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Monosaccharide
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Structure and nomenclature
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While most stereoisomers can be arranged in pairs of mirror-image forms, there are some non-chiral stereoisomers that are identical to their mirror images, in spite of having chiral centers. This happens whenever the molecular graph is symmetrical, as in the 3-ketopentoses H(CHOH)2(CO)(CHOH)2H, and the two halves are mirror images of each other. In that case, mirroring is equivalent to a half-turn rotation. For this reason, there are only three distinct 3-ketopentose stereoisomers, even though the molecule has two chiral carbons.
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Monosaccharide
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Structure and nomenclature
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Distinct stereoisomers that are not mirror-images of each other usually have different chemical properties, even in non-chiral environments. Therefore, each mirror pair and each non-chiral stereoisomer may be given a specific monosaccharide name. For example, there are 16 distinct aldohexose stereoisomers, but the name "glucose" means a specific pair of mirror-image aldohexoses. In the Fischer projection, one of the two glucose isomers has the hydroxyl at left on C3, and at right on C4 and C5; while the other isomer has the reversed pattern. These specific monosaccharide names have conventional three-letter abbreviations, like "Glu" for glucose and "Thr" for threose.
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Monosaccharide
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Structure and nomenclature
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Generally, a monosaccharide with n asymmetrical carbons has 2n stereoisomers. The number of open chain stereoisomers for an aldose monosaccharide is larger by one than that of a ketose monosaccharide of the same length. Every ketose will have 2(n−3) stereoisomers where n > 2 is the number of carbons. Every aldose will have 2(n−2) stereoisomers where n > 2 is the number of carbons.
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Monosaccharide
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Structure and nomenclature
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These are also referred to as epimers which have the different arrangement of −OH and −H groups at the asymmetric or chiral carbon atoms (this does not apply to those carbons having the carbonyl functional group).
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Monosaccharide
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Structure and nomenclature
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Configuration of monosaccharides Like many chiral molecules, the two stereoisomers of glyceraldehyde will gradually rotate the polarization direction of linearly polarized light as it passes through it, even in solution. The two stereoisomers are identified with the prefixes D- and L-, according to the sense of rotation: D-glyceraldehyde is dextrorotatory (rotates the polarization axis clockwise), while L-glyceraldehyde is levorotatory (rotates it counterclockwise).
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Monosaccharide
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Structure and nomenclature
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The D- and L- prefixes are also used with other monosaccharides, to distinguish two particular stereoisomers that are mirror-images of each other. For this purpose, one considers the chiral carbon that is furthest removed from the C=O group. Its four bonds must connect to −H, −OH, −C(OH)H, and the rest of the molecule. If the molecule can be rotated in space so that the directions of those four groups match those of the analog groups in D-glyceraldehyde's C2, then the isomer receives the D- prefix. Otherwise, it receives the L- prefix.
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Monosaccharide
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Structure and nomenclature
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In the Fischer projection, the D- and L- prefixes specifies the configuration at the carbon atom that is second from bottom: D- if the hydroxyl is on the right side, and L- if it is on the left side.
Note that the D- and L- prefixes do not indicate the direction of rotation of polarized light, which is a combined effect of the arrangement at all chiral centers. However, the two enantiomers will always rotate the light in opposite directions, by the same amount. See also D/L system.
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Monosaccharide
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Structure and nomenclature
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Cyclisation of monosaccharides (hemiacetal formation) A monosaccharide often switches from the acyclic (open-chain) form to a cyclic form, through a nucleophilic addition reaction between the carbonyl group and one of the hydroxyl groups of the same molecule. The reaction creates a ring of carbon atoms closed by one bridging oxygen atom. The resulting molecule has a hemiacetal or hemiketal group, depending on whether the linear form was an aldose or a ketose. The reaction is easily reversed, yielding the original open-chain form.
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Monosaccharide
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Structure and nomenclature
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In these cyclic forms, the ring usually has five or six atoms. These forms are called furanoses and pyranoses, respectively—by analogy with furan and pyran, the simplest compounds with the same carbon-oxygen ring (although they lack the double bonds of these two molecules). For example, the aldohexose glucose may form a hemiacetal linkage between the aldehyde group on carbon 1 and the hydroxyl on carbon 4, yielding a molecule with a 5-membered ring, called glucofuranose. The same reaction can take place between carbons 1 and 5 to form a molecule with a 6-membered ring, called glucopyranose. Cyclic forms with a seven-atom ring (the same of oxepane), rarely encountered, are called heptoses.
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Monosaccharide
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Structure and nomenclature
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For many monosaccharides (including glucose), the cyclic forms predominate, in the solid state and in solutions, and therefore the same name commonly is used for the open- and closed-chain isomers. Thus, for example, the term "glucose" may signify glucofuranose, glucopyranose, the open-chain form, or a mixture of the three.
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Monosaccharide
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Structure and nomenclature
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Cyclization creates a new stereogenic center at the carbonyl-bearing carbon. The −OH group that replaces the carbonyl's oxygen may end up in two distinct positions relative to the ring's midplane. Thus each open-chain monosaccharide yields two cyclic isomers (anomers), denoted by the prefixes α- and β-. The molecule can change between these two forms by a process called mutarotation, that consists in a reversal of the ring-forming reaction followed by another ring formation.
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Monosaccharide
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Structure and nomenclature
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Haworth projection The stereochemical structure of a cyclic monosaccharide can be represented in a Haworth projection. In this diagram, the α-isomer for the pyranose form of a D-aldohexose has the −OH of the anomeric carbon below the plane of the carbon atoms, while the β-isomer has the −OH of the anomeric carbon above the plane. Pyranoses typically adopt a chair conformation, similar to that of cyclohexane. In this conformation, the α-isomer has the −OH of the anomeric carbon in an axial position, whereas the β-isomer has the −OH of the anomeric carbon in equatorial position (considering D-aldohexose sugars).
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Monosaccharide
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Derivatives
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A large number of biologically important modified monosaccharides exist: Amino sugars such as: galactosamine glucosamine sialic acid N-acetylglucosamine Sulfosugars such as: sulfoquinovose Others such as: ascorbic acid mannitol glucuronic acid
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Boron porphyrins
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Boron porphyrins
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Boron porphyrins are a variety of porphyrin, a common macrocycle used for photosensitization and metal trapping applications, that incorporate boron. The central four nitrogen atoms in a porphyrin macrocycle form a unique molecular pocket which is known to accommodate transition metals of various sizes and oxidation states. Due to the diversity of binding modes available to porphyrin, there is a growing interest in introducing other elements (i.e. main group elements) into this pocket.
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Boron porphyrins
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Boron porphyrins
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Boron in particular has been shown to prefer binding to porphyrin in a 2:1 stoichiometry, primarily due to its small atomic radius, but the Group XIII element will bind in a 1:1 ratio with corrole, a macromolecule with a structure similar to porphyrin but with a smaller N4 pocket.
Boron porphyrins are of interest because of the unique geometric environment to which both boron and porphyrin are subjected upon B-N(pyrrole) bond formation. These new geometric motifs lead to novel reactivity, one of the most surprising examples being sterically-induced reductive coupling. Possible applications for boron porphyrins include BNCT delivery agents and OLED devices.
Also of interest are molecules containing both boron and porphyrin moieties, but without B-N(pyrrole) bonds. Examples include diketonate-porphyrin compounds and dyads (two-component molecules) containing the classic BODIPY dye.
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Boron porphyrins
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Synthesis
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Boron porphyrins first appeared in the literature during the 1960's and 1970's, in initially available literature the complex was never well characterized. The Boron porphyrin compounds can be synthesized either from the free base porphyrin or from a lithium porphyrin complex as starting material. Two representative examples are shown here. The first is the porphyrin free base reacted with BX3 in the presence of water.
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Boron porphyrins
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Synthesis
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The second is Li2(ttp) reacted with BX3. The (BX2)2(por) can undergo reduction to form a B-B bond and eliminate X2, giving (BX)2(por). From here, the halides can be replaced with BuLi to give (B-Bu)2(por), reacted with alcohols to give (B-OR)2(por), or even undergo halogen abstraction via weakly-coordinating anions to give [(B-B)(por)]2+.
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Boron porphyrins
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Geometry
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One of the major differences between p-block-element-centered porphyrins and transition-metal-centered porphyrins is the far smaller size of the interstitial atom, especially in the case of the first-row p-block. Other than protons, the next smallest atom known to bind to the central N4 pocket is lithium. The first two isolated lithium porphyrin complexes each reported a 2:1 metal to base ratio, and XRD suggested both lithium atoms reside out of the porphyrin plane.Boron has a covalent radius of 85 pm, significantly smaller than lithium's 133 pm. This suggests the porphyrin pocket is more likely to accommodate two boron atoms rather than one. Indeed, each boron porphyrin synthesized thus far has adopted a ratio of 2:1, with a range of orientations relative to the N4 plane. The boron atoms can exist in the same plane as the porphyrin (both with and without additional out-of-plane B-X bonds), or out of N4 plane in either a cisoid or transoid geometry.
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Boron porphyrins
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Geometry
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This coordination motif is interesting because it introduces both boron and porphyrin to geometries they do not regularly adopt. Porphyrin readily binds to transition metals, which are capable of octahedral or square planar geometries. Boron, without available d-orbitals, typically adopts a trigonal planar or tetrahedral local bonding environment. Diboryl porphyrins, on the other hand, find boron in a pseudo-tetrahedral local environment and introduce a tetragonal distortion to the porphyrin, as can be seen in the DFT image above.
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Boron porphyrins
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Geometry
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Corroles are distinct from porphyrins in that they contain one less methine to bridge between pyrrole units, creating a lower-symmetry compound and a smaller N4 pocket. For boron chemistry, this slightly smaller core allows for the possibility of binding to a single boron, whereas the porphyrin pocket has thus far always bound two. For such monoboryl corroles, DFT studies have suggested the boron preferentially binds to the dipyrromethene (A) site shown here, in which stability is attained by maximizing both BX—HN hydrogen bonding and BH—HN dihydrogen bonding, in addition to minimizing steric crowding.
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Boron porphyrins
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Geometry
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The Brothers group has shown the stereochemical implications of comparing diboryl porphyrin with diboryl corrole: porphyrin prefers transoid orientation of the diboryl unit, whereas corrole prefers the cisoid orientation.
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Boron porphyrins
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Non-central boron-porphyrin interactions
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Two examples of boron-containing compounds that have been linked to porphyrin are BODIPY and diketonate.
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Boron porphyrins
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Non-central boron-porphyrin interactions
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The BODIPY chromophore acts as an antenna: it absorbs a broad range of UV-visible light, then emits at a wavelength compatible with porphyrin absorption, allowing for efficient energy transfer.This work has been extended to triads and to porphyrins with various core transition metals, some displaying multiphoton excitation.On the other hand, when boron difluoride β-diketonate is used for an antenna, the emission-absorption overlap is small and little change in the porphyrin's optical properties is observed. Though this chromophore is preferable to BODIPY in certain applications, it is not an effective antenna for porphyrin.
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Boron porphyrins
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Reactivity
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Reduction One consequence of geometric strain on both the boron and the porphyrin moieties is unique reactivity. The Brothers group was able to demonstrate reductive coupling, wherein two BX2 units inside the porphyrin pocket become X-B-B-X, only occurs with X=Br and when the substrates are within the porphyrin pocket. DFT calculations show that for X=Cl or F, the reaction is endothermic and non-spontaneous. However, for X=Br, the reduction is spontaneous, which was consistent with experimental findings. Further, when the same reaction is simulated with two porphyrin halves ((dipyrromethene)BX2), it is non-spontaneous even for X=Br, suggesting the steric strain of the porphyrin ring to be the driving force behind the reduction reaction.
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Boron porphyrins
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Reactivity
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Hydrolysis Hydrolysis is one of the primary reactions to occur in diboryl porphyrin complexes. In this reaction, RBOBR(por) reacts with water to exchange a B-OH bond for a B-R bond, liberating the R group.
Hydrolysis products are important intermediates in the synthesis of the B-O-B(por) compounds from BX2(por) compounds. In fact, simply performing column chromatography on (BF2)2(por) on silica gives the partial hydrolysis product B2OF2(por).
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Boron porphyrins
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Reactivity
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DFT computations show that hydrolysis, as in the scheme shown here, is energetically favorable (breaking of a relatively weak B-C bond, formation of a strong B-O bond, formation of benzene). However, only one of the two phenyl groups is observed to undergo hydrolysis. This suggests thermodynamic favorability is not the only factor at play. Rather, as Belcher et al. suggest, there is a significant steric component to this reaction. The boron in the porphyrin ring plane undergoes substitution, while the out-of-plane boron retains its phenyl bond.
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Boron porphyrins
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Reactivity
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Halogen abstraction (Also see Geometry section above for a discussion of the B-B bonding environment.) Abstraction of halogens with two equivalents of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate gives the dication with both boron atoms within the porphyrin plane. Two reversible reduction waves occur at reduction potentials lower than that of the free base.
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Deep diving
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Deep diving
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Deep diving is underwater diving to a depth beyond the norm accepted by the associated community. In some cases this is a prescribed limit established by an authority, while in others it is associated with a level of certification or training, and it may vary depending on whether the diving is recreational, technical or commercial. Nitrogen narcosis becomes a hazard below 30 metres (98 ft) and hypoxic breathing gas is required below 60 metres (200 ft) to lessen the risk of oxygen toxicity.
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Deep diving
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Deep diving
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For some recreational diving agencies, "Deep diving", or "Deep diver" may be a certification awarded to divers that have been trained to dive to a specified depth range, generally deeper than 30 metres (98 ft). However, the Professional Association of Diving Instructors (PADI) defines anything from 18 to 30 metres (59 to 98 ft) as a "deep dive" in the context of recreational diving (other diving organisations vary), and considers deep diving a form of technical diving. In technical diving, a depth below about 60 metres (200 ft) where hypoxic breathing gas becomes necessary to avoid oxygen toxicity may be considered a deep dive. In professional diving, a depth that requires special equipment, procedures, or advanced training may be considered a deep dive.
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Deep diving
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Deep diving
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Deep diving can mean something else in the commercial diving field. For instance early experiments carried out by COMEX using heliox and trimix attained far greater depths than any recreational technical diving. One example being its "Janus 4" open-sea dive to 501 metres (1,640 ft) in 1977.The open-sea diving depth record was achieved in 1988 by a team of COMEX and French Navy divers who performed pipeline connection exercises at a depth of 534 metres (1,750 ft) in the Mediterranean Sea as part of the "Hydra 8" programme employing heliox and hydrox. The latter avoids the high-pressure nervous syndrome (HPNS) caused by helium and eases breathing due to its lower density. These divers needed to breathe special gas mixtures because they were exposed to very high ambient pressure (more than 54 times atmospheric pressure).
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Deep diving
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Deep diving
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An atmospheric diving suit (ADS) allows very deep dives of up to 700 metres (2,300 ft). These suits are capable of withstanding the pressure at great depth permitting the diver to remain at normal atmospheric pressure. This eliminates the problems associated with breathing pressurised gases. In 2006 Chief Navy Diver Daniel Jackson set a record of 610 metres (2,000 ft) in an ADS.On 20 November 1992 COMEX's "Hydra 10" experiment simulated a dive in an onshore hyperbaric chamber with hydreliox. Théo Mavrostomos spent two hours at an simulated depth of 701 metres (2,300 ft).
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Deep diving
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Depth ranges in underwater diving
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Assumed is the surface of the waterbody to be at or near sea level and underlies atmospheric pressure.
Not included are the differing ranges of freediving – without breathing during a dive.
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Deep diving
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Particular problems associated with deep dives
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Deep diving has more hazards and greater risk than basic open-water diving. Nitrogen narcosis, the "narks" or "rapture of the deep", starts with feelings of euphoria and over-confidence but then leads to numbness and memory impairment similar to alcohol intoxication. Decompression sickness, or the "bends", can happen if a diver ascends too rapidly, when excess inert gas leaves solution in the blood and tissues and forms bubbles. These bubbles produce mechanical and biochemical effects that lead to the condition. The onset of symptoms depends on the severity of the tissue gas loading and may develop during ascent in severe cases, but is frequently delayed until after reaching the surface. Bone degeneration (dysbaric osteonecrosis) is caused by the bubbles forming inside the bones; most commonly the upper arm and the thighs. Deep diving involves a much greater danger of all of these, and presents the additional risk of oxygen toxicity, which may lead to convulsions underwater. Very deep diving using a helium-oxygen mixture (heliox) carries a risk of high-pressure nervous syndrome. Coping with the physical and physiological stresses of deep diving requires good physical conditioning.Using open-circuit scuba equipment, consumption of breathing gas is proportional to ambient pressure – so at 50 metres (164 ft), where the pressure is 6 bars (87 psi), a diver breathes six times as much as on the surface (1 bar, 14.5 psi). Heavy physical exertion makes the diver breathe even more gas, and gas becomes denser requiring increased effort to breathe with depth, leading to increased risk of hypercapnia – an excess of carbon dioxide in the blood. The need to do decompression stops increases with depth. A diver at 6 metres (20 ft) may be able to dive for many hours without needing to do decompression stops. At depths greater than 40 metres (131 ft), a diver may have only a few minutes at the deepest part of the dive before decompression stops are needed. In the event of an emergency, the diver cannot make an immediate ascent to the surface without risking decompression sickness. All of these considerations result in the amount of breathing gas required for deep diving being much greater than for shallow open water diving. The diver needs a disciplined approach to planning and conducting dives to minimise these additional risks.
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Deep diving
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Particular problems associated with deep dives
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Many of these problems are avoided by the use of surface supplied breathing gas, closed diving bells, and saturation diving, at the cost of logistical complexity, reduced maneuverability of the diver, and greater expense.
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Deep diving
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Dealing with depth
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Both equipment and procedures can be adapted to deal with the problems of greater depth. Usually the two are combined, as the procedures must be adapted to suit the equipment, and in some cases the equipment is needed to facilitate the procedures.
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Deep diving
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Dealing with depth
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Equipment adaptations for deeper diving The equipment used for deep diving depends on both the depth and the type of diving. Scuba is limited to equipment that can be carried by the diver or is easily deployed by the dive team, while surface-supplied diving equipment can be more extensive, and much of it stays above the water where it is operated by the diving support team.
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Deep diving
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Dealing with depth
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Scuba divers carry larger volumes of breathing gas to compensate for the increased gas consumption and decompression stops.
Rebreathers, though more complex, manage gas much more efficiently than open-circuit scuba.
Use of helium-based breathing gases such as trimix reduces nitrogen narcosis and reduces the toxic effects of oxygen at depth.
A diving shot, a decompression trapeze, or a decompression buoy can help divers control their ascent and return to the surface at a position that can be monitored by their surface support team at the end of a dive.
Decompression can be accelerated by using specially blended breathing gas mixtures containing lower proportions of inert gas.
Surface supply of breathing gases reduces the risk of running out of gas.
In-water decompression can be minimized by using dry bells and decompression chambers.
Hot-water suits can prevent hypothermia due to the high heat loss when using helium-based breathing gases.
Diving bells and lockout submersibles expose the diver to the direct underwater environment for less time, and provide a relatively safe shelter that does not require decompression, with a dry environment where the diver can rest, take refreshment, and if necessary, receive first aid in an emergency.
Breathing gas reclaim systems reduce the cost of using helium-based breathing gases, by recovering and recycling exhaled surface supplied gas, analogous to rebreathers for scuba diving.
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Deep diving
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Dealing with depth
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The most radical equipment adaptation for deep diving is to isolate the diver from the direct pressure of the environment, using armoured atmospheric diving suits that allow diving to depths beyond those currently possible at ambient pressure. These rigid, articulated exoskeleton suits are sealed against water and withstand external pressure while providing life support to the diver for several hours at an internal pressure of approximately normal surface atmospheric pressure. This avoids the problems of inert gas narcosis, decompression sickness, barotrauma, oxygen toxicity, high work of breathing, compression arthralgia, high-pressure nervous syndrome and hypothermia, but at the cost of reduced mobility and dexterity, logistical problems due to the bulk and mass of the suits, and high equipment costs.
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Deep diving
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Dealing with depth
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Procedural adaptations for deeper diving Procedural adaptations for deep diving can be classified as those procedures for operating specialized equipment, and those that apply directly to the problems caused by exposure to high ambient pressures.
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Deep diving
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Dealing with depth
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The most important procedure for dealing with physiological problems of breathing at high ambient pressures associated with deep diving is decompression. This is necessary to prevent inert gas bubble formation in the body tissues of the diver, which can cause severe injury. Decompression procedures have been derived for a large range of pressure exposures, using a large range of gas mixtures. These basically entail a slow and controlled reduction in pressure during ascent by using a restricted ascent rate and decompression stops, so that the inert gases dissolved in the tissues of the diver can be eliminated harmlessly during normal respiration.
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Deep diving
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Dealing with depth
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Gas management procedures are necessary to ensure that the diver has access to suitable and sufficient breathing gas at all times during the dive, both for the planned dive profile and for any reasonably foreseeable contingency. Scuba gas management is logistically more complex than surface supply, as the diver must either carry all the gas, must follow a route where previously arranged gas supply depots have been set up (stage cylinders). or must rely on a team of support divers who will provide additional gas at pre-arranged signals or points on the planned dive. On very deep scuba dives or on occasions where long decompression times are planned, it is a common practice for support divers to meet the primary team at decompression stops to check if they need assistance, and these support divers will often carry extra gas supplies in case of need.Rebreather diving can reduce the bulk of the gas supplies for long and deep scuba dives, at the cost of more complex equipment with more potential failure modes, requiring more demanding procedures and higher procedural task loading.
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Deep diving
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Dealing with depth
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Surface supplied diving distributes the task loading between the divers and the support team, who remain in the relative safety and comfort of the surface control position. Gas supplies are limited only by what is available at the control position, and the diver only needs to carry sufficient bailout capacity to reach the nearest place of safety, which may be a diving bell or lockout submersible.
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Deep diving
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Dealing with depth
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Saturation diving is a procedure used to reduce the high-risk decompression a diver is exposed to during a long series of deep underwater exposures. By keeping the diver under high pressure for the whole job, and only decompressing at the end of several days to weeks of underwater work, a single decompression can be done at a slower rate without adding much overall time to the job. During the saturation period, the diver lives in a pressurized environment at the surface, and is transported under pressure to the underwater work site in a closed diving bell.
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Deep diving
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Ultra-deep diving
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Mixed gas Amongst technical divers, there are divers who participate in ultra-deep diving on scuba below 200 metres (656 ft). This practice requires high levels of training, experience, discipline, fitness and surface support. Only twenty-six people are known to have ever dived to at least 240 metres (790 ft) on self-contained breathing apparatus recreationally. The "Holy Grail" of deep scuba diving was the 300 metres (980 ft) mark, first achieved by John Bennett in 2001, and has only been achieved five times since.
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Deep diving
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Ultra-deep diving
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The difficulties involved in ultra-deep diving are numerous. Although commercial and military divers often operate at those depths, or even deeper, they are surface supplied. All of the complexities of ultra-deep diving are magnified by the requirement of the diver to carry (or provide for) their own gas underwater. These lead to rapid descents and "bounce dives". Unsurprisingly, this has led to extremely high mortality rates amongst those who practise ultra-deep diving. Notable ultra-deep diving fatalities include Sheck Exley, John Bennett, Dave Shaw and Guy Garman. Mark Ellyatt, Don Shirley and Pascal Bernabé were involved in serious incidents and were fortunate to survive their dives. Despite the extremely high mortality rate, the Guinness World Records continues to maintain a record for scuba diving (although the record for deep diving with compressed air has not been updated since 1999, given the high accident rate). Amongst those who do survive significant health issues are reported. Mark Ellyatt is reported to have suffered permanent lung damage; Pascal Bernabé (who was injured on his dive when a light on his mask imploded) and Nuno Gomes reported short to medium term hearing loss.Serious issues that confront divers engaging in ultra-deep diving on self-contained breathing apparatus include: Compression arthralgia Deep aching pain in the knees, shoulders, fingers, back, hips, neck, and ribs caused by exposure to high ambient pressure at a relatively high rate of descent (i.e., in "bounce dives").
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Deep diving
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Ultra-deep diving
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High-pressure nervous syndrome (HPNS) HPNS, brought on by breathing helium under extreme pressure causes tremors, myoclonic jerking, somnolence, EEG changes, visual disturbance, nausea, dizziness, and decreased mental performance. Symptoms of HPNS are exacerbated by rapid compression, a feature common to ultra-deep "bounce" dives.
Isobaric counterdiffusion (ICD) ICD is the diffusion of one inert gas into body tissues while another inert gas is diffusing out. It is a complication that can occur during decompression, and that can result in the formation or growth of bubbles without changes in the environmental pressure.
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Deep diving
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Ultra-deep diving
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Decompression algorithm There are no reliable decompression algorithms tested for such depths on the assumption of an immediate surfacing. Almost all decompression methodology for such depths is based upon saturation, and calculates ascent times in days rather than hours. Accordingly, ultra-deep dives are almost always a partly experimental basis.In addition, "ordinary" risks like gas reserves, hypothermia, dehydration and oxygen toxicity are compounded by extreme depth and exposure. Much technical equipment is simply not designed for the necessarily greater stresses at depths, and reports of key equipment (including submersible pressure gauges) imploding are not uncommon.
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Deep diving
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Ultra-deep diving
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Air A severe risk in ultra-deep air diving is deep water blackout, or depth blackout, a loss of consciousness at depths below 50 metres (160 ft) with no clear primary cause, associated with nitrogen narcosis, a neurological impairment with anaesthetic effects caused by high partial pressure of nitrogen dissolved in nerve tissue, and possibly acute oxygen toxicity. The term is not in widespread use at present, as where the actual cause of blackout is known, a more specific term is preferred. The depth at which deep water blackout occurs is extremely variable and unpredictable. Before the popular availability of trimix, attempts were made to set world record depths using air. The extreme risk of both narcosis and oxygen toxicity in the divers contributed to a high fatality rate in those attempting records. In his book, Deep Diving, Bret Gilliam chronicles the various fatal attempts to set records as well as the smaller number of successes. From the comparatively few who survived extremely deep air dives: In deference to the high accident rate, the Guinness World Records have ceased to publish records for deep air dives, after Manion's dive.
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Deep diving
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Fatalities during depth record attempts
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Maurice Fargues, a member of the GRS (Groupement de Recherches Sous-marines, Underwater Research Group headed by Jacques Cousteau), died in 1947 after losing consciousness at depth in an experiment to see how deep a scuba diver could go. He reached 120 m (394 ft) before failing to return line signals. He became the first diver to perish using an Aqua-Lung.
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Deep diving
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Fatalities during depth record attempts
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Hope Root died on 3 December 1953 off the coast of Miami Beach trying set a deep diving record of 125 m (410 ft) with an Aqua-Lung; he passed 152 m (500 ft) and was not seen again.
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Deep diving
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Fatalities during depth record attempts
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Archie Forfar and Ann Gunderson died on 11 December 1971 off the coast of Andros Island, while attempting to dive to 146 m (479 ft), which would have been the world record at the time. Their third team member, Jim Lockwood, only survived due to his use of a safety weight that dropped when he lost consciousness at 122 m (400 ft), causing him to start an uncontrolled ascent before being intercepted by a safety diver at a depth of around 91 m (300 ft). Sheck Exley, who was acting as another safety diver at 300 feet, inadvertently managed to set the depth record when he descended towards Forfar and Gunderson, who were both still alive at the 480-foot level, although completely incapacitated by narcosis. Exley was forced to give up his attempt at around 142 m (465 ft) when the narcosis very nearly overcame him as well. The bodies of Forfar and Gunderson were never recovered.
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Deep diving
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Fatalities during depth record attempts
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Sheck Exley died in 1994 at 268 m (879 ft) in an attempt to reach the bottom of Zacatón in a dive that would have extended his own world record (at the time) for deep diving.
Dave Shaw died in 2005 in an attempt at the deepest ever body recovery and deepest ever dive on a rebreather at 270 m (886 ft).
Brigitte Lenoir, planning to attempt the deepest dive ever made by a woman with a rebreather to 230 m (750 ft), died on 14 May 2010 in Dahab while ascending from a training dive at 147 m (482 ft).
Guy Garman died on 15 August 2015 in an unsuccessful attempt to dive to 370 m (1,200 ft). The Virgin Island Police Department confirmed that Guy Garman's body was recovered on 18 August 2015.
Theodora Balabanova died at Toroneos Bay, Greece, in September 2017 attempting to break the women's deep dive record with 231 m (758 ft). She did not complete the decompression stops and surfaced too early.
Wacław Lejko attempting 275 m (902 ft) in Lake Garda, died in September 2017. His body was recovered with a ROV at 230 m (750 ft).
Adam Krzysztof Pawlik, attempting a 316 m (1,037 ft) dive in Lake Garda, died on 18 October 2018. His body was located at 284 m (932 ft).
Sebastian Marczewski reached the target depth of 275 m (902 ft) in Lake Garda but his tanks became entangled in his ascent line at 150 m (490 ft). He died on 6 July 2019.
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OR2A1
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OR2A1
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Olfactory receptor 2A1/2A42 is a protein that in humans is encoded by the OR2A1 gene.Olfactory receptors interact with odorant molecules in the nose, to initiate a neuronal response that triggers the perception of a smell. The olfactory receptor proteins are members of a large family of G-protein-coupled receptors (GPCR) arising from single coding-exon genes. Olfactory receptors share a 7-transmembrane domain structure with many neurotransmitter and hormone receptors and are responsible for the recognition and G protein-mediated transduction of odorant signals. The olfactory receptor gene family is the largest in the genome. The nomenclature assigned to the olfactory receptor genes and proteins for this organism is independent of other organisms.
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Anthropological science fiction
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Anthropological science fiction
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The anthropologist Leon E. Stover says of science fiction's relationship to anthropology: "Anthropological science fiction enjoys the philosophical luxury of providing answers to the question "What is man?" while anthropology the science is still learning how to frame it".: 472 The editors of a collection of anthropological SF stories observed: Anthropology is the science of man. It tells the story from ape-man to spaceman, attempting to describe in detail all the epochs of this continuing history. Writers of fiction, and in particular science fiction, peer over the anthropologists' shoulders as the discoveries are made, then utilize the material in fictional works. Where the scientist must speculate reservedly from known fact and make a small leap into the unknown, the writer is free to soar high on the wings of fancy.: 12 Charles F. Urbanowicz, Professor of Anthropology, California State University, Chico has said of anthropology and SF: Anthropology and science fiction often present data and ideas so bizarre and unusual that readers, in their first confrontation with both, often fail to appreciate either science fiction or anthropology. Intelligence does not merely consist of fact, but in the integration of ideas -- and ideas can come from anywhere, especially good science fiction! The difficulty in describing category boundaries for 'anthropological SF' is illustrated by a reviewer of an anthology of anthropological SF, written for the journal American Anthropologist, which warned against too broad a definition of the subgenre, saying: "Just because a story has anthropologists as protagonists or makes vague references to 'culture' does not qualify it as anthropological science fiction, although it may be 'pop' anthropology." The writer concluded the book review with the opinion that only "twelve of the twenty-six selections can be considered as examples of anthropological science fiction.": 798 This difficulty of categorization explains the exclusions necessary when seeking the origins of the subgenre. Thus: Nineteenth-century utopian writings and lost-race sagas notwithstanding, anthropological science fiction is generally considered a late-twentieth-century phenomenon, best exemplified by the work of writers such as Ursula K. Le Guin, Michael Bishop, Joanna Russ, Ian Watson, and Chad Oliver.: 243 Again, questions of description are not simple as Gary Westfahl observes: ... others present hard science fiction as the most rigorous and intellectually demanding form of science fiction, implying that those who do not produce it are somehow failing to realize the true potential of science fiction. This is objectionable ...; writers like Chad Oliver and Ursula K. Le Guin, for example, bring to their writing a background in anthropology that makes their extrapolated aliens and future societies every bit as fascinating and intellectually involving as the technological marvels and strange planets of hard science fiction. Because anthropology is a social science, not a natural science, it is hard to classify their works as hard science fiction, but one cannot justly construe this observation as a criticism.: 189 Despite being described as a "late-twentieth-century phenomenon" (above) anthropological SF's roots can be traced further back in history. H. G. Wells (1866–1946) has been called "the Shakespeare of SF": 133 and his first anthropological story has been identified by anthropologist Leon E. Stover as "The Grisly Folk". Stover notes that this story is about Neanderthal Man, and writing in 1973,: 472 continues: "[the story] opens with the line 'Can these bones live?' Writers are still trying to make them live, the latest being Golding. Some others in between have been de Camp, Del Rey, Farmer, and Klass." A more contemporary example of the Neanderthal as subject is Robert J. Sawyer's trilogy "The Neanderthal Parallax" – here "scientists from an alternative earth in which Neanderthals superseded homo sapiens cross over to our world. The series as a whole allows Sawyer to explore questions of evolution and humanity's relationship to the environment.": 317
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Anthropological science fiction
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Authors and works
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Chad Oliver Anthropological science fiction is best exemplified by the work of writers such as Ursula K. Le Guin, Michael Bishop, Joanna Russ, Ian Watson, and Chad Oliver. Of this pantheon, Oliver is alone in being also a professional anthropologist, author of academic tomes such as Ecology and Cultural Continuity as Contributing Factors in the Social Organization of the Plains Indians (1962) and The Discovery of Anthropology (1981) in addition to his anthropologically-inflected science fiction. Although he tried, in a superficial way, to separate these two aspects of his career, signing his anthropology texts with his given name "Symmes C. Oliver", he nonetheless saw them as productively interrelated. "I like to think," he commented in a 1984 interview, "that there's a kind of feedback ... that the kind of open-minded perspective in science fiction conceivably has made me a better anthropologist. And on the other side of the coin, the kind of rigor that anthropology has, conceivably has made me a better science fiction writer.": 243 Thus "Oliver's Unearthly Neighbors (1960) highlights the methods of ethnographic fieldwork by imagining their application to a nonhuman race on another world. His Blood's a Rover (1955 [1952]) spells out the problems of applied anthropology by sending a technical-assistance team to an underdeveloped planet. His Rite of Passage (1966 [1954]) is a lesson in the patterning of culture, how humans everywhere unconsciously work out a blueprint for living. Anthropological wisdom is applied to the conscious design of a new blueprint for American society in his Mother of Necessity (1972 [1955])". Oliver's The Winds of Time is a "science fiction novel giving an excellent introduction to the field methods of descriptive linguistics".: 96 In 1993 a journal of SF criticism requested from writers and critics of SF a list of their 'most neglected' writers, and Chad Oliver was listed in three replies. Among the works chosen were: Shadows in the Sun, Unearthly Neighbors, and The Shores of Another Sea. One respondent declared that "Oliver's anthropological SF is the precursor of more recent novels by Ursula K. Le Guin, Michael Bishop, and others"; another that "Chad Oliver was developing quiet, superbly crafted anthropological fictions long before anyone had heard of Le Guin; maybe his slight output and unassuming plots (and being out of print) have caused people to overlook the carefully thought-out ideas behind his fiction".In the novel Shadows in the Sun the protagonist, Paul Ellery, is an anthropologist doing field work in the town of Jefferson Springs, Texas—a place where he discovers extraterrestrial aliens. It has been remarked that: Not only are these aliens comprehensible in anthropological terms, but it is anthropology, rather than the physical sciences, that promises a solution to the problem of alien colonization. According to the science of anthropology, every society, regardless of its level of development, has to functionally meet certain human needs. The aliens of Jefferson Springs "had learned, long ago, that it was the cultural core that counted-the deep and underlying spirit and belief and knowledge, the tone and essence of living. Once you had that, the rest was window dressing. Not only that, but the rest, the cultural superstructure, was relatively equal in all societies (115; emphasis in original). For Ellery, the aliens are not "supermen" (a favorite Campbellian conceit): despite their fantastic technologies, they are ultimately ordinary people with the expected array of weaknesses – laziness, factionalism, arrogance – whose cultural life is as predictable as any Earth society's. Since they are not superior, they are susceptible to defeat, but the key lies not in the procurement of advanced technologies, but in the creative cultural work of Earth people themselves.: 248 A reviewer of The Shores of Another Sea finds the book "curiously flat despite its exploration of an almost mythical, and often horrific, theme".: 202 The reviewer's reaction is not surprising because, as Samuel Gerald Collins points out in the 'New Wave Anthropology' section of his comprehensive review of Chad Oliver's work: "In many ways, the novel is very much unlike Oliver's previous work; there is little moral resolution, nor is anthropology of much help in determining what motivates the aliens. In striking contrast to the familiar chumminess of the aliens in Shadows in the Sun and The Winds of Time, humans and aliens in Shores of Another Sea systematically misunderstand one another.": 253 Collins continues: In fact, the intervening decade between Oliver's field research and the publication of Shores [1971] had been one of critical self-reflection in the field of anthropology. In the United States, qualms about the Vietnam war, together with evidence that anthropologists had been employed as spies and propagandists by the US government, prompted critiques of anthropology's role in systems of national and global power. Various strains of what came to be known as dependency theory disrupted the self-congratulatory evolutionism of modernization models, evoking and critiquing a world system whose political economy structurally mandated unequal development. Less narrowly academic works such as Vine Deloria, Jr.'s, Custer Died for Your Sins (1969), combined with the efforts of civil-rights groups like the American Indian Movement, skewered anthropology's paternalist pretensions. Two major collections of essays -- Dell Hymes's Reinventing Anthropology (1972) and Talal Asad's Anthropology and the Colonial Encounter (1973) -- explored anthropology's colonial legacy and precipitated a critical engagement with the ethics and politics of ethnographic representation.: 253 At the conclusion of his essay, discussing Chad Oliver's legacy Collins says: The lesson of Chad Oliver for sf is that his Campbell-era commitments to the power of technology, rational thinking, and the evolutionary destiny of "humanity" came to seem an enshrinement of a Western imperialist vision that needed to be transcended, through a rethinking of otherness driven by anthropological theory and practice. Above all, Oliver's career speaks to many of the shared impulses and assumptions of anthropology and sf, connections that have only grown more multifarious and complex since his death in 1993.: 257 Ursula K. Le Guin It has often been observed that Ursula K. Le Guin's interest in anthropology and its influence on her fiction derives from the influence of both her mother Theodora Kroeber, and of her father, Alfred L. Kroeber.: 410 : 61 : 1 Warren G. Rochelle in his essay on Le Guin notes that from her parents she: acquired the "anthropological attitude" necessary for the observation of another culture – or for her, the invention of another culture: the recognition and appreciation of cultural diversity, the necessity to be a "close and impartial observer", who is objective, yet recognizes the inescapable subjectivity that comes with participation in an alien culture.: 410 Another critic has observed that Le Guin's "concern with cultural biases is evident throughout her literary career", and continues, In The Word for World is Forest (1972), for example, she explicitly demonstrates the failure of colonialists to comprehend other cultures, and shows how the desire to dominate and control interferes with the ability to perceive the other. Always Coming Home (1985) is an attempt to allow another culture to speak for itself through songs and music (available in cassette form), writings, and various unclassifiable fragments. Like a documentary, the text presents the audience with pieces of information that they can sift through and examine. But unlike a traditional anthropological documentary, there is no "voice-over" to interpret that information and frame it for them. The absence of "voice-over" commentary in the novel forces the reader to draw conclusions rather than rely on a scientific analysis which would be tainted with cultural blind spots. The novel, consequently, preserves the difference of the alien culture and removes the observing neutral eye from the scene until the very end.
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Anthropological science fiction
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Authors and works
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Le Guin's novel The Left Hand of Darkness has been called "the most sophisticated and technically plausible work of anthropological science fiction, insofar as the relationship of culture and biology is concerned",: 472 and also rated as "perhaps her most notable book".: 244 This novel forms part of Le Guin's Hainish Cycle (so termed because it develops as a whole "a vast story about diverse planets seeded with life by the ancient inhabitants of Hain").: 46–47 The series is "a densely textured anthropology, unfolding through a cycle of novels and stories and actually populated by several anthropologists and ethnologists".": 183 Le Guin employs the SF trope of inter-stellar travel which allows for fictional human colonies on other worlds developing widely differing social systems. For example, in The Left Hand of Darkness "a human envoy to the snowbound planet of Gethan struggles to understand its sexually ambivalent inhabitants".: 180 Published in 1969, this Le Guin novel: is only one of many subsequent novels that have dealt with androgyny and multiple gender/sex identities through a variety of approaches, from Samuel R. Delany's Triton (1976), Joanna Russ's Female Man (1975), Marge Piercy's Woman at the Edge of Time (1976), Marion Zimmer Bradley's Darkover series (1962–1996) and Octavia Butler's Xenogenesis Trilogy (1987-89). Though innovative in its time, it is not its construction of androgyny itself that is remarkable about Le Guin's text. Rather, it is her focus on the way that the androgynes are perceived and how they are constructed within a particular discourse, that of scientific observation. This discourse is manifested specifically in the language of anthropology, the social sciences as a whole, and diplomacy. This focus, in turn, places Le Guin's novel within a body of later works – such as Mary Gentle's Golden Witchbreed novels (1984-87) and C. J. Cherryh's Foreigner series (1994-96) – that deal with an outside observer's arrival on an alien planet, all of which indicate the difficulty of translating the life-style of an alien species into a language and cultural experience that is comprehensible. As such, these texts provide critiques of anthropological discourse that are similar to Trinh Minh-ha's attempts to problematize the colonialist beginnings and imperialistic undertones of anthropology as a science.
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Anthropological science fiction
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Authors and works
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Geoffery Samuel has pointed out some specific anthropological aspect to Le Guin's fiction, noting that: the culture of the people of Gethen in The Left Hand of Darkness clearly owes a lot to North-West Coast Indian and Eskimo culture; the role of dreams of Athshe (in The Word for World is Forest) is very reminiscent of that described for the Temiar people of Malaysia; and the idea of a special vocabulary of terms of address correlated with a hierarchy of knowledge, in City of Illusions, recalls the honorific terminologies of many Far Eastern cultures (such as Java or Tibet).
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Anthropological science fiction
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Authors and works
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However, Fredric Jameson says of The Left Hand of Darkness that the novel is "constructed from a heterogeneous group of narratives modes ...", and that: ... we find here intermingled: the travel narrative (with anthropological data), the pastiche myth, the political novel (in the restricted sense of the drama of court intrigue), straight SF (the Hainish colonization, the spaceship in orbit around Gethen's sun), Orwellian dystopia ..., adventure story ..., and finally even, something like a multiracial love story (the drama of communication between the two cultures and species).: 267 Similarly Adam Roberts warns against a too narrow an interpretation of Le Guin's fiction, pointing out that her writing is always balanced and that "balance as such forms one of her major concerns. Both Left Hand and The Dispossed (1974) balance form to theme, of symbol to narration, flawlessly".: 244–245 Nevertheless, there is no doubt that the novel The Left Hand of Darkness is steeped in anthropological thought, with one academic critic noting that "the theories of [French anthropologist] Claude Lévi-Strauss provide an access to understanding the workings of the myths" in the novel. Later in the essay the author explains: Unlike the openended corpus of actual myths that anthropologists examine, the corpus of myths in The Left Hand of Darkness is closed and complete. Therefore, it is possible to analyze the entire set of Gethenian myths and establish the ways in which they are connected. Kinship exchange, in the Lévi-Straussian sense, comprises their dominant theme. In them, Le Guin articulates the theme of exchange by employing contrary images – heat and cold, dark and light, home and exile, name and namelessness, life and death, murder and sex – so as finally to reconcile their contrariety. The myths present wholeness, or unity, as an ideal; but that wholeness is never merely the integrity of an individual who stands apart from society. Instead, it consists of the tenuous and temporary integration of individuals into social units.: 181
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Compact Reconnaissance Imaging Spectrometer for Mars
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Compact Reconnaissance Imaging Spectrometer for Mars
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The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) was a visible-infrared spectrometer aboard the Mars Reconnaissance Orbiter searching for mineralogic indications of past and present water on Mars. The CRISM instrument team comprised scientists from over ten universities and was led by principal investigator Scott Murchie. CRISM was designed, built, and tested by the Johns Hopkins University Applied Physics Laboratory.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Objectives
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CRISM was being used to identify locations on Mars that may have hosted water, a solvent considered important in the search for past or present life on Mars. In order to do this, CRISM was mapping the presence of minerals and chemicals that may indicate past interaction with water - low-temperature or hydrothermal. These materials include iron and oxides, which can be chemically altered by water, and phyllosilicates and carbonates, which form in the presence of water. All of these materials have characteristic patterns in their visible-infrared reflections and were readily seen by CRISM. In addition, CRISM was monitoring ice and dust particulates in the Martian atmosphere to learn more about its climate and seasons.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Instrument overview
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CRISM measured visible and infrared electromagnetic radiation from 362 to 3920 nanometers in 6.55 nanometer increments. The instrument had two modes, a multispectral untargeted mode and a hyperspectral targeted mode. In the untargeted mode, CRISM reconnoiters Mars, recording approximately 50 of its 544 measurable wavelengths at a resolution of 100 to 200 meters per pixel. In this mode CRISM mapped half of Mars within a few months after aerobraking and most of the planet after one year. The objective of this mode is to identify new scientifically interesting locations that could be further investigated. In targeted mode, the spectrometer measured energy in all 544 wavelengths. When the MRO spacecraft is at an altitude of 300 km, CRISM detects a narrow but long strip on the Martian surface about 18 kilometers across and 10,800 kilometers long. The instrument swept this strip across the surface as MRO orbits Mars to image the surface.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Instrument design
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The data collecting part of CRISM was called the Optical Sensor Unit (OSU) and consisted of two spectrographs, one that detected visible light from 400 to 830 nm and one that detected infrared light from 830 to 4050 nm. The infrared detector was cooled to –173° Celsius (–280° Fahrenheit) by a radiator plate and three cryogenic coolers. While in targeted mode, the instrument gimbals in order to continue pointing at one area even though the MRO spacecraft is moving. The extra time collecting data over a targeted area increases the signal-to-noise ratio as well as the spatial and spectral resolution of the image. This scanning ability also allowed the instrument to perform emission phase functions, viewing the same surface through variable amounts of atmosphere, which would be used to determine atmospheric properties. The Data Processing Unit (DPU) of CRISM performs in-flight data processing including compressing the data before transmission.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Investigations
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CRISM began its exploration of Mars in late 2006. Results from the OMEGA visible/near-infrared spectrometer on Mars Express (2003–present), the Mars Exploration Rovers (MER; 2003–2019), the TES thermal emission spectrometer on Mars Global Surveyor (MGS; 1997-2006), and the THEMIS thermal imaging system on Mars Odyssey (2004–present) helped to frame the themes for CRISM's exploration: Where and when did Mars have persistently wet environments? What is the composition of Mars' crust? What are the characteristics of Mars' modern climate?In November 2018, it was announced that CRISM had fabricated some additional pixels representing the minerals alunite, kieserite, serpentine and perchlorate. The instrument team found that some false positives were caused by a filtering step when the detector switches from a high luminosity area to shadows. Reportedly, 0.05% of the pixels were indicating perchlorate, now known to be a false high estimate by this instrument. However, both the Phoenix lander and the Curiosity rover measured 0.5% perchlorates in the soil, suggesting a global distribution of these salts. Perchlorate is of interest to astrobiologists, as it sequesters water molecules from the atmosphere and reduces its freezing point, potentially creating thin films of watery brine that —although toxic to most Earth life— it could potentially offer habitats for native Martian microbes in the shallow subsurface. (See: Life on Mars#Perchlorates) Persistently wet environments Aqueous minerals are minerals that form in water, either by chemical alteration of pre-existing rock or by precipitation out of solution. The minerals indicate where liquid water existed long enough to react chemically with rock. Which minerals form depends on temperature, salinity, pH, and composition of the parent rock. Which aqueous minerals are present on Mars therefore provides important clues to understanding past environments. The OMEGA spectrometer on the Mars Express orbiter and the MER rovers both uncovered evidence for aqueous minerals. OMEGA revealed two distinct kinds of past aqueous deposits. The first, containing sulfates such as gypsum and kieserite, is found in layered deposits of Hesperian age (Martian middle age, roughly from 3.7 to 3 billion years ago). The second, rich in several different kinds of phyllosilicates, instead occurs rocks of Noachian age (older than about 3.7 billion years). The different ages and mineral chemistries suggest an early water-rich environment in which phyllosilicates formed, followed by a dryer, more saline and acidic environment in which sulfates formed. The MER Opportunity rover spent years exploring sedimentary rocks formed in the latter environment, full of sulfates, salts, and oxidized iron minerals.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Investigations
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Soil forms from parent rocks through physical disintegration of rocks and by chemical alteration of the rock fragments. The types of soil minerals can reveal if the environment was cool or warm, wet or dry, or whether the water was fresh or salty. Because CRISM is able to detect many minerals in the soil or regolith, the instrument is being used to help decipher ancient Martian environments. CRISM has found a characteristic layering pattern of aluminum-rich clays overlying iron- and magnesium-rich clays in many areas scattered through Mars' highlands. Surrounding Mawrth Vallis, these "layered clays" cover hundreds of thousands of square kilometers. Similar layering occurs near the Isidis basin, in the Noachian plains surrounding Valles Marineris, and in Noachian plains surrounding the Tharsis plateau. The global distribution of layered clays suggests a global process. Layered clays are late Noachian in age, dating from the same time as water-carved valley networks. The layered clay composition is similar to what is expected for soil formation on Earth - a weathered upper layer leached of soluble iron and magnesium, leaving an insoluble aluminum-rich residue, with a lower layer that still retains its iron and magnesium. Some researchers have suggested that the Martian clay "layer cake" was created by soil-forming processes, including rainfall, at the time that valley networks formed. Lake and marine environments on Earth are favorable for fossil preservation, especially where the sediments they left behind are rich in carbonates or clays. Hundreds of highland craters on Mars have horizontally layered, sedimentary rocks that may have formed in lakes. CRISM has taken many targeted observations of these rocks to measure their mineralogy and how the minerals vary between layers. Variation between layers helps us to understand the sequence of events that formed the sedimentary rocks. The Mars Orbiter Camera found that where valley networks empty into craters, commonly the craters contain fan-shaped deposits. However it was not completely clear if the fans formed by sediment deposition on dry crater floors (alluvial fans) or in crater lakes (deltas). CRISM discovered that in the fans' lowermost layers, there are concentrated deposits of clay. More clay occurs beyond the end of the fans on the crater floors, and in some cases there is also opal. On Earth, the lowermost layers of deltas are called bottom set beds, and they are made of clays that settled out of inflowing river water in quiet, deep parts of the lakes. This discovery supports the idea that many fans formed in crater lakes where, potentially, evidence for habitable environments could be preserved.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Investigations
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Not all ancient Martian lakes were fed by inflowing valley networks. CRISM discovered several craters on the western slope of Tharsis that contain "bathtub rings" of sulfate minerals and a kind of phyllosilicate called kaolinite. Both minerals can form together by precipitating out of acidic, saline water. These craters lack inflowing valley networks, showing that they were not fed by rivers - instead, they must have been fed by inflowing groundwater.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Investigations
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The identification of hot spring deposits was a priority for CRISM, because hot springs would have had energy (geothermal heat) and water, two basic requirements for life. One of the signatures of hot springs on Earth is deposits of silica. The MER Spirit rover explored a silica-rich deposit called "Home Plate" that is thought to have formed in a hot spring. CRISM has discovered other silica-rich deposits in many locations. Some are associated with central peaks of impact craters, which are sites of heating driven by meteor impact. Silica has also been identified on the flanks of volcanic inside the caldera of the Syrtis Major shield volcano, forming light-colored mounds that look like scaled-up versions of Home Plate. Elsewhere, in the westernmost parts of Valles Marineris, near the core of the Tharsis volcanic province, there are sulfate and clay deposits suggestive of "warm" springs. Hot spring deposits are one of the most promising areas on Mars to search for evidence for past life.One of the leading hypotheses for why ancient Mars was wetter than today is that a thick, carbon dioxide-rich atmosphere created a global greenhouse, that warmed the surface enough for liquid water to occur in large amounts. Carbon dioxide ice in today's polar caps is too limited in volume to hold that ancient atmosphere. If a thick atmosphere ever existed, it was either blown into space by solar wind or impacts, or reacted with silicate rocks to become trapped as carbonates in Mars' crust. One of the goals that drove CRISM's design was to find carbonates, to try to solve this question about what happened to Mars' atmosphere. And one of CRISM's most important discoveries was the identification of carbonate bedrock in Nili Fossae in 2008. Soon thereafter, landed missions to Mars started identifying carbonates on the surface; the Phoenix Mars lander found between 3–5 wt% calcite (CaCO3) at its northern lowland landing site, while the MER Spirit rover identified outcrops rich in magnesium-iron carbonate (16–34 wt%) in the Columbia Hills of Gusev crater. Later CRISM analyses identified carbonates in the rim of Huygens crater which suggested that there could be extensive deposits of buried carbonates on Mars. However, a study by CRISM scientists estimated that all of the carbonate rock on Mars holds less than the present Martian atmosphere worth of carbon dioxide. They determined that if a dense ancient Martian atmosphere did exist, it is probably not trapped in the crust.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Investigations
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Crustal composition Understanding the composition of Mars' crust and how it changed with time tells us about many aspects of Mars' evolution as a planet, and was a major goal of CRISM. Remote and landed measurements prior to CRISM, and analysis of Martian meteorites, all suggest that the Martian crust is made mostly of basaltic igneous rock composed mostly of feldspar and pyroxene. Images from the Mars Orbiter Camera on MGS showed that in some places the upper few kilometers of the crust is composed of hundreds of thin volcanic lava flows. TES and THEMIS both found mostly basaltic igneous rock, with scattered olivine-rich and even some quartz-rich rocks.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Investigations
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The first recognition of widespread sedimentary rock on Mars came from the Mars Orbiter Camera which found that several areas of the planet - including Valles Marineris and Terra Arabia - have horizontally layered, light-toned rocks. Follow-up observations of those rocks' mineralogy by OMEGA found that some are rich in sulfate minerals, and that other layered rocks around Mawrth Vallis are rich in phyllosilicates. Both class of minerals are signatures of sedimentary rocks. CRISM had used its improved spatial resolution to look for other deposits of sedimentary rock on Mars' surface, and for layers of sedimentary rock buried between layers of volcanic rock in Mars' crust.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Investigations
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Modern climates To understand Mars' ancient climate, and whether it might have created environments habitable for life, first we need to understand Mars' climate today. Each mission to Mars has made new advances in understanding its climate. Mars has seasonal variations in the abundances of water vapor, water ice clouds and hazes, and atmospheric dust. During southern summer, when Mars is closest to the Sun (at perihelion), solar heating can raise massive dust storms. Regional dust storms - ones having a 1000-kilometer scale - show surprising repeatability Mars-year to Mars-year. Once every decade or so, they grow into global-scale events. In contrast, during northern summer when Mars is furthest from the Sun (at aphelion), there is an equatorial water-ice cloud belt and very little dust in the atmosphere. Atmospheric water vapor varies in abundance seasonally, with the greatest abundances in each hemisphere's summer after the seasonal polar caps have sublimated into the atmosphere. During winter, both water and carbon dioxide frost and ices form on Mars' surface. These ices form the seasonal and residual polar caps. The seasonal caps - which form each autumn and sublimate each spring - are dominated by carbon dioxide ice. The residual caps - which persist year after year - consist mostly of water ice at the north pole and water ice with a thin veneer (a few 10's of meters thick) of carbon dioxide ice at the south pole.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Investigations
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Mars' atmosphere is so thin and wispy that solar heating of dust and ice in the atmosphere - not heating of the atmospheric gases - is more important in driving weather. Small, suspended particles of dust and water ice - aerosols - intercept 20–30% of incoming sunlight, even under relatively clear conditions. So variations in the amounts of these aerosols have a huge influence on climate. CRISM had taken three major kinds of measurements of dust and ice in the atmosphere: targeted observations whose repeated views of the surface provide a sensitive estimate of aerosol abundance; special global grids of targeted observations every couple of months designed especially to track spatial and seasonal variations; and scans across the planet's limb to show how dust and ice vary with height above the surface.
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Compact Reconnaissance Imaging Spectrometer for Mars
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Investigations
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The south polar seasonal cap has a bizarre variety of bright and dark streaks and spots that appear during spring, as carbon dioxide ice sublimates. Prior to MRO there were various ideas for processes that could form these strange features, a leading model being carbon dioxide geysers. CRISM had watched the dark spots grow during southern spring, and found that bright streaks forming alongside the dark spots are made of fresh, new carbon dioxide frost, pointing like arrows back to their sources - the same sources as the dark spots. The bright streaks probably form by expansion, cooling, and freezing of the carbon dioxide gas, forming a "smoking gun" to support the geyser hypothesis.
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International Journal on Artificial Intelligence Tools
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International Journal on Artificial Intelligence Tools
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The International Journal on Artificial Intelligence Tools was founded in 1992 and is published by World Scientific. It covers research on artificial intelligence (AI) tools or tools that use AI, including architectures, languages and algorithms. Topics include AI in Bioinformatics, Cognitive Informatics, Knowledge-Based/Expert Systems and Object-Oriented Programming for AI.
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International Journal on Artificial Intelligence Tools
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Abstracting and indexing
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The journal is abstracted and indexed in: Inspec Science Citation Index Expanded ISI Alerting Services CompuMath Citation Index Current Contents/Engineering, Computing, and Technology
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P-form electrodynamics
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P-form electrodynamics
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In theoretical physics, p-form electrodynamics is a generalization of Maxwell's theory of electromagnetism.
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P-form electrodynamics
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Ordinary (via. one-form) Abelian electrodynamics
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We have a one-form A , a gauge symmetry A→A+dα, where α is any arbitrary fixed 0-form and d is the exterior derivative, and a gauge-invariant vector current J with density 1 satisfying the continuity equation d⋆J=0, where ⋆ is the Hodge star operator.
Alternatively, we may express J as a closed (n − 1)-form, but we do not consider that case here.
F is a gauge-invariant 2-form defined as the exterior derivative F=dA .F satisfies the equation of motion d⋆F=⋆J (this equation obviously implies the continuity equation).
This can be derived from the action S=∫M[12F∧⋆F−A∧⋆J], where M is the spacetime manifold.
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P-form electrodynamics
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p-form Abelian electrodynamics
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We have a p-form B , a gauge symmetry B→B+dα, where α is any arbitrary fixed (p − 1)-form and d is the exterior derivative, and a gauge-invariant p-vector J with density 1 satisfying the continuity equation d⋆J=0, where ⋆ is the Hodge star operator.
Alternatively, we may express J as a closed (n − p)-form.
C is a gauge-invariant (p + 1)-form defined as the exterior derivative C=dB .B satisfies the equation of motion d⋆C=⋆J (this equation obviously implies the continuity equation).
This can be derived from the action S=∫M[12C∧⋆C+(−1)pB∧⋆J] where M is the spacetime manifold.
Other sign conventions do exist.
The Kalb–Ramond field is an example with p = 2 in string theory; the Ramond–Ramond fields whose charged sources are D-branes are examples for all values of p. In 11-dimensional supergravity or M-theory, we have a 3-form electrodynamics.
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P-form electrodynamics
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Non-abelian generalization
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Just as we have non-abelian generalizations of electrodynamics, leading to Yang–Mills theories, we also have nonabelian generalizations of p-form electrodynamics. They typically require the use of gerbes.
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MBASIC
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MBASIC
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MBASIC is the Microsoft BASIC implementation of BASIC for the CP/M operating system. MBASIC is a descendant of the original Altair BASIC interpreters that were among Microsoft's first products. MBASIC was one of the two versions of BASIC bundled with the Osborne 1 computer. The name "MBASIC" is derived from the disk file name MBASIC.COM of the BASIC interpreter.
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MBASIC
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Environment
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MBASIC version 5 required a CP/M system with at least 28 kB of random access memory (RAM) and at least one diskette drive.
Unlike versions of Microsoft BASIC-80 that were customized by home computer manufacturers to use the particular hardware features of the computer, MBASIC relied only on the CP/M operating system calls for all input and output. Only the CP/M console (screen and keyboard), line printer, and disk devices were available.
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MBASIC
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Environment
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MBASIC in the uncustomized form had no functions for graphics, color, joysticks, mice, serial communications, networking, sound, or even a real-time clock function. MBASIC did not fully support the features of the host CP/M operating system, for example, it did not support CP/M's user areas for organizing files on a diskette. Since CP/M systems were typically single-user and stand alone, there was no provision for file or record locking, or any form of multitasking. Apart from these limitations, MBASIC was considered at the time to be a powerful and useful implementation of BASIC.
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MBASIC
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Features
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Language system MBASIC is an interpreter. Program source text was stored in memory in tokenized form, with BASIC keywords replaced by one-byte tokens which saved memory space and speeded execution. Any line prefixed with a line number was stored as program text; BASIC statements not prefixed with a line number were executed immediately as commands. Programs could be listed on the screen for editing, or saved to disk in either a compressed binary format or as plain ASCII text. Every source line was identified with a number, which could be used as the target of a GOTO or GOSUB transfer. Only line editing commands were provided. It was often beneficial to save a program as plain text and edit it with a full featured editor.
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MBASIC
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Features
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Program text, variables, disk buffers and the CP/M operating system itself all had to share the 64 kilobyte address space of the 8080 processor. Typically when first starting MBASIC there would be less than 32 kB memory available for programs and data, even on a machine equipped with a full 64 kilobytes of RAM. Comment lines, prefixed with the REM keyword or an apostrophe, could be placed in the program text but took up valuable memory space, which discouraged BASIC users from fully documenting their code. To allow larger and more complex programs to be run, later versions of MBASIC supported functions that allowed portions of program text to be read in and executed under program control (the " CHAIN " and MERGE statements). No support for "shell" command execution was provided, though this functionality could be duplicated by a determined programmer.
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MBASIC
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Features
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A particular advantage of MBASIC was the full-text error messages provided for syntax and run-time errors. MBASIC also had a "trace" function that displayed line numbers as they were executed. While this occupied the same screen space as normal program output, it was useful for detecting conditions such as endless loops.
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MBASIC
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Features
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Files and input/output Data could be read and stored to disk as either sequential files (delimited by the CP/M convention of CR/LF at the end of each line) or else as fixed-record-length random access files, which, given a sufficiently determined programmer, could be used to perform database-type record manipulation. The Microsoft Binary Format for floating point numbers was proprietary to the implementation, which meant that data could only be interchanged with other programs using ASCII text representation or else with extensive programming to convert the binary format.
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MBASIC
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Features
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Variables and data types MBASIC supported the following data types: 8-bit character data, in strings of length 0 to 255 characters; 16-bit integers; 32-bit floating point (single precision), equivalent to six decimal digits, with a two-digit exponent; 64-bit floating point (double precision), equivalent to sixteen decimal digits, with a two-digit exponent.String operators included substring selection, concatenation, assignment, and testing for equality.
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MBASIC
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Features
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Arrays of the above types were allowed with up to 7 dimensions, but no functions or operators worked on arrays; for example, there was no assignment of arrays. Unlike some other BASIC implementations of the time, MBASIC did not provide support for matrix operations, complex numbers, or a decimal (BCD) data type for financial calculations. All floating point operations were carried out in software since typical CP/M systems did not have floating point hardware. The built-in mathematics functions (sine, cosine, tangent, natural log, exponential, square root) only gave single precision results. A software pseudorandom number generator was provided; this relied on the user to key in a seed number to obtain a sequence of numbers useful for games and some simulations. MBASIC permitted but did not require the LET keyword for assignment statements.
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MBASIC
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Features
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Early versions of BASIC on microcomputers were infamous for one- or two-character variable names, which made the meanings of variables difficult to recall in complex programs. MBASIC version 5 allowed identifiers up to 40 characters long, which permitted programmers to give variables readable names.
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MBASIC
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Features
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Program flow control Program flow control in MBASIC was controlled by IF...THEN...ELSE... conditional tests, WHILE...WEND loops, and GOTO and GOSUB instructions. No CASE statement was available, although an ON...GOTO... (computed GOTO) provided multi-way branches. Subroutines had no parameters and all variables were global. MBASIC did not make structured programming mandatory for programmers and it was easy to write spaghetti code.
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MBASIC
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PEEKs, POKEs, and user functions
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No discussion of BASICs on the 8-bit computers of the late '70s and early '80s would be complete without mentioning the importance of the PEEK and POKE functions for directly reading and writing to memory. Since these systems typically had no memory protection, this allowed a programmer to access portions of the operating system, or functions that would not otherwise be available. This also provided opportunities for user programs to hang the system (by accident, usually). For example, a CP/M programmer might use a POKE function to allow BASIC to switch the console device to the serial port, if the system BIOS supported this. For machines with real-time clocks, a set of PEEK instructions might have been used to access the time.
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MBASIC
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PEEKs, POKEs, and user functions
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For more complex operations, MBASIC allowed user-defined functions that could be called from a BASIC program. These were typically placed in a reserved area of memory, or POKEd into string constants, as a series of machine codes (op codes). MBASIC also provided hardware INP and OUT instructions that read and wrote directly to the 8080 hardware input/output ports. This could be used to control peripheral devices from a BASIC program if the system hardware permitted. Any MBASIC programs that made use of PEEK and POKE, and of machine code user functions, were not portable between machines without modifications.
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MBASIC
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Successors to MBASIC
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Besides Microsoft's BASIC-80 for CP/M, a variant of MBASIC was also available as for the ISIS-II operating system.
MSX-BASIC is also a well known successor of MBASIC, featuring several extensions specific to the MSX machines.
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MBASIC
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Successors to MBASIC
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All the functions of CP/M MBASIC were available in the IBM PC disk-based BASICA or GWBASIC which made migration of programs from CP/M systems to PC-compatibles possible. The tokens used to represent keywords were different, so CP/M programs had to be saved in ASCII source form. Typically screen formatting escape sequences put into the CP/M version would be replaced with the cursor positioning commands found in the PC versions of BASIC, otherwise little rewriting would be needed.
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MBASIC
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BASCOM
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Microsoft sold a CP/M BASIC compiler (known as BASCOM) which used a similar source language to MBASIC. A program debugged under MBASIC could be compiled with BASCOM. Since program text was no longer in memory and the run-time elements of the compiler were smaller than the interpreter, more memory was available for user data. Speed of real program execution increased about 3 fold.
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MBASIC
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BASCOM
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Developers welcomed BASCOM as an alternative to the popular but slow and clumsy CBASIC. Unlike CBASIC, BASCOM did not need a preprocessor for MBASIC source code so could be debugged interactively. A disadvantage was Microsoft's requirement of a 9% royalty for each compiled copy of a program and $40 for hardware-software combinations. The company also reserved the right to audit developers' financial records. Because authors' typical royalty rates for software was 10-25%, InfoWorld in 1980 stated that BASCOM's additional 9% royalty rate "could make software development downright unprofitable", concluding that "Microsoft has the technical solution [to CBASIC's flaws], but not the economic one".
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MBASIC
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Importance of MBASIC
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MBASIC was an important tool during the era of 8-bit CP/M computers. Skilled users could write routines in MBASIC to automate tasks that in modern-day systems would be performed by powerful application program commands or scripting languages. Exchange of useful MBASIC programs was a common function of computer users' groups. Keying in long BASIC listings from a magazine article was one way of "bootstrapping" software into a new CP/M system. At least one compiler for a high-level language was written in MBASIC, and many small games and utility programs ranging from a few lines to a few thousand lines of code were written.
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MBASIC
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Other uses
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MBASIC is also the name of a commercial BASIC compiler for the Microchip Technology PIC microcontroller family developed by Basic Micro, Inc., unrelated to the CP/M interpreter.
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ANKRD35
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ANKRD35
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Ankyrin repeat domain 35 also known as ANKRD35 is a protein which in humans is encoded by the ANKRD35 gene.
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ANKRD35
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Related gene problems
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TAR syndrome 1q21.1 deletion syndrome 1q21.1 duplication syndrome
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ArcGIS Pro
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ArcGIS Pro
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ArcGIS Pro is desktop GIS software developed by Esri, which replaces their ArcMap software generation. The product was announced as part of Esri's ArcGIS 10.3 release, ArcGIS Pro is notable in having a 64 bit architecture, combined 2-D, 3-D support, ArcGIS Online integration and Python 3 support.A major version update occurred with the release of ArcGIS Pro 3.0 in June, 2022. Several major changes include: the dropping of support for geocoders created with ArcMap 10.x and versions of ArcGIS Pro 2.9.x and earlier; project files created or modified with ArcGIS Pro 3.0 are not readable by versions 2.9.x and earlier; geodatabases created in 3.0 may not be fully compatible with prior versions; and perhaps most significantly, Parcel Fabric datasets created in prior versions must be upgraded to be fully compatible in version 3.0.
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4-Chlorobenzonitrile
|
4-Chlorobenzonitrile
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4-Chlorobenzonitrile is an organic compound with the formula ClC6H4CN. It is a white solid. The compound, one of three isomers of chlorobenzonitrile, is produced industrially by ammoxidation of 4-chlorotoluene. The compound is of commercial interest as a precursor to pigments.
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