-Picard-Ballot) froth flotation process at its Broken Hill plant, the primacy of the Minerals Separation over other process contenders was assured. Henry Livingston Sulman was later recognized by his peers in his election as President of the (British) Institution of Mining and Metallurgy, which also awarded him its gold medal.
20th century
Developments in the United States had been less than spectacular. Butters's failures, as well as others, was followed after 1904, with Scotsman Stanley MacQuisten's process (a surface tension based method), which was developed with a modicum of success in Nevada and Idaho, but this would not work when slimes were present, a major fault. Henry E. Wood of Denver had developed his flotation process along the same lines in 1907, patented 1911, with some success on molybdenum ores. For the most part, however, these were isolated attempts without fanfare for what can only be called marginal successes.
In 1911, James M. Hyde, a former employee of Minerals Separation, Ltd., modified the Minerals Separation process and installed a test plant in the Butte and Superior Mill in Basin, Montana, the first such installation in the USA. In 1912, he designed the Butte & Superior zinc works, Butte, Montana, the first great flotation plant in America. Minerals Separation, Ltd., which had set up an office in San Francisco, sued Hyde for infringement as well as the Butte & Superior company, both cases were eventually won by the firm in the U. S. Supreme Court. Daniel Cowan Jackling and partners, who controlled Butte & Superior, also refuted the Minerals Separation patent and funded the ensuing legal battles that lasted over a decade. They - Utah Copper (Kennecott), Nevada Consolidated, Chino Copper, Ray Con and other Jackling firms - eventually settled, in 1922, paying a substantial fee for licenses to use the Minerals Separation process. One unfortunate result of the dispute was professional divisiveness among the mining engineering community for a generation.
In 1913, the Minerals Separation paid for a test plant for the Inspiration Copper Company at Miami, Arizona. Built under the San Francisco office director, Edward Nutter, it proved a success. Inspiration engineer L. D. Ricketts ripped out a gravity concentration mill and replaced it with the Minerals Separation process, the first major use of the process at an American copper mine. A major holder of Inspiration stock were men who controlled the great Anaconda mine of Butte. They immediately followed the Inspiration success to build a Minerals Separation licensed plant at Butte, in 1915–1916, a major statement about the final acceptance of the Minerals Separation patented process.
John M. Callow, of General Engineering of Salt Lake City, had followed flotation from technical papers and the introduction in both the Butte and Superior Mill, and at Inspiration Copper in Arizona and determined that mechanical agitation was a drawback to the existing technology. Introducing a porous brick with compressed air, and a mechanical stirring mechanism, Callow applied for a patent in 1914 (some say that Callow, a Jackling partisan, invented his cell as a means to avoid paying royalties to Minerals Separation, which firms using his cell eventually were forced to do by the courts). This method, known as Pneumatic Flotation, was recognized as an alternative to the Minerals Separation process of flotation concentration. The American Institute of Mining Engineers presented Callow the James Douglas Gold Medal in 1926 for his contributions to the field of flotation. By that time, flotation technology was changing, especially with the discovery of the use of xanthates and other reagents, which made the Callow cell and his process obsolete.
Montana Tech professor Antoine Marc Gaudin defined the early period of flotation as the mechanical phase while by the late 1910s it entered the chemical phase. Discoveries in reagents, especially the use of xanthates patented by Minerals Separations chemist Cornelius H. Keller, not so much increased the capture of minerals through the process as making it far more manageable in day-to-day operations. Minerals Separation's initial flotation patents ended 1923, and new ones for chemical processes gave it a significant position into the 1930s. During this period the company also developed and patented flotation processes for iron out of its Hibbing lab and of phosphate in its Florida lab. Another rapid phase of flotation process innovation did not occur until after 1960.
In the 1960s the froth flotation technique was adapted for deinking recycled paper.
The success of the process is evinced by the number of claimants as "discoverers" of flotation. In 1961, American engineers celebrated "50 years of flotation" and enshrined James Hyde and his Butte & Superior mill. In 1977, German engineers celebrated the "hundredth anniversary of flotation" based on the brothers Bessel patent of 1877. The historic Glasdir copper mine site advertises its tours in Wales as site of the "discovery of flotation" based upon the Elmore brothers work. Recent writers, because of the interest in celebrating women in science, champion Carrie Everson of Denver as mother of the process based on her 1885 patent. Omitted from this list are the engineers, metallurgists and chemists of Minerals Separation, Ltd., which, at least in the American and Australian courts, won control of froth flotation patents as well as right of claimant as discoverers of froth flotation. But, as historian Martin Lynch writes, "Mineral Separation would eventually prevail after taking the case to the US Supreme Court [and the House of Lords], and in so doing earned for itself the cordial detestation of many in the mining world."
Theory
Froth flotation efficiency is determined by a series of probabilities: those of particle–bubble contact, particle–bubble attachment, transport between the pulp and the froth, and froth collection into the product launder. In a conventional mechanically-agitated cell, the void fraction (i.e. volume occupied by air bubbles) is low (5 to 10 percent) and the bubble size is usually greater than 1 mm. This results in a relatively low interfacial area and a low probability of particle–bubble contact. Consequently, several cells in series are required to increase the particle residence time, thus increasing the probability of particle–bubble contact.
Selective adhesion
Froth flotation depends on the selective adhesion of air bubbles to mineral surfaces in a mineral/water slurry. The air bubbles attach to more hydrophobic particles, as determined by the interfacial energies between the solid, liquid, and gas phases. This energy is determined by the Young–Dupré equation:
where:
γlv is the surface energy of the liquid/vapor interface
γsv is the surface energy of the solid/vapor interface
γsl is the surface energy of the solid/liquid interface,
θ is the contact angle, the angle formed at the junction between vapor, solid, and liquid phases.
Minerals targeted for separation may be chemically surface-modified with collectors so that they are more hydrophobic. Collectors are a type of surfactant that increase the natural hydrophobicity of the surface, increasing the separability of the hydrophobic and hydrophilic particles. Collectors either chemically bond via chemisorption to the mineral or adsorb onto the surface via physisorption.
IMFs and surface forces in bubble-particle interactions
Collision
The collision rates for fine particles (50 - 80 μm) can be accurately modeled, but there is no current theory that accurately models bubble-particle collision for particles as large as 300 μm, which are commonly used in flotation processes.
For fine particles, Stokes law underestimates collision probability while the potential equation based on surface charge overestimates collision probability so an intermediate equation is used.
It is important to know the collision rates in the system since this step precedes the adsorption where a three phase system is formed.
Adsorption (attachment)
The effectiveness of a medium to adsorb to a particle is influenced by the relationship between the surfaces of both materials. There are multiple factors that affect the efficiency of adsorption in chemical, thermodynamic, and physical domains. These factors can range from surface energy and polarity to the shape, size, and roughness of the particle. In froth flotation, adsorption is a strong consequence of surface energy, since the small particles have a high surface area to size ratio, resulting in higher energy surfaces to form attractions with adsorbates. The air bubbles must selectively adhere to the desired minerals to elevate them to the surface of the slurry while wetting the other minerals and leaving them in the aqueous slurry medium.
Particles that can be easily wetted by water are called hydrophilic, while particles that are not easily wetted by water are called hydrophobic. Hydrophobic particles have a tendency to form a separate phase in aqueous media. In froth flotation the effectiveness of an air bubble to adhere to a particle is based on how hydrophobic the particle is. Hydrophobic particles have an affinity to air bubbles, leading to adsorption. The bubble-particle combinations are elevated to the froth zone driven by buoyancy forces.
The attachment of the bubbles to the particles is determined by the interfacial energies of between the solid, liquid, and vapor phases, as modeled by the Young/Dupre Equation. The interfacial energies can be based on the natural structure of the materials, or the addition of chemical treatments can improve energy compatibility.
Collectors are the main additives used to improve particle surfaces. They function as surfactants to selectively isolate and aid adsorption between the particles of interest and bubbles rising through the slurry. Common collectors used in flotation are anionic sulfur ligands, which have a bifunctional structure with an ionic portion which shares attraction with metals, and a hydrophobic portion such as a long hydrocarbon tail. These collectors coat a particle's surface with a monolayer of non-polar substance to aid separation from the aqueous phase by decreasing the adsorbed particle solubility in water. The adsorbed ligands can form micelles around the particles and form small-particle colloids improving stability and phase separation further.
Desorption (detachment)
The adsorption of particles to bubbles is essential to separating the minerals from the slurry, but the minerals must be purified from the additives used in separation, such as the collectors, frothers, and modifiers. The product of the cleaning, or desorption process, is known as the cleaner concentrate.
The detachment of a particle and bubble requires adsorption bond cleavage driven by shear forces. Depending on the flotation cell type, shear forces are applied by a variety of mechanical systems. Among the most common are impellers and mixers. Some systems combine the functionalities of these components by placing them at key locations where they can take part in multiple froth flotation mechanisms. Cleaning cells also take advantage of gravitational forces to improve separation efficiency.
Desorption itself is a chemical phenomenon where compounds are just physically attached to each other without having any chemical bond.
Performance calculations
Relevant equations
A common quantity used to describe the collection efficiency of a froth flotation process is flotation recovery (). This quantity incorporates the probabilities of collision and attachment of particles to gas flotation bubbles.
where:
, which is the product of the probability of the particle being collected () and the number of possible particle collisions ()
is particle diameter
is bubble diameter
is a specified height within the flotation which the recovery was calculated
is the particle concentration
The following are several additional mathematical methods often used to evaluate the effectiveness of froth flotation processes. These equations are more simple than the calculation for flotation recovery, as they are based solely on the amounts of inputs and outputs of the processes.
For the following equations:
is the weight percent of feed
is the weight percent concentrate
is the weight percent of tailings
, , and are the metallurgical assays of the concentrate, tailings, and feed, respectively
Ratio of feed weight to concentrate weight (unitless)
Percent of metal recovered () in wt%
Percent of metal lost () in wt%
Percent of weight recovered in wt%
This can be calculated using weights and assays, as . Or, since , the percent of metal recovered () can be calculated from assays alone using .
Percent of metal lost is the opposite of the percent of metal recovered, and represents the material lost to the tailings.
See also
Deinking
Dissolved air flotation (DAF)
Flocculation
List of waste-water treatment technologies
References
Further reading
Froth Flotation: A Century of Innovation, by Maurice C. Fuerstenau et al. 2007, SME, 891 pp. . Google Books preview
D N Nihill, C M Stewart and P Bowen, "The McArthur River mine—the first years of operation," in: AusIMM ’98 – The Mining Cycle, Mount Isa, 19–23 April 1998 (The Australasian Institute of Mining and Metallurgy: Melbourne, 1998), 73–82.
E V Manlapig, C Green, J W Parkinson and A S Murphy, "The technology and economic incentives for recovering coal from tailings impoundments," SME Annual Meeting, Denver, Colorado, 26–28 February 2001, Preprint 01-70 (Society of Mining, Metallurgy and Exploration: Littleton, Colorado, 2001).
Industrial processes
Water treatment
Metallurgical processes
Australian inventions | Froth flotation | [
"Chemistry",
"Materials_science",
"Engineering",
"Environmental_science"
] | 7,175 | [
"Water treatment",
"Metallurgical processes",
"Metallurgy",
"Water pollution",
"Environmental engineering",
"Oil refining",
"Flotation processes",
"Water technology"
] |
1,567,889 | https://en.wikipedia.org/wiki/Triparental%20mating | Triparental mating is a form of bacterial conjugation where a conjugative plasmid present in one bacterial strain assists the transfer of a mobilizable plasmid present in a second bacterial strain into a third bacterial strain. Plasmids are introduced into bacteria for such purposes as transformation, cloning, or transposon mutagenesis. Triparental matings can help overcome some of the barriers to efficient plasmid mobilization. For instance, if the conjugative plasmid and the mobilizable plasmid are members of the same incompatibility group they do not need to stably coexist in the second bacterial strain for the mobilizable plasmid to be transferred.
History
Triparental mating was identified in yeasts in 1960 and then in Escherichia coli in 1962.
Process
Requirements
A helper strain, carrying a conjugative plasmid (such as the F-plasmid) that codes for genes required for conjugation and DNA transfer.
A donor strain, carrying a mobilizable plasmid that can utilize the transfer functions of the conjugative plasmid.
A recipient strain, you wish to introduce the mobilizable plasmid into.
Five to seven days are required to determine if the
plasmid was successfully introduced into the new bacterial
strain and confirm that there is no carryover of the helper or
donor strain.
In contrast, electroporation does not require a helper or
donor strain. This helps
avoid possible contamination with other strains. The introduction
of the plasmid can be verified in the recipient
strain in two days, making electroporation a faster and
more efficient method of transformation. Electroporation however does not work with all bacteria and is mostly limited to well-characterized model organisms.
See also
Bacterial conjugation
Plasmid
Transposon (applications)
Bacteriophage
Three-parent baby
External links
Protocol for P. aeruginosa
References
Molecular biology | Triparental mating | [
"Chemistry",
"Biology"
] | 426 | [
"Biochemistry",
"Molecular biology"
] |
1,568,133 | https://en.wikipedia.org/wiki/Automatic%20Performance%20Control | Automatic Performance Control (APC) was the first engine knock and boost control system. The APC was invented by Per Gillbrand at the Swedish car maker SAAB.
SAAB introduced it on the turbo charged Saab H engines in 1982, and the APC was fitted to all subsequent 900 Turbos through 1993 (and 1994 convertibles), as well as 9000 Turbos through 1989.
The APC was sold to Maserati to equip the carbureted Maserati Biturbo, with different settings for the Biturbo, and was known as the Maserati Automatic Boost Controller (MABC).
The APC allowed a higher compression ratio (initially, 8.5:1 as opposed to 7.2:1, and, on 16-valve variants introduced in 1985, 9.0:1). This improved fuel economy and allowed the use of low-octane petrol without causing engine damage caused by knock.
The APC controls boost pressure and the overall performance, specifically the rate of rise and maximum boost level - and it detects and manages harmful knock events.
To control the turbocharger, the APC monitors the engine's RPM and inlet manifold pressure via a pressure transducer, and uses these inputs to control a solenoid valve that trims the rate of rise of pressure as well as the maximum pressure by directing boost pressure to the turbocharger's pneumatic wastegate actuator.
To detect knock, a piezoelectric knock sensor (basically a microphone) bolted to the engine block responds to unique frequencies caused by engine knock. The sensor generates a small voltage that is sent to the electronic control unit, which processes the signal to determine if, in fact, knock is occurring. If it is, then the control unit activates a solenoid valve that directs boost pressure to the turbocharger's pneumatically controlled wastegate, that opens to bypass exhaust gases from the turbocharger directly to the exhaust pipe, lowering turbo boost pressure until the knock subsides. Knock events that are managed by the APC can be discerned when the in-dash boost needle "twitches" slightly. The APC unit has a 'knock' output where an LED may be connected. This LED will then light up if knock is detected. Because the knock sensor becomes less accurate at high revolutions, the APC tapers maximum boost pressure after approximately 4,500 RPM.
APC boost gauge
Saab Full Pressure Turbo (FPT) models with this unit include the APC name displayed on a non-numeric boost pressure gauge in the instrument panel. Although knock sensors are common even on non-turbocharged and turbocharged engines today, Saab has continued to use the APC name prominently as a differentiating feature.
The white area on the left side of the scale shows manifold vacuum under normal driving conditions, the short white dash is atmospheric pressure (engine off), the orange scale is where there is safe turbo boost, the red scale is boost above 0.5 - 0.7 bar where the wastegate may be opened or a fuel cut due to overboost may occur.
Saab integrated the APC's boost control functionality with ignition control in 1990 with the introduction of the DI/APC system, available in 9000 models only. The DI/APC system managed knock not only by decreasing boost via a solenoid but by retarding ignition timing as well; DI/APC also managed the engine's basic ignition timing.
See also
Saab Information Display
Trionic
References
Engine technology
Saab | Automatic Performance Control | [
"Technology"
] | 738 | [
"Engine technology",
"Engines"
] |
1,568,394 | https://en.wikipedia.org/wiki/Mayor%27s%20Award%20for%20Excellence%20in%20Science%20and%20Technology | The Mayor's Award for Excellence in Science and Technology is given annually to recognise important members of the science and engineering communities in New York City. Candidates must live or work in the city.
Nominations are submitted in five categories:
Biological and Medical Sciences
Mathematical, Physical, Engineering Sciences
Technology
Public Understanding of Science and Technology
Young Investigator (for scientists and engineers under the age of 40)
The Mayor chooses winners from a list of finalists submitted by the New York Academy of Sciences and the New York City Department of Cultural Affairs.
References
Science and technology awards
American awards | Mayor's Award for Excellence in Science and Technology | [
"Technology"
] | 111 | [
"Science and technology awards",
"Science award stubs"
] |
1,568,414 | https://en.wikipedia.org/wiki/RuleML | RuleML is a global initiative, led by a non-profit organization RuleML Inc., that is devoted to advancing research and industry standards design activities in the technical area of rules that are semantic and highly inter-operable. The standards design takes the form primarily of a markup language, also known as RuleML. The research activities include an annual research conference, the RuleML Symposium, also known as RuleML for short. Founded in fall 2000 by Harold Boley, Benjamin Grosof, and Said Tabet, RuleML was originally devoted purely to standards design, but then quickly branched out into the related activities of coordinating research and organizing an annual research conference starting in 2002. The M in RuleML is sometimes interpreted as standing for Markup and Modeling. The markup language was developed to express both forward (bottom-up) and backward (top-down) rules in XML for deduction, rewriting, and further inferential-transformational tasks. It is defined by the Rule Markup Initiative, an open network of individuals and groups from both industry and academia that was formed to develop a canonical Web language for rules using XML markup and transformations from and to other rule standards/systems.
Markup standards and initiatives related to RuleML include:
Rule Interchange Format (RIF): The design and overall purpose of W3C's Rule Interchange Format (RIF) industry standard is based primarily on the RuleML industry standards design. Like RuleML, RIF embraces a multiplicity of potentially useful rule dialects that nevertheless share common characteristics.
RuleML Technical Committee from Oasis-Open: An industry standards effort devoted to legal automation utilizing RuleML.
Semantic Web Rule Language (SWRL): An industry standards design, based primarily on an early version of RuleML, whose development was funded in part by the DARPA Agent Markup Language (DAML) research program.
Semantic Web Services Framework, particularly its Semantic Web Services Language: An industry standards design, based primarily on a medium-mature version of RuleML, whose development was funded in part by the DARPA Agent Markup Language (DAML) research program and the WSMO research effort of the EU.
Mathematical Markup Language (MathML): However, MathML's Content Markup is better suited for defining functions rather than relations or general rules
Predictive Model Markup Language (PMML): With this XML-based language one can define and share various models for data-mining results, including association rules
Attribute Grammars in XML (AG-markup): For AG's semantic rules, there are various possible XML markups that are similar to Horn-rule markup
Extensible Stylesheet Language Transformations (XSLT): This is a restricted term-rewriting system of rules, written in XML, for transforming XML documents into other text documents
See also
RuleML Symposium
Ontology (information science)
Business rules
Business rules approach
Semantic Web Rule Language
R2ML
Flora-2
References
External links
AG-markup
Rules Portal
Computer science organizations
Events (computing)
Rule engines
XML markup languages
Knowledge representation languages | RuleML | [
"Technology"
] | 630 | [
"Information systems",
"Computer science",
"Events (computing)",
"Computer science organizations"
] |
1,568,513 | https://en.wikipedia.org/wiki/Dendrite%20%28crystal%29 | A crystal dendrite is a crystal that develops with a typical multi-branching form, resembling a fractal. The name comes from the Ancient Greek word (), which means "tree", since the crystal's structure resembles that of a tree. These crystals can be synthesised by using a supercooled pure liquid, however they are also quite common in nature. The most common crystals in nature exhibit dendritic growth are snowflakes and frost on windows, but many minerals and metals can also be found in dendritic structures.
History
Maximum velocity principle
The first dendritic patterns were discovered in palaeontology and are often mistaken for fossils because of their appearance. The first theory for the creation of these patterns was published by Nash and Glicksman in 1974, they used a very mathematical method and derived a non-linear integro-differential equation for a classical needle growth. However they only found an inaccurate numerical solution close to the tip of the needle and they found that under a given growth condition, the tip velocity has a unique maximum value. This became known as the maximum velocity principle (MVP) but was ruled out by Glicksman and Nash themselves very quickly. In the following two years Glicksman improved the numerical methods used, but did not realise the non-linear integro-differential equation had no mathematical solutions making his results meaningless.
Marginal stability hypothesis
Four years later, in 1978, Langer and Müller-Krumbhaar proposed the marginal stability hypothesis (MSH). This hypothesis used a stability parameter σ which depended on the thermal diffusivity, the surface tension and the radius of the tip of the dendrite. They claimed a system would be unstable for small σ causing it to form dendrites. At the time however Langer and Müller-Krumbhaar were unable to obtain a stability criterion for certain growth systems which lead to the MSH theory being abandoned.
Microscopic solvability condition
A decade later several groups of researchers went back to the Nash-Glicksman problem and focused on simplified versions of it. Through this they found that the problem for isotropic surface tension had no solutions. This result meant that a system with a steady needle growth solution necessarily needed to have some type of anisotropic surface tension. This breakthrough lead to the microscopic solvability condition theory (MSC), however this theory still failed since although for isotropic surface tension there could not be a steady solution, it was experimentally shown that there were nearly steady solutions which the theory did not predict.
Macroscopic continuum model
Nowadays the best understanding for dendritic crystals comes in the form of the macroscopic continuum model which assumes that both the solid and the liquid parts of the system are continuous media and the interface is a surface. This model uses the microscopic structure of the material and uses the general understanding of nucleation to accurately predict how a dendrite will grow.
Dendrite formation
Dendrite formation starts with some nucleation, i.e. the first appearance of solid growth, in the supercooled liquid. This formation will at first grow spherically until this shape is no longer stable. This instability has two causes: anisotropy in the surface energy of the solid/liquid interface and the attachment kinetics of particles to crystallographic planes when they have formed.
On the solid-liquid interface, we can define a surface energy, , which is the excess energy at the liquid-solid interface to accommodate the structural changes at the interface.
For a spherical interface, the Gibbs–Thomson equation then gives a melting point depression compared to a flat interface , which has the relation
where is the radius of the sphere. This curvature undercooling, the effective lowering of the melting point at the interface, sustains the spherical shape for small radii.
However, anisotropy in the surface energy implies that the interface will deform to find the energetically most favourable shape. For cubic symmetry in 2D we can express this anisotropy int the surface energy as
This gives rise to a surface stiffness
where we note that this quantity is positive for all angles when . In this case we speak of "weak anisotropy". For larger values of , the "strong anisotropy" causes the surface stiffness to be negative for some . This means that these orientations cannot appear, leading to so-called 'faceted' crystals, i.e. the interface would be a crystallographic plane inhibiting growth along this part of the interface due to attachment kinetics.
Wulff construction
For both above and below the critical anisotropy the Wulff construction provides a method to determine the shape of the crystal. In principle, we can understand the deformation as an attempt by the system to minimise the area with the highest effective surface energy.
Growth velocity
Taking into account attachment kinetics, we can derive that both for spherical growth and for flat surface growth, the growth velocity decreases with time by . We do however find stable parabolic growth, where the length grows with and the width with . Therefore, growth mainly takes place at the tip the parabolic interface, which draws out longer and longer. Eventually, the sides of this parabolic tip will also exhibit instabilities giving a dendrite its characteristic shape.
Preferred growth direction
When dendrites start to grow with tips in different directions, they display their underlying crystal structure, as this structure causes the anisotropy in surface energy. For instance, a dendrite growing with BCC crystal structure will have a preferred growth direction along the directions. The table below gives an overview of preferred crystallographic directions for dendritic growth. Note that when the strain energy minimisation effect dominates over surface energy minimisation, one might find a different growth direction, such as with Cr, which has as a preferred growth direction , even though it is a BCC latice.
Metal dendrites
For metals the process of forming dendrites is very similar to other crystals, but the kinetics of attachment play a much smaller role. This is because the interface is atomically rough; because of the small difference in structure between the liquid and the solid state, the transition from liquid to solid is somewhat gradual and one observes some interface thickness. Consequently, the surface energy will become nearly isotropic. For this reason, one would not expect faceted crystals as found for atomically smooth interfaces observed in crystals of more complex molecules.
Mineralogy and paleontology
In paleontology, dendritic mineral crystal forms are often mistaken for fossils. These pseudofossils form as naturally occurring fissures in the rock are filled by percolating mineral solutions. They form when water rich in manganese and iron flows along fractures and bedding planes between layers of limestone and other rock types, depositing dendritic crystals as the solution flows through. A variety of manganese oxides and hydroxides are involved, including:
birnessite ()
coronadite ()
cryptomelane ()
hollandite ()
romanechite ()
todorokite () and others.
A three-dimensional form of dendrite develops in fissures in quartz, forming moss agate
NASA microgravity experiment
The Isothermal Dendritic Growth Experiment (IDGE) was a materials science solidification experiment that researchers used on Space Shuttle missions to investigate dendritic growth in an environment where the effect of gravity (convection in the liquid) could be excluded. The experimental results indicated that at lower supercooling (up to 1.3 K), these convective effects are indeed significant. Compared to the growth in microgravity, the tip velocity during dendritic growth under normal gravity was found to be up to several times greater.
See also
Brownian tree
Monocrystalline whisker
Patterns in nature
STS-87—Space Shuttle mission featuring the Isothermal Dendritic Growth Experiment
Whisker (metallurgy)
References
External links
Mindat Manganese Dendrites
What are manganese dendrites?
The Isothermal Dendritic Growth Experiment
Snow crystals
Dendritic Solidification
Dendritic growth in Local-Nonequilibrium Solidification Model
All About Manganese Dendrites
Crystals | Dendrite (crystal) | [
"Chemistry",
"Materials_science"
] | 1,690 | [
"Crystallography",
"Crystals"
] |
1,568,586 | https://en.wikipedia.org/wiki/HD%206434 | HD 6434 is a star in the southern constellation of Phoenix. Yellow dwarfs such as this are not very luminous, so at a distance of 138 light years it is not visible to the unaided eye. However, with binoculars it is readily visible under ideal observing conditions, having an apparent visual magnitude of 7.71. The star is drifting further from the Sun with a radial velocity of +23 km/s.
The star HD 6434 is named Nenque. The name was selected in the NameExoWorlds campaign by Ecuador, during the 100th anniversary of the IAU. Nenque means the Sun in the language spoken by the Indigenous Waorani tribes.
This object is a Sun-like G-type main-sequence star with a stellar classification of G2/G3V. It is an ancient population II star with an estimated age of 12 billion years, and is one of the most metal-deficient stars known to host a planet. This star is spinning at a leisurely rate with a projected rotational velocity of 2.2 km/s. It has 88% of the mass of the Sun but is nearly the same size. HD 6434 is radiating 1.2 times the luminosity of the Sun from its photosphere at an effective temperature of 5,907 K.
Planetary system
In 2000, a planet, designated , was detected in a close orbit around the star. The peer-reviewed scientific paper was published four years later.
See also
94 Ceti
List of extrasolar planets
References
External links
G-type main-sequence stars
Planetary systems with one confirmed planet
Phoenix (constellation)
CD–40 239
9037
006434
005054
J01044015-3929173 | HD 6434 | [
"Astronomy"
] | 354 | [
"Phoenix (constellation)",
"Constellations"
] |
1,568,592 | https://en.wikipedia.org/wiki/Albertite | Albertite is a variety of asphalt found in the Albert Formation in Albert County, New Brunswick, and in a deposit at Dingwall, in the north-east of Scotland. It is a type of solid hydrocarbon.
Albertite has a black colour, a resinous luster, and a hardness of 2½. It is less soluble in turpentine than the usual type of asphalt. It was from a mixture of albertite and pitch that kerosene was first distilled in 1846 by Abraham Gesner, a New Brunswick geologist who had heard stories of rocks that burned in the area and gave the material its first scientific study.
Origin
Albertite is formed from oil shale in which some of the hydrocarbons have been remobilised as liquid asphalt. The process is as follows:
Crude oil (petroleum) is produced from source rocks (in the case of Albert Mines, oil shale).
The petroleum migrates through fractures and becomes trapped in the apex of an anticline.
The lighter oils gradually leak out through the weakly permeable caprock.
The bituminous residues (tars, asphaltanes, etc.) are left behind in the fractures as albertite.
Occurrence
Albertite is named after Albert County in New Brunswick, Canada, where it was first found in the area that became known as Albert Mines. There, the albertite occurs as discordant, cross-cutting veins in the core of an anticline. It was initially mistaken for coal. Most geologists of the 1800s were puzzled by how this "coal" came to be discordant to the local strata, as they did not understand the nature of its oil shale source rock, or the fact that the albertite was essentially solidified asphaltum.
Extraterrestrial albertite has also been detected on the dwarf planet Ceres.
References
External links
Albertite occurrences, Albert Mines
Oil Shows of Nova Scotia, including Albertite leads
Solid Hydrocarbon References
Asphaltic substances in Turkey; their physical properties
Petroleum industry in Canada
Oil shale in Canada
Oil shale geology
Bitumen-impregnated rocks | Albertite | [
"Chemistry"
] | 426 | [
"Asphalt",
"Bitumen-impregnated rocks"
] |
1,568,608 | https://en.wikipedia.org/wiki/Half-integer | In mathematics, a half-integer is a number of the form
where is an integer. For example,
are all half-integers. The name "half-integer" is perhaps misleading, as each integer is itself half of the integer . A name such as "integer-plus-half" may be more accurate, but while not literally true, "half integer" is the conventional term. Half-integers occur frequently enough in mathematics and in quantum mechanics that a distinct term is convenient.
Note that halving an integer does not always produce a half-integer; this is only true for odd integers. For this reason, half-integers are also sometimes called half-odd-integers. Half-integers are a subset of the dyadic rationals (numbers produced by dividing an integer by a power of two).
Notation and algebraic structure
The set of all half-integers is often denoted
The integers and half-integers together form a group under the addition operation, which may be denoted
However, these numbers do not form a ring because the product of two half-integers is not a half-integer; e.g. The smallest ring containing them is , the ring of dyadic rationals.
Properties
The sum of half-integers is a half-integer if and only if is odd. This includes since the empty sum 0 is not half-integer.
The negative of a half-integer is a half-integer.
The cardinality of the set of half-integers is equal to that of the integers. This is due to the existence of a bijection from the integers to the half-integers: , where is an integer
Uses
Sphere packing
The densest lattice packing of unit spheres in four dimensions (called the D4 lattice) places a sphere at every point whose coordinates are either all integers or all half-integers. This packing is closely related to the Hurwitz integers: quaternions whose real coefficients are either all integers or all half-integers.
Physics
In physics, the Pauli exclusion principle results from definition of fermions as particles which have spins that are half-integers.
The energy levels of the quantum harmonic oscillator occur at half-integers and thus its lowest energy is not zero.
Sphere volume
Although the factorial function is defined only for integer arguments, it can be extended to fractional arguments using the gamma function. The gamma function for half-integers is an important part of the formula for the volume of an -dimensional ball of radius ,
The values of the gamma function on half-integers are integer multiples of the square root of pi:
where denotes the double factorial.
References
Rational numbers
Elementary number theory
Parity (mathematics) | Half-integer | [
"Mathematics"
] | 543 | [
"Elementary mathematics",
"Elementary number theory",
"Number theory"
] |
1,568,646 | https://en.wikipedia.org/wiki/HD%20187123 | HD 187123 is a single, yellow-hued star with two exoplanetary companions in the northern constellation of Cygnus. It has an apparent visual magnitude of 7.83, making it an 8th magnitude star that is too faint to be visible with the naked eye. However, it should be easy target with binoculars or small telescope. The system is located at a distance of 150 light years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of −17 km/s.
This is an ordinary G-type main-sequence star with a stellar classification of G2V. The physical properties of this star are sufficiently similar to the Sun that it has been considered a solar analog, although the metallicity is higher. It is estimated to be five or six billion years old and is spinning with a projected rotational velocity of 2 km/s. The star has a similar mass to the Sun but is slightly larger with 117% of the Sun's radius. It is radiating 1.44 times the luminosity of the Sun from its photosphere at an effective temperature of 5,853 K.
Planetary system
In 1998 the California and Carnegie Planet Search team, after following a suggestion by Kevin Apps, a Briton who at the time was an undergraduate student found a possible planet orbiting the star. There were also indications of another, more distant body orbiting the star and this claim was published in 2006. This planet was confirmed in 2009. The presence of water has been detected in the atmosphere of HD 187123 b with high confidence.
See also
List of extrasolar planets
List of exoplanets discovered before 2000 - HD 187123 b
List of exoplanets discovered between 2000–2009 - HD 187123 c
References
External links
G-type main-sequence stars
Solar analogs
Planetary systems with two confirmed planets
Cygnus (constellation)
Durchmusterung objects
187123
097336 | HD 187123 | [
"Astronomy"
] | 394 | [
"Cygnus (constellation)",
"Constellations"
] |
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