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Topic Review
Former Constellation
Former constellations are old historical Western constellations that for various reasons are no longer widely recognised or are not officially recognised by the International Astronomical Union (IAU). Prior to 1930, many of these defunct constellations were traditional in one or more countries or cultures. Some only lasted decades but others were referred to over many centuries. All are now recognised only for having classical or historical value. Many former constellations had complex Latinised names after objects, people, or mythological or zoological creatures. Others with unwieldy names were shortened for convenience. For example, Scutum Sobiescianum was reduced to Scutum, Mons Mensae to Mensa, and Apparatus Sculptoris to Sculptor. Some of the Northern Sky's former constellations were placed in the less populated regions between the traditional brighter constellations just to fill gaps. In the Southern Sky, new constellations were often created from about the 15th century by voyagers who began journeying south of the Equator. European countries like England, France, the Netherlands, German or Italian states, etc., often supported and popularised their own constellation outlines. In some cases, different constellations occupied overlapping areas and included the same stars. These former constellations are often found in older books, star charts, or star catalogues. The 88 modern constellation names and boundaries were standardised by Eugene Delporte for the IAU in 1930, under an international agreement, removing any possible astronomical ambiguities between astronomers from different countries. Nearly all former or defunct constellations differ in their designated boundaries in as much as they have outlines that do not follow the exact lines of right ascension and declination.
  • 830
  • 05 Nov 2022
Topic Review
Aether Drag Hypothesis
In the 19th century, the theory of the luminiferous aether as the hypothetical medium for the propagation of light was widely discussed. An important part of this discussion was the question concerning the state of motion of Earth with respect to this medium. The aether drag hypothesis dealt with the question of whether or not the luminiferous aether is dragged by or entrained within moving matter. According to the first variant no relative motion exists between Earth and aether; according to the second one, relative motion exists and thus the speed of light should depend on the speed of this motion ("aether wind"), which should be measurable by instruments at rest on Earth's surface. Specific aether models were invented by Augustin-Jean Fresnel who in 1818 proposed that the aether is partially entrained by matter. The other one was proposed by George Stokes in 1845, in which the aether is completely entrained within or in the vicinity of matter. While Fresnel's almost stationary theory was apparently confirmed by the Fizeau experiment (1851), Stokes' theory was apparently confirmed by the Michelson–Morley experiment (1881, 1887). This contradictory situation was resolved by the works of Hendrik Antoon Lorentz (1895, 1904) whose Lorentz ether theory banished any form of aether dragging, and finally with the work of Albert Einstein (1905) whose theory of special relativity does not contain the aether as a mechanical medium at all.
  • 1.2K
  • 04 Nov 2022
Topic Review
KinITC
The method kinITC for kinetic Isothermal Titration Calorimetry is an extension of the classical ITC technique in view of obtaining kinetic information in addition to thermodynamic information. It has been described in full in, and in a simplified and less general form in.
  • 397
  • 04 Nov 2022
Topic Review
Types of Snow
Types of snow can be designated by the shape of its flakes, description of how it is falling, and by how it collects on the ground. A blizzard and snow storm indicate heavy snowfalls over a large area, snow squalls give heavy snowfalls over narrow bands, while flurries are used for the lightest snowfall. Types which fall in the form of a ball, rather than a flake, are known as graupel, with sleet and snow grains as types of graupel. Once on the ground, snow can be categorized as powdery when fluffy, granular when it begins the cycle of melting and refreezing, and crud or eventually ice once it packs down into a dense drift after multiple melting and refreezing cycles. When powdering, snow drifts with the wind or ground blizzard, sometimes to the depth of several metres. After attaching to hillsides, blown snow can evolve into a snow slab, which is an avalanche hazard on steep slopes.
  • 2.8K
  • 04 Nov 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
Direct Methods (Electron Microscopy)
In crystallography, direct methods is a set of techniques used for structure determination using diffraction data and a priori information. It is a solution to the crystallographic phase problem, where phase information is lost during a diffraction measurement. Direct methods provides a method of estimating the phase information by establishing statistical relationships between the recorded amplitude information and phases of strong reflections.
  • 322
  • 04 Nov 2022
Topic Review
Spatial Memory
In cognitive psychology and neuroscience, spatial memory is a form of memory responsible for the recording of information about one's environment and spatial orientation. For example, a person's spatial memory is required in order to navigate around a familiar city, just as a rat's spatial memory is needed to learn the location of food at the end of a maze. It is often argued that in both humans and animals, spatial memories are summarized as a cognitive map. Spatial memory has representations within working, short-term memory and long-term memory. Research indicates that there are specific areas of the brain associated with spatial memory. Many methods are used for measuring spatial memory in children, adults, and animals.
  • 2.9K
  • 04 Nov 2022
Topic Review
Working Fluids
Heat engines, refrigeration cycles and heat pumps usually involve a fluid to and from which heat is transferred while undergoing a thermodynamic cycle. This fluid is called the working fluid. Refrigeration and heat pump technologies often refer to working fluids as refrigerants. Most thermodynamic cycles make use of the latent heat (adventages of phase change) of the working fluid. In case of other cycles the working fluid remains in gaseous phase while undergoing all the processes of the cycle. When it comes to heat engines, working fluid generally undergoes a combustion process as well, for example in internal combustion engines or gas turbines. There are also technologies in heat pump and refrigeration, where working fluid does not change phase, such as reverse Brayton or Stirling cycle. This article summarises the main critera of selecting working fluids for a thermodynamic cycle, such as heat engines including low grade heat recovery using Organic Rankine Cycle (ORC) for geothermal energy, waste heat, thermal solar energy or biomass and heat pumps and refrigeration cycles. The article addresses how working fluids affect technological applications, where the working fluid undergoes a phase transition and does not remain in its original (mainly gaseous) phase during all the processes of the thermodynamic cycle. Finding the optimal working fluid for a given purpose – which is essential to achieve higher energy efficiency in the energy conversion systems – has great impact on the technology, namely it does not just influence operational variables of the cycle but also alters the layout and modifies the design of the equipment. Selection criteria of working fluids generally include thermodynamic and physical properties besides economical and environmental factors, but most often all of these criteria are used together.
  • 2.3K
  • 04 Nov 2022
Topic Review
Composition (Objects)
Compositional objects are wholes instantiated by collections of parts. If an ontology wishes to permit the inclusion of compositional objects it must define which collections of objects are to be considered parts composing a whole. Mereology, the study of relationships between parts and their wholes, provides specifications on how parts must relate to one another in order to compose a whole.
  • 265
  • 04 Nov 2022
Topic Review
Thermodynamic Potential
A thermodynamic potential (or more accurately, a thermodynamic potential energy) is a scalar quantity used to represent the thermodynamic state of a system. The concept of thermodynamic potentials was introduced by Pierre Duhem in 1886. Josiah Willard Gibbs in his papers used the term fundamental functions. One main thermodynamic potential that has a physical interpretation is the internal energy U. It is the energy of configuration of a given system of conservative forces (that is why it is called potential) and only has meaning with respect to a defined set of references (or data). Expressions for all other thermodynamic energy potentials are derivable via Legendre transforms from an expression for U. In thermodynamics, external forces, such as gravity, are typically disregarded when formulating expressions for potentials. For example, while all the working fluid in a steam engine may have higher energy due to gravity while sitting on top of Mount Everest than it would at the bottom of the Mariana Trench, the gravitational potential energy term in the formula for the internal energy would usually be ignored because changes in gravitational potential within the engine during operation would be negligible. In a large system under even homogeneous external force, like the earth atmosphere under gravity, the intensive parameters ([math]\displaystyle{ p, T, \rho }[/math]) should be studied locally having even in equilibrium different values in different places far from each other (see thermodynamic models of troposphere].
  • 1.3K
  • 04 Nov 2022
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