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Evolution of metal ions in biological systems refers to the incorporation of metallic ions into living organisms and how it has changed over time. Metal ions have been associated with biological systems for billions of years, but only in the last century have scientists began to truly appreciate the scale of their influence. Major (iron, manganese, magnesium and zinc) and minor (copper, cobalt, nickel, molybdenum, tungsten) metal ions have become aligned with living organisms through the interplay of biogeochemical weathering and metabolic pathways involving the products of that weathering. The associated complexes have evolved over time.

Natural development of chemicals and elements challenged organisms to adapt or die. Current organisms require redox reactions to induce metabolism and other life processes. Metals have a tendency to lose electrons and are important for redox reactions.

Metals have become so central to cellular function that the collection of metal-binding proteins (referred to as the metallomes) accounts for over 30% of all proteins in the cell. Metals are known to be involved in over 40% of enzymatic reactions, and metal-binding proteins carry out at least one step in almost all biological pathways.

Metals are also toxic so a balance must be acquired to regulate where the metals are in an organism as well as in what quantities. Many organisms have flexible systems in which they can exchange one metal for another if one is scarce. Metals in this discussion are naturally occurring elements that have a tendency to undergo oxidation. Vanadium, molybdenum, cobalt, copper, chromium, iron, manganese, nickel, and zinc are deemed essential because without them biological function is impaired.

The TP-82 (Russian: ТП-82) was a triple-barrelled Soviet pistol that was carried by cosmonauts on space missions.

It was intended as a survival aid to be used after landings and before recovery in the Siberian wilderness. The TP-82 was the result of cosmonaut Alexei Leonov's concerns after being stranded in the Siberian wilderness when his Voskhod capsule malfunctioned. He feared that the 9mm pistol that was provided in the survival kit would be ineffective against the Siberian wildlife, namely bears and wolves.

The upper two shotgun barrels used 12.5×70 mm ammunition (40 gauge), and the lower rifled barrel used 5.45×39mm ammunition developed for the AK-74 assault rifle. The TP-82 has a large lever on the left side of the receiver that opens the action and a small grip-safety under the trigger-guard that resembles a secondary trigger.

The pistol could be used for hunting, to defend against predators and for visible and audible distress signals. The detachable buttstock was also a machete that came with a canvas sheath. TP-82s were carried regularly on Soviet and Russian space missions from 1986 to 2007. They were part of the Soyuz Portable Emergency-Survival Kit (Носимый аварийный запас, Nosimyi Avariynyi Zapas, NAZ). In 2007, the media reported that the remaining ammunition for the TP-82 had become unusable and that a regular semi-automatic pistol would be used on future missions.

Mach () is a kernel developed at Carnegie Mellon University to support operating system research, primarily distributed and parallel computing. Mach is often mentioned as one of the earliest examples of a microkernel. However, not all versions of Mach are microkernels. Mach's derivatives are the basis of the operating system kernel in GNU Hurd and of Apple's XNU kernel used in macOS, iOS, iPadOS, tvOS, and watchOS.

The project at Carnegie Mellon ran from 1985 to 1994, ending with Mach 3.0, which is a true microkernel. Mach was developed as a replacement for the kernel in the BSD version of Unix, so no new operating system would have to be designed around it. Mach and its derivatives exist within a number of commercial operating systems. These include all using the XNU operating system kernel which incorporates an earlier non-microkernel Mach as a major component. The Mach virtual memory management system was also adopted in 4.4BSD by the BSD developers at CSRG, and appears in modern BSD-derived Unix systems, such as FreeBSD.

Mach is the logical successor to Carnegie Mellon's Accent kernel. The lead developer on the Mach project, Richard Rashid, has been working at Microsoft since 1991 in various top-level positions revolving around the Microsoft Research division. Another of the original Mach developers, Avie Tevanian, was formerly head of software at NeXT, then Chief Software Technology Officer at Apple Inc. until March 2006.

A sun dog (or sundog) or mock sun, formally called a parhelion (plural parhelia) in meteorology, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Sun. Two sun dogs often flank the Sun within a 22° halo.

The sun dog is a member of the family of halos, caused by the refraction of sunlight by ice crystals in the atmosphere. Sun dogs typically appear as a pair of subtly colored patches of light, around 22° to the left and right of the Sun, and at the same altitude above the horizon as the Sun. They can be seen anywhere in the world during any season, but are not always obvious or bright. Sun dogs are best seen and most conspicuous when the Sun is near the horizon.

A kleroterion (Ancient Greek: κληρωτήριον) was a randomization device used by the Athenian polis during the period of democracy to select citizens to the boule, to most state offices, to the nomothetai, and to court juries.

The kleroterion was a slab of stone incised with rows of slots and with an attached tube. Citizens' tokens—pinakia—were placed randomly in the slots so that every member of each of the tribes of Athens had their tokens placed in the same column. There was a pipe attached to the stone which could then be fed dice that were coloured differently (assumed to be black and white) and could be released individually by a mechanism that has not survived to posterity (but is speculated to be by two nails; one used to block the open end and another to separate the next die to fall from the rest of the dice above it). When a die was released, a complete row of tokens (so, one citizen from each of the tribes of Athens) was either selected if the die was coloured one colour, or discarded if it was the alternate colour. This process continued until the requisite number of citizens was selected.

The Phaistos Disc (also spelled Phaistos Disk, Phaestos Disc) is a disk of fired clay from the Minoan palace of Phaistos on the island of Crete, possibly dating to the middle or late Minoan Bronze Age (second millennium B.C.). The disk is about 15 cm (5.9 in) in diameter and covered on both sides with a spiral of stamped symbols. Its purpose and meaning, and even its original geographical place of manufacture, remain disputed, making it one of the most famous mysteries of archaeology. This unique object is now on display at the archaeological museum of Heraklion.

The disc was discovered in 1908 by the Italian archaeologist Luigi Pernier in the Minoan palace-site of Phaistos, and features 241 tokens, comprising 45 distinct signs, which were apparently made by pressing hieroglyphic "seals" into a disc of soft clay, in a clockwise sequence spiraling toward the center of the disk.

The Phaistos Disc captured the imagination of amateur and professional archaeologists, and many attempts have been made to decipher the code behind the disc's signs. While it is not clear that it is a script, most attempted decipherments assume that it is; most additionally assume a syllabary, others an alphabet or logography. Attempts at decipherment are generally thought to be unlikely to succeed unless more examples of the signs are found, as it is generally agreed that there is not enough context available for a meaningful analysis.

Although the Phaistos Disc is generally accepted as authentic by archaeologists, a few scholars believe that the disc is a forgery or a hoax.

Gödel's completeness theorem is a fundamental theorem in mathematical logic that establishes a correspondence between semantic truth and syntactic provability in first-order logic. It makes a close link between model theory that deals with what is true in different models, and proof theory that studies what can be formally proven in particular formal systems.

It was first proved by Kurt Gödel in 1929. It was then simplified in 1947, when Leon Henkin observed in his Ph.D. thesis that the hard part of the proof can be presented as the Model Existence Theorem (published in 1949). Henkin's proof was simplified by Gisbert Hasenjaeger in 1953.

A quasiperiodic crystal, or quasicrystal, is a structure that is ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry. While crystals, according to the classical crystallographic restriction theorem, can possess only two-, three-, four-, and six-fold rotational symmetries, the Bragg diffraction pattern of quasicrystals shows sharp peaks with other symmetry orders—for instance, five-fold.

Aperiodic tilings were discovered by mathematicians in the early 1960s, and, some twenty years later, they were found to apply to the study of natural quasicrystals. The discovery of these aperiodic forms in nature has produced a paradigm shift in the fields of crystallography. Quasicrystals had been investigated and observed earlier, but, until the 1980s, they were disregarded in favor of the prevailing views about the atomic structure of matter. In 2009, after a dedicated search, a mineralogical finding, icosahedrite, offered evidence for the existence of natural quasicrystals.

Roughly, an ordering is non-periodic if it lacks translational symmetry, which means that a shifted copy will never match exactly with its original. The more precise mathematical definition is that there is never translational symmetry in more than n – 1 linearly independent directions, where n is the dimension of the space filled, e.g., the three-dimensional tiling displayed in a quasicrystal may have translational symmetry in two directions. Symmetrical diffraction patterns result from the existence of an indefinitely large number of elements with a regular spacing, a property loosely described as long-range order. Experimentally, the aperiodicity is revealed in the unusual symmetry of the diffraction pattern, that is, symmetry of orders other than two, three, four, or six. In 1982 materials scientist Dan Shechtman observed that certain aluminium-manganese alloys produced the unusual diffractograms which today are seen as revelatory of quasicrystal structures. Due to fear of the scientific community's reaction, it took him two years to publish the results for which he was awarded the Nobel Prize in Chemistry in 2011. On 25 October 2018, Luca Bindi and Paul Steinhardt were awarded the Aspen Institute 2018 Prize for collaboration and scientific research between Italy and the United States.

Entropic gravity, also known as emergent gravity, is a theory in modern physics that describes gravity as an entropic force—a force with macro-scale homogeneity but which is subject to quantum-level disorder—and not a fundamental interaction. The theory, based on string theory, black hole physics, and quantum information theory, describes gravity as an emergent phenomenon that springs from the quantum entanglement of small bits of spacetime information. As such, entropic gravity is said to abide by the second law of thermodynamics under which the entropy of a physical system tends to increase over time.

At its simplest, the theory holds that when gravity becomes vanishingly weak—levels seen only at interstellar distances—it diverges from its classically understood nature and its strength begins to decay linearly with distance from a mass.

Entropic gravity provides the underlying framework to explain Modified Newtonian Dynamics, or MOND, which holds that at a gravitational acceleration threshold of approximately 1.2×10⁻¹⁰ m/s², gravitational strength begins to vary inversely (linearly) with distance from a mass rather than the normal inverse-square law of the distance. This is an exceedingly low threshold, measuring only 12 trillionths gravity's strength at earth's surface; an object dropped from a height of one meter would fall for 36 hours were earth's gravity this weak. It is also 3,000 times less than exists at the point where Voyager 1 crossed our solar system's heliopause and entered interstellar space.

The theory claims to be consistent with both the macro-level observations of Newtonian gravity as well as Einstein's theory of general relativity and its gravitational distortion of spacetime. Importantly, the theory also explains (without invoking the existence of dark matter and its accompanying math featuring new free parameters that are tweaked to obtain the desired outcome) why galactic rotation curves differ from the profile expected with visible matter.

The theory of entropic gravity posits that what has been interpreted as unobserved dark matter is the product of quantum effects that can be regarded as a form of positive dark energy that lifts the vacuum energy of space from its ground state value. A central tenet of the theory is that the positive dark energy leads to a thermal-volume law contribution to entropy that overtakes the area law of anti-de Sitter space precisely at the cosmological horizon.

The theory has been controversial within the physics community but has sparked research and experiments to test its validity.

The Matthew effect of accumulated advantage, Matthew principle, or Matthew effect for short, is sometimes summarized by the adage "the rich get richer and the poor get poorer". The concept is applicable to matters of fame or status, but may also be applied literally to cumulative advantage of economic capital. In the beginning, Matthew effects were primarily focused on the inequality in the way scientists were recognized for their work. However, Norman Storer, of Columbia University, led a new wave of research. He believed he discovered that the inequality that existed in the social sciences also existed in other institutions.

The term was coined by sociologist Robert K. Merton in 1968 and takes its name from the Parable of the talents or minas in the biblical Gospel of Matthew. Merton credited his collaborator and wife, sociologist Harriet Zuckerman, as co-author of the concept of the Matthew effect.