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Opal | Sources | Andamooka in South Australia is also a major producer of matrix opal, crystal opal, and black opal. Another Australian town, Lightning Ridge in New South Wales, is the main source of black opal, opal containing a predominantly dark background (dark gray to blue-black displaying the play of color), collected from the Griman Creek Formation. Boulder opal consists of concretions and fracture fillings in a dark siliceous ironstone matrix. It is found sporadically in western Queensland, from Kynuna in the north, to Yowah and Koroit in the south. Its largest quantities are found around Jundah and Quilpie in South West Queensland. Australia also has opalized fossil remains, including dinosaur bones in New South Wales and South Australia, and marine creatures in South Australia. |
Opal | Sources | Ethiopia It has been reported that Northern African opal was used to make tools as early as 4000 BC. The first published report of gem opal from Ethiopia appeared in 1994, with the discovery of precious opal in the Menz Gishe District, North Shewa Province. The opal, found mostly in the form of nodules, was of volcanic origin and was found predominantly within weathered layers of rhyolite. This Shewa Province opal was mostly dark brown in color and had a tendency to crack. These qualities made it unpopular in the gem trade. In 2008, a new opal deposit was found approximately 180 km north of Shewa Province, near the town of Wegel Tena, in Ethiopia's Wollo Province. The Wollo Province opal was different from the previous Ethiopian opal finds in that it more closely resembled the sedimentary opals of Australia and Brazil, with a light background and often vivid play-of-color. Wollo Province opal, more commonly referred to as "Welo" or "Wello" opal, has become the dominant Ethiopian opal in the gem trade. |
Opal | Sources | Virgin Valley, Nevada The Virgin Valley opal fields of Humboldt County in northern Nevada produce a wide variety of precious black, crystal, white, fire, and lemon opal. The black fire opal is the official gemstone of Nevada. Most of the precious opal is partial wood replacement. The precious opal is hosted and found in situ within a subsurface horizon or zone of bentonite, which is considered a "lode" deposit. Opals which have weathered out of the in situ deposits are alluvial and considered placer deposits. Miocene-age opalised teeth, bones, fish, and a snake head have been found. Some of the opal has high water content and may desiccate and crack when dried. The largest producing mines of Virgin Valley have been the famous Rainbow Ridge, Royal Peacock, Bonanza, Opal Queen, and WRT Stonetree/Black Beauty mines. The largest unpolished black opal in the Smithsonian Institution, known as the "Roebling opal", came out of the tunneled portion of the Rainbow Ridge Mine in 1917, and weighs 2,585 carats (517.0 g; 18.24 oz). The largest polished black opal in the Smithsonian Institution comes from the Royal Peacock opal mine in the Virgin Valley, weighing 160 carats (32 g; 1.1 oz), known as the "Black Peacock". |
Opal | Sources | Mexico Fire opal is a transparent to translucent opal with warm body colors of yellow to orange to red. Although fire opals don't usually show any play of color, they occasionally exhibit bright green flashes. The most famous source of fire opals is the state of Querétaro in Mexico; these opals are commonly called Mexican fire opals. Fire opals that do not show a play of color are sometimes referred to as jelly opals. Mexican opals are sometimes cut in their rhyolitic host material if it is hard enough to allow cutting and polishing. This type of Mexican opal is referred to as a Cantera opal. Another type of opal from Mexico, referred to as Mexican water opal, is a colorless opal that exhibits either a bluish or golden internal sheen.Opal occurs in significant quantity and variety in central Mexico, where mining and production first originated in the state of Querétaro. In this region the opal deposits are located mainly in the mountain ranges of three municipalities: Colón, Tequisquiapan and Ezequiel Montes. During the 1960s through to the mid-1970s, the Querétaro mines were heavily mined. Today's opal miners report that it was much easier to find quality opals with a lot of fire and play of color back then, whereas today the gem-quality opals are very hard to come by and command hundreds of US dollars or more. The orange-red background color is characteristic of all "fire opals," including "Mexican fire opal". |
Opal | Sources | The oldest mine in Querétaro is Santa Maria del Iris. This mine was opened around 1870 and has been reopened at least 28 times since. At the moment there are about 100 mines in the regions around Querétaro, but most of them are now closed. The best quality of opals came from the mine Santa Maria del Iris, followed by La Hacienda la Esperanza, Fuentezuelas, La Carbonera, and La Trinidad. Important deposits in the state of Jalisco were not discovered until the late 1950s. |
Opal | Sources | In 1957, Alfonso Ramirez (of Querétaro) accidentally discovered the first opal mine in Jalisco: La Unica, located on the outer area of the volcano of Tequila, near the Huitzicilapan farm in Magdalena. By 1960 there were around 500 known opal mines in this region alone. Other regions of the country that also produce opals (of lesser quality) are Guerrero, which produces an opaque opal similar to the opals from Australia (some of these opals are carefully treated with heat to improve their colors so high-quality opals from this area may be suspect). There are also some small opal mines in Morelos, Durango, Chihuahua, Baja California, Guanajuato, Puebla, Michoacán, and Estado de México. |
Opal | Sources | Other locations Another source of white base opal or creamy opal in the United States is Spencer, Idaho. A high percentage of the opal found there occurs in thin layers.
Other significant deposits of precious opal around the world can be found in the Czech Republic, Canada, Slovakia, Hungary, Turkey, Indonesia, Brazil (in Pedro II, Piauí), Honduras (more precisely in Erandique), Guatemala and Nicaragua.
In late 2008, NASA announced the discovery of opal deposits on Mars. |
Opal | Synthetic opal | Opals of all varieties have been synthesized experimentally and commercially. The discovery of the ordered sphere structure of precious opal led to its synthesis by Pierre Gilson in 1974. The resulting material is distinguishable from natural opal by its regularity; under magnification, the patches of color are seen to be arranged in a "lizard skin" or "chicken wire" pattern. Furthermore, synthetic opals do not fluoresce under ultraviolet light. Synthetics are also generally lower in density and are often highly porous. |
Opal | Synthetic opal | Opals which have been created in a laboratory are often termed "lab-created opals", which, while classifiable as man-made and synthetic, are very different from their resin-based counterparts which are also considered man-made and synthetic. The term "synthetic" implies that a stone has been created to be chemically and structurally indistinguishable from a genuine one, and genuine opal contains no resins or polymers. The finest modern lab-created opals do not exhibit the lizard skin or columnar patterning of earlier lab-created varieties, and their patterns are non-directional. They can still be distinguished from genuine opals, however, by their lack of inclusions and the absence of any surrounding non-opal matrix. While many genuine opals are cut and polished without a matrix, the presence of irregularities in their play-of-color continues to mark them as distinct from even the best lab-created synthetics. |
Opal | Synthetic opal | Other research in macroporous structures have yielded highly ordered materials that have similar optical properties to opals and have been used in cosmetics. Synthetic opals are also deeply investigated in photonics for sensing and light management purposes. |
Opal | Local atomic structure of opals | The lattice of spheres of opal that cause interference with light is several hundred times larger than the fundamental structure of crystalline silica. As a mineraloid, no unit cell describes the structure of opal. Nevertheless, opals can be roughly divided into those that show no signs of crystalline order (amorphous opal) and those that show signs of the beginning of crystalline order, commonly termed cryptocrystalline or microcrystalline opal. Dehydration experiments and infrared spectroscopy have shown that most of the H2O in the formula of SiO2·nH2O of opals is present in the familiar form of clusters of molecular water. Isolated water molecules, and silanols, structures such as SiOH, generally form a lesser proportion of the total and can reside near the surface or in defects inside the opal. |
Opal | Local atomic structure of opals | The structure of low-pressure polymorphs of anhydrous silica consists of frameworks of fully corner bonded tetrahedra of SiO4. The higher temperature polymorphs of silica cristobalite and tridymite are frequently the first to crystallize from amorphous anhydrous silica, and the local structures of microcrystalline opals also appear to be closer to that of cristobalite and tridymite than to quartz. The structures of tridymite and cristobalite are closely related and can be described as hexagonal and cubic close-packed layers. It is therefore possible to have intermediate structures in which the layers are not regularly stacked. |
Opal | Local atomic structure of opals | Microcrystalline opal Microcrystalline opal or Opal-CT has been interpreted as consisting of clusters of stacked cristobalite and tridymite over very short length scales. The spheres of opal in microcrystalline opal are themselves made up of tiny nanocrystalline blades of cristobalite and tridymite. Microcrystalline opal has occasionally been further subdivided in the literature. Water content may be as high as 10 wt%. Opal-CT, also called lussatine or lussatite, is interpreted as consisting of localized order of α-cristobalite with a lot of stacking disorder. Typical water content is about 1.5 wt%. |
Opal | Local atomic structure of opals | Noncrystalline opal Two broad categories of noncrystalline opals, sometimes just referred to as "opal-A" ("A" stands for "amorphous"), have been proposed. The first of these is opal-AG consisting of aggregated spheres of silica, with water filling the space in between. Precious opal and potch opal are generally varieties of this, the difference being in the regularity of the sizes of the spheres and their packing. The second "opal-A" is opal-AN or water-containing amorphous silica-glass. Hyalite is another name for this. |
Opal | Local atomic structure of opals | Noncrystalline silica in siliceous sediments is reported to gradually transform to opal-CT and then opal-C as a result of diagenesis, due to the increasing overburden pressure in sedimentary rocks, as some of the stacking disorder is removed.
Opal surface chemical groups The surface of opal in contact with water is covered by siloxane bonds (≡Si–O–Si≡) and silanol groups (≡Si–OH). This makes the opal surface very hydrophilic and capable of forming numerous hydrogen bonds. |
Opal | Etymology | The word 'opal' is adapted from the Latin term opalus. The origin of this word in turn is a matter of debate, but most modern references suggest it is adapted from the Sanskrit word úpala meaning ‘precious stone’.References to the gem are made by Pliny the Elder. It is suggested to have been adapted from Ops, the wife of Saturn, and goddess of fertility. The portion of Saturnalia devoted to Ops was "Opalia", similar to opalus. |
Opal | Etymology | Another common claim that the term is adapted from the Ancient Greek word, opallios. This word has two meanings, one is related to "seeing" and forms the basis of the English words like "opaque"; the other is "other" as in "alias" and "alter". It is claimed that opalus combined these uses, meaning "to see a change in color". However, historians have noted the first appearances of opallios do not occur until after the Romans had taken over the Greek states in 180 BC and they had previously used the term paederos.However, the argument for the Sanskrit origin is strong. The term first appears in Roman references around 250 BC, at a time when the opal was valued above all other gems. The opals were supplied by traders from the Bosporus, who claimed the gems were being supplied from India. Before this, the stone was referred to by a variety of names, but these fell from use after 250 BC. |
Opal | Historical superstitions | In the Middle Ages, opal was considered a stone that could provide great luck because it was believed to possess all the virtues of each gemstone whose color was represented in the color spectrum of the opal. It was also said to grant invisibility if wrapped in a fresh bay leaf and held in the hand. As a result, the opal was seen as the patron gemstone for thieves during the medieval period. Following the publication of Sir Walter Scott's Anne of Geierstein in 1829, opal acquired a less auspicious reputation. In Scott's novel, the Baroness of Arnheim wears an opal talisman with supernatural powers. When a drop of holy water falls on the talisman, the opal turns into a colorless stone and the Baroness dies soon thereafter. Due to the popularity of Scott's novel, people began to associate opals with bad luck and death. Within a year of the publishing of Scott's novel in April 1829, the sale of opals in Europe dropped by 50%, and remained low for the next 20 years or so.Even as recently as the beginning of the 20th century, it was believed that when a Russian saw an opal among other goods offered for sale, he or she should not buy anything more, as the opal was believed to embody the evil eye.Opal is considered the birthstone for people born in October. |
Opal | Examples | The Olympic Australis, the world's largest and most valuable gem opal, found in Coober Pedy The Andamooka Opal, presented to Queen Elizabeth II, also known as the Queen's Opal The Addyman Plesiosaur from Andamooka, "the finest known opalised skeleton on Earth" The Burning of Troy, the now-lost opal presented to Joséphine de Beauharnais by Napoleon I of France and the first named opal The Flame Queen Opal The Halley's Comet Opal, the world's largest uncut black opal Although the clock faces above the information stand in Grand Central Terminal in New York City are often said to be opal, they are in fact opalescent glass The Roebling Opal, Smithsonian Institution The Galaxy Opal, listed as the "World's Largest Polished Opal" in the 1992 Guinness Book of Records The Rainbow Virgin, "the finest crystal opal specimen ever unearthed" The Sea of Opal, the largest black opal in the world The Fire of Australia, assumed to be "the finest uncut opal in existence" Beverly the Bug, the first known example of an opal with an insect inclusion |
Trophic level | Trophic level | The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it is from the start of the chain. A food web starts at trophic level 1 with primary producers such as plants, can move to herbivores at level 2, carnivores at level 3 or higher, and typically finish with apex predators at level 4 or 5. The path along the chain can form either a one-way flow or a food "web". Ecological communities with higher biodiversity form more complex trophic paths. |
Trophic level | Trophic level | The word trophic derives from the Greek τροφή (trophē) referring to food or nourishment. |
Trophic level | History | The concept of trophic level was developed by Raymond Lindeman (1942), based on the terminology of August Thienemann (1926): "producers", "consumers", and "reducers" (modified to "decomposers" by Lindeman). |
Trophic level | Overview | The three basic ways in which organisms get food are as producers, consumers, and decomposers. |
Trophic level | Overview | Producers (autotrophs) are typically plants or algae. Plants and algae do not usually eat other organisms, but pull nutrients from the soil or the ocean and manufacture their own food using photosynthesis. For this reason, they are called primary producers. In this way, it is energy from the sun that usually powers the base of the food chain. An exception occurs in deep-sea hydrothermal ecosystems, where there is no sunlight. Here primary producers manufacture food through a process called chemosynthesis. |
Trophic level | Overview | Consumers (heterotrophs) are species that cannot manufacture their own food and need to consume other organisms. Animals that eat primary producers (like plants) are called herbivores. Animals that eat other animals are called carnivores, and animals that eat both plants and other animals are called omnivores. |
Trophic level | Overview | Decomposers (detritivores) break down dead plant and animal material and wastes and release it again as energy and nutrients into the ecosystem for recycling. Decomposers, such as bacteria and fungi (mushrooms), feed on waste and dead matter, converting it into inorganic chemicals that can be recycled as mineral nutrients for plants to use again.Trophic levels can be represented by numbers, starting at level 1 with plants. Further trophic levels are numbered subsequently according to how far the organism is along the food chain. |
Trophic level | Overview | Level 1 Plants and algae make their own food and are called producers.
Level 2 Herbivores eat plants and are called primary consumers.
Level 3 Carnivores that eat herbivores are called secondary consumers.
Level 4 Carnivores that eat other carnivores are called tertiary consumers.
Apex predator By definition, healthy adult apex predators have no predators (with members of their own species a possible exception) and are at the highest numbered level of their food web. |
Trophic level | Overview | In real-world ecosystems, there is more than one food chain for most organisms, since most organisms eat more than one kind of food or are eaten by more than one type of predator. A diagram that sets out the intricate network of intersecting and overlapping food chains for an ecosystem is called its food web. Decomposers are often left off food webs, but if included, they mark the end of a food chain. Thus food chains start with primary producers and end with decay and decomposers. Since decomposers recycle nutrients, leaving them so they can be reused by primary producers, they are sometimes regarded as occupying their own trophic level.The trophic level of a species may vary if it has a choice of diet. Virtually all plants and phytoplankton are purely phototrophic and are at exactly level 1.0. Many worms are at around 2.1; insects 2.2; jellyfish 3.0; birds 3.6. A 2013 study estimates the average trophic level of human beings at 2.21, similar to pigs or anchovies. This is only an average, and plainly both modern and ancient human eating habits are complex and vary greatly. For example, a traditional Inuit living on a diet consisting primarily of seals would have a trophic level of nearly 5. |
Trophic level | Biomass transfer efficiency | In general, each trophic level relates to the one below it by absorbing some of the energy it consumes, and in this way can be regarded as resting on, or supported by, the next lower trophic level. Food chains can be diagrammed to illustrate the amount of energy that moves from one feeding level to the next in a food chain. This is called an energy pyramid. The energy transferred between levels can also be thought of as approximating to a transfer in biomass, so energy pyramids can also be viewed as biomass pyramids, picturing the amount of biomass that results at higher levels from biomass consumed at lower levels. However, when primary producers grow rapidly and are consumed rapidly, the biomass at any one moment may be low; for example, phytoplankton (producer) biomass can be low compared to the zooplankton (consumer) biomass in the same area of ocean.The efficiency with which energy or biomass is transferred from one trophic level to the next is called the ecological efficiency. Consumers at each level convert on average only about 10% of the chemical energy in their food to their own organic tissue (the ten-per cent law). For this reason, food chains rarely extend for more than 5 or 6 levels. At the lowest trophic level (the bottom of the food chain), plants convert about 1% of the sunlight they receive into chemical energy. It follows from this that the total energy originally present in the incident sunlight that is finally embodied in a tertiary consumer is about 0.001% |
Trophic level | Evolution | Both the number of trophic levels and the complexity of relationships between them evolve as life diversifies through time, the exception being intermittent mass extinction events. |
Trophic level | Fractional trophic levels | Food webs largely define ecosystems, and the trophic levels define the position of organisms within the webs. But these trophic levels are not always simple integers, because organisms often feed at more than one trophic level. For example, some carnivores also eat plants, and some plants are carnivores. A large carnivore may eat both smaller carnivores and herbivores; the bobcat eats rabbits, but the mountain lion eats both bobcats and rabbits. Animals can also eat each other; the bullfrog eats crayfish and crayfish eat young bullfrogs. The feeding habits of a juvenile animal, and, as a consequence, its trophic level, can change as it grows up. |
Trophic level | Fractional trophic levels | The fisheries scientist Daniel Pauly sets the values of trophic levels to one in plants and detritus, two in herbivores and detritivores (primary consumers), three in secondary consumers, and so on. The definition of the trophic level, TL, for any consumer species is: TLi=1+∑j(TLj⋅DCij) where TLj is the fractional trophic level of the prey j, and DCij represents the fraction of j in the diet of i. That is, the consumer trophic level is one plus the weighted average of how much different trophic levels contribute to its food. |
Trophic level | Fractional trophic levels | In the case of marine ecosystems, the trophic level of most fish and other marine consumers takes a value between 2.0 and 5.0. The upper value, 5.0, is unusual, even for large fish, though it occurs in apex predators of marine mammals, such as polar bears and orcas.In addition to observational studies of animal behavior, and quantification of animal stomach contents, trophic level can be quantified through stable isotope analysis of animal tissues such as muscle, skin, hair, bone collagen. This is because there is a consistent increase in the nitrogen isotopic composition at each trophic level caused by fractionations that occur with the synthesis of biomolecules; the magnitude of this increase in nitrogen isotopic composition is approximately 3–4‰. |
Trophic level | Mean trophic level | In fisheries, the mean trophic level for the fisheries catch across an entire area or ecosystem is calculated for year y as: TLy=∑i(TLi⋅Yiy)∑iYiy where Yiy is the annual catch of the species or group i in year y, and TLi is the trophic level for species i as defined above.Fish at higher trophic levels usually have a higher economic value, which can result in overfishing at the higher trophic levels. Earlier reports found precipitous declines in mean trophic level of fisheries catch, in a process known as fishing down the food web. However, more recent work finds no relation between economic value and trophic level; and that mean trophic levels in catches, surveys and stock assessments have not in fact declined, suggesting that fishing down the food web is not a global phenomenon. However Pauly et al. note that trophic levels peaked at 3.4 in 1970 in the northwest and west-central Atlantic, followed by a subsequent decline to 2.9 in 1994. They report a shift away from long-lived, piscivorous, high-trophic-level bottom fishes, such as cod and haddock, to short-lived, planktivorous, low-trophic-level invertebrates (e.g., shrimp) and small, pelagic fish (e.g., herring). This shift from high-trophic-level fishes to low-trophic-level invertebrates and fishes is a response to changes in the relative abundance of the preferred catch. They consider that this is part of the global fishery collapse, which finds an echo in the overfished Mediterranean Sea.Humans have a mean trophic level of about 2.21, about the same as a pig or an anchovy. |
Trophic level | FiB index | Since biomass transfer efficiencies are only about 10%, it follows that the rate of biological production is much greater at lower trophic levels than it is at higher levels. Fisheries catch, at least, to begin with, will tend to increase as the trophic level declines. At this point the fisheries will target species lower in the food web. In 2000, this led Pauly and others to construct a "Fisheries in Balance" index, usually called the FiB index. The FiB index is defined, for any year y, by log Yy/(TE)TLyY0/(TE)TL0 where Yy is the catch at year y, TLy is the mean trophic level of the catch at year y, Y0 is the catch, TL0 the mean trophic level of the catch at the start of the series being analyzed, and TE is the transfer efficiency of biomass or energy between trophic levels. |
Trophic level | FiB index | The FiB index is stable (zero) over periods of time when changes in trophic levels are matched by appropriate changes in the catch in the opposite direction. The index increases if catches increase for any reason, e.g. higher fish biomass, or geographic expansion. Such decreases explain the "backward-bending" plots of trophic level versus catch originally observed by Pauly and others in 1998. |
Trophic level | Tritrophic and other interactions | One aspect of trophic levels is called tritrophic interaction. Ecologists often restrict their research to two trophic levels as a way of simplifying the analysis; however, this can be misleading if tritrophic interactions (such as plant–herbivore–predator) are not easily understood by simply adding pairwise interactions (plant-herbivore plus herbivore–predator, for example). Significant interactions can occur between the first trophic level (plant) and the third trophic level (a predator) in determining herbivore population growth, for example. Simple genetic changes may yield morphological variants in plants that then differ in their resistance to herbivores because of the effects of the plant architecture on enemies of the herbivore. Plants can also develop defenses against herbivores such as chemical defenses. |
Cetrimonium bromide | Cetrimonium bromide | Cetrimonium bromide ([(C16H33)N(CH3)3]Br; cetyltrimethylammonium bromide; hexadecyltrimethylammonium bromide; CTAB) is a quaternary ammonium surfactant. |
Cetrimonium bromide | Cetrimonium bromide | It is one of the components of the topical antiseptic cetrimide. The cetrimonium (hexadecyltrimethylammonium) cation is an effective antiseptic agent against bacteria and fungi. It is also one of the main components of some buffers for the extraction of DNA. It has been widely used in synthesis of gold nanoparticles (e.g., spheres, rods, bipyramids), mesoporous silica nanoparticles (e.g., MCM-41), and hair conditioning products. The closely related compounds cetrimonium chloride and cetrimonium stearate are also used as topical antiseptics and may be found in many household products such as shampoos and cosmetics. CTAB, due to its relatively high cost, is typically only used in select cosmetics. |
Cetrimonium bromide | Cetrimonium bromide | As with most surfactants, CTAB forms micelles in aqueous solutions. At 303 K (30 °C) it forms micelles with aggregation number 75-120 (depending on method of determination; average ~95) and degree of ionization, α = 0.2–0.1 (fractional charge; from low to high concentration). The binding constant (K°) of Br− counterion to a CTA+ micelle at 303 K (30 °C) is ca. 400 M-1. This value is calculated from Br− and CTA+ ion selective electrode measurements and conductometry data by using literature data for micelle size (r = ~3 nm), extrapolated to the critical micelle concentration of 1 mM. However, K° varies with total surfactant concentration so it is extrapolated to the point at which micelle concentration is zero. |
Cetrimonium bromide | Applications | Biological Cell lysis is a convenient tool to isolate certain macromolecules that exist primarily inside of the cell. Cell membranes consist of hydrophilic and lipophilic endgroups. Therefore, detergents are often used to dissolve these membranes since they interact with both polar and nonpolar endgroups. CTAB has emerged as the preferred choice for biological use because it maintains the integrity of precipitated DNA during its isolation. Cells typically have high concentrations of macromolecules, such as glycoproteins and polysaccharides, that co-precipitate with DNA during the extraction process, causing the extracted DNA to lose purity. The positive charge of the CTAB molecule allows it to denature these molecules that would interfere with this isolation. |
Cetrimonium bromide | Applications | Medical CTAB has been shown to have potential use as an apoptosis-promoting anticancer agent for head and neck cancer (HNC). In vitro, CTAB interacted additively with γ radiation and cisplatin, two standard HNC therapeutic agents. CTAB exhibited anticancer cytotoxicity against several HNC cell lines with minimal effects on normal fibroblasts, a selectivity that exploits cancer-specific metabolic aberrations. In vivo, CTAB ablated tumor-forming capacity of FaDu cells and delayed growth of established tumors. Thus, using this approach, CTAB was identified as a potential apoptogenic quaternary ammonium compound possessing in vitro and in vivo efficacy against HNC models. CTAB is also recommended by the World Health Organisation (WHO) as a purification agent in the downstream vaccine processing of polysaccharide vaccines. |
Cetrimonium bromide | Applications | Protein electrophoresis Glycoproteins form broad, fuzzy bands in SDS-PAGE (Laemmli-electrophoresis) because of their broad distribution of negative charges. Using positively charged detergents such as CTAB will avoid issues associated with glycoproteins. Proteins can be blotted from CTAB-gels in analogy to western blots ("eastern blot"), and Myelin-associated high hydrophobic protein can be analyzed using CTAB 2-DE. |
Cetrimonium bromide | Applications | DNA extraction CTAB serves as an important surfactant in the DNA extraction buffer system to remove membrane lipids and promote cell lysis. Separation is also successful when the tissue contains high amounts of polysaccharides. CTAB binds to the polysaccharides when the salt concentration is high, thus removing polysaccharides from solution. A typical recipe can be to combine 100 mL of 1 M Tris HCl (pH 8.0), 280 mL 5 M NaCl, 40 mL of 0.5 M EDTA, and 20 g of CTAB then add double distilled water (ddH2O) to bring total volume to 1 L. |
Cetrimonium bromide | Nanoparticle synthesis | Surfactants play a key role in nanoparticle synthesis by adsorbing to the surface of the forming nanoparticle and lowering its surface energy. Surfactants also help to prevent aggregation (e.g. via DLVO mechanisms). |
Cetrimonium bromide | Nanoparticle synthesis | Au nanoparticle synthesis Gold (Au) nanoparticles are interesting to researchers because of their unique properties that can be used in applications such as catalysis, optics, electronics, sensing, and medicine. Control of nanoparticle size and shape is important in order to tune its properties. CTAB has been a widely used reagent to both impart stability to these nanoparticles as well as control their morphologies. CTAB may play a role in controlling nanoparticle size and shape by selectively or more strongly binding to various emerging crystal facets. |
Cetrimonium bromide | Nanoparticle synthesis | Some of this control originates from the reaction of CTAB with other reagents in the gold nanoparticle synthesis. For example, in aqueous gold nanoparticle syntheses, chlorauric acid (HAuCl4) may react with CTAB to create a CTA+-AuCl−4 complex. The gold complex is then reacted with ascorbic acid to produce hydrochloric acid, an ascorbic acid radical, and CTA-AuCl3. The ascorbic acid radical and CTA-AuCl3 react spontaneously to create metallic Au0 nanoparticles and other byproducts. An alternative or simultaneous reaction is the substitution of Cl− with Br− about the Au(III) center. Both complexation with the ammonium cation and/or speciation of the Au(III) precursor influence the kinetics of the nanoparticle formation reaction and therefore influence the size, shape, and (size and shape) distributions of the resulting particles. |
Cetrimonium bromide | Nanoparticle synthesis | Mesoporous materials CTAB is used as the template for the first report of ordered mesoporous materials. Microporous and mesoporous inorganic solids (with pore diameters of ≤20 Å and ~20–500 Å respectively) have found great utility as catalysts and sorption media because of their large internal surface area. Typical microporous materials are crystalline framework solids, such as zeolites, but the largest pore dimensions are still below 2 nm which greatly limit application. Examples of mesoporous solids include silicas and modified layered materials, but these are invariably amorphous or paracrystalline, with pores that are irregularly spaced and broadly distributed in size. There is a need to prepare highly ordered mesoporous material with good mesoscale crystallinity. The synthesis of mesoporous solids from the calcination of aluminosilicate gels in the presence of surfactants was reported. The material possesses regular arrays of uniform channels, the dimensions of which can be tailored (in the range of 16 Å to >100 Å) through the choice of surfactant, auxiliary chemicals, and reaction conditions. It was proposed that the formation of these materials takes place by means of a liquid-crystal 'templating' mechanism, in which the silicate material forms inorganic walls between ordered surfactant micelles. CTAB formed micelles in the solution and these micelles further formed a two dimensional hexagonal mesostructure. The silicon precursor began to hydrolyze between the micelles and finally filled the gap with silicon dioxide. The template could be further removed by calcination and left a pore structure behind. These pores mimicked exactly the structure of mesoscale soft template and led to highly ordered mesoporous silica materials. |
Cetrimonium bromide | Toxicity | CTAB has been used for applications from nanoparticle synthesis to cosmetics. Due to its use in human products, along with other applications, it is essential to be made aware of the hazards this agent contains. The Santa Cruz Biotechnology, Inc. offers a comprehensive MSDS for CTAB and should be referred to for additional questions or concerns. Animal testing has shown ingestion of less than 150 g of the agent can lead to adverse health effects or possibly death by CTAB causing chemical burns throughout the esophagus and gastrointestinal tract that can be followed by nausea and vomiting. If the substance continues through the gastrointestinal tract, it will be poorly absorbed in the intestines followed by excretion in feces. Toxicity has also been tested on aquatic life including Brachydanio rerio (zebra fish) and Daphnia magna (Water flea). Zebra fish showed CTAB toxicity when exposed to 0.3 mg/L for 96 hours, and water fleas showed CTAB toxicity when exposed to 0.03 mg/L for 48 hours.CTAB along with other quaternary ammonium salts have frequently been used in cosmetics at concentrations up to 10%. Cosmetics at that concentration must only be used as rinse-off types such as shampoos. Other leave-on cosmetics are considered only safe at or below 0.25% concentrations. Injections into the body cavity of pregnant mice showed embryotoxic and teratogenic effects. Only teratogenic effects were seen with 10 mg/kg doses, while both effects were seen at 35 mg/kg doses. Oral doses of 50 mg/kg/day showed embryotoxic effects as well. Similar tests were completed by giving rats 10, 20, and 45 mg/kg/day of CTAB in their drinking water for one year. At the 10 and 20 mg/kg/day doses, the rats did not have any toxic symptoms. At the highest dose, the rats began experiencing weight loss. The weight loss in the male rats was attributed to less efficient food conversion. The tests showed no microscopic alterations to the gastrointestinal tract of the rats.Other toxicity tests have been conducted using incubated human skin HaCaT keratinocyte cells. These human cells were incubated with gold nanorods that were synthesized using seed-mediated, surfactant-assisted growth of gold nanoparticles. Gold nanoparticles are shown to be nontoxic, however once the nanoparticles are put through the growth solutions, the newly formed nanorods are highly toxic. This large increase in toxicity is attributed to the CTAB that is used in the growth solutions to cause anisotropic growth. Experiments also showed the toxicity of bulk CTAB and the synthesized gold nanorods to be equivalent. Toxicity tests showed CTAB remaining toxic with concentrations as low as 10 μM. The human cells show CTAB being nontoxic at concentrations less than 1 μM. Without the use of CTAB in this synthesis, the gold nanorods are not stable; they break into nanoparticles or undergo aggregation.The mechanism for cytotoxicity has not been extensively studied, but there has been possible mechanisms proposed. One proposal showed two methods that led to the cytotoxicity in U87 and A172 glioblastoma cells. The first method showed CTAB exchanging with phospholipids causing rearrangement of the membrane allowing β-galactoside to enter into the cell by way of cavities. At low concentrations, there are not enough cavities to cause death to the cells, but with increasing the CTAB concentration, more phospholipids are displaced causing more cavities in the membrane leading to cell death. The second proposed method is based on the dissociation of CTAB into CTA+ and Br− within the mitochondrial membrane. The positively charged CTA+ binds to the ATP synthase not allowing H+ to bind stopping the synthesis of ATP and resulting in cell death. |
Lithium ion manganese oxide battery | Lithium ion manganese oxide battery | A lithium ion manganese oxide battery (LMO) is a lithium-ion cell that uses manganese dioxide, MnO2, as the cathode material. They function through the same intercalation/de-intercalation mechanism as other commercialized secondary battery technologies, such as LiCoO2. Cathodes based on manganese-oxide components are earth-abundant, inexpensive, non-toxic, and provide better thermal stability. |
Lithium ion manganese oxide battery | Compounds | Spinel LiMn2O4 One of the more studied manganese oxide-based cathodes is LiMn2O4, a cation ordered member of the spinel structural family (space group Fd3m). In addition to containing inexpensive materials, the three-dimensional structure of LiMn2O4 lends itself to high rate capability by providing a well connected framework for the insertion and de-insertion of Li+ ions during discharge and charge of the battery. In particular, the Li+ ions occupy the tetrahedral sites within the Mn2O4 polyhedral frameworks adjacent to empty octahedral sites. As a consequence of this structural arrangement, batteries based on LiMn2O4 cathodes have demonstrated a higher rate-capability compared to materials with two-dimensional frameworks for Li+ diffusion.A significant disadvantage of cathodes based on LiMn2O4 is the surface degradation observed when the average oxidation state of the manganese drops below Mn+3.5. At this concentration, the formally Mn(III) at the surface can disproportionate to form Mn(IV) and Mn(II) by the Hunter mechanism. The Mn(II) formed is soluble in most electrolytes and its dissolution degrades the cathode. With this in mind many manganese cathodes are substituted or doped to keep the average manganese oxidation state above +3.5 during battery use or they will suffer from lower overall capacities as a function of cycle life and temperature. |
Lithium ion manganese oxide battery | Compounds | Layered Li2MnO3 Li2MnO3 is a lithium rich layered rocksalt structure that is made of alternating layers of lithium ions and lithium and manganese ions in a 1:2 ratio, similar to the layered structure of LiCoO2. In the nomenclature of layered compounds it can be written Li(Li0.33Mn0.67)O2. Although Li2MnO3 is electrochemically inactive, it can be charged to a high potential (4.5 V v.s Li0) in order to undergo lithiation/de-lithiation or delithiated using an acid leaching process followed by mild heat treatment. However, extracting lithium from Li2MnO3 at such a high potential can also be charge compensated by loss of oxygen from the electrode surface which leads to poor cycling stability. New allotropes of Li2MnO3 have been discovered which have better structural stability against oxygen release (longer cycle-life). |
Lithium ion manganese oxide battery | Compounds | Layered LiMnO2 The layered manganese oxide LiMnO2 is constructed from corrugated layers of manganese/oxide octahedra and is electrochemically unstable. The distortions and deviation from truly planar metal oxide layers are a manifestation of the electronic configuration of the Mn(III) Jahn-Teller ion. A layered variant, isostructural with LiCoO2, was prepared in 1996 by ion exchange from the layered compound NaMnO2, however long term cycling and the defect nature of the charged compound led to structural degradation and cation equilibration to other phases. |
Lithium ion manganese oxide battery | Compounds | Layered Li2MnO2 The layered manganese oxide Li2MnO2 is structurally related to Li2MnO3 and LiCoO2 with similar transition metal oxide layers separated by a layer containing two lithium cations occupying the available two tetrahedral sites in the lattice rather the one octahedral site. The material is typically made by low voltage lithiation of the parent compound, direct lithiation using liquid ammonia, or via use of an organic lithiating reagent. Stability on cycling has been demonstrated in symmetric cells although due to Mn(II) formation and dissolution cycling degradation is expected. Stabilization of the structure using dopants and substitutions to decrease the amount of reduced manganese cations has been a successful route to extending the cycle life of these lithium rich reduced phases. These layered manganese oxide layers are so rich in lithium. |
Lithium ion manganese oxide battery | Compounds | x Li2MnO3 • y Li1+aMn2-aO4 • z LiMnO2 composites One of the main research efforts in the field of lithium-manganese oxide electrodes for lithium-ion batteries involves developing composite electrodes using structurally integrated layered Li2MnO3, layered LiMnO2, and spinel LiMn2O4, with a chemical formula of x Li2MnO3 • y Li1+aMn2-aO4 • z LiMnO2, where x+y+z=1. The combination of these structures provides increased structural stability during electrochemical cycling while achieving higher capacity and rate-capability. A rechargeable capacity in excess of 250 mAh/g was reported in 2005 using this material, which has nearly twice the capacity of current commercialized rechargeable batteries of the same dimensions. |
L(R) | L(R) | In set theory, L(R) (pronounced L of R) is the smallest transitive inner model of ZF containing all the ordinals and all the reals. |
L(R) | Construction | It can be constructed in a manner analogous to the construction of L (that is, Gödel's constructible universe), by adding in all the reals at the start, and then iterating the definable powerset operation through all the ordinals. |
L(R) | Assumptions | In general, the study of L(R) assumes a wide array of large cardinal axioms, since without these axioms one cannot show even that L(R) is distinct from L. But given that sufficient large cardinals exist, L(R) does not satisfy the axiom of choice, but rather the axiom of determinacy. However, L(R) will still satisfy the axiom of dependent choice, given only that the von Neumann universe, V, also satisfies that axiom. |
L(R) | Results | Given the assumptions above, some additional results of the theory are: Every projective set of reals – and therefore every analytic set and every Borel set of reals – is an element of L(R).
Every set of reals in L(R) is Lebesgue measurable (in fact, universally measurable) and has the property of Baire and the perfect set property.
L(R) does not satisfy the axiom of uniformization or the axiom of real determinacy.
R#, the sharp of the set of all reals, has the smallest Wadge degree of any set of reals not contained in L(R).
While not every relation on the reals in L(R) has a uniformization in L(R), every such relation does have a uniformization in L(R#).
Given any (set-size) generic extension V[G] of V, L(R) is an elementary submodel of L(R) as calculated in V[G]. Thus the theory of L(R) cannot be changed by forcing.
L(R) satisfies AD+. |
Viruses of the Mind | Viruses of the Mind | "Viruses of the Mind" is an essay by British evolutionary biologist Richard Dawkins, first published in the book Dennett and His Critics: Demystifying Mind (1993). Dawkins originally wrote the essay in 1991 and delivered it as a Voltaire Lecture on 6 November 1992 at the Conway Hall Humanist Centre. The essay discusses how religion can be viewed as a meme, an idea previously expressed by Dawkins in The Selfish Gene (1976). Dawkins analyzes the propagation of religious ideas and behaviors as a memetic virus, analogous to how biological and computer viruses spread. The essay was later published in A Devil's Chaplain (2003) and its ideas are further explored in the television programme, The Root of All Evil? (2006). |
Viruses of the Mind | Content | Dawkins defines the "symptoms" of being infected by the "virus of religion", providing examples for most of them, and tries to define a connection between the elements of religion and its survival value (invoking Zahavi's handicap principle of sexual selection, applied to believers of a religion). Dawkins also describes religious beliefs as "mind-parasites", and as "gangs [that] will come to constitute a package, which may be sufficiently stable to deserve a collective name such as Roman Catholicism ... or ... component parts to a single virus". |
Viruses of the Mind | Content | Dawkins suggests that religious belief in the "faith-sufferer" typically shows the following elements: It is impelled by some deep, inner conviction that something is true, or right, or virtuous: a conviction that doesn't seem to owe anything to evidence or reason, but which, nevertheless, the believer feels as totally compelling and convincing.
The believer typically makes a positive virtue of faith's being strong and unshakable, despite it not being based upon evidence.
There is a conviction that "mystery", per se, is a good thing; the belief that it is not a virtue to solve mysteries but to enjoy them and revel in their insolubility.
There may be intolerant behaviour towards perceived rival faiths, in extreme cases even the killing of opponents or advocating of their deaths. Believers may be similarly violent in disposition towards apostates or heretics, even if those espouse only a slightly different version of the faith.
The particular convictions that the believer holds, while having nothing to do with evidence, are likely to resemble those of the believer's parents.
If the believer is one of the rare exceptions who follows a different religion from his parents, the explanation may be cultural transmission from a charismatic individual. |
Viruses of the Mind | Content | The internal sensations of the 'faith-sufferer' may be reminiscent of those more ordinarily associated with sexual love.Dawkins stresses his claim that religious beliefs do not spread as a result of evidence in their support, but typically by cultural transmission, in most cases from parents or from charismatic individuals. He refers to this as involving "epidemiology, not evidence". Further Dawkins distinguishes this process from the spread of scientific ideas, which, he suggests, is constrained by the requirement to conform with certain virtues of standard methodology: "testability, evidential support, precision, quantifiability, consistency, intersubjectivity, repeatability, universality, progressiveness, independence of cultural milieu, and so on". He points out that faith "spreads despite a total lack of every single one of these virtues". |
Viruses of the Mind | Critical reactions | Alister McGrath, a Christian theologian, has commented critically on Dawkins' analysis, suggesting that "memes have no place in serious scientific reflection", that there is strong evidence that such ideas are not spread by random processes, but by deliberate intentional actions, that "evolution" of ideas is more Lamarckian than Darwinian, and suggests there is no evidence that epidemiological models usefully explain the spread of religious ideas. McGrath also cites a meta-review of 100 studies and argues that "If religion is reported as having a positive effect on human well-being by 79% of recent studies in the field, how can it conceivably be regarded as analogous to a virus?" |
Carbyl sulfate | Carbyl sulfate | Carbyl sulfate is an organosulfur compound. The white solid is the product of the reaction of sulfur trioxide and ethylene. It is used in preparation of some dyes and other organosulfur compounds. Carbyl sulfate is a colorless, crystalline, hygroscopic substance although commercial product can appear as a liquid. Because of its unpleasant properties carbyl sulfate is difficult to handle and is usually not isolated but further processed to give secondary products. |
Carbyl sulfate | Production | Regnault and Heinrich Gustav Magnus reported first in the years 1838 to 1839 on the compound as reaction product of anhydrous ethanol and anhydrous sulfuric acid.
Carbyl sulfate is produced in the highly exothermic (about 800 kcal/kg) reaction of ethylene and sulfur trioxide in the vapor phase in nearly quantitative yield. |
Carbyl sulfate | Production | Disulfuric acid and chlorosulfuric acid can also be used as a sulfonating agent, replacing sulfur trioxide. Instead of ethylene, ethylene-forming agents can be used, e.g. ethanol or diethyl ether.The product of industrial processes is a water-clear liquid which has - in accordance with D.S. Breslow (107.5 to 109 °C) - a melting range from 102 to 108 °C. Previously stated melting point of about 80 °C results from adhering sulfur trioxide. |
Carbyl sulfate | Reactions and use | As a cyclic sulfate ester, it is an alkylating agent. Hydrolysis affords ethionic acid, which retains one sulfate ester group. Ethionic acid undergoes further hydrolysis to isethionic acid: Carbyl sulfate is used as precursor for vinylsulfonic acid and sodium vinyl sulfonate, which are important activated alkenes and are used e. g. as anionic comonomers. A number of functional compounds with a variety of applications are available by nucleophilic addition at the activated double bond of the vinyl sulfonic acid and its derivatives. |
Carbyl sulfate | Safety | The material is highly reactive. It can decompose explosively when heated above 170 °C. |
Wharton's jelly | Wharton's jelly | Wharton's jelly (substantia gelatinea funiculi umbilicalis) is a gelatinous substance within the umbilical cord, largely made up of mucopolysaccharides (hyaluronic acid and chondroitin sulfate). It acts as a mucous connective tissue containing some fibroblasts and macrophages, and is derived from extra-embryonic mesoderm of the connecting stalk. |
Wharton's jelly | Umbilical cord occlusion | As a mucous connective tissue, it is rich in proteoglycans, and protects and insulates umbilical blood vessels. Wharton's jelly, when exposed to temperature changes, collapses structures within the umbilical cord and thus provides a physiological clamping of the cord, typically three minutes after birth. |
Wharton's jelly | Stem cells | Cells in Wharton's jelly express several stem cell genes, including telomerase. They can be extracted, cultured, and induced to differentiate into mature cell types such as neurons. Wharton's jelly is therefore a potential source of adult stem cells, often collected from cord blood. Wharton's jelly-derived mesenchymal stem cells may have immunomodulatory effect on lymphocytes.
Wharton's jelly tissue transplantation has shown to be able to reduce traumatic brain injury in rats. |
Wharton's jelly | Etymology | It is named for the English physician and anatomist Thomas Wharton (1614–1673) who first described it in his publication Adenographia, or "The Description of the Glands of the Entire Body", first published in 1656. |
GPR156 | GPR156 | GPR156 (G protein-coupled receptor 156), is a human gene which encodes a G protein-coupled receptor belonging to metabotropic glutamate receptor subfamily. By sequence homology, this gene was proposed as being a possible GABAB receptor subunit, however when expressed in cells alone or with other GABAB subunits, no response to GABAB ligands could be detected. Therefore, the function of this protein remains to be elucidated. In vitro studies on GPR156 constitutive activity revealed a high level of basal activation and coupling with members of the Gi/Go heterotrimeric G protein family. |
Bastnäsite | Bastnäsite | The mineral bastnäsite (or bastnaesite) is one of a family of three carbonate-fluoride minerals, which includes bastnäsite-(Ce) with a formula of (Ce, La)CO3F, bastnäsite-(La) with a formula of (La, Ce)CO3F, and bastnäsite-(Y) with a formula of (Y, Ce)CO3F. Some of the bastnäsites contain OH− instead of F− and receive the name of hydroxylbastnasite. Most bastnäsite is bastnäsite-(Ce), and cerium is by far the most common of the rare earths in this class of minerals. Bastnäsite and the phosphate mineral monazite are the two largest sources of cerium and other rare-earth elements. |
Bastnäsite | Bastnäsite | Bastnäsite was first described by the Swedish chemist Wilhelm Hisinger in 1838. It is named for the Bastnäs mine near Riddarhyttan, Västmanland, Sweden.
Bastnäsite also occurs as very high-quality specimens at the Zagi Mountains, Pakistan.
Bastnäsite occurs in alkali granite and syenite and in associated pegmatites. It also occurs in carbonatites and in associated fenites and other metasomatites. |
Bastnäsite | Composition | Bastnäsite has cerium, lanthanum and yttrium in its generalized formula but officially the mineral is divided into three minerals based on the predominant rare-earth element. There is bastnäsite-(Ce) with a more accurate formula of (Ce, La)CO3F. There is also bastnäsite-(La) with a formula of (La, Ce)CO3F. And finally there is bastnäsite-(Y) with a formula of (Y, Ce)CO3F. There is little difference in the three in terms of physical properties and most bastnäsite is bastnäsite-(Ce). Cerium in most natural bastnäsites usually dominates the others. Bastnäsite and the phosphate mineral monazite are the two largest sources of cerium, an important industrial metal. |
Bastnäsite | Composition | Bastnäsite is closely related to the mineral series parisite. The two are both rare-earth fluorocarbonates, but parisite's formula of Ca(Ce, La, Nd)2(CO3)3F2 contains calcium (and a small amount of neodymium) and a different ratio of constituent ions. Parisite could be viewed as a formula unit of calcite (CaCO3) added to two formula units of bastnäsite. In fact, the two have been shown to alter back and forth with the addition or loss of CaCO3 in natural environments.Bastnäsite forms a series with the minerals hydroxylbastnäsite-(Ce) [(Ce,La)CO3(OH,F)] and hydroxylbastnäsite-(Nd). The three are members of a substitution series that involves the possible substitution of fluoride (F−) ions with hydroxyl (OH−) ions. |
Bastnäsite | Name | Bastnäsite gets its name from its type locality, the Bastnäs Mine, Riddarhyttan, Västmanland, Sweden. Ore from the Bastnäs Mine led to the discovery of several new minerals and chemical elements by Swedish scientists such as Jöns Jakob Berzelius, Wilhelm Hisinger and Carl Gustav Mosander. Among these are the chemical elements cerium, which was described by Hisinger in 1803, and lanthanum in 1839. Hisinger, who was also the owner of the Bastnäs mine, chose to name one of the new minerals bastnäsit when it was first described by him in 1838. |
Bastnäsite | Occurrence | Although a scarce mineral and never in great concentrations, it is one of the more common rare-earth carbonates. Bastnäsite has been found in karst bauxite deposits in Hungary, Greece and the Balkans region. Also found in carbonatites, a rare carbonate igneous intrusive rock, at the Fen Complex, Norway; Bayan Obo, Mongolia; Kangankunde, Malawi; Kizilcaoren, Turkey and the Mountain Pass rare earth mine in California, US. At Mountain Pass, bastnäsite is the leading ore mineral. Some bastnäsite has been found in the unusual granites of the Langesundsfjord area, Norway; Kola Peninsula, Russia; Mont Saint-Hilaire mines, Ontario, and Thor Lake deposits, Northwest Territories, Canada. Hydrothermal sources have also been reported. |
Bastnäsite | Occurrence | The formation of hydroxylbastnasite (NdCO3OH) can also occur via the crystallization of a rare-earth bearing amorphous precursor. With increasing temperature, the habit of NdCO3OH crystals changes progressively to more complex spherulitic or dendritic morphologies. The development of these crystal morphologies has been suggested to be controlled by the level at which supersaturation is reached in the aqueous solution during the breakdown of the amorphous precursor. At higher temperature (e.g., 220 °C) and after rapid heating (e.g. < 1 h) the amorphous precursor breaks down rapidly and the fast supersaturation promotes spherulitic growth. At a lower temperature (e.g., 165 °C) and slow heating (100 min) the supersaturation levels are approached more slowly than required for spherulitic growth, and thus more regular triangular pyramidal shapes form. |
Bastnäsite | Mining history | In 1949, the huge carbonatite-hosted bastnäsite deposit was discovered at Mountain Pass, San Bernardino County, California. This discovery alerted geologists to the existence of a whole new class of rare earth deposit: the rare earth containing carbonatite. Other examples were soon recognized, particularly in Africa and China. The exploitation of this deposit began in the mid-1960s after it had been purchased by Molycorp (Molybdenum Corporation of America). The lanthanide composition of the ore included 0.1% europium oxide, which was needed by the color television industry, to provide the red phosphor, to maximize picture brightness. The composition of the lanthanides was about 49% cerium, 33% lanthanum, 12% neodymium, and 5% praseodymium, with some samarium and gadolinium, or distinctly more lanthanum and less neodymium and heavies as compared to commercial monazite. The europium content was at least double that of a typical monazite. Mountain Pass bastnäsite was the world's major source of lanthanides from the 1960s to the 1980s. Thereafter, China became an increasingly important rare earth supply. Chinese deposits of bastnäsite include several in Sichuan Province, and the massive deposit at Bayan Obo, Inner Mongolia, which had been discovered early in the 20th century, but not exploited until much later. Bayan Obo is currently (2008) providing the majority of the world's lanthanides. Bayan Obo bastnäsite occurs in association with monazite (plus enough magnetite to sustain one of the largest steel mills in China), and unlike carbonatite bastnäsites, is relatively closer to monazite lanthanide compositions, with the exception of its generous 0.2% content of europium. |
Bastnäsite | Ore technology | At Mountain Pass, bastnäsite ore was finely ground, and subjected to flotation to separate the bulk of the bastnäsite from the accompanying barite, calcite, and dolomite. Marketable products include each of the major intermediates of the ore dressing process: flotation concentrate, acid-washed flotation concentrate, calcined acid washed bastnäsite, and finally a cerium concentrate, which was the insoluble residue left after the calcined bastnäsite had been leached with hydrochloric acid. The lanthanides that dissolved as a result of the acid treatment were subjected to solvent extraction, to capture the europium, and purify the other individual components of the ore. A further product included a lanthanide mix, depleted of much of the cerium, and essentially all of samarium and heavier lanthanides. The calcination of bastnäsite had driven off the carbon dioxide content, leaving an oxide-fluoride, in which the cerium content had become oxidized to the less basic quadrivalent state. However, the high temperature of the calcination gave less-reactive oxide, and the use of hydrochloric acid, which can cause reduction of quadrivalent cerium, led to an incomplete separation of cerium and the trivalent lanthanides. By contrast, in China, processing of bastnäsite, after concentration, starts with heating with sulfuric acid. |
Bastnäsite | Ore technology | Extraction of rare-earth metals Bastnäsite ore is typically used to produce rare-earth metals. The following steps and process flow diagram detail the rare-earth-metal extraction process from the ore.
After extraction, bastnasite ore is typically used in this process, with an average of 7% REO (rare-earth oxides).
The ore goes through comminution using rod mills, ball mills, or autogenous mills.
Steam is consistently used to condition the ground ore, along with soda ash fluosilicate, and usually Tail Oil C-30. This is done to coat the various types of rare earth metals with either flocculent, collectors, or modifiers for easier separation in the next step.
Flotation using the previous chemicals to separate the gangue from the rare-earth metals.
Concentrate the rare-earth metals and filter out large particles.
Remove excess water by heating to ~100 °C.
Add HCl to solution to reduce pH to < 5. This enables certain REM (rare-earth metals) to become soluble (Ce is an example).
Oxidizing roast further concentrates the solution to approximately 85% REO. This is done at ~100 °C and higher if necessary.
Enables solution to concentrate further and filters out large particles again.
Reduction agents (based on area) are used to remove Ce as Ce carbonate or CeO2, typically.
Solvents are added (solvent type and concentration based on area, availability, and cost) to help separate Eu, Sm, and Gd from La, Nd, and Pr.
Reduction agents (based on area) are used to oxidize Eu, Sm, and Gd.
Eu is precipitated and calcified.
Gd is precipitated as an oxide.
Sm is precipitated as an oxide.
Solvent is recycled into step 11. Additional solvent is added based on concentration and purity.
La separated from Nd, Pr, and SX.
Nd and Pr separated. SX goes on for recovery and recycle.
One way to collect La is adding HNO3, creating La(NO3)3. HNO3 typically added at a very high molarity (1–5 M), depending on La concentration and amount.
Another method is to add HCl to La, creating LaCl3. HCl is added at 1 M to 5 M depending on La concentration.
Solvent from La, Nd, and Pr separation is recycled to step 11.
Nd is precipitated as an oxide product.
Pr is precipitated as an oxide product. |
3DXRD | 3DXRD | Three-dimensional X-ray diffraction (3DXRD) is a microscopy technique using hard X-rays (with energy in the 30-100 keV range) to investigate the internal structure of polycrystalline materials in three dimensions. For a given sample, 3DXRD returns the shape, juxtaposition, and orientation of the crystallites ("grains") it is made of. 3DXRD allows investigating micrometer- to millimetre-sized samples with resolution ranging from hundreds of nanometers to micrometers. Other techniques employing X-rays to investigate the internal structure of polycrystalline materials include X-ray diffraction contrast tomography (DCT) and high energy X-ray diffraction (HEDM).Compared with destructive techniques, e.g. three-dimensional electron backscatter diffraction (3D EBSD), with which the sample is serially sectioned and imaged, 3DXRD and similar X-ray nondestructive techniques have the following advantages: They require less sample preparation, thus limiting the introduction of new structures in the sample. |
3DXRD | 3DXRD | They can be used to investigate larger samples and to employ more complicated sample environments.
They enable to study how 3D grain structures evolve with time.
Since measurements do not alter the sample, different types of analysis can be made in sequence. |
3DXRD | Experimental setup | 3DXRD measurements are performed using various experimental geometries. The classical 3DXRD setup is similar to the conventional tomography setting used at synchrotrons: the sample, mounted on a rotation stage, is illuminated using quasi-parallel monochromatic X-ray beam. Each time a certain grain within the sample satisfies the Bragg condition, a diffracted beam is generated. This signal is transmitted through the sample and collected by two-dimensional detectors. Since different grains satisfy the Bragg condition at different angles, the sample is rotated to probe the complete sample structure. Crucial for 3DXRD is the idea to mimic a three-dimensional detector by positioning a number of two-dimensional detectors at different distances from the centre of rotation of the sample, and exposing these either simultaneously (many detectors are semi-transparent to hard X-rays) or at different times. |
3DXRD | Experimental setup | At present (April 2017), a 3DXRD microscope is installed at the Materials Science beamline of the ESRF. |
3DXRD | Software | To determine the crystallographic orientation of the grains in the considered sample, the following software packages are in use: Fable and GrainSpotter. Reconstructing the 3D shape of the grains is nontrivial and three approaches are available to do so, respectively based on simple back-projection, forward projection, algebraic reconstruction technique and Monte Carlo method-based reconstruction. |
3DXRD | Applications | With 3DXRD, it is possible to study in situ the time evolution of materials under different conditions. Among others, the technique has been used to map the elastic strains and stresses in a pre-strained nickel-titanium wire. |
3DXRD | Related techniques | The scientists involved in developing 3DXRD contributed to the development of three other three-dimensional non-destructive techniques for the material sciences, respectively using electrons and neutrons as a probe: three-dimensional orientation mapping in the transmission electron microscope (3D-OMiTEM), time-of-flight 3D neutron diffraction for multigrain crystallography (ToF 3DND) and laue 3D neutron diffraction (Laue3DND).Using a system of lenses, the synchrotron technique dark-field X-ray microscopy (DFXRM) extends the capabilities of 3DXRD, allowing to focus on a deeply embedded single grain and to reconstruct its 3D structure and its crystalline properties. DFXRM is under development at the European Synchrotron Research Facility (ESRF), beamline ID06.In a laboratory setting, 3D grain maps using X-rays as a probe can be obtained using laboratory diffraction contrast tomography (LabDCT), a technique derived from 3DXRD. |
SYBL1 | SYBL1 | Vesicle-associated membrane protein 7 (VAMP-7), is a protein that in humans is encoded by the VAMP7 gene also known as the or SYBL1 gene. |
SYBL1 | Function | VAMP-7 is a transmembrane protein that is a member of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) family. VAMP-7 localizes to late endosomes and lysosomes and is involved in the fusion of transport vesicles to their target membranes. |
SYBL1 | Interactions | VAMP-7 has been shown to interact with SNAP23 and AP3D1. |
Blood–gas partition coefficient | Blood–gas partition coefficient | Blood–gas partition coefficient, also known as Ostwald coefficient for blood–gas, is a term used in pharmacology to describe the solubility of inhaled general anesthetics in blood. According to Henry's law, the ratio of the concentration in blood to the concentration in gas that is in contact with that blood, when the partial pressure in both compartments is equal, is nearly constant at sufficiently low concentrations. The partition coefficient is defined as this ratio and, therefore, has no units. The concentration of the anesthetic in blood includes the portion that is undissolved in plasma and the portion that is dissolved (bound to plasma proteins). The more soluble the inhaled anesthetic is in blood compared to in air, the more it binds to plasma proteins in the blood and the higher the blood–gas partition coefficient. |
Blood–gas partition coefficient | Blood–gas partition coefficient | It is inversely related to induction rate. Induction rate is defined as the speed at which an agent produces anesthesia. The higher the blood:gas partition coefficient, the lower will be the induction rate. |
Blood–gas partition coefficient | Blood–gas partition coefficient | Newer anesthetics (such as desflurane) typically have smaller blood–gas partition coefficients than older ones (such as ether); this leads to faster onset of anesthesia and faster emergence from anesthesia once application of the anesthetic is stopped, which may be preferable in certain clinical scenarios. If an anesthetic has a high coefficient, then a large amount of it will have to be taken up in the body's blood before being passed on to the fatty (lipid) tissues of the brain where it can exert its effect. |
Blood–gas partition coefficient | Blood–gas partition coefficient | The potency of an anesthetic is associated with its lipid solubility, which is measured by its oil/gas partition coefficient.Minimum alveolar concentration (MAC) is defined as the alveolar concentration of anesthetic gas that prevents a movement response in half of subjects undergoing a painful (surgical) stimulus; simplified, it is the exhaled gas concentration required to produce anaesthetic effects – an inverse indicator of anesthetic gas potency. |
Old Nassau reaction | Old Nassau reaction | The Old Nassau reaction or Halloween reaction is a chemical clock reaction in which a clear solution turns orange and then black. This reaction was discovered by two undergraduate students at Princeton University researching the inhibition of the iodine clock reaction (or Landolt reaction) by Hg2+, resulting in the formation of orange HgI2. Orange and black are the school colors of Princeton University, and "Old Nassau" is a nickname for Princeton, named for its historic administration building, Nassau Hall. |
Old Nassau reaction | Chemical equation | The reactions involved are as follows: Na2S2O5 + H2O → 2 NaHSO3 IO3− + 3 HSO3− → I− + 3 SO42− + 3 H+ This reaction reduces iodate ions to iodide ions.
Hg2+ + 2 I− → HgI2 Orange mercury iodide solid is precipitated until the mercury is used up.
IO3− + 5 I− + 6 H+ → 3 I2 + 3 H2O The excess I− and IO3− undergo the iodide-iodate reaction I2 + starch → a blue/black complex A blue/black starch-iodine complex is formed. |