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where is the plaintext and the ciphertext, with r being the number of rounds.
Frequently, key whitening is used in addition to this. At the beginning and the end, the data is modified with key material (often with XOR):
Given one of the standard iterated block cipher design schemes, it is fairly easy to construct a... | Block cipher | Wikipedia | 499 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Decryption is done by simply reversing the process (using the inverses of the S-boxes and P-boxes and applying the round keys in reversed order).
Feistel ciphers
In a Feistel cipher, the block of plain text to be encrypted is split into two equal-sized halves. The round function is applied to one half, using a subkey... | Block cipher | Wikipedia | 509 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Other operations
Other operations often used in block ciphers include data-dependent rotations as in RC5 and RC6, a substitution box implemented as a lookup table as in Data Encryption Standard and Advanced Encryption Standard, a permutation box, and multiplication as in IDEA.
Modes of operation
A block cipher by its... | Block cipher | Wikipedia | 510 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
From a security-theoretic point of view, modes of operation must provide what is known as semantic security. Informally, it means that given some ciphertext under an unknown key one cannot practically derive any information from the ciphertext (other than the length of the message) over what one would have known withou... | Block cipher | Wikipedia | 457 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Integral cryptanalysis is a cryptanalytic attack that is particularly applicable to block ciphers based on substitution–permutation networks. Unlike differential cryptanalysis, which uses pairs of chosen plaintexts with a fixed XOR difference, integral cryptanalysis uses sets or even multisets of chosen plaintexts of w... | Block cipher | Wikipedia | 490 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
To be a bit more precise, let E be an n-bit block cipher. We imagine the following game:
The person running the game flips a coin.
If the coin lands on heads, he chooses a random key K and defines the function f = EK.
If the coin lands on tails, he chooses a random permutation on the set of n-bit strings and define... | Block cipher | Wikipedia | 411 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
These definitions have proven useful for analyzing various modes of operation. For example, one can define a similar game for measuring the security of a block cipher-based encryption algorithm, and then try to show (through a reduction argument) that the probability of an adversary winning this new game is not much mo... | Block cipher | Wikipedia | 443 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
DES was designed to, among other things, resist a certain cryptanalytic attack known to the NSA and rediscovered by IBM, though unknown publicly until rediscovered again and published by Eli Biham and Adi Shamir in the late 1980s. The technique is called differential cryptanalysis and remains one of the few general att... | Block cipher | Wikipedia | 451 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
The designers analysed IDEA to measure its strength against differential cryptanalysis and concluded that it is immune under certain assumptions. No successful linear or algebraic weaknesses have been reported. , the best attack which applies to all keys can break a full 8.5-round IDEA using a narrow-bicliques attack a... | Block cipher | Wikipedia | 409 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Adopted by NIST in 2001, AES has a fixed block size of 128 bits and a key size of 128, 192, or 256 bits, whereas Rijndael can be specified with block and key sizes in any multiple of 32 bits, with a minimum of 128 bits. The block size has a maximum of 256 bits, but the key size has no theoretical maximum. AES operates ... | Block cipher | Wikipedia | 461 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Block ciphers traditionally work over a binary alphabet. That is, both the input and the output are binary strings, consisting of n zeroes and ones. In some situations, however, one may wish to have a block cipher that works over some other alphabet; for example, encrypting 16-digit credit card numbers in such a way th... | Block cipher | Wikipedia | 482 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Just as block ciphers can be used to build hash functions, like SHA-1 and SHA-2 are based on block ciphers which are also used independently as SHACAL, hash functions can be used to build block ciphers. Examples of such block ciphers are BEAR and LION. | Block cipher | Wikipedia | 58 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
The Boeing 747 is a long-range wide-body airliner designed and manufactured by Boeing Commercial Airplanes in the United States between 1968 and 2023.
After the introduction of the 707 in October 1958, Pan Am wanted a jet times its size, to reduce its seat cost by 30%. In 1965, Joe Sutter left the 737 development pro... | Boeing 747 | Wikipedia | 348 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Boeing introduced the -200 in 1971, with uprated engines for a heavier maximum takeoff weight (MTOW) of from the initial , increasing the maximum range from . It was shortened for the longer-range 747SP in 1976, and the 747-300 followed in 1983 with a stretched upper deck for up to 400 seats in three classes. The heav... | Boeing 747 | Wikipedia | 505 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The desire to keep the number of engines to four required new engine designs with greatly increased power and better fuel economy. In May 1964, airframe proposals arrived from Boeing, Douglas, General Dynamics, Lockheed, and Martin Marietta; engine proposals were submitted by General Electric, Curtiss-Wright, and Pratt... | Boeing 747 | Wikipedia | 494 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
In April 1966, Pan Am ordered 25 Boeing 747-100 aircraft for US$525 million (equivalent to $ billion in dollars). During the ceremonial 747 contract-signing banquet in Seattle on Boeing's 50th Anniversary, Juan Trippe predicted that the 747 would be "…a great weapon for peace, competing with intercontinental missiles ... | Boeing 747 | Wikipedia | 453 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The project was designed with a new methodology called fault tree analysis, which allowed the effects of a failure of a single part to be studied to determine its impact on other systems. To address concerns about safety and flyability, the 747's design included structural redundancy, redundant hydraulic systems, quadr... | Boeing 747 | Wikipedia | 405 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Developing the 747 had been a major challenge, and building its assembly plant was also a huge undertaking. Boeing president William M. Allen asked Malcolm T. Stamper, then head of the company's turbine division, to oversee construction of the Everett factory and to start production of the 747. To level the site, more ... | Boeing 747 | Wikipedia | 494 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
During later stages of the flight test program, flutter testing showed that the wings suffered oscillation under certain conditions. This difficulty was partly solved by reducing the stiffness of some wing components. However, a particularly severe high-speed flutter problem was solved only by inserting depleted uraniu... | Boeing 747 | Wikipedia | 497 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
On January 15, 1970, First Lady Pat Nixon christened Pan Am's first 747 at Dulles International Airport in the presence of Pan Am chairman Najeeb Halaby. Instead of champagne, red, white, and blue water was sprayed on the aircraft. The 747 entered service on January 22, 1970, on Pan Am's New York–London route; the flig... | Boeing 747 | Wikipedia | 429 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
In 1985, development of the longer range 747-400 began. The variant had a new glass cockpit, which allowed for a cockpit crew of two instead of three, new engines, lighter construction materials, and a redesigned interior. Development costs soared, and production delays occurred as new technologies were incorporated at... | Boeing 747 | Wikipedia | 487 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
On November 14, 2005, Boeing announced it was launching the 747 Advanced as the Boeing 747-8. The last 747-400s were completed in 2009. , most orders of the 747-8 were for the freighter variant. On February 8, 2010, the 747-8 Freighter made its maiden flight. The first delivery of the 747-8 went to Cargolux in 2011. Th... | Boeing 747 | Wikipedia | 478 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
On July 2, 2020, it was reported that Boeing planned to end 747 production in 2022 upon delivery of the remaining jets on order to UPS and the Volga-Dnepr Group due to low demand. On July 29, 2020, Boeing confirmed that the final 747 would be delivered in 2022 as a result of "current market dynamics and outlook" stemmi... | Boeing 747 | Wikipedia | 448 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The 747 has redundant structures along with four redundant hydraulic systems and four main landing gears each with four wheels; these provide a good spread of support on the ground and safety in case of tire blow-outs. The main gear are redundant so that landing can be performed on two opposing landing gears if the oth... | Boeing 747 | Wikipedia | 337 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The recession of 1969–1970, despite having been characterized as relatively mild, greatly affected Boeing. For the year and a half after September 1970, it only sold two 747s in the world, both to Irish flag carrier Aer Lingus.
No 747s were sold to any American carrier for almost three years. When economic problems in ... | Boeing 747 | Wikipedia | 428 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The first 747-100s were built with six upper deck windows (three per side) to accommodate upstairs lounge areas. Later, as airlines began to use the upper deck for premium passenger seating instead of lounge space, Boeing offered an upper deck with ten windows on either side as an option. Some early -100s were retrofit... | Boeing 747 | Wikipedia | 480 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Following the -100SR, Boeing produced the -100BSR, a 747SR variant with increased takeoff weight capability. Debuting in 1978, the -100BSR also incorporated structural modifications for a high cycle-to-flying hour ratio; a related standard -100B model debuted in 1979. The -100BSR first flew on November 3, 1978, with fi... | Boeing 747 | Wikipedia | 512 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The development of the 747SP stemmed from a joint request between Pan American World Airways and Iran Air, who were looking for a high-capacity airliner with enough range to cover Pan Am's New York–Middle Eastern routes and Iran Air's planned Tehran–New York route. The Tehran–New York route, when launched, was the long... | Boeing 747 | Wikipedia | 496 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The 747-200B was the basic passenger version, with increased fuel capacity and more powerful engines; it entered service in February 1971. In its first three years of production, the -200 was equipped with Pratt & Whitney JT9D-7 engines (initially the only engine available). Range with a full passenger load started at ... | Boeing 747 | Wikipedia | 483 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
A total of 393 of the 747-200 versions had been built when production ended in 1991. Of these, 225 were -200B, 73 were -200F, 13 were -200C, 78 were -200M, and 4 were military. Iran Air retired the last passenger in May 2016, 36 years after it was delivered. , five 747-200s remain in service as freighters.
747-300
... | Boeing 747 | Wikipedia | 324 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Swissair placed the first order for the on June 11, 1980. The variant revived the 747-300 designation, which had been previously used on a design study that did not reach production. The 747-300 first flew on October 5, 1982, and the type's first delivery went to Swissair on March 23, 1983. In 1982, its unit cost was ... | Boeing 747 | Wikipedia | 468 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The 747-400 is an improved model with increased range. It has wingtip extensions of and winglets of , which improve the type's fuel efficiency by four percent compared to previous 747 versions. The 747-400 introduced a new glass cockpit designed for a flight crew of two instead of three, with a reduction in the number... | Boeing 747 | Wikipedia | 473 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
In March 2007, Boeing announced that it had no plans to produce further passenger versions of the -400. However, orders for 36 -400F and -400ERF freighters were already in place at the time of the announcement. The last passenger version of the 747-400 was delivered in April 2005 to China Airlines. Some of the last bui... | Boeing 747 | Wikipedia | 417 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The 747-8 Freighter, or 747-8F, has 16% more payload capacity than its predecessor, allowing it to carry seven more standard air cargo containers, with a maximum payload capacity of of cargo. As on previous 747 freighters, the 747-8F features a flip up nose-door, a side-door on the main deck, and a side-door on the lo... | Boeing 747 | Wikipedia | 347 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
VC-25 – This aircraft is the U.S. Air Force very important person (VIP) version of the 747-200B. The U.S. Air Force operates two of them in VIP configuration as the VC-25A. Tail numbers 28000 and 29000 are popularly known as Air Force One, which is technically the air-traffic call sign for any United States Air Force a... | Boeing 747 | Wikipedia | 454 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
KC-25/33 – A proposed 747-200F was also adapted as an aerial refueling tanker and was bid against the DC-10-30 during the 1970s Advanced Cargo Transport Aircraft (ACTA) program that produced the KC-10 Extender. Before the 1979 Iranian Revolution, Iran bought four 747-100 aircraft with air-refueling boom conversions to ... | Boeing 747 | Wikipedia | 497 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Stratospheric Observatory for Infrared Astronomy (SOFIA) – A former Pan Am Boeing 747SP modified to carry a large infrared-sensitive telescope, in a joint venture of NASA and DLR. High altitudes are needed for infrared astronomy, to rise above infrared-absorbing water vapor in the atmosphere.
A number of other governm... | Boeing 747 | Wikipedia | 123 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Proposed variants
Boeing has studied a number of 747 variants that have not gone beyond the concept stage.
747 trijet
During the late 1960s and early 1970s, Boeing studied the development of a shorter 747 with three engines, to compete with the smaller Lockheed L-1011 TriStar and McDonnell Douglas DC-10. The center ... | Boeing 747 | Wikipedia | 487 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The 747-500X concept featured a fuselage length increased by to , and the aircraft was to carry 462 passengers over a range up to , with a gross weight of over 1.0 Mlb (450 tonnes). The 747-600X concept featured a greater stretch to with seating for 548 passengers, a range of up to , and a gross weight of 1.2 Mlb (54... | Boeing 747 | Wikipedia | 454 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
747-400XQLR
After the end of the 747X program, Boeing continued to study improvements that could be made to the 747. The 747-400XQLR (Quiet Long Range) was meant to have an increased range of , with improvements to boost efficiency and reduce noise. Improvements studied included raked wingtips similar to those used on... | Boeing 747 | Wikipedia | 459 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
, the 747 has been involved in 173 aviation accidents and incidents, including 64 hull losses (52 in-flight accidents), causing fatalities. There have been several hijackings of Boeing 747s, such as Pan Am Flight 73, a 747-100 hijacked by four terrorists, causing 20 deaths. The 747 also fell victim to three mid-air bo... | Boeing 747 | Wikipedia | 308 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The lack of adequate warning systems combined with flight crew error led to a preventable crash of Lufthansa Flight 540 in November 1974, which was the first fatal crash of a 747, while an instrument malfunction leading to disorientation of the crew led to the crash of Air India Flight 855 on New Years Day in 1978. TWA... | Boeing 747 | Wikipedia | 286 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Other incidents did not result in any hull losses, but the planes suffered certain damages and were put back into service after repair. On July 30, 1971, Pan Am Flight 845 struck approach lighting system structures while taking off from San Francisco for Tokyo, Japan; the plane dumped fuel and landed back. The cause wa... | Boeing 747 | Wikipedia | 257 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
As increasing numbers of "classic" 747-100 and series aircraft have been retired, some have been used for other uses such as museum displays. Some older 747-300s and 747-400s were later added to museum collections.
20235/001 – 747-121 registration N7470 City of Everett, the first 747 and prototype, is at the Museum o... | Boeing 747 | Wikipedia | 488 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
21549/336 – 747-206B registration PH-BUK at the Aviodrome, Lelystad, Netherlands.
21588/342 – 747-230B(M) registration D-ABYM preserved at Technik Museum Speyer, Germany.
21650/354 – 747-2R7F/SCD registration G-MKGA preserved at Cotswold Airport, UK as an event space.
22145/410 – 747-238B registration VH-EBQ at the ... | Boeing 747 | Wikipedia | 384 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Other uses
Upon its retirement from service, the 747 which was number two in the production line was dismantled and shipped to Hopyeong, Namyangju, Gyeonggi-do, South Korea where it was re-assembled, repainted in a livery similar to that of Air Force One and converted into a restaurant. Originally flown commercially ... | Boeing 747 | Wikipedia | 490 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
A black hole is a region of spacetime wherein gravity is so strong that no matter or electromagnetic energy (e.g. light) can escape it. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizo... | Black hole | Wikipedia | 440 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
The presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Any matter that falls toward a black hole can form an external accretion disk heated by friction, forming quasars, some of the brightest objects in the universe. Stars passing... | Black hole | Wikipedia | 469 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
In 1915, Albert Einstein developed his theory of general relativity, having earlier shown that gravity does influence light's motion. Only a few months later, Karl Schwarzschild found a solution to the Einstein field equations that describes the gravitational field of a point mass and a spherical mass. A few months aft... | Black hole | Wikipedia | 465 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
In 1939, Robert Oppenheimer and others predicted that neutron stars above another limit, the Tolman–Oppenheimer–Volkoff limit, would collapse further for the reasons presented by Chandrasekhar, and concluded that no law of physics was likely to intervene and stop at least some stars from collapsing to black holes. Thei... | Black hole | Wikipedia | 478 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
These results came at the beginning of the golden age of general relativity, which was marked by general relativity and black holes becoming mainstream subjects of research. This process was helped by the discovery of pulsars by Jocelyn Bell Burnell in 1967, which, by 1969, were shown to be rapidly rotating neutron sta... | Black hole | Wikipedia | 499 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Observation
On 11 February 2016, the LIGO Scientific Collaboration and the Virgo collaboration announced the first direct detection of gravitational waves, representing the first observation of a black hole merger. On 10 April 2019, the first direct image of a black hole and its vicinity was published, following obser... | Black hole | Wikipedia | 431 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
These properties are special because they are visible from outside a black hole. For example, a charged black hole repels other like charges just like any other charged object. Similarly, the total mass inside a sphere containing a black hole can be found by using the gravitational analogue of Gauss's law (through the ... | Black hole | Wikipedia | 475 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Solutions describing more general black holes also exist. Non-rotating charged black holes are described by the Reissner–Nordström metric, while the Kerr metric describes a non-charged rotating black hole. The most general stationary black hole solution known is the Kerr–Newman metric, which describes a black hole with... | Black hole | Wikipedia | 489 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
As predicted by general relativity, the presence of a mass deforms spacetime in such a way that the paths taken by particles bend towards the mass. At the event horizon of a black hole, this deformation becomes so strong that there are no paths that lead away from the black hole.
To a distant observer, clocks near a b... | Black hole | Wikipedia | 452 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Observers falling into a Schwarzschild black hole (i.e., non-rotating and not charged) cannot avoid being carried into the singularity once they cross the event horizon. They can prolong the experience by accelerating away to slow their descent, but only up to a limit. When they reach the singularity, they are crushed ... | Black hole | Wikipedia | 488 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
While light can still escape from the photon sphere, any light that crosses the photon sphere on an inbound trajectory will be captured by the black hole. Hence any light that reaches an outside observer from the photon sphere must have been emitted by objects between the photon sphere and the event horizon. For a Kerr... | Black hole | Wikipedia | 397 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
In Newtonian gravity, test particles can stably orbit at arbitrary distances from a central object. In general relativity, however, there exists an innermost stable circular orbit (often called the ISCO), for which any infinitesimal inward perturbations to a circular orbit will lead to spiraling into the black hole, an... | Black hole | Wikipedia | 475 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Gravitational collapse occurs when an object's internal pressure is insufficient to resist the object's own gravity. For stars this usually occurs either because a star has too little "fuel" left to maintain its temperature through stellar nucleosynthesis, or because a star that would have been stable receives extra ma... | Black hole | Wikipedia | 446 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
While most of the energy released during gravitational collapse is emitted very quickly, an outside observer does not actually see the end of this process. Even though the collapse takes a finite amount of time from the reference frame of infalling matter, a distant observer would see the infalling material slow and ha... | Black hole | Wikipedia | 512 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
This would put the creation of black holes firmly out of reach of any high-energy process occurring on or near the Earth. However, certain developments in quantum gravity suggest that the minimum black hole mass could be much lower: some braneworld scenarios for example put the boundary as low as . This would make it c... | Black hole | Wikipedia | 505 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
A stellar black hole of has a Hawking temperature of 62 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of... | Black hole | Wikipedia | 483 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Observational evidence
By nature, black holes do not themselves emit any electromagnetic radiation other than the hypothetical Hawking radiation, so astrophysicists searching for black holes must generally rely on indirect observations. For example, a black hole's existence can sometimes be inferred by observing its g... | Black hole | Wikipedia | 410 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
The brightening of this material in the 'bottom' half of the processed EHT image is thought to be caused by Doppler beaming, whereby material approaching the viewer at relativistic speeds is perceived as brighter than material moving away. In the case of a black hole, this phenomenon implies that the visible material i... | Black hole | Wikipedia | 482 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
More importantly, the signal observed by LIGO also included the start of the post-merger ringdown, the signal produced as the newly formed compact object settles down to a stationary state. Arguably, the ringdown is the most direct way of observing a black hole. From the LIGO signal, it is possible to extract the frequ... | Black hole | Wikipedia | 484 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Due to conservation of angular momentum, gas falling into the gravitational well created by a massive object will typically form a disk-like structure around the object. Artists' impressions such as the accompanying representation of a black hole with corona commonly depict the black hole as if it were a flat-space bod... | Black hole | Wikipedia | 494 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
In November 2011 the first direct observation of a quasar accretion disk around a supermassive black hole was reported.
X-ray binaries
X-ray binaries are binary star systems that emit a majority of their radiation in the X-ray part of the spectrum. These X-ray emissions are generally thought to result when one of th... | Black hole | Wikipedia | 426 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
The X-ray emissions from accretion disks sometimes flicker at certain frequencies. These signals are called quasi-periodic oscillations and are thought to be caused by material moving along the inner edge of the accretion disk (the innermost stable circular orbit). As such their frequency is linked to the mass of the c... | Black hole | Wikipedia | 402 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Microlensing
Another way the black hole nature of an object may be tested is through observation of effects caused by a strong gravitational field in their vicinity. One such effect is gravitational lensing: The deformation of spacetime around a massive object causes light rays to be deflected, such as light passing t... | Black hole | Wikipedia | 481 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
The evidence for the existence of stellar and supermassive black holes implies that in order for black holes not to form, general relativity must fail as a theory of gravity, perhaps due to the onset of quantum mechanical corrections. A much anticipated feature of a theory of quantum gravity is that it will not feature... | Black hole | Wikipedia | 362 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
The link with the laws of thermodynamics was further strengthened by Hawking's discovery in 1974 that quantum field theory predicts that a black hole radiates blackbody radiation at a constant temperature. This seemingly causes a violation of the second law of black hole mechanics, since the radiation will carry away e... | Black hole | Wikipedia | 415 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Because a black hole has only a few internal parameters, most of the information about the matter that went into forming the black hole is lost. Regardless of the type of matter which goes into a black hole, it appears that only information concerning the total mass, charge, and angular momentum are conserved. As long ... | Black hole | Wikipedia | 437 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
This seemingly creates a paradox: a principle called "monogamy of entanglement" requires that, like any quantum system, the outgoing particle cannot be fully entangled with two other systems at the same time; yet here the outgoing particle appears to be entangled both with the infalling particle and, independently, wit... | Black hole | Wikipedia | 210 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an a... | Beta decay | Wikipedia | 494 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Beta decay conserves a quantum number known as the lepton number, or the number of electrons and their associated neutrinos (other leptons are the muon and tau particles). These particles have lepton number +1, while their antiparticles have lepton number −1. Since a proton or neutron has lepton number zero, β+ decay (... | Beta decay | Wikipedia | 467 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Discovery and initial characterization
Radioactivity was discovered in 1896 by Henri Becquerel in uranium, and subsequently observed by Marie and Pierre Curie in thorium and in the new elements polonium and radium. In 1899, Ernest Rutherford separated radioactive emissions into two types: alpha and beta (now beta minus... | Beta decay | Wikipedia | 321 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
The study of beta decay provided the first physical evidence for the existence of the neutrino. In both alpha and gamma decay, the resulting alpha or gamma particle has a narrow energy distribution, since the particle carries the energy from the difference between the initial and final nuclear states. However, the kine... | Beta decay | Wikipedia | 509 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
In a famous letter written in 1930, Wolfgang Pauli attempted to resolve the beta-particle energy conundrum by suggesting that, in addition to electrons and protons, atomic nuclei also contained an extremely light neutral particle, which he called the neutron. He suggested that this "neutron" was also emitted during bet... | Beta decay | Wikipedia | 487 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Non-conservation of parity
In 1956, Tsung-Dao Lee and Chen Ning Yang noticed that there was no evidence that parity was conserved in weak interactions, and so they postulated that this symmetry may not be preserved by the weak force. They sketched the design for an experiment for testing conservation of parity in the l... | Beta decay | Wikipedia | 428 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
However, decay cannot occur in an isolated proton because it requires energy, due to the mass of the neutron being greater than the mass of the proton. decay can only happen inside nuclei when the daughter nucleus has a greater binding energy (and therefore a lower total energy) than the mother nucleus. The differenc... | Beta decay | Wikipedia | 456 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
:{|border="0"
|- style="height:2em;"
| || || ||→ || ||+ || ||+ || ||(beta minus decay)
|- style="height:2em;"
| || || ||→ || ||+ || ||+ || ||(beta plus decay)
|- style="height:2em;"
| ||+ || ||→ || ||+ || || || ||(electron capture)
|}
Beta decay does not change the number () of nucleons in the nucleus, but changes onl... | Beta decay | Wikipedia | 294 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Competition of beta decay types
Usually unstable nuclides are clearly either "neutron rich" or "proton rich", with the former undergoing beta decay and the latter undergoing electron capture (or more rarely, due to the higher energy requirements, positron decay). However, in a few cases of odd-proton, odd-neutron radio... | Beta decay | Wikipedia | 487 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
The electron and antineutrino are fermions, spin-1/2 objects, therefore they may couple to total (parallel) or (anti-parallel).
For forbidden decays, orbital angular momentum must also be taken into consideration.
Energy release
The value is defined as the total energy released in a given nuclear decay. In beta de... | Beta decay | Wikipedia | 508 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Because the reaction will proceed only when the value is positive, β+ decay can occur when the mass of atom exceeds that of by at least twice the mass of the electron.
Electron capture
The analogous calculation for electron capture must take into account the binding energy of the electrons. This is because the atom... | Beta decay | Wikipedia | 444 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
A Kurie plot (also known as a Fermi–Kurie plot) is a graph used in studying beta decay developed by Franz N. D. Kurie, in which the square root of the number of beta particles whose momenta (or energy) lie within a certain narrow range, divided by the Fermi function, is plotted against beta-particle energy. It is a str... | Beta decay | Wikipedia | 445 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Fermi transitions
A Fermi transition is a beta decay in which the spins of the emitted electron (positron) and anti-neutrino (neutrino) couple to total spin , leading to an angular momentum change between the initial and final states of the nucleus (assuming an allowed transition). In the non-relativistic limit, the n... | Beta decay | Wikipedia | 453 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
For fully ionized atoms (bare nuclei), it is possible in likewise manner for electrons to fail to escape the atom, and to be emitted from the nucleus into low-lying atomic bound states (orbitals). This cannot occur for neutral atoms with low-lying bound states which are already filled by electrons.
Bound-state β decay... | Beta decay | Wikipedia | 488 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Some nuclei can undergo double beta decay (2β) where the charge of the nucleus changes by two units. Double beta decay is difficult to study, as it has an extremely long half-life. In nuclei for which both β decay and 2β are possible, the rarer 2β process is effectively impossible to observe. However, in nuclei where β... | Beta decay | Wikipedia | 223 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyletic lineage within the superfamily Apoidea. They are currently considered a clade, called Anthophila. There are ... | Bee | Wikipedia | 457 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Evolution
The immediate ancestors of bees were stinging wasps in the family Crabronidae, which were predators of other insects. The switch from insect prey to pollen may have resulted from the consumption of prey insects which were flower visitors and were partially covered with pollen when they were fed to the wasp l... | Bee | Wikipedia | 422 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Following the K-Pg extinction, surviving bee lineages continued to spread into the Northern Hemisphere, colonizing Europe from Africa by the Paleocene, and then spreading east to Asia. This was facilitated by the warming climate around the same time, allowing bees to move to higher latitudes following the spread of tro... | Bee | Wikipedia | 452 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
The earliest animal-pollinated flowers were shallow, cup-shaped blooms pollinated by insects such as beetles, so the syndrome of insect pollination was well established before the first appearance of bees. The novelty is that bees are specialized as pollination agents, with behavioral and physical modifications that sp... | Bee | Wikipedia | 507 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Bees differ from closely related groups such as wasps by having branched or plume-like setae (hairs), combs on the forelimbs for cleaning their antennae, small anatomical differences in limb structure, and the venation of the hind wings; and in females, by having the seventh dorsal abdominal plate divided into two half... | Bee | Wikipedia | 468 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
In haplodiploid species, females develop from fertilized eggs and males from unfertilized eggs. Because a male is haploid (has only one copy of each gene), his daughters (which are diploid, with two copies of each gene) share 100% of his genes and 50% of their mother's. Therefore, they share 75% of their genes with eac... | Bee | Wikipedia | 338 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Bees may be solitary or may live in various types of communities. Eusociality appears to have originated from at least three independent origins in halictid bees. The most advanced of these are species with eusocial colonies; these are characterized by cooperative brood care and a division of labour into reproductive a... | Bee | Wikipedia | 457 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
There are many more species of primitively eusocial than highly eusocial bees, but they have been studied less often. Most are in the family Halictidae, or "sweat bees". Colonies are typically small, with a dozen or fewer workers, on average. Queens and workers differ only in size, if at all. Most species have a single... | Bee | Wikipedia | 460 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Most solitary bees are fossorial, digging nests in the ground in a variety of soil textures and conditions, while others create nests in hollow reeds or twigs, or holes in wood. The female typically creates a compartment (a "cell") with an egg and some provisions for the resulting larva, then seals it off. A nest may c... | Bee | Wikipedia | 322 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
The life cycle of a bee, be it a solitary or social species, involves the laying of an egg, the development through several moults of a legless larva, a pupation stage during which the insect undergoes complete metamorphosis, followed by the emergence of a winged adult. The number of eggs laid by a female during her li... | Bee | Wikipedia | 342 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
In most species, larvae are whitish grubs, roughly oval and bluntly-pointed at both ends. They have 15 segments and spiracles in each segment for breathing. They have no legs but move within the cell, helped by tubercles on their sides. They have short horns on the head, jaws for chewing food and an appendage on either... | Bee | Wikipedia | 425 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
The ethologist Karl von Frisch studied navigation in the honey bee. He showed that honey bees communicate by the waggle dance, in which a worker indicates the location of a food source to other workers in the hive. He demonstrated that bees can recognize a desired compass direction in three different ways: by the Sun, ... | Bee | Wikipedia | 391 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
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