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Physical Information
Physical information is a form of information. In physics, it refers to the information of a physical system. Physical information is an important concept used in a number of fields of study in physics. For example, in quantum mechanics, the form of physical information known as quantum information is used in many descriptions of quantum phenomena, such as quantum observation, quantum entanglement and the causal relationship between quantum objects that carry out either or both close and long-range interactions with one another. In a general sense, information is that which resolves uncertainty, which is due to the fact that it describes the details of that which is associated with the uncertainty. The description itself is, however, divorced from any type of language. When clarifying the subject of information, care should be taken to distinguish between the following specific cases: As the above usages are all conceptually distinct from each other, overloading the word "information" (by itself) to denote (or connote) several of these concepts simultaneously can lead to confusion. Accordingly, this article uses more detailed phrases, such as those shown in bold above, whenever the intended meaning is not made clear by the context.
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  • 09 Oct 2022
Topic Review
Biological Small-Angle Scattering
Biological small-angle scattering is a small-angle scattering method for structure analysis of biological materials. Small-angle scattering is used to study the structure of a variety of objects such as solutions of biological macromolecules, nanocomposites, alloys, and synthetic polymers. Small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) are the two complementary techniques known jointly as small-angle scattering (SAS). SAS is an analogous method to X-ray and neutron diffraction, wide angle X-ray scattering, as well as to static light scattering. In contrast to other X-ray and neutron scattering methods, SAS yields information on the sizes and shapes of both crystalline and non-crystalline particles. When used to study biological materials, which are very often in aqueous solution, the scattering pattern is orientation averaged. SAS patterns are collected at small angles of a few degrees. SAS is capable of delivering structural information in the resolution range between 1 and 25 nm, and of repeat distances in partially ordered systems of up to 150 nm in size. Ultra small-angle scattering (USAS) can resolve even larger dimensions. The grazing-incidence small-angle scattering (GISAS) is a powerful technique for studying of biological molecule layers on surfaces. In biological applications SAS is used to determine the structure of a particle in terms of average particle size and shape. One can also get information on the surface-to-volume ratio. Typically, the biological macromolecules are dispersed in a liquid. The method is accurate, mostly non-destructive and usually requires only a minimum of sample preparation. However, biological molecules are always susceptible to radiation damage. In comparison to other structure determination methods, such as solution NMR or X-ray crystallography, SAS allows one to overcome some restraints. For example, solution NMR is limited to protein size, whereas SAS can be used for small molecules as well as for large multi-molecular assemblies. Solid-State NMR is still an indispensable tool for determining atomic level information of macromolecules greater than 40 kDa or non-crystalline samples such as amyloid fibrils. Structure determination by X-ray crystallography may take several weeks or even years, whereas SAS measurements take days. SAS can also be coupled to other analytical techniques like size-exclusion chromatography to study heterogeneous samples. However, with SAS it is not possible to measure the positions of the atoms within the molecule.
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Topic Review
Defining Equation
In physics, defining equations are equations that define new quantities in terms of base quantities. This article uses the current SI system of units, not natural or characteristic units.
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Topic Review
Alpha Crucis
Alpha Crucis (α Crucis, abbreviated Alpha Cru, α Cru) is a multiple star system 321 light-years from the Sun in the constellation of Crux and part of the asterism known as the Southern Cross. With a combined visual magnitude of 0.76, it is the brightest star in Crux and the 13th brightest star in the night sky. It is the southernmost first-magnitude star, 2.3 degrees more southerly than Alpha Centauri. To the naked eye Alpha Crucis appears as a single star, but it is actually a multiple star system. Two components are visually distinguishable: α1 Crucis and α2 Crucis; alternatively designated α Crucis A and α Crucis B. Both are B-type stars, and are many times more massive and luminous than the Sun. α1 Crucis is itself a spectroscopic binary with components designated α Crucis Aa (also named Acrux) and α Crucis Ab. Its two component stars orbit every 76 days at a separation of about 1 astronomical unit (au).
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Topic Review
Troppy Effect
Troppy effect – a phenomenon of formation of irregular residual surface wave-like damages resulting from a non-stationary process of cyclic elastoplastic deformation in the zone of contact at rolling friction. It was openly and studied by professor L. A. Sosnovskiy with staff in the framework of Tribo-Fatigue.
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Topic Review
Horror Vacui
In physics, horror vacui, or plenism (/ˈpliːnɪzəm/), commonly stated as "nature abhors a vacuum", is a postulate attributed to Aristotle, who articulated a belief, later criticized by the atomism of Epicurus and Lucretius, that nature contains no vacuums because the denser surrounding material continuum would immediately fill the rarity of an incipient void. He also argued against the void in a more abstract sense (as "separable"), for example, that by definition a void, itself, is nothing, and following Plato, nothing cannot rightly be said to exist. Furthermore, insofar as it would be featureless, it could neither be encountered by the senses, nor could its supposition lend additional explanatory power. Hero of Alexandria challenged the theory in the first century CE, but his attempts to create an artificial vacuum failed. The theory was debated in the context of 17th-century fluid mechanics, by Thomas Hobbes and Robert Boyle, among others, and through the early 18th century by Sir Isaac Newton and Gottfried Leibniz.
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Topic Review
Stellar Magnetic Field
A stellar magnetic field is a magnetic field generated by the motion of conductive plasma inside a star. This motion is created through convection, which is a form of energy transport involving the physical movement of material. A localized magnetic field exerts a force on the plasma, effectively increasing the pressure without a comparable gain in density. As a result, the magnetized region rises relative to the remainder of the plasma, until it reaches the star's photosphere. This creates starspots on the surface, and the related phenomenon of coronal loops.
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Topic Review
88 Modern Constellations
In contemporary astronomy, the sky is divided into 88 regions called constellations, generally based on the asterisms (which are also called "constellations") of Greek and Roman mythology. The number of 88, along with the contemporary scientific notion of "constellation", was conventioned in 1922 by the International Astronomical Union in order to establish a universal pattern for professional astronomers, who defined constellations from then on as regions of the sky separated by arcs of right ascensions and declinations and grouped by asterisms of their historically most important stars, which cover the entire celestial sphere. The constellations along the ecliptic are called the zodiac. The ancient Sumerians, and later the Greeks (as recorded by Ptolemy), established most of the northern constellations in international use today. When explorers mapped the stars of the southern skies, European and American astronomers proposed new constellations for that region, as well as ones to fill gaps between the traditional constellations. Not all of these proposals caught on, but in 1922, the International Astronomical Union (IAU) adopted the modern list of 88 constellations. After this, Eugène Joseph Delporte drew up precise boundaries for each constellation, so that every point in the sky belonged to exactly one constellation.
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Topic Review
Beta (Plasma Physics)
The beta of a plasma, symbolized by β, is the ratio of the plasma pressure (p = n kB T) to the magnetic pressure (pmag = B²/2μ0). The term is commonly used in studies of the Sun and Earth's magnetic field, and in the field of fusion power designs. In the fusion power field, plasma is often confined using strong magnets. Since the temperature of the fuel scales with pressure, reactors attempt to reach the highest pressures possible. The costs of large magnets roughly scales like β½. Therefore, beta can be thought of as a ratio of money out to money in for a reactor, and beta can be thought of (very approximately) as an economic indicator of reactor efficiency. For tokamaks, betas of larger than 0.05 or 5% are desired for economically viable electrical production. The same term is also used when discussing the interactions of the solar wind with various magnetic fields. For example, beta in the corona of the Sun is about 0.01.
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Topic Review
Liquid Mirror Telescope
Liquid mirror telescopes are telescopes with mirrors made with a reflective liquid. The most common liquid used is mercury, but other liquids will work as well (for example, low melting alloys of gallium). The liquid and its container are rotated at a constant speed around a vertical axis, which causes the surface of the liquid to assume a paraboloidal shape, suitable for use as the primary mirror of a reflecting telescope. The rotating liquid assumes the paraboloidal shape regardless of the container's shape. To reduce the amount of liquid metal needed, and thus weight, a rotating mercury mirror uses a container that is as close to the necessary parabolic shape as possible. Liquid mirrors can be a low cost alternative to conventional large telescopes. Compared to a solid glass mirror that must be cast, ground, and polished, a rotating liquid metal mirror is much less expensive to manufacture. Isaac Newton noted that the free surface of a rotating liquid forms a circular paraboloid and can therefore be used as a telescope, but he could not actually build one because he had no way to stabilize the speed of rotation. The concept was further developed by Ernesto Capocci of the Naples Observatory (1850), but it was not until 1872 that Henry Skey of Dunedin, New Zealand constructed the first working laboratory liquid mirror telescope. Another difficulty is that a liquid metal mirror can only be used in zenith telescopes, i.e., that look straight up, so it is not suitable for investigations where the telescope must remain pointing at the same location of inertial space (a possible exception to this rule may exist for a mercury mirror space telescope, where the effect of Earth's gravity is replaced by artificial gravity, perhaps by rotating the telescope on a very long tether, or propelling it gently forward with rockets). Only a telescope located at the North Pole or South Pole would offer a relatively static view of the sky, although the freezing point of mercury and the remoteness of the location would need to be considered. A very large telescope already exists at the South Pole, but the North Pole is located in the Arctic Ocean. The mercury mirror of the Large Zenith Telescope in Canada was the largest liquid metal mirror ever built. It had a diameter of six meters, and rotated at a rate of about 8.5 revolutions per minute. It is now decommissioned. This mirror was a test, built for $1 million but it was not suitable for astronomy because of the test site's weather. They are now planning to build a larger 8 meter liquid mirror telescope ALPACA for astronomical use and a larger project called LAMA with 66 individual 6.15 meter telescopes with a total collecting power equal to a 55 meter telescope, resolving power of a 70 meter scope.
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