id int64 39 79M | url stringlengths 31 227 | text stringlengths 6 334k | source stringlengths 1 150 ⌀ | categories listlengths 1 6 | token_count int64 3 71.8k | subcategories listlengths 0 30 |
|---|---|---|---|---|---|---|
16,341,729 | https://en.wikipedia.org/wiki/Tape%20transport | A tape transport is the collection of parts of a magnetic tape player or recorder that move the tape and play or record it. Transport parts include the head, capstan, pinch roller, tape pins, and tape guide. The tape transport as a whole is called the transport mechanism.
Tape head
The tape head is the part of a tape recording or playback device which converts the magnetic fluctuations present in the tape into an electrical signal, which is then amplified and sent to speakers or headphones. The tape head is set off-center in a multitrack device in order to record or play one or more tracks running in each direction of the tape (e.g. the two different tracks present on most, if not all, compact cassettes).
Capstan
The capstan is a rotating spindle used to move recording tape through the mechanism of a tape recorder. The tape is threaded between the capstan and one or more rubber-covered wheels, called pinch rollers, which press against the capstan, thus providing friction necessary for the capstan to pull the tape. The capstan is always placed downstream (in the direction of tape motion) from the tape heads. To maintain the required tension against the tape heads and other part of the tape transport, a small amount of drag is placed on the supply reel. Tape recorder capstans have a function similar to nautical capstans, which however have no pinch rollers, the line simply being wound around them.
The use of a capstan allows the tape to run at a precise and constant speed. Capstans are precision-machined spindles, and polished very smooth: any out-of-roundness or imperfections can cause uneven motion and an audible effect called flutter. The alternative to capstan drive, simply driving the tape takeup reel (which was used on some cheap tape recorders), causes problems both with the speed difference between a full and empty reel and with speed variations as described.
Dual capstans, where one is on each side of the heads, are claimed to provide even smoother tape travel across the heads and result in less variance in the recorded/playback signal.
Pinch roller
The pinch roller is a rubberized, free-spinning wheel typically used to press magnetic tape against a capstan shaft in order to create friction necessary to drive the tape along the magnetic heads (erase, write, read).
Most magnetic tape recorders use one capstan motor and one pinch roller located after the magnetic heads in the direction of the moving tape. However multiple pinch rollers may also be employed in association with one or more capstans. An example of the application of multiple pinch rollers is the Technics RS-1520 tape recorder, which utilizes two pinch rollers located on opposite sides of a single capstan shaft, providing a more stable transport across two sets of magnetic heads. Dual pinch rollers are also used (along with dual capstans) in auto-reverse cassette decks to drive the tape in both directions as needed. In this case, only one pinch roller is pressed against its corresponding capstan at a time.
Tension arm
A tension arm is a device used in magnetic tape recorders/reproducers to control the tension of the magnetic tape during machine operation. The recorders equipped with a tension arm can utilize more than one of them to control tape tension in different direction of winding or during different modes of tape operation. Tension arms can also be found on digital data recorders and other types of recorders/reproducers using continuous tape media such as magnetic digital tape, perforated paper tape, and analog magnetic tape.
References
One of many US Patents pertaining to Tension arm
Workbench Guide to Tape Recorder Servicing. G. Howard Poteet, 1977
Wheels
Sound recording technology
Sound production technology
Tape recording | Tape transport | [
"Technology"
] | 768 | [
"Recording devices",
"Sound recording technology",
"Tape recording"
] |
16,342,785 | https://en.wikipedia.org/wiki/Wiener%20sausage | In the mathematical field of probability, the Wiener sausage is a neighborhood of the trace of a Brownian motion up to a time t, given by taking all points within a fixed distance of Brownian motion. It can be visualized as a sausage of fixed radius whose centerline is Brownian motion. The Wiener sausage was named after Norbert Wiener by because of its relation to the Wiener process; the name is also a pun on Vienna sausage, as "Wiener" is German for "Viennese".
The Wiener sausage is one of the simplest non-Markovian functionals of Brownian motion. Its applications include stochastic phenomena including heat conduction. It was first described by , and it was used by to explain results of a Bose–Einstein condensate, with proofs published by .
Definitions
The Wiener sausage Wδ(t) of radius δ and length t is the set-valued random variable on Brownian paths b (in some Euclidean space) defined by
is the set of points within a distance δ of some point b(x) of the path b with 0≤x≤t.
Volume
There has been a lot of work on the behavior of the volume (Lebesgue measure) |Wδ(t)| of the Wiener sausage as it becomes thin (δ→0); by rescaling, this is essentially equivalent to studying the volume as the sausage becomes long (t→∞).
showed that in 3 dimensions the expected value of the volume of the sausage is
In dimension d at least 3 the volume of the Wiener sausage is asymptotic to
as t tends to infinity. In dimensions 1 and 2 this formula gets replaced by and respectively. , a student of Spitzer, proved similar results for generalizations of Wiener sausages with cross sections given by more general compact sets than balls.
References
Especially chapter 22.
(Reprint of 1964 edition)
An advanced monograph covering the Wiener sausage.
Mathematical physics
Statistical mechanics
Wiener process | Wiener sausage | [
"Physics",
"Mathematics"
] | 397 | [
"Applied mathematics",
"Statistical mechanics",
"Theoretical physics",
"Mathematical physics"
] |
620,712 | https://en.wikipedia.org/wiki/Landau%E2%80%93Ramanujan%20constant | In mathematics and the field of number theory, the Landau–Ramanujan constant is the positive real number b that occurs in a theorem proved by Edmund Landau in 1908, stating that for large , the number of positive integers below that are the sum of two square numbers behaves asymptotically as
This constant b was rediscovered in 1913 by Srinivasa Ramanujan, in the first letter he wrote to G.H. Hardy.
Sums of two squares
By the sum of two squares theorem, the numbers that can be expressed as a sum of two squares of integers are the ones for which each prime number congruent to 3 mod 4 appears with an even exponent in their prime factorization. For instance, 45 = 9 + 36 is a sum of two squares; in its prime factorization, 32 × 5, the prime 3 appears with an even exponent, and the prime 5 is congruent to 1 mod 4, so its exponent can be odd.
Landau's theorem states that if is the number of positive integers less than that are the sum of two squares, then
,
where is the Landau–Ramanujan constant.
The Landau-Ramanujan constant can also be written as an infinite product:
History
This constant was stated by Landau in the limit form above; Ramanujan instead approximated as an integral, with the same constant of proportionality, and with a slowly growing error term.
References
Additive number theory
Analytic number theory
Mathematical constants
Srinivasa Ramanujan | Landau–Ramanujan constant | [
"Mathematics"
] | 308 | [
"Analytic number theory",
"Mathematical objects",
"nan",
"Mathematical constants",
"Numbers",
"Number theory"
] |
620,746 | https://en.wikipedia.org/wiki/Interface%20%28computing%29 | In computing, an interface is a shared boundary across which two or more separate components of a computer system exchange information. The exchange can be between software, computer hardware, peripheral devices, humans, and combinations of these. Some computer hardware devices, such as a touchscreen, can both send and receive data through the interface, while others such as a mouse or microphone may only provide an interface to send data to a given system.
Hardware interfaces
Hardware interfaces exist in many components, such as the various buses, storage devices, other I/O devices, etc. A hardware interface is described by the mechanical, electrical, and logical signals at the interface and the protocol for sequencing them (sometimes called signaling). A standard interface, such as SCSI, decouples the design and introduction of computing hardware, such as I/O devices, from the design and introduction of other components of a computing system, thereby allowing users and manufacturers great flexibility in the implementation of computing systems. Hardware interfaces can be parallel with several electrical connections carrying parts of the data simultaneously or serial where data are sent one bit at a time.
Software interfaces
A software interface may refer to a wide range of different types of interfaces at different "levels". For example, an operating system may interface with pieces of hardware. Applications or programs running on the operating system may need to interact via data streams, filters, and pipelines. In object oriented programs, objects within an application may need to interact via methods.
In practice
A key principle of design is to prohibit access to all resources by default, allowing access only through well-defined entry points, i.e., interfaces. Software interfaces provide access to computer resources (such as memory, CPU, storage, etc.) of the underlying computer system; direct access (i.e., not through well-designed interfaces) to such resources by software can have major ramifications—sometimes disastrous ones—for functionality and stability.
Interfaces between software components can provide constants, data types, types of procedures, exception specifications, and method signatures. Sometimes, public variables are also defined as part of an interface.
The interface of a software module A is deliberately defined separately from the implementation of that module. The latter contains the actual code of the procedures and methods described in the interface, as well as other "private" variables, procedures, etc. Another software module B, for example the client to A, that interacts with A is forced to do so only through the published interface. One practical advantage of this arrangement is that replacing the implementation of A with another implementation of the same interface should not cause B to fail—how A internally meets the requirements of the interface is not relevant to B, which is only concerned with the specifications of the interface. (See also Liskov substitution principle.)
In object-oriented languages
In some object-oriented languages, especially those without full multiple inheritance, the term interface is used to define an abstract type that acts as an abstraction of a class. It contains no data, but defines behaviours as method signatures. A class having code and data for all the methods corresponding to that interface and declaring so is said to implement that interface. Furthermore, even in single-inheritance-languages, one can implement multiple interfaces, and hence can be of different types at the same time.
An interface is thus a type definition; anywhere an object can be exchanged (for example, in a function or method call) the type of the object to be exchanged can be defined in terms of one of its implemented interfaces or base-classes rather than specifying the specific class. This approach means that any class that implements that interface can be used. For example, a dummy implementation may be used to allow development to progress before the final implementation is available. In another case, a fake or mock implementation may be substituted during testing. Such stub implementations are replaced by real code later in the development process.
Usually, a method defined in an interface contains no code and thus cannot itself be called; it must be implemented by non-abstract code to be run when it is invoked. An interface called "Stack" might define two methods: push() and pop(). It can be implemented in different ways, for example, FastStack and GenericStack—the first being fast, working with a data structure of fixed size, and the second using a data structure that can be resized, but at the cost of somewhat lower speed.
Though interfaces can contain many methods, they may contain only one or even none at all. For example, the Java language defines the interface that has the single method; various implementations are used for different purposes, including , , , , and . Marker interfaces like contain no methods at all and serve to provide run-time information to generic processing using Reflection.
Programming to the interface
The use of interfaces allows for a programming style called programming to the interface. The idea behind this approach is to base programming logic on the interfaces of the objects used, rather than on internal implementation details. Programming to the interface reduces dependency on implementation specifics and makes code more reusable.
Pushing this idea to the extreme, inversion of control leaves the context to inject the code with the specific implementations of the interface that will be used to perform the work.
User interfaces
A user interface is a point of interaction between a computer and humans; it includes any number of modalities of interaction (such as graphics, sound, position, movement, etc.) where data is transferred between the user and the computer system.
See also
Abstraction inversion
Application binary interface
Application programming interface
Business Interoperability Interface
Computer bus
Hard disk drive interface
Implementation (computer science)
Implementation inheritance
Interoperability
Inheritance semantics
Modular programming
Software componentry
Virtual inheritance
References
Object-oriented programming
Programming constructs | Interface (computing) | [
"Technology"
] | 1,164 | [
"Interfaces"
] |
620,785 | https://en.wikipedia.org/wiki/Council%20of%20Laodicea | The Council of Laodicea was a regional Christian synod of approximately thirty clerics from Asia Minor which assembled about 363–364 in Laodicea, Phrygia Pacatiana.
Historical context
The council took place soon after the conclusion of the war between the Roman Empire and the Persian Empire, waged by Emperor Julian. Julian, the last Constantinian emperor, attempted a revival of paganism. After his death in battle on 26 June 363, officers of the army elected the Christian Jovian as his successor. Jovian, in a precarious position, far from supplies, ended the war with Persia unfavorably for Rome. He was soon succeeded by Valentinian I, who named his brother Valens as Emperor of the East.
Major concerns
The major concerns of the council involved regulating the conduct of church members. The council expressed its decrees in the form of written rules or canons. Among the sixty canons decreed, several aimed at:
Maintaining order among bishops, clerics and laypeople (canons 3–5, 11–13, 21–27, 40–44, 56–57)
Enforcing modest behavior of clerics and laypeople (4, 27, 30, 36, 53–55)
Regulating approach to heretics (canons 6–10, 31–34, 37), Jews (canons 16, 37–38) and pagans (canon 39)
Outlawing the keeping of the Sabbath (Saturday), and encouraging rest on Sunday (canon 29)
Outlining liturgical practices (canons 14–20, 21–23, 25, 28, 58–59)
Restrictions during lent (canons 45, 49–52)
Admission and instruction of catechumens and neophytes (canons 45–48)
Specifying a biblical canon (canons 59–60)
Biblical canon
The 59th canon forbade the readings in churches of uncanonical books. The 60th canon listed canonical books, with the New Testament containing 26 books, omitting the Book of Revelation, and the Old Testament including 22 books from the Tanakh and some deuterocanonical books as the Book of Baruch, and the Epistle of Jeremiah.
The authenticity of the 60th canon is doubtful, as it is missing from various Greek manuscripts and may have been added later to specify the extent of the preceding 59th canon. The Latin version of the canons of Laodicea consistently omit the canon list. Around 350, Cyril of Jerusalem produced a list of biblical books matching that from the Council of Laodicea.
Astrology
The council marks the first occasion in Christianity of the explicit condemnation of astrology, a matter on which theologians and legislators had not yet reached consensus.
References
External links
"Synod of Laodicea (4th Century)", The Canons with annotations, from Schaff
Philip Schaff (ed.), The Seven Ecumenical Councils (A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church, vol. XIV), "The Canons of the Councils of Ancyra, Gangra, Neocæsarea, Antioch and Laodicea, which Canons were Accepted and Received by the Ecumenical Synods". Synod of Laodicea.
Laodicea
Laodicea
Laodicea
Laodicea
Laodicea
363
364 | Council of Laodicea | [
"Astronomy"
] | 671 | [
"History of astrology",
"History of astronomy"
] |
620,957 | https://en.wikipedia.org/wiki/Water%20dispenser | A water dispenser, sometimes referred to as a water cooler (if used for cooling only), is a machine that dispenses and often also cools or heats up water with a refrigeration unit. It is commonly located near the restroom due to closer access to plumbing. A drain line is also provided from the water cooler into the sewer system.
Water dispensers come in a variety of form factors, ranging from wall-mounted to bottle filler water dispenser combination units, to bi-level units and other formats. They are generally broken up into two categories: point-of-use (POU) water dispensers and bottled water dispensers. POU water dispensers are connected to a water supply, while bottled water dispensers require delivery (or self-pick-up) of water in large bottles from vendors. Bottled water dispensers can be top-mounted or bottom-loaded, depending on the design of the model.
Bottled water dispensers typically use 11- or 22-liter (5- or 10-gallon) dispensers commonly found on top of the unit. Pressure coolers are a subcategory of water dispensers encompassing drinking water fountains and direct-piping water dispensers. Water cooler may also refer to a primitive device for keeping water cool.
History
Dispenser types
Wall-mounted / recessed
The wall-mounted type is connected to the building's water supply for a continuous supply of water and electricity to run a refrigeration unit to cool the incoming water, and to the building's waste disposal system to dispose of unused water. Wall-mounted water coolers are frequently used in commercial buildings like hospitals, schools, businesses, and other facilities where a facility manager is present to monitor its installation and maintenance.
In the standard wall-mounted cooler, also commonly referred to as a water fountain or drinking fountain, a small tank in the machine holds chilled water so the user does not have to wait for chilled water. Water is delivered by turning or pressing a button on a spring-loaded valve located on the top of the unit, that turns off the water when released. Some devices also offer a large button on the front or side. Newer machines may not have a button at all; instead, a sensor that detects when someone is near and activates the water. Water is delivered in a stream that arches up, allowing the user to drink directly from the top of the stream of water. These devices usually dispense water directly from the municipal water supply, without treatment or filtering.
Wall mount water coolers come in a wide variety of styles, from recessed models to splash resistant, contoured basins protruding out from the wall, traditional rounded square edge designs, bottle filler and water cooler combination units, bi-level designs, with other features and options. These are sometimes installed to meet local, state or federal codes.
Bottom-load water dispenser
Water dispensers commonly have the water supply vessel mounted at the top of the unit. Bottom-load water dispensers have the vessel mounted at the bottom of the unit to make loading easier.
Tabletop water dispenser
There are also smaller versions of the water dispensers where the dispenser can be placed directly on top of a table. These dispensers are commonly classified as household appliances and can often be found in household kitchens and office pantries.
Direct-piping water dispenser (POU)
Water dispensers can be directly connected to the in-house water source for continuous dispensing of hot and cold drinking water.
It is commonly referred to as POU () water dispensers. POU units are generally more hygienic than bottled water coolers, provided the end user has access to clean water sources.
Freestanding
A freestanding design generally involves bottles of water placed spout-down into the dispensing machine.
Tabletop or kitchen worktop versions are available which utilize readily available five-liter water bottles from supermarkets. These coolers use air pumps to push the water into the cooling chamber and Peltier devices to chill the water.
New development within the water cooler market is the advent of countertop appliances which are connected to the mains and provide an instant supply of not only chilled water but also hot and boiling water. This is often visible in the horeca industry.
Water will flow faster when the handle is in the upright position. The water is aerated which allows the water to come through the spout at a faster rate.
Water source
Water dispensed from water coolers may originate from many different sources, but are often classified into two major categories, namely natural mineral and spring water, and purified water.
Natural mineral and spring water
Natural mineral and spring water are waters emanating from underground geological rock formations collected from boreholes or emerging springs. Legislation in each respective country further differentiates between these two types of water and stipulates strict naming and labeling criteria based on natural source protection, total dissolved solids, and the amount of processing the water may undergo prior to bottling.
Purified water
Purified water is water from groundwater or municipal water supply and is produced by any one of several methods of purification including reverse osmosis, distillation, deionization, and filtration. The water is often treated by ultraviolet light or ozone for antimicrobial reasons and re-mineralized by injection of soluble inorganic salts.
Water delivery
The delivery of water in a water cooler comes in two main forms, namely bottled variants, or plumbed directly from the main water supply. The water is normally pumped into a water tank to be heated or chilled, depending on the model of the water cooler. Modern versions include hybrid models that are able to utilize both methods.
Bottled water coolers
To install the bottle, the bottle is tipped upside down and set onto the dispenser; a probe punctures the cap of the bottle
and allows the water to flow into the machine's internal reservoir.
These gravity-powered systems have a device to dispense water in a controlled manner.
These machines come in different sizes and vary from table units, intended for occasional use to floor-mounted units intended for heavier use. Bottled water is normally delivered to households or businesses on a regular basis, where empty returnable polycarbonate bottles are exchanged for full ones. In developing markets, PET is often used for large bottles despite shrinkage and lower washing temperature will lead to making it a more challenging material to use.
The bottle size varies with the size of the unit, with the larger versions in the US using bottles. This is also the most common size elsewhere, labeled as 18.9 liters in countries that use the metric system. Originally, these bottles were manufactured at 3,5 or 6 US gallon capacity (11.4, 18.9 or 22.7 liters) and supplied to rented water cooler units. These units usually do not have a place to dump excess water, only offering a small basin to catch minor spills. On the front, a lever or pushbutton dispenses the water into a cup held beneath the spigot. When the water container is empty, it is lifted off the top of the dispenser, and automatically seals to prevent any excess water still in the bottle from leaking.
Material
For many years and throughout the 20th century, glass was the main material used for bottling until the evolution of thermoplastics following World War II. PVC evolved as a multi-purpose plastic material and gained mass adoption as an ideal mass production material. Only dark green glass bottles were retained for packaging carbonated waters. The 1980s saw the re-development of PVC bottles due to cost reduction. Advances in manufacturing and materials technology such as new blow and injection molding techniques have reduced the wall thickness and weight of bottles while improving durability and increasing service life.
Direct plumbed
Directly plumbed water coolers use tap water and therefore do not need bottles due to their use of the main water supply. Usually, some method of purification is used. Log reduction (e.g. 6-log reduction or 99.9999% effective) is used as a measure on the effectiveness of sanitization and disinfection.
Purification
Filtration
Filtration methods include reverse osmosis, ion exchange, and activated carbon. Reverse osmosis works differently from chemical or ultraviolet protection, using a membrane that has fine pores, passing H2O while preventing larger molecules such as salts, carbonates, and other micro-organisms from passing through it. If there is insufficient energy to naturally force the water through the membrane, a powerful pump is required, resulting in potential high energy costs. In addition, RO units are capable of softening water. Some living micro-organisms, including viruses, are capable of passing through an RO unit filter.
Deionizers or demineralizers use resins exchange to remove ions from the stream of water and are most commonly twin-bed or mixed-bed deionizers. It is often used in sterile manufacturing environments such as computer chips, where deionized water is a poor conductor of electricity.
In activated carbon, raw materials such as lignite, coal, bone charcoal, coconut shells, and wood charcoal are used, developing pores during activation when partly burning away carbon layers. In most cases, activated carbon is a single-use material as regeneration is often not possible on-site. Granular activated carbon (GAC) is most commonly used in the filtration of the water cooler. Regular sanitization using hot water and steam is required to limit bacterial growth.
Sanitization & disinfection
The sanitization of water is defined by the reduction of the number of micro-organisms to a safe level. According to the AOAC suspension test method, a sanitizer should be capable of killing 99.999% of a specific bacterial test population within 30 seconds at 25 °C (77 °F). Sanitizers may or may not necessarily destroy pathogenic or disease-causing bacteria. The sanitizer used must comply with regulations applicable in the geographic location. In the US, sanitizers are regulated by the EPA and FDA, and must pass the AOAC test in the reduction of microbial activity of two standard test organisms (Staphylococcus aureus and Escherichia coli) from a designated microbial load by a 5-log reduction.
The main difference between a sanitizer and a disinfectant is that at a specific use dilution, the disinfectant must have a higher kill capability for pathogenic bacteria than that of a sanitizer. If these micro-organisms are not destroyed, the bottled water being produced may be contaminated.
UVGI (ultraviolet germicidal irradiation) is a commonly used disinfection method to kill or inactivate micro-organisms and leaving them unable to perform vital cellular functions. Drawbacks to UV light water purifiers include turbidity. If the fluid is unclear, the UV light will not pass through completely, leaving the stream partially sterilized.
Cooling and heating methods
Cooling
Most modern units offer a refrigeration function to chill the water, using Vapor compression refrigeration or Thermoelectric cooling.
Vapor compression refrigeration
Water coolers using vapor compression refrigeration come in one of the following systems:
Reservoir System - A tank where water is held, to be used for cooling or heating and is fitted with a float mechanism to prevent overflowing.
Removable Reservoir - a removable reservoir is an open-end tank with cooling coils that come into contact with the external tank surface. It operates on the basis of a modular system, allowing one to easily detach and refill water instead of keeping it in a closed system. One of the advantages in using a removable reservoir is the ease of sanitization. This allows end users to replace the reservoir completely rather than sending an entire water cooler back for servicing. A similar technology can be found in many modern water dispensers and coffee machines.
Stainless Steel - open end tank with cooling coils that come into contact with the external tank surface
Pressure Vessel Direct Chill System - The combination of a pressure vessel, which protects the water in the tank from air-borne contamination, and a direct chill system which cools water coming from the mains quickly.
Pressure Vessel - A sealed pressure vessel is filled at a lower pressure within the water cooler. As such, the water does not come into contact with the atmosphere, allowing a larger amount of cold water (depending on the size of the tank) to be dispensed at the expense of a slower cooling system.
Direct Chill - In a standard direct chill system, water is passed through a stainless steel coil that is in contact with a copper evaporator that circulates refrigerant gas. The refrigeration system is attached outside of the coil and the cold transfers through the pipe walls to chill the water in the coil through conduction. When the taps are operated, the chilled water is dispensed at mains pressure. The water never comes into contact with the atmosphere as the cold temperature emitted by the refrigerant gas is transferred through the copper coil which transfers the cold temperatures to water passing through the stainless steel coil without touching each other. This allows the water to get cold more quickly again at the expense of having a lower volume of cold water available.
Ice-bank Cooling System - A pressurized stainless steel coil and a copper coil is immersed in a reservoir full of pre-chilled water. The copper coil containing the refrigerant gas freezes the water contained within the reservoir producing a cold supply, which in turns cools the drinking water flowing through stainless steel coil.
Thermoelectric cooling
Thermoelectric cooling is a green alternative to HFC refrigerant that uses a solid state device that acts as a heat pump to transfer heat from one side of the device to another using the Peltier effect. It is made up of numerous pairs of semiconductors enclosed by ceramic wafers. Thermoelectric coolers use direct current power rather than refrigerant gas and a compressor and have no moving parts or complex assemblies.
Heating
Some versions also have a second dispenser that delivers room-temperature water or even heated water that can be used for tea, hot chocolate or other uses. The water in the alternate hot tap is generally heated with a heating element and stored in a hot tank (much like the traditional hot water heaters used in residential homes). Additionally, the hot tap is usually equipped with a push-in safety valve to prevent burns from an accidental or inadvertent pressing of the lever.
Additional features
Bottle filler
Newer variants of water coolers include an additional dispenser designed to fill water bottles directly on wall-mounted units. This is increasingly common in public water coolers as they have also been spotted in public places such as airports and railway stations. These bottle filling units also can indicate the number of single-use plastic bottles saved as part of an ongoing public effort to reduce plastic pollution.
Carbonation
Modern variants of water coolers have been equipped with options for sparkling water as a result of increasing demand for carbonated beverages and also a greater awareness to healthy living, resulting in preference for carbonated water over sweetened carbonated beverages. This works with the addition of a mixer tank filled with compressed CO2 located inside the cooling tank. This brings the temperature of the CO2 gas down to the temperature of the cooling tank. As carbonated water is dispensed, the mixer tank is automatically refilled with cold water and carbon dioxide, ensuring a continuous supply of carbonated water is readily available.
Maintenance
All bottled water coolers need to be periodically cleaned to prevent mineral build-up inside the heating tank, also known as scaling. The frequency of the cleaning can be determined by the concentration of the minerals and the amount of water used. Descaling agents such as citric acid can be used for this cleaning process.
Heating tanks will require cleaning when normal hot water flow appears to be restricted or when noisy heating cycles can be heard during operation. Additional symptoms include water coming from the cooling tank is very warm as well as a change of taste in the water resulting from mineral build-up.
See also
Drinking fountain
Instant hot water dispenser
International Bottled Water Association
Refrigerator with built-in water dispenser.
Soda fountain
Tutedhara
Vending machine
References
External links
Dispenser
Coolers
Home appliances
20th-century inventions
Dispensers | Water dispenser | [
"Physics",
"Technology"
] | 3,435 | [
"Physical systems",
"Machines",
"Home appliances"
] |
620,991 | https://en.wikipedia.org/wiki/Plummer%20model | The Plummer model or Plummer sphere is a density law that was first used by H. C. Plummer to fit observations of globular clusters. It is now often used as toy model in N-body simulations of stellar systems.
Description of the model
The Plummer 3-dimensional density profile is given by
where is the total mass of the cluster, and a is the Plummer radius, a scale parameter that sets the size of the cluster core. The corresponding potential is
where G is Newton's gravitational constant. The velocity dispersion is
The isotropic distribution function reads
if , and otherwise, where is the specific energy.
Properties
The mass enclosed within radius is given by
Many other properties of the Plummer model are described in Herwig Dejonghe's comprehensive article.
Core radius , where the surface density drops to half its central value, is at .
Half-mass radius is
Virial radius is .
The 2D surface density is:
and hence the 2D projected mass profile is:
In astronomy, it is convenient to define 2D half-mass radius which is the radius where the 2D projected mass profile is half of the total mass: .
For the Plummer profile: .
The escape velocity at any point is
For bound orbits, the radial turning points of the orbit is characterized by specific energy and specific angular momentum are given by the positive roots of the cubic equation
where , so that . This equation has three real roots for : two positive and one negative, given that , where is the specific angular momentum for a circular orbit for the same energy. Here can be calculated from single real root of the discriminant of the cubic equation, which is itself another cubic equation
where underlined parameters are dimensionless in Henon units defined as , , and .
Applications
The Plummer model comes closest to representing the observed density profiles of star clusters, although the rapid falloff of the density at large radii () is not a good description of these systems.
The behavior of the density near the center does not match observations of elliptical galaxies, which typically exhibit a diverging central density.
The ease with which the Plummer sphere can be realized as a Monte-Carlo model has made it a favorite choice of N-body experimenters, in spite of the model's lack of realism.
References
Astrophysics
Equations of astronomy | Plummer model | [
"Physics",
"Astronomy"
] | 471 | [
"Concepts in astronomy",
"Astronomical sub-disciplines",
"Astrophysics",
"Equations of astronomy"
] |
621,090 | https://en.wikipedia.org/wiki/Photophore | A photophore is a glandular organ that appears as luminous spots on marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye, equipped with lenses, shutters, color filters, and reflectors; unlike an eye, however, it is optimized to produce light, not absorb it.
Mechanism
The bioluminescence can be produced from compounds during the digestion of prey, from specialized mitochondrial cells in the organism called photocytes ("light producing" cells), or, similarly, associated with symbiotic bacteria in the organism that are cultured.
The character of photophores is important in the identification of deep sea fishes. Photophores on fish are used for attracting food or for camouflage from predators by counter-illumination.
Photophores are found on some cephalopods including the firefly squid, which can create impressive light displays, as well as numerous other deep sea organisms, such as the pocket shark Mollisquama mississippiensis and the strawberry squid.
See also
Bioluminescence
Chromatophore
Chromophore, part of a molecule
References
External links
Bioluminescence
Cephalopod zootomy
Fish anatomy | Photophore | [
"Chemistry",
"Biology"
] | 251 | [
"Biochemistry",
"Luminescence",
"Bioluminescence"
] |
621,132 | https://en.wikipedia.org/wiki/Priority%20inheritance | In real-time computing, priority inheritance is a method for eliminating unbounded priority inversion. Using this programming method, a process scheduling algorithm increases the priority of a process (A) to the maximum priority of any other process waiting for any resource on which A has a resource lock (if it is higher than the original priority of A).
The basic idea of the priority inheritance protocol is that when a job blocks one or more high-priority jobs, it ignores its original priority assignment and executes its critical section at an elevated priority level. After executing its critical section and releasing its locks, the process returns to its original priority level.
Example
Consider three jobs:
Suppose that both H and L require some shared resource. If L acquires this shared resource (entering a critical section), and H subsequently requires it, H will block until L releases it (leaving its critical section). Without priority inheritance, process M could preempt process L during the critical section and delay its completion, in effect causing the lower-priority process M to indirectly preempt the high-priority process H. This is a priority inversion bug.
With priority inheritance, L will execute its critical section at H's high priority whenever H is blocked on the shared resource. As a result, M will be unable to preempt L and will be blocked. That is, the higher-priority job M must wait for the critical section of the lower priority job L to be executed, because L has inherited H's priority. When L exits its critical section, it regains its original (low) priority and awakens H (which was blocked by L). H, having high priority, preempts L and runs to completion. This enables M and L to resume in succession and run to completion without priority inversion.
Operating systems supporting priority inheritance
ERIKA Enterprise
FreeRTOS
Microsoft Azure RTOS, formerly Express Logic's ThreadX
Linux
VxWorks
iRMX
See also
Priority ceiling protocol
References
External links
"Priority Inheritance: The Real Story" by Doug Locke
"Against Priority Inheritance" by Victor Yodaiken
"Implementing Concurrency Control With Priority Inheritance in Real-Time CORBA" by Steven Wohlever, Victor Fay Wolfe and Russell Johnston
"Priority Inheritance Spin Locks for Multiprocessor Real-Time Systems" by Cai-Dong Wang, Hiroaki Takada and Ken Sakamura
"Hardware Support for Priority Inheritance" by Bilge E. S. Akgul, Vincent J. Mooney, Henrik Thane and Pramote Kuacharoen
Real-time computing
Concurrency control | Priority inheritance | [
"Technology"
] | 520 | [
"Computing stubs",
"Computer science",
"Real-time computing",
"Computer science stubs"
] |
621,163 | https://en.wikipedia.org/wiki/International%20Standard%20Bibliographic%20Description | The International Standard Bibliographic Description (ISBD) is a set of rules produced by the International Federation of Library Associations and Institutions (IFLA) to create a bibliographic description in a standard, human-readable form, especially for use in a bibliography or a library catalog. A preliminary consolidated edition of the ISBD was published in 2007 and the consolidated edition was published in 2011, superseding earlier separate ISBDs for monographs, older monographic publications, cartographic materials, serials and other continuing resources, electronic resources, non-book materials, and printed music. In 2022, IFLA published the 2021 update to the 2011 consolidated edition, which includes expanding ISBD to include unpublished resources, integrating stipulations for the application of ISBD to the description of component parts, clarifying cartographic resources stipulations, as well as added examples and updates to the Areas and glossary sections. IFLA's ISBD Review Group is responsible for maintaining the ISBD.
One of the original purposes of the ISBD was to provide a standard form of bibliographic description that could be used to exchange records internationally. This would support IFLA's Universal Bibliographic Control program.
Structure of an ISBD record
The ISBD defines nine areas of description. Each area, except area 7, is composed of multiple elements with structured classifications. Elements and areas that do not apply to a particular resource are omitted from the description. Standardized punctuation (colons, semicolons, slashes, dashes, commas, and periods) is used to identify and separate the elements and areas. The order of elements and standardized punctuation make it easier to interpret bibliographic records when one does not understand the language of the description.
0: Content form and media type area
1: Title and statement of responsibility area, consisting of
1.1 Title proper
1.2 Parallel title
1.3 Other title information
1.4 Statement of responsibility
2: Edition area
3: Material or type of resource specific area (e.g., the scale of a map or the numbering of a periodical)
4: Publication, production, distribution, etc., area
5: Material description area (e.g., number of pages in a book or number of CDs issued as a unit)
6: Series area
7: Notes area
8: Resource identifier and terms of availability area (e.g., ISBN, ISSN)
Example
A typical ISBD record looks like this:
Text : unmediated
A manual for writers of research papers, theses, and dissertations : Chicago style for students and researchers / Kate L. Turabian; revised by Wayne C. Booth, Gregory G. Colomb, Joseph M. Williams, and University of Chicago Press editorial staff. — 7th edition. — Chicago : University of Chicago Press, 2007. — xviii, 466 pages : illustrations; 23 cm. — (Chicago guides to writing, editing, and publishing). — Includes bibliographical references (pages 409-435) and index. — (cloth : alk. paper) : USD35.00. — (pbk. : alk. paper) : USD17.00
See also
Bibliographic control
ISO 690
Supply chain management
Anglo-American Cataloguing Rules (AACR)
Resource Description and Access (RDA)
Library catalog
MARC standards
BIBFRAME
Paris Principles (PP)
References
External links
ISBD Review Group
ISBD Consolidated edition (2011 version, full text)
ISBD Consolidated edition (2011 version, contents only)
Full ISBD Examples (2013 version, full examples in 16 languages)
ISBD 2021 Update to the 2011 Consolidated Edition (2022 version, full text)
Library cataloging and classification
Metadata | International Standard Bibliographic Description | [
"Technology"
] | 789 | [
"Metadata",
"Data"
] |
621,176 | https://en.wikipedia.org/wiki/Interpretability | In mathematical logic, interpretability is a relation between formal theories that expresses the possibility of interpreting or translating one into the other.
Informal definition
Assume T and S are formal theories. Slightly simplified, T is said to be interpretable in S if and only if the language of T can be translated into the language of S in such a way that S proves the translation of every theorem of T. Of course, there are some natural conditions on admissible translations here, such as the necessity for a translation to preserve the logical structure of formulas.
This concept, together with weak interpretability, was introduced by Alfred Tarski in 1953. Three other related concepts are cointerpretability, logical tolerance, and cotolerance, introduced by Giorgi Japaridze in 1992–93.
See also
Conservative extension
Interpretation (logic)
Interpretation (model theory)
Interpretability logic
References
Japaridze, G., and De Jongh, D. (1998) "The logic of provability" in Buss, S., ed., Handbook of Proof Theory. North-Holland: 476–546.
Alfred Tarski, Andrzej Mostowski, and Raphael Robinson (1953) Undecidable Theories. North-Holland.
Proof theory | Interpretability | [
"Mathematics"
] | 256 | [
"Mathematical logic",
"Proof theory"
] |
621,215 | https://en.wikipedia.org/wiki/Cointerpretability | In mathematical logic, cointerpretability is a binary relation on formal theories: a formal theory T is cointerpretable in another such theory S, when the language of S can be translated into the language of T in such a way that S proves every formula whose translation is a theorem of T. The "translation" here is required to preserve the logical structure of formulas.
This concept, in a sense dual to interpretability, was introduced by , who also proved that, for theories of Peano arithmetic and any stronger theories with effective axiomatizations, cointerpretability is equivalent to -conservativity.
See also
Cotolerance
Interpretability logic
Tolerance (in logic)
References
.
.
Mathematical relations
Mathematical logic | Cointerpretability | [
"Mathematics"
] | 151 | [
"Mathematical analysis",
"Predicate logic",
"Mathematical logic",
"Basic concepts in set theory",
"Mathematical relations"
] |
621,230 | https://en.wikipedia.org/wiki/Tolerant%20sequence | In mathematical logic, a tolerant sequence is a sequence
,...,
of formal theories such that there are consistent extensions
,...,
of these theories with each interpretable in . Tolerance naturally generalizes from sequences of theories to trees of theories. Weak interpretability can be shown to be a special, binary case of tolerance.
This concept, together with its dual concept of cotolerance, was introduced by Japaridze in 1992, who also proved that, for Peano arithmetic and any stronger theories with effective axiomatizations, tolerance is equivalent to -consistency.
See also
Interpretability
Cointerpretability
Interpretability logic
References
G. Japaridze, The logic of linear tolerance. Studia Logica 51 (1992), pp. 249–277.
G. Japaridze, A generalized notion of weak interpretability and the corresponding logic. Annals of Pure and Applied Logic 61 (1993), pp. 113–160.
G. Japaridze and D. de Jongh, The logic of provability. Handbook of Proof Theory. S. Buss, ed. Elsevier, 1998, pp. 476–546.
Proof theory | Tolerant sequence | [
"Mathematics"
] | 244 | [
"Mathematical logic",
"Proof theory"
] |
621,321 | https://en.wikipedia.org/wiki/Chamber%20%28firearms%29 | The chamber of a firearm is the cavity at the back end of a breechloading weapon's barrel or cylinder, where the ammunition is inserted before being fired. The rear opening of the chamber is the breech, and is sealed by the breechblock or the bolt.
Function
The act of chambering a cartridge means the insertion of a round into the chamber, either manually or through the action of the weapon, e.g., pump-action, lever-action, bolt action, or autoloading operation generally in anticipation of firing the weapon, without need to "load" the weapon upon decision to use it (reducing the number of actions needed to discharge).
Automatic and single-shot pistols (such as Derringers), rifles, and shotguns generally have a single chamber integral to their barrels, but revolvers have multiple chambers in their cylinder, and no chamber in their barrel. Thus, pistols, rifles, and shotguns can usually still be fired with the magazine removed as long as a cartridge is inserted into the chamber, while a revolver cannot be fired at all with its cylinder swung out or broken open.
In firearms design or modification, "chambering" is fitting a weapon's chamber for a particular caliber or round, so a Colt Model 1911 is chambered for .45 ACP or .38 Super, or re-chambered for .38/.45 Clerke. While the majority of firearms are chambered for one caliber, some are chambered for multiple calibers; however firing an oversized or undersized cartridge can be hazardous.
Fluted chamber
In the barrel chamber, fluting refers to gas relief flutes/grooves used to ease the extraction of cartridges. They may also come in annular and helical forms. Notable firearms using fluted chambers are the roller-delayed blowback Heckler & Koch G3 and lever-delayed blowback FAMAS and AA-52.
Roller or lever-delayed blowback arms require that the bolt starts moving while the bullet is still in the barrel and the spent case is fully pressurized. Fluting the end of the chamber allows combustion gasses to float the neck and front of the cartridge case providing pressure equalization between the front outer surface of the cartridge case and its interior. The roller-delayed blowback StG 45(M) assault rifle prototypes proved pressure equalization fluting is desirable, since the breech of roller or lever-delayed blowback arms is opened whilst under very high internal cartridge case pressure that presses a spent (bloated) cartridge casing against the chamber walls which can cause significant problems during the cartridge extraction phase. Using traditionally cut (non-fluted) chambers in the StG 45(M) resulted in separated cartridge case heads during testing.
Ported chamber
A barrel chamber with pressure relief ports that allows gas to leak around the cartridge during extraction. Basically, the opposite of a fluted chamber, as it is intended for the cartridge to stick to the chamber wall making a slight delay of extraction. This requires a welded-on sleeve with an annular groove to contain the pressure.
Multi chamber
Mostly used on artillery guns. Multi chambered is where the barrel has a series of chambers to propel the round down the barrel to increase speed and range. The Lymann-Haskell multi chamber gun is an example.
Forensics
The chamber is a key component to the practice of forensic firearm examination. The chamber is known to imprint its surface striations irregularities on the cartridge case, in what are called chamber marks, due to the pressure produced when shooting. Such imperfections in chamber may be produced in the manufacturing process or through extensive use. Such chamber marks are more pronounced on substandard firearms or when firing from an undersized chamber.
In recent years there has been a push to automate this process via the use of automated firearms databases. Ballistics identification has also seen the development of microstamping technology which purposefully creates chamber marks through engravings on the firing pin and breech face.
See also
Glossary of firearms terms
References
External links
Chamber
Firearms
Firearm terminology
Firearm components | Chamber (firearms) | [
"Technology"
] | 828 | [
"Firearm components",
"Components"
] |
621,346 | https://en.wikipedia.org/wiki/Breechface | The breechface is the front part of the breechblock that makes contact with the cartridge in a firearm. The breech block (or breechblock) in a gun is what holds a round in the chamber, and absorbs the recoil of the cartridge when the round is fired, preventing the cartridge case from moving.
Footnotes
Firearm components | Breechface | [
"Technology"
] | 72 | [
"Firearm components",
"Components"
] |
621,348 | https://en.wikipedia.org/wiki/Natural%20Resources%20Canada | Natural Resources Canada (NRCan; ; ) is the department of the Government of Canada responsible for natural resources, energy, minerals and metals, forests, earth sciences, mapping, and remote sensing. It was formed in 1994 by amalgamating the Department of Energy, Mines and Resources with the Department of Forestry.
Under the Constitution Act, 1867, primary responsibility for natural resources falls to provincial governments, however, the federal government has jurisdiction over off-shore resources, trade and commerce in natural resources, statistics, international relations, and boundaries. The department administers federal legislation relating to natural resources, including energy, forests, minerals and metals. The department also collaborates with American and Mexican government scientists, along with the Commission for Environmental Cooperation, to produce the North American Environmental Atlas, which is used to depict and track environmental issues for a continental perspective.
The current minister of natural resources is Jonathan Wilkinson. The department is governed by the Resources and Technical Surveys Act and the Department of Natural Resources Act.
Structure
The department currently has these sectors:
Corporate Management and Services Sector
Land and Minerals Sector
Strategic Policy and Innovation Sector
Low Carbon Energy Sector
Energy Efficiency and Technology Sector
Strategic Petroleum Policy and Investment Office
Canadian Forest Service
Indigenous Affairs and Reconciliation Sector
Office of the Chief Scientist
Major Projects Management Office
Communications and Portfolio Sector
Legal Services
Audit and Evaluation Branch
Geographical Names Board of Canada
Space Weather Canada
The following sub-agencies are attached to the department:
Canadian Forest Service
Northern Pipeline Agency Canada
Canadian Energy Regulator
Canadian Nuclear Safety Commission
Atomic Energy of Canada Limited
Related legislation
Acts for which Natural Resources Canada has responsibility
Arctic Waters Pollution Prevention Act
Canada Foundation for Sustainable Development Technology Act
Canada Labour Code
Canada Lands Surveyors Act
Canada Lands Surveys Act
Canada-Newfoundland Atlantic Accord Implementation Act
Canada-Nova Scotia Offshore Petroleum Resources Accord Implementation Act
Canada Oil and Gas Operations Act
Canada Petroleum Resources Act
Canadian Energy Regulator Act
Canadian Ownership and Control Determination Act
Cape Breton Development Corporation Act
Cape Breton Development Corporation Divestiture Authorization and Dissolution Act
Cooperative Energy Act
Department of Natural Resources Act
Energy Administration Act
Energy Efficiency Act
Energy Supplies Emergency Act
Explosives Act
Export and Import of Rough Diamonds Act
Forestry Act
Hibernia Development Project Act
International Boundary Commission Act
Northern Pipeline Act
Nuclear Energy Act
Nuclear Fuel Waste Act
Nuclear Liability Act
Nuclear Safety and Control Act
Oil Substitution and Conservation Act
Resources and Technical Surveys Act
Not in force
Greenhouse Gas Technology Investment Fund Act
See also
EnerGuide for Houses
Canada Green Building Council
Minister of Energy and Natural Resources
R-2000 program
Notes
References
External links
Natural Resources Canada Map Publication Website
Federal departments and agencies of Canada
Energy in Canada
Canada
Energy-related government agencies of Canada
Canada
Ministries established in 1842
Canada
Forestry agencies in Canada
1842 establishments in Canada
Mining in Canada | Natural Resources Canada | [
"Engineering"
] | 531 | [
"Energy organizations",
"Energy ministries"
] |
621,429 | https://en.wikipedia.org/wiki/Infomorph | An infomorph is a virtual body of information that possesses self-awareness and sentience. The term was coined in Charles Platt's 1991 novel The Silicon Man, where it refers to a single biological consciousness transferred into a computer through a process of mind transfer. In the book, a character defines an infomorph as "intelligence held in a computer memory", and an "information entity".
In the 2002 game Transhuman Space, an infomorph is any form of sentient or near-sentient computer program, which may exist either only in the computer networks or occupy a physical body: robot, android, a living thing ("wetware", "bioshell"). They may be of two main types: mind emulations (mind-uploaded human intelligencies) and "native" artificial intelligencies. These types are further classified into subtypes.
In EVE Online, players are posthuman entities known as capsuleers: immortal spacecraft commanders who can cheat death by scanning and transferring their consciousness into remote clones. "Infomorph Psychology" and "Advanced Infomorph Psychology" are neural enhancement skills for pilots using "jump clones" to alleviate the unsettling effect of the detaching of one's consciousness and transferring it into a remote clone.
See also
Ascension (Stargate)
Mind uploading
Omega Point
Simulated reality
References
Science fiction themes
Transhumanism
Posthumanism
1991 neologisms | Infomorph | [
"Technology",
"Engineering",
"Biology"
] | 304 | [
"Genetic engineering",
"Transhumanism",
"Ethics of science and technology"
] |
621,447 | https://en.wikipedia.org/wiki/List%20of%20computer%20graphics%20and%20descriptive%20geometry%20topics | This is a list of computer graphics and descriptive geometry topics, by article name.
2D computer graphics
2D geometric model
3D computer graphics
3D projection
Alpha compositing
Anisotropic filtering
Anti-aliasing
Axis-aligned bounding box
Axonometric projection
Bézier curve
Bézier surface
Bicubic interpolation
Bilinear interpolation
Binary space partitioning
Bitmap graphics editor
Bounding volume
Bresenham's line algorithm
Bump mapping
Collision detection
Color space
Colour banding
Computational geometry
Computer animation
Computer-generated art
Computer painting
Convex hull
Curvilinear perspective
Cylindrical perspective
Data compression
Digital raster graphic
Dimetric projection
Distance fog
Dithering
Elevation
Engineering drawing
Flat shading
Flood fill
Geometric model
Geometric primitive
Global illumination
Gouraud shading
Graphical projection
Graphics suite
Heightfield
Hidden face removal
Hidden line removal
High-dynamic-range rendering
Isometric projection
Lathe (graphics)
Line drawing algorithm
Linear perspective
Mesh generation
Motion blur
Orthographic projection
Orthographic projection (geometry)
Orthogonal projection
Perspective (graphical)
Phong reflection model
Phong shading
Pixel shaders
Polygon (computer graphics)
Procedural surface
Projection
Projective geometry
Quadtree
Radiosity
Raster graphics
Raytracing
Rendering (computer graphics)
Reverse perspective
Scan line rendering
Scrolling
Technical drawing
Texture mapping
Trimetric projection
Vanishing point
Vector graphics
Vector graphics editor
Vertex shaders
Volume rendering
Voxel
See also
List of geometry topics
List of graphical methods
Computing-related lists
Mathematics-related lists | List of computer graphics and descriptive geometry topics | [
"Technology"
] | 287 | [
"Computing-related lists"
] |
621,512 | https://en.wikipedia.org/wiki/Ergoline | Ergoline is a core structure in many alkaloids and their synthetic derivatives. Ergoline alkaloids were first characterized in ergot. Some of these are implicated in the condition of ergotism, which can take a convulsive form or a gangrenous form. Even so, many ergoline alkaloids have been found to be clinically useful. Annual world production of ergot alkaloids has been estimated at 5,000–8,000 kg of all ergopeptines and 10,000–15,000 kg of lysergic acid, used primarily in the manufacture of semi-synthetic derivatives.
Others, such as lysergic acid diethylamide, better known as LSD, a semi-synthetic derivative, and ergine, a natural derivative found in Argyreia nervosa, Ipomoea tricolor and related species, are known psychedelic substances.
Natural occurrence
Ergoline alkaloids are found in fungi such as Claviceps purpurea, Claviceps paspali, and the related Periglandula, which have a permanent, symbiotic bond with numerous flowering vines, most notably, Turbina corymbosa and Ipomoea tricolor (“morning glory”). Ergolines are concentrated in the seeds, which have been used for ages by indigenous central/south Americans (i.e. T. corymbosa seeds are known as ololiuhqui) The principal alkaloids in the seeds appear to be ergine and isoergine, but they're just decomposition products of lysergic acid hydroxyethylamide, isolysergic hydroxyethylamide, lysergic acid hydroxymethylethylamide (syn. ergonovine), and isolysergic acid hydroxymethylethylamide (syn. ergonovinine). All of the other ergolines have been quantified in very small amts. except for penniclavine, which was found to be the predominant ergoline in a 2016 assay of I. tricolor seeds. Ergolines have been identified in 42 Morning Glory species. The only ergolines of these seeds that have been trialed as isolates are ergine, ergonovine, and lysergol, with lysergol showing the weakest effect (refs: Ergine / Psychedelic Effects, Ergometrine / Psychedelic Effects).
History
Ergoline alkaloids were first isolated from ergot, a fungus that infects rye and causes ergotism or St. Anthony's fire. Reports of the toxic effects due to ergoline alkaloids date back to the 12th century. Ergot also has a long history of medicinal use, which led to attempts to characterize its activity chemically. First reports of its use date back to 1582, where preparations of ergot were used in small doses by midwives to induce strong uterine contractions. The first use of ergoline alkaloids in modern medicine was described in 1808 by John Stearns, an American physician, who had reported on the uterine contractile actions of a preparation of ergot as a remedy for "quickening birth".
Attempts to characterize the activity of ergoline alkaloids began in 1907, with the isolation of ergotoxine by G. Barger and F. H. Carrin. However, the industrial production of ergot alkaloids didn't begin until 1918, when Arthur Stoll patented the isolation of ergotamine tartrate, which was marketed by Sandoz in 1921. Following the determination of the basic chemical structure of the ergot alkaloids in 1930, an era of intensive exploration of synthetic derivatives began and industrial production of ergoline alkaloids exploded, with Sandoz continuing to be the leading company in their production worldwide, up until 1950 when other competitors arose. The company, now renamed Novartis, still retains its leadership in the product of ergot alkaloids. In 1943, Arthur Stoll and Albert Hofmann reported the first total synthesis of an ergot alkaloid, ergometrine. Though the synthesis found no industrial application, this was a huge leap forward in the industry.
Uses
There are a variety of clinically useful ergoline derivatives for the purpose of vasoconstriction, the treatment of migraines, and treatment of Parkinson's disease. Ergoline alkaloids found their place in pharmacology long before modern medicine as preparations of ergot were often used by midwives in the 12th century to stimulate childbirth. Following Arthur Stoll's isolation of ergometrine, the therapeutic use of ergoline derivatives became well explored.
The induction of uterine contractions via the preparation of ergot was attributed to ergonovine, an ergoline derivative found in ergot, which is a powerful oxytocic. From this, methergine, a synthetic derivative, was elucidated. While used to facilitate child birth, ergoline derivatives can pass into breast milk and should not be used during breastfeeding. They are uterine contractors that can increase the risk of miscarriage during pregnancy.
Another example of medically relevant ergoline alkaloids is ergotamine, an alkaloid also found in ergot. It acts as a vasoconstrictor and has been reported to control migraines. From ergotamine, the anti-migraine drugs dihydroergotamine and methysergide were developed by Albert Hofmann.
Ergoline derivatives, such as hydergine, a mixture of dihydroergotoxine mesylates or ergoline mesylates, have also been used in the treatment of dementia. The use of these alkaloids in the treatment of Parkinson's disease has also been prominent. Drugs such as bromocriptine act as a dopamine receptor agonist, stimulating the nerves that control movement. Newer synthetic ergoline derivatives that have been synthesized for the treatment of Parkinson's disease include pergolide and lisuride, which both act as dopamine agonists as well.
A famous ergoline derivative is the psychedelic drug LSD, a semi-synthetic ergoline alkaloid that was discovered by Albert Hofmann. LSD is considered a Schedule I controlled substance. Ergometrine and ergotamine are included as schedule I precursors in the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances.
Mechanism of action
The mechanism of ergoline alkaloids varies for each derivative. A variety of modifications can be made to the ergoline skeleton to produce medically relevant derivatives. Types of potential ergoline-based drugs include dopaminergic, antidopaminergic, serotonergic, and antiserotonergic. Ergoline alkaloids often interfere with multiple receptor sites, leading to negative side effects and adding to the challenge of drug development.
Dopaminergic/antidopaminergic
Ergolines, such as ergotoxin, have been reported to inhibit the deciduoma reaction, which is reversed through injection of progesterone. Thus, it was concluded that ergotoxin, and related ergolines, act via the hypothalamus and pituitary gland to inhibit the secretion of prolactin. Drugs such as bromocriptine interact with the dopaminergic receptor sites as agonists with selectivity for D2 receptors, making them effective in treating Parkinson's disease. While the part of the ergoline alkaloid structure responsible for dopaminergic properties has yet to be identified, some reason that it is due to the pyroleethylamine moiety while others assert that it is due to the indoleethylamine partial structure.
Antidopaminergic ergolines have found use in antiemetics and in the treatment of schizophrenia. These substances are neuroleptic and are either an antagonist of dopamine at the postsynaptic level at the D2 receptor site or an agonist of dopamine at the presynaptic level at the D1 receptor site. The antagonist or agonist behavior of the ergolines are substrate dependent and mixed agonist/antagonist behaviors of ergoline derivatives have been reported.
Serotonergic/antiserotonergic
The primary challenges of developing serotonergic/antiserotonergic ergolines is attributed to serotonin, or 5-HT, acting on various distinct receptor sites. Similarly, ergoline alkaloids have been shown to exhibit both 5-HT agonist and antagonist behaviors for multiple receptors, such as metergoline, a 5-HT1A agonist/5-HT2A antagonist, and mesulergine, a 5-HT2A/2C antagonist. The selectivity and affinity of ergolines for certain 5-HT receptors can be improved by introducing a bulky group on the phenyl ring of the ergoline skeleton, which would prevent the interaction of ergoline derivatives with receptors. This methodology has been used to develop selective 5-HT1A and 5-HT2A ergolines in particular.
Ergoline derivatives
There are three main classes of ergoline derivatives, or substituted ergolines: (1) the water-soluble amides of lysergic acid (i.e., lysergamides); (2) the water-insoluble ergopeptines (i.e., ergopeptides); and (3) the clavine group. Only the lysergamides have been known to have psychedelic effects.
Lysergic acid amides
Ergine (LSA, D-lysergic acid amide, LAA, LA-111)
IUPAC name: 9,10-didehydro-6-methylergoline-8beta-carboxamide
CAS number:
Ergonovine (ergobasine)
INN: ergometrine
IUPAC name: (8beta(S))-9,10-didehydro-N-(2-hydroxy-1-methylethyl)-6-methyl-ergoline-8-carboxamide
CAS number:
Methergine (ME-277)
INN: methylergometrine
IUPAC name: (8beta(S))-9,10-didehydro-N-(1-(hydroxymethyl)propyl)-6-methyl-ergoline-8-carboxamide
CAS number:
Methysergide (UML-491)
INN: methysergide
IUPAC name: (8beta)-9,10-didehydro-N-(1-(hydroxymethyl)propyl)-1,6-dimethyl-ergoline-8-carboxamide
CAS number:
LSD (D-lysergic acid diethylamide, LSD-25)
INN: lysergide
IUPAC name: (8beta)-9,10-didehydro-N,N-diethyl-6-methyl-ergoline-8-carboxamide
CAS number:
LSH (D-lysergic acid α-hydroxyethylamide)
IUPAC name: 9,10-didehydro-N-(1-hydroxyethyl)-6-methylergoline-8-carboxamide
CAS number:
The relationship between these compounds is summarized in the following structural formula and table of substitutions.
Peptide alkaloids
Peptide ergot alkaloids or ergopeptines (also known as ergopeptides) are ergoline derivatives that contain a tripeptide structure attached to the basic ergoline ring in the same location as the amide group of the lysergic acid derivatives. This structure consists of proline and two other α-amino acids, linked in an unusual cyclol formation >N-C(OH)< with the carboxyl carbon of proline, at the juncture between the two lactam rings. Some of the important ergopeptines are summarized below. In addition to the following ergopeptines, a commonly encountered term is ergotoxine, which refers to a mixture of equal proportions of ergocristine, ergocornine and ergocryptine, the latter being a 2:1 mixture of alpha- and beta-ergocryptine. Ergopeptines are considered to be the most toxic and are capable of inducing gangrene: “The low molecular ergolines are lacking the complex peptide moiety, which is apparently responsible for the persistence of the ergopeptines at the receptor molecules.”
Ergotoxine group (valine as the amino acid attached to the ergoline moiety, at R2 below)
Ergocristine
IUPAC name: Ergotaman-3',6',18-trione, 12'-hydroxy-2'-(1-methylethyl)-5'-(phenylmethyl)-, (5'-alpha)-
CAS number:
Ergocornine
IUPAC name: Ergotaman-3',6',18-trione, 12'-hydroxy-2',5'-bis(1-methylethyl)-, (5'-alpha)-
CAS number:
alpha-Ergocryptine
IUPAC name: Ergotaman-3',6',18-trione, 12'-hydroxy-2'-(1-methylethyl)-5'-(2-methylpropyl)-, (5'alpha)-
CAS number:
beta-Ergocryptine
IUPAC name: Ergotaman-3',6',18-trione, 12'-hydroxy-2'-(1-methylethyl)-5'-(1-methylpropyl)-, (5'alpha(S))-
CAS number:
Ergotamine group (alanine at R2)
Ergotamine
IUPAC name: Ergotaman-3',6',18-trione, 12'-hydroxy-2'-methyl-5'-(phenylmethyl)-, (5'-alpha)-
CAS number:
Ergovaline
IUPAC name: Ergotaman-3',6',18-trione, 12'-hydroxy-2'-methyl-5'-(1-methylethyl)-, (5'alpha)-
CAS number:
alpha-Ergosine
IUPAC name: Ergotaman-3',6',18-trione, 12'-hydroxy-2'-methyl-5'-(2-methylpropyl)-, (5'-alpha)-
CAS number:
beta-Ergosine
IUPAC name: Ergotaman-3',6',18-trione, 12'-hydroxy-2'-methyl-5'-(1-methylpropyl)-, (5'-alpha(S))-
CAS number:
Clavines
A variety of modifications to the basic ergoline are seen in nature, for example agroclavine, elymoclavine, lysergol. Those deriving from dimethylergoline are referred to as clavines. Examples of clavines, include festuclavine, fumigaclavine A, fumigaclavine B and fumigaclavine C.
Others
Some synthetic ergoline derivatives do not fall easily into any of the above groups. Some examples are:
Cabergoline (INN)
IUPAC name: 1-[(6-Allylergolin-8β-yl)-carbonyl]-1-[3-(dimethylamino)propyl]-3-ethylurea
CAS number:
Pergolide (INN)
IUPAC name: (8β)-8-((methylthio)methyl)-6-propyl-ergoline
CAS number:
Lisuride (INN)
IUPAC name: 3-(9,10-didehydro-6-methylergolin-8α-yl)-1,1-diethylurea
CAS number:
See also
Ergotism
Ergot
LSD
Ergine
Migraine
Albert Hofmann
References
External links
The Ergot Alkaloids (A. T. Sneden)
The Ergot Alkaloids Story (Z. Madlom)
The Psychoactive Ergot Alkaloids and their occurrence in the Microfungi — M. P. Bock and D. G. Parbery
Hofmann, A. Teonanácatl and Ololiuqui, two ancient magic drugs of Mexico Bulletin on Narcotics 1971 1 3
TiHKAL (A & A Shulgin) #26
Tryptamine alkaloids
Quinoline alkaloids
Alkaloids found in fungi | Ergoline | [
"Chemistry"
] | 3,698 | [
"Quinoline alkaloids",
"Tryptamine alkaloids",
"Alkaloids by chemical classification"
] |
621,523 | https://en.wikipedia.org/wiki/Lysergic%20acid | Lysergic acid, also known as -lysergic acid and (+)-lysergic acid, is a precursor for a wide range of ergoline alkaloids that are produced by the ergot fungus and found in the seeds of Argyreia nervosa (Hawaiian baby woodrose), and Ipomoea species (morning glories, ololiuhqui, tlitliltzin).
Amides of lysergic acid, lysergamides, are widely used as pharmaceuticals and as psychedelic drugs, e.g. lysergic acid diethylamide (LSD). Lysergic acid is listed as a Table I precursor under the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances.
The name Lysergic acid comes from the fact that the this carboxylic acid was first made by hydrolysis of various ergot alkaloids.
Synthesis
Laboratory
Lysergic acid is generally produced by hydrolysis of natural lysergamides, but can also be synthesized in the laboratory by a complex total synthesis, for example by Robert Burns Woodward's team in 1956. An enantioselective total synthesis based on a palladium-catalyzed domino cyclization reaction has been described in 2011 by Fujii and Ohno. Lysergic acid monohydrate crystallizes in very thin hexagonal leaflets when recrystallized from water. Lysergic acid monohydrate, when dried (140 °C at ) forms anhydrous lysergic acid.
Biosynthesis
The biosynthetic route is based on the alkylation of the amino acid tryptophan with dimethylallyl diphosphate (isoprene derived from 3R-mevalonic acid) giving 4-dimethylallyl--tryptophan which is N-methylated with S-adenosyl--methionine. Oxidative ring closure followed by decarboxylation, reduction, cyclization, oxidation, and allylic isomerization yields -(+)-lysergic acid. The biosynthetic pathway has been reconsituted in transgenic baker's yeast.
Isomers
Lysergic acid is a chiral compound with two stereocenters. The isomer with inverted configuration at carbon atom 8 close to the carboxyl group is called isolysergic acid. Inversion at carbon 5 close to the nitrogen atom leads to -lysergic acid and -isolysergic acid, respectively.
Legality
In the United States, Lysergic acid and Lysergic acid amide are Schedule III substances.
See also
Ergine
Lysergamides
References
Beta-Amino acids
Ergolines
Tryptamines
Total synthesis | Lysergic acid | [
"Chemistry"
] | 599 | [
"Total synthesis",
"Chemical synthesis"
] |
621,531 | https://en.wikipedia.org/wiki/Ergotamine | Ergotamine, sold under the brand name Ergomar among others, is an ergopeptine and part of the ergot family of alkaloids; it is structurally and biochemically closely related to ergoline. It is structurally similar to several neurotransmitters, and it acts as a vasoconstrictor. It is used for acute migraines, sometimes with caffeine as the combination ergotamine/caffeine.
Medicinal use of ergot fungus began in the 16th century, for the induction of childbirth; but dosage uncertainty discouraged its use. It has been used to prevent post-partum hemorrhage (bleeding after childbirth). It was first isolated from the ergot fungus by Arthur Stoll, at Sandoz in 1918, and was marketed as Gynergen in 1921.
Medical uses
Ergotamine is indicated as therapy to abort or prevent vascular headache.
Available forms
Ergotamine is available as a suppository and as a tablet, sometimes in combination with caffeine.
Contraindications
Contraindications include: atherosclerosis, Buerger's syndrome, coronary artery disease, hepatic disease, pregnancy, pruritus, Raynaud's syndrome, and renal disease.
It's also contraindicated if patient is taking macrolide antibiotics (e.g., erythromycin), certain HIV protease inhibitors (e.g., ritonavir, nelfinavir, indinavir), certain azole antifungals (e.g., ketoconazole, itraconazole, voriconazole) delavirdine, efavirenz, or a 5-HT1 receptor agonist (e.g., sumatriptan).
Side effects
Side effects of ergotamine include nausea and vomiting. At higher doses, it can cause raised arterial blood pressure, vasoconstriction (including coronary vasospasm) and bradycardia or tachycardia. Severe vasoconstriction may cause symptoms of intermittent claudication.
Pharmacology
Pharmacodynamics
Ergotamine interacts with serotonin, adrenergic, and dopamine receptors. It is an agonist of serotonin receptors including the 5-HT1 and 5-HT2 subtypes. Ergotamine is an agonist of the serotonin 5-HT2B receptor and has been associated with cardiac valvulopathy. Despite acting as a potent 5-HT2A receptor agonist, ergotamine is said to be non-hallucinogenic similarly to lisuride. This is thought to be due to functional selectivity at the 5-HT2A receptor. However, an alternative possibility is that it is due to peripheral selectivity.
Pharmacokinetics
The bioavailability of ergotamine is around 2% orally, 6% rectally, and 100% by intramuscular or intravenous injection. The low oral and rectal bioavailability is due to low gastrointestinal absorption and high first-pass metabolism.
Ergotamine may not readily cross the blood–brain barrier.
Biosynthesis
Ergotamine is a secondary metabolite (natural product) and the principal alkaloid produced by the ergot fungus, Claviceps purpurea, and related fungi in the family Clavicipitaceae. Its biosynthesis in these fungi requires the amino acid L-tryptophan and dimethylallyl pyrophosphate. These precursor compounds are the substrates for the enzyme, tryptophan dimethylallyltransferase, catalyzing the first step in ergot alkaloid biosynthesis, i.e., the prenylation of L-tryptophan. Further reactions, involving methyltransferase and oxygenase enzymes, yield the ergoline, lysergic acid. Lysergic acid (LA) is the substrate of lysergyl peptide synthetase, a nonribosomal peptide synthetase, which covalently links LA to the amino acids, L-alanine, L-proline, and L-phenylalanine. Enzyme-catalyzed or spontaneous cyclizations, oxygenations/oxidations, and isomerizations at selected residues precede, and give rise to, formation of ergotamine.
Society and culture
Legal status
Ergotamine is a List I regulated chemical in the United States.
References
External links
Alpha-1 blockers
Alpha-2 adrenergic receptor agonists
Antimigraine drugs
Biased ligands
Cardiotoxins
Ergot alkaloids
Lactams
Lysergamides
Non-hallucinogenic 5-HT2A receptor agonists
Oxazolopyrrolopyrazines
Peripherally selective drugs
Serotonin receptor agonists
Vasoconstrictors | Ergotamine | [
"Chemistry"
] | 1,078 | [
"Biased ligands",
"Signal transduction"
] |
621,599 | https://en.wikipedia.org/wiki/Playboy%20Bunny | A Playboy Bunny is a cocktail waitress who works at a Playboy Club and selected through standardized training. Their costumes were made up of lingerie, inspired by the tuxedo-wearing Playboy rabbit mascot. This costume consisted of a strapless corset teddy, bunny ears, black sheer-to-waist pantyhose, a bow tie, a collar, cuffs and a fluffy cottontail. In more recent Playboy Clubs, such as Sin City that was re-opened in 2006, Playboy bunnies wore slightly altered costumes that were based on the original bunny suit.
Origins
The original Playboy Bunny costume was designed by the mother of Ilse Taurins, who was a Latvian émigrée. At the time, Taurins was dating one of the Playboy Club co-founders, Victor Lownes III.
Taurins had suggested a costume modeled after the Playboy Magazine trademark, either a rabbit or bunny, and she had her seamstress mother make a costume prototype. The prototype was reviewed at a meeting attended by Playboy Club co-founders Hugh Hefner, Victor Lownes and Arnold Morton, as well as frequent Playboy illustrator LeRoy Neiman.
The outfits were initially not received well by the co-founders, but Hefner advised that it could work once changes were made. The initial costume looked similar to a one piece swimsuit, with a white yarn puff tail and a headband with bunny ears, and Hefner suggested cutting the leg higher on the hip to expose more of the leg, and sharpening the v-shape of the costume. His suggested modifications were in an attempt to make the costumes more visually appealing, and the tightly laced corsets added to the feminine appeal, cinching in the Bunny's waist by at least two inches. This redesign of the bunny costume tied in directly with the need for a show-girl type of costume, achieving this look with an addition of bow ties, collars and a fluffy cottontail.
For mass production, the costume was manufactured for the Playboy Clubs by the Chicago-based Kabo Corset Company, and was based upon a "merry widow" style of corset within their line.
Later, in 1962, French fashion designer Renee Blot was further employed to refine the design, and her revisions included making the ears smaller, adding a collar with bow tie and cuffs with rabbit-head cufflinks, and a satin rosette with the bunny's name, worn on the hip. The original costumes were made in twelve colours of rayon satin. Several years later, Playboy engaged a prominent manufacturer of lingerie and swimwear to create a modified bunny costume that used washable stretch knit fabrics, allowing for costumes in vibrant prints as well as solid colors. The standard stockings also evolved from fishnet material to a special sheer pantyhose style supplied by Danskin. Bunnies wore two pairs of these sheer stockings, a black pair worn on top of a taupe toned pair.
In the 1970s, Lownes used his country mansion, Stocks House in Hertfordshire, England, as a training camp for Bunnies. The Bunnies acted as hostesses at lavish parties thrown in the house.
Since 2013, rumours have suggested the original design of the Playboy bunny costume was by New York fashion designer Zelda Wynn Valdes, however, there exists no evidence to support this. This is also contradicted by recounts in much earlier publications such as "Big Bunny" by Joe Goldberg (1967) and "The Bunny Years" by Kathryn Leigh Scott (1998).
The bunny costume became a symbol of the Playboy Clubs, and was also the first commercial uniform to be registered by the United States Patent and Trademark Office (U.S. trademark registration number 0762884).
Training and qualifications
The Playboy Bunnies are waitresses who serve drinks at Playboy Clubs. There are different types of Bunnies, including the Door Bunny, Cigarette Bunny, Floor Bunny, Pool Bunny, Fine Dining Bunny, Playmate Bunny, and the Jet Bunnies (specially selected Bunnies trained as flight attendants; they served on the Playboy "Big Bunny" Jet).
To become a Bunny, women are first carefully chosen and selected from auditions. Bunnies then undergo thorough and strict training before officially becoming a Bunny. Bunnies are required to be able to identify 143 brands of liquor and know how to garnish 20 cocktail variations. Customers are not allowed to touch the Bunnies, demerits are given if a Bunny's appearance does not meet requirements, and dating or mingling with customers is forbidden.
A Bunny also has to master the required maneuvers to work. These include the "Bunny Stance", a posture that is required in front of patrons, where the Bunny must stand with legs together, back arched and hips tucked under. When the Bunny is resting or waiting to be of service, she must do the "Bunny Perch," where she must sit on the back of a chair, sofa, or railing without sitting too close to a patron. The most famous maneuver of all, the "Bunny Dip", was invented by Kelly Collins, once renowned for being the "Perfect Bunny." To do the "Bunny Dip," the Bunny gracefully leans backwards while bending at the knees with the left knee lifted and tucked behind the right leg. This maneuver allows the Bunny to serve drinks while keeping her low-cut costume in place. Strict regulations were enforced by special workers in the guise of patrons.
Description
The uniforms were tailored to each Bunny at the clubs in which they worked, and a full-time seamstress always remained on duty whenever the club opened. The costumes were stocked in two pieces, the front part being pre-sewn in different bra cup sizes, and the seamstress would match the Bunnies' figure to the correct fitting front and back pieces. The two pieces were then sewn together to fit each person with great precision.
A woman, also known as the "Bunny Mother", took responsibility for the welfare of the women working as Playboy Bunnies. This was a human-resources role and a management position as the Bunny Mother was in charge of scheduling work shifts, hiring, firing and training. The Club Manager carried two responsibilities for the Bunnies – floor service and weigh-in. Before every shift, the Manager would weigh each Bunny, and bunnies could not gain or lose more than one pound, with exceptions only being made for water retention. Playboy Enterprises required all employees to turn in their costumes at the end of employment and Playboy still retains some of these costumes in storage. Occasionally, costumes are offered for sale on the Playboy Auction site or eBay, but some of the costumes on eBay are known to be counterfeit or damaged. The only two costumes on public display are in the collections of the Smithsonian and the Chicago History Museum.
Image
Reception and review
The treatment of Playboy Bunnies was exposed in a piece written by Gloria Steinem and reprinted in her 1983 book Outrageous Acts and Everyday Rebellions. The article featured a photo of Steinem in Bunny uniform and detailed how women were treated at those clubs. The article was published in 1963 in Show magazine as "A Bunny's Tale". Steinem has maintained that she is proud of the work she did publicizing the exploitative working conditions of the Bunnies and especially the sexual demands made of them, which skirted the edge of the law.
Clive James wrote of the "callous fatuity of the selection process" and observed that "to make it as a Bunny, a girl need[ed] more than just looks. She need[ed] idiocy, too."
International icon
The costume of a Playboy Bunny gained huge popularity in Japan, where it has lost much of its association with Playboy and is accordingly referred to simply as the or . It has frequently been featured in manga and anime; notable examples of characters who have been depicted wearing it include the title character of Haruhi Suzumiya, Kallen Stadtfeld of Code Geass, Bulma of Dragon Ball, Haruko Haruhara of FLCL, and the unnamed protagonist of the Daicon III and Daicon IV Opening Animations. The outfit is alluded to in the title of the series Rascal Does Not Dream of Bunny Girl Senpai, and the character Mai Sakurajima is seen wearing one in its first episode. The suit is also popularly depicted in anime and manga fan art and merchandise, even for characters who are never seen wearing it in official works. Bunny suits are most frequently worn by female characters, but they are occasionally worn by male characters, usually for comedic effect.
There are no Playboy Clubs in Brazil, but Playboy's Brazilian division has Bunnies who attend its events. For most of the 2000s there were three official Bunnies, and they were also Playmates — both separately, and together in the cover pictorial for the December 2008 edition. The last printed issue of the magazine, in 2018, featured the five Bunnies of the period on the cover.
Playboy Bunnies are a separate entity from Playboy Playmates, women who appear in the centerfold pictorials of Playboy magazine, however, a few Playboy Bunnies went on to become Playmates and vice versa (see below).
Return of the Bunnies
In 2006, The Palms Hotel-Casino in Las Vegas opened the first new Playboy Club in over a quarter-century, located on the 52nd floor of the Fantasy Tower. Italian fashion designer Roberto Cavalli was chosen to re-design the original Bunny suit. It closed in 2012.
Notable Bunnies
Prominent women who had careers as a Playboy Bunnies include:
Bunnies who were also Playboy Playmates
Helena Antonaccio
Deanna Baker
Lannie Balcom
Kai Brendlinger
Jessica Burciaga
Dianne Chandler
Karen Christy
Sharon Clark
June Cochran
Marilyn Cole
Candace Collins
Debbie Ellison
Ava Fabian
Jennifer Jackson
Terri Kimball
Avis Kimble
Shay Knuth
China Lee
Janet Lupo
Laura Lyons
Connie Mason
Avis Miller
Laura Misch
Kara Monaco
Dolly Read
Patti Reynolds
Mercy Rooney
Janis Schmitt
Dorothy Stratten
Heather Van Every
Carol Vitale
Delores Wells
Gallery
See also
Animal roleplay
Breastaurant
Nyotaimori
Wet T-shirt contest
Notes
References
Further reading
Goldberg, Joe (1967). Big Bunny: The Inside Story of Playboy. New York: Ballantine Books.
Scott, Kathryn Leigh. The Bunny Years. Los Angeles: Pomegranate Press, 1998. .
External links
Official Playboy Bunnies Website at Playboy
Ex-Playboy Bunnies Website
"Playboy Bunnies: The Early Years"—slideshow by Life
"Playboy Bunnies: Today"—slideshow by Life
1960 introductions
Female characters in advertising
Mascots introduced in 1960
Food services occupations
Magazine mascots
Playboy
Restaurant staff
Costume design
Fetish clothing
Uniforms | Playboy Bunny | [
"Engineering"
] | 2,176 | [
"Costume design",
"Design"
] |
621,655 | https://en.wikipedia.org/wiki/Cartan%27s%20theorem | Cartan's theorem may refer to several mathematical results by Élie Cartan:
Closed-subgroup theorem, 1930, that any closed subgroup of a Lie group is a Lie subgroup
Theorem of the highest weight, that the irreducible representations of Lie algebras or Lie groups are classified by their highest weights
Lie's third theorem, an equivalence between Lie algebras and simply-connected Lie groups
See also
Cartan's theorems A and B, c.1931 results by Henri Cartan concerning a coherent sheaf on a Stein manifold
Cartan's lemma, several results by Élie or Henri Cartan
Cartan–Dieudonné theorem, a result on orthogonal transformations and reflections
Lie groups
Theorems in abstract algebra | Cartan's theorem | [
"Mathematics"
] | 148 | [
"Lie groups",
"Mathematical structures",
"Theorems in algebra",
"Algebraic structures",
"Theorems in abstract algebra"
] |
621,677 | https://en.wikipedia.org/wiki/Cartan%27s%20theorems%20A%20and%20B | In mathematics, Cartan's theorems A and B are two results proved by Henri Cartan around 1951, concerning a coherent sheaf on a Stein manifold . They are significant both as applied to several complex variables, and in the general development of sheaf cohomology.
Theorem B is stated in cohomological terms (a formulation that Cartan (1953, p. 51) attributes to J.-P. Serre):
Analogous properties were established by Serre (1957) for coherent sheaves in algebraic geometry, when is an affine scheme. The analogue of Theorem B in this context is as follows :
These theorems have many important applications. For instance, they imply that a holomorphic function on a closed complex submanifold, , of a Stein manifold can be extended to a holomorphic function on all of . At a deeper level, these theorems were used by Jean-Pierre Serre to prove the GAGA theorem.
Theorem B is sharp in the sense that if for all coherent sheaves on a complex manifold (resp. quasi-coherent sheaves on a noetherian scheme ), then is Stein (resp. affine); see (resp. and ).
See also
Cousin problems
References
.
.
.
Several complex variables
Topological methods of algebraic geometry
Theorems in algebraic geometry | Cartan's theorems A and B | [
"Mathematics"
] | 272 | [
"Theorems in algebraic geometry",
"Functions and mappings",
"Several complex variables",
"Mathematical objects",
"Mathematical relations",
"Theorems in geometry"
] |
621,704 | https://en.wikipedia.org/wiki/Lumen%20%28website%29 | Lumen, formerly Chilling Effects, is an American collaborative archive created by Wendy Seltzer and operated by the Berkman Klein Center for Internet & Society at Harvard University. It allows recipients of cease-and-desist notices to submit them to the site and receive information about their legal rights and responsibilities.
The archive was founded in 2001 with several law school clinics and the Electronic Frontier Foundation to protect lawful online activity from legal threats. Originally located in San Francisco, California, Lumen later moved its operations to Massachusetts.
Inception
The archive was founded in 2001 by Internet activists who were concerned that the unregulated private practice of sending cease-and-desist letters seemed to be increasing and was having an unstudied, but potentially significant, "chilling effect" on free speech.
The archive got a boost when Google began submitting its notices to the site in 2002. Google began to do so in response when the Church of Scientology convinced Google to remove references and links to an anti-Scientology web site, Operation Clambake, in April 2002. The incident inspired vocal Internet users and groups to complain to Google, and links to the Clambake site were restored. Google subsequently began to contribute its notices to Chilling Effects, archiving the Scientology complaints and linking to the archive.
Starting in 2002, researchers used the clearinghouse to study the use of cease-and-desist letters, primarily looking at Digital Millennium Copyright Act (DMCA) 512 takedown notices, non-DMCA copyright issues, and trademark claims.
On November 2, 2015, Chilling Effects announced its renaming to Lumen, as well as a number of international partnerships.
Reception
Lumen has been praised for providing and promoting transparency on the use of copyright takedowns.
The Copyright Alliance has criticized Lumen for republishing lists of URLs named in takedowns as part of its database. It argued that this defeats the purpose and intent of sending takedown notices to search engines in the first place, as they would subsequently be added to "the largest repository of URLs hosting infringing content on the internet.". While the Lumen database formerly used to show full URLs, in 2019 the URLs were redacted to only display the website names and the number of URLs from each site, with the full URLs only to be made available to authorised users.
Members
Berkman Center for Internet and Society, Harvard Law School
Electronic Frontier Foundation
George Washington University Law School
Samuelson Law, Technology and Public Policy Clinic, Boalt Hall
Santa Clara University School of Law High Tech Law Institute
Stanford Center for Internet and Society, Stanford Law School
University of Maine School of Law
IIP Justice Project, University of San Francisco School of Law
See also
Censorship by Google
References
External links
Internet-related activism
Internet-based activism
Freedom of expression organizations
Organizations established in 2001
2001 establishments in the United States
Digital Millennium Copyright Act takedown incidents
Scientology and the Internet
Internet censorship
Information society | Lumen (website) | [
"Technology"
] | 602 | [
"Computing and society",
"Information society"
] |
621,732 | https://en.wikipedia.org/wiki/Geometric%20topology | In mathematics, geometric topology is the study of manifolds and maps between them, particularly embeddings of one manifold into another.
History
Geometric topology as an area distinct from algebraic topology may be said to have originated in the 1935 classification of lens spaces by Reidemeister torsion, which required distinguishing spaces that are homotopy equivalent but not homeomorphic. This was the origin of simple homotopy theory. The use of the term geometric topology to describe these seems to have originated rather recently.
Differences between low-dimensional and high-dimensional topology
Manifolds differ radically in behavior in high and low dimension.
High-dimensional topology refers to manifolds of dimension 5 and above, or in relative terms, embeddings in codimension 3 and above. Low-dimensional topology is concerned with questions in dimensions up to 4, or embeddings in codimension up to 2.
Dimension 4 is special, in that in some respects (topologically), dimension 4 is high-dimensional, while in other respects (differentiably), dimension 4 is low-dimensional; this overlap yields phenomena exceptional to dimension 4, such as exotic differentiable structures on R4. Thus the topological classification of 4-manifolds is in principle tractable, and the key questions are: does a topological manifold admit a differentiable structure, and if so, how many? Notably, the smooth case of dimension 4 is the last open case of the generalized Poincaré conjecture; see Gluck twists.
The distinction is because surgery theory works in dimension 5 and above (in fact, in many cases, it works topologically in dimension 4, though this is very involved to prove), and thus the behavior of manifolds in dimension 5 and above may be studied using the surgery theory program. In dimension 4 and below (topologically, in dimension 3 and below), surgery theory does not work.
Indeed, one approach to discussing low-dimensional manifolds is to ask "what would surgery theory predict to be true, were it to work?" – and then understand low-dimensional phenomena as deviations from this.
The precise reason for the difference at dimension 5 is because the Whitney embedding theorem, the key technical trick which underlies surgery theory, requires 2+1 dimensions. Roughly, the Whitney trick allows one to "unknot" knotted spheres – more precisely, remove self-intersections of immersions; it does this via a homotopy of a disk – the disk has 2 dimensions, and the homotopy adds 1 more – and thus in codimension greater than 2, this can be done without intersecting itself; hence embeddings in codimension greater than 2 can be understood by surgery. In surgery theory, the key step is in the middle dimension, and thus when the middle dimension has codimension more than 2 (loosely, 2½ is enough, hence total dimension 5 is enough), the Whitney trick works. The key consequence of this is Smale's h-cobordism theorem, which works in dimension 5 and above, and forms the basis for surgery theory.
A modification of the Whitney trick can work in 4 dimensions, and is called Casson handles – because there are not enough dimensions, a Whitney disk introduces new kinks, which can be resolved by another Whitney disk, leading to a sequence ("tower") of disks. The limit of this tower yields a topological but not differentiable map, hence surgery works topologically but not differentiably in dimension 4.
Important tools in geometric topology
Fundamental group
In all dimensions, the fundamental group of a manifold is a very important invariant, and determines much of the structure; in dimensions 1, 2 and 3, the possible fundamental groups are restricted, while in dimension 4 and above every finitely presented group is the fundamental group of a manifold (note that it is sufficient to show this for 4- and 5-dimensional manifolds, and then to take products with spheres to get higher ones).
Orientability
A manifold is orientable if it has a consistent choice of orientation, and a connected orientable manifold has exactly two different possible orientations. In this setting, various equivalent formulations of orientability can be given, depending on the desired application and level of generality. Formulations applicable to general topological manifolds often employ methods of homology theory, whereas for differentiable manifolds more structure is present, allowing a formulation in terms of differential forms. An important generalization of the notion of orientability of a space is that of orientability of a family of spaces parameterized by some other space (a fiber bundle) for which an orientation must be selected in each of the spaces which varies continuously with respect to changes in the parameter values.
Handle decompositions
A handle decomposition of an m-manifold M is a union
where each is obtained from
by the attaching of -handles. A handle decomposition is to a manifold what a CW-decomposition is to a topological space—in many regards the purpose of a handle decomposition is to have a language analogous to CW-complexes, but adapted to the world of smooth manifolds. Thus an i-handle is the smooth analogue of an i-cell. Handle decompositions of manifolds arise naturally via Morse theory. The modification of handle structures is closely linked to Cerf theory.
Local flatness
Local flatness is a property of a submanifold in a topological manifold of larger dimension. In the category of topological manifolds, locally flat submanifolds play a role similar to that of embedded submanifolds in the category of smooth manifolds.
Suppose a d dimensional manifold N is embedded into an n dimensional manifold M (where d < n). If we say N is locally flat at x if there is a neighborhood of x such that the topological pair is homeomorphic to the pair , with a standard inclusion of as a subspace of . That is, there exists a homeomorphism such that the image of coincides with .
Schönflies theorems
The generalized Schoenflies theorem states that, if an (n − 1)-dimensional sphere S is embedded into the n-dimensional sphere Sn in a locally flat way (that is, the embedding extends to that of a thickened sphere), then the pair (Sn, S) is homeomorphic to the pair (Sn, Sn−1), where Sn−1 is the equator of the n-sphere. Brown and Mazur received the Veblen Prize for their independent proofs of this theorem.
Branches of geometric topology
Low-dimensional topology
Low-dimensional topology includes:
Surfaces (2-manifolds)
3-manifolds
4-manifolds
each have their own theory, where there are some connections.
Low-dimensional topology is strongly geometric, as reflected in the uniformization theorem in 2 dimensions – every surface admits a constant curvature metric; geometrically, it has one of 3 possible geometries: positive curvature/spherical, zero curvature/flat, negative curvature/hyperbolic – and the geometrization conjecture (now theorem) in 3 dimensions – every 3-manifold can be cut into pieces, each of which has one of 8 possible geometries.
2-dimensional topology can be studied as complex geometry in one variable (Riemann surfaces are complex curves) – by the uniformization theorem every conformal class of metrics is equivalent to a unique complex one, and 4-dimensional topology can be studied from the point of view of complex geometry in two variables (complex surfaces), though not every 4-manifold admits a complex structure.
Knot theory
Knot theory is the study of mathematical knots. While inspired by knots which appear in daily life in shoelaces and rope, a mathematician's knot differs in that the ends are joined together so that it cannot be undone. In mathematical language, a knot is an embedding of a circle in 3-dimensional Euclidean space, R3 (since we're using topology, a circle isn't bound to the classical geometric concept, but to all of its homeomorphisms). Two mathematical knots are equivalent if one can be transformed into the other via a deformation of R3 upon itself (known as an ambient isotopy); these transformations correspond to manipulations of a knotted string that do not involve cutting the string or passing the string through itself.
To gain further insight, mathematicians have generalized the knot concept in several ways. Knots can be considered in other three-dimensional spaces and objects other than circles can be used; see knot (mathematics). Higher-dimensional knots are n-dimensional spheres in m-dimensional Euclidean space.
High-dimensional geometric topology
In high-dimensional topology, characteristic classes are a basic invariant, and surgery theory is a key theory.
A characteristic class is a way of associating to each principal bundle on a topological space X a cohomology class of X. The cohomology class measures the extent to which the bundle is "twisted" — particularly, whether it possesses sections or not. In other words, characteristic classes are global invariants which measure the deviation of a local product structure from a global product structure. They are one of the unifying geometric concepts in algebraic topology, differential geometry and algebraic geometry.
Surgery theory is a collection of techniques used to produce one manifold from another in a 'controlled' way, introduced by . Surgery refers to cutting out parts of the manifold and replacing it with a part of another manifold, matching up along the cut or boundary. This is closely related to, but not identical with, handlebody decompositions. It is a major tool in the study and classification of manifolds of dimension greater than 3.
More technically, the idea is to start with a well-understood manifold M and perform surgery on it to produce a manifold M ′ having some desired property, in such a way that the effects on the homology, homotopy groups, or other interesting invariants of the manifold are known.
The classification of exotic spheres by led to the emergence of surgery theory as a major tool in high-dimensional topology.
See also
:Category:Maps of manifolds
List of geometric topology topics
Plumbing (mathematics)
References
R. B. Sher and R. J. Daverman (2002), Handbook of Geometric Topology, North-Holland. .
Geometry processing | Geometric topology | [
"Mathematics"
] | 2,096 | [
"Topology",
"Geometric topology"
] |
621,749 | https://en.wikipedia.org/wiki/Radioactive%20contamination | Radioactive contamination, also called radiological pollution, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids, or gases (including the human body), where their presence is unintended or undesirable (from the International Atomic Energy Agency (IAEA) definition).
Such contamination presents a hazard because the radioactive decay of the contaminants produces ionizing radiation (namely alpha, beta, gamma rays and free neutrons). The degree of hazard is determined by the concentration of the contaminants, the energy of the radiation being emitted, the type of radiation, and the proximity of the contamination to organs of the body. It is important to be clear that the contamination gives rise to the radiation hazard, and the terms "radiation" and "contamination" are not interchangeable.
The sources of radioactive pollution can be classified into two groups: natural and man-made. Following an atmospheric nuclear weapon discharge or a nuclear reactor containment breach, the air, soil, people, plants, and animals in the vicinity will become contaminated by nuclear fuel and fission products. A spilled vial of radioactive material like uranyl nitrate may contaminate the floor and any rags used to wipe up the spill. Cases of widespread radioactive contamination include the Bikini Atoll, the Rocky Flats Plant in Colorado, the area near the Fukushima Daiichi nuclear disaster, the area near the Chernobyl disaster, and the area near the Mayak disaster.
Sources of contamination
The sources of radioactive pollution can be natural or man-made.
Radioactive contamination can be due to a variety of causes. It may occur due to the release of radioactive gases, liquids or particles. For example, if a radionuclide used in nuclear medicine is spilled (accidentally or, as in the case of the Goiânia accident, through ignorance), the material could be spread by people as they walk around.
Radioactive contamination may also be an inevitable result of certain processes, such as the release of radioactive xenon in nuclear fuel reprocessing. In cases that radioactive material cannot be contained, it may be diluted to safe concentrations. For a discussion of environmental contamination by alpha emitters please see actinides in the environment.
Nuclear fallout is the distribution of radioactive contamination by the 520 atmospheric nuclear explosions that took place from the 1950s to the 1980s.
In nuclear accidents, a measure of the type and amount of radioactivity released, such as from a reactor containment failure, is known as the source term. The United States Nuclear Regulatory Commission defines this as "Types and amounts of radioactive or hazardous material released to the environment following an accident."
Contamination does not include residual radioactive material remaining at a site after the completion of decommissioning. Therefore, radioactive material in sealed and designated containers is not properly referred to as contamination, although the units of measurement might be the same.
Containment
Containment is the primary way of preventing contamination from being released into the environment or coming into contact with or being ingested by humans.
Being within the intended Containment differentiates radioactive material from radioactive contamination. When radioactive materials are concentrated to a detectable level outside a containment, the area affected is generally referred to as "contaminated".
There are a large number of techniques for containing radioactive materials so that it does not spread beyond the containment and become contaminated. In the case of liquids, this is by the use of high integrity tanks or containers, usually with a sump system so that leakage can be detected by radiometric or conventional instrumentation.
Where the material is likely to become airborne, then extensive use is made of the glovebox, which is a common technique in hazardous laboratory and process operations in many industries. The gloveboxes are kept under slight negative pressure and the vent gas is filtered in high-efficiency filters, which are monitored by radiological instrumentation to ensure they are functioning correctly.
Naturally occurring radioactivity
A variety of radionuclides occur naturally in the environment. Elements like uranium and thorium, and their decay products, are present in rock and soil. Potassium-40, a primordial nuclide, makes up a small percentage of all potassium and is present in the human body. Other nuclides, like carbon-14, which is present in all living organisms, are continuously created by cosmic rays.
These levels of radioactivity pose little bit danger but can confuse measurement. A particular problem is encountered with naturally generated radon gas which can affect instruments that are set to detect contamination close to normal background levels and can cause false alarms. Because of this skill is required by the operator of radiological survey equipment to differentiate between background radiation and the radiation which emanates from contamination.
Naturally occurring radioactive materials (NORM) can be brought to the surface or concentrated by human activities such as mining, oil and gas extraction, and coal consumption.
Control and monitoring of contamination
Radioactive contamination may exist on surfaces or in volumes of material or air, and specialized techniques are used to measure the levels of contamination by detection of the emitted radiation.
Contamination monitoring
Contamination monitoring depends entirely upon the correct and appropriate deployment and utilisation of radiation monitoring instruments.
Surface contamination
Surface contamination may either be fixed or "free". In the case of fixed contamination, the radioactive material cannot by definition be spread, but its radiation is still measurable. In the case of free contamination, there is the hazard of contamination spread to other surfaces such as skin or clothing, or entrainment in the air. A concrete surface contaminated by radioactivity can be shaved to a specific depth, removing the contaminated material for disposal.
For occupational workers, controlled areas are established where there may be a contamination hazard. Access to such areas is controlled by a variety of barrier techniques, sometimes involving changes of clothing and footwear as required. The contamination within a controlled area is normally regularly monitored. Radiological protection instrumentation (RPI) plays a key role in monitoring and detecting any potential contamination spread, and combinations of hand held survey instruments and permanently installed area monitors such as Airborne particulate monitors and area gamma monitors are often installed. Detection and measurement of surface contamination of personnel and plant are normally by Geiger counter, scintillation counter or proportional counter. Proportional counters and dual phosphor scintillation counters can discriminate between alpha and beta contamination, but the Geiger counter cannot. Scintillation detectors are generally preferred for hand-held monitoring instruments and are designed with a large detection window to make monitoring of large areas faster. Geiger detectors tend to have small windows, which are more suited to small areas of contamination.
Exit monitoring
The spread of contamination by personnel exiting controlled areas in which nuclear material is used or processed is monitored by specialised installed exit control instruments such as frisk probes, hand contamination monitors and whole body exit monitors. These are used to check that persons exiting controlled areas do not carry contamination on their bodies or clothes.
In the United Kingdom, HSE has issued a user guidance note on selecting the correct portable radiation measurement instrument for the application concerned. This covers all radiation instrument technologies and is a useful comparative guide for selecting the correct technology for the contamination type.
The UK NPL publishes a guide on the alarm levels to be used with instruments for checking personnel exiting controlled areas in which contamination may be encountered.
Surface contamination is usually expressed in units of radioactivity per unit of area for alpha or beta emitters. For SI, this is becquerels per square meter (or Bq/m2). Other units such as picoCuries per 100 cm2 or disintegrations per minute per square centimeter (1 dpm/cm2 = 167 Bq/m2) may be used.
Airborne contamination
The air can be contaminated with radioactive isotopes in particulate form, which poses a particular inhalation hazard. Respirators with suitable air filters or completely self-contained suits with their own air supply can mitigate these dangers.
Airborne contamination is measured by specialist radiological instruments that continuously pump the sampled air through a filter. Airborne particles accumulate on the filter and can be measured in a number of ways:
The filter paper is periodically manually removed to an instrument such as a "scaler" which measures any accumulated radioactivity.
The filter paper is static and is measured in situ by a radiation detector.
The filter is a slowly moving strip and is measured by a radiation detector. These are commonly called "moving filter" devices and automatically advance the filter to present a clean area for accumulation, and thereby allow a plot of airborne concentration over time.
Commonly a semiconductor radiation detection sensor is used that can also provide spectrographic information on the contamination being collected.
A particular problem with airborne contamination monitors designed to detect alpha particles is that naturally occurring radon can be quite prevalent and may appear as contamination when low contamination levels are being sought. Modern instruments consequently have "radon compensation" to overcome this effect.
Internal human contamination
Radioactive contamination can enter the body through ingestion, inhalation, absorption, or injection. This will result in a committed dose.
For this reason, it is important to use personal protective equipment when working with radioactive materials. Radioactive contamination may also be ingested as the result of eating contaminated plants and animals or drinking contaminated water or milk from exposed animals. Following a major contamination incident, all potential pathways of internal exposure should be considered.
Successfully used on Harold McCluskey, chelation therapy and other treatments exist for internal radionuclide contamination.
Decontamination
Cleaning up contamination results in radioactive waste unless the radioactive material can be returned to commercial use by reprocessing. In some cases of large areas of contamination, the contamination may be mitigated by burying and covering the contaminated substances with concrete, soil, or rock to prevent further spread of the contamination to the environment. If a person's body is contaminated by ingestion or by injury and standard cleaning cannot reduce the contamination further, then the person may be permanently contaminated.
Contamination control products have been used by the U.S. Department of Energy (DOE) and the commercial nuclear industry for decades to minimize contamination on radioactive equipment and surfaces and fix contamination in place. "Contamination control products" is a broad term that includes fixatives, strippable coatings, and decontamination gels. A fixative product functions as a permanent coating to stabilize residual loose/transferable radioactive contamination by fixing it in place; this aids in preventing the spread of contamination and reduces the possibility of the contamination becoming airborne, reducing workforce exposure and facilitating future deactivation and decommissioning (D&D) activities. Strippable coating products are loosely adhered to paint-like films and are used for their decontamination abilities. They are applied to surfaces with loose/transferable radioactive contamination and then, once dried, are peeled off, which removes the loose/transferable contamination along with the product. The residual radioactive contamination on the surface is significantly reduced once the strippable coating is removed. Modern strippable coatings show high decontamination efficiency and can rival traditional mechanical and chemical decontamination methods. Decontamination gels work in much the same way as other strippable coatings. The results obtained through the use of contamination control products are variable and depend on the type of substrate, the selected contamination control product, the contaminants, and the environmental conditions (e.g., temperature, humidity, etc.).
Some of the largest areas committed to be decontaminated are in the Fukushima Prefecture, Japan. The national government is under pressure to clean up radioactivity due to the Fukushima nuclear accident of March 2011 from as much land as possible so that some of the 110,000 displaced people can return. Stripping out the key radioisotope threatening health (caesium-137) from low-level waste could also dramatically decrease the volume of waste requiring special disposal. A goal is to find techniques that might be able to strip out 80 to 95% of the caesium from contaminated soil and other materials, efficiently and without destroying the organic content in the soil. One being investigated is termed hydrothermal blasting. The caesium is broken away from soil particles and then precipitated with ferric ferricyanide (Prussian blue). It would be the only component of the waste requiring special burial sites. The aim is to get annual exposure from the contaminated environment down to one millisievert (mSv) above background. The most contaminated area where radiation doses are greater than 50 mSv/year must remain off-limits, but some areas that are currently less than 5 mSv/year may be decontaminated allowing 22,000 residents to return.
To help protect people living in geographical areas which have been radioactively contaminated, the International Commission on Radiological Protection has published a guide: "Publication 111 – Application of the Commission's Recommendations to the Protection of People Living in Long-term Contaminated Areas after a Nuclear Accident or a Radiation Emergency".
Contamination hazards
Low-level contamination
The hazards to people and the environment from radioactive contamination depend on the nature of the radioactive contaminant, the level of contamination, and the extent of the spread of contamination. Low levels of radioactive contamination pose little risk, but can still be detected by radiation instrumentation. If a survey or map is made of a contaminated area, random sampling locations may be labeled with their activity in becquerels or curies on contact. Low levels may be reported in counts per minute using a scintillation counter.
In the case of low-level contamination by isotopes with a short half-life, the best course of action may be to simply allow the material to naturally decay. Longer-lived isotopes should be cleaned up and properly disposed of because even a very low level of radiation can be life-threatening when in long exposure to it.
Facilities and physical locations that are deemed to be contaminated may be cordoned off by a health physicist and labeled "Contaminated area." Persons coming near such an area would typically require anti-contamination clothing ("anti-Cs").
High-level contamination
High levels of contamination may pose major risks to people and the environment. People can be exposed to potentially lethal radiation levels, both externally and internally, from the spread of contamination following an accident (or a deliberate initiation) involving large quantities of radioactive material. The biological effects of external exposure to radioactive contamination are generally the same as those from an external radiation source not involving radioactive materials, such as x-ray machines, and are dependent on the absorbed dose.
When radioactive contamination is being measured or mapped in situ, any location that appears to be a point source of radiation is likely to be heavily contaminated. A highly contaminated location is colloquially referred to as a "hot spot." On a map of a contaminated place, hot spots may be labeled with their "on contact" dose rate in mSv/h. In a contaminated facility, hot spots may be marked with a sign, shielded with bags of lead shot, or cordoned off with warning tape containing the radioactive trefoil symbol.
The hazard from contamination is the emission of ionizing radiation. The principal radiations which will be encountered are alpha, beta and gamma, but these have quite different characteristics. They have widely differing penetrating powers and radiation effects, and the accompanying diagram shows the penetration of these radiations in simple terms. For an understanding of the different ionising effects of these radiations and the weighting factors applied, see the article on absorbed dose.
Radiation monitoring involves the measurement of radiation dose or radionuclide contamination for reasons related to the assessment or control of exposure to radiation or radioactive substances, and the interpretation of the results. The methodological and technical details of the design and operation of environmental radiation monitoring programmes and systems for different radionuclides, environmental media and types of facility are given in IAEA Safety Standards Series No. RS–G-1.8 and in IAEA Safety Reports Series No. 64.
Health effects of contamination
Biological effects
Radioactive contamination by definition emits ionizing radiation, which can irradiate the human body from an external or internal origin.
External irradiation
This is due to radiation from contamination located outside the human body. The source can be in the vicinity of the body or can be on the skin surface. The level of health risk is dependent on duration and the type and strength of irradiation. Penetrating radiation such as gamma rays, X-rays, neutrons or beta particles pose the greatest risk from an external source. Low penetrating radiation such as alpha particles have a low external risk due to the shielding effect of the top layers of skin. See the article on sievert for more information on how this is calculated.
Internal irradiation
Radioactive contamination can be ingested into the human body if it is airborne or is taken in as contamination of food or drink, and will irradiate the body internally. The art and science of assessing internally generated radiation dose is Internal dosimetry.
The biological effects of ingested radionuclides depend greatly on the activity, the biodistribution, and the removal rates of the radionuclide, which in turn depends on its chemical form, the particle size, and route of entry. Effects may also depend on the chemical toxicity of the deposited material, independent of its radioactivity. Some radionuclides may be generally distributed throughout the body and rapidly removed, as is the case with tritiated water.
Some organs concentrate certain elements and hence radionuclide variants of those elements. This action may lead to much lower removal rates. For instance, the thyroid gland takes up a large percentage of any iodine that enters the body. Large quantities of inhaled or ingested radioactive iodine may impair or destroy the thyroid, while other tissues are affected to a lesser extent. Radioactive iodine-131 is a common fission product; it was a major component of the radioactivity released from the Chernobyl disaster, leading to nine fatal cases of pediatric thyroid cancer and hypothyroidism. On the other hand, radioactive iodine is used in the diagnosis and treatment of many diseases of the thyroid precisely because of the thyroid's selective uptake of iodine.
The radiation risk proposed by the International Commission on Radiological Protection (ICRP) predicts that an effective dose of one sievert (100 rem) carries a 5.5% chance of developing cancer. Such a risk is the sum of both internal and external radiation doses.
The ICRP states "Radionuclides incorporated in the human body irradiate the tissues over time periods determined by their physical half-life and their biological retention within the body. Thus they may give rise to doses to body tissues for many months or years after the intake. The need to regulate exposures to radionuclides and the accumulation of radiation dose over extended periods of time has led to the definition of committed dose quantities".
The ICRP further states "For internal exposure, committed effective doses are generally determined from an assessment of the intakes of radionuclides from bioassay measurements or other quantities (e.g., activity retained in the body or in daily excreta). The radiation dose is determined from the intake using recommended dose coefficients".
The ICRP defines two dose quantities for individual committed dose:
Committed equivalent dose, H T(t) is the time integral of the equivalent dose rate in a particular tissue or organ that will be received by an individual following intake of radioactive material into the body by a Reference Person, where t is the integration time in years.
This refers specifically to the dose in a specific tissue or organ, in a similar way to external equivalent dose.
Committed effective dose, E(t) is the sum of the products of the committed organ or tissue equivalent doses and the appropriate tissue weighting factors WT, where t is the integration time in years following the intake. The commitment period is taken to be 50 years for adults, and to age 70 years for children. This refers specifically to the dose to the whole body, in a similar way to external effective dose.
Social and psychological effects
A 2015 report in Lancet explained that serious impacts of nuclear accidents were often not directly attributable to radiation exposure, but rather social and psychological effects. The consequences of low-level radiation are often more psychological than radiological. Because damage from very low-level radiation cannot be detected, people exposed to it are left in anguished uncertainty about what will happen to them. Many believe they have been fundamentally contaminated for life and may refuse to have children for fear of birth defects. They may be shunned by others in their community who fear a sort of mysterious contagion.
Forced evacuation from a radiological or nuclear accident may lead to social isolation, anxiety, depression, psychosomatic medical problems, reckless behavior, even suicide. Such was the outcome of the 1986 Chernobyl nuclear disaster in Ukraine. A comprehensive 2005 study concluded that "the mental health impact of Chernobyl is the largest public health problem unleashed by the accident to date". Frank N. von Hippel, a U.S. scientist, commented on 2011 Fukushima nuclear disaster, saying that "fear of ionizing radiation could have long-term psychological effects on a large portion of the population in the contaminated areas". Evacuation and long-term displacement of affected populations create problems for many people, especially the elderly and hospital patients.
Such great psychological danger does not accompany other materials that put people at risk of cancer and other deadly illness. Visceral fear is not widely aroused by, for example, the daily emissions from coal burning, although, as a National Academy of Sciences study found, this causes 10,000 premature deaths a year in the US population of 317,413,000. Medical errors leading to death in U.S. hospitals are estimated to be between 44,000 and 98,000. It is "only nuclear radiation that bears a huge psychological burden – for it carries a unique historical legacy".
See also
Chemical hazard
Criticality accident
Human decontamination
Lists of nuclear disasters and radioactive incidents
Low-background steel
Nuclear and radiation accidents
Nuclear debate (disambiguation)
Nuclear power
Radiation biology
Radiation exposure (disambiguation)
Radiophobia
Relative biological effectiveness
Rongelap Atoll
Soviet submarine K-19
Washdown
:Category:Deaths by acute radiation syndrome
References
Measurement Good Practice Guide No. 30 "Practical Radiation Monitoring" Oct 2002 – National Physical Laboratory, Teddington
External links
Q&A: Health effects of radiation exposure, BBC News, 21 July 2011.
Alliance for Nuclear Responsibility
training guide Brookhaven National Laboratory Training Guide.
International Fund for Animal Welfare report on impact of radiation on animals
Radioactive waste
Nuclear safety and security
Radiobiology
Pollution
Radiation accidents and incidents
Radiation protection | Radioactive contamination | [
"Chemistry",
"Technology",
"Biology"
] | 4,625 | [
"Radioactive contamination",
"Radiobiology",
"Environmental impact of nuclear power",
"Hazardous waste",
"Radioactivity",
"Radioactive waste"
] |
621,769 | https://en.wikipedia.org/wiki/List%20of%20amateur%20mathematicians | This is a list of amateur mathematicians—people whose primary vocation did not involve mathematics (or any similar discipline) yet made notable, and sometimes important, contributions to the field of mathematics.
Ahmes (scribe)
Ashutosh Mukherjee (lawyer)
Robert Ammann (programmer and postal worker)
John Arbuthnot (surgeon and author)
Jean-Robert Argand (shopkeeper)
Leon Bankoff (Beverly Hills dentist)
Rev. Thomas Bayes (Presbyterian minister)
Andrew Beal (businessman)
Isaac Beeckman (candlemaker)
Chester Ittner Bliss (biologist)
Napoléon Bonaparte (general)
Mary Everest Boole (homemaker, librarian)
William Bourne (innkeeper)
Nathaniel Bowditch (indentured bookkeeper)
Achille Brocot (clockmaker)
Jost Bürgi (clockmaker)
Marvin Ray Burns (veteran)
Gerolamo Cardano (medical doctor)
D. G. Champernowne (college student)
Thomas Clausen (technical assistant)
Sir James Cockle (judge)
Federico Commandino (medical doctor)
William Crabtree (merchant)
Nathan Daboll (cooper)
Henri Delannoy (army officer)
Felix Delastelle (bonded warehouseman)
Martin Demaine (goldsmith and glass artist)
Humphry Ditton (minister)
Harvey Dubner (engineer)
Henry Dudeney (civil servant)
Albrecht Dürer (painter)
Greg Egan (writer)
M. C. Escher (graphic artist)
Eugène Ehrhart (mathematics teacher)
John Ernest (painter)
Pasquale Joseph Federico (patent attorney)
Pierre de Fermat (lawyer)
Sarah Flannery (high school student)
Reo Fortune (anthropologist)
John G.F. Francis (research assistant)
Benjamin Franklin (printer and diplomat)
Bernard Frenicle de Bessy
Gemma Frisius (medical doctor)
Britney Gallivan (high school student)
James Garfield (United States President)
Antoine Gombaud (essayist)
Thorold Gosset (lawyer)
Jørgen Pedersen Gram (actuary)
Hermann Grassmann (school teacher)
John Graunt (haberdasher)
George Green (miller)
Aubrey de Grey (gerontologist)
André-Michel Guerry (lawyer)
Charles James Hargreave (judge)
Oliver Heaviside (telegraph operator)
Kurt Heegner (private scholar)
John R. Hendricks (meteorologist)
Anthony Hill (painter)
Paul Jaccard (botanist)
Alfred Bray Kempe (lawyer)
Thomas Kirkman (church rector)
Laurence Monroe Klauber (herpetologist)
Harry Lindgren (civil servant)
Ada Lovelace (countess)
Lu Jiaxi (high school physics teacher)
Kenneth McIntyre (lawyer)
Danica McKellar (actress)
Anderson Gray McKendrick (medical doctor)
Marin Mersenne (theologian)
George Phillips Odom Jr. (artist)
B. Nicolò I. Paganini (schoolboy)
Pāṇini (linguist)
Blaise Pascal (heir, private scholar)
Padmakumar (technician)
Henry Perigal (stockbroker)
Kenneth Perko (lawyer)
Ivan Pervushin (priest)
Piero della Francesca (painter)
Pingala (musician)
William Playfair (draftsman)
Henry Cabourn Pocklington (schoolmaster)
François Proth (farmer)
Ramchundra (head master)
Marjorie Rice (homemaker)
Olinde Rodrigues (banker, social reformer)
Lee Sallows (engineer)
Robert Schlaifer (classics scholar)
Robert Schneider (musician and record producer)
William Shanks (landlord)
Abraham Sharp (schoolmaster)
Simon Stevin (merchants clerk)
Alicia Boole Stott (secretary)
Paul Tannery (tobacco factory director)
Gaston Tarry (civil servant)
Niccolò Fontana Tartaglia (bookkeeper)
Nikola Tesla (engineer, inventor)
Sébastien Truchet (monk)
Franciscus Vieta (lawyer)
Giordano Vitale (soldier)
Walter Frank Raphael Weldon (evolutionary biologist)
Johannes Werner (parish priest)
Caspar Wessel (lawyer)
Leo Wiener (linguist)
Frank Wilcoxon (chemist)
Edouard Zeckendorf (medical doctor)
References
Amateur mathematicians | List of amateur mathematicians | [
"Technology"
] | 847 | [
"Lists of people in STEM fields",
"Lists of mathematicians"
] |
621,774 | https://en.wikipedia.org/wiki/Low-dimensional%20topology | In mathematics, low-dimensional topology is the branch of topology that studies manifolds, or more generally topological spaces, of four or fewer dimensions. Representative topics are the structure theory of 3-manifolds and 4-manifolds, knot theory, and braid groups. This can be regarded as a part of geometric topology. It may also be used to refer to the study of topological spaces of dimension 1, though this is more typically considered part of continuum theory.
History
A number of advances starting in the 1960s had the effect of emphasising low dimensions in topology. The solution by Stephen Smale, in 1961, of the Poincaré conjecture in five or more dimensions made dimensions three and four seem the hardest; and indeed they required new methods, while the freedom of higher dimensions meant that questions could be reduced to computational methods available in surgery theory. Thurston's geometrization conjecture, formulated in the late 1970s, offered a framework that suggested geometry and topology were closely intertwined in low dimensions, and Thurston's proof of geometrization for Haken manifolds utilized a variety of tools from previously only weakly linked areas of mathematics. Vaughan Jones' discovery of the Jones polynomial in the early 1980s not only led knot theory in new directions but gave rise to still mysterious connections between low-dimensional topology and mathematical physics. In 2002, Grigori Perelman announced a proof of the three-dimensional Poincaré conjecture, using Richard S. Hamilton's Ricci flow, an idea belonging to the field of geometric analysis.
Overall, this progress has led to better integration of the field into the rest of mathematics.
Two dimensions
A surface is a two-dimensional, topological manifold. The most familiar examples are those that arise as the boundaries of solid objects in ordinary three-dimensional Euclidean space R3—for example, the surface of a ball. On the other hand, there are surfaces, such as the Klein bottle, that cannot be embedded in three-dimensional Euclidean space without introducing singularities or self-intersections.
Classification of surfaces
The classification theorem of closed surfaces states that any connected closed surface is homeomorphic to some member of one of these three families:
the sphere;
the connected sum of g tori, for ;
the connected sum of k real projective planes, for .
The surfaces in the first two families are orientable. It is convenient to combine the two families by regarding the sphere as the connected sum of 0 tori. The number g of tori involved is called the genus of the surface. The sphere and the torus have Euler characteristics 2 and 0, respectively, and in general the Euler characteristic of the connected sum of g tori is .
The surfaces in the third family are nonorientable. The Euler characteristic of the real projective plane is 1, and in general the Euler characteristic of the connected sum of k of them is .
Teichmüller space
In mathematics, the Teichmüller space TX of a (real) topological surface X, is a space that parameterizes complex structures on X up to the action of homeomorphisms that are isotopic to the identity homeomorphism. Each point in TX may be regarded as an isomorphism class of 'marked' Riemann surfaces where a 'marking' is an isotopy class of homeomorphisms from X to X.
The Teichmüller space is the universal covering orbifold of the (Riemann) moduli space.
Teichmüller space has a canonical complex manifold structure and a wealth of natural metrics. The underlying topological space of Teichmüller space was studied by Fricke, and the Teichmüller metric on it was introduced by .
Uniformization theorem
In mathematics, the uniformization theorem says that every simply connected Riemann surface is conformally equivalent to one of the three domains: the open unit disk, the complex plane, or the Riemann sphere. In particular it admits a Riemannian metric of constant curvature. This classifies Riemannian surfaces as elliptic (positively curved—rather, admitting a constant positively curved metric), parabolic (flat), and hyperbolic (negatively curved) according to their universal cover.
The uniformization theorem is a generalization of the Riemann mapping theorem from proper simply connected open subsets of the plane to arbitrary simply connected Riemann surfaces.
Three dimensions
A topological space X is a 3-manifold if every point in X has a neighbourhood that is homeomorphic to Euclidean 3-space.
The topological, piecewise-linear, and smooth categories are all equivalent in three dimensions, so little distinction is made in whether we are dealing with say, topological 3-manifolds, or smooth 3-manifolds.
Phenomena in three dimensions can be strikingly different from phenomena in other dimensions, and so there is a prevalence of very specialized techniques that do not generalize to dimensions greater than three. This special role has led to the discovery of close connections to a diversity of other fields, such as knot theory, geometric group theory, hyperbolic geometry, number theory, Teichmüller theory, topological quantum field theory, gauge theory, Floer homology, and partial differential equations. 3-manifold theory is considered a part of low-dimensional topology or geometric topology.
Knot and braid theory
Knot theory is the study of mathematical knots. While inspired by knots that appear in daily life in shoelaces and rope, a mathematician's knot differs in that the ends are joined together so that it cannot be undone. In mathematical language, a knot is an embedding of a circle in 3-dimensional Euclidean space, R3 (since we're using topology, a circle isn't bound to the classical geometric concept, but to all of its homeomorphisms). Two mathematical knots are equivalent if one can be transformed into the other via a deformation of R3 upon itself (known as an ambient isotopy); these transformations correspond to manipulations of a knotted string that do not involve cutting the string or passing the string through itself.
Knot complements are frequently-studied 3-manifolds. The knot complement of a tame knot K is the three-dimensional space surrounding the knot. To make this precise, suppose that K is a knot in a three-manifold M (most often, M is the 3-sphere). Let N be a tubular neighborhood of K; so N is a solid torus. The knot complement is then the complement of N,
A related topic is braid theory. Braid theory is an abstract geometric theory studying the everyday braid concept, and some generalizations. The idea is that braids can be organized into groups, in which the group operation is 'do the first braid on a set of strings, and then follow it with a second on the twisted strings'. Such groups may be described by explicit presentations, as was shown by . For an elementary treatment along these lines, see the article on braid groups. Braid groups may also be given a deeper mathematical interpretation: as the fundamental group of certain configuration spaces.
Hyperbolic 3-manifolds
A hyperbolic 3-manifold is a 3-manifold equipped with a complete Riemannian metric of constant sectional curvature -1. In other words, it is the quotient of three-dimensional hyperbolic space by a subgroup of hyperbolic isometries acting freely and properly discontinuously. See also Kleinian model.
Its thick-thin decomposition has a thin part consisting of tubular neighborhoods of closed geodesics and/or ends that are the product of a Euclidean surface and the closed half-ray. The manifold is of finite volume if and only if its thick part is compact. In this case, the ends are of the form torus cross the closed half-ray and are called cusps. Knot complements are the most commonly studied cusped manifolds.
Poincaré conjecture and geometrization
Thurston's geometrization conjecture states that certain three-dimensional topological spaces each have a unique geometric structure that can be associated with them. It is an analogue of the uniformization theorem for two-dimensional surfaces, which states that every simply-connected Riemann surface can be given one of three geometries (Euclidean, spherical, or hyperbolic).
In three dimensions, it is not always possible to assign a single geometry to a whole topological space. Instead, the geometrization conjecture states that every closed 3-manifold can be decomposed in a canonical way into pieces that each have one of eight types of geometric structure. The conjecture was proposed by , and implies several other conjectures, such as the Poincaré conjecture and Thurston's elliptization conjecture.
Four dimensions
A 4-manifold is a 4-dimensional topological manifold. A smooth 4-manifold is a 4-manifold with a smooth structure. In dimension four, in marked contrast with lower dimensions, topological and smooth manifolds are quite different. There exist some topological 4-manifolds that admit no smooth structure and even if there exists a smooth structure it need not be unique (i.e. there are smooth 4-manifolds that are homeomorphic but not diffeomorphic).
4-manifolds are of importance in physics because, in General Relativity, spacetime is modeled as a pseudo-Riemannian 4-manifold.
Exotic R4
An exotic R4 is a differentiable manifold that is homeomorphic but not diffeomorphic to the Euclidean space R4. The first examples were found in the early 1980s by Michael Freedman, by using the contrast between Freedman's theorems about topological 4-manifolds, and Simon Donaldson's theorems about smooth 4-manifolds. There is a continuum of non-diffeomorphic differentiable structures of R4, as was shown first by Clifford Taubes.
Prior to this construction, non-diffeomorphic smooth structures on spheres—exotic spheres—were already known to exist, although the question of the existence of such structures for the particular case of the 4-sphere remained open (and still remains open to this day). For any positive integer n other than 4, there are no exotic smooth structures on Rn; in other words, if n ≠ 4 then any smooth manifold homeomorphic to Rn is diffeomorphic to Rn.
Other special phenomena in four dimensions
There are several fundamental theorems about manifolds that can be proved by low-dimensional methods in dimensions at most 3, and by completely different high-dimensional methods in dimension at least 5, but which are false in four dimensions. Here are some examples:
In dimensions other than 4, the Kirby–Siebenmann invariant provides the obstruction to the existence of a PL structure; in other words a compact topological manifold has a PL structure if and only if its Kirby–Siebenmann invariant in H4(M,Z/2Z) vanishes. In dimension 3 and lower, every topological manifold admits an essentially unique PL structure. In dimension 4 there are many examples with vanishing Kirby–Siebenmann invariant but no PL structure.
In any dimension other than 4, a compact topological manifold has only a finite number of essentially distinct PL or smooth structures. In dimension 4, compact manifolds can have a countable infinite number of non-diffeomorphic smooth structures.
Four is the only dimension n for which Rn can have an exotic smooth structure. R4 has an uncountable number of exotic smooth structures; see exotic R4.
The solution to the smooth Poincaré conjecture is known in all dimensions other than 4 (it is usually false in dimensions at least 7; see exotic sphere). The Poincaré conjecture for PL manifolds has been proved for all dimensions other than 4, but it is not known whether it is true in 4 dimensions (it is equivalent to the smooth Poincaré conjecture in 4 dimensions).
The smooth h-cobordism theorem holds for cobordisms provided that neither the cobordism nor its boundary has dimension 4. It can fail if the boundary of the cobordism has dimension 4 (as shown by Donaldson). If the cobordism has dimension 4, then it is unknown whether the h-cobordism theorem holds.
A topological manifold of dimension not equal to 4 has a handlebody decomposition. Manifolds of dimension 4 have a handlebody decomposition if and only if they are smoothable.
There are compact 4-dimensional topological manifolds that are not homeomorphic to any simplicial complex. In dimension at least 5 the existence of topological manifolds not homeomorphic to a simplicial complex was an open problem. In 2013, Ciprian Manolescu posted a preprint on the ArXiv showing that there are manifolds in each dimension greater than or equal to 5, that are not homeomorphic to a simplicial complex.
A few typical theorems that distinguish low-dimensional topology
There are several theorems that in effect state that many of the most basic tools used to study high-dimensional manifolds do not apply to low-dimensional manifolds, such as:
Steenrod's theorem states that an orientable 3-manifold has a trivial tangent bundle. Stated another way, the only characteristic class of a 3-manifold is the obstruction to orientability.
Any closed 3-manifold is the boundary of a 4-manifold. This theorem is due independently to several people: it follows from the Dehn–Lickorish theorem via a Heegaard splitting of the 3-manifold. It also follows from René Thom's computation of the cobordism ring of closed manifolds.
The existence of exotic smooth structures on R4. This was originally observed by Michael Freedman, based on the work of Simon Donaldson and Andrew Casson. It has since been elaborated by Freedman, Robert Gompf, Clifford Taubes and Laurence Taylor to show there exists a continuum of non-diffeomorphic smooth structures on R4. Meanwhile, Rn is known to have exactly one smooth structure up to diffeomorphism provided n ≠ 4.
See also
List of geometric topology topics
References
External links
Rob Kirby's Problems in Low-Dimensional Topologygzipped postscript file (1.4 MB)
Mark Brittenham's links to low dimensional topologylists of homepages, conferences, etc.
Geometric topology | Low-dimensional topology | [
"Mathematics"
] | 2,908 | [
"Topology",
"Low-dimensional topology",
"Geometric topology"
] |
621,827 | https://en.wikipedia.org/wiki/Grigory%20Shajn | Grigory Abramovich Shajn () (April 19, 1892 – August 4, 1956) was a Soviet/Russian astronomer. In modern English transliteration, his surname would be given as Shayn, but his astronomical discoveries are credited under the name G. Shajn. Nonetheless, his last name is sometimes given as Schayn.
He earned a masters degree from Tomsk University in 1920.
He was the husband of Pelageya Shajn (Пелагея Фёдоровна Шайн) née Sannikova (Санникова), who was also a Russian astronomer.
He worked on stellar spectroscopy and the physics of gaseous nebulas. Together with Otto Struve, he studied the rapid rotation of stars of young spectral types and measured the radial velocities of stars. He discovered new gaseous nebulas and the anomalous abundance of 13C in stellar atmospheres.
He became a member of the Soviet Academy of Sciences in 1939, and was also a member of various foreign societies such as the Royal Astronomical Society. From 1945 to 1952 he was the director of the Crimean Astrophysical Observatory.
He also discovered a few asteroids. He also co-discovered the non-periodic comet C/1925 F1 (Shajn-Comas Solá), also known as Comet 1925 VI or Comet 1925a. However, the periodic comet 61P/Shajn–Schaldach was co-discovered by his wife rather than by him.
The crater Shayn on the Moon is named after him. He and his wife were also honoured by the minor planet 1648 Shajna.
References
Further reading
External links
Obituaries
Obs 76 (1956) 205 (one sentence)
PASP 68 (1956) 561 (one paragraph)
1892 births
1956 deaths
Jewish astronomers
Soviet astronomers
Discoverers of asteroids
Discoverers of comets
Academic staff of Perm State University
Academic staff of Tomsk State University
Full Members of the USSR Academy of Sciences
Scientists from Odesa
Jewish Ukrainian scientists
Russian scientists | Grigory Shajn | [
"Astronomy"
] | 418 | [
"Astronomers",
"Jewish astronomers"
] |
621,887 | https://en.wikipedia.org/wiki/Tectonophysics | Tectonophysics, a branch of geophysics, is the study of the physical processes that underlie tectonic deformation. This includes measurement or calculation of the stress- and strain fields on Earth’s surface and the rheologies of the crust, mantle, lithosphere and asthenosphere.
Overview
Tectonophysics is concerned with movements in the Earth's crust and deformations over scales from meters to thousands of kilometers. These govern processes on local and regional scales and at structural boundaries, such as the destruction of continental crust (e.g. gravitational instability) and oceanic crust (e.g. subduction), convection in the Earth's mantle (availability of melts), the course of continental drift, and second-order effects of plate tectonics such as thermal contraction of the lithosphere. This involves the measurement of a hierarchy of strains in rocks and plates as well as deformation rates; the study of laboratory analogues of natural systems; and the construction of models for the history of deformation.
History
Tectonophysics was adopted as the name of a new section of AGU on April 19, 1940, at AGU's 21st Annual Meeting. According to the AGU website (https://tectonophysics.agu.org/agu-100/section-history/), using the words from Norman Bowen, the main goal of the tectonophysics section was to “designate this new borderline field between geophysics, physics and geology … for the solution of problems of tectonics.” Consequently, the claim below that the term was defined in 1954 by Gzolvskii is clearly incorrect. Since 1940 members of AGU had been presenting papers at AGU meetings, the contents of which defined the meaning of the field.
Tectonophysics was defined as a field in 1954 when Mikhail Vladimirovich Gzovskii published three papers in the journal Izvestiya Akad. Nauk SSSR, Sireya Geofizicheskaya: "On the tasks and content of tectonophysics", "Tectonic stress fields", and "Modeling of tectonic stress fields". He defined the main goals of tectonophysical research to be study of the mechanisms of folding and faulting as well as large structural units of the Earth's crust. He later created the Laboratory of Tectonophysics at the Institute of Physics of the Earth, Academy of Sciences of the USSR, Moscow.
Applications
In coal mines, large amounts of horizontal stress on the rock (around two to three times greater than the vertical pressure from the overlying rock) are caused by tectonic stress and can be predicted with plate tectonics stress maps. For example, because West Virginia experiences tectonic stress from east to west, as of around the 1990s significantly more roof collapses occurred in mines running north to south than in mines running east to west.
See also
Geodynamics
Palaeogeography
Rock mechanics
Seafloor spreading
Structural geology
Tectonophysics (journal)
Notes
References
External links
American Geophysical Union Tectonophysics Section
Geophysics
Tectonics | Tectonophysics | [
"Physics"
] | 669 | [
"Applied and interdisciplinary physics",
"Geophysics"
] |
621,989 | https://en.wikipedia.org/wiki/Viktor%20Ambartsumian | Viktor Amazaspovich Ambartsumian (; , Viktor Hamazaspi Hambardzumyan; 12 August 1996) was a Soviet and Armenian astrophysicist and science administrator. One of the 20th century's leading astronomers, he is widely regarded as the founder of theoretical astrophysics in the Soviet Union.
Educated at Leningrad State University (LSU) and the Pulkovo Observatory, Ambartsumian taught at LSU and founded the Soviet Union's first department of astrophysics there in 1934. He subsequently moved to Soviet Armenia, where he founded the Byurakan Observatory in 1946. It became his institutional base for the decades to come and a major center of astronomical research. He also co-founded the Armenian Academy of Sciences and led it for almost half a century—the entire post-war period. One commentator noted that "science in Armenia was synonymous with the name Ambartsumian." In 1965 Ambartsumian founded the journal Astrofizika and served as its editor for over 20 years.
Ambartsumian began retiring from the various positions he held only from the age of 80. He died at his house in Byurakan and was buried on the grounds of the observatory. He was awarded the title of National Hero of Armenia in 1994.
Background
Ambartsumian was born in Tiflis on , to Armenian parents Hripsime Khakhanian (1885–1972) and Hamazasp Hambardzumyan (1880–1966). Hripsime's father was an Armenian Apostolic priest from Tskhinvali, while Hamazasp hailed from Vardenis (Basargechar). His ancestors had moved from Diyadin, what is now Turkey, to the southern shores of Lake Sevan in 1830, in the aftermath of the Russo-Turkish War. Hamazasp was an educated man of letters who studied law at Saint Petersburg University. He was also a writer and translator and notably translated Homer's Iliad into Armenian from Classical Greek. In 1912 he co-founded the Caucasian Society of Armenian Writers, which lasted until 1921. Ambartsumian was the secretary, while Hovhannes Tumanyan, the famed poet, served as its president. Ambartsumian knew Tumanyan personally. In 1922, after the 14-year-old boy described Sirius to him, Tumanyan wrote a short poem about the star.
Ambartsumian's parents married in 1904. He had a brother, Levon, and sister, Gohar. Levon, a geophysics student, died at 23-24 while on an expedition in the Urals. Gohar (1907–1979) was a mathematician and Chair of Probability Theory and Mathematical Statistics at Yerevan State University towards the end of her life.
Education
Ambartsumian developed an early interest in mathematics and was able to multiply by the age of 4. His interest in astronomy began with reading a Russian translation of a book by Ormsby M. Mitchel at 11. By his own account, he considered himself an astronomer by the age of 12. Between 1917 and 1924 he studied at Tiflis gymnasiums #3 and #4 where schooling was done in both Russian and Armenian. In 1921 he transferred to gymnasium #4 to study under Nikolay Ignatievich Sudakov, a Moscow-educated astronomer, whom Ambartsumian called a "very serious teacher of astronomy." Ambartsumian worked with Sudakov at the school observatory the latter had built. At school, Ambartsumian wrote several papers on astronomy and delivered lectures on the origin of the Solar System and extraterrestrial life at "first in school and then in the various clubs and houses of culture" beginning at 12–13. In 1924 Ambartsumian delivered a lecture at Yerevan State University about the theory of relativity. He also met Ashot Hovhannisyan and Alexander Miasnikian, Armenia's communist leaders.
In 1924 Ambartsumian moved to Leningrad, where he began attending the Herzen Pedagogical Institute. Shakhbazyan suggests that his non-peasant, non-proletarian background prevented him from entering Leningrad State University (LSU). However, Ambartsumian explained in an interview that by the time he arrived in August, LSU's admissions were already closed. To avoid losing a year, he opted to study in the physics and mathematics department of the pedagogical institute. After one year, he transferred to LSU's physics and mathematics department. At university, Ambartsumian was interested in both astronomy and mathematics. "I loved mathematics, but at the same time I felt that my profession would be astronomy. Mathematics was like a hobby, but I did complete the full mathematics curriculum. Thus you could say that I graduated with a major in mathematics, but in fact it is recorded that I graduated as an astronomer," he said in an interview in 1987. At LSU among his professors were the physicist Orest Khvolson and mathematician Vladimir Smirnov. He studied alongside other major Soviet scientists such as Lev Landau, Sergei Sobolev, Sergey Khristianovich and George Gamow. In 1926 he published the first of his 16 scholarly papers as a student. He graduated in 1928, although he received his diploma only fifty years later—in 1978. His undergraduate thesis was "devoted to a study of radiative transfer radiative equilibrium." He completed his postgraduate studies at the Pulkovo Observatory under Aristarkh Belopolsky between 1928 and 1931.
Career
Leningrad
After completing his postgraduate studies in 1931, Ambartsumian began working at the Pulkovo Observatory and teaching part-time at LSU. In 1931 Ambartsumian began reading the first course on theoretical astrophysics in the Soviet Union. He also served as Pulkovo's scientific secretary in 1931–32, which involved mostly administrative work. Ambartsumian later characterized Pulkovo as being a "very old institution, and for this reason there were certain elements of ossification and stagnation. Nevertheless, this was the best qualified astronomical institution in the Soviet Union."
In 1934 Ambartsumian was fired by Pulkovo director Boris Gerasimovich for alleged "laziness." Gerasimovich viewed Ambartsumian and other young astrophysicists as "undisciplined and in too much of a rush to publish untested theories and poorly documented research." Gerasimovich himself had a "tendency to non-cooperativeness." Gerasimovich was not taken seriously by them. When in 1934 Subrahmanyan Chandrasekhar visited Leningrad, he was told by Ambartsumian, "Look here, here is a set of papers by Gerasimovich. I turn to an arbitrary paper and to an arbitrary line. I am sure you will find a mistake." Chandrasekhar stated in 1977 that during his visit in 1934 Ambartsumian "was very free and very open. He was extremely critical of his seniors."
After leaving Pulkovo, Ambartsumian founded the first department of astrophysics in the Soviet Union at Leningrad State University in 1934. In 1934 he was named professor at LSU and in 1935 he was named doctor of physical-mathematical sciences without having to defend a thesis "based on his scientific work through that date." He headed the department until 1946 or 1947.
Between 1939 and 1941 Ambartsumian was the director of the Astronomical Observatory of LSU. He was simultaneously prorector (deputy president) of the university. Among his graduate students were Viktor Sobolev, Benjamin Markarian, Grigor Gurzadyan, and others. Ambartsumian considered Sobolev his "most brilliant graduate student."
Stalin's purges
Many of Ambartsumian's colleagues and friends suffered during the Great Purge under Stalin, most notably Nikolai Aleksandrovich Kozyrev (1908–83), with whom he became close friends in the mid-1920s. Kozyrev was sentenced to ten years in a forced-labor camp, but survived the repressions. Others such as Matvei Petrovich Bronstein and Pulkovo director Boris Gerasimovich did not survive. Ambartsumian's relations with Kozyrev were "strained for the remainder of his life." McCutcheon notes that while in the West some have questioned Ambartsumian's possible role in the terror, "there is no hard evidence to suggest that he was guilty of anything more serious than surviving at a time when others did not."
World War II
Ambartsumian led the evacuation of part of the faculty of Leningrad State University to Elabuga, Tatarstan in 1941, after the Nazi invasion of the Soviet Union. There a branch of LSU operated under Ambartsumian's leadership until 1944. He served as the dean of the branch.
Armenia
In 1943 Ambartsumian moved with his family to Yerevan, Soviet Armenia, where he lived until the end of his life. In the same year, he co-founded the Armenian Academy of Sciences along with scientists and scholars Hovsep Orbeli, Hrachia Acharian, Artem Alikhanian, Abram Alikhanov, Manuk Abeghian and others. He served as vice president of the academy until 1947 and as president from 1947 to 1993.
Since 1943 Ambartsumian served as director of the Yerevan Astronomical Observatory. The small observatory was affiliated with Yerevan State University. Ambartsumian had secured a nine-inch telescope from Leningrad for the observatory. Ambartsumian said that before the war "this observatory did not rise significantly above the level of amateur variable star observations. During the war they also carried out photographic observations of variable stars using a small camera." In 1945–1946 Ambartsumian founded the department of astrophysics at Yerevan State University (YSU). He was named professor of astrophysics at YSU in 1947. He served as chair of the department until 1994.
In 1965 Ambartsumian founded the journal Astrofizika (Armenian: Աստղաֆիզիկա, Russian: Астрофизика), which has been published by the Armenian Academy of Sciences since then. It was originally published in Russian, subsequently articles in English began to appear. He served as its editor-in-chief until 1987. The journal has also been published since the first issue in English by Springer in the US as Astrophysics.
Byurakan
In 1946 Ambartsumian founded the Byurakan Astrophysical Observatory in the village of Byurakan, at an altittude of , on the slopes of Mount Aragats, some from Yerevan. The first buildings were completed in 1951, though the official inauguration took place in 1956. Observations began to be carried out simultaneous with the construction of the observatory. "Our instruments stood under the open sky, covered with tarpaulin," said Ambartsumian. Ambartsumian initially lived at a house in the village of Byurakan then build a house within the observatory grounds with the money awarded with the 1950 Stalin Prize. Ambartsumian directed the Byurakan Observatory until 1988 and was named its honorary director that year. From 1946 until his death in 1996, the Byurakan Observatory served as Ambartsumian's "institutional base."
In 1960 Ambartsumian secured a Schmidt telescope with 40І (102 cm) correcting plate and 52І (132 cm) mirror for Byurakan. The telescope was reportedly made by Carl Zeiss AG in Nazi Germany in the 1930s and was transferred to Leningrad as spoils of war. It was completed in Leningrad and sent to Armenia. Beginning with 1965, on Ambartsumian's initiative, Benjamin Markarian started the First Byurakan Survey that resulted in the discovery of the Markarian galaxies. A number of international symposiums and meetings were held at Byurakan under Ambartsumian's supervision. In 1968 the observatory was awarded the Order of Lenin, the Soviet Union's highest civilian order for its great merit to the development of science. In 1961 Ambartsumian supervised the establishment of an astrophysical station of Leningrad State University, his alma mater, within the grounds of the Byurakan Observatory. It is where graduate students of the LSU did their summer internships until the late 1980s. It was shut down in 1993.
Ambartsumian and his disciples at the Byurakan Observatory became known in the scholarly literature as the "Byurakan School." From 1977 to 1996 Ambartsumian headed a specialized council for theses defenses at Byurakan. Over 50 scientists defended their PhD (Candidate) and Doctoral theses on astronomy, astrophysics and theoretical physics in those years under Ambartsumian. Though most of the students were graduates of the astrophysics department of Yerevan State University, many came from Russia, Georgia, Ukraine, Azerbaijan, Hungary, Bulgaria, and elsewhere. Several symposiums of the International Astronomical Union and numerous conferences were held in Byurakan in attendance of Jan Oort, Fritz Zwicky, Subrahmanyan Chandrasekhar, Pyotr Kapitsa, Vitaly Ginzburg, and others. It was also visited by Soviet leaders Nikita Khrushchev and Leonid Brezhnev.
With the Byurakan Observatory, Ambartsumian "put Armenia on the astronomical map" and made Soviet Armenia "one of the world's centers for the study of astrophysics." By the time of his death in 1996, The New York Times described Byurakan as "one of the world's leading astronomical research centers." As of 1960 the Byurakan Observatory maintained regular contact with 350 research institutions and with scientists from 50 countries.
Research
Ambartsumian carried out basic research in astronomy and cosmogony. It covered astrophysics, theoretical physics and mathematical physics, and mostly focused on the physics of nebulae, star systems, and extragalactic astronomy. He is best known for having discovered stellar associations and predicted activity of galactic nuclei. In his later career, Ambartsumian held views in contradiction to the consequences of the general relativity, such as rejecting the existence of black holes.
Stellar associations
In 1947 Ambartsumian discovered stellar associations, a new type of stellar system, which led to the conclusion that star formation continues to take place in the Milky Way galaxy. At the time the "idea of star formation as an ongoing process was regarded as very speculative." His discovery was announced in a short publication by the Armenian Academy Sciences. Ambartsumian's discovery was based on his observation of stars of O and B spectral types and T Tauri and flare stars that cluster very loosely. This is significantly different from open clusters, which have a higher density of stars, while stellar associations have lower than average density. Ambartsumian divided stellar associations into OB and T groups and concluded that the "associations have to be dynamically unstable configurations, and must expand subsequently, dissolving to form field stars." He thus argued that star forming is ongoing in the galaxy and that stars are born explosively and in groups.
Ambartsumian's concept was not immediately accepted. Chandrasekhar noted the "early scepticism with which this discovery was received by the astronomers of the 'establishment' when I first gave an account of [Ambartsumian's] paper at the colloquium at the Yerkes Observatory in late 1950." Chandrasekhar noted that Ambartsumian's discovery of stellar associations had "far-reaching implications for subsequent theories relating to star formation." McCutcheon noted that the discovery "opened an entirely new field of astrophysical research."
Active galactic nuclei (AGN)
Ambartsumian began studying nuclei of galaxies in the mid-1950s. He found that clusters of galaxies are unstable and that galaxy formation is still ongoing. At the 1958 Solvay Conference on Physics in Brussels he gave a famous report in which he emphasized the extraordinary character of the activity of galactic nuclei (AGN). He claimed "enormous explosions take place in galactic nuclei and as a result a huge amount of mass is expelled. In addition, if this is so, these galactic nuclei must contain bodies of huge mass and unknown nature." Lynden-Bell and Gurzadyan note that Ambartsumian was "perhaps the first to emphasize explosive phenomena in galactic nuclei." Evidence for the activity included the Markarian galaxies, discovered at Byurakan. The concept of AGN was widely accepted some years later, especially after quasars were discovered in 1963. Ambartsumian developed and summarized his views on activity of galaxies in the 1960s.
Radiative transfer
Ambartsumian discovered basic results in radiative transfer in astronomy. He was the first or one of the first to study stellar radiation transfer in gaseous nebulae. He devised techniques for calculating the rates of star cluster decay and the time needed to reach statistical equilibrium in double star systems.
In 1943 he introduced the principle of invariance, a method introduced by Ambartsumian in a theory of radiation transfer. Lynden-Bell and Gurzadyan describe it as the "law that diffuse reflection by a semi-infinite, plane-parallel atmosphere must be invariant to the addition or subtraction of layers of arbitrary thickness to the atmosphere." It has been applied in other areas, including optics, mathematical physics, radiophysics, geophysics, oceanology, "allowing people to handle easily very complex mathematical problems." It was further developed by Chandrasekhar in his Radiative Transfer (1950). According to Chandrasekhar, the formulation of the principles of invariance in the theory of radiative transfer is a "theoretical innovation that is of the greatest significance." He admitted that Ambartsumian's ideas influenced his own.
Astronomy from space
Ambartsumian was a "pioneer of astronomical research from Soviet spacecraft." The program was directed by his disciple Grigor Gurzadyan and was launched in 1961. In April 1971 the Salyut 1 space station carried Orion 1, the "first space telescope with an objective prism, into orbit." In December 1973 the crewed Soyuz 13 mission operated the "Orion-2 ultraviolet Cassegrain telescope with a quartz objective prism built in the Byurakan Observatory. Spectra of thousands of stars to as faint as thirteenth magnitude were obtained, as was the first satellite ultraviolet spectrogram of a planetary nebula, revealing lines of aluminium and titanium-elements not previously observed in planetary nebulae."
These activities, especially the space missions, when for example a special crewed spaceship had to be devoted to an experiment from the smallest Soviet republic, needed powerful backing, both in Kremlin corridors and within the top-secret rocket industry establishment. This was achieved due to Ambartsumian's political skills, with the active support of Mstislav Keldish, the then President of the Academy of Sciences of the USSR.
Mathematics
Ambartsumian also made contributions to mathematics, most notably with his 1929 paper in Zeitschrift für Physik. In it, Ambartsumian first introduced the inverse Sturm-Liouville problem. He proved that "among all vibrating strings only the homogeneous vibrating string has eigenvalues that are specific to it—that is, homogeneous vibrating strings have a spectrum of eigenvalues." It was only in the mid-1940s when his paper received attention and became a "significant research topic in the ensuing decades." He commented: "when an astronomer is publishing a mathematical paper in a physical journal, he cannot expect to attract too many readers."
Ambartsumian had made an independent discovery of Radon's problem in 1936. He did so in a three dimensional velocity space rather than ordinary space and gave the solution in two and three dimensions. Allan MacLeod Cormack, the 1979 Nobel Prize Laureate in Physiology or Medicine for his work on X-ray computed tomography, noted that it is the "first numerical inversion of the Radon transform" and suggested that it disproves the "often made statement that computed tomography would be impossible without computers." Ambartsumian's calculations, Cormack argued, "suggest that even in 1936 computed tomography might have been able to make significant contributions to, say, the diagnosis of tumors in the head." Ambartsumian told Cormack that he was informed of Radon's results two years after he published his work.
Science administration
Soviet Academy of Sciences
Ambartsumian was elected corresponding member of the USSR Academy of Sciences in 1939 and full member (academician) in 1953. In 1955 he became a member of the academy's presidium, the governing body. He also chaired the Academy's Joint Coordinating Scientific Council on astronomy, which was responsible for the priorities and all major decisions in all of astronomy. He was also chairman of the academy's commissions on astronomy (1944–46) and cosmogony (1952–64).
In these positions, Ambartsumian was "one of the most powerful scientists of his time." McCutcheon noted that Ambartsumian's "towering authority as an astrophysicist combined with his position in the Soviet establishment made him arguably the most powerful Soviet astronomer of his day." He was often the "official head of Soviet delegations at many conferences, not only on astronomy but also on natural philosophy."
From 1944 to 1979 Ambartsumian was a member of the editorial board of Astronomicheskii zhurnal (also known as Astronomy Reports), the Soviet Union's main astronomy journal. He was also on the editorial board of Doklady Akademii Nauk SSSR (Proceedings of the USSR Academy of Sciences).
Armenian Academy of Sciences
Although the Armenian branch of the Soviet Academy of Sciences was established in 1935, it was not until 1943 that the National Academy of Sciences of the Armenian SSR was found. Ambartsumian was one of its original co-founders along with other prominent scholars and scientists, including Hovsep Orbeli, who became its first president. Ambartsumian initially served as vice president and in 1947 he became the academy's second president, serving for 46 years until 1993. When he stepped down, Ambartsumian was declared honorary president of the academy.
Rouben Paul Adalian wrote that Ambartsumian "exercised enormous influence in the advancement of science in Soviet Armenia, and was revered as his country's leading scientist." McCutcheon went on to note that "From that point forward, science in Armenia was synonymous with the name Ambartsumian." As president of the principal coordinating body for scientific research in Soviet Armenia, Ambartsumian played a significant role in promoting the sciences in the country. He actively promoted the natural and exact sciences, including physics and mathematics, radioelectronics, chemistry, mechanics and engineering. Artashes Shahinian noted that Ambartsumian played a significant role in the development of the physical and mathematical sciences. He played an instrumental role in the establishment and development of the Yerevan Scientific Research Institute of Mathematical Machines (YerNIIMM) in 1956, popularly known as the "Mergelyan Institute" after its first director, mathematician Sergey Mergelyan. Apoyan rejects that Ambartsumian had a direct involvement in its creation and characterizes his role as "favorable neutrality." Overall, Apoyan criticizes Ambartsumian's role in science administration, arguing that he had a tendency to "fail projects that did not directly serve his fame." He went as far as call Ambartsumian a "tyrant."
Ambartsumian and Mergelyan had a complicated relationship. In 1971 Ambartsumian persuaded him to return to Armenia from Moscow and become vice president of the Armenian Academy of Sciences. However, in 1974 Mergelyan was not reelected to the presidium of the academy and was forced to leave it. Some academicians called for a revote, but Ambartsumian rejected any such attempts. Oganjanyan and Silantiev note that Ambartsumian was rumored to have seen Mergelyan as a rival for the academy's president and decided to "get rid of the competitor forever."
Ambartsumian was the Chairman of the Editorial Board of the Armenian Soviet Encyclopedia, published in 13 volumes in 1974–87.
International
According to Jean-Claude Pecker Ambartsumian "had a very strong influence on world astropolitics" and is one of the few astronomers who have had such a "deep influence on the life of the international bodies devoted to the promotion and defense of astronomy and science in general."
International Astronomical Union
Ambartsumian was a member of the International Astronomical Union (IAU) since 1946. He served as vice-president of the IAU from 1948 to 1955, then as president from 1961 to 1964. As Vice President Ambartsumian attempted to have the IAU General Assembly be held in Leningrad in 1951, however, the IAU Executive Committee canceled the assembly, increasing tensions within the IAU. An IAU General Assembly eventually took place in Moscow in 1958. Ambartsumian headed the organizing committee. Blaauw noted that "During these years, Ambartsumian, although violently opposing the IAU's policy, remained loyal to the Executive Committee's majority decisions for the sake of safeguarding international collaboration, an attitude that contributed to his election as President of the IAU in 1961." He continued to support it as "the world-wide organization embracing astronomers from all countries. His election as President of the IAU in 1961 reflected both the appreciation for his efforts in this respect and his outstanding scientific achievements."
Ambartsumian was outspoken about the importance of international cooperation. At the 1952 IAU General Assembly in Rome he declared: "We believe that the joint study of such large problems as that of the evolution of celestial bodies will contribute to the cultural rapprochement of different nations, and to a better understanding among them. This is our modest contribution to the noble efforts toward maintaining peace throughout the world." At the 1963 IAU symposium in Sydney he stated that while competition between nations is important, it should be associated with co-operation.
International Council of Scientific Unions
Ambartsumian also served as president of the International Council of Scientific Unions (ICSU) between 1968 and 1972, being elected twice for two-year terms in 1968 and 1970. He was the first individual from the Eastern bloc to be elected to that post.
Philosophical and cosmological views
Ambartsumian made "philosophical excursions", and published several books and articles on philosophy, including Philosophical Questions About the Science of the Universe (1973). In a 1968 paper Ambartsumian wrote that he believes in a close collaboration of philosophy and the natural sciences to solve the main scientific problems about nature. Ambartsumian became a member of the administration of the Philosophical Society of the Soviet Union when it was established in 1971. In 1990 he became honorary president of the Philosophical Society of Armenia, which was created through his efforts.
Science and religion
Ambartsumian was an atheist and believed that science and religion are irreconcilable. Ambartsumian wrote in 1959 that the "idea of the existence of God, the idea of world-creation has been defeated entirely." In an interview months before his death, Ambartsumian said that "God is an idea [...] the embodiment of morality [...] an idea that gives meaning to life, profound meaning, and thus, it must be acknowledged that it exists."
For over four decades, he headed Gitelik, the Armenian branch of the all-Soviet organization Znaniye (Knowledge), founded in 1947 to continue the pre-war atheist work of the League of Militant Godless. The organization engaged in what it called "scientific-atheistic propaganda" by publishing atheist novels and journals, producing films and organizing lectures on the supremacy of science over religion. As of 1986, the society had around 20,000 members.
According to one associate, Ambartsumian self-identified as an "Armenian Christian" but was not religious. He felt that Christianity has been important in preserving Armenian identity. Ambartsumian had friendly relations with Vazgen I, the long-time head (Catholicos) of the Armenian Apostolic Church, especially since at least the late 1980s. In 1969 Ambartsumian visited San Lazzaro degli Armeni in Venice, home of the Armenian Catholic congregation of the Mekhitarists and was declared an honorary member of its academy.
Marxism–Leninism and dialectical materialism
Ambartsumian accepted and followed Marxist-Leninist philosophy and staunchly promoted dialectical materialism and projected it on his astrophysical interpretations. Helge Kragh described Ambartsumian as a "convinced Marxist." He wrote on Marxism–Leninism and dialectical materialism in 1959:
Dialectical materialism influenced Ambartsumian's cosmological views and ideas. According to Loren Graham, "perhaps no great Soviet scientist has made more outspoken statements in favor of dialectical materialism" than Ambartsumian. Mark H. Teeter wrote in a 1981 report that Ambartsumian is "one of a rather limited group of Soviet scholars of international stature who claim that dialectical materialism has assisted them in their work." Kragh noted that Ambartsumian was not a cosmologist, but an astrophysicist, and that "his ideas of the universe were influenced both by his background in astrophysics and his adherence to Marxist–Leninist philosophy." Graham notes that his "praise of dialectical materialism has been voiced again and again over the years; these affirmations have come when political controls were rather lax as well as when they were tight. We have every reason to believe that they reflect, at root, his own approach to nature."
Political career and views
Ambartsumian is often referred to as a politician; Donald Lynden-Bell called him a skillful one. In a 1977 interview Subrahmanyan Chandrasekhar went as far as to opine that Ambartsumian has been "much more of a politician than an astronomer" since the mid-1940s.
Lyudvig Mirzoyan, a colleague and friend, wrote that "Ambartsumian was a true patriot of his native land, Soviet Armenia and all the Soviet Union, and simultaneously, he was a convinced internationalist." He was described by a Soviet-run magazine as an "ardent advocate of the widest possible international scientific exchange."
Soviet politics
McCutcheon noted that Ambartsumian's life was "shaped and directed by the Soviet system" and he was politically loyal to the Soviet regime. Adriaan Blaauw wrote that "his political views harmonized to a considerable degree with those of Soviet rulers." Loren Graham argued that, simultaneously, he was "not afraid to reprimand the Communist Party ideologues when they obstructed his research." In favor with the Communist Party, he enjoyed the freedom to regularly travel to the West. McCutcheon noted that Ambartsumian's "scientific genius combined with his political loyalty took him to the heights of the Soviet scientific establishment."
Ambartsumian jointed the Communist Party of the Soviet Union (CPSU) in 1940. In 1948 he became a member of the Central Committee (the executive branch) of the Communist Party of the Armenian SSR. Ambartsumian was also a member of the Supreme Soviet from 1950 to 1989 (3rd to 11th convocation sessions). In 1989 he was elected as a representative from Armenia to the Congress of People's Deputies of the Soviet Union in the first relatively free elections.
Ambartsumian was a delegate to the 19th (1952), 20th (1956), 22nd (1961), 23rd (1966), 24th (1971), 25th (1976) and 26th (1981) congresses of the CPSU.
Cold War politics
Ambartsumian often signed open letters in support of the official line of the Soviet authorities. In 1971 he was among leading 14 Soviet scientists who signed a letter to U.S. President Richard Nixon in support of Angela Davis and appealed him to "give her an opportunity of continuing her scientific work." In 1983 Ambartsumian was among 244 Soviet scientists who signed a statement attacking U.S. President Ronald Reagan's Strategic Defense Initiative ("Star Wars"), namely Reagan's plan for an effective defense against nuclear attack. The scientists stated that Reagan is "creating a most dangerous illusion that may turn into an even more threatening spiral of the arms race."
Ambartsumian's relationship with dissidents was complicated. In 1973 he refused to meet Yuri Orlov, nuclear physicist and a prominent dissident, after having offered him a job in Yerevan. Ambartsumian told him through subordinate that "there are situations when even an Academy member is helpless." In 1975 he was among 72 Soviet scientists who denounced the award of the Nobel Peace Prize to Soviet physicist and dissident Andrei Sakharov.
Armenian causes
Ambartsumian revered the Armenian language and supported its usage. He insisted all internal communication of the Armenian Academy of Sciences be done in Armenian when he became president in 1947. As president of the Armenian Academy of Sciences, Ambartsumian often gave speeches at major events, such as during the commemorations of the 1600th anniversary of Mesrop Mashtots, the inventor of the Armenian alphabet, in 1962 and the 100th anniversary of Hovhannes Tumanyan, Armenia's national poet, in 1969. Ambartsumian stated: "The history of our culture has given many outstanding figures, but of all these figures, the Armenian people owe the most to Mashtots."
Armenian genocide
Ambartsumian delivered a speech on 24 April 1965, on the 50th anniversary of the Armenian genocide, describing it as "extermination of the Armenian population of Western Armenia." He linked it to the 45th anniversary of Soviet Armenia and the revival of the Armenian people as a result of the October Revolution. In an article published in Pravda on 24 April 1975 Ambartsumian linked the Armenian genocide to the Holocaust and blamed German imperialism during World War I for inspiring the Young Turks and the capitalist states for failing to defend the innocent Armenian population and praised the October Revolution for saving the Armenian nation.
Nagorno-Karabakh
Ambartsumian played a role in the Karabakh movement and was vocal in the initial phase of the Nagorno-Karabakh conflict. In November 1989, the Ambartsumian-led Armenian Academy of Sciences issued a statement protesting the decision of the Supreme Soviet of the Soviet Union to return Nagorno-Karabakh under the direct control of Soviet Azerbaijan.
In September 1990 Ambartsumian and four other Armenians, including writer Zori Balayan and actor Sos Sargsyan, went on a hunger strike at the Hotel Moskva in Moscow to protest the military rule over Nagorno-Karabakh declared by Mikhail Gorbachev. Ambartsumian celebrated his 82nd birthday hunger striking. He insisted that Gorbachev had violated the Soviet constitution by keeping Nagorno-Karabakh under direct rule from Moscow. "This is a bad thing when a government does not abide by its own laws," he argued. He also stated: "My desire is that Karabakh be part of Armenia. This is a problem that has to be solved with a long process and with concessions." Ambartsumian stated that his only demand is that the "elected leaders of Nagorno-Karabakh regain control." Ambartsumian called the hunger strike a "modest step" aimed at making a "huge resonance in the world—to let the world know." The Soviet authorities "totally ignored" the strike. He ended it after 9 days only when Catholicos Vazgen I persuaded him to do so.
On 11 May 1991 Ambartsumian and a number of members of the Armenian Academy of Sciences wrote a letter to Soviet President Mikhail Gorbachev expressing their concern with the forced expulsion of ethnic Armenians from parts of NKAO and Shahumian rayon as part of Operation Ring.
Soviet collapse and independence of Armenia
In June 1991 the session of the Armenian Academy of Sciences issued a statement on its views on Armenian independence and the future of the Soviet Union. The Academy stated its unconditional support for the independence of Armenia, pushed at the time by the Pan-Armenian National Movement (HHSh). However, it argued that because Armenia is economically interconnected with and dependent on other Soviet republics, an abrupt disruption in the existing relations would result in "unimaginable levels of economic collapse, unemployment and emigration." Thus, they called for Armenia to join the New Union Treaty proposed by Gorbachev. The session also argued that leaving the Soviet Union would mean to abandon Nagorno-Karabakh.
As a communist, Ambartsumian reportedly regretted the collapse of the Soviet Union, but voted for Armenia's independence in the 1991 referendum. He appreciated independent Armenia, but reminded Armenians that they will be paying a high price for it. In 1995 he congratulated Armenians worldwide with Armenia's independence and stated that the newly independent republic is "moving forward." According to Yuri Shahbazyan, a friend and biographer of Ambartsumian, he remained sympathetic towards the Communist Party of Russia and was critical of Western-sponsored economic liberalization in Russia and other post-Soviet countries.
Personal life
When Ambartsumian was referred to by foreigners as a Russian scientist, he corrected them by saying he was Armenian. He spoke perfect Armenian, albeit with an accent.
Between 1946 and 1996 Ambartsumian mostly divided his time between Yerevan and Byurakan. He built himself a house within the Byurakan Observatory with the award money that came with his second Stalin Prize in 1950. Since 1960 he also maintained a house next to the building of the Academy of Sciences in Yerevan, on Baghramyan Avenue.
Personality
Donald Lynden-Bell characterized Ambartsumian as a "broad-shouldered thickset man of medium height, quick intellect and strong character." Lynden-Bell and Vahe Gurzadyan wrote that Ambartsumian was modest in private life and behaved simply in public. Fadey Sargsyan described Ambartsumian as an "extremely modest" man. Anthony Astrachan wrote in The New Yorker that Ambartsumian is "by all reports an engaging human being." Ambartsumian admitted to not having any hobbies: "My only passion is science, astronomy. Like a jealous wife, it expects a man to give all of himself." However, he loved poetry and music, and "could enliven even the most abstract mathematical lectures with quotations from classical and contemporary poets."
Family
In 1930 or 1931 Ambartsumian married Vera Fyodorovna (née Klochikhina), an ethnic Russian, who was the niece and the adopted daughter of Pelageya Shajn, the wife of Grigory Shajn, both Russian astronomers. She was an English teacher who taught him to read his papers in English when he visited the U.S. and Britain. However, she could not reconcile with his "barbarous pronunciation," as she described it. He was deeply depressed by her death in 1995. They had four children: daughters Karine (b. 1933) and Yelena (b. 1936) and sons Rafayel (b. 1940) and Rouben (b. 1941). All four became either mathematicians or physicists. As of 1987 he had eight grandchildren.
Retirement and death
Ambartsumian began retiring from the various positions he held in 1988, at 80. He left the position of the director of the Byurakan Observatory that year. In 1993 he stepped down as president of the Armenian Academy of Sciences and in 1994 as chair of astrophysics at Yerevan State University.
Ambartsumian died at his Byurakan house on August 12, 1996, a month short of his 88th birthday. He was buried at the observatory grounds, next to his wife and parents. His funeral was attended by thousands of people, including Armenia's president Levon Ter-Petrosyan.
His house was inaugurated as a museum in August 1998.
Recognition
Ambartsumian was one of the 20th century's leading astrophysicists and astronomers. He was the leading astronomer of the Soviet Union and is universally recognized as the founder of the Soviet school of theoretical astrophysics. Ambartsumian was also well-regarded internationally. Loren Graham called him "one of the best-known abroad of all Soviet scientists." He was an honorary or foreign member of academies of sciences of over 25 countries.
Despite being a Soviet scientist, he was well-regarded in the United States. During the Cold War, Ambartsumian was the first Soviet scientist to become foreign honorary member of the American Academy of Arts and Sciences and foreign associate of the National Academy of Sciences in 1958 and 1959, respectively. In January 1971 Ambartsumian was invited to the U.S. House Committee on Science and Astronautics, where he was introduced by Fred Lawrence Whipple as a "man who is rated the world's greatest astronomer or at least among the very greatest."
In 1977 Subrahmanyan Chandrasekhar stated: "My own impression has always been that he was, when he was in his prime, one of the most perceptive and elegant of astronomers." Chandrasekhar opined in 1988:
In Armenia
After he visited Byurakan for the First Soviet-American Conference on Communication with Extraterrestrial Intelligence in 1971, William H. McNeill wrote that Ambartsumian is a "world famous astronomer and a man of enormous local prestige." One of the "modern icons of Armenian pride," Ambartsumian is recognized as the most prominent scientist in 20th century Armenia, and the most important since the seventh century polymath Anania Shirakatsi. Fadey Sargsyan, Ambartsumian's successor as President of the Armenian Academy of Sciences, stated in 1998 that he went "beyond the limits of his scientific fields and in his own lifetime [became] a great national figure."
On 11 October 1994 Armenia's President Levon Ter-Petrosyan awarded Ambartsumian the title of a National Hero of Armenia for his scientific work of international significance, science administration and patriotic activism. His official obituary was signed by Armenia's president, government and parliament.
Tribute
An asteroid discovered at the Crimean Astrophysical Observatory in 1972 by Tamara Smirnova is named 1905 Ambartsumian. Ambartsumian's Knot is a small tidal dwarf galaxy located in NGC 3561 in the constellation Ursa Major.
In 1998 Ambartsumian's 90th anniversary was celebrated in Armenia; the International Astronomical Union held a symposium at the Byurakan Observatory and the Central Bank of Armenia issued a 100 dram banknote depicting Ambartsumian and the Byurakan Observatory. The Byurakan Observatory was officially named after him that year. Other things named after Ambartsumian include Chair of General Physics and Astrophysics at Yerevan State University, a street, park, and public school in Yerevan, and the Pedagogical Institute of Vardenis.
In 2009 a bronze statue of Ambartsumian was unveiled in Yerevan at the park around the Yerevan Observatory in attendance of President Serzh Sargsyan and other officials. Busts of Ambartsumian stand at the Byurakan Observatory, the city of Vardenis (1978), and at the central campus of Yerevan State University.
In 2009 Armenian President Serzh Sargsyan established an international prize in Ambartsumian's memory. It was first awarded in 2010 and is awarded every two years. The prize was initially $500,000, but was reduced to $300,000 in 2018. It is considered one of the prestigious awards in astronomy and related fields.
Awards and honors
State awards
Soviet Union
Hero of Socialist Labour (1968, 1978)
Honored Scientist of the Armenian SSR (1940) and the Georgian SSR (1968)
Order of Lenin (1945, 1958, 1968, 1974, 1978)
Order of the Red Banner of Labour (1944, 1953)
Order of the Badge of Honour (1988)
Order of the October Revolution (1983)
Medal "For Labour Valour" (1960)
USSR State Prize (1946, 1950)
Armenia
National Hero of Armenia (1994)
Foreign countries
Order of Merit of the Republic of Poland 3rd class, Polish People's Republic (1973)
Order of the Flag of the People's Republic of Hungary, People's Republic of Bulgaria (1975)
Order of Cyril and Methodius, People's Republic of Bulgaria (1969)
State Prize of the Russian Federation (1995)
Professional awards
Janssen Prize (Prix Jules-Janssen) of Société astronomique de France (1956)
Gold Medal of the Royal Astronomical Society (1960) "for outstanding contributions to astrophysics"
Bruce Medal of the Astronomical Society of the Pacific (1960)
Lomonosov Gold Medal of the Soviet Academy of Sciences, "for outstanding achievements in the field of astronomy and astrophysics" (1971)
Helmholtz Medal (Helmholtz-Medaille) of the Academy of Sciences of the German Democratic Republic (1971)
Cothenius Medal (Cothenius-Medaille) of the Academy of Sciences Leopoldina (1974)
Membership
Soviet Union
Corresponding Member of the USSR Academy of Sciences (1939)
Full member (Academician) of the Armenian SSR Academy of Sciences (1943)
Full member (Academician) of the USSR Academy of Sciences (1953)
Honorary member of the Academies of Sciences of the Georgian SSR and Azerbaijan SSR
Abroad
Ambartsumian was elected honorary and foreign member of 28 Academies of Sciences, including:
Honorary Member of the American Astronomical Society (1947)
Associate of the Royal Astronomical Society (1953)
Corresponding member (1958) and foreign associate (1978) of the French Academy of Sciences
Foreign Honorary Member of the American Academy of Arts and Sciences (1958)
Foreign Associate of the U.S. National Academy of Sciences (1959)
Honorary Member of the Royal Astronomical Society of Canada (1959)
Foreign Member of the Royal Society (1969)
Honorary degrees
Ambartsumian received honorary doctorates from several universities: Australian National University (1963), University of Paris (1967), University of Liège (1967), Charles University in Prague (1967), Nicolaus Copernicus University in Toruń (1973), National University of La Plata (1974).
Publications
Throughout his career, Ambartsumian authored some 20 books and booklets and over 200 academic papers.
Theoretical Astrophysics (1952)
Ambartsumian served as editor and senior author of the 1952 book Teoreticheskaia Astrofizika (Теоретическая астрофизика). It is an extended version of his 1939 book on theoretical astrophysics—the first systematic textbook on the subject in Russian—based on his lectures at Leningrad State University. It was translated into a number of languages, including English, German, and Chinese. The English translation appeared in 1958 as Theoretical Astrophysics. It became a bible for a generation of astronomers and astrophysicists and was well received by reviewers. Roderick Oliver Redman called it "a welcome addition to the comparatively few general texts of solid worth which are now available" and noted that in a short time it had found "many appreciative readers in both German and English speaking countries." Cecilia Payne-Gaposchkin wrote that it is the "only advanced book of this scope in English, it will be of the greatest value." George B. Field described the book as "comprehensively and competently constructed." A. David Andrews described it as a "valuable textbook", which "contains examples of [Ambartsumian's] unique and fruitful approaches to stubborn astronomical problems." Leonard Searle lauded the sections on stellar atmospheres, but criticized the section on interstellar material, especially the constitution of stars as outdated for ignoring fundamental post-war western contributions.
See also
Armenians in Tbilisi
References
Notes
Citations
Bibliography
Books on Ambartsumian
Journal articles
; translated in
General books
External links
Oral history interview transcript with Viktor Amazaspovich Ambartsumian on 2 October 1987, American Institute of Physics, Niels Bohr Library & Archives
Ambartsumian bibliography at Sonoma State University
Ambartsumian bibliography at ambartsumian.ru
Further reading
1908 births
1996 deaths
Scientists from Tbilisi
Armenian astronomers
Armenian scientists
Armenian astrophysicists
Fellows of the American Academy of Arts and Sciences
Foreign associates of the National Academy of Sciences
Foreign members of the Bulgarian Academy of Sciences
Foreign members of the Royal Society
Members of the French Academy of Sciences
Foreign fellows of the Indian National Science Academy
Members of the Royal Netherlands Academy of Arts and Sciences
Full Members of the Russian Academy of Sciences
Full Members of the USSR Academy of Sciences
Heroes of Socialist Labour
Recipients of the Stalin Prize
Recipients of the Gold Medal of the Royal Astronomical Society
Recipients of the Lomonosov Gold Medal
Recipients of the Order of Lenin
Recipients of the Order of the Red Banner of Labour
National Hero of Armenia
Soviet Armenians
Soviet astronomers
Soviet astrophysicists
Soviet politicians
Communist Party of Armenia (Soviet Union) politicians
Party leaders of the Soviet Union
Members of the German Academy of Sciences at Berlin
Presidents of the International Astronomical Union
Members of the Royal Swedish Academy of Sciences
Recipients of the Cothenius Medal | Viktor Ambartsumian | [
"Astronomy",
"Technology"
] | 10,222 | [
"Science and technology awards",
"Astronomers",
"Presidents of the International Astronomical Union",
"Recipients of the Lomonosov Gold Medal"
] |
622,034 | https://en.wikipedia.org/wiki/Connecting%20rod | A connecting rod, also called a 'con rod', is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the crankshaft. The connecting rod is required to transmit the compressive and tensile forces from the piston. In its most common form, in an internal combustion engine, it allows pivoting on the piston end and rotation on the shaft end.
The predecessor to the connecting rod is a mechanic linkage used by water mills to convert rotating motion of the water wheel into reciprocating motion.
The most common usage of connecting rods is in internal combustion engines or on steam engines.
Origins
A connecting rod crank has been found in the Celtic Oppida at Paule in Brittany, dated to 69BC
The predecessor to the connecting length is the mechanical linkage used by Roman-era watermills. An early example of this linkage has been found at the late 3rd century Hierapolis sawmill in Roman Asia (modern Turkey) and the 6th century saw mills at Ephesus in Asia Minor (modern Turkey) and at Gerasa in Roman Syria. The crank and connecting rod mechanism of these machines converted the rotary motion of the waterwheel into the linear movement of the saw blades.
An early documentation of the design occurred sometime between 1174 and 1206 AD in the Artuqid State (modern Turkey), when inventor Al-Jazari described a machine which incorporated the connecting rod with a crankshaft to pump water as part of a water-raising machine, though the device was more complex than typical crank and connecting rod designs. There is also documentation of cranks with connecting rods in the sketch books of Taccola from Renaissance Italy and 15th century painter Pisanello.
Steam engines
The 1712 Newcomen atmospheric engine (the first steam engine) used chain drive instead of a connecting rod, since the piston only produced force in one direction. However, most steam engines after this are double-acting, therefore the force is produced in both directions, leading to the use of a connecting rod. The typical arrangement uses a large sliding bearing block called a crosshead with the hinge between the piston and connecting rod placed outside the cylinder, requiring a seal around the piston rod.
In a steam locomotive, the cranks are usually mounted directly on the driving wheels. The connecting rod is used between the crank pin on the wheel and the crosshead (where it connects to the piston rod). On smaller steam locomotives, the connecting rods are usually of rectangular cross-section, however marine-type rods of circular cross-section have occasionally been used.
On paddle steamers, the connecting rods are called 'pitmans' (not to be mistaken for pitman arms).
Internal combustion engines
A connecting rod for an internal combustion engine consists of the 'big end', 'rod' and 'small end'. The small end attaches to the gudgeon pin (also called 'piston pin' or 'wrist pin' in the U.S.), which allows for rotation between the connecting rod and the piston. Typically, the big end connects to the crankpin using a plain bearing to reduce friction; however some smaller engines may instead use a rolling-element bearing, in order to avoid the need for a pumped lubrication system. Connecting rods with rolling element bearings are typically a one piece design where the crankshaft must be pressed together through them, rather than a two piece design that can be bolted around the journal of a one piece crankshaft.
Typically there is a pinhole bored through the bearing on the big end of the connecting rod so that lubricating oil squirts out onto the thrust side of the cylinder wall to lubricate the travel of the pistons and piston rings.
A connecting rod can rotate at both ends, so that the angle between the connecting rod and the piston can change as the rod moves up and down and rotates around the crankshaft.
Materials
The materials used for connecting rods widely vary, including carbon steel, iron base sintered metal, micro-alloyed steel, spheroidized graphite cast iron. In mass-produced automotive engines, the connecting rods are most usually made of steel. In high performance applications, "billet" connecting rods can be used, which are machined out of a solid billet of metal, rather than being cast or forged.
Other materials include T6-2024 aluminium alloy or T651-7075 aluminium alloy, which are used for lightness and the ability to absorb high impact at the expense of durability. Titanium is a more expensive option which reduces the weight. Cast iron can be used for cheaper, lower performance applications such as motor scooters.
Failure during operation
During each rotation of the crankshaft, a connecting rod is often subject to large and repetitive forces: shear forces due to the angle between the piston and the crankpin, compression forces as the piston moves downwards, and tensile forces as the piston moves upwards. These forces are proportional to the engine speed (RPM) squared.
Failure of a connecting rod, often called "throwing a rod", often forces the broken rod through the side of the crankcase and thereby renders the engine irreparable. Common causes of connecting rod failure are tensile failure from high engine speeds, the impact force when the piston hits a valve (due to a valvetrain problem), rod bearing failure (usually due to a lubrication problem), or incorrect installation of the connecting rod.
Cylinder wear
The sideways force exerted on the piston through the connecting rod by the crankshaft can cause the cylinders to wear into an oval shape. This significantly reduces engine performance, since the circular piston rings are unable to properly seal against the oval-shaped cylinder walls.
The amount of sideways force is proportional to the angle of the connecting rod, therefore longer connecting rods will reduce the amount of sideways force and engine wear. However, the maximum length of a connecting rod is constrained by the engine block size; the stroke length plus the connecting rod length must not result in the piston travelling past the top of the engine block.
Master-and-slave rods
Radial engines typically use master-and-slave connecting rods, whereby one piston (the uppermost piston in the animation), has a master rod with a direct attachment to the crankshaft. The remaining pistons pin their connecting rods' attachments to rings around the edge of the master rod.
Multi-bank engines with many cylinders, such as V12 engines, have little space available for many connecting rod journals on a limited length of crankshaft. The simplest solution, as used in most road car engines, is for each pair of cylinders to share a crank journal, but this reduces the size of the rod bearings and means that matching (i.e. opposite) cylinders in the different banks are slightly offset along the crankshaft axis (which creates a rocking couple). Another solution is to use master-and-slave connecting rods, where the master rod also includes one or more ring pins which are connected to the big ends of slave rods on other cylinders. A drawback of master-slave rods is that the stroke lengths of all slave pistons not located 180° from the master piston will always be slightly longer than that of the master piston, which increases vibration in V engines.
One of the most complicated examples of master-and-slave connecting rods is the 24-cylinder Junkers Jumo 222 experimental airplane engine developed for World War II. This engine consisted of six banks of cylinders, each with four cylinders per bank. Each "layer" of six cylinders used one master connecting rod, with the other five cylinders using slave rods. Approximately 300 test engines were built, however the engine did not reach production.
Fork-and-blade rods
Fork-and-blade rods, also known as "split big-end rods", have been used on V-twin motorcycle engines and V12 aircraft engines. For each pair of cylinders, a "fork" rod is split in two at the big end and the "blade" rod from the opposing cylinder is thinned to fit into this gap in the fork. This arrangement removes the rocking couple that is caused when cylinder pairs are offset along the crankshaft.
A common arrangement for the big-end bearing is for the fork rod to have a single wide bearing sleeve that spans the whole width of the rod, including the central gap. The blade rod then runs, not directly on the crankpin, but on the outside of this sleeve. This causes the two rods to oscillate back and forth (instead of rotating relative to each other), which reduces the forces on the bearing and the surface speed. However the bearing movement also becomes reciprocating rather than continuously rotating, which is a more difficult problem for lubrication.
Notable engines to use fork-and-blade rods include the Rolls-Royce Merlin V12 aircraft engine, EMD two-stroke Diesel engines, and various Harley Davidson V-twin motorcycle engines.
See also
Hydrolock
List of auto parts
Steam locomotive components
References
Engine technology
Locomotive parts
Linkages (mechanical) | Connecting rod | [
"Technology"
] | 1,860 | [
"Engine technology",
"Engines"
] |
622,053 | https://en.wikipedia.org/wiki/S-matrix | In physics, the S-matrix or scattering matrix is a matrix that relates the initial state and the final state of a physical system undergoing a scattering process. It is used in quantum mechanics, scattering theory and quantum field theory (QFT).
More formally, in the context of QFT, the S-matrix is defined as the unitary matrix connecting sets of asymptotically free particle states (the in-states and the out-states) in the Hilbert space of physical states: a multi-particle state is said to be free (or non-interacting) if it transforms under Lorentz transformations as a tensor product, or direct product in physics parlance, of one-particle states as prescribed by equation below. Asymptotically free then means that the state has this appearance in either the distant past or the distant future.
While the S-matrix may be defined for any background (spacetime) that is asymptotically solvable and has no event horizons, it has a simple form in the case of the Minkowski space. In this special case, the Hilbert space is a space of irreducible unitary representations of the inhomogeneous Lorentz group (the Poincaré group); the S-matrix is the evolution operator between (the distant past), and (the distant future). It is defined only in the limit of zero energy density (or infinite particle separation distance).
It can be shown that if a quantum field theory in Minkowski space has a mass gap, the state in the asymptotic past and in the asymptotic future are both described by Fock spaces.
History
The initial elements of S-matrix theory are found in Paul Dirac's 1927 paper "Über die Quantenmechanik der Stoßvorgänge". The S-matrix was first properly introduced by John Archibald Wheeler in the 1937 paper "On the Mathematical Description of Light Nuclei by the Method of Resonating Group Structure". In this paper Wheeler introduced a scattering matrix – a unitary matrix of coefficients connecting "the asymptotic behaviour of an arbitrary particular solution [of the integral equations] with that of solutions of a standard form", but did not develop it fully.
In the 1940s, Werner Heisenberg independently developed and substantiated the idea of the S-matrix. Because of the problematic divergences present in quantum field theory at that time, Heisenberg was motivated to isolate the essential features of the theory that would not be affected by future changes as the theory developed. In doing so, he was led to introduce a unitary "characteristic" S-matrix.
Today, however, exact S-matrix results are important for conformal field theory, integrable systems, and several further areas of quantum field theory and string theory. S-matrices are not substitutes for a field-theoretic treatment, but rather, complement the end results of such.
Motivation
In high-energy particle physics one is interested in computing the probability for different outcomes in scattering experiments. These experiments can be broken down into three stages:
Making a collection of incoming particles collide (usually two kinds of particles with high energies).
Allowing the incoming particles to interact. These interactions may change the types of particles present (e.g. if an electron and a positron annihilate they may produce two photons).
Measuring the resulting outgoing particles.
The process by which the incoming particles are transformed (through their interaction) into the outgoing particles is called scattering. For particle physics, a physical theory of these processes must be able to compute the probability for different outgoing particles when different incoming particles collide with different energies.
The S-matrix in quantum field theory achieves exactly this. It is assumed that the small-energy-density approximation is valid in these cases.
Use
The S-matrix is closely related to the transition probability amplitude in quantum mechanics and to cross sections of various interactions; the elements (individual numerical entries) in the S-matrix are known as scattering amplitudes. Poles of the S-matrix in the complex-energy plane are identified with bound states, virtual states or resonances. Branch cuts of the S-matrix in the complex-energy plane are associated to the opening of a scattering channel.
In the Hamiltonian approach to quantum field theory, the S-matrix may be calculated as a time-ordered exponential of the integrated Hamiltonian in the interaction picture; it may also be expressed using Feynman's path integrals. In both cases, the perturbative calculation of the S-matrix leads to Feynman diagrams.
In scattering theory, the S-matrix is an operator mapping free particle in-states to free particle out-states (scattering channels) in the Heisenberg picture. This is very useful because often we cannot describe the interaction (at least, not the most interesting ones) exactly.
In one-dimensional quantum mechanics
A simple prototype in which the S-matrix is 2-dimensional is considered first, for the purposes of illustration. In it, particles with sharp energy scatter from a localized potential according to the rules of 1-dimensional quantum mechanics. Already this simple model displays some features of more general cases, but is easier to handle.
Each energy yields a matrix that depends on . Thus, the total S-matrix could, figuratively speaking, be visualized, in a suitable basis, as a "continuous matrix" with every element zero except for -blocks along the diagonal for a given .
Definition
Consider a localized one dimensional potential barrier , subjected to a beam of quantum particles with energy . These particles are incident on the potential barrier from left to right.
The solutions of Schrödinger's equation outside the potential barrier are plane waves given by
for the region to the left of the potential barrier, and
for the region to the right to the potential barrier, where
is the wave vector. The time dependence is not needed in our overview and is hence omitted. The term with coefficient represents the incoming wave, whereas term with coefficient represents the outgoing wave. stands for the reflecting wave. Since we set the incoming wave moving in the positive direction (coming from the left), is zero and can be omitted.
The "scattering amplitude", i.e., the transition overlap of the outgoing waves with the incoming waves is a linear relation defining the S-matrix,
The above relation can be written as
where
The elements of completely characterize the scattering properties of the potential barrier .
Unitary property
The unitary property of the S-matrix is directly related to the conservation of the probability current in quantum mechanics.
The probability current density of the wave function is defined as
The probability current density of to the left of the barrier is
while the probability current density of to the right of the barrier is
For conservation of the probability current, . This implies the S-matrix is a unitary matrix.
Time-reversal symmetry
If the potential is real, then the system possesses time-reversal symmetry. Under this condition, if is a solution of Schrödinger's equation, then is also a solution.
The time-reversed solution is given by
for the region to the left to the potential barrier, and
for the region to the right to the potential barrier,
where the terms with coefficient , represent incoming wave, and terms with coefficient , represent outgoing wave.
They are again related by the S-matrix,
that is,
Now, the relations
together yield a condition
This condition, in conjunction with the unitarity relation, implies that the S-matrix is symmetric, as a result of time reversal symmetry,
By combining the symmetry and the unitarity, the S-matrix can be expressed in the form:
with and . So the S-matrix is determined by three real parameters.
Transfer matrix
The transfer matrix relates the plane waves and on the right side of scattering potential to the plane waves and on the left side:
and its components can be derived from the components of the S-matrix via: and , whereby time-reversal symmetry is assumed.
In the case of time-reversal symmetry, the transfer matrix can be expressed by three real parameters:
with and (in case there would be no connection between the left and the right side)
Finite square well
The one-dimensional, non-relativistic problem with time-reversal symmetry of a particle with mass m that approaches a (static) finite square well, has the potential function with
The scattering can be solved by decomposing the wave packet of the free particle into plane waves with wave numbers for a plane wave coming (faraway) from the left side or likewise (faraway) from the right side.
The S-matrix for the plane wave with wave number has the solution:
and ; hence and therefore and in this case.
Whereby is the (increased) wave number of the plane wave inside the square well, as the energy eigenvalue associated with the plane wave has to stay constant:
The transmission is
In the case of then and therefore and i.e. a plane wave with wave number k passes the well without reflection if for a
Finite square barrier
The square barrier is similar to the square well with the difference that for .
There are three different cases depending on the energy eigenvalue of the plane waves (with wave numbers resp. ) far away from the barrier:
Transmission coefficient and reflection coefficient
The transmission coefficient from the left of the potential barrier is, when ,
The reflection coefficient from the left of the potential barrier is, when ,
Similarly, the transmission coefficient from the right of the potential barrier is, when ,
The reflection coefficient from the right of the potential barrier is, when ,
The relations between the transmission and reflection coefficients are
and
This identity is a consequence of the unitarity property of the S-matrix.
With time-reversal symmetry, the S-matrix is symmetric and hence and .
Optical theorem in one dimension
In the case of free particles , the S-matrix is
Whenever is different from zero, however, there is a departure of the S-matrix from the above form, to
This departure is parameterized by two complex functions of energy, and .
From unitarity there also follows a relationship between these two functions,
The analogue of this identity in three dimensions is known as the optical theorem.
Definition in quantum field theory
Interaction picture
A straightforward way to define the S-matrix begins with considering the interaction picture. Let the Hamiltonian be split into the free part and the interaction , . In this picture, the operators behave as free field operators and the state vectors have dynamics according to the interaction . Let
denote a state that has evolved from a free initial state
The S-matrix element is then defined as the projection of this state on the final state
Thus
where is the S-operator. The great advantage of this definition is that the time-evolution operator evolving a state in the interaction picture is formally known,
where denotes the time-ordered product. Expressed in this operator,
from which
Expanding using the knowledge about gives a Dyson series,
or, if comes as a Hamiltonian density ,
Being a special type of time-evolution operator, is unitary. For any initial state and any final state one finds
This approach is somewhat naïve in that potential problems are swept under the carpet. This is intentional. The approach works in practice and some of the technical issues are addressed in the other sections.
In and out states
Here a slightly more rigorous approach is taken in order to address potential problems that were disregarded in the interaction picture approach of above. The final outcome is, of course, the same as when taking the quicker route. For this, the notions of in and out states are needed. These will be developed in two ways, from vacuum, and from free particle states. Needless to say, the two approaches are equivalent, but they illuminate matters from different angles.
From vacuum
If is a creation operator, its hermitian adjoint is an annihilation operator and destroys the vacuum,
In Dirac notation, define
as a vacuum quantum state, i.e. a state without real particles. The asterisk signifies that not all vacua are necessarily equal, and certainly not equal to the Hilbert space zero state . All vacuum states are assumed Poincaré invariant, invariance under translations, rotations and boosts, formally,
where is the generator of translation in space and time, and is the generator of Lorentz transformations. Thus the description of the vacuum is independent of the frame of reference. Associated to the in and out states to be defined are the in and out field operators (aka fields) and . Attention is here focused to the simplest case, that of a scalar theory in order to exemplify with the least possible cluttering of the notation. The in and out fields satisfy
the free Klein–Gordon equation. These fields are postulated to have the same equal time commutation relations (ETCR) as the free fields,
where is the field canonically conjugate to . Associated to the in and out fields are two sets of creation and annihilation operators, and , acting in the same Hilbert space, on two distinct complete sets (Fock spaces; initial space , final space ). These operators satisfy the usual commutation rules,
The action of the creation operators on their respective vacua and states with a finite number of particles in the in and out states is given by
where issues of normalization have been ignored. See the next section for a detailed account on how a general state is normalized. The initial and final spaces are defined by
The asymptotic states are assumed to have well defined Poincaré transformation properties, i.e. they are assumed to transform as a direct product of one-particle states. This is a characteristic of a non-interacting field. From this follows that the asymptotic states are all eigenstates of the momentum operator ,
In particular, they are eigenstates of the full Hamiltonian,
The vacuum is usually postulated to be stable and unique,
The interaction is assumed adiabatically turned on and off.
Heisenberg picture
The Heisenberg picture is employed henceforth. In this picture, the states are time-independent. A Heisenberg state vector thus represents the complete spacetime history of a system of particles. The labeling of the in and out states refers to the asymptotic appearance. A state is characterized by that as the particle content is that represented collectively by . Likewise, a state will have the particle content represented by for . Using the assumption that the in and out states, as well as the interacting states, inhabit the same Hilbert space and assuming completeness of the normalized in and out states (postulate of asymptotic completeness), the initial states can be expanded in a basis of final states (or vice versa). The explicit expression is given later after more notation and terminology has been introduced. The expansion coefficients are precisely the S-matrix elements to be defined below.
While the state vectors are constant in time in the Heisenberg picture, the physical states they represent are not. If a system is found to be in a state at time , then it will be found in the state at time . This is not (necessarily) the same Heisenberg state vector, but it is an equivalent state vector, meaning that it will, upon measurement, be found to be one of the final states from the expansion with nonzero coefficient. Letting vary one sees that the observed (not measured) is indeed the Schrödinger picture state vector. By repeating the measurement sufficiently many times and averaging, one may say that the same state vector is indeed found at time as at time . This reflects the expansion above of an in state into out states.
From free particle states
For this viewpoint, one should consider how the archetypical scattering experiment is performed. The initial particles are prepared in well defined states where they are so far apart that they don't interact. They are somehow made to interact, and the final particles are registered when they are so far apart that they have ceased to interact. The idea is to look for states in the Heisenberg picture that in the distant past had the appearance of free particle states. This will be the in states. Likewise, an out state will be a state that in the distant future has the appearance of a free particle state.
The notation from the general reference for this section, will be used. A general non-interacting multi-particle state is given by
where
is momentum,
is spin z-component or, in the massless case, helicity,
is particle species.
These states are normalized as
Permutations work as such; if is a permutation of objects (for a state) such that
then a nonzero term results. The sign is plus unless involves an odd number of fermion transpositions, in which case it is minus. The notation is usually abbreviated letting one Greek letter stand for the whole collection describing the state. In abbreviated form the normalization becomes
When integrating over free-particle states one writes in this notation
where the sum includes only terms such that no two terms are equal modulo a permutation of the particle type indices. The sets of states sought for are supposed to be complete. This is expressed as
which could be paraphrased as
where for each fixed , the right hand side is a projection operator onto the state . Under an inhomogeneous Lorentz transformation , the field transforms according to the rule
where is the Wigner rotation and is the representation of . By putting , for which is , in , it immediately follows that
so the in and out states sought after are eigenstates of the full Hamiltonian that are necessarily non-interacting due to the absence of mixed particle energy terms. The discussion in the section above suggests that the in states and the out states should be such that
for large positive and negative has the appearance of the corresponding package, represented by , of free-particle states, assumed smooth and suitably localized in momentum. Wave packages are necessary, else the time evolution will yield only a phase factor indicating free particles, which cannot be the case. The right hand side follows from that the in and out states are eigenstates of the Hamiltonian per above. To formalize this requirement, assume that the full Hamiltonian can be divided into two terms, a free-particle Hamiltonian and an interaction , such that the eigenstates of have the same appearance as the in- and out-states with respect to normalization and Lorentz transformation properties,
The in and out states are defined as eigenstates of the full Hamiltonian,
satisfying
for or respectively. Define
then
This last expression will work only using wave packages.From these definitions follow that the in and out states are normalized in the same way as the free-particle states,
and the three sets are unitarily equivalent. Now rewrite the eigenvalue equation,
where the terms has been added to make the operator on the LHS invertible. Since the in and out states reduce to the free-particle states for , put
on the RHS to obtain
Then use the completeness of the free-particle states,
to finally obtain
Here has been replaced by its eigenvalue on the free-particle states. This is the Lippmann–Schwinger equation.
In states expressed as out states
The initial states can be expanded in a basis of final states (or vice versa). Using the completeness relation,
where is the probability that the interaction transforms
into
By the ordinary rules of quantum mechanics,
and one may write
The expansion coefficients are precisely the S-matrix elements to be defined below.
The S-matrix
The S-matrix is now defined by
Here and are shorthands that represent the particle content but suppresses the individual labels. Associated to the S-matrix there is the S-operator defined by
where the are free particle states. This definition conforms with the direct approach used in the interaction picture. Also, due to unitary equivalence,
As a physical requirement, must be a unitary operator. This is a statement of conservation of probability in quantum field theory. But
By completeness then,
so S is the unitary transformation from in-states to out states.
Lorentz invariance is another crucial requirement on the S-matrix. The S-operator represents the quantum canonical transformation of the initial in states to the final out states. Moreover, leaves the vacuum state invariant and transforms in-space fields to out-space fields,
In terms of creation and annihilation operators, this becomes
hence
A similar expression holds when operates to the left on an out state. This means that the S-matrix can be expressed as
If describes an interaction correctly, these properties must be also true:
If the system is made up with a single particle in momentum eigenstate , then . This follows from the calculation above as a special case.
The S-matrix element may be nonzero only where the output state has the same total momentum as the input state. This follows from the required Lorentz invariance of the S-matrix.
Evolution operator U
Define a time-dependent creation and annihilation operator as follows,
so, for the fields,
where
We allow for a phase difference, given by
because for ,
Substituting the explicit expression for , one has
where is the interaction part of the Hamiltonian and is the time ordering.
By inspection, it can be seen that this formula is not explicitly covariant.
Dyson series
The most widely used expression for the S-matrix is the Dyson series. This expresses the S-matrix operator as the series:
where:
denotes time-ordering,
denotes the interaction Hamiltonian density which describes the interactions in the theory.
The not-S-matrix
Since the transformation of particles from black hole to Hawking radiation could not be described with an S-matrix, Stephen Hawking proposed a "not-S-matrix", for which he used the dollar sign ($), and which therefore was also called "dollar matrix".
See also
Feynman diagram
LSZ reduction formula
Wick's theorem
Haag's theorem
Interaction picture
Levinson's theorem
Initial and final state radiation
Remarks
Notes
References
§125
Quantum field theory
Scattering theory
Matrices
Mathematical physics | S-matrix | [
"Physics",
"Chemistry",
"Mathematics"
] | 4,527 | [
"Quantum field theory",
"Scattering theory",
"Applied mathematics",
"Theoretical physics",
"Mathematical objects",
"Quantum mechanics",
"Matrices (mathematics)",
"Scattering",
"Mathematical physics"
] |
622,061 | https://en.wikipedia.org/wiki/Moroccan%20Western%20Sahara%20Wall | The Moroccan Western Sahara Wall or the Berm, also called the Moroccan sand wall (), is an approximately berm running south to north through Western Sahara and the southwestern portion of Morocco. It separates the Moroccan-controlled areas (the Southern Provinces) on the west from the Polisario-controlled areas (Free Zone, nominally Sahrawi Arab Democratic Republic) on the east. The main function of the barriers is to exclude guerrilla fighters of the Polisario Front, who have sought Western Saharan independence since before Spain ended its colonial occupation in 1975, from the Moroccan-controlled western part of the territory.
According to maps from the United Nations Mission for the Referendum in Western Sahara (MINURSO) or the United Nations High Commissioner for Refugees (UNHCR), in some places the wall extends several kilometers into internationally recognized Mauritanian territory.
Names
The wall is also called the Western Sahara berm and the Western Sahara separation barrier.
Physical structure
The fortifications lie in uninhabited or very sparsely inhabited territory. They consist of sand and stone walls or berms about in height, with bunkers, fences, and landmines throughout. The barrier minebelt that runs along the structure is thought to be the longest continuous minefield in the world. Military bases, artillery posts and airfields dot the Moroccan-controlled side of the wall at regular intervals, and radar masts and other electronic surveillance equipment scan the areas in front of it.
The following is one observer's description of the berm from 2001:
In all, six lines of berms have been constructed. The main ("external") line of fortifications extends for about . It runs east from Guerguerat on the coast in the extreme south of Western Sahara near the Mauritanian town of Nouadhibou, closely parallelling the Mauritanian border for about , before turning north beyond Tichla. It then runs generally northeastward, leaving Guelta Zemmur and Smara, again crossing Mauritanian territory and reaching Haouza in Moroccan-held territory, before turning east and again closely following the Algerian border as it approaches Morocco. A section extends about into southeastern Morocco.
Significant lines of fortifications also lie deep within the Moroccan-controlled area. Their exact number and location have been ignored and not well understood until 2004 by international commentators.
All major settlements in Western Sahara, the capital Laayoune, and the phosphate mine at Bou Craa lie far into the Moroccan-held side.
History
Construction
The fortifications were progressively built by Moroccan forces starting in 1980, with help from South African, South Korean, and Israeli advisors, and formally ending on 16 April 1987. The wall was built in six stages, and the area behind the wall was expanded from a small area near Morocco in the north to most of the western and central part of the country gradually. The walls built were:
1st wall (August 1980 – June 1982) surrounding the "useful triangle" of El Aaiún, Smara, and the phosphate mines at Bou Craa, built with the help of South African military engineers and Portuguese and French renegade mercenaries (c. ).
2nd wall (December 1983 – January 1984) surrounding Amgala (c. ).
3rd wall (April 1984 – May 1984) surrounding Jdiriya and Haouza (c. ).
4th wall (December 1984 – January 1985) surrounding Mahbes and Farciya (c. ).
5th wall (May–September 1985) surrounding Guelta Zemmur, Bir Anzarane, and Dakhla, again with the help of South African and Israeli experts (c. )
6th wall (February–April 1987) surrounding Auserd, Tichla, and Bir Ganduz (c. ).
7th wall (November–December 2020) from 6th wall to Mauritanian frontier (c. ).
2005 expulsion incident
In the summer of 2005, the Moroccan Army accelerated the expulsion (begun in late 2004) of illegal immigrants detained in northern Morocco to the eastern side of the wall, into the Free Zone. The Polisario Front and the MINURSO rescued several dozen lost in the desert, who had run out of water. Others died of thirst. By October, the Polisario had received 22 immigrants in Mehaires, 46 in Tifariti and 97 in Bir Lehlu. They were from African countries (Gambia, Cameroon, Nigeria, Ghana, etc.), except a group of 48 who were from Bangladesh.
The Thousand Column demonstration
Since 2008, a demonstration called "The Thousand Column" is held annually in the desert against the barrier by international human rights activists and Sahrawi refugees. In the 2008 demonstration, more than 2,000 people (most of them Sahrawis and Spaniards, but also Algerians, Italians, and others) made a human chain demanding the demolition of the wall, the celebration of the self-determination referendum accorded by the UN and the parts in 1991, and the end of the Moroccan occupation of the territory.
During the 2009 demonstration, a teenage Sahrawi refugee named Ibrahim Hussein Leibeit lost half of his right leg in a landmine explosion. The incident happened when Leibeit and dozens of young Sahrawis crossed the line into a minefield while aiming to throw stones to the other side of the wall.
Effect
Effectively, after the completion of the wall, Morocco has controlled the bulk of Western Sahara territory that lies to the north and west of it, calling these the kingdom's "Southern Provinces". The Polisario-founded Sahrawi Arab Democratic Republic controls the mostly uninhabited "Free Zone", which comprises all areas to the east of the barrier. Units from the United Nations mission MINURSO separate the two sides, and enforce cease-fire regulations.
External reactions and opinions
Western attention to the wall, and to the Moroccan annexation of Western Sahara in general, has been minimal, apart from Spain. In Africa, the annexation of Western Sahara by Morocco has attracted somewhat more attention. Algeria supports the Polisario Front "in its long-running desert war to oppose Moroccan control of the disputed area". The Organization of African Unity/African Union (AU) and United Nations have proposed negotiated solutions.
The AU's stance on Western Sahara led to Morocco's exit from the organization. After a 33-year absence, Morocco rejoined on 30 January 2017, despite 9 member states voting against, but 39 supporting. Morocco was re-admitted with the understanding that Western Sahara will remain an AU member.
See also
Defensive wall
List of walls
Wall of Shame
References and notes
External links
Map of Western Sahara, with the location of the wall marked Produced by the United Nations, showing the deployment of the MINURSO mission as of January 2014. Map No. 3691 Rev. 72 United Nations, January 2014 (Colour), Department of Peacekeeping Operations, Cartographic Section
Landmine Monitor, LM Report 2006, Morocco
Landmine Monitor, LM Report 2006, Western Sahara
Landmine Monitor, LM Report 2006, Algeria
Profile – Created by the United Nations MINURSO mission
Walls
Western Sahara conflict
Buildings and structures in Western Sahara
Separation barriers
Borders of Morocco
Borders of Western Sahara
Politics of Morocco
Politics of Western Sahara | Moroccan Western Sahara Wall | [
"Engineering"
] | 1,476 | [
"Separation barriers"
] |
622,503 | https://en.wikipedia.org/wiki/Maturation%20promoting%20factor | Maturation-promoting factor (abbreviated MPF, also called mitosis-promoting factor or M-Phase-promoting factor) is the cyclin–Cdk complex that was discovered first in frog eggs. It stimulates the mitotic and meiotic phases of the cell cycle. MPF promotes the entrance into mitosis (the M phase) from the G2 phase by phosphorylating multiple proteins needed during mitosis. MPF is activated at the end of G2 by a phosphatase, which removes an inhibitory phosphate group added earlier.
The MPF is also called the M phase kinase because of its ability to phosphorylate target proteins at a specific point in the cell cycle and thus control their ability to function.
Discovery
In 1971, two independent teams of researchers (Yoshio Masui and Clement Markert, as well as L. Dennis Smith and Robert Ecker) found that frog oocytes arrested in G2 could be induced to enter M phase by microinjection of cytoplasm from oocytes that had been hormonally stimulated with progesterone. Because the entry of oocytes into meiosis is frequently referred to as oocyte maturation, this cytoplasmic factor was called maturation promoting factor (MPF). Further studies showed, however, that the activity of MPF is not restricted to the entry of oocytes into meiosis. To the contrary, MPF is also present in somatic cells, where it induces entry into M phase of the mitotic cycle.
Evidence that a diffusible factor regulates the entry into mitosis had been previously obtained in 1966 using the slime mold Physarum polycephalum in which the nuclei of the multi-nucleate plasmodial form undergo synchronous mitoses. Fusing plasmodia whose cell cycles were out of phase with each other led to a synchronous mitosis in the next mitotic cycle. This result demonstrated that mitotic entry was controlled by a diffusible cytoplasmic factor and not by a "nuclear clock."
Structure
MPF is composed of two subunits:
Cyclin-dependent kinase 1 (CDK1), the cyclin-dependent kinase subunit. It uses ATP to phosphorylate specific serine and threonine residues of target proteins.
Cyclin, a regulatory subunit. The cyclins are necessary for the kinase subunit to function with the appropriate substrate. The mitotic cyclins can be grouped as cyclins A & B. These cyclins have a nine residue sequence in the N-terminal region called the “destruction box”, which can be recognized by the ubiquitin ligase enzyme which destroys the cyclins when appropriate.
Role in the cell cycle
During G1 and S phase, the CDK1 subunit of MPF is inactive due to an inhibitory enzyme, Wee1. Wee1 phosphorylates the Tyr-15 residue of CDK1, rendering MPF inactive. During the transition of G2 to M phase, cdk1 is de-phosphorylated by CDC25. The CDK1 subunit is now free and can bind to cyclin B, activate MPF, and make the cell enter mitosis. There is also a positive feedback loop that inactivates wee1.
Activation
MPF must be activated in order for the cell to transition from G2 to M phase. There are three amino acid residues responsible for this G2 to M phase transition. The Threonine-161 (Thr-161) on CDK1 must be phosphorylated by a CDK-activating kinase (CAK). CAK only phosphorylates Thr-161 when cyclin B is attached to CDK1.
In addition, two other residues on the CDK1 subunit must be activated by dephosphorylation. CDC25 removes a phosphate from residues Threonine-14 (Thr-14) and Tyrosine-15 (Tyr-15) and adds a hydroxyl group. Cyclin B/CDK1 activates CDC25 resulting in a positive feedback loop.
Overview of functions
Triggers the formation of mitotic spindle through microtubule instability.
Promotes mitosis i.e. chromatin condensation through phosphorylation of condensins.
The three lamins present in the nuclear lamina, lamin A, B & C, are phosphorylated by MPF at serine amino residues. This leads to depolymerisation of the nuclear lamina & breakdown of nuclear envelope into small vesicles.
Causes phosphorylation of GM130, which leads to the fragmentation of the Golgi and the ER.
Targets
The following are affected by MPF.
condensins, which enable chromatin condensation (see prophase)
various microtubule-associated proteins involved in mitotic spindle formation
lamins, interaction contributing to degradation of the nuclear envelope
Histones, H1 and H3
Golgi matrix, to cause fragmentation
Inhibition of myosin
MPF phosphorylates inhibitory sites on myosin early in mitosis. This prevents cytokinesis. When MPF activity falls at anaphase, the inhibitory sites are dephosphorylated and cytokinesis proceeds.
Disassembly by anaphase-promoting complex
MPF is disassembled when anaphase-promoting complex (APC) polyubiquitinates cyclin B, marking it for degradation in a negative feedback loop. In intact cells, cyclin degradation begins shortly after the onset of anaphase (late anaphase), the period of mitosis when sister chromatids are separated and pulled toward opposite spindle poles. As the concentration of Cyclin B/CDK1 increases, the heterodimer promotes APC to polyubiquitinate Cyclin B/CDK1.
References
Protein complexes
Cell cycle | Maturation promoting factor | [
"Biology"
] | 1,268 | [
"Cell cycle",
"Cellular processes"
] |
622,529 | https://en.wikipedia.org/wiki/Logical%20atomism | Logical atomism is a philosophical view that originated in the early 20th century with the development of analytic philosophy. It holds that the world consists of ultimate logical "facts" (or "atoms") that cannot be broken down any further, each of which can be understood independently of other facts.
Its principal exponent was the British philosopher Bertrand Russell. It is also widely held that the early works of his Austrian-born pupil and colleague, Ludwig Wittgenstein, defend a version of logical atomism, though he went on to reject it in his later Philosophical Investigations. Some philosophers in the Vienna Circle were also influenced by logical atomism (particularly Rudolf Carnap, who was deeply sympathetic to some of its philosophical aims, especially in his earlier works). Gustav Bergmann also developed a form of logical atomism that focused on an ideal phenomenalistic language, particularly in his discussions of J.O. Urmson's work on analysis.
The name for this kind of theory was coined in March 1911 by Russell, in a work published in French titled "Le Réalisme analytique" (published in translation as "Analytic Realism" in Volume 6 of The Collected Papers of Bertrand Russell). Russell was developing and responding to what he called "logical holism"—i.e., the belief that the world operates in such a way that no part can be known without the whole being known first. This belief is related to monism, and is associated with the absolute idealism which was dominant in Britain at the time. The criticism of monism seen in the works of Russell and his colleague G. E. Moore can therefore be seen as an extension of their criticism of absolute idealism, particularly as it appeared in the works of F. H. Bradley and J. M. E. McTaggart. Logical atomism can thus be understood as a developed alternative to logical holism, or the "monistic logic" of the absolute idealists.
Origin
As mentioned above, the term "logical atomism" was first coined by Russell in 1911. However, since the paper in which it was first introduced was published only in French during Russell's lifetime, the view was not widely associated with Russell in the English-speaking world until Russell gave a series of lectures in early 1918 under the title "The Philosophy of Logical Atomism". These lectures were subsequently published in 1918 and 1919 in The Monist (Volumes 28 and 29), which at the time was edited by Phillip Jourdain. Russell's ideas as presented in 1918 were also influenced by Wittgenstein, as he explicitly acknowledges in his introductory note. This has partly contributed to the widely-held view that Wittgenstein was also a logical atomist, as has Wittgenstein's atomistic metaphysics developed in the Tractatus.
However, logical atomism has older roots. Russell and Moore broke themselves free from British Idealism in the 1890s. And Russell's break developed along its own logical and mathematical path. His views on philosophy and its methods were heavily influenced by revolutionary nineteenth-century mathematics by figures like Cantor, Dedekind, Peano, and Weierstrass. As he says in his 1901 essay, republished in his 1917 collection Mysticism and Logic, and Other Essays under the title "Mathematics and the Metaphysicians":What is now required is to give the greatest possible development to mathematical logic, to allow to the full the importance of relations, and then to found upon this secure basis a new philosophical logic, which may hope to borrow some of the exactitude and certainty of its mathematical foundation. If this can be successfully accomplished, there is every reason to hope that the near future will be as great an epoch in pure philosophy as the immediate past has been in the principles of mathematics. Great triumphs inspire great hopes; and pure thought may achieve, within our generation, such results as will place our time, in this respect, on a level with the greatest age of Greece. (pg. 96)
With the operations of the calculus of relations as atoms or indefinables (primitive notions), Russell described logicism, or mathematics as logic, in The Principles of Mathematics (1903). Russell thought the revolutionary mathematical work could, through the development of relations, produce a similar revolution in philosophy. This ambition overlays the character of Russell's work from 1900 onward. Russell believes in fact that logical atomism, fully carried out and implemented throughout philosophy, is the realization of his 1901 ambition. As he says in the 1911 piece where he coins the phrase "logical atomism":The true method, in philosophy as in science, should be inductive, meticulous, respectful of detail, and should reject the belief that it is the duty of each philosophy to solve all problems by himself. It is this method which has inspired analytic realism [a.k.a. logical atomism], and it is the only method, if I am not mistaken, with which philosophy will succeed in obtaining results as solid as those obtained in science. (pg. 139)Logical atomism rightly makes logic central to philosophy. In doing so, it makes philosophy scientific, at least in Russell's view. As he says in his 1924 "Logical Atomism":The technical methods of mathematical logic, as developed in this book [Principia Mathematica], seem to me very powerful, and capable of providing a new instrument for the discussion of many problems that have hitherto remained subject to philosophical vagueness.In summary, Russell thought that a moral of the revolutionary work in mathematics was this: equally revolutionary work in philosophy could occur, if we only make logic the essence of philosophizing. This aspiration lies at the origin, and motivates and runs through, logical atomism.
Principles
Russell referred to his atomistic doctrine as contrary to the tier "of the people who more or less follow Hegel" (PLA 178).
The first principle of logical atomism is that the World contains "facts". The facts are complex structures consisting of objects ("particulars"). A fact may be that an object has a property or that it stands in some relation to other objects. In addition, there are judgments ("beliefs"), which are in a relationship to the facts, and by this relationship either true or false.
According to this theory, even ordinary objects of daily life "are apparently complex entities". According to Russell, words like "this" and "that" are used to denote particulars. In contrast, ordinary names such as "Socrates" actually are definitive descriptions. In the analysis of "Plato talks with his pupils", "Plato" needs to be replaced with something like "the man who was the teacher of Aristotle".
In 1905, Russell had already criticized Alexius Meinong, whose theories led to the paradox of the simultaneous existence and non-existence of fictional objects. This theory of descriptions was crucial to logical atomism, as Russell believed that language mirrored reality.
Russell's principles
Bertrand Russell's theory of logical atomism consists of three interworking parts: the atomic proposition, the atomic fact, and the atomic complex. An atomic proposition, also known as an elemental judgement, is a fundamental statement describing a single entity. Russell refers to this entity as an atomic fact, and recognizes a range of elements within each fact that he refers to as particulars and universals. A particular denotes a signifier such as a name, many of which may apply to a single atomic fact, while a universal lends quality to these particulars, e.g. color, shape, disposition. In Russell's Theory of Acquaintance, awareness and thereby knowledge of these particulars and universals comes through sense data. Every system consists of many atomic propositions and their corresponding atomic facts, known together as an atomic complex. In respect to the nomenclature that Russell used for his theory, these complexes are also known as molecular facts in that they possess multiple atoms. Rather than decoding the complex in a top-down manner, logical atomism analyzes its propositions individually before considering their collective effect. According to Russell, the atomic complex is a product of human thought and ideation that combines the various atomic facts in a logical manner.
Russell's perspective on belief proved a point of contention between him and Wittgenstein, causing it to shift throughout his career. In logical atomism, belief is a complex that possesses both true and untrue propositions. Initially, Russell plotted belief as the special relationship between a subject and a complex proposition. Later, he amended this to say that belief lacks a proposition, and instead associates with universals and particulars directly. Here, the link between psychological experience – sense data – and components of logical atomism – universals and particulars – causes a breach in the typical logic of the theory; Russell's logical atomism is in some respects defined by the crossover of metaphysics and analytical philosophy, which characterizes the field of naturalized epistemology.
In his theory of Logical Atomism, Russell posited the highly controversial idea that for every positive fact exists a parallel negative fact: a fact that is untrue. The correspondence theory maintains that every atomic proposition coordinates with exactly one atomic fact, and that all atomic facts exist. The Theory of Acquaintance says that for any given statement taking the form of an atomic proposition, we must be familiar with the assertion it makes. For example, in the positive statement, "the leaf is green," we must be acquainted with the atomic fact that the leaf is green, and we know that this statement corresponds to exactly this one fact. Along this same line, the complementary negative statement, "the leaf is not green," is clearly false given what we know about the color of the leaf, but our ability to form a statement of this nature means that a corresponding fact must exist. Regardless of whether the second statement is or isn't true, the connection between its proposition and a fact must itself be true. One central doctrine of Logical Atomism, known as the Logically Perfect Language Principle, enables this conclusion. This principle establishes that everything exists as atomic proposition and fact, and that all language signifies reality. In Russell's viewpoint, this necessitates the negative fact, whereas Wittgenstein maintained the more conventional Principle of Bivalence, in which the states "P" and "Not (P)" cannot coexist.
Wittgenstein's principles
In his Tractatus Logico-Philosophicus, Ludwig Wittgenstein explains his version of logical atomism as the relationship between proposition, state of affairs, object, and complex, often referred to as "Picture theory". In view of Russell's version, the propositions are congruent in that they are both clear statements about an atomic entity. Every atomic proposition is constructed from "names" that correspond to "objects", and the interaction of these objects generates "states of affairs," which are analogous to what Russell called atomic facts. Where Russell identifies both particulars and universals, Wittgenstein amalgamates these into objects for the sake of protecting the truth-independence of his propositions; a self-contained state of affairs defines each proposition, and the truth of a proposition cannot be proven by the sharing or exclusion of objects between propositions. In Russell's work, his concept of universals and particulars denies truth-independence, as each universal accounts for a specific set of particulars, and the exact matching of any two sets implies equality, difference implies inequality, and this acts as a qualifier of truth. In Wittgenstein's theory, an atomic complex is a layered proposition subsuming many atomic propositions, each representing its own state of affairs.
Wittgenstein's handling of belief was dismissive and reflects his abstention from the epistemology that concerned Russell. Because his theory dealt with understanding the nature of reality, and because any item or process of the mind barring positive fact, i.e. something absolute and without interpretation, may become altered and thus divorced from reality, belief exists as a sign of reality but not reality itself. Wittgenstein was decidedly skeptical of epistemology, which tends to value unifying metaphysical ideas while depreciating the casewise and methodological inspection of philosophy that dominates his Tractatus Logico-Philosophicus. Furthermore, Wittgenstein concerned himself with defining the exact correspondence between language and reality wherein any explanation of reality that defies or overburdens these semantic structures, namely metaphysics, becomes unhinged. Wittgenstein's work bears the exact philosophical determinants that he openly dismissed, hence his later abandonment of this theory altogether.
Differences between Russell's and Wittgenstein's atomism
At the time Russell delivered his lectures on logical atomism, he had lost contact with Wittgenstein. After World War I, Russell met with Wittgenstein again and helped him publish the Tractatus Logico Philosophicus, Wittgenstein's own version of Logical Atomism.
Although Wittgenstein did not use the expression Logical Atomism, the book espouses most of Russell's logical atomism except for Russell's Theory of Knowledge (T 5.4 and 5.5541). By 1918 Russell had moved away from this position. Nevertheless, the Tractatus differed so fundamentally from the philosophy of Russell that Wittgenstein always believed that Russell misunderstood the work.
The differences relate to many details, but the crucial difference is in a fundamentally different understanding of the task of philosophy. Wittgenstein believed that the task of philosophy was to clean up linguistic mistakes. Russell was ultimately concerned with establishing sound epistemological foundations. Epistemological questions such as how practical knowledge is possible did not interest Wittgenstein. Wittgenstein investigated the "limits of the world" and later on meaning. For Wittgenstein, metaphysics and ethics were nonsensical - as they did not "speak of facts" - though he did not mean to devalue their importance in life by describing them in this way. Russell, on the other hand, believed that these subjects, particularly ethics, though belonging not to philosophy nor science and possessing an inferior epistemological foundation, were not only of certain interest, but also meaningful.
Influence and decline
The immediate effect of the Tractatus was enormous, particularly by the reception it received by the Vienna Circle. However, it is now claimed by many contemporary analytic philosophers, that the Vienna Circle misunderstood certain sections of the Tractatus. The indirect effect of the method, however, was perhaps even greater long-term, especially on logical positivism. Wittgenstein eventually rejected the "atomism" of logical atomism in his posthumously published book, Philosophical Investigations, and it is still debated whether or not he ever held the wide-ranging version that Russell expounded in his 1918 logical atomism lectures. Russell, on the other hand, never abandoned logical atomism. In his 1959 My Philosophical Development, Russell said that his philosophy evolved and changed many times in his life, but he described all these changes as an "evolution" stemming from his original "revolution" into logical atomism in 1899-1900: There is one major division in my philosophical work: in the years 1899-1900, I adopted the philosophy of logical atomism and the technique of Peano in mathematical logic. This was so great a revolution as to make my previous work, except such as was purely mathematical, irrelevant to everything that I did later. The change in these years was a revolution; subsequent changes have been of the nature of an evolution. (Chapter 1: "Introductory Outline")Even into the 1960s, Russell claimed that he "rather avoided labels" in describing his views—with the exception of "logical atomism."
Philosophers such as Willard Van Orman Quine, Hubert Dreyfus and Richard Rorty went on to adopt logical holism.
See also
Logical positivism
Philosophy of language
Logic
Ordinary language philosophy
Theory of descriptions
"On Denoting"
Definitions of philosophy
Notes
References
External links
Peter Schulte: Bertrand Russell: Philosophie des Logischen Atomismus
Kevin Klement: Russell's Logical Atomism
Ian Proops: Wittgenstein's Logical Atomism
Jeff Speaks: Russell on logical constructions and logical atomism, McGill University 2004
Logical Atomism Overview:
Lecture on Bertrand Russell at Wheaton College:
Lecture on Ludwig Wittgenstein at Wheaton College:
Bertrand Russell
Theories of language
Theories of deduction
Reductionism | Logical atomism | [
"Mathematics"
] | 3,402 | [
"Theories of deduction"
] |
622,535 | https://en.wikipedia.org/wiki/Frank%20Thring | Francis William Thring IV (11 May 1926 – 29 December 1994) was an Australian character actor in radio, stage, television and film; as well as a theatre director. His early career started in London in theatre productions, before he starred in Hollywood film, where he became best known for roles in Ben-Hur in 1959 and King of Kings in 1961. He was known for always wearing black and styling his home in black decor.
Early life
Thring was born in Melbourne. Although sometimes referred to as Frank Thring Jr. because of his well-known father, F. W. Thring, he was actually Francis William Thring (or William Francis Thring) IV. His forebears were Francis William Thring (1812–1887), Francis William Thring (known as William Thring) (1858–1920); William Frank Thring, known as Francis William Thring or F. W. Thring, (1882–1936).
Thring was the son of F. W. Thring and Olive (née Kreitmeyer), and was educated at the Melbourne Grammar School. His father was the head of the theatrical firm J. C. Williamson's in the 1920s, and subsequently founded the theatre film production studio Efftee Studios in the 1930s, in Melbourne, Australia. He has been anachronistically claimed to have been the inventor of the clapperboard. Thring Sr. was also a noted film producer (The Sentimental Bloke), and partner in the nationwide Australian theatre circuit Hoyts. Thring Sr. died in July 1936 at the age of 53, when Frank Jr. was 10 years old. His second wife (Frank Jr.'s mother) inherited all the businesses. Frank said his earliest memory is of his mother standing on a stepladder in the foyer of the Regent Theatre in Melbourne, and arranging gladioli in the vases attached to the pillars.
Career
His career spanned more than 45 years, much of it spent alternating between stage, film and television. Perhaps his most famous roles were that of Pontius Pilate in Ben-Hur (1959) and Herod Antipas in King of Kings (1961).
Radio
Thring's family operated Melbourne radio station 3XY, from the opening of the station in 1935. He commenced working at 3XY as both a thespian and radio announcer in 1941, as a young man of 15. His numerous jobs at the microphone included being Uncle Frankie in the children's session. When Thring Sr died in 1936 (see above), Thring Jr.'s mother inherited the businesses. However, Thring Jr. incorrectly told people that he owned 3XY.
Stage
He began acting in professional stage roles after his discharge from the Royal Australian Air Force in 1945. He was memorable as Herod in Irene Mitchell's production of Oscar Wilde's Salome at Melbourne's Arrow Theatre in 1951, and made his British theatrical debut in the same part in 1954. Two years later, he played Sir Lancelot Spratt in Doctor in the House, which ran for 240 performances at the Victoria Palace in London.
He was Saturninus in the Royal Shakespeare Theatre production of Titus Andronicus with Laurence Olivier, Vivien Leigh and Anthony Quayle. He also played Captain Hook opposite Peggy Cummins' Peter Pan. Among his other acclaimed stage roles were George Bernard Shaw's Arms and the Man, Captain Ahab in Orson Welles's Moby-Dick, Falstaff in Henry IV, Part 1, and Bertolt Brecht's Life of Galileo. Another stage role was in the musical Robert and Elizabeth opposite June Bronhill and Denis Quilley.
Later in life he returned to the stage playing the butler in the Melbourne Theatre Company's production of The Importance of Being Earnest in 1988. His final stage appearance was in Humorists Read the Humorists at the Melbourne International Comedy Festival in 1992.
Film
Thring first appeared on screen as a child in the 1932 Australian film The Sentimental Bloke, directed by his father F. W. Thring. One of Thring's most well-known screen roles was as Pontius Pilate in Ben-Hur (1959). He also appeared as Al-Kadir, Emir of Valencia in El Cid (1961). Thring was also awarded the Erik Kuttner Award for Acting (1965). In addition to these roles, Thring played a barrister in The Case of Mrs. Loring (1958), the usurping king Aella (Ælla of Northumbria) in The Vikings (1958) and Herod Antipas in King of Kings (1961). Thring is the only actor to portray on film both of the historical figures directly responsible for authorizing the crucifixion of Christ according to the Gospels. He played numerous glowering bad guys in Hollywood epics of the 1950s and 1960s.
Back in Australia, he starred opposite James Mason and a young Helen Mirren in Michael Powell's film Age of Consent (1969), and appeared in two biographical films about famous bushrangers: Ned Kelly (1970) and Mad Dog Morgan (1976). He played suave gangsters in Alvin Rides Again (1974) and The Man from Hong Kong (1975). In his later years, his screen roles included the devilish Collector in Mad Max Beyond Thunderdome (1985), and a comedic role as an Alfred Hitchcock-like film director in the horror movie spoof, Howling III (1987).
Television
Thring's television credits include the Australian miniseries Against the Wind and Bodyline. He was also the recurring villain Doctor Stark who would use mischievous means in attempts to steal Skippy and other animals out of Waratah National Park in several episodes of Skippy the Bush Kangaroo.
He also acted in commercials, particularly one in which he would glare at the camera saying "You do have your television licence. Don't you?".
He had the lead roles in the 1959 ABC TV play Treason, and the 1962 ABC play Light Me A Lucifer.
Personal life
Off-screen, Thring was known for his flamboyant, often waspish, persona. He was featured in numerous TV commercials and guest-starring roles on popular weekly series, variety programs and quiz shows, often dressed in black funereal attire and other sinister costumes - the interior of his house was featured in an Australian TV program and the walls were also black. However, his acting career was interrupted by bouts of alcoholism and periods of ill health.
Thring was appointed 1982 King of Moomba, "this doyenne [sic] of film and theatre looked nothing short of majestic in his regal garb and riding on a thespian-inspired float".
Thring was briefly married to actress Joan Cunliffe during the 1950s. The marriage ended in divorce. Cunliffe lived in London and was manager of both Rudolf Nureyev and Margot Fonteyn. Thring was flamboyantly gay, but he wanted children and was greatly distressed when his marriage ended without issue.
On 29 December 1994, Thring died from oesophageal cancer, aged 68. He was cremated and his ashes scattered off the coast of Queenscliff, Victoria. A celebration of his life was held at the Victorian Arts Centre, Melbourne, in 1995.
Filmography
The Vikings (1958) – Aella
A Question of Adultery (1958) – Mr. Stanley
The Flaming Sword (1958) – Gar
Dick and the Duchess – "The Courtroom" (1958 TV series) – Wembler
Treason (1959) – Karl Albrecht
Ben Hur (1959) – Pontius Pilate
This Is Television (1960) - as himself
King of Kings (1961) – Herod Antipas
El Cid (1961) – Al Kadir
Light Me a Lucifer (1962, TV Movie) – The Devil.
Photo Finish (1965 TV movie) – Sam Kinsale
Hey You! – "The Soup Kitchen" (1967 TV series) – Mr Goodly
Australian Playhouse – "The Heat's On" (1967 TV series) – Mr Paisley
Skippy the Bush Kangaroo – "Double Trouble"; "Trapped"; "Long Way Home" (1967 TV series) – Dr Stark
Salome (1968) – Herod
Age of Consent (1969) – Godfrey
Delta – The Initiates (1969 TV series) – Dr Spencer
The Link Men – "See Amsterdam and Die" (1970 TV series) – Bruce Crane
Ned Kelly (1970) – Judge Barry
The Man Who Shot the Albatross (1970 TV Movie)
Alvin Rides Again (1974) – Fingers
The Cherry Orchard (1974 TV movie)
The Man from Hong Kong (1975) – Willard
Mad Dog Morgan (1976) – Superintendent Cobham
Up the Convicts (1976 TV series) – Sgt Bastion
The Importance of Keeping Perfectly Still (1977 short film)
Against the Wind – "The Seeds of Fire"; "The Wild Goose" (1978 TV mini-series) – Magistrate
Outbreak of Love (1981 TV mini-series) – Arthur Langton
At Last... Bullamakanka: The Motion Picture (1983) – TV Producer
Eureka Stockade (1984 TV mini-series) – Judge
Bodyline – Episode 1.1 (1984 TV mini-series) – Lord Harris
Mad Max Beyond Thunderdome (1985) – The Collector
Death of a Soldier (1986) – Religious speaker
The Steam-Driven Adventures of Riverboat Bill (1986) – voice
Howling III (1987) – Jack Citron
The Devil in Evening Dress (1987) – Host
Mission: Impossible – "Bayou" (1989 TV series) – Jake Morgan
Hercules Returns (1993) – Zeus (voice) (final film role)
Further reading
The Dictionary of Performing Arts in Australia – Theatre . Film . Radio . Television – Volume 1 – Ann Atkinson, Linsay Knight, Margaret McPhee – Allen & Unwin Pty. Ltd., 1996.
The Australian Film and Television Companion – compiled by Tony Harrison – Simon & Schuster Australia, 1994.
The Two Frank Thrings – Peter Fitzpatrick – Monash University Publishing, 2012.
Notes
References
External links
The Frank Thring Collection , at the Performing Arts Collection, Arts Centre Melbourne
Frank Thring at liveperformance
1926 births
1994 deaths
Australian male film actors
Australian male television actors
Male actors from Melbourne
People educated at Melbourne Grammar School
Australian gay actors
Deaths from cancer in Victoria (state)
20th-century Australian male actors
Australian people of German descent
Royal Australian Air Force personnel of World War II
20th-century Australian LGBTQ people
Eccentricity (behavior)
Military personnel from Melbourne | Frank Thring | [
"Biology"
] | 2,166 | [
"Behavior",
"Human behavior",
"Eccentricity (behavior)"
] |
622,571 | https://en.wikipedia.org/wiki/Ubiquitin%20ligase | A ubiquitin ligase (also called an E3 ubiquitin ligase) is a protein that recruits an E2 ubiquitin-conjugating enzyme that has been loaded with ubiquitin, recognizes a protein substrate, and assists or directly catalyzes the transfer of ubiquitin from the E2 to the protein substrate. In simple and more general terms, the ligase enables movement of ubiquitin from a ubiquitin carrier to another protein (the substrate) by some mechanism. The ubiquitin, once it reaches its destination, ends up being attached by an isopeptide bond to a lysine residue, which is part of the target protein. E3 ligases interact with both the target protein and the E2 enzyme, and so impart substrate specificity to the E2. Commonly, E3s polyubiquitinate their substrate with Lys48-linked chains of ubiquitin, targeting the substrate for destruction by the proteasome. However, many other types of linkages are possible and alter a protein's activity, interactions, or localization. Ubiquitination by E3 ligases regulates diverse areas such as cell trafficking, DNA repair, and signaling and is of profound importance in cell biology. E3 ligases are also key players in cell cycle control, mediating the degradation of cyclins, as well as cyclin dependent kinase inhibitor proteins. The human genome encodes over 600 putative E3 ligases, allowing for tremendous diversity in substrates.
Ubiquitination system
The ubiquitin ligase is referred to as an E3, and operates in conjunction with an E1 ubiquitin-activating enzyme and an E2 ubiquitin-conjugating enzyme. There is one major E1 enzyme, shared by all ubiquitin ligases, that uses ATP to activate ubiquitin for conjugation and transfers it to an E2 enzyme. The E2 enzyme interacts with a specific E3 partner and transfers the ubiquitin to the target protein. The E3, which may be a multi-protein complex, is, in general, responsible for targeting ubiquitination to specific substrate proteins.
The ubiquitylation reaction proceeds in three or four steps depending on the mechanism of action of the E3 ubiquitin ligase. In the conserved first step, an E1 cysteine residue attacks the ATP-activated C-terminal glycine on ubiquitin, resulting in a thioester Ub-S-E1 complex. The energy from ATP and diphosphate hydrolysis drives the formation of this reactive thioester, and subsequent steps are thermoneutral. Next, a transthiolation reaction occurs, in which an E2 cysteine residue attacks and replaces the E1. HECT domain type E3 ligases will have one more transthiolation reaction to transfer the ubiquitin molecule onto the E3, whereas the much more common RING finger domain type ligases transfer ubiquitin directly from E2 to the substrate. The final step in the first ubiquitylation event is an attack from the target protein lysine amine group, which will remove the cysteine, and form a stable isopeptide bond. One notable exception to this is p21 protein, which appears to be ubiquitylated using its N-terminal amine, thus forming a peptide bond with ubiquitin.
Ubiquitin ligase families
Humans have an estimated 500-1000 E3 ligases, which impart substrate specificity onto the E1 and E2. The E3 ligases are classified into four families: HECT, RING-finger, U-box, and PHD-finger. The RING-finger E3 ligases are the largest family and contain ligases such as the anaphase-promoting complex (APC) and the SCF complex (Skp1-Cullin-F-box protein complex). SCF complexes consist of four proteins: Rbx1, Cul1, Skp1, which are invariant among SCF complexes, and an F-box protein, which varies. Around 70 human F-box proteins have been identified. F-box proteins contain an F-box, which binds the rest of the SCF complex, and a substrate binding domain, which gives the E3 its substrate specificity.
Mono- and poly-ubiquitylation
Ubiquitin signaling relies on the diversity of ubiquitin tags for the specificity of its message. A protein can be tagged with a single ubiquitin molecule (monoubiquitylation), or variety of different chains of ubiquitin molecules (polyubiquitylation). E3 ubiquitin ligases catalyze polyubiquitination events much in the same way as the single ubiquitylation mechanism, using instead a lysine residue from a ubiquitin molecule currently attached to substrate protein to attack the C-terminus of a new ubiquitin molecule. For example, a common 4-ubiquitin tag, linked through the lysine at position 48 (K48) recruits the tagged protein to the proteasome, and subsequent degradation. However, all seven of the ubiquitin lysine residues (K6, K11, K27, K29, K33, K48, and K63), as well as the N-terminal methionine are used in chains in vivo.
Monoubiquitination has been linked to membrane protein endocytosis pathways. For example, phosphorylation of the Tyrosine at position 1045 in the Epidermal Growth Factor Receptor (EGFR) can recruit the RING type E3 ligase c-Cbl, via an SH2 domain. C-Cbl monoubiquitylates EGFR, signaling for its internalization and trafficking to the lysosome.
Monoubiquitination also can regulate cytosolic protein localization. For example, the E3 ligase MDM2 ubiquitylates p53 either for degradation (K48 polyubiquitin chain), or for nuclear export (monoubiquitylation). These events occur in a concentration dependent fashion, suggesting that modulating E3 ligase concentration is a cellular regulatory strategy for controlling protein homeostasis and localization.
Substrate recognition
Ubiquitin ligases are the final, and potentially the most important determinant of substrate specificity in ubiquitination of proteins. The ligases must simultaneously distinguish their protein substrate from thousands of other proteins in the cell, and from other (ubiquitination-inactive) forms of the same protein. This can be achieved by different mechanisms, most of which involve recognition of degrons: specific short amino acid sequences or chemical motifs on the substrate.
N-degrons
Proteolytic cleavage can lead to exposure of residues at the N-terminus of a protein. According to the N-end rule, different N-terminal amino acids (or N-degrons) are recognized to a different extent by their appropriate ubiquitin ligase (N-recognin), influencing the half-life of the protein. For instance, positively charged (Arg, Lys, His) and bulky hydrophobic amino acids (Phe, Trp, Tyr, Leu, Ile) are recognized preferentially and thus considered destabilizing degrons since they allow faster degradation of their proteins.
Phosphodegrons
A degron can be converted into its active form by a post-translational modification such as phosphorylation of a tyrosine, serine or threonine residue. In this case, the ubiquitin ligase exclusively recognizes the phosphorylated version of the substrate due to stabilization within the binding site. For example, FBW7, the F-box substrate recognition unit of an SCFFBW7ubiquitin ligase, stabilizes a phosphorylated substrate by hydrogen binding its arginine residues to the phosphate, as shown in the figure to the right. In absence of the phosphate, residues of FBW7 repel the substrate.
Oxygen and small molecule dependent degrons
The presence of oxygen or other small molecules can influence degron recognition. The von Hippel-Lindau (VHL) protein (substrate recognition part of a specific E3 ligase), for instance, recognizes the hypoxia-inducible factor alpha (HIF-α) only under normal oxygen conditions, when its proline is hydroxylated. Under hypoxia, on the other hand, HIF-a is not hydroxylated, evades ubiquitination and thus operates in the cell at higher concentrations which can initiate transcriptional response to hypoxia. Another example of small molecule control of protein degradation is phytohormone auxin in plants. Auxin binds to TIR1 (the substrate recognition domain of SCFTIR1ubiquitin ligase) increasing the affinity of TIR1 for its substrates (transcriptional repressors: Aux/IAA), and promoting their degradation.
Misfolded and sugar degrons
In addition to recognizing amino acids, ubiquitin ligases can also detect unusual features on substrates that serve as signals for their destruction. For example, San1 (Sir antagonist 1), a nuclear protein quality control in yeast, has a disordered substrate binding domain, which allows it to bind to hydrophobic domains of misfolded proteins. Misfolded or excess unassembled glycoproteins of the ERAD pathway, on the other hand, are recognized by Fbs1 and Fbs2, mammalian F-box proteins of E3 ligases SCFFbs1and SCFFbs2. These recognition domains have small hydrophobic pockets allowing them to bind high-mannose containing glycans.
Structural motifs
In addition to linear degrons, the E3 ligase can in some cases also recognize structural motifs on the substrate. In this case, the 3D motif can allow the substrate to directly relate its biochemical function to ubiquitination. This relation can be demonstrated with TRF1 protein (regulator of human telomere length), which is recognized by its corresponding E3 ligase (FBXO4) via an intermolecular beta sheet interaction. TRF1 cannot be ubiquinated while telomere bound, likely because the same TRF1 domain that binds to its E3 ligase also binds to telomeres.
Disease relevance
E3 ubiquitin ligases regulate homeostasis, cell cycle, and DNA repair pathways, and as a result, a number of these proteins are involved in a variety of cancers, including famously MDM2, BRCA1, and Von Hippel-Lindau tumor suppressor. For example, a mutation of MDM2 has been found in stomach cancer, renal cell carcinoma, and liver cancer (amongst others) to deregulate MDM2 concentrations by increasing its promoter’s affinity for the Sp1 transcription factor, causing increased transcription of MDM2 mRNA. Several proteomics-based experimental techniques are available for identifying E3 ubiquitin ligase-substrate pairs, such as proximity-dependent biotin identification (BioID), ubiquitin ligase-substrate trapping, and tandem ubiquitin-binding entities (TUBEs).
Examples
A RING (Really Interesting New Gene) domain binds the E2 conjugase and might be found to mediate enzymatic activity in the E2-E3 complex
An F-box domain (as in the SCF complex) binds the ubiquitinated substrate. (e.g., Cdc 4, which binds the target protein Sic1; Grr1, which binds Cln).
A HECT domain, which is involved in the transfer of ubiquitin from the E2 to the substrate.
Individual E3 ubiquitin ligases
E3A
mdm2
Anaphase-promoting complex (APC)
UBR5 (EDD1)
SOCS/ BC-box/ eloBC/ CUL5/ RING
LNXp80
CBX4, CBLL1
HACE1
HECTD1, HECTD2, HECTD3, HECTD4
HECW1, HECW2
HERC1, HERC2, HERC3, HERC4, HERC5, HERC6
HUWE1, ITCH
NEDD4, NEDD4L
PPIL2
PRPF19
PIAS1, PIAS2, PIAS3, PIAS4
RANBP2
RNF4, RNF167
RBX1
SMURF1, SMURF2
STUB1
TOPORS
TRIP12
UBE3A, UBE3B, UBE3C, UBE3D
UBE4A, UBE4B
UBOX5
UBR5
VHL
WWP1, WWP2
Parkin
MKRN1
See also
ERAD
Ubiquitin
Ubiquitin-activating enzyme
Ubiquitin-conjugating enzyme
References
External links
Quips article describing E3 Ligase function at PDBe
EC 6.3
Post-translational modification | Ubiquitin ligase | [
"Chemistry"
] | 2,810 | [
"Post-translational modification",
"Gene expression",
"Biochemical reactions"
] |
622,714 | https://en.wikipedia.org/wiki/Brillouin%20scattering | In electromagnetism, Brillouin scattering (also known as Brillouin light scattering or BLS), named after Léon Brillouin, refers to the interaction of light with the material waves in a medium (e.g. electrostriction and magnetostriction). It is mediated by the refractive index dependence on the material properties of the medium; as described in optics, the index of refraction of a transparent material changes under deformation (compression-distension or shear-skewing).
The result of the interaction between the light-wave and the carrier-deformation wave is that a fraction of the transmitted light-wave changes its momentum (thus its frequency and energy) in preferential directions, as if by diffraction caused by an oscillating 3-dimensional diffraction grating.
If the medium is a solid crystal, a macromolecular chain condensate or a viscous liquid or gas, then the low frequency atomic-chain-deformation waves within the transmitting medium (not the transmitted electro-magnetic wave) in the carrier (represented as a quasiparticle) could be for example:
mass oscillation (acoustic) modes (called phonons);
charge displacement modes (in dielectrics, called polarons);
magnetic spin oscillation modes (in magnetic materials, called magnons).
Mechanism
From the perspective of solid state physics, Brillouin scattering is an interaction between an electromagnetic wave and one of the three above-mentioned crystalline lattice waves (e.g. electrostriction and magnetostriction). The scattering is inelastic i.e. the photon may lose energy (Stokes process) and in the process create one of the three quasiparticle types (phonon, polariton, magnon) or it may gain energy (anti-Stokes process) by absorbing one of those quasiparticle types. Such a shift in photon energy, corresponding to a Brillouin shift in frequency, is equal to the energy of the released or absorbed quasiparticle. Thus, Brillouin scattering can be used to measure the energies, wavelengths and frequencies of various atomic chain oscillation types ('quasiparticles'). To measure a Brillouin shift a commonly employed device called the Brillouin spectrometer is used, the design of which is derived from a Fabry–Pérot interferometer. Alternatively, high-speed photodiodes, such as those recovered from inexpensive 25-gigabit Ethernet optical transceivers, may be used in combination with a software-defined radio or RF spectrum analyzer.
Contrast with Rayleigh scattering
Rayleigh scattering, too, can be considered to be due to fluctuations in the density, composition and orientation of molecules within the transmitting medium, and hence of its refraction index, in small volumes of matter (particularly in gases or liquids). The difference is that Rayleigh scattering involves only the random and incoherent thermal fluctuations, in contrast with the correlated, periodic fluctuations (phonons) that cause Brillouin scattering. Moreover, Rayleigh scattering is elastic in that no energy is lost or gained.
Contrast with Raman scattering
Raman scattering is another phenomenon that involves inelastic scattering of light caused by the vibrational properties of matter. The detected range of frequency shifts and other effects are very different compared to Brillouin scattering. In Raman scattering, photons are scattered by the effect of vibrational and rotational transitions in the bonds between first-order neighboring atoms, while Brillouin scattering results from the scattering of photons caused by large scale, low-frequency phonons. The effects of the two phenomena provide very different information about the sample: Raman spectroscopy can be used to determine the transmitting medium's chemical composition and molecular structure, while Brillouin scattering can be used to measure the material's properties on a larger scale – such as its elastic behavior. The frequency shifts from Brillouin scattering, a technique known as Brillouin spectroscopy, are detected with an interferometer while Raman scattering uses either an interferometer or a dispersive (grating) spectrometer.
Stimulated Brillouin scattering
For intense beams of light (e.g. laser) traveling in a medium or in a waveguide, such as an optical fiber, the variations in the electric field of the beam itself may induce acoustic vibrations in the medium via electrostriction or radiation pressure. The beam may display Brillouin scattering as a result of those vibrations, usually in the direction opposite the incoming beam, a phenomenon known as stimulated Brillouin scattering (SBS). For liquids and gases, the frequency shifts typically created are of the order of 1–10 GHz resulting in wavelength shifts of ~1–10 pm in the visible light. Stimulated Brillouin scattering is one effect by which optical phase conjugation can take place.
Discovery
Inelastic scattering of light caused by acoustic phonons was first predicted by Léon Brillouin in 1914
. Leonid Mandelstam is believed to have recognised the possibility of such scattering as early as 1918, but he published his idea only in 1926.
In order to credit Mandelstam, the effect is also called Brillouin-Mandelstam scattering (BMS). Other commonly used names are Brillouin light scattering (BLS) and Brillouin-Mandelstam light scattering (BMLS).
The process of stimulated Brillouin scattering (SBS) was first observed by Chiao et al. in 1964. The optical phase conjugation aspect of the SBS process was discovered by Boris Yakovlevich Zeldovich et al. in 1972.
Fiber optic sensing
Brillouin scattering can also be employed to sense mechanical strain and temperature in optical fibers.
See also
Brillouin spectroscopy
Scattering
Raman scattering
Nonlinear optics
References
Notes
Sources
L.I. Mandelstam, Zh. Russ. Fiz-Khim., Ova. 58, 381 (1926).
B.Ya. Zel’dovich, V.I.Popovichev, V.V.Ragulskii and F.S.Faisullov, "Connection between the wavefronts of the reflected and exciting light in stimulated Mandel’shtam Brillouin scattering," Sov. Phys. JETP, 15, 109 (1972)
External links
CIMIT Center for Integration of Medicine and Innovative Technology
Brillouin scattering in the Encyclopedia of Laser Physics and Technology
Surface Brillouin Scattering, U. Hawaii
List of labs performing Brillouin scattering measurements (source BS Lab in ICMM-CSIC)
Scattering, absorption and radiative transfer (optics)
Scattering
Fiber-optic communications | Brillouin scattering | [
"Physics",
"Chemistry",
"Materials_science"
] | 1,387 | [
" absorption and radiative transfer (optics)",
"Scattering",
"Condensed matter physics",
"Particle physics",
"Nuclear physics"
] |
622,805 | https://en.wikipedia.org/wiki/Navigational%20database | A navigational database is a type of database in which records or objects are found primarily by following references from other objects. The term was popularized by the title of Charles Bachman's 1973 Turing Award paper, The Programmer as Navigator. This paper emphasized the fact that the new disk-based database systems allowed the programmer to choose arbitrary navigational routes following relationships from record to record, contrasting this with the constraints of earlier magnetic-tape and punched card systems where data access was strictly sequential.
One of the earliest navigational databases was Integrated Data Store (IDS), which was developed by Bachman for General Electric in the 1960s. IDS became the basis for the CODASYL database model in 1969.
Although Bachman described the concept of navigation in abstract terms, the idea of navigational access came to be associated strongly with the procedural design of the CODASYL Data Manipulation Language. Writing in 1982, for example, Tsichritzis and Lochovsky state that "The notion of currency is central to the concept of navigation." By the notion of currency, they refer to the idea that a program maintains (explicitly or implicitly) a current position in any sequence of records that it is processing, and that operations such as GET NEXT and GET PRIOR retrieve records relative to this current position, while also changing the current position to the record that is retrieved.
Navigational database programming thus came to be seen as intrinsically procedural; and moreover to depend on the maintenance of an implicit set of global variables (currency indicators) holding the current state. As such, the approach was seen as diametrically opposed to the declarative programming style used by the relational model. The declarative nature of relational languages such as SQL offered better programmer productivity and a higher level of data independence (that is, the ability of programs to continue working as the database structure evolves.) Navigational interfaces, as a result, were gradually eclipsed during the 1980s by declarative query languages.
During the 1990s it started becoming clear that for certain applications handling complex data (for example, spatial databases and engineering databases), the relational calculus had limitations. At that time, a reappraisal of the entire database market began, with several companies describing the new systems using the marketing term NoSQL. Many of these systems introduced data manipulation languages which, while far removed from the CODASYL DML with its currency indicators, could be understood as implementing Bachman's "navigational" vision. Some of these languages are procedural; others (such as XPath) are entirely declarative. Offshoots of the navigational concept, such as the graph database, found new uses in modern transaction processing workloads.
Description
Navigational access is traditionally associated with the network model and hierarchical model of database, and conventionally describes data manipulation APIs in which records (or objects) are processed one at a time, iteratively. The essential characteristic as described by Bachman, however, is finding records by virtue of their relationship to other records: so an interface can still be navigational if it has set-oriented features. From this viewpoint, the key difference between navigational data manipulation languages and relational languages is the use of explicit named relationships rather than value-based joins: for department with name="Sales", find all employees in set department-employees versus find employees, departments where employee.department-code = department.code and department.name="Sales".
In practice, however, most navigational APIs have been procedural: the above query would be executed using procedural logic along the lines of the following pseudo-code:
get department with name='Sales'
get first employee in set department-employees
until end-of-set do {
get next employee in set department-employees
process employee
}
On this viewpoint, the key difference between navigational APIs and the relational model (implemented in relational databases) is that relational APIs use "declarative" or logic programming techniques that ask the system what to fetch, while navigational APIs instruct the system in a sequence of steps how to reach the required records.
Most criticisms of navigational APIs fall into one of two categories:
Usability: application code quickly becomes unreadable and difficult to debug
Data independence: application code needs to change whenever the data structure changes
For many years the primary defence of navigational APIs was performance. Database systems that support navigational APIs often use internal storage structures that contain physical links or pointers from one record to another. While such structures may allow very efficient navigation, they have disadvantages because it becomes difficult to reorganize the physical placement of data. It is quite possible to implement navigational APIs without low-level pointer chasing (Bachman's paper envisaged logical relationships being implemented just as in relational systems, using primary keys and foreign keys), so the two ideas should not be conflated. But without the performance benefits of low-level pointers, navigational APIs become harder to justify.
Hierarchical models often construct primary keys for records by concatenating the keys that appear at each level in the hierarchy. Such composite identifiers are found in computer file names (/usr/david/docs/index.txt), in URIs, in the Dewey decimal system, and for that matter in postal addresses. Such a composite key can be considered as representing a navigational path to a record; but equally, it can be considered as a simple primary key allowing associative access.
As relational systems came to prominence in the 1980s, navigational APIs (and in particular, procedural APIs) were criticized and fell out of favour. The 1990s, however, brought a new wave of object-oriented databases that often provided both declarative and procedural interfaces. One explanation for this is that they were often used to represent graph-structured information (for example spatial data and engineering data) where access is inherently recursive: the mathematics underpinning SQL (specifically, first-order predicate calculus) does not have sufficient power to support recursive queries, even those as simple as a transitive closure.
A current example of a popular navigational API can be found in the Document Object Model (DOM) often used in web browsers and closely associated with JavaScript. The DOM is essentially an in-memory hierarchical database with an API that is both procedural and navigational. By contrast, the same data (XML or HTML) can be accessed using XPath, which can be categorized as declarative and navigational: data is accessed by following relationships, but the calling program does not issue a sequence of instructions to be followed in order. Languages such as SPARQL used to retrieve Linked Data from the Semantic Web are also simultaneously declarative and navigational.
Examples
IBM Information Management System
IDMS
See also
CODASYL
Graph database
Network database
Object database
Relational database
References
External links
DB-Engines Ranking of Navigational DBMS by popularity, updated by month
Data management
Types of databases | Navigational database | [
"Technology"
] | 1,431 | [
"Data management",
"Data"
] |
622,844 | https://en.wikipedia.org/wiki/Homogeneous%20function | In mathematics, a homogeneous function is a function of several variables such that the following holds: If each of the function's arguments is multiplied by the same scalar, then the function's value is multiplied by some power of this scalar; the power is called the degree of homogeneity, or simply the degree. That is, if is an integer, a function of variables is homogeneous of degree if
for every and This is also referred to a th-degree or th-order homogeneous function.
For example, a homogeneous polynomial of degree defines a homogeneous function of degree .
The above definition extends to functions whose domain and codomain are vector spaces over a field : a function between two -vector spaces is homogeneous of degree if
for all nonzero and This definition is often further generalized to functions whose domain is not , but a cone in , that is, a subset of such that implies for every nonzero scalar .
In the case of functions of several real variables and real vector spaces, a slightly more general form of homogeneity called positive homogeneity is often considered, by requiring only that the above identities hold for and allowing any real number as a degree of homogeneity. Every homogeneous real function is positively homogeneous. The converse is not true, but is locally true in the sense that (for integer degrees) the two kinds of homogeneity cannot be distinguished by considering the behavior of a function near a given point.
A norm over a real vector space is an example of a positively homogeneous function that is not homogeneous. A special case is the absolute value of real numbers. The quotient of two homogeneous polynomials of the same degree gives an example of a homogeneous function of degree zero. This example is fundamental in the definition of projective schemes.
Definitions
The concept of a homogeneous function was originally introduced for functions of several real variables. With the definition of vector spaces at the end of 19th century, the concept has been naturally extended to functions between vector spaces, since a tuple of variable values can be considered as a coordinate vector. It is this more general point of view that is described in this article.
There are two commonly used definitions. The general one works for vector spaces over arbitrary fields, and is restricted to degrees of homogeneity that are integers.
The second one supposes to work over the field of real numbers, or, more generally, over an ordered field. This definition restricts to positive values the scaling factor that occurs in the definition, and is therefore called positive homogeneity, the qualificative positive being often omitted when there is no risk of confusion. Positive homogeneity leads to considering more functions as homogeneous. For example, the absolute value and all norms are positively homogeneous functions that are not homogeneous.
The restriction of the scaling factor to real positive values allows also considering homogeneous functions whose degree of homogeneity is any real number.
General homogeneity
Let and be two vector spaces over a field . A linear cone in is a subset of such that
for all and all nonzero
A homogeneous function from to is a partial function from to that has a linear cone as its domain, and satisfies
for some integer , every and every nonzero The integer is called the degree of homogeneity, or simply the degree of .
A typical example of a homogeneous function of degree is the function defined by a homogeneous polynomial of degree . The rational function defined by the quotient of two homogeneous polynomials is a homogeneous function; its degree is the difference of the degrees of the numerator and the denominator; its cone of definition is the linear cone of the points where the value of denominator is not zero.
Homogeneous functions play a fundamental role in projective geometry since any homogeneous function from to defines a well-defined function between the projectivizations of and . The homogeneous rational functions of degree zero (those defined by the quotient of two homogeneous polynomial of the same degree) play an essential role in the Proj construction of projective schemes.
Positive homogeneity
When working over the real numbers, or more generally over an ordered field, it is commonly convenient to consider positive homogeneity, the definition being exactly the same as that in the preceding section, with "nonzero " replaced by "" in the definitions of a linear cone and a homogeneous function.
This change allow considering (positively) homogeneous functions with any real number as their degrees, since exponentiation with a positive real base is well defined.
Even in the case of integer degrees, there are many useful functions that are positively homogeneous without being homogeneous. This is, in particular, the case of the absolute value function and norms, which are all positively homogeneous of degree . They are not homogeneous since if This remains true in the complex case, since the field of the complex numbers and every complex vector space can be considered as real vector spaces.
Euler's homogeneous function theorem is a characterization of positively homogeneous differentiable functions, which may be considered as the fundamental theorem on homogeneous functions.
Examples
Simple example
The function is homogeneous of degree 2:
Absolute value and norms
The absolute value of a real number is a positively homogeneous function of degree , which is not homogeneous, since if and if
The absolute value of a complex number is a positively homogeneous function of degree over the real numbers (that is, when considering the complex numbers as a vector space over the real numbers). It is not homogeneous, over the real numbers as well as over the complex numbers.
More generally, every norm and seminorm is a positively homogeneous function of degree which is not a homogeneous function. As for the absolute value, if the norm or semi-norm is defined on a vector space over the complex numbers, this vector space has to be considered as vector space over the real number for applying the definition of a positively homogeneous function.
Linear Maps
Any linear map between vector spaces over a field is homogeneous of degree 1, by the definition of linearity:
for all and
Similarly, any multilinear function is homogeneous of degree by the definition of multilinearity:
for all and
Homogeneous polynomials
Monomials in variables define homogeneous functions For example,
is homogeneous of degree 10 since
The degree is the sum of the exponents on the variables; in this example,
A homogeneous polynomial is a polynomial made up of a sum of monomials of the same degree. For example,
is a homogeneous polynomial of degree 5. Homogeneous polynomials also define homogeneous functions.
Given a homogeneous polynomial of degree with real coefficients that takes only positive values, one gets a positively homogeneous function of degree by raising it to the power So for example, the following function is positively homogeneous of degree 1 but not homogeneous:
Min/max
For every set of weights the following functions are positively homogeneous of degree 1, but not homogeneous:
(Leontief utilities)
Rational functions
Rational functions formed as the ratio of two polynomials are homogeneous functions in their domain, that is, off of the linear cone formed by the zeros of the denominator. Thus, if is homogeneous of degree and is homogeneous of degree then is homogeneous of degree away from the zeros of
Non-examples
The homogeneous real functions of a single variable have the form for some constant . So, the affine function the natural logarithm and the exponential function are not homogeneous.
Euler's theorem
Roughly speaking, Euler's homogeneous function theorem asserts that the positively homogeneous functions of a given degree are exactly the solution of a specific partial differential equation. More precisely:
As a consequence, if is continuously differentiable and homogeneous of degree its first-order partial derivatives are homogeneous of degree
This results from Euler's theorem by differentiating the partial differential equation with respect to one variable.
In the case of a function of a single real variable (), the theorem implies that a continuously differentiable and positively homogeneous function of degree has the form for and for The constants and are not necessarily the same, as it is the case for the absolute value.
Application to differential equations
The substitution converts the ordinary differential equation
where and are homogeneous functions of the same degree, into the separable differential equation
Generalizations
Homogeneity under a monoid action
The definitions given above are all specialized cases of the following more general notion of homogeneity in which can be any set (rather than a vector space) and the real numbers can be replaced by the more general notion of a monoid.
Let be a monoid with identity element let and be sets, and suppose that on both and there are defined monoid actions of Let be a non-negative integer and let be a map. Then is said to be if for every and
If in addition there is a function denoted by called an then is said to be if for every and
A function is (resp. ) if it is homogeneous of degree over (resp. absolutely homogeneous of degree over ).
More generally, it is possible for the symbols to be defined for with being something other than an integer (for example, if is the real numbers and is a non-zero real number then is defined even though is not an integer). If this is the case then will be called if the same equality holds:
The notion of being is generalized similarly.
Distributions (generalized functions)
A continuous function on is homogeneous of degree if and only if
for all compactly supported test functions ; and nonzero real Equivalently, making a change of variable is homogeneous of degree if and only if
for all and all test functions The last display makes it possible to define homogeneity of distributions. A distribution is homogeneous of degree if
for all nonzero real and all test functions Here the angle brackets denote the pairing between distributions and test functions, and is the mapping of scalar division by the real number
Glossary of name variants
Let be a map between two vector spaces over a field (usually the real numbers or complex numbers ). If is a set of scalars, such as or for example, then is said to be if
for every and scalar
For instance, every additive map between vector spaces is although it might not be
The following commonly encountered special cases and variations of this definition have their own terminology:
() : for all and all real
When the function is valued in a vector space or field, then this property is logically equivalent to , which by definition means: for all and all real It is for this reason that positive homogeneity is often also called nonnegative homogeneity. However, for functions valued in the extended real numbers which appear in fields like convex analysis, the multiplication will be undefined whenever and so these statements are not necessarily always interchangeable.
This property is used in the definition of a sublinear function.
Minkowski functionals are exactly those non-negative extended real-valued functions with this property.
: for all and all real
This property is used in the definition of a linear functional.
: for all and all scalars
It is emphasized that this definition depends on the scalar field underlying the domain
This property is used in the definition of linear functionals and linear maps.
: for all and all scalars
If then typically denotes the complex conjugate of . But more generally, as with semilinear maps for example, could be the image of under some distinguished automorphism of
Along with additivity, this property is assumed in the definition of an antilinear map. It is also assumed that one of the two coordinates of a sesquilinear form has this property (such as the inner product of a Hilbert space).
All of the above definitions can be generalized by replacing the condition with in which case that definition is prefixed with the word or
For example,
: for all and all scalars
This property is used in the definition of a seminorm and a norm.
If is a fixed real number then the above definitions can be further generalized by replacing the condition with (and similarly, by replacing with for conditions using the absolute value, etc.), in which case the homogeneity is said to be (where in particular, all of the above definitions are ).
For instance,
: for all and all real
: for all and all scalars
: for all and all real
: for all and all scalars
A nonzero continuous function that is homogeneous of degree on extends continuously to if and only if
See also
Homogeneous space
Notes
Proofs
References
Sources
External links
Linear algebra
Differential operators
Types of functions
Leonhard Euler | Homogeneous function | [
"Mathematics"
] | 2,533 | [
"Functions and mappings",
"Mathematical analysis",
"Mathematical objects",
"Mathematical relations",
"Linear algebra",
"Types of functions",
"Differential operators",
"Algebra"
] |
622,880 | https://en.wikipedia.org/wiki/Bromocriptine | Bromocriptine, originally marketed as Parlodel and subsequently under many brand names, is an ergoline derivative and dopamine agonist that is used in the treatment of pituitary tumors, Parkinson's disease, hyperprolactinaemia, neuroleptic malignant syndrome, and, as an adjunct, type 2 diabetes.
It was patented in 1968 and approved for medical use in 1975.
Medical uses
Bromocriptine is used to treat acromegaly and conditions associated with hyperprolactinemia like amenorrhea, infertility, hypogonadism, and prolactin-secreting adenomas. It is also used to prevent ovarian hyperstimulation syndrome and to treat Parkinson's disease.
Since the late 1980s it has been used, off-label, to reduce the symptoms of cocaine withdrawal but the evidence for this use is poor. Bromocriptine has been successfully used in cases of galactorrhea precipitated by dopamine antagonists like risperidone.
A quick-release formulation of bromocriptine, Cycloset, is also used to treat type 2 diabetes. When administered within 2 hours of awakening, it increases hypothalamic dopamine level. That results to a significant weight loss as well as decreases in blood glucose levels, hepatic glucose production, and insulin resistance. It therefore acts as an adjunct to diet and exercise to improve glycemic control and cardiovascular risk.
Side effects
Most frequent side effects are nausea, orthostatic hypotension, headaches, and vomiting through stimulation of the brainstem vomiting centre. Vasospasms with serious consequences such as myocardial infarction and stroke that have been reported in connection with the puerperium, appear to be extremely rare events. Peripheral vasospasm (of the fingers or toes) can cause Raynaud's phenomenon.
Bromocriptine use has been anecdotally associated with causing or worsening psychotic symptoms (its mechanism is in opposition of most antipsychotics, whose mechanisms generally block dopamine receptors). It should be understood, however, that the greater affinity bromocriptine and many similar antiparkinson's drugs have for the D2S receptor form (considered to be mostly present at inhibitory D2 autoreceptor locatations) relative to the D2L form, sufficiently low partial agonist activity (ie where a molecule binding to a receptor induces limited effects while preventing a stronger ligand like dopamine from binding), and, possibly, the functional selectivity of a particular drug may generate antidopaminergic effects that are more similar than oppositional in nature to antipsychotics.
Pulmonary fibrosis has been reported when bromocriptine was used in high doses for the treatment of Parkinson's disease.
Use to suppress milk production after childbirth was reviewed in 2014 and it was concluded that in this context a causal association with serious cardiovascular, neurological or psychiatric events could not be excluded with an overall incidence estimated to range between 0.005% and 0.04%. Additional safety precautions and stricter prescribing rules were suggested based on the data. It is a bile salt export pump inhibitor.
After long-term use of dopamine agonists, a withdrawal syndrome may occur during dose reduction or discontinuation with the following possible side effects: anxiety, panic attacks, dysphoria, depression, agitation, irritability, suicidal ideation, fatigue, orthostatic hypotension, nausea, vomiting, diaphoresis, generalized pain, and drug cravings. For some individuals, these withdrawal symptoms are short-lived and they make a full recovery, for others a protracted withdrawal syndrome may occur with withdrawal symptoms persisting for months or years.
Pharmacology
Pharmacodynamics
Bromocriptine is a partial agonist of the dopamine D2 receptor. It also interacts with other dopamine receptors and with various serotonin and adrenergic receptors. Bromocriptine has additionally been found to inhibit the release of glutamate by reversing the GLT1 glutamate transporter.
Despite acting as a serotonin 5-HT2A receptor agonist, bromocriptine is described as non-hallucinogenic.
As a silent antagonist of the serotonin 5-HT2B receptor, bromocriptine has been said not to pose a risk of cardiac valvulopathy. This is in contrast to other ergolines acting instead as 5-HT2B receptor agonists such as cabergoline and pergolide but is similar to lisuride which likewise acts as a 5-HT2B receptor antagonist. However, in other research, bromocriptine has subsequently been found to be a partial agonist of the serotonin 5-HT2B receptor and has been associated with cardiac valvulopathy and related complications. In any case, bromocriptine seems to have lower risk than certain other drugs.
Chemistry
Like all ergopeptides, bromocriptine is a cyclol; two peptide groups of its tripeptide moiety are crosslinked, forming the >N-C(OH)< juncture between the two rings with the amide functionality.
Bromocriptine is a semisynthetic derivative of a natural ergot alkaloid, ergocryptine (a derivative of lysergic acid), which is synthesized by bromination of ergocryptine using N-bromosuccinimide.
History
Bromocriptine was discovered by scientists at Sandoz in 1965 and was first published in 1968; it was first marketed under the brand name Parlodel.
A quick-release formulation of bromocriptine was approved by the FDA in 2009.
Society and culture
Brand names
As of July 2017, bromocriptine was marketed under many brand names worldwide, including Abergin, Barlolin, Brameston, Brocriptin, Brom, Broma-Del, Bromergocryptine, Bromergon, Bromicon, Bromocorn, Bromocriptin, Bromocriptina, Bromocriptine, Bromocriptine mesilate, Bromocriptine mesylate, Bromocriptine methanesulfonate, Bromocriptini mesilas, Bromocriptinmesilat, Bromodel, Bromokriptin, Bromolac, Bromotine, Bromtine, Brotin, Butin, Corpadel, Cripsa, Criptine, Criten, Cycloset, Degala, Demil, Deparo, Deprolac, Diacriptin, Dopagon, Erenant, Grifocriptina, Gynodel, kirim, Kriptonal, Lactodel, Medocriptine, Melen, Padoparine, Palolactin, Parlodel, Pravidel, Proctinal, Ronalin, Semi-Brom, Serocriptin, Serocryptin, Suplac, Syntocriptine, Umprel, Unew, Updopa, Upnol B, and Volbro.
As of July 2017 it was also marketed as a combination drug with metformin as Diacriptin-M, and as a veterinary drug under the brand Pseudogravin.
References
External links
5-HT2B agonists
5-HT2C agonists
Antimigraine drugs
Bromoarenes
Cardiotoxins
Dopamine agonists
Isopropyl compounds
Lysergamides
Non-hallucinogenic 5-HT2A receptor agonists
Oxazolopyrrolopyrazines
Prolactin inhibitors
Respiratory toxins
Serotonin receptor agonists | Bromocriptine | [
"Chemistry"
] | 1,661 | [
"Respiratory toxins",
"Cellular respiration"
] |
622,942 | https://en.wikipedia.org/wiki/Pergolide | Pergolide, sold under the brand name Permax and Prascend (veterinary) among others, is an ergoline-based dopamine receptor agonist used in some countries for the treatment of Parkinson's disease. Parkinson's disease is associated with reduced dopamine synthesis in the substantia nigra of the brain. Pergolide acts on many of the same receptors as dopamine to increase receptor activity.
It was patented in 1978 and approved for medical use in 1989. In 2007, pergolide was withdrawn from the U.S. market for human use after several published studies revealed a link between the drug and increased rates of valvular heart disease. However, a veterinary form of pergolide, marketed under the trade name Prascend, is permitted for the treatment of pituitary pars intermedia dysfunction (PPID) also known as equine Cushing's syndrome (ECS) in horses.
Medical uses
Pergolide is no longer available for use by humans in the United States, however, it is still used in various other countries, where it is used to treat various conditions including Parkinson's disease, hyperprolactinemia, and restless leg syndrome.
Pergolide is available for veterinary use. Under the trade name Prascend, manufactured by Boehringer Ingelheim, it is commonly used for the treatment of pituitary hyperplasia at the pars intermedia or Equine Cushing's Syndrome (ECS) in horses.
Pharmacology
Pharmacodynamics
Pergolide acts as an agonist of dopamine D2 and D1 and serotonin 5-HT1A, 5-HT1B, 5-HT2A, 5-HT2B, and 5-HT2C receptors. It may possess agonist activity at other dopamine receptor subtypes as well, similar to cabergoline. Although pergolide is more potent as an agonist of the D2 receptor, it has high D1 receptor affinity and is one of the most potent D1 receptor agonists of the dopamine receptor agonists that are clinically available. The agonist activity of pergolide at the D1 receptor somewhat alters its clinical and side effect profile in the treatment of Parkinson's disease. Pergolide has been said to be hallucinogenic due to activation of 5-HT2A receptors. However, other sources have stated that the drug is non-hallucinogenic. It has been associated with cardiac valvulopathy due to activation of 5-HT2B receptors.
Side effects
The drug is in decreasing use, as it was reported in 2003 to be associated with a form of heart disease called cardiac fibrosis. In 2007, the United States Food and Drug Administration announced a voluntary withdrawal of the drug by manufacturers due to the possibility of heart valve damage. Pergolide is not currently available in the United States for human use. This problem is thought to be due to pergolide's action at the 5-HT2B serotonin receptors of cardiac myocytes, causing proliferative valve disease by the same mechanism as ergotamine, methysergide, fenfluramine, and other serotonin 5-HT2B agonists, including serotonin itself when elevated in the blood in carcinoid syndrome. Pergolide can rarely cause Raynaud's phenomenon. Among similar antiparkinsonian drugs, cabergoline, but not lisuride, exhibit this same type of serotonin receptor binding. In January 2007, cabergoline (Dostinex) was also reported to be associated with valvular proliferation heart damage. In March 2007, pergolide was withdrawn from the U.S. market for human use due to serious valvular damage that was shown in two independent studies.
Pergolide has also been shown to impair associative learning.
Addictive behaviors
At least one British pergolide user has attracted some media attention with claims that it has caused him to develop a gambling addiction. In June 2010, it was reported that more than 100 Australian users of the drug are suing the manufacturer over both gambling and sex addiction problems they claim are the result of the drug's side effects.
Society and culture
Brand names
Brand names of pergolide include Permax and Prascend (veterinary), among others.
Research
Pergolide has been studied in the treatment of social anxiety disorder in one small study but was found to be ineffective.
References
5-HT2B agonists
D2-receptor agonists
D3 receptor agonists
D4 receptor agonists
Dopamine receptor modulators
Equine medications
Ergolines
Non-hallucinogenic 5-HT2A receptor agonists
Prolactin inhibitors
Thioethers
Withdrawn drugs
Cardiotoxins | Pergolide | [
"Chemistry"
] | 1,030 | [
"Drug safety",
"Withdrawn drugs"
] |
622,966 | https://en.wikipedia.org/wiki/Cousin%20problems | In mathematics, the Cousin problems are two questions in several complex variables, concerning the existence of meromorphic functions that are specified in terms of local data. They were introduced in special cases by Pierre Cousin in 1895. They are now posed, and solved, for any complex manifold M, in terms of conditions on M.
For both problems, an open cover of M by sets Ui is given, along with a meromorphic function fi on each Ui.
First Cousin problem
The first Cousin problem or additive Cousin problem assumes that each difference
is a holomorphic function, where it is defined. It asks for a meromorphic function f on M such that
is holomorphic on Ui; in other words, that f shares the singular behaviour of the given local function. The given condition on the is evidently necessary for this; so the problem amounts to asking if it is sufficient. The case of one variable is the Mittag-Leffler theorem on prescribing poles, when M is an open subset of the complex plane. Riemann surface theory shows that some restriction on M will be required. The problem can always be solved on a Stein manifold.
The first Cousin problem may be understood in terms of sheaf cohomology as follows. Let K be the sheaf of meromorphic functions and O the sheaf of holomorphic functions on M. A global section of K passes to a global section of the quotient sheaf K/O. The converse question is the first Cousin problem: given a global section of K/O, is there a global section of K from which it arises? The problem is thus to characterize the image of the map
By the long exact cohomology sequence,
is exact, and so the first Cousin problem is always solvable provided that the first cohomology group H1(M,O) vanishes. In particular, by Cartan's theorem B, the Cousin problem is always solvable if M is a Stein manifold.
Second Cousin problem
The second Cousin problem or multiplicative Cousin problem assumes that each ratio
is a non-vanishing holomorphic function, where it is defined. It asks for a meromorphic function f on M such that
is holomorphic and non-vanishing. The second Cousin problem is a multi-dimensional generalization of the Weierstrass theorem on the existence of a holomorphic function of one variable with prescribed zeros.
The attack on this problem by means of taking logarithms, to reduce it to the additive problem, meets an obstruction in the form of the first Chern class (see also exponential sheaf sequence). In terms of sheaf theory, let be the sheaf of holomorphic functions that vanish nowhere, and the sheaf of meromorphic functions that are not identically zero. These are both then sheaves of abelian groups, and the quotient sheaf is well-defined. The multiplicative Cousin problem then seeks to identify the image of quotient map
The long exact sheaf cohomology sequence associated to the quotient is
so the second Cousin problem is solvable in all cases provided that The quotient sheaf is the sheaf of germs of Cartier divisors on M. The question of whether every global section is generated by a meromorphic function is thus equivalent to determining whether every line bundle on M is trivial.
The cohomology group for the multiplicative structure on can be compared with the cohomology group with its additive structure by taking a logarithm. That is, there is an exact sequence of sheaves
where the leftmost sheaf is the locally constant sheaf with fiber . The obstruction to defining a logarithm at the level of H1 is in , from the long exact cohomology sequence
When M is a Stein manifold, the middle arrow is an isomorphism because for so that a necessary and sufficient condition in that case for the second Cousin problem to be always solvable is that
See also
Cartan's theorems A and B
References
.
.
.
Complex analysis
Several complex variables
Sheaf theory | Cousin problems | [
"Mathematics"
] | 841 | [
"Functions and mappings",
"Mathematical structures",
"Several complex variables",
"Mathematical objects",
"Sheaf theory",
"Topology",
"Mathematical relations",
"Category theory"
] |
622,986 | https://en.wikipedia.org/wiki/Compile%20farm | A compile farm is a server farm, a collection of one or more servers, which has been set up to compile computer programs remotely for various reasons. Uses of a compile farm include:
Cross-platform development: When writing software that runs on multiple processor architectures and operating systems, it can be infeasible for each developer to have their own machine for each architecture — for example, one platform might have an expensive or obscure type of CPU. In this scenario, a compile farm is useful as a tool for developers to build and test their software on a shared server running the target operating system and CPU. Compile farms may be preferable to cross-compilation as cross compilers are often complicated to configure, and in some cases compilation is only possible on the target, making cross-compilation impossible.
Cross-platform continuous integration testing: in this scenario, each server has a different processor architecture or runs a different operating system; scripts automatically build the latest version of a source tree from a version control repository. One of the difficulties of cross-platform development is that a programmer may unintentionally introduce an error that causes the software to stop functioning on a different CPU/OS platform from the one they are using. By using a cross-platform compile farm, such errors can be identified and fixed.
Distributed compilation: Building software packages typically requires operations that can be run in parallel (for example, compiling individual source code files). By using a compile farm, these operations can be run in parallel on separate machines. An example of a program which can be used to do this is distcc.
One example of a compile farm was the service provided by SourceForge until 2006. The SourceForge compile farm was composed of twelve machines of various computer architectures running a variety of operating systems, and was intended to allow developers to test and use their programs on a variety of platforms before releasing them to the public. After a power spike destroyed several of the machines it became non-operational some time in 2006, and was officially discontinued in February 2007.
Other examples are:
GCC Compile Farm https://gcc.gnu.org/wiki/CompileFarm
OpenSUSE Build Service
FreeBSD reports service which lets package maintainers test their own changes on a variety of versions and architectures.
Launchpad Build Farm https://launchpad.net/builders
Mozilla has a build farm, but it is not public https://wiki.mozilla.org/ReleaseEngineering
Debian has a build farm https://buildd.debian.org/
OpenCSW build farm for Solaris x86 and Sparc
References
Cluster computing
Servers (computing) | Compile farm | [
"Technology"
] | 562 | [
"Computing stubs",
"Computer science",
"Computer science stubs"
] |
623,008 | https://en.wikipedia.org/wiki/Kangla%20fort | The with diacritic Kanglā, officially known as the Kangla Fort, is an old fortified palace at Imphal, in the Manipur state of India. It was formerly situated on both sides (western and eastern) of the bank of the Imphal River, now remaining only on the western side in ruined conditions. Kangla means "the prominent part of the dry land" in old Meetei. It was the traditional seat of the past Meetei rulers of Manipur.
Kangla (Imphal) was the ancient capital of pre-modern Manipur.
The Kangla is a revered spot for the people of Manipur, reminding them of the days of their independence. It is a sacred place to the Meiteis.
The Kangla is being proposed to be declared as a UNESCO World Heritage Site, for which there are discussions ongoing in the Indian Parliament.
History
The Kangla was the seat of administration of the Meitei rulers of the Ningthouja dynasty (33 CE to 1891 CE).
Flora and fauna
The Kangla possesses a sobriquet, "Lungs of Imphal" as it is heavily forested, providing oxygen at a massive level in the heart of the metropolis of Manipur.
Unfortunately, due to some developmental construction activities in the last few years, some minor but significant deforestation occurred inside the Kangla.
In the year 2009, the Kangla Herbal Garden was set up by the Kangla Fort Board, in order to carry out the plan of planting medicinal plants inside the Kangla into action. The responsibility for bringing up the botanical garden was held by the Lamphel based sub-branch of the North East Institute of Science and Technology, Jorhat (NEIST).
In the year 2010, the Government of Manipur financed out of to the NEIST to carry out the task. It planted around 131 different plants, (including around 20 medicinal plant species) in the garden. Notable plant species nurtured in the Kangla Herbal Garden include "heigru" (), "kihori" (), agar (Aquilaria agallocha Lamp), neem (Azadirachta indica A Zuss), tera (), singairei () and leihao (). An area covering 3.5 acres of land was allocated for the development of the botanical garden by the Manipur Government.
During the month of June in 2019, around 700 indigenous fruit-bearing tree saplings were planted inside the , formerly known as "Biodiversity Park" of the Kangla) of the Kangla by the Government of Manipur, under the initiative of Green Manipur Mission.
During the month of September in 2019, around 120 trees, including mayokfa, agar, uningthou, teak, chahui and samba, were planted inside the Kangla by the editorial board and the management team of "The Sangai Express" (TSE), a newspaper daily of Manipur, on its 20th foundation day.
There's another garden named "Engellei Leikol" (formerly known as "Rock Garden" of the Kangla) located in the southern part of the Kangla.
During the month of May in 2022, around 50 fruit-bearing plants were planted inside the Kangla by the Institute of Bioresources and Sustainable Development (IBSD).
There's a plan for planting 10,000 saplings of fruit bearing trees inside the Kangla by the Kangla Fort Board, under the leadership of Nongthombam Biren, the Chief Minister of Manipur.
Places
See also
Kangla Nongpok Torban
Museums in Kangla
Notes
References
External links
Kangla Fort at Imphal Free Press
The ancient capital of Manipur : E-Pao.Net
Rediscovering a heritage- By SUSHANTA TALUKDAR
Kangla Fort Beautiful Photos - KanglaOnline.com
Meitei architecture
Ancient archaeological sites
Manipur Kingdom
Ancient cities
Ancient peoples
Ancient culture
Archaeological monuments in India
Archaeological sites in India
British India
Buildings and structures in Imphal
Cultural history of India
Imphal West district
Indian Army bases
Former capital cities in India
Forts in India
Meitei pilgrimage sites
Military installations of India
Monuments and memorials in Imphal
Monuments and memorials to Meitei royalty
Palaces in Manipur
Public art in India
Religious places
Royal residences in India
Tourist attractions in Manipur | Kangla fort | [
"Engineering"
] | 891 | [
"Meitei architecture",
"Architecture"
] |
623,068 | https://en.wikipedia.org/wiki/Foreach%20loop | In computer programming, foreach loop (or for-each loop) is a control flow statement for traversing items in a collection. is usually used in place of a standard loop statement. Unlike other loop constructs, however, loops usually maintain no explicit counter: they essentially say "do this to everything in this set", rather than "do this times". This avoids potential off-by-one errors and makes code simpler to read. In object-oriented languages, an iterator, even if implicit, is often used as the means of traversal.
The statement in some languages has some defined order, processing each item in the collection from the first to the last.
The statement in many other languages, especially array programming languages, does not have any particular order. This simplifies loop optimization in general and in particular allows vector processing of items in the collection concurrently.
Syntax
Syntax varies among languages. Most use the simple word for, although other use the more logical word foreach, roughly as follows:
foreach(key, value) in collection {
# Do something to value #
}
Language support
Programming languages which support foreach loops include ABC, ActionScript, Ada, C++ (since C++11), C#, ColdFusion Markup Language (CFML), Cobra, D, Daplex (query language), Delphi, ECMAScript, Erlang, Java (since 1.5), JavaScript, Lua, Objective-C (since 2.0), ParaSail, Perl, PHP, Prolog, Python, R, REALbasic, Rebol, Red, Ruby, Scala, Smalltalk, Swift, Tcl, tcsh, Unix shells, Visual Basic (.NET), and Windows PowerShell. Notable languages without foreach are C, and C++ pre-C++11.
ActionScript 3.0
ActionScript supports the ECMAScript 4.0 Standard for for each .. in which pulls the value at each index.
var foo:Object = {
"apple":1,
"orange":2
};
for each (var value:int in foo) {
trace(value);
}
// returns "1" then "2"
It also supports for .. in which pulls the key at each index.
for (var key:String in foo) {
trace(key);
}
// returns "apple" then "orange"
Ada
Ada supports foreach loops as part of the normal for loop. Say X is an array:
for I in X'Range loop
X (I) := Get_Next_Element;
end loop;
This syntax is used on mostly arrays, but will also work with other types when a full iteration is needed.
Ada 2012 has generalized loops to foreach loops on any kind of container (array, lists, maps...):
for Obj of X loop
-- Work on Obj
end loop;
C
The C language does not have collections or a foreach construct. However, it has several standard data structures that can be used as collections, and foreach can be made easily with a macro.
However, two obvious problems occur:
The macro is unhygienic: it declares a new variable in the existing scope which remains after the loop.
One foreach macro cannot be defined that works with different collection types (e.g., array and linked list) or that is extensible to user types.
C string as a collection of char
#include <stdio.h>
/* foreach macro viewing a string as a collection of char values */
#define foreach(ptrvar, strvar) \
char* ptrvar; \
for (ptrvar = strvar; (*ptrvar) != '\0'; *ptrvar++)
int main(int argc, char** argv) {
char* s1 = "abcdefg";
char* s2 = "123456789";
foreach (p1, s1) {
printf("loop 1: %c\n", *p1);
}
foreach (p2, s2) {
printf("loop 2: %c\n", *p2);
}
return 0;
}
C int array as a collection of int (array size known at compile-time)
#include <stdio.h>
/* foreach macro viewing an array of int values as a collection of int values */
#define foreach(intpvar, intarr) \
int* intpvar; \
for (intpvar = intarr; intpvar < (intarr + (sizeof(intarr)/sizeof(intarr[0]))); ++intpvar)
int main(int argc, char** argv) {
int a1[] = {1, 1, 2, 3, 5, 8};
int a2[] = {3, 1, 4, 1, 5, 9};
foreach (p1, a1) {
printf("loop 1: %d\n", *p1);
}
foreach (p2, a2) {
printf("loop 2: %d\n", *p2);
}
return 0;
}
Most general: string or array as collection (collection size known at run-time)
can be removed and typeof(col[0]) used in its place with GCC
#include <stdio.h>
#include <string.h>
/* foreach macro viewing an array of given type as a collection of values of given type */
#define arraylen(arr) (sizeof(arr)/sizeof(arr[0]))
#define foreach(idxtype, idxpvar, col, colsiz) \
idxtype* idxpvar; \
for (idxpvar = col; idxpvar < (col + colsiz); ++idxpvar)
int main(int argc, char** argv) {
char* c1 = "collection";
int c2[] = {3, 1, 4, 1, 5, 9};
double* c3;
int c3len = 4;
c3 = (double*)calloc(c3len, sizeof(double));
c3[0] = 1.2; c3[1] = 3.4; c3[2] = 5.6; c3[3] = 7.8;
foreach (char, p1, c1, strlen(c1)) {
printf("loop 1: %c\n", *p1);
}
foreach (int, p2, c2, arraylen(c2)) {
printf("loop 2: %d\n", *p2);
}
foreach (double, p3, c3, c3len) {
printf("loop 3: %.1lf\n", *p3);
}
return 0;
}
C#
In C#, assuming that myArray is an array of integers:
foreach (int x in myArray) { Console.WriteLine(x); }
Language Integrated Query (LINQ) provides the following syntax, accepting a delegate or lambda expression:
myArray.ToList().ForEach(x => Console.WriteLine(x));
C++
C++11 provides a foreach loop. The syntax is similar to that of Java:
#include <iostream>
int main()
{
int myint[] = {1, 2, 3, 4, 5};
for (int i : myint)
{
std::cout << i << '\n';
}
}
C++11 range-based for statements have been implemented in GNU Compiler Collection (GCC) (since version 4.6), Clang (since version 3.0) and Visual C++ 2012 (version 11 )
The range-based for is syntactic sugar equivalent to:
for (auto __anon = begin(myint); __anon != end(myint); ++__anon)
{
auto i = *__anon;
std::cout << i << '\n';
}
The compiler uses argument-dependent lookup to resolve the begin and end functions.
The C++ Standard Library also supports for_each, that applies each element to a function, which can be any predefined function or a lambda expression. While range-based for is only from the start to the end, the range or direction can be changed by altering the first two parameters.
#include <iostream>
#include <algorithm> // contains std::for_each
#include <vector>
int main()
{
std::vector<int> v {1, 2, 3, 4, 5};
std::for_each(v.begin(), v.end(), [](int i)
{
std::cout << i << '\n';
});
std::cout << "reversed but skip 2 elements:\n";
std::for_each(v.rbegin()+2, v.rend(), [](int i)
{
std::cout << i << '\n';
});
}
Qt, a C++ framework, offers a macro providing foreach loops using the STL iterator interface:
#include <QList>
#include <QDebug>
int main()
{
QList<int> list;
list << 1 << 2 << 3 << 4 << 5;
foreach (int i, list)
{
qDebug() << i;
}
}
Boost, a set of free peer-reviewed portable C++ libraries also provides foreach loops:
#include <boost/foreach.hpp>
#include <iostream>
int main()
{
int myint[] = {1, 2, 3, 4, 5};
BOOST_FOREACH(int &i, myint)
{
std::cout << i << '\n';
}
}
C++/CLI
The C++/CLI language proposes a construct similar to C#.
Assuming that myArray is an array of integers:
for each (int x in myArray)
{
Console::WriteLine(x);
}
ColdFusion Markup Language (CFML)
Script syntax
// arrays
arrayeach([1,2,3,4,5], function(v){
writeOutput(v);
});
// or
for (v in [1,2,3,4,5]){
writeOutput(v);
}
// or
// (Railo only; not supported in ColdFusion)
letters = ["a","b","c","d","e"];
letters.each(function(v){
writeOutput(v); // abcde
});
// structs
for (k in collection){
writeOutput(collection[k]);
}
// or
structEach(collection, function(k,v){
writeOutput("key: #k#, value: #v#;");
});
// or
// (Railo only; not supported in ColdFusion)
collection.each(function(k,v){
writeOutput("key: #k#, value: #v#;");
});
Tag syntax
<!--- arrays --->
<cfloop index="v" array="#['a','b','c','d','e']#">
<cfoutput>#v#</cfoutput><!--- a b c d e --->
</cfloop>
CFML incorrectly identifies the value as "index" in this construct; the index variable does receive the actual value of the array element, not its index.
<!--- structs --->
<cfloop item="k" collection="#collection#">
<cfoutput>#collection[k]#</cfoutput>
</cfloop>
Common Lisp
Common Lisp provides foreach ability either with the dolist macro:
(dolist (i '(1 3 5 6 8 10 14 17))
(print i))
or the powerful loop macro to iterate on more data types
(loop for i in '(1 3 5 6 8 10 14 17)
do (print i))
and even with the mapcar function:
(mapcar #'print '(1 3 5 6 8 10 14 17))
D
foreach(item; set) {
// do something to item
}
or
foreach(argument) {
// pass value
}
Dart
for (final element in someCollection) {
// do something with element
}
Object Pascal, Delphi
Foreach support was added in Delphi 2005, and uses an enumerator variable that must be declared in the var section.
for enumerator in collection do
begin
//do something here
end;
Eiffel
The iteration (foreach) form of the Eiffel loop construct is introduced by the keyword across.
In this example, every element of the structure my_list is printed:
across my_list as ic loop print (ic.item) end
The local entity ic is an instance of the library class ITERATION_CURSOR. The cursor's feature item provides access to each structure element. Descendants of class ITERATION_CURSOR can be created to handle specialized iteration algorithms. The types of objects that can be iterated across (my_list in the example) are based on classes that inherit from the library class ITERABLE.
The iteration form of the Eiffel loop can also be used as a boolean expression when the keyword loop is replaced by either all (effecting universal quantification) or some (effecting existential quantification).
This iteration is a boolean expression which is true if all items in my_list have counts greater than three:
across my_list as ic all ic.item.count > 3 end
The following is true if at least one item has a count greater than three:
across my_list as ic some ic.item.count > 3 end
Go
Go's foreach loop can be used to loop over an array, slice, string, map, or channel.
Using the two-value form gets the index/key (first element) and the value (second element):
for index, value := range someCollection {
// Do something to index and value
}
Using the one-value form gets the index/key (first element):
for index := range someCollection {
// Do something to index
}
Groovy
Groovy supports for loops over collections like arrays, lists and ranges:
def x = [1,2,3,4]
for (v in x) // loop over the 4-element array x
{
println v
}
for (v in [1,2,3,4]) // loop over 4-element literal list
{
println v
}
for (v in 1..4) // loop over the range 1..4
{
println v
}
Groovy also supports a C-style for loop with an array index:
for (i = 0; i < x.size(); i++)
{
println x[i]
}
Collections in Groovy can also be iterated over using the each keyword
and a closure. By default, the loop dummy is named it
x.each{ println it } // print every element of the x array
x.each{i-> println i} // equivalent to line above, only loop dummy explicitly named "i"
Haskell
Haskell allows looping over lists with monadic actions using mapM_ and forM_ (mapM_ with its arguments flipped) from Control.Monad:
It's also possible to generalize those functions to work on applicative functors rather than monads and any data structure that is traversable using traverse (for with its arguments flipped) and mapM (forM with its arguments flipped) from Data.Traversable.
Haxe
for (value in iterable) {
trace(value);
}
Lambda.iter(iterable, function(value) trace(value));
Java
In Java, a foreach-construct was introduced in Java Development Kit (JDK) 1.5.0.
Official sources use several names for the construct. It is referred to as the "Enhanced for Loop", the "For-Each Loop", and the "foreach statement".
for (Type item : iterableCollection) {
// Do something to item
}
Java also provides the stream api since java 8:
List<Integer> intList = List.of(1, 2, 3, 4);
intList.stream().forEach(i -> System.out.println(i));
JavaScript
In ECMAScript 5, a callback-based forEach() method was added to the array prototype:myArray.forEach(function (item, index) {
// Do stuff with item and index
// The index variable can be omitted from the parameter list if not needed
});The ECMAScript 6 standard introduced a more conventional for..of syntax that works on all iterables rather than operating on only array instances. However, no index variable is available with the syntax.
for (const item of myArray) {
// Do stuff with item
}
For unordered iteration over the keys in an object, JavaScript features the for..in loop:
for (const key in myObject) {
// Do stuff with myObject[key]
}
To limit the iteration to the object's own properties, excluding those inherited through the prototype chain, it's often useful to add a hasOwnProperty() test (or a hasOwn() test if supported).
for (const key in myObject) {
// Available in older browsers
if (myObject.hasOwnProperty(key)) {
// Do stuff with object[key]
}
// Preferred in modern browsers
if (Object.hasOwn(myObject, key)) {
// Do stuff with object[key]
}
}
Alternatively, the Object.keys() method combined with the for..of loop can be used for a less verbose way to iterate over the keys of an object.
const book = {
name: "A Christmas Carol",
author: "Charles Dickens"
};
for (const key of Object.keys(book)) {
console.log(`Key: ${key}, Value: ${book[key]}`);
}
Lua
Source:
Iterate only through numerical index values:for index, value in ipairs(array) do
-- do something
endIterate through all index values:for index, value in pairs(array) do
-- do something
end
Mathematica
In Mathematica, Do will simply evaluate an expression for each element of a list, without returning any value.
In[]:= Do[doSomethingWithItem, {item, list}]
It is more common to use Table, which returns the result of each evaluation in a new list.
In[]:= list = {3, 4, 5};
In[]:= Table[item^2, {item, list}]
Out[]= {9, 16, 25}
MATLAB
for item = array
%do something
end
Mint
For each loops are supported in Mint, possessing the following syntax:
for each element of list
/* 'Do something.' */
end
The for (;;) or while (true) infinite loop
in Mint can be written using a for each loop and an infinitely long list.
import type
/* 'This function is mapped to'
* 'each index number i of the'
* 'infinitely long list.'
*/
sub identity(x)
return x
end
/* 'The following creates the list'
* '[0, 1, 2, 3, 4, 5, ..., infinity]'
*/
infiniteList = list(identity)
for each element of infiniteList
/* 'Do something forever.' */
end
Objective-C
Foreach loops, called Fast enumeration, are supported starting in Objective-C 2.0. They can be used to iterate over any object that implements the NSFastEnumeration protocol, including NSArray, NSDictionary (iterates over keys), NSSet, etc.
NSArray *a = [NSArray new]; // Any container class can be substituted
for(id obj in a) { // Dynamic typing is used. The type of object stored
// in 'a' can be unknown. The array can hold many different
// types of object.
printf("%s\n", [[obj description] UTF8String]); // Must use UTF8String with %s
NSLog(@"%@", obj); // Leave as an object
}
NSArrays can also broadcast a message to their members:
NSArray *a = [NSArray new];
[a makeObjectsPerformSelector:@selector(printDescription)];
Where blocks are available, an NSArray can automatically perform a block on every contained item:
[myArray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop)
{
NSLog(@"obj %@", obj);
if ([obj shouldStopIterationNow])
*stop = YES;
}];
The type of collection being iterated will dictate the item returned with each iteration.
For example:
NSDictionary *d = [NSDictionary new];
for(id key in d) {
NSObject *obj = [d objectForKey:key]; // We use the (unique) key to access the (possibly nonunique) object.
NSLog(@"%@", obj);
}
OCaml
OCaml is a functional programming language. Thus, the equivalent of a foreach loop can be achieved as a library function over lists and arrays.
For lists:
List.iter (fun x -> print_int x) [1;2;3;4];;
or in short way:
List.iter print_int [1;2;3;4];;
For arrays:
Array.iter (fun x -> print_int x) [|1;2;3;4|];;
or in short way:
Array.iter print_int [|1;2;3;4|];;
ParaSail
The ParaSail parallel programming language supports several kinds of iterators, including a general "for each" iterator over a container:
var Con : Container<Element_Type> := ...
// ...
for each Elem of Con concurrent loop // loop may also be "forward" or "reverse" or unordered (the default)
// ... do something with Elem
end loop
ParaSail also supports filters on iterators, and the ability to refer to both the key and the value of a map. Here is a forward iteration over the elements of "My_Map" selecting only elements where the keys are in "My_Set":
var My_Map : Map<Key_Type => Univ_String, Value_Type => Tree<Integer>> := ...
const My_Set : Set<Univ_String> := ["abc", "def", "ghi"];
for each [Str => Tr] of My_Map {Str in My_Set} forward loop
// ... do something with Str or Tr
end loop
Pascal
In Pascal, ISO standard 10206:1990 introduced iteration over set types, thus:
var
elt: ElementType;
eltset: set of ElementType;
{...}
for elt in eltset do
{ ... do something with elt }
Perl
In Perl, foreach (which is equivalent to the shorter for) can be used to traverse elements of a list. The expression which denotes the collection to loop over is evaluated in list-context and each item of the resulting list is, in turn, aliased to the loop variable.
List literal example:
foreach (1, 2, 3, 4) {
print $_;
}
Array examples:
foreach (@arr) {
print $_;
}
foreach $x (@arr) { #$x is the element in @arr
print $x;
}
Hash example:
foreach $x (keys %hash) {
print $x . " = " . $hash{$x}; # $x is a key in %hash and $hash{$x} is its value
}
Direct modification of collection members:
@arr = ( 'remove-foo', 'remove-bar' );
foreach $x (@arr){
$x =~ s/remove-//;
}
# Now @arr = ('foo', 'bar');
PHP
foreach ($set as $value) {
// Do something to $value;
}
It is also possible to extract both keys and values using the alternate syntax:
foreach ($set as $key => $value) {
echo "{$key} has a value of {$value}";
}
Direct modification of collection members:
$arr = array(1, 2, 3);
foreach ($arr as &$value) { // The &, $value is a reference to the original value inside $arr
$value++;
}
// Now $arr = array(2, 3, 4);
// also works with the full syntax
foreach ($arr as $key => &$value) {
$value++;
}
More information
Python
for item in iterable_collection:
# Do something with item
Python's tuple assignment, fully available in its foreach loop, also makes it trivial to iterate on (key, value) pairs in dictionaries:
for key, value in some_dict.items(): # Direct iteration on a dict iterates on its keys
# Do stuff
As for ... in is the only kind of for loop in Python, the equivalent to the "counter" loop found in other languages is...
for i in range(len(seq)):
# Do something to seq[i]
... although using the enumerate function is considered more "Pythonic":
for i, item in enumerate(seq):
# Do stuff with item
# Possibly assign it back to seq[i]
R
for (item in object) {
# Do something with item
}
As for ... in is the only kind of for loop in R, the equivalent to the "counter" loop found in other languages is...
for (i in seq_along(object)) {
# Do something with object[[i]]
}
Racket
(for ([item set])
(do-something-with item))
or using the conventional Scheme for-each function:
(for-each do-something-with a-list)
do-something-with is a one-argument function.
Raku
In Raku, a sister language to Perl, for must be used to traverse elements of a list (foreach is not allowed). The expression which denotes the collection to loop over is evaluated in list-context, but not flattened by default, and each item of the resulting list is, in turn, aliased to the loop variable(s).
List literal example:
for 1..4 {
.say;
}
Array examples:
for @arr {
.say;
}
The for loop in its statement modifier form:
.say for @arr;
for @arr -> $x {
say $x;
}
for @arr -> $x, $y { # more than one item at a time
say "$x, $y";
}
Hash example:
for keys %hash -> $key {
say "$key: $hash{$key}";
}
or
for %hash.kv -> $key, $value {
say "$key: $value";
}
or
for %hash -> $x {
say "$x.key(): $x.value()"; # Parentheses needed to inline in double quoted string
}
Direct modification of collection members with a doubly pointy block, <->:
my @arr = 1,2,3;
for @arr <-> $x {
$x *= 2;
}
# Now @arr = 2,4,6;
Ruby
set.each do |item|
# do something to item
end
or
for item in set
# do something to item
end
This can also be used with a hash.
set.each do |key,value|
# do something to key
# do something to value
end
Rust
The for loop has the structure for <pattern> in <expression> { /* optional statements */ }. It implicitly calls the IntoIterator::into_iter method on the expression, and uses the resulting value, which must implement the Iterator trait. If the expression is itself an iterator, it is used directly by the for loop through an implementation of IntoIterator for all Iterators that returns the iterator unchanged. The loop calls the Iterator::next method on the iterator before executing the loop body. If Iterator::next returns Some(_), the value inside is assigned to the pattern and the loop body is executed; if it returns None, the loop is terminated.
let mut numbers = vec![1, 2, 3];
// Immutable reference:
for number in &numbers { // calls IntoIterator::into_iter(&numbers)
println!("{}", number);
}
for square in numbers.iter().map(|x| x * x) { // numbers.iter().map(|x| x * x) implements Iterator
println!("{}", square);
}
// Mutable reference:
for number in &mut numbers { // calls IntoIterator::into_iter(&mut numbers)
*number *= 2;
}
// prints "[2, 4, 6]":
println!("{:?}", numbers);
// Consumes the Vec and creates an Iterator:
for number in numbers { // calls IntoIterator::into_iter(numbers)
// ...
}
// Errors with "borrow of moved value":
// println!("{:?}", numbers);
Scala
// return list of modified elements
items map { x => doSomething(x) }
items map multiplyByTwo
for {x <- items} yield doSomething(x)
for {x <- items} yield multiplyByTwo(x)
// return nothing, just perform action
items foreach { x => doSomething(x) }
items foreach println
for {x <- items} doSomething(x)
for {x <- items} println(x)
// pattern matching example in for-comprehension
for ((key, value) <- someMap) println(s"$key -> $value")
Scheme
(for-each do-something-with a-list)
do-something-with is a one-argument function.
Smalltalk
collection do: [:item| "do something to item" ]
Swift
Swift uses the for…in construct to iterate over members of a collection.
for thing in someCollection {
// do something with thing
}
The for…in loop is often used with the closed and half-open range constructs to iterate over the loop body a certain number of times.
for i in 0..<10 {
// 0..<10 constructs a half-open range, so the loop body
// is repeated for i = 0, i = 1, …, i = 9.
}
for i in 0...10 {
// 0...10 constructs a closed range, so the loop body
// is repeated for i = 0, i = 1, …, i = 9, i = 10.
}
SystemVerilog
SystemVerilog supports iteration over any vector or array type of any dimensionality using the foreach keyword.
A trivial example iterates over an array of integers:
A more complex example iterates over an associative array of arrays of integers:
Tcl
Tcl uses foreach to iterate over lists. It is possible to specify more than one iterator variable, in which case they are assigned sequential values from the list.
It is also possible to iterate over more than one list simultaneously. In the following i assumes sequential values of the first list, j sequential values of the second list:
Visual Basic (.NET)
For Each item In enumerable
' Do something with item.
Next
or without type inference
For Each item As type In enumerable
' Do something with item.
Next
Windows
Conventional command processor
Invoke a hypothetical frob command three times, giving it a color name each time.
C:\>FOR %%a IN ( red green blue ) DO frob %%a
Windows PowerShell
foreach ($item in $set) {
# Do something to $item
}
From a pipeline
$list | ForEach-Object {Write-Host $_}
# or using the aliases
$list | foreach {write $_}
$list | % {write $_}
XSLT
<xsl:for-each select="set">
<!-- do something for the elements in <set> -->
</xsl:for-each>
See also
Do while loop
For loop
While loop
Map (higher-order function)
References
Control flow
Iteration in programming
Programming language comparisons
Articles with example Ada code
Articles with example C code
Articles with example C++ code
Articles with example C Sharp code
Articles with example D code
Articles with example Eiffel code
Articles with example Haskell code
Articles with example Java code
Articles with example JavaScript code
Articles with example Lisp (programming language) code
Articles with example MATLAB/Octave code
Articles with example Objective-C code
Articles with example OCaml code
Articles with example Pascal code
Articles with example Perl code
Articles with example PHP code
Articles with example Python (programming language) code
Articles with example R code
Articles with example Racket code
Articles with example Ruby code
Articles with example Rust code
Articles with example Scala code
Articles with example Scheme (programming language) code
Articles with example Smalltalk code
Articles with example Swift code
Articles with example Tcl code
ru:Цикл просмотра | Foreach loop | [
"Technology"
] | 7,596 | [
"Programming language comparisons",
"Computing comparisons"
] |
623,112 | https://en.wikipedia.org/wiki/Robotic%20mapping | Robotic mapping is a discipline related to computer vision and cartography. The goal for an autonomous robot is to be able to construct (or use) a map (outdoor use) or floor plan (indoor use) and to localize itself and its recharging bases or beacons in it. Robotic mapping is that branch which deals with the study and application of ability to localize itself in a map / plan and sometimes to
construct the map or floor plan by the autonomous robot.
Evolutionarily shaped blind action may suffice to keep some animals alive. For some insects for example, the environment is not interpreted as a map, and they survive only with a triggered response. A slightly more elaborated navigation strategy dramatically enhances the capabilities of the robot. Cognitive maps enable planning capacities and use of current perceptions, memorized events, and expected consequences.
Operation
The robot has two sources of information: the idiothetic and the allothetic sources. When in motion, a robot can use dead reckoning methods such as tracking the number of revolutions of its wheels; this corresponds to the idiothetic source and can give the absolute position of the robot, but it is subject to cumulative error which can grow quickly.
The allothetic source corresponds the sensors of the robot, like a camera, a microphone, laser, lidar or sonar. The problem here is "perceptual aliasing". This means that two different places can be perceived as the same. For example, in a building, it is nearly impossible to determine a location solely with the visual information, because all the corridors may look the same. 3-dimensional models of a robot's environment can be generated using range imaging sensors or 3D scanners.
Map representation
The internal representation of the map can be "metric" or "topological":
The metric framework is the most common for humans and considers a two-dimensional space in which it places the objects. The objects are placed with precise coordinates. This representation is very useful, but is sensitive to noise and it is difficult to calculate the distances precisely.
The topological framework only considers places and relations between them. Often, the distances between places are stored. The map is then a graph, in which the nodes corresponds to places and arcs correspond to the paths.
Many techniques use probabilistic representations of the map, in order to handle uncertainty.
There are three main methods of map representations, i.e., free space maps, object maps, and composite maps. These employ the notion of a grid, but permit the resolution of the grid to vary so that it can become finer where more accuracy is needed and more coarse where the map is uniform.
Map learning
Map learning cannot be separated from the localization process, and a difficulty arises when errors in localization are incorporated into the map. This problem is commonly referred to as Simultaneous localization and mapping (SLAM).
An important additional problem is to determine whether the robot is in a part of environment already stored or never visited. One way to solve this problem is by using electric beacons, Near field communication (NFC), WiFi, Visible light communication (VLC) and Li-Fi and Bluetooth.
Path planning
Path planning is an important issue as it allows a robot to get from point A to point B. Path planning algorithms are measured by their computational complexity. The feasibility of real-time motion planning is dependent on the accuracy of the map (or floorplan), on robot localization and on the number of obstacles. Topologically, the problem of path planning is related to the shortest path problem of finding a route between two nodes in a graph.
Robot navigation
Outdoor robots can use GPS in a similar way to automotive navigation systems.
Alternative systems can be used with floor plan and beacons instead of maps for indoor robots, combined with localization wireless hardware. Electric beacons can help for cheap robot navigational systems.
See also
Automotive navigation system
Domestic robot
AVM Navigator
Dead reckoning
Electric beacon
GPS
Home automation for the elderly and disabled
Internet of Things (IoT)
Indoor positioning system
Map database management
Maze Simulator
Mobile robot
Neato Robotics
PatrolBot
Real-time locating system (RTLS).
Robotics suite
Occupancy grid
Simultaneous localization and mapping (SLAM)
Multi Autonomous Ground-robotic International Challenge: A challenge requiring multiple vehicles to collaboratively map a large dynamic urban environment
Wayfinding
Wi-Fi positioning system (WPS)
References
Cartography
Indoor positioning system | Robotic mapping | [
"Technology"
] | 897 | [
"Wireless networking",
"Wireless locating",
"Indoor positioning system"
] |
623,150 | https://en.wikipedia.org/wiki/Windage | Windage is a term used in aerodynamics, firearms ballistics, and automobiles that mainly relates to the effects of air (e.g., wind) on an object of interest. The term is also used for the similar effects of liquids, such as oil.
Usage
Aerodynamics
Windage is a force created on an object by friction when there is relative movement between air and the object. Windage loss is the reduction in efficiency due to windage forces.
For example, electric motors are affected by friction between the rotor and air. Large alternators have significant losses due to windage. To reduce losses, hydrogen gas may be used, since it is less dense.
There are two causes of windage:
The object is moving and being slowed by resistance from the air.
A wind is blowing, producing a force on the object.
The term can refer to:
The effect of the force, for example the deflection of a missile or an aircraft by a cross wind.
The area and shape of the object that make it susceptible to friction, for example those parts of a boat that are exposed to the wind.
Aerodynamic streamlining can be used to reduce windage.
There is a hydrodynamic effect similar to windage, hydrodynamic drag.
Ballistics
In firearms parlance, the word windage refers to the sight adjustment used to compensate for the horizontal deviation of the projectile trajectory from the intended point of impact due to wind drift or Coriolis effect. By contrast, the adjustment for the vertical deviation is the elevation.
The colloquial term "Kentucky windage" refers to the practice of holding the aim to the upwind side of the target (also known as deflection shooting or "leading" the wind) to compensate for wind drift, without actually changing the existing adjustment settings on the gunsight.
In muzzleloading firearms, windage also refers to the difference in diameter between the bore and the ball, especially in muskets and cannons. The bore gap allows the shot to be loaded quickly, but reduces the efficiency of the weapon's internal ballistics, as it allows gas to leak past the projectile. It also reduces the accuracy, as the ball takes a zig-zag path along the barrel, emerging out of the muzzle at an unpredictable angle.
Automobiles
In automotive parlance, windage refers to parasitic drag on the crankshaft due to sump oil splashing on the crank train during rough driving, as well as dissipating energy in turbulence from the crank train moving the crankcase gas and oil mist at high RPM. Windage may also inhibit the migration of oil into the sump and back to the oil pump, creating lubrication problems. Some manufacturers and aftermarket vendors have developed special scrapers to remove excess oil from the counterweights and windage screens to create a barrier between the crankshaft and oil sump.
See also
Deflection (ballistics)
Drag (physics)
References
Navigation
Ballistics
Nautical terminology
Engines | Windage | [
"Physics",
"Technology"
] | 608 | [
"Machines",
"Applied and interdisciplinary physics",
"Engines",
"Physical systems",
"Ballistics"
] |
623,154 | https://en.wikipedia.org/wiki/Assessment%20of%20kidney%20function | Assessment of kidney function occurs in different ways, using the presence of symptoms and signs, as well as measurements using urine tests, blood tests, and medical imaging.
Functions of a healthy kidney include maintaining a person's fluid balance, maintaining an acid-base balance; regulating electrolytes sodium, and other electrolytes; clearing toxins; regulating blood pressure; and regulating hormones, such as erythropoietin; and activation of vitamin D. The kidney is also involved in maintaining blood pH balance.
Description
The functions of the kidney include maintenance of acid-base balance; regulation of fluid balance; regulation of sodium, potassium, and other electrolytes; clearance of toxins; absorption of glucose, amino acids, and other small molecules; regulation of blood pressure; production of various hormones, such as erythropoietin; and activation of vitamin D.
The Glomerular filtration rate (GFR) is regarded as the best overall measure of the kidney's ability to carry out these numerous functions. An estimate of the GFR is used clinically to determine the degree of kidney impairment and to track the progression of the disease. The GFR, however, does not reveal the source of the kidney disease. This is accomplished by urinalysis, measurement of urine protein excretion, kidney imaging, and, if necessary, kidney biopsy.
Much of renal physiology is studied at the level of the nephron the smallest functional unit of the kidney. Each nephron begins with a filtration component that filters the blood entering the kidney. This filtrate then flows along the length of the nephron, which is a tubular structure lined by a single layer of specialized cells and surrounded by capillaries. The major functions of these lining cells are the reabsorption of water and small molecules from the filtrate into the blood, and the secretion of wastes from the blood into the urine.
Proper function of the kidney requires that it receives and adequately filters blood. This is performed at the microscopic level by many hundreds of thousands of filtration units called renal corpuscles, each of which is composed of a glomerulus and a Bowman's capsule. A global assessment of renal function is often ascertained by estimating the rate of filtration, called the glomerular filtration rate (GFR).
Clinical assessment
Clinical assessment can be used to assess the function of the kidneys. This is because a person with abnormally functioning kidneys may have symptoms that develop. For example, a person with chronic kidney disease may develop oedema due to failure of the kidneys to regulate water balance. They may develop evidence of chronic kidney disease, that can be used to assess its severity, for example high blood pressure, osteoporosis or anaemia. If the kidneys are unable to excrete urea, a person may develop a widespread itch or confusion.
Urine tests
Part of the assessment of kidney function includes the measurement of urine and its contents. Abnormal kidney function may cause too much or too little urine to be produced. The ability of the kidneys to filter protein is often measured, as urine albumin or urine protein levels, measured either at a single instance or, because of variation throughout the day, as 24-hour urine tests.
Blood tests
Blood tests are also used to assess kidney function. These include tests that are intended to directly measure the function of the kidneys, as well as tests that assess the function of the kidneys by looking for evidence of problems associated with abnormal function. One of the measures of kidney function is the glomerular filtration rate (GFR). Other tests that can assess the function of the kidneys include assessment of electrolyte levels such as potassium and phosphate, assessment of acid-base status by the measurement of bicarbonate levels from a vein, and assessment of the full blood count for anaemia.
Glomerular filtration rate
The glomerular filtration rate (GFR) describes the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman's capsule per unit time. Creatinine clearance (CCr) is the volume of blood plasma that is cleared of creatinine per unit time and is a useful measure for approximating the GFR. Creatinine clearance exceeds GFR due to creatinine secretion, which can be blocked by cimetidine. Both GFR and CCr may be accurately calculated by comparative measurements of substances in the blood and urine, or estimated by formulas using just a blood test result (eGFR and eCCr) The results of these tests are used to assess the excretory function of the kidneys. Staging of chronic kidney disease is based on categories of GFR as well as albuminuria and cause of kidney disease.
Central to the physiologic maintenance of GFR is the differential basal tone of the afferent and efferent arterioles (see diagram). In other words, the filtration rate is dependent on the difference between the higher blood pressure created by vasoconstriction of the input or afferent arteriole versus the lower blood pressure created by lesser vasoconstriction of the output or efferent arteriole.
GFR is equal to the renal clearance ratio when any solute is freely filtered and is neither reabsorbed nor secreted by the kidneys. The rate therefore measured is the quantity of the substance in the urine that originated from a calculable volume of blood. Relating this principle to the below equation – for the substance used, the product of urine concentration and urine flow equals the mass of substance excreted during the time that urine has been collected. This mass equals the mass filtered at the glomerulus as nothing is added or removed in the nephron. Dividing this mass by the plasma concentration gives the volume of plasma which the mass must have originally come from, and thus the volume of plasma fluid that has entered Bowman's capsule within the aforementioned period of time. The GFR is typically recorded in units of volume per time, e.g., milliliters per minute (mL/min). Compare to filtration fraction.
There are several different techniques used to calculate or estimate the glomerular filtration rate (GFR or eGFR). The above formula only applies for GFR calculation when it is equal to the clearance rate.
The normal range of GFR, adjusted for body surface area, is 100–130 average 125 (mL/min)/(1.73 m2) in men and 90–120 (mL/min)/(1.73 m2) in women younger than the age of 40. In children, GFR measured by inulin clearance is 110 (mL/min)/(1.73 m2) until 2 years of age in both sexes, and then it progressively decreases. After age 40, GFR decreases progressively with age, by 0.4–1.2 mL/min per year.
Estimated GFR (eGFR) is now recommended by clinical practice guidelines and regulatory agencies for routine evaluation of GFR whereas measured GFR (mGFR) is recommended as a confirmatory test when more accurate assessment is required.
Medical imaging
The kidney function can also be assessed with medical imaging. Some forms of imaging, such as kidney ultrasound or CT scans, may assess kidney function by indicating chronic disease that can impact function, by showing a small or shrivelled kidney.. Other tests, such as nuclear medicine tests, directly assess the function of the kidney by measuring the perfusion and excretion of radioactive substances through the kidneys.
Kidney function in disease
A decreased renal function can be caused by many types of kidney disease. Upon presentation of decreased renal function, it is recommended to perform a history and physical examination, as well as performing a renal ultrasound and a urinalysis. The most relevant items in the history are medications, edema, nocturia, gross hematuria, family history of kidney disease, diabetes and polyuria. The most important items in a physical examination are signs of vasculitis, lupus erythematosus, diabetes, endocarditis and hypertension.
A urinalysis is helpful even when not showing any pathology, as this finding suggests an extrarenal etiology. Proteinuria and/or urinary sediment usually indicates the presence of glomerular disease. Hematuria may be caused by glomerular disease or by a disease along the urinary tract.
The most relevant assessments in a renal ultrasound are renal sizes, echogenicity and any signs of hydronephrosis. Renal enlargement usually indicates diabetic nephropathy, focal segmental glomerular sclerosis or myeloma. Renal atrophy suggests longstanding chronic renal disease.
Chronic kidney disease stages
Risk factors for kidney disease include diabetes, high blood pressure, family history, older age, ethnic group and smoking.
For most patients, a GFR over 60 (mL/min)/(1.73 m2) is adequate. But significant decline of the GFR from a previous test result can be an early indicator of kidney disease requiring medical intervention. The sooner kidney dysfunction is diagnosed and treated the greater odds of preserving remaining nephrons, and preventing the need for dialysis.
The severity of chronic kidney disease (CKD) is described by six stages; the most severe three are defined by the MDRD-eGFR value, and first three also depend on whether there is other evidence of kidney disease (e.g., proteinuria):
0) Normal kidney function – GFR above 90 (mL/min)/(1.73 m2) and no proteinuria
1) CKD1 – GFR above 90 (mL/min)/(1.73 m2) with evidence of kidney damage
2) CKD2 (mild) – GFR of 60 to 89 (mL/min)/(1.73 m2) with evidence of kidney damage
3) CKD3 (moderate) – GFR of 30 to 59 (mL/min)/(1.73 m2)
4) CKD4 (severe) – GFR of 15 to 29 (mL/min)/(1.73 m2)
5) CKD5 kidney failure – GFR less than 15 (mL/min)/(1.73 m2) Some people add CKD5D for those stage 5 patients requiring dialysis; many patients in CKD5 are not yet on dialysis.
Note: others add a "T" to patients who have had a transplant regardless of stage.
Not all clinicians agree with the above classification, suggesting that it may mislabel patients with mildly reduced kidney function, especially the elderly, as having a disease. A conference was held in 2009 regarding these controversies by Kidney Disease: Improving Global Outcomes (KDIGO) on CKD: Definition, Classification and Prognosis, gathering data on CKD prognosis to refine the definition and staging of CKD.
See also
References
External links
Online calculators
Online GFR Calculator
Schwartz formula for estimating pediatric renal function
Creatinine clearance calculator (Cockcroft-Gault Equation)- by MDCalc
MDRD GFR Equation
GFR calculator using Cystatin C
Reference links
National Kidney Disease Education Program website. Includes professional references and GFR calculators
eGFR at Lab Tests Online
Renal physiology
Blood tests | Assessment of kidney function | [
"Chemistry"
] | 2,383 | [
"Blood tests",
"Chemical pathology"
] |
623,174 | https://en.wikipedia.org/wiki/Von%20Willebrand%20factor | Von Willebrand factor (VWF) () is a blood glycoprotein that promotes primary hemostasis, specifically, platelet adhesion. It is deficient and/or defective in von Willebrand disease and is involved in many other diseases, including thrombotic thrombocytopenic purpura, Heyde's syndrome, and possibly hemolytic–uremic syndrome. Increased plasma levels in many cardiovascular, neoplastic, metabolic (e.g. diabetes), and connective tissue diseases are presumed to arise from adverse changes to the endothelium, and may predict an increased risk of thrombosis.
Biochemistry
Synthesis
VWF is a large multimeric glycoprotein present in blood plasma and produced constitutively as ultra-large VWF in endothelium (in the Weibel–Palade bodies) and megakaryocytes (α-granules of platelets).
Structure
VWF is synthesized as a prepropeptide comprising 2813 amino acids in endothelial cells and megakaryocytes. The prepropeptide includes a 22-amino acid signal peptide (SP), a 741-amino acid propeptide (VWFpp), and a 2050-amino acid mature VWF monomer. The signal peptide directs the prepropeptide to the endoplasmic reticulum, where it is cleaved, resulting in the formation of pro-VWF. Pro-VWF undergoes glycosylation, forms disulfide bonds, and dimerizes under neutral pH and the influence of Protein Disulfide Isomerase A1 (PDIA1).
Dimerized pro-VWF is then transported to the Golgi apparatus, where it forms "dimeric bouquets" and undergoes further glycosylation. The propeptide is cleaved by furin, but remains associated with the mature VWF in a non-covalent manner. This association persists until the propeptide dissociates, yielding mature VWF monomers, which subsequently dimerize and multimerize. Although the fundamental structure of mature VWF is monomeric, the smallest form detectable in blood plasma is a VWF dimer.
The basic monomer of VWF, a 2050-amino acid protein, contains several key domains with specific functions:
The D'/D3 domain: Binds to factor VIII, heparin, and P-selectin.
The A1 domain: Binds to the platelet GPIb-receptor, collagen types IV and VI, heparin, and osteoprotegerin.
The A2 domain: Unfolds to expose the cleavage site for ADAMTS13 protease, which cleaves VWF into smaller multimers. Unfolding is influenced by blood shear flow, calcium binding, and a "vicinal disulfide" at the A2-domain’s C-terminus.
The A3 domain: Acts as the primary collagen binding site for VWF, binding to collagen types I and III.
The C4 domain: Contains an RGD motif that binds to platelet integrin αIIbβ3.
The CK (cystine knot) domain at the protein’s C-terminal end: Involved in VWF dimerization.
VWF is one of the few proteins carrying ABO blood group antigens. After glycosylation in the Golgi apparatus, VWF is packaged into storage granules, Weibel-Palade bodies (WPBs) in endothelial cells, and α-granules in platelets.
Function
Von Willebrand Factor's primary function is binding to other proteins, in particular factor VIII, and it is important in platelet adhesion to wound sites. It is not an enzyme and, thus, has no catalytic activity.
VWF binds to a number of cells and molecules. The most important ones are:
Factor VIII is bound to VWF while inactive in circulation; factor VIII degrades rapidly when not bound to VWF. Factor VIII is released from VWF by the action of thrombin. In the absence of VWF, factor VIII has a half-life of 1–2 hours; when carried by intact VWF, factor VIII has a half-life of 8–12 hours.
VWF binds to collagen, e.g., when collagen is exposed beneath endothelial cells due to damage occurring to the blood vessel. Endothelium also releases VWF which forms additional links between the platelets' glycoprotein Ib/IX/V and the collagen fibrils
VWF binds to platelet GpIb when it forms a complex with gpIX and gpV; this binding occurs under all circumstances, but is most efficient under high shear stress (i.e., rapid blood flow in narrow blood vessels, see below).
VWF binds to other platelet receptors when they are activated, e.g., by thrombin (i.e., when coagulation has been stimulated).
VWF plays a major role in blood coagulation. Therefore, VWF deficiency or dysfunction (von Willebrand disease) leads to a bleeding tendency, which is most apparent in tissues having high blood flow shear in narrow vessels. From studies it appears that VWF uncoils under these circumstances, decelerating passing platelets. Recent research also suggests that von Willebrand Factor is involved in the formation of blood vessels themselves, which would explain why some people with von Willebrand disease develop vascular malformations (predominantly in the digestive tract) that can bleed excessively.
Catabolism
The biological breakdown (catabolism) of VWF is largely mediated by the enzyme ADAMTS13 (acronym of "a disintegrin-like and metalloprotease with thrombospondin type 1 motif no. 13"). It is a metalloproteinase that cleaves VWF between tyrosine at position 842 and methionine at position 843 (or 1605–1606 of the gene) in the A2 domain. This breaks down the multimers into smaller units, which are degraded by other peptidases.
The half-life of vWF in human plasma is around 16 hours; glycosylation variation on vWF molecules from different individuals result in a larger range of 4.2 to 26 hours. Liver cells as well as macrophages take up vWF for clearance via ASGPRs and LRP1. SIGLEC5 and CLEC4M also recognize vWF.
Role in disease
Hereditary or acquired defects of VWF lead to von Willebrand disease (vWD), a bleeding diathesis of the skin and mucous membranes, causing nosebleeds, menorrhagia, and gastrointestinal bleeding. The point at which the mutation occurs determines the severity of the bleeding diathesis. There are three types (I, II and III), and type II is further divided in several subtypes. Treatment depends on the nature of the abnormality and the severity of the symptoms. Most cases of vWD are hereditary, but abnormalities of VWF may be acquired; aortic valve stenosis, for instance, has been linked to vWD type IIA, causing gastrointestinal bleeding - an association known as Heyde's syndrome.
In thrombotic thrombocytopenic purpura (TTP) and hemolytic–uremic syndrome (HUS), ADAMTS13 either is deficient or has been inhibited by antibodies directed at the enzyme. This leads to decreased breakdown of the ultra-large multimers of VWF and microangiopathic hemolytic anemia with deposition of fibrin and platelets in small vessels, and capillary necrosis. In TTP, the organ most obviously affected is the brain; in HUS, the kidney.
Higher levels of VWF are more common among people that have had ischemic stroke (from blood-clotting) for the first time. Occurrence is not affected by ADAMTS13, and the only significant genetic factor is the person's blood group. High plasma VWF levels were found to be an independent predictor of major bleeding in anticoagulated atrial fibrillation patients. VWF is a marker of endothelial dysfunction, and is consistently elevated in atrial fibrillation, associated with adverse outcomes.
History
VWF is named after Erik Adolf von Willebrand, a Finnish physician who in 1926 first described a hereditary bleeding disorder in families from Åland. Although von Willebrand did not identify the definite cause, he distinguished von Willebrand disease (vWD) from hemophilia and other forms of bleeding diathesis.
In the 1950s, vWD was shown to be caused by a plasma factor deficiency (instead of being caused by platelet disorders), and, in the 1970s, the VWF protein was purified.
Harvey J. Weiss and coworkers developed a quantitative assay for VWF function that remains a mainstay of laboratory
evaluation for VWD to this day.
Interactions
Von Willebrand Factor has been shown to interact with Collagen, type I, alpha 1.
Recently, It has been reported that the cooperation and interactions within the von Willebrand Factors enhances the adsorption probability in the primary haemostasis. Such cooperation is proven by calculating the adsorption probability of flowing VWF once it crosses another adsorbed one. Such cooperation is held within a wide range of shear rates.
See also
von Willebrand disease
Bernard–Soulier syndrome
References
External links
GeneReviews/NCBI/NIH/UW entry on von Willebrand Factor Deficiency. Includes: Type 1 von Willebrand Disease, Type 2A von Willebrand Disease, Type 2B von Willebrand Disease, Type 2M von Willebrand Disease, Type 2N von Willebrand Disease, Type 3 von Willebrand Disease
Blood proteins
Coagulation system
Glycoproteins | Von Willebrand factor | [
"Chemistry"
] | 2,149 | [
"Glycoproteins",
"Glycobiology"
] |
623,199 | https://en.wikipedia.org/wiki/Radial%20arm%20saw | A radial arm saw is a cutting machine consisting of a circular saw mounted on a sliding horizontal arm. Invented by Raymond DeWalt in 1922, the radial arm saw was the primary tool used for cutting long pieces of stock to length until the introduction of the power miter saw in the 1970s.
In addition to making length cuts, a radial arm saw may be configured with a dado blade to create cuts for dado, rabbet or half lap joints. In addition some radial arm saws allow the blade to be turned parallel to the back fence, allowing a rip cut to be performed.
Origins
Unlike most types of woodworking machinery, the radial arm saw has a clear genesis: it was invented by Raymond DeWalt of Leola, Pennsylvania. DeWalt applied for patents in 1923, which were issued in 1925 (US Patent 1,528,536). DeWalt and others subsequently patented many variations on the original, but DeWalt's original design (sold under the moniker Wonder Worker) remained the most successful: a circular saw blade directly driven by an electric motor held in a yoke sliding along a horizontal arm that is some distance above a horizontal table surface. A saw which combines the sliding and compound features is known as a sliding compound miter saw or SCMS.
Before the advent of the radial arm saw, table saws and hand saws were most commonly used for crosscutting lumber. Table saws can easily rip stock, but it is awkward to push a long piece of stock widthwise through a table saw blade. In contrast, when a radial arm saw is used for crosscutting, the stock remains stationary on the saw's table, and the blade is pulled through it.
During the late 1970s, the compound miter saw began to replace the radial arm saw, but only for crosscuts and miter cuts since miter saws are unable to perform rip cuts. The radial arm saw can be less safe when used by an inexperienced or untrained operator, but is not as dangerous when used properly. In the hands of an experienced operator, the radial arm saw can safely cut compound miters necessary for picture and door frames, rip lumber precisely to width, cut tongues and grooves, and make variable dadoes. Like the compound miter saw, the radial arm saw can make these cuts with absolute precision, but is capable of making a wider variety of cuts, including more complex ones.
In the home shop the radial arm saw is an alternative to the table saw. Both machines can rip, crosscut, do simple and compound miters, dado, mold or shape, make tenons, make open mortises, taper cut, and rabbet. The radial arm saw requires less clearance or space in the shop to handle long stock, since it only requires clearance on the sides, whereas a table saw needs clearance to the sides, in front and at the back. The radial saw is perfectly effective backed up against a wall, whereas the table saw needs to be placed in the center of the shop to give all around clearance. With some accessories the former can be used as a shaper, a disk or drum sander, a grinder, a surface planer, a router, a horizontal boring machine and even as a power unit for a lathe; whereas a table saw's secondary uses are limited to shaper and disk sander.
The major shortcoming of most current radial arm saws for home-use is that, most radial arm saws that have been built after the early 1960s are manufactured with stamped sheet metal parts and are machined to loose tolerances, hence they are not precise for doing accurate work without 'tuning'. A high-quality radial arm saw has carefully machined track arm ways and locking mechanisms, and a motor that runs very smoothly; under 'no-load' conditions most of the sound and vibration will originate from the whisper/whistling and the imbalance of the saw blade upon the arbor.
The saw tilts on all axes except vertical slope – see photo (all points of rotation are not clear in photo).
If machining depth cuts, the radial arm saw allows one to see the progress. With the (wood) clamped and using the arm (not hand feeding, which is also possible), the cuts are better machined and require no jig setup; the advantage is not widely needed however. Cutting full depth is less convenient, as the saw lowers into the table, cutting the table (often a wood table for that reason).
"Top cutting" machined saw table with differing axis designs are still made and sold.
Safety
Power saws can easily cut off fingers. Furthermore, a dull blade will grab lumber with enough force to kick it through a wall. A new blade has less tendency to grab but still requires proper feeding.
Radial arm saws are safer with a blade with a very low or negative hook angle, to inhibit overly fast feed rate, binding, and the blade's tendency to try to "climb" the material. Also, a 10 degree positive hook blade with a "triple chip profile" works well on the radial arm saw and can be considered a universal blade. If the saw climbs with this blade, the yoke roller bearings need to be adjusted and tightened.
Occupational Safety and Health Association (OSHA) Requirements in the United States
According to OSHA regulation 1910.213(h)(1): The upper hood shall completely enclose the upper portion of the blade down to a point that will include the end of the saw arbor. The upper hood shall be constructed in such a manner and of such material that it will protect the operator from flying splinters, broken saw teeth, etc., and will deflect sawdust away from the operator. The sides of the lower exposed portion of the blade shall be guarded to the full diameter of the blade by a device that will automatically adjust itself to the thickness of the stock and remain in contact with stock being cut to give maximum protection possible for the operation being performed.
References
External links
Link to DeWalt's 1925 patent
Link to Radial Arm Saw Discussion Forum
Saws
Woodworking machines
American inventions | Radial arm saw | [
"Physics",
"Technology"
] | 1,258 | [
"Physical systems",
"Machines",
"Woodworking machines"
] |
623,238 | https://en.wikipedia.org/wiki/Netherlands%20Agency%20for%20Aerospace%20Programmes | The Netherlands Agency for Aerospace Programmes (in Dutch language, Nederlands Instituut voor Vliegtuigontwikkeling en Ruimtevaart (NIVR)) was the official space exploration agency of the Dutch government until 2009.
Since 1 July 2009, the space-exploration activities of the NIVR are merged into the newly formed Netherlands Space Office (NSO).
See also
European Space Agency (ESA)
Netherlands Space Office (NSO)
References
External links
nivr.nl, Nederlands Instituut voor Vliegtuigontwikkeling en Ruimtevaart (NIVR) (Netherlands Agency for Aerospace Programmes) official website (website in Dutch language). Accessed 12 February 2010.
spaceoffice.nl, Netherlands Space Office (NSO) official website (website in Dutch language; toggle switch to English-language version offered in top bar). Accessed 12 February 2010.
Government agencies of the Netherlands
Government agencies disestablished in 2009
Science and technology in the Netherlands
Space agencies | Netherlands Agency for Aerospace Programmes | [
"Astronomy"
] | 217 | [
"Astronomy stubs",
"Astronomy organizations",
"Astronomy organization stubs"
] |
623,243 | https://en.wikipedia.org/wiki/Science%20and%20Engineering%20Research%20Council | The Science and Engineering Research Council (SERC) and its predecessor the Science Research Council (SRC) were the UK agencies in charge of publicly funded scientific and engineering research activities, including astronomy, biotechnology and biological sciences, space research and particle physics, between 1965 and 1994.
History
The SERC also had oversight of:
the Royal Greenwich Observatory (RGO)
the Royal Observatory Edinburgh (ROE)
the Rutherford Appleton Laboratory (RAL)
the Daresbury Laboratory
From its formation in 1965 until 1981 it was known as the Science Research Council (SRC). The SRC had been formed in 1965 as a result of the Trend Committee enquiry into the organisation of civil science in the UK. Previously the Minister for Science had been responsible for various research activities in the Department of Scientific and Industrial Research (DSIR) and more loosely with a variety of agencies concerned with the formulation of civil scientific policy. One of the main problems addressed by the enquiry was how to decide the priorities for government funding across all areas of scientific research. Previously this task had been the responsibility of the Treasury without direct scientific advice. The other Research Councils formed in 1965 were:
the Natural Environment Research Council (NERC)
the Social Science Research Council (SSRC)
the Agricultural Research Council (ARC)
These bodies joined the Medical Research Council (MRC) which had existed since 1920. In 1981, to reflect the increased emphasis on engineering research, the SRC was renamed the Science and Engineering Research Council. In 1994, the new Director General of Research Councils was charged with reorganization of the four existing research councils, and this resulted in the SERC being split three bodies:
the Particle Physics and Astronomy Research Council (PPARC)
the Engineering and Physical Sciences Research Council (EPSRC)
the Biotechnology and Biological Sciences Research Council (BBSRC)
The two Observatories were moved under the aegis of PPARC, and the Laboratories initially into EPSRC and later into their own organization, the Council for the Central Laboratory of the Research Councils (CCLRC).
In 2007 CCLRC and PPARC were merged to form the Science and Technology Facilities Council (STFC), with responsibility for nuclear physics being transferred from EPSRC to STFC.
See also
ORRF Risk Research Forum
Packet switching § SRCnet/SERCnet
References
Science and technology in the United Kingdom
Research councils
1965 establishments in the United Kingdom
1994 disestablishments in the United Kingdom
Organizations established in 1984
Organizations disestablished in 1991
Engineering organizations
Research in the United Kingdom | Science and Engineering Research Council | [
"Engineering"
] | 513 | [
"nan"
] |
623,281 | https://en.wikipedia.org/wiki/HOOD%20method | HOOD (Hierarchic Object-Oriented Design) is a detailed software design method. It is based on hierarchical decomposition of a software problem. It comprises textual and graphical representations of the design.
HOOD was initially created for the European Space Agency and is used in such varied domains as aerospace (Eurofighter Typhoon, Helios 2 Earth Observation ground control, Ariane 5 on-board computer), ground transportation, and nuclear plants.
HOOD main target languages are Ada, Fortran and C.
External links
Introduction to HOOD HOOD page at ESA
ESA's HOOD user manual, gzipped postscript
Software design
Data modeling languages
Specification languages | HOOD method | [
"Technology",
"Engineering"
] | 129 | [
"Specification languages",
"Computer science stubs",
"Software engineering",
"Computer science",
"Computing stubs",
"Design",
"Software design"
] |
623,379 | https://en.wikipedia.org/wiki/Haldane%27s%20rule | Haldane's rule is an observation about the early stage of speciation, formulated in 1922 by the British evolutionary biologist J. B. S. Haldane, that states that if — in a species hybrid — only one sex is inviable or sterile, that sex is more likely to be the heterogametic sex. The heterogametic sex is the one with two different sex chromosomes; in therian mammals, for example, this is the male.
Overview
Haldane himself described the rule as:
Haldane's rule applies to the vast majority of species that have heterogametic chromosomal sex determination (e.g. XX females vs. XY males, or ZW females vs. ZZ males).
The rule includes both male heterogametic (XY or XO-type sex determination, such as found in mammals and Drosophila fruit flies) and female heterogametic (ZW or Z0-type sex determination, as found in birds and butterflies), and some dioecious plants such as campions.
Hybrid dysfunction (sterility and inviability) is a major form of post-zygotic reproductive isolation, which occurs in early stages of speciation. Evolution can produce a similar pattern of isolation in a vast array of different organisms. However, the actual mechanisms leading to Haldane's rule in different taxa remain largely undefined.
Hypotheses
Many different hypotheses have been advanced to address the evolutionary mechanisms to produce Haldane's rule. Currently, the most popular explanation for Haldane's rule is the composite hypothesis, which divides Haldane's rule into multiple subdivisions, including sterility, inviability, male heterogamety, and female heterogamety. The composite hypothesis states that Haldane's rule in different subdivisions has different causes. Individual genetic mechanisms may not be mutually exclusive, and these mechanisms may act together to cause Haldane's rule in any given subdivision. In contrast to these views that emphasize genetic mechanisms, another view hypothesizes that population dynamics during population divergence may cause Haldane's rule.
The main genetic hypotheses are:
Dominance: Heterogametic hybrids are affected by all X-linked alleles (be they recessive or dominant) causing incompatibilities due to divergent alleles being brought together. However, homogametic hybrids are only affected by dominant deleterious X-linked alleles. Heterogametic hybrids, which carry only a single copy of a given X-linked gene, will be affected by mutations regardless of dominance. Thus, an X-linked incompatibility between diverging populations is more likely to be expressed in the heterogametic sex than in the homogametic sex.
The "faster male": Male genes are thought to evolve faster due to sexual selection. As a result, male sterility becomes more evident in male heterogametic taxa (XY sex determination). This hypothesis conflicts with Haldane's rule in male homogametic taxa, in which females are more affected by hybrid inferiority. It therefore only applies to male sterility in taxa with XY sex determination, according to the composite theory.
Meiotic drive: In hybrid populations, selfish genetic elements inactivate sperm cells (i.e.: an X-linked drive factor inactivates a Y-bearing sperm and vice versa).
The "faster X": Genes on hemizygous chromosomes may evolve more quickly by enhancing selection on possible recessive alleles causing a larger effect in reproductive isolation.
Differential selection: Hybrid incompatibilities affecting the heterogametic sex and homogametic sex are fundamentally different isolating mechanisms, which makes heterogametic inferiority (sterility/inviability) more visible or preserved in nature.
Data from multiple phylogenetic groups support a combination of dominance and faster X-chromosome theories. However, it has recently been argued that dominance theory can not explain Haldane's rule in marsupials since both sexes experience the same incompatibilities due to paternal X-inactivation in females.
The dominance hypothesis is the core of the composite theory, and X-linked recessive/dominance effects have been demonstrated in many cases to cause hybrid incompatibilities. There is also supporting evidence for the faster male and meiotic drive hypotheses. For example, a significant reduction of male-driven gene flow is observed in Asian elephants, suggesting faster evolution of male traits.
Although the rule was initially stated in context of diploid organisms with chromosomal sex determination, it has recently been argued that it can be extended to certain species lacking chromosomal sex determination, such as haplodiploids and hermaphrodites.
Exceptions
In some instances, the homogametic sex turns out to be inviable while the heterogametic sex is viable and fertile. This is seen in some Drosophila fruit flies.
Notes
References
Further reading
Evolutionary biology
Rules of thumb
Works by J. B. S. Haldane
Biological rules
Hybridisation (biology) | Haldane's rule | [
"Biology"
] | 1,067 | [
"Evolutionary biology",
"Biological rules",
"nan"
] |
623,465 | https://en.wikipedia.org/wiki/Metallate | Metallate or metalate is the name given to any complex anion containing a metal ligated to several atoms or small groups.
Typically, the metal will be one of the transition elements and the ligand will be oxygen or another chalcogenide or a cyanide group (though others are known). The chalcogenide metallates are known as oxometallates, thiometallates, selenometallates and tellurometallates; the cyanide metallates are known as cyanometallates.
Oxometallates include permanganate (), chromate () and vanadate ( or ).
Thiometallates include tetrathiovanadate (), tetrathiomolybdate (), tetrathiotungstate () and similar ions.
Cyanometallates include ferricyanide and ferrocyanide.
Metallate is also used as a verb by bioinorganic chemistry to describe the act of adding metal atoms or ions to a site (synthetic ligand or protein).
References
Anions | Metallate | [
"Physics",
"Chemistry"
] | 230 | [
"Matter",
"Metallates",
"Inorganic compounds",
"Anions",
"Coordination chemistry",
"Inorganic compound stubs",
"Ions"
] |
623,472 | https://en.wikipedia.org/wiki/The%20Palace%20of%20Auburn%20Hills | The Palace of Auburn Hills, commonly known as the Palace, was a multi-purpose arena located in Auburn Hills, Michigan. Opened in 1988, it was the home of the Detroit Pistons of the National Basketball Association (NBA), the Detroit Shock of the Women's National Basketball Association (WNBA), the Detroit Vipers of the International Hockey League, the Detroit Rockers of the National Professional Soccer League, the Detroit Neon/Detroit Safari of the Continental Indoor Soccer League, and the Detroit Fury of the Arena Football League.
The Palace was one of eight basketball arenas owned by their respective NBA franchises. The Pistons moved to Little Caesars Arena in Midtown Detroit in 2017 and the Palace was demolished in 2020.
Naming
By the time it closed as an NBA venue, the Palace was one of only two arenas that had not sold its naming rights to a corporate sponsor. The other was Madison Square Garden.
The court was previously named the "William Davidson Court", in honor of late owner Bill Davidson, prior to the Pistons' home opener on October 30, 2009. His signature, along with the retired numbers, were removed from the hardwood when Tom Gores bought the Palace and were re-retired on its rafters as replacement banners.
History
Background
From 1957 to 1978, the Pistons competed in Detroit's Olympia Stadium, Memorial Building, and Cobo Arena. In 1978, owner Bill Davidson elected not to share the new Joe Louis Arena with the National Hockey League's Detroit Red Wings, instead opting to relocate the team to the Pontiac Silverdome in suburban Pontiac, a venue constructed for football, where it remained for the next decade. While the Silverdome could accommodate massive crowds, it offered substandard sight lines for basketball games. In late 1985, a group led by Davidson decided to build a new arena in Auburn Hills. Groundbreaking for the arena took place in June 1986. Using entirely private funding, The Palace cost a relatively low price of $90 million. The Davidson family held a controlling interest in the arena until Tom Gores bought it as part of his purchase of the Pistons in 2011.
Construction
Then-Pistons owner Bill Davidson and two developers privately financed the $90 million construction of The Palace, and did not require public funds.
The Palace was built with 180 luxury suites, considered an exorbitant number when it opened, virtually all later consistently leased. In December 2005, the Palace added five underground luxury suites, each containing of space and renting for $450,000 per year. Eight more luxury suites, also located below arena level, were opened in February 2006. They range in size from and were rented for $350,000 annually. The architectural design of the Palace, including its multiple tiers of luxury suites, has been used as the basis for many other arenas in North America since its construction.
Basketball
The Palace opened in 1988. When one of its basketball occupants won a championship, the number on its address changed. Its address was 6 Championship Drive, reflecting the Pistons' three NBA titles and the Shock's three WNBA titles.
The Palace was widely considered to be the first of the modern-style NBA arenas, and its large number of luxury suites was a major reason for the building boom of new NBA arenas in the 1990s. Although the Palace became one of the oldest arenas in the NBA, its foresighted design contained the amenities that most NBA teams have sought in new arenas built since that time. By contrast, of the other NBA venues that opened during the 1988–89 season, Charlotte Coliseum, Miami Arena, the Bradley Center and ARCO Arena were considered obsolete relatively quickly, due to a lack of luxury suites and club seating, lucrative revenue-generating features that made pro sports teams financially successful in order to remain competitive long-term.
Nonetheless, Palace Sports & Entertainment (PS&E) had spent $117.5 million in upgrades and renovations to keep the arena updated. A new high definition JumboTron monitor, new LED video monitors, and more than of ribbon display technology from Daktronics was installed in the mid-2000s.
The Malice at the Palace
On November 19, 2004, a fight broke out between members of the Pistons and Indiana Pacers after Pacers forward Ron Artest committed a hard foul on Pistons center Ben Wallace. As the on-court fight died down, a fan, John Green, threw a cup of Diet Coke at Artest, who then ran into the stands to fight another fan, Michael Ryan, whom he mistakenly believed to be responsible, and this immediately escalated into a full-scale brawl between other fans and players. The fight lasted for several minutes and resulted in the suspension of nine players (including Artest, who was suspended for the remainder of the 2004–05 NBA season and also the playoffs), criminal charges against five players, and criminal charges against five spectators. The offending fans, including Green, Charlie Haddad and A.J. Shackleford, were banned for life from attending games at the Palace. In the aftermath of the fight, the NBA decided to increase the security presence between players and spectators. The fact that the fight took place at the Palace led to it becoming colloquially referred to as the "Malice at the Palace" and the "Basketbrawl".
On July 22, 2008, nearly four years after this incident, another fight took place at the Palace, this time between the Detroit Shock and Los Angeles Sparks of the WNBA. This fight was dubbed "The Malice at the Palace II".
Select concerts
During his ...Nothing Like the Sun Tour on August 13, 1988, Sting became the first musician to perform at the Palace.
Pink Floyd performed here on August 16–17, 1988, as part of their A Momentary Lapse of Reason Tour.
Michael Jackson performed three sold-out shows during his Bad World Tour on October 24–26, 1988.
Janet Jackson performed two shows here on August 22–23, 1990, as part of her Rhythm Nation World Tour. She returned July 30–31, 2001, on her All for You Tour.
On October 21, 1990 MC Hammer made a stop at the Palace as part of his Please Hammer Don't Hurt 'Em World Tour.
Aerosmith played the venue 14 times from 1990 to 2012.
Grateful Dead performed at the Palace eight times from 1992 to 1995.
Van Halen performed four shows on their For Unlawful Carnal Knowledge Tour on February 21–22, 1992, and on April 3–4, 1992. They also performed consecutive shows during their The Balance "Ambulance" Tour on April 15–16, 1995.
U2 performed at The Palace on March 27, 1992, on the first leg of their Zoo TV Tour. During the performance, Bono called a local pizza bar from the stage and ordered 10,000 pizzas for the crowd in attendance. Approximately 100 pizzas were delivered. They returned on May 30, 2001, for their Elevation Tour, and on October 24 and 25, 2005 for their Vertigo Tour.
The Cure performed two consecutive shows, during their Wish Tour on July 18–19, 1992, with The Cranes as their opening act. The shows were recorded and released as a live album, entitled Show.
Bon Jovi performed during their Keep the Faith world tour on March 2, 1993, their Crush Tour on November 18, 2000, their Lost Highway Tour on February 20 and July 7, 2008, and their Circle Tour in 2010.
The Palace was the site of an attempt on the life of Led Zeppelin guitarist Jimmy Page, while he was on tour, with former bandmate Robert Plant, during their No Quarter Tour. On March 31, 1995, Lance Alworth Cunningham, a 23-year-old who thought Led Zeppelin's music contained Satanic messages, tried to rush the stage with a knife. He was subdued about 50 feet from the stage.
Grand Funk Railroad performed a benefit show for Bosnia and Herzegovina in March 1997 on their Reunion Tour. The show also featured Peter Frampton, Alto Reed, Paul Shaffer, and the Detroit Symphony Orchestra. The performance was recorded, and released as the double-live Bosnia album in October of that year.
Phish played at the Palace during their fall 1997 tour on December 6, 1997.
The British group the Spice Girls performed at The Palace during their Spiceworld Tour on July 26, 1998.
Madonna performed two sold-out shows during her Drowned World Tour on August 25–26, 2001. The shows were recorded and broadcast live on HBO and were later released as a DVD, entitled Drowned World Tour 2001.
Prince brought his Musicology Live 2004ever tour to the Palace on June 20–21, 2004. He returned to the venue on July 31.
Australian children's music group The Wiggles performed at the Palace on August 15, 2005, with their "Sailing Around the World Live!" tour, August 11, 2006, with their "Wiggledancing! Live On Stage" tour, August 15, 2007, with their "Racing to The Rainbow Live!" tour, August 12, 2008, with their "Pop Go The Wiggles Live!" tour, August 14, 2009, with their "The Wiggles Go Bananas! Live in Concert" tour, August 27, 2010, with their "Wiggly Circus" tour, July 29, 2011, with their "Ukulele Baby! Live In Concert" tour, and August 10, 2012, with "The Celebration Tour!".
Three Days Grace held a concert at the Palace on March 21, 2008, which was recorded and released on DVD. Live at the Palace 2008 is their only full concert video to date.
Taylor Swift, who opened for Brad Paisley at the Palace on October 4, 2007, returned on March 26–27, 2010, playing back-to-back sold-out shows during her Fearless Tour.
Coldplay performed a sold-out show at the arena on August 1, 2012, as part of their Mylo Xyloto Tour. The band came back to the arena on August 3, 2016, to perform for a sold-out crowd of 15,436 as part of their A Head Full of Dreams Tour.
Replacement and demolition
In October 2016, it was reported that the Pistons' ownership were negotiating a possible relocation to Little Caesars Arena, a new multi-purpose venue then under construction in Midtown Detroit, for the 2017–18 season. Little Caesars Arena was initially designed for ice hockey to replace Joe Louis Arena as home of the National Hockey League's Detroit Red Wings, so some design modifications were needed to accommodate the Pistons. On November 22, 2016, the team officially announced that they would play at Little Caesars Arena in 2017. The final NBA game at The Palace was played on April 10, 2017, with the Pistons losing to the Washington Wizards, 105–101. This game ended a 42-year history of professional sports in Oakland County.
Bob Seger held the final concert at the venue on September 23, 2017. The last scheduled event at the venue was the Taste of Auburn Hills on October 12, 2017. Palace Sports & Entertainment entered into a joint venture with Olympia Entertainment known as 313 Presents to jointly manage entertainment bookings and promotions for Little Caesars Arena and other venues owned by the firms.
At its closure, the Palace was still in top condition as a sporting and concert venue, but its location in a northern suburb, far from the city center, conflicted with a trend of "walkable urbanism" that the Pistons thought would grow their fanbase. It was speculated that the Palace would likely end up being demolished, and the site would be redeveloped to accommodate a possible new auto supplier headquarters and research and development parks.
In August 2018, the arena's Palace360 scoreboard, installed in 2014, was sold to the Arizona Coyotes to replace the old one at Desert Diamond Arena in time for the 2018–19 season.
In October 2018, it was reported Oakland University considered purchasing the arena. Ultimately, a deal never went through.
On June 24, 2019, the arena was sold to a joint venture, which planned to redevelop the property into a mixed-use office park. Demolition of the arena began in February 2020. Demolition was completed on July 11, 2020, when the roof was demolished using explosives by Controlled Demolition, Inc. General Motors purchased the site in 2023, to build a parts plant in support of its electric cars.
See also
Pine Knob Music Theatre
List of indoor arenas in the United States
Sports in Detroit
Tourism in metropolitan Detroit
Notes
References
1988 establishments in Michigan
2017 disestablishments in Michigan
Basketball venues in Michigan
Defunct basketball venues in the United States
Defunct boxing venues in the United States
Defunct college basketball venues in the United States
Defunct indoor arenas in the United States
Demolished music venues in the United States
Demolished sports venues in Michigan
Detroit Pistons
Detroit Shock venues
Former NBA venues
Gymnastics venues in the United States
Indoor arenas in Michigan
Ice hockey venues in Michigan
Indoor soccer venues in Michigan
Sports in Auburn Hills, Michigan
Sports venues completed in 1988
Sports venues demolished in 2020
Sports venues in Oakland County, Michigan
Buildings and structures demolished by controlled implosion | The Palace of Auburn Hills | [
"Engineering"
] | 2,639 | [
"Buildings and structures demolished by controlled implosion",
"Architecture"
] |
623,488 | https://en.wikipedia.org/wiki/Polyoxometalate | In chemistry, a polyoxometalate (abbreviated POM) is a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions linked together by shared oxygen atoms to form closed 3-dimensional frameworks. The metal atoms are usually group 6 (Mo, W) or less commonly group 5 (V, Nb, Ta) and group 7 (Tc, Re) transition metals in their high oxidation states. Polyoxometalates are often colorless, orange or red diamagnetic anions. Two broad families are recognized, isopolymetalates, composed of only one kind of metal and oxide, and heteropolymetalates, composed of one or more metals, oxide, and eventually a main group oxyanion (phosphate, silicate, etc.). Many exceptions to these general statements exist.
Formation
The oxides of d0 metals such as , , dissolve at high pH to give orthometalates, , , . For and , the nature of the dissolved species at high pH is less clear, but these oxides also form polyoxometalates.
As the pH is lowered, orthometalates protonate to give oxide–hydroxide compounds such as and . These species condense via the process called olation. The replacement of terminal M=O bonds, which in fact have triple bond character, is compensated by the increase in coordination number. The nonobservation of polyoxochromate cages is rationalized by the small radius of Cr(VI), which may not accommodate octahedral coordination geometry.
Condensation of the species entails loss of water and the formation of linkages. The stoichiometry for hexamolybdate is shown:
An abbreviated condensation sequence illustrated with vanadates is:
When such acidifications are conducted in the presence of phosphate or silicate, heteropolymetalate result. For example, the phosphotungstate anion consists of a framework of twelve octahedral tungsten oxyanions surrounding a central phosphate group.
History
Ammonium phosphomolybdate, anion, was reported in 1826. The isostructural phosphotungstate anion was characterized by X-ray crystallography 1934. This structure is called the Keggin structure after its discoverer.
The 1970s witnessed the introduction of quaternary ammonium salts of POMs. This innovation enabled systematic study without the complications of hydrolysis and acid/base reactions. The introduction of 17O NMR spectroscopy allowed the structural characterization of POMs in solution.
Ramazzoite, the first example of a mineral with a polyoxometalate cation, was described in 2016 in Mt. Ramazzo Mine, Liguria, Italy.
Structure and bonding
The typical framework building blocks are polyhedral units, with 6-coordinate metal centres. Usually, these units share edges and/or vertices. The coordination number of the oxide ligands varies according to their location in the cage. Surface oxides tend to be terminal or doubly bridging oxo ligands. Interior oxides are typically triply bridging or even octahedral. POMs are sometimes viewed as soluble fragments of metal oxides.
Recurring structural motifs allow POMs to be classified. Iso-polyoxometalates (isopolyanions) feature octahedral metal centers. The heteropolymetalates form distinct structures because the main group center is usually tetrahedral. The Lindqvist and Keggin structures are common motifs for iso- and heteropolyanions, respectively.
Polyoxometalates typically exhibit coordinate metal-oxo bonds of different multiplicity and strength. In a typical POM such as the Keggin structure , each addenda center connects to single terminal oxo ligand, four bridging μ2-O ligands and one bridging μ3-O deriving from the central heterogroup. Metal–metal bonds in polyoxometalates are normally absent and owing to this property, F. Albert Cotton opposed to consider polyoxometalates as form of cluster materials. However, metal-metal bonds are not completely absent in polyoxometalates and they are often present among the highly reduced species.
Polymolybdates and tungstates
The polymolybdates and polytungstates are derived, formally at least, from the dianionic [MO4]2- precursors. The most common units for polymolybdates and polyoxotungstates are the octahedral {MO6} centers, sometimes slightly distorted. Some polymolybdates contain pentagonal bipyramidal units. These building blocks are found in the molybdenum blues, which are mixed valence compounds.
Polyoxotechnetates and rhenates
Polyoxotechnetates form only in strongly acidic conditions, such as in or trifluoromethanesulfonic acid solutions. The first empirically isolated polyoxotechnetate was the red . It contains both Tc(V) and Tc(VII) in ratio 4: 16 and is obtained as the hydronium salt by concentrating an solution. Corresponding ammonium polyoxotechnetate salt was recently isolated from trifluoromethanesulfonic acid and it has very similar structure.
The only polyoxorhenate formed in acidic conditions in presence of pyrazolium cation. The first empirically isolated polyoxorhenate was the white . It contains Re(VII) in both octahedral and tetrahedral coordination.
Polyoxotantalates, niobates, and vanadates
The polyniobates, polytantalates, and vanadates are derived, formally at least, from highly charged [MO4]3- precursors. For Nb and Ta, most common members are (M = Nb, Ta), which adopt the Lindqvist structure. These octaanions form in strongly basic conditions from alkali melts of the extended metal oxides (M2O5), or in the case of Nb even from mixtures of niobic acid and alkali metal hydroxides in aqueous solution. The hexatantalate can also be prepared by condensation of peroxotantalate in alkaline media. These polyoxometalates display an anomalous aqueous solubility trend of their alkali metal salts inasmuch as their Cs+ and Rb+ salts are more soluble than their Na+ and Li+ salts. The opposite trend is observed in group 6 POMs.
The decametalates with the formula (M = Nb, Ta) are isostructural with decavanadate. They are formed exclusively by edge-sharing {MO6} octahedra (the structure of decatungstate comprises edge-sharing and corner-sharing tungstate octahedra).
Heteroatoms
Heteroatoms aside from the transition metal are a defining feature of heteropolymetalates. Many different elements can serve as heteroatoms but most common are , , and .
Giant structures
Polyoxomolybdates include the wheel-shaped molybdenum blue anions and spherical keplerates. The cluster consists of more than 700 atoms and is the size of a small protein. The anion is in the form of a tire (the cavity has a diameter of more than 20 Å) and an extremely large inner and outer surface. The incorporation of lanthanide ions in molybdenum blues is particularly intriguing. Lanthanides can behave like Lewis acids and perform catalytic properties. Lanthanide-containing polyoxometalates show chemoselectivity and are also able to form inorganic–organic adducts, which can be exploited in chiral recognition.
Oxoalkoxometalates
Oxoalkoxometalates are clusters that contain both oxide and alkoxide ligands. Typically they lack terminal oxo ligands. Examples include the dodecatitanate Ti12O16(OPri)16 (where OPri stands for an alkoxy group), the iron oxoalkoxometalates and iron and copper Keggin ions.
Sulfido, imido, and other O-replaced oxometalates
The terminal oxide centers of polyoxometalate framework can in certain cases be replaced with other ligands, such as S2−, Br−, and NR2−. Sulfur-substituted POMs are called polyoxothiometalates. Other ligands replacing the oxide ions have also been demonstrated, such as nitrosyl and alkoxy groups.
Polyfluoroxometalate are yet another class of O-replaced oxometalates.
Other
Numerous hybrid organic–inorganic materials that contain POM cores,
Illustrative of the diverse structures of POM is the ion , which has face-shared octahedra with Mo atoms at the vertices of an icosahedron.
Use and aspirational applications
Oxidation catalysts
POMs are employed as commercial catalysts for oxidation of organic compounds.
Efforts continue to extend this theme. POM-based aerobic oxidations have been promoted as alternatives to chlorine-based wood pulp bleaching processes, a method of decontaminating water, and a method to catalytically produce formic acid from biomass (OxFA process). Polyoxometalates have been shown to catalyse water splitting.
Molecular electronics
Some POMs exhibit unusual magnetic properties, which has prompted visions of many applications. One example is storage devices called qubits. non-volatile (permanent) storage components, also known as flash memory devices.
Drugs
Potential antitumor and antiviral drugs. The Anderson-type polyoxomolybdates and heptamolybdates exhibit activity for suppressing the growth of some tumors. In the case of (NH3Pr)6[Mo7O24], activity appears related to its redox properties. The Wells-Dawson structure can efficiently inhibit amyloid β (Aβ) aggregation in a therapeutic strategy for Alzheimer's disease. antibacterial and antiviral uses.
See also
Superatom
Perovskite
Metal aromaticity
References
Further reading
Oxyanions
Oxometallates
Cluster chemistry
Catalysts | Polyoxometalate | [
"Chemistry"
] | 2,156 | [
"Catalysis",
"Catalysts",
"Cluster chemistry",
"Chemical kinetics",
"Organometallic chemistry"
] |
623,501 | https://en.wikipedia.org/wiki/Forb | A forb or phorb is a herbaceous flowering plant that is not a graminoid (grass, sedge, or rush). The term is used in botany and in vegetation ecology especially in relation to grasslands and understory. Typically, these are eudicots without woody stems.
Etymology
The word forb is derived from Greek () 'pasture; fodder'. The Hellenic spelling phorb is sometimes used, and in older usage this sometimes includes graminids and other plants currently not regarded as forbs.
Guilds
Forbs are members of a guilda group of plant species with broadly similar growth forms. In certain contexts in ecology, guild membership may often be more important than the taxonomic relationships between organisms.
In informal classification
In addition to its use in ecology, the term "forb" may be used for subdividing popular guides to wildflowers, distinguishing them from other categories such as grasses, sedges, shrubs, and trees. Some examples of forbs are clovers, sunflowers, daylilies, and milkweed.
Forb Adaptation Zones:
Kale and turnip are examples of forb adaptations distributed over much of Europe, southern Oceania, northern Asia, and northern North America. In cooler climates, these crops are grown year-round, while in warmer climates, they are used as winter forage.
Examples
Linnaean taxonomy family names are given.
Acanthaceae,
Aizoaceae,
Amaranthaceae,
Apiaceae,
Apocynaceae,
Asclepiadaceae,
Asteraceae,
Balsaminaceae,
Begoniaceae,
Boraginaceae,
Brassicaceae,
Buxaceae,
Campanulaceae,
Cannabaceae,
Caryophyllaceae,
Chenopodiaceae,
Clusiaceae,
Convolvulaceae,
Crassulaceae,
Cucurbitaceae,
Cuscutaceae,
Dipsacaceae,
Ericaceae,
Euphorbiaceae,
Fabaceae,
Gentianaceae,
Geraniaceae,
Gunneraceae,
Haloragaceae,
Hydrophyllaceae,
Lamiaceae,
Lentibulariaceae,
Limnanthaceae,
Linaceae,
Lythraceae,
Malvaceae,
Moraceae,
Nyctaginaceae,
Onagraceae,
Orobanchaceae,
Oxalidaceae,
Papaveraceae,
Phytolaccaceae,
Plantaginaceae,
Plumbaginaceae,
Polemoniaceae,
Polygonaceae,
Portulacaceae,
Primulaceae,
Ranunculaceae,
Resedaceae,
Rosaceae,
Rubiaceae,
Scrophulariaceae,
Solanaceae,
Thymelaeaceae,
Urticaceae,
Valerianaceae,
Verbenaceae,
Violaceae,
Zygophyllaceae
See also
Tapestry lawn
References
External links
United States Department of Agriculture Natural Resources Conservation Service link to Growth habits Codes and Definitions.
Plant morphology
Plants by habit
Plant life-forms | Forb | [
"Biology"
] | 603 | [
"Plant morphology",
"Plant life-forms",
"Plants"
] |
623,560 | https://en.wikipedia.org/wiki/Henry%20Draper%20Medal | The Henry Draper Medal is awarded every 4 years by the United States National Academy of Sciences "for investigations in astronomical physics". Named after Henry Draper, the medal is awarded with a gift of USD $15,000. The medal was established under the Draper Fund by his widow, Anna Draper, in honor of her husband, and was first awarded in 1886 to Samuel Pierpont Langley "for numerous investigations of a high order of merit in solar physics, and especially in the domain of radiant energy". It has since been awarded 45 times.
The medal has been awarded to multiple individuals in the same year: in 1977 it was awarded to Arno Allan Penzias and Robert Woodrow Wilson "for their discovery of the cosmic microwave radiation (a remnant of the very early universe), and their leading role in the discovery of interstellar molecules"; in 1989 to Riccardo Giovanelli and Martha P. Haynes "for the first three-dimensional view of some of the remarkable large-scale filamentary structures of our visible universe"; in 1993 to Ralph Asher Alpher and Robert Herman "for their insight and skill in developing a physical model of the evolution of the universe and in predicting the existence of a microwave background radiation years before this radiation was serendipitously discovered" and in 2001 to R. Paul Butler and Geoffrey Marcy "for their pioneering investigations of planets orbiting other stars via high-precision radial velocities".
List of recipients
Source: National Academy of Sciences
See also
List of astronomy awards
List of physics awards
References
Astronomy prizes
Awards established in 1886
Awards of the United States National Academy of Sciences
1886 establishments in the United States | Henry Draper Medal | [
"Astronomy",
"Technology"
] | 337 | [
"Science and technology awards",
"Astronomy prizes"
] |
623,686 | https://en.wikipedia.org/wiki/Brain%E2%80%93computer%20interface | A brain–computer interface (BCI), sometimes called a brain–machine interface (BMI), is a direct communication link between the brain's electrical activity and an external device, most commonly a computer or robotic limb. BCIs are often directed at researching, mapping, assisting, augmenting, or repairing human cognitive or sensory-motor functions. They are often conceptualized as a human–machine interface that skips the intermediary of moving body parts (hands...), although they also raise the possibility of erasing the distinction between brain and machine. BCI implementations range from non-invasive (EEG, MEG, MRI) and partially invasive (ECoG and endovascular) to invasive (microelectrode array), based on how physically close electrodes are to brain tissue.
Research on BCIs began in the 1970s by Jacques Vidal at the University of California, Los Angeles (UCLA) under a grant from the National Science Foundation, followed by a contract from the Defence Advanced Research Projects Agency (DARPA). Vidal's 1973 paper introduced the expression brain–computer interface into scientific literature.
Due to the cortical plasticity of the brain, signals from implanted prostheses can, after adaptation, be handled by the brain like natural sensor or effector channels. Following years of animal experimentation, the first neuroprosthetic devices were implanted in humans in the mid-1990s.
Studies in human-computer interaction via the application of machine learning to statistical temporal features extracted from the frontal lobe (EEG brainwave) data has achieved success in classifying mental states (relaxed, neutral, concentrating), mental emotional states (negative, neutral, positive), and thalamocortical dysrhythmia.
History
The history of brain-computer interfaces (BCIs) starts with Hans Berger's discovery of the brain's electrical activity and the development of electroencephalography (EEG). In 1924 Berger was the first to record human brain activity utilizing EEG. Berger was able to identify oscillatory activity, such as the alpha wave (8–13 Hz), by analyzing EEG traces.
Berger's first recording device was rudimentary. He inserted silver wires under the scalps of his patients. These were later replaced by silver foils attached to the patient's head by rubber bandages. Berger connected these sensors to a Lippmann capillary electrometer, with disappointing results. However, more sophisticated measuring devices, such as the Siemens double-coil recording galvanometer, which displayed voltages as small as 10−4 volt, led to success.
Berger analyzed the interrelation of alternations in his EEG wave diagrams with brain diseases. EEGs permitted completely new possibilities for brain research.
Although the term had not yet been coined, one of the earliest examples of a working brain-machine interface was the piece Music for Solo Performer (1965) by American composer Alvin Lucier. The piece makes use of EEG and analog signal processing hardware (filters, amplifiers, and a mixing board) to stimulate acoustic percussion instruments. Performing the piece requires producing alpha waves and thereby "playing" the various instruments via loudspeakers that are placed near or directly on the instruments.
Vidal coined the term "BCI" and produced the first peer-reviewed publications on this topic. He is widely recognized as the inventor of BCIs. A review pointed out that Vidal's 1973 paper stated the "BCI challenge" of controlling external objects using EEG signals, and especially use of Contingent Negative Variation (CNV) potential as a challenge for BCI control. Vidal's 1977 experiment was the first application of BCI after his 1973 BCI challenge. It was a noninvasive EEG (actually Visual Evoked Potentials (VEP)) control of a cursor-like graphical object on a computer screen. The demonstration was movement in a maze.
1988 was the first demonstration of noninvasive EEG control of a physical object, a robot. The experiment demonstrated EEG control of multiple start-stop-restart cycles of movement, along an arbitrary trajectory defined by a line drawn on a floor. The line-following behavior was the default robot behavior, utilizing autonomous intelligence and an autonomous energy source.
In 1990, a report was given on a closed loop, bidirectional, adaptive BCI controlling a computer buzzer by an anticipatory brain potential, the Contingent Negative Variation (CNV) potential. The experiment described how an expectation state of the brain, manifested by CNV, used a feedback loop to control the S2 buzzer in the S1-S2-CNV paradigm. The resulting cognitive wave representing the expectation learning in the brain was termed Electroexpectogram (EXG). The CNV brain potential was part of Vidal's 1973 challenge.
Studies in the 2010s suggested neural stimulation's potential to restore functional connectivity and associated behaviors through modulation of molecular mechanisms. This opened the door for the concept that BCI technologies may be able to restore function.
Beginning in 2013, DARPA funded BCI technology through the BRAIN initiative, which supported work out of teams including University of Pittsburgh Medical Center, Paradromics, Brown, and Synchron.
Neuroprosthetics
Neuroprosthetics is an area of neuroscience concerned with neural prostheses, that is, using artificial devices to replace the function of impaired nervous systems and brain-related problems, or of sensory or other organs (bladder, diaphragm, etc.). As of December 2010, cochlear implants had been implanted as neuroprosthetic devices in some 736,900 people worldwide. Other neuroprosthetic devices aim to restore vision, including retinal implants. The first neuroprosthetic device, however, was the pacemaker.
The terms are sometimes used interchangeably. Neuroprosthetics and BCIs seek to achieve the same aims, such as restoring sight, hearing, movement, ability to communicate, and even cognitive function. Both use similar experimental methods and surgical techniques.
Animal research
Several laboratories have managed to read signals from monkey and rat cerebral cortices to operate BCIs to produce movement. Monkeys have moved computer cursors and commanded robotic arms to perform simple tasks simply by thinking about the task and seeing the results, without motor output. In May 2008 photographs that showed a monkey at the University of Pittsburgh Medical Center operating a robotic arm by thinking were published in multiple studies. Sheep have also been used to evaluate BCI technology including Synchron's Stentrode.
In 2020, Elon Musk's Neuralink was successfully implanted in a pig. In 2021, Musk announced that the company had successfully enabled a monkey to play video games using Neuralink's device.
Early work
In 1969 operant conditioning studies by Fetz et al. at the Regional Primate Research Center and Department of Physiology and Biophysics, University of Washington School of Medicine showed that monkeys could learn to control the deflection of a biofeedback arm with neural activity. Similar work in the 1970s established that monkeys could learn to control the firing rates of individual and multiple neurons in the primary motor cortex if they were rewarded accordingly.
Algorithms to reconstruct movements from motor cortex neurons, which control movement, date back to the 1970s. In the 1980s, Georgopoulos at Johns Hopkins University found a mathematical relationship between the electrical responses of single motor cortex neurons in rhesus macaque monkeys and the direction in which they moved their arms. He also found that dispersed groups of neurons, in different areas of the monkey's brains, collectively controlled motor commands. He was able to record the firings of neurons in only one area at a time, due to equipment limitations.
Several groups have been able to capture complex brain motor cortex signals by recording from neural ensembles (groups of neurons) and using these to control external devices.
Research
Kennedy and Yang Dan
Phillip Kennedy (Neural Signals founder (1987) and colleagues built the first intracortical brain–computer interface by implanting neurotrophic-cone electrodes into monkeys.In 1999, Yang Dan et al. at University of California, Berkeley decoded neuronal firings to reproduce images from cats. The team used an array of electrodes embedded in the thalamus (which integrates the brain's sensory input). Researchers targeted 177 brain cells in the thalamus lateral geniculate nucleus area, which decodes signals from the retina. Neuron firings were recorded from watching eight short movies. Using mathematical filters, the researchers decoded the signals to reconstruct recognizable scenes and moving objects.
Nicolelis
Duke University professor Miguel Nicolelis advocates using multiple electrodes spread over a greater area of the brain to obtain neuronal signals.
After initial studies in rats during the 1990s, Nicolelis and colleagues developed BCIs that decoded brain activity in owl monkeys and used the devices to reproduce monkey movements in robotic arms. Monkeys' advanced reaching and grasping abilities and hand manipulation skills, made them good test subjects.
By 2000, the group succeeded in building a BCI that reproduced owl monkey movements while the monkey operated a joystick or reached for food. The BCI operated in real time and could remotely control a separate robot. But the monkeys received no feedback (open-loop BCI).
Later experiments on rhesus monkeys included feedback and reproduced monkey reaching and grasping movements in a robot arm. Their deeply cleft and furrowed brains made them better models for human neurophysiology than owl monkeys. The monkeys were trained to reach and grasp objects on a computer screen by manipulating a joystick while corresponding movements by a robot arm were hidden. The monkeys were later shown the robot and learned to control it by viewing its movements. The BCI used velocity predictions to control reaching movements and simultaneously predicted gripping force.
In 2011 O'Doherty and colleagues showed a BCI with sensory feedback with rhesus monkeys. The monkey controlled the position of an avatar arm while receiving sensory feedback through direct intracortical stimulation (ICMS) in the arm representation area of the sensory cortex.
Donoghue, Schwartz, and Andersen
Other laboratories that have developed BCIs and algorithms that decode neuron signals include John Donoghue at the Carney Institute for Brain Science at Brown University, Andrew Schwartz at the University of Pittsburgh, and Richard Andersen at Caltech. These researchers produced working BCIs using recorded signals from far fewer neurons than Nicolelis (15–30 neurons versus 50–200 neurons).
The Carney Institute reported training rhesus monkeys to use a BCI to track visual targets on a computer screen (closed-loop BCI) with or without a joystick. The group created a BCI for three-dimensional tracking in virtual reality and reproduced BCI control in a robotic arm. The same group demonstrated that a monkey could feed itself pieces of fruit and marshmallows using a robotic arm controlled by the animal's brain signals.
Andersen's group used recordings of premovement activity from the posterior parietal cortex, including signals created when experimental animals anticipated receiving a reward.
Other research
In addition to predicting kinematic and kinetic parameters of limb movements, BCIs that predict electromyographic or electrical activity of the muscles of primates are in process. Such BCIs could restore mobility in paralyzed limbs by electrically stimulating muscles.
Nicolelis and colleagues demonstrated that large neural ensembles can predict arm position. This work allowed BCIs to read arm movement intentions and translate them into actuator movements. Carmena and colleagues programmed a BCI that allowed a monkey to control reaching and grasping movements by a robotic arm. Lebedev and colleagues argued that brain networks reorganize to create a new representation of the robotic appendage in addition to the representation of the animal's own limbs.
In 2019, a study reported a BCI that had the potential to help patients with speech impairment caused by neurological disorders. Their BCI used high-density electrocorticography to tap neural activity from a patient's brain and used deep learning to synthesize speech. In 2021, those researchers reported the potential of a BCI to decode words and sentences in an anarthric patient who had been unable to speak for over 15 years.
The biggest impediment to BCI technology is the lack of a sensor modality that provides safe, accurate and robust access to brain signals. The use of a better sensor expands the range of communication functions that can be provided using a BCI.
Development and implementation of a BCI system is complex and time-consuming. In response to this problem, Gerwin Schalk has been developing BCI2000, a general-purpose system for BCI research, since 2000.
A new 'wireless' approach uses light-gated ion channels such as channelrhodopsin to control the activity of genetically defined subsets of neurons in vivo. In the context of a simple learning task, illumination of transfected cells in the somatosensory cortex influenced decision-making in mice.
BCIs led to a deeper understanding of neural networks and the central nervous system. Research has reported that despite neuroscientists' inclination to believe that neurons have the most effect when working together, single neurons can be conditioned through the use of BCIs to fire in a pattern that allows primates to control motor outputs. BCIs led to development of the single neuron insufficiency principle that states that even with a well-tuned firing rate, single neurons can only carry limited information and therefore the highest level of accuracy is achieved by recording ensemble firings. Other principles discovered with BCIs include the neuronal multitasking principle, the neuronal mass principle, the neural degeneracy principle, and the plasticity principle.
BCIs are proposed to be applied by users without disabilities. Passive BCIs allow for assessing and interpreting changes in the user state during Human-Computer Interaction (HCI). In a secondary, implicit control loop, the system adapts to its user, improving its usability.
BCI systems can potentially be used to encode signals from the periphery. These sensory BCI devices enable real-time, behaviorally-relevant decisions based upon closed-loop neural stimulation.
The BCI Award
The BCI Research Award is awarded annually in recognition of innovative research. Each year, a renowned research laboratory is asked to judge projects. The jury consists of BCI experts recruited by that laboratory. The jury selects twelve nominees, then chooses a first, second, and third-place winner, who receive awards of $3,000, $2,000, and $1,000, respectively.
Human research
Invasive BCIs
Invasive BCI requires surgery to implant electrodes under the scalp for accessing brain signals. The main advantage is to increase accuracy. Downsides include side effects from the surgery, including scar tissue that can obstruct brain signals or the body may not accept the implanted electrodes.
Vision
Invasive BCI research has targeted repairing damaged sight and providing new functionality for people with paralysis. Invasive BCIs are implanted directly into the grey matter of the brain during neurosurgery. Because they lie in the grey matter, invasive devices produce the highest quality signals of BCI devices but are prone to scar-tissue build-up, causing the signal to weaken, or disappear, as the body reacts to the foreign object.
In vision science, direct brain implants have been used to treat non-congenital (acquired) blindness. One of the first scientists to produce a working brain interface to restore sight was private researcher William Dobelle. Dobelle's first prototype was implanted into "Jerry", a man blinded in adulthood, in 1978. A single-array BCI containing 68 electrodes was implanted onto Jerry's visual cortex and succeeded in producing phosphenes, the sensation of seeing light. The system included cameras mounted on glasses to send signals to the implant. Initially, the implant allowed Jerry to see shades of grey in a limited field of vision at a low frame-rate. This also required him to be hooked up to a mainframe computer, but shrinking electronics and faster computers made his artificial eye more portable and now enable him to perform simple tasks unassisted.
In 2002, Jens Naumann, also blinded in adulthood, became the first in a series of 16 paying patients to receive Dobelle's second generation implant, one of the earliest commercial uses of BCIs. The second generation device used a more sophisticated implant enabling better mapping of phosphenes into coherent vision. Phosphenes are spread out across the visual field in what researchers call "the starry-night effect". Immediately after his implant, Jens was able to use his imperfectly restored vision to drive an automobile slowly around the parking area of the research institute. Dobelle died in 2004 before his processes and developments were documented, leaving no one to continue his work. Subsequently, Naumann and the other patients in the program began having problems with their vision, and eventually lost their "sight" again.
Movement
BCIs focusing on motor neuroprosthetics aim to restore movement in individuals with paralysis or provide devices to assist them, such as interfaces with computers or robot arms.
Kennedy and Bakay were first to install a human brain implant that produced signals of high enough quality to simulate movement. Their patient, Johnny Ray (1944–2002), developed 'locked-in syndrome' after a brain-stem stroke in 1997. Ray's implant was installed in 1998 and he lived long enough to start working with the implant, eventually learning to control a computer cursor; he died in 2002 of a brain aneurysm.
Tetraplegic Matt Nagle became the first person to control an artificial hand using a BCI in 2005 as part of the first nine-month human trial of Cyberkinetics's BrainGate chip-implant. Implanted in Nagle's right precentral gyrus (area of the motor cortex for arm movement), the 96-electrode implant allowed Nagle to control a robotic arm by thinking about moving his hand as well as a computer cursor, lights and TV. One year later, Jonathan Wolpaw received the Altran Foundation for Innovation prize for developing a Brain Computer Interface with electrodes located on the surface of the skull, instead of directly in the brain.
Research teams led by the BrainGate group and another at University of Pittsburgh Medical Center, both in collaborations with the United States Department of Veterans Affairs (VA), demonstrated control of prosthetic limbs with many degrees of freedom using direct connections to arrays of neurons in the motor cortex of tetraplegia patients.
Communication
In May 2021, a Stanford University team reported a successful proof-of-concept test that enabled a quadraplegic participant to produce English sentences at about 86 characters per minute and 18 words per minute. The participant imagined moving his hand to write letters, and the system performed handwriting recognition on electrical signals detected in the motor cortex, utilizing Hidden Markov models and recurrent neural networks.
A 2021 study reported that a paralyzed patient was able to communicate 15 words per minute using a brain implant that analyzed vocal tract motor neurons.
In a review article, authors wondered whether human information transfer rates can surpass that of language with BCIs. Language research has reported that information transfer rates are relatively constant across many languages. This may reflect the brain's information processing limit. Alternatively, this limit may be intrinsic to language itself, as a modality for information transfer.
In 2023 two studies used BCIs with recurrent neural network to decode speech at a record rate of 62 words per minute and 78 words per minute.
Technical challenges
There exist a number of technical challenges to recording brain activity with invasive BCIs. Advances in CMOS technology are pushing and enabling integrated, invasive BCI designs with smaller size, lower power requirements, and higher signal acquisition capabilities. Invasive BCIs involve electrodes that penetrate brain tissue in an attempt to record action potential signals (also known as spikes) from individual, or small groups of, neurons near the electrode. The interface between a recording electrode and the electrolytic solution surrounding neurons has been modelled using the Hodgkin-Huxley model.
Electronic limitations to invasive BCIs have been an active area of research in recent decades. While intracellular recordings of neurons reveal action potential voltages on the scale of hundreds of millivolts, chronic invasive BCIs rely on recording extracellular voltages which typically are three orders of magnitude smaller, existing at hundreds of microvolts. Further adding to the challenge of detecting signals on the scale of microvolts is the fact that the electrode-tissue interface has a high capacitance at small voltages. Due to the nature of these small signals, for BCI systems that incorporate functionality onto an integrated circuit, each electrode requires its own amplifier and ADC, which convert analog extracellular voltages into digital signals. Because a typical neuron action potential lasts for one millisecond, BCIs measuring spikes must have sampling rates ranging from 300 Hz to 5 kHz. Yet another concern is that invasive BCIs must be low-power, so as to dissipate less heat to surrounding tissue; at the most basic level more power is traditionally needed to optimize signal-to-noise ratio. Optimal battery design is an active area of research in BCIs.Challenges existing in the area of material science are central to the design of invasive BCIs. Variations in signal quality over time have been commonly observed with implantable microelectrodes. Optimal material and mechanical characteristics for long term signal stability in invasive BCIs has been an active area of research. It has been proposed that the formation of glial scarring, secondary to damage at the electrode-tissue interface, is likely responsible for electrode failure and reduced recording performance. Research has suggested that blood-brain barrier leakage, either at the time of insertion or over time, may be responsible for the inflammatory and glial reaction to chronic microelectrodes implanted in the brain. As a result, flexible and tissue-like designs have been researched and developed to minimize foreign-body reaction by means of matching the Young's modulus of the electrode closer to that of brain tissue.
Partially invasive BCIs
Partially invasive BCI devices are implanted inside the skull but rest outside the brain rather than within the grey matter. They produce higher resolution signals than non-invasive BCIs where the bone tissue of the cranium deflects and deforms signals and have a lower risk of forming scar-tissue in the brain than fully invasive BCIs. Preclinical demonstration of intracortical BCIs from the stroke perilesional cortex has been conducted.
Endovascular
A systematic review published in 2020 detailed multiple clinical and non-clinical studies investigating the feasibility of endovascular BCIs.
In 2010, researchers affiliated with University of Melbourne began developing a BCI that could be inserted via the vascular system. Australian neurologist Thomas Oxley conceived the idea for this BCI, called Stentrode, earning funding from DARPA. Preclinical studies evaluated the technology in sheep.
Stentrode is a monolithic stent electrode array designed to be delivered via an intravenous catheter under image-guidance to the superior sagittal sinus, in the region which lies adjacent to the motor cortex. This proximity enables Stentrode to measure neural activity. The procedure is most similar to how venous sinus stents are placed for the treatment of idiopathic intracranial hypertension. Stentrode communicates neural activity to a battery-less telemetry unit implanted in the chest, which communicates wirelessly with an external telemetry unit capable of power and data transfer. While an endovascular BCI benefits from avoiding a craniotomy for insertion, risks such as clotting and venous thrombosis exist.
Human trials with Stentrode were underway as of 2021. In November 2020, two participants with amyotrophic lateral sclerosis were able to wirelessly control an operating system to text, email, shop, and bank using direct thought using Stentrode, marking the first time a brain-computer interface was implanted via the patient's blood vessels, eliminating the need for brain surgery. In January 2023, researchers reported no serious adverse events during the first year for all four patients, who could use it to operate computers.
Electrocorticography
Electrocorticography (ECoG) measures brain electrical activity from beneath the skull in a way similar to non-invasive electroencephalography, using electrodes embedded in a thin plastic pad placed above the cortex, beneath the dura mater. ECoG technologies were first trialled in humans in 2004 by Eric Leuthardt and Daniel Moran from Washington University in St. Louis. In a later trial, the researchers enabled a teenage boy to play Space Invaders. This research indicates that control is rapid, requires minimal training, balancing signal fidelity and level of invasiveness.
Signals can be either subdural or epidural, but are not taken from within the brain parenchyma. Patients are required to have invasive monitoring for localization and resection of an epileptogenic focus.
ECoG offers higher spatial resolution, better signal-to-noise ratio, wider frequency range, and less training requirements than scalp-recorded EEG, and at the same time has lower technical difficulty, lower clinical risk, and may have superior long-term stability than intracortical single-neuron recording. This feature profile and evidence of the high level of control with minimal training requirements shows potential for real world application for people with motor disabilities.
Edward Chang and Joseph Makin from UCSF reported that ECoG signals could be used to decode speech from epilepsy patients implanted with high-density ECoG arrays over the peri-Sylvian cortices. They reported word error rates of 3% (a marked improvement from prior efforts) utilizing an encoder-decoder neural network, which translated ECoG data into one of fifty sentences composed of 250 unique words.
Non-invasive BCIs
Human experiments have used non-invasive neuroimaging interfaces. The majority of published BCI research involves noninvasive EEG-based BCIs. EEG-based technologies and interfaces have been used for the broadest variety of applications. Although EEG-based interfaces are easy to wear and do not require surgery, they have relatively poor spatial resolution and cannot effectively use higher-frequency signals because the skull interferes, dispersing and blurring the electromagnetic waves created by the neurons. EEG-based interfaces also require some time and effort prior to each usage session, while others require no prior-usage training. The choice of a specific BCI for a patient depends on numerous factors.
Functional near-infrared spectroscopy
In 2014, a BCI using functional near-infrared spectroscopy for "locked-in" patients with amyotrophic lateral sclerosis (ALS) was able to restore basic ability to communicate.
Electroencephalography (EEG)-based brain-computer interfaces
After Vidal stated the BCI challenge, the initial reports on non-invasive approaches included control of a cursor in 2D using VEP, control of a buzzer using CNV, control of a physical object, a robot, using a brain rhythm (alpha), control of a text written on a screen using P300.
In the early days of BCI research, another substantial barrier to using EEG was that extensive training was required. For example, in experiments beginning in the mid-1990s, Niels Birbaumer at the University of Tübingen in Germany trained paralysed people to self-regulate the slow cortical potentials in their EEG to such an extent that these signals could be used as a binary signal to control a computer cursor. (Birbaumer had earlier trained epileptics to prevent impending fits by controlling this low voltage wave.) The experiment trained ten patients to move a computer cursor. The process was slow, requiring more than an hour for patients to write 100 characters with the cursor, while training often took months. The slow cortical potential approach has fallen away in favor of approaches that require little or no training, are faster and more accurate, and work for a greater proportion of users.
Another research parameter is the type of oscillatory activity that is measured. Gert Pfurtscheller founded the BCI Lab 1991 and conducted the first online BCI based on oscillatory features and classifiers. Together with Birbaumer and Jonathan Wolpaw at New York State University they focused on developing technology that would allow users to choose the brain signals they found easiest to operate a BCI, including mu and beta rhythms.
A further parameter is the method of feedback used as shown in studies of P300 signals. Patterns of P300 waves are generated involuntarily (stimulus-feedback) when people see something they recognize and may allow BCIs to decode categories of thoughts without training.
A 2005 study reported EEG emulation of digital control circuits, using a CNV flip-flop. A 2009 study reported noninvasive EEG control of a robotic arm using a CNV flip-flop. A 2011 study reported control of two robotic arms solving Tower of Hanoi task with three disks using a CNV flip-flop. A 2015 study described EEG-emulation of a Schmitt trigger, flip-flop, demultiplexer, and modem.
Advances by Bin He and his team at University of Minnesota suggest the potential of EEG-based brain-computer interfaces to accomplish tasks close to invasive brain-computer interfaces. Using advanced functional neuroimaging including BOLD functional MRI and EEG source imaging, They identified the co-variation and co-localization of electrophysiological and hemodynamic signals. Refined by a neuroimaging approach and a training protocol, They fashioned a non-invasive EEG based brain-computer interface to control the flight of a virtual helicopter in 3-dimensional space, based upon motor imagination. In June 2013 they announced a technique to guide a remote-control helicopter through an obstacle course. They also solved the EEG inverse problem and then used the resulting virtual EEG for BCI tasks. Well-controlled studies suggested the merits of such a source analysis-based BCI.
A 2014 study reported that severely motor-impaired patients could communicate faster and more reliably with non-invasive EEG BCI than with muscle-based communication channels.
A 2019 study reported that the application of evolutionary algorithms could improve EEG mental state classification with a non-invasive Muse device, enabling classification of data acquired by a consumer-grade sensing device.
In a 2021 systematic review of randomized controlled trials using BCI for post-stroke upper-limb rehabilitation, EEG-based BCI was reported to have efficacy in improving upper-limb motor function compared to control therapies. More specifically, BCI studies that utilized band power features, motor imagery, and functional electrical stimulation were reported to be more effective than alternatives. Another 2021 systematic review focused on post-stroke robot-assisted EEG-based BCI for hand rehabilitation. Improvement in motor assessment scores was observed in three of eleven studies.
Dry active electrode arrays
In the early 1990s Babak Taheri, at University of California, Davis demonstrated the first single and multichannel dry active electrode arrays. The arrayed electrode was demonstrated to perform well compared to silver/silver chloride electrodes. The device consisted of four sensor sites with integrated electronics to reduce noise by impedance matching. The advantages of such electrodes are:
no electrolyte used,
no skin preparation,
significantly reduced sensor size,
compatibility with EEG monitoring systems.
The active electrode array is an integrated system containing an array of capacitive sensors with local integrated circuitry packaged with batteries to power the circuitry. This level of integration was required to achieve the result.
The electrode was tested on a test bench and on human subjects in four modalities, namely:
spontaneous EEG,
sensory event-related potentials,
brain stem potentials,
cognitive event-related potentials.
Performance compared favorably with that of standard wet electrodes in terms of skin preparation, no gel requirements (dry), and higher signal-to-noise ratio.
In 1999 Hunter Peckham and others at Case Western Reserve University used a 64-electrode EEG skullcap to return limited hand movements to a quadriplegic. As he concentrated on simple but opposite concepts like up and down. A basic pattern was identified in his beta-rhythm EEG output and used to control a switch: Above average activity was interpreted as on, below average off. The signals were also used to drive nerve controllers embedded in his hands, restoring some movement.
SSVEP mobile EEG BCIs
In 2009, the NCTU Brain-Computer-Interface-headband was announced. Those researchers also engineered silicon-based microelectro-mechanical system (MEMS) dry electrodes designed for application to non-hairy body sites. These electrodes were secured to the headband's DAQ board with snap-on electrode holders. The signal processing module measured alpha activity and transferred it over Bluetooth to a phone that assessed the patients' alertness and cognitive capacity. When the subject became drowsy, the phone sent arousing feedback to the operator to rouse them.
In 2011, researchers reported a cellular based BCI that could cause a phone to ring. The wearable system was composed of a four channel bio-signal acquisition/amplification module, a communication module, and a Bluetooth phone. The electrodes were placed to pick up steady state visual evoked potentials (SSVEPs). SSVEPs are electrical responses to flickering visual stimuli with repetition rates over 6 Hz that are best found in the parietal and occipital scalp regions of the visual cortex. It was reported that all study participants were able to initiate the phone call with minimal practice in natural environments.
The scientists reported that a single channel fast Fourier transform (FFT) and multiple channel system canonical correlation analysis (CCA) algorithm can support mobile BCIs. The CCA algorithm has been applied in experiments investigating BCIs with claimed high accuracy and speed. Cellular BCI technology can reportedly be translated for other applications, such as picking up sensorimotor mu/beta rhythms to function as a motor-imagery based BCI.
In 2013, comparative tests performed on Android cell phone, tablet, and computer based BCIs, analyzed the power spectrum density of resultant EEG SSVEPs. The stated goals of this study were to "increase the practicability, portability, and ubiquity of an SSVEP-based BCI, for daily use". It was reported that the stimulation frequency on all mediums was accurate, although the phone's signal was not stable. The amplitudes of the SSVEPs for the laptop and tablet were reported to be larger than those of the cell phone. These two qualitative characterizations were suggested as indicators of the feasibility of using a mobile stimulus BCI.
One of the difficulties with EEG readings is susceptibility to motion artifacts. In most research projects, the participants were asked to sit still in a laboratory setting, reducing head and eye movements as much as possible. However, since these initiatives were intended to create a mobile device for daily use, the technology had to be tested in motion. In 2013, researchers tested mobile EEG-based BCI technology, measuring SSVEPs from participants as they walked on a treadmill. Reported results were that as speed increased, SSVEP detectability using CCA decreased. Independent component analysis (ICA) had been shown to be efficient in separating EEG signals from noise. The researchers stated that CCA data with and without ICA processing were similar. They concluded that CCA demonstrated robustness to motion artifacts. EEG-based BCI applications offer low spatial resolution. Possible solutions include: EEG source connectivity based on graph theory, EEG pattern recognition based on Topomap and EEG-fMRI fusion.
Prosthesis and environment control
Non-invasive BCIs have been applied to prosthetic upper and lower extremity devices in people with paralysis. For example, Gert Pfurtscheller of Graz University of Technology and colleagues demonstrated a BCI-controlled functional electrical stimulation system to restore upper extremity movements in a person with tetraplegia due to spinal cord injury. Between 2012 and 2013, researchers at University of California, Irvine demonstrated for the first time that BCI technology can restore brain-controlled walking after spinal cord injury. In their study, a person with paraplegia operated a BCI-robotic gait orthosis to regain basic ambulation. In 2009 independent researcher Alex Blainey used the Emotiv EPOC to control a 5 axis robot arm. He made several demonstrations of mind controlled wheelchairs and home automation.
Magnetoencephalography and fMRI
Magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) have both been used as non-invasive BCIs. In a widely reported experiment, fMRI allowed two users to play Pong in real-time by altering their haemodynamic response or brain blood flow through biofeedback.
fMRI measurements of haemodynamic responses in real time have also been used to control robot arms with a seven-second delay between thought and movement.
In 2008 research developed in the Advanced Telecommunications Research (ATR) Computational Neuroscience Laboratories in Kyoto, Japan, allowed researchers to reconstruct images from brain signals at a resolution of 10x10 pixels.
A 2011 study reported second-by-second reconstruction of videos watched by the study's subjects, from fMRI data. This was achieved by creating a statistical model relating videos to brain activity. This model was then used to look up 100 one-second video segments, in a database of 18 million seconds of random YouTube videos, matching visual patterns to brain activity recorded when subjects watched a video. These 100 one-second video extracts were then combined into a mash-up image that resembled the video.
BCI control strategies in neurogaming
Motor imagery
Motor imagery involves imagining the movement of body parts, activating the sensorimotor cortex, which modulates sensorimotor oscillations in the EEG. This can be detected by the BCI and used to infer user intent. Motor imagery typically requires training to acquire acceptable control. Training sessions typically consume hours over several days. Regardless of the duration of the training session, users are unable to master the control scheme. This results in very slow pace of the gameplay. Machine learning methods were used to compute a subject-specific model for detecting motor imagery performance. The top performing algorithm from BCI Competition IV in 2022 dataset 2 for motor imagery was the Filter Bank Common Spatial Pattern, developed by Ang et al. from A*STAR, Singapore.
Bio/neurofeedback for passive BCI designs
Biofeedback can be used to monitor a subject's mental relaxation. In some cases, biofeedback does not match EEG, while parameters such as electromyography (EMG), galvanic skin resistance (GSR), and heart rate variability (HRV) can do so. Many biofeedback systems treat disorders such as attention deficit hyperactivity disorder (ADHD), sleep problems in children, teeth grinding, and chronic pain. EEG biofeedback systems typically monitor four brainwave bands (theta: 4–7 Hz, alpha:8–12 Hz, SMR: 12–15 Hz, beta: 15–18 Hz) and challenge the subject to control them. Passive BCI uses BCI to enrich human–machine interaction with information on the user's mental state, for example, simulations that detect when users intend to push brakes during emergency vehicle braking. Game developers using passive BCIs understand that through repetition of game levels the user's cognitive state adapts. During the first play of a given level, the player reacts differently than during subsequent plays: for example, the user is less surprised by an event that they expect.
Visual evoked potential (VEP)
A VEP is an electrical potential recorded after a subject is presented with a visual stimuli. The types of VEPs include SSVEPs and P300 potential.
Steady-state visually evoked potentials (SSVEPs) use potentials generated by exciting the retina, using visual stimuli modulated at certain frequencies. SSVEP stimuli are often formed from alternating checkerboard patterns and at times use flashing images. The frequency of the phase reversal of the stimulus used can be distinguished by EEG; this makes detection of SSVEP stimuli relatively easy. SSVEP is used within many BCI systems. This is due to several factors. The signal elicited is measurable in as large a population as the transient VEP and blink movement. Electrocardiographic artefacts do not affect the frequencies monitored. The SSVEP signal is robust; the topographic organization of the primary visual cortex is such that a broader area obtains afferents from the visual field's central or fovial region. SSVEP comes with problems. As SSVEPs use flashing stimuli to infer user intent, the user must gaze at one of the flashing or iterating symbols in order to interact with the system. It is, therefore, likely that the symbols become irritating and uncomfortable during longer play sessions.
Another type of VEP is the P300 potential. This potential is a positive peak in the EEG that occurs roughly 300 ms after the appearance of a target stimulus (a stimulus for which the user is waiting or seeking) or oddball stimuli. P300 amplitude decreases as the target stimuli and the ignored stimuli grow more similar. P300 is thought to be related to a higher level attention process or an orienting response. Using P300 requires fewer training sessions. The first application to use it was the P300 matrix. Within this system, a subject chooses a letter from a 6 by 6 grid of letters and numbers. The rows and columns of the grid flashed sequentially and every time the selected "choice letter" was illuminated the user's P300 was (potentially) elicited. However, the communication process, at approximately 17 characters per minute, was slow. P300 offers a discrete selection rather than continuous control. The advantage of P300 within games is that the player does not have to learn how to use a new control system, requiring only short training instances to learn gameplay mechanics and the basic BCI paradigm.
Non-brain-based human–computer interface (physiological computing)
Human-computer interaction can exploit other recording modalities, such as electrooculography and eye-tracking. These modalities do not record brain activity and therefore do not qualify as BCIs.
Electrooculography (EOG)
In 1989, a study reported control of a mobile robot by eye movement using electrooculography signals. A mobile robot was driven to a goal point using five EOG commands, interpreted as forward, backward, left, right, and stop.
Pupil-size oscillation
A 2016 article described a new non-EEG-based HCI that required no visual fixation, or ability to move the eyes. The interface is based on covert interest; directing attention to a chosen letter on a virtual keyboard, without the need to look directly at the letter. Each letter has its own (background) circle which micro-oscillates in brightness differently from the others. Letter selection is based on best fit between unintentional pupil-size oscillation and the background circle's brightness oscillation pattern. Accuracy is additionally improved by the user's mental rehearsal of the words 'bright' and 'dark' in synchrony with the brightness transitions of the letter's circle.
Brain-to-brain communication
In the 1960s a researcher after training used EEG to create Morse code using alpha waves. On 27 February 2013 Miguel Nicolelis's group at Duke University and IINN-ELS connected the brains of two rats, allowing them to share information, in the first-ever direct brain-to-brain interface.
Gerwin Schalk reported that ECoG signals can discriminate vowels and consonants embedded in spoken and imagined words, shedding light on the mechanisms associated with their production and could provide a basis for brain-based communication using imagined speech.
In 2002 Kevin Warwick had an array of 100 electrodes fired into his nervous system in order to link his nervous system to the Internet. Warwick carried out a series of experiments. Electrodes were implanted into his wife's nervous system, allowing them to conduct the first direct electronic communication experiment between the nervous systems of two humans.
Other researchers achieved brain-to-brain communication between participants at a distance using non-invasive technology attached to the participants' scalps. The words were encoded in binary streams by the cognitive motor input of the person sending the information. Pseudo-random bits of the information carried encoded words "hola" ("hi" in Spanish) and "ciao" ("goodbye" in Italian) and were transmitted mind-to-mind.
Cell-culture BCIs
Researchers have built devices to interface with neural cells and entire neural networks in vitro. Experiments on cultured neural tissue focused on building problem-solving networks, constructing basic computers and manipulating robotic devices. Research into techniques for stimulating and recording individual neurons grown on semiconductor chips is neuroelectronics or neurochips.
Development of the first neurochip was claimed by a Caltech team led by Jerome Pine and Michael Maher in 1997. The Caltech chip had room for 16 neurons.
In 2003 a team led by Theodore Berger, at the University of Southern California, worked on a neurochip designed to function as an artificial or prosthetic hippocampus. The neurochip was designed for rat brains. The hippocampus was chosen because it is thought to be the most structured and most studied part of the brain. Its function is to encode experiences for storage as long-term memories elsewhere in the brain.
In 2004 Thomas DeMarse at the University of Florida used a culture of 25,000 neurons taken from a rat's brain to fly a F-22 fighter jet aircraft simulator. After collection, the cortical neurons were cultured in a petri dish and reconnected themselves to form a living neural network. The cells were arranged over a grid of 60 electrodes and used to control the pitch and yaw functions of the simulator. The study's focus was on understanding how the human brain performs and learns computational tasks at a cellular level.
Collaborative BCIs
The idea of combining/integrating brain signals from multiple individuals was introduced at Humanity+ @Caltech, in December 2010, by Adrian Stoica, who referred to the concept as multi-brain aggregation. A patent was applied for in 2012. Stoica's first paper on the topic appeared in 2012, after the publication of his patent application.
Ethical considerations
BCIs present ethical questions, including concerns about privacy, autonomy, consent, and the consequences of merging human cognition with external devices. Exploring these ethical considerations highlights the complex interplay between advancing technology and preserving fundamental human rights and values. The concerns can be broadly categorized into user-centric issues and legal and social issues.
Concerns center on the safety and long-term effects on users. These include obtaining informed consent from individuals with communication difficulties, the impact on patients' and families' quality of life, health-related side effects, misuse of therapeutic applications, safety risks, and the non-reversible nature of some BCI-induced changes. Additionally, questions arise about access to maintenance, repair, and spare parts, particularly in the event of a company's bankruptcy.
The legal and social aspects of BCIs complicate mainstream adoption. Concerns include issues of accountability and responsibility, such as claims that BCI influence overrides free will and control over actions, inaccurate translation of cognitive intentions, personality changes resulting from deep-brain stimulation, and the blurring of the line between human and machine. Other concerns involve the use of BCIs in advanced interrogation techniques, unauthorized access ("brain hacking"), social stratification through selective enhancement, privacy issues related to mind-reading, tracking and "tagging" systems, and the potential for mind, movement, and emotion control. Researchers have also theorized that BCIs could exacerbate existing social inequalities.
In their current form, most BCIs are more akin to corrective therapies that engage few of such ethical issues. Bioethics is well-equipped to address the challenges posed by BCI technologies, with Clausen suggesting in 2009 that "BCIs pose ethical challenges, but these are conceptually similar to those that bioethicists have addressed for other realms of therapy." Haselager and colleagues highlighted the importance of managing expectations and value. Standard protocols can ensure ethically sound informed-consent procedures for locked-in patients.
The evolution of BCIs mirrors that of pharmaceutical science, which began as a means to address impairments and now enhances focus and reduces the need for sleep. As BCIs progress from therapies to enhancements, the BCI community is working to create consensus on ethical guidelines for research, development, and dissemination. Ensuring equitable access to BCIs will be crucial in preventing generational inequalities that could hinder the right to human flourishing.
Low-cost systems
Various companies are developing inexpensive BCIs for research and entertainment. Toys such as the NeuroSky and Mattel MindFlex have seen some commercial success.
In 2006, Sony patented a neural interface system allowing radio waves to affect signals in the neural cortex.
In 2007, NeuroSky released the first affordable consumer based EEG along with the game NeuroBoy. It was the first large scale EEG device to use dry sensor technology.
In 2008, OCZ Technology developed a device for use in video games relying primarily on electromyography.
In 2008, Final Fantasy developer Square Enix announced that it was partnering with NeuroSky to create Judecca, a game.
In 2009, Mattel partnered with NeuroSky to release Mindflex, a game that used an EEG to steer a ball through an obstacle course. It was by far the best selling consumer based EEG at the time.
In 2009, Uncle Milton Industries partnered with NeuroSky to release the Star Wars Force Trainer, a game designed to create the illusion of possessing the Force.
In 2009, Emotiv released the EPOC, a 14 channel EEG device that can read 4 mental states, 13 conscious states, facial expressions, and head movements. The EPOC was the first commercial BCI to use dry sensor technology, which can be dampened with a saline solution for a better connection.
In November 2011, Time magazine selected "necomimi" produced by Neurowear as one of the year's best inventions.
In February 2014, They Shall Walk (a nonprofit organization fixed on constructing exoskeletons, dubbed LIFESUITs, for paraplegics and quadriplegics) began a partnership with James W. Shakarji on the development of a wireless BCI.
In 2016, a group of hobbyists developed an open-source BCI board that sends neural signals to the audio jack of a smartphone, dropping the cost of entry-level BCI to £20. Basic diagnostic software is available for Android devices, as well as a text entry app for Unity.
In 2020, NextMind released a dev kit including an EEG headset with dry electrodes at $399. The device can run various visual-BCI demonstration applications or developers can create their own. It was later acquired by Snap Inc. in 2022.
In 2023, PiEEG released a shield that allows converting a single-board computer Raspberry Pi to a brain-computer interface for $350.
Future directions
A consortium of 12 European partners completed a roadmap to support the European Commission in their funding decisions for the Horizon 2020 framework program. The project was funded by the European Commission. It started in November 2013 and published a roadmap in April 2015. A 2015 publication describes this project, as well as the Brain-Computer Interface Society. It reviewed work within this project that further defined BCIs and applications, explored recent trends, discussed ethical issues, and evaluated directions for new BCIs.
Other recent publications too have explored future BCI directions for new groups of disabled users.
Disorders of consciousness (DOC)
Some people have a disorder of consciousness (DOC). This state is defined to include people in a coma and those in a vegetative state (VS) or minimally conscious state (MCS). BCI research seeks to address DOC. A key initial goal is to identify patients who can perform basic cognitive tasks, which would change their diagnosis, and allow them to make important decisions (such as whether to seek therapy, where to live, and their views on end-of-life decisions regarding them). Patients incorrectly diagnosed may die as a result of end-of-life decisions made by others. The prospect of using BCI to communicate with such patients is a tantalizing prospect.
Many such patients cannot use BCIs based on vision. Hence, tools must rely on auditory and/or vibrotactile stimuli. Patients may wear headphones and/or vibrotactile stimulators placed on responsive body parts. Another challenge is that patients may be able to communicate only at unpredictable intervals. Home devices can allow communications when the patient is ready.
Automated tools can ask questions that patients can easily answer, such as "Is your father named George?" or "Were you born in the USA?" Automated instructions inform patients how to convey yes or no, for example by focusing their attention on stimuli on the right vs. left wrist. This focused attention produces reliable changes in EEG patterns that can help determine whether the patient is able to communicate.
Motor recovery
People may lose some of their ability to move due to many causes, such as stroke or injury. Research in recent years has demonstrated the utility of EEG-based BCI systems in aiding motor recovery and neurorehabilitation in patients who have had a stroke. Several groups have explored systems and methods for motor recovery that include BCIs. In this approach, a BCI measures motor activity while the patient imagines or attempts movements as directed by a therapist. The BCI may provide two benefits: (1) if the BCI indicates that a patient is not imagining a movement correctly (non-compliance), then the BCI could inform the patient and therapist; and (2) rewarding feedback such as functional stimulation or the movement of a virtual avatar also depends on the patient's correct movement imagery.
So far, BCIs for motor recovery have relied on the EEG to measure the patient's motor imagery. However, studies have also used fMRI to study different changes in the brain as persons undergo BCI-based stroke rehab training. Imaging studies combined with EEG-based BCI systems hold promise for investigating neuroplasticity during motor recovery post-stroke. Future systems might include the fMRI and other measures for real-time control, such as functional near-infrared, probably in tandem with EEGs. Non-invasive brain stimulation has also been explored in combination with BCIs for motor recovery. In 2016, scientists out of the University of Melbourne published preclinical proof-of-concept data related to a potential brain-computer interface technology platform being developed for patients with paralysis to facilitate control of external devices such as robotic limbs, computers and exoskeletons by translating brain activity.
Functional brain mapping
In 2014, some 400,000 people underwent brain mapping during neurosurgery. This procedure is often required for people who do not respond to medication. During this procedure, electrodes are placed on the brain to precisely identify the locations of structures and functional areas. Patients may be awake during neurosurgery and asked to perform tasks, such as moving fingers or repeating words. This is necessary so that surgeons can remove the desired tissue while sparing other regions. Removing too much brain tissue can cause permanent damage, while removing too little can mandate additional neurosurgery.
Researchers explored ways to improve neurosurgical mapping. This work focuses largely on high gamma activity, which is difficult to detect non-invasively. Results improved methods for identifying key functional areas.
Flexible devices
Flexible electronics are polymers or other flexible materials (e.g. silk, pentacene, PDMS, Parylene, polyimide) printed with circuitry; the flexibility allows the electronics to bend. The fabrication techniques used to create these devices resembles those used to create integrated circuits and microelectromechanical systems (MEMS).
Flexible neural interfaces may minimize brain tissue trauma related to mechanical mismatch between electrode and tissue.
Neural dust
Neural dust is millimeter-sized devices operated as wirelessly powered nerve sensors that were proposed in a 2011 paper from the University of California, Berkeley Wireless Research Center. In one model, local field potentials could be distinguished from action potential "spikes", which would offer greatly diversified data vs conventional techniques.
See also
Informatics
Intendix (2009)
AlterEgo, a system that reads unspoken verbalizations and responds with bone-conduction headphones
Augmented learning
Biological machine
Cortical implants
Deep brain stimulation
Human senses
Experience machine
Kernel (neurotechnology company)
Lie detection
Microwave auditory effect
Neural engineering
Neuralink
Neurorobotics
Neurostimulation
Nootropic
Paradromics
Precision Neuroscience
Project Cyborg
Simulated reality
Stent-electrode recording array
Telepresence
Thought identification
Wetware computer (Uses similar technology for IO)
Whole brain emulation
Wirehead (science fiction)
Notes
References
Further reading
Brouse, Andrew. "A Young Person's Guide to Brainwave Music: Forty years of audio from the human EEG". eContact! 14.2 – Biotechnological Performance Practice / Pratiques de performance biotechnologique (July 2012). Montréal: CEC.
Gupta, Cota Navin and Ramaswamy Palanappian. "Using High-Frequency Electroencephalogram in Visual and Auditory-Based Brain-Computer Interface Designs". eContact! 14.2 – Biotechnological Performance Practice / Pratiques de performance biotechnologique (July 2012). Montréal: CEC.
Ouzounian, Gascia. "The Biomuse Trio in Conversation: An Interview with R. Benjamin Knapp and Eric Lyon". eContact! 14.2 – Biotechnological Performance Practice / Pratiques de performance biotechnologique (July 2012). Montréal: CEC.
External links
The Unlock Project
CIA - Wireless BCI
DARPA projects
Human–computer interaction
Implants (medicine)
User interface techniques
Virtual reality
Augmented reality
Spatial computing | Brain–computer interface | [
"Engineering"
] | 12,157 | [
"Human–computer interaction",
"Human–machine interaction"
] |
623,694 | https://en.wikipedia.org/wiki/American%20Sailboat%20Hall%20of%20Fame | The American Sailboat Hall of Fame is a defunct hall of fame honoring 26 production sailboats built-in the United States. The hall of fame was established in 1994 by Sail America, a trade association for the U.S. sailing industry, to recognize ingenuity in designs by American boat builders. The last year of induction was 2004.
Half-hull models of each Hall of Fame inductee was housed in a permanent exhibit at The Museum of Yachting located in Fort Adams State Park in Newport, Rhode Island prior to the museum's dismantling after a 2007 acquisition by the IYRS School of Technology & Trades. The collection also traveled around the country each year to be displayed at the various Strictly Sail boat shows sponsored by Sail America, and at Sail Expo in Atlantic City, New Jersey.
Inducted sailboats were required to be production models built in the U.S. introduced at least 15 years prior to induction, and to have made a lasting impact on sailing. Selections to the hall of fame were made by a committee composed of magazine editors of Sailing Magazine, Sailing World, and SAIL.
Inductees
See also
National Sailing Hall of Fame
ISAF World Sailor of the Year Awards
List of maritime museums in the United States
Footnotes
References
US Boats Magazine(online) Retrieved 1/7/07
Sail Magazine (online), New Old Boats, Retrieved 1/7/07
Sailing Magazine (online), Full and By, Bill Schanen, Retrieved 1/7/07
Practical Sailor Magazine, Retrieved 1/7/07
Boat US (online boat review) retrieved 1/7/07
Strictly Sail (website), 15 November 2003,11th Annual Atlantic SAIL EXPO Draws Crowd of 13,000, retrieved 1/7/07
Yahoo Travel retrieved 1/7/07
Rhode Island Tourist Guide (location & contact)
Description of Award - Sail America
Marston, Red (May 3, 1996). "Kudos to sailboat designer Morgan". St. Petersburg Times, p. 8C.
Staff. (June 25, 1996). "East Bay Briefings". Providence Journal-Bulletin, p. 3C.
External links
The American Sailboat Hall of Fame
Sail America
Sailing in the United States
Science and technology halls of fame
American science and technology awards
Sailboat
Organizations established in 1994
Maritime museums in Rhode Island
Museums in Newport, Rhode Island
Sailing museums and halls of fame | American Sailboat Hall of Fame | [
"Technology"
] | 484 | [
"Science and technology awards",
"Science and technology halls of fame"
] |
623,831 | https://en.wikipedia.org/wiki/Eval | In some programming languages, eval , short for evaluate, is a function which evaluates a string as though it were an expression in the language, and returns a result; in others, it executes multiple lines of code as though they had been included instead of the line including the eval. The input to eval is not necessarily a string; it may be structured representation of code, such as an abstract syntax tree (like Lisp forms), or of special type such as code (as in Python). The analog for a statement is exec, which executes a string (or code in other format) as if it were a statement; in some languages, such as Python, both are present, while in other languages only one of either eval or exec is.
Security risks
Using eval with data from an untrusted source may introduce security vulnerabilities. For instance, assuming that the get_data() function gets data from the Internet, this Python code is insecure:
session['authenticated'] = False
data = get_data()
foo = eval(data)
An attacker could supply the program with the string "session.update(authenticated=True)" as data, which would update the session dictionary to set an authenticated key to be True. To remedy this, all data which will be used with eval must be escaped, or it must be run without access to potentially harmful functions.
Implementation
In interpreted languages, eval is almost always implemented with the same interpreter as normal code. In compiled languages, the same compiler used to compile programs may be embedded in programs using the eval function; separate interpreters are sometimes used, though this results in code duplication.
Programming languages
ECMAScript
JavaScript
In JavaScript, eval is something of a hybrid between an expression evaluator and a statement executor. It returns the result of the last expression evaluated.
Example as an expression evaluator:
foo = 2;
alert(eval('foo + 2'));
Example as a statement executor:
foo = 2;
eval('foo = foo + 2;alert(foo);');
One use of JavaScript's eval is to parse JSON text, perhaps as part of an Ajax framework. However, modern browsers provide JSON.parse as a more secure alternative for this task.
ActionScript
In ActionScript (Flash's programming language), eval cannot be used to evaluate arbitrary expressions. According to the Flash 8 documentation, its usage is limited to expressions which represent "the name of a variable, property, object, or movie clip to retrieve. This parameter can be either a String or a direct reference to the object instance."
ActionScript 3 does not support eval.
The ActionScript 3 Eval Library and the D.eval API were development projects to create equivalents to eval in ActionScript 3. Both have ended, as Adobe Flash Player has reached its end-of-life.
Lisp
Lisp was the original language to make use of an eval function in 1958. In fact, definition of the eval function led to the first implementation of the language interpreter.
Before the eval function was defined, Lisp functions were manually compiled to assembly language statements. However, once the eval function had been manually compiled it was then used as part of a simple read-eval-print loop which formed the basis of the first Lisp interpreter.
Later versions of the Lisp eval function have also been implemented as compilers.
The eval function in Lisp expects a form to be evaluated as its argument. The resulting value of the given form will be the returned value of the call to eval.
This is an example Lisp code:
; A form which calls the + function with 1,2 and 3 as arguments.
; It returns 6.
(+ 1 2 3)
; In Lisp any form is meant to be evaluated, therefore
; the call to + was performed.
; We can prevent Lisp from performing evaluation
; of a form by prefixing it with "'", for example:
(setq form1 '(+ 1 2 3))
; Now form1 contains a form that can be used by eval, for
; example:
(eval form1)
; eval evaluated (+ 1 2 3) and returned 6.
Lisp is well known to be very flexible and so is the eval function. For example, to evaluate the content of a string, the string would first have to be converted into a Lisp form using the read-from-string function and then the resulting form would have to be passed to eval:
(eval (read-from-string "(format t \"Hello World!!!~%\")"))
One major point of confusion is the question, in which context the symbols in the form will be evaluated. In the above example, form1 contains the symbol +. Evaluation of this symbol must yield the function for addition to make the example work as intended. Thus some dialects of Lisp allow an additional parameter for eval to specify the context of evaluation (similar to the optional arguments to Python's eval function - see below). An example in the Scheme dialect of Lisp (R5RS and later):
;; Define some simple form as in the above example.
(define form2 '(+ 5 2))
;Value: form2
;; Evaluate the form within the initial context.
;; A context for evaluation is called an "environment" in Scheme slang.
(eval form2 user-initial-environment)
;Value: 7
;; Confuse the initial environment, so that + will be
;; a name for the subtraction function.
(environment-define user-initial-environment '+ -)
;Value: +
;; Evaluate the form again.
;; Notice that the returned value has changed.
(eval form2 user-initial-environment)
;Value: 3
Perl
In Perl, the eval function is something of a hybrid between an expression evaluator and a statement executor. It returns the result of the last expression evaluated (all statements are expressions in Perl programming), and allows the final semicolon to be left off.
Example as an expression evaluator:
$foo = 2;
print eval('$foo + 2'), "\n";
Example as a statement executor:
$foo = 2;
eval('$foo += 2; print "$foo\n";');
Perl also has eval blocks, which serves as its exception handling mechanism (see Exception handling syntax#Perl). This differs from the above use of eval with strings in that code inside eval blocks is interpreted at compile-time instead of run-time, so it is not the meaning of eval used in this article.
PHP
In PHP, eval executes code in a string almost exactly as if it had been put in the file instead of the call to eval(). The only exception is that errors are reported as coming from a call to eval(), and return statements become the result of the function.
Unlike some languages, the argument to eval must be a string of one or more complete statements, not just expressions; however, one can get the "expression" form of eval by putting the expression in a return statement, which causes eval to return the result of that expression.
Unlike some languages, PHP's eval is a "language construct" rather than a function, and so cannot be used in some contexts where functions can be, like higher-order functions.
Example using echo:
<?php
$foo = "Hello, world!\n";
eval('echo "$foo";');
?>
Example returning a value:
<?php
$foo = "Goodbye, world!\n"; //does not work in PHP5
echo eval('return $foo;');
?>
Lua
In Lua 5.1, loadstring compiles Lua code into an anonymous function.
Example as an expression evaluator:
loadstring("print('Hello World!')")()
Example to do the evaluation in two steps:
a = 1
f = loadstring("return a + 1") -- compile the expression to an anonymous function
print(f()) -- execute (and print the result '2')
Lua 5.2 deprecates loadstring in favor of the existing load function, which has been augmented to accept strings. In addition, it allows providing the function's environment directly, as environments are now upvalues.
load("print('Hello ' .. a)", "", "t", { a = "World!", print = print })()
PostScript
PostScript's exec operator takes an operand — if it is a simple literal it pushes it back on the stack. If one takes a string containing a PostScript expression however, one can convert the string to an executable which then can be executed by the interpreter, for example:
((Hello World) =) cvx exec
converts the PostScript expression
(Hello World) =
which pops the string "Hello World" off the stack and displays it on the screen, to have an executable type, then is executed.
PostScript's run operator is similar in functionality but instead the interpreter interprets PostScript expressions in a file, itself.
(file.ps) run
Python
In Python, the eval function in its simplest form evaluates a single expression.
eval example (interactive shell):
>>> x = 1
>>> eval('x + 1')
2
>>> eval('x')
1
The eval function takes two optional arguments, global and locals, which allow the programmer to set up a restricted environment for the evaluation of the expression.
The exec statement (or the exec function in Python 3.x) executes statements:
exec example (interactive shell):
>>> x = 1
>>> y = 1
>>> exec "x += 1; y -= 1"
>>> x
2
>>> y
0
The most general form for evaluating statements/expressions is using code objects. Those can be created by invoking the compile() function and by telling it what kind of input it has to compile: an "exec" statement, an "eval" statement or a "single" statement:
compile example (interactive shell):
>>> x = 1
>>> y = 2
>>> eval (compile ("print 'x + y = ', x + y", "compile-sample.py", "single"))
x + y = 3
D
D is a statically compiled language and therefore does not include an "eval" statement in the traditional sense, but does include the related "mixin" statement. The difference is that, where "eval" interprets a string as code at runtime, with a "mixin" the string is statically compiled like ordinary code and must be known at compile time. For example:
import std.stdio;
void main() {
int num = 0;
mixin("num++;");
writeln(num); // Prints 1.
}
The above example will compile to exactly the same assembly language instructions as if "num++;" had been written directly instead of mixed in. The argument to mixin doesn't need to be a string literal, but arbitrary expressions resulting in a string value, including function calls, that can be evaluated at compile time.
ColdFusion
ColdFusion's evaluate function lets you evaluate a string expression at runtime.
<cfset x = "int(1+1)">
<cfset y = Evaluate(x)>
It is particularly useful when you need to programmatically choose the variable you want to read from.
<cfset x = Evaluate("queryname.#columnname#[rownumber]")>
Ruby
The Ruby programming language interpreter offers an eval function similar to Python or Perl, and also allows a scope, or binding, to be specified.
Aside from specifying a function's binding, eval may also be used to evaluate an expression within a specific class definition binding or object instance binding, allowing classes to be extended with new methods specified in strings.
a = 1
eval('a + 1') # (evaluates to 2)
# evaluating within a context
def get_binding(a)
binding
end
eval('a+1',get_binding(3)) # (evaluates to 4, because 'a' in the context of get_binding is 3)
class Test; end
Test.class_eval("def hello; return 'hello';end") # add a method 'hello' to this class
Test.new.hello # evaluates to "hello"
Forth
Most standard implementations of Forth have two variants of eval: EVALUATE and INTERPRET.
Win32FORTH code example:
S" 2 2 + ." EVALUATE \ Outputs "4"
BASIC
REALbasic
In REALbasic, there is a class called RBScript which can execute REALbasic code at runtime. RBScript is very sandboxed—only the most core language features are there, and you have to allow it access to things you want it to have. You can optionally assign an object to the context property. This allows for the code in RBScript to call functions and use properties of the context object. However, it is still limited to only understanding the most basic types, so if you have a function that returns a Dictionary or MySpiffyObject, RBScript will be unable to use it. You can also communicate with your RBScript through the Print and Input events.
VBScript
Microsoft's VBScript, which is an interpreted language, has two constructs. Eval is a function evaluator that can include calls to user-defined functions. (These functions may have side-effects such as changing the values of global variables.) Execute executes one or more colon-separated statements, which can change global state.
Both VBScript and JScript eval are available to developers of compiled Windows applications (written in languages which do not support Eval) through an ActiveX control called the Microsoft Script Control, whose Eval method can be called by application code. To support calling of user-defined functions, one must first initialize the control with the AddCode method, which loads a string (or a string resource) containing a library of user-defined functions defined in the language of one's choice, prior to calling Eval.
Visual Basic for Applications
Visual Basic for Applications (VBA), the programming language of Microsoft Office, is a virtual machine language where the runtime environment compiles and runs p-code. Its flavor of Eval supports only expression evaluation, where the expression may include user-defined functions and objects (but not user-defined variable names). Of note, the evaluator is different from VBS, and invocation of certain user-defined functions may work differently in VBA than the identical code in VBScript.
Smalltalk
As Smalltalk's compiler classes are part of the standard class library and usually present at run time, these can be used to evaluate a code string.
Compiler evaluate:'1 + 2'
Because class and method definitions are also implemented by message-sends (to class objects), even code changes are possible:
Compiler evaluate:'Object subclass:#Foo'
Tcl
The Tcl programming language has a command called eval, which executes the source code provided as an argument. Tcl represents all source code as strings, with curly braces acting as quotation marks, so that the argument to eval can have the same formatting as any other source code.
set foo {
while {[incr i]<10} {
puts "$i squared is [expr $i*$i]"
}
}
eval $foo
bs
bs has an eval function that takes one string argument. The function is both an expression evaluator and a statement executor. In the latter role, it can also be used for error handling. The following examples and text are from the bs man page as appears in the UNIX System V Release 3.2 Programmer's Manual.
Command-line interpreters
Unix shells
The eval command is present in all Unix shells, including the original "sh" (Bourne shell). It concatenates all the arguments with spaces, then re-parses and executes the result as a command.
PowerShell
In PowerShell, the Invoke-Expression Cmdlet serves the same purpose as the eval function in programming languages like JavaScript, PHP and Python.
The Cmdlet runs any PowerShell expression that is provided as a command parameter in the form of a string and outputs the result of the specified expression.
Usually, the output of the Cmdlet is of the same type as the result of executing the expression. However, if the result is an empty array, it outputs $null. In case the result is a single-element array, it outputs that single element. Similar to JavaScript, PowerShell allows the final semicolon to be left off.
Example as an expression evaluator:
PS > $foo = 2
PS > Invoke-Expression '$foo + 2'
Example as a statement executor:
PS > $foo = 2
PS > Invoke-Expression '$foo += 2; $foo'
Microcode
In 1966 IBM Conversational Programming System (CPS) introduced a microprogrammed function EVAL to perform "interpretive evaluation of expressions which are written in a modified Polish-string notation" on an IBM System/360 Model 50. Microcoding this function was "substantially more" than five times faster compared to a program that interpreted an assignment statement.
Theory
In theoretical computer science, a careful distinction is commonly made between eval and apply. Eval is understood to be the step of converting a quoted string into a callable function and its arguments, whereas apply is the actual call of the function with a given set of arguments. The distinction is particularly noticeable in functional languages, and languages based on lambda calculus, such as LISP and Scheme. Thus, for example, in Scheme, the distinction is between
(eval '(f x) )
where the form (f x) is to be evaluated, and
(apply f (list x))
where the function f is to be called with argument x.
Eval and apply are the two interdependent components of the eval-apply cycle, which is the essence of evaluating Lisp, described in SICP.
In category theory, the eval morphism is used to define the closed monoidal category. Thus, for example, the category of sets, with functions taken as morphisms, and the cartesian product taken as the product, forms a Cartesian closed category. Here, eval (or, properly speaking, apply) together with its right adjoint, currying, form the simply typed lambda calculus, which can be interpreted to be the morphisms of Cartesian closed categories.
See also
Data as code
References
External links
ANSI and GNU Common Lisp Document: eval function
Python Library Reference: eval built-in function
Jonathan Johnson on exposing classes to RBScript
Examples of runtime evaluation in several languages on Rosetta Code
Control flow
Unix SUS2008 utilities
IBM i Qshell commands | Eval | [
"Technology"
] | 4,121 | [
"IBM i Qshell commands",
"Computing commands"
] |
623,870 | https://en.wikipedia.org/wiki/Raman%20scattering | In chemistry and physics, Raman scattering or the Raman effect () is the inelastic scattering of photons by matter, meaning that there is both an exchange of energy and a change in the light's direction. Typically this effect involves vibrational energy being gained by a molecule as incident photons from a visible laser are shifted to lower energy. This is called normal Stokes-Raman scattering.
Light has a certain probability of being scattered by a material. When photons are scattered, most of them are elastically scattered (Rayleigh scattering), such that the scattered photons have the same energy (frequency, wavelength, and therefore color) as the incident photons, but different direction. Rayleigh scattering usually has an intensity in the range 0.1% to 0.01% relative to that of a radiation source. An even smaller fraction of the scattered photons (about 1 in a million) can be scattered inelastically, with the scattered photons having an energy different (usually lower) from those of the incident photons—these are Raman scattered photons. Because of conservation of energy, the material either gains or loses energy in the process.
The effect is exploited by chemists and physicists to gain information about materials for a variety of purposes by performing various forms of Raman spectroscopy. Many other variants of Raman spectroscopy allow rotational energy to be examined, if gas samples are used, and electronic energy levels may be examined if an X-ray source is used, in addition to other possibilities. More complex techniques involving pulsed lasers, multiple laser beams and so on are known.
The Raman effect is named after Indian scientist C. V. Raman, who discovered it in 1928 with assistance from his student K. S. Krishnan. Raman was awarded the 1930 Nobel Prize in Physics for his discovery of Raman scattering. The effect had been predicted theoretically by Adolf Smekal in 1923.
History
The elastic light scattering phenomena called Rayleigh scattering, in which light retains its energy, was described in the 19th century. The intensity of Rayleigh scattering is about 10−3 to 10−4 compared to the intensity of the exciting source. In 1908, another form of elastic scattering, called Mie scattering was discovered.
The inelastic scattering of light was predicted by Adolf Smekal in 1923 and in older German-language literature it has been referred to as the Smekal-Raman-Effekt. In 1922, Indian physicist C. V. Raman published his work on the "Molecular Diffraction of Light", the first of a series of investigations with his collaborators that ultimately led to his discovery (on 16 February 1928) of the radiation effect that bears his name. The Raman effect was first reported by Raman and his coworker K. S. Krishnan, and independently by Grigory Landsberg and Leonid Mandelstam, in Moscow on 21 February 1928 (5 days after Raman and Krishnan). In the former Soviet Union, Raman's contribution was always disputed; thus in Russian scientific literature the effect is usually referred to as "combination scattering" or "combinatory scattering". Raman received the Nobel Prize in 1930 for his work on the scattering of light.
In 1998 the Raman effect was designated a National Historic Chemical Landmark by the American Chemical Society in recognition of its significance as a tool for analyzing the composition of liquids, gases, and solids.
Instrumentation
Modern Raman spectroscopy nearly always involves the use of lasers as an exciting light source. Because lasers were not available until more than three decades after the discovery of the effect, Raman and Krishnan used a mercury lamp and photographic plates to record spectra. Early spectra took hours or even days to acquire due to weak light sources, poor sensitivity of the detectors and the weak Raman scattering cross-sections of most materials. The most common modern detectors are charge-coupled devices (CCDs). Photodiode arrays and photomultiplier tubes were common prior to the adoption of CCDs.
Theory
The following focuses on the theory of normal (non-resonant, spontaneous, vibrational) Raman scattering of light by discrete molecules. X-ray Raman spectroscopy is conceptually similar but involves excitation of electronic, rather than vibrational, energy levels.
Molecular vibrations
Raman scattering generally gives information about vibrations within a molecule. In the case of gases, information about rotational energy can also be gleaned. For solids, phonon modes may also be observed. The basics of infrared absorption regarding molecular vibrations apply to Raman scattering although the selection rules are different.
Degrees of freedom
For any given molecule, there are a total of 3 degrees of freedom, where is the number of atoms. This number arises from the ability of each atom in a molecule to move in three dimensions. When dealing with molecules, it is more common to consider the movement of the molecule as a whole. Consequently, the 3 degrees of freedom are partitioned into molecular translational, rotational, and vibrational motion. Three of the degrees of freedom correspond to translational motion of the molecule as a whole (along each of the three spatial dimensions). Similarly, three degrees of freedom correspond to rotations of the molecule about the , , and -axes. Linear molecules only have two rotations because rotations along the bond axis do not change the positions of the atoms in the molecule. The remaining degrees of freedom correspond to molecular vibrational modes. These modes include stretching and bending motions of the chemical bonds of the molecule. For a linear molecule, the number of vibrational modes is 3-5, whereas for a non-linear molecule the number of vibrational modes is 3-6.
Vibrational energy
Molecular vibrational energy is known to be quantized and can be modeled using the quantum harmonic oscillator (QHO) approximation or a Dunham expansion when anharmonicity is important.
The vibrational energy levels according to the QHO are
,
where n is a quantum number. Since the selection rules for Raman and infrared absorption generally dictate that only fundamental vibrations are observed, infrared excitation or Stokes Raman excitation results in an energy change of
The energy range for vibrations is in the range of approximately 5 to 3500 cm−1. The fraction of molecules occupying a given vibrational mode at a given temperature follows a Boltzmann distribution. A molecule can be excited to a higher vibrational mode through the direct absorption of a photon of the appropriate energy, which falls in the terahertz or infrared range. This forms the basis of infrared spectroscopy. Alternatively, the same vibrational excitation can be produced by an inelastic scattering process. This is called Stokes Raman scattering, by analogy with the Stokes shift in fluorescence discovered by George Stokes in 1852, with light emission at longer wavelength (now known to correspond to lower energy) than the absorbed incident light. Conceptually similar effects can be caused by neutrons or electrons rather than light. An increase in photon energy which leaves the molecule in a lower vibrational energy state is called anti-Stokes scattering.
Raman scattering
Raman scattering is conceptualized as involving a virtual electronic energy level which corresponds to the energy of the exciting laser photons. Absorption of a photon excites the molecule to the imaginary state and re-emission leads to Raman or Rayleigh scattering. In all three cases the final state has the same electronic energy as the initial state but is higher in vibrational energy in the case of Stokes Raman scattering, lower in the case of anti-Stokes Raman scattering or the same in the case of Rayleigh scattering. Normally this is thought of in terms of wavenumbers, where is the wavenumber of the laser and is the wavenumber of the vibrational transition. Thus Stokes scattering gives a wavenumber of while is given for anti-Stokes. When the exciting laser energy corresponds to an actual electronic excitation of the molecule then the resonance Raman effect occurs.
A classical physics based model is able to account for Raman scattering and predicts an increase in the intensity which scales with the fourth-power of the light frequency. Light scattering by a molecule is associated with oscillations of an induced electric dipole. The oscillating electric field component of electromagnetic radiation may bring about an induced dipole in a molecule which follows the alternating electric field which is modulated by the molecular vibrations. Oscillations at the external field frequency are therefore observed along with beat frequencies resulting from the external field and normal mode vibrations.
The spectrum of the scattered photons is termed the Raman spectrum. It shows the intensity of the scattered light as a function of its frequency difference Δν to the incident photons, more commonly called a Raman shift. The locations of corresponding Stokes and anti-Stokes peaks form a symmetric pattern around the RayleighΔν=0 line. The frequency shifts are symmetric because they correspond to the energy difference between the same upper and lower resonant states. The intensities of the pairs of features will typically differ, though. They depend on the populations of the initial states of the material, which in turn depend on the temperature. In thermodynamic equilibrium, the lower state will be more populated than the upper state. Therefore, the rate of transitions from the more populated lower state to the upper state (Stokes transitions) will be higher than in the opposite direction (anti-Stokes transitions). Correspondingly, Stokes scattering peaks are stronger than anti-Stokes scattering peaks. Their ratio depends on the temperature, and can therefore be exploited to measure it:
Selection rules
In contrast to IR spectroscopy, where there is a requirement for a change in dipole moment for vibrational excitation to take place, Raman scattering requires a change in polarizability. A Raman transition from one state to another is allowed only if the molecular polarizability of those states is different. For a vibration, this means that the derivative of the polarizability with respect to the normal coordinate associated to the vibration is non-zero: . In general, a normal mode is Raman active if it transforms with the same symmetry of the quadratic forms , which can be verified from the character table of the molecule's point group. As with IR spectroscopy, only fundamental excitations () are allowed according to the QHO. There are however many cases where overtones are observed. The rule of mutual exclusion, which states that vibrational modes cannot be both IR and Raman active, applies to certain molecules.
The specific selection rules state that the allowed rotational transitions are , where is the rotational state. This generally is only relevant to molecules in the gas phase where the Raman linewidths are small enough for rotational transitions to be resolved.
A selection rule relevant only to ordered solid materials states that only phonons with zero phase angle can be observed by IR and Raman, except when phonon confinement is manifest.
Symmetry and polarization
Monitoring the polarization of the scattered photons is useful for understanding the connections between molecular symmetry and Raman activity which may assist in assigning peaks in Raman spectra. Light polarized in a single direction only gives access to some Raman–active modes, but rotating the polarization gives access to other modes. Each mode is separated according to its symmetry.
The symmetry of a vibrational mode is deduced from the depolarization ratio , which is the ratio of the Raman scattering with polarization orthogonal to the incident laser and the Raman scattering with the same polarization as the incident laser: Here is the intensity of Raman scattering when the analyzer is rotated 90 degrees with respect to the incident light's polarization axis, and the intensity of Raman scattering when the analyzer is aligned with the polarization of the incident laser. When polarized light interacts with a molecule, it distorts the molecule which induces an equal and opposite effect in the plane-wave, causing it to be rotated by the difference between the orientation of the molecule and the angle of polarization of the light wave. If , then the vibrations at that frequency are depolarized; meaning they are not totally symmetric.
Stimulated Raman scattering and Raman amplification
The Raman-scattering process as described above takes place spontaneously; i.e., in random time intervals, one of the many incoming photons is scattered by the material. This process is thus called spontaneous Raman scattering.
On the other hand, stimulated Raman scattering can take place when some Stokes photons have previously been generated by spontaneous Raman scattering (and somehow forced to remain in the material), or when deliberately injecting Stokes photons ("signal light") together with the original light ("pump light"). In that case, the total Raman-scattering rate is increased beyond that of spontaneous Raman scattering: pump photons are converted more rapidly into additional Stokes photons. The more Stokes photons that are already present, the faster more of them are added. Effectively, this amplifies the Stokes light in the presence of the pump light, which is exploited in Raman amplifiers and Raman lasers.
Stimulated Raman scattering is a nonlinear optical effect.
Requirement for space-coherence
Suppose that the distance between two points A and B of an exciting beam is . Generally, as the exciting frequency is not equal to the scattered Raman frequency, the corresponding relative wavelengths and are not equal. Thus, a phase-shift appears. For , the scattered amplitudes are opposite, so that the Raman scattered beam remains weak.
A crossing of the beams may limit the path .
Several tricks may be used to get a larger amplitude:
In an optically anisotropic crystal, a light ray may have two modes of propagation with different polarizations and different indices of refraction. If energy may be transferred between these modes by a quadrupolar (Raman) resonance, phases remain coherent along the whole path, transfer of energy may be large. It is an Optical parametric generation.
Light may be pulsed, so that beats do not appear. In Impulsive Stimulated Raman Scattering (ISRS), the length of the pulses must be shorter than all relevant time constants. Interference of Raman and incident lights is too short to allow beats, so that it produces a frequency shift roughly, in best conditions, inversely proportional to the cube of the pulse length.
In labs, femtosecond laser pulses must be used because the ISRS becomes very weak if the pulses are too long. Thus ISRS cannot be observed using nanosecond pulses making ordinary time-incoherent light.
Inverse Raman effect
The inverse Raman effect is a form of Raman scattering first noted by W. J. Jones and Boris P. Stoicheff. In some circumstances, Stokes scattering can exceed anti-Stokes scattering; in these cases the continuum (on leaving the material) is observed to have an absorption line (a dip in intensity) at νL+νM. This phenomenon is referred to as the inverse Raman effect; the application of the phenomenon is referred to as inverse Raman spectroscopy, and a record of the continuum is referred to as an inverse Raman spectrum.
In the original description of the inverse Raman effect, the authors discuss both absorption from a continuum of higher frequencies and absorption from a continuum of lower frequencies. They note that absorption from a continuum of lower frequencies will not be observed if the Raman frequency of the material is vibrational in origin and if the material is in thermal equilibrium.
Supercontinuum generation
For high-intensity continuous wave (CW) lasers, stimulated Raman scattering can be used to produce a broad bandwidth supercontinuum. This process can also be seen as a special case of four-wave mixing, in which the frequencies of the two incident photons are equal and the emitted spectra are found in two bands separated from the incident light by the phonon energies. The initial Raman spectrum is built up with spontaneous emission and is amplified later on. At high pumping levels in long fibers, higher-order Raman spectra can be generated by using the Raman spectrum as a new starting point, thereby building a chain of new spectra with decreasing amplitude. The disadvantage of intrinsic noise due to the initial spontaneous process can be overcome by seeding a spectrum at the beginning, or even using a feedback loop as in a resonator to stabilize the process. Since this technology easily fits into the fast evolving fiber laser field and there is demand for transversal coherent high-intensity light sources (i.e., broadband telecommunication, imaging applications), Raman amplification and spectrum generation might be widely used in the near-future.
Applications
Raman spectroscopy employs the Raman effect for substances analysis. The spectrum of the Raman-scattered light depends on the molecular constituents present and their state, allowing the spectrum to be used for material identification and analysis. Raman spectroscopy is used to analyze a wide range of materials, including gases, liquids, and solids. Highly complex materials such as biological organisms and human tissue can also be analyzed by Raman spectroscopy.
For solid materials, Raman scattering is used as a tool to detect high-frequency phonon and magnon excitations.
Raman lidar is used in atmospheric physics to measure the atmospheric extinction coefficient and the water vapour vertical distribution.
Stimulated Raman transitions are also widely used for manipulating a trapped ion's energy levels, and thus basis qubit states.
Raman spectroscopy can be used to determine the force constant and bond length for molecules that do not have an infrared absorption spectrum.
Raman amplification is used in optical amplifiers.
The Raman effect is also involved in producing the appearance of the blue sky (see Rayleigh Scattering: 'Rayleigh scattering of molecular nitrogen and oxygen in the atmosphere includes elastic scattering as well as the inelastic contribution from rotational Raman scattering in air').
Raman spectroscopy has been used to chemically image small molecules, such as nucleic acids, in biological systems by a vibrational tag.
See also
References
Further reading
External links
Explanation from Hyperphysics in Astronomy section of gsu.edu
Prof. R. W. Wood Demonstrating the New "Raman Effect" in Physics (Scientific American, December 1930)
Scattering, absorption and radiative transfer (optics)
Fiber-optic communications | Raman scattering | [
"Chemistry"
] | 3,750 | [
"Scattering",
" absorption and radiative transfer (optics)"
] |
623,891 | https://en.wikipedia.org/wiki/Blastomere | In biology, a blastomere is a type of cell produced by cell division (cleavage) of the zygote after fertilization; blastomeres are an essential part of blastula formation, and blastocyst formation in mammals.
Human blastomere characteristics
In humans, blastomere formation begins immediately following fertilization and continues through the first week of embryonic development. About 90 minutes after fertilization, the zygote divides into two cells. The two-cell blastomere state, present after the zygote first divides, is considered the earliest mitotic product of the fertilized oocyte. These mitotic divisions continue and result in a grouping of cells called blastomeres. During this process, the total size of the embryo does not increase, so each division results in smaller and smaller cells. When the zygote contains 16 to 32 blastomeres it is referred to as a morula. These are the preliminary stages in the embryo beginning to form. Once this begins, microtubules within the morula's cytosolic material in the blastomere cells can develop into important membrane functions, such as sodium pumps. These pumps allow the inside of the embryo to fill with blastocoelic fluid, which supports the further growth of life.
The blastomere is considered totipotent; that is, blastomeres are capable of developing from a single cell into a fully fertile adult organism. This has been demonstrated through studies and conjectures made with mouse blastomeres, which have been accepted as true for most mammalian blastomeres as well. Studies have analyzed monozygotic twin mouse blastomeres in their two-cell state, and have found that when one of the twin blastomeres is destroyed, a fully fertile adult mouse can still develop. Thus, it can be assumed that since one of the twin cells was totipotent, the destroyed one originally was as well.
Relative blastomere size within the embryo is dependent not only on the stage of the cleavage, but also on the regularity of the cleavage amongst the cells. If the number of blastomeres in the cellular mass is even, then the sizes of the cells should be congruent. However, if the number of blastomeres in the cellular mass is not even, then the division should be asynchronous such that the sizes of the cells best support the mass's specific stage of differentiation. Blastomere size is typically considered uneven when one blastomere has a diameter over 25% larger than that of the other being compared.
Blastomere differentiation
The division of blastomeres from the zygote allows a single fertile cell to continue to cleave and differentiate until a blastocyst forms. The differentiation of the blastomere allows for the development of two distinct cell populations: the inner cell mass, which becomes the precursor to the embryo, and the trophectoderm, which becomes the precursor to the placenta. These precursors typically appear when the blastomere differentiates into the 8- and 16-cell masses.
During the 8-cell differentiation period, the blastomeres form adheren junctions, and subsequently polarize along the apical-basal axis. This polarization permanently changes the morphology of these cells, and starts the differentiation process. After this, the 8-cell blastomere mass begins to compact by forming tight junctions between themselves, and cytosolic components of the cell accumulate in the apical region while the nucleus of each cell moves to the basal region. The adhesive lateral junction is then formed, and the blastomere is flattened to establish the apical cortical domain. Once the transition begins to a 16-cell mass, the apical cortical domain disappears, but elements of polarity are preserved. This allows for approximately half of the blastomeres to inherit polar regions that can rebuild the apical cortical domain. The other blastomeres that differentiate, then, will become apolar. Polar blastomere cells that differentiate will move to an outer position in the developing blastocyst and show precursors for the trophectoderm, while the apolar cells will move to an inner position and begin developing into the embryo. The cells will then fully commit to their individual states in one of these two domains at the 32-cell stage.
Models of differentiation
There are two main models for differentiation that determine which blastomere cells will divide into either the inner cell mass or the trophectoderm. The first conjecture is known as the "inside-outside model", and states that the cells differentiate based on their state in the 16-cell stage or later. This means that, under this model, blastomere cells do not differentiate based on cellular differences, but rather they do so because of mechanical and chemical stimuli based on where they are positioned at that time.
The other, more widely accepted model is known as the "cell-polarity model". This model states that the orientation of the cleavage plane at the 8-cell and 16-cell stages determines their later differentiation. There are two main ways in which blastomeres typically divide: symmetrically, meaning perpendicular to the apical-basal axis, or asymmetrically, meaning horizontal to the apical-basal axis. Many potential hypotheses and conjectures that attempt to explain why these cells orient themselves the way that they do. Some researchers have stated that early-dividing blastomeres tend to divide asymmetrically, while others have proposed that the orientation of 8-cell stage blastomeres is random and cannot be predicted on a larger scale. One study in particular states that the position of the nucleus in each blastomere can be used to indicate how the cell will divide: if the nucleus is in the apical region then the cell will likely divide symmetrically, while if the nucleus is located in the basal region then the cell will likely divide asymmetrically.
Related disorders
It is possible for errors to occur during this process of repetitive cell division. Common among these errors is for the genetic material to not be divided evenly. Normally, when a cell divides each daughter cell has the same genetic material as the parent cell; if the genetic material does not split evenly between the two daughter cells, an event called "nondisjunction" occurs. Since this event occurs in only one of the several cells that exist at this point, the embryo will continue to develop but will have some normal cells and some abnormal cells. This disorder is called "numerical mosaicism".
This mosaicism, especially of diploidy and polyploidy, can lead to the failure of cell cleavage and mitosis. When these necessary early cell divisions do not occur, the embryo can begin to form polyploid giant cancer cells that function very similarly to blastomere cells in order to grow and evolve in response to mechanical and chemical signals just like blastocyst precursors do. Studies have shown that these giant cancer cells are often also the genetic equivalent to somatic blastomeres.
Diagnostics
Oftentimes, clinicians and researchers will use blastomere biopsies in at-risk pregnant women as a way to test for genetic disorders. These biopsies are invasive, however, and have a major disadvantage when compared to other forms of invasive genetic testing in that only a few number of cells can be extracted at a time. Over time many specialists have switched to blastocyst biopsies, which provide a lower level of mosaicism, but blastomere biopsies can still be used for earlier-stage studies and genetic diagnostics.
References
Sources
"Blastomere." Stedman's Medical Dictionary, 28th ed. (2006).
Moore, Keith L., Torchia, Mark G., and T. Persaud. The Developing Human: Clinically Oriented Embryology, 8th ed. (2008).
Sermon, Karen, and Viville, Stéphane, editors. Textbook of Human Reproductive Genetics. (2014).
Bradshaw, Ralph, and Stahl, Philip, editors. Encyclopedia of Cell Biology (2015).
Singh, Vishram. Textbook of Clinical Embryology, 2nd Updated Edition.'' (2020).
Developmental biology
Embryology | Blastomere | [
"Biology"
] | 1,683 | [
"Behavior",
"Developmental biology",
"Reproduction"
] |
624,033 | https://en.wikipedia.org/wiki/Reynolds-averaged%20Navier%E2%80%93Stokes%20equations | The Reynolds-averaged Navier–Stokes equations (RANS equations) are time-averaged
equations of motion for fluid flow. The idea behind the equations is Reynolds decomposition, whereby an instantaneous quantity is decomposed into its time-averaged and fluctuating quantities, an idea first proposed by Osborne Reynolds. The RANS equations are primarily used to describe turbulent flows. These equations can be used with approximations based on knowledge of the properties of flow turbulence to give approximate time-averaged solutions to the Navier–Stokes equations.
For a stationary flow of an incompressible Newtonian fluid, these equations can be written in Einstein notation in Cartesian coordinates as:
The left hand side of this equation represents the change in mean momentum of a fluid element owing to the unsteadiness in the mean flow and the convection by the mean flow. This change is balanced by the mean body force, the isotropic stress owing to the mean pressure field, the viscous stresses, and apparent stress owing to the fluctuating velocity field, generally referred to as the Reynolds stress. This nonlinear Reynolds stress term requires additional modeling to close the RANS equation for solving, and has led to the creation of many different turbulence models. The time-average operator is a Reynolds operator.
Derivation of RANS equations
The basic tool required for the derivation of the RANS equations from the instantaneous Navier–Stokes equations is the Reynolds decomposition. Reynolds decomposition refers to separation of the flow variable (like velocity ) into the mean (time-averaged) component () and the fluctuating component (). Because the mean operator is a Reynolds operator, it has a set of properties. One of these properties is that the mean of the fluctuating quantity is equal to zero . Thus,
where is the position vector. Some authors prefer using instead of for the mean term (since an overbar is sometimes used to represent a vector). In this case, the fluctuating term is represented instead by . This is possible because the two terms do not appear simultaneously in the same equation. To avoid confusion, the notation , , and will be used to represent the instantaneous, mean, and fluctuating terms, respectively.
The properties of Reynolds operators are useful in the derivation of the RANS equations. Using these properties, the Navier–Stokes equations of motion, expressed in tensor notation, are (for an incompressible Newtonian fluid):
where is a vector representing external forces.
Next, each instantaneous quantity can be split into time-averaged and fluctuating components, and the resulting equation time-averaged,
to yield:
The momentum equation can also be written as,
On further manipulations this yields,
where, is the mean rate of strain tensor.
Finally, since integration in time removes the time dependence of the resultant terms, the time derivative must be eliminated, leaving:
Equations of Reynolds stress
The time evolution equation of Reynolds stress is given by:
This equation is very complicated. If is traced, turbulence kinetic energy is obtained.
The last term is turbulent dissipation rate. All RANS models are based on the above equation.
Applications (RANS modelling)
A model for testing performance was determined that, when combined with the vortex lattice (VLM) or boundary element method (BEM), RANS was found useful for modelling the flow of water between two contrary rotation propellers, where VLM or BEM are applied to the propellers and RANS is used for the dynamically fluxing inter-propeller state.
The RANS equations have been widely utilized as a model for determining flow characteristics and assessing wind comfort in urban environments. This computational approach can be executed through direct calculations involving the solution of the RANS equations, or through an indirect method involving the training of machine learning algorithms using the RANS equations as a basis. The direct approach is more accurate than the indirect approach but it requires expertise in numerical methods and computational fluid dynamics (CFD), as well as substantial computational resources to handle the complexity of the equations.
Notes
See also
Favre averaging
References
Fluid dynamics
Turbulence
Turbulence models
Computational fluid dynamics | Reynolds-averaged Navier–Stokes equations | [
"Physics",
"Chemistry",
"Engineering"
] | 829 | [
"Turbulence",
"Computational fluid dynamics",
"Chemical engineering",
"Computational physics",
"Piping",
"Fluid dynamics"
] |
624,038 | https://en.wikipedia.org/wiki/James%20Craig%20Watson%20Medal | The James Craig Watson Medal was established by the bequest of James Craig Watson, an astronomer the University of Michigan between 1863 and 1879, and is awarded every 1-4 years by the U.S. National Academy of Sciences for contributions to astronomy.
Recipients
Source:National Academy of Sciences
See also
List of astronomy awards
List of awards named after people
References
Watson
Awards established in 1887
Awards of the United States National Academy of Sciences
1887 establishments in the United States | James Craig Watson Medal | [
"Astronomy",
"Technology"
] | 92 | [
"Science and technology awards",
"Astronomy prizes"
] |
624,083 | https://en.wikipedia.org/wiki/Player%20versus%20player | Player versus player (PvP) is a type of multiplayer interactive conflict within a game between human players. This is often compared to player versus environment (PvE), in which the game itself controls its players' opponents. The terms are most often used in games where both activities exist, particularly MMORPGs, MUDs, and other role-playing video games, to distinguish between gamemodes. PvP can be broadly used to describe any game, or aspect of a game, where players compete against each other. PvP is often controversial when used in role-playing games. In most cases, there are vast differences in abilities between players. PvP can even encourage experienced players to immediately attack and kill inexperienced players. PvP is often referred to as player killing in the cases of games which contain, but do not focus on, such interaction.
History
PvP combat in CRPGs has its roots in various MUDs like Gemstone II and Avalon: The Legend Lives. While the ability to kill another player existed in many MUDs, it was usually frowned upon because of general strict adherences and heavy influences from tabletop role-playing games such as Dungeons & Dragons. The term PvP originated in text based MUDs played on bulletin board systems like MajorMUD and Usurper. These games had open worlds where any player could attack any other player as long as they were not at a safe spot in town like the Bank. Player versus player was coined sometime in the late 1980s to refer to the combat between players that resulted in the loser being penalized in some way.
The first graphical MMORPG was Neverwinter Nights, which began development in 1989 and ran on AOL 1991–1997, and which included PvP, which was initially limited to magical attacks in the game. Later modifications expanded its use to limited areas so that players who wished to avoid it could do so. Much of the PvP activity was coordinated events by the game's guilds, which were the first such organized user groups in MMORPGs.
Genocide, an LPMud launched in 1992, was a pioneer in PvP conflict as the first "pure PK" MUD, removing all non-PvP gameplay and discarding the RPG-style character development normally found in MUDs in favor of placing characters on an even footing, with only player skill providing an advantage. Extremely popular, its ideas influenced the MUD world heavily. 80 percent of multiplayer games have pvp
Other early MMORPGs, including Meridian 59 (1996), Ultima Online (1997), and Tibia (1997) also had PvP combat as a feature. In Ultima Online, the goal was to allow players to police themselves in a "frontier justice" way. This system also exists in Tibia, where death includes significant penalty, and killing someone inflicts considerable harm to their character. In Meridian 59, the game tried to focus PvP by having different political factions for players to join. The later Eve Online (2003) refined Ultima Onlines original approach of "PvP anywhere but in town" (where attacking another player is dangerous in and around towns due to interference from NPC "guards"). However, these games tended to be unfriendly to more casual players. With the popularity of EverQuest in 1999, primarily consisting of PvE elements (with the exception of limited PvP on one specific server), PvP became a negative for some newer/casual MMORPG players and developers looking to draw a larger crowd. In 2000, in response to complaints about malicious player-killers, Ultima Online controversially added an extra copy of the game world to each server in which open PvP was disabled.
In addition to this, not all PvP games feature a player's avatar experiencing death. An example of this type of PvP element can be found on MMOs such as Audition Online (2004) where while players are not directly killing each other's avatars as traditionally found in MMOs, they are still competing against each other during certain game modes in a Player versus Player setting.
PvP has been included in other games such as Asheron's Call in late 1999, Diablo II in 2000, Dark Age of Camelot and RuneScape in 2001, Asheron's Call 2 in 2002, Shadowbane in 2003, and Dragon Nest in 2011. While these games included PvP, they still contained large portions of prerequisite PvE, mostly to build characters.
DOOM was one of the most influential instances of PvP, coining the term "Deathmatch". This MMO-esque mode helped inspire the now-iconic PvP modes found in the FPS genre, such as battle royale and team deathmatch while popularizing PvP as a whole.
Classifications
Player KillingPlayer killing, or PKing, is unrestricted PvP resulting in a character's death. Some games offer open PvP (also sometimes called world PvP), where one player can attack another without warning anywhere in the game world. A pure PK game is one where PvP conflict is the only gameplay offered. Ganking (short for gang killing) is a type of PKing in which the killer has a significant advantage over his victim, such as being part of a group, being a higher level, or attacking the victim while they are at low health.
PvP can also create additional facets in the community. In Ultima Online and Asheron's Call, a rift formed between those who enjoyed PKing, those who enjoyed hunting the PKs and those who simply did not want to fight at all. The Renaissance expansion later added a Trammel facet where PvP was not allowed, giving some out to the UO crowd that did not wish to engage in PvP at all. Asheron's Call contained a server that was completely unrestricted in player interactions where massive "PK" and "Anti (PK)" dynasties formed.
Character death in an online game usually comes with a penalty (though some games remove it from PvP combat), so habitual PKers can find themselves ostracized by the local community. In some games a character will die many times and the player must often sacrifice some experience points (XP) or in-game currency to restore that character to life. Permanent death (such that the player must create a new character) is relatively uncommon in online games, especially if PKing is permitted. An example of such a mode is Hardcore mode on the game Diablo II.
Anti-Player Killing
Anti-PKing, also known as Player Killer Killing, PK Killing, or PKK''', is a form of in-game player justice. Often motivated by an overpopulation of in-game player killers, vigilante Anti-PKs hunt Player Killers and Player Griefers with vengeance.
Some players, known as "friendlies", choose to befriend other players with pacifism. Voice chat or in-game emotes are often utilized to demonstrate peacefulness and keep others from attacking.
Dueling
Dueling is both voluntary and competitive. Dueling ladders and leagues set up by fans are common for most MMORPGs that have PvP. Dark Age of Camelot was the first graphical MMORPG to debut a formal dueling system in-game (Ballista); other MMORPGs such as City of Heroes, Anarchy Online, World of Warcraft, Guild Wars, Lineage 2, Wurm Online, and RuneScape feature PvP as competitive dueling in a group setting.
Flagging
Through various means, "flags" can be turned on or off, allowing PvP combat with other people who have also turned on their flag. In EverQuest, there is no way to turn the flag off once it has been turned on. In Star Wars Galaxies, the flag may be turned off by interacting with faction specific NPCs located throughout the game or by typing an in-game command (/pvp). In World of Warcraft, flagging is selectable or can be activated by attacking certain flagged players until a cool-off period ends, though this can be exploited by griefers via corpse camping. Some games have a bounty system where players that kill or heal other players open themselves up to being killed in return. This is sometimes called the "revenge flag". Use of this 'bounty' system is not standardized among MMORPGs, and there are debates raging about how to 'police' the system to avoid abuse.
Sometimes the PvP flag gets automatically 'ON' on any player who initiates a PK. Other players who attacks a player who has the PvP flag on will NOT get their PvP flag 'ON'.
RvR (realm versus realm) combat
In 2001, Mythic Entertainment introduced a new team-based form of PvP combat with the release of Dark Age of Camelot. In RvR, players of each realm team up to fight against players from the opposing realms in team-based combat. This can include normal skirmishes between rival groups that is common in other PvP systems, but also consists of objective-based battles such as taking and holding keeps or capturing enemy relics.
This was a new concept to graphical MMORPGs, but was first introduced in the game that preceded DAoC, Darkness Falls: The Crusade, which has since been shut down in favor of building on DAoC. Other MMORPG games now also feature this type of gameplay.
PvP in tabletop role-playing games
Tabletop role-playing games (RPGs) have also often featured PvP action. These are usually considered a reasonable part of play so long as the fight is based on "in-character" reasons. Games are often written to balance playable characters, ensuring that the players are able to pick their favorite characters rather than being forced into a metagame to succeed.
This approach to PvP in tabletop games is not universal. For example, in the highly satirical Paranoia'', lethal PvP conflict is a core game element, considered normal and heavily encouraged by the rules and support materials.
Ethical issues
Player-vs-player dynamics involve ethical issues with players. Because of ganking, some game developers view PvP with contempt. Despite the advantage experienced players have over new players, many game developers have assumed an honor code would prevent PKing.
See also
Deathmatch
Last man standing (video games)
Player versus environment
References
Esports terminology
MUD terminology
Role-playing game terminology
Video game terminology | Player versus player | [
"Technology"
] | 2,156 | [
"Computing terminology",
"Video game terminology"
] |
624,144 | https://en.wikipedia.org/wiki/Control%20logic | Control logic is a key part of a software program that controls the operations of the program. The control logic responds to commands from the user, and it also acts on its own to perform automated tasks that have been structured into the program.
Control logic can be modeled using a state diagram, which is a form of hierarchical state machine. These state diagrams can also be combined with flow charts to provide a set of computational semantics for describing complex control logic. This mix of state diagrams and flow charts is illustrated in the figure on the right, which shows the control logic for a simple stopwatch. The control logic takes in commands from the user, as represented by the event named “START”, but also has automatic recurring sample time events, as represented by the event named “TIC”.
References
Computing terminology | Control logic | [
"Technology"
] | 162 | [
"Computing terminology"
] |
9,588,527 | https://en.wikipedia.org/wiki/Engine%20power | Engine power is the power that an engine can put out. It can be expressed in power units, most commonly kilowatt, pferdestärke (metric horsepower), or horsepower. In terms of internal combustion engines, the engine power usually describes the rated power, which is a power output that the engine can maintain over a long period of time according to a certain testing method, for example ISO 1585. In general though, an internal combustion engine has a power take-off shaft (the crankshaft), therefore, the rule for shaft power applies to internal combustion engines: Engine power is the product of the engine torque and the crankshaft's angular velocity.
Definition
Power is the product of torque and angular velocity:
Let:
Power in Watt (W)
Torque in Newton-metre (N·m)
Crankshaft speed per Second (s−1)
Angular velocity =
Power is then:
In internal combustion engines, the crankshaft speed is a more common figure than , so we can use instead, which is equivalent to :
Note that is per Second (s−1). If we want to use the common per Minute (min−1) instead, we have to divide by 60:
Usage
Numerical value equations
The approximate numerical value equations for engine power from torque and crankshaft speed are:
International unit system (SI)
Let:
Power in Kilowatt (kW)
Torque in Newton-metre (N·m)
Crankshaft speed per Minute (min−1)
Then:
Technical unit system (MKS)
Power in Pferdestärke (PS)
Torque in Kilopondmetre (kp·m)
Crankshaft speed per Minute (min−1)
Then:
Imperial/U.S. Customary unit system
Power in Horsepower (hp)
Torque in Pound-force foot (lbf·ft)
Crankshaft speed in Revolutions per Minute (rpm)
Then:
Example
A diesel engine produces a torque of 234 N·m at 4200 min−1, which is the engine's rated speed.
Let:
Then:
or using the numerical value equation:
The engine's rated power output is 103 kW.
Units
See also
List of production cars by power output
Bibliography
References
Mechanics
Power (physics)
Engines | Engine power | [
"Physics",
"Mathematics",
"Technology",
"Engineering"
] | 447 | [
"Machines",
"Force",
"Physical quantities",
"Engines",
"Quantity",
"Physical systems",
"Power (physics)",
"Energy (physics)",
"Mechanics",
"Mechanical engineering",
"Wikipedia categories named after physical quantities"
] |
9,589,549 | https://en.wikipedia.org/wiki/The%20Revelation%20in%20Storm%20and%20Thunder | In March 1907 the Russian astronomer Nikolai Alexandrovich Morozov published the book Revelation In Thunderstorm And Tempest. History of the Apocalypses Origin. (; German title Die Offenbarung Johannis – Eine astronomisch-historische Untersuchung, meaning in ). After intervention by the Orthodox clergy, the book was added to the index of prohibited books the next year. In his book Morozov makes the case that the Book of Revelation is describing the astronomical constellation over the island of Patmos on Sunday, September 30, 395 (Julian date). Morozov presumes that the educated John was able to calculate the Saros cycle and, therefore, did observe the sky on this day in attendance of a solar eclipse. (This eclipse did occur indeed—over South America, however.)
Morozov's claims
1. The weekday of the event is named explicitly:
Rev. 1,10: "I was in the Spirit on the Lords Day" (believed to be Sunday).
2. The description of the skies starts systematically at the Pole with a constellation named Throne (presently Ursa Minor):
Rev. 4,2: And a throne was set in heaven...
3. The text continues mentioning the Milky Way and the signs of the zodiac denoting the four seasons: Lion, Taurus, Sagittarius and Eagle (presently Aquarius):
Rev. 4,6-7: And before the throne there was a sea of glass like unto crystal: and in the midst of the throne, and round about the throne, were four beasts full of eyes before and behind. And the first beast was like a lion, and the second beast like a calf, and the third beast had a face as a man, and the fourth beast was like a flying eagle.
4. The four horses were interpreted by Morozov as traditional metaphors for the planets Jupiter, Mars, Mercury and Saturn. The constellations Sagittarius, Perseus, Libra and Scorpion were sitting on them:
Rev. 6,2: And I saw, and behold a white horse: and he that sat on him had a bow;
Rev. 6,4: And there went out another horse that was red: and power was given to him that sat thereon to take peace from the earth, and that they should kill one another: and there was given unto him a great sword.
Rev. 6,5: And I beheld, and lo a black horse; and he that sat on him had a pair of balances in his hand.
Rev. 6,8: And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him.
5. Sun and Moon were named explicitly. The only female character of the zodiac is Virgo:
Rev. 12,1: A woman clothed with the sun, and the moon under her feet, and upon her head a crown of twelve stars.
6. The planet Venus , used as a symbol of female eroticism and harlotry, united with the red star Antares (Anti-Mars) within the constellation Scorpion:
Rev. 17,3-4: and I saw a woman sit upon a scarlet colored beast, full of names of blasphemy, having seven heads and ten horns. And the woman was arrayed in purple and scarlet color, and decked with gold and precious stones and pearls, having a golden cup in her hand full of abominations and filthiness of her fornication.
The description within the Book of Revelation matches exactly the Constellation for the Julian date 30-9-395.
Right ascension and Declination for the island of Patmos at 15:00 UTC on this day were calculated using the program Yoursky. (Due to precession R.A. of the stars has been shifted since 395).
Sun, Moon and the 3 outer and 2 inner planets will produce 3.732.480 combinations within the 12 signs of the zodiac (125 × 5 × 3).
Therefore, an accidental match is quite unlikely.
At this point criticism of Chronology begins: Common understanding says, referring to Irenaeus (Haer. V,30,3), that the Revelation to John was written near the end of the reign of the Roman emperor Domitian (81-96). Consequently, either the Revelation has been dated some three centuries too old, or the reign of Domitian has. Unless of course real prophecy was occurring and the constellations of 30th Sept 395 were predicted in it. Such confirmation by astronomy may have contributed to its acceptance as canonical.
Literature
Nikolai A. Morozov: "The Revelation to John - An astronomic historical Investigation" (Die Offenbarung Johannis – Eine astronomisch-historische Untersuchung, 223 pages, Stuttgart 1912.)
Nikolai A. Morozov: "Revelation within Thunderstorm and Tempest. History of the Apocalypses Origin." (Откровение в грозе и буре. История возникновения Апокалипсиса. СПб.: Былое, 1907.)
References
Notes
This article is a translation from the German Wikipedia.
1905 non-fiction books
Ancient astronomy
Astronomy books
Astrological texts
Book of Revelation | The Revelation in Storm and Thunder | [
"Astronomy"
] | 1,121 | [
"Works about astronomy",
"Ancient astronomy",
"Astronomy books",
"History of astronomy"
] |
9,590,201 | https://en.wikipedia.org/wiki/Valve%20actuator | A valve actuator is the mechanism for opening and closing a valve. Manually operated valves require someone in attendance to adjust them using a direct or geared mechanism attached to the valve stem. Power-operated actuators, using gas pressure, hydraulic pressure or electricity, allow a valve to be adjusted remotely, or allow rapid operation of large valves. Power-operated valve actuators may be the final elements of an automatic control loop which automatically regulates some flow, level or other process. Actuators may be only to open and close the valve, or may allow intermediate positioning; some valve actuators include switches or other ways to remotely indicate the position of the valve.
Used for the automation of industrial valves, actuators can be found in all kinds of process plants. They are used in waste water treatment plants, power plants, refineries, mining and nuclear processes, food factories, and pipelines. Valve actuators play a major part in automating process control. The valves to be automated vary both in design and dimension. The diameters of the valves range from one-tenth of an inch to several feet.
Types
The common types of actuators are: manual, pneumatic, hydraulic, electric and spring.
Manual
A manual actuator employs levers, gears, or wheels to move the valve stem with a certain action. Manual actuators are powered by hand. Manual actuators are inexpensive, typically self-contained, and easy to operate by humans. However, some large valves are impossible to operate manually and some valves may be located in remote, toxic, or hostile environments that prevent manual operations in some conditions. As a safety feature, certain types of situations may require quicker operation than manual actuators can provide to close the valve.
Pneumatic
Air (or other gas) pressure is the power source for pneumatic valve actuators. They are used on linear or quarter-turn valves. Air pressure acts on a piston or bellows diaphragm creating linear force on a valve stem. Alternatively, a quarter-turn vane-type actuator produces torque to provide rotary motion to operate a quarter-turn valve. A pneumatic actuator may be arranged to be spring-closed or spring-opened, with air pressure overcoming the spring to provide movement. A "double acting" actuator use air applied to different inlets to move the valve in the opening or closing direction. A central compressed air system can provide the clean, dry, compressed air needed for pneumatic actuators. In some types, for example, regulators for compressed gas, the supply pressure is provided from the process gas stream and waste gas either vented to air or dumped into lower-pressure process piping.
Hydraulic
Hydraulic actuators convert fluid pressure into motion. Similar to pneumatic actuators, they are used on linear or quarter-turn valves. Fluid pressure acting on a piston provides linear thrust for gate or globe valves. A quarter-turn actuator produces torque to provide rotary motion to operate a quarter-turn valve. Most types of hydraulic actuators can be supplied with fail-safe features to close or open a valve under emergency circumstances. Hydraulic pressure can be supplied by a self-contained hydraulic pressure pump. In some applications, such as water pumping stations, the process fluid can provide hydraulic pressure, although the actuators must use materials compatible with the fluid.
Electric
The electric actuator uses an electric motor to provide torque to operate a valve. They are quiet, non-toxic and energy efficient. However, electricity must be available, which is not always the case, they can also operate on batteries.
Spring
Spring-based actuators hold back a spring. Once any anomaly is detected, or power is lost, the spring is released, operating the valve. They can only operate once, without resetting, and so are used for one-use purposes such as emergencies. They have the advantage that they do not require a powerful electric supply to move the valve, so they can operate from restricted battery power, or automatically when all power has been lost.
Actuator movement
A linear actuator opens and closes valves that can be operated via linear force, the type sometimes called a "rising stem" valve. These types of valves include globe valves, rising stem ball valves, control valves and gate valves. The two main types of linear actuators are diaphragm and piston.
Diaphragm actuators are made out of a round piece of rubber and squeezed around its edges between two side of a cylinder or chamber that allows air pressure to enter either side pushing the piece of rubber one direction or the other. A rod is connected to the center of the diaphragm so that it moves as the pressure is applied. The rod is then connected to a valve stem which allows the valve to experience the linear motion thereby opening or closing. A diaphragm actuator is useful if the supply pressure is moderate and the valve travel and thrust required are low.
Piston actuators use a piston which moves along the length of a cylinder. The piston rod conveys the force on the piston to the valve stem. Piston actuators allow higher pressures, longer travel ranges, and higher thrust forces than diaphragm actuators.
A spring is used to provide defined behavior in the case of loss of power. This is important in safety related incidents and is sometimes the driving factor in specifications. An example of loss of power is when the air compressor (the main source of compressed air that provides the fluid for the actuator to move) shuts down. If there is a spring inside of the actuator, it will force the valve open or closed and will keep it in that position while power is restored. An actuator may be specified "fail open" or "fail close" to describe its behavior. In the case of an electric actuator, losing power will keep the valve stationary unless there is a backup power supply.
A typical representative of the valves to be automated is a plug-type control valve. Just like the plug in the bathtub is pressed into the drain, the plug is pressed into the plug seat by a stroke movement. The pressure of the medium acts upon the plug while the thrust unit has to provide the same amount of thrust to be able to hold and move the plug against this pressure.
Features of an electric actuator
Motor (1)
Robust asynchronous three-phase AC motors are mostly used as the driving force, for some applications also single-phase AC or DC motors are used. These motors are specially adapted for valve automation as they provide higher torques from standstill than comparable conventional motors, a necessary requirement to unseat sticky valves. The actuators are expected to operate under extreme ambient conditions, however they are generally not used for continuous operation since the motor heat buildup can be excessive.
Limit and torque sensors (2)
The limit switches signal when an end position has been reached. The torque switching measures the torque present in the valve. When exceeding a set limit, this is signaled in the same way. Actuators are often equipped with a remote position transmitter which indicates the valve position as continuous 4-20mA current or voltage signal.
Gearing (3)
Often a worm gearing is used to reduce the high output speed of the electric motor. This enables a high reduction ratio within the gear stage, leading to a low efficiency which is desired for the actuators. The gearing is therefore self-locking i.e. it prevents accidental and undesired changes of the valve position by acting upon the valve’s closing element.
Valve attachment (4)
The valve attachment consists of two elements. First: The flange used to firmly connect the actuator to the counterpart on the valve side. The higher the torque to be transmitted, the larger the flange required.
Second: The output drive type used to transmit the torque or the thrust from the actuator to the valve shaft. Just like there is a multitude of valves there is also a multitude of valve attachments.
Dimensions and design of valve mounting flange and valve attachments are stipulated in the standards EN ISO 5210 for multi-turn actuators or EN ISO 5211 for part-turn actuators. The design of valve attachments for linear actuators is generally based on DIN 3358.
Manual operation (5)
In their basic version most electric actuators are equipped with a handwheel for operating the actuators during commissioning or power failure. The handwheel does not move during motor operation.
The electronic torque limiting switches are not functional during manual operation. Mechanical torque-limiting devices are commonly used to prevent torque overload during manual operation.
Actuator controls (6)
Both actuator signals and operation commands of the DCS are processed within the actuator controls. This task can in principle be assumed by external controls, e.g. a PLC. Modern actuators include integral controls which process signals locally without any delay. The controls also include the switchgear required to control the electric motor. This can either be reversing contactors or thyristors which, being an electric component, are not subject to mechanic wear. Controls use the switchgear to switch the electric motor on or off depending on the signals or commands present. Another task of the actuator controls is to provide the DCS with feedback signals, e.g. when reaching a valve end position.
Electrical connection (7)
The supply cables of the motor and the signal cables for transmitting the commands to the actuator and sending feedback signals on the actuator status are connected to the electrical connection. The electrical connection can be designed as a separately sealed terminal bung or plug/socket connector. For maintenance purposes, the wiring should be easily disconnected and reconnected.
Fieldbus connection (8)
Fieldbus technology is increasingly used for data transmission in process automation applications. Electric actuators can therefore be equipped with all common fieldbus interfaces used in process automation. Special connections are required for the connection of fieldbus data cables.
Functions
Automatic switching off in the end positions
After receiving an operation command, the actuator moves the valve in direction OPEN or CLOSE. When reaching the end position, an automatic switch-off procedure is started. Two fundamentally different switch-off mechanisms can be used. The controls switch off the actuator as soon as the set tripping point has been reached. This is called limit seating. However, there are valve types for which the closing element has to be moved in the end position at a defined force or a defined torque to ensure that the valve seals tightly. This is called torque seating. The controls are programmed as to ensure that the actuator is switched off when exceeding the set torque limit. The end position is signalled by a limit switch.
Safety functions
The torque switching is not only used for torque seating in the end position, but it also serves as overload protection over the whole travel and protects the valve against excessive torque. If excessive torque acts upon the closing element in an intermediate position, e.g. due to a trapped object, the torque switching will trip when reaching the set tripping torque. In this situation the end position is not signalled by the limit switch. The controls can therefore distinguish between normal operation torque switch tripping in one of the end positions and switching off in an intermediate position due to excessive torque.
Temperature sensors are required to protect the motor against overheating. For some applications by other manufacturers, the increase of the motor current is also monitored. Thermoswitches or PTC thermistors which are embedded in the motor windings mostly reliably fulfil this task. They trip when the temperature limit has been exceeded and the controls switch off the motor.
]
Process control functions
Due to increasing decentralisation in automation technology and the introduction of micro processors, more and more functions have been transferred from the DCS to the field devices. The data volume to be transmitted was reduced accordingly, in particular by the introduction of fieldbus technology. Electric actuators whose functions have been considerably expanded are also affected by this development.
The simplest example is the position control. Modern positioners are equipped with self-adaptation i.e. the positioning behaviour is monitored and continuously optimised via controller parameters.
Meanwhile, electric actuators are equipped with fully-fledged process controllers (PID controllers). Especially for remote installations, e.g. the flow control to an elevated tank, the actuator can assume the tasks of a PLC which otherwise would have to be additionally installed.
Diagnosis
Modern actuators have extensive diagnostic functions which can help identify the cause of a failure. They also log the operating data. Study of the logged data allows the operation to be optimised by changing the parameters and the wear of both actuator and valve to be reduced.
Duty types
Open-close duty
If a valve is used as a shut-off valve, then it will be either open or closed and intermediate positions are not held...
Positioning duty
Defined intermediate positions are approached for setting a static flow through a pipeline. The same running time limits as in open-close duty apply.
Modulating duty
The most distinctive feature of a closed-loop application is that changing conditions require frequent adjustment of the actuator, for example, to set a certain flow rate. Sensitive closed-loop applications require adjustments within intervals of a few seconds. The demands on the actuator are higher than in open-close or positioning duty. Actuator design must be able to withstand the high number of starts without any deterioration in control accuracy.
Service conditions
Actuators are specified for the desired life and reliability for a given set of application service conditions. In addition to the static and dynamic load and response time required for the valve, the actuator must withstand the temperature range, corrosion environment and other conditions of a specific application. Valve actuator applications are often safety related, therefore the plant operators put high demands on the reliability of the devices. Failure of an actuator may cause accidents in process-controlled plants and toxic substances may leak into the environment.
Process-control plants are often operated for several decades which justifies the higher demands put on the lifetime of the devices.
For this reason, actuators are always designed in high enclosure protection. The manufacturers put a lot of work and knowledge into corrosion protection.
Enclosure protection
The enclosure protection types are defined according to the IP codes of EN 60529. The basic versions of most electric actuators are designed to the second highest enclosure protection IP 67. This means they are protected against the ingress of dust and water during immersion (30 min at a max. head of water of 1 m). Most actuator manufacturers also supply devices to enclosure protection IP 68 which provides protection against submersion up to a max. head of water of 6 m.
Ambient temperatures
In Siberia, temperatures down to – 60 °C may occur, and in technical process plants + 100 °C may be exceeded. Using the proper lubricant is crucial for full operation under these conditions. Greases which may be used at room temperature can become too solid at low temperatures for the actuator to overcome the resistance within the device. At high temperatures, these greases can liquify and lose their lubricating power. When sizing the actuator, the ambient temperature and the selection of the correct lubricant are of major importance.
Explosion protection
Actuators are used in applications where potentially explosive atmospheres may occur. This includes among others refineries, pipelines, oil and gas exploration or even mining. When a potentially explosive gas-air-mixture or gas-dust-mixture occurs, the actuator must not act as ignition source. Hot surfaces on the actuator as well as ignition sparks created by the actuator have to be avoided. This can be achieved by a flameproof enclosure, where the housing is designed to prevent ignition sparks from leaving the housing even if there is an explosion inside.
Actuators designed for these applications, being explosion-proof devices, have to be qualified by a test authority (notified body). Explosion protection is not standardized worldwide. Within the European Union, ATEX 94/9/EC applies, in US, the NEC (approval by FM) or the CEC in Canada (approval by the CSA). Explosion-proof actuators have to meet the design requirements of these directives and regulations.
Additional uses
Small electric actuators can be used in a wide variety of assembly, packaging and testing applications. Such actuators can be linear, rotary, or a combination of the two, and can be combined to perform work in three dimensions. Such actuators are often used to replace pneumatic cylinders.
References
Actuators
Fluid technology
Actuators | Valve actuator | [
"Physics",
"Chemistry",
"Engineering"
] | 3,449 | [
"Fluid technology",
"Physical systems",
"Valves",
"Hydraulics",
"Mechanical engineering by discipline",
"Piping"
] |
9,590,204 | https://en.wikipedia.org/wiki/Doctor%20sweetening%20process | The doctor sweetening process is an industrial chemical process for converting mercaptans in sour gasoline into disulfides. Sulfur compounds darken gasoline, give it an offensive odor and increase toxic sulfur dioxide engine emissions. However, this process only reduces the odor.
These sulfur compounds can be removed with the following chemical reactions:
\overset{sour~gasoline}{2RSH} + {Na2PbO2} + S ->[\text{in the presence of NaOH}] \overset{alkyl~disulfide}{R-S-S-R} + {PbS} + 2NaOH
Chemistry of the process
The chemistry of 'doctor sweetening' was described in detail by G. Wendt and S. Diggs in 1924. They also showed that the lead oxide solution brought about oxidation of the mercaptans to the corresponding organic disulfides, which are comparatively odourless. Lead oxide (litharge) dissolves in reasonably concentrated solutions of sodium hydroxide or potassium hydroxide owing to formation of a soluble compound, sodium plumbite:
PbO + 2NaOH -> Na2PbO2 + H2O
When this alkaline solution is agitated with petroleum, the two liquids do not dissolve in one another, but any mercaptan in the oil will unite with an equivalent amount of the lead (which then passes into the petroleum) to form what is called a lead mercaptide, soluble in the oil:
2RSH + Na2PbO2 -> (RS)2Pb + 2NaOH
If the mixture is now treated with powdered sulfur, which has a high affinity for lead, a black suspension of lead sulfide forms, and conversion of the mercaptide into a so-called disulfide (which remains in the oil) is induced:
-(RS)2Pb + S -> RS-SR + PbS
With no sulfur added, but in the presence of atmospheric oxygen, the same conversion occurs, but only slowly, and probably not completely:
2(RS)2Pb + 4NaOH + O2 -> 2RS-SR + 2Na2PbO2 + 2H2O
It is evident that the process does not remove the sulfur from the oil but even may increase the sulfur content if too much powdered sulfur is added, and some of the lead may remain in the petroleum.
The described chemistry is also the basis of the doctor test for the sweetness or sourness of gasoline (i.e., the extent of sulfur contamination). A gasoline is described as doctor sweet if, after shaking with sodium plumbite solutions, the addition of powdered sulfur fails to produce a dark precipitate of lead sulfide.
Literature
McBryde, W.A.E.: Petroleum deodorized: Early canadian history of the ‘doctor sweetening’ process, Annals of Science, Vol. 48, Issue 2, Taylor & Francis, 1991
L. M. Henderson, W. B. Ross, C. M. Ridgway: Tetraethyllead Susceptibilities of Gasoline Doctor Treatment vs. Caustic Washing, Ind. Eng. Chem., 1939, 31 (1), p. 27–30
Naphtali, Max: Fortschritte auf dem Gebiete der Mineralöle. Die technische Entwicklung der Erdölindustrie nach dem Kriege, Angewandte Chemie, Band 42, Ausgabe 20, p. 508-518, WILEY-VCH Verlag GmbH, May 18, 1929
Otto Rotton, William Archer: Deodorizing Petroleum, American Artisan and Patent Record (New York), new series 5, p. 310, 1867
G.L. Wendt, S.H. Diggs: The Chemistry of "Sweetening" in the Petroleum Industry, Industrial and Engineering Chemistry, Ausgabe 16, pp. 1113-1115, 1924
M.L. Kalinowski: Doctor sweetening process using sulfur, US patent 2871187 January 27, 1957
References
External links
Fuel technology
Oil refining | Doctor sweetening process | [
"Chemistry"
] | 865 | [
"Petroleum technology",
"Oil refining"
] |
9,590,241 | https://en.wikipedia.org/wiki/Wobbulator | A wobbulator is an electronic device primarily used for the alignment of receiver or transmitter intermediate frequency strips. It is usually used in conjunction with an oscilloscope, to enable a visual representation of a receiver's passband to be seen, hence simplifying alignment; it was used to tune early consumer AM radios. The term "wobbulator" is a portmanteau of wobble and oscillator. A "wobbulator" (without capitalization) is a generic term for the swept-output RF oscillator described above, a frequency-modulated oscillator, also called a "sweep generator" by most professional electronics engineers and technicians. A wobbulator was used in some old microwave signal generators to create what amounted to frequency modulation. It physically altered the size of the klystron cavity, therefore changing the frequency.
When capitalized, "Wobbulator" refers to the trade name of a specific brand of RF/IF alignment generator. The Wobbulator was made by a company known as "TIC" (Tel-Instrument Company) although some units branded "Allen B. Du Mont Laboratories" and "Stromberg-Carlson" are rumoured to exist. These were apparently made under some form of license and branded with the name of the licensee, much as Radio Corporation of America through subsidiary Hazeltine Corp., licensed its KCS-20A television chassis design (used in models 630TS, 8TS30, etc.) to other television manufacturers (Air King, Crosley, Fada, et al.) for production under their brand names. The Wobbulator generator, designated model 1200A, combined sweep and marker functions into a single self-contained pushbutton controlled device which, when connected to an oscilloscope and television receiver under test, would display a representation of the receiver's RF/IF response curves with "markers" defining critical frequency reference points as a response curve on the oscilloscope screen. Such an amplitude-versus-frequency graph is also often referred to as a Bode (pronounced "bodee") graph or Bode plot.
In the 1960s a device described as a wobbulator was made by instrument company Brüel & Kjær. It was an audio-frequency oscillator with an adjustable frequency modulation. The purpose of the modulation was in acoustic characterisation of architectural spaces, where it prevented the build-up of resonances during measurement.
Another implementation of wobbulators were designed and implemented in the mid-1980's at Singer-Link Flight Simulation. It was determined that due to the orientation of the CRT's checklists and other similarly formatted text at the simulator's control panels created a situation where checklists had to be scrolled through, line-by-line or page-by-page, to complete. Checklists that could fit on one screen made it more efficient to follow and/or troubleshoot. The implementation of x- and y- axis wobbulators overcame the problems encountered.
References
Electronic oscillators
Wireless tuning and filtering | Wobbulator | [
"Engineering"
] | 640 | [
"Radio electronics",
"Wireless tuning and filtering"
] |
9,590,289 | https://en.wikipedia.org/wiki/Systems%20Tool%20Kit | Systems Tool Kit (formerly Satellite Tool Kit), often referred to by its initials STK, is a multi-physics software application from Analytical Graphics, Inc. (an Ansys company) that enables engineers and scientists to perform complex analyses of ground, sea, air, and space platforms, and to share results in one integrated environment. At the core of STK is a geometry engine for determining the time-dynamic position and attitude of objects ("assets"), and the spatial relationships among the objects under consideration including their relationships or accesses given a number of complex, simultaneous constraining conditions. STK has been developed since 1989 as a commercial off the shelf software tool. Originally created to solve problems involving Earth-orbiting satellites, it is now used in the aerospace and defense communities and for many other applications.
STK is used in government, commercial, and defense applications around the world. Clients of AGI are organizations such as NASA, ESA, CNES, DLR, Boeing, JAXA, ISRO, Lockheed Martin, Northrop Grumman, Airbus, The US DoD, and Civil Air Patrol.
History
In 1989, the three founders of Analytical Graphics, Inc. — Paul Graziani, Scott Reynolds, and Jim Poland, left GE Aerospace to create Satellite Tool Kit (STK) as an alternative to bespoke, project-specific aerospace software.
The original version of STK ran only on Sun Microsystems computers, but as PCs became more powerful, the code was converted to run on Windows.
STK was first adopted by the aerospace community for orbit analysis and access calculations (when a satellite can see a ground-station or image target), but as the software was expanded, more modules were added that included the ability to perform calculations for communications systems, radar, interplanetary missions and orbit collision avoidance.
The addition of 3D viewing capabilities led to the adoption of the STK by military users for real-time visualization of air, land and sea forces as well as the space domain. STK has also been used by news organizations to graphically depict current events to a wider audience, including the deorbit of Russia's Mir Space Station, the Space Shuttle Columbia disaster, the Iridium/Cosmos collision, the asteroid 2012 DA14 close approach and various North Korea missile tests.
As of version 12.1 (released in 2020), the software underwent a name change from Satellite Tool Kit to Systems Tool Kit to reflect its applicability in land, sea, air, and space systems.
In 2019, Dutch amateur skywatcher Marco Langbroek used STK to analyze a high-resolution photograph of an Iranian launch site accident tweeted by former US President Donald Trump. It was "the first time in three and a half decades that an image [had] become public that [revealed] the sophistication of US spy satellites in orbit." Langbroek and astronomer Cees Bassa, identified the specific classified spysat (USA-224, a KH-11 satellite with an objective mirror as large as the Hubble Space Telescope) that had taken the photograph, and the time when it was taken on a particular satellite pass.
Interface
The STK interface is a standard GUI display with customizable toolbars and dockable maps and 3D graphic windows. All analysis can be done through mouse and keyboard interaction.
The STK Integration module provides a scripting interface named Connect that enables STK to act within a client/server environment (via TCP/IP) and is language independent. Users also have the option of using STK programmatically via OLE automation.
Each analysis or design space within STK is called a scenario. Within each scenario any number of satellites, aircraft, targets, ships, communications systems or other objects can be created. Each scenario defines the default temporal limits to the child objects, as well as the base unit selection and properties. All of these properties can be overridden for each child object individually, as necessary. Only one scenario may exist at any one time, although data can be exported and reused in subsequent analyses.
For each object within a scenario, reports and graphics (both static and dynamic) may be created. Relative parameters, between one object and another can also be reported and the effect of real-world restrictions (constraints) enabled so that more accurate reporting is obtained. Through the use of the constellation and chains objects, multiple child objects may be grouped together and the multipath interactions between them investigated.
AGI also offers software development kits for embedding STK capabilities into third-party applications or creating new applications based on AGI technology.
Modules
STK is a modular product, in much the same way as MATLAB and Simulink, and allows users to add modules to the baseline package to enhance specific functions.
Integration
STK can be embedded within another application (as an ActiveX component) or controlled from an external application (through TCP/IP or Component Object Model (COM)). Both integration techniques can make use of the Connect scripting language to accomplish this task. There is also an object model for more "programmer oriented" integration methodologies. STK can be driven from a script that is run from the STK internal web browser in the free version of the tool. To control STK from an external source, or embed STK in another application requires the STK Integration module.
Connect
Since Connect is a messaging format, it has the advantage of being completely language independent. This allows applications and client tools to be created in the programming language of the user's or developer's choice. In practice, as long as it is possible to create a socket connection, send information through that socket and then receive information that way then STK can be controlled with connect using that language.
Applications have been developed in C, C++, C#, Perl, Visual Basic, VBScript, Java, JavaScript and MATLAB. Examples can also be found in the STK help files or downloaded from the AGI website.
See also
TRACE (computer program)
References
External links
STK at AGI.com
1989 software
3D graphics software
Astronomy software
Mathematical software
Physics software | Systems Tool Kit | [
"Physics",
"Astronomy",
"Mathematics"
] | 1,255 | [
"Works about astronomy",
"Physics software",
"Computational physics",
"Astronomy software",
"Mathematical software"
] |
9,590,785 | https://en.wikipedia.org/wiki/Feature-oriented%20positioning | Feature-oriented positioning (FOP) is a method of precise movement of the scanning microscope probe across the surface under investigation. With this method, surface features (objects) are used as reference points for microscope probe attachment. Actually, FOP is a simplified variant of the feature-oriented scanning (FOS). With FOP, no topographical image of a surface is acquired. Instead, a probe movement by surface features is only carried out from the start surface point A (neighborhood of the start feature) to the destination point B (neighborhood of the destination feature) along some route that goes through intermediate features of the surface. The method may also be referred to by another name—object-oriented positioning (OOP).
To be distinguished are a "blind" FOP when the coordinates of features used for probe movement are unknown in advance and FOP by existing feature "map" when the relative coordinates of all features are known, for example, in case they were obtained during preliminary FOS. Probe movement by a navigation structure is a combination of the above-pointed methods.
FOP method may be used in bottom-up nanofabrication to implement high-precision movement of the nanolithograph/nanoassembler probe along the substrate surface. Moreover, once made along some route, FOP may be then exactly repeated the required number of times. After movement in the specified position, an influence on the surface or manipulation of a surface object (nanoparticle, molecule, atom) is performed. All the operations are carried out in automatic mode. With multiprobe instruments, FOP approach allows to apply any number of specialized technological and/or analytical probes successively to a surface feature/object or to a specified point of the feature/object neighborhood. That opens a prospect for building a complex nanofabrication consisting of a large number of technological, measuring, and checking operations.
See also
Feature-oriented scanning
References
External links
Feature-oriented positioning, Research section, Lapshin's Personal Page on SPM & Nanotechnology
Microscopes
Nanotechnology
Scanning probe microscopy
ru:ООП | Feature-oriented positioning | [
"Chemistry",
"Materials_science",
"Technology",
"Engineering"
] | 429 | [
"Materials science",
"Measuring instruments",
"Microscopes",
"Scanning probe microscopy",
"Microscopy",
"Nanotechnology"
] |
9,590,793 | https://en.wikipedia.org/wiki/Procedure%20word | Procedure words (abbreviated to prowords) are words or phrases limited to radiotelephony procedure used to facilitate communication by conveying information in a condensed standard verbal format. Prowords are voice versions of the much older procedural signs for Morse code which were first developed in the 1860s for Morse telegraphy, and their meaning is identical.
The NATO communications manual ACP-125 contains the most formal and perhaps earliest modern (post-World War II) glossary of prowords, but its definitions have been adopted by many other organizations, including the United Nations Development Programme, the U.S. Coast Guard, US Civil Air Patrol, US Military Auxiliary Radio System, and others.
Prowords are one of several structured parts of radio voice procedures, including brevity codes and plain language radio checks.
Examples
According to the U.S. Marine Corps training document FMSO 108, "understanding the following PROWORDS and their respective definitions is the key to clear and concise communication procedures".
This is ...
This transmission is from the station whose designator immediately follows. For clarity, the station called should be named before the station calling. So, "Victor Juliet zero, THIS IS Golf Mike Oscar three...", or for brevity, "Victor Juliet zero, Golf Mike Oscar three, ...". One can never say, "This is GMO3 calling VJ0".
Over
"This is the end of my transmission to you and a response is necessary. Go ahead: transmit."
"Over" and "Out" are never used at the same time, since their meanings are mutually exclusive. With spring-loaded Push to talk (PTT) buttons on modern combined transceivers, the same meaning can be communicated with just "OUT", as in "Ops, Alpha, ETA five minutes. OUT."
Out
"This is the end of my transmission to you and no answer is required or expected."
Do you read?
A question about whether the receiver can hear and understand the transmission.
Example: "Bob, you read me? What is the situation from your position?"
Example:
Roger
"ROGER" may be used to mean "yes" with regard to confirming a command; however, in Air Traffic Control phraseology, it does not signify that a clearance has been given.
The term originates from the practice of telegraphers sending an "R" to stand for "received" after successfully getting a message. This was extended into spoken radio during World War II, with the "R" changed to the spelling alphabet equivalent word "Roger". The modern NATO spelling alphabet uses the word "Romeo" for "R" instead of "Roger", and "Romeo" is sometimes used for the same purpose as "Roger", mainly in Australian maritime operations.
Wilco
"I understand and will comply." It is used on receipt of an order. "Roger" and "Wilco" used together (e.g. "Roger, Wilco") are redundant, since "Wilco" includes the acknowledgement element of "Roger".
Say again
"I have not understood your message, please SAY AGAIN". Usually used with prowords "ALL AFTER" or "ALL BEFORE". Example: radio working between Solent Coastguard and a motor vessel, call-sign EG 93, where part of the initial transmission is unintelligible.
Example:
At this juncture, Solent Coastguard would reply, preceding the message with the prowords "I SAY AGAIN":
The word "REPEAT" should not be used in place of "SAY AGAIN", especially in the vicinity of naval or other firing ranges, as "REPEAT" is an artillery proword defined in ACP 125 U.S. Supp-2(A) with the wholly different meaning of "request for the same volume of fire to be fired again with or without corrections or changes" (e.g., at the same coordinates as the previous round).
All after...
"Please repeat the message you just sent me beginning after the word or phrase said after this proword."
Example:
At this juncture, Solent Coastguard would reply, preceding the message after "position" with the prowords "I SAY AGAIN":
All before...
"Please repeat the message you just sent me ending before the word or phrase said after this proword."
Wait over
"Wait for some time."
Standby
"I must pause for a few seconds."
Wait out
"I must pause for longer than a few seconds.."
Read back
"Please repeat my entire transmission back to me."
I read back
"The following is my response to your READ BACK proword."
Correction
"I made an error in this transmission. Transmission will continue with the last word correctly sent."
Radio check
"What is my signal strength and readability; how do you hear me?"
The sender requests a response indicating the strength and readability of their transmission, according to plain language radio check standards:
A response of ROGER is shorthand for the prowords LOUD AND CLEAR.
A response of WEAK BUT READABLE ("WEAK READABLE" is also used) indicates a weak signal but I can understand.
A response of WEAK AND DISTORTED indicates a weak signal and unreadable.
A response of STRONG BUT DISTORTED indicates a strong signal but unreadable. One of the two stations might be slightly off frequency, there might be multipath distortion, or there might be a problem with the audio circuits on one or both of the radios.
"5 by 5" is an older term used to assess radio signals, as in 5 out of 5 units for both signal strength and readability. Other terms similar to 5x5 are "LOUD AND CLEAR" or "Lima and Charlie". Example:
Similar example in shorter form:
If the initiating station (Alpha 12 in the example) cannot hear the responding station (X-ray 23 above), then the initiator attempts a radio-check again, or if the responder's signal was not heard, the initiator replies to the responder with "Negative contact, Alpha 12 OUT".
The following readability scale is used: 1 = bad (unreadable); 2 = poor (readable now and then); 3 = fair (readable, but with difficulty); 4 = good (readable); 5 = excellent (perfectly readable).
Example of correct US Army radio check, for receiver A-11 (Alpha 11) and sender D-12 (Delta 12):
Article 32 Radio Regulations distress and rescue
International Telecommunication Union (ITU) Radio Regulations and the International Civil Aviation Organization (ICAO) Convention and Procedures for Air Navigation Services set out "distress, urgency and safety procedures".
On the radio, distress (emergency) and rescue usage takes precedence above all other usage, and the radio stations at the scene of the disaster (on land, in a plane, or on a boat) are authorized to commandeer the frequency and prohibit all transmissions that are not involved in assisting them. These procedure words originate in the International Radio Regulations.
The Combined Communications-Electronics Board (representing military use by Australia, Canada, New Zealand, United Kingdom and United States) sets out their usage in the Allied Communications Publications "ACP 135(F) Communications instructions Distress and Rescue Procedures".
Mayday
Mayday is used internationally as the official SOS/distress call for voice. It means that the caller, their vessel or a person aboard the vessel is in grave and imminent danger, send immediate assistance. This call takes priority over all other calls.
The correct format for a Mayday call is as follows:
[The first part of the signal is known as the "call"]
Mayday, Mayday, Mayday,
This is (vessel name repeated three times, followed by call sign if available)
[The subsequent part of the signal is known as the "message"]
Mayday (vessel name)
My position is (position as a lat-long position or bearing and distance from a fixed point)
I am (type of distress, e.g. on fire and sinking)
I require immediate assistance
I have (number of people on board and their condition)
(Any other information e.g. "I am abandoning to life rafts")
Over
VHF instructors, specifically those working for the Royal Yachting Association, often suggest the mnemonic MIPDANIO for learning the message of a Mayday signal: mayday, identify, position, distress, assistance, number-of-crew, information, over.
In aviation a different format is used:
[First part of the message] Mayday, Mayday, Mayday
[Second part of the message] Callsign
[Third part of the message] Nature of the emergency
For example: "Mayday, Mayday, Mayday, Wiki Air 999, we have lost both of our engines due to a bird strike, we are gliding now."
After that pilot can give, or the controller can ask for, additional information, such as, fuel and number of passengers on board.
Pan-Pan
Pan-pan (pronounced ) is the official urgency voice call.
Meaning "I, my vessel or a person aboard my vessel requires assistance but is not in distress." This overrides all but a mayday call, and is used, as an example, for calling for medical assistance or if the station has no means of propulsion. The correct usage is:
Pan-Pan, Pan-Pan, Pan-Pan
All stations, all stations, all stations
This is [vessel name repeated three times]
My position is [position as a lat-long position or bearing and distance from a fixed point]
I am [type of urgency, e.g. drifting without power in a shipping lane]
I require [type of assistance required]
[Any other information e.g. size of vessel, which may be important for towing]
Over
SÉCURITÉ
Pronounced , this is the official safety voice call.
"I have important meteorological, navigational or safety information to pass on."
This call is normally broadcast on a defined channel (channel 16 for maritime VHF) and then moved onto another channel to pass the message. Example:
[On channel 16]
SÉCURITÉ, SÉCURITÉ, SÉCURITÉ
All stations, all stations, all stations.
This is Echo Golf niner three, Echo Golf niner three, Echo Golf niner three.
For urgent navigational warning, listen on channel six-seven.
OUT
[Then on channel 67]
SÉCURITÉ, SÉCURITÉ, SÉCURITÉ
All stations, all stations, all stations.
This is Echo Golf niner tree (three), Echo Golf niner tree, Echo Golf niner tree.
Floating debris sighted off Calshot Spit.
Considered a danger to surface navigation.
OUT
SEELONCE MAYDAY
"Seelonce" is an approximation rendition of the French word silence. Indicates that your vessel has an emergency and that you are requiring radio silence from all other stations not assisting you.
SEELONCE DISTRESS
Indicates that you are relaying or assisting a station that has placed a MAYDAY call and you are requiring radio silence from all other stations not assisting you or the station in distress.
When the emergency issue is winding down and then has been resolved, these prowords are used to open up the frequency for use by stations not involved in the emergency:
PRU-DONCE
From the French word prudence. Indicates that complete radio silence is no longer required and restricted (limited) use of the frequency may resume, but immediately giving way to all further distress communications.
SEELONCE FEENEE
From the French word silence and fini (ended). Indicates that emergency communications have ceased and normal use of the frequency may resume.
ACP 125(F)
Aviation radio
More formally known as "Aeronautical Mobile communications", radio communications from and to aircraft are governed by rules created by the International Civil Aviation Organization. ICAO defines a very similar but shorter list of prowords in Annex 10 of its Radiotelephony Procedures (to the Convention on International Civil Aviation). Material in the following table is quoted from their list. ICAO also defines "ICAO Radio Telephony Phraseology".
Marine radio
Marine radio procedure words follow from the ACP-125 definition, and those in the International Radio Regulations published by the ITU, and should be used by small vessels as their standard radio procedure. Beginning in 2001, large vessels, defined as being 500 gross tonnage or greater, the International Convention on Standards of Training, Certification and Watchkeeping for Seafarers has required that a restricted and simplified English vocabulary with pre-set phrases, called Standard Marine Communication Phrases (SMCP), be used and understood by all officers in charge of a navigational watch. These rules are enforced by the International Maritime Organization (IMO). The IMO describes the purpose of SMCP, explaining "The IMO SMCP includes phrases which have been developed to cover the most important safety-related fields of verbal shore-to-ship (and vice-versa), ship-to-ship and on-board communications. The aim is to get round the problem of language barriers at sea and avoid misunderstandings which can cause accidents."
The SMCP language is not free-form like the standard radio voice procedures and procedure words. Instead, it consists of entire pre-formed phrases carefully designed for each situation, and watch officers must pass a test of their usage in order to be certified under international maritime regulations. For example, ships in their own territorial waters might be allowed to use their native language, but when navigating at sea or communicating with foreign vessels in their own territorial waters, they should switch to SMCP, and will state the switch over the radio before using the procedures. When it is necessary to indicate that the SMCP are to be used, the following message may be sent: "Please use Standard Marine Communication Phrases." "I will use Standard Marine Communication Phrases."
SMCP
"Yes" when the answer to a question is in the affirmative
"No" when the answer to a question is in the negative
"Stand by" when the information requested is not immediately available
"No information" when the information requested cannot be obtained
Misusages
Clear
"Clear" is sometimes heard in amateur radio transmissions to indicate the sending station is done transmitting and leaving the airways, i.e. turning off the radio, but the Clear proword is reserved for a different purpose, that of specifying the classification of a 16-line format radio message as one which can be sent 'in clear [language]' (without encryption), as well as being reserved for use in responding to the Radio Check proword to indicate the readability of the radio transmission.
Affirmative
"Confirm" or "yes" and sometimes shortened to Affirm is heard in several radio services, but is not listed in ACP-125 as a proword. In poor radio conditions Affirmative can be confused with Negative. Instead, the proword Correct is used.
Negative
Means "no", and can be abbreviated to Negat. Because over a poor quality connection the words "affirmative" and "negative" can be mistaken for one another (for example over a sound-powered telephone circuit), United States Navy instruction omits the use of either as prowords. Sailors are instructed to instead use "yes" and "no".
Example of usage
Example 1
Two helicopters, call signs "Swiss 610" and "Swiss 613", are flying in formation :
Swiss 610: "613, I have a visual on you at my 3 o'clock. 610"
Swiss 613: "Roger 613"
Swiss 610: "613, Turn right to a heading of 090. 610"
Swiss 613: "Wilco 613"
Anytime a radio call is made (excepting "standby", where the correct response is silence), there is some kind of response indicating that the original call was heard. 613's "Roger" confirms to 610 that the information was heard. In the second radio call from 610, direction was given. 613's "Wilco" means "will comply."
Reading back an instruction confirms that it was heard correctly. For example, if all 613 says is "Wilco", 610 cannot be certain that he correctly heard the heading as 090. If 613 replies with a read back and the word "Wilco" ("Turn right zero-niner-zero, Wilco") then 610 knows that the heading was correctly understood, and that 613 intends to comply.
Example 2
The following is the example of working between two stations, EG93 and VJ50 demonstrating how to confirm information:
EG93: "Victor Juliet five zero, Victor Juliet five zero, this is Echo Golf niner three. Request rendezvous at 51 degrees 37.0N, 001 degrees 49.5W. Read back for check. Over"
VJ50: "Echo Golf niner three, this is Victor Juliet five zero. I read back: five one degrees three seven decimal zero north, zero zero one degrees four niner decimal five west. Over."
EG93: "Victor Juliet five zero, this is Echo Golf niner three. Correct, Out"
Example 3
The following is the example of working between MACV-SOG operator and a gunship demonstrating how to confirm information:
MACV-SOG: "Texas, this is Sierra Oscar Golf X-Ray. Priority one, ordnance on my command. I authenticate, golf shoe, over."
RT Texas: "Affirmative, X-Ray. Let us know when you need us."
See also
Allied Communication Procedures
Brevity code
NATO phonetic alphabet
Prosigns for Morse code
Ten-code
Distress signal
Plain language radio checks
References
Notes
Bibliography
FM 21-75
Handbook for Marine Radio Communication, Fifth Edition
Military communications
Amateur radio
Parts of speech
Operating signals | Procedure word | [
"Technology",
"Engineering"
] | 3,671 | [
"Parts of speech",
"Military communications",
"Telecommunications engineering",
"Components"
] |
9,591,272 | https://en.wikipedia.org/wiki/Counter-scanning | Counter-scanning (CS) is a scanning method that allows correcting raster distortions caused by drift of the probe of scanning microscope relative to the measured surface. During counter-scanning two surface scans, viz., direct scan and counter scan are obtained (see Fig. 1). The counter scan starts in the point where the direct scan ends. This point is called the coincidence point (CP). With the counter scan, the probe movement along the raster line and the probe movement from one raster line to the other raster line are carried out along the directions that are opposite to the movements in the direct scan. The obtained pair of images is called counter-scanned images (CSIs).
Principles
When the raster distortions are linear, i. e., when the drift velocity is constant, to correct drift, it is sufficient to measure coordinates of only one common feature in the direct and the counter scans. In case of nonlinear distortion, when the drift velocity varies during the scan, the number of common features on CSIs whose coordinates need to be measured increases in proportion to the degree of the nonlinearity.
Typically, the drift of the microscope probe relative to the measured surface consists of two components: one is associated with creep of the scanner piezoceramics, the other is caused by a thermal deformation of the instrument due to change in temperature. The first component is nonlinear (it can be approximated by logarithm), the second component can be considered as linear in most practical applications.
The use of the counter-scanning method allows, even in the case of a strong drift leading to errors in tens of percents, measuring the surface topography with error of few tenths of a percent.
Fig. 1. Counter-scanning with (a) an idle line (shown by the dotted line), (b) no idle line. Digits 1…4 designate the numbers of the images obtained. 1, 3 are direct images, 2, 4 are counter images corresponding to the direct ones. CP is a coincidence point of the counter-scanned image pair. The raster presented conditionally consists of four lines.
Counter-scanned images
Counter-scanned images (CSI, CSIs) are a pair of images obtained during counter-scanning. During the counter-scanning it is possible to obtain one or two pairs of CSIs (see Fig. 1). Each pair consists of a direct image and the image counter to it. First, a conventional image is obtained called the direct image, after that a counter image is obtained by reversing the movement direction along a raster line and the movement direction from line to line of the raster. The direct image of the second pair is formed by the retrace lines of the direct image of the first pair. The counter image of the second pair is formed by the retrace lines of the counter image of the first pair. CSIs are intended for correction of distortions caused by drift of the scanning microscope probe relative to the surface under investigation. To implement correction, it is sufficient to have at least one common feature between the direct and the counter images. As compared to a single CSI pair, the use of two pairs requires twice as much memory and processing time but on the other hand it allows increasing precision of correction and reducing noise level in the corrected image.
Fig. 1. Counter-scanned images of porous alumina (AFM, 128×128 pixels): (a) direct and (b) counter images of the first pair; (c) direct and (d) counter images of the second pair. Drift induced error makes 25%. (e) Corrected image, residual error makes 0.1%.
See also
Feature-oriented scanning
References
Microscopes
Scanning probe microscopy | Counter-scanning | [
"Chemistry",
"Materials_science",
"Technology",
"Engineering"
] | 764 | [
"Measuring instruments",
"Microscopes",
"Scanning probe microscopy",
"Microscopy",
"Nanotechnology"
] |
9,591,516 | https://en.wikipedia.org/wiki/Seer%20%28unit%29 | A Seer (also sihr) is a traditional unit of mass and volume used in large parts of Asia prior to the middle of the 20th century. It remains in use only in a few countries such as Afghanistan, Iran, and parts of India although in Iran it indicates a smaller unit of weight than the one used in India.
India
In India, the seer was a traditional unit used mostly in Northern India including Hindi speaking region, Telangana in South. Officially, seer was defined by the Standards of Weights and Measures Act (No. 89 of 1956, amended in 1960 and 1964) as being exactly equal to . However, there were many local variants of the seer in India. Note the chart below gives maund weight for Mumbai, divide by 40 to get a seer.
Aden, Nepal and Pakistan
In Aden (Oman), Nepal, and Pakistan a seer was approximately derived from the Government seer of British colonial days.
Afghanistan
In Afghanistan, it was a unit of mass, approximately .
Persia/Iran
In Persia (and later Iran), it was and remains in two units:
The metric seer was
The seer (sihr) was
The smaller weight is now part of the national weight system in Iran and is used on daily basis for small measures of delicate foodstuff and choice produce.
Sri Lanka
In Sri Lanka, it was a measure of capacity, approximately .
See also
List of customary units of measurement in South Asia
References
Units of mass
Units of volume
Customary units in India
Obsolete units of measurement | Seer (unit) | [
"Physics",
"Mathematics"
] | 309 | [
"Obsolete units of measurement",
"Matter",
"Units of volume",
"Quantity",
"Units of mass",
"Mass",
"Units of measurement"
] |
9,591,673 | https://en.wikipedia.org/wiki/Unglie | A unglie ("finger") is an obsolete unit of length equal to three-fourths of an inch (1.905 cm) that was used in India and Pakistan. After metrification in both countries, the unit became obsolete.
See also
List of customary units of measurement in South Asia
References
Units of length
Customary units in India
Obsolete units of measurement | Unglie | [
"Mathematics"
] | 77 | [
"Obsolete units of measurement",
"Quantity",
"Units of measurement",
"Units of length"
] |
9,591,722 | https://en.wikipedia.org/wiki/Buddam%20%28unit%29 | A buddam (also known as a chow) was an obsolete unit of mass used in the pearl trade in Mumbai (formerly Bombay) during the 19th century. One buddam was equivalent to 1/1600 of a chow, or 1/16 of a docra.
See also
List of customary units of measurement in South Asia
References
Units of mass
Customary units in India
Obsolete units of measurement | Buddam (unit) | [
"Physics",
"Mathematics"
] | 79 | [
"Obsolete units of measurement",
"Matter",
"Quantity",
"Units of mass",
"Mass",
"Units of measurement"
] |
9,591,772 | https://en.wikipedia.org/wiki/Corgee | A corgee is an obsolete unit of mass equal to 212 moodahs, or rush mat bundles of rice. The unit was used in the Canara (now Kanara) region of Karnataka in India.
See also
List of customary units of measurement in South Asia
List of obsolete units of measurement
References
Further reading
Units of mass
Customary units in India
Obsolete units of measurement | Corgee | [
"Physics",
"Mathematics"
] | 76 | [
"Obsolete units of measurement",
"Matter",
"Quantity",
"Units of mass",
"Mass",
"Units of measurement"
] |
9,591,787 | https://en.wikipedia.org/wiki/Punishment%20%28psychology%29 | Punishment is any change in a human or animal's surroundings which, occurring after a given behavior or response, reduces the likelihood of that behavior occurring again in the future. Reinforcement, referring to any behavior that increases the likelihood that a response will occurs, plays a large role in punishment. Motivating operations (MO) can be categorized in abolishing operations, decrease the effectiveness of the stimuli and establishing, increase the effectiveness of the stimuli. For example, a painful stimulus which would act as a punisher for most people may actually reinforce some behaviors of masochistic individuals.
There are two types of punishment: positive and negative. Positive punishment involves the introduction of a stimulus to decrease behavior while negative punishment involves the removal of a stimulus to decrease behavior. While similar to reinforcement, punishment's goal is to decrease behaviors while reinforcement's goal is to increase behaviors. Different kinds of stimuli exist as well. Rewarding stimuli are considered pleasant; however, aversive stimuli are considered unpleasant. There are also two types of punishers: Primary and secondary punishers. Primary punishers directly affect the individual such as pain and are a natural response. Secondary punishers are things that are learned to be negative like a buzzing sound when getting an answer wrong on a game show.
Conflicting findings have been found on the effectiveness of the use of punishment. Some have found that punishment can be a useful tool in suppressing behavior while some have found it to have a weak effect on suppressing behavior. Punishment can also lead to lasting negative unintended side effects as well. In countries that are wealthy, high in trust, cooperation, and democracy, punishment has been found to be effective.
Punishment has been used in a lot of different applications. It has been used in applied behavioral analysis, specifically in situations to try and punish dangerous behaviors like head banging. Punishment has also been used to psychologically manipulate individuals to gain control over victims. For example: in trauma bonding, an abuser may try punishment in order keep control over their victim. Signs of trauma bonding include the following:
an intense emotional connection between the victim and abuser
the victim is isolated from supportive relationship such as parents and sibling
the victim having obsessive through about their abuser
difficulty setting boundaries
resistant to outside help
In some situations, punishment techniques have been seen as effective. Children with intellectual disabilities, such as autism and those who participate in stuttering therapy have had a positive outcome using punishment as a means to learn. Stuttering therapy can help a child improve their speech fluency, develop communication effectively, and be able to participate in all class activities.
Types
There are two basic types of punishment in operant conditioning:
positive punishment, punishment by application, or type I punishment, an experimenter punishes a response by presenting an aversive stimulus into the animal's surroundings (a brief electric shock, for example).
negative punishment, punishment by removal, or type II punishment, a valued, appetitive stimulus is removed (as in the removal of a feeding dish). As with reinforcement, it is not usually necessary to speak of positive and negative in regard to punishment.
Punishment is not a mirror effect of reinforcement. In experiments with laboratory animals and studies with children, punishment decreases the likelihood of a previously reinforced response only temporarily, and it can produce other "emotional" behavior (wing-flapping in pigeons, for example) and physiological changes (increased heart rate, for example) that have no clear equivalents in reinforcement.
Punishment is considered by some behavioral psychologists to be a "primary process" – a completely independent phenomenon of learning, distinct from reinforcement. Others see it as a category of negative reinforcement, creating a situation in which any punishment-avoiding behavior (even standing still) is reinforced.
Positive
Positive punishment occurs when a response produces a stimulus and that response decreases in probability in the future
in similar circumstances.
Example: A mother yells at a child when they run into the street. If the child stops running into the street, the yelling ceases. The yelling acts as positive punishment because the mother presents (adds) an unpleasant stimulus in the form of yelling.
Example: A barefoot person walks onto a hot asphalt surface, creating pain, a positive punishment. When the person leaves the asphalt, the pain subsides. The pain acts as positive punishment because it is the addition of an unpleasant stimulus that reduces the future likelihood of the person walking barefoot on a hot surface.
Negative
Negative punishment occurs when a response produces the removal of a stimulus and that response decreases in probability in the future in similar circumstances.
Example: A teenager comes home after curfew and the parents take away a privilege, such as cell phone usage. If the frequency of the child coming home late decreases, the privilege is gradually restored. The removal of the phone is negative punishment because the parents are taking away a pleasant stimulus (the phone) and motivating the child to return home earlier.
Example: A child throws a temper tantrum because they want ice cream. Their mother subsequently ignores them, making it less likely the child will throw a temper tantrum in the future when they want something. The removal of attention from his mother is a negative punishment because a pleasant stimulus (attention) is taken away.
Versus reinforcement
Simply put, reinforcers serve to increase behaviors whereas punishers serve to decrease behaviors; thus, positive reinforcers are stimuli that the subject will work to attain, and negative reinforcers are stimuli that the subject will work to be rid of or to end. The table below illustrates the adding and subtracting of stimuli (pleasant or aversive) in relation to reinforcement vs. punishment.
Types of stimuli and punishers
Rewarding stimuli (pleasant)
A rewarding stimuli is a stimulus that is considered pleasant. For example, a child may be allowed TV time everyday. Punishment often involves the removal of a rewarding stimuli if an undesired action is done. If the child were to misbehave, this rewarding stimulus of TV time would be removed which would result in negative punishment.
Aversive stimuli (unpleasant)
Aversive Stimuli, punisher, and punishing stimulus are somewhat synonymous. Punishment may be used to mean
An aversive stimulus
The occurrence of any punishing change
The part of an experiment in which a particular response is punished.
Some things considered aversive can become reinforcing. In addition, some things that are aversive may not be punishing if accompanying changes are reinforcing. A classic example would be mis-behavior that is 'punished' by a teacher but actually increases over time due to the reinforcing effects of attention on the student.
Primary punishers
Pain, loud noises, foul tastes, bright lights, and exclusion are all things that would pass the "caveman test" as an aversive stimulus, and are therefore primary punishers. Primary punishers can also be loss of money and receiving negative feedback from people.
Secondary punishers
The sound of someone booing, the wrong-answer buzzer on a game show, and a ticket on your car windshield are all things society has learned to think about as negative, and are considered secondary punishers.
Effectiveness
Contrary to suggestions by Skinner and others that punishment typically has weak or impermanent effects, a large body of research has shown that it can have a powerful and lasting effect in suppressing the punished behavior. Furthermore, more severe punishments are more effective, and very severe ones may even produce complete suppression. However, it may also have powerful and lasting side effects. For example, an aversive stimulus used to punish a particular behavior may also elicit a strong emotional response that may suppress unpunished behavior and become associated with situational stimuli through classical conditioning. Such side effects suggest caution and restraint in the use of punishment to modify behavior. Spanking in particular has been found to have lasting side effects. Parents often use spanking to try make their child act better but there is minimal evidence suggesting that spanking is effective in doing so. Some lasting side effects of spanking include lower cognitive ability, lower self-esteem, and more mental health problems for the child. Some side effects can reach into adulthood as well such as antisocial behavior and support for punishment that involves physical force such as spanking. Punishment is more effective in increasing cooperation in high-trust societies than low-trust societies. Punishment was also more effective in countries that have stronger norms for cooperation, high in wealth, and countries that are high-democratic rather than low-democratic.
Importance of contingency and contiguity
One variable affecting punishment is contingency, which is defined as the dependency of events. A behavior may be dependent on a stimulus or dependent on a response. The purpose of punishment is to reduce a behavior, and the degree to which punishment is effective in reducing a targeted behavior is dependent on the relationship between the behavior and a punishment. For example, if a rat receives an aversive stimulus, such as a shock each time it presses a lever, then it is clear that contingency occurs between lever pressing and shock. In this case, the punisher (shock) is contingent upon the appearance of the behavior (lever pressing). Punishment is most effective when contingency is present between a behavior and a punisher. A second variable affecting punishment is contiguity, which is the closeness of events in time and/or space. Contiguity is important to reducing behavior because the longer the time interval between an unwanted behavior and a punishing effect, the less effective the punishment will be. One major problem with a time delay between a behavior and a punishment is that other behaviors may present during that time delay. The subject may then associate the punishment given with the unintended behaviors, and thus suppressing those behaviors instead of the targeted behavior. Therefore, immediate punishment is more effective in reducing a targeted behavior than a delayed punishment would be. However, there may be ways to improve the effectiveness of delayed punishment, such as providing verbal explanation, reenacting the behavior, increasing punishment intensity, or other methods.
Applications
Applied behavior analysis
Punishment is sometimes used for in applied behavior analysis under the most extreme cases, to reduce dangerous behaviors such as head banging or biting exhibited most commonly by children or people with special needs. Punishment is considered one of the ethical challenges to autism treatment, has led to significant controversy, and is one of the major points for professionalizing behavior analysis. Professionalizing behavior analysis through licensure would create a board to ensure that consumers or families had a place to air disputes, and would ensure training in how to use such tactics properly. (see Professional practice of behavior analysis)
Controversy regarding ABA persists in the autism community. A 2017 study found that 46% of people with autism spectrum undergoing ABA appeared to meet the criteria for post-traumatic stress disorder (PTSD), a rate 86% higher than the rate of those who had not undergone ABA (28%). According to the researcher, the rate of apparent PTSD increased after exposure to ABA regardless of the age of the patient. However, the quality of this study has been disputed by other researchers.
Psychological manipulation
Braiker identified the following ways that manipulators control their victims:
Positive reinforcement: includes praise, superficial charm, superficial sympathy (crocodile tears), excessive apologizing, money, approval, gifts, attention, facial expressions such as a forced laugh or smile, and public recognition.
Negative reinforcement: may involve removing one from a negative situation
Intermittent or partial reinforcement: Partial or intermittent negative reinforcement can create an effective climate of fear and doubt. Partial or intermittent positive reinforcement can encourage the victim to persist - for example in most forms of gambling, the gambler is likely to win now and again but still lose money overall.
Punishment: includes nagging, yelling, the silent treatment, intimidation, threats, swearing, emotional blackmail, the guilt trip, sulking, crying, and playing the victim.
Traumatic one-trial learning: using verbal abuse, explosive anger, or other intimidating behavior to establish dominance or superiority; even one incident of such behavior can condition or train victims to avoid upsetting, confronting or contradicting the manipulator.
Traumatic bonding
Traumatic bonding occurs as the result of ongoing cycles of abuse in which the intermittent reinforcement of reward and punishment creates powerful emotional bonds that are resistant to change.
Punishment used in stuttering therapy
Early studies in the late 60's to early 70's have shown that punishment via time-out (a form of negative punishment) can reduce the severity of stuttering in patients. Since the punishment in these studies was time-out which resulted in the removal of the permission to speak, speaking itself was seen as reinforcing which thus made the time-out an effective form of punishment. Some research has also shown that it is not the time-out that is considered punishing but rather the fact that the removal of the permission to speak was seen as punishing because it interrupted the individual's speech.
Punishment in children with disabilities
Some studies have found effective punishment techniques concerning children with disabilities, such as autism and intellectual disabilities. The targeted behaviors were self-injurious behaviors such as head banging, motor, stereotypy, aggression, emesis, or breaking the rules. Some techniques that were used are timeout, overcorrection, contingent aversive, response blocking, and response interruption and redirection (RIRD). Most punishment techniques were used alone or combined with other punishment techniques; however, the use of punishment techniques alone was less effective in reducing targeted behaviors. Timeout was used the most even though it was less effective in reducing targeted behaviors; however, contingent aversive was used the least even though it was more effective in reducing targeted behaviors. Using punishment techniques in combination with reinforcement-based interventions was more effective than a punishment technique alone or using multiple punishment techniques.
See also
References
Further reading
Behavioral concepts
Punishments
Behaviorism | Punishment (psychology) | [
"Biology"
] | 2,814 | [
"Behavior",
"Behavioral concepts",
"Behaviorism"
] |
9,591,814 | https://en.wikipedia.org/wiki/Munjandie | A munjandie is an obsolete unit of mass in India approximately equal to 4 grains (0.259 g). After metrication in the mid-20th century, the unit became obsolete.
See also
List of customary units of measurement in South Asia
References
Units of mass
Customary units in India
Obsolete units of measurement | Munjandie | [
"Physics",
"Mathematics"
] | 65 | [
"Obsolete units of measurement",
"Matter",
"Quantity",
"Units of mass",
"Mass",
"Units of measurement"
] |
9,591,879 | https://en.wikipedia.org/wiki/Katha%20%28unit%29 | Katha or Biswa (also spelled kattha or cottah; Hindi: कट्ठा, Assamese: কঠা, Bengali: কাঠা) is a unit of area mostly used for land measurement in India, Nepal, and Bangladesh. After metrication in the mid-20th century by these countries, the unit became officially obsolete. But this unit is still in use in much of Bangladesh, Northern India, Eastern India and Nepal. The measurement of katha varies significantly from place to place.
In Purvanchal, 1 Katha = or 151.25 square yard. One Bigha is made up of 5 to 20 Katha. Katha is divided into 20 Dhur and Dhur is subdivided into 20 Dhurki.
Bangladesh
In Bangladesh, one katha is standardized to , and 20 katha equals 1 bigha.
1 Katha (কাঠা) = 720 sq. feet = 66.88 sq. metre = 1.652 Decimal (শতাংশ/ শতক)
1 Bigha (বিঘা) = 20 Katha (কাঠা) = 14,400 square feet = 1,338 sq m = 1,600 sq yard
1 Acre (একর) = 3.025 Bigha (বিঘা) = 60.5 Katha (কাঠা) = 4,047 square metre
1 Hectare (হেক্টর) = 2.47 Acre (একর) = 7.475 Bigha (বিঘা) = 149.5 Katha (কাঠা)
1 Chattak (ছটাক) = 16
India
Assam
In Assam, 1 Katha is equal to 2,880 ft2 and 1 Bigha = 5 Katha; 1 bigha = 14,400 ft2 and in lower assam such as cachar it is 720 square feet.
Bihar
In Bihar, one Katha may vary from 720 to 3,267 square feet (ft2). 1 Bigha = 20 Katha. One katha is divided in 20 dhur. One dhur is subdivided in 20 dhurki. The origin of the term and measurement unit was during the Pala Empire. 1 Decimal = 435.6 square feet & 1 Acre = 100 decimal.
In Patna & Arrah, 1 Katha is equal to 1,361.25 ft2 or 3.125 decimal.
1 Hectare = 3.95 bigha = 79 Katha
1 Acre = 1.6 bigha = 32 Katha
1 Bigha = 27,225 ft2 = 20 Katha
1 Katha = 1,361.25 ft2 = 20 dhur (Patna)
1 Dhur = 68.0625 ft2 = 20 Dhurki
In Bettiah, 1 Katha = 7.5 decimal = 3,267 ft2 and 1 bigha = 65,340 ft2
In Chhapra, 1 Katha = 4 decimal = 1,742.4 ft2 and 1 bigha = 34,848.0 ft2
In Hajipur, 1 Katha = 1,901.25 ft2 and 1 Bigha = 38,025 ft2.
Jharkhand
In Jharkhand, 1 Katha ranges from 720 to 1,742 square feet. In Ranchi, 1 Katha is equal to 720 ft2. 1 bigha is equal to 20 Katha; 1 bigha = 14,400 ft2.
Punjab
In Punjab and Haryana, Katha is known as Biswa. 1 Bigha = 20 Biswa and 1 Biswa = 20 Biswansi.
1 Acre = 2 bigha = 4,840 square yard
1 Bigha = 2,420 square yard
1 biswa = 121 square yard
1 biswansi = 6.05 square yard
Uttar Pradesh
In Uttar Pradesh, Katha is also known as Biswa. One Katha is equal to 1,361.25 ft2 or 151.25 square yard or 126.46 square metre. One Bigha in UP can range from 5 to 20 Katha.
In Western UP, 1 Bigha can be 5.0 Katha (756.25 square yard) or 6.6667 Katha (1,008.33 square yard). In Eastern UP, 1 Bigha is 20 Katha (3,025 square yard).
1 Katha or 1 Biswa = 20 Dhur or 20 Biswansi
1 Dhur = 1 Biswansi
1 Dhur = 20 Dhurki
1 Katha = 3.125 Decimal
1 Acre = 100 Decimal
1 Acre = 32 Katha
West Bengal
In West Bengal, 1 Katha is equal to 720 ft2. 1 bigha is equal to 20 Katha; 1 bigha = 14,400 ft2.
1 Acre = 3.025 Bigha, 1 katha= 16 chatak, 1 chatak=45 sq.ft
Nepal
In Nepal, 1 Katha is equivalent to 338.55 m2 With Manoj Chhetri
See also
List of customary units of measurement in South Asia
Nepalese customary units of measurement
References
Units of area
Customary units in India
Obsolete units of measurement | Katha (unit) | [
"Mathematics"
] | 1,038 | [
"Obsolete units of measurement",
"Quantity",
"Units of area",
"Units of measurement"
] |
9,591,926 | https://en.wikipedia.org/wiki/Jow%20%28unit%29 | A jow (also called a jacob) is an obsolete unit of length in India approximately equal 0.25 inch (about 0.63 cm). After metrication in India in the mid-20th century, the unit became obsolete.
See also
List of customary units of measurement in South Asia
References
Units of length
Customary units in India
Obsolete units of measurement | Jow (unit) | [
"Mathematics"
] | 73 | [
"Obsolete units of measurement",
"Quantity",
"Units of measurement",
"Units of length"
] |
9,591,966 | https://en.wikipedia.org/wiki/Groundwater-related%20subsidence | Groundwater-related subsidence is the subsidence (or the sinking) of land resulting from unsustainable groundwater extraction. It is a growing problem in the developing world as cities increase in population and water use, without adequate pumping regulation and enforcement. One estimate has 80% of serious U.S. land subsidence problems associated with the excessive extraction of groundwater.
Groundwater can be considered one of the last free resources, as anyone who can afford to drill can usually draw up merely according to their ability to pump (depending on local regulations). However, as seen in the figure, pumping-induced draw down causes a depression of the groundwater surface around the production well. This can ultimately affect a large region by making it more difficult and expensive to pump the deeper water. Thus, the extraction of groundwater becomes a tragedy of the commons, with resulting economic externalities.
Mechanism
The cause of the long-term surface changes associated with this phenomenon are fairly well known. As shown in the USGS figure, aquifers are frequently associated with compressible layers of silt or clay.
As the groundwater is pumped out, the effective stress changes, precipitating consolidation, which is often non-reversible. Thus, the total volume of the silts and clays is reduced, resulting in the lowering of the surface. The damage at the surface is much greater if there is differential settlement, or large-scale features, such as sinkholes and fissures.
Aquifer compaction is a significant concern along with pumping-induced land subsidence. A large portion of the groundwater storage potential of many aquifers can be significantly reduced when longterm groundwater extraction, and the resulting groundwater level decline, causes permanent compaction of fine sediment layers (silts and clays). A study in an arid agricultural region of Arizona showed that, even with a water level recovery of 100 ft after groundwater pumping was stopped, the land surface continued to subside for decades. This is a result of the continued dewatering of aquitards (fine-grain layers that slow the movement of groundwater) from stresses mentioned in the previous paragraph.
The only known method to prevent this condition is by pumping less groundwater, which is extremely difficult to enforce when many people own water wells. Attempts are being made to directly recharge aquifers but this is still a preliminary effort.
Impacted geographies
The arid areas of the world are requiring more and more water for growing populations and agriculture. In the San Joaquin Valley of the United States, groundwater pumping for crops has gone on for generations. This has resulted in the entire valley sinking an extraordinary amount, as shown in the figure. This has not come without consequences. Any large-scale change of topography, no matter how slight it may seem, has the potential to drastically change the surface-water hydrology. This has happened in the Joaquin Valley and other regions of the world, such as New Orleans and Bangkok. These areas are now subject to severe flooding due to subsidence associated with groundwater removal. Total subsidence can usually be determined by ground-surface elevation surveys and GPS measurements. Potential impact on the aquifers and other resulting geohazards such as fissures can be assessed through long-term hydrologic studies and models.
Groundwater-related subsidence often results in major damage to urban areas. In Mexico City, the buildings interact with the settlement, and cause cracking, tilting, and other major damage. In many places, large sinkholes open up, as well as surface cavities. Damage from Hurricane Katrina was exacerbated due to coastal sinking, associated with groundwater withdrawal.
Major areas affected include the San Joaquin Valley in California, Central Arizona, Mexico City, and Jakarta, Indonesia.
See also
Sea level rise
List of aquifers in the United States
References
Aquifers
Environmental issues with water
Soil mechanics
de:Grundwasserabsenkung#Folgen der Grundwasserabsenkung | Groundwater-related subsidence | [
"Physics",
"Environmental_science"
] | 814 | [
"Soil mechanics",
"Hydrology",
"Applied and interdisciplinary physics",
"Aquifers"
] |
9,591,993 | https://en.wikipedia.org/wiki/Marabba | A marabba is a customary unit of area in India and Pakistan approximately equal to 25 acres, (10.117 hectares).
Defined as a square with sides measuring 200 karam. The karam was standardised as 5 1/2 feet by the British making each side 1100 feet. The unit is now used customarily as the visual size of an average crop field. It is thought to derive from the size of crop field necessary to sustain 3 generations of an average family.
After metrification by both countries in the 20th century, the unit was superseded.
See also
List of customary units of measurement in South Asia
References
Units of area
Customary units in India
Obsolete units of measurement | Marabba | [
"Mathematics"
] | 139 | [
"Obsolete units of measurement",
"Quantity",
"Units of area",
"Units of measurement"
] |
9,592,061 | https://en.wikipedia.org/wiki/Tank%20%28unit%29 | A tank is an obsolete unit of mass in India approximately equal to 4.4 g (69 gr). After metrication in the mid-20th century, the unit became obsolete.
See also
List of customary units of measurement in South Asia
References
Units of mass
Customary units in India
Obsolete units of measurement | Tank (unit) | [
"Physics",
"Mathematics"
] | 62 | [
"Obsolete units of measurement",
"Matter",
"Quantity",
"Units of mass",
"Mass",
"Units of measurement"
] |
9,592,106 | https://en.wikipedia.org/wiki/Ser%20%28unit%29 | A ser is an obsolete unit of dry volume in India. In 1871 it was defined as being exactly 1 litre. After metrication in the mid-20th century, the unit became obsolete. It was the unit in pre-modern India which was so close to the metric values of volume approx equal to a litre.
See also
List of customary units of measurement in South Asia
References
Units of volume
Customary units in India
Obsolete units of measurement | Ser (unit) | [
"Mathematics"
] | 88 | [
"Units of volume",
"Obsolete units of measurement",
"Quantity",
"Units of measurement"
] |
9,592,142 | https://en.wikipedia.org/wiki/Cawnie | A cawnie is an obsolete unit of land area used in Chennai (formerly Madras) in India. It was approximately equal to 1.322 acres. In SI units that is 5349 square metres. After metrication in the mid-20th century, the unit became obsolete. It is also known as Kani. 1 kani is equal to 57600 Square Feet.
See also
List of customary units of measurement in South Asia
References
External links
Units of area
Customary units in India
Obsolete units of measurement | Cawnie | [
"Mathematics"
] | 103 | [
"Obsolete units of measurement",
"Quantity",
"Units of area",
"Units of measurement"
] |
9,592,241 | https://en.wikipedia.org/wiki/Bamboo%20%28unit%29 | A bamboo is an obsolete unit of length in India and Myanmar.
India
In India, the unit was fixed by the reforms of Akbar the Great (1556–1605) at approximately 12.8 m (42 ft). After Metrication in India in the mid-20th century, the unit became obsolete.
Myanmar
In Myanmar (formerly Burma) it was approximately 3.912 meters (154 in, or 12.86 ft). It was also known as the dha.
One thousand bamboos = one dain (A dain is sometimes referred to as a "Burmese league")
One dain = 7 saundaungs
See also
List of customary units of measurement in South Asia
References
Units of length
Customary units in India
Obsolete units of measurement | Bamboo (unit) | [
"Mathematics"
] | 154 | [
"Obsolete units of measurement",
"Quantity",
"Units of measurement",
"Units of length"
] |
9,592,375 | https://en.wikipedia.org/wiki/Decimal%20%28unit%29 | A decimal (also spelled decimil or dismil; ) is a unit of area in India and Bangladesh. After metrication in the mid-20th century by both countries, the unit became officially obsolete. However, it is still in use among the rural population in Northern Bangladesh and West Bengal.
A decimal is one hundredth of an acre of land, and is equal to 48.4 square yards or . Decimals are also used as a measure of land in West Africa.
Conversion chart
See also
List of customary units of measurement in South Asia
References
Customary units in India
Obsolete units of measurement
Units of area
External Links
Decimal to Square Feet Calculator | Decimal (unit) | [
"Mathematics"
] | 134 | [
"Obsolete units of measurement",
"Quantity",
"Units of area",
"Units of measurement"
] |
9,592,436 | https://en.wikipedia.org/wiki/Hat%27h | A hat'h (hath, hand, cubit, moolum or mulam) is an obsolete unit of length in India equal to 24 angli (approximately 18 inches) or 2 hat'h to a gaz (approximately 1 yard). The unit was used in Mumbai (formerly Bombay) and in Bengal After metrication in the mid-20th century, the unit became obsolete.
See also
List of customary units of measurement in South Asia
References
External links
Units of length
Customary units in India
Obsolete units of measurement | Hat'h | [
"Mathematics"
] | 108 | [
"Obsolete units of measurement",
"Quantity",
"Units of measurement",
"Units of length"
] |
9,592,779 | https://en.wikipedia.org/wiki/Pocket%20PC%202002 | Pocket PC 2002, originally codenamed "Merlin", was a member of the Windows Mobile family of mobile operating systems, released on October 4, 2001. Like Pocket PC 2000, it was based on Windows CE 3.0, and was modified version of Windows 95. Although mainly targeted for (QVGA) Pocket PC devices, Pocket PC 2002 was also used for Pocket PC phones (Pocket PC 2002 Phone Edition), devices that combined the PDA with cellular connectivity.
Aesthetically, Pocket PC 2002 was meant to be similar in design to the then newly released Windows XP. Newly added or updated programs include Windows Media Player 8 with streaming capability, MSN Messenger, and Microsoft Reader 2, with digital rights management support. Upgrades to the bundled version of Office Mobile include a spell checker and word count tool in Pocket Word and improved Pocket Outlook. Connectivity was improved with file beaming on non-Microsoft devices such as Palm OS, the inclusion of Terminal Services and Virtual Private Networking support, and the ability to synchronize folders. Other upgrades include an enhanced UI with theme support and savable downloads and WAP in Pocket Internet Explorer.
On the technical side of things, Pocket PC 2002 removed MIPS and SuperH CPU support, only supporting the ARM architecture. Another software platform on the same base designed for smartphones (Smartphone 2002) was also released, which were mainly keypad-style GSM devices. With future releases, the Pocket PC and Smartphone lines would increasingly collide as the licensing terms were relaxed allowing OEMs to take advantage of more innovative, individual design ideas.
See also
References
Windows CE
Windows Mobile
Discontinued versions of Microsoft Windows
Products and services discontinued in 2008 | Pocket PC 2002 | [
"Technology"
] | 340 | [
"Operating system stubs",
"Computing stubs"
] |
9,593,786 | https://en.wikipedia.org/wiki/Dihydroorotate%20dehydrogenase | Dihydroorotate dehydrogenase (DHODH) is an enzyme that in humans is encoded by the DHODH gene on chromosome 16. The protein encoded by this gene catalyzes the fourth enzymatic step, the ubiquinone-mediated oxidation of dihydroorotate to orotate, in de novo pyrimidine biosynthesis. This protein is a mitochondrial protein located on the outer surface of the inner mitochondrial membrane (IMM). Inhibitors of this enzyme are used to treat autoimmune diseases such as rheumatoid arthritis.
Structure
DHODH can vary in cofactor content, oligomeric state, subcellular localization, and membrane association. An overall sequence alignment of these DHODH variants presents two classes of DHODHs: the cytosolic Class 1 and the membrane-bound Class 2. In Class 1 DHODH, a basic cysteine residue catalyzes the oxidation reaction, whereas in Class 2, the serine serves this catalytic function. Structurally, Class 1 DHODHs can also be divided into two subclasses, one of which forms homodimers and uses fumarate as its electron acceptor, and the other which forms heterotetramers and uses NAD+ as its electron acceptor. This second subclass contains an addition subunit (PyrK) containing an iron-sulfur cluster and a flavin adenine dinucleotide (FAD). Meanwhile, Class 2 DHODHs use coenzyme Q/ubiquinones for their oxidant.
In higher eukaryotes, this class of DHODH contains an N-terminal bipartite signal comprising a cationic, amphipathic mitochondrial targeting sequence of about 30 residues and a hydrophobic transmembrane sequence. The targeting sequence is responsible for this protein's localization to the IMM, possibly from recruiting the import apparatus and mediating ΔΨ-driven transport across the inner and outer mitochondrial membranes, while the transmembrane sequence is essential for its insertion into the IMM. This sequence is adjacent to a pair of α-helices, α1 and α2, which are connected by a short loop. Together, this pair forms a hydrophobic funnel that is suggested to serve as the insertion site for ubiquinone, in conjunction with the FMN binding cavity at the C-terminal. The two terminal domains are directly connected by an extended loop. The C-terminal domain is the larger of the two and folds into a conserved α/β-barrel structure with a core of eight parallel β-strands surrounded by eight α helices.
Function
Human DHODH is a ubiquitous FMN flavoprotein. In bacteria (gene pyrD), it is located on the inner side of the cytosolic membrane. In some yeasts, such as in Saccharomyces cerevisiae (gene URA1), it is a cytosolic protein, whereas, in other eukaryotes, it is found in the mitochondria. It is also the only enzyme in the pyrimidine biosynthesis pathway located in the mitochondria rather than the cytosol.
As an enzyme associated with the electron transport chain, DHODH links mitochondrial bioenergetics, cell proliferation, ROS production, and apoptosis in certain cell types. DHODH depletion also resulted in increased ROS production, decreased membrane potential and cell growth retardation. Also, due to its role in DNA synthesis, inhibition of DHODH may provide a means to regulate transcriptional elongation.
Mechanism
In mammalian species, DHODH catalyzes the fourth step in de novo pyrimidine biosynthesis, which involves the ubiquinone-mediated oxidation of dihydroorotate to orotate and the reduction of FMN to dihydroflavin mononucleotide (FMNH2):
(S)-dihydroorotate + O2 orotate + H2O2
The particular mechanism for the dehydrogenation of dihydroorotic acid by DHODH differs between the two classes of DHODH. Class 1 DHODHs follow a concerted mechanism, in which the two C–H bonds of dihydroorotic acid break in concert. Class 2 DHODHs follow a stepwise mechanism, in which the breaking of the C–H bonds precedes the equilibration of iminium into orotic acid.
Inhibitors
Brequinar
Teriflunomide
Leflunomide
S416
Vidofludimus Calcium
Olorofim
Orludodstat
Clinical significance
Brequinar, a potent and selective inhibitor of the enzyme dihydroorotate dehydrogenase, has been shown to inhibit completely vaccinia virus in human cells. The immunomodulatory drugs teriflunomide and leflunomide have been shown to inhibit DHODH. Human DHODH has two domains: an alpha/beta-barrel domain containing the active site and an alpha-helical domain that forms the opening of a tunnel leading to the active site. Leflunomide has been shown to bind in this tunnel. Leflunomide is being used for treatment of rheumatoid and psoriatic arthritis, as well as multiple sclerosis. Its immunosuppressive effects have been attributed to the depletion of the pyrimidine supply for T cells or to more complex interferon or interleukin-mediated pathways, but nonetheless require further research.
Additionally, DHODH may play a role in retinoid N-(4-hydroxyphenyl)retinamide (4HPR)-mediated cancer suppression. Inhibition of DHODH activity with teriflunomide or expression with RNA interference resulted in reduced ROS generation in, and thus apoptosis of, transformed skin and prostate epithelial cells.
Mutations in this gene have been shown to cause Miller syndrome, also known as Genee-Wiedemann syndrome, Wildervanck-Smith syndrome or post-axial acrofacial dystosis.
Interactions
DHODH binds to its FMN cofactor in conjunction with ubiquinone to catalyze the oxidation of dihydroorotate to orotate.
References
Further reading
External links
Protein domains
Peripheral membrane proteins | Dihydroorotate dehydrogenase | [
"Biology"
] | 1,329 | [
"Protein domains",
"Protein classification"
] |
9,593,892 | https://en.wikipedia.org/wiki/Carbamoyl%20aspartic%20acid | Carbamoyl aspartic acid (or ureidosuccinic acid) is a carbamate derivative, serving as an intermediate in pyrimidine biosynthesis.
References
Ureas
Dicarboxylic acids | Carbamoyl aspartic acid | [
"Chemistry"
] | 50 | [
"Organic compounds",
"Organic compound stubs",
"Organic chemistry stubs",
"Ureas"
] |
9,593,941 | https://en.wikipedia.org/wiki/4%2C5-Dihydroorotic%20acid | 4,5-Dihydroorotic acid is a derivative of orotic acid which serves as an intermediate in pyrimidine biosynthesis.
References
Pyrimidinediones
Carboxylic acids | 4,5-Dihydroorotic acid | [
"Chemistry",
"Biology"
] | 46 | [
"Biotechnology stubs",
"Carboxylic acids",
"Functional groups",
"Biochemistry stubs",
"Biochemistry"
] |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.