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The function composition operation satisfies the axioms of a group. It is associative, meaning , and products of more than two permutations are usually written without parentheses. The composition operation also has an identity element (the identity permutation ), and each permutation has an inverse (its inverse func... | Permutation | Wikipedia | 460 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
If M is a finite multiset, then a multiset permutation is an ordered arrangement of elements of M in which each element appears a number of times equal exactly to its multiplicity in M. An anagram of a word having some repeated letters is an example of a multiset permutation. If the multiplicities of the elements of M ... | Permutation | Wikipedia | 446 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
The cycles (including the fixed points) of a permutation of a set with elements partition that set; so the lengths of these cycles form an integer partition of , which is called the cycle type (or sometimes cycle structure or cycle shape) of . There is a "1" in the cycle type for every fixed point of , a "2" for ever... | Permutation | Wikipedia | 470 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
A permutation matrix is an n × n matrix that has exactly one entry 1 in each column and in each row, and all other entries are 0. There are several ways to assign a permutation matrix to a permutation of {1, 2, ..., n}. One natural approach is to define to be the linear transformation of which permutes the standard b... | Permutation | Wikipedia | 488 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
An ascending run of a permutation is a nonempty increasing contiguous subsequence that cannot be extended at either end; it corresponds to a maximal sequence of successive ascents (the latter may be empty: between two successive descents there is still an ascending run of length 1). By contrast an increasing subsequenc... | Permutation | Wikipedia | 489 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
As a first corollary, the number of n-permutations with exactly k records is equal to the number of n-permutations with exactly k cycles: this last number is the signless Stirling number of the first kind, . Furthermore, Foata's mapping takes an n-permutation with k weak exceedances to an n-permutation with ascents. ... | Permutation | Wikipedia | 291 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
The number of inversions is an important measure for the degree to which the entries of a permutation are out of order; it is the same for σ and for σ−1. To bring a permutation with k inversions into order (that is, transform it into the identity permutation), by successively applying (right-multiplication by) adjacent... | Permutation | Wikipedia | 423 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
One way to represent permutations of n things is by an integer N with 0 ≤ N < n!, provided convenient methods are given to convert between the number and the representation of a permutation as an ordered arrangement (sequence). This gives the most compact representation of arbitrary permutations, and in computing is pa... | Permutation | Wikipedia | 445 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
Both encodings can be visualized by an n by n Rothe diagram (named after Heinrich August Rothe) in which dots at (i,σi) mark the entries of the permutation, and a cross at (i,σj) marks the inversion (i,j); by the definition of inversions a cross appears in any square that comes both before the dot (j,σj) in its column,... | Permutation | Wikipedia | 378 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
Converting successive natural numbers to the factorial number system produces those sequences in lexicographic order (as is the case with any mixed radix number system), and further converting them to permutations preserves the lexicographic ordering, provided the Lehmer code interpretation is used (using inversion tab... | Permutation | Wikipedia | 364 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
An obvious way to generate permutations of n is to generate values for the Lehmer code (possibly using the factorial number system representation of integers up to n!), and convert those into the corresponding permutations. However, the latter step, while straightforward, is hard to implement efficiently, because it re... | Permutation | Wikipedia | 355 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
The basic idea to generate a random permutation is to generate at random one of the n! sequences of integers d1,d2,...,dn satisfying (since d1 is always zero it may be omitted) and to convert it to a permutation through a bijective correspondence. For the latter correspondence one could interpret the (reverse) sequenc... | Permutation | Wikipedia | 495 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
However, Fisher-Yates is not the fastest algorithm for generating a permutation, because Fisher-Yates is essentially a sequential algorithm and "divide and conquer" procedures can achieve the same result in parallel.
Generation in lexicographic order
There are many ways to systematically generate all permutations of a... | Permutation | Wikipedia | 246 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
Find the largest index k such that . If no such index exists, the permutation is the last permutation.
Find the largest index l greater than k such that .
Swap the value of a[k] with that of a[l].
Reverse the sequence from a[k + 1] up to and including the final element a[n].
For example, given the sequence [1, 2, 3... | Permutation | Wikipedia | 380 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
An alternative to the above algorithm, the Steinhaus–Johnson–Trotter algorithm, generates an ordering on all the permutations of a given sequence with the property that any two consecutive permutations in its output differ by swapping two adjacent values. This ordering on the permutations was known to 17th-century Engl... | Permutation | Wikipedia | 456 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
Generation of permutations in nested swap steps
Explicit sequence of swaps (transpositions, 2-cycles ), is described here, each swap applied (on the left) to the previous chain providing a new permutation, such that all the permutations can be retrieved, each only once. This counting/generating procedure has an additio... | Permutation | Wikipedia | 510 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
Because multiplying by swap permutation takes short computing time and every new generated permutation requires only one such swap multiplication, this generation procedure is quite efficient. Moreover as there is a simple formula, having the last permutation in each can save even more time to go directly to a perm... | Permutation | Wikipedia | 184 | 44027 | https://en.wikipedia.org/wiki/Permutation | Mathematics | Discrete mathematics | null |
Solvations describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the solute, including solubility, reactivity, and color, as well as influencing the properties o... | Solvation | Wikipedia | 494 | 44041 | https://en.wikipedia.org/wiki/Solvation | Physical sciences | Mixture | Chemistry |
Which of these forces are at play depends on the molecular structure and properties of the solvent and solute. The similarity or complementary character of these properties between solvent and solute determines how well a solute can be solvated by a particular solvent.
Solvent polarity is the most important factor in ... | Solvation | Wikipedia | 345 | 44041 | https://en.wikipedia.org/wiki/Solvation | Physical sciences | Mixture | Chemistry |
Hydrogen bonding among solvent and solute molecules depends on the ability of each to accept H-bonds, donate H-bonds, or both. Solvents that can donate H-bonds are referred to as protic, while solvents that do not contain a polarized bond to a hydrogen atom and cannot donate a hydrogen bond are called aprotic. H-bond... | Solvation | Wikipedia | 484 | 44041 | https://en.wikipedia.org/wiki/Solvation | Physical sciences | Mixture | Chemistry |
The enthalpy of solution is the solution enthalpy minus the enthalpy of the separate systems, whereas the entropy of solution is the corresponding difference in entropy. The solvation energy (change in Gibbs free energy) is the change in enthalpy minus the product of temperature (in Kelvin) times the change in entropy.... | Solvation | Wikipedia | 473 | 44041 | https://en.wikipedia.org/wiki/Solvation | Physical sciences | Mixture | Chemistry |
In general, thermodynamic analysis of solutions is done by modeling them as reactions. For example, if you add sodium chloride to water, the salt will dissociate into the ions sodium(+aq) and chloride(-aq). The equilibrium constant for this dissociation can be predicted by the change in Gibbs energy of this reaction.
... | Solvation | Wikipedia | 512 | 44041 | https://en.wikipedia.org/wiki/Solvation | Physical sciences | Mixture | Chemistry |
As computer power increased, it became possible to try and incorporate the effects of solvation within a simulation and the simplest way to do this is to surround the molecule being simulated with a "skin" of solvent molecules, akin to simulating the molecule within a drop of solvent if the skin is sufficiently deep. | Solvation | Wikipedia | 61 | 44041 | https://en.wikipedia.org/wiki/Solvation | Physical sciences | Mixture | Chemistry |
Oceanography (), also known as oceanology, sea science, ocean science, and marine science, is the scientific study of the ocean, including its physics, chemistry, biology, and geology.
It is an Earth science, which covers a wide range of topics, including ocean currents, waves, and geophysical fluid dynamics; fluxe... | Oceanography | Wikipedia | 511 | 44044 | https://en.wikipedia.org/wiki/Oceanography | Physical sciences | Oceanography | null |
His credibility rests on being personally involved in the instruction of pilots and senior seafarers from 1527 onwards by Royal appointment, along with his recognized competence as mathematician and astronomer.
The main problem in navigating back from the south of the Canary Islands (or south of Boujdour) by sail alone... | Oceanography | Wikipedia | 348 | 44044 | https://en.wikipedia.org/wiki/Oceanography | Physical sciences | Oceanography | null |
The secrecy involving the Portuguese navigations, with the death penalty for the leaking of maps and routes, concentrated all sensitive records in the Royal Archives, completely destroyed by the Lisbon earthquake of 1775. However, the systematic nature of the Portuguese campaign, mapping the currents and winds of the A... | Oceanography | Wikipedia | 277 | 44044 | https://en.wikipedia.org/wiki/Oceanography | Physical sciences | Oceanography | null |
The documents relating to the supplying of ships, and the ordering of sun declination tables for the southern Atlantic for as early as 1493–1496, all suggest a well-planned and systematic activity happening during the decade long period between Bartolomeu Dias finding the southern tip of Africa, and Gama's departure; a... | Oceanography | Wikipedia | 424 | 44044 | https://en.wikipedia.org/wiki/Oceanography | Physical sciences | Oceanography | null |
Information on the currents of the Pacific Ocean was gathered by explorers of the late 18th century, including James Cook and Louis Antoine de Bougainville. James Rennell wrote the first scientific textbooks on oceanography, detailing the current flows of the Atlantic and Indian oceans. During a voyage around the Cape ... | Oceanography | Wikipedia | 488 | 44044 | https://en.wikipedia.org/wiki/Oceanography | Physical sciences | Oceanography | null |
The seminal event in the founding of the modern science of oceanography was the 1872–1876 Challenger expedition. As the first true oceanographic cruise, this expedition laid the groundwork for an entire academic and research discipline. In response to a recommendation from the Royal Society, the British Government ann... | Oceanography | Wikipedia | 510 | 44044 | https://en.wikipedia.org/wiki/Oceanography | Physical sciences | Oceanography | null |
The first acoustic measurement of sea depth was made in 1914. Between 1925 and 1927 the "Meteor" expedition gathered 70,000 ocean depth measurements using an echo sounder, surveying the Mid-Atlantic Ridge.
In 1934, Easter Ellen Cupp, the first woman to have earned a PhD (at Scripps) in the United States, completed a m... | Oceanography | Wikipedia | 512 | 44044 | https://en.wikipedia.org/wiki/Oceanography | Physical sciences | Oceanography | null |
From the 1970s, there has been much emphasis on the application of large scale computers to oceanography to allow numerical predictions of ocean conditions and as a part of overall environmental change prediction. Early techniques included analog computers (such as the Ishiguro Storm Surge Computer) generally now repla... | Oceanography | Wikipedia | 401 | 44044 | https://en.wikipedia.org/wiki/Oceanography | Physical sciences | Oceanography | null |
Ocean acidification describes the decrease in ocean pH that is caused by anthropogenic carbon dioxide () emissions into the atmosphere. Seawater is slightly alkaline and had a preindustrial pH of about 8.2. More recently, anthropogenic activities have steadily increased the carbon dioxide content of the atmosphere; abo... | Oceanography | Wikipedia | 416 | 44044 | https://en.wikipedia.org/wiki/Oceanography | Physical sciences | Oceanography | null |
Since the early ocean expeditions in oceanography, a major interest was the study of ocean currents and temperature measurements. The tides, the Coriolis effect, changes in direction and strength of wind, salinity, and temperature are the main factors determining ocean currents. The thermohaline circulation (THC) (ther... | Oceanography | Wikipedia | 321 | 44044 | https://en.wikipedia.org/wiki/Oceanography | Physical sciences | Oceanography | null |
The earliest international organizations of oceanography were founded at the turn of the 20th century, starting with the International Council for the Exploration of the Sea created in 1902, followed in 1919 by the Mediterranean Science Commission. Marine research institutes were already in existence, starting with the... | Oceanography | Wikipedia | 269 | 44044 | https://en.wikipedia.org/wiki/Oceanography | Physical sciences | Oceanography | null |
Galactic astronomy is the study of the Milky Way galaxy and all its contents. This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies.
Galactic astronomy should not be confused with galaxy formation and evolution, which is the general study of g... | Galactic astronomy | Wikipedia | 420 | 44057 | https://en.wikipedia.org/wiki/Galactic%20astronomy | Physical sciences | Basics_2 | Astronomy |
In physical cosmology, Big Bang nucleosynthesis (also known as primordial nucleosynthesis, and abbreviated as BBN) is the production of nuclei other than those of the lightest isotope of hydrogen (hydrogen-1, 1H, having a single proton as a nucleus) during the early phases of the universe. This type of nucleosynthesis ... | Big Bang nucleosynthesis | Wikipedia | 393 | 44058 | https://en.wikipedia.org/wiki/Big%20Bang%20nucleosynthesis | Physical sciences | Physical cosmology | Astronomy |
The key parameter which allows one to calculate the effects of Big Bang nucleosynthesis is the baryon/photon number ratio, which is a small number of order 6 × 10−10. This parameter corresponds to the baryon density and controls the rate at which nucleons collide and react; from this it is possible to calculate element... | Big Bang nucleosynthesis | Wikipedia | 478 | 44058 | https://en.wikipedia.org/wiki/Big%20Bang%20nucleosynthesis | Physical sciences | Physical cosmology | Astronomy |
At times much earlier than 1 sec, these reactions were fast and maintained the n/p ratio close to 1:1. As the temperature dropped, the equilibrium shifted in favour of protons due to their slightly lower mass, and the n/p ratio smoothly decreased.
These reactions continued until the decreasing temperature and density... | Big Bang nucleosynthesis | Wikipedia | 479 | 44058 | https://en.wikipedia.org/wiki/Big%20Bang%20nucleosynthesis | Physical sciences | Physical cosmology | Astronomy |
Big Bang nucleosynthesis began roughly about 20 seconds after the big bang, when the universe had cooled sufficiently to allow deuterium nuclei to survive disruption by high-energy photons. (Note that the neutron–proton freeze-out time was earlier). This time is essentially independent of dark matter content, since the... | Big Bang nucleosynthesis | Wikipedia | 461 | 44058 | https://en.wikipedia.org/wiki/Big%20Bang%20nucleosynthesis | Physical sciences | Physical cosmology | Astronomy |
History of theory
The history of Big Bang nucleosynthesis began with the calculations of Ralph Alpher in the 1940s. Alpher published the Alpher–Bethe–Gamow paper that outlined the theory of light-element production in the early universe.
Heavy elements
Big Bang nucleosynthesis produced very few nuclei of elements hea... | Big Bang nucleosynthesis | Wikipedia | 319 | 44058 | https://en.wikipedia.org/wiki/Big%20Bang%20nucleosynthesis | Physical sciences | Physical cosmology | Astronomy |
Big Bang nucleosynthesis predicts a primordial abundance of about 25% helium-4 by mass, irrespective of the initial conditions of the universe. As long as the universe was hot enough for protons and neutrons to transform into each other easily, their ratio, determined solely by their relative masses, was about 1 neutro... | Big Bang nucleosynthesis | Wikipedia | 456 | 44058 | https://en.wikipedia.org/wiki/Big%20Bang%20nucleosynthesis | Physical sciences | Physical cosmology | Astronomy |
Deuterium is in some ways the opposite of helium-4, in that while helium-4 is very stable and difficult to destroy, deuterium is only marginally stable and easy to destroy. The temperatures, time, and densities were sufficient to combine a substantial fraction of the deuterium nuclei to form helium-4 but insufficient t... | Big Bang nucleosynthesis | Wikipedia | 439 | 44058 | https://en.wikipedia.org/wiki/Big%20Bang%20nucleosynthesis | Physical sciences | Physical cosmology | Astronomy |
It is very hard to come up with another process that would produce deuterium other than by nuclear fusion. Such a process would require that the temperature be hot enough to produce deuterium, but not hot enough to produce helium-4, and that this process should immediately cool to non-nuclear temperatures after no more... | Big Bang nucleosynthesis | Wikipedia | 393 | 44058 | https://en.wikipedia.org/wiki/Big%20Bang%20nucleosynthesis | Physical sciences | Physical cosmology | Astronomy |
As noted above, in the standard picture of BBN, all of the light element abundances depend on the amount of ordinary matter (baryons) relative to radiation (photons). Since the universe is presumed to be homogeneous, it has one unique value of the baryon-to-photon ratio. For a long time, this meant that to test BBN the... | Big Bang nucleosynthesis | Wikipedia | 453 | 44058 | https://en.wikipedia.org/wiki/Big%20Bang%20nucleosynthesis | Physical sciences | Physical cosmology | Astronomy |
There have been, and continue to be, various reasons for researching non-standard BBN. The first, which is largely of historical interest, is to resolve inconsistencies between BBN predictions and observations. This has proved to be of limited usefulness in that the inconsistencies were resolved by better observations,... | Big Bang nucleosynthesis | Wikipedia | 200 | 44058 | https://en.wikipedia.org/wiki/Big%20Bang%20nucleosynthesis | Physical sciences | Physical cosmology | Astronomy |
X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. X-ray astron... | X-ray astronomy | Wikipedia | 470 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
In 1927, E.O. Hulburt of the US Naval Research Laboratory and associates Gregory Breit and Merle A. Tuve of the Carnegie Institution of Washington explored the possibility of equipping Robert H. Goddard's rockets to explore the upper atmosphere. "Two years later, he proposed an experimental program in which a rocket mi... | X-ray astronomy | Wikipedia | 366 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
An Aerobee 150 rocket launched on June 19, 1962 (UTC) detected the first X-rays emitted from a source outside our solar system (Scorpius X-1). It is now known that such X-ray sources as Sco X-1 are compact stars, such as neutron stars or black holes. Material falling into a black hole may emit X-rays, but the black hol... | X-ray astronomy | Wikipedia | 355 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
Of interest is the hot ionized medium (HIM) consisting of a coronal cloud ejection from star surfaces at 106-107 K which emits X-rays. The ISM is turbulent and full of structure on all spatial scales. Stars are born deep inside large complexes of molecular clouds, typically a few parsecs in size. During their lives and... | X-ray astronomy | Wikipedia | 410 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
The high-energy focusing telescope (HEFT) is a balloon-borne experiment to image astrophysical sources in the hard X-ray (20–100 keV) band. Its maiden flight took place in May 2005 from Fort Sumner, New Mexico, USA. The angular resolution of HEFT is c. 1.5'. Rather than using a grazing-angle X-ray telescope, HEFT makes... | X-ray astronomy | Wikipedia | 466 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
Satellites are needed because X-rays are absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. X-ray telescopes (XRTs) have varying directionality or imaging ability based on glancing angle reflection rather than refraction or l... | X-ray astronomy | Wikipedia | 340 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
Several types of astrophysical objects emit, fluoresce, or reflect X-rays, from galaxy clusters, through black holes in active galactic nuclei (AGN) to galactic objects such as supernova remnants, stars, and binary stars containing a white dwarf (cataclysmic variable stars and super soft X-ray sources), neutron star or... | X-ray astronomy | Wikipedia | 389 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
The celestial sphere has been divided into 88 constellations. The International Astronomical Union (IAU) constellations are areas of the sky. Each of these contains remarkable X-ray sources. Some of them have been identified from astrophysical modeling to be galaxies or black holes at the centers of galaxies. Some are ... | X-ray astronomy | Wikipedia | 477 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
Usually observational astronomy is considered to occur on Earth's surface (or beneath it in neutrino astronomy). The idea of limiting observation to Earth includes orbiting the Earth. As soon as the observer leaves the cozy confines of Earth, the observer becomes a deep space explorer. Except for Explorer 1 and Explore... | X-ray astronomy | Wikipedia | 511 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
The Ulysses soft X-ray detectors consisted of 2.5-mm thick × 0.5 cm2 area Si surface barrier detectors. A 100 mg/cm2 beryllium foil front window rejected the low energy X-rays and defined a conical FOV of 75° (half-angle). These detectors were passively cooled and operate in the temperature range −35 to −55 °C. This de... | X-ray astronomy | Wikipedia | 425 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
From the observed X-ray spectrum, combined with spectral emission results for other wavelength ranges, an astronomical model addressing the likely source of X-ray emission can be constructed. For example, with Scorpius X-1 the X-ray spectrum steeply drops off as X-ray energy increases up to 20 keV, which is likely for ... | X-ray astronomy | Wikipedia | 408 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
Analytical X-ray astronomy
High-mass X-ray binaries (HMXBs) are composed of OB supergiant companion stars and compact objects, usually neutron stars (NS) or black holes (BH). Supergiant X-ray binaries (SGXBs) are HMXBs in which the compact objects orbit massive companions with orbital periods of a few days (3–15 d), an... | X-ray astronomy | Wikipedia | 481 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
In 1977 Proxima Centauri is discovered to be emitting high-energy radiation in the XUV. In 1978, α Cen was identified as a low-activity coronal source. With the operation of the Einstein observatory, X-ray emission was recognized as a characteristic feature common to a wide range of stars covering essentially the whole... | X-ray astronomy | Wikipedia | 509 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
X-ray emission as an indicator of stellar youth is important for studies of star-forming regions. Most star-forming regions in the Milky Way Galaxy are projected on Galactic-Plane fields with numerous unrelated field stars. It is often impossible to distinguish members of a young stellar cluster from field-star contami... | X-ray astronomy | Wikipedia | 443 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
K giants
The FK Com stars are giants of spectral type K with an unusually rapid rotation and signs of extreme activity. Their X-ray coronae are among the most luminous (LX ≥ 1032 erg·s−1 or 1025 W) and the hottest known with dominant temperatures up to 40 MK. However, the current popular hypothesis involves a merger of... | X-ray astronomy | Wikipedia | 440 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
Collectively, amateur astronomers observe a variety of celestial objects and phenomena sometimes with equipment that they build themselves. The United States Air Force Academy (USAFA) is the home of the US's only undergraduate satellite program, and has and continues to develop the FalconLaunch sounding rockets. In add... | X-ray astronomy | Wikipedia | 440 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
X‐ray source counterparts to stars can be identified by calculating the angular separation between source centroids and the position of the star. The maximum allowable separation is a compromise between a larger value to identify as many real matches as possible and a smaller value to minimize the probability of spurio... | X-ray astronomy | Wikipedia | 421 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
Coronal mass ejection
A coronal mass ejection (CME) is an ejected plasma consisting primarily of electrons and protons (in addition to small quantities of heavier elements such as helium, oxygen, and iron), plus the entraining coronal closed magnetic field regions. Evolution of these closed magnetic structures in respo... | X-ray astronomy | Wikipedia | 404 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
A microquasar is a smaller cousin of a quasar that is a radio emitting X-ray binary, with an often resolvable pair of radio jets.
LSI+61°303 is a periodic, radio-emitting binary system that is also the gamma-ray source, CG135+01.
Observations are revealing a growing number of recurrent X-ray transients, characterized b... | X-ray astronomy | Wikipedia | 216 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
During the solar cycle, as shown in the sequence of images at right, at times the Sun is almost X-ray dark, almost an X-ray variable. Betelgeuse, on the other hand, appears to be always X-ray dark. Hardly any X-rays are emitted by red giants. There is a rather abrupt onset of X-ray emission around spectral type A7-F0, ... | X-ray astronomy | Wikipedia | 421 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
NASA's Swift Gamma-Ray Burst Mission satellite was monitoring Comet Lulin as it closed to 63 Gm of Earth. For the first time, astronomers can see simultaneous UV and X-ray images of a comet. "The solar wind—a fast-moving stream of particles from the sun—interacts with the comet's broader cloud of atoms. This causes the... | X-ray astronomy | Wikipedia | 173 | 44062 | https://en.wikipedia.org/wiki/X-ray%20astronomy | Physical sciences | High-energy astronomy | Astronomy |
Extragalactic astronomy is the branch of astronomy concerned with objects outside the Milky Way galaxy. In other words, it is the study of all astronomical objects which are not covered by galactic astronomy.
The closest objects in extragalactic astronomy include the galaxies of the Local Group, which are close enough... | Extragalactic astronomy | Wikipedia | 412 | 44063 | https://en.wikipedia.org/wiki/Extragalactic%20astronomy | Physical sciences | Basics_2 | Astronomy |
A gyroscope (from Ancient Greek γῦρος gŷros, "round" and σκοπέω skopéō, "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rotation (spin axis) is free to assume any orientation by itself. When rotating, the orientation of this ... | Gyroscope | Wikipedia | 400 | 44125 | https://en.wikipedia.org/wiki/Gyroscope | Technology | Navigation | null |
In the case of a gyroscope with two gimbals, the outer gimbal, which is the gyroscope frame, is mounted so as to pivot about an axis in its own plane determined by the support. This outer gimbal possesses one degree of rotational freedom and its axis possesses none. The second gimbal, inner gimbal, is mounted in the gy... | Gyroscope | Wikipedia | 507 | 44125 | https://en.wikipedia.org/wiki/Gyroscope | Technology | Navigation | null |
Early similar devices
Essentially, a gyroscope is a top combined with a pair of gimbals. Tops were invented in many different civilizations, including classical Greece, Rome, and China. Most of these were not utilized as instruments.
The first known apparatus similar to a gyroscope (the "Whirling Speculum" or "Serson'... | Gyroscope | Wikipedia | 467 | 44125 | https://en.wikipedia.org/wiki/Gyroscope | Technology | Navigation | null |
Circa 1911 the L. T. Hurst Mfg Co of Indianapolis started producing the "Hurst gyroscope" a toy gyroscope with a pull string and pedestal. Manufacture was at some point switched to Chandler Mfg Co (still branded Hurst). The product was later renamed to a “Chandler gyroscope”, presumably because Chandler Mfg Co. took ov... | Gyroscope | Wikipedia | 509 | 44125 | https://en.wikipedia.org/wiki/Gyroscope | Technology | Navigation | null |
Gyroscopic principles
All spinning objects have gyroscopic properties. The main properties that an object can experience in any gyroscopic motion are rigidity in space and precession.
Rigidity in space
Rigidity in space describes the principle that a gyroscope remains in the fixed position on the plane in which it ... | Gyroscope | Wikipedia | 460 | 44125 | https://en.wikipedia.org/wiki/Gyroscope | Technology | Navigation | null |
Unlike a directional gyro or heading indicator, a gyrocompass seeks north. It detects the rotation of the Earth about its axis and seeks the true north, rather than the magnetic north. Gyrocompasses usually have built-in damping to prevent overshoot when re-calibrating from sudden movement.
Accelerometer
By determini... | Gyroscope | Wikipedia | 456 | 44125 | https://en.wikipedia.org/wiki/Gyroscope | Technology | Navigation | null |
In modern times, the gyrostat concept is used in the design of attitude control systems for orbiting spacecraft and satellites. For instance, the Mir space station had three pairs of internally mounted flywheels known as gyrodynes or control moment gyroscopes.
In physics, there are several systems whose dynamical equa... | Gyroscope | Wikipedia | 473 | 44125 | https://en.wikipedia.org/wiki/Gyroscope | Technology | Navigation | null |
DTG
A dynamically tuned gyroscope (DTG) is a rotor suspended by a universal joint with flexure pivots. The flexure spring stiffness is independent of spin rate. However, the dynamic inertia (from the gyroscopic reaction effect) from the gimbal provides negative spring stiffness proportional to the square of the spin s... | Gyroscope | Wikipedia | 475 | 44125 | https://en.wikipedia.org/wiki/Gyroscope | Technology | Navigation | null |
A fiber optic gyroscope also uses the interference of light to detect mechanical rotation. The two-halves of the split beam travel in opposite directions in a coil of fiber optic cable as long as 5 km. Like the ring laser gyroscope, it makes use of the Sagnac effect.
London moment
A London moment gyroscope relies on... | Gyroscope | Wikipedia | 478 | 44125 | https://en.wikipedia.org/wiki/Gyroscope | Technology | Navigation | null |
The main rotor of a helicopter acts like a gyroscope. Its motion is influenced by the principle of gyroscopic precession which is the concept that a force applied to a spinning object will have a maximum reaction approximately 90 degrees later. The reaction may differ from 90 degrees when other stronger forces are in p... | Gyroscope | Wikipedia | 500 | 44125 | https://en.wikipedia.org/wiki/Gyroscope | Technology | Navigation | null |
Cruise ships use gyroscopes to level motion-sensitive devices such as self-leveling pool tables.
An electric powered flywheel gyroscope inserted in a bicycle wheel is sold as an alternative to training wheels. | Gyroscope | Wikipedia | 46 | 44125 | https://en.wikipedia.org/wiki/Gyroscope | Technology | Navigation | null |
The metric system is a system of measurement that standardizes a set of base units and a nomenclature for describing relatively large and small quantities via decimal-based multiplicative unit prefixes. Though the rules governing the metric system have changed over time, the modern definition, the International System ... | Metric system | Wikipedia | 466 | 44142 | https://en.wikipedia.org/wiki/Metric%20system | Physical sciences | Measurement systems | null |
In the SI system and generally in older metric systems, multiples and fractions of a unit can be described via a prefix on a unit name that implies a decimal (base-10), multiplicative factor. The only exceptions are for the SI-accepted units of time (minute and hour) and angle (degree, arcminute, arcsecond) which, base... | Metric system | Wikipedia | 440 | 44142 | https://en.wikipedia.org/wiki/Metric%20system | Physical sciences | Measurement systems | null |
Metric systems have evolved since the 1790s, as science and technology have evolved, in providing a single universal measuring system. Before and in addition to the SI, other metric systems include: the MKS system of units and the MKSA systems, which are the direct forerunners of the SI; the centimetre–gram–second (CGS... | Metric system | Wikipedia | 429 | 44142 | https://en.wikipedia.org/wiki/Metric%20system | Physical sciences | Measurement systems | null |
In 1791 the commission originally defined the metre based on the size of the earth, equal to one ten-millionth of the distance from the equator to the North Pole. In the SI, the standard metre is now defined as exactly of the distance that light travels in a second. The metre can be realised by measuring the length th... | Metric system | Wikipedia | 431 | 44142 | https://en.wikipedia.org/wiki/Metric%20system | Physical sciences | Measurement systems | null |
Decimal ratios
A significant characteristic of the metric system is its use of decimal multiples powers of 10. For example, a length that is significantly longer or shorter than 1 metre can be represented in units that are a power of 10 or 1000 metres. This differs from many older systems in which the ratio of differ... | Metric system | Wikipedia | 479 | 44142 | https://en.wikipedia.org/wiki/Metric%20system | Physical sciences | Measurement systems | null |
The CGS system had two units of energy, the erg that was related to mechanics and the calorie that was related to thermal energy; so only one of them (the erg) could bear a coherent relationship to the base units. Coherence was a design aim of SI, which resulted in only one unit of energy being defined – the joule.
Ra... | Metric system | Wikipedia | 482 | 44142 | https://en.wikipedia.org/wiki/Metric%20system | Physical sciences | Measurement systems | null |
Candela and Watt relationship
Candela is about the luminous intensity of a moderately bright candle, or 1 candle power. A 60 Watt tungsten-filament incandescent light bulb has a luminous intensity of about 800 lumens which is radiated equally in all directions (i.e. 4 steradians), thus is equal to .
Watt, Volt and Amp... | Metric system | Wikipedia | 429 | 44142 | https://en.wikipedia.org/wiki/Metric%20system | Physical sciences | Measurement systems | null |
19th century
In 1832, Gauss used the astronomical second as a base unit in defining the gravitation of the Earth, and together with the milligram and millimetre, this became the first system of mechanical units. He showed that the strength of a magnet could also be quantified in terms of these units, by measuring the ... | Metric system | Wikipedia | 494 | 44142 | https://en.wikipedia.org/wiki/Metric%20system | Physical sciences | Measurement systems | null |
The metre–tonne–second system of units (MTS) was based on the metre, tonne and second – the unit of force was the sthène and the unit of pressure was the pièze. It was invented in France for industrial use and from 1933 to 1955 was used both in France and in the Soviet Union. Gravitational metric systems use the kilogr... | Metric system | Wikipedia | 464 | 44142 | https://en.wikipedia.org/wiki/Metric%20system | Physical sciences | Measurement systems | null |
Today, the International system of units consists of 7 base units and innumerable coherent derived units including 22 with special names. The last new derived unit, the katal for catalytic activity, was added in 1999. All the base units except the second are now defined in terms of exact and invariant constants of phys... | Metric system | Wikipedia | 176 | 44142 | https://en.wikipedia.org/wiki/Metric%20system | Physical sciences | Measurement systems | null |
In physics, a conservative force is a force with the property that the total work done by the force in moving a particle between two points is independent of the path taken. Equivalently, if a particle travels in a closed loop, the total work done (the sum of the force acting along the path multiplied by the displacem... | Conservative force | Wikipedia | 481 | 44158 | https://en.wikipedia.org/wiki/Conservative%20force | Physical sciences | Classical mechanics | Physics |
For non-conservative forces, the mechanical energy that is lost (not conserved) has to go somewhere else, by conservation of energy. Usually the energy is turned into heat, for example the heat generated by friction. In addition to heat, friction also often produces some sound energy. The water drag on a moving boat co... | Conservative force | Wikipedia | 495 | 44158 | https://en.wikipedia.org/wiki/Conservative%20force | Physical sciences | Classical mechanics | Physics |
Many forces (particularly those that depend on velocity) are not force fields. In these cases, the above three conditions are not mathematically equivalent. For example, the magnetic force satisfies condition 2 (since the work done by a magnetic field on a charged particle is always zero), but does not satisfy conditio... | Conservative force | Wikipedia | 352 | 44158 | https://en.wikipedia.org/wiki/Conservative%20force | Physical sciences | Classical mechanics | Physics |
Ozone depletion consists of two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere, and a much larger springtime decrease in stratospheric ozone (the ozone layer) around Earth's polar regions. The latter phenomenon is referred to as t... | Ozone depletion | Wikipedia | 442 | 44183 | https://en.wikipedia.org/wiki/Ozone%20depletion | Physical sciences | Atmosphere | null |
The ban came into effect in 1989. Ozone levels stabilized by the mid-1990s and began to recover in the 2000s, as the shifting of the jet stream in the southern hemisphere towards the south pole has stopped and might even be reversing. Recovery was projected to continue over the next century, with the ozone hole expecte... | Ozone depletion | Wikipedia | 457 | 44183 | https://en.wikipedia.org/wiki/Ozone%20depletion | Physical sciences | Atmosphere | null |
While all of the relevant radicals have both natural and man-made sources, human activity has impacted some more than others. As of 2020, most of the OH· and NO· in the stratosphere is naturally occurring, but human activity has drastically increased the levels of chlorine and bromine. These elements are found in stabl... | Ozone depletion | Wikipedia | 365 | 44183 | https://en.wikipedia.org/wiki/Ozone%20depletion | Physical sciences | Atmosphere | null |
A single chlorine atom would continuously destroy ozone (thus a catalyst) for up to two years (the time scale for transport back down to the troposphere) except for reactions that remove it from this cycle by forming reservoir species such as hydrogen chloride (HCl) and chlorine nitrate (). Bromine is even more efficie... | Ozone depletion | Wikipedia | 487 | 44183 | https://en.wikipedia.org/wiki/Ozone%20depletion | Physical sciences | Atmosphere | null |
The amount lost is more variable year-to-year in the Arctic than in the Antarctic. The greatest Arctic declines are in the winter and spring, reaching up to 30 percent when the stratosphere is coldest.
Reactions that take place on polar stratospheric clouds (PSCs) play an important role in enhancing ozone depletion. P... | Ozone depletion | Wikipedia | 473 | 44183 | https://en.wikipedia.org/wiki/Ozone%20depletion | Physical sciences | Atmosphere | null |
CFCs and related compounds
Chlorofluorocarbons (CFCs) and other halogenated ozone-depleting substances (ODS) are mainly responsible for man-made chemical ozone depletion. The total amount of effective halogens (chlorine and bromine) in the stratosphere can be calculated and are known as the equivalent effective strato... | Ozone depletion | Wikipedia | 507 | 44183 | https://en.wikipedia.org/wiki/Ozone%20depletion | Physical sciences | Atmosphere | null |
Aluminum oxide
Satellites burning up upon re-entry into Earth's atmosphere produce aluminum oxide (Al2O3) nanoparticles that endure in the atmosphere for decades. Estimates for 2022 alone were ~17 metric tons (~30kg of nanoparticles per ~250kg satellite). Increasing populations of satellite constellations can eventuall... | Ozone depletion | Wikipedia | 506 | 44183 | https://en.wikipedia.org/wiki/Ozone%20depletion | Physical sciences | Atmosphere | null |
The photochemical processes involved are complex but well understood. The key observation is that, ordinarily, most of the chlorine in the stratosphere resides in "reservoir" compounds, primarily chlorine nitrate () as well as stable end products such as HCl. The formation of end products essentially removes Cl from th... | Ozone depletion | Wikipedia | 368 | 44183 | https://en.wikipedia.org/wiki/Ozone%20depletion | Physical sciences | Atmosphere | null |
Effects
Since the ozone layer absorbs UVB ultraviolet light from the sun, ozone layer depletion increases surface UVB levels (all else equal), which could lead to damage, including an increase in skin cancer. This was the reason for the Montreal Protocol. Although decreases in stratospheric ozone are well-tied to CFCs... | Ozone depletion | Wikipedia | 393 | 44183 | https://en.wikipedia.org/wiki/Ozone%20depletion | Physical sciences | Atmosphere | null |
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