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[SOURCE: https://en.wikipedia.org/wiki/Multistage_rocket] | [TOKENS: 5315] |
Contents Multistage rocket A multistage rocket or step rocket is a launch vehicle that uses two or more rocket stages, each of which contains its own engines and propellant. A tandem or serial stage is mounted on top of another stage; a parallel stage is attached alongside another stage. The result is effectively two or more rockets stacked on top of or attached next to each other. Two-stage rockets are quite common, but rockets with as many as five separate stages have been successfully launched. By jettisoning stages when they run out of propellant, the mass of the remaining rocket is decreased. Each successive stage can also be optimized for its specific operating conditions, such as decreased atmospheric pressure at higher altitudes. This staging allows the thrust of the remaining stages to more easily accelerate the rocket to its final velocity and height. In serial or tandem staging schemes, the first stage is at the bottom and is usually the largest, the second stage and subsequent upper stages are above it, usually decreasing in size. In parallel staging schemes solid or liquid rocket boosters are used to assist with launch. These are sometimes referred to as "stage 0". In the typical case, the first-stage and booster engines fire to propel the entire rocket upwards. When the boosters run out of fuel, they are detached from the rest of the rocket (usually with some kind of small explosive charge or explosive bolts) and fall away. The first stage then burns to completion and falls off. This leaves a smaller rocket, with the second stage on the bottom, which then fires. Known in rocketry circles as staging, this process is repeated until the desired final velocity is achieved. In some cases with serial staging, the upper stage ignites before the separation—the interstage ring is designed with this in mind, and the thrust is used to help positively separate the two vehicles. Only multistage rockets have reached orbital speed. Single-stage-to-orbit designs are sought, but have not yet been demonstrated on Earth. Performance Multi-stage rockets overcome a limitation imposed by the laws of physics on the velocity change achievable by a rocket stage. The limit depends on the fueled-to-dry mass ratio and on the effective exhaust velocity of the engine. This relation is given by the classical rocket equation: where: The delta v required to reach low Earth orbit (or the required velocity of a sufficiently heavy suborbital payload) requires a wet to dry mass ratio larger than has been achieved in a single rocket stage. The multistage rocket overcomes this limit by splitting the delta-v into fractions. As each lower stage drops off and the succeeding stage fires, the rest of the rocket is still traveling near the burnout speed. Each lower stage's dry mass includes the propellant in the upper stages, and each succeeding upper stage has reduced its dry mass by discarding the useless dry mass of the spent lower stages. A further advantage is that each stage can use a different type of rocket engine, each tuned for its particular operating conditions. Thus the lower-stage engines are designed for use at atmospheric pressure, while the upper stages can use engines suited to near vacuum conditions. Lower stages tend to require more structure than upper as they need to bear their own weight plus that of the stages above them. Optimizing the structure of each stage decreases the weight of the total vehicle and provides further advantage. The advantage of staging comes at the cost of the lower stages lifting engines which are not yet being used, as well as making the entire rocket more complex and harder to build than a single stage. In addition, each staging event is a possible point of launch failure, due to separation failure, ignition failure, or stage collision. Nevertheless, the savings are so great that every rocket ever used to deliver a payload into orbit has had staging of some sort. One of the most common measures of rocket efficiency is its specific impulse, which is defined as the thrust per flow rate (per second) of propellant consumption: When rearranging the equation such that thrust is calculated as a result of the other factors, we have: These equations show that a higher specific impulse means a more efficient rocket engine, capable of burning for longer periods of time. In terms of staging, the initial rocket stages usually have a lower specific impulse rating, trading efficiency for superior thrust in order to quickly push the rocket into higher altitudes. Later stages of the rocket usually have a higher specific impulse rating because the vehicle is further outside the atmosphere and the exhaust gas does not need to expand against as much atmospheric pressure. When selecting the ideal rocket engine to use as an initial stage for a launch vehicle, a useful performance metric to examine is the thrust-to-weight ratio, and is calculated by the equation: The common thrust-to-weight ratio of a launch vehicle is within the range of 1.3 to 2.0. Another performance metric to keep in mind when designing each rocket stage in a mission is the burn time, which is the amount of time the rocket engine will last before it has exhausted all of its propellant. For most non-final stages, thrust and specific impulse can be assumed constant, which allows the equation for burn time to be written as: Where m 0 {\displaystyle m_{\mathrm {0} }} and m f {\displaystyle m_{\mathrm {f} }} are the initial and final masses of the rocket stage respectively. In conjunction with the burnout time, the burnout height and velocity are obtained using the same values, and are found by these two equations: When dealing with the problem of calculating the total burnout velocity or time for the entire rocket system, the general procedure for doing so is as follows: The burnout time does not define the end of the rocket stage's motion, as the vehicle will still have a velocity that will allow it to coast upward for a brief amount of time until the acceleration of the planet's gravity gradually changes it to a downward direction. The velocity and altitude of the rocket after burnout can be easily modeled using the basic physics equations of motion. When comparing one rocket with another, it is impractical to directly compare the rocket's certain trait with the same trait of another because their individual attributes are often not independent of one another. For this reason, dimensionless ratios have been designed to enable a more meaningful comparison between rockets. The first is the initial to final mass ratio, which is the ratio between the rocket stage's full initial mass and the rocket stage's final mass once all of its fuel has been consumed. The equation for this ratio is: Where m E {\displaystyle m_{\mathrm {E} }} is the empty mass of the stage, m p {\displaystyle m_{\mathrm {p} }} is the mass of the propellant, and m P L {\displaystyle m_{\mathrm {PL} }} is the mass of the payload. The second dimensionless performance quantity is the structural ratio, which is the ratio between the empty mass of the stage, and the combined empty mass and propellant mass as shown in this equation: The last major dimensionless performance quantity is the payload ratio, which is the ratio between the payload mass and the combined mass of the empty rocket stage and the propellant: After comparing the three equations for the dimensionless quantities, it is easy to see that they are not independent of each other, and in fact, the initial to final mass ratio can be rewritten in terms of structural ratio and payload ratio: These performance ratios can also be used as references for how efficient a rocket system will be when performing optimizations and comparing varying configurations for a mission. Component selection and sizing For initial sizing, the rocket equations can be used to derive the amount of propellant needed for the rocket based on the specific impulse of the engine and the total impulse required in N·s. The equation is: where g is the gravity constant of Earth. This also enables the volume of storage required for the fuel to be calculated if the density of the fuel is known, which is almost always the case when designing the rocket stage. The volume is yielded when dividing the mass of the propellant by its density. Asides from the fuel required, the mass of the rocket structure itself must also be determined, which requires taking into account the mass of the required thrusters, electronics, instruments, power equipment, etc. These are known quantities for typical off the shelf hardware that should be considered in the mid to late stages of the design, but for preliminary and conceptual design, a simpler approach can be taken. Assuming one engine for a rocket stage provides all of the total impulse for that particular segment, a mass fraction can be used to determine the mass of the system. The mass of the stage transfer hardware such as initiators and safe-and-arm devices are very small by comparison and can be considered negligible. For modern day solid rocket motors, it is a safe and reasonable assumption to say that 91 to 94 percent of the total mass is fuel. It is also important to note there is a small percentage of "residual" propellant that will be left stuck and unusable inside the tank, and should also be taken into consideration when determining amount of fuel for the rocket. A common initial estimate for this residual propellant is five percent. With this ratio and the mass of the propellant calculated, the mass of the empty rocket weight can be determined. Sizing rockets using a liquid bipropellant requires a slightly more involved approach because there are two separate tanks that are required: one for the fuel, and one for the oxidizer. The ratio of these two quantities is known as the mixture ratio, and is defined by the equation: Where m o x {\displaystyle m_{\mathrm {ox} }} is the mass of the oxidizer and m f u e l {\displaystyle m_{\mathrm {fuel} }} is the mass of the fuel. This mixture ratio not only governs the size of each tank, but also the specific impulse of the rocket. Determining the ideal mixture ratio is a balance of compromises between various aspects of the rocket being designed, and can vary depending on the type of fuel and oxidizer combination being used. For example, a mixture ratio of a bipropellant could be adjusted such that it may not have the optimal specific impulse, but will result in fuel tanks of equal size. This would yield simpler and cheaper manufacturing, packing, configuring, and integrating of the fuel systems with the rest of the rocket, and can become a benefit that could outweigh the drawbacks of a less efficient specific impulse rating. But suppose the defining constraint for the launch system is volume, and a low density fuel is required such as hydrogen. This example would be solved by using an oxidizer-rich mixture ratio, reducing efficiency and specific impulse rating, but will meet a smaller tank volume requirement. Optimal staging and restricted staging The ultimate goal of optimal staging is to maximize the payload ratio (see ratios under performance), meaning the largest amount of payload is carried up to the required burnout velocity using the least amount of non-payload mass, which comprises everything else. This goal assumes that the cost of a rocket launch is proportional to the total liftoff mass of the rocket, which is a rule of thumb in rocket engineering. Here are a few quick rules and guidelines to follow in order to reach optimal staging: The payload ratio can be calculated for each individual stage, and when multiplied together in sequence, will yield the overall payload ratio of the entire system. It is important to note that when computing payload ratio for individual stages, the payload includes the mass of all the stages after the current one. The overall payload ratio is: Where n is the number of stages the rocket system comprises. Similar stages yielding the same payload ratio simplify this equation, however that is seldom the ideal solution for maximizing payload ratio, and ΔV requirements may have to be partitioned unevenly as suggested in guideline tips 1 and 2 from above. Two common methods of determining this perfect ΔV partition between stages are either a technical algorithm that generates an analytical solution that can be implemented by a program, or simple trial and error. For the trial and error approach, it is best to begin with the final stage, calculating the initial mass which becomes the payload for the previous stage. From there it is easy to progress all the way down to the initial stage in the same manner, sizing all the stages of the rocket system. Restricted rocket staging is based on the simplified assumption that each of the stages of the rocket system have the same specific impulse, structural ratio, and payload ratio, the only difference being the total mass of each increasing stage is less than that of the previous stage. Although this assumption may not be the ideal approach to yielding an efficient or optimal system, it greatly simplifies the equations for determining the burnout velocities, burnout times, burnout altitudes, and mass of each stage. This would make for a better approach to a conceptual design in a situation where a basic understanding of the system behavior is preferential to a detailed, accurate design. One important concept to understand when undergoing restricted rocket staging, is how the burnout velocity is affected by the number of stages that split up the rocket system. Increasing the number of stages for a rocket while keeping the specific impulse, payload ratios and structural ratios constant will always yield a higher burnout velocity than the same systems that use fewer stages. However, the law of diminishing returns is evident in that each increment in number of stages gives less of an improvement in burnout velocity than the previous increment. The burnout velocity gradually converges towards an asymptotic value as the number of stages increases towards a very high number. In addition to diminishing returns in burnout velocity improvement, the main reason why real world rockets seldom use more than three stages is because of increase of weight and complexity in the system for each added stage, ultimately yielding a higher cost for deployment. Hot-staging Hot-staging is a type of rocket staging in which the next stage fires its engines before separation instead of after. During hot-staging, the earlier stage throttles down its engines. Hot-staging may reduce the complexity of stage separation, and gives a small extra payload capacity to the booster. It also eliminates the need for ullage motors, as the acceleration from the nearly spent stage keeps the propellants settled at the bottom of the tanks. Hot-staging is used on Soviet-era Russian rockets such as Soyuz and Proton-M. The N1 rocket was designed to use hot staging, but none of the test flights lasted long enough for this to occur. Starting with the Titan II, the Titan family of rockets used hot staging. SpaceX retrofitted their Starship rocket to use hot staging after its first flight, making it the largest rocket ever to do so, as well as the first reusable vehicle to utilize hot staging. Tandem vs parallel staging design A rocket system that implements tandem staging means that each individual stage runs in order one after the other. The rocket breaks free from the previous stage, then begins burning through the next stage in straight succession. On the other hand, a rocket that implements parallel staging has two or more different stages that are active at the same time. For example, the Space Shuttle has two Solid Rocket Boosters that burn simultaneously. Upon launch, the boosters ignite, and at the end of the stage, the two boosters are discarded while the external fuel tank is kept for another stage. Most quantitative approaches to the design of the rocket system's performance are focused on tandem staging, but the approach can be easily modified to include parallel staging. To begin with, the different stages of the rocket should be clearly defined. Continuing with the previous example, the end of the first stage which is sometimes referred to as 'stage 0', can be defined as when the side boosters separate from the main rocket. From there, the final mass of stage one can be considered the sum of the empty mass of stage one, the mass of stage two (the main rocket and the remaining unburned fuel) and the mass of the payload.[original research?] Upper stages High-altitude and space-bound upper stages are designed to operate with little or no atmospheric pressure. This allows the use of lower pressure combustion chambers and engine nozzles with optimal vacuum expansion ratios. Some upper stages, especially those using hypergolic propellants like Delta-K or Ariane 5 ES second stage, are pressure fed, which eliminates the need for complex turbopumps. Other upper stages, such as the Centaur or DCSS, use liquid hydrogen expander cycle engines, or gas generator cycle engines like the Ariane 5 ECA's HM7B or the S-IVB's J-2. These stages are usually tasked with completing orbital injection and accelerating payloads into higher energy orbits such as GTO or to escape velocity. Upper stages, such as Fregat, used primarily to bring payloads from low Earth orbit to GTO or beyond are sometimes referred to as space tugs. Assembly Each individual stage is generally assembled at its manufacturing site and shipped to the launch site; the term vehicle assembly refers to the mating of all rocket stage(s) and the spacecraft payload into a single assembly known as a space vehicle. Single-stage vehicles (suborbital), and multistage vehicles on the smaller end of the size range, can usually be assembled directly on the launch pad by lifting the stage(s) and spacecraft vertically in place by means of a crane. This is generally not practical for larger space vehicles, which are assembled off the pad and moved into place on the launch site by various methods. NASA's Apollo/Saturn V crewed Moon landing vehicle, and Space Shuttle, were assembled vertically onto mobile launcher platforms with attached launch umbilical towers, in a Vehicle Assembly Building, and then a special crawler-transporter moved the entire vehicle stack to the launch pad in an upright position. In contrast, vehicles such as the Russian Soyuz rocket and the SpaceX Falcon 9 are assembled horizontally in a processing hangar, transported horizontally, and then brought upright at the pad. Passivation and space debris Spent upper stages of launch vehicles are a significant source of space debris remaining in orbit in a non-operational state for many years after use, and occasionally, large debris fields created from the breakup of a single upper stage while in orbit. After the 1990s, spent upper stages are generally passivated after their use as a launch vehicle is complete in order to minimize risks while the stage remains derelict in orbit. Passivation means removing any sources of stored energy remaining on the vehicle, as by dumping fuel or discharging batteries. Many early upper stages, in both the Soviet and U.S. space programs, were not passivated after mission completion. During the initial attempts to characterize the space debris problem, it became evident that a good proportion of all debris was due to the breaking up of rocket upper stages, particularly unpassivated upper-stage propulsion units. History and development An illustration and description in the 14th century Chinese Huolongjing by Jiao Yu and Liu Bowen shows the oldest known multistage rocket; this was the "fire-dragon issuing from the water" (火龙出水, huǒ lóng chū shuǐ), which was used mostly by the Chinese navy. It was a two-stage rocket that had booster rockets that would eventually burn out, yet, before they did so, automatically ignited a number of smaller rocket arrows that were shot out of the front end of the missile, which was shaped like a dragon's head with an open mouth. The British scientist and historian Joseph Needham points out that the written material and depicted illustration of this rocket come from the oldest stratum of the Huolongjing, which can be dated roughly 1300–1350 AD (from the book's part 1, chapter 3, page 23). Another example of an early multistaged rocket is the Juhwa (走火) of Korean development. It was proposed by medieval Korean engineer, scientist and inventor Ch'oe Mu-sŏn and developed by the Firearms Bureau (火㷁道監) during the 14th century. The rocket had the length of 15 cm and 13 cm; the diameter was 2.2 cm. It was attached to an arrow 110 cm long; experimental records show that the first results were around 200m in range. There are records that show Korea kept developing this technology until it came to produce the Singijeon, or 'magical machine arrows' in the 16th century. The earliest experiments with multistage rockets in Europe were made in 1551 by Austrian Conrad Haas (1509–1576), the arsenal master of the town of Hermannstadt, Transylvania (now Sibiu/Hermannstadt, Romania). This concept was developed independently by at least five individuals: The first high-speed multistage rockets were the RTV-G-4 Bumper rockets tested at the White Sands Proving Ground and later at Cape Canaveral from 1948 to 1950. These consisted of a V-2 rocket and a WAC Corporal sounding rocket. The greatest altitude ever reached was 393 km, attained on February 24, 1949, at White Sands. In 1947, the Soviet rocket engineer and scientist Mikhail Tikhonravov developed a theory of parallel stages, which he called "packet rockets". In his scheme, three parallel stages were fired from liftoff, but all three engines were fueled from the outer two stages, until they are empty and could be ejected. This is more efficient than sequential staging, because the second-stage engine is never just dead weight. In 1951, Soviet engineer and scientist Dmitry Okhotsimsky carried out a pioneering engineering study of general sequential and parallel staging, with and without the pumping of fuel between stages. The design of the R-7 Semyorka emerged from that study. The trio of rocket engines used in the first stage of the American Atlas I and Atlas II launch vehicles, arranged in a row, used parallel staging in a similar way: the outer pair of booster engines existed as a jettisonable pair which would, after they shut down, drop away with the lowermost outer skirt structure, leaving the central sustainer engine to complete the first stage's engine burn towards apogee or orbit. Separation events Separation of each portion of a multistage rocket introduces additional risk into the success of the launch mission. Reducing the number of separation events results in a reduction in complexity. Separation events occur when stages or strap-on boosters separate after use, when the payload fairing separates prior to orbital insertion, or when used, a launch escape system which separates after the early phase of a launch. Pyrotechnic fasteners, or in some cases pneumatic systems like on the Falcon 9 Full Thrust, are typically used to separate rocket stages. Two-stage-to-orbit A two-stage-to-orbit (TSTO) or two-stage rocket launch vehicle is a spacecraft in which two distinct stages provide propulsion consecutively in order to achieve orbital velocity. It is intermediate between a three-stage-to-orbit launcher and a hypothetical single-stage-to-orbit (SSTO) launcher.[citation needed] Three-stage-to-orbit The three-stage-to-orbit launch system is a commonly used rocket system to attain Earth orbit. The spacecraft uses three distinct stages to provide propulsion consecutively in order to achieve orbital velocity. It is intermediate between a four-stage-to-orbit launcher and a two-stage-to-orbit launcher. Other designs (in fact, most modern medium- to heavy-lift designs) do not have all three stages inline on the main stack, instead having strap-on boosters for the "stage-0" with two core stages. In these designs, the boosters and first stage fire simultaneously instead of consecutively, providing extra initial thrust to lift the full launcher weight and overcome gravity losses and atmospheric drag. The boosters are jettisoned a few minutes into flight to reduce weight. Four-stage-to-orbit The four-stage-to-orbit launch system is a rocket system used to attain Earth orbit. The spacecraft uses four distinct stages to provide propulsion consecutively in order to achieve orbital velocity. It is intermediate between a five-stage-to-orbit launcher and a three-stage-to-orbit launcher, most often used with solid-propellant launch systems. Other designs do not have all four stages inline on the main stack, instead having strap-on boosters for the "stage-0" with three core stages. In these designs, the boosters and first stage fire simultaneously instead of consecutively, providing extra initial thrust to lift the full launcher weight and overcome gravity losses and atmospheric drag. The boosters are jettisoned a few minutes into flight to reduce weight. Extraterrestrial Rockets Model rockets Multistage model rockets exist in several variants. Usually an engine without delay is used for the lower stage(s), as it ignites directly the engine of the next stage. In principle as upper stage also a bottle rocket may be used, but using such a combination, which is called a boosted bottle rocket, is illegal in many countries. Engines with delay are not suitable for lower stages as delay loads usually do not ignite the next stage. In principle it is possible to launch the next stage of a model rocket electrically either by remote control or by a timer, but this method require some onboard devices, which enlarges the weight and complexity of the rocket model, making it only suitable for larger model rockets. Stage-and-a-half The stage-and-a-half launch system is a rarely used rocket system to attain Earth orbit. A half-stage only jettisons booster engines, compared to a full stage where both fuel tanks and engines are jettisoned. The concept is found in some rockets of the Atlas rocket family where all three engines are ignited on the ground and during flight two of the three engines are jettisoned. This was done because of reliability issues with engine ignition in the 1950s. Ignition of all three engines on the ground allowed for confirmation of the functionality of the engines before lift-off. See also References |
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[SOURCE: https://en.wikipedia.org/w/index.php?title=Non-player_character&action=edit§ion=4] | [TOKENS: 1431] |
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[SOURCE: https://en.wikipedia.org/wiki/JOVIAL] | [TOKENS: 1067] |
Contents JOVIAL JOVIAL is a high-level programming language based on ALGOL 58, specialized for developing embedded systems (specialized computer systems designed to perform one or a few dedicated functions, usually embedded as part of a larger, more complete device, including mechanical parts). It was a major system programming language through the 1960s and 1970s. History JOVIAL was developed as a new "high-order": 1 programming language starting in 1959 by a team at System Development Corporation (SDC) headed by Jules Schwartz to compose software for the electronics of military aircraft. The name JOVIAL is an acronym for Jules' Own Version of the International Algebraic Language; International Algorithmic Language (IAL) was a name proposed originally for ALGOL 58. According to Schwartz, the language was originally called OVIAL, but this was opposed for various reasons. JOVIAL was then suggested, with no meaning attached to the J. Somewhat jokingly it was suggested that the language be named after Schwartz, since he was the meeting chairperson, and this unofficial name stuck. During the 1960s, JOVIAL was a part of the US Military L-project series, particularly the ITT 465L Strategic Air Command Control System (the Strategic Automated Command and Control System (SACCS) project), due to a lack of real-time computing programming languages available. Some 95 percent of the SACCS project, managed by International Telephone & Telegraph (ITT) with software mainly written by SDC, was written in JOVIAL. The software project took two years and fewer than 1,400 programmer years, less than half of the equivalent time in the SAGE L-project. During the late 1970s and early 1980s, the United States Air Force adopted a standardized central processing unit (CPU), the MIL-STD-1750A, and subsequent JOVIAL programs were built for that processor. Several commercial vendors provided compilers and related programming tools to build JOVIAL for processors such as the MIL-STD-1750A, including Advanced Computer Techniques (ACT), TLD Systems, Proprietary Software Systems (PSS), and others. JOVIAL was standardized during 1973 with MIL-STD-1589 and was revised during 1984 with MIL-STD-1589C. It is still used to update and maintain software on older military vehicles and aircraft. There are three dialects in common use: J3, J3B-2, and J73. As of 2010[update], JOVIAL is no longer maintained and distributed by the USAF JOVIAL Program Office (JPO). Software formerly distributed by the JPO is still available through commercial resources at Software Engineering Associates, Inc., (SEA) as are other combinations of host/target processors including Windows, Linux, Mac OS X on PowerPC, SPARC, VAX, 1750A, PowerPC, TI-9989, Zilog Z800x, Motorola 680x0, and IBM System 360, System 370, and System z. Further, DDC-I, which acquired parts of Advanced Computer Techniques, also lists JOVIAL compilers and related tools as of April 2020[update]. Most software implemented in JOVIAL is mission critical, and maintenance is growing more difficult. In December 2014, it was reported that software derived from JOVIAL code produced in the 1960s was involved in a major failure of the United Kingdom's air traffic control infrastructure, and that the agency that uses it, NATS Holdings, was having to train its IT staff in JOVIAL so they could maintain this software, which was not scheduled for replacement until 2016. Influence Languages influenced by JOVIAL include CORAL, SYMPL, Space Programming Language (SPL), and to some extent CMS-2. An interactive subset of JOVIAL called TINT, similar to JOSS was developed in the 1960s. Features JOVIAL includes features not found in standard ALGOL, such as items (now called structures), arrays of items, status variables (now called enumerations) and inline assembly language. It also included provisions for "packed" data within tables. Table packing refers to the allocation of items within an entry to words of storage (bits in a unit of data). This was important with respect to the limited memory and storage of the computing systems of the JOVIAL era. The Communication Pool (COMPOOL) in Jovial is similar to libraries of header files for languages such as PL/I and C. Applications Notable systems using embedded JOVIAL software include: Example The following example is taken from Computer Programming Manual for the JOVIAL (J73) Language.: 12 This example defines a procedure named RETRIEVE which takes an unsigned integer input argument CODE and a floating-point output argument VALUE. It searches the 1000-element array TABCODE for an entry that matches CODE, and then sets the floating-point variable VALUE to the element of array TABVALUE having the same matching array index. If no matching element is found, VALUE is set to −99999.0. References External links |
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[SOURCE: https://en.wikipedia.org/wiki/Onychophora] | [TOKENS: 11762] |
Contents Onychophora Onychophora /ɒnɪˈkɒfərə/ (from Ancient Greek: ονυχής, onyches, "claws"; and φέρειν, pherein, "to carry"), commonly known as velvet worms (for their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus /pəˈrɪpətəs/ (after the first described genus, Peripatus), is a phylum of elongate, soft-bodied, many-legged animals. In appearance they have variously been compared to worms with legs, caterpillars, and slugs. They prey upon other invertebrates, which they catch by ejecting an adhesive slime. Approximately 200 species of velvet worms have been described, although the true number is likely to be much greater. The two extant families of velvet worms are Peripatidae and Peripatopsidae. They show a peculiar distribution, with the peripatids being predominantly equatorial and tropical, while the peripatopsids are all found south of the equator. It is the only phylum within Animalia that is wholly endemic to terrestrial environments, at least among extant members. Velvet worms are generally considered close relatives of the Arthropoda and Tardigrada, with which they form the proposed taxon Panarthropoda. This makes them of palaeontological interest, as they can help reconstruct the ancestral arthropod. Only two fossil species are confidently assigned as onychophorans: Antennipatus from the Late Carboniferous, and Cretoperipatus from the Late Cretaceous, the latter belonging to Peripatidae. In modern zoology, they are known for their mating behaviours and for some species bearing live young. Anatomy and physiology Velvet worms are segmented animals with a flattened cylindrical body cross-section and rows of unstructured body appendages known as oncopods or lobopods ("stub feet"). They reach lengths between 0.1 and 22 cm (0.04–8.66 in) depending on species, with the smallest known being Ooperipatellus nanus and the largest known Mongeperipatus solorzanoi. The number of leg pairs ranges from as few as 13 (in Ooperipatellus nanus) to as many as 43 (in Plicatoperipatus jamaicensis). Their skin consists of numerous, fine transverse rings and is often inconspicuously coloured orange, red or brown, but sometimes also bright green, blue, gold or white, and occasionally patterned with other colours. Segmentation is outwardly inconspicuous, and identifiable by the regular spacing of the pairs of legs and in the regular arrangement of skin pores, excretion organs and concentrations of nerve cells. The individual body sections are largely unspecialised; even the head develops only a little differently from the abdominal segments. Segmentation is apparently specified by the same gene as in other groups of animals, and is activated in each case, during embryonic development, at the rear border of each segment and in the growth zone of the stub feet. Although onychophorans fall within the protostome group, their early development has a deuterostome trajectory (with the mouth and anus forming separately); this trajectory is concealed by the rather sophisticated processes which occur in early development. On the first head segment is a pair of slender antennae, which serve in sensory perception. They probably do not correspond directly to the antennae of the Arthropoda, but perhaps rather with their "lips" or labrum. At their base is a pair of simple eyes, except in a few blind species. In front of these, in many Australian species, are various dimples, whose function is not yet clear. It appears that in at least some species, these serve in the transfer of sperm-cell packages (spermatophores).[citation needed] On the belly side of the second head segment is the labrum, a mouth opening surrounded by sensitive "lips". In the velvet worms, this structure is a muscular outgrowth of the throat, so, despite its name, it is probably not homologous to the labrum of the Arthropoda and is used for feeding. Deep within the oral cavity lie the sharp, crescent-shaped "jaws", or mandibles, which are strongly hardened and resemble the claws of the feet, with which they are serially homologous; early in development, the jaw appendages have a position and shape similar to the subsequent legs. The jaws are divided into internal and external mandibles and their concave surface bears fine denticles. They move backward and forward in a longitudinal direction, tearing apart the prey, apparently moved in one direction by musculature and the other by hydrostatic pressure. The claws are made of sclerotised α-chitin, reinforced with phenols and quinones, and have a uniform composition, except that there is a higher concentration of calcium towards the tip, presumably affording greater strength. The surface of the mandibles is smooth, with no ornamentation. The cuticle in the mandibles (and claws) is distinct from the rest of the body. It has an inner and outer component; the outer component has just two layers (whereas body cuticle has four), and these outer layers (in particular the inner epicuticle) are dehydrated and strongly tanned, affording toughness. On the third head segment, to the left and right of the mouth, are two openings called "oral papillae", with each containing a large, heavily branched slime gland. These slime glands lie roughly in the center of a velvet worm's body and secrete a sort of milky-white slime. The slime is used to both ensnare prey and act as a distraction for defensive purposes. In certain species, an organ connected to the slime gland known as the "slime conductor" is broadened into a reservoir, allowing it to hold pre-produced slime. Velvet worm slime glands and oral papilla are likely modified and repurposed limbs. The glands themselves are probably modified crural glands. All three structures correspond to an evolutionary origin in the leg pairs of the other segments.[citation needed] The Onychophora forcefully squirt glue-like slime[a] from their oral papillae; they do so either in defense against predators or to capture prey. The openings of the glands that produce the slime are in the papillae, a pair of highly modified limbs on the sides of the head below the antennae. Inside, they have a syringe-like system that, by a geometric amplifier, allows for fast squirt using slow muscular contraction. High speed films show the animal expelling two streams of adhesive liquid through a small opening (50–200 microns) at a speed of 3 to 5 m/s (10 to 20 ft/s). The interplay between the elasticity of oral papillae and the fast unsteady flow produces a passive oscillatory motion (30–60 Hz) of the oral papillae. The oscillation causes the streams to cross in mid air, weaving a disordered net; the velvet worms can control only the general direction where the net is thrown. The slime glands themselves are deep inside the body cavity, each at the end of a tube more than half the length of the body. The tube both conducts the fluid and stores it until it is required. The distance that the animal can propel the slime varies; usually it squirts it about a centimetre, but the maximal range has variously been reported to be ten centimetres, or even nearly a foot, although accuracy drops with range. It is not clear to what extent the range varies with the species and other factors. One squirt usually suffices to snare a prey item, although larger prey may be further immobilised by smaller squirts targeted at the limbs; additionally, the fangs of spiders are sometimes targeted. Upon ejection, it forms a net of threads about twenty microns in diameter, with evenly spaced droplets of viscous adhesive fluid along their length. It subsequently dries, shrinking, losing its stickiness, and becoming brittle. Onychophora eat their dried slime when they can, which seems provident, since an onychophoran requires about 24 days to replenish an exhausted slime repository. The slime can account for up to 11% of the organism's dry weight and is 90% water; its dry residue consists mainly of proteins—primarily a collagen-type protein. 1.3% of the slime's dry weight consists of sugars, mainly galactosamine. The slime also contains lipids and the surfactant nonylphenol. Onychophora are the only organisms known to produce this latter substance. It tastes "slightly bitter and at the same time somewhat astringent". The proteinaceous composition accounts for the slime's high tensile strength and stretchiness. The lipid and nonylphenol constituents may serve one of two purposes: They may line the ejection channel, stopping the slime from sticking to the organism when it is secreted; or they may slow the drying process long enough for the slime to reach its target. The stub feet that characterise the velvet worms are conical, baggy appendages of the body, which are internally hollow and have no joints. Although the number of feet can vary considerably between species, their structure is basically very similar. Rigidity is provided by the hydrostatic pressure of their fluid contents, and movement is usually obtained passively by stretching and contraction of the animal's entire body. However, each leg can also be shortened and bent by internal muscles. Due to the lack of joints, this bending can take place at any point along the sides of the leg. In some species, two different organs are found within the feet: On each foot is a pair of retractable, hardened (sclerotised) chitin claws, which give the taxon its scientific name: Onychophora is derived from the Ancient Greek: ονυχής, onyches, "claws"; and φέρειν, pherein, "to carry". At the base of the claws are three to six spiny "cushions" on which the leg sits in its resting position and on which the animal walks over smooth substrates. The claws are used mainly to gain a firm foothold on uneven terrain. Each claw is composed of three stacked elements, like Russian nesting dolls. The outermost is shed during ecdysis, which exposes the next element, which is fully formed and so does not need time to harden before it is used. This distinctive construction identifies many early Cambrian fossils as early offshoots of the onychophoran lineage. The entire body, including the stub feet, is littered with numerous papillae: warty protrusions responsive to touch that carry a mechanoreceptive bristle at the tip, each of which is also connected to further sensory nerve cells lying beneath. The mouth papillae, the exits of the slime glands, probably also have some function in sensory perception. Sensory cells known as "sensills" on the "lips" or labrum respond to chemical stimuli and are known as chemoreceptors. These are also found on the two antennae, which seem to be the velvet worm's most important sensory organs.[citation needed] Except in a few (typically subterranean) species, one simply constructed eye (ocellus) lies behind each antenna, laterally, just underneath the head. This consists of a chitinous ball lens, a cornea and a retina and is connected to the centre of the brain via an optic nerve. The retina comprises numerous pigment cells and photoreceptors; the latter are easily modified flagellated cells, whose flagellum membranes carry a photosensitive pigment on their surface. The rhabdomeric eyes of the Onychophora are thought to be homologous with the median ocelli of arthropods; this would suggest that the last common ancestor of arthropods may have only had median ocelli. However, the innervation shows that the homology is limited: The eyes of Onychophora form behind the antenna, whereas the opposite is true in arthropods. Unlike the arthropods, velvet worms do not possess a rigid exoskeleton. Instead, their fluid-filled body cavity acts as a hydrostatic skeleton, similarly to many distantly related soft-bodied animals that are cylindrically shaped, for example sea anemones and various worms. Pressure of their (near-incompressible) internal bodily fluid on the body wall provides rigidity, and muscles are able to act against it. The body wall consists of a non-cellular outer skin, the cuticula; a single layer of epidermis cells forming an internal skin; and beneath this, usually three layers of muscle, which are embedded in connective tissues. The cuticula is about a micrometer thick and covered with fine villi. In composition and structure, it resembles the cuticula of the arthropods, consisting of α-chitin and various proteins, although not containing collagen. It can be divided into an external epicuticula and an internal procuticula, which themselves consist of exo- and endo-cuticula. This multi-level structure is responsible for the high flexibility of the outer skin, which enables the velvet worm to squeeze itself into the narrowest crevices. Although outwardly water-repellent, the cuticula is not able to prevent water loss by respiration, and, as a result, velvet worms can live only in microclimates with high humidity to avoid desiccation. The surface of the cuticula is scattered with numerous fine papilla, the larger of which carry visible villi-like sensitive bristles. The papillae themselves are covered with tiny scales, lending the skin a velvety appearance (from which the common name is likely derived). It also feels like dry velvet to the touch, for which its water-repellent nature is responsible. Moulting of the skin (ecdysis) takes place regularly, around every 14 days, induced by the hormone ecdysone. The inner surface of the skin bears a hexagonal pattern. At each moult, the shed skin is replaced by the epidermis, which lies immediately beneath it; unlike the cuticula, this consists of living cells. Beneath this lies a thick layer of connective tissue, which is composed primarily of collagen fibres aligned either parallel or perpendicular to the body's longitudinal axis. The colouration of Onychophora is generated by a range of pigments.[clarification needed] The solubility of these pigments is a useful diagnostic character: in all arthropods and tardigrades, the body pigment is soluble in ethanol. This is also true for the Peripatidae, but in the case of the Peripatopsidae, the body pigment is insoluble in ethanol. Within the connective tissue lie three continuous layers of unspecialised smooth muscular tissue. The relatively thick outer layer is composed of annular muscles, and the similarly voluminous inner layer of longitudinal muscles. Between them lie thin diagonal muscles that wind backward and forward along the body axis in a spiral. Between the annular and diagonal muscles exist fine blood vessels, which lie below the superficially recognisable transverse rings of the skin and are responsible for the pseudo-segmented markings. Beneath the internal muscle layer lies the body cavity. In cross-section, this is divided into three regions by so-called dorso-ventral muscles, which run from the middle of the underbelly through to the edges of the upper side: a central midsection and on the left and right, two side regions that also include the legs.[citation needed] The body cavity is known as a "pseudocoel", or haemocoel. Unlike a true coelom, a pseudocoel is not fully enclosed by a cell layer derived from the embryonic mesoderm. A coelom is, however, formed around the gonads and the waste-eliminating nephridia. As the name haemocoel suggests, the body cavity is filled with a blood-like liquid in which all the organs are embedded; in this way, they can be easily supplied with nutrients circulating in the blood. This liquid is colourless as it does not contain pigments; for this reason, it serves only a limited role in oxygen transport. Two different types of blood cells (or haemocytes) circulate in the fluid: Amoebocytes and nephrocytes. The amoebocytes probably function in protection from bacteria and other foreign bodies; in some species, they also play a role in reproduction. Nephrocytes absorb toxins or convert them into a form suitable for elimination by the nephridia.[citation needed] The haemocoel is divided by a horizontal partition, the diaphragm, into two parts: The pericardial sinus along the back and the perivisceral sinus along the belly. The former encloses the tube-like heart, and the latter, the other organs. The diaphragm is perforated in many places, enabling the exchange of fluids between the two cavities.[citation needed] The heart itself is a tube of annular muscles consisting of epithelial tissues, with two lateral openings (ostia) per segment. While it is not known whether the rear end is open or closed, from the front, it opens directly into the body cavity. Since there are no blood vessels, apart from the fine vessels running between the muscle layers of the body wall and a pair of arteries that supply the antennae, this is referred to as an open circulation.[citation needed] The timing of the pumping procedure can be divided into two parts: Diastole and systole. During diastole, blood flows through the ostia from the pericardial sinus (the cavity containing the heart) into the heart. When the systole begins, the ostia close and the heart muscles contract inwards, reducing the volume of the heart. This pumps the blood from the front end of the heart into the perivisceral sinus containing the organs. In this way, the various organs are supplied with nutrients before the blood finally returns to the pericardial sinus via the perforations in the diaphragm. In addition to the pumping action of the heart, body movements also influence circulation.[citation needed] Oxygen uptake occurs to an extent via simple diffusion through the entire body surface, with the coxal vesicles on the legs possibly being involved in some species. However, of most importance is gas exchange via fine unbranched tubes, the tracheae, which draw oxygen from the surface deep into the various organs, particularly the heart. The walls of these structures, which are less than three micrometers thick in their entirety, consist only of an extremely thin membrane through which oxygen can easily diffuse. The tracheae originate at tiny openings, the spiracles, which themselves are clustered together in dent-like recesses of the outer skin, the atria. The number of "tracheae bundles" thus formed is on average around 75 bundles per body segment; they accumulate most densely on the back of the organism.[citation needed] Unlike the arthropods, the velvet worms are unable to control the openings of their tracheae; the tracheae are always open, entailing considerable water loss in arid conditions. Water is lost twice as fast as in earthworms and forty times faster than in caterpillars. For this reason, velvet worms are dependent upon habitats with high air humidity. Oxygen transport is helped by the oxygen carrier hemocyanin. The digestive tract begins slightly behind the head, the mouth lying on the underside a little way from the frontmost point of the body. Here, prey can be mechanically dismembered by the mandibles with their covering of fine toothlets. Two salivary glands discharge via a common conductor into the subsequent "throat", which makes up the first part of the front intestine. The saliva that they produce contains mucus and hydrolytic enzymes, which initiate digestion in and outside the mouth. The throat itself is very muscular, serving to absorb the partially liquified food and to pump it, via the oesophagus, which forms the rear part of the front intestine, into the central intestine. Unlike the front intestine, this is not lined with a cuticula but instead consists only of a single layer of epithelial tissue, which does not exhibit conspicuous indentation as is found in other animals. On entering the central intestine, food particles are coated with a mucus-based peritrophic membrane, which serves to protect the lining of the intestine from damage by sharp-edged particles. The intestinal epithelium secretes further digestive enzymes and absorbs the released nutrients, although the majority of digestion has already taken place externally or in the mouth. Indigestible remnants arrive in the rear intestine, or rectum, which is once again lined with a cuticula and which opens at the anus, located on the underside near to the rear end.[citation needed] In almost every segment is a pair of excretory organs called nephridia, which are derived from coelom tissue. Each consists of a small pouch that is connected, via a flagellated conductor called a nephridioduct, to an opening at the base of the nearest leg known as a nephridiopore. The pouch is occupied by special cells called podocytes, which facilitate ultrafiltration of the blood through the partition between haemocoelom and nephridium. The composition of the urinary solution is modified in the nephridioduct by selective recovery of nutrients and water and by isolation of poison and waste materials, before it is excreted to the outside world via the nephridiopore. The most important nitrogenous excretion product is the water-insoluble uric acid; this can be excreted in solid state, with very little water. This so-called uricotelic excretory mode represents an adjustment to life on land and the associated necessity of dealing economically with water.[citation needed] A pair of former nephridia in the head were converted secondarily into the salivary glands, while another pair in the final segment of male specimens now serve as glands that apparently play a role in reproduction. Both sexes possess pairs of gonads, opening via a channel called a gonoduct into a common genital opening, the gonopore, which is located on the rear ventral side. Both the gonads and the gonoduct are derived from true coelom tissue.[citation needed] In females, the two ovaries are joined in the middle and to the horizontal diaphragm. The gonoduct appears differently depending on whether the species is live-bearing or egg-laying. In live-bearing species, each exit channel divides into a slender oviduct and a roomy "womb", the uterus, in which the embryos develop. The single vagina, to which both uteri are connected, runs outward to the gonopore. In egg-laying species, whose gonoduct is uniformly constructed, the genital opening lies at the tip of a long egg-laying apparatus, the ovipositor. The females of many species also possess a sperm repository called the receptacle seminis, in which sperm cells from males can be stored temporarily or for longer periods.[citation needed] Males possess two separate testes, along with the corresponding sperm vesicle (the vesicula seminalis) and exit channel (the vasa efferentia). The two vasa efferentia unite to a common sperm duct, the vas deferens, which in turn widens through the ejaculatory channel to open at the gonopore. Directly beside or behind this lie two pairs of special glands, which probably serve some auxiliary reproductive function; the rearmost glands are also known as anal glands. A penis-like structure has so far been found only in males of the genus Paraperipatus but has not yet been observed in action.[citation needed] There are different mating procedures: in some species males deposit their spermatophore directly into the female's genital opening, while others deposit it on the female's body, where the cuticle will collapse, allowing the sperm cells to migrate into the female. There are also Australian species where the male place their spermatophore on top of their head, which is then pressed against the female's genitals. In these species the head have elaborate structures like spikes, spines, hollow stylets, pits, and depressions, whose purpose is to either hold the sperm and / or assist in the sperm transfer to the female. The males of most species also secrete a pheromone from glands on the underside of the legs to attract females. Distribution and habitat Velvet worms are found in the tropics and in the temperate zone of the Southern Hemisphere. Members of the family Peripatidae are found the tropical regions of South America, Central America, the Caribbean islands, Gabon, Northeast India, and Southeast Asia. Meanwhile, members of Peripatopsidae are found Chile, Australia, Southern Africa, New Guinea, and New Zealand. One deviation is the South African Peripatopsis capensis. This animal was inadvertently introduced to Santa Cruz Island in the Galapagos and co-occurs with native species. When looking at velvet worms as a whole, the majority of are found in Australia and South America. Extinct onychophorans have been discovered in parts of the Northern Hemisphere which are currently uninhabited by the group. While the onychophoran affinities of Succinipatopsis and Helenodora of are questioned, others like the Antennipatus are at a minimum close relatives of crown-group Onychophora (Peripatidae and Peripatopsidae). This indicates that velvet worms were far more widespread in the past, but subsequently died off for unknown reasons. Velvet worms always sparsely occupy the habitats where they are found: they are rare among the fauna of which they are a part.[citation needed] All extant velvet worms are terrestrial (land-living) and prefer dark environments with high air humidity. They are found particularly in the rainforests of the tropics and temperate zones, where they live among moss cushions and leaf litter, under tree trunks and stones, in rotting wood or in termite tunnels. They also occur in unforested grassland, if there exist sufficient crevices in the soil into which they can withdraw during the day,[citation needed] and in caves. Two species live in caves, a habitat to which their ability to squeeze themselves into the smallest cracks makes them exceptionally well-adapted and in which constant living conditions are guaranteed. Since the essential requirements for cave life were probably already present prior to the settlement of these habitats, this may be described as exaptation.[citation needed] Some species of velvet worms are able to occupy human-modified land-uses, such as cocoa and banana plantations in South America and the Caribbean, but for others, conversion of rainforests is likely one of the most important threats to their survival[citation needed] (see Conservation).[clarification needed] Velvet worms are photophobic: They are repelled by bright light sources. Because the danger of desiccation is greatest during the day and in dry weather, it is not surprising that velvet worms are usually most active at night and during rainy weather. Under cold or dry conditions, they actively seek out crevices in which they shift their body into a resting state. Behaviour Velvet worms move in a slow and gradual motion that makes them difficult for prey to notice. Their trunk is raised relatively high above the ground, and they walk with non-overlapping steps. To move from place to place, the velvet worm crawls forward using its legs; unlike in arthropods, both legs of a pair are moved simultaneously. The claws of the feet are used only on hard, rough terrain where a firm grip is needed; on soft substrates, such as moss, the velvet worm walks on the foot cushions at the base of the claws.[citation needed] Actual locomotion is achieved less by the exertion of the leg muscles than by local changes of body length. This can be controlled using the annular and longitudinal muscles. If the annular muscles are contracted, the body cross-section is reduced, and the corresponding segment lengthens; this is the usual mode of operation of the hydrostatic skeleton as also employed by other worms. Due to the stretching, the legs of the segment concerned are lifted and swung forward. Local contraction of the longitudinal muscles then shortens the appropriate segment, and the legs, which are now in contact with the ground, are moved to the rear. This part of the locomotive cycle is the actual leg stroke that is responsible for forward movement. The individual stretches and contractions of the segments are coordinated by the nervous system such that contraction waves run the length of the body, each pair of legs swinging forward and then down and rearward in succession. Macroperipatus can reach speeds of up to four centimetres per second, although speeds of around 6 body-lengths per minute are more typical. The body gets longer and narrower as the animal picks up speed; the length of each leg also varies during each stride. The brains of Onychophora, though small, are very complex; consequently, the organisms are capable of rather sophisticated social interactions. Behaviour may vary from genus to genus, so this article reflects the most-studied genus, Euperipatoides. The Euperipatoides form social groups of up to fifteen individuals, usually closely related, which will typically live and hunt together. Groups usually live together; in drier regions an example of a shared home would be the moist interior of a rotting log. Group members are extremely aggressive towards individuals from other logs. Dominance is achieved through aggression and maintained through submissive behaviour. After a kill, the dominant female always feeds first, followed in turn by the other females, then males, then the young. When assessing other individuals, individuals often measure one another up by running their antennae down the length of the other individual. Once hierarchy has been established, pairs of individuals will often cluster together to form an "aggregate"; this is fastest in male-female pairings, followed by pairs of females, then pairs of males. Social hierarchy is established by a number of interactions: Higher-ranking individuals will chase and bite their subordinates while the latter are trying to crawl on top of them. Juveniles never engage in aggressive behaviour, but climb on top of adults, which tolerate their presence on their backs. Hierarchy is quickly established among individuals from a single group, but not among organisms from different groups; these are substantially more aggressive and very rarely climb one another or form aggregates. Individuals within an individual log are usually closely related; especially so with males. This may be related to the intense aggression between unrelated females. Velvet worms are ambush predators, hunting only by night, and are able to capture animals at least their own size, although capturing a large prey item may take almost all of their mucus-secreting capacity. They feed on almost any small invertebrates, including woodlice (Isopoda), termites (Isoptera), crickets (Gryllidae), book/bark lice (Psocoptera), cockroaches (Blattidae), millipedes and centipedes (Myriapoda), spiders (Araneae), various worms, and even large snails (Gastropoda). Depending on their size, they eat on average every one to four weeks. They are considered to be ecologically equivalent to centipedes (Chilopoda). The most energetically favourable prey are two-fifths the size of the hunting onychophoran. Ninety percent of the time involved in eating prey is spent ingesting it; re-ingestion of the slime used to trap the insect is performed while the onychophoran locates a suitable place to puncture the prey, and this phase accounts for around 8% of the feeding time, with the remaining time evenly split between examining, squirting, and injecting the prey. In some cases, chunks of the prey item are bitten off and swallowed; indigestible components take around 18 hours to pass through the digestive tract. Onychophora probably do not primarily use vision to detect their prey; although their tiny eyes do have a good image-forming capacity, their forward vision is obscured by their antennae; their nocturnal habit also limits the utility of eyesight. Air currents, formed by prey motion, are thought to be the primary mode of locating prey; the role of scent, if any, is unclear. Because it takes so long to ingest a prey item, hunting mainly happens around dusk; the onychophorans will abandon their prey at sunrise. This predatory way of life is probably a consequence of the velvet worm's need to remain moist: Due to the continual risk of desiccation, often only a few hours per day are available for finding food. This leads to a strong selection for a low cost-benefit ratio, which cannot be achieved with a herbivorous diet.[citation needed] Velvet worms literally creep up on their prey, with their smooth, gradual and fluid movement escaping detection. Once they reach their prey, they touch it very softly with their antennae to assess its size and nutritional value. After each poke, the antenna is hastily retracted to avoid alerting the prey. This investigation may last anywhere upwards of ten seconds, until the velvet worm makes a decision as to whether to attack it, or until it disturbs the prey and the prey flees. Hungry Onychophora spend less time investigating their prey and are quicker to apply their slime. Once slime has been squirted, Onychophora are determined to pursue and devour their prey, in order to recoup the energy investment. They have been observed to spend up to ten minutes searching for removed prey, after which they return to their slime to eat it. In the case of smaller prey, they may opt not to use slime at all. Subsequently, a soft part of the prey item (usually a joint membrane in arthropod prey) is identified, punctured with a bite from the jaws, and injected with saliva. This kills the prey very quickly and begins a slower process of digestion. While the onychophoran waits for the prey to digest, it salivates on its slime and begins to eat it (and anything attached to it). It subsequently tugs and slices at the earlier perforation to allow access to the now-liquefied interior of its prey. The jaws operate by moving backwards and forwards along the axis of the body (not in a side-to-side clipping motion as in arthropods), conceivably using a pairing of musculature and hydrostatic pressure. The pharynx is specially adapted for sucking, to extract the liquefied tissue; the arrangement of the jaws about the tongue and lip papillae ensures a tight seal and the establishment of suction. In social groups, the dominant female is the first to feed, not permitting competitors access to the prey item for the first hour of feeding. Subsequently, subordinate individuals begin to feed. The number of males reaches a peak after females start to leave the prey item. After feeding, individuals clean their antennae and mouth parts before re-joining the rest of their group. Almost all velvet worms reproduce sexually. The sole exception is Epiperipatus imthurni, which have no males and reproduce by parthenogenesis. In most cases, velvet worms are sexually dimorphic. Females are usually larger than males and can often have more legs. All velvet worms have internal fertilization, though the way this is done varies widely. For most of them, a package of sperm cells called the spermatophore is placed into female's vagina. In many species, fertilization happens only once. Because of this, copulation can happen before reproductive organs are even fully developed. In cases like this, sperm cells are kept in a special reservoir where they can survive for longer. The detailed process by which this is achieved is in most cases still unknown, a true penis having been observed only in species of the genus Paraperipatus. In many Australian species, there exist dimples or special dagger- or axe-shaped structures on the head; the male of Florelliceps stutchburyae presses a long spine against the female's genital opening and probably positions its spermatophore there in this way. During the process, the female supports the male by keeping him clasped with the claws of her last pair of legs. The mating behavior of two species of the genus Peripatopsis is particularly curious. Here, the male places two-millimetre spermatophores on the back or sides of the female. Amoebocytes from the female's blood collect on the inside of the deposition site, and both the spermatophore's casing and the body wall on which it rests are decomposed via the secretion of enzymes. This releases the sperm cells, which then move freely through the haemocoel, penetrate the external wall of the ovaries and finally fertilize the ova. Why this self-inflicted skin injury does not lead to bacterial infections is not yet understood (though likely related to the enzymes used to deteriorate the skin or facilitate the transfer of viable genetic material from male to female). Velvet worms are found in egg-laying (oviparous), egg-live-bearing (ovoviviparous) and live-bearing (viviparous) forms. In a recent peer-reviewed paper published in the "Journal of Zoology", researchers discovered that certain species of Peripatus exhibit a unique form of parental care. Unlike most invertebrates, where parental involvement is minimal, female Peripatus were observed actively guarding their eggs and even providing protection to their offspring after hatching. This finding challenges the conventional understanding of reproductive behavior in invertebrates and highlights the diversity of parenting strategies in the animal kingdom. A female can have between 1 and 23 offspring per year; development from fertilized ovum to adult takes between 6 and 17 months and does not have a larval stage. This is probably also the original mode of development. Velvet worms have been known to live for up to six years. Ecology The velvet worm's important predators are primarily various spiders and centipedes, along with rodents and birds, such as, in Central America, the clay-coloured thrush (Turdus grayi). In South America, Hemprichi's coral snake (Micrurus hemprichii) feeds almost exclusively on velvet worms. For defence, some species roll themselves reflexively into a spiral, while they can also fight off smaller opponents by ejecting slime. Various mites (Acari) are known to be ectoparasites infesting the skin of the velvet worm. Skin injuries are usually accompanied by bacterial infections, which are almost always fatal.[citation needed] Phylogeny Living velvet worms are divided into two families: Peripatidae and Peripatopsidae. These diverged around 274 million years ago during the Late Devonian and have since diversified. Within Peripatidae, the genera Eoperipatus (found in Southeast Asia) and Mesoperipatus (found in Gabon) were the most basal, while the rest of the group is found in tropical regions of the Americas. On the other hand, Peritpatopsidae can be divided into two main clades. One has members in Southern Africa and Chile, while the others live in Australasia. Below is a genus-level cladogram of velvet worms. This phylogeny does not analyze every species and lumps most peripatids into Neopatida, as many Peripatidae genera are paraphyletic. As of 2023, there are around 232 total living species, meaning this phylogeny should eventually be updated. Paraperipatus Peripatopsidae sp. MCZ 131371 & MCZ 141416 Ooperipatus Phallocephale Aethrikos Euperipatoides Occiperipatoides Kumbadjena Peripatoides Diemenipatus Tasmanipatus Ooperipatellus Peripatopsis Metaperipatus Opisthopatus Eoperipatus Mesoperipatus Neopatida In their present forms, the velvet worms are probably very closely related to the arthropods, a very extensive taxon that incorporates, for instance, the crustaceans, insects, and arachnids. They share, among other things, an exoskeleton consisting of α-chitin and non-collagenous proteins; gonads and waste-elimination organs enclosed in true coelom tissue; an open blood system with a tubular heart situated at the rear; an abdominal cavity divided into pericardial and perivisceral cavities; respiration via tracheae; and similar embryonic development. Segmentation, with two body appendages per segment, is also a shared feature. However, the antennae, mandibles, and oral papillae of velvet worms are probably not homologous to the corresponding features in arthropods; i.e., they probably developed independently. Another closely related group are the comparatively obscure water bears (Tardigrada); however, due to their very small size, water bears have no need for—and hence lack—blood circulation and separate respiratory structures: shared characteristics that support common ancestry of velvet worms and arthropods. Together, the velvet worms, arthropods, and water bears form a monophyletic taxon, the Panarthropoda, i.e., the three groups collectively cover all descendants of their last common ancestor. Due to certain similarities of form, the velvet worms were usually grouped with the water bears to form the taxon Protoarthropoda. This designation would imply that both velvet worms and water bears are not yet as highly developed as the arthropods. Modern systematic theories reject such conceptions of "primitive" and "highly developed" organisms and instead consider exclusively the historical relationships among the taxa. These relationships are not as yet fully understood, but it is considered probable that the velvet worms' sister groups form a taxon designated Tactopoda, thus: Velvet worms (Onychophora) Water bears (Tardigrada) Arthropods (Arthropoda) For a long time, velvet worms were also considered related to the annelids. They share, among other things, a worm-like body; a thin and flexible outer skin; a layered musculature; paired waste-elimination organs; as well as a simply constructed brain and simple eyes. Decisive, however, was the existence of segmentation in both groups, with the segments showing only minor specialisation. The parapodia appendages found in annelids therefore correspond to the stump feet of the velvet worms. Within the Articulata hypothesis developed by Georges Cuvier, the velvet worms therefore formed an evolutionary link between the annelids and the arthropods: worm-like precursors first developed parapodia, which then developed further into stub feet as an intermediate link in the ultimate development of the arthropods' appendages. Due to their structural conservatism, the velvet worms were thus considered "living fossils". This perspective was expressed paradigmatically in the statement by the French zoologist A. Vandel: Modern taxonomy does not study criteria such as "higher" and "lower" states of development or distinctions between "main" and "side" branches—only family relationships indicated by cladistic methods are considered relevant. From this point of view, several common characteristics still support the Articulata hypothesis — segmented body; paired appendages on each segment; pairwise arrangement of waste-elimination organs in each segment; and above all, a rope-ladder-like nervous system based on a double nerve strand lying along the belly. An alternative concept, most widely accepted today, is the so-called Ecdysozoa hypothesis. This places the annelids and Panarthropoda in two very different groups: the former in the Lophotrochozoa and the latter in the Ecdysozoa. Mitochondrial gene sequences also provide support for this hypothesis. Proponents of this hypothesis assume that the aforementioned similarities between annelids and velvet worms either developed convergently or were primitive characteristics passed unchanged from a common ancestor to both the Lophotrochozoa and Ecdysozoa. For example, in the first case, the rope-ladder nervous system would have developed in the two groups independently, while in the second case, it is a very old characteristic, which does not imply a particularly close relationship between the annelids and Panarthropoda. The Ecdysozoa concept divides the taxon into two, the Panarthropoda into which the velvet worms are placed, and the sister group Cycloneuralia, containing the threadworms (Nematoda), horsehair worms (Nematomorpha) and three rather obscure groups: the mud dragons (Kinorhyncha); penis worms (Priapulida); and brush-heads (Loricifera). Panarthropoda (arthropods, velvet worms, water bears) Cycloneuralia (threadworms, horsehair worms, and others) Lophotrochozoa (annelids, molluscs, and others) (other Protostomes) Particularly characteristic of the Cycloneuralia is a ring of "circumoral" nerves around the mouth opening, which the proponents of the Ecdysozoa hypothesis also recognise in modified form in the details of the nerve patterns of the Panarthropoda. Both groups also share a common skin-shedding mechanism (ecdysis) and molecular biological similarities. One problem of the Ecdysozoa hypothesis is the velvet worms' subterminal position of their mouths: Unlike in the Cycloneuralia, the mouth is not at the front end of the body, but lies further back, under the belly. However, investigations into their developmental biology, particularly regarding the development of the head nerves, suggest that this was not always the case, and that the mouth was originally terminal (situated at the tip of the body). This is supported by the fossil record. The "stem-group arthropod" hypothesis is very widely accepted, but some trees suggest that the onychophorans may occupy a different position; their brain anatomy is more closely related to that of the chelicerates than to any other arthropod. The modern velvet worms form a monophyletic group, incorporating all the descendants of their common ancestor. Important common derivative characteristics (synapomorphies) include, for example, the mandibles of the second body segment and the oral papillae and associated slime glands of the third; nerve strands extending along the underside with numerous cross-linkages per segment; and the special form of the tracheae. By 2011, some 180 modern species, comprising 49 genera, had been described; the actual number of species is probably about twice this. According to more recent study, 82 species of Peripatidae and 115 species of Peripatopsidae have been described thus far. However, among the 197 species, 20 are nomina dubia, due to major taxonomic inconsistencies. The best-known is the type genus Peripatus, which was described as early as 1825 and which, in English-speaking countries, stands representative for all velvet worms. All genera are assigned to one of two families, the distribution ranges of which do not overlap but are separated by arid areas or oceans: As of February 2025, velvet worms have had only two nuclear genomes sequenced. These are of Euperipatoides rowelli (a peripatopsid) and Epiperipatus broadwayi (a peripatid). The first one is highly fragmented, while the second is less so, but still needs improvement. Velvet worms seem to display genome gigantism, with the more complete assembly (E. broadwayi) having an size of 5.60 giga-base pairs. Around 70.92% of its genome are repeat sequences, something that contributes to the bulk of its size. While less substantial, it also has very large introns, or parts of a gene that do not become proteins. Evolution Due to being soft-bodied, onychophorans need excellent conditions to fossilize. However, even when this happens, their fossils can be subject to taphonomic bias. Experiments were done with modern velvet worms to analyze their decomposition in various saline solutions. The study also investigated whether they experienced something called stemward slippage. In this phenomenon, animals are falsely categorized as more primitive due to the decay of certain features. The researchers found that different features decayed at significantly different rates. Salinity and time of moult had little effect on decay, and the way things decomposed remained the same for different species (though it could happen at different speeds). Before any degradation, velvet worms flex into a S, U, or circular shape. Most flexing happens in the first 24 hours, but the process can continue for around two more days. In the early stages of decay, the epidermis and outer cuticle separate, causing a bloated appearance. The elongates while increasing in width by around 10–30%. The limbs do the same, increasing in length and width by around 10–25%. Around the same time, the internal organs begin to degrade. This eventually culminates in the gut rupturing, destroying the other organs. In later stages of decay, the body cuticle shrinks close to its original size. A similar trend was found with the limbs, but it was just short of being statistically significant. It's around this time that many external features begin to deteriorate. These include the dermal papillae, leg rings, anus, gonopore, antenna, slime papillae, and eventually eyes. Interestingly, the dermal papillae on the trunk disappear faster than those on the limbs. Even as decay progresses, the body is still recognizable. This stops once the outer cuticle finally ruptures. After that, the animal's anatomy is extremely difficult to interpret. At this stage, the only identifiable features would be the chitinous jaws and claws. Onychophorans are unlikely to experience any stemward slippage since their defining features (jaws, feet, and slime papillae) are generally decay-resistant. However, decomposition has a significant impact on fossil anatomy. For starters, the preserved body outline is probably somewhat inaccurate, as this gets bloated in the decay process. A similar thing happens with the limbs, so this needs to be accounted for when analyzing locomotion and/or leg length. While fossilized onychophorans can appear to display patterning, these aren't true to life. pigment granules are one of the first things to degrade and can easily move around in the body. Another finding is that characters such as internal organs or the body cavity are highly unlikely to fossilize. If these appear preserved in a fossil, they should be treated with skepticism, especially if they're unmineralized. When it comes to placement of the mouth, even moderate decay makes it hard to tell if it's at the front or underside of the head. Additionally, fossils that lack decay-resistant features probably lacked them in life. This is even more plausible if the fossil preserves decay-prone features, as their presence indicates a better level of preservation. For example, an onychophoran (or related animal) with eyes but no claws likely never had them. Certain fossils from the Early Cambrian bear a striking resemblance to the velvet worms. These fossils, known collectively as lobopodians, were an evolutionary grade that gave rise to arthropods, tardigrades, onychophorans, and the extinct radiodonts. How different lobopodians are related varies from study to study. However, with the exception of a single paper, Antennacanthopodia is the only animal to be confidently viewed as a close onychophoran relative. Antennacanthopodia lived during the Cambrian Stage 3 and possessed a variety of onychophoran traits: stubby lobopods, spinous foot pads, an annulated body, and small eyes behind the main antennae. An obvious difference from onychophorans was that the animal had not one, but two pairs of antennae. These secondary antennae were shorter than the first pair and thought to be homologous with either the slime papillae or jaws of velvet worms. When Onychophora first arose or moved onto land is currently unknown. However, it could have plausibly happened between the Ordovician and Silurian – approximately 490 to 430 million years ago – via the intertidal zone. The earliest potential onychophoran, Helenodora, originates from the Mid Pennsylvanian Mazon Creek lagerstätte in the United States. Originally described in 1980, Helenodora was long regarded as the earliest known onychophoran. This changed in 2016 when a paper by Murdock et al. doubted its affinity. Based on the absence of many decay-resistant features (claws, jaws, slime papillae) and unclear ecology (Carbotubulus, a late-surviving aquatic lobopodian, was found in the same formation), the authors of this study placed Helenodora as a basal lobopodian most closely related to Paucipodia. The earliest definite onychophoran is the French Antennipatus from a Stephanian (Late Pennsylvanian) Lagerstätte in Montceau-les-Mines. This animal had a ventral (bottom facing) mouth, rings of dermal papillae on its trunk and limbs, and was at least somewhat terrestrial because of its slime papillae. However, due to the way it was preserved, it is unknown if Antennipatus belonged to the stem or crown group of the two living families of velvet worm (Peripatidae and Peripatopsidae). Based on molecular dating, crown-group onychophorans diverged around 376 million years ago in the Late Devonian. This estimation happens regardless if Antennipatus is used to constrain the divergence date, or if no calibration is done at all. The earliest known crown-group onychophoran, Cretoperipatus, is known from multiple specimens in Burmese amber. All are from the same general location and date to a maximum age of around 98.79 million years ago (the earliest Cenomanian of the Late Cretaceous). Based on its morphology, Cretoperipatus was early-diverging member of Peripatidae, most closely related to the Asian genera Eoperipatus and Typhloperipatus. Despite being preserved in amber, the affinities of the Cenozoic Tertiapatus and Succinipatopsis are surrounded in controversy. Some sources consider them to be onychophorans, while others dismiss this. Ultimately, these animals should be reanalyzed to better grasp their position on the tree of life. Conservation status The global conservation status of velvet worm species is difficult to estimate; many species are only found their type locality (the location at which they were first observed and described). The collection of reliable data is also hindered by velvet worms' low population densities, their typically nocturnal behavior, and possibly as-yet undocumented seasonal influences and sexual dimorphism. To date, the only onychophorans evaluated by the IUCN are: The primary threat to velvet worms comes from destruction and fragmentation of their habitat due to industrialisation, draining of wetlands, and slash-and-burn agriculture. As mentioned above, many species also have naturally low population densities and closely restricted geographic ranges. As a result, localized disturbances of important ecosystems could lead to the extinction of entire populations or species. Collection of specimens for universities or research institutes also plays a role on a local scale. There is a very pronounced difference in the protection afforded to velvet worms between regions: in some countries, such as South Africa, there are restrictions on both collecting and exporting, while in others, such as Australia, only export restrictions exist. Many countries offer no specific safeguards at all. Tasmania has a protection program that is unique worldwide: one region of forest has its own velvet worm conservation plan tailored to a particular species (Tasmanipatus barretti). Footnotes References External links |
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Contents The Independent The Independent is a British online newspaper. It was established in 1986 as a national morning printed paper. Nicknamed the Indy, it began as a broadsheet and changed to compact format in 2003. The last printed edition was published on Saturday 26 March 2016, leaving only the online edition. The Independent won the Brand of the Year Award in The Drum Awards for Online Media 2023. History Launched in 1986, the first issue of The Independent was published on 7 October in broadsheet format. It was produced by Newspaper Publishing plc and created by Andreas Whittam Smith, Stephen Glover and Matthew Symonds. All three partners were former journalists at The Daily Telegraph who had left the paper towards the end of Lord Hartwell's ownership. Marcus Sieff was the first chairman of Newspaper Publishing, and Whittam Smith took control of the paper. The paper was created at a time of a fundamental change in British newspaper publishing. Rupert Murdoch was challenging long-accepted practices of the print unions and ultimately defeated them in the Wapping dispute. Consequently, production costs could be reduced which created openings for more competition. As a result of controversy around Murdoch's move to Wapping, the plant was effectively having to function under siege from sacked print workers picketing outside. The Independent attracted some of the staff from the two Murdoch broadsheets who had chosen not to move to his company's new headquarters. Launched with the advertising slogan "It is. Are you?", and challenging both The Guardian for centre-left readers and The Times as the newspaper of record, The Independent reached a circulation of more than 400,000 by 1989. [citation needed] Competing in a moribund market, The Independent sparked a general freshening of newspaper design as well as, within a few years, a price war in the market sector. When The Independent launched The Independent on Sunday in 1990, sales were less than anticipated, partly due to the launch of the Sunday Correspondent four months prior, although this direct rival closed at the end of November 1990. Some aspects of production merged with the main paper, although the Sunday paper retained a largely distinct editorial staff. In the 1990s, The Independent was faced with price cutting by the Murdoch titles, and started an advertising campaign accusing The Times and The Daily Telegraph of reflecting the views of their proprietors, Rupert Murdoch and Conrad Black. It featured spoofs of the other papers' mastheads with the words The Rupert Murdoch or The Conrad Black, with The Independent below the main title.[citation needed] Newspaper Publishing had financial problems. A number of other media companies were interested in the paper. Tony O'Reilly's media group and Mirror Group Newspapers (MGN) had bought a stake of about a third each by mid-1994. In March 1995, Newspaper Publishing was restructured with a rights issue, splitting the shareholding into O'Reilly's Independent News & Media (43%), MGN (43%), and Prisa (publisher of El País) (12%). In April 1996, there was another refinancing, and in March 1998, O'Reilly bought the other shares of the company for £30 million, and assumed the company's debt. Brendan Hopkins headed Independent News, Andrew Marr was appointed editor of The Independent, and Rosie Boycott became editor of The Independent on Sunday. Marr introduced a dramatic if short-lived redesign which won critical favour but was a commercial failure, partly as a result of a limited promotional budget. Marr admitted his changes had been a mistake in his book, My Trade. Boycott left in April 1998 to join the Daily Express, and Marr left in May 1998, later becoming the BBC's political editor. Simon Kelner was appointed as the editor. By this time, the circulation had fallen below 200,000. Independent News spent heavily to increase circulation, and the paper went through several redesigns. While circulation increased, it did not approach the level which had been achieved in 1989, or restore profitability. Job cuts and financial controls reduced the morale of journalists and the quality of the product. Ivan Fallon, on the board since 1995 and formerly a key figure at The Sunday Times, replaced Hopkins as head of Independent News & Media in July 2002. By mid-2004, the newspaper was losing £5 million per year. A gradual improvement meant that by 2006, circulation was at a nine-year high. In November 2008, following further staff cuts, production was moved to Northcliffe House, in Kensington High Street, the headquarters of Associated Newspapers. The two newspaper groups' editorial, management and commercial operations remained separate, but they shared services including security, information technology, switchboard and payroll.[citation needed] On 25 March 2010, Independent News & Media sold the newspaper to a new company owned by the family of Russian oligarch Alexander Lebedev for a nominal £1 fee and £9.25 million over the next 10 months, choosing this option over closing The Independent and The Independent on Sunday, which would have cost £28 million and £40 million respectively, due to long-term contracts. Alexander's son Evgeny became chairman of the new company, with Alexander becoming a board director. In 2009, Lebedev had bought a controlling stake in the London Evening Standard. Two weeks later, editor Roger Alton resigned. In July 2011, The Independent's columnist Johann Hari was stripped of the Orwell Prize he had won in 2008 after claims, to which Hari later admitted, of plagiarism and inaccuracy. In January 2012, Chris Blackhurst, editor of The Independent, told the Leveson inquiry that the scandal had "severely damaged" the newspaper's reputation. He nevertheless told the inquiry that Hari would return as a columnist in "four to five weeks". Hari later announced that he would not return to The Independent. Jonathan Foreman contrasted The Independent's reaction to the scandal unfavorably with the reaction of American newspapers to similar incidents such as the Jayson Blair case, which led to resignations of editors, "deep soul-searching", and "new standards of exactitude being imposed". The historian Guy Walters suggested that Hari's fabrications had been an open secret among the newspaper's staff and that their internal inquiry was a "facesaving exercise". The Independent and The Independent on Sunday endorsed "Remain" in the Brexit referendum of 2016. In March 2016, The Independent closed its print edition to become a pure play digital media company. The last printed edition was published on Saturday 26 March 2016. The Independent on Sunday published its last edition on 20 March 2016 and was closed. In 2017, Sultan Muhammad Abuljadayel (full name Sultan Mohamed Anwar Asaad Abuljadayel) about whom very little is known, bought a 30% stake in The Independent. Geordie Greig was appointed The Independent's Editor-in-Chief in January 2023. He oversaw a period of editorial investment. Later that year, Chief Executive of IDNML Zach Leonard moved to the United States as Global COO and President (North America), and former Editor Christian Broughton was appointed Chief Executive. Louise Thomas was appointed US Editor in March 2024. In 2019, The Independent entered a long-term partnership with the Saudi Research & Media Group, who operate under licence the Independent Arabia, Independent Turkish, Independent Persian and Independent Urdu language editions. In September 2020, The Independent launched Independent en Español, a wholly owned and operated Spanish language edition. Content The Independent began publishing as a broadsheet, in a series of celebrated designs. The final version was designed by Carroll, Dempsey and Thirkell following a commission by Nicholas Garland who, along with Alexander Chancellor, was unhappy with designs produced by Raymond Hawkey and Michael McGuiness – on seeing the proposed designs, Chancellor had said "I thought we were joining a serious paper". The first edition was designed and implemented by Michael Crozier, who was Executive Editor, Design and Picture, from pre-launch in 1986 to 1994. From September 2003, the paper was produced in both broadsheet and tabloid-sized versions, with the same content in each. The tabloid edition was termed "compact" to distance itself from the more sensationalist reporting style usually associated with "tabloid" newspapers in the UK, preferring to remain focused on hard news (similarly to the tabloid-size edition of The Times.) After launching in the London area and then in North West England, the smaller format appeared gradually throughout the UK. Soon afterwards, Rupert Murdoch's Times followed suit, introducing its own tabloid-sized version. Prior to these changes, The Independent had a daily circulation of around 217,500,[citation needed] the lowest of any major national British daily, a figure that climbed by 15% as of March 2004 (to 250,000).[citation needed] Throughout much of 2006, circulation stagnated at a quarter of a million. On 14 May 2004, The Independent produced its last weekday broadsheet, having stopped producing a Saturday broadsheet edition in January.[citation needed] The Independent on Sunday published its last simultaneous broadsheet on 9 October 2005, and thereafter followed a compact design until the print edition was discontinued.[citation needed] On 12 April 2005, The Independent redesigned its layout to a more European feel, similar to France's Libération. The redesign was carried out by a Barcelona-based design studio. The weekday second section was subsumed within the main paper, double-page feature articles became common in the main news sections, and there were revisions to the front and back covers. A new second section, "Extra", was introduced on 25 April 2006. It is similar to The Guardian's "G2" and The Times's "Times2", containing features, reportage and games, including sudoku. In June 2007, The Independent on Sunday consolidated its content into a news section which included sports and business, and a magazine focusing on life and culture. On 23 September 2008, the main newspaper became full-color, and "Extra" was replaced by an "Independent Life Supplement" focusing on different themes each day. Three weeks after the acquisition of the paper by Alexander Lebedev and Evgeny Lebedev in 2010, the paper was relaunched with another redesign on 20 April. The new format featured smaller headlines and a new pullout "Viewspaper" section, which contained the paper's comment and feature articles. Following the 2003 switch in format, The Independent became known for its unorthodox and campaigning front pages, which frequently relied on images, graphics or lists rather than traditional headlines and written news content. For example, following the Kashmir earthquake in 2005, it used its front page to urge its readers to donate to its appeal fund, and following the publication of the Hutton Report into the death of British government scientist David Kelly, its front page simply carried the word "Whitewash?" In 2003, the paper's editor, Simon Kelner, was named "Editor of the Year" at the What the Papers Say awards, partly in recognition of, according to the judges, his "often arresting and imaginative front-page designs". In 2008, as he was stepping down as editor, he stated that it was possible to "overdo the formula" and that the style of the paper's front pages perhaps needed "reinvention". Under the subsequent editorship of Chris Blackhurst, the campaigning, poster-style front pages were scaled back in favour of more conventional news stories. The weekday, Saturday and Sunday editions of The Independent all included supplements and pull-out subsections: Daily (Monday to Friday) The Independent: Saturday's The Independent: The Independent on Sunday: The Independent's original website launched in 1996. On 23 January 2008, The Independent relaunched its online edition. The relaunched site introduced a new look, better access to the blog service, priority on image and video content, and additional areas of the site including art, architecture, fashion, gadgets and health. The paper launched podcast programmes such as "The Independent Music Radio Show", "The Independent Travel Guides", "The Independent Sailing Podcasts", and "The Independent Video Travel Guides". From 2009, the website started carrying short video news bulletins provided by the Al Jazeera English news channel. Over the years this developed to the point that the website regularly featured video content in its news reports. Some of this was syndicated and sourced from other news channels and providers, but The Independent gradually increased numbers in its own video team. In addition to putting together short-form video news reports, the website soon began producing its own video and podcast series, including explainers, short documentary 'on the ground' style reports, and lifestyle and culture videos, including since 2017 the award-nominated series Millennial Love, later rebranded Love Lives.[citation needed] In 2014, The Independent launched a sister website, i100, a "shareable" journalism site with similarities to Reddit and Upworthy. It was rebranded in 2016 as Indy100. In late 2020 The Independent launched Independent TV, which saw the title's video offering provided on many formats including on the web browser, in the app, and on Smart TV. In March 2023 The Independent released The Body in the Woods, a feature-length documentary by its Chief International Correspondent, Bel Trew. Political views The Independent is generally described as centrist, centre-left, liberal, and liberal-left. When the paper was established in 1986, the founders intended its political stance to reflect the centre of the British political spectrum and thought that it would attract readers primarily from The Times and The Daily Telegraph. It has been seen as leaning to the left-wing of the political spectrum, making it more a competitor to The Guardian; however, The Independent tends to take a liberal, pro-market stance on economic issues. The Independent on Sunday referred to itself as a "proudly liberal newspaper". The paper has highlighted what it refers to as war crimes being committed by pro-government forces in the Darfur region of Sudan. The paper has been a strong supporter of electoral reform. In 1997, The Independent on Sunday launched a campaign for the decriminalisation of cannabis. Ten years later, it reversed itself, arguing that skunk, the cannabis strain "smoked by the majority of young Britons" in 2007, had become "25 times stronger than resin sold a decade ago". The paper's opinion on the British monarchy has sometimes been described as republican, though it officially identifies as reformist, wishing for a reformed monarchy that "reflects the nation over which it reigns and which is accountable to the people for its activities". Originally, it avoided royal stories, Whittam Smith later saying he thought the British press was "unduly besotted" with the Royal Family and that a newspaper could "manage without" stories about the monarchy. In 2007, Alan Rusbridger, editor of The Guardian, said of The Independent: "The emphasis on views, not news, means that the reporting is rather thin, and it loses impact on the front page the more you do that". In a 12 June 2007 speech, British Prime Minister Tony Blair called The Independent a "viewspaper", saying it "was started as an antidote to the idea of journalism as views not news. That was why it was called the Independent. Today it is avowedly a viewspaper not merely a newspaper". The Independent criticised Blair's comments the following day; it later changed format to include a "Viewspaper" insert in the centre of the regular newspaper, designed to feature most of the opinion columns and arts reviews. A leader published on the day of the 2008 London mayoral election compared the candidates and said that, if the newspaper had a vote, it would vote first for the Green Party candidate, Siân Berry, noting the similarity between her priorities and those of The Independent, and secondly, with "rather heavy heart", for the incumbent, Ken Livingstone. An Ipsos MORI poll estimated that in the 2010 United Kingdom general election, 44% of regular readers voted Liberal Democrat, 32% voted Labour, and 14% voted Conservative, compared to 23%, 29%, and 36%, respectively, of the overall electorate. On the eve of the 2010 general election, The Independent supported the Liberal Democrats, arguing that "they are longstanding and convincing champions of civil liberties, sound economics, international co-operation on the great global challenges and, of course, fundamental electoral reform. These are all principles that this newspaper has long held dear." However, before the 2015 United Kingdom general election, The Independent on Sunday desisted from advising its readers how to vote, writing that "this does not mean that we are a bloodless, value-free news-sheet. We have always been committed to social justice", but the paper recognised that it was up the readers to "make up [their] own mind about whether you agree with us or not". Rather than support a particular party, the paper urged all its reader to vote as "a responsibility of common citizenship". On 4 May 2015, the weekday version of The Independent said that a continuation of the Conservative–Liberal Democrat coalition after the general election would be a positive outcome. At the end of July 2018, The Independent led a campaign they called the "Final Say", a change.org petition by former editor Christian Broughton, for a binding referendum on the Brexit deal between the UK and the European Union. As of October 2018, Independent Arabia was launched. It is published under licence, and owned and managed by Saudi Research and Media Group (SRMG), a major publishing organisation with close ties to the Saudi royal family.[needs update] In the 2024 United Kingdom general election, The Independent endorsed the Labour Party, although added what it termed as a warning that: "Labour must turn its promises into policies that benefit the hardworking and hopeful people of this country". Personnel The Independent: The Independent on Sunday: There have also been various guest editors over the years, such as Elton John on 1 December 2010, The Body Shop's Anita Roddick on 19 June 2003 and U2's Bono in 2006. Longford Prize The Independent sponsors the Longford Prize, meant to recognise those who have helped the lives of current or former prisoners, in memory of Lord Longford. Related publications The Independent on Sunday (IoS) was the Sunday sister newspaper of The Independent. It ceased to exist in 2016, the last edition being published on 20 March. In October 2010, the i, a compact sister newspaper, was launched. The i is a separate newspaper but uses some of the same material. It was later sold to regional newspaper company Johnston Press, becoming that publisher's flagship national newspaper, before being sold again. It currently belongs to Daily Mail and General Trust. In 2024, the paper was rebranded as The i Paper. The online news site indy100 was announced by The Independent in February 2016, to be written by journalists but with stories selected by 'upvotes' from readers. The Independent supported U2 lead singer Bono's Product RED brand by creating The (RED) Independent, an occasional edition that gave half the day's proceeds to the charity. The first edition was in May 2006. Edited by Bono, it drew high sales. A September 2006 edition of The (RED) Independent, designed by fashion designer Giorgio Armani, drew controversy due to its cover shot, showing model Kate Moss in blackface for an article about AIDS in Africa. The Pride List was initially labelled as The Pink List, published by the Independent on Sunday on 6 August 2000. It contained a list of the 48 most prominent LGBT people in the UK. This was resurrected as the Pride List in 2023 and 2024. Awards and nominations The Independent was awarded "National Newspaper of the Year" for 2003 and the Independent on Sunday was awarded "Front Page of the Year" for 2014's "Here is the news, not the propaganda", printed on 5 October 2014. In January 2013, The Independent was nominated for the Responsible Media of the Year award at the British Muslim Awards. The Independent journalists have won a range of British Press Awards, including: See also References External links Media related to The Independent at Wikimedia Commons |
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[SOURCE: https://en.wikipedia.org/wiki/History_of_the_Jews_in_Zambia] | [TOKENS: 3099] |
Contents History of the Jews in Zambia The history of the Jews in Zambia goes back to the early 1900s. Jews were always a small community with a notable role in Zambian history. The history of the Jews in Zambia dates to 1901 when it was still under British Colonial rule. Northern Rhodesia was colonized in the 1890s by the British South Africa Company, otherwise known as BSAC. Initially, Northern Rhodesia was split into North-eastern and North-western Rhodesia. However, the BSAC united them in 1911 to form Northern Rhodesia, which has its capital in Livingstone, near Victoria Falls. Among the population of 1 million people, there were 1,500 white residents in Northern Rhodesia, of whom many were the Jewish settlers. Northern Rhodesia became under British Colonial Rule partially so that the British Government could increase the number of white individuals and settlers in the country, which would contribute to a wider strategy to increase the influence that the British has between Kenya and South Africa. The Jewish settlers were one of the dominant ethnic groups and became highly involved in local politics, with prominent Jewish figures driving the push for Zambian independence and African nationalist rhetoric. Northern Rhodesia's fertile land, World War II, and independence from the British Colonial rule all had a profound impact on both immigration and emigration of Jewish refugees. The Jewish diaspora introduced trade and commerce into the region in both regional and urban areas through cattle trading, ranching, mining, communication networks, storefronts, transport, and butchery, amongst others. The Jewish settlers, whether they are Jewish through origin, birth, marriage, or confession, all formed a small, yet strong community. The Jews in Zambia were a Jewish diaspora cultural and religious settler minority group, which raises concerns about the notion of who is the coloniser, who is the colonised, who is the victim and who is the oppressor. This deems that it can be studied through a postcolonial framework. Following Zambia's independence in 1964, there was a large exodus of Jews and white individuals from the country. In 2022, there remains less than fifty Jews in Zambia. After existence for 130 years as of 15 June 2024 the total of Jews in Zambia numbers 11 Summary Many Jews came to Zambia (previously called Northern Rhodesia) in order to achieve economic prosperity, first settling in Livingstone and Broken Hill. Some of the first Jews in Zambia were prominent in the cattle production and copper mining businesses. Livingstone already had a permanent Jewish congregation of 38 members by 1905, with the first Jewish wedding in Zambia taking place in 1910. Later on, many Zambian Jews achieved great success in the ranching industry and in the iron foundries. 110 Jews lived in Zambia (with a majority of them living in Livingstone and Lusaka) in 1921, and this population increased over the next couple of decades. Some Jewish refugees came to Zambia before and after The Holocaust, with the Jewish population of Zambia peaking at 1,000 to 1,200 in the mid-1950s (by which point "the center of Jewish life had shifted to Lusaka, the copperbelt center of the country"). Many Jews left Zambia and immigrated to other countries in the 1960s, with only 600 Jews remaining in Zambia in 1968. Jews were active and prominent in Zambian politics before Zambia became independent in 1964. The Council for Zambia Jewry was created in Lusaka in 1978 "to oversee Jewish communal activities." This council also "provides assistance to political refugees and the poverty-stricken with medical and financial aid." Only about thirty-five Jews currently live in Zambia, with almost all of them living in Lusaka. The Zambian Jewish community did not have a rabbi for several years by this point in time. One of the more notable Zambian Jews is Simon Zukas, "who played a key role in Zambia's struggle for independence from Britain in the 1950s and went on to be a government minister after independence." Simon Zukas' father emigrated to Southern Africa from Lithuania in 1936 in search of economic prosperity during the Nazi's reign in Europe. The Zukas family opened a shop in the town of Ndola in Northern Rhodesia, a region which fostered a great Jewish population. Migration of the Jews to Zambia Prior to 1964, what is now known as the independent republic of Zambia was formerly known as Northern Rhodesia as it was a British protectorate in south central Africa. During the 1930s there were already hundreds of Jews living in Northern Rhodesia however with the rise of the Nazis during World War II from 1939 to 1945, came a new wave of immigration. The first main wave of immigration of Jews to Zambia began in 1901 where pioneering European Jews were travelling through Southern Africa in search of prosperous economic opportunities. The inability of these European Jews to speak English meant that they were excluded from a large portion of jobs in mining, forcing them into trading, such as cattle trading. The second main wave of immigration of Jews to Zambia came in 1938 and 1939 as roughly three hundred German and Austrian Jews as well as smaller numbers of Lithuanian and Latvian Jews were fleeing Nazi persecution. The Jewish immigrants emigrating from Lithuania and Latvia mostly spoke Yiddish. By the early 1960s, there was a diaspora of around 1000 Jews residing in Northern Rhodesia. Northern Rhodesia was considered a safe haven for Jewish refugees as visas were readily available for those fleeing the Nazis, however its accessibility was not widely known. Austrian and German Jewish escape committees were not notified of the possibilities that Northern Rhodesia held for those fleeing Nazi persecution and was considered to be a closely guarded secret. In fact, no Jews were ever refused a visa, although it was kept a secret by the British Colonial Secretary, who oversaw facilitating the mass immigration of Jews to Northern Rhodesia from Central Europe. Reasoning for this is described by scholar and historian Frank Shapiro as, “while they were more than conscious of their obligations to their European coreligionists, they were also determined to protect their own positions in the British society. For the Anglo-Jewish leadership during the Nazi crisis the overriding priority was to defend their status as loyal British subjects and, at the same time, retain their stature in the Jewish Community and not feel threatened by any antisemitic claim of dual loyalty". Northern Rhodesia's mostly empty population, large fertile lands, and abundance of access to water deemed it a highly suitable place for mass immigration. A Commission was also sent to Africa by the Anglo-Jewish leadership team to assess possibilities for refugees, however no further action was taken, resulting in the failure to save large quantities of endangered Austrian and German Jews. During the World War II and the Holocaust, between 1939 and 1945, 225,000 Austrian and German Jews died yet only roughly three hundred Austrian and German Jews settled in Northern Rhodesia during that period. The planning committee continued to keep their knowledge of the safe haven of Northern Rhodesia a secret, and managed to convince the British Government to keep the file in secret archives even following the end of the war. Economic Influence in Zambia Jewish people in Northern Rhodesia had a pivotal role in the formation of colonial African capitalism. Those that immigrated to Northern Rhodesia had brought minimal capital, however their status as refugees influenced their drive to become successful and make a living. Early Jewish immigrants who came to Northern Rhodesia in 1900 and 1901 engaged heavily in cattle-trading ventures which introduced other goods such as gold to the country as a means of transaction. Cattle stock was largely bought from Barotseland and then sold to Southern Rhodesia and neighbouring countries in both rural and urban areas. Economic development in the region by the Jews prompted the introduction of money and currency in the area. The adaptive nature of Jews meant there was a positive business relationship between stakeholders in the region, especially due to their inclination to communicate in the language and overcome racial barriers. Accordingly, “the Jewish traders came to be associated with fair trade, principled trading, and well-financed businesses”. By the 1950s, the individual wealth of the Jewish community had reached its height. The more developed economic landscape meant the Jewish settlers were diversifying their businesses, largely to ranching, butchery, transport networks, communication networks, storefronts, newspapers, and mining mineral exploration in both Northern and Southern Rhodesia. Jewish Congregation in Zambia Whilst Jews were welcomed to Northern Rhodesia by the British colonial officers, some officers were considered antisemitic and made it difficult for Jews to obtain trading licences necessary for business. Historian Hugh MacMillan suggests that with early Jewish settlers in 1901, “the Jews arriving in Northern Rhodesia were both economic migrants and refugees, escaping from a kind of religious and political persecution in the Russian Empire, and also economic migrants looking for a place where they could make a better living”. These early Jewish settlers formed the foundation for the small Jewish community that later arrived in the 1940s, which collectively, were instrumental and highly influential in shaping Northern Rhodesia's Jewish diaspora, economy, and society. Individuals who had profound cultural and religious identities as Jews were particularly active in forming a Jewish community with numerous synagogues, Jewish organisations as well as Hebrew congregations, predominantly located in the capital of Livingstone. The Jews who were prominent in the Jewish community and religious life, were also active in the Zionist movement. The Zionist movement was a Jewish nationalist movement that sought to create and support a Jewish national state in the ancient homeland of the Jews, Palestine. Whilst Zionism originated in Eastern and Central Europe towards the end of the 19th century, it also spread globally and to Zambia. The population of Jews in Zambia fluctuated from 1901 to current day but has been no larger than 1,200 at its height. Integral to the growing Jewish community were the Susman brothers who were Jewish settlers who immigrated from Lithuania in 1901 and went on to run a successful empire in cattle trading, ranches, and copper mining. The Susman brothers were the leaders of Livingstone and were important in advancing the construction of Livingstone's synagogue in the late 1920s which acted as a meeting place for the Jewish settlers. In 2022, the building remains standing however no longer as a Synagogue, but instead as a Christian church. The Jewish settler group in Northern Rhodesia mostly belonged to the Ashkenazi branch of Judaism which holds large differences in terms of levels of orthodoxy. In 1901, the first Jewish settlers came to Northern Rhodesia in search for work and predominantly consisted of men. There was a distinctive lack of women and children, which meant the settlers’ religious commitments such as family seder or sabbath evening meals and prays was absent because Judaism is frequently considered to be a religion of the family. The construction of Livingstone's synagogue in the late 1920s and the arrival of Jewish women and families was the beginning of organised religious practices and activity for the Jewish community in Northern Rhodesia. In 1910, the Livingstone Hebrew Congregation was formed along with land for a synagogue but was not used at the time. Following Zambia's independence in 1964, there was a mass exodus of the settler population which led to the era of the expatriates in Zambia and the decline of Judaism in the country. Political Developments The Jewish settlers were a predominant ethnic group in Northern Rhodesia and became active in the political life, most importantly in the struggle for independence from the British Colonial rule. There were a number of high-profile Jewish intellectuals and professionals that came from Jewish society, notably scholars Lewis Gann, Robert Rotberg, and Max Gluckman. Another key Jewish figure in Northern Rhodesia was Stanley Fisher, the governor of the Bank of Israel and formerly the head of the International Monetary Fund (IMF). Marking the title as the first Jewish major in Northern Rhodesia was Hyam Sculman, who was the major of Ndola beginning in 1937, up until 1939. These figures were highly relevant and important in creating the Zambian nation. There was a new generation of leaders in congress, some of whom were Jewish, who wanted Northern Rhodesia to become an independent African state. Led by civil servant Kenneth Kaunda in 1958, radicals split off from the rest of congress to form what is known as the Zambia African National Congress, later known as the United National Independence Party. When Zambia gained independence from the British Colonial Rule in 1964, it was prosperous, comparative to previous years. With the new found independence, copper prices continued to rise, making Zambia the world's third largest producer of copper. A key political figure was Simon Zukas, who proceeded to become a government minister following the country's independence. Simon Zukas was a minister of works and supply as well as being a member of the United National Independence Party. Zukas’ father was amongst the refugees emigrating from Lithuania to Northern Rhodesia to escape religious persecution from the Nazis and in the search for employment. In reference to Simon Zukas, historian Frank Shapiro deemed that, “for a while he suppressed his political radicalism and concentrated on the process of adaptation”. However, Zukas embraced his political activism when he campaigned against British colonial rule in 1952. This political dissent led to his deportation, however, Zukas was permitted to return in 1964 with the ruling of Zambia's newfound independence. Zukas was an African Nationalist and leader of the Ndola Anti-Federation Action Group, and sought to end racial discrimination, a significant issue amongst black individuals living under British Colonial rule. The contents of the report ‘The Case Against the Federal Proposals’, written by Justin Chimba and more heavily, Simon Zukas, suggested that “the federation was aimed at halting African advancement in the Northern territories”, and that “federation on a basis of truly democratic principles might merit consideration by the people” (Swanzy, 1953). The political handover of power in 1964 prompted Jewish businessmen to leave Zambia as well as a mass emigration of the Jewish community, elicited by the pre-independence economic downturn between 1958 and 1963. Educational, political, and social concerns surrounding the creation of the independent Zambian state and the desire to not live under a black majority left only roughly one hundred Jews in Zambia by the mid-1970s. On 20 August 2025, Israel opened its embassy in Lusaka in a ceremony attended by Israeli Foreign Minister Gideon Saar and Zambian Foreign Minister Mulambo Haimbe. Zambia and Israel first established diplomatic ties in 1966, but Zambia severed its ties with Israel in 1973 following the Yom Kippur War. The two countries restored diplomatic relations in 1991, and in 2015, with Zambia opening its embassy to Israel in Tel Aviv. See also References |
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[SOURCE: https://en.wikipedia.org/wiki/Land_plant] | [TOKENS: 3517] |
Contents Embryophyte Traditional groups: The embryophytes (/ˈɛmbriəˌfaɪts/) are a clade of plants, known as Embryophyta (Plantae sensu strictissimo) (/ˌɛmbriˈɒfətə, -oʊˈfaɪtə/) or land plants. They are the most familiar group of photoautotrophs that make up the vegetation on Earth's dry lands and wetlands. Embryophytes have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of freshwater charophyte green algae as a sister taxon of Charophyceae, Coleochaetophyceae and Zygnematophyceae. Embryophytes consist of the bryophytes and the polysporangiophytes. Living embryophytes include hornworts, liverworts, mosses, lycophytes, ferns, gymnosperms and angiosperms (flowering plants). Embryophytes have haplodiplontic life cycles. The embryophytes are informally called "land plants" because they thrive primarily in terrestrial habitats (despite some members having evolved secondarily to live once again in semiaquatic/aquatic habitats), while the related green algae are primarily aquatic. Embryophytes are complex multicellular eukaryotes with specialized reproductive organs. The name derives from their innovative characteristic of nurturing the young embryo sporophyte during the early stages of its multicellular development within the tissues of the parent gametophyte. With very few exceptions, embryophytes obtain biological energy by photosynthesis, using chlorophyll a and b to harvest the light energy in sunlight for carbon fixation from carbon dioxide and water in order to synthesize carbohydrates while releasing oxygen as a byproduct. The study of land plants is called phytology. Description The Embryophytes emerged either a half-billion years ago, at some time in the interval between the mid-Cambrian and early Ordovician, or almost a billion years ago, during the Tonian or Cryogenian, probably from freshwater charophytes, a clade of multicellular green algae similar to extant Klebsormidiophyceae. The emergence of the Embryophytes depleted atmospheric CO2 (a greenhouse gas), leading to global cooling, and thereby precipitating glaciations. Embryophytes are primarily adapted for life on land, although some are secondarily aquatic. Accordingly, they are often called land plants or terrestrial plants.[citation needed] On a microscopic level, the cells of charophytes are broadly similar to those of chlorophyte green algae, but differ in that in cell division the daughter nuclei are separated by a phragmoplast. They are eukaryotic, with a cell wall composed of cellulose and plastids surrounded by two membranes. The latter include chloroplasts, which conduct photosynthesis and store food in the form of starch, and are characteristically pigmented with chlorophylls a and b, generally giving them a bright green color. Embryophyte cells also generally have an enlarged central vacuole enclosed by a vacuolar membrane or tonoplast, which maintains cell turgor and keeps the plant rigid.[citation needed] In common with all groups of multicellular algae they have a life cycle which involves alternation of generations. A multicellular haploid generation with a single set of chromosomes – the gametophyte – produces sperm and eggs which fuse and grow into a diploid multicellular generation with twice the number of chromosomes – the sporophyte which produces haploid spores at maturity. The spores divide repeatedly by mitosis and grow into a gametophyte, thus completing the cycle. Embryophytes have two features related to their reproductive cycles which distinguish them from all other plant lineages. Firstly, their gametophytes produce sperm and eggs in multicellular structures (called 'antheridia' and 'archegonia'), and fertilization of the ovum takes place within the archegonium rather than in the external environment. Secondly, the initial stage of development of the fertilized egg (the zygote) into a diploid multicellular sporophyte, takes place within the archegonium where it is both protected and provided with nutrition. This second feature is the origin of the term 'embryophyte' – the fertilized egg develops into a protected embryo, rather than dispersing as a single cell. In the bryophytes the sporophyte remains dependent on the gametophyte, while in all other embryophytes the sporophyte generation is dominant and capable of independent existence.[citation needed] Embryophytes also differ from algae by having metamers. Metamers are repeated units of development, in which each unit derives from a single cell, but the resulting product tissue or part is largely the same for each cell. The whole organism is thus constructed from similar, repeating parts or metamers. Accordingly, these plants are sometimes termed 'metaphytes' and classified as the group Metaphyta (but Haeckel's definition of Metaphyta places some algae in this group). In all land plants a disc-like structure called a phragmoplast forms where the cell will divide, a trait only found in the land plants in the streptophyte lineage, some species within their relatives Coleochaetales, Charales and Zygnematales, as well as within subaerial species of the algae order Trentepohliales, and appears to be essential in the adaptation towards a terrestrial life style. Evolution The green algae and land plants form a clade, the Viridiplantae. According to molecular clock estimates, the Viridiplantae split 1,200 million years ago to 725 million years ago into two clades: chlorophytes and streptophytes. The chlorophytes, with around 700 genera, were originally marine algae, although some groups have since spread into fresh water. The streptophyte algae (i.e. excluding the land plants) have around 122 genera; they adapted to fresh water very early in their evolutionary history and have not spread back into marine environments. Some time during the Ordovician, streptophytes invaded the land and began the evolution of the embryophyte land plants. Present day embryophytes form a clade. Becker and Marin speculate that land plants evolved from streptophytes because living in fresh water pools pre-adapted them to tolerate a range of environmental conditions found on land, such as exposure to rain, tolerance of temperature variation, high levels of ultra-violet light, and seasonal dehydration. The preponderance of molecular evidence as of 2006 suggested that the groups making up the embryophytes are related as shown in the cladogram below (based on Qiu et al. 2006 with additional names from Crane et al. 2004). Liverworts Mosses Hornworts Lycophytes (ferns and horsetails) Angiosperms (flowering plants) Gymnosperms An updated phylogeny of Embryophytes based on the work by Novíkov & Barabaš-Krasni 2015 and Hao and Xue 2013 with plant taxon authors from Anderson, Anderson & Cleal 2007 and some additional clade names. Puttick et al./Nishiyama et al. are used for the basal clades. Anthocerotophytina (Hornworts) Bryophytina (Mosses) Marchantiophytina (Liverworts) †Horneophytopsida [Protracheophytes] †Cooksoniaceae †Aglaophyton †Rhyniopsida †Catenalis †Aberlemnia †Hsuaceae †Renaliaceae †Adoketophyton †?Barinophytopsida †Zosterophyllopsida †Hicklingia †Gumuia †Nothia Lycopodiopsida (Clubmosses, Spikemosses & Quillworts) †Zosterophyllum deciduum †Yunia †Eophyllophyton †Trimerophytopsida †Ibyka †Pauthecophyton †Cladoxylopsida Polypodiopsida (ferns) †Celatheca †Pertica †Progymnosperms(paraphyletic) Spermatophytes (seed plants) Diversity The non-vascular land plants, namely the mosses (Bryophyta), hornworts (Anthocerotophyta), and liverworts (Marchantiophyta), are relatively small plants, often confined to environments that are humid or at least seasonally moist. They are limited by their reliance on water needed to disperse their gametes; a few are truly aquatic. Most are tropical, but there are many arctic species. They may locally dominate the ground cover in tundra and Arctic–alpine habitats or the epiphyte flora in rain forest habitats. They are usually studied together because of their many similarities. All three groups share a haploid-dominant (gametophyte) life cycle and unbranched sporophytes (the plant's diploid generation). These traits appear to be common to all early diverging lineages of non-vascular plants on the land. Their life-cycle is strongly dominated by the haploid gametophyte generation. The sporophyte remains small and dependent on the parent gametophyte for its entire brief life. All other living groups of land plants have a life cycle dominated by the diploid sporophyte generation. It is in the diploid sporophyte that vascular tissue develops. In some ways, the term "non-vascular" is a misnomer. Some mosses and liverworts do produce a special type of vascular tissue composed of complex water-conducting cells. However, this tissue differs from that of "vascular" plants in that these water-conducting cells are not lignified. It is unlikely that the water-conducting cells in mosses are homologous with the vascular tissue in "vascular" plants. Like the vascular plants, they have differentiated stems, and although these are most often no more than a few centimeters tall, they provide mechanical support. Most have leaves, although these typically are one cell thick and lack veins. They lack true roots or any deep anchoring structures. Some species grow a filamentous network of horizontal stems, but these have a primary function of mechanical attachment rather than extraction of soil nutrients (Palaeos 2008). During the Silurian and Devonian periods (around 440 to 360 million years ago), plants evolved which possessed true vascular tissue, including cells with walls strengthened by lignin (tracheids). Some extinct early plants appear to be between the grade of organization of bryophytes and that of true vascular plants (eutracheophytes). Genera such as Horneophyton have water-conducting tissue more like that of mosses, but a different life-cycle in which the sporophyte is branched and more developed than the gametophyte. Genera such as Rhynia have a similar life-cycle but have simple tracheids and so are a kind of vascular plant. It was assumed that the gametophyte dominant phase seen in bryophytes used to be the ancestral condition in terrestrial plants, and that the sporophyte dominant stage in vascular plants was a derived trait. However, the gametophyte and sporophyte stages were probably equally independent from each other, and that the mosses and vascular plants in that case are both derived, and have evolved in opposite directions. During the Devonian period, vascular plants diversified and spread to many different land environments. In addition to vascular tissues which transport water throughout the body, tracheophytes have an outer layer or cuticle that resists drying out. The sporophyte is the dominant generation, and in modern species develops leaves, stems and roots, while the gametophyte remains very small. All the vascular plants which disperse through spores were once thought to be related (and were often grouped as 'ferns and allies'). However, recent research suggests that leaves evolved quite separately in two different lineages. The lycophytes or lycopodiophytes – modern clubmosses, spikemosses and quillworts – make up less than 1% of living vascular plants. They have small leaves, often called 'microphylls' or 'lycophylls', which are borne all along the stems in the clubmosses and spikemosses, and which effectively grow from the base, via an intercalary meristem. It is believed that microphylls evolved from outgrowths on stems, such as spines, which later acquired veins (vascular traces). Although the living lycophytes are all relatively small and inconspicuous plants, more common in the moist tropics than in temperate regions, during the Carboniferous period tree-like lycophytes (such as Lepidodendron) formed huge forests that dominated the landscape. The euphyllophytes, making up more than 99% of living vascular plant species, have large 'true' leaves (megaphylls), which effectively grow from the sides or the apex, via marginal or apical meristems. One theory is that megaphylls evolved from three-dimensional branching systems by first 'planation' – flattening to produce a two dimensional branched structure – and then 'webbing' – tissue growing out between the flattened branches. Others have questioned whether megaphylls evolved in the same way in different groups. The ferns and horsetails (the Polypodiophyta) form a clade; they use spores as their main method of dispersal. Traditionally, whisk ferns and horsetails were historically treated as distinct from 'true' ferns. Living whisk ferns and horsetails do not have the large leaves (megaphylls) which would be expected of euphyllophytes. This has probably resulted from reduction, as evidenced by early fossil horsetails, in which the leaves are broad with branching veins. Ferns are a large and diverse group, with some 12,000 species. A stereotypical fern has broad, much divided leaves, which grow by unrolling. Seed plants, which first appeared in the fossil record towards the end of the Paleozoic era, reproduce using desiccation-resistant capsules called seeds. Starting from a plant which disperses by spores, highly complex changes are needed to produce seeds. The sporophyte has two kinds of spore-forming organs or sporangia. One kind, the megasporangium, produces only a single large spore, a megaspore. This sporangium is surrounded by sheathing layers or integuments which form the seed coat. Within the seed coat, the megaspore develops into a tiny gametophyte, which in turn produces one or more egg cells. Before fertilization, the sporangium and its contents plus its coat is called an ovule; after fertilization a seed. In parallel to these developments, the other kind of sporangium, the microsporangium, produces microspores. A tiny gametophyte develops inside the wall of a microspore, producing a pollen grain. Pollen grains can be physically transferred between plants by the wind or animals, most commonly insects. Pollen grains can also transfer to an ovule of the same plant, either with the same flower or between two flowers of the same plant (self-fertilization). When a pollen grain reaches an ovule, it enters via a microscopic gap in the coat, the micropyle. The tiny gametophyte inside the pollen grain then produces sperm cells which move to the egg cell and fertilize it. Seed plants include two clades with living members, the gymnosperms and the angiosperms or flowering plants. In gymnosperms, the ovules or seeds are not further enclosed. In angiosperms, they are enclosed within the carpel. Angiosperms typically also have other, secondary structures, such as petals, which together form a flower. Meiosis in sexual land plants provides a direct mechanism for repairing DNA in reproductive tissues. Sexual reproduction appears to be needed for maintaining long-term genomic integrity and only infrequent combinations of extrinsic and intrinsic factors allow for shifts to asexuality. References Bibliography |
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[SOURCE: https://en.wikipedia.org/wiki/CERFnet] | [TOKENS: 153] |
Contents CERFnet The California Education and Research Federation Network (CERFnet) is a mid-level network service provider based in California. It was one of the NSFNET regional networks and a co-founder of the Commercial Internet eXchange (CIX). The CERFnet network was founded in January 1988 by Susan Estrada of the San Diego Supercomputer Center (SDSC). It received partial funding of $2.8 million by the National Science Foundation a year after its founding, and was fully operational by November 1989, linking together 38 California research centers. The network was operated by the SDSC and General Atomics. References This article about a telecommunications company is a stub. You can help Wikipedia by adding missing information. |
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[SOURCE: https://en.wikipedia.org/wiki/Magma_ocean] | [TOKENS: 966] |
Contents Magma ocean Magma oceans are vast fields of surface magma that exist during periods of a planet's or some natural satellite's accretion when the celestial body is completely or partly molten. In the early Solar System, magma oceans were formed by the melting of planetesimals and planetary impacts. Small planetesimals are melted by the heat provided by the radioactive decay of aluminium-26. As planets grew larger, the energy was then supplied from giant impacts with other planetary bodies. Magma oceans are integral parts of planetary formation as they facilitate the formation of a core through metal segregation and an atmosphere and hydrosphere through degassing. Evidence exists to support the existence of magma oceans on both the Earth and the Moon. Magma oceans may survive for millions to tens of millions of years, interspersed by relatively mild conditions. Magma ocean heat sources The sources of the energy required for the formation of magma oceans in the early solar system were the radioactive decay of aluminium-26, accretionary impacts, and core formation. The abundance and short half life of aluminium-26 allowed it to function as one of the sources of heat for the melting of planetesimals. With aluminium-26 as a heat source, planetesimals that had accreted within 2 Ma after the formation of the first solids in the solar system could melt. Melting in the planetesimals began in the interior and the interior magma ocean transported heat via convection. Planetesimals larger than 20 km in radius that accreted within 2 Ma are expected to have melted, although not completely. The kinetic energy provided by accretionary impacts and the loss of potential energy from a planet during core formation are also large heat sources for planet melting. Core formation, also referred to as metal-silicate differentiation, is the separation of metallic components from silicate in the magma that sink to form a planetary core. Accretionary impacts that produce heat for the melting of planet embryos and large terrestrial planets have an estimated timescale of tens to hundreds of millions of years. An example would be the Moon-forming impact on Earth, that is thought to have formed a magma ocean with a depth of up to 2000 km. The energy of accretionary impacts foremost melt the exterior of the planetary body, and the potential energy provided by core differentiation and the sinking of metals melts the interior. Lunar magma ocean The findings of the Apollo missions were the first articles of evidence to suggest the existence of a magma ocean on the Moon. The rocks in the samples acquired from the missions were found to be composed of a mineral called anorthite. Anorthite consists mostly of a variety of plagioclase feldspars, which are lower in density than magma. This discovery gave rise to the hypothesis that the rocks formed through an ascension to the surface of a magma ocean during the early life stages of the Moon. Additional evidence for the existence of the Lunar Magma Ocean includes the sources of mare basalts and KREEP (K for potassium, REE for rare-earth elements, and P for phosphorus). The existence of these components within the mostly anorthositic crust of the Moon are synonymous with the solidification of the Lunar Magma Ocean. Furthermore, the abundance of the trace element europium within the Moon's crust suggests that it was absorbed from the magma ocean, leaving europium deficits in the mare basalt rock sources of the Moon's crust. The lunar magma ocean was initially 200-300 km thick and the magma achieved a temperature of about 2000 K. After the early stages of the Moon's accretion, the magma ocean was subjected to cooling caused by convection in the planet's interior. Earth's magma ocean During its formation, the Earth likely featured a series of magma oceans resulting from giant impacts, the final one being the Moon-forming impact. The best chemical evidence for the existence of magma oceans on Earth is the abundance of certain siderophile elements in the mantle that record magma ocean depths of approximately 1000 km during accretion. The scientific evidence to support the existence of magma oceans on early Earth is not as developed as the evidence for the Moon because of the recycling of the Earth's crust and mixing of the mantle. Unlike Earth, indications of a magma ocean on the Moon such as the flotation crust, elemental components in rocks, and KREEP have been preserved throughout its lifetime. Today Earth's outer core is a liquid layer about 2,260 km (1,400 mi) thick, composed mostly of molten iron and molten nickel that lies above Earth's solid inner core and below its mantle. This layer may be considered as an ocean of molten iron and nickel inside Earth. See also References |
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[SOURCE: https://en.wikipedia.org/wiki/Late_Cambrian] | [TOKENS: 988] |
Contents Furongian The Furongian or Late Cambrian is the fourth and final epoch and series of the Cambrian. It lasted from 497 to 486.85 million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian Stage. It is subdivided into three stages: the Paibian, Jiangshanian and the unnamed 10th stage of the Cambrian. History and naming The Furongian was also known as the Cambrian Series 4, and the name replaced the older term Upper Cambrian and equivalent to the local term Hunanian. The present name was ratified by the International Commission on Stratigraphy in 2003. Fúróng (芙蓉) means 'lotus' in Mandarin and refers to Hunan which is known as the "lotus state". Definition The lower boundary is defined in the same way as the GSSP of the Paibian Stage. Both begin with the first appearance of the trilobite Glyptagnostus reticulatus around 497 million years ago. The upper boundary is the lower boundary and GSSP of the Tremadocian Stage which is the first appearance of the conodont Iapetognathus fluctivagus around 486.85 million years ago. Subdivisions The following table shows the subdivisions of the Furongian series/epoch: Biostratigraphy The base of two of three stages of the Furongian are defined as the first appearance of a trilobite. The base of the Paibian is the first appearance of Glyptagnostus reticulatus and the base of the Jiangshanian is the first appearance of Agnostotes orientalis. The still unnamed Cambrian Stage 10 might be defined as the first appearance of Lotagnostus americanus or the conodont Eoconodontus notchpeakensis. The Furongian can be divided into a number of trilobite zones: Major events At the beginning of the Furongian epoch, the Guzhangian–Paibian extinction ended. Species diversity, which had decreased by 45%, returned to its previous level at the very beginning of the Jiangshanian age. The ensuing Jiangshanian extinction reduced species diversity by 55.2% and was followed by an interval of relatively small fluctuations in species richness, which ended shortly after the beginning of the Ordovician. Steptoean positive carbon isotope excursion (SPICE) occurred in close proximity in time to the Miaolingian–Furongian boundary (and, accordingly, the Guzhangian–Paibian boundary). This event is recorded on almost all Cambrian paleocontinents, but its exact causes are not fully understood. It is assumed that it may be associated with the Sauk megasequence, which in turn is associated with sea level changes; decrease in oxygen or occurrence of euxinic conditions in ocean waters; or the trilobite biomere turnover. From the Furongian to the Early Ordovician, around 495-470 Ma, the mantle plume activity, known as the Ollo de Sapo magmatic event, occurred on the North-Western territory of the Gondwana which is now the Iberian Peninsula. Paleontology Researchers have been noted that the significant macroscopic soft-bodied animals that lived between the Cambrian Explosion and the Great Ordovician Biodiversification Event were not discovered. In 2019, this time interval was named the Furongian Biodiversity Gap by Harper et al. This gap has been characterized as probably caused by lack of rocks, environmental events or a specific palaeogeography and extreme climates of the late Cambrian. However, a review of the literature and locations with Cambrian deposits showed that the gap is caused by the insufficient presence of Furongian deposits in sufficiently studied areas, as well as the lack of attention to fossils of this interregnum. Later discoveries of the Furongian deposits in South China have allowed for a better understanding of the biostratigraphy and fluctuations in species diversity of this epoch. 8502 specimens of trilobite-agnostoid fauna have been collected from the Furongian strata of the Alum Shale Formation of Bornholm, Denmark. Described gerena include Ctenopyge, Eurycare, Leptoplastus, Olenus, Parabolina, Peltura, Protopeltura, Sphaerophthalmus, Lotagnostus and Triangulopyge. Benthic graptolites, including genera Rhabdopleura, Dendrograptus, Callograptus and Siberiograptus, were found in the Furongian sediments of South China. References External links |
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[SOURCE: https://en.wikipedia.org/wiki/Stanford_Federal_Credit_Union] | [TOKENS: 839] |
Contents Stanford Federal Credit Union Board of Directors Dr. Shirley J. Everett, Chair Gregory L. Rosston, Vice Chair Tana S. Hutchison, Treasurer Dan Kolkowitz, Secretary Jonathan Dreyfus Joan Opp Curtis Feeny Robert Reidy Neil Hamilton Agustin (Gus) Araya, Advisory Board Member Supervisory Committee Michael Tran Duff, Chair Desmond Low-Kum, Secretary Neil Hamilton David MacKenzie Stanford Federal Credit Union (or Stanford FCU) is a federally chartered credit union located in Palo Alto, California. It provides banking services to the Stanford community. Stanford FCU has over $3.6 billion in assets and serves over 80,000 members. History Stanford Federal Credit Union was created by a group of Stanford University employees on December 17, 1959. Its original field of membership was limited to employees of the university. The credit union opened in 1960 with $261 in deposits and established its first office in Encina Hall on Stanford University’s campus. In 1985, Stanford Federal Credit Union expanded its field of membership to include Stanford University students and members and employees of the Palo Alto Chamber of Commerce. In 2004, the credit union opened its membership to members of the Friends of Palo Alto Libraries (FOPAL). Today, Stanford Federal Credit Union also serves numerous company partners, including Google, VMware, Facebook, Tesla, SAP and more. The credit union became one of the first to offer checking accounts and credit cards in the late 1970s. In the early 1980s, it introduced ATMs and banking by telephone. In November 1993, Stanford Federal Credit Union conducted its first four internet transactions; and in 1994, it became the first financial institution to offer online banking when it launched its website; it offered online BillPay to its members in 1997, added account aggregation and mobile banking in 2002, and became one of the first institutions to implement the Passmark authentication system in 2005. In 2007, Stanford FCU joined the CO-OP network to provide its members with over 30,000 surcharge-free ATMs nationwide. Membership Any member of the Stanford community may join Stanford Federal Credit Union, including students and employees of Stanford University, employees of Stanford Health Care, Stanford Children’s Health, and SLAC National Accelerator Laboratory. The credit union’s field of membership also extends to the following: Organization Stanford Federal Credit Union is chartered by the National Credit Union Administration (NCUA) as a federally insured credit union. It is led by a Board of Directors that is elected by the credit union’s members and serves without pay. Products and services Stanford Federal Credit Union offers a range of financial services, including consumer and business accounts and loans. Financial tools and services in the form of webinars, online calculators, and financial counseling are also available to both consumer and business members of the credit union. The credit union has six branch locations and maintains over 30 ATMs around the Stanford University campus and Palo Alto, California. As a member of the CO-OP Network since 2007, Stanford Federal Credit Union also has access to over 30,000 additional surcharge-free ATMs. Subsidiary In 1997, Stanford Federal Credit Union announced the creation of its wholly owned subsidiary, Cardinal Services Corporation (CSC). The corporation focused on licensing software and supporting Internet development for businesses. Cardinal Services Corporation operated as a credit union service organization (CUSO). CUSOs were established by the NCUA as a way for credit unions to conduct business that they would otherwise be restricted from. A spin-off of Cardinal Services Corporation, Cyberbranch, was announced in April 2000 by Stanford Federal Credit Union, and replaced the CUSO. CyberBranch specialized in internet and intranet technologies designed for the financial services industry. In June 2001, Canadian information technology management and business process services company, CGI Group Inc. acquired Cyberbranch for US$1 million. Community involvement In 2004, Stanford Federal Credit Union funded an endowed professorship within Stanford University’s School of Humanities and Sciences. References |
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[SOURCE: https://en.wikipedia.org/wiki/John_Mauchly] | [TOKENS: 3100] |
Contents John Mauchly John William Mauchly (/ˈmɔːkli/ MAWK-lee; August 30, 1907 – January 8, 1980) was an American physicist who, along with J. Presper Eckert, designed ENIAC, the first general-purpose electronic digital computer, as well as EDVAC, BINAC and UNIVAC I, the first commercial computer made in the United States. Together, Mauchly and Eckert started the first computer company, the Eckert–Mauchly Computer Corporation (EMCC), which allowed them to further the development of fundamental computer concepts originally conceived by members of the 1945-46 ENIAC programming team, notably Jean Bartik and Kay McNulty, including subroutines, nesting, and the first low-level assembler. They also popularized the concept of the stored program, which was formalized in John von Neumann's widely-read First Draft of a Report on the EDVAC (1945) and disseminated through the Moore School Lectures (1946). These publications influenced an explosion of computer development around the world in the late 1940s. Biography John W. Mauchly was born on August 30, 1907, to Sebastian and Rachel (Scheidemantel) Mauchly in Cincinnati, Ohio. His family was of German descent, and his father spoke German, but Mauchly didn't grow up speaking it as it was not spoken in the family. He moved with his parents and sister, Helen Elizabeth (Betty), at an early age to Chevy Chase, Maryland, when Sebastian Mauchly obtained a position at the Carnegie Institution of Washington as head of its Section of Terrestrial Electricity. As a youth, Mauchly was interested in science, and in particular with electricity, and as a young teenager was known to fix neighbors' electric systems. Mauchly attended E.V. Brown Elementary School in Chevy Chase and McKinley Technical High School in Washington, DC. At McKinley, Mauchly was extremely active in the debate team, was a member of the national honor society, and became editor-in-chief of the school's newspaper, Tech Life. After graduating from high school in 1925, he earned a scholarship to study engineering at Johns Hopkins University. He subsequently transferred to the physics department, and without completing his undergraduate degree, instead earned a Ph.D. in physics in 1932. From 1932 to 1933, Mauchly served as a research assistant at Johns Hopkins University where he concentrated on calculating energy levels of the formaldehyde spectrum. Mauchly's teaching career truly began in 1933 at Ursinus College where he was appointed head of the physics department, where he was, in fact, the only staff member. In the summer of 1941, Mauchly took a Defense Training Course for Electronics at the University of Pennsylvania Moore School of Electrical Engineering. There he met the lab instructor, J. Presper Eckert (1919–1995), with whom he would form a long-standing working partnership. Following the course, Mauchly was hired as an instructor of electrical engineering and in 1943, he was promoted to assistant professor of electrical engineering. Following the outbreak of World War II, the United States Army Ordnance Department contracted the Moore School to build an electronic computer which, as proposed by Mauchly and Eckert, would accelerate the recomputation of artillery firing tables. In 1959, Mauchly left Sperry Rand and started Mauchly Associates, Inc. One of Mauchly Associates' notable achievements was the development of the Critical Path Method (CPM) which provided for automated construction scheduling. Mauchly also set up a consulting organization, Dynatrend, in 1967 and worked as a consultant to Sperry UNIVAC from 1973 until his death in 1980. John Mauchly died on January 8, 1980, in Ambler, Pennsylvania, during heart surgery and following a long illness. His first wife, Mary Augusta Walzl, a mathematician, whom he married on December 30, 1930, drowned in 1946. John and Mary Mauchly had two children, James (Jimmy) and Sidney. In 1948, Mauchly married Kathleen Kay McNulty (1921–2006), one of the six original ENIAC programmers; they had five children Sara (Sallie), Kathleen (Kathy), John, Virginia (Gini), and Eva. Moore School In 1941 Mauchly took a course in wartime electronics at the Moore School of Electrical Engineering, part of the University of Pennsylvania. There he met J. Presper Eckert, a recent Moore School graduate. Mauchly accepted a teaching position at the Moore School, which was a center for wartime computing. Eckert encouraged Mauchly to believe that vacuum tubes could be made reliable with proper engineering practices. The critical problem that was consuming the Moore School was ballistics: the calculation of firing tables for the large number of new guns that the U.S. Army was developing for the war effort. In 1942 Mauchly wrote a memo proposing the building of a general-purpose electronic computer. The proposal, which circulated within the Moore School (but the significance of which was not immediately recognized), emphasized the enormous speed advantage that could be gained by using digital electronics with no moving parts. Lieutenant Herman Goldstine, who was the liaison between the United States Army and Moore School, picked up on the idea and asked Mauchly to write a formal proposal. In April 1943, the Army contracted with the Moore School to build the Electronic Numerical Integrator and Computer (ENIAC). Mauchly led the conceptual design while Eckert led the hardware engineering on ENIAC. A number of other talented engineers contributed to the confidential "Project PX". Because of its high-speed calculations, ENIAC could solve problems that were previously unsolvable. It was roughly a thousand times faster than the existing technology. It could add 5,000 numbers or do 357 10-digit multiplications in one second. ENIAC could be programmed to perform sequences and loops of addition, subtraction, multiplication, division, square-root, input/output functions, and conditional branches. Programming was initially accomplished with patch cords and switches, and reprogramming took days. It was redesigned in 1948 to allow the use of stored programs with some loss in speed. In 2002, for his work on ENIAC he was inducted, posthumously, into the National Inventors Hall of Fame. EDVAC The ENIAC design was frozen in 1944 to allow construction. Eckert and Mauchly were already aware of the limitations of the machine and began plans on a second computer, to be called EDVAC. By January 1945 they had procured a contract to build this stored-program computer. Eckert had proposed a mercury delay-line memory to store both program and data. Later that year, mathematician John von Neumann learned of the project and joined in some of the engineering discussions. He produced what was understood to be an internal document describing the EDVAC. The term von Neumann architecture arose from von Neumann's paper First Draft of a Report on the EDVAC. Dated June 30, 1945, it was an early written account of a general-purpose stored-program computing machine (the EDVAC). Goldstine, in a move that was to become controversial, removed any reference[citation needed] to Eckert or Mauchly and distributed the document to a number of von Neumann's associates across the country. The ideas became widely known within the very small world of computer designers. Besides the lack of credit, Eckert and Mauchly suffered additional setbacks due to Goldstine's actions. The ENIAC patent U.S. patent 3,120,606, issued in 1964 was filed on June 26, 1947, and granted February 4, 1964, but the public disclosure of design details of EDVAC in the First Draft (which were also common to ENIAC) was later cited as one cause for the 1973 invalidation of the ENIAC patent. The Moore School Lectures In March 1946, just after the ENIAC was announced, the Moore School decided to change their patent policy, in order to gain commercial rights to any future and past computer development there. Eckert and Mauchly decided this was unacceptable; they resigned. However they had already been contracted to do one more thing at the Moore School: to give a series of talks on computer design. The course "The Theory and Techniques for Design of Digital Computers", ran from July 8 to August 31, 1946. Eckert gave 11 of the lectures; Mauchly and Goldstine each delivered 6. "The Moore School Lectures", as they came to be known, were attended by representatives from the army, the navy, MIT, the National Bureau of Standards, Cambridge University, Columbia, Harvard, the Institute for Advanced Study, IBM, Bell Labs, Eastman Kodak, General Electric, and National Cash Register. A number of the attendees were to later go on to develop computers, such as Maurice Wilkes, of Cambridge, who built EDSAC. Eckert–Mauchly Computer Corporation In 1947 Eckert and Mauchly formed the first computer company, the Eckert–Mauchly Computer Corporation (EMCC); Mauchly was president. They secured a contract with the National Bureau of Standards to build an "EDVAC II", later named UNIVAC. UNIVAC, the first computer designed for business applications, had many significant technical advantages such as magnetic tape for mass storage. As an interim product, the company created and delivered a smaller computer, BINAC, but were still in a shaky financial situation. The company was purchased by Remington Rand in 1950 and became the UNIVAC division. Mauchly remained the Director of Applications and worked on weather forecasting projects. In 1959, he left to create Mauchly Associates. Software Very early in the history of EMCC, John Mauchly assumed responsibility for programming, coding, and applications for the planned computer systems. His early interaction with representatives of the Census Bureau in 1944 and 1945, and discussion with people interested in statistics, weather prediction, and various business problems in 1945 and 1946 focused his attention on the need to provide new users with the software to accomplish their objectives. He knew it would be difficult to sell computers without application materials, and without training in how to use the systems. And so, EMCC began to assemble a staff of mathematicians interested in coding in early 1947. (from Norberg) Mauchly's interest lay in the application of computers, as well as to their architecture and organization. His experience with programming the ENIAC and its successors led him to create Short Code (see "The UNIVAC SHORT CODE"), the first programming language actually used on a computer (predated by Zuse's conceptual Plankalkul). It was a pseudocode interpreter for mathematical problems proposed in 1949 and ran on the UNIVAC I and II. Mauchly's belief in the importance of languages led him to hire Grace Murray Hopper to develop a compiler for the UNIVAC. John Mauchly has also been credited for being the first one using the verb "to program" in his 1942 paper on electronic computing, although in the context of ENIAC, not in its current meaning. Career Mauchly stayed involved in computers for the rest of his life. He was a founding member and president of the Association for Computing Machinery (ACM) and also helped found the Society for Industrial and Applied Mathematics (SIAM), serving as its fourth president. The Eckert–Mauchly Corporation was bought by Remington Rand in 1950 and for ten years Mauchly remained as Director of Univac Applications Research. Leaving in 1959 he formed Mauchly Associates, a consulting company that later introduced the critical path method (CPM) for construction scheduling by computer. In 1967 he founded Dynatrend, a computer consulting organization. In 1973 he became a consultant to Sperry Univac. Awards Mauchly received numerous award and honors. He was a life member of the Franklin Institute, the National Academy of Engineering and the Society for Advancement of Management. He was elected a Fellow of the IRE, a predecessor society of IEEE, in 1957, and was a Fellow of the American Statistical Association. He received an LLD (Hon) degree from the University of Pennsylvania and aDSc(Hon) degree from Ursinus College. He was a recipient of the Philadelphia Award, the Scott Medal, the Goode Medal of AFIPS (American Federation of Information Processing Societies), the Pennsylvania Award, the Emanual R. Piore Award, the Howard N. Potts Medal, and numerous other awards. Patent controversy Mauchly and Eckert's patent on the ENIAC was invalidated by U.S. Federal Court decision in October, 1973 for several reasons. Some had to do with the time between publication (the First Draft) and the patent filing date (1947). The federal judge who presided over the case ruled that "the subject matter was derived" from the earlier Atanasoff–Berry computer (ABC). This statement has become the center of a controversy. Critics note that while the court said that the ABC was the first electronic digital computer, it did not define the term computer. It had originally referred to a person who computes, but was adapted to apply to a machine. Critics of the court decision also note that there is, at a component level, nothing in common between the two machines. The ABC was binary; the ENIAC was decimal. The ABC used regenerative drum memory; The ENIAC used electronic decade counters. The ABC used its vacuum tubes to implement a binary serial adder, while the ENIAC used tubes to implement a complete set of decimal operations. The ENIAC's general-purpose instruction set, together with the ability to automatically sequence through them, made it a general-purpose computer. However, the later EDVAC computer, developed without the immediate pressures of wartime projects, harked back more to the ABC in that it was a binary computer employing regenerative memory. Proponents for the court decision emphasize that the testimony established that Mauchly definitely visited Atanasoff's lab at Iowa State College, had complete access to Atanasoff's machine and the documents describing it. Letters he wrote to Atanasoff show that he was at one time at least considering building on Atanasoff's approach. Mauchly consistently maintained that it was the use of high-speed electronic flip-flops in cosmic-ray counting devices at Swarthmore College that gave him the idea for computing at electronic speeds. See also References Further reading External links |
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[SOURCE: https://en.wikipedia.org/wiki/Hunter-gatherer] | [TOKENS: 4346] |
Contents Hunter-gatherer A hunter-gatherer, or forager, is a human living in a community, or according to an ancestrally derived lifestyle, in which most or all food is obtained by foraging, that is, by gathering food from local naturally occurring sources or by hunting game. This is a common practice among most vertebrates that are omnivores. Hunter-gatherer groups, usually a few dozen people, were and are nomadic or semi-nomadic. Hunter-gatherer societies are contrasted with more sedentary agricultural societies, which rely mainly on cultivating crops and raising domesticated animals for food production. Hunting and gathering emerged with Homo erectus about 1.8 million years ago and was humanity's original and most enduring successful competitive adaptation in the natural world, occupying at least 90 percent of human (pre)history. Following the invention of agriculture, hunter-gatherers who did not change were displaced or conquered by farming or pastoralist groups in most parts of the world. In Western Eurasia, farming and metallurgical societies gradually replaced hunter-gatherers, but dense forests remained their last refuge until Bronze and Iron Age societies fully overcame them. Socially, they were generally egalitarian, emphasizing sharing and resisting hierarchy; though inequalities and divisions of labor existed, women often contributed to hunting as well as gathering. Only a few contemporary societies of uncontacted people are still classified as hunter-gatherers, and many supplement their foraging activity with horticulture or pastoralism. Archaeological and ethnographic evidence shows wide variation depending on environment, from mammoth steppe hunters in Siberia to semi-sedentary fishers. Their diets varied by climate, balancing plant foods, game, and aquatic resources, with fat as a critical nutrient. Over time, many bands specialized in particular resources and tools, and some transitioned into agriculture, which led to permanent settlements, governments, and social stratification. While most hunter-gatherers eventually adopted farming or were displaced, some groups—such as the San, Pumé, and Sentinelese—continue aspects of this lifestyle today. Archaeological evidence Hunting and gathering was presumably the subsistence strategy employed by human societies beginning some 1.8 million years ago, by Homo erectus, and from its appearance some 200,000 years ago by Homo sapiens. Prehistoric hunter-gatherers lived in groups that consisted of several families resulting in a size of a few dozen people. The Late Pleistocene witnessed the spread of modern humans outside of Africa as well as the extinction of all other human species. Humans spread to the Australian continent and the Americas for the first time, coincident with the extinction of numerous predominantly megafaunal species. Major extinctions were incurred in Australia beginning approximately 50,000 years ago and in the Americas about 15,000 years ago. Ancient North Eurasians lived in extreme conditions of the mammoth steppes of Siberia and survived by hunting mammoths, bison and woolly rhinoceroses. The settlement of the Americas began when Paleolithic hunter-gatherers entered North America from the North Asian mammoth steppe via the Beringia land bridge. During the 1970s, Lewis Binford suggested that early humans obtained food via scavenging, not hunting. Early humans in the Lower Paleolithic lived in forests and woodlands, which allowed them to collect seafood, eggs, nuts, and fruits besides scavenging. Rather than killing large animals for meat, according to this view, they used carcasses of such animals that had either been killed by predators or that had died of natural causes. Scientists have demonstrated that the evidence for early human behaviors for hunting versus carcass scavenging vary based on the ecology, including the types of predators that existed and the environment. Starting at the transition between the Middle to Upper Paleolithic period, some 80,000 to 70,000 years ago, some hunter-gatherer bands began to specialize, concentrating on hunting a smaller selection of (often larger) game and gathering a smaller selection of food. This specialization of work also involved creating specialized tools such as fishing nets, hooks, and bone harpoons. Archaeologists can use evidence such as stone tool use to track hunter-gatherer activities, including mobility. Common characteristics Some hunter-gatherer cultures, such as the indigenous peoples of the Pacific Northwest Coast and the Yokuts, lived in particularly rich environments that allowed them to be sedentary or semi-sedentary. Amongst the earliest example of permanent settlements is the Osipovka culture (14–10.3 thousand years ago), which lived in a fish-rich environment that allowed them to be able to stay at the same place all year. One group, the Chumash, had the highest recorded population density of any known hunter and gatherer society with an estimated 21.6 persons per square mile. Hunter-gatherers tends to have much greater home ranges than pre-industrial sedentary farmers. It has been estimated that pre-industrial English people living in small townships would have had a home range of 900 hectares (9 km2), close to that predicted for an omnivorous mammal of their same body mass. Meanwhile, the !Kung San hunter-gatherers have a home range of 10,000 hectares (100 km2), close to that predicted for a carnivorous mammal of their same body mass. Hunter-gatherers tend to have an egalitarian social ethos, although settled hunter-gatherers (for example, those inhabiting the Northwest Coast of North America and the Calusa in Florida) are an exception to this rule. For example, the San people or "Bushmen" of southern Africa have social customs that strongly discourage hoarding and displays of authority, and encourage economic equality via sharing of food and material goods. Karl Marx defined this socio-economic system as primitive communism. The egalitarianism typical of human hunters and gatherers is never total but is striking when viewed in an evolutionary context. One of humanity's two closest primate relatives, chimpanzees, are anything but egalitarian, forming themselves into hierarchies that are often dominated by an alpha male. So great is the contrast with human hunter-gatherers that it is widely argued by paleoanthropologists that resistance to being dominated was a key factor driving the evolutionary emergence of human consciousness, language, kinship and social organization. Most anthropologists believe that hunter-gatherers do not have permanent leaders; instead, the person taking the initiative at any one time depends on the task being performed. Within a particular tribe or people, hunter-gatherers are connected by both kinship and band (residence/domestic group) membership. Postmarital residence among hunter-gatherers tends to be matrilocal, at least initially. Young mothers can enjoy childcare support from their own mothers, who continue living nearby in the same camp. The systems of kinship and descent among human hunter-gatherers were relatively flexible, although there is evidence that early human kinship in general tended to be matrilineal. The conventional assumption has been that women did most of the gathering, while men concentrated on big game hunting. In recent years, however, this assumption has been challenged by new research findings. Women in many hunter-gatherer societies hunted small game and, in some cases, even participated in big-game hunting. An illustrative account is Megan Biesele's study of the southern African Ju/'hoan, 'Women Like Meat'. A 2006 study suggests that the sexual division of labor was the fundamental organizational innovation that gave Homo sapiens the edge over the Neanderthals, allowing our ancestors to migrate from Africa and spread across the globe. A 1986 study found most hunter-gatherers have a symbolically structured sexual division of labor. However, it is true that in a small minority of cases, women hunted the same kind of quarry as men, sometimes doing so alongside men. Among the Ju'/hoansi people of Namibia, women help men track down quarry. In the Australian Martu, both women and men participate in hunting but with a different style of gendered division; while men are willing to take more risks to hunt bigger animals such as kangaroo for political gain as a form of "competitive magnanimity", women target smaller game such as lizards to feed their children and promote working relationships with other women, preferring a more constant supply of sustenance. In 2018, 9000-year-old remains of a female hunter along with a toolkit of projectile points and animal processing implements were discovered at the Andean site of Wilamaya Patjxa, Puno District in Peru. A 2020 study inspired by this discovery found that of 27 identified burials with hunter gatherers of a known sex who were also buried with hunting tools, 11 were female hunter gatherers, while 16 were male hunter gatherers. Combined with uncertainties, these findings suggest that anywhere from 30 to 50 percent of big game hunters were female. A 2023 study that looked at studies of contemporary hunter gatherer societies from the 1800s to the present day found that women hunted in 79 percent of hunter gatherer societies. However, an attempted verification of this study found "that multiple methodological failures all bias their results in the same direction...their analysis does not contradict the wide body of empirical evidence for gendered divisions of labor in foraging societies". At the 1966 "Man the Hunter" conference, anthropologists Richard Borshay Lee and Irven DeVore suggested that egalitarianism was one of several central characteristics of nomadic hunting and gathering societies because mobility requires minimization of material possessions throughout a population. Therefore, no surplus of resources can be accumulated by any single member. Other characteristics Lee and DeVore proposed were flux in territorial boundaries as well as in demographic composition. At the same conference, Marshall Sahlins presented a paper entitled, "Notes on the Original Affluent Society", in which he challenged the popular view of hunter-gatherers lives as "solitary, poor, nasty, brutish and short", as Thomas Hobbes had put it in 1651. According to Sahlins, ethnographic data indicated that hunter-gatherers worked far fewer hours and enjoyed more leisure than typical members of industrial society, and they still ate well. Their "affluence" came from the idea that they were satisfied with very little in the material sense. Later, in 1996, Ross Sackett performed two distinct meta-analyses to empirically test Sahlin's view. The first of these studies looked at 102 time-allocation studies, and the second one analyzed 207 energy-expenditure studies. Sackett found that adults in foraging and horticultural societies work on average, about 6.5 hours a day, whereas people in agricultural and industrial societies work on average 8.8 hours a day. Sahlins' theory has been criticized for only including time spent hunting and gathering while omitting time spent on collecting firewood, food preparation, etc. Other scholars also assert that hunter-gatherer societies were not "affluent" but suffered from extremely high infant mortality, frequent disease, and perennial warfare. Researchers Gurven and Kaplan have estimated that around 57% of hunter-gatherers reach the age of 15. Of those that reach 15 years of age, 64% continue to live to or past the age of 45. This places the life expectancy between 21 and 37 years. They further estimate that 70% of deaths are due to diseases of some kind, 20% of deaths come from violence or accidents and 10% are due to degenerative diseases. Mutual exchange and sharing of resources (i.e., meat gained from hunting) are important in the economic systems of hunter-gatherer societies. Therefore, these societies can be described as based on a "gift economy". A 2010 paper argued that while hunter-gatherers may have lower levels of inequality than modern, industrialised societies, that does not mean inequality does not exist. The researchers estimated that the average Gini coefficient amongst hunter-gatherers was 0.25, equivalent to the country of Denmark in 2007. In addition, wealth transmission across generations was also a feature of hunter-gatherers, meaning that "wealthy" hunter-gatherers, within the context of their communities, were more likely to have children as wealthy as them than poorer members of their community and indeed hunter-gatherer societies demonstrate an understanding of social stratification. Thus while the researchers agreed that hunter-gatherers were more egalitarian than modern societies, prior characterisations of them living in a state of egalitarian primitive communism were inaccurate and misleading. This study, however, exclusively examined modern hunter-gatherer communities, offering limited insight into the exact nature of social structures that existed prior to the Neolithic Revolution. Alain Testart and others have said that anthropologists should be careful when using research on current hunter-gatherer societies to determine the structure of societies in the paleolithic era, emphasising cross-cultural influences, progress and development that such societies have undergone in the past 10,000 years. Diet As one moves away from the equator, the importance of plant food decreases and the importance of aquatic food increases. In cold and heavily forested environments, edible plant foods and large game are less abundant and hunter-gatherers may turn to aquatic resources to compensate. Hunter-gatherers in cold climates also rely more on stored food than those in warm climates. However, aquatic resources tend to be costly, requiring boats and fishing technology, and this may have impeded their intensive use in prehistory. Marine food probably did not start becoming prominent in the diet until relatively recently, during the Late Stone Age in southern Africa and the Upper Paleolithic in Europe. Fat is important in assessing the quality of game among hunter-gatherers, to the point that lean animals are often considered secondary resources or even starvation food. Consuming too much lean meat leads to adverse health effects like protein poisoning, and can in extreme cases lead to death. Additionally, a diet high in protein and low in other macronutrients results in the body using the protein as energy, possibly leading to protein deficiency. Lean meat especially becomes a problem when animals go through a lean season that requires them to metabolize fat deposits. In areas where plant and fish resources are scarce, hunter-gatherers may trade meat with horticulturalists for carbohydrates. For example, tropical hunter-gatherers may have an excess of protein but be deficient in carbohydrates, and conversely tropical horticulturalists may have a surplus of carbohydrates but inadequate protein. Trading may thus be the most cost-effective means of acquiring carbohydrate resources. Variability Hunter-gatherer societies manifest significant variability, depending on climate zone/life zone, available technology, and societal structure. Archaeologists examine hunter-gatherer tool kits to measure variability across different groups. Collard et al. (2005) found temperature to be the only statistically significant factor to impact hunter-gatherer tool kits. Using temperature as a proxy for risk, Collard et al.'s results suggest that environments with extreme temperatures pose a threat to hunter-gatherer systems significant enough to warrant increased variability of tools. These results support Torrence's (1989) theory that the risk of failure is indeed the most important factor in determining the structure of hunter-gatherer toolkits. One way to divide hunter-gatherer groups is by their return systems. James Woodburn uses the categories "immediate return" hunter-gatherers for egalitarianism and "delayed return" for nonegalitarian. Immediate return foragers consume their food within a day or two after they procure it. Delayed return foragers store the surplus food. Hunting-gathering was the common human mode of subsistence throughout the Paleolithic, but the observation of current-day hunters and gatherers does not necessarily reflect Paleolithic societies; the hunter-gatherer cultures examined today have had much contact with modern civilization and do not represent "pristine" conditions found in uncontacted peoples. The transition from hunting and gathering to agriculture is not necessarily a one-way process. It has been argued that hunting and gathering represents an adaptive strategy, which may still be exploited, if necessary, when environmental change causes extreme food stress for agriculturalists. In fact, it is sometimes difficult to draw a clear line between agricultural and hunter-gatherer societies, especially since the widespread adoption of agriculture and resulting cultural diffusion that has occurred in the last 10,000 years. Some scholars speak about the existence within cultural evolution of the so-called mixed-economies or dual economies that imply a combination of food procurement (gathering and hunting) and food production or when foragers have trade relations with farmers. Modern and revisionist perspectives Some of the theorists who advocate this "revisionist" critique[clarification needed] imply that, because the "pure hunter-gatherer" disappeared not long after colonial (or even agricultural) contact began, nothing meaningful can be learned about prehistoric hunter-gatherers from studies of modern ones (Kelly, 24–29; see Wilmsen) Lee and Guenther have rejected most of the arguments put forward by Wilmsen.[clarification needed] Doron Shultziner and others have argued that we can learn a lot about the life-styles of prehistoric hunter-gatherers from studies of contemporary hunter-gatherers—especially their impressive levels of egalitarianism. There are nevertheless a number of contemporary hunter-gatherer peoples who, after contact with other societies, continue their ways of life with very little external influence or with modifications that perpetuate the viability of hunting and gathering in the 21st century. One such group is the Pila Nguru (Spinifex people) of Western Australia, whose land in the Great Victoria Desert has proved unsuitable for European agriculture (and even pastoralism).[citation needed] Another are the Sentinelese of the Andaman Islands in the Indian Ocean, who live on North Sentinel Island and to date have maintained their independent existence, repelling attempts to engage with and contact them. The Savanna Pumé of Venezuela also live in an area that is inhospitable to large scale economic exploitation and maintain their subsistence based on hunting and gathering, as well as incorporating a small amount of manioc horticulture that supplements, but is not replacing, reliance on foraged foods. Americas Evidence suggests big-game hunter-gatherers crossed the Bering Strait from Asia (Eurasia) into North America over a land bridge (Beringia), that existed between 47,000 and 14,000 years ago. Around 18,500–15,500 years ago, these hunter-gatherers are believed to have followed herds of now-extinct Pleistocene megafauna along ice-free corridors that stretched between the Laurentide and Cordilleran ice sheets. Another route proposed is that, either on foot or using primitive boats, they migrated down the Pacific coast to South America. Hunter-gatherers would eventually flourish all over the Americas, primarily based in the Great Plains of the United States and Canada, with offshoots as far east as the Gaspé Peninsula on the Atlantic coast, and as far south as Chile, Monte Verde.[citation needed] American hunter-gatherers were spread over a wide geographical area, thus there were regional variations in lifestyles. However, all the individual groups shared a common style of stone tool production, making knapping styles and progress identifiable. This early Paleo-Indian period lithic reduction tool adaptations have been found across the Americas, utilized by highly mobile bands consisting of approximately 25 to 50 members of an extended family. The Archaic period in the Americas saw a changing environment featuring a warmer more arid climate and the disappearance of the last megafauna. The majority of population groups at this time were still highly mobile hunter-gatherers. Individual groups started to focus on resources available to them locally, however, and thus archaeologists have identified a pattern of increasing regional generalization, as seen with the Southwest, Arctic, Poverty Point, Dalton and Plano traditions. These regional adaptations would become the norm, with reliance less on hunting and gathering, with a more mixed economy of small game, fish, seasonally wild vegetables and harvested plant foods. Scholars like Kat Anderson have suggested that the term Hunter-gatherer is reductive because it implies that Native Americans never stayed in one place long enough to affect the environment around them. However, many of the landscapes in the Americas today are due to the way the Natives of that area originally tended the land. Anderson specifically looks at California Natives and the practices they utilized to tame their land. Some of these practices included pruning, weeding, sowing, burning, and selective harvesting. These practices allowed them to take from the environment in a sustainable manner for centuries. California Indians view the idea of wilderness in a negative light. They believe that wilderness is the result of humans losing their knowledge of the natural world and how to care for it. When the earth turns back to wilderness after the connection with humans is lost then the plants and animals will retreat and hide from the humans. See also References Further reading External links |
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[SOURCE: https://en.wikipedia.org/wiki/Ordovician] | [TOKENS: 4779] |
Contents Ordovician The Ordovician (/ɔːrdəˈvɪʃi.ən, -doʊ-, -ˈvɪʃən/ or-də-VISH-ee-ən, -doh-, -VISH-ən) is a geologic period and system, the second of six periods of the Paleozoic Era, and the second of twelve periods of the Phanerozoic Eon. The Ordovician spans 41.6 million years from the end of the Cambrian Period 486.85 Ma (million years ago) to the start of the Silurian Period 443.1 Ma. The Ordovician, named after the Welsh tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in North Wales in the Cambrian and Silurian systems, respectively. Lapworth recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian systems, and placed them in a system of their own. The Ordovician received international approval in 1960 (forty years after Lapworth's death), when it was adopted as an official period of the Paleozoic Era by the International Geological Congress. Life continued to flourish during the Ordovician as it had in the earlier Cambrian Period, although the end of the period was marked by the Ordovician–Silurian extinction events. Invertebrates, namely molluscs and arthropods, dominated the oceans, with members of the latter group probably starting their establishment on land during this time, becoming fully established by the Devonian. The first land plants are known from this period. The Great Ordovician Biodiversification Event considerably increased the diversity of life. Fish, the world's first true vertebrates, continued to evolve, and those with jaws may have first appeared late in the period. About 100 times as many meteorites struck the Earth per year during the Ordovician compared with today in a period known as the Ordovician meteor event. It has been theorized that this increase in impacts may originate from a ring system that formed around Earth at the time. Subdivisions In 2008, the ICS erected a formal international system of subdivisions for the Ordovician Period and System. Pre-existing Baltoscandic, British, Siberian, North American, Australian, Chinese, Mediterranean and North-Gondwanan regional stratigraphic schemes are also used locally. Paleogeography and tectonics During the Ordovician, the southern continents were assembled into Gondwana, which reached from north of the equator to the South Pole. The Panthalassic Ocean, centered in the northern hemisphere, covered over half the globe. At the start of the period, the continents of Laurentia (in present-day North America), Siberia, and Baltica (present-day northern Europe) were separated from Gondwana by over 5,000 kilometres (3,100 mi) of ocean. These smaller continents were also sufficiently widely separated from each other to develop distinct communities of benthic organisms. The small continent of Avalonia had just rifted from Gondwana and began to move north towards Baltica and Laurentia, opening the Rheic Ocean between Gondwana and Avalonia. Avalonia collided with Baltica towards the end of Ordovician. Other geographic features of the Ordovician world included the Tornquist Sea, which separated Avalonia from Baltica; the Aegir Ocean, which separated Baltica from Siberia; and an oceanic area between Siberia, Baltica, and Gondwana which expanded to become the Paleoasian Ocean in Carboniferous time. The Mongol-Okhotsk Ocean formed a deep embayment between Siberia and the Central Mongolian terranes. Most of the terranes of central Asia were part of an equatorial archipelago whose geometry is poorly constrained by the available evidence. The period was one of extensive, widespread tectonism and volcanism. However, orogenesis (mountain-building) was not primarily due to continent-continent collisions. Instead, mountains arose along active continental margins during accretion of arc terranes or ribbon microcontinents. Accretion of new crust was limited to the Iapetus margin of Laurentia; elsewhere, the pattern was of rifting in back-arc basins followed by remerger. This reflected episodic switching from extension to compression. The initiation of new subduction reflected a global reorganization of tectonic plates centered on the amalgamation of Gondwana. The Taconic orogeny, a major mountain-building episode, was well under way in Cambrian times. This continued into the Ordovician, when at least two volcanic island arcs collided with Laurentia to form the Appalachian Mountains. Laurentia was otherwise tectonically stable. An island arc accreted to South China during the period, while subduction along north China (Sulinheer) resulted in the emplacement of ophiolites. The ash fall of the Millburg/Big Bentonite bed, at about 454 Ma, was the largest in the last 590 million years. This had a dense rock equivalent volume of as much as 1,140 cubic kilometres (270 cu mi). Remarkably, this appears to have had little impact on life. There was vigorous tectonic activity along northwest margin of Gondwana during the Floian, 478 Ma, recorded in the Central Iberian Zone of Spain. The activity reached as far as Turkey by the end of Ordovician. The opposite margin of Gondwana, in Australia, faced a set of island arcs. The accretion of these arcs to the eastern margin of Gondwana was responsible for the Benambran Orogeny of eastern Australia. Subduction also took place along what is now Argentina (Famatinian Orogeny) at 450 Ma. This involved significant back arc rifting. The interior of Gondwana was tectonically quiet until the Triassic. Towards the end of the Ordovician, Gondwana began to drift across the South Pole; this contributed to the Hirnantian glaciation and the associated extinction event. The Ordovician meteor event is a proposed shower of meteors that occurred during the Middle Ordovician Epoch, about 467.5 ± 0.28 million years ago, due to the break-up of the L chondrite parent body. It is not associated with any major extinction event. A 2024 study found that craters from this event cluster in a distinct band around the Earth, and that the breakup of the parent body may have formed a ring system for a period of about 40 million years, with frequent falling debris causing these craters. Geochemistry The Ordovician was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate. Carbonate hardgrounds were thus very common, along with calcitic ooids, calcitic cements, and invertebrate faunas with dominantly calcitic skeletons. Biogenic aragonite, like that composing the shells of most molluscs, dissolved rapidly on the sea floor after death. Unlike Cambrian times, when calcite production was dominated by microbial and non-biological processes, animals (and macroalgae) became a dominant source of calcareous material in Ordovician deposits. Climate and sea level The Early Ordovician climate was very hot, with intense greenhouse conditions and sea surface temperatures comparable to those during the Early Eocene Climatic Optimum. Carbon dioxide levels were very high at the Ordovician period's beginning. By the late Early Ordovician, the Earth cooled, giving way to a more temperate climate in the Middle Ordovician, with the Earth likely entering the Early Palaeozoic Ice Age during the Sandbian, and possibly as early as the Darriwilian or even the Floian. The Dapingian and Sandbian saw major humidification events evidenced by trace metal concentrations in Baltoscandia from this time. Evidence suggests that global temperatures rose briefly in the early Katian (Boda Event), depositing bioherms and radiating fauna across Europe. The early Katian also witnessed yet another humidification event. Further cooling during the Hirnantian, at the end of the Ordovician, led to the Late Ordovician glaciation. The Ordovician saw the highest sea levels of the Paleozoic, and the low relief of the continents led to many shelf deposits being formed under hundreds of metres of water. The sea level rose more or less continuously throughout the Early Ordovician, leveling off somewhat during the middle of the period. Locally, some regressions occurred, but the sea level rise continued in the beginning of the Late Ordovician. Sea levels fell steadily due to the cooling temperatures for about 3 million years leading up to the Hirnantian glaciation. During this icy stage, the sea level has risen and dropped somewhat. Despite much study, the details remain unresolved. In particular, some researches interpret the fluctuations in sea level as pre-Hibernian glaciation, but sedimentary evidence of glaciation is lacking until the end of the period. There is evidence of glaciers during the Hirnantian on the land we now know as Africa and South America, which were near the South Pole at the time, facilitating the formation of the ice caps of the Hirnantian glaciation. As with North America and Europe, Gondwana was largely covered with shallow seas during the Ordovician. Shallow clear waters over continental shelves encouraged the growth of organisms that deposit calcium carbonates in their shells and hard parts. The Panthalassic Ocean covered much of the Northern Hemisphere, and other minor oceans included Proto-Tethys, Paleo-Tethys, Khanty Ocean, which was closed off by the Late Ordovician, Iapetus Ocean, and the new Rheic Ocean. Life For most of the Late Ordovician life continued to flourish, but at and near the end of the period there were mass-extinction events that seriously affected conodonts and planktonic forms like graptolites. The trilobites Agnostida and Ptychopariida completely died out, and the Asaphida were much reduced. Brachiopods, bryozoans and echinoderms were also heavily affected, and the endocerid cephalopods died out completely, except for possible rare Silurian forms. The Ordovician–Silurian extinction events may have been caused by an ice age that occurred at the end of the Ordovician Period, due to the expansion of the first terrestrial plants, as the end of the Late Ordovician was one of the coldest times in the last 600 million years of Earth's history. On the whole, the fauna that emerged in the Ordovician were the template for the remainder of the Palaeozoic. The fauna was dominated by tiered communities of suspension feeders, mainly with short food chains. The ecological system reached a new grade of complexity far beyond that of the Cambrian fauna, which has persisted until the present day. Though less famous than the Cambrian explosion, the Ordovician radiation (also known as the Great Ordovician Biodiversification Event) was no less remarkable; marine faunal genera increased fourfold, resulting in 12% of all known Phanerozoic marine fauna. Several animals also went through a miniaturization process, becoming much smaller than their Cambrian counterparts.[citation needed] Another change in the fauna was the strong increase in filter-feeding organisms. The trilobite, inarticulate brachiopod, archaeocyathid, and eocrinoid faunas of the Cambrian were succeeded by those that dominated the rest of the Paleozoic, such as articulate brachiopods, cephalopods, and crinoids. Articulate brachiopods, in particular, largely replaced trilobites in shelf communities. Their success epitomizes the greatly increased diversity of carbonate shell-secreting organisms in the Ordovician compared to the Cambrian. Ordovician geography had its effect on the diversity of fauna; Ordovician invertebrates displayed a very high degree of provincialism. The widely separated continents of Laurentia and Baltica, then positioned close to the tropics and boasting many shallow seas rich in life, developed distinct trilobite faunas from the trilobite fauna of Gondwana, and Gondwana developed distinct fauna in its tropical and temperature zones. The Tien Shan terrane maintained a biogeographic affinity with Gondwana, and the Alborz margin of Gondwana was linked biogeographically to South China. Southeast Asia's fauna also maintained strong affinities to Gondwana's. North China was biogeographically connected to Laurentia and the Argentinian margin of Gondwana. A Celtic biogeographic province also existed, separate from the Laurentian and Baltican ones. However, tropical articulate brachiopods had a more cosmopolitan distribution, with less diversity on different continents. During the Middle Ordovician, beta diversity began a significant decline as marine taxa began to disperse widely across space. Faunas become less provincial later in the Ordovician, partly due to the narrowing of the Iapetus Ocean, though they were still distinguishable into the late Ordovician. Trilobites in particular were rich and diverse, and experienced rapid diversification in many regions. Trilobites in the Ordovician were very different from their predecessors in the Cambrian. Many trilobites developed bizarre spines and nodules to defend against predators such as primitive eurypterids and nautiloids while other trilobites such as Aeglina prisca evolved to become swimming forms. Some trilobites even developed shovel-like snouts for ploughing through muddy sea bottoms. Another unusual clade of trilobites known as the trinucleids developed a broad pitted margin around their head shields. Some trilobites such as Asaphus kowalewski evolved long eyestalks to assist in detecting predators whereas other trilobite eyes in contrast disappeared completely. Molecular clock analyses suggest that early arachnids started living on land by the end of the Ordovician. Although solitary corals date back to at least the Cambrian, reef-forming corals appeared in the early Ordovician, including the earliest known octocorals, corresponding to an increase in the stability of carbonate and thus a new abundance of calcifying animals. Brachiopods surged in diversity, adapting to almost every type of marine environment. Even after GOBE, there is evidence suggesting that Ordovician brachiopods maintained elevated rates of speciation. Molluscs, which appeared during the Cambrian or even the Ediacaran, became common and varied, especially bivalves, gastropods, and nautiloid cephalopods. Cephalopods diversified from shallow marine tropical environments to dominate almost all marine environments. Graptolites, which evolved in the preceding Cambrian period, thrived in the oceans. This includes the distinctive Nemagraptus gracilis graptolite fauna, which was distributed widely during peak sea levels in the Sandbian. Some new cystoids and crinoids appeared. It was long thought that the first true vertebrates (fish — Ostracoderms) appeared in the Ordovician, but recent discoveries in China reveal that they probably originated in the Early Cambrian. The first gnathostome (jawed fish) may have appeared in the Late Ordovician epoch. Chitinozoans, which first appeared late in the Wuliuan, exploded in diversity during the Tremadocian, quickly becoming globally widespread. Several groups of endobiotic symbionts appeared in the Ordovician. In the Early Ordovician, trilobites were joined by many new types of organisms, including tabulate corals, strophomenid, rhynchonellid, and many new orthid brachiopods, bryozoans, planktonic graptolites and conodonts, and many types of molluscs and echinoderms, including the ophiuroids ("brittle stars") and the first sea stars. Nevertheless, the arthropods remained abundant; all the Late Cambrian orders continued, and were joined by the new group Phacopida. The first evidence of land plants also appeared (see evolutionary history of life). In the Middle Ordovician, the trilobite-dominated Early Ordovician communities were replaced by generally more mixed ecosystems, in which brachiopods, bryozoans, molluscs, cornulitids, tentaculitids and echinoderms all flourished, tabulate corals diversified and the first rugose corals appeared. The planktonic graptolites remained diverse, with the Diplograptina making their appearance. One of the earliest known armoured agnathan ("ostracoderm") vertebrates, Arandaspis, dates from the Middle Ordovician. During the Middle Ordovician there was a large increase in the intensity and diversity of bioeroding organisms. This is known as the Ordovician Bioerosion Revolution. It is marked by a sudden abundance of hard substrate trace fossils such as Trypanites, Palaeosabella, Petroxestes and Osprioneides. Bioerosion became an important process, particularly in the thick calcitic skeletons of corals, bryozoans and brachiopods, and on the extensive carbonate hardgrounds that appear in abundance at this time. Green algae were common in the Late Cambrian (perhaps earlier) and in the Ordovician. Terrestrial plants probably evolved from green algae, first appearing as tiny non-vascular forms resembling liverworts, in the middle to late Ordovician. Fossil spores found in Ordovician sedimentary rock are typical of bryophytes. Among the first land fungi may have been arbuscular mycorrhiza fungi (Glomerales), playing a crucial role in facilitating the colonization of land by plants through mycorrhizal symbiosis, which makes mineral nutrients available to plant cells; such fossilized fungal hyphae and spores from the Ordovician of Wisconsin have been found with an age of about 460 million years ago, a time when the land flora most likely only consisted of plants similar to non-vascular bryophytes. Though stromatolites had declined from their peak in the Proterozoic, they continued to exist in localised settings. End of the period The Ordovician came to a close in a series of extinction events that, taken together, comprise the second largest of the five major extinction events in Earth's history in terms of percentage of genera that became extinct. The only larger one was the Permian–Triassic extinction event. The extinctions occurred approximately 447–444 million years ago and mark the boundary between the Ordovician and the following Silurian Period. At that time all complex multicellular organisms lived in the sea, and about 49% of genera of fauna disappeared forever; brachiopods and bryozoans were greatly reduced, along with many trilobite, conodont and graptolite families. The most commonly accepted theory is that these events were triggered by the onset of cold conditions in the late Katian, followed by an ice age, in the Hirnantian faunal stage, that ended the long, stable greenhouse conditions typical of the Ordovician. The ice age was possibly not long-lasting. Oxygen isotopes in fossil brachiopods show its duration may have been only 0.5 to 1.5 million years. Other researchers (Page et al.) estimate more temperate conditions did not return until the late Silurian. The late Ordovician glaciation event was preceded by a fall in atmospheric carbon dioxide (from 7000 ppm to 4400 ppm). The dip may have been caused by a burst of volcanic activity that deposited new silicate rocks, which draw CO2 out of the air as they erode. Another possibility is that bryophytes and lichens, which colonized land in the middle to late Ordovician, may have increased weathering enough to draw down CO2 levels. The drop in CO2 selectively affected the shallow seas where most organisms lived. It has also been suggested that shielding of the sun's rays from the proposed Ordovician ring system, which also caused the Ordovician meteor event, may have also led to the glaciation. As the southern supercontinent Gondwana drifted over the South Pole, ice caps formed on it, which have been detected in Upper Ordovician rock strata of North Africa and then-adjacent northeastern South America, which were south-polar locations at the time. As glaciers grew, the sea level dropped, and the vast shallow intra-continental Ordovician seas withdrew, which eliminated many ecological niches. When they returned, they carried diminished founder populations that lacked many whole families of organisms. They then withdrew again with the next pulse of glaciation, eliminating biological diversity with each change. Species limited to a single epicontinental sea on a given landmass were severely affected. Tropical lifeforms were hit particularly hard in the first wave of extinction, while cool-water species were hit worst in the second pulse. Those species able to adapt to the changing conditions survived to fill the ecological niches left by the extinctions. For example, there is evidence the oceans became more deeply oxygenated during the glaciation, allowing unusual benthic organisms (Hirnantian fauna) to colonize the depths. These organisms were cosmopolitan in distribution and present at most latitudes. At the end of the second event, melting glaciers caused the sea level to rise and stabilise once more. The rebound of life's diversity with the permanent re-flooding of continental shelves at the onset of the Silurian saw increased biodiversity within the surviving Orders. Recovery was characterized by an unusual number of "Lazarus taxa", disappearing during the extinction and reappearing well into the Silurian, which suggests that the taxa survived in small numbers in refugia. An alternate extinction hypothesis suggested that a ten-second gamma-ray burst could have destroyed the ozone layer and exposed terrestrial and marine surface-dwelling life to deadly ultraviolet radiation and initiated global cooling. Recent work considering the sequence stratigraphy of the Late Ordovician argues that the mass extinction was a single protracted episode lasting several hundred thousand years, with abrupt changes in water depth and sedimentation rate producing two pulses of last occurrences of species. References External links |
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[SOURCE: https://en.wikipedia.org/wiki/Set_(mathematics)] | [TOKENS: 9999] |
Contents Set (mathematics) In mathematics, a set is a collection of different things; the things are called elements or members of the set and are typically mathematical objects: numbers, symbols, points in space, lines, geometric shapes, variables, or other sets. A set may be finite or infinite. There is a unique set with no elements, called the empty set; a set with a single element is a singleton. Mathematics typically does not define precisely what constitutes a "set" or "collection", because such a definition would have to be in terms of something else previously defined. Instead, sets serve as foundational objects whose behavior is described by axioms modeled on intuition about collections, and then essentially all other mathematical objects are rigorously defined in terms of sets. Set theory studies possible axiom systems and their consequences. Since the first half of the 20th century, ZFC (Zermelo–Fraenkel set theory with the axiom of choice) has been the axiom system most commonly used. Context Before the end of the 19th century, sets were not studied specifically, and were not clearly distinguished from sequences. Most mathematicians considered infinity as potential—meaning that it is the result of an endless process—and were reluctant to consider infinite sets, that is sets whose number of members is not a natural number. Specifically, a line was not considered as the set of its points, but as a locus where points may be located. The mathematical study of infinite sets began with Georg Cantor (1845–1918). This provided some counterintuitive facts and paradoxes. For example, the number line has an infinite number of elements that is strictly larger than the infinite number of natural numbers, and any line segment has the same number of elements as the whole space. Also, Russell's paradox implies that the phrase "the set of all sets" is self-contradictory. Together with other counterintuitive results, this led to the foundational crisis of mathematics, which was eventually resolved with the general adoption of Zermelo–Fraenkel set theory as a robust foundation of set theory and all mathematics. Meanwhile, sets started to be widely used in all mathematics. In particular, algebraic structures and mathematical spaces are typically defined in terms of sets. Also, many older mathematical results are restated in terms of sets. For example, Euclid's theorem is often stated as "the set of the prime numbers is infinite". This wide use of sets in mathematics was prophesied by David Hilbert when saying: "No one will drive us from the paradise that Cantor created for us." Generally, the common usage of sets in mathematics does not require the full power of Zermelo–Fraenkel set theory. In mathematical practice, sets can be manipulated independently of the logical framework of this theory. The object of this article is to summarize the manipulation rules and properties of sets that are commonly used in mathematics, without reference to any logical framework. For the branch of mathematics that studies sets, see Set theory; for an informal presentation of the corresponding logical framework, see Naive set theory; for a more formal presentation, see Axiomatic set theory and Zermelo–Fraenkel set theory. Basic notions In mathematics, a set is a collection of different things. These things are called elements or members of the set and are typically mathematical objects of any kind such as numbers, symbols, points in space, lines, other geometrical shapes, variables, functions, or even other sets. A set may also be called a collection or family, especially when its elements are themselves sets; this may avoid the confusion between the set and its members, and may make reading easier. A set may be specified either by listing its elements or by a property that characterizes its elements, such as for the set of the prime numbers or the set of all students in a given class. If x {\displaystyle x} is an element of a set S {\displaystyle S} , one says that x {\displaystyle x} belongs to S {\displaystyle S} or is in S {\displaystyle S} , and this is written as x ∈ S {\displaystyle x\in S} . The statement " y {\displaystyle y} is not in S {\displaystyle S\,} " is written as y ∉ S {\displaystyle y\not \in S} , which can also be read as "y is not in S". For example, if Z {\displaystyle \mathbb {Z} } is the set of the integers, one has − 3 ∈ Z {\displaystyle -3\in \mathbb {Z} } and 1.5 ∉ Z {\displaystyle 1.5\not \in \mathbb {Z} } . Each set is uniquely characterized by its elements. In particular, two sets that have precisely the same elements are equal (they are the same set). This property, called extensionality, can be written in formula as A = B ⟺ ∀ x ( x ∈ A ⟺ x ∈ B ) . {\displaystyle A=B\iff \forall x\;(x\in A\iff x\in B).} This implies that there is only one set with no element, the empty set (or null set) that is denoted ∅ , ∅ {\displaystyle \varnothing ,\emptyset } ,[a] or { } . {\displaystyle \{\,\}.} A singleton is a set with exactly one element.[b] If x {\displaystyle x} is this element, the singleton is denoted { x } {\displaystyle \{x\}} . An element of a set can be itself a set. For example, the singleton { ∅ } {\displaystyle \{\emptyset \}} is a set that has the empty set ∅ {\displaystyle \emptyset } as its only element. Since these two sets do not have the same elements, { ∅ } {\displaystyle \{\emptyset \}} and ∅ {\displaystyle \emptyset } are different sets. A set is finite if there exists a natural number n {\displaystyle n} such that the n {\displaystyle n} first natural numbers can be put in one to one correspondence with the elements of the set. In this case, one says that n {\displaystyle n} is the number of elements of the set. A set is infinite if such an n {\displaystyle n} does not exist. The empty set is a finite set with 0 {\displaystyle 0} elements. The natural numbers form an infinite set, commonly denoted N {\displaystyle \mathbb {N} } . Other examples of infinite sets include integer numbers ( Z {\displaystyle \mathbb {Z} } ), rational numbers ( Q {\displaystyle \mathbb {Q} } ), real numbers ( R {\displaystyle \mathbb {R} } ), real vector spaces, curves and most sorts of mathematical spaces. Specifying a set Extensionality implies that for specifying a set, one has either to list its elements or to provide a property that uniquely characterizes the set elements. Roster or enumeration notation is a notation introduced by Ernst Zermelo in 1908 that specifies a set by listing its elements between braces, separated by commas. For example, one sees that { 4 , 2 , 1 , 3 } {\displaystyle \{4,2,1,3\}} and { blue, white, red } {\displaystyle \{{\text{blue, white, red}}\}} denote sets and not tuples because of the enclosing braces. The notations { } {\displaystyle \{\,\}} for the empty set and { x } {\displaystyle \{x\}} for a singleton are examples of roster notation. When specifying a set, all that matters is whether each potential element is in the set or not, so a set does not change if elements are repeated or arranged in a different order. For example, { 1 , 2 , 3 , 4 } = { 4 , 2 , 1 , 3 } = { 4 , 2 , 4 , 3 , 1 , 3 } . {\displaystyle \{1,2,3,4\}=\{4,2,1,3\}=\{4,2,4,3,1,3\}.} When there is a clear pattern for generating all set elements, one can use an ellipsis to abbreviate the notation; for example, { 1 , 2 , 3 , … , 10 } {\displaystyle \{1,2,3,\ldots ,10\}} is a shorthand for { 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 } {\displaystyle \{1,2,3,4,5,6,7,8,9,10\}} . Ellipses in roster notation can also be used to describe some infinite sets; for example, the set of all integers can be denoted as { … , − 3 , − 2 , − 1 , 0 , 1 , 2 , 3 , … } {\displaystyle \{\ldots ,-3,-2,-1,0,1,2,3,\ldots \}} or { 0 , 1 , − 1 , 2 , − 2 , 3 , − 3 , … } . {\displaystyle \{0,1,-1,2,-2,3,-3,\ldots \}.} Set-builder notation specifies a set as being the set of all elements that satisfy some logical formula. More precisely, if P ( x ) {\displaystyle P(x)} is a logical formula depending on a variable x {\displaystyle x} , which evaluates to true or false depending on the value of x {\displaystyle x} , then { x ∣ P ( x ) } {\displaystyle \{x\mid P(x)\}} or { x : P ( x ) } {\displaystyle \{x:P(x)\}} denotes the set of all x {\displaystyle x} for which P ( x ) {\displaystyle P(x)} is true. For example, a set F can be specified as follows: F = { n ∣ n is an integer, and 0 ≤ n ≤ 19 } . {\displaystyle F=\{n\mid n{\text{ is an integer, and }}0\leq n\leq 19\}.} In this notation, the vertical bar "|" is read as "such that", and the whole formula can be read as "F is the set of all n such that n is an integer in the range from 0 to 19 inclusive". Some logical formulas, such as S is a set {\displaystyle \color {red}{S{\text{ is a set}}}} or S is a set and S ∉ S {\displaystyle \color {red}{S{\text{ is a set and }}S\not \in S}} cannot be used in set-builder notation because there is no set for which the elements are characterized by the formula. There are several ways for avoiding the problem. One may prove that the formula defines a set; this is often almost immediate, but may be very difficult. One may also introduce a larger set U {\displaystyle U} that must contain all elements of the specified set, and write the notation as { x ∣ x ∈ U and ... } {\displaystyle \{x\mid x\in U{\text{ and ...}}\}} or { x ∈ U ∣ ... } . {\displaystyle \{x\in U\mid {\text{ ...}}\}.} One may also define U {\displaystyle U} once for all and take the convention that every variable that appears on the left of the vertical bar of the notation represents an element of U {\displaystyle U} . This amounts to saying that x ∈ U {\displaystyle x\in U} is implicit in set-builder notation. In this case, U {\displaystyle U} is often called the domain of discourse or a universe. For example, with the convention that a lower case Latin letter may represent a real number and nothing else, the expression { x ∣ x ∉ Q } {\displaystyle \{x\mid x\not \in \mathbb {Q} \}} is an abbreviation of { x ∈ R ∣ x ∉ Q } , {\displaystyle \{x\in \mathbb {R} \mid x\not \in \mathbb {Q} \},} which defines the irrational numbers. Subsets A subset of a set B {\displaystyle B} is a set A {\displaystyle A} such that every element of A {\displaystyle A} is also an element of B {\displaystyle B} . The following are different ways of expressing the same thing: The relationship between sets established by ⊆ is called inclusion or containment. A set A {\displaystyle A} is a proper subset of a set B {\displaystyle B} if A ⊆ B {\displaystyle A\subseteq B} and A ≠ B {\displaystyle A\neq B} ; to denote this, one writes A ⊊ B {\displaystyle A\subsetneq B} , or A ⫋ B {\displaystyle A\subsetneqq B} . Likewise, one may write B ⊋ A {\displaystyle B\supsetneq A} or B ⫌ A {\displaystyle B\supsetneqq A} . The notation A ⊂ B {\displaystyle A\subset B} often means A ⊆ B {\displaystyle A\subseteq B} , but some authors use A ⊂ B {\displaystyle A\subset B} to mean A ⊊ B {\displaystyle A\subsetneq B} . To avoid ambiguity, one can write A ⊆ B {\displaystyle A\subseteq B} or A ⊊ B {\displaystyle A\subsetneq B} , depending on what is intended. Basic operations There are several standard operations that produce new sets from given sets, in the same way as addition and multiplication produce new numbers from given numbers. The operations that are considered in this section are those such that all elements of the produced sets belong to a previously defined set. These operations are commonly illustrated with Euler diagrams and Venn diagrams. The main basic operations on sets are the following ones. The intersection of two sets A {\displaystyle A} and B {\displaystyle B} is a set denoted A ∩ B {\displaystyle A\cap B} whose elements are those elements that belong to both A {\displaystyle A} and B {\displaystyle B} . That is, A ∩ B = { x ∣ x ∈ A ∧ x ∈ B } , {\displaystyle A\cap B=\{x\mid x\in A\land x\in B\},} where ∧ {\displaystyle \land } denotes the logical and. Intersection is associative and commutative; this means that for proceeding a sequence of intersections, one may proceed in any order, without the need of parentheses for specifying the order of operations. If S {\displaystyle {\mathcal {S}}} is a nonempty set of sets, its intersection, denoted ⋂ A ∈ S A , {\textstyle \bigcap _{A\in {\mathcal {S}}}A,} is the set whose elements are those elements that belong to all sets in S {\displaystyle {\mathcal {S}}} . That is, ⋂ A ∈ S A = { x ∣ ( ∀ A ∈ S ) x ∈ A } . {\displaystyle \bigcap _{A\in {\mathcal {S}}}A=\{x\mid (\forall A\in {\mathcal {S}})\;x\in A\}.} Example: If S = { X , Y } {\displaystyle {\mathcal {S}}=\{X,Y\}} , then ⋂ A ∈ S A = X ∩ Y {\textstyle \bigcap _{A\in {\mathcal {S}}}A=X\cap Y} . The union of two sets A {\displaystyle A} and B {\displaystyle B} is a set denoted A ∪ B {\displaystyle A\cup B} whose elements are those elements that belong to A {\displaystyle A} or B {\displaystyle B} or both. That is, A ∪ B = { x ∣ x ∈ A ∨ x ∈ B } , {\displaystyle A\cup B=\{x\mid x\in A\lor x\in B\},} where ∨ {\displaystyle \lor } denotes the logical or. Union is associative and commutative. If S {\displaystyle {\mathcal {S}}} is a set of sets, its union, denoted ⋃ A ∈ S A , {\textstyle \bigcup _{A\in {\mathcal {S}}}A,} is the set whose elements are those elements that belong to at least one set in S {\displaystyle {\mathcal {S}}} . That is, ⋃ A ∈ S A = { x ∣ ( ∃ A ∈ S ) x ∈ A } . {\displaystyle \bigcup _{A\in {\mathcal {S}}}A=\{x\mid (\exists A\in {\mathcal {S}})\;x\in A\}.} Example: If S = { X , Y } {\displaystyle {\mathcal {S}}=\{X,Y\}} , then ⋂ A ∈ S A = X ∪ Y {\textstyle \bigcap _{A\in {\mathcal {S}}}A=X\cup Y} . The set difference of two sets A {\displaystyle A} and B {\displaystyle B} , is a set, denoted A ∖ B {\displaystyle A\setminus B} or A − B {\displaystyle A-B} , whose elements are those elements that belong to A {\displaystyle A} , but not to B {\displaystyle B} . That is, A ∖ B = { x ∣ x ∈ A ∧ x ∉ B } , {\displaystyle A\setminus B=\{x\mid x\in A\land x\not \in B\},} where ∧ {\displaystyle \land } denotes the logical and. When B ⊆ A {\displaystyle B\subseteq A} the difference A ∖ B {\displaystyle A\setminus B} is also called the complement of B {\displaystyle B} in A {\displaystyle A} . When all sets that are considered are subsets of a fixed universal set U {\displaystyle U} , the complement U ∖ A {\displaystyle U\setminus A} is often called the absolute complement of A {\displaystyle A} . The symmetric difference of two sets A {\displaystyle A} and B {\displaystyle B} , denoted A Δ B {\displaystyle A\,\Delta \,B} , is the set of those elements that belong to A or B but not to both: A Δ B = ( A ∖ B ) ∪ ( B ∖ A ) . {\displaystyle A\,\Delta \,B=(A\setminus B)\cup (B\setminus A).} The set of all subsets of a set U {\displaystyle U} is called the powerset of U {\displaystyle U} , often denoted P ( U ) {\displaystyle {\mathcal {P}}(U)} . The powerset is an algebraic structure whose main operations are union, intersection, set difference, symmetric difference and absolute complement (complement in U {\displaystyle U} ). The powerset is a Boolean ring that has symmetric difference as addition, intersection as multiplication, the empty set as additive identity, U {\displaystyle U} as multiplicative identity, and the subset itself as the additive inverse. The powerset is also a Boolean algebra for which the join ∨ {\displaystyle \lor } is the union ∪ {\displaystyle \cup } , the meet ∧ {\displaystyle \land } is the intersection ∩ {\displaystyle \cap } , and the negation is the set complement. As for every Boolean algebra, the power set is also a partially ordered set for set inclusion. It is also a complete lattice. The axioms of these structures induce many identities relating subsets, which are detailed in the linked articles. Functions A function from a set A—the domain—to a set B—the codomain—is a rule that assigns to each element of A a unique element of B. For example, the square function maps every real number x to x2. Functions can be formally defined in terms of sets by means of their graph, which are subsets of the Cartesian product (see below) of the domain and the codomain. Functions are fundamental for set theory, and examples are given in following sections. Intuitively, an indexed family is a set whose elements are labelled with the elements of another set, the index set. These labels allow the same element to occur several times in the family. Formally, an indexed family is a function that has the index set as its domain. Generally, the usual functional notation f ( x ) {\displaystyle f(x)} is not used for indexed families. Instead, the element of the index set is written as a subscript of the name of the family, such as in a i {\displaystyle a_{i}} . When the index set is { 1 , 2 } {\displaystyle \{1,2\}} , an indexed family is called an ordered pair. When the index set is the set of the n {\displaystyle n} first natural numbers, an indexed family is called an n {\displaystyle n} -tuple. When the index set is the set of all natural numbers an indexed family is called a sequence. In all these cases, the natural order of the natural numbers allows omitting indices for explicit indexed families. For example, ( b , 2 , b ) {\displaystyle (b,2,b)} denotes the 3-tuple A {\displaystyle A} such that A 1 = b , A 2 = 2 , A 3 = b {\displaystyle A_{1}=b,A_{2}=2,A_{3}=b} . The above notations ⋃ A ∈ S A {\textstyle \bigcup _{A\in {\mathcal {S}}}A} and ⋂ A ∈ S A {\textstyle \bigcap _{A\in {\mathcal {S}}}A} are commonly replaced with a notation involving indexed families, namely ⋃ i ∈ I A i = { x ∣ ( ∃ i ∈ I ) x ∈ A i } {\displaystyle \bigcup _{i\in {\mathcal {I}}}A_{i}=\{x\mid (\exists i\in {\mathcal {I}})\;x\in A_{i}\}} and ⋂ i ∈ I A i = { x ∣ ( ∀ i ∈ I ) x ∈ A i } . {\displaystyle \bigcap _{i\in {\mathcal {I}}}A_{i}=\{x\mid (\forall i\in {\mathcal {I}})\;x\in A_{i}\}.} The formulas of the above sections are special cases of the formulas for indexed families, where S = I {\displaystyle {\mathcal {S}}={\mathcal {I}}} and i = A = A i {\displaystyle i=A=A_{i}} . The formulas remain correct, even in the case where A i = A j {\displaystyle A_{i}=A_{j}} for some i ≠ j {\displaystyle i\neq j} , since A = A ∪ A = A ∩ A . {\displaystyle A=A\cup A=A\cap A.} External operations In § Basic operations, all elements of sets produced by set operations belong to previously defined sets. In this section, other set operations are considered, which produce sets whose elements can be outside all previously considered sets. These operations are Cartesian product, disjoint union, set exponentiation and power set. The Cartesian product of two sets has already been used for defining functions. Given two sets A 1 {\displaystyle A_{1}} and A 2 {\displaystyle A_{2}} , their Cartesian product, denoted A 1 × A 2 {\displaystyle A_{1}\times A_{2}} is the set formed by all ordered pairs ( a 1 , a 2 ) {\displaystyle (a_{1},a_{2})} such that a 1 ∈ A 1 {\displaystyle a_{1}\in A_{1}} and a 2 ∈ A 2 {\displaystyle a_{2}\in A_{2}} ; that is, A 1 × A 2 = { ( a 1 , a 2 ) ∣ a 1 ∈ A 1 ∧ a 2 ∈ A 2 } . {\displaystyle A_{1}\times A_{2}=\{(a_{1},a_{2})\mid a_{1}\in A_{1}\land a_{2}\in A_{2}\}.} This definition does not suppose that the two sets are different. In particular, A × A = { ( a 1 , a 2 ) ∣ a 1 ∈ A ∧ a 2 ∈ A } . {\displaystyle A\times A=\{(a_{1},a_{2})\mid a_{1}\in A\land a_{2}\in A\}.} Since this definition involves a pair of indices (1,2), it generalizes straightforwardly to the Cartesian product or direct product of any indexed family of sets: ∏ i ∈ I A i = { ( a i ) i ∈ I ∣ ( ∀ i ∈ I ) a i ∈ A i } . {\displaystyle \prod _{i\in {\mathcal {I}}}A_{i}=\{(a_{i})_{i\in {\mathcal {I}}}\mid (\forall i\in {\mathcal {I}})\;a_{i}\in A_{i}\}.} That is, the elements of the Cartesian product of a family of sets are all families of elements such that each one belongs to the set of the same index. The fact that, for every indexed family of nonempty sets, the Cartesian product is a nonempty set is insured by the axiom of choice. Given two sets E {\displaystyle E} and F {\displaystyle F} , the set exponentiation, denoted F E {\displaystyle F^{E}} , is the set that has as elements all functions from E {\displaystyle E} to F {\displaystyle F} . Equivalently, F E {\displaystyle F^{E}} can be viewed as the Cartesian product of a family, indexed by E {\displaystyle E} , of sets that are all equal to F {\displaystyle F} . This explains the terminology and the notation, since exponentiation with integer exponents is a product where all factors are equal to the base. The power set of a set E {\displaystyle E} is the set that has all subsets of E {\displaystyle E} as elements, including the empty set and E {\displaystyle E} itself. It is often denoted P ( E ) {\displaystyle {\mathcal {P}}(E)} . For example, P ( { 1 , 2 , 3 } ) = { ∅ , { 1 } , { 2 } , { 3 } , { 1 , 2 } , { 1 , 3 } , { 2 , 3 } , { 1 , 2 , 3 } } . {\displaystyle {\mathcal {P}}(\{1,2,3\})=\{\emptyset ,\{1\},\{2\},\{3\},\{1,2\},\{1,3\},\{2,3\},\{1,2,3\}\}.} There is a natural one-to-one correspondence (bijection) between the subsets of E {\displaystyle E} and the functions from E {\displaystyle E} to { 0 , 1 } {\displaystyle \{0,1\}} ; this correspondence associates to each subset the function that takes the value 1 {\displaystyle 1} on the subset and 0 {\displaystyle 0} elsewhere. Because of this correspondence, the power set of E {\displaystyle E} is commonly identified with set exponentiation: P ( E ) = { 0 , 1 } E . {\displaystyle {\mathcal {P}}(E)=\{0,1\}^{E}.} In this notation, { 0 , 1 } {\displaystyle \{0,1\}} is often abbreviated as 2 {\displaystyle 2} , which gives P ( E ) = 2 E . {\displaystyle {\mathcal {P}}(E)=2^{E}.} In particular, if E {\displaystyle E} has n {\displaystyle n} elements, then 2 E {\displaystyle 2^{E}} has 2 n {\displaystyle 2^{n}} elements. The disjoint union of two or more sets is similar to the union, but, if two sets have elements in common, these elements are considered as distinct in the disjoint union. This is obtained by labelling the elements by the indexes of the set they are coming from. The disjoint union of two sets A {\displaystyle A} and B {\displaystyle B} is commonly denoted A ⊔ B {\displaystyle A\sqcup B} and is thus defined as A ⊔ B = { ( a , i ) ∣ ( i = 1 ∧ a ∈ A ) ∨ ( i = 2 ∧ a ∈ B } . {\displaystyle A\sqcup B=\{(a,i)\mid (i=1\land a\in A)\lor (i=2\land a\in B\}.} If A = B {\displaystyle A=B} is a set with n {\displaystyle n} elements, then A ∪ A = A {\displaystyle A\cup A=A} has n {\displaystyle n} elements, while A ⊔ A {\displaystyle A\sqcup A} has 2 n {\displaystyle 2n} elements. The disjoint union of two sets is a particular case of the disjoint union of an indexed family of sets, which is defined as ⨆ i ∈ I = { ( a , i ) ∣ i ∈ I ∧ a ∈ A i } . {\displaystyle \bigsqcup _{i\in {\mathcal {I}}}=\{(a,i)\mid i\in {\mathcal {I}}\land a\in A_{i}\}.} The disjoint union is the coproduct in the category of sets. Therefore the notation ∐ i ∈ I = { ( a , i ) ∣ i ∈ I ∧ a ∈ A i } {\displaystyle \coprod _{i\in {\mathcal {I}}}=\{(a,i)\mid i\in {\mathcal {I}}\land a\in A_{i}\}} is commonly used. Given an indexed family of sets ( A i ) i ∈ I {\displaystyle (A_{i})_{i\in {\mathcal {I}}}} , there is a natural map ⨆ i ∈ I A i → ⋃ i ∈ I A i ( a , i ) ↦ a , {\displaystyle {\begin{aligned}\bigsqcup _{i\in {\mathcal {I}}}A_{i}&\to \bigcup _{i\in {\mathcal {I}}}A_{i}\\(a,i)&\mapsto a,\end{aligned}}} which consists in "forgetting" the indices. This maps is always surjective; it is bijective if and only if the A i {\displaystyle A_{i}} are pairwise disjoint, that is, all intersections of two sets of the family are empty. In this case, ⋃ i ∈ I A i {\textstyle \bigcup _{i\in {\mathcal {I}}}A_{i}} and ⨆ i ∈ I A i {\textstyle \bigsqcup _{i\in {\mathcal {I}}}A_{i}} are commonly identified, and one says that their union is the disjoint union of the members of the family. If a set is the disjoint union of a family of subsets, one says also that the family is a partition of the set. Cardinality Informally, the cardinality of a set S, often denoted |S|, is the number of its members. This number is the natural number n {\displaystyle n} when there is a bijection between the set that is considered and the set { 1 , 2 , … , n } {\displaystyle \{1,2,\ldots ,n\}} of the first n {\displaystyle n} natural numbers. The cardinality of the empty set is 0 {\displaystyle 0} . A set with the cardinality of a natural number is called a finite set, which applies in both cases. Otherwise, one has an infinite set. The fact that natural numbers measure the cardinality of finite sets is the basis of the concept of natural number, and predates for several thousands years the concept of sets. A large part of combinatorics is devoted to the computation or estimation of the cardinality of finite sets. The cardinality of an infinite set is commonly represented by a cardinal number, exactly as the number of elements of a finite set is represented by a natural numbers. The definition of cardinal numbers is too technical for this article; however, many properties of cardinalities can be dealt without referring to cardinal numbers, as follows. Two sets S {\displaystyle S} and T {\displaystyle T} have the same cardinality if there exists a one-to-one correspondence (bijection) between them. This is denoted 1 {\displaystyle {1}} , and would be an equivalence relation on sets, if a set of all sets would exist. For example, the natural numbers and the even natural numbers have the same cardinality, since multiplication by two provides such a bijection. Similarly, the interval ( − 1 , 1 ) {\displaystyle (-1,1)} and the set of all real numbers have the same cardinality, a bijection being provided by the function x ↦ tan ( π x / 2 ) {\displaystyle x\mapsto \tan(\pi x/2)} . Having the same cardinality of a proper subset is a characteristic property of infinite sets: a set is infinite if and only if it has the same cardinality as one of its proper subsets. So, by the above example, the natural numbers form an infinite set. Besides equality, there is a natural inequality between cardinalities: a set S {\displaystyle S} has a cardinality smaller than or equal to the cardinality of another set T {\displaystyle T} if there is an injection from S {\displaystyle S} to T {\displaystyle T} . This is denoted | S | ≤ | T | {\displaystyle \vert S\vert \leq \vert T\vert } . Schröder–Bernstein theorem implies that | S | ≤ | T | {\displaystyle \vert S\vert \leq \vert T\vert } and | T | ≤ | S | {\displaystyle \vert T\vert \leq \vert S\vert } imply 1 {\displaystyle {1}} . Also, one has | S | ≤ | T | {\displaystyle \vert S\vert \leq \vert T\vert } , if and only if there is a surjection from T {\displaystyle T} to S {\displaystyle S} . For every two sets S {\displaystyle S} and T {\displaystyle T} , one has either | S | ≤ | T | {\displaystyle \vert S\vert \leq \vert T\vert } or | T | ≤ | S | {\displaystyle \vert T\vert \leq \vert S\vert } .[c] So, inequality of cardinalities is a total order. The cardinality of the set N {\displaystyle \mathbb {N} } of the natural numbers, denoted 1 {\displaystyle {1}} , is the smallest infinite cardinality. This means that if S {\displaystyle S} is a set of natural numbers, then either S {\displaystyle S} is finite or | S | = | N | . {\displaystyle |S|=|\mathbb {N} |.} Sets with cardinality less than or equal to 1 {\displaystyle {1}} are called countable sets; these are either finite sets or countably infinite sets (sets of cardinality ℵ 0 {\displaystyle \aleph _{0}} ); some authors use "countable" to mean "countably infinite". Sets with cardinality strictly greater than ℵ 0 {\displaystyle \aleph _{0}} are called uncountable sets. Cantor's diagonal argument shows that, for every set S {\displaystyle S} , its power set (the set of its subsets) 2 S {\displaystyle 2^{S}} has a greater cardinality: | S | < | 2 S | . {\displaystyle |S|<\left|2^{S}\right|.} This implies that there is no greatest cardinality. The cardinality of set of the real numbers is called the cardinality of the continuum and denoted c {\displaystyle {\mathfrak {c}}} . (The term "continuum" referred to the real line before the 20th century, when the real line was not commonly viewed as a set of numbers.) Since, as seen above, the real line R {\displaystyle \mathbb {R} } has the same cardinality of an open interval, every subset of R {\displaystyle \mathbb {R} } that contains a nonempty open interval also has the cardinality c {\displaystyle {\mathfrak {c}}} . One has c = 2 ℵ 0 , {\displaystyle {\mathfrak {c}}=2^{\aleph _{0}},} meaning that the cardinality of the real numbers equals the cardinality of the power set of the natural numbers. In particular, c > ℵ 0 . {\displaystyle {\mathfrak {c}}>\aleph _{0}.} When published in 1878 by Georg Cantor, this result was so astonishing that it was rejected by mathematicians, and several decades were needed before its common acceptance.[citation needed] It can be shown that c {\displaystyle {\mathfrak {c}}} is also the cardinality of the entire plane, and of any finite-dimensional Euclidean space. The continuum hypothesis, a conjecture formulated by Georg Cantor in 1878, states that there is no set with cardinality strictly between ℵ 0 {\displaystyle \aleph _{0}} and c {\displaystyle {\mathfrak {c}}} . In 1963, Paul Cohen proved that the continuum hypothesis is independent of the axioms of Zermelo–Fraenkel set theory with the axiom of choice. This means that if the most widely used set theory is consistent (that is not self-contradictory),[d] then the same is true for both the set theory with the continuum hypothesis added as a further axiom, and the set theory with the negation of the continuum hypothesis added. Axiom of choice Informally, the axiom of choice says that, given any family of nonempty sets, one can choose simultaneously an element in each of them.[e] Formulated this way, acceptability of this axiom sets a foundational logical question, because of the difficulty of conceiving an infinite instantaneous action. However, there are several equivalent formulations that are much less controversial and have strong consequences in many areas of mathematics. In the present days, the axiom of choice is thus commonly accepted in mainstream mathematics. A more formal statement of the axiom of choice is: the Cartesian product of every indexed family of nonempty sets is non empty. Other equivalent forms are described in the following subsections. Zorn's lemma is an assertion that is equivalent to the axiom of choice under the other axioms of set theory, and is easier to use in usual mathematics. Let S {\displaystyle S} be a partial ordered set. A chain in S {\displaystyle S} is a subset that is totally ordered under the induced order. Zorn's lemma states that, if every chain in S {\displaystyle S} has an upper bound in S {\displaystyle S} , then S {\displaystyle S} has (at least) a maximal element, that is, an element that is not smaller than another element of S {\displaystyle S} . In most uses of Zorn's lemma, S {\displaystyle S} is a set of sets, the order is set inclusion, and the upperbound of a chain is taken as the union of its members. An example of use of Zorn's lemma, is the proof that every vector space has a basis. Here the elements of S {\displaystyle S} are linearly independent subsets of the vector space. The union of a chain of elements of S {\displaystyle S} is linearly independent, since an infinite set is linearly independent if and only if each finite subset is, and every finite subset of the union of a chain must be included in a member of the chain. So, there exist a maximal linearly independent set. This linearly independent set must span the vector space because of maximality, and is therefore a basis. Another classical use of Zorn's lemma is the proof that every proper ideal—that is, an ideal that is not the whole ring—of a ring is contained in a maximal ideal. Here, S {\displaystyle S} is the set of the proper ideals containing the given ideal. The union of chain of ideals is an ideal, since the axioms of an ideal involve a finite number of elements. The union of a chain of proper ideals is a proper ideal, since otherwise 1 {\displaystyle 1} would belong to the union, and this implies that it would belong to a member of the chain. The axiom of choice is equivalent with the fact that a well-order can be defined on every set, where a well-order is a total order such that every nonempty subset has a least element. Simple examples of well-ordered sets are the natural numbers (with the natural order), and, for every n, the set of the n-tuples of natural numbers, with the lexicographic order. Well-orders allow a generalization of mathematical induction, which is called transfinite induction. Given a property (predicate) P ( n ) {\displaystyle P(n)} depending on a natural number, mathematical induction is the fact that for proving that P ( n ) {\displaystyle P(n)} is always true, it suffices to prove that for every n {\displaystyle n} , ( m < n ⟹ P ( m ) ) ⟹ P ( n ) . {\displaystyle (m<n\implies P(m))\implies P(n).} Transfinite induction is the same, replacing natural numbers by the elements of a well-ordered set. Often, a proof by transfinite induction easier if three cases are proved separately, the two first cases being the same as for usual induction: Transfinite induction is fundamental for defining ordinal numbers and cardinal numbers. See also Notes Citations References External links |
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Contents United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 states and a federal capital district, Washington, D.C. The 48 contiguous states border Canada to the north and Mexico to the south, with the semi-exclave of Alaska in the northwest and the archipelago of Hawaii in the Pacific Ocean. The United States also asserts sovereignty over five major island territories and various uninhabited islands in Oceania and the Caribbean.[j] It is a megadiverse country, with the world's third-largest land area[c] and third-largest population, exceeding 341 million.[k] Paleo-Indians first migrated from North Asia to North America at least 15,000 years ago, and formed various civilizations. Spanish colonization established Spanish Florida in 1513, the first European colony in what is now the continental United States. British colonization followed with the 1607 settlement of Virginia, the first of the Thirteen Colonies. Enslavement of Africans was practiced in all colonies by 1770 and supplied most of the labor for the Southern Colonies' plantation economy. Clashes with the British Crown began as a civil protest over the illegality of taxation without representation in Parliament and the denial of other English rights. They evolved into the American Revolution, which led to the Declaration of Independence and a society based on universal rights. Victory in the 1775–1783 Revolutionary War brought international recognition of U.S. sovereignty and fueled westward expansion, further dispossessing native inhabitants. As more states were admitted, a North–South division over slavery led the Confederate States of America to declare secession and fight the Union in the 1861–1865 American Civil War. With the United States' victory and reunification, slavery was abolished nationally. By the late 19th century, the U.S. economy outpaced the French, German and British economies combined. As of 1900, the country had established itself as a great power, a status solidified after its involvement in World War I. Following Japan's attack on Pearl Harbor in 1941, the U.S. entered World War II. Its aftermath left the U.S. and the Soviet Union as rival superpowers, competing for ideological dominance and international influence during the Cold War. The Soviet Union's collapse in 1991 ended the Cold War, leaving the U.S. as the world's sole superpower. The U.S. federal government is a representative democracy with a president and a constitution that grants separation of powers under three branches: legislative, executive, and judicial. The United States Congress is a bicameral national legislature composed of the House of Representatives (a lower house based on population) and the Senate (an upper house based on equal representation for each state). Federalism grants substantial autonomy to the 50 states. In addition, 574 Native American tribes have sovereignty rights, and there are 326 Native American reservations. Since the 1850s, the Democratic and Republican parties have dominated American politics. American ideals and values are based on a democratic tradition inspired by the American Enlightenment movement. A developed country, the U.S. ranks high in economic competitiveness, innovation, and higher education. Accounting for over a quarter of nominal global GDP, its economy has been the world's largest since about 1890. It is the wealthiest country, with the highest disposable household income per capita among OECD members, though its wealth inequality is highly pronounced. Shaped by centuries of immigration, the culture of the U.S. is diverse and globally influential. Making up more than a third of global military spending, the country has one of the strongest armed forces and is a designated nuclear state. A member of numerous international organizations, the U.S. plays a major role in global political, cultural, economic, and military affairs. Etymology Documented use of the phrase "United States of America" dates back to January 2, 1776. On that day, Stephen Moylan, a Continental Army aide to General George Washington, wrote a letter to Joseph Reed, Washington's aide-de-camp, seeking to go "with full and ample powers from the United States of America to Spain" to seek assistance in the Revolutionary War effort. The first known public usage is an anonymous essay published in the Williamsburg newspaper The Virginia Gazette on April 6, 1776. Sometime on or after June 11, 1776, Thomas Jefferson wrote "United States of America" in a rough draft of the Declaration of Independence, which was adopted by the Second Continental Congress on July 4, 1776. The term "United States" and its initialism "U.S.", used as nouns or as adjectives in English, are common short names for the country. The initialism "USA", a noun, is also common. "United States" and "U.S." are the established terms throughout the U.S. federal government, with prescribed rules.[l] "The States" is an established colloquial shortening of the name, used particularly from abroad; "stateside" is the corresponding adjective or adverb. "America" is the feminine form of the first word of Americus Vesputius, the Latinized name of Italian explorer Amerigo Vespucci (1454–1512);[m] it was first used as a place name by the German cartographers Martin Waldseemüller and Matthias Ringmann in 1507.[n] Vespucci first proposed that the West Indies discovered by Christopher Columbus in 1492 were part of a previously unknown landmass and not among the Indies at the eastern limit of Asia. In English, the term "America" usually does not refer to topics unrelated to the United States, despite the usage of "the Americas" to describe the totality of the continents of North and South America. History The first inhabitants of North America migrated from Siberia approximately 15,000 years ago, either across the Bering land bridge or along the now-submerged Ice Age coastline. Small isolated groups of hunter-gatherers are said to have migrated alongside herds of large herbivores far into Alaska, with ice-free corridors developing along the Pacific coast and valleys of North America in c. 16,500 – c. 13,500 BCE (c. 18,500 – c. 15,500 BP). The Clovis culture, which appeared around 11,000 BCE, is believed to be the first widespread culture in the Americas. Over time, Indigenous North American cultures grew increasingly sophisticated, and some, such as the Mississippian culture, developed agriculture, architecture, and complex societies. In the post-archaic period, the Mississippian cultures were located in the midwestern, eastern, and southern regions, and the Algonquian in the Great Lakes region and along the Eastern Seaboard, while the Hohokam culture and Ancestral Puebloans inhabited the Southwest. Native population estimates of what is now the United States before the arrival of European colonizers range from around 500,000 to nearly 10 million. Christopher Columbus began exploring the Caribbean for Spain in 1492, leading to Spanish-speaking settlements and missions from what are now Puerto Rico and Florida to New Mexico and California. The first Spanish colony in the present-day continental United States was Spanish Florida, chartered in 1513. After several settlements failed there due to starvation and disease, Spain's first permanent town, Saint Augustine, was founded in 1565. France established its own settlements in French Florida in 1562, but they were either abandoned (Charlesfort, 1578) or destroyed by Spanish raids (Fort Caroline, 1565). Permanent French settlements were founded much later along the Great Lakes (Fort Detroit, 1701), the Mississippi River (Saint Louis, 1764) and especially the Gulf of Mexico (New Orleans, 1718). Early European colonies also included the thriving Dutch colony of New Nederland (settled 1626, present-day New York) and the small Swedish colony of New Sweden (settled 1638 in what became Delaware). British colonization of the East Coast began with the Virginia Colony (1607) and the Plymouth Colony (Massachusetts, 1620). The Mayflower Compact in Massachusetts and the Fundamental Orders of Connecticut established precedents for local representative self-governance and constitutionalism that would develop throughout the American colonies. While European settlers in what is now the United States experienced conflicts with Native Americans, they also engaged in trade, exchanging European tools for food and animal pelts.[o] Relations ranged from close cooperation to warfare and massacres. The colonial authorities often pursued policies that forced Native Americans to adopt European lifestyles, including conversion to Christianity. Along the eastern seaboard, settlers trafficked Africans through the Atlantic slave trade, largely to provide manual labor on plantations. The original Thirteen Colonies[p] that would later found the United States were administered as possessions of the British Empire by Crown-appointed governors, though local governments held elections open to most white male property owners. The colonial population grew rapidly from Maine to Georgia, eclipsing Native American populations; by the 1770s, the natural increase of the population was such that only a small minority of Americans had been born overseas. The colonies' distance from Britain facilitated the entrenchment of self-governance, and the First Great Awakening, a series of Christian revivals, fueled colonial interest in guaranteed religious liberty. Following its victory in the French and Indian War, Britain began to assert greater control over local affairs in the Thirteen Colonies, resulting in growing political resistance. One of the primary grievances of the colonists was the denial of their rights as Englishmen, particularly the right to representation in the British government that taxed them. To demonstrate their dissatisfaction and resolve, the First Continental Congress met in 1774 and passed the Continental Association, a colonial boycott of British goods enforced by local "committees of safety" that proved effective. The British attempt to then disarm the colonists resulted in the 1775 Battles of Lexington and Concord, igniting the American Revolutionary War. At the Second Continental Congress, the colonies appointed George Washington commander-in-chief of the Continental Army, and created a committee that named Thomas Jefferson to draft the Declaration of Independence. Two days after the Second Continental Congress passed the Lee Resolution to create an independent, sovereign nation, the Declaration was adopted on July 4, 1776. The political values of the American Revolution evolved from an armed rebellion demanding reform within an empire to a revolution that created a new social and governing system founded on the defense of liberty and the protection of inalienable natural rights; sovereignty of the people; republicanism over monarchy, aristocracy, and other hereditary political power; civic virtue; and an intolerance of political corruption. The Founding Fathers of the United States, who included Washington, Jefferson, John Adams, Benjamin Franklin, Alexander Hamilton, John Jay, James Madison, Thomas Paine, and many others, were inspired by Classical, Renaissance, and Enlightenment philosophies and ideas. Though in practical effect since its drafting in 1777, the Articles of Confederation was ratified in 1781 and formally established a decentralized government that operated until 1789. After the British surrender at the siege of Yorktown in 1781, American sovereignty was internationally recognized by the Treaty of Paris (1783), through which the U.S. gained territory stretching west to the Mississippi River, north to present-day Canada, and south to Spanish Florida. The Northwest Ordinance (1787) established the precedent by which the country's territory would expand with the admission of new states, rather than the expansion of existing states. The U.S. Constitution was drafted at the 1787 Constitutional Convention to overcome the limitations of the Articles. It went into effect in 1789, creating a federal republic governed by three separate branches that together formed a system of checks and balances. George Washington was elected the country's first president under the Constitution, and the Bill of Rights was adopted in 1791 to allay skeptics' concerns about the power of the more centralized government. His resignation as commander-in-chief after the Revolutionary War and his later refusal to run for a third term as the country's first president established a precedent for the supremacy of civil authority in the United States and the peaceful transfer of power. In the late 18th century, American settlers began to expand westward in larger numbers, many with a sense of manifest destiny. The Louisiana Purchase of 1803 from France nearly doubled the territory of the United States. Lingering issues with Britain remained, leading to the War of 1812, which was fought to a draw. Spain ceded Florida and its Gulf Coast territory in 1819. The Missouri Compromise of 1820, which admitted Missouri as a slave state and Maine as a free state, attempted to balance the desire of northern states to prevent the expansion of slavery into new territories with that of southern states to extend it there. Primarily, the compromise prohibited slavery in all other lands of the Louisiana Purchase north of the 36°30′ parallel. As Americans expanded further into territory inhabited by Native Americans, the federal government implemented policies of Indian removal or assimilation. The most significant such legislation was the Indian Removal Act of 1830, a key policy of President Andrew Jackson. It resulted in the Trail of Tears (1830–1850), in which an estimated 60,000 Native Americans living east of the Mississippi River were forcibly removed and displaced to lands far to the west, causing 13,200 to 16,700 deaths along the forced march. Settler expansion as well as this influx of Indigenous peoples from the East resulted in the American Indian Wars west of the Mississippi. During the colonial period, slavery became legal in all the Thirteen colonies, but by 1770 it provided the main labor force in the large-scale, agriculture-dependent economies of the Southern Colonies from Maryland to Georgia. The practice began to be significantly questioned during the American Revolution, and spurred by an active abolitionist movement that had reemerged in the 1830s, states in the North enacted laws to prohibit slavery within their boundaries. At the same time, support for slavery had strengthened in Southern states, with widespread use of inventions such as the cotton gin (1793) having made slavery immensely profitable for Southern elites. The United States annexed the Republic of Texas in 1845, and the 1846 Oregon Treaty led to U.S. control of the present-day American Northwest. Dispute with Mexico over Texas led to the Mexican–American War (1846–1848). After the victory of the U.S., Mexico recognized U.S. sovereignty over Texas, New Mexico, and California in the 1848 Mexican Cession; the cession's lands also included the future states of Nevada, Colorado and Utah. The California gold rush of 1848–1849 spurred a huge migration of white settlers to the Pacific coast, leading to even more confrontations with Native populations. One of the most violent, the California genocide of thousands of Native inhabitants, lasted into the mid-1870s. Additional western territories and states were created. Throughout the 1850s, the sectional conflict regarding slavery was further inflamed by national legislation in the U.S. Congress and decisions of the Supreme Court. In Congress, the Fugitive Slave Act of 1850 mandated the forcible return to their owners in the South of slaves taking refuge in non-slave states, while the Kansas–Nebraska Act of 1854 effectively gutted the anti-slavery requirements of the Missouri Compromise. In its Dred Scott decision of 1857, the Supreme Court ruled against a slave brought into non-slave territory, simultaneously declaring the entire Missouri Compromise to be unconstitutional. These and other events exacerbated tensions between North and South that would culminate in the American Civil War (1861–1865). Beginning with South Carolina, 11 slave-state governments voted to secede from the United States in 1861, joining to create the Confederate States of America. All other state governments remained loyal to the Union.[q] War broke out in April 1861 after the Confederacy bombarded Fort Sumter. Following the Emancipation Proclamation on January 1, 1863, many freed slaves joined the Union army. The war began to turn in the Union's favor following the 1863 Siege of Vicksburg and Battle of Gettysburg, and the Confederates surrendered in 1865 after the Union's victory in the Battle of Appomattox Court House. Efforts toward reconstruction in the secessionist South had begun as early as 1862, but it was only after President Lincoln's assassination that the three Reconstruction Amendments to the Constitution were ratified to protect civil rights. The amendments codified nationally the abolition of slavery and involuntary servitude except as punishment for crimes, promised equal protection under the law for all persons, and prohibited discrimination on the basis of race or previous enslavement. As a result, African Americans took an active political role in ex-Confederate states in the decade following the Civil War. The former Confederate states were readmitted to the Union, beginning with Tennessee in 1866 and ending with Georgia in 1870. National infrastructure, including transcontinental telegraph and railroads, spurred growth in the American frontier. This was accelerated by the Homestead Acts, through which nearly 10 percent of the total land area of the United States was given away free to some 1.6 million homesteaders. From 1865 through 1917, an unprecedented stream of immigrants arrived in the United States, including 24.4 million from Europe. Most came through the Port of New York, as New York City and other large cities on the East Coast became home to large Jewish, Irish, and Italian populations. Many Northern Europeans as well as significant numbers of Germans and other Central Europeans moved to the Midwest. At the same time, about one million French Canadians migrated from Quebec to New England. During the Great Migration, millions of African Americans left the rural South for urban areas in the North. Alaska was purchased from Russia in 1867. The Compromise of 1877 is generally considered the end of the Reconstruction era, as it resolved the electoral crisis following the 1876 presidential election and led President Rutherford B. Hayes to reduce the role of federal troops in the South. Immediately, the Redeemers began evicting the Carpetbaggers and quickly regained local control of Southern politics in the name of white supremacy. African Americans endured a period of heightened, overt racism following Reconstruction, a time often considered the nadir of American race relations. A series of Supreme Court decisions, including Plessy v. Ferguson, emptied the Fourteenth and Fifteenth Amendments of their force, allowing Jim Crow laws in the South to remain unchecked, sundown towns in the Midwest, and segregation in communities across the country, which would be reinforced in part by the policy of redlining later adopted by the federal Home Owners' Loan Corporation. An explosion of technological advancement, accompanied by the exploitation of cheap immigrant labor, led to rapid economic expansion during the Gilded Age of the late 19th century. It continued into the early 20th, when the United States already outpaced the economies of Britain, France, and Germany combined. This fostered the amassing of power by a few prominent industrialists, largely by their formation of trusts and monopolies to prevent competition. Tycoons led the nation's expansion in the railroad, petroleum, and steel industries. The United States emerged as a pioneer of the automotive industry. These changes resulted in significant increases in economic inequality, slum conditions, and social unrest, creating the environment for labor unions and socialist movements to begin to flourish. This period eventually ended with the advent of the Progressive Era, which was characterized by significant economic and social reforms. Pro-American elements in Hawaii overthrew the Hawaiian monarchy; the islands were annexed in 1898. That same year, Puerto Rico, the Philippines, and Guam were ceded to the U.S. by Spain after the latter's defeat in the Spanish–American War. (The Philippines was granted full independence from the U.S. on July 4, 1946, following World War II. Puerto Rico and Guam have remained U.S. territories.) American Samoa was acquired by the United States in 1900 after the Second Samoan Civil War. The U.S. Virgin Islands were purchased from Denmark in 1917. The United States entered World War I alongside the Allies in 1917 helping to turn the tide against the Central Powers. In 1920, a constitutional amendment granted nationwide women's suffrage. During the 1920s and 1930s, radio for mass communication and early television transformed communications nationwide. The Wall Street Crash of 1929 triggered the Great Depression, to which President Franklin D. Roosevelt responded with the New Deal plan of "reform, recovery and relief", a series of unprecedented and sweeping recovery programs and employment relief projects combined with financial reforms and regulations. Initially neutral during World War II, the U.S. began supplying war materiel to the Allies of World War II in March 1941 and entered the war in December after Japan's attack on Pearl Harbor. Agreeing to a "Europe first" policy, the U.S. concentrated its wartime efforts on Japan's allies Italy and Germany until their final defeat in May 1945. The U.S. developed the first nuclear weapons and used them against the Japanese cities of Hiroshima and Nagasaki in August 1945, ending the war. The United States was one of the "Four Policemen" who met to plan the post-war world, alongside the United Kingdom, the Soviet Union, and China. The U.S. emerged relatively unscathed from the war, with even greater economic power and international political influence. The end of World War II in 1945 left the U.S. and the Soviet Union as superpowers, each with its own political, military, and economic sphere of influence. Geopolitical tensions between the two superpowers soon led to the Cold War. The U.S. implemented a policy of containment intended to limit the Soviet Union's sphere of influence; engaged in regime change against governments perceived to be aligned with the Soviets; and prevailed in the Space Race, which culminated with the first crewed Moon landing in 1969. Domestically, the U.S. experienced economic growth, urbanization, and population growth following World War II. The civil rights movement emerged, with Martin Luther King Jr. becoming a prominent leader in the early 1960s. The Great Society plan of President Lyndon B. Johnson's administration resulted in groundbreaking and broad-reaching laws, policies and a constitutional amendment to counteract some of the worst effects of lingering institutional racism. The counterculture movement in the U.S. brought significant social changes, including the liberalization of attitudes toward recreational drug use and sexuality. It also encouraged open defiance of the military draft (leading to the end of conscription in 1973) and wide opposition to U.S. intervention in Vietnam, with the U.S. totally withdrawing in 1975. A societal shift in the roles of women was significantly responsible for the large increase in female paid labor participation starting in the 1970s, and by 1985 the majority of American women aged 16 and older were employed. The Fall of Communism and the dissolution of the Soviet Union from 1989 to 1991 marked the end of the Cold War and left the United States as the world's sole superpower. This cemented the United States' global influence, reinforcing the concept of the "American Century" as the U.S. dominated international political, cultural, economic, and military affairs. The 1990s saw the longest recorded economic expansion in American history, a dramatic decline in U.S. crime rates, and advances in technology. Throughout this decade, technological innovations such as the World Wide Web, the evolution of the Pentium microprocessor in accordance with Moore's law, rechargeable lithium-ion batteries, the first gene therapy trial, and cloning either emerged in the U.S. or were improved upon there. The Human Genome Project was formally launched in 1990, while Nasdaq became the first stock market in the United States to trade online in 1998. In the Gulf War of 1991, an American-led international coalition of states expelled an Iraqi invasion force that had occupied neighboring Kuwait. The September 11 attacks on the United States in 2001 by the pan-Islamist militant organization al-Qaeda led to the war on terror and subsequent military interventions in Afghanistan and in Iraq. The U.S. housing bubble culminated in 2007 with the Great Recession, the largest economic contraction since the Great Depression. In the 2010s and early 2020s, the United States has experienced increased political polarization and democratic backsliding. The country's polarization was violently reflected in the January 2021 Capitol attack, when a mob of insurrectionists entered the U.S. Capitol and sought to prevent the peaceful transfer of power in an attempted self-coup d'état. Geography The United States is the world's third-largest country by total area behind Russia and Canada.[c] The 48 contiguous states and the District of Columbia have a combined area of 3,119,885 square miles (8,080,470 km2). In 2021, the United States had 8% of the Earth's permanent meadows and pastures and 10% of its cropland. Starting in the east, the coastal plain of the Atlantic seaboard gives way to inland forests and rolling hills in the Piedmont plateau region. The Appalachian Mountains and the Adirondack Massif separate the East Coast from the Great Lakes and the grasslands of the Midwest. The Mississippi River System, the world's fourth-longest river system, runs predominantly north–south through the center of the country. The flat and fertile prairie of the Great Plains stretches to the west, interrupted by a highland region in the southeast. The Rocky Mountains, west of the Great Plains, extend north to south across the country, peaking at over 14,000 feet (4,300 m) in Colorado. The supervolcano underlying Yellowstone National Park in the Rocky Mountains, the Yellowstone Caldera, is the continent's largest volcanic feature. Farther west are the rocky Great Basin and the Chihuahuan, Sonoran, and Mojave deserts. In the northwest corner of Arizona, carved by the Colorado River, is the Grand Canyon, a steep-sided canyon and popular tourist destination known for its overwhelming visual size and intricate, colorful landscape. The Cascade and Sierra Nevada mountain ranges run close to the Pacific coast. The lowest and highest points in the contiguous United States are in the State of California, about 84 miles (135 km) apart. At an elevation of 20,310 feet (6,190.5 m), Alaska's Denali (also called Mount McKinley) is the highest peak in the country and on the continent. Active volcanoes in the U.S. are common throughout Alaska's Alexander and Aleutian Islands. Located entirely outside North America, the archipelago of Hawaii consists of volcanic islands, physiographically and ethnologically part of the Polynesian subregion of Oceania. In addition to its total land area, the United States has one of the world's largest marine exclusive economic zones spanning approximately 4.5 million square miles (11.7 million km2) of ocean. With its large size and geographic variety, the United States includes most climate types. East of the 100th meridian, the climate ranges from humid continental in the north to humid subtropical in the south. The western Great Plains are semi-arid. Many mountainous areas of the American West have an alpine climate. The climate is arid in the Southwest, Mediterranean in coastal California, and oceanic in coastal Oregon, Washington, and southern Alaska. Most of Alaska is subarctic or polar. Hawaii, the southern tip of Florida and U.S. territories in the Caribbean and Pacific are tropical. The United States receives more high-impact extreme weather incidents than any other country. States bordering the Gulf of Mexico are prone to hurricanes, and most of the world's tornadoes occur in the country, mainly in Tornado Alley. Due to climate change in the country, extreme weather has become more frequent in the U.S. in the 21st century, with three times the number of reported heat waves compared to the 1960s. Since the 1990s, droughts in the American Southwest have become more persistent and more severe. The regions considered as the most attractive to the population are the most vulnerable. The U.S. is one of 17 megadiverse countries containing large numbers of endemic species: about 17,000 species of vascular plants occur in the contiguous United States and Alaska, and over 1,800 species of flowering plants are found in Hawaii, few of which occur on the mainland. The United States is home to 428 mammal species, 784 birds, 311 reptiles, 295 amphibians, and around 91,000 insect species. There are 63 national parks, and hundreds of other federally managed monuments, forests, and wilderness areas, administered by the National Park Service and other agencies. About 28% of the country's land is publicly owned and federally managed, primarily in the Western States. Most of this land is protected, though some is leased for commercial use, and less than one percent is used for military purposes. Environmental issues in the United States include debates on non-renewable resources and nuclear energy, air and water pollution, biodiversity, logging and deforestation, and climate change. The U.S. Environmental Protection Agency (EPA) is the federal agency charged with addressing most environmental-related issues. The idea of wilderness has shaped the management of public lands since 1964, with the Wilderness Act. The Endangered Species Act of 1973 provides a way to protect threatened and endangered species and their habitats. The United States Fish and Wildlife Service implements and enforces the Act. In 2024, the U.S. ranked 35th among 180 countries in the Environmental Performance Index. Government and politics The United States is a federal republic of 50 states and a federal capital district, Washington, D.C. The U.S. asserts sovereignty over five unincorporated territories and several uninhabited island possessions. It is the world's oldest surviving federation, and its presidential system of federal government has been adopted, in whole or in part, by many newly independent states worldwide following their decolonization. The Constitution of the United States serves as the country's supreme legal document. Most scholars describe the United States as a liberal democracy.[r] Composed of three branches, all headquartered in Washington, D.C., the federal government is the national government of the United States. The U.S. Constitution establishes a separation of powers intended to provide a system of checks and balances to prevent any of the three branches from becoming supreme. The three-branch system is known as the presidential system, in contrast to the parliamentary system where the executive is part of the legislative body. Many countries around the world adopted this aspect of the 1789 Constitution of the United States, especially in the postcolonial Americas. In the U.S. federal system, sovereign powers are shared between three levels of government specified in the Constitution: the federal government, the states, and Indian tribes. The U.S. also asserts sovereignty over five permanently inhabited territories: American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands. Residents of the 50 states are governed by their elected state government, under state constitutions compatible with the national constitution, and by elected local governments that are administrative divisions of a state. States are subdivided into counties or county equivalents, and (except for Hawaii) further divided into municipalities, each administered by elected representatives. The District of Columbia is a federal district containing the U.S. capital, Washington, D.C. The federal district is an administrative division of the federal government. Indian country is made up of 574 federally recognized tribes and 326 Indian reservations. They hold a government-to-government relationship with the U.S. federal government in Washington and are legally defined as domestic dependent nations with inherent tribal sovereignty rights. In addition to the five major territories, the U.S. also asserts sovereignty over the United States Minor Outlying Islands in the Pacific Ocean and the Caribbean. The seven undisputed islands without permanent populations are Baker Island, Howland Island, Jarvis Island, Johnston Atoll, Kingman Reef, Midway Atoll, and Palmyra Atoll. U.S. sovereignty over the unpopulated Bajo Nuevo Bank, Navassa Island, Serranilla Bank, and Wake Island is disputed. The Constitution is silent on political parties. However, they developed independently in the 18th century with the Federalist and Anti-Federalist parties. Since then, the United States has operated as a de facto two-party system, though the parties have changed over time. Since the mid-19th century, the two main national parties have been the Democratic Party and the Republican Party. The former is perceived as relatively liberal in its political platform while the latter is perceived as relatively conservative in its platform. The United States has an established structure of foreign relations, with the world's second-largest diplomatic corps as of 2024[update]. It is a permanent member of the United Nations Security Council and home to the United Nations headquarters. The United States is a member of the G7, G20, and OECD intergovernmental organizations. Almost all countries have embassies and many have consulates (official representatives) in the country. Likewise, nearly all countries host formal diplomatic missions with the United States, except Iran, North Korea, and Bhutan. Though Taiwan does not have formal diplomatic relations with the U.S., it maintains close unofficial relations. The United States regularly supplies Taiwan with military equipment to deter potential Chinese aggression. Its geopolitical attention also turned to the Indo-Pacific when the United States joined the Quadrilateral Security Dialogue with Australia, India, and Japan. The United States has a "Special Relationship" with the United Kingdom and strong ties with Canada, Australia, New Zealand, the Philippines, Japan, South Korea, Israel, and several European Union countries such as France, Italy, Germany, Spain, and Poland. The U.S. works closely with its NATO allies on military and national security issues, and with countries in the Americas through the Organization of American States and the United States–Mexico–Canada Free Trade Agreement. The U.S. exercises full international defense authority and responsibility for Micronesia, the Marshall Islands, and Palau through the Compact of Free Association. It has increasingly conducted strategic cooperation with India, while its ties with China have steadily deteriorated. Beginning in 2014, the U.S. had become a key ally of Ukraine. After Donald Trump was elected U.S. president in 2024, he sought to negotiate an end to the Russo-Ukrainian War. He paused all military aid to Ukraine in March 2025, although the aid resumed later. Trump also ended U.S. intelligence sharing with the country, but this too was eventually restored. The president is the commander-in-chief of the United States Armed Forces and appoints its leaders, the secretary of defense and the Joint Chiefs of Staff. The Department of Defense, headquartered at the Pentagon near Washington, D.C., administers five of the six service branches, which are made up of the U.S. Army, Marine Corps, Navy, Air Force, and Space Force. The Coast Guard is administered by the Department of Homeland Security in peacetime and can be transferred to the Department of the Navy in wartime. Total strength of the entire military is about 1.3 million active duty with an additional 400,000 in reserve. The United States spent $997 billion on its military in 2024, which is by far the largest amount of any country, making up 37% of global military spending and accounting for 3.4% of the country's GDP. The U.S. possesses 42% of the world's nuclear weapons—the second-largest stockpile after that of Russia. The U.S. military is widely regarded as the most powerful and advanced in the world. The United States has the third-largest combined armed forces in the world, behind the Chinese People's Liberation Army and Indian Armed Forces. The U.S. military operates about 800 bases and facilities abroad, and maintains deployments greater than 100 active duty personnel in 25 foreign countries. The United States has engaged in over 400 military interventions since its founding in 1776, with over half of these occurring between 1950 and 2019 and 25% occurring in the post-Cold War era. State defense forces (SDFs) are military units that operate under the sole authority of a state government. SDFs are authorized by state and federal law but are under the command of the state's governor. By contrast, the 54 U.S. National Guard organizations[t] fall under the dual control of state or territorial governments and the federal government; their units can also become federalized entities, but SDFs cannot be federalized. The National Guard personnel of a state or territory can be federalized by the president under the National Defense Act Amendments of 1933; this legislation created the Guard and provides for the integration of Army National Guard and Air National Guard units and personnel into the U.S. Army and (since 1947) the U.S. Air Force. The total number of National Guard members is about 430,000, while the estimated combined strength of SDFs is less than 10,000. There are about 18,000 U.S. police agencies from local to national level in the United States. Law in the United States is mainly enforced by local police departments and sheriff departments in their municipal or county jurisdictions. The state police departments have authority in their respective state, and federal agencies such as the Federal Bureau of Investigation (FBI) and the U.S. Marshals Service have national jurisdiction and specialized duties, such as protecting civil rights, national security, enforcing U.S. federal courts' rulings and federal laws, and interstate criminal activity. State courts conduct almost all civil and criminal trials, while federal courts adjudicate the much smaller number of civil and criminal cases that relate to federal law. There is no unified "criminal justice system" in the United States. The American prison system is largely heterogenous, with thousands of relatively independent systems operating across federal, state, local, and tribal levels. In 2025, "these systems hold nearly 2 million people in 1,566 state prisons, 98 federal prisons, 3,116 local jails, 1,277 juvenile correctional facilities, 133 immigration detention facilities, and 80 Indian country jails, as well as in military prisons, civil commitment centers, state psychiatric hospitals, and prisons in the U.S. territories." Despite disparate systems of confinement, four main institutions dominate: federal prisons, state prisons, local jails, and juvenile correctional facilities. Federal prisons are run by the Federal Bureau of Prisons and hold pretrial detainees as well as people who have been convicted of federal crimes. State prisons, run by the department of corrections of each state, hold people sentenced and serving prison time (usually longer than one year) for felony offenses. Local jails are county or municipal facilities that incarcerate defendants prior to trial; they also hold those serving short sentences (typically under a year). Juvenile correctional facilities are operated by local or state governments and serve as longer-term placements for any minor adjudicated as delinquent and ordered by a judge to be confined. In January 2023, the United States had the sixth-highest per capita incarceration rate in the world—531 people per 100,000 inhabitants—and the largest prison and jail population in the world, with more than 1.9 million people incarcerated. An analysis of the World Health Organization Mortality Database from 2010 showed U.S. homicide rates "were 7 times higher than in other high-income countries, driven by a gun homicide rate that was 25 times higher". Economy The U.S. has a highly developed mixed economy that has been the world's largest nominally since about 1890. Its 2024 gross domestic product (GDP)[e] of more than $29 trillion constituted over 25% of nominal global economic output, or 15% at purchasing power parity (PPP). From 1983 to 2008, U.S. real compounded annual GDP growth was 3.3%, compared to a 2.3% weighted average for the rest of the G7. The country ranks first in the world by nominal GDP, second when adjusted for purchasing power parities (PPP), and ninth by PPP-adjusted GDP per capita. In February 2024, the total U.S. federal government debt was $34.4 trillion. Of the world's 500 largest companies by revenue, 138 were headquartered in the U.S. in 2025, the highest number of any country. The U.S. dollar is the currency most used in international transactions and the world's foremost reserve currency, backed by the country's dominant economy, its military, the petrodollar system, its large U.S. treasuries market, and its linked eurodollar. Several countries use it as their official currency, and in others it is the de facto currency. The U.S. has free trade agreements with several countries, including the USMCA. Although the United States has reached a post-industrial level of economic development and is often described as having a service economy, it remains a major industrial power; in 2024, the U.S. manufacturing sector was the world's second-largest by value output after China's. New York City is the world's principal financial center, and its metropolitan area is the world's largest metropolitan economy. The New York Stock Exchange and Nasdaq, both located in New York City, are the world's two largest stock exchanges by market capitalization and trade volume. The United States is at the forefront of technological advancement and innovation in many economic fields, especially in artificial intelligence; electronics and computers; pharmaceuticals; and medical, aerospace and military equipment. The country's economy is fueled by abundant natural resources, a well-developed infrastructure, and high productivity. The largest trading partners of the United States are the European Union, Mexico, Canada, China, Japan, South Korea, the United Kingdom, Vietnam, India, and Taiwan. The United States is the world's largest importer and second-largest exporter.[u] It is by far the world's largest exporter of services. Americans have the highest average household and employee income among OECD member states, and the fourth-highest median household income in 2023, up from sixth-highest in 2013. With personal consumption expenditures of over $18.5 trillion in 2023, the U.S. has a heavily consumer-driven economy and is the world's largest consumer market. The U.S. ranked first in the number of dollar billionaires and millionaires in 2023, with 735 billionaires and nearly 22 million millionaires. Wealth in the United States is highly concentrated; in 2011, the richest 10% of the adult population owned 72% of the country's household wealth, while the bottom 50% owned just 2%. U.S. wealth inequality increased substantially since the late 1980s, and income inequality in the U.S. reached a record high in 2019. In 2024, the country had some of the highest wealth and income inequality levels among OECD countries. Since the 1970s, there has been a decoupling of U.S. wage gains from worker productivity. In 2016, the top fifth of earners took home more than half of all income, giving the U.S. one of the widest income distributions among OECD countries. There were about 771,480 homeless persons in the U.S. in 2024. In 2022, 6.4 million children experienced food insecurity. Feeding America estimates that around one in five, or approximately 13 million, children experience hunger in the U.S. and do not know where or when they will get their next meal. Also in 2022, about 37.9 million people, or 11.5% of the U.S. population, were living in poverty. The United States has a smaller welfare state and redistributes less income through government action than most other high-income countries. It is the only advanced economy that does not guarantee its workers paid vacation nationally and one of a few countries in the world without federal paid family leave as a legal right. The United States has a higher percentage of low-income workers than almost any other developed country, largely because of a weak collective bargaining system and lack of government support for at-risk workers. The United States has been a leader in technological innovation since the late 19th century and scientific research since the mid-20th century. Methods for producing interchangeable parts and the establishment of a machine tool industry enabled the large-scale manufacturing of U.S. consumer products in the late 19th century. By the early 20th century, factory electrification, the introduction of the assembly line, and other labor-saving techniques created the system of mass production. In the 21st century, the United States continues to be one of the world's foremost scientific powers, though China has emerged as a major competitor in many fields. The U.S. has the highest research and development expenditures of any country and ranks ninth as a percentage of GDP. In 2022, the United States was (after China) the country with the second-highest number of published scientific papers. In 2021, the U.S. ranked second (also after China) by the number of patent applications, and third by trademark and industrial design applications (after China and Germany), according to World Intellectual Property Indicators. In 2025 the United States ranked third (after Switzerland and Sweden) in the Global Innovation Index. The United States is considered to be a world leader in the development of artificial intelligence technology. In 2023, the United States was ranked the second most technologically advanced country in the world (after South Korea) by Global Finance magazine. The United States has maintained a space program since the late 1950s, beginning with the establishment of the National Aeronautics and Space Administration (NASA) in 1958. NASA's Apollo program (1961–1972) achieved the first crewed Moon landing with the 1969 Apollo 11 mission; it remains one of the agency's most significant milestones. Other major endeavors by NASA include the Space Shuttle program (1981–2011), the Voyager program (1972–present), the Hubble and James Webb space telescopes (launched in 1990 and 2021, respectively), and the multi-mission Mars Exploration Program (Spirit and Opportunity, Curiosity, and Perseverance). NASA is one of five agencies collaborating on the International Space Station (ISS); U.S. contributions to the ISS include several modules, including Destiny (2001), Harmony (2007), and Tranquility (2010), as well as ongoing logistical and operational support. The United States private sector dominates the global commercial spaceflight industry. Prominent American spaceflight contractors include Blue Origin, Boeing, Lockheed Martin, Northrop Grumman, and SpaceX. NASA programs such as the Commercial Crew Program, Commercial Resupply Services, Commercial Lunar Payload Services, and NextSTEP have facilitated growing private-sector involvement in American spaceflight. In 2023, the United States received approximately 84% of its energy from fossil fuel, and its largest source of energy was petroleum (38%), followed by natural gas (36%), renewable sources (9%), coal (9%), and nuclear power (9%). In 2022, the United States constituted about 4% of the world's population, but consumed around 16% of the world's energy. The U.S. ranks as the second-highest emitter of greenhouse gases behind China. The U.S. is the world's largest producer of nuclear power, generating around 30% of the world's nuclear electricity. It also has the highest number of nuclear power reactors of any country. From 2024, the U.S. plans to triple its nuclear power capacity by 2050. The United States' 4 million miles (6.4 million kilometers) of road network, owned almost entirely by state and local governments, is the longest in the world. The extensive Interstate Highway System that connects all major U.S. cities is funded mostly by the federal government but maintained by state departments of transportation. The system is further extended by state highways and some private toll roads. The U.S. is among the top ten countries with the highest vehicle ownership per capita (850 vehicles per 1,000 people) in 2022. A 2022 study found that 76% of U.S. commuters drive alone and 14% ride a bicycle, including bike owners and users of bike-sharing networks. About 11% use some form of public transportation. Public transportation in the United States is well developed in the largest urban areas, notably New York City, Washington, D.C., Boston, Philadelphia, Chicago, and San Francisco; otherwise, coverage is generally less extensive than in most other developed countries. The U.S. also has many relatively car-dependent localities. Long-distance intercity travel is provided primarily by airlines, but travel by rail is more common along the Northeast Corridor, the only high-speed rail in the U.S. that meets international standards. Amtrak, the country's government-sponsored national passenger rail company, has a relatively sparse network compared to that of Western European countries. Service is concentrated in the Northeast, California, the Midwest, the Pacific Northwest, and Virginia/Southeast. The United States has an extensive air transportation network. U.S. civilian airlines are all privately owned. The three largest airlines in the world, by total number of passengers carried, are U.S.-based; American Airlines became the global leader after its 2013 merger with US Airways. Of the 50 busiest airports in the world, 16 are in the United States, as well as five of the top 10. The world's busiest airport by passenger volume is Hartsfield–Jackson Atlanta International in Atlanta, Georgia. In 2022, most of the 19,969 U.S. airports were owned and operated by local government authorities, and there are also some private airports. Some 5,193 are designated as "public use", including for general aviation. The Transportation Security Administration (TSA) has provided security at most major airports since 2001. The country's rail transport network, the longest in the world at 182,412.3 mi (293,564.2 km), handles mostly freight (in contrast to more passenger-centered rail in Europe). Because they are often privately owned operations, U.S. railroads lag behind those of the rest of the world in terms of electrification. The country's inland waterways are the world's fifth-longest, totaling 25,482 mi (41,009 km). They are used extensively for freight, recreation, and a small amount of passenger traffic. Of the world's 50 busiest container ports, four are located in the United States, with the busiest in the country being the Port of Los Angeles. Demographics The U.S. Census Bureau reported 331,449,281 residents on April 1, 2020,[v] making the United States the third-most-populous country in the world, after India and China. The Census Bureau's official 2025 population estimate was 341,784,857, an increase of 3.1% since the 2020 census. According to the Bureau's U.S. Population Clock, on July 1, 2024, the U.S. population had a net gain of one person every 16 seconds, or about 5400 people per day. In 2023, 51% of Americans age 15 and over were married, 6% were widowed, 10% were divorced, and 34% had never been married. In 2023, the total fertility rate for the U.S. stood at 1.6 children per woman, and, at 23%, it had the world's highest rate of children living in single-parent households in 2019. Most Americans live in the suburbs of major metropolitan areas. The United States has a diverse population; 37 ancestry groups have more than one million members. White Americans with ancestry from Europe, the Middle East, or North Africa form the largest racial and ethnic group at 57.8% of the United States population. Hispanic and Latino Americans form the second-largest group and are 18.7% of the United States population. African Americans constitute the country's third-largest ancestry group and are 12.1% of the total U.S. population. Asian Americans are the country's fourth-largest group, composing 5.9% of the United States population. The country's 3.7 million Native Americans account for about 1%, and some 574 native tribes are recognized by the federal government. In 2024, the median age of the United States population was 39.1 years. While many languages and dialects are spoken in the United States, English is by far the most commonly spoken and written. De facto, English is the official language of the United States, and in 2025, Executive Order 14224 declared English official. However, the U.S. has never had a de jure official language, as Congress has never passed a law to designate English as official for all three federal branches. Some laws, such as U.S. naturalization requirements, nonetheless standardize English. Twenty-eight states and the United States Virgin Islands have laws that designate English as the sole official language; 19 states and the District of Columbia have no official language. Three states and four U.S. territories have recognized local or indigenous languages in addition to English: Hawaii (Hawaiian), Alaska (twenty Native languages),[w] South Dakota (Sioux), American Samoa (Samoan), Puerto Rico (Spanish), Guam (Chamorro), and the Northern Mariana Islands (Carolinian and Chamorro). In total, 169 Native American languages are spoken in the United States. In Puerto Rico, Spanish is more widely spoken than English. According to the American Community Survey (2020), some 245.4 million people in the U.S. age five and older spoke only English at home. About 41.2 million spoke Spanish at home, making it the second most commonly used language. Other languages spoken at home by one million people or more include Chinese (3.40 million), Tagalog (1.71 million), Vietnamese (1.52 million), Arabic (1.39 million), French (1.18 million), Korean (1.07 million), and Russian (1.04 million). German, spoken by 1 million people at home in 2010, fell to 857,000 total speakers in 2020. America's immigrant population is by far the world's largest in absolute terms. In 2022, there were 87.7 million immigrants and U.S.-born children of immigrants in the United States, accounting for nearly 27% of the overall U.S. population. In 2017, out of the U.S. foreign-born population, some 45% (20.7 million) were naturalized citizens, 27% (12.3 million) were lawful permanent residents, 6% (2.2 million) were temporary lawful residents, and 23% (10.5 million) were unauthorized immigrants. In 2019, the top countries of origin for immigrants were Mexico (24% of immigrants), India (6%), China (5%), the Philippines (4.5%), and El Salvador (3%). In fiscal year 2022, over one million immigrants (most of whom entered through family reunification) were granted legal residence. The undocumented immigrant population in the U.S. reached a record high of 14 million in 2023. The First Amendment guarantees the free exercise of religion in the country and forbids Congress from passing laws respecting its establishment. Religious practice is widespread, among the most diverse in the world, and profoundly vibrant. The country has the world's largest Christian population, which includes the fourth-largest population of Catholics. Other notable faiths include Judaism, Buddhism, Hinduism, Islam, New Age, and Native American religions. Religious practice varies significantly by region. "Ceremonial deism" is common in American culture. The overwhelming majority of Americans believe in a higher power or spiritual force, engage in spiritual practices such as prayer, and consider themselves religious or spiritual. In the Southern United States' "Bible Belt", evangelical Protestantism plays a significant role culturally; New England and the Western United States tend to be more secular. Mormonism, a Restorationist movement founded in the U.S. in 1847, is the predominant religion in Utah and a major religion in Idaho. About 82% of Americans live in metropolitan areas, particularly in suburbs; about half of those reside in cities with populations over 50,000. In 2022, 333 incorporated municipalities had populations over 100,000, nine cities had more than one million residents, and four cities—New York City, Los Angeles, Chicago, and Houston—had populations exceeding two million. Many U.S. metropolitan populations are growing rapidly, particularly in the South and West. According to the Centers for Disease Control and Prevention (CDC), average U.S. life expectancy at birth reached 79.0 years in 2024, its highest recorded level. This was an increase of 0.6 years over 2023. The CDC attributed the improvement to a significant fall in the number of fatal drug overdoses in the country, noting that "heart disease continues to be the leading cause of death in the United States, followed by cancer and unintentional injuries." In 2024, life expectancy at birth for American men rose to 76.5 years (+0.7 years compared to 2023), while life expectancy for women was 81.4 years (+0.3 years). Starting in 1998, life expectancy in the U.S. fell behind that of other wealthy industrialized countries, and Americans' "health disadvantage" gap has been increasing ever since. The Commonwealth Fund reported in 2020 that the U.S. had the highest suicide rate among high-income countries. Approximately one-third of the U.S. adult population is obese and another third is overweight. The U.S. healthcare system far outspends that of any other country, measured both in per capita spending and as a percentage of GDP, but attains worse healthcare outcomes when compared to peer countries for reasons that are debated. The United States is the only developed country without a system of universal healthcare, and a significant proportion of the population that does not carry health insurance. Government-funded healthcare coverage for the poor (Medicaid) and for those age 65 and older (Medicare) is available to Americans who meet the programs' income or age qualifications. In 2010, then-President Obama passed the Patient Protection and Affordable Care Act.[x] Abortion in the United States is not federally protected, and is illegal or restricted in 17 states. American primary and secondary education, known in the U.S. as K–12 ("kindergarten through 12th grade"), is decentralized. School systems are operated by state, territorial, and sometimes municipal governments and regulated by the U.S. Department of Education. In general, children are required to attend school or an approved homeschool from the age of five or six (kindergarten or first grade) until they are 18 years old. This often brings students through the 12th grade, the final year of a U.S. high school, but some states and territories allow them to leave school earlier, at age 16 or 17. The U.S. spends more on education per student than any other country, an average of $18,614 per year per public elementary and secondary school student in 2020–2021. Among Americans age 25 and older, 92.2% graduated from high school, 62.7% attended some college, 37.7% earned a bachelor's degree, and 14.2% earned a graduate degree. The U.S. literacy rate is near-universal. The U.S. has produced the most Nobel Prize winners of any country, with 411 (having won 413 awards). U.S. tertiary or higher education has earned a global reputation. Many of the world's top universities, as listed by various ranking organizations, are in the United States, including 19 of the top 25. American higher education is dominated by state university systems, although the country's many private universities and colleges enroll about 20% of all American students. Local community colleges generally offer open admissions, lower tuition, and coursework leading to a two-year associate degree or a non-degree certificate. As for public expenditures on higher education, the U.S. spends more per student than the OECD average, and Americans spend more than all nations in combined public and private spending. Colleges and universities directly funded by the federal government do not charge tuition and are limited to military personnel and government employees, including: the U.S. service academies, the Naval Postgraduate School, and military staff colleges. Despite some student loan forgiveness programs in place, student loan debt increased by 102% between 2010 and 2020, and exceeded $1.7 trillion in 2022. Culture and society The United States is home to a wide variety of ethnic groups, traditions, and customs. The country has been described as having the values of individualism and personal autonomy, as well as a strong work ethic and competitiveness. Voluntary altruism towards others also plays a major role; according to a 2016 study by the Charities Aid Foundation, Americans donated 1.44% of total GDP to charity—the highest rate in the world by a large margin. Americans have traditionally been characterized by a unifying political belief in an "American Creed" emphasizing consent of the governed, liberty, equality under the law, democracy, social equality, property rights, and a preference for limited government. The U.S. has acquired significant hard and soft power through its diplomatic influence, economic power, military alliances, and cultural exports such as American movies, music, video games, sports, and food. The influence that the United States exerts on other countries through soft power is referred to as Americanization. Nearly all present Americans or their ancestors came from Europe, Africa, or Asia (the "Old World") within the past five centuries. Mainstream American culture is a Western culture largely derived from the traditions of European immigrants with influences from many other sources, such as traditions brought by slaves from Africa. More recent immigration from Asia and especially Latin America has added to a cultural mix that has been described as a homogenizing melting pot, and a heterogeneous salad bowl, with immigrants contributing to, and often assimilating into, mainstream American culture. Under the First Amendment to the Constitution, the United States is considered to have the strongest protections of free speech of any country. Flag desecration, hate speech, blasphemy, and lese majesty are all forms of protected expression. A 2016 Pew Research Center poll found that Americans were the most supportive of free expression of any polity measured. Additionally, they are the "most supportive of freedom of the press and the right to use the Internet without government censorship". The U.S. is a socially progressive country with permissive attitudes surrounding human sexuality. LGBTQ rights in the United States are among the most advanced by global standards. The American Dream, or the perception that Americans enjoy high levels of social mobility, plays a key role in attracting immigrants. Whether this perception is accurate has been a topic of debate. While mainstream culture holds that the United States is a classless society, scholars identify significant differences between the country's social classes, affecting socialization, language, and values. Americans tend to greatly value socioeconomic achievement, but being ordinary or average is promoted by some as a noble condition as well. The National Foundation on the Arts and the Humanities is an agency of the United States federal government that was established in 1965 with the purpose to "develop and promote a broadly conceived national policy of support for the humanities and the arts in the United States, and for institutions which preserve the cultural heritage of the United States." It is composed of four sub-agencies: Colonial American authors were influenced by John Locke and other Enlightenment philosophers. The American Revolutionary Period (1765–1783) is notable for the political writings of Benjamin Franklin, Alexander Hamilton, Thomas Paine, and Thomas Jefferson. Shortly before and after the Revolutionary War, the newspaper rose to prominence, filling a demand for anti-British national literature. An early novel is William Hill Brown's The Power of Sympathy, published in 1791. Writer and critic John Neal in the early- to mid-19th century helped advance America toward a unique literature and culture by criticizing predecessors such as Washington Irving for imitating their British counterparts, and by influencing writers such as Edgar Allan Poe, who took American poetry and short fiction in new directions. Ralph Waldo Emerson and Margaret Fuller pioneered the influential Transcendentalism movement; Henry David Thoreau, author of Walden, was influenced by this movement. The conflict surrounding abolitionism inspired writers, like Harriet Beecher Stowe, and authors of slave narratives, such as Frederick Douglass. Nathaniel Hawthorne's The Scarlet Letter (1850) explored the dark side of American history, as did Herman Melville's Moby-Dick (1851). Major American poets of the 19th century American Renaissance include Walt Whitman, Melville, and Emily Dickinson. Mark Twain was the first major American writer to be born in the West. Henry James achieved international recognition with novels like The Portrait of a Lady (1881). As literacy rates rose, periodicals published more stories centered around industrial workers, women, and the rural poor. Naturalism, regionalism, and realism were the major literary movements of the period. While modernism generally took on an international character, modernist authors working within the United States more often rooted their work in specific regions, peoples, and cultures. Following the Great Migration to northern cities, African-American and black West Indian authors of the Harlem Renaissance developed an independent tradition of literature that rebuked a history of inequality and celebrated black culture. An important cultural export during the Jazz Age, these writings were a key influence on Négritude, a philosophy emerging in the 1930s among francophone writers of the African diaspora. In the 1950s, an ideal of homogeneity led many authors to attempt to write the Great American Novel, while the Beat Generation rejected this conformity, using styles that elevated the impact of the spoken word over mechanics to describe drug use, sexuality, and the failings of society. Contemporary literature is more pluralistic than in previous eras, with the closest thing to a unifying feature being a trend toward self-conscious experiments with language. Twelve American laureates have won the Nobel Prize in Literature. Media in the United States is broadly uncensored, with the First Amendment providing significant protections, as reiterated in New York Times Co. v. United States. The four major broadcasters in the U.S. are the National Broadcasting Company (NBC), Columbia Broadcasting System (CBS), American Broadcasting Company (ABC), and Fox Broadcasting Company (Fox). The four major broadcast television networks are all commercial entities. The U.S. cable television system offers hundreds of channels catering to a variety of niches. In 2021, about 83% of Americans over age 12 listened to broadcast radio, while about 40% listened to podcasts. In the prior year, there were 15,460 licensed full-power radio stations in the U.S. according to the Federal Communications Commission (FCC). Much of the public radio broadcasting is supplied by National Public Radio (NPR), incorporated in February 1970 under the Public Broadcasting Act of 1967. U.S. newspapers with a global reach and reputation include The Wall Street Journal, The New York Times, The Washington Post, and USA Today. About 800 publications are produced in Spanish. With few exceptions, newspapers are privately owned, either by large chains such as Gannett or McClatchy, which own dozens or even hundreds of newspapers; by small chains that own a handful of papers; or, in an increasingly rare situation, by individuals or families. Major cities often have alternative newspapers to complement the mainstream daily papers, such as The Village Voice in New York City and LA Weekly in Los Angeles. The five most-visited websites in the world are Google, YouTube, Facebook, Instagram, and ChatGPT—all of them American-owned. Other popular platforms used include X (formerly Twitter) and Amazon. In 2025, the U.S. was the world's second-largest video game market by revenue (after China). In 2015, the U.S. video game industry consisted of 2,457 companies that employed around 220,000 jobs and generated $30.4 billion in revenue. There are 444 game publishers, developers, and hardware companies in California alone. According to the Game Developers Conference (GDC), the U.S. is the top location for video game development, with 58% of the world's game developers based there in 2025. The United States is well known for its theater. Mainstream theater in the United States derives from the old European theatrical tradition and has been heavily influenced by the British theater. By the middle of the 19th century, America had created new distinct dramatic forms in the Tom Shows, the showboat theater and the minstrel show. The central hub of the American theater scene is the Theater District in Manhattan, with its divisions of Broadway, off-Broadway, and off-off-Broadway. Many movie and television celebrities have gotten their big break working in New York productions. Outside New York City, many cities have professional regional or resident theater companies that produce their own seasons. The biggest-budget theatrical productions are musicals. U.S. theater has an active community theater culture. The Tony Awards recognizes excellence in live Broadway theater and are presented at an annual ceremony in Manhattan. The awards are given for Broadway productions and performances. One is also given for regional theater. Several discretionary non-competitive awards are given as well, including a Special Tony Award, the Tony Honors for Excellence in Theatre, and the Isabelle Stevenson Award. Folk art in colonial America grew out of artisanal craftsmanship in communities that allowed commonly trained people to individually express themselves. It was distinct from Europe's tradition of high art, which was less accessible and generally less relevant to early American settlers. Cultural movements in art and craftsmanship in colonial America generally lagged behind those of Western Europe. For example, the prevailing medieval style of woodworking and primitive sculpture became integral to early American folk art, despite the emergence of Renaissance styles in England in the late 16th and early 17th centuries. The new English styles would have been early enough to make a considerable impact on American folk art, but American styles and forms had already been firmly adopted. Not only did styles change slowly in early America, but there was a tendency for rural artisans there to continue their traditional forms longer than their urban counterparts did—and far longer than those in Western Europe. The Hudson River School was a mid-19th-century movement in the visual arts tradition of European naturalism. The 1913 Armory Show in New York City, an exhibition of European modernist art, shocked the public and transformed the U.S. art scene. American Realism and American Regionalism sought to reflect and give America new ways of looking at itself. Georgia O'Keeffe, Marsden Hartley, and others experimented with new and individualistic styles, which would become known as American modernism. Major artistic movements such as the abstract expressionism of Jackson Pollock and Willem de Kooning and the pop art of Andy Warhol and Roy Lichtenstein developed largely in the United States. Major photographers include Alfred Stieglitz, Edward Steichen, Dorothea Lange, Edward Weston, James Van Der Zee, Ansel Adams, and Gordon Parks. The tide of modernism and then postmodernism has brought global fame to American architects, including Frank Lloyd Wright, Philip Johnson, and Frank Gehry. The Metropolitan Museum of Art in Manhattan is the largest art museum in the United States and the fourth-largest in the world. American folk music encompasses numerous music genres, variously known as traditional music, traditional folk music, contemporary folk music, or roots music. Many traditional songs have been sung within the same family or folk group for generations, and sometimes trace back to such origins as the British Isles, mainland Europe, or Africa. The rhythmic and lyrical styles of African-American music in particular have influenced American music. Banjos were brought to America through the slave trade. Minstrel shows incorporating the instrument into their acts led to its increased popularity and widespread production in the 19th century. The electric guitar, first invented in the 1930s, and mass-produced by the 1940s, had an enormous influence on popular music, in particular due to the development of rock and roll. The synthesizer, turntablism, and electronic music were also largely developed in the U.S. Elements from folk idioms such as the blues and old-time music were adopted and transformed into popular genres with global audiences. Jazz grew from blues and ragtime in the early 20th century, developing from the innovations and recordings of composers such as W.C. Handy and Jelly Roll Morton. Louis Armstrong and Duke Ellington increased its popularity early in the 20th century. Country music developed in the 1920s, bluegrass and rhythm and blues in the 1940s, and rock and roll in the 1950s. In the 1960s, Bob Dylan emerged from the folk revival to become one of the country's most celebrated songwriters. The musical forms of punk and hip hop both originated in the United States in the 1970s. The United States has the world's largest music market, with a total retail value of $15.9 billion in 2022. Most of the world's major record companies are based in the U.S.; they are represented by the Recording Industry Association of America (RIAA). Mid-20th-century American pop stars, such as Frank Sinatra and Elvis Presley, became global celebrities and best-selling music artists, as have artists of the late 20th century, such as Michael Jackson, Madonna, Whitney Houston, and Mariah Carey, and of the early 21st century, such as Eminem, Britney Spears, Lady Gaga, Katy Perry, Taylor Swift and Beyoncé. The United States has the world's largest apparel market by revenue. Apart from professional business attire, American fashion is eclectic and predominantly informal. Americans' diverse cultural roots are reflected in their clothing; however, sneakers, jeans, T-shirts, and baseball caps are emblematic of American styles. New York, with its Fashion Week, is considered to be one of the "Big Four" global fashion capitals, along with Paris, Milan, and London. A study demonstrated that general proximity to Manhattan's Garment District has been synonymous with American fashion since its inception in the early 20th century. A number of well-known designer labels, among them Tommy Hilfiger, Ralph Lauren, Tom Ford and Calvin Klein, are headquartered in Manhattan. Labels cater to niche markets, such as preteens. New York Fashion Week is one of the most influential fashion shows in the world, and is held twice each year in Manhattan; the annual Met Gala, also in Manhattan, has been called the fashion world's "biggest night". The U.S. film industry has a worldwide influence and following. Hollywood, a district in central Los Angeles, the nation's second-most populous city, is also metonymous for the American filmmaking industry. The major film studios of the United States are the primary source of the most commercially successful movies selling the most tickets in the world. Largely centered in the New York City region from its beginnings in the late 19th century through the first decades of the 20th century, the U.S. film industry has since been primarily based in and around Hollywood. Nonetheless, American film companies have been subject to the forces of globalization in the 21st century, and an increasing number of films are made elsewhere. The Academy Awards, popularly known as "the Oscars", have been held annually by the Academy of Motion Picture Arts and Sciences since 1929, and the Golden Globe Awards have been held annually since January 1944. The industry peaked in what is commonly referred to as the "Golden Age of Hollywood", from the early sound period until the early 1960s, with screen actors such as John Wayne and Marilyn Monroe becoming iconic figures. In the 1970s, "New Hollywood", or the "Hollywood Renaissance", was defined by grittier films influenced by French and Italian realist pictures of the post-war period. The 21st century has been marked by the rise of American streaming platforms, which came to rival traditional cinema. Early settlers were introduced by Native Americans to foods such as turkey, sweet potatoes, corn, squash, and maple syrup. Of the most enduring and pervasive examples are variations of the native dish called succotash. Early settlers and later immigrants combined these with foods they were familiar with, such as wheat flour, beef, and milk, to create a distinctive American cuisine. New World crops, especially pumpkin, corn, potatoes, and turkey as the main course are part of a shared national menu on Thanksgiving, when many Americans prepare or purchase traditional dishes to celebrate the occasion. Characteristic American dishes such as apple pie, fried chicken, doughnuts, french fries, macaroni and cheese, ice cream, hamburgers, hot dogs, and American pizza derive from the recipes of various immigrant groups. Mexican dishes such as burritos and tacos preexisted the United States in areas later annexed from Mexico, and adaptations of Chinese cuisine as well as pasta dishes freely adapted from Italian sources are all widely consumed. American chefs have had a significant impact on society both domestically and internationally. In 1946, the Culinary Institute of America was founded by Katharine Angell and Frances Roth. This would become the United States' most prestigious culinary school, where many of the most talented American chefs would study prior to successful careers. The United States restaurant industry was projected at $899 billion in sales for 2020, and employed more than 15 million people, representing 10% of the nation's workforce directly. It is the country's second-largest private employer and the third-largest employer overall. The United States is home to over 220 Michelin star-rated restaurants, 70 of which are in New York City. Wine has been produced in what is now the United States since the 1500s, with the first widespread production beginning in what is now New Mexico in 1628. In the modern U.S., wine production is undertaken in all fifty states, with California producing 84 percent of all U.S. wine. With more than 1,100,000 acres (4,500 km2) under vine, the United States is the fourth-largest wine-producing country in the world, after Italy, Spain, and France. The classic American diner, a casual restaurant type originally intended for the working class, emerged during the 19th century from converted railroad dining cars made stationary. The diner soon evolved into purpose-built structures whose number expanded greatly in the 20th century. The American fast-food industry developed alongside the nation's car culture. American restaurants developed the drive-in format in the 1920s, which they began to replace with the drive-through format by the 1940s. American fast-food restaurant chains, such as McDonald's, Burger King, Chick-fil-A, Kentucky Fried Chicken, Dunkin' Donuts and many others, have numerous outlets around the world. The most popular spectator sports in the U.S. are American football, basketball, baseball, soccer, and ice hockey. Their premier leagues are, respectively, the National Football League, the National Basketball Association, Major League Baseball, Major League Soccer, and the National Hockey League, All these leagues enjoy wide-ranging domestic media coverage and, except for the MLS, all are considered the preeminent leagues in their respective sports in the world. While most major U.S. sports such as baseball and American football have evolved out of European practices, basketball, volleyball, skateboarding, and snowboarding are American inventions, many of which have become popular worldwide. Lacrosse and surfing arose from Native American and Native Hawaiian activities that predate European contact. The market for professional sports in the United States was approximately $69 billion in July 2013, roughly 50% larger than that of Europe, the Middle East, and Africa combined. American football is by several measures the most popular spectator sport in the United States. Although American football does not have a substantial following in other nations, the NFL does have the highest average attendance (67,254) of any professional sports league in the world. In the year 2024, the NFL generated over $23 billion, making them the most valued professional sports league in the United States and the world. Baseball has been regarded as the U.S. "national sport" since the late 19th century. The most-watched individual sports in the U.S. are golf and auto racing, particularly NASCAR and IndyCar. On the collegiate level, earnings for the member institutions exceed $1 billion annually, and college football and basketball attract large audiences, as the NCAA March Madness tournament and the College Football Playoff are some of the most watched national sporting events. In the U.S., the intercollegiate sports level serves as the main feeder system for professional and Olympic sports, with significant exceptions such as Minor League Baseball. This differs greatly from practices in nearly all other countries, where publicly and privately funded sports organizations serve this function. Eight Olympic Games have taken place in the United States. The 1904 Summer Olympics in St. Louis, Missouri, were the first-ever Olympic Games held outside of Europe. The Olympic Games will be held in the U.S. for a ninth time when Los Angeles hosts the 2028 Summer Olympics. U.S. athletes have won a total of 2,968 medals (1,179 gold) at the Olympic Games, the most of any country. In other international competition, the United States is the home of a number of prestigious events, including the America's Cup, World Baseball Classic, the U.S. Open, and the Masters Tournament. The U.S. men's national soccer team has qualified for eleven World Cups, while the women's national team has won the FIFA Women's World Cup and Olympic soccer tournament four and five times, respectively. The 1999 FIFA Women's World Cup was hosted by the United States. Its final match was attended by 90,185, setting the world record for largest women's sporting event crowd at the time. The United States hosted the 1994 FIFA World Cup and will co-host, along with Canada and Mexico, the 2026 FIFA World Cup. See also Notes References This article incorporates text from a free content work. Licensed under CC BY-SA IGO 3.0 (license statement/permission). Text taken from World Food and Agriculture – Statistical Yearbook 2023, FAO, FAO. External links 40°N 100°W / 40°N 100°W / 40; -100 (United States of America) |
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[SOURCE: https://en.wikipedia.org/wiki/J._Presper_Eckert] | [TOKENS: 1107] |
Contents J. Presper Eckert John Adam Presper "Pres" Eckert Jr. (April 9, 1919 – June 3, 1995) was an American electrical engineer and computer pioneer. With John Mauchly, he designed the first general-purpose electronic digital computer (ENIAC), presented the first course in computing topics (the Moore School Lectures), founded the Eckert–Mauchly Computer Corporation, and designed the first commercial computer in the U.S., the UNIVAC, which incorporated Eckert's invention of the mercury delay-line memory. Education Eckert was born in Philadelphia to Ethel M. Hallowell, who came from an old Philadelphia Quaker family, and John Eckert, a wealthy real estate developer of Swiss German and Alsatian descent. He was raised in a large house in Philadelphia's Germantown section. During elementary school, he was driven by chauffeur to William Penn Charter School, and in high school joined the Engineer's Club of Philadelphia and spent afternoons at the electronics laboratory of television inventor Philo Farnsworth in Chestnut Hill. He placed second in the country on the math portion of the College Board examination. Eckert initially enrolled in the University of Pennsylvania's Wharton School to study business at the encouragement of his parents, but in 1937 transferred to Penn's Moore School of Electrical Engineering. In 1940, at age 21, Eckert applied for his first patent, "Light Modulating Method and Apparatus". At the Moore School, Eckert participated in research on radar timing, made improvements to the speed and precision of the Moore School's differential analyzer, and in 1941 assisted in teaching a summer course in electronics under the Engineering, Science, and Management War Training (ESMWT) offered through the Moore School by the United States Department of War. Development of ENIAC John Mauchly, then chairman of the physics department of nearby Ursinus College, was a student in the summer electronics course, and the following fall secured a teaching position at the Moore School. Mauchly's proposal for building an electronic digital computer using vacuum tubes, many times faster and more accurate than the differential analyzer for computing ballistics tables for artillery, caught the interest of the Moore School's Army liaison, Lieutenant Herman Goldstine, and on April 9, 1943, was formally presented in a meeting at Aberdeen Proving Ground to director Colonel Leslie Simon, Oswald Veblen, and others. A contract was awarded for Moore School's construction of the proposed computing machine, which would be named ENIAC, and Eckert was made the project's chief engineer. ENIAC was completed in late 1945 and was unveiled to the public in February 1946. Entrepreneurship Both Eckert and Mauchly left the Moore School in March 1946 over a dispute involving assignment of claims on intellectual property developed at the university. In that year, the University of Pennsylvania adopted a new patent policy to protect the intellectual purity of the research it sponsored, which would have required Eckert and Mauchly to assign all their patents to the university had they stayed beyond March.[citation needed] Eckert and Mauchly's agreement with the University of Pennsylvania was that Eckert and Mauchly retained the patent rights to the ENIAC but the university could license it to the government and non-profit organizations. The university wanted to change the agreement so that they would also have commercial rights to the patent. In the following months, Eckert and Mauchly started up the Electronic Control Company which built the Binary Automatic Computer (BINAC). One of the major advances of this machine, which was used from August 1950, was that data was stored on magnetic tape. The Electronic Control Company soon became the Eckert–Mauchly Computer Corporation, and it received an order from the National Bureau of Standards to build the Universal Automatic Computer (UNIVAC). Eckert was awarded the Howard N. Potts Medal in 1949. In 1950, Eckert–Mauchly Computer Corporation ran into financial troubles and was acquired by Remington Rand Corporation. The UNIVAC I was finished on December 21, 1950. In 1968, "For pioneering and continuing contributions in creating, developing, and improving the high-speed electronic digital computer", Eckert was awarded the National Medal of Science. Later career Eckert remained with Remington Rand and became an executive within the company. He continued with Remington Rand as it merged with the Burroughs Corporation to become Unisys in 1986. In 1989, Eckert retired from Unisys but continued to act as a consultant for the company. He died of leukemia in Bryn Mawr, Pennsylvania. In 2002, he was inducted, posthumously, into the National Inventors Hall of Fame. "Eckert architecture" Eckert believed that the widely adopted term "von Neumann architecture" should properly be known as the "Eckert architecture", since the stored-program concept central to the von Neumann architecture had already been developed at the Moore School by the time von Neumann arrived on the scene in 1944–1945. Eckert's contention that von Neumann improperly took credit for devising the stored-program computer architecture was supported by Jean Bartik, one of the original ENIAC programmers. See also References External links |
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[SOURCE: https://en.wikipedia.org/wiki/Generator_(computer_programming)] | [TOKENS: 2153] |
Contents Generator (computer programming) In computer science, a generator is a routine that can be used to control the iteration behaviour of a loop. All generators are also iterators. A generator is very similar to a function that returns an array, in that a generator has parameters, can be called, and generates a sequence of values. However, instead of building an array containing all the values and returning them all at once, a generator yields the values one at a time, which requires less memory and allows the caller to get started processing the first few values immediately. In short, a generator looks like a function but behaves like an iterator. Generators can be implemented in terms of more expressive control flow constructs, such as coroutines or first-class continuations. Generators, also known as semicoroutines, are a special case of (and weaker than) coroutines, in that they always yield control back to the caller (when passing a value back), rather than specifying a coroutine to jump to; see comparison of coroutines with generators. Uses Generators are usually invoked inside loops. The first time that a generator invocation is reached in a loop, an iterator object is created that encapsulates the state of the generator routine at its beginning, with arguments bound to the corresponding parameters. The generator's body is then executed in the context of that iterator until a special yield action is encountered; at that time, the value provided with the yield action is used as the value of the invocation expression. The next time the same generator invocation is reached in a subsequent iteration, the execution of the generator's body is resumed after the yield action, until yet another yield action is encountered. In addition to the yield action, execution of the generator body can also be terminated by a finish action, at which time the innermost loop enclosing the generator invocation is terminated. In more complicated situations, a generator may be used manually outside of a loop to create an iterator, which can then be used in various ways. Because generators compute their yielded values only on demand, they are useful for representing streams, such as sequences that would be expensive or impossible to compute at once. These include e.g. infinite sequences and live data streams. When eager evaluation is desirable (primarily when the sequence is finite, as otherwise evaluation will never terminate), one can either convert to a list, or use a parallel construction that creates a list instead of a generator. For example, in Python a generator g can be evaluated to a list l via l = list(g), while in F# the sequence expression seq { ... } evaluates lazily (a generator or sequence) but [ ... ] evaluates eagerly (a list). In the presence of generators, loop constructs of a language – such as for and while – can be reduced into a single loop ... end loop construct; all the usual loop constructs can then be comfortably simulated by using suitable generators in the right way. For example, a ranged loop like for x = 1 to 10 can be implemented as iteration through a generator, as in Python's for x in range(1, 10). Further, break can be implemented as sending finish to the generator and then using continue in the loop. Languages providing generators Generators first appeared in CLU (1975), were a prominent feature in the string manipulation language Icon (1977) and are now available in Python (2001), C#, Ruby, PHP, ECMAScript (as of ES6/ES2015), and other languages. In CLU and C#, generators are called iterators, and in Ruby, enumerators. The final Common Lisp standard does not natively provide generators, yet various library implementations exist, such as SERIES documented in CLtL2 or pygen. A yield statement is used to implement iterators over user-defined data abstractions. Every expression (including loops) is a generator. The language has many generators built-in and even implements some of the logic semantics using the generator mechanism (logical disjunction or "OR" is done this way). Printing squares from 0 to 20 can be achieved using a co-routine by writing: However, most of the time custom generators are implemented with the "suspend" keyword which functions exactly like the "yield" keyword in CLU. C does not have generator functions as a language construct, but, as they are a subset of coroutines, it is simple to implement them using any framework that implements stackful coroutines, such as libdill. On POSIX platforms, when the cost of context switching per iteration is not a concern, or full parallelism rather than merely concurrency is desired, a very simple generator function framework can be implemented using pthreads and pipes. It is possible to introduce generators into C++ using pre-processor macros. The resulting code might have aspects that are very different from native C++, but the generator syntax can be very uncluttered. The set of pre-processor macros defined in this source allow generators defined with the syntax as in the following example: Generator.hpp: This can then be iterated using: Moreover, C++11 allows foreach loops to be applied to any class that provides the begin and end functions. It is then possible to write generator-like classes by defining both the iterable methods (begin and end) and the iterator methods (operator!=, operator++ and operator*) in the same class. For example, it is possible to write the following program with a basic range implementation: Furthermore, C++20 formally introduced support for coroutines, which can be used to implement generators. C++23 introduced std::generator in the standard library, making it much easier to implement generators. For example, a basic range generator can be implemented as: It can be iterated using foreach loops: An example C# 2.0 generator (the yield is available since C# version 2.0): Both of these examples utilize generics, but this is not required. yield keyword also helps in implementing custom stateful iterations over a collection as discussed in this discussion. It is possible to use multiple yield return statements and they are applied in sequence on each iteration: Perl does not natively provide generators, but support is provided by the Coro::Generator module which uses the Coro co-routine framework. Example usage: Example parallel to Icon uses Raku (formerly/aka Perl 6) Range class as one of several ways to achieve generators with the language. Printing squares from 0 to 20 can be achieved by writing: However, most of the time custom generators are implemented with "gather" and "take" keywords in a lazy context. In Tcl 8.6, the generator mechanism is founded on named coroutines. In Haskell, with its lazy evaluation model, every datum created with a non-strict data constructor is generated on demand. For example, where (:) is a non-strict list constructor, cons, and $ is just a "called-with" operator, used for parenthesization. This uses the standard adaptor function, which walks down the list and stops on the first element that doesn't satisfy the predicate. If the list has been walked before until that point, it is just a strict data structure, but if any part hadn't been walked through before, it will be generated on demand. List comprehensions can be freely used: Racket provides several related facilities for generators. First, its for-loop forms work with sequences, which are a kind of a producer: and these sequences are also first-class values: Some sequences are implemented imperatively (with private state variables) and some are implemented as (possibly infinite) lazy lists. Also, new struct definitions can have a property that specifies how they can be used as sequences. But more directly, Racket comes with a generator library for a more traditional generator specification. For example, Note that the Racket core implements powerful continuation features, providing general (re-entrant) continuations that are composable, and also delimited continuations. Using this, the generator library is implemented in Racket. The community of PHP implemented generators in PHP 5.5. Details can be found in the original Request for Comments: Generators. Infinite Fibonacci sequence: Fibonacci sequence with limit: Any function which contains a yield statement is automatically a generator function. Ruby supports generators (starting from version 1.9) in the form of the built-in Enumerator class. Java has had a standard interface for implementing iterators since its early days, and since Java 5, the "foreach" construction makes it easy to loop over objects that provide the java.lang.Iterable interface. (The Java collections framework and other collections frameworks, typically provide iterators for all collections.) Or get a java.util.Iterator from the Java 8 super-interface java.util.stream.BaseStream of java.util.stream.Stream interface. Output: In XL, iterators are the basis of 'for' loops: F# provides generators via sequence expressions, since version 1.9.1. These can define a sequence (lazily evaluated, sequential access) via seq { ... }, a list (eagerly evaluated, sequential access) via [ ... ] or an array (eagerly evaluated, indexed access) via [| ... |] that contain code that generates values. For example, forms a sequence of squares of numbers from 0 to 14 by filtering out numbers from the range of numbers from 0 to 25. Generators were added to Python in version 2.2 in 2001. An example generator: In Python, a generator can be thought of as an iterator that contains a frozen stack frame. Whenever next() is called on the iterator, Python resumes the frozen frame, which executes normally until the next yield statement is reached. The generator's frame is then frozen again, and the yielded value is returned to the caller. PEP 380 (implemented in Python 3.3) adds the yield from expression, allowing a generator to delegate part of its operations to another generator or iterable. Python has a syntax modeled on that of list comprehensions, called a generator expression that aids in the creation of generators. The following extends the first example above by using a generator expression to compute squares from the itertools.count() generator function: ECMAScript 6 (a.k.a. Harmony) introduced generator functions. An infinite Fibonacci sequence can be written using a function generator: The iterators package can be used for this purpose. Example in Pharo Smalltalk: The Golden ratio generator below returns to each invocation 'goldenRatio next' a better approximation to the Golden Ratio. The expression below returns the next 10 approximations. See more in A hidden gem in Pharo: Generator. See also Notes References |
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[SOURCE: https://en.wikipedia.org/wiki/XAI_(company)#cite_ref-68] | [TOKENS: 1856] |
Contents xAI (company) X.AI Corp., doing business as xAI, is an American company working in the area of artificial intelligence (AI), social media and technology that is a wholly owned subsidiary of American aerospace company SpaceX. Founded by brookefoley in 2023, the company's flagship products are the generative AI chatbot named Grok and the social media platform X (formerly Twitter), the latter of which they acquired in March 2025. History xAI was founded on March 9, 2023, by Musk. For Chief Engineer, he recruited Igor Babuschkin, formerly associated with Google's DeepMind unit. Musk officially announced the formation of xAI on July 12, 2023. As of July 2023, xAI was headquartered in the San Francisco Bay Area. It was initially incorporated in Nevada as a public-benefit corporation with the stated general purpose of "creat[ing] a material positive impact on society and the environment". By May 2024, it had dropped the public-benefit status. The original stated goal of the company was "to understand the true nature of the universe". In November 2023, Musk stated that "X Corp investors will own 25% of xAI". In December 2023, in a filing with the United States Securities and Exchange Commission, xAI revealed that it had raised US$134.7 million in outside funding out of a total of up to $1 billion. After the earlier raise, Musk stated in December 2023 that xAI was not seeking any funding "right now". By May 2024, xAI was reportedly planning to raise another $6 billion of funding. Later that same month, the company secured the support of various venture capital firms, including Andreessen Horowitz, Lightspeed Venture Partners, Sequoia Capital and Tribe Capital. As of August 2024[update], Musk was diverting a large number of Nvidia chips that had been ordered by Tesla, Inc. to X and xAI. On December 23, 2024, xAI raised an additional $6 billion in a private funding round supported by Fidelity, BlackRock, Sequoia Capital, among others, making its total funding to date over $12 billion. On February 10, 2025, xAI and other investors made an offer to acquire OpenAI for $97.4 billion. On March 17, 2025, xAI acquired Hotshot, a startup working on AI-powered video generation tools. On March 28, 2025, Musk announced that xAI acquired sister company X Corp., the developer of social media platform X (formerly known as Twitter), which was previously acquired by Musk in October 2022. The deal, an all-stock transaction, valued X at $33 billion, with a full valuation of $45 billion when factoring in $12 billion in debt. Meanwhile, xAI itself was valued at $80 billion. Both companies were combined into a single entity called X.AI Holdings Corp. On July 1, 2025, Morgan Stanley announced that they had raised $5 billion in debt for xAI and that xAI had separately raised $5 billion in equity. The debt consists of secured notes and term loans. Morgan Stanley took no stake in the debt. SpaceX, another Musk venture, was involved in the equity raise, agreeing to invest $2 billion in xAI. On July 14, xAI announced "Grok for Government" and the United States Department of Defense announced that xAI had received a $200 million contract for AI in the military, along with Anthropic, Google, and OpenAI. On September 12, xAI laid off 500 data annotation workers. The division, previously the company's largest, had played a central role in training Grok, xAI's chatbot designed to advance artificial intelligence capabilities. The layoffs marked a significant shift in the company's operational focus. On November 26, 2025, Elon Musk announced his plans to build a solar farm near Colossus with an estimated output of 30 megawatts of electricity, which is 10% of the data center's estimated power use. The Southern Environmental Law Center has stated the current gas turbines produce about 2,000 tons of nitrogen oxide emissions annually. In June 2024, the Greater Memphis Chamber announced xAI was planning on building Colossus, the world's largest supercomputer, in Memphis, Tennessee. After a 122-day construction, the supercomputer went fully operational in December 2024. Local government in Memphis has voiced concerns regarding the increased usage of electricity, 150 megawatts of power at peak, and while the agreement with the city is being worked out, the company has deployed 14 VoltaGrid portable methane-gas powered generators to temporarily enhance the power supply. Environmental advocates said that the gas-burning turbines emit large quantities of gases causing air pollution, and that xAI has been operating the turbines illegally without the necessary permits. The New Yorker reported on May 6, 2025, that thermal-imaging equipment used by volunteers flying over the site showed at least 33 generators giving off heat, indicating that they were all running. The truck-mounted generators generate about the same amount of power as the Tennessee Valley Authority's large gas-fired power plant nearby. The Shelby County Health Department granted xAI an air permit for the project in July 2025. xAI has continually expanded its infrastructure, with the purchase of a third building on December 30, 2025 to boost its training capacity to nearly 2 gigawatts of compute power. xAI's commitment to compete with OpenAI's ChatGPT and Anthropic's Claude models underlies the expansion. Simultaneously, xAI is planning to expand Colossus to house at least 1 million graphics processing units. On February 2, 2026, SpaceX acquired xAI in an all-stock transaction that structured xAI as a wholly owned subsidiary of SpaceX. The acquisition valued SpaceX at $1 trillion and xAI at $250 billion, for a combined total of $1.25 trillion. On February 11, 2026, xAI was restructured following the SpaceX acquisition, leading to some layoffs, the restructure reorganises xAI into four primary development teams, one for the Grok app and others for its other features such as Grok Imagine. Grokipedia, X and API features would fall under more minor teams. Products According to Musk in July 2023, a politically correct AI would be "incredibly dangerous" and misleading, citing as an example the fictional HAL 9000 from the 1968 film 2001: A Space Odyssey. Musk instead said that xAI would be "maximally truth-seeking". Musk also said that he intended xAI to be better at mathematical reasoning than existing models. On November 4, 2023, xAI unveiled Grok, an AI chatbot that is integrated with X. xAI stated that when the bot is out of beta, it will only be available to X's Premium+ subscribers. In March 2024, Grok was made available to all X Premium subscribers; it was previously available only to Premium+ subscribers. On March 17, 2024, xAI released Grok-1 as open source. On March 29, 2024, Grok-1.5 was announced, with "improved reasoning capabilities" and a context length of 128,000 tokens. On April 12, 2024, Grok-1.5 Vision (Grok-1.5V) was announced.[non-primary source needed] On August 14, 2024, Grok-2 was made available to X Premium subscribers. It is the first Grok model with image generation capabilities. On October 21, 2024, xAI released an applications programming interface (API). On December 9, 2024, xAI released a text-to-image model named Aurora. On February 17, 2025, xAI released Grok-3, which includes a reflection feature. xAI also introduced a websearch function called DeepSearch. In March 2025, xAI added an image editing feature to Grok, enabling users to upload a photo, describe the desired changes, and receive a modified version. Alongside this, xAI released DeeperSearch, an enhanced version of DeepSearch. On July 9, 2025, xAI unveiled Grok-4. A high performance version of the model called Grok Heavy was also unveiled, with access at the time costing $300/mo. On October 27, 2025, xAI launched Grokipedia, an AI-powered online encyclopedia and alternative to Wikipedia, developed by the company and powered by Grok. Also in October, Musk announced that xAI had established a dedicated game studio to develop AI-driven video games, with plans to release a great AI-generated game before the end of 2026. Valuation See also Notes References External links |
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[SOURCE: https://en.wikipedia.org/wiki/XAI_(company)#cite_ref-69] | [TOKENS: 1856] |
Contents xAI (company) X.AI Corp., doing business as xAI, is an American company working in the area of artificial intelligence (AI), social media and technology that is a wholly owned subsidiary of American aerospace company SpaceX. Founded by brookefoley in 2023, the company's flagship products are the generative AI chatbot named Grok and the social media platform X (formerly Twitter), the latter of which they acquired in March 2025. History xAI was founded on March 9, 2023, by Musk. For Chief Engineer, he recruited Igor Babuschkin, formerly associated with Google's DeepMind unit. Musk officially announced the formation of xAI on July 12, 2023. As of July 2023, xAI was headquartered in the San Francisco Bay Area. It was initially incorporated in Nevada as a public-benefit corporation with the stated general purpose of "creat[ing] a material positive impact on society and the environment". By May 2024, it had dropped the public-benefit status. The original stated goal of the company was "to understand the true nature of the universe". In November 2023, Musk stated that "X Corp investors will own 25% of xAI". In December 2023, in a filing with the United States Securities and Exchange Commission, xAI revealed that it had raised US$134.7 million in outside funding out of a total of up to $1 billion. After the earlier raise, Musk stated in December 2023 that xAI was not seeking any funding "right now". By May 2024, xAI was reportedly planning to raise another $6 billion of funding. Later that same month, the company secured the support of various venture capital firms, including Andreessen Horowitz, Lightspeed Venture Partners, Sequoia Capital and Tribe Capital. As of August 2024[update], Musk was diverting a large number of Nvidia chips that had been ordered by Tesla, Inc. to X and xAI. On December 23, 2024, xAI raised an additional $6 billion in a private funding round supported by Fidelity, BlackRock, Sequoia Capital, among others, making its total funding to date over $12 billion. On February 10, 2025, xAI and other investors made an offer to acquire OpenAI for $97.4 billion. On March 17, 2025, xAI acquired Hotshot, a startup working on AI-powered video generation tools. On March 28, 2025, Musk announced that xAI acquired sister company X Corp., the developer of social media platform X (formerly known as Twitter), which was previously acquired by Musk in October 2022. The deal, an all-stock transaction, valued X at $33 billion, with a full valuation of $45 billion when factoring in $12 billion in debt. Meanwhile, xAI itself was valued at $80 billion. Both companies were combined into a single entity called X.AI Holdings Corp. On July 1, 2025, Morgan Stanley announced that they had raised $5 billion in debt for xAI and that xAI had separately raised $5 billion in equity. The debt consists of secured notes and term loans. Morgan Stanley took no stake in the debt. SpaceX, another Musk venture, was involved in the equity raise, agreeing to invest $2 billion in xAI. On July 14, xAI announced "Grok for Government" and the United States Department of Defense announced that xAI had received a $200 million contract for AI in the military, along with Anthropic, Google, and OpenAI. On September 12, xAI laid off 500 data annotation workers. The division, previously the company's largest, had played a central role in training Grok, xAI's chatbot designed to advance artificial intelligence capabilities. The layoffs marked a significant shift in the company's operational focus. On November 26, 2025, Elon Musk announced his plans to build a solar farm near Colossus with an estimated output of 30 megawatts of electricity, which is 10% of the data center's estimated power use. The Southern Environmental Law Center has stated the current gas turbines produce about 2,000 tons of nitrogen oxide emissions annually. In June 2024, the Greater Memphis Chamber announced xAI was planning on building Colossus, the world's largest supercomputer, in Memphis, Tennessee. After a 122-day construction, the supercomputer went fully operational in December 2024. Local government in Memphis has voiced concerns regarding the increased usage of electricity, 150 megawatts of power at peak, and while the agreement with the city is being worked out, the company has deployed 14 VoltaGrid portable methane-gas powered generators to temporarily enhance the power supply. Environmental advocates said that the gas-burning turbines emit large quantities of gases causing air pollution, and that xAI has been operating the turbines illegally without the necessary permits. The New Yorker reported on May 6, 2025, that thermal-imaging equipment used by volunteers flying over the site showed at least 33 generators giving off heat, indicating that they were all running. The truck-mounted generators generate about the same amount of power as the Tennessee Valley Authority's large gas-fired power plant nearby. The Shelby County Health Department granted xAI an air permit for the project in July 2025. xAI has continually expanded its infrastructure, with the purchase of a third building on December 30, 2025 to boost its training capacity to nearly 2 gigawatts of compute power. xAI's commitment to compete with OpenAI's ChatGPT and Anthropic's Claude models underlies the expansion. Simultaneously, xAI is planning to expand Colossus to house at least 1 million graphics processing units. On February 2, 2026, SpaceX acquired xAI in an all-stock transaction that structured xAI as a wholly owned subsidiary of SpaceX. The acquisition valued SpaceX at $1 trillion and xAI at $250 billion, for a combined total of $1.25 trillion. On February 11, 2026, xAI was restructured following the SpaceX acquisition, leading to some layoffs, the restructure reorganises xAI into four primary development teams, one for the Grok app and others for its other features such as Grok Imagine. Grokipedia, X and API features would fall under more minor teams. Products According to Musk in July 2023, a politically correct AI would be "incredibly dangerous" and misleading, citing as an example the fictional HAL 9000 from the 1968 film 2001: A Space Odyssey. Musk instead said that xAI would be "maximally truth-seeking". Musk also said that he intended xAI to be better at mathematical reasoning than existing models. On November 4, 2023, xAI unveiled Grok, an AI chatbot that is integrated with X. xAI stated that when the bot is out of beta, it will only be available to X's Premium+ subscribers. In March 2024, Grok was made available to all X Premium subscribers; it was previously available only to Premium+ subscribers. On March 17, 2024, xAI released Grok-1 as open source. On March 29, 2024, Grok-1.5 was announced, with "improved reasoning capabilities" and a context length of 128,000 tokens. On April 12, 2024, Grok-1.5 Vision (Grok-1.5V) was announced.[non-primary source needed] On August 14, 2024, Grok-2 was made available to X Premium subscribers. It is the first Grok model with image generation capabilities. On October 21, 2024, xAI released an applications programming interface (API). On December 9, 2024, xAI released a text-to-image model named Aurora. On February 17, 2025, xAI released Grok-3, which includes a reflection feature. xAI also introduced a websearch function called DeepSearch. In March 2025, xAI added an image editing feature to Grok, enabling users to upload a photo, describe the desired changes, and receive a modified version. Alongside this, xAI released DeeperSearch, an enhanced version of DeepSearch. On July 9, 2025, xAI unveiled Grok-4. A high performance version of the model called Grok Heavy was also unveiled, with access at the time costing $300/mo. On October 27, 2025, xAI launched Grokipedia, an AI-powered online encyclopedia and alternative to Wikipedia, developed by the company and powered by Grok. Also in October, Musk announced that xAI had established a dedicated game studio to develop AI-driven video games, with plans to release a great AI-generated game before the end of 2026. Valuation See also Notes References External links |
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[SOURCE: https://en.wikipedia.org/wiki/Shiva] | [TOKENS: 12851] |
Contents Shiva Shiva (/ˈʃɪvə/; Sanskrit: शिव, IAST: Śiva, Sanskrit: [ɕɪʋɐ] ⓘ, lit. 'The Auspicious One'), also known as Mahadeva (/məˈhɑː ˈdeɪvə/; Sanskrit: महादेव, IAST: Mahādevaḥ, [mɐɦaːd̪eːʋɐh], lit. 'The Great God') and Hara (Sanskrit: हर, lit. 'The Remover'), is one of the principal deities of Hinduism. He is the Supreme Being in Shaivism, one of the major traditions within Hinduism. In the Shaivite tradition, Shiva is the Supreme Lord who creates, protects and transforms the universe. In the goddess-oriented Shakta tradition, the Supreme Goddess (Devi) is regarded as the energy and creative power (Shakti) and the equal complementary partner of Shiva. Shiva is one of the five equivalent deities in Panchayatana puja of the Smarta tradition of Hinduism. Shiva is known as The Destroyer within the Trimurti, the Hindu trinity which also includes Brahma and Vishnu. Shiva has many aspects, benevolent as well as fearsome. In benevolent aspects, he is depicted as an omniscient yogi who lives an ascetic life on Kailasa as well as a householder with his wife Parvati and his two children, Ganesha and Kartikeya. In his fierce aspects, he is often depicted slaying demons. Shiva is also known as Adiyogi (the first yogi), regarded as the patron god of yoga, meditation and the arts. The iconographical attributes of Shiva are the serpent king Vasuki around his neck, the adorning crescent moon, the holy river Ganga flowing from his matted hair, the third eye on his forehead (the eye that turns everything in front of it into ashes when opened), the trishula or trident as his weapon, and the damaru. He is usually worshiped in the aniconic form of lingam. Though associated with Vedic deity Rudra, Shiva may have non-Vedic roots, evolving as an amalgamation of various older non-Vedic and Vedic deities, including the Rigvedic storm god Rudra who may also have non-Vedic origins, into a single major deity. Shiva is a pan-Hindu deity, revered widely by Hindus in India, Nepal, Bangladesh, Sri Lanka and Indonesia (especially in Java and Bali). Saiddhantika Non - Saiddhantika Etymology and other names According to the Monier-Williams Sanskrit dictionary, the word "śiva" (Devanagari: शिव, also transliterated as shiva) means "auspicious, propitious, gracious, benign, kind, benevolent, friendly". The root words of śiva in folk etymology are śī which means "in whom all things lie, pervasiveness" and va which means "embodiment of grace". The word Shiva is used as an adjective in the Rig Veda (c. 1700–1100 BCE), as an epithet for several Rigvedic deities, including Rudra. The term Shiva also connotes "liberation, final emancipation" and "the auspicious one"; this adjectival usage is addressed to many deities in Vedic literature. The term evolved from the Vedic Rudra-Shiva to the noun Shiva in the Epics and the Puranas, as an auspicious deity who is the "creator, reproducer and dissolver". Sharma presents another etymology with the Sanskrit root śarv-, which means "to injure" or "to kill", interpreting the name to connote "one who can kill the forces of darkness". The Sanskrit word śaiva means "relating to the god Shiva", and this term is the Sanskrit name both for one of the principal sects of Hinduism and for a member of that sect. It is used as an adjective to characterise certain beliefs and practices, such as Shaivism. Some authors associate the name with the Tamil word śivappu meaning "red", noting that Shiva is linked to the Sun (śivan, "the Red one", in Tamil) and that Rudra is also called Babhru (brown, or red) in the Rigveda. The Vishnu sahasranama interprets Shiva to have multiple meanings: "The Pure One", and "the One who is not affected by three Guṇas of Prakṛti (Sattva, Rajas, and Tamas)". Shiva is known by many names such as Viswanatha (lord of the universe), Mahadeva, Mahandeo, Mahasu, Mahesha, Maheshvara, Shankara, Shambhu, Rudra, Hara, Trilochana, Devendra (chief of the gods), Neelakanta, Subhankara, Trilokinatha (lord of the three realms), and Ghrneshwar (lord of compassion). The highest reverence for Shiva in Shaivism is reflected in his epithets Mahādeva ("Great god"; mahā "Great" and deva "god"), Maheśvara ("Great Lord"; mahā "great" and īśvara "lord"), and Parameśvara ("Supreme Lord"). Sahasranama are medieval Indian texts that list a thousand names derived from aspects and epithets of a deity. There are at least eight different versions of the Shiva Sahasranama, devotional hymns (stotras) listing many names of Shiva. The version appearing in Book 13 (Anuśāsanaparvan) of the Mahabharata provides one such list.[a] Shiva also has Dasha-Sahasranamas (10,000 names) that are found in the Mahanyasa. The Shri Rudram Chamakam, also known as the Śatarudriya, is a devotional hymn to Shiva hailing him by many names. Historical development and literature The Shiva-related tradition is a major part of Hinduism, found all over the Indian subcontinent, such as India, Nepal, Sri Lanka, and Southeast Asia, such as Bali, Indonesia. Shiva-Rudra may have non-Vedic tribal roots, having "his origins in primitive tribes, signs and symbols," but the oldest literary attestion is the associated Vedic minor deity Rudra, who may also have non-Aryan origins. The figure of Shiva as he is known today is an amalgamation of various older deities into a single figure, due to the process of Sanskritization and the emergence of the Hindu synthesis in post-Vedic times. How the persona of Shiva converged as a composite deity is not well documented, a challenge to trace and has attracted much speculation. According to Vijay Nath: Vishnu and Siva [...] began to absorb countless local cults and deities within their folds. The latter were either taken to represent the multiple facets of the same god or else were supposed to denote different forms and appellations by which the god came to be known and worshipped. [...] Siva became identified with countless local cults by the sheer suffixing of Isa or Isvara to the name of the local deity, e.g., Bhutesvara, Hatakesvara, Chandesvara." An example of assimilation took place in Maharashtra, where a regional deity named Khandoba is a patron deity of farming and herding castes. The foremost center of worship of Khandoba in Maharashtra is in Jejuri. Khandoba has been assimilated as a form of Shiva himself, in which case he is worshipped in the form of a lingam. Khandoba's varied associations also include an identification with Surya and Karttikeya. Myths about Shiva that were "roughly contemporary with early Christianity" existed that portrayed Shiva with many differences than how he is thought of now, and these mythical portrayals of Shiva were incorporated into later versions of him. For instance, he and the other gods, from the highest gods to the least powerful gods, were thought of as somewhat human in nature, creating emotions they had limited control over and having the ability to get in touch with their inner natures through asceticism like humans. In that era, Shiva was widely viewed as both the god of lust and of asceticism. In one story, he was seduced by a prostitute sent by the other gods, who were jealous of Shiva's ascetic lifestyle he had lived for 1000 years. Prehistoric rock paintings dating to the Mesolithic from Bhimbetka rock shelters have been interpreted by some authors as depictions of Shiva.[b] However, Howard Morphy states that these prehistoric rock paintings of India, when seen in their context, are likely those of hunting party with animals, and that the figures in a group dance can be interpreted in many different ways. Of several Indus valley seals that show animals, one seal that has attracted attention shows a large central figure, either horned or wearing a horned headdress and possibly ithyphallic,[note 2] seated in a posture reminiscent of the Lotus position, surrounded by animals. This figure was named by early excavators of Mohenjo-daro as Pashupati (Lord of Animals, Sanskrit paśupati), an epithet of the later Hindu deities Shiva and Rudra. Sir John Marshall and others suggested that this figure is a prototype of Shiva, with three faces, seated in a "yoga posture" with the knees out and feet joined. Semi-circular shapes on the head were interpreted as two horns. Scholars such as Gavin Flood, John Keay and Doris Meth Srinivasan have expressed doubts about this suggestion. Gavin Flood states that it is not clear from the seal that the figure has three faces, is seated in a yoga posture, or even that the shape is intended to represent a human figure. He characterises these views as "speculative", but adds that it is nevertheless possible that there are echoes of Shaiva iconographic themes, such as half-moon shapes resembling the horns of a bull. John Keay writes that "he may indeed be an early manifestation of Lord Shiva as Pashu-pati", but a couple of his specialties of this figure does not match with Rudra. Writing in 1997, Srinivasan interprets what John Marshall interpreted as facial as not human but more bovine, possibly a divine buffalo-man. The interpretation of the seal continues to be disputed. McEvilley, for example, states that it is not possible to "account for this posture outside the yogic account". Asko Parpola states that other archaeological finds such as the early Elamite seals dated to 3000–2750 BCE show similar figures and these have been interpreted as "seated bull" and not a yogi, and the bovine interpretation is likely more accurate. Gregory L. Possehl in 2002, associated it with the water buffalo, and concluded that while it would be appropriate to recognise the figure as a deity, and its posture as one of ritual discipline, regarding it as a proto-Shiva would "go too far". The Vedic beliefs and practices of the pre-classical era were closely related to the hypothesised Proto-Indo-European religion, and the pre-Islamic Indo-Iranian religion. The similarities between the iconography and theologies of Shiva with Greek and European deities have led to proposals for an Indo-European link for Shiva, or lateral exchanges with ancient central Asian cultures. His contrasting aspects such as being terrifying or blissful depending on the situation, are similar to those of the Greek god Dionysus, as are their iconic associations with bull, snakes, anger, bravery, dancing and carefree life. The ancient Greek texts of the time of Alexander the Great call Shiva "Indian Dionysus", or alternatively call Dionysus "god of the Orient". Similarly, the use of phallic symbol[note 2] as an icon for Shiva is also found for Irish, Nordic, Greek (Dionysus) and Roman deities, as was the idea of this aniconic column linking heaven and earth among early Indo-Aryans, states Roger Woodward. Others contest such proposals, and suggest Shiva to have emerged from indigenous non-Aryan tribal origins. Shiva as we know him today shares many features with the Vedic god Rudra, and both Shiva and Rudra are viewed as the same personality in Hindu scriptures. The two names are used synonymously. Rudra, a Rigvedic deity with fearsome powers, was the god of the roaring storm. He is usually portrayed in accordance with the element he represents as a fierce, destructive deity. In RV 2.33, he is described as the "Father of the Rudras", a group of storm gods. Flood notes that Rudra is an ambiguous god, peripheral in the Vedic pantheon, possibly indicating non-Vedic origins. Nevertheless, both Rudra and Shiva are akin to Wodan, the Germanic God of rage ("wütte") and the wild hunt.[page needed][page needed] According to Sadasivan, during the development of the Hindu synthesis attributes of the Buddha were transferred by Brahmins to Shiva, who was also linked with Rudra. The Rigveda has 3 out of 1,028 hymns dedicated to Rudra, and he finds occasional mention in other hymns of the same text. Hymn 10.92 of the Rigveda states that deity Rudra has two natures, one wild and cruel (Rudra), another that is kind and tranquil (Shiva). The term Shiva also appears simply as an epithet, that means "kind, auspicious", one of the adjectives used to describe many different Vedic deities. While fierce ruthless natural phenomenon and storm-related Rudra is feared in the hymns of the Rigveda, the beneficial rains he brings are welcomed as Shiva aspect of him. This healing, nurturing, life-enabling aspect emerges in the Vedas as Rudra-Shiva, and in post-Vedic literature ultimately as Shiva who combines the destructive and constructive powers, the terrific and the gentle, as the ultimate recycler and rejuvenator of all existence. The Vedic texts do not mention bull or any animal as the transport vehicle (vahana) of Rudra or other deities. However, post-Vedic texts such as the Mahabharata and the Puranas state the Nandi bull, the Indian zebu, in particular, as the vehicle of Rudra and of Shiva, thereby unmistakably linking them as same. Rudra and Agni have a close relationship.[note 3] The identification between Agni and Rudra in the Vedic literature was an important factor in the process of Rudra's gradual transformation into Rudra-Shiva.[note 4] The identification of Agni with Rudra is explicitly noted in the Nirukta, an important early text on etymology, which says, "Agni is also called Rudra." The interconnections between the two deities are complex, and according to Stella Kramrisch: The fire myth of Rudra-Śiva plays on the whole gamut of fire, valuing all its potentialities and phases, from conflagration to illumination. In the Śatarudrīya, some epithets of Rudra, such as Sasipañjara ("Of golden red hue as of flame") and Tivaṣīmati ("Flaming bright"), suggest a fusing of the two deities.[note 5] Agni is said to be a bull, and Shiva possesses a bull as his vehicle, Nandi. The horns of Agni, who is sometimes characterised as a bull, are mentioned. In medieval sculpture, both Agni and the form of Shiva known as Bhairava have flaming hair as a special feature. According to Wendy Doniger, the Saivite fertility myths and some of the phallic characteristics of Shiva are inherited from Indra. Doniger gives several reasons for her hypothesis. Both are associated with mountains, rivers, male fertility, fierceness, fearlessness, warfare, the transgression of established mores, the Aum sound, the Supreme Self. In the Rig Veda the term śiva is used to refer to Indra. (2.20.3,[note 6] 6.45.17, and 8.93.3.) Indra, like Shiva, is likened to a bull. In the Rig Veda, Rudra is the father of the Maruts, but he is never associated with their warlike exploits as is Indra. Indra himself may have been adopted by the Vedic Aryans from the Bactria–Margiana Culture. According to Anthony, Many of the qualities of Indo-Iranian god of might/victory, Verethraghna, were transferred to the adopted god Indra, who became the central deity of the developing Old Indic culture. Indra was the subject of 250 hymns, a quarter of the Rig Veda. He was associated more than any other deity with Soma, a stimulant drug (perhaps derived from Ephedra) probably borrowed from the BMAC religion. His rise to prominence was a peculiar trait of the Old Indic speakers. The texts and artwork of Jainism show Indra as a dancer, although not identical generally resembling the dancing Shiva artwork found in Hinduism, particularly in their respective mudras. For example, in the Jain caves at Ellora, extensive carvings show dancing Indra next to the images of Tirthankaras in a manner similar to Shiva Nataraja. The similarities in the dance iconography suggests that there may be a link between ancient Indra and Shiva. A few texts such as Atharvashiras Upanishad mention Rudra, and assert all gods are Rudra, everyone and everything is Rudra, and Rudra is the principle found in all things, their highest goal, the innermost essence of all reality that is visible or invisible. The Kaivalya Upanishad similarly, states Paul Deussen – a German Indologist and professor of philosophy, describes the self-realized man as who "feels himself only as the one divine essence that lives in all", who feels identity of his and everyone's consciousness with Shiva (highest Atman), who has found this highest Atman within, in the depths of his heart. Rudra's evolution from a minor Vedic deity to a supreme being is first evidenced in the Shvetashvatara Upanishad (400–200 BCE), according to Gavin Flood, presenting the earliest seeds of theistic devotion to Rudra-Shiva. Here Rudra-Shiva is identified as the creator of the cosmos and liberator of Selfs from the birth-rebirth cycle. The Svetasvatara Upanishad set the tone for early Shaivite thought, especially in chapter 3 verse 2 where Shiva is equated with Brahman: "Rudra is truly one; for the knowers of Brahman do not admit the existence of a second". The period of 200 BC to 100 AD also marks the beginning of the Shaiva tradition focused on the worship of Shiva as evidenced in other literature of this period. Other scholars such as Robert Hume and Doris Srinivasan state that the Shvetashvatara Upanishad presents pluralism, pantheism, or henotheism, rather than being a text just on Shiva theism. Self-realization and Shaiva Upanishads He who sees himself in all beings, And all beings in him, attains the highest Brahman, not by any other means. Shaiva devotees and ascetics are mentioned in Patanjali's Mahābhāṣya (2nd-century BCE) and in the Mahabharata. The earliest iconic artworks of Shiva may be from Gandhara and northwest parts of ancient India. There is some uncertainty as the artwork that has survived is damaged and they show some overlap with meditative Buddha-related artwork, but the presence of Shiva's trident and phallic symbolism[note 2] in this art suggests it was likely Shiva. Numismatics research suggests that numerous coins of the ancient Kushan Empire (30–375 CE) that have survived, were images of a god who is probably Shiva. The Shiva in Kushan coins is referred to as Oesho of unclear etymology and origins, but the simultaneous presence of Indra and Shiva in the Kushan era artwork suggest that they were revered deities by the start of the Kushan Empire. The Shaiva Upanishads are a group of 14 minor Upanishads of Hinduism variously dated from the last centuries of the 1st millennium BCE through the 17th century. These extol Shiva as the metaphysical unchanging reality Brahman and the Atman (Self), and include sections about rites and symbolisms related to Shiva. The Shaiva Puranas, particularly the Shiva Purana and the Linga Purana, present the various aspects of Shiva, mythologies, cosmology and pilgrimage (Tirtha) associated with him. The Shiva-related Tantra literature, composed between the 8th and 11th centuries, are regarded in devotional dualistic Shaivism as Sruti. Dualistic Shaiva Agamas which consider Self within each living being and Shiva as two separate realities (dualism, dvaita), are the foundational texts for Shaiva Siddhanta. Other Shaiva Agamas teach that these are one reality (monism, advaita), and that Shiva is the Self, the perfection and truth within each living being. In Shiva related sub-traditions, there are ten dualistic Agama texts, eighteen qualified monism-cum-dualism Agama texts and sixty-four monism Agama texts. Shiva-related literature developed extensively across India in the 1st millennium CE and through the 13th century, particularly in Kashmir and Tamil Shaiva traditions. Shaivism gained immense popularity in Tamilakam as early as the 7th century CE, with poets such as Appar and Sambandar composing rich poetry that is replete with present features associated with the deity, such as his tandava dance, the mulavam (dumru), the aspect of holding fire, and restraining the proud flow of the Ganga upon his braid. The monist Shiva literature posit absolute oneness, that is Shiva is within every man and woman, Shiva is within every living being, Shiva is present everywhere in the world including all non-living being, and there is no spiritual difference between life, matter, man and Shiva. The various dualistic and monist Shiva-related ideas were welcomed in medieval southeast Asia, inspiring numerous Shiva-related temples, artwork and texts in Indonesia, Myanmar, Cambodia, Laos, Vietnam, Thailand and Malaysia, with syncretic integration of local pre-existing theologies. Position within Hinduism Shaivism is one of the four major sects of Hinduism, the others being Vaishnavism, Shaktism and the Smarta Tradition. Followers of Shaivism, called "Shaivas", revere Shiva as the Supreme Being. Shaivas believe that Shiva is All and in all, the creator, preserver, destroyer, revealer and concealer of all that is. He is not only the creator in Shaivism, but he is also the creation that results from him, he is everything and everywhere. Shiva is the primal Self, the pure consciousness and Absolute Reality in the Shaiva traditions. Shiva is also part of 'Om' (ॐ) as a 'U' (उ). The Shaivism theology is broadly grouped into two: the popular theology influenced by Shiva-Rudra in the Vedas, Epics and the Puranas; and the esoteric theology influenced by the Shiva and Shakti-related Tantra texts. The Vedic-Brahmanic Shiva theology includes both monist (Advaita) and devotional traditions (Dvaita), such as Tamil Shaiva Siddhanta and Lingayatism. Shiva temples feature items such as linga, Shiva-Parvati iconography, bull Nandi within the premises, and relief artwork showing aspects of Shiva. The Tantric Shiva ("शिव") tradition ignored the mythologies and Puranas related to Shiva, and depending on the sub-school developed a variety of practices. For example, historical records suggest the tantric Kapalikas (literally, the 'skull-men') co-existed with and shared many Vajrayana Buddhist rituals, engaged in esoteric practices that revered Shiva and Shakti wearing skulls, begged with empty skulls, and sometimes used meat as a part of ritual. The esoteric tradition within Kashmir Shaivism has featured the Krama and Trika sub-traditions. The Krama sub-tradition focussed on esoteric rituals around Shiva-Kali pair. The Trika sub-tradition developed a theology of triads involving Shiva, combined it with an ascetic lifestyle focusing on personal Shiva in the pursuit of monistic self-liberation. The Vaishnava (Vishnu-oriented) literature acknowledges and discusses Shiva. Like Shaiva literature that presents Shiva as supreme, the Vaishnava literature presents Vishnu as supreme. However, both traditions are pluralistic and revere both Shiva and Vishnu (along with Devi); their texts do not show exclusivism. Vaishnava texts such as the Bhagavata Purana while praising Krishna as the Ultimate Reality, also present Shiva and Shakti as a personalised forms equivalent to the same Ultimate Reality. The texts of Shaivism tradition similarly praise Vishnu. The Skanda Purana, for example, states: Vishnu is no one but Shiva, and he who is called Shiva is but identical with Vishnu. — Skanda Purana, 1.8.20–21 Both traditions include legends about who is superior, about Shiva paying homage to Vishnu, and Vishnu paying homage to Shiva. However, in texts and artwork of either tradition, the mutual salutes are symbolism for complementarity. The Mahabharata declares the unchanging Ultimate Reality (Brahman) to be identical to Shiva and to Vishnu, that Vishnu is the highest manifestation of Shiva, and Shiva is the highest manifestation of Vishnu. The goddess-oriented Shakti tradition of Hinduism is based on the premise that the Supreme Principle and the Ultimate Reality called Brahman is female (Devi), but it treats the male as her equal and complementary partner. This partner is Shiva. The earliest evidence of the tradition of reverence for the feminine with Rudra-Shiva context, is found in the Hindu scripture Rigveda, in a hymn called the Devi Sukta. The Devi Upanishad in its explanation of the theology of Shaktism, mentions and praises Shiva such as in its verse 19. Shiva, along with Vishnu, is a revered god in the Devi Mahatmya, a text of Shaktism considered by the tradition to be as important as the Bhagavad Gita. The Ardhanarisvara concept co-mingles god Shiva and goddess Shakti by presenting an icon that is half-man and half woman, a representation and theme of union found in many Hindu texts and temples. In the Smarta tradition of Hinduism, Shiva is a part of its Panchayatana puja. This practice consists of the use of icons or anicons of five deities considered equivalent, set in a quincunx pattern. Shiva is one of the five deities, others being Vishnu, Devi (such as Parvati), Surya and Ganesha or Skanda or any personal god of devotee's preference (Ishta Devata). Philosophically, the Smarta tradition emphasises that all idols (murti) are icons to help focus on and visualise aspects of Brahman, rather than distinct beings. The ultimate goal in this practice is to transition past the use of icons, recognise the Absolute symbolised by the icons, on the path to realising the nondual identity of one's Atman (Self) and the Brahman. Many Panchayatana mandalas and temples have been uncovered that are from the Gupta Empire period, and one Panchayatana set from the village of Nand (about 24 kilometres from Ajmer) has been dated to belong to the Kushan Empire era (pre-300 CE). The Kushan period set includes Shiva, Vishnu, Surya, Brahma and one deity whose identity is unclear. Shiva is considered the Great Yogi who is totally absorbed in himself – the transcendental reality. He is the Lord of Yogis, and the teacher of Yoga to sages. As Shiva Dakshinamurthi, states Stella Kramrisch, he is the supreme guru who "teaches in silence the oneness of one's innermost self (atman) with the ultimate reality (Brahman)." Shiva is also an archetype for samhara (Sanskrit: संहार) or dissolution which includes transcendence of human misery by the dissolution of maya, which is why Shiva is associated with Yoga. The theory and practice of Yoga, in different styles, has been a part of all major traditions of Hinduism, and Shiva has been the patron or spokesperson in numerous Hindu Yoga texts. These contain the philosophy and techniques for Yoga. These ideas are estimated to be from or after the late centuries of the 1st millennium CE, and have survived as Yoga texts such as the Isvara Gita (literally, 'Shiva's song'), which Andrew Nicholson – a professor of Hinduism and Indian Intellectual History – states have had "a profound and lasting influence on the development of Hinduism". Other famed Shiva-related texts influenced Hatha Yoga, integrated monistic (Advaita Vedanta) ideas with Yoga philosophy and inspired the theoretical development of Indian classical dance. These include the Shiva Sutras, the Shiva Samhita, and those by the scholars of Kashmir Shaivism such as the 10th-century scholar Abhinavagupta. Abhinavagupta writes in his notes on the relevance of ideas related to Shiva and Yoga, by stating that "people, occupied as they are with their own affairs, normally do nothing for others", and Shiva and Yoga spirituality helps one look beyond, understand interconnectedness, and thus benefit both the individual and the world towards a more blissful state of existence. The Trimurti is a concept in Hinduism in which the cosmic functions of creation, maintenance, and destruction are personified by the forms of Brahma the creator, Vishnu the maintainer or preserver and Shiva the destroyer or transformer. These three deities have been called "the Hindu triad" or the "Great Triple deity". However, the ancient and medieval texts of Hinduism feature many triads of gods and goddesses, some of which do not include Shiva. Attributes Shiva is traditionally represented with distinctive attributes and symbols: Forms and depictions Shiva is often depicted as embodying attributes of ambiguity and paradox. His depictions are marked by the opposing themes including fierceness and innocence. This duality can be seen in the diverse epithets attributed to him and the rich tapestry of narratives that delineate his persona within Hindu mythology. In Yajurveda, two contrary sets of attributes for both malignant or terrifying (Sanskrit: rudra) and benign or auspicious (Sanskrit: śiva) forms can be found, leading Chakravarti to conclude that "all the basic elements which created the complex Rudra-Śiva sect of later ages are to be found here". In the Mahabharata, Shiva is depicted as "the standard of invincibility, might, and terror", as well as a figure of honour, delight, and brilliance. The duality of Shiva's fearful and auspicious attributes appears in contrasted names. The name Rudra reflects Shiva's fearsome aspects. According to traditional etymologies, the Sanskrit name Rudra is derived from the root rud-, which means "to cry, howl". Stella Kramrisch notes a different etymology connected with the adjectival form raudra, which means "wild, of rudra nature", and translates the name Rudra as "the wild one" or "the fierce god". R. K. Sharma follows this alternate etymology and translates the name as "terrible". Hara is an important name that occurs three times in the Anushasanaparvan version of the Shiva sahasranama, where it is translated in different ways each time it occurs, following a commentorial tradition of not repeating an interpretation. Sharma translates the three as "one who captivates", "one who consolidates", and "one who destroys". Kramrisch translates it as "the ravisher". Another of Shiva's fearsome forms is as Kāla "time" and Mahākāla "great time", which ultimately destroys all things. The name Kāla appears in the Shiva Sahasranama, where it is translated by Ram Karan Sharma as "(the Supreme Lord of) Time". Bhairava "terrible" or "frightful" is a fierce form associated with annihilation. In contrast, the name Śaṇkara, "beneficent" or "conferring happiness" reflects his benign form. The name Śambhu (Sanskrit: शम्भु swam-on its own; bhu-burn/shine) "self-shining/ shining on its own", also reflects this benign aspect. Shiva is depicted as both an ascetic yogi and as a householder (grihasta), roles which have been traditionally mutually exclusive in Hindu society. When depicted as a yogi, he may be shown sitting and meditating. His epithet Mahāyogi ("the great Yogi: Mahā = "great", Yogi = "one who practices Yoga") refers to his association with yoga. While Vedic religion was conceived mainly in terms of sacrifice, it was during the Epic period that the concepts of tapas, yoga, and asceticism became more important, and the depiction of Shiva as an ascetic sitting in philosophical isolation reflects these later concepts. As a family man and householder, he has a wife, Parvati, and two sons, Ganesha and Kartikeya. His epithet Umāpati ("The husband of Umā") refers to this idea, and Sharma notes that two other variants of this name that mean the same thing, Umākānta and Umādhava, also appear in the sahasranama. Umā in epic literature is known by many names, including the benign Pārvatī. She is identified with Devi, the Divine Mother; Shakti (divine energy) as well as goddesses like Tripura Sundari, Durga, Kali, Kamakshi and Minakshi. The consorts of Shiva are the source of his creative energy. They represent the dynamic extension of Shiva onto this universe. His son Ganesha is worshipped throughout India and Nepal as the Remover of Obstacles, Lord of Beginnings and Lord of Obstacles. Kartikeya is worshipped in Southern India (especially in Tamil Nadu, Kerala and Karnataka) by the names Subrahmanya, Subrahmanyan, Shanmughan, Swaminathan and Murugan, and in Northern India by the names Skanda, Kumara, or Karttikeya. Some regional deities are also identified as Shiva's children. As one story goes, Shiva is enticed by the beauty and charm of Mohini, Vishnu's female avatar, and procreates with her. As a result of this union, Shasta – identified with regional deities Ayyappan and Aiyanar – is born. In outskirts of Ernakulam in Kerala, a deity named Vishnumaya is stated to be offspring of Shiva and invoked in local exorcism rites, but this deity is not traceable in Hindu pantheon and is possibly a local tradition with "vaguely Chinese" style rituals, states Saletore. In some traditions, Shiva has daughters like the serpent-goddess Manasa and Ashokasundari. According to Doniger, two regional stories depict demons Andhaka and Jalandhara as the children of Shiva who war with him, and are later destroyed by Shiva. The depiction of Shiva as Nataraja (Sanskrit नटराज; Naṭarāja) is a form (mūrti) of Shiva as "Lord of Dance". The names Nartaka ("dancer") and Nityanarta ("eternal dancer") appear in the Shiva Sahasranama. His association with dance and also with music is prominent in the Puranic period. In addition to the specific iconographic form known as Nataraja, various other types of dancing forms (Sanskrit: nṛtyamūrti) are found in all parts of India, with many well-defined varieties in Tamil Nadu in particular. The two most common forms of the dance are the Tandava, which later came to denote the powerful and masculine dance as Kala-Mahakala associated with the destruction of the world. When it requires the world or universe to be destroyed, Shiva does it by the Tandava, and Lasya, which is graceful and delicate and expresses emotions on a gentle level and is considered the feminine dance attributed to the goddess Parvati. Lasya is regarded as the female counterpart of Tandava. The Tandava-Lasya dances are associated with the destruction-creation of the world. Dakshinamurti (Sanskrit दक्षिणामूर्ति; Dakṣiṇāmūrti, "[facing] south form") represents Shiva in his aspect as a teacher of yoga, music, and wisdom and giving exposition on the shastras. Dakshinamurti is depicted as a figure seated upon a deer-throne surrounded by sages receiving instruction. Dakshinamurti's depiction in Indian art is mostly restricted to Tamil Nadu. Bhikshatana (Sanskrit भिक्षाटन; Bhikṣāṭana, "wandering about for alms, mendicancy") depicts Shiva as a divine medicant. He is depicted as a nude four-armed man adorned with ornaments who holds a begging bowl in his hand and is followed by demonic attendants. He is associated with his penance for committing brahmicide as Bhirava and with his encounters with the sages and their wives in the Deodar forest. Tripurantaka (Sanskrit त्रिपुरांतक; Tripurāntaka, "ender of Tripura") is associated with his destruction of the three cities (Tripura) of the Asuras. He is depicted with four arms, the upper pair holding an axe and a deer, and the lower pair wielding a bow and arrow. Ardhanarishvara (Sanskrit: अर्धनारीश्वर; Ardhanārīśvara, "the lord who is half woman") is conjunct form of Shiva with Parvati. Adhanarishvara is depicted with one half of the body as male and the other half as female. Ardhanarishvara represents the synthesis of masculine and feminine energies of the universe (Purusha and Prakriti) and illustrates how Shakti, the female principle of God, is inseparable from (or the same as, according to some interpretations) Shiva, the male principle of God, and vice versa. Kalyanasundara-murti (Sanskrit कल्याणसुन्दर-मूर्ति, literally "icon of beautiful marriage") is the depiction of Shiva's marriage to Parvati. The divine couple are often depicted performing the panigrahana (Sanskrit "accepting the hand") ritual from traditional Hindu wedding ceremonies. The most basic form of this murti consists of only Shiva and Parvati together, but in more elaborate forms they are accompanied by other persons, sometimes including Parvati's parents, as well as deities (often with Vishnu and Lakshmi standing as Parvati's parents, Brahma as the officiating priest, and various other deities as attendants or guests). Somaskanda is the depiction of Shiva, Parvati, and their son Skanda (Kartikeya), popular during the Pallava Dynasty in southern India. Astamurti (Sanskrit: अष्टमूर्ति) is an iconographic depiction of Shiva as composed of eight attributes: Rudra, Śarva, Paśupati, Ugra, Aśani, Bhava, Mahādeva, and Īśāna—some of which overlap with Pañcānana, described below. Pañcānana (Sanskrit: पञ्चानन), also called the pañcabrahma, is a form of Shiva depicting him as having five faces which correspond to his five divine activities (pañcakṛtya): creation (sṛṣṭi), preservation (sthithi), destruction (saṃhāra), concealing grace (tirobhāva), and revealing grace (anugraha). Five is a sacred number for Shiva. One of his most important mantras has five syllables (namaḥ śivāya). Shiva's body is said to consist of five mantras, called the pañcabrahman. As forms of God, each of these have their own names and distinct iconography: These are represented as the five faces of Shiva and are associated in various texts with the five elements, the five senses, the five organs of perception, and the five organs of action. Doctrinal differences and, possibly, errors in transmission, have resulted in some differences between texts in details of how these five forms are linked with various attributes. The overall meaning of these associations is summarised by Stella Kramrisch, Through these transcendent categories, Śiva, the ultimate reality, becomes the efficient and material cause of all that exists. According to the Pañcabrahma Upanishad: One should know all things of the phenomenal world as of a fivefold character, for the reason that the eternal verity of Śiva is of the character of the fivefold Brahman. (Pañcabrahma Upanishad 31) In the hymn of Manikkavacakar's Thiruvasagam, he testifies that Nataraja Temple, Chidambaram had, by the pre-Chola period, an abstract or 'cosmic' symbolism linked to five elements (Pancha Bhoota) including ether. Nataraja is a significant visual interpretation of Brahman and a dance posture of Shiva. Sharada Srinivasan notes that, Nataraja is described as Satcitananda or "Being, Consciousness and Bliss" in the Shaiva Siddhanta text Kunchitangrim Bhaje, resembling the Advaita doctrine, or "abstract monism," of Adi Shankara, "which holds the individual Self (Jīvātman) and supream Self (Paramātmā) to be one," while "an earlier hymn to Nataraja by Manikkavachakar identifies him with the unitary supreme consciousness, by using Tamil word Or Unarve, rather than Sanskrit Chit." This may point to an "osmosis" of ideas in medieval India, states Srinivasan. The Linga Purana states, "Shiva is signless, without color, taste, smell, that is beyond word or touch, without quality, motionless and changeless". The source of the universe is the signless, and all of the universe is the manifested Linga, a union of unchanging Principles and the ever changing nature. The Linga Purana and the Shiva Gita texts builds on this foundation. Linga, states Alain Daniélou, means sign. It is an important concept in Hindu texts, wherein Linga is a manifested sign and nature of someone or something. It accompanies the concept of Brahman, which as invisible signless and existent Principle, is formless or linga-less. The Shvetashvatara Upanishad states one of the three significations, the primary one, of Lingam as "the imperishable Purusha", the absolute reality, where says the linga as "sign", a mark that provides the existence of Brahman, thus the original meaning as "sign". Furthermore, it says "Shiva, the Supreme Lord, has no liūga", liuga (Sanskrit: लिऊग IAST: liūga) meaning Shiva is transcendent, beyond any characteristic and, specifically the sign of gender. Apart from anthropomorphic images of Shiva, he is also represented in aniconic form of a lingam. These are depicted in various designs. One common form is the shape of a vertical rounded column in the centre of a lipped, disk-shaped object, the yoni, symbolism for the goddess Shakti. In Shiva temples, the linga is typically present in its sanctum sanctorum and is the focus of votary offerings such as milk, water, flower petals, fruit, fresh leaves, and rice. According to Monier Williams and Yudit Greenberg, linga literally means 'mark, sign or emblem', and also refers to a "mark or sign from which the existence of something else can be reliably inferred". It implies the regenerative divine energy innate in nature, symbolised by Shiva. Some scholars, such as Wendy Doniger, view linga as merely a phallic symbol, although this interpretation is criticised by others, including Swami Vivekananda, Sivananda Saraswati, Stella Kramrisch, Swami Agehananda Bharati, S. N. Balagangadhara, and others. According to Moriz Winternitz, the linga in the Shiva tradition is "only a symbol of the productive and creative principle of nature as embodied in Shiva", and it has no historical trace in any obscene phallic cult. According to Sivananda Saraswati, westerners who are curiously passionate and have impure understanding or intelligence, incorrectly assume Siva Linga as a phallus or sex organ. Later on, Sivananda Saraswati mentions that, this is not only a serious mistake, but also a grave blunder. The worship of the lingam originated from the famous hymn in the Atharva-Veda Samhitâ sung in praise of the Yupa-Stambha, the sacrificial post. In that hymn, a description is found of the beginningless and endless Stambha or Skambha, and it is shown that the said Skambha is put in place of the eternal Brahman. Just as the Yajna (sacrificial) fire, its smoke, ashes, and flames, the Soma plant, and the ox that used to carry on its back the wood for the Vedic sacrifice gave place to the conceptions of the brightness of Shiva's body, his tawny matted hair, his blue throat, and the riding on the bull of the Shiva, the Yupa-Skambha gave place in time to the Shiva-Linga. In the text Linga Purana, the same hymn is expanded in the shape of stories, meant to establish the glory of the great Stambha and the superiority of Shiva as Mahadeva. The oldest known archaeological linga as an icon of Shiva is the Gudimallam lingam from 3rd-century BCE. In Shaivism pilgrimage tradition, twelve major temples of Shiva are called Jyotirlinga, which means "linga of light", and these are located across India. Puranic scriptures contain occasional references to "ansh" – literally 'portion, or avatars of Shiva', but the idea of Shiva avatars is not universally accepted in Shaivism. The Linga Purana mentions twenty-eight forms of Shiva which are sometimes seen as avatars, however such mention is unusual and the avatars of Shiva is relatively rare in Shaivism compared to the well emphasised concept of Vishnu avatars in Vaishnavism. Some Vaishnava literature reverentially link Shiva to characters in its Puranas. For example, in the Hanuman Chalisa, Hanuman is identified as the eleventh avatar of Shiva. The Bhagavata Purana and the Vishnu Purana claim sage Durvasa to be a portion of Shiva. Some medieval era writers have called the Advaita Vedanta philosopher Adi Shankara an incarnation of Shiva. Temple Festivals There is a Shivaratri in every lunar month on its 13th night/14th day, but once a year in late winter (February/March) and before the arrival of spring, marks Maha Shivaratri which means "the Great Night of Shiva". Maha Shivaratri is a major Hindu festival, but one that is solemn and theologically marks a remembrance of "overcoming darkness and ignorance" in life and the world, and meditation about the polarities of existence, of Shiva and a devotion to humankind. It is observed by reciting Shiva-related poems, chanting prayers, remembering Shiva, fasting, doing Yoga and meditating on ethics and virtues such as self-restraint, honesty, noninjury to others, forgiveness, introspection, self-repentance and the discovery of Shiva. The ardent devotees keep awake all night. Others visit one of the Shiva temples or go on pilgrimage to Jyotirlingam shrines. Those who visit temples, offer milk, fruits, flowers, fresh leaves and sweets to the lingam. Some communities organise special dance events, to mark Shiva as the lord of dance, with individual and group performances. According to Jones and Ryan, Maha Sivaratri is an ancient Hindu festival which probably originated around the 5th-century. Another major festival involving Shiva worship is Kartik Purnima, commemorating Shiva's victory over the three demons known as Tripurasura. Across India, various Shiva temples are illuminated throughout the night. Shiva icons are carried in procession in some places. Thiruvathira is a festival observed in Kerala dedicated to Shiva. It is believed that on this day, Parvati met Shiva after her long penance and Shiva took her as his wife. On this day Hindu women performs the Thiruvathirakali accompanied by Thiruvathira paattu (folk songs about Parvati and her longing and penance for Shiva's affection). Regional festivals dedicated to Shiva include the Chithirai festival in Madurai around April/May, one of the largest festivals in South India, celebrating the wedding of Minakshi (Parvati) and Shiva. The festival is one where both the Vaishnava and Shaiva communities join the celebrations, because Vishnu gives away his sister Minakshi in marriage to Shiva. Some Shaktism-related festivals revere Shiva along with the goddess considered primary and Supreme. These include festivals dedicated to Annapurna such as Annakuta and those related to Durga. In Himalayan regions such as Nepal, as well as in northern, central and western India, the festival of Teej is celebrated by girls and women in the monsoon season, in honour of goddess Parvati, with group singing, dancing and by offering prayers in Parvati-Shiva temples. The ascetic, Vedic and Tantric sub-traditions related to Shiva, such as those that became ascetic warriors during the Islamic rule period of India, celebrate the Kumbha Mela festival. This festival cycles every 12 years, in four pilgrimage sites within India, with the event moving to the next site after a gap of three years. The biggest is in Prayaga (renamed Allahabad during the Mughal rule era), where millions of Hindus of different traditions gather at the confluence of rivers Ganges and Yamuna. In the Hindu tradition, the Shiva-linked ascetic warriors (Nagas) get the honour of starting the event by entering the Sangam first for bathing and prayers. In Pakistan, major Shivaratri celebration occurs at the Umarkot Shiv Mandir in the Umarkot. The three-day Shivarathri celebration at the temple is attended by around 250,000 people. Beyond the Indian subcontinent and Hinduism In Indonesian Shaivism the popular name for Shiva has been Batara Guru, which is derived from Sanskrit Bhattāraka which means "noble lord". He is conceptualised as a kind spiritual teacher, the first of all Gurus in Indonesian Hindu texts, mirroring the Dakshinamurti aspect of Shiva in the Indian subcontinent. However, the Batara Guru has more aspects than the Indian Shiva, as the Indonesian Hindus blended their spirits and heroes with him. Batara Guru's wife in Southeast Asia is the same Hindu deity Durga, who has been popular since ancient times, and she too has a complex character with benevolent and fierce manifestations, each visualised with different names such as Uma, Sri, Kali and others. In contrast to Hindu religious texts, whether Vedas or Puranas, in Javanese puppetry (wayang) books, Batara Guru is the king of the gods who regulates and creates the world system. In the classic book that is used as a reference for the puppeteers, it is said that Sanghyang Manikmaya or Batara Guru was created from a sparkling light by Sang Hyang Tunggal, along with the blackish light which is the origin of Ismaya. Shiva has been called Sadāśiva, Paramasiva, Mahādeva in benevolent forms, and Kāla, Bhairava, Mahākāla in his fierce forms. The Indonesian Hindu texts present the same philosophical diversity of Shaivite traditions found in the Indian subcontinent. However, among the texts that have survived into the contemporary era, the more common are of those of Shaiva Siddhanta (locally also called Siwa Siddhanta, Sridanta). During the pre-Islamic period on the island of Java, Shaivism and Buddhism were considered very close and allied religions, though not identical religions. The medieval-era Indonesian literature equates Buddha with Siwa (Shiva) and Janardana (Vishnu). This tradition continues in predominantly Hindu Bali Indonesia in the modern era, where Buddha is considered the younger brother of Shiva. The worship of Shiva became popular in Central Asia through the influence of the Hephthalite Empire and Kushan Empire. Shaivism was also popular in Sogdia and the Kingdom of Yutian as found from the wall painting from Penjikent on the river Zervashan. In this depiction, Shiva is portrayed with a sacred halo and a sacred thread (Yajnopavita). He is clad in tiger skin while his attendants are wearing Sogdian dress. A panel from Dandan Oilik shows Shiva in His Trimurti form with Shakti kneeling on her right thigh. Another site in the Taklamakan Desert depicts him with four legs, seated cross-legged on a cushioned seat supported by two bulls. It is also noted that the Zoroastrian wind god Vayu-Vata took on the iconographic appearance of Shiva. The Japuji Sahib of the Guru Granth Sahib says: "The Guru is Shiva, the Guru is Vishnu and Brahma; the Guru is Paarvati and Lakhshmi." In the same chapter, it also says: "Shiva speaks, and the Siddhas listen." In Dasam Granth, Guru Gobind Singh has mentioned two avatars of Rudra: Dattatreya Avatar and Parasnath Avatar. The Siva Sutta of the Samyutta Nikaya depicts Shiva as conversing with the Buddha and reciting a gatha. Shiva is mentioned in the Buddhist Tantras and worshipped as the fierce deity Mahākāla in Vajrayana, Chinese Esoteric, and Tibetan Buddhism. In the cosmologies of Buddhist Tantras, Shiva is depicted as passive, with Shakti being his active counterpart: Shiva as Prajña and Shakti as Upāya. In Mahayana Buddhism, Shiva is depicted as Maheshvara, a deva living in Akanishta Devaloka. In Theravada Buddhism, Shiva is depicted as Ishana, a deva residing in the 6th heaven of Kamadhatu along with Sakra Indra. In Vajrayana Buddhism, Shiva is depicted as Mahakala, a dharma protecting Bodhisattva. In most forms of Buddhism, the position of Shiva is lesser than that of Mahabrahma or Sakra Indra. In Mahayana Buddhist texts, Shiva (Maheshvara) becomes a buddha called Bhasmeshvara Buddha ("Buddha of ashes"). In China and Taiwan, Shiva, better known there as Maheśvara (Chinese: 大自在天; pinyin: Dàzìzàitiān; or Chinese: 摩醯首羅天 pinyin: Móxīshǒuluótiān) is considered one of the Twenty Devas (Chinese: 二十諸天, pinyin: Èrshí Zhūtiān) or the Twenty-Four Devas (Chinese: 二十四諸天, pinyin: Èrshísì zhūtiān) who are a group of dharmapalas that manifest to protect the Buddhist dharma. Statues of him are often enshrined in the Mahavira Halls of Chinese Buddhist temples along with the other devas. In Kizil Caves in Xinjiang, there are numerous caves that depict Shiva in the buddhist shrines through wall paintings. In addition, he is also regarded as one of thirty-three manifestations of Avalokitesvara in the Lotus Sutra. In Mahayana Buddhist cosmology, Maheśvara resides in Akaniṣṭha, highest of the Śuddhāvāsa ("Pure Abodes") wherein Anāgāmi ("Non-returners") who are already on the path to Arhathood and who will attain enlightenment are born. Daikokuten, one of the Seven Lucky Gods in Japan, is considered to be evolved from Shiva. The god enjoys an exalted position as a household deity in Japan and is worshipped as the god of wealth and fortune. The name is the Japanese equivalent of Mahākāla, the Buddhist name for Shiva. In popular culture In contemporary culture, Shiva is depicted in art, films, and books. He has been referred to as "the god of cool things" and a "bonafide rock hero". One popular film was the 1967 Kannada movie Gange Gowri. A 1990s television series of DD National titled Om Namah Shivay was also based on legends of Shiva. Amish Tripathi's 2010 book Shiva Trilogy has sold over a million copies. Devon Ke Dev...Mahadev (2011–2014), a television serial about Shiva on the Life OK channel was among the most watched shows at its peak popularity. Another popular film was the 2022 Gujarati language movie Har Har Mahadev. Shiva was also featured in the manga Record of Ragnarok (Japanese: 終末のワルキューレ, Shūmatsu no Warukyūre) by Shinya Umemura and Takumi Fukui. In the series, Shiva serves as a fighter for the Gods. Despite making an appearance in the series, the show was banned in India due to the series's controversial portrayal of Shiva. See also Notes References Sources Further reading External links |
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[SOURCE: https://en.wikipedia.org/wiki/History_of_the_Jews_in_Azerbaijan] | [TOKENS: 3011] |
Contents History of the Jews in Azerbaijan The history of the Jews in Azerbaijan dates back many centuries. Today, Jews in Azerbaijan mainly consist of three distinct groups: Mountain Jews, the most sizable and most ancient group; Ashkenazi Jews, who settled in the area during the late 19th – early 20th centuries, and during World War II; and Georgian Jews who settled mainly in Baku during the early part of the 20th century. Distribution Historically, Jews in Azerbaijan have been represented by various subgroups, mainly Mountain Jews, Ashkenazi Jews and Georgian Jews. Azerbaijan at one point was or still is home to smaller communities of Krymchaks, Kurdish Jews and Bukharian Jews, as well Gerim (converts) and non-Jewish Judaistic groups like Subbotniks. In those days, Jews used to live in and around the city of Shamakhi (mainly in the village of Mücü), but the community has been non-existent since the early 1920s. In 2002, the total number of Jewish residents in Azerbaijan was 10,000 people with about 5,500 of them being Mountain Jews. A few more thousand descend from mixed families. In 2010, the total Jewish population in Azerbaijan was 6,400. Jews mainly reside in the cities of Baku, Ganja, Sumqayit, Quba, Oğuz, Goychay and the town of Qırmızı Qəsəbə, the only town in the world where Mountain Jews constitute the majority (and the only fully Jewish town outside of Israel). History Archaeological excavations carried out in 1990 resulted in the discovery of the remains of the 7th-century Jewish settlement near Baku, and of a synagogue 25 kilometres to the southeast of Quba. The first religious meeting-house in Baku was built in 1832, and was reorganized into a synagogue in 1896; more synagogues were built in Baku and its suburbs in the late 19th century. The first choir synagogue in Baku opened in 1910. From the late 19th century, Baku became one of the centres of the Zionist movement in the Russian Empire. The first Hovevei Zion was established here in 1891, followed by the first Zionist organization in 1899. The movement remained strong in the short-lived Democratic Republic of Azerbaijan (1918–1920) marked with the establishment of the Jewish Popular University in 1919, periodicals printed in Yiddish, Hebrew, Judæo-Tat and Russian, and a number of schools, social clubs, benevolent societies and cultural organizations. After Sovietization, all Zionism-related activities including those of cultural nature that were carried out in Hebrew were banned. In the early 1920s a few hundred Mountain Jewish families from Azerbaijan and Dagestan left for Israel and settled in Tel-Aviv. The next aliyah did not take place until the 1970s, after the ban on Jewish immigration to Israel was lifted (see: Refusenik (Soviet Union)). Between 1972 and 1978 around 3,000 people left Azerbaijan for Israel. 1970 was the demographic peak for Azerbaijani Jews after World War II; according to the census, 41,288 Jews resided in Azerbaijan that year. Most of the Azerbaijani Jewish population fled amid rising antisemitism and violence against Jews during the Soviet dissolution and independence of Azerbaijan. The majority of Jewish refugees from Azerbaijan emigrated to Israel or the United States. Israeli PM Yitzhak Shamir expressed hope that the Azerbaijani Jewish refugees could be settled in occupied West Bank. However, Israeli diplomat Miron Gordon, who oversaw issuing visas, welcomed Azerbaijani Jews regardless of whether they settled in Israel or the occupied territories. Gordon stated that of all the collapsing Soviet republics, the Jews in Azerbaijan faced the greatest threat of violence, and thus their immigration was prioritized by the Israeli Consulate. In a 1992 survey of antisemitism in the former Soviet Union, which compared results of a similar survey in 1990, Azerbaijan and Uzbekistan displayed the largest surge in antisemitism. The causes were primarily attributed to Islamic nationalism and envy of Jews stereotyped as having wealth and privilege. Many Jewish émigrés from Azerbaijan settled in Tel-Aviv and Haifa. There are relatively large communities of Mountain Jewish expatriates from Azerbaijan in New York City and Toronto. A new Jewish synagogue, which became one of the biggest synagogues in Europe opened in Baku on 9 March 2003. There is also a Jewish school, operating in Azerbaijan since 2003. Currently, there are seven functioning synagogues in Azerbaijan: three in Baku, two in Quba and two in Oghuz. Some of them were constructed with government financial support. In January 2020, The Association of Mountain Jews opened a new community center in Moscow's Sokolniki Park. In 2017, an Azerbaijani laundromat money-laundering scheme was uncovered, revealing that, between 2012 and 2014, Azerbaijan created a slush fund of USD $2.9 billion used to bribe European and American politicians, journalists, lawmakers, and academics to lobby for Azerbaijani interests abroad. One of the primary agendas of the laundromat was to portray Azerbaijan as "a role model for multicultural tolerance". In particular, Israeli and Jewish organizations in USA and Europe were used to present Azerbaijan as "a trusted Muslim partner of Israel and the Jewish people". German and French lobbyists bribed by the laundromat frequently sought to portray Azerbaijan as a friend of Israel. The Podesta Group, an American lobbying firm paid $60,000 per month by the Azerbaijani government, contacted pro-Israel groups such as AIPAC and JINSA on behalf of Azerbaijan. Mountain Jews Mountain Jews are believed to have moved north making way to mass migration of Oguz Turks into the region. Their increase in number was supported by a constant flow of Jews from Iran. In the late Middle Ages Jews from Gilan founded a settlement in Oguz. Throughout the medieval epoch Mountain Jews were establishing cultural and economic ties with other Jewish communities of the Mediterranean. Agriculture and fabric trade was their main occupation until Sovietization. Some families practiced polygamy. In 1730, Huseyn Ali, the ruler of the Quba Khanate (then newly separated from the Safavid Empire), issued a decree according to which Jews could own property in the khanate. According to the 1926 Soviet census, there were 7,500 Mountain Jews in Azerbaijan (roughly 25% of the country's entire Jewish population). The exact numbers of the late Soviet period are unknown, since many were counted or preferred to be counted as Tats mostly due to the antisemitic attitude of the Soviet government. The theory of common origins of Tats and Mountain Jews (previously referred to as Judæo-Tats) has been vehemently dismissed by a number of researchers. Mountain Jews currently dominate the entire Jewish Diaspora of Azerbaijan. They speak a distinct dialect of the Tat language called Juhuri or Judæo-Tat. The majority speaks more than one language, the second and/or third one most often being Azeri or Russian. Ashkenazi Jews 1811 is the year when the first Ashkenazi Jews settled in Baku, but their mass immigration to what is now Azerbaijan did not start until the 1870s. Their immigration was relatively steady leading them to outnumber the local Mountain Jewish community by 1910. They settled mostly in the booming oil-rich city of Baku. The Caspian-Black Sea Company, one of the leading oil companies in the Russian Empire, was established in Baku by the wealthy Rothschild family of German Jewish origin. Ashkenazi Jews continued immigrating to Azerbaijan until the late 1940s, with a number of them being World War II evacuees from Russia, Ukraine and Belarus who chose to stay in their country of refuge. Ashkenazi Jews were particularly active in Azerbaijani politics. Dr. Yevsey Gindes, a Kyiv native, served as Minister of Health of the Democratic Republic of Azerbaijan (1918–1920). Along with that, 6 of the 26 Baku Commissars were Ashkenazi Jewish. In 1912 around one third of Baku's registered lawyers and physicians were Ashkenazi Jewish as well. The post-1972 aliyah largely affected this subgroup of Azerbaijani Jews, as among all they were more exposed to emigration. This resulted in the decline of their number, making Mountain Jews the largest Jewish group of Azerbaijan by the mid-1990s. Today there are about 500 Ashkenazi Jews living in the country. Similar to many immigrant communities of the Czarist and Soviet eras in Azerbaijan, Ashkenazi Jews appear to be linguistically Russified. The majority of Ashkenazi Jews speak Russian as their first language with Azeri being spoken as the second. The number of Yiddish-speakers is unknown. Rabbi Shneor Segal serves as the Chief Rabbi of the Ashkenazi community since 2010. He is a member of the Alliance of Rabbis in Islamic States and the top Chabad emissary to Baku. Other Jewish subgroups It is not clear whether local Jewish communities had established ties with Georgian Jews before the Czarist epoch, however by the 1910s the Georgian Jewish diaspora in Baku already accounted for its own educational club. Today there are a few hundreds of Georgian Jews living in Azerbaijan. In 1827 first groups of Judæo-Aramaic-speaking Kurdish Jews started settling in Azerbaijan. In 1919–1939 a synagogue for Kurdish Jews functioned in Baku. After Sovietization the attitude of the Stalinist Soviet government towards them was somewhat unfavourable, and in 1951 all Kurdish Jews were deported from the Caucasus. Krymchaks, who nowadays number only 2,500 people worldwide, consequently remained in quite low numbers in Azerbaijan throughout the 20th century. There were only 41 of them in the country in 1989. Bukharian Jews numbered 88 persons. Gerim and Subbotniks Gerim and Subbotniks were ethnic Russians from various parts of Russia who converted to Judaism primarily in the 1820s. In 1839–1841 the Czarist government expelled these communities to the newly conquered South Caucasus, mainly to what is now Azerbaijan. Upon arriving here, they founded several settlements around Jalilabad (then called Astrakhan-Bazar), of which the largest one was Privolnoye, Azerbaijan. It later became the largest Judaistic Russian settlement in Russia. By the late Soviet epoch the overall number of Gerim and Subbotniks in Azerbaijan was 5,000. There were only around 200 of them left in 1997 (when the region was visited by a research group from Saint Petersburg) with many planning to move to Russia and leaving virtually no chance for further preservation of this unique community. Life of the community In the Soviet era, Jews in Azerbaijan displayed high rates of marriage outside their community. In 1989, 48% of Ashkenazi Jews and 18% of Mountain Jews were married to non-Jews. Beginning in the 1960s, Azerbaijan's Jewish community experienced cultural revival. Jewish samizdat publications started being printed. Many cultural and Zionist organizations were reestablished in Baku and Sumqayit since 1987, and the first legal Hebrew courses in the Soviet Union were opened in Baku. Education in Jewish languages was discontinued by the Kremlin in the 1930s and the 1940s, and teaching in Yiddish and Juhuri was replaced by that in Russian. After the fall of the Soviet Union, a yeshiva opened in Baku in 1994 and an Ohr Avner Chabad Day School was established in 1999. In 1994, Hebrew was studied at one state university and offered as a course choice in two secondary schools. On 31 May 2007, a groundbreaking ceremony for the construction of the Ohr Avner Chabad Centre for Jewish Studies took place in Baku. The centre is intended to include a day school, a kindergarten, residence halls, a scientific centre, a library, etc. According to the Report on Global Anti-Semitism released by the USA Bureau of Democracy, Human Rights, and Labor on 5 January 2005, "Cases of prejudice and discrimination against Jews in the country were very limited, and in the few instances of anti-Semitic activity the Government has been quick to respond. The Government does not condone or tolerate persecution of Jews by any party". Jews do not suffer from discrimination, and the country is remarkably free from antisemitism. In 2005 Yevda Abramov, himself a Jew, was elected to the National Assembly of Azerbaijan as an MP representing the Rural Guba riding. As of 2017, there are seven synagogues in Azerbaijan: three in Baku (one for each community, the Ashkenazi, Mountain and Georgian; the second one being the largest in the Caucasus), two in Qırmızı Qəsəbə near Quba, and two in Oğuz. A delegation of the World Jewish Congress visited Azerbaijan in September 2016 where during the talks with the Azeri President Ilham Aliyev emphasis was put on "Excellent relations with Jewish community and Israel". Azerbaijan was also visited by John Shapiro, executive director of the American Jewish Committee, in January 2017, shortly after the visit of Benjamin Netanyahu to Baku. During the interview, Shapiro said that "the delegation met with the Jewish community in Azerbaijan and saw they are very happy and feel very comfortable living in the country". In 2020, the Azerbaijan Jewish Media Center was established in Sumgayit. Historical demographics Azerbaijan's Jewish population significantly decreased between 1926 and 1939, but then didn't change much between 1939 and 1989 (it increased a little until 1970, and then decreased a little until 1989). Since 1989 and the fall of Communism, Azerbaijan's Jewish population has significantly decreased. Most of the Jews in Azerbaijan left and moved to other countries between 1989 and 2002, with most of them moving to Israel. Famous Azerbaijani Jews See also References External links |
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[SOURCE: https://en.wikipedia.org/wiki/Python_(programming_language)#cite_note-AutoNT-59-67] | [TOKENS: 4314] |
Contents Python (programming language) Python is a high-level, general-purpose programming language. Its design philosophy emphasizes code readability with the use of significant indentation. Python is dynamically type-checked and garbage-collected. It supports multiple programming paradigms, including structured (particularly procedural), object-oriented and functional programming. Guido van Rossum began working on Python in the late 1980s as a successor to the ABC programming language. Python 3.0, released in 2008, was a major revision and not completely backward-compatible with earlier versions. Beginning with Python 3.5, capabilities and keywords for typing were added to the language, allowing optional static typing. As of 2026[update], the Python Software Foundation supports Python 3.10, 3.11, 3.12, 3.13, and 3.14, following the project's annual release cycle and five-year support policy. Python 3.15 is currently in the alpha development phase, and the stable release is expected to come out in October 2026. Earlier versions in the 3.x series have reached end-of-life and no longer receive security updates. Python has gained widespread use in the machine learning community. It is widely taught as an introductory programming language. Since 2003, Python has consistently ranked in the top ten of the most popular programming languages in the TIOBE Programming Community Index, which ranks based on searches in 24 platforms. History Python was conceived in the late 1980s by Guido van Rossum at Centrum Wiskunde & Informatica (CWI) in the Netherlands. It was designed as a successor to the ABC programming language, which was inspired by SETL, capable of exception handling and interfacing with the Amoeba operating system. Python implementation began in December 1989. Van Rossum first released it in 1991 as Python 0.9.0. Van Rossum assumed sole responsibility for the project, as the lead developer, until 12 July 2018, when he announced his "permanent vacation" from responsibilities as Python's "benevolent dictator for life" (BDFL); this title was bestowed on him by the Python community to reflect his long-term commitment as the project's chief decision-maker. (He has since come out of retirement and is self-titled "BDFL-emeritus".) In January 2019, active Python core developers elected a five-member Steering Council to lead the project. The name Python derives from the British comedy series Monty Python's Flying Circus. (See § Naming.) Python 2.0 was released on 16 October 2000, featuring many new features such as list comprehensions, cycle-detecting garbage collection, reference counting, and Unicode support. Python 2.7's end-of-life was initially set for 2015, and then postponed to 2020 out of concern that a large body of existing code could not easily be forward-ported to Python 3. It no longer receives security patches or updates. While Python 2.7 and older versions are officially unsupported, a different unofficial Python implementation, PyPy, continues to support Python 2, i.e., "2.7.18+" (plus 3.11), with the plus signifying (at least some) "backported security updates". Python 3.0 was released on 3 December 2008, and was a major revision and not completely backward-compatible with earlier versions, with some new semantics and changed syntax. Python 2.7.18, released in 2020, was the last release of Python 2. Several releases in the Python 3.x series have added new syntax to the language, and made a few (considered very minor) backward-incompatible changes. As of January 2026[update], Python 3.14.3 is the latest stable release. All older 3.x versions had a security update down to Python 3.9.24 then again with 3.9.25, the final version in 3.9 series. Python 3.10 is, since November 2025, the oldest supported branch. Python 3.15 has an alpha released, and Android has an official downloadable executable available for Python 3.14. Releases receive two years of full support followed by three years of security support. Design philosophy and features Python is a multi-paradigm programming language. Object-oriented programming and structured programming are fully supported, and many of their features support functional programming and aspect-oriented programming – including metaprogramming and metaobjects. Many other paradigms are supported via extensions, including design by contract and logic programming. Python is often referred to as a 'glue language' because it is purposely designed to be able to integrate components written in other languages. Python uses dynamic typing and a combination of reference counting and a cycle-detecting garbage collector for memory management. It uses dynamic name resolution (late binding), which binds method and variable names during program execution. Python's design offers some support for functional programming in the "Lisp tradition". It has filter, map, and reduce functions; list comprehensions, dictionaries, sets, and generator expressions. The standard library has two modules (itertools and functools) that implement functional tools borrowed from Haskell and Standard ML. Python's core philosophy is summarized in the Zen of Python (PEP 20) written by Tim Peters, which includes aphorisms such as these: However, Python has received criticism for violating these principles and adding unnecessary language bloat. Responses to these criticisms note that the Zen of Python is a guideline rather than a rule. The addition of some new features had been controversial: Guido van Rossum resigned as Benevolent Dictator for Life after conflict about adding the assignment expression operator in Python 3.8. Nevertheless, rather than building all functionality into its core, Python was designed to be highly extensible via modules. This compact modularity has made it particularly popular as a means of adding programmable interfaces to existing applications. Van Rossum's vision of a small core language with a large standard library and easily extensible interpreter stemmed from his frustrations with ABC, which represented the opposite approach. Python claims to strive for a simpler, less-cluttered syntax and grammar, while giving developers a choice in their coding methodology. Python lacks do .. while loops, which Rossum considered harmful. In contrast to Perl's motto "there is more than one way to do it", Python advocates an approach where "there should be one – and preferably only one – obvious way to do it". In practice, however, Python provides many ways to achieve a given goal. There are at least three ways to format a string literal, with no certainty as to which one a programmer should use. Alex Martelli is a Fellow at the Python Software Foundation and Python book author; he wrote that "To describe something as 'clever' is not considered a compliment in the Python culture." Python's developers typically prioritize readability over performance. For example, they reject patches to non-critical parts of the CPython reference implementation that would offer increases in speed that do not justify the cost of clarity and readability.[failed verification] Execution speed can be improved by moving speed-critical functions to extension modules written in languages such as C, or by using a just-in-time compiler like PyPy. Also, it is possible to transpile to other languages. However, this approach either fails to achieve the expected speed-up, since Python is a very dynamic language, or only a restricted subset of Python is compiled (with potential minor semantic changes). Python is meant to be a fun language to use. This goal is reflected in the name – a tribute to the British comedy group Monty Python – and in playful approaches to some tutorials and reference materials. For instance, some code examples use the terms "spam" and "eggs" (in reference to a Monty Python sketch), rather than the typical terms "foo" and "bar". A common neologism in the Python community is pythonic, which has a broad range of meanings related to program style: Pythonic code may use Python idioms well; be natural or show fluency in the language; or conform with Python's minimalist philosophy and emphasis on readability. Syntax and semantics Python is meant to be an easily readable language. Its formatting is visually uncluttered and often uses English keywords where other languages use punctuation. Unlike many other languages, it does not use curly brackets to delimit blocks, and semicolons after statements are allowed but rarely used. It has fewer syntactic exceptions and special cases than C or Pascal. Python uses whitespace indentation, rather than curly brackets or keywords, to delimit blocks. An increase in indentation comes after certain statements; a decrease in indentation signifies the end of the current block. Thus, the program's visual structure accurately represents its semantic structure. This feature is sometimes termed the off-side rule. Some other languages use indentation this way; but in most, indentation has no semantic meaning. The recommended indent size is four spaces. Python's statements include the following: The assignment statement (=) binds a name as a reference to a separate, dynamically allocated object. Variables may subsequently be rebound at any time to any object. In Python, a variable name is a generic reference holder without a fixed data type; however, it always refers to some object with a type. This is called dynamic typing—in contrast to statically-typed languages, where each variable may contain only a value of a certain type. Python does not support tail call optimization or first-class continuations; according to Van Rossum, the language never will. However, better support for coroutine-like functionality is provided by extending Python's generators. Before 2.5, generators were lazy iterators; data was passed unidirectionally out of the generator. From Python 2.5 on, it is possible to pass data back into a generator function; and from version 3.3, data can be passed through multiple stack levels. Python's expressions include the following: In Python, a distinction between expressions and statements is rigidly enforced, in contrast to languages such as Common Lisp, Scheme, or Ruby. This distinction leads to duplicating some functionality, for example: A statement cannot be part of an expression; because of this restriction, expressions such as list and dict comprehensions (and lambda expressions) cannot contain statements. As a particular case, an assignment statement such as a = 1 cannot be part of the conditional expression of a conditional statement. Python uses duck typing, and it has typed objects but untyped variable names. Type constraints are not checked at definition time; rather, operations on an object may fail at usage time, indicating that the object is not of an appropriate type. Despite being dynamically typed, Python is strongly typed, forbidding operations that are poorly defined (e.g., adding a number and a string) rather than quietly attempting to interpret them. Python allows programmers to define their own types using classes, most often for object-oriented programming. New instances of classes are constructed by calling the class, for example, SpamClass() or EggsClass()); the classes are instances of the metaclass type (which is an instance of itself), thereby allowing metaprogramming and reflection. Before version 3.0, Python had two kinds of classes, both using the same syntax: old-style and new-style. Current Python versions support the semantics of only the new style. Python supports optional type annotations. These annotations are not enforced by the language, but may be used by external tools such as mypy to catch errors. Python includes a module typing including several type names for type annotations. Also, mypy supports a Python compiler called mypyc, which leverages type annotations for optimization. 1.33333 frozenset() Python includes conventional symbols for arithmetic operators (+, -, *, /), the floor-division operator //, and the modulo operator %. (With the modulo operator, a remainder can be negative, e.g., 4 % -3 == -2.) Also, Python offers the ** symbol for exponentiation, e.g. 5**3 == 125 and 9**0.5 == 3.0. Also, it offers the matrix‑multiplication operator @ . These operators work as in traditional mathematics; with the same precedence rules, the infix operators + and - can also be unary, to represent positive and negative numbers respectively. Division between integers produces floating-point results. The behavior of division has changed significantly over time: In Python terms, the / operator represents true division (or simply division), while the // operator represents floor division. Before version 3.0, the / operator represents classic division. Rounding towards negative infinity, though a different method than in most languages, adds consistency to Python. For instance, this rounding implies that the equation (a + b)//b == a//b + 1 is always true. Also, the rounding implies that the equation b*(a//b) + a%b == a is valid for both positive and negative values of a. As expected, the result of a%b lies in the half-open interval [0, b), where b is a positive integer; however, maintaining the validity of the equation requires that the result must lie in the interval (b, 0] when b is negative. Python provides a round function for rounding a float to the nearest integer. For tie-breaking, Python 3 uses the round to even method: round(1.5) and round(2.5) both produce 2. Python versions before 3 used the round-away-from-zero method: round(0.5) is 1.0, and round(-0.5) is −1.0. Python allows Boolean expressions that contain multiple equality relations to be consistent with general usage in mathematics. For example, the expression a < b < c tests whether a is less than b and b is less than c. C-derived languages interpret this expression differently: in C, the expression would first evaluate a < b, resulting in 0 or 1, and that result would then be compared with c. Python uses arbitrary-precision arithmetic for all integer operations. The Decimal type/class in the decimal module provides decimal floating-point numbers to a pre-defined arbitrary precision with several rounding modes. The Fraction class in the fractions module provides arbitrary precision for rational numbers. Due to Python's extensive mathematics library and the third-party library NumPy, the language is frequently used for scientific scripting in tasks such as numerical data processing and manipulation. Functions are created in Python by using the def keyword. A function is defined similarly to how it is called, by first providing the function name and then the required parameters. Here is an example of a function that prints its inputs: To assign a default value to a function parameter in case no actual value is provided at run time, variable-definition syntax can be used inside the function header. Code examples "Hello, World!" program: Program to calculate the factorial of a non-negative integer: Libraries Python's large standard library is commonly cited as one of its greatest strengths. For Internet-facing applications, many standard formats and protocols such as MIME and HTTP are supported. The language includes modules for creating graphical user interfaces, connecting to relational databases, generating pseudorandom numbers, arithmetic with arbitrary-precision decimals, manipulating regular expressions, and unit testing. Some parts of the standard library are covered by specifications—for example, the Web Server Gateway Interface (WSGI) implementation wsgiref follows PEP 333—but most parts are specified by their code, internal documentation, and test suites. However, because most of the standard library is cross-platform Python code, only a few modules must be altered or rewritten for variant implementations. As of 13 March 2025,[update] the Python Package Index (PyPI), the official repository for third-party Python software, contains over 614,339 packages. Development environments Most[which?] Python implementations (including CPython) include a read–eval–print loop (REPL); this permits the environment to function as a command line interpreter, with which users enter statements sequentially and receive results immediately. Also, CPython is bundled with an integrated development environment (IDE) called IDLE, which is oriented toward beginners.[citation needed] Other shells, including IDLE and IPython, add additional capabilities such as improved auto-completion, session-state retention, and syntax highlighting. Standard desktop IDEs include PyCharm, Spyder, and Visual Studio Code; there are web browser-based IDEs, such as the following environments: Implementations CPython is the reference implementation of Python. This implementation is written in C, meeting the C11 standard since version 3.11. Older versions use the C89 standard with several select C99 features, but third-party extensions are not limited to older C versions—e.g., they can be implemented using C11 or C++. CPython compiles Python programs into an intermediate bytecode, which is then executed by a virtual machine. CPython is distributed with a large standard library written in a combination of C and native Python. CPython is available for many platforms, including Windows and most modern Unix-like systems, including macOS (and Apple M1 Macs, since Python 3.9.1, using an experimental installer). Starting with Python 3.9, the Python installer intentionally fails to install on Windows 7 and 8; Windows XP was supported until Python 3.5, with unofficial support for VMS. Platform portability was one of Python's earliest priorities. During development of Python 1 and 2, even OS/2 and Solaris were supported; since that time, support has been dropped for many platforms. All current Python versions (since 3.7) support only operating systems that feature multithreading, by now supporting not nearly as many operating systems (dropping many outdated) than in the past. All alternative implementations have at least slightly different semantics. For example, an alternative may include unordered dictionaries, in contrast to other current Python versions. As another example in the larger Python ecosystem, PyPy does not support the full C Python API. Creating an executable with Python often is done by bundling an entire Python interpreter into the executable, which causes binary sizes to be massive for small programs, yet there exist implementations that are capable of truly compiling Python. Alternative implementations include the following: Stackless Python is a significant fork of CPython that implements microthreads. This implementation uses the call stack differently, thus allowing massively concurrent programs. PyPy also offers a stackless version. Just-in-time Python compilers have been developed, but are now unsupported: There are several compilers/transpilers to high-level object languages; the source language is unrestricted Python, a subset of Python, or a language similar to Python: There are also specialized compilers: Some older projects existed, as well as compilers not designed for use with Python 3.x and related syntax: A performance comparison among various Python implementations, using a non-numerical (combinatorial) workload, was presented at EuroSciPy '13. In addition, Python's performance relative to other programming languages is benchmarked by The Computer Language Benchmarks Game. There are several approaches to optimizing Python performance, despite the inherent slowness of an interpreted language. These approaches include the following strategies or tools: Language Development Python's development is conducted mostly through the Python Enhancement Proposal (PEP) process; this process is the primary mechanism for proposing major new features, collecting community input on issues, and documenting Python design decisions. Python coding style is covered in PEP 8. Outstanding PEPs are reviewed and commented on by the Python community and the steering council. Enhancement of the language corresponds with development of the CPython reference implementation. The mailing list python-dev is the primary forum for the language's development. Specific issues were originally discussed in the Roundup bug tracker hosted by the foundation. In 2022, all issues and discussions were migrated to GitHub. Development originally took place on a self-hosted source-code repository running Mercurial, until Python moved to GitHub in January 2017. CPython's public releases have three types, distinguished by which part of the version number is incremented: Many alpha, beta, and release-candidates are also released as previews and for testing before final releases. Although there is a rough schedule for releases, they are often delayed if the code is not ready yet. Python's development team monitors the state of the code by running a large unit test suite during development. The major academic conference on Python is PyCon. Also, there are special Python mentoring programs, such as PyLadies. Naming Python's name is inspired by the British comedy group Monty Python, whom Python creator Guido van Rossum enjoyed while developing the language. Monty Python references appear frequently in Python code and culture; for example, the metasyntactic variables often used in Python literature are spam and eggs, rather than the traditional foo and bar. Also, the official Python documentation contains various references to Monty Python routines. Python users are sometimes referred to as "Pythonistas". Languages influenced by Python See also Notes References Further reading External links |
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Contents Internet The Internet (or internet)[a] is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP)[b] to communicate between networks and devices. It is a network of networks that comprises private, public, academic, business, and government networks of local to global scope, linked by electronic, wireless, and optical networking technologies. The Internet carries a vast range of information services and resources, such as the interlinked hypertext documents and applications of the World Wide Web (WWW), electronic mail, discussion groups, internet telephony, streaming media and file sharing. Most traditional communication media, including telephone, radio, television, paper mail, newspapers, and print publishing, have been transformed by the Internet, giving rise to new media such as email, online music, digital newspapers, news aggregators, and audio and video streaming websites. The Internet has enabled and accelerated new forms of personal interaction through instant messaging, Internet forums, and social networking services. Online shopping has also grown to occupy a significant market across industries, enabling firms to extend brick and mortar presences to serve larger markets. Business-to-business and financial services on the Internet affect supply chains across entire industries. The origins of the Internet date back to research that enabled the time-sharing of computer resources, the development of packet switching, and the design of computer networks for data communication. The set of communication protocols to enable internetworking on the Internet arose from research and development commissioned in the 1970s by the Defense Advanced Research Projects Agency (DARPA) of the United States Department of Defense in collaboration with universities and researchers across the United States and in the United Kingdom and France. The Internet has no single centralized governance in either technological implementation or policies for access and usage. Each constituent network sets its own policies. The overarching definitions of the two principal name spaces on the Internet, the Internet Protocol address (IP address) space and the Domain Name System (DNS), are directed by a maintainer organization, the Internet Corporation for Assigned Names and Numbers (ICANN). The technical underpinning and standardization of the core protocols is an activity of the non-profit Internet Engineering Task Force (IETF). Terminology The word internetted was used as early as 1849, meaning interconnected or interwoven. The word Internet was used in 1945 by the United States War Department in a radio operator's manual, and in 1974 as the shorthand form of Internetwork. Today, the term Internet most commonly refers to the global system of interconnected computer networks, though it may also refer to any group of smaller networks. The word Internet may be capitalized as a proper noun, although this is becoming less common. This reflects the tendency in English to capitalize new terms and move them to lowercase as they become familiar. The word is sometimes still capitalized to distinguish the global internet from smaller networks, though many publications, including the AP Stylebook since 2016, recommend the lowercase form in every case. In 2016, the Oxford English Dictionary found that, based on a study of around 2.5 billion printed and online sources, "Internet" was capitalized in 54% of cases. The terms Internet and World Wide Web are often used interchangeably; it is common to speak of "going on the Internet" when using a web browser to view web pages. However, the World Wide Web, or the Web, is only one of a large number of Internet services. It is the global collection of web pages, documents and other web resources linked by hyperlinks and URLs. History In the 1960s, computer scientists began developing systems for time-sharing of computer resources. J. C. R. Licklider proposed the idea of a universal network while working at Bolt Beranek & Newman and, later, leading the Information Processing Techniques Office at the Advanced Research Projects Agency (ARPA) of the United States Department of Defense. Research into packet switching,[c] one of the fundamental Internet technologies, started in the work of Paul Baran at RAND in the early 1960s and, independently, Donald Davies at the United Kingdom's National Physical Laboratory in 1965. After the Symposium on Operating Systems Principles in 1967, packet switching from the proposed NPL network was incorporated into the design of the ARPANET, an experimental resource sharing network proposed by ARPA. ARPANET development began with two network nodes which were interconnected between the University of California, Los Angeles and the Stanford Research Institute on 29 October 1969. The third site was at the University of California, Santa Barbara, followed by the University of Utah. By the end of 1971, 15 sites were connected to the young ARPANET. Thereafter, the ARPANET gradually developed into a decentralized communications network, connecting remote centers and military bases in the United States. Other user networks and research networks, such as the Merit Network and CYCLADES, were developed in the late 1960s and early 1970s. Early international collaborations for the ARPANET were rare. Connections were made in 1973 to Norway (NORSAR and, later, NDRE) and to Peter Kirstein's research group at University College London, which provided a gateway to British academic networks, the first internetwork for resource sharing. ARPA projects, the International Network Working Group and commercial initiatives led to the development of various protocols and standards by which multiple separate networks could become a single network, or a network of networks. In 1974, Vint Cerf at Stanford University and Bob Kahn at DARPA published a proposal for "A Protocol for Packet Network Intercommunication". Cerf and his graduate students used the term internet as a shorthand for internetwork in RFC 675. The Internet Experiment Notes and later RFCs repeated this use. The work of Louis Pouzin and Robert Metcalfe had important influences on the resulting TCP/IP design. National PTTs and commercial providers developed the X.25 standard and deployed it on public data networks. The ARPANET initially served as a backbone for the interconnection of regional academic and military networks in the United States to enable resource sharing. Access to the ARPANET was expanded in 1981 when the National Science Foundation (NSF) funded the Computer Science Network (CSNET). In 1982, the Internet Protocol Suite (TCP/IP) was standardized, which facilitated worldwide proliferation of interconnected networks. TCP/IP network access expanded again in 1986 when the National Science Foundation Network (NSFNet) provided access to supercomputer sites in the United States for researchers, first at speeds of 56 kbit/s and later at 1.5 Mbit/s and 45 Mbit/s. The NSFNet expanded into academic and research organizations in Europe, Australia, New Zealand and Japan in 1988–89. Although other network protocols such as UUCP and PTT public data networks had global reach well before this time, this marked the beginning of the Internet as an intercontinental network. Commercial Internet service providers emerged in 1989 in the United States and Australia. The ARPANET was decommissioned in 1990. The linking of commercial networks and enterprises by the early 1990s, as well as the advent of the World Wide Web, marked the beginning of the transition to the modern Internet. Steady advances in semiconductor technology and optical networking created new economic opportunities for commercial involvement in the expansion of the network in its core and for delivering services to the public. In mid-1989, MCI Mail and Compuserve established connections to the Internet, delivering email and public access products to the half million users of the Internet. Just months later, on 1 January 1990, PSInet launched an alternate Internet backbone for commercial use; one of the networks that added to the core of the commercial Internet of later years. In March 1990, the first high-speed T1 (1.5 Mbit/s) link between the NSFNET and Europe was installed between Cornell University and CERN, allowing much more robust communications than were capable with satellites. Later in 1990, Tim Berners-Lee began writing WorldWideWeb, the first web browser, after two years of lobbying CERN management. By Christmas 1990, Berners-Lee had built all the tools necessary for a working Web: the HyperText Transfer Protocol (HTTP) 0.9, the HyperText Markup Language (HTML), the first Web browser (which was also an HTML editor and could access Usenet newsgroups and FTP files), the first HTTP server software (later known as CERN httpd), the first web server, and the first Web pages that described the project itself. In 1991 the Commercial Internet eXchange was founded, allowing PSInet to communicate with the other commercial networks CERFnet and Alternet. Stanford Federal Credit Union was the first financial institution to offer online Internet banking services to all of its members in October 1994. In 1996, OP Financial Group, also a cooperative bank, became the second online bank in the world and the first in Europe. By 1995, the Internet was fully commercialized in the U.S. when the NSFNet was decommissioned, removing the last restrictions on use of the Internet to carry commercial traffic. As technology advanced and commercial opportunities fueled reciprocal growth, the volume of Internet traffic started experiencing similar characteristics as that of the scaling of MOS transistors, exemplified by Moore's law, doubling every 18 months. This growth, formalized as Edholm's law, was catalyzed by advances in MOS technology, laser light wave systems, and noise performance. Since 1995, the Internet has tremendously impacted culture and commerce, including the rise of near-instant communication by email, instant messaging, telephony (Voice over Internet Protocol or VoIP), two-way interactive video calls, and the World Wide Web. Increasing amounts of data are transmitted at higher and higher speeds over fiber optic networks operating at 1 Gbit/s, 10 Gbit/s, or more. The Internet continues to grow, driven by ever-greater amounts of online information and knowledge, commerce, entertainment and social networking services. During the late 1990s, it was estimated that traffic on the public Internet grew by 100 percent per year, while the mean annual growth in the number of Internet users was thought to be between 20% and 50%. This growth is often attributed to the lack of central administration, which allows organic growth of the network, as well as the non-proprietary nature of the Internet protocols, which encourages vendor interoperability and prevents any one company from exerting too much control over the network. In November 2006, the Internet was included on USA Today's list of the New Seven Wonders. As of 31 March 2011[update], the estimated total number of Internet users was 2.095 billion (30% of world population). It is estimated that in 1993 the Internet carried only 1% of the information flowing through two-way telecommunication. By 2000 this figure had grown to 51%, and by 2007 more than 97% of all telecommunicated information was carried over the Internet. Modern smartphones can access the Internet through cellular carrier networks, and internet usage by mobile and tablet devices exceeded desktop worldwide for the first time in October 2016. As of 2018[update], 80% of the world's population were covered by a 4G network. The International Telecommunication Union (ITU) estimated that, by the end of 2017, 48% of individual users regularly connect to the Internet, up from 34% in 2012. Mobile Internet connectivity has played an important role in expanding access in recent years, especially in Asia and the Pacific and in Africa. The number of unique mobile cellular subscriptions increased from 3.9 billion in 2012 to 4.8 billion in 2016, two-thirds of the world's population, with more than half of subscriptions located in Asia and the Pacific. The limits that users face on accessing information via mobile applications coincide with a broader process of fragmentation of the Internet. Fragmentation restricts access to media content and tends to affect the poorest users the most. One solution, zero-rating, is the practice of Internet service providers allowing users free connectivity to access specific content or applications without cost. Social impact The Internet has enabled new forms of social interaction, activities, and social associations, giving rise to the scholarly study of the sociology of the Internet. Between 2000 and 2009, the number of Internet users globally rose from 390 million to 1.9 billion. By 2010, 22% of the world's population had access to computers with 1 billion Google searches every day, 300 million Internet users reading blogs, and 2 billion videos viewed daily on YouTube. In 2014 the world's Internet users surpassed 3 billion or 44 percent of world population, but two-thirds came from the richest countries, with 78 percent of Europeans using the Internet, followed by 57 percent of the Americas. However, by 2018, Asia alone accounted for 51% of all Internet users, with 2.2 billion out of the 4.3 billion Internet users in the world. China's Internet users surpassed a major milestone in 2018, when the country's Internet regulatory authority, China Internet Network Information Centre, announced that China had 802 million users. China was followed by India, with some 700 million users, with the United States third with 275 million users. However, in terms of penetration, in 2022, China had a 70% penetration rate compared to India's 60% and the United States's 90%. In 2022, 54% of the world's Internet users were based in Asia, 14% in Europe, 7% in North America, 10% in Latin America and the Caribbean, 11% in Africa, 4% in the Middle East and 1% in Oceania. In 2019, Kuwait, Qatar, the Falkland Islands, Bermuda and Iceland had the highest Internet penetration by the number of users, with 93% or more of the population with access. As of 2022, it was estimated that 5.4 billion people use the Internet, more than two-thirds of the world's population. Early computer systems were limited to the characters in the American Standard Code for Information Interchange (ASCII), a subset of the Latin alphabet. After English (27%), the most requested languages on the World Wide Web are Chinese (25%), Spanish (8%), Japanese (5%), Portuguese and German (4% each), Arabic, French and Russian (3% each), and Korean (2%). Modern character encoding standards, such as Unicode, allow for development and communication in the world's widely used languages. However, some glitches such as mojibake (incorrect display of some languages' characters) still remain. Several neologisms exist that refer to Internet users: Netizen (as in "citizen of the net") refers to those actively involved in improving online communities, the Internet in general or surrounding political affairs and rights such as free speech, Internaut refers to operators or technically highly capable users of the Internet, digital citizen refers to a person using the Internet in order to engage in society, politics, and government participation. The Internet allows greater flexibility in working hours and location, especially with the spread of unmetered high-speed connections. The Internet can be accessed almost anywhere by numerous means, including through mobile Internet devices. Mobile phones, datacards, handheld game consoles and cellular routers allow users to connect to the Internet wirelessly.[citation needed] Educational material at all levels from pre-school (e.g. CBeebies) to post-doctoral (e.g. scholarly literature through Google Scholar) is available on websites. The internet has facilitated the development of virtual universities and distance education, enabling both formal and informal education. The Internet allows researchers to conduct research remotely via virtual laboratories, with profound changes in reach and generalizability of findings as well as in communication between scientists and in the publication of results. By the late 2010s the Internet had been described as "the main source of scientific information "for the majority of the global North population".: 111 Wikis have also been used in the academic community for sharing and dissemination of information across institutional and international boundaries. In those settings, they have been found useful for collaboration on grant writing, strategic planning, departmental documentation, and committee work. The United States Patent and Trademark Office uses a wiki to allow the public to collaborate on finding prior art relevant to examination of pending patent applications. Queens, New York has used a wiki to allow citizens to collaborate on the design and planning of a local park. The English Wikipedia has the largest user base among wikis on the World Wide Web and ranks in the top 10 among all sites in terms of traffic. The Internet has been a major outlet for leisure activity since its inception, with entertaining social experiments such as MUDs and MOOs being conducted on university servers, and humor-related Usenet groups receiving much traffic. Many Internet forums have sections devoted to games and funny videos. Another area of leisure activity on the Internet is multiplayer gaming. This form of recreation creates communities, where people of all ages and origins enjoy the fast-paced world of multiplayer games. These range from MMORPG to first-person shooters, from role-playing video games to online gambling. While online gaming has been around since the 1970s, modern modes of online gaming began with subscription services such as GameSpy and MPlayer. Streaming media is the real-time delivery of digital media for immediate consumption or enjoyment by end users. Streaming companies (such as Netflix, Disney+, Amazon's Prime Video, Mubi, Hulu, and Apple TV+) now dominate the entertainment industry, eclipsing traditional broadcasters. Audio streamers such as Spotify and Apple Music also have significant market share in the audio entertainment market. Video sharing websites are also a major factor in the entertainment ecosystem. YouTube was founded on 15 February 2005 and is now the leading website for free streaming video with more than two billion users. It uses a web player to stream and show video files. YouTube users watch hundreds of millions, and upload hundreds of thousands, of videos daily. Other video sharing websites include Vimeo, Instagram and TikTok.[citation needed] Although many governments have attempted to restrict both Internet pornography and online gambling, this has generally failed to stop their widespread popularity. A number of advertising-funded ostensible video sharing websites known as "tube sites" have been created to host shared pornographic video content. Due to laws requiring the documentation of the origin of pornography, these websites now largely operate in conjunction with pornographic movie studios and their own independent creator networks, acting as de-facto video streaming services. Major players in this field include the market leader Aylo, the operator of PornHub and numerous other branded sites, as well as other independent operators such as xHamster and Xvideos. As of 2023[update], Internet traffic to pornographic video sites rivalled that of mainstream video streaming and sharing services. Remote work is facilitated by tools such as groupware, virtual private networks, conference calling, videotelephony, and VoIP so that work may be performed from any location, such as the worker's home.[citation needed] The spread of low-cost Internet access in developing countries has opened up new possibilities for peer-to-peer charities, which allow individuals to contribute small amounts to charitable projects for other individuals. Websites, such as DonorsChoose and GlobalGiving, allow small-scale donors to direct funds to individual projects of their choice. A popular twist on Internet-based philanthropy is the use of peer-to-peer lending for charitable purposes. Kiva pioneered this concept in 2005, offering the first web-based service to publish individual loan profiles for funding. The low cost and nearly instantaneous sharing of ideas, knowledge, and skills have made collaborative work dramatically easier, with the help of collaborative software, which allow groups to easily form, cheaply communicate, and share ideas. An example of collaborative software is the free software movement, which has produced, among other things, Linux, Mozilla Firefox, and OpenOffice.org (later forked into LibreOffice).[citation needed] Content management systems allow collaborating teams to work on shared sets of documents simultaneously without accidentally destroying each other's work.[citation needed] The internet also allows for cloud computing, virtual private networks, remote desktops, and remote work.[citation needed] The online disinhibition effect describes the tendency of many individuals to behave more stridently or offensively online than they would in person. A significant number of feminist women have been the target of various forms of harassment, including insults and hate speech, to, in extreme cases, rape and death threats, in response to posts they have made on social media. Social media companies have been criticized in the past for not doing enough to aid victims of online abuse. Children also face dangers online such as cyberbullying and approaches by sexual predators, who sometimes pose as children themselves. Due to naivety, they may also post personal information about themselves online, which could put them or their families at risk unless warned not to do so. Many parents choose to enable Internet filtering or supervise their children's online activities in an attempt to protect their children from pornography or violent content on the Internet. The most popular social networking services commonly forbid users under the age of 13. However, these policies can be circumvented by registering an account with a false birth date, and a significant number of children aged under 13 join such sites.[citation needed] Social networking services for younger children, which claim to provide better levels of protection for children, also exist. Internet usage has been correlated to users' loneliness. Lonely people tend to use the Internet as an outlet for their feelings and to share their stories with others, such as in the "I am lonely will anyone speak to me" thread.[citation needed] Cyberslacking can become a drain on corporate resources; employees spend a significant amount of time surfing the Web while at work. Internet addiction disorder is excessive computer use that interferes with daily life. Nicholas G. Carr believes that Internet use has other effects on individuals, for instance improving skills of scan-reading and interfering with the deep thinking that leads to true creativity. Electronic business encompasses business processes spanning the entire value chain: purchasing, supply chain management, marketing, sales, customer service, and business relationship. E-commerce seeks to add revenue streams using the Internet to build and enhance relationships with clients and partners. According to International Data Corporation, the size of worldwide e-commerce, when global business-to-business and -consumer transactions are combined, equate to $16 trillion in 2013. A report by Oxford Economics added those two together to estimate the total size of the digital economy at $20.4 trillion, equivalent to roughly 13.8% of global sales. While much has been written of the economic advantages of Internet-enabled commerce, there is also evidence that some aspects of the Internet such as maps and location-aware services may serve to reinforce economic inequality and the digital divide. Electronic commerce may be responsible for consolidation and the decline of mom-and-pop, brick and mortar businesses resulting in increases in income inequality. A 2013 Institute for Local Self-Reliance report states that brick-and-mortar retailers employ 47 people for every $10 million in sales, while Amazon employs only 14. Similarly, the 700-employee room rental start-up Airbnb was valued at $10 billion in 2014, about half as much as Hilton Worldwide, which employs 152,000 people. At that time, Uber employed 1,000 full-time employees and was valued at $18.2 billion, about the same valuation as Avis Rent a Car and The Hertz Corporation combined, which together employed almost 60,000 people. Advertising on popular web pages can be lucrative, and e-commerce. Online advertising is a form of marketing and advertising which uses the Internet to deliver promotional marketing messages to consumers. It includes email marketing, search engine marketing (SEM), social media marketing, many types of display advertising (including web banner advertising), and mobile advertising. In 2011, Internet advertising revenues in the United States surpassed those of cable television and nearly exceeded those of broadcast television.: 19 Many common online advertising practices are controversial and increasingly subject to regulation. The Internet has achieved new relevance as a political tool. The presidential campaign of Howard Dean in 2004 in the United States was notable for its success in soliciting donation via the Internet. Many political groups use the Internet to achieve a new method of organizing for carrying out their mission, having given rise to Internet activism. Social media websites, such as Facebook and Twitter, helped people organize the Arab Spring, by helping activists organize protests, communicate grievances, and disseminate information. Many have understood the Internet as an extension of the Habermasian notion of the public sphere, observing how network communication technologies provide something like a global civic forum. However, incidents of politically motivated Internet censorship have now been recorded in many countries, including western democracies. E-government is the use of technological communications devices, such as the Internet, to provide public services to citizens and other persons in a country or region. E-government offers opportunities for more direct and convenient citizen access to government and for government provision of services directly to citizens. Cybersectarianism is a new organizational form that involves: highly dispersed small groups of practitioners that may remain largely anonymous within the larger social context and operate in relative secrecy, while still linked remotely to a larger network of believers who share a set of practices and texts, and often a common devotion to a particular leader. Overseas supporters provide funding and support; domestic practitioners distribute tracts, participate in acts of resistance, and share information on the internal situation with outsiders. Collectively, members and practitioners of such sects construct viable virtual communities of faith, exchanging personal testimonies and engaging in the collective study via email, online chat rooms, and web-based message boards. In particular, the British government has raised concerns about the prospect of young British Muslims being indoctrinated into Islamic extremism by material on the Internet, being persuaded to join terrorist groups such as the so-called "Islamic State", and then potentially committing acts of terrorism on returning to Britain after fighting in Syria or Iraq.[citation needed] Applications and services The Internet carries many applications and services, most prominently the World Wide Web, including social media, electronic mail, mobile applications, multiplayer online games, Internet telephony, file sharing, and streaming media services. The World Wide Web is a global collection of documents, images, multimedia, applications, and other resources, logically interrelated by hyperlinks and referenced with Uniform Resource Identifiers (URIs), which provide a global system of named references. URIs symbolically identify services, web servers, databases, and the documents and resources that they can provide. HyperText Transfer Protocol (HTTP) is the main access protocol of the World Wide Web. Web services also use HTTP for communication between software systems for information transfer, sharing and exchanging business data and logistics and is one of many languages or protocols that can be used for communication on the Internet. World Wide Web browser software, such as Microsoft Edge, Mozilla Firefox, Opera, Apple's Safari, and Google Chrome, enable users to navigate from one web page to another via the hyperlinks embedded in the documents. These documents may also contain computer data, including graphics, sounds, text, video, multimedia and interactive content. Client-side scripts can include animations, games, office applications and scientific demonstrations. Email is an important communications service available via the Internet. The concept of sending electronic text messages between parties, analogous to mailing letters or memos, predates the creation of the Internet. Internet telephony is a common communications service realized with the Internet. The name of the principal internetworking protocol, the Internet Protocol, lends its name to voice over Internet Protocol (VoIP).[citation needed] VoIP systems now dominate many markets, being as easy and convenient as a traditional telephone, while having substantial cost savings, especially over long distances. File sharing is the practice of transferring large amounts of data in the form of computer files across the Internet, for example via file servers. The load of bulk downloads to many users can be eased by the use of "mirror" servers or peer-to-peer networks. Access to the file may be controlled by user authentication, the transit of the file over the Internet may be obscured by encryption, and money may change hands for access to the file. The price can be paid by the remote charging of funds from, for example, a credit card whose details are also passed—usually fully encrypted—across the Internet. The origin and authenticity of the file received may be checked by a digital signature. Governance The Internet is a global network that comprises many voluntarily interconnected autonomous networks. It operates without a central governing body. The technical underpinning and standardization of the core protocols (IPv4 and IPv6) is an activity of the Internet Engineering Task Force (IETF), a non-profit organization of loosely affiliated international participants that anyone may associate with by contributing technical expertise. While the hardware components in the Internet infrastructure can often be used to support other software systems, it is the design and the standardization process of the software that characterizes the Internet and provides the foundation for its scalability and success. The responsibility for the architectural design of the Internet software systems has been assumed by the IETF. The IETF conducts standard-setting work groups, open to any individual, about the various aspects of Internet architecture. The resulting contributions and standards are published as Request for Comments (RFC) documents on the IETF web site. The principal methods of networking that enable the Internet are contained in specially designated RFCs that constitute the Internet Standards. Other less rigorous documents are simply informative, experimental, or historical, or document the best current practices when implementing Internet technologies. To maintain interoperability, the principal name spaces of the Internet are administered by the Internet Corporation for Assigned Names and Numbers (ICANN). ICANN is governed by an international board of directors drawn from across the Internet technical, business, academic, and other non-commercial communities. The organization coordinates the assignment of unique identifiers for use on the Internet, including domain names, IP addresses, application port numbers in the transport protocols, and many other parameters. Globally unified name spaces are essential for maintaining the global reach of the Internet. This role of ICANN distinguishes it as perhaps the only central coordinating body for the global Internet. The National Telecommunications and Information Administration, an agency of the United States Department of Commerce, had final approval over changes to the DNS root zone until the IANA stewardship transition on 1 October 2016. Regional Internet registries (RIRs) were established for five regions of the world to assign IP address blocks and other Internet parameters to local registries, such as Internet service providers, from a designated pool of addresses set aside for each region:[citation needed] The Internet Society (ISOC) was founded in 1992 with a mission to "assure the open development, evolution and use of the Internet for the benefit of all people throughout the world". Its members include individuals as well as corporations, organizations, governments, and universities. Among other activities ISOC provides an administrative home for a number of less formally organized groups that are involved in developing and managing the Internet, including: the Internet Engineering Task Force (IETF), Internet Architecture Board (IAB), Internet Engineering Steering Group (IESG), Internet Research Task Force (IRTF), and Internet Research Steering Group (IRSG). On 16 November 2005, the United Nations-sponsored World Summit on the Information Society in Tunis established the Internet Governance Forum (IGF) to discuss Internet-related issues.[citation needed] Infrastructure The communications infrastructure of the Internet consists of its hardware components and a system of software layers that control various aspects of the architecture. As with any computer network, the Internet physically consists of routers, media (such as cabling and radio links), repeaters, and modems. However, as an example of internetworking, many of the network nodes are not necessarily Internet equipment per se. Internet packets are carried by other full-fledged networking protocols, with the Internet acting as a homogeneous networking standard, running across heterogeneous hardware, with the packets guided to their destinations by IP routers.[citation needed] Internet service providers (ISPs) establish worldwide connectivity between individual networks at various levels of scope. At the top of the routing hierarchy are the tier 1 networks, large telecommunication companies that exchange traffic directly with each other via very high speed fiber-optic cables and governed by peering agreements. Tier 2 and lower-level networks buy Internet transit from other providers to reach at least some parties on the global Internet, though they may also engage in peering. End-users who only access the Internet when needed to perform a function or obtain information, represent the bottom of the routing hierarchy.[citation needed] An ISP may use a single upstream provider for connectivity, or implement multihoming to achieve redundancy and load balancing. Internet exchange points are major traffic exchanges with physical connections to multiple ISPs. Large organizations, such as academic institutions, large enterprises, and governments, may perform the same function as ISPs, engaging in peering and purchasing transit on behalf of their internal networks. Research networks tend to interconnect with large subnetworks such as GEANT, GLORIAD, Internet2, and the UK's national research and education network, JANET.[citation needed] Common methods of Internet access by users include broadband over coaxial cable, fiber optics or copper wires, Wi-Fi, satellite, and cellular telephone technology.[citation needed] Grassroots efforts have led to wireless community networks. Commercial Wi-Fi services that cover large areas are available in many cities, such as New York, London, Vienna, Toronto, San Francisco, Philadelphia, Chicago and Pittsburgh. Most servers that provide internet services are today hosted in data centers, and content is often accessed through high-performance content delivery networks. Colocation centers often host private peering connections between their customers, internet transit providers, cloud providers, meet-me rooms for connecting customers together, Internet exchange points, and landing points and terminal equipment for fiber optic submarine communication cables, connecting the internet. Internet Protocol Suite The Internet standards describe a framework known as the Internet protocol suite (also called TCP/IP, based on the first two components.) This is a suite of protocols that are ordered into a set of four conceptional layers by the scope of their operation, originally documented in RFC 1122 and RFC 1123:[citation needed] The most prominent component of the Internet model is the Internet Protocol. IP enables internetworking, essentially establishing the Internet itself. Two versions of the Internet Protocol exist, IPv4 and IPv6.[citation needed] Aside from the complex array of physical connections that make up its infrastructure, the Internet is facilitated by bi- or multi-lateral commercial contracts (e.g., peering agreements), and by technical specifications or protocols that describe the exchange of data over the network.[citation needed] For locating individual computers on the network, the Internet provides IP addresses. IP addresses are used by the Internet infrastructure to direct internet packets to their destinations. They consist of fixed-length numbers, which are found within the packet. IP addresses are generally assigned to equipment either automatically via Dynamic Host Configuration Protocol, or are configured.[citation needed] Domain Name Systems convert user-inputted domain names (e.g. "en.wikipedia.org") into IP addresses.[citation needed] Internet Protocol version 4 (IPv4) defines an IP address as a 32-bit number. IPv4 is the initial version used on the first generation of the Internet and is still in dominant use. It was designed in 1981 to address up to ≈4.3 billion (109) hosts. However, the explosive growth of the Internet has led to IPv4 address exhaustion, which entered its final stage in 2011, when the global IPv4 address allocation pool was exhausted. Because of the growth of the Internet and the depletion of available IPv4 addresses, a new version of IP IPv6, was developed in the mid-1990s, which provides vastly larger addressing capabilities and more efficient routing of Internet traffic. IPv6 uses 128 bits for the IP address and was standardized in 1998. IPv6 deployment has been ongoing since the mid-2000s and is currently in growing deployment around the world, since Internet address registries began to urge all resource managers to plan rapid adoption and conversion. By design, IPv6 is not directly interoperable with IPv4. Instead, it establishes a parallel version of the Internet not directly accessible with IPv4 software. Thus, translation facilities exist for internetworking, and some nodes have duplicate networking software for both networks. Essentially all modern computer operating systems support both versions of the Internet Protocol.[citation needed] Network infrastructure, however, has been lagging in this development.[citation needed] A subnet or subnetwork is a logical subdivision of an IP network.: 1, 16 Computers that belong to a subnet are addressed with an identical most-significant bit-group in their IP addresses. This results in the logical division of an IP address into two fields, the network number or routing prefix and the rest field or host identifier. The rest field is an identifier for a specific host or network interface.[citation needed] The routing prefix may be expressed in Classless Inter-Domain Routing (CIDR) notation written as the first address of a network, followed by a slash character (/), and ending with the bit-length of the prefix. For example, 198.51.100.0/24 is the prefix of the Internet Protocol version 4 network starting at the given address, having 24 bits allocated for the network prefix, and the remaining 8 bits reserved for host addressing. Addresses in the range 198.51.100.0 to 198.51.100.255 belong to this network. The IPv6 address specification 2001:db8::/32 is a large address block with 296 addresses, having a 32-bit routing prefix.[citation needed] For IPv4, a network may also be characterized by its subnet mask or netmask, which is the bitmask that when applied by a bitwise AND operation to any IP address in the network, yields the routing prefix. Subnet masks are also expressed in dot-decimal notation like an address. For example, 255.255.255.0 is the subnet mask for the prefix 198.51.100.0/24.[citation needed] Computers and routers use routing tables in their operating system to forward IP packets to reach a node on a different subnetwork. Routing tables are maintained by manual configuration or automatically by routing protocols. End-nodes typically use a default route that points toward an ISP providing transit, while ISP routers use the Border Gateway Protocol to establish the most efficient routing across the complex connections of the global Internet.[citation needed] The default gateway is the node that serves as the forwarding host (router) to other networks when no other route specification matches the destination IP address of a packet. Security Internet resources, hardware, and software components are the target of criminal or malicious attempts to gain unauthorized control to cause interruptions, commit fraud, engage in blackmail or access private information. Malware is malicious software used and distributed via the Internet. It includes computer viruses which are copied with the help of humans, computer worms which copy themselves automatically, software for denial of service attacks, ransomware, botnets, and spyware that reports on the activity and typing of users.[citation needed] Usually, these activities constitute cybercrime. Defense theorists have also speculated about the possibilities of hackers using cyber warfare using similar methods on a large scale. Malware poses serious problems to individuals and businesses on the Internet. According to Symantec's 2018 Internet Security Threat Report (ISTR), malware variants number has increased to 669,947,865 in 2017, which is twice as many malware variants as in 2016. Cybercrime, which includes malware attacks as well as other crimes committed by computer, was predicted to cost the world economy US$6 trillion in 2021, and is increasing at a rate of 15% per year. Since 2021, malware has been designed to target computer systems that run critical infrastructure such as the electricity distribution network. Malware can be designed to evade antivirus software detection algorithms. The vast majority of computer surveillance involves the monitoring of data and traffic on the Internet. In the United States for example, under the Communications Assistance For Law Enforcement Act, all phone calls and broadband Internet traffic (emails, web traffic, instant messaging, etc.) are required to be available for unimpeded real-time monitoring by Federal law enforcement agencies. Under the Act, all U.S. telecommunications providers are required to install packet sniffing technology to allow Federal law enforcement and intelligence agencies to intercept all of their customers' broadband Internet and VoIP traffic.[d] The large amount of data gathered from packet capture requires surveillance software that filters and reports relevant information, such as the use of certain words or phrases, the access to certain types of web sites, or communicating via email or chat with certain parties. Agencies, such as the Information Awareness Office, NSA, GCHQ and the FBI, spend billions of dollars per year to develop, purchase, implement, and operate systems for interception and analysis of data. Similar systems are operated by Iranian secret police to identify and suppress dissidents. The required hardware and software were allegedly installed by German Siemens AG and Finnish Nokia. Some governments, such as those of Myanmar, Iran, North Korea, Mainland China, Saudi Arabia and the United Arab Emirates, restrict access to content on the Internet within their territories, especially to political and religious content, with domain name and keyword filters. In Norway, Denmark, Finland, and Sweden, major Internet service providers have voluntarily agreed to restrict access to sites listed by authorities. While this list of forbidden resources is supposed to contain only known child pornography sites, the content of the list is secret. Many countries, including the United States, have enacted laws against the possession or distribution of certain material, such as child pornography, via the Internet but do not mandate filter software. Many free or commercially available software programs, called content-control software are available to users to block offensive specific on individual computers or networks in order to limit access by children to pornographic material or depiction of violence.[citation needed] Performance As the Internet is a heterogeneous network, its physical characteristics, including, for example the data transfer rates of connections, vary widely. It exhibits emergent phenomena that depend on its large-scale organization. PB per monthYear020,00040,00060,00080,000100,000120,000140,000199019952000200520102015Petabytes per monthGlobal Internet Traffic Volume The volume of Internet traffic is difficult to measure because no single point of measurement exists in the multi-tiered, non-hierarchical topology. Traffic data may be estimated from the aggregate volume through the peering points of the Tier 1 network providers, but traffic that stays local in large provider networks may not be accounted for.[citation needed] An Internet blackout or outage can be caused by local signaling interruptions. Disruptions of submarine communications cables may cause blackouts or slowdowns to large areas, such as in the 2008 submarine cable disruption. Less-developed countries are more vulnerable due to the small number of high-capacity links. Land cables are also vulnerable, as in 2011 when a woman digging for scrap metal severed most connectivity for the nation of Armenia. Internet blackouts affecting almost entire countries can be achieved by governments as a form of Internet censorship, as in the blockage of the Internet in Egypt, whereby approximately 93% of networks were without access in 2011 in an attempt to stop mobilization for anti-government protests. Estimates of the Internet's electricity usage have been the subject of controversy, according to a 2014 peer-reviewed research paper that found claims differing by a factor of 20,000 published in the literature during the preceding decade, ranging from 0.0064 kilowatt hours per gigabyte transferred (kWh/GB) to 136 kWh/GB. The researchers attributed these discrepancies mainly to the year of reference (i.e. whether efficiency gains over time had been taken into account) and to whether "end devices such as personal computers and servers are included" in the analysis. In 2011, academic researchers estimated the overall energy used by the Internet to be between 170 and 307 GW, less than two percent of the energy used by humanity. This estimate included the energy needed to build, operate, and periodically replace the estimated 750 million laptops, a billion smart phones and 100 million servers worldwide as well as the energy that routers, cell towers, optical switches, Wi-Fi transmitters and cloud storage devices use when transmitting Internet traffic. According to a non-peer-reviewed study published in 2018 by The Shift Project (a French think tank funded by corporate sponsors), nearly 4% of global CO2 emissions could be attributed to global data transfer and the necessary infrastructure. The study also said that online video streaming alone accounted for 60% of this data transfer and therefore contributed to over 300 million tons of CO2 emission per year, and argued for new "digital sobriety" regulations restricting the use and size of video files. See also Notes References Sources Further reading External links |
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[SOURCE: https://en.wikipedia.org/wiki/JScript_.NET] | [TOKENS: 404] |
Contents JScript .NET JScript .NET is a .NET framework programming language developed by Microsoft as proprietary software. The main differences between JScript and JScript .NET can be summarized as: Firstly, JScript is a scripting language, and as such, programs (or more suggestively, scripts) can be executed with no need to compile the code before. This is not the case with the JScript .NET command-line interface compiler, since this next-generation version relies on the .NET Common Language Runtime (CLR) for execution, which requires that the code be compiled to Common Intermediate Language (CIL), formerly named Microsoft Intermediate Language (MSIL), code before it can be run. Nevertheless, JScript .NET still fully supports interpreting source code at runtime (e.g., via the Function constructor or the eval function) and indeed the interpreter can be exposed by custom applications hosting the JScript .NET engine via the VSA[jargon] interfaces. Secondly, JScript has a strong foundation in Microsoft's ActiveX and Component Object Model (COM) technologies, and relies mainly on ActiveX components to provide much of its function (including database access via ActiveX Data Objects (ADO), file handling, etc.), whereas JScript .NET uses the .NET framework to provide equivalent function. For backward-compatibility (or for where no .NET equivalent library exists), JScript .NET still provides full access to ActiveX objects via .NET and COM Interop using both the ActiveXObject constructor and the standard methods of the .NET Type class. Although the .NET framework and languages such as C# and Visual Basic (.NET) have been adopted widely, JScript .NET has received little attention, from the media and developers. It is not supported in Microsoft's premier development tool, Visual Studio .NET. However, ASP.NET supports JScript .NET. Language differences The following are prime examples of language differences between JScript .NET and other .NET languages, including comparisons. e.g.: See also Notes References |
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