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Topic Review
Outline of Nanotechnology
The following outline is provided as an overview of and topical guide to nanotechnology: Nanotechnology is science, engineering, and technology conducted at the nanoscale, which is about 1 to 100 nanometers.
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  • 26 Oct 2022
Topic Review
Strategies for Engineered Negligible Senescence
Strategies for Engineered Negligible Senescence (SENS) is the term coined by British biogerontologist Aubrey de Grey for the diverse range of regenerative medical therapies, either planned or currently in development, for the periodical repair of all age-related damage to human tissue with the ultimate purpose of maintaining a state of negligible senescence in the patient, thereby postponing age-associated disease for as long as the therapies are reapplied. The term "negligible senescence" was first used in the early 1990s by professor Caleb Finch to describe organisms such as lobsters and hydras, which do not show symptoms of aging. The term "engineered negligible senescence" first appeared in print in Aubrey de Grey's 1999 book The Mitochondrial Free Radical Theory of Aging. De Grey called SENS a "goal-directed rather than curiosity-driven" approach to the science of aging, and "an effort to expand regenerative medicine into the territory of aging". While many biogerontologists find it "worthy of discussion", some contend that the ultimate goals of de Grey's programme are too speculative given the current state of technology, referring to it as "fantasy rather than science".
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  • 26 Oct 2022
Topic Review
Street Canyon
A street canyon (also known as an urban canyon) is a place where the street is flanked by buildings on both sides creating a canyon-like environment. Classic examples of these human-built canyons are made when streets separate dense blocks of structures, especially skyscrapers. These include the Magnificent Mile in Chicago, Toronto's Financial District, the Canyon of Heroes in Manhattan and Hong Kong's Kowloon and Central districts. Urban canyons affect various local conditions, including temperature, wind, air quality, and radio reception, including satellite navigation signals.
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  • 26 Oct 2022
Topic Review
Actinopterygii
Actinopterygii (/ˌæktɪnɒptəˈrɪdʒiaɪ/; from actino- 'having rays', and grc πτέρυξ (ptérux) 'wing, fins'), members of which are known as ray-finned fishes, is a clade (traditionally class or subclass) of the bony fishes. They comprise over 50% of living vertebrate species. The ray-finned fishes are so-called because their fins are webs of skin supported by bony or horny spines (rays), as opposed to the fleshy, lobed fins that characterize the class Sarcopterygii (lobe-finned fish). These actinopterygian fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the link or connection between these fins and the internal skeleton (e.g., pelvic and pectoral girdles). By species count, actinopterygians dominate the vertebrates, and they comprise nearly 99% of the over 30,000 species of fish. They are ubiquitous throughout freshwater and marine environments from the deep sea to the highest mountain streams. Extant species can range in size from Paedocypris, at 8 mm (0.3 in), to the massive ocean sunfish, at 2,300 kg (5,070 lb), and the long-bodied oarfish, at 11 m (36 ft). The vast majority of Actinopterygii (~95%) are teleosts.
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  • 27 Oct 2022
Topic Review
Localization of a Ring
In commutative algebra, localization is a systematic method of adding multiplicative inverses to a ring. Given a ring R and a subset S, one wants to construct some ring R* and ring homomorphism from R to R*, such that the image of S consists of units (invertible elements) in R*. Further one wants R* to be the 'best possible' or 'most general' way to do this—in the usual fashion this should be expressed by a universal property. The localization of R by S is usually denoted by S −1R; however other notations are used in some important special cases. If S is the set of the non zero elements of an integral domain, then the localization is the field of fractions and thus usually denoted Frac(R). If S is the complement of a prime ideal I the localization is denoted by RI, and Rf is used to denote the localization by the powers of an element f. The two latter cases are fundamental in algebraic geometry and scheme theory. In particular the definition of an affine scheme is based on the properties of these two kinds of localizations.
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  • 26 Oct 2022
Topic Review
USS Adelante (SP-765)
The iron-hulled, single-screw steam yacht Utowana was completed in 1883 at Chester, Pennsylvania, by the Delaware River Iron Ship Building and Engine Works for Washington Everett Connor. On sale to Elias Cornelius Benedict the yacht's name was changed to Oneida (1887), then when Benedict bought a new yacht to be named Oneida and sale of the old yacht and conversion to a tow boat the name was changed to Adelante (1913). During Benedict's ownership Oneida was the covert site of an operation on President Grover Cleveland, a friend of Benedict's and frequent guest on the yacht, to remove a cancerous tumor in his mouth. She was taken over by the U.S. Navy in August 1918 and commissioned as USS Adelante (SP-765) in December 1918. Employed in setting up radio compass stations along the Maine coast, she was also used as a boarding boat, meeting vessels arriving off the port of Boston. USS Adelante was decommissioned in August 1919 and sold in March 1920, subsequently operating as a commercial tow boat under the names John Gully and Salvager. The ship was abandoned in 1941.
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  • 26 Oct 2022
Topic Review
Reduction (Recursion Theory)
In computability theory, many reducibility relations (also called reductions, reducibilities, and notions of reducibility) are studied. They are motivated by the question: given sets A and B of natural numbers, is it possible to effectively convert a method for deciding membership in B into a method for deciding membership in A? If the answer to this question is affirmative then A is said to be reducible to B. The study of reducibility notions is motivated by the study of decision problems. For many notions of reducibility, if any noncomputable set is reducible to a set A then A must also be noncomputable. This gives a powerful technique for proving that many sets are noncomputable.
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  • 26 Oct 2022
Topic Review
Hidden Surface Determination
In 3D computer graphics, shown surface determination (also known as hidden surface removal (HSR), occlusion culling (OC) or visible surface determination (VSD)) is the process used to determine which surfaces and parts of surfaces are not visible from a certain viewpoint. A hidden surface determination algorithm is a solution to the visibility problem, which was one of the first major problems in the field of 3D computer graphics. The process of hidden surface determination is sometimes called hiding, and such an algorithm is sometimes called a hider. The analogue for line rendering is hidden line removal. Hidden surface determination is necessary to render an image correctly, so that one may not view features hidden behind the model itself, allowing only the naturally viewable portion of the graphic to be visible.
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  • 26 Oct 2022
Topic Review
Intermittent Energy Source
An intermittent energy source is any source of energy that is not continuously available for conversion into electricity and outside direct control because the used primary energy cannot be stored. Intermittent energy sources may be predictable but cannot be dispatched to meet the demand of an electric power system. The use of intermittent sources in an electric power system usually displaces storable primary energy that would otherwise be consumed by other power stations. Another option is to store electricity generated by non-dispatchable energy sources for later use when needed, e.g. in the form of pumped storage, compressed air or in batteries. A third option is the sector coupling e.g. by electric heating for district heating schemes. The use of small amounts of intermittent power has little effect on grid operations. Using larger amounts of intermittent power may require upgrades or even a redesign of the grid infrastructure.
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  • 26 Oct 2022
Topic Review
Free-Space Path Loss
In telecommunication, the free-space path loss (FSPL) is the attenuation of radio energy between the feedpoints of two antennas that results from the combination of the receiving antenna's capture area plus the obstacle free, line-of-sight path through free space (usually air). The "Standard Definitions of Terms for Antennas", IEEE Std 145-1993, defines "free-space loss" as "The loss between two isotropic radiators in free space, expressed as a power ratio." It does not include any power loss in the antennas themselves due to imperfections such as resistance. Free space loss increases with the square of distance between the antennas because the radio waves spread out due the inverse square law and decreases with the square of the wavelength of the radio waves. The FSPL is rarely used standalone, but rather as a part of the Friis transmission formula, which includes the gain of antennas. It is a factor that must be included in the power link budget of a radio communication system, to ensure that sufficient radio power reaches the receiver that the transmitted signal is received intelligibly.
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  • 02 Jun 2023
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