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Topic Review
Jiles–Atherton Model
The Jiles–Atherton model of magnetic hysteresis was introduced in 1984 by David Jiles and D. L. Atherton. This is one of the most popular models of magnetic hysteresis. Its main advantage is the fact that this model enables connection with physical parameters of the magnetic material. Jiles–Atherton model enables calculation of minor and major hysteresis loops. The original Jiles–Atherton model is suitable only for isotropic materials. However, an extension of this model presented by Ramesh et al. and corrected by Szewczyk enables the modeling of anisotropic magnetic materials.
  • 1.4K
  • 02 Nov 2022
Topic Review
JPL Mars Helicopter Scout
The Mars Helicopter Scout (MHS) is a planned robotic helicopter that will test the technology to scout interesting targets for study on Mars, and help plan the best driving route for future Mars rovers. The small drone helicopter will be deployed in 2021 from the planned Mars 2020 rover. It is expected to fly up to five times during its 30-day test campaign, early in the rover's mission, as it is primarily a technology demonstration. Each flight will take no more than 3 minutes, at altitudes ranging from 3 m to 10 m above the ground, but it could potentially cover a maximum distance of about 600 m (2,000 ft) per flight. It will use autonomous control and communicate with the Mars 2020 rover directly after each landing. If it works as expected, NASA will be able to build on the design for future Mars missions. MiMi Aung is the project lead. Other team members are AeroVironment Inc., NASA Ames Research Center, and NASA Langley Research Center.
  • 313
  • 24 Nov 2022
Topic Review
Jpsi Meson
The J/ψ (J/psi) meson /ˈdʒeɪ ˈsaɪ ˈmiːzɒn/ or psion is a subatomic particle, a flavor-neutral meson consisting of a charm quark and a charm antiquark. Mesons formed by a bound state of a charm quark and a charm anti-quark are generally known as "charmonium". The J/ψ is the most common form of charmonium, due to its spin of 1 and its low rest mass. The J/ψ has a rest mass of 3.0969 GeV/c2, just above that of the ηc (2.9836 GeV/c2), and a mean lifetime of 7.2×10−21 s. This lifetime was about a thousand times longer than expected. Its discovery was made independently by two research groups, one at the Stanford Linear Accelerator Center, headed by Burton Richter, and one at the Brookhaven National Laboratory, headed by Samuel Ting of MIT. They discovered they had actually found the same particle, and both announced their discoveries on 11 November 1974. The importance of this discovery is highlighted by the fact that the subsequent, rapid changes in high-energy physics at the time have become collectively known as the "November Revolution". Richter and Ting were awarded the 1976 Nobel Prize in Physics.
  • 499
  • 29 Nov 2022
Topic Review
Jyotisha
Jyotisha (Sanskrit: ज्योतिष, IAST: Jyotiṣa), now the term for traditional Hindu astrology, historically was the branch of knowledge dedicated to the observation of astronomical bodies in order to keep the right time for the Vedic sacrifices. It is one of the six Vedangas, or ancillary science connected with the Vedas that developed . This field of study was concerned with fixing the days and hours of Vedic rituals. Hindu astrology from the 3rd century BCE was greatly influenced by Greek tradition,. But the concept of Vedanga predates Greek contact, and there have also been later independent developments. Hindu astrology as it stands today is inherently a study of karma, which gives it a very different foundation compared to Greek astrology. In addition to this, the predictive techniques such as Dashas (planetary and sign-based time periods), Vargas (harmonic divisions of the horoscope) are not that evolved in Greek astrology.
  • 872
  • 27 Sep 2022
Topic Review
K-Theory
In string theory, K-theory classification refers to a conjectured application of K-theory (in abstract algebra and algebraic topology) to superstrings, to classify the allowed Ramond–Ramond field strengths as well as the charges of stable D-branes. In condensed matter physics K-theory has also found important applications, specially in the topological classification of topological insulators, superconductors and stable Fermi surfaces ((Kitaev 2009), (Horava 2005)).
  • 412
  • 30 Nov 2022
Topic Review
Kairos
Kairos (καιρός) is an Ancient Greek word meaning the right, critical, or opportune moment. The ancient Greeks had two words for time: chronos (χρόνος) and kairos. The former refers to chronological or sequential time, while the latter signifies a proper or opportune time for action. While chronos is quantitative, kairos has a qualitative, permanent nature. Kairos also means weather in Modern Greek. The plural, καιροί (kairoi (Ancient and Modern Greek)) means the times. Kairos is a term, idea, and practice that has been applied in several fields including classical rhetoric, modern rhetoric, digital media, Christian theology, and science.
  • 2.2K
  • 07 Oct 2022
Topic Review
Kaleidoscope
A kaleidoscope (/kəˈlaɪdəskoʊp/) is an optical instrument with two or more reflecting surfaces (or mirrors) tilted to each other at an angle, so that one or more (parts of) objects on one end of the mirrors are seen as a regular symmetrical pattern when viewed from the other end, due to repeated reflection. The reflectors are usually enclosed in a tube, often containing on one end a cell with loose, colored pieces of glass or other transparent (and/or opaque) materials to be reflected into the viewed pattern. Rotation of the cell causes motion of the materials, resulting in an ever-changing view being presented.
  • 1.7K
  • 04 Nov 2022
Topic Review
Kelvin–Stokes Theorem
The Kelvin–Stokes theorem, named after Lord Kelvin and George Stokes, also known as the Stokes' theorem, the fundamental theorem for curls or simply the curl theorem, is a theorem in vector calculus on [math]\displaystyle{ \mathbb{R}^3 }[/math]. Given a vector field, the theorem relates the integral of the curl of the vector field over some surface, to the line integral of the vector field around the boundary of the surface. If a vector field [math]\displaystyle{ \mathbf{A} = (P(x, y, z), Q(x, y, z), R(x, y, z)) }[/math] is defined in a region with smooth oriented surface [math]\displaystyle{ \Sigma }[/math] and has first order continuous partial derivatives then: where [math]\displaystyle{ \partial \Sigma }[/math] is boundary of region with smooth surface [math]\displaystyle{ \Sigma }[/math]. The above classical Kelvin-Stokes theorem can be stated in one sentence: The line integral of a vector field over a loop is equal to the flux of its curl through the enclosed surface. The Kelvin–Stokes theorem is a special case of the "generalized Stokes' theorem." In particular, a vector field on [math]\displaystyle{ \mathbb{R}^3 }[/math] can be considered as a 1-form in which case its curl is its exterior derivative, a 2-form.
  • 1.6K
  • 02 Nov 2022
Topic Review
Kepler-86
Kepler-86, PH2 or KIC 12735740 (2MASS 19190326+5157453), is a G-type star 1,130 ly (350 pc) distant within the constellation Cygnus. Roughly the size and temperature of the Sun, PH2 gained prominence when it was known to be the host of one of 42 planet candidates detected by the Planet Hunters citizen science project in its second data release. The candidate orbiting around PH2, known as PH2 b, had been determined to have a spurious detection probability of only 0.08%, thus effectively confirming its existence as a planet. Located in its parent star's habitable zone, PH2 b (or Kepler-86b) is a "Jupiter-size" gas giant which may have a natural satellite suitable for hosting life. The report of the confirmed detection of PH2 b was submitted on January 3, 2013. It was discovered by amateur Pole Rafał Herszkowicz using his laptop and access to the Internet project with data from the Kepler space observatory.
  • 413
  • 24 Oct 2022
Topic Review
KIC 8462852
KIC 8462852 (also Tabby's Star or Boyajian's Star) is an F-type main-sequence star located in the constellation Cygnus approximately 1,470 light-years (450 pc) from Earth. Unusual light fluctuations of the star, including up to a 22% dimming in brightness, were discovered by citizen scientists as part of the Planet Hunters project. In September 2015, astronomers and citizen scientists associated with the project posted a preprint of an article describing the data and possible interpretations. The discovery was made from data collected by the Kepler space telescope, which observes changes in the brightness of distant stars to detect exoplanets. Several hypotheses have been proposed to explain the star's large irregular changes in brightness as measured by its light curve, but none to date fully explain all aspects of the curve. One explanation is that an "uneven ring of dust" orbits KIC 8462852. In another explanation, the star's luminosity is modulated by changes in the efficiency of heat transport to its photosphere, so no external obscuration is required. A third hypothesis, based on a lack of observed infrared light, posits a swarm of cold, dusty comet fragments in a highly eccentric orbit, however, the notion that disturbed comets from such a cloud could exist in high enough numbers to obscure 22% of the star's observed luminosity has been doubted. Another hypothesis is that a large number of small masses in "tight formation" are orbiting the star. Furthermore, spectroscopic study of the system has found no evidence for coalescing material or hot close-in dust or circumstellar matter from an evaporating or exploding planet within a few astronomical units of the mature central star. It has also been hypothesized that the changes in brightness could be signs of activity associated with intelligent extraterrestrial life constructing a Dyson swarm. The scientists involved are very skeptical, however, with others describing it as implausible. KIC 8462852 is not the only star that has large irregular dimmings, but all other such stars are young stellar objects called YSO dippers, which have different dimming patterns. An example of such an object is EPIC 204278916. New light fluctuation events of KIC 8462852 began in the middle of May 2017. Except for a period between late-December 2017 and mid-February 2018 when the star was obscured by the Sun, the fluctuations have continued (As of July 2018).
  • 2.2K
  • 15 Nov 2022
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