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Topic Review
Transition of State
In quantum mechanics, particularly Perturbation theory, a transition of state is a change from an initial quantum state to a final one.
  • 304
  • 08 Nov 2022
Topic Review
List of Objects at Lagrangian Points
This is a list of known objects which occupy, have occupied, or are planned to occupy any of the five Lagrangian points of two-body systems in space.
  • 1.2K
  • 08 Nov 2022
Topic Review
Corona
A corona (meaning 'crown' in Latin derived from Ancient Greek 'κορώνη' (korōnè, “garland, wreath”)) is an aura of plasma that surrounds the Sun and other stars. The Sun's corona extends millions of kilometres into outer space and is most easily seen during a total solar eclipse, but it is also observable with a coronagraph. Spectroscopy measurements indicate strong ionization in the corona and a plasma temperature in excess of 1000000 kelvin, much hotter than the surface of the Sun. Light from the corona comes from three primary sources, from the same volume of space. The K-corona (K for kontinuierlich, "continuous" in German) is created by sunlight scattering off free electrons; Doppler broadening of the reflected photospheric absorption lines spreads them so greatly as to completely obscure them, giving the spectral appearance of a continuum with no absorption lines. The F-corona (F for Fraunhofer) is created by sunlight bouncing off dust particles, and is observable because its light contains the Fraunhofer absorption lines that are seen in raw sunlight; the F-corona extends to very high elongation angles from the Sun, where it is called the zodiacal light. The E-corona (E for emission) is due to spectral emission lines produced by ions that are present in the coronal plasma; it may be observed in broad or forbidden or hot spectral emission lines and is the main source of information about the corona's composition.
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Topic Review
Laboratory B in Sungul’
Laboratory B in Sungul' was one of the laboratories under the 9th Chief Directorate of the NKVD (MVD after 1946) that contributed to the Soviet atomic bomb project. It was created in 1946 and closed in 1955, when some of its personnel were merged with the second Soviet nuclear design and assembly facility. It was run as a sharashka – a secret scientific facility run as a prison. Laboratory B employed German scientists from 1947 to 1953. It had two scientific divisions, radiochemistry and radiobiophysics; the latter was headed by the world-renowned geneticist N. V. Timofeev-Resovskij. For two years, the renowned German chemist, Nikolaus Riehl was the scientific director.
  • 372
  • 08 Nov 2022
Topic Review
Public Transport in Shanghai
Shanghai has an extensive public transport system, largely based on buses, trolley buses, taxis, and a rapidly expanding metro system. Shanghai has invested heavily in public transportation before and after the 2010 World Expo, including the construction of the Hongqiao transportation hub of high-speed rail, air, metro and bus routes. Public transport is the major mode of transport in Shanghai as limitations on car purchases were introduced in 1994 in order to limit the growth of automobile traffic and alleviate congestion. New private cars cannot be driven without a license plate, which are sold in monthly license plate auctions which is only accessible for locally registered residents and those who have paid social insurance or individual income taxes for over three years. Around 9,500 license plates are auctioned each month, and the average price is about CN¥89,600 (US$12,739) in 2019. Shanghai (population of 25 million) has over four million cars on the road, the fifth-largest number of any Chinese city. Despite this the city remains plagued by congestion and vehicle pollution. The results of the "2011 Shanghai Public Transport Passenger Flow Survey" released by the Municipal Transportation and Port Bureau showed that the city's public transport travel time was gradually reduced. The average travel distance of public transport in 2011 was 8.5 kilometers, the travel time 50.8 minutes per trip and the travel cost of public transport is gradually reduced: in 2011, the cost of rail transit was 2.4 yuan per trip, down 14% from 2005; the cost of bus and tram trips was 1.8 yuan, down 5% from 2005. Metro accounted for 33% of the public transport passenger volume. In 2018 the public transportation system handled a total of 16.05 million rides on average each day, among which 10.17 million (63%) were made via the Metro and 5.76 million (36%) via buses. Shanghai expressway traffic volume was 1.215 million vehicles on an average day.
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Topic Review
Two-Ray Ground-Reflection Model
The Two-Rays Ground Reflected Model is a radio propagation model which predicts the path losses between a transmitting antenna and a receiving antenna when they are in LOS (line of sight). Generally, the two antenna each have different height. The received signal having two components, the LOS component and the multipath component formed predominantly by a single ground reflected wave.
  • 7.0K
  • 08 Nov 2022
Topic Review
Gastropoda
The gastropods (/ˈɡæstrəpɒdz/), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (/ɡæsˈtrɒpədə/). This class comprises snails and slugs from saltwater, from freshwater, and from the land. There are many thousands of species of sea snails and slugs, as well as freshwater snails, freshwater limpets, and land snails and slugs. The class Gastropoda contains a vast total of named species, second only to the insects in overall number. The fossil history of this class goes back to the Late Cambrian. (As of 2017), 721 families of gastropods are known, of which 245 are extinct and appear only in the fossil record, while 476 are currently extant with or without a fossil record. Gastropoda (previously known as univalves and sometimes spelled "Gasteropoda") are a major part of the phylum Mollusca, and are the most highly diversified class in the phylum, with 65,000 to 80,000 living snail and slug species. The anatomy, behavior, feeding, and reproductive adaptations of gastropods vary significantly from one clade or group to another, so stating many generalities for all gastropods is difficult. The class Gastropoda has an extraordinary diversification of habitats. Representatives live in gardens, woodland, deserts, and on mountains; in small ditches, great rivers, and lakes; in estuaries, mudflats, the rocky intertidal, the sandy subtidal, the abyssal depths of the oceans, including the hydrothermal vents, and numerous other ecological niches, including parasitic ones. Although the name "snail" can be, and often is, applied to all the members of this class, commonly this word means only those species with an external shell big enough that the soft parts can withdraw completely into it. Those gastropods without a shell, and those with only a very reduced or internal shell, are usually known as slugs; those with a shell into which they can partly but not completely withdraw are termed semislugs. The marine shelled species of gastropods include species such as abalone, conches, periwinkles, whelks, and numerous other sea snails that produce seashells that are coiled in the adult stage—though in some, the coiling may not be very visible, for example in cowries. In a number of families of species, such as all the various limpets, the shell is coiled only in the larval stage, and is a simple conical structure after that.
  • 3.2K
  • 08 Nov 2022
Topic Review
Nanotechnology in Agriculture
Research has shown nanoparticles to be a groundbreaking tool for tackling many arising global issues, the agricultural industry being no exception. In general, a nanoparticle is defined as any particle where one characteristic dimension is 100nm or less. Because of their unique size, these particles begin to exhibit properties that their larger counterparts may not. Due to their scale, quantum mechanical interactions become more important than classic mechanical forces, allowing for the prevalence of unique physical and chemical properties due to their extremely high surface-to-body ratio. Properties such as cation exchange capacity, enhanced diffusion, ion adsorption, and complexation are enhanced when operating at nanoscale. This is primarily the consequence of a high proportion of atoms being present on the surface, with an increased proportion of sites operating at higher reactivities with respect to processes such as adsorption processes and electrochemical interactions. Nanoparticles are promising candidates for implementation in agriculture. Because many organic functions such as ion exchange and plant gene expression operate on small scales, nanomaterials offer a toolset that works at just the right scale to provide efficient, targeted delivery to living cells. Current areas of focus of nanotechnology development in the agricultural industry include development of environmentally conscious nanofertilizers to provide efficient ion, nutrient delivery into plant cells, and plant gene transformations to produce plants with desirable genes such as drought resistance and accelerated growth cycles. With the global population on the rise, it is necessary to make advancements in sustainable farming methods that generate higher yields in order to meet the rising food demand. However, it must be done without generating long-term consequences such as depletion of arable land or water sources, toxic runoff, or bioaccumulative toxicity. In order to meet these demands, research is being done into the incorporation of nanotechnology agriculture.
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Topic Review
Osmium-191
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
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Topic Review
Wake
In fluid dynamics, a wake may either be: 1. the region of recirculating flow immediately behind a moving or stationary blunt body, caused by viscosity, which may be accompanied by flow separation and turbulence, or 2. the wave pattern on the water surface downstream of an object in a flow, or produced by a moving object (e.g. a ship), caused by density differences of the fluids above and below the free surface and gravity (or surface tension).
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  • 08 Nov 2022
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