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  • Polya, George (American mathematician)

    combinatorics: Polya’s theorem: mathematician George Polya in a famous 1937 memoir in which he established connections between groups, graphs, and chemical bonds. It has been applied to enumeration problems in physics, chemistry, and mathematics.

  • polyacetal (chemical compound)

    major industrial polymers: Polyacetal: Also called polyoxymethylene (POM) or simply acetal, polyacetal has the simplest structure of all the polyethers. It is manufactured in a solution process by anionic or cationic chain-growth polymerization of formaldehyde (H2C=O), a reaction analogous to vinyl polymerization. By itself, the polymer is unstable…

  • polyacetyglucosamine (chemical compound)

    Chitin, white, horny substance found in the outer skeleton of insects, crabs, and lobsters and in the internal structures of other invertebrates. It is a polysaccharide consisting of units of the amino sugar glucosamine. As a by-product of crustacean processing, chitin is used as a flocculating

  • polyacetylene (polymer)

    Asterales: Asteraceae: …flowering plants, Asteraceae heavily exploits polyacetylenes, bitter sesquiterpenes (especially sesquiterpene lactones), terpenoid volatile oils, latex, several kinds of alkaloids (notably pyrrolizidine alkaloids in the tribe Senecioneae), and various other compounds. Members of the genus Tagetes (marigolds) kill plant-parasitic nematodes in the soil by releasing terpenoid compounds from their roots. The…

  • polyacrylamide (chemical compound)

    Polyacrylamide, an acrylic resin that has the unique property of being soluble in water. It is employed in the treatment of industrial and municipal wastewater. Polyacrylamides are produced by the polymerization of acrylamide (C3H5NO), a compound obtained by the hydration of acrylonitrile.

  • polyacrylate (polymer)

    Polyacrylate, any of a number of synthetic resins produced by the polymerization of acrylic esters. Forming plastic materials of notable clarity and flexibility under certain methods, the polyacrylates are employed primarily in paints and other surface coatings, in adhesives, and in textiles. The

  • polyacrylate elastomer (polymer)

    Polyacrylate elastomer, any of a class of synthetic rubbers produced by the copolymerization of ethyl acrylate and other acrylates, in addition to small amounts (approximately 5 percent) of another compound containing a reactive halogen such as chlorine. Other acrylates used in the elastomers

  • polyacrylic compound (chemical compound)

    major industrial polymers: Acrylic polymers: Acrylic is a generic term denoting derivatives of acrylic and methacrylic acid, including acrylic esters and compounds containing nitrile and amide groups. Polymers based on acrylics were discovered before many other polymers that are now widely employed. In 1880 the Swiss chemist Georg…

  • polyacrylonitrile (chemical compound)

    Polyacrylonitrile (PAN), a synthetic resin prepared by the polymerization of acrylonitrile. A member of the important family of acrylic resins, it is a hard, rigid thermoplastic material that is resistant to most solvents and chemicals, slow to burn, and of low permeability to gases. Most

  • polyacrylonitrile fibre

    major industrial polymers: Polyacrylonitrile (PAN): Acrylic fibres are soft and flexible, producing lightweight, lofty yarns. Such properties closely resemble those of wool, and hence the most common use of acrylics in apparel and carpets is as a wool replacement—for example, in knitwear such as sweaters and socks. Acrylics can be…

  • Polyaenus (Macedonian rhetorician)

    Polyaenus, Macedonian rhetorician and pleader who lived in Rome and was the author of a work entitled Strategica (or Strategemata), which he dedicated to the emperors Marcus Aurelius and Lucius Verus on the outbreak of the Parthian War (162–165). The Strategica, still extant, is a historical

  • Polyakov, Valery Vladimirovich (Soviet cosmonaut)

    Valery Vladimirovich Polyakov, Russian cosmonaut who holds the record for the longest single spaceflight in history. Polyakov had an early interest in spaceflight, and in 1971 he joined the Institute of Biomedical Problems in Moscow, the leading Soviet institution for space biomedicine. In 1972 he

  • polyalkene (chemical compound)

    Polyolefin, any of a class of synthetic resins prepared by the polymerization of olefins. Olefins are hydrocarbons (compounds containing hydrogen [H] and carbon [C]) whose molecules contain a pair of carbon atoms linked together by a double bond. They are most often derived from natural gas or from

  • Polyalthia longifolia (plant)

    Magnoliales: Timber: Polyalthia longifolia is a tall, handsome tree with pendent linear leaves that is cultivated in most parts of Sri Lanka and India as an avenue tree and around temples for its religious significance. Although the wood is not very durable, it is utilized to some…

  • Polyalthia longifolia pendula (tree)

    Annonaceae: …of the mast tree (Polyalthia longifolia, variety pendula), of Sri Lanka. Its shining, brilliant green, willowy, wavy-edged leaves hang from pendant branches that almost clasp the tall straight trunk. The leaves are used as temple decorations in India.

  • polyamide (chemistry)

    Polyamide, any polymer (substance composed of long, multiple-unit molecules) in which the repeating units in the molecular chain are linked together by amide groups. Amide groups have the general chemical formula CO-NH. They may be produced by the interaction of an amine (NH2) group and a carboxyl

  • polyamide ink

    flexography: …or some other volatile solvent), polyamide inks, acrylic inks, and water-based inks. These are superior to oil-based printing inks because they adhere to the surface of the material, while oil-based inks must be absorbed into the material.

  • polyamideimide (chemical compound)

    major industrial polymers: Polyimides: Related commercial products are polyamideimide (PAI; trademarked as Torlon by Amoco Corporation) and polyetherimide (PEI; trademark Ultem); these two compounds combine the imide function with amide and ether groups, respectively.

  • polyandry (marriage)

    Polyandry, marriage of a woman to two or more men at the same time; the term derives from the Greek polys, “many,” and anēr, andros, “man.” When the husbands in a polyandrous marriage are brothers or are said to be brothers, the institution is called adelphic, or fraternal, polyandry. Polygyny, the

  • polyandry (animal behaviour)

    animal social behaviour: Social interactions involving sex: …a phenomenon referred to as polyandry, examples of which include spotted sandpipers (Actitis macularia), phalaropes (Phalaropus), jacanas (tropical species in the family Jacanidae), and a few human societies such as those once found in the Ladakh region of the Tibetan plateau. Monogamy, where a single male and female form a…

  • Polyanov, Treaty of (Europe [1634])

    Thirty Years' War: The Russo-Polish Peace of Polyanov in 1634 ended Poland’s claim to the tsarist throne but freed Poland to resume hostilities against its Baltic archenemy, Sweden, which was now deeply embroiled in Germany. Here, in the heartland of Europe, three denominations vied for dominance: Roman Catholicism, Lutheranism, and Calvinism. This…

  • polyantha rose (plant)

    rose: Major species and hybrids: Polyantha roses are a class of very hardy roses that produce dense bunches of tiny blossoms. Floribunda roses are hardy hybrids that resulted from crossing hybrid teas with polyanthas. Grandiflora roses are relatively new hybrids resulting from the crossbreeding of hybrid teas and floribunda roses.…

  • polyarchy (political science)

    Polyarchy, concept coined by the American political scientist Robert Dahl to denote the acquisition of democratic institutions within a political system that leads to the participation of a plurality of actors. Polyarchy, which means “rule by many,” describes the process of democratization, in

  • polyarteritis nodosa (pathology)

    Polyarteritis nodosa, inflammation of blood vessels and surrounding tissue; it may affect functioning of adjacent organs. The cause of polyarteritis nodosa is unknown. The word nodosa (“knotty”) forms part of the name because of the fibrous nodules along the medium-sized arteries that are affected.

  • polyarthralgia (pathology)

    connective tissue disease: Scleroderma: …stiffness of the joints (polyarthralgia)—often mistaken for rheumatoid arthritis—and paroxysmal blanching and cyanosis (becoming blue) of the fingers induced by exposure to cold (Raynaud syndrome). The skin changes may be restricted to the fingers (sclerodactyly) and face but often spread. Although there may be spontaneous improvement in the condition…

  • polyarylate (chemical compound)

    Polyarylate, a family of high-performance engineering plastics noted for their strength, toughness, chemical resistance, and high melting points. They are employed in automotive parts, ovenware, and electronic devices, among other applications. Polyarylates are a type of aromatic polyester. As in

  • polyatomic ion (chemistry)

    chemical compound: Ionic compounds containing polyatomic ions: A special type of ionic compound is exemplified by ammonium nitrate (NH4NO3), which contains two polyatomic ions, NH4+ and NO3−. As the name suggests, a polyatomic ion is a charged entity composed of several atoms bound together. Polyatomic ions have special names that…

  • polyatomic molecule (chemistry)

    molecule: …than two atoms are termed polyatomic molecules, e.g., carbon dioxide (CO2) and water (H2O). Polymer molecules may contain many thousands of component atoms.

  • polybasite (mineral)

    Polybasite, heavy, black sulfosalt mineral, a sulfide of the elements silver, copper, and antimony ([Ag, Cu]16Sb2S11), that occurs as monoclinic crystals and masses in silver veins, sometimes in large amounts. Polybasite is found in Chile, Peru, the Czech Republic, and many localities in Mexico

  • polybenzimidazole (chemical compound)

    Carl Shipp Marvel: …during the 1960s, Marvel synthesized polybenzimidazoles (PBIs), a type of polyimide that is resistant to temperatures as high as 600 °C (1,100 °F) and is used in suits for astronauts and firefighters. In 1980 PBIs became the first man-made fibres to be produced commercially in almost a decade. Marvel continued…

  • Polybia (insect genus)

    hymenopteran: Social forms: …division of labour occurs in Polybia. Some female Polybia only lay eggs. In others, called assisting females, the gonads are poorly developed; these females take charge of repair and construction, larvae care, and food gathering. They thus are useful in the society, even though they produce no offspring. This society…

  • polybisphenol-A terephthalate (chemical compound)

    polyarylate: Polybisphenol-A terephthalate does not begin to soften until heated above approximately 170 °C (340 °F). Its transparency and resistance to degradation from ultraviolet radiation make it suitable for use in solar-energy panels. Poly-4-hydroxybenzoate, a highly crystalline polymer consisting solely of aromatic rings linked by ester…

  • Polybius (Greek historian)

    Polybius, Greek statesman and historian who wrote of the rise of Rome to world prominence. Polybius was the son of Lycortas, a distinguished Achaean statesman, and he received the upbringing considered appropriate for a son of rich landowners. His youthful biography of Philopoemen reflected his

  • Polybius checkerboard (device)

    cryptology: Early cryptographic systems and applications: …by a device called the Polybius checkerboard, which is a true biliteral substitution and presages many elements of later cryptographic systems. Similar examples of primitive substitution or transposition ciphers abound in the history of other civilizations. The Romans used monoalphabetic substitution with a simple cyclic displacement of the alphabet. Julius…

  • Polyboroides typus (bird)

    hawk: The African harrier hawk (Polyboroides typus) and the crane hawk (Geranospiza nigra) of tropical America are medium-sized gray birds resembling the harriers but having short, broad wings.

  • Polyborus plancus (bird)

    caracara: …crested caracara (Caracara plancus or Polyborus plancus) occurs from Florida, Texas, Arizona, Cuba, and the Isle of Pines south to the Falkland Islands and Tierra del Fuego. Some authorities classify the entire population of caracaras within this range as crested caracaras, dividing them into several subspecies, while others define only…

  • polybrominated diphenyl ether (chemical compound)

    biomonitoring: Studies and surveillance programs: …that human milk levels of polybrominated diphenyl ethers (PBDEs), chemicals used as flame retardants in many consumer products, had doubled every five years. Other studies detected these chemicals in breast milk from women in Japan, Germany, the United States, and Canada, as well as in killer whales and polar bears…

  • polybutadiene (chemistry)

    butadiene rubber: It consists of polybutadiene, an elastomer (elastic polymer) built up by chemically linking multiple molecules of butadiene to form giant molecules, or polymers. The polymer is noted for its high resistance to abrasion, low heat buildup, and resistance to cracking.

  • polybutylene pipe (technology)

    polybutylene terephthalate: Pipe made with PBT (so-called polybutylene pipe, or PB pipe) was formerly popular for residential plumbing as a low-cost and easily handled substitute for copper, but it was found to degrade after prolonged contact with oxidizing chemicals such as chlorine in municipal water supplies, so it is no longer used.…

  • polybutylene terephthalate (chemical compound)

    Polybutylene terephthalate (PBT), a strong and highly crystalline synthetic resin, produced by the polymerization of butanediol and terephthalic acid. PBT is similar in structure to polyethylene terephthalate (PET)—the difference being in the number of methylene (CH2) groups present in the

  • Polycaon (beetle)

    branch and twig borer: …dead wood, and the genus Polycaon is often destructive in orchards.

  • polycaprolactam (fibre)

    major industrial polymers: Nylon: …the DuPont fibre was marketed, nylon 6 (polycaprolactam) was produced in Europe based on the polymerization of caprolactam. Nylon 6 and nylon 6,6 have almost the same structure and similar properties and are still the most important polyamide fibres worldwide. Their repeating units have the following structure:

  • polycaprolactone (chemical compound)

    major industrial polymers: Degradable polyesters: … (PLA), poly-2-hydroxy butyrate (PHB), and polycaprolactone (PCL), as well as their copolymers:

  • polycarbonate (chemical compound)

    Polycarbonate (PC), a tough, transparent synthetic resin employed in safety glass, eyeglass lenses, and compact discs, among other applications. PC is a special type of polyester used as an engineering plastic owing to its exceptional impact resistance, tensile strength, ductility, dimensional

  • polycarboxylic acid (chemical compound)

    carboxylic acid: Polycarboxylic acids: Unbranched-chain dicarboxylic acids contain two COOH groups. As a result they can yield two kinds of salts. For example, if oxalic acid, HOOCCOOH, is half-neutralized with sodium hydroxide, NaOH (i.e., the acid and base are in a 1:1 molar ratio), HOOCCOONa, called

  • Polycarp, Martyrdom of (patristic literature)

    Martyrdom of Polycarp, letter that describes the death by burning of Polycarp, bishop of Smyrna in Asia Minor. It was sent to the Christian church in Philomelium, Asia Minor, from the church in Smyrna (modern İzmir, Tur.) and is the oldest authentic account of an early Christian martyr’s death.

  • Polycarp, Saint (Greek bishop)

    Saint Polycarp, ; feast day February 23), Greek bishop of Smyrna who was the leading 2nd-century Christian figure in Roman Asia by virtue of his work during the initial appearance of the fundamental theological literature of Christianity. Historically, he formed a link between the apostolic and

  • polycentrism (political concept)

    Democrats of the Left: …proposing the concept of “polycentrism,” a form of limited independence among communist parties. After Togliatti’s death in 1964, the PCI nearly split into “Russian” and “Italian” wings over this concept. Despite this conflict and other splits to the left, the PCI won 27 percent of the vote in the…

  • Polychaeta (annelid)

    Polychaete, any worm of the class Polychaeta (phylum Annelida). About 8,000 living species are known. Polychaetes, which include rag worms, lugworms, bloodworms, sea mice, and others, are marine worms notable for well-defined segmentation of the body. Unique among annelids, most polychaete body

  • polychaete (annelid)

    Polychaete, any worm of the class Polychaeta (phylum Annelida). About 8,000 living species are known. Polychaetes, which include rag worms, lugworms, bloodworms, sea mice, and others, are marine worms notable for well-defined segmentation of the body. Unique among annelids, most polychaete body

  • polychaete hypothesis (paleontology)

    Polychaete hypothesis, theory that conodonts (minute toothlike structures found as fossils in marine rocks) are parts of the jaw apparatus of polychaete worms, a class of the annelid, or segmented, worms. Conodonts resemble the jaws (scolecodonts) of polychaete worms in form, and they are found in

  • polychlorinated biphenyl (chemical compound)

    Polychlorinated biphenyl (PCB), any of a class of organohalogen compounds prepared by the reaction of chlorine with biphenyl. A typical mixture of PCBs may contain over 100 compounds and is a colourless, viscous liquid. The mixture is relatively insoluble in water, is stable at high temperatures,

  • polychlorinated dibenzodioxin (chemical compound)

    Dioxin, any of a group of aromatic hydrocarbon compounds known to be environmental pollutants that are generated as undesirable by-products in the manufacture of herbicides, disinfectants, and other agents. In popular terminology, dioxin has become a synonym for one specific dioxin,

  • polychloroethene (chemical compound)

    Polyvinyl chloride (PVC), a synthetic resin made from the polymerization of vinyl chloride. Second only to polyethylene among the plastics in production and consumption, PVC is used in an enormous range of domestic and industrial products, from raincoats and shower curtains to window frames and

  • polychloroprene (chemical compound)

    Neoprene (CR), synthetic rubber produced by the polymerization (or linking together of single molecules into giant, multiple-unit molecules) of chloroprene. A good general-purpose rubber, neoprene is valued for its high tensile strength, resilience, oil and flame resistance, and resistance to

  • polychlorotrifluoroethylene (chemical compound)

    Polychlorotrifluoroethylene (PCTFE), synthetic resin formed by the polymerization of chlorotrifluoroethylene. It is a moldable, temperature-resistant, and chemical-resistant plastic that finds specialty applications in the chemical, electrical, and aerospace industries. PCTFE can be prepared as a

  • polychondritis (pathology)

    Polychondritis, chronic disease characterized by inflammation and destruction of the cartilage of various tissues of the body. The cause of polychondritis is unknown, but the disease may be the result of an abnormal immune response. Symptoms include pain, redness, and swelling of the affected

  • polychromatism (biological pigmentation)

    coloration: Coloration changes in populations: …species is said to be polychromatic. The white-throated sparrow (Zonotrichia albicollis) of North America, for example, has individuals with white-and-black head stripes and other individuals with tan-and-brown head stripes. The different colorations are not associated with age, sex, or geographic region. Polychromatism may evolve in response to predation. A predator…

  • polychromy (visual arts)

    Aegean civilizations: Period of the Early Palaces in Crete (c. 2000–1700): …red to create a striking polychrome effect. This kind of pottery, which flourished in Crete throughout the time of the first palaces and later (c. 2200 to 1600), is known as Kamáres ware from a sacred cave of that name on Mount Ida, where vases with fine polychrome decoration were…

  • Polychronicon (work by Higden)

    Ranulf Higden: …and chronicler remembered for his Polychronicon, a compilation of much of the knowledge of his age.

  • Polycillin (drug)

    Ampicillin, drug used in the treatment of various infections, including otitis media (middle ear infection), sinusitis, and acute bacterial cystitis. Ampicillin (or alpha-aminobenzylpenicillin) is a semisynthetic penicillin, one of the first such antibiotics developed. Similar in action to

  • Polycladida (flatworm order)

    flatworm: Annotated classification: Order Polycladida Pharynx simple, bulbose, or plicate (many ridges); intestine may have short diverticula, or pockets; protonephridia paired; testes usually numerous; penis papilla generally present; nervous system with 3–4 trunks; nearly 800 species. Class Monogenea Oral sucker lacking or weakly developed; posterior end with large

  • Polycleitus (Greek sculptor)

    Polyclitus, Greek sculptor from the school of Árgos, known for his masterly bronze sculptures of young athletes; he was also one of the most significant aestheticians in the history of art. Polyclitus’s two greatest statues were the Diadumenus (430 bce; “Man Tying on a Fillet”) and the Doryphoros

  • polyclinic (medicine)

    medicine: Russia: …in varying specialties work from polyclinics or outpatient units, where many types of diseases are treated. Small towns usually have one polyclinic to serve all purposes. Large cities commonly have separate polyclinics for children and adults, as well as clinics with specializations such as women’s health care, mental illnesses, and…

  • Polyclitus (Greek sculptor)

    Polyclitus, Greek sculptor from the school of Árgos, known for his masterly bronze sculptures of young athletes; he was also one of the most significant aestheticians in the history of art. Polyclitus’s two greatest statues were the Diadumenus (430 bce; “Man Tying on a Fillet”) and the Doryphoros

  • polycrase (mineral)

    euxenite: …to form the similar mineral polycrase; both it and euxenite often contain rare earths. These minerals are widespread in Norway, Madagascar, and Canada and also occur in Sweden, Finland, Greenland, Australia, Brazil, and the U.S. For chemical formula and detailed physical properties, see oxide mineral (table).

  • Polycrates (bishop of Ephesus)

    councils of Ephesus: First Council of Ephesus: In 190 Polycrates, bishop of Ephesus, convened a synod to establish the 14th of Nisan (the date of the Jewish Passover) as the official date of Easter. Pope Victor I, preferring a Sunday as more convenient and desiring uniformity, repudiated the decision and separated those who disagreed…

  • Polycrates (tyrant of Samos)

    Polycrates, tyrant (c. 535–522 bc) of the island of Samos, in the Aegean Sea, who established Samian naval supremacy in the eastern Aegean and strove for control of the archipelago and mainland towns of Ionia. Polycrates seized control of the city of Samos during a celebration of a festival of Hera

  • polycrystal (crystallography)

    Polycrystal, any solid object composed of randomly oriented crystalline regions, called crystallites, especially as distinguished from a single crystal (q.v.). Polycrystalline materials result when a substance solidifies rapidly; crystallization commences at many sites (see nucleation), and the

  • Polyctenidae (insect)

    Bat bug, (family Polyctenidae), any of about 20 species of bloodsucking insects (order Heteroptera) that are external parasites found mainly in the fur of tropical bats. The adult (between 3.5 and 5 mm [0.14 and 0.2 inch] long) lacks eyes and wings. Its forelegs are short and thick, and its middle

  • polycyclic aromatic hydrocarbon (chemical compound)

    David S. McKay: First was the presence of polycyclic aromatic hydrocarbons (PAHs). While these organic compounds are commonplace, found throughout the solar system, the PAHs in the meteorite were unusual in appearance, resembling the type that result from the decay of organic matter. The presence of the molecules within the rock and their…

  • polycyclic dictyostele (botany)

    fern: Vascular tissues: … fern (Pteridium), which has a polycyclic dictyostele, in which one stele occurs within another stele. Large strands of fibrelike cells running between the two steles form mechanically specialized hard tissue, or sclerenchyma.

  • polycyclic nonaromatic compound (chemical compound)

    hydrocarbon: Polycyclic nonaromatic compounds: The Hückel rule is not designed to apply to polycyclic compounds. Nevertheless, a similar dependence on the number of π electrons is apparent. The bicyclic hydrocarbon azulene has the same number of π electrons (10) as naphthalene and, like naphthalene, is aromatic.…

  • polycyclic quinone (chemical compound)

    coloration: Polycyclic quinones: The polycyclic quinones occur in some bacteria, fungi, and parts of higher plants. One of the more interesting representatives is the aphin group, so called because of their initial recovery from the hemolymph (circulating fluid) of several coloured species of aphids; aphids parasitize…

  • polycystic ovary syndrome (medical disorder)

    Stein-Leventhal syndrome, disorder in women that is characterized by an elevated level of male hormones (androgens) and infrequent or absent ovulation (anovulation). About 5 percent of women are affected by Stein-Leventhal syndrome, which is responsible for a substantial proportion of cases of

  • polycystic renal disease

    renal system disease: Other tumours: The form of polycystic (multiple-cyst) renal disease that allows survival into adult life is a familial condition, in which several members of the family have little trouble until middle life but then are progressively affected by kidney malfunction. Episodes of blood in the urine and urinary infection are…

  • Polycystinea (protozoan)

    Radiolarian, any protozoan of the class Polycystinea (superclass Actinopoda), found in the upper layers of all oceans. Radiolarians, which are mostly spherically symmetrical, are known for their complex and beautifully sculptured, though minute, skeletons, referred to as tests. Usually composed of

  • polycythemia (pathology)

    Polycythemia, abnormal increase in red blood cells (erythrocytes) and hemoglobin in the circulation, a situation that results in thickened blood, retarded flow, and an increased danger of clot formation within the circulatory system. The condition often results in an increase in the volume of

  • polycythemia vera (pathology)

    polycythemia: Polycythemia vera: Polycythemia differs from a disease called polycythemia vera (erythremia, or primary polycythemia), in which excess red blood cells occur without known cause. In polycythemia vera there is usually an increase in other blood elements as well; for example, the number of red cells…

  • polycythemia, absolute (pathology)

    polycythemia: Types of polycythemia: …cause is known, is called erythrocytosis.

  • polydactylism (congenital disorder)

    cat: Other characters: Polydactylism, the presence of extra toes, is inherited and behaves as a dominant to the normal condition. It seems to be due to a single gene. The extra toes occur on the inner, or thumb, side of the foot.

  • polydactyly (congenital disorder)

    cat: Other characters: Polydactylism, the presence of extra toes, is inherited and behaves as a dominant to the normal condition. It seems to be due to a single gene. The extra toes occur on the inner, or thumb, side of the foot.

  • polydaemonistic magical religion

    classification of religions: Morphological: …the nature religions is called polydaemonistic (many spirits) magical religion, which is dominated by animism and characterized by a confused mythology, a firm faith in magic, and the preeminence of fear above other religious emotions. At a higher stage of nature religions is therianthropic polytheism, in which the deities are…

  • Polydectes (Greek mythology)

    Perseus: …the chest had grounded, King Polydectes of Seriphus, who desired Danaë, tricked Perseus into promising to obtain the head of Medusa, the only mortal among the Gorgons.

  • polydentate ligand (chemistry)

    coordination compound: Ligands and chelates: Because a polydentate ligand is joined to the metal atom in more than one place, the resulting complex is said to be cyclic—i.e., to contain a ring of atoms. Coordination compounds containing polydentate ligands are called chelates (from Greek chele, “claw”), and their formation is termed chelation.…

  • Polydeuces (astronomy)

    Dione: …much smaller moons, Helene and Polydeuces (also named for Greek mythological figures). Helene, which has a diameter of about 30 km (20 miles), maintains a gravitationally stable position 60° ahead of Dione. Polydeuces has less than half the diameter of Helene and follows Dione by 60°, though with large deviations…

  • polydimethylsiloxane (chemical compound)

    major industrial polymers: Polysiloxanes (silicones): The most common siloxane polymer, polydimethylsiloxane, is formed when the chlorine atoms of the monomer, dichlorodimethylsilane (Cl2Si[CH3]2), are replaced by hyroxyl (OH) groups by hydrolysis. The resultant unstable compound, silanol (Cl2Si[OH]2), condenses in step-growth fashion to form the polymer, with concomitant loss of water. Some cyclic products are also formed,…

  • Polydora (polychaete genus)

    annelid: Annotated classification: …cm; examples of genera: Spio, Polydora. Order Chaetopterida Two to 3 distinct body regions; prostomium with palpi; modified setae on segment 4; tube dweller; examples of genera: Chaetopterus (parchment worm), Spiochaetopterus. Order Magelonida

  • Polydorian (Turkey)

    Burdur, city, southwestern Turkey. It is located near the eastern shore of Lake Burdur. Called Polydorion in the Middle Ages, it fell to the Seljuq Turks in the 12th century and came under Ottoman domination in the 15th. Its size and economy expanded after World War II. Industries include textiles,

  • Polydoúre, Maria (Greek poet)

    Maria Polidoúri, Greek poet known for her impassioned, eloquent farewell to life. Polidoúri was orphaned as a small child, and in 1921 she went to Athens to study law. There she began a friendship with another poet, Kóstas Kariotákis. In 1926 she went to Paris, returning two years later, fatally

  • Polyeidus (Greek mythology)

    Glaucus: The seer Polyeidus finally discovered the child but on confessing his inability to restore him to life was shut up in a vault with the corpse. There he killed a serpent and, seeing it revived by a companion that laid a certain herb upon it, brought the…

  • polyelectrolyte (chemical compound)

    liquid: Solutions of electrolytes: …charges; such molecules are called polyelectrolytes. In solution, the conformation (i.e., the three-dimensional structure) of a large, charged molecule is strongly dependent on the ionic strength of the dissolving medium; for example, depending on the nature and concentration of salts present in the solvent, a polyelectrolyte molecule may coagulate into…

  • polyembryony (biology)

    Polyembryony, a condition in which two or more embryos develop from a single fertilized egg, forming what in humans is known as identical twins. A common phenomenon in many plant and animal species, polyembryony occurs regularly in the nine-banded armadillo, which usually gives birth to four

  • polyene (chemical compound)

    antifungal drug: The polyenes: Polyenes, such as amphotericin B and nystatin, are macrolide antibiotics made up of alternating conjugated double bonds. The polyene drugs work by interacting with ergosterol, a type of steroid that is found in fungal membranes; this binding causes channels to form in

  • polyepiphyseal dysplasia (pathology)

    joint disease: Congenital and hereditary abnormalities: Polyepiphyseal dysplasias (abnormal development in childhood of a number of epiphyses—the ends or outlying portions of bones separated from the main body of the bone by cartilage) are a vaguely similar, though much milder, group of conditions in which precocious osteoarthritis and spondylosis are the…

  • polyester (chemical compound)

    Polyester, a class of synthetic polymers built up from multiple chemical repeating units linked together by ester (CO-O) groups. Polyesters display a wide array of properties and practical applications. Permanent-press fabrics, disposable soft-drink bottles, compact discs, rubber tires, and enamel

  • polyesterurethane

    materials science: General requirements of biomaterials: In addition, degradable polyesterurethane foam was abandoned as a fixation patch for breast prostheses, because it offered a distinct possibility for the release of carcinogenic by-products as it degraded.

  • polyestrous (zoology)

    estrus: , ground squirrels) are polyestrous: if not impregnated, they will come into heat repeatedly during the breeding season. Males can recognize a female in heat by smell; certain substances (pheromones) are secreted only at this portion of her cycle. The female’s genital area may be swollen during estrus, and…

  • polyethene (chemical compound)

    Polyethylene (PE), light, versatile synthetic resin made from the polymerization of ethylene. Polyethylene is a member of the important family of polyolefin resins. It is the most widely used plastic in the world, being made into products ranging from clear food wrap and shopping bags to detergent

  • polyether (chemical compound)

    Polyether, any of a class of organic substances prepared by joining together or polymerizing many molecules of simpler compounds (monomers) by establishing ether links between them; polyethers, which may be either chainlike or networklike in molecular structure, comprise an unusually diverse group

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