phonon \'fo-,nan\ In solid-state physics, a quantum of lattice vibrational energy. In analogy to a photon (a quantum of light), a phonon is viewed
as a wave packet with particlelike properties (see wave-particle duality). The way phonons behave determines or affects various properties of sol¬ ids. Thermal conductivity, for instance, is explained by phonon interac¬ tions. Phonons also provide the basis for understanding superconductivity in certain metals.
Phony War (1939—40) Early months of World War II, marked by no major hostilities. The term was coined by journalists to derisively describe the six-month period (October 1939-March 1940) during which no land operations were undertaken by the Allies or the Germans after the Ger¬ man conquest of Poland in September 1939.
phosgene Vfaz- jen\ or carbonyl chloride Vkar-bs-.nilV Colourless, highly toxic gas used in chemical warfare as well as in industrial processes including the making of dyestuffs and polyurethane resins. Either alone or in combination with chlorine, it was used against troops in World War I. It smells like musty hay. Inhalation causes severe lung injury several hours after exposure. First prepared in 1811, it is manufactured by the reaction of carbon monoxide and chlorine in the presence of a catalyst. Gaseous phosgene is usually stored and transported as a liquid under pressure in steel cylinders or as a solution in toluene. Mixed with water, it forms carbon dioxide and hydrochloric acid.
phosphate Any of numerous chemical compounds related to phospho¬ ric acid (H3PO4). Phosphate salts are inorganic compounds containing the phosphate ion (PO4 - ), the hydrogen phosphate ion (HPO4 - ), or the dihy¬ drogen phosphate ion (H2PO4), along with any cation. Phosphate esters are organic compounds in which the hydrogens of phosphoric acid are replaced by organic groups (e.g., methyl, ethyl, phenyl), with one of their carbon atoms bonding to an oxygen atom in the phosphate group. Nucleic acids and ATP both contain phosphate; bones and teeth contain calcium phosphate. Phosphate rock (mainly calcium phosphate) is one of the four most important basic chemical commodities. Phosphates were formerly used in detergents, which washed into rivers and lakes, causing water blooms of algae and bacteria (see eutrophication); such use is now gener¬ ally outlawed or regulated. Phosphates are still used in fertilizers, baking powder, and toothpaste.
phospholipid \,fas-fo-Ti-p3d\ or phosphatide Any member of a large class of fatlike organic compounds that in their molecular structure resemble the triglycerides, except for the replacement of a fatty acid with a PHOSPHATE-containing polar group. The polar end of the molecule is soluble in water (hydrophilic) and water solutions (including cytoplasm); the other, fatty-acid end is soluble in fats (hydrophobic). In a watery envi¬ ronment phospholipids naturally combine to form a two-layer structure (upid bilayer) with the fat-soluble ends sandwiched in the middle and the water-soluble ends sticking out. Such lipid bilayers are the structural basis of cell membranes. Phospholipids are the principal components of the mye¬ lin sheaths of neurons. Examples of phospholipids include lecithin, ceph- alins, phosphoinositides (in the brain), and cardiolipin (in the heart). See also DETERGENT.
phosphorescence Emission of light from a substance exposed to radiation and persisting as an afterglow after the exciting radiation has been removed. Unlike fluorescence, in which the absorbed light is emit¬ ted about 10 -8 second after excitation, in phosphorescence the extra energy absorbed is stored in metastable states and reemitted later. Phos¬ phorescence may last from about 10~ 3 second to days or even years. The term phosphorescence is often applied to luminescence of living organisms, as well.
phosphorite Vfas-for-.itV or phosphate rock Rock with a high con¬ centration of phosphates in nodular or compact masses. The phosphates may be derived from a variety of sources, including marine invertebrates that secrete shells of calcium phosphate and the bones and excrement of vertebrates. Typical phosphorite beds contain about 30% phosphorus pen- toxide (P 2 0 5 ) and constitute the primary source of raw materials for phos¬ phate fertilizers. Significant deposits in the U.S. include the Phosphoria Formation in Idaho and the Monterey Formation in California. Major deposits also occur in the Sechura Desert in Peru.
phosphorus Nonmetallic chemical element, chemical symbol P, atomic number 15. The ordinary allotrope, called white phosphorus, is a poison¬ ous, colourless, semitransparent, soft, waxy solid that glows in the dark (see phosphorescence) and combusts spontaneously in air, producing dense white fumes of the oxide P 4 0 10 ; it is used as a rodenticide and a military smokescreen. Heat or sunlight converts it to the red phosphorus allotrope,
© 2006 Encyclopaedia Britannica, Inc.
1492 I Photian Schism ► photometry
a violet-red powder that does not phosphoresce or ignite spontaneously. Much less reactive and soluble than white phosphorus, it is used in manu¬ facturing other phosphorus compounds and in semiconductors, fertilizers, safety matches, and fireworks. Black phosphorus, made by heating the white form under pressure, is flaky like graphite. Phosphorus seldom occurs uncombined in nature. As the phosphate ion, it is abundant and widely distributed, in apatite, phosphorite, and many other minerals. Phos¬ phorus has valence 3 or 5 in compounds, which have many uses in indus¬ try. Phosphine (PH 3 ) is a chemical raw material and a doping agent (deliberately added impurity) for solid-state electronics components. Organic phosphorus compounds are used as plasticizers, gasoline addi¬ tives, insecticides (e.g., parathion), and nerve gases. In living organisms the role of phosphorus is essential; it is a component of DNA and RNA, ATP, and bone.
Photian Schism See Photian Schism
Photius \'fo-she-3s. Saint (b. c. 820, Constantinople—d. 10th century; feast day February 6) Patriarch of Constantinople (858-867, 877-886). A high-ranking civil servant, he was promoted swiftly through the ecclesi¬ astical orders to become patriarch after the deposition of Ignatius, an action that offended Pope Nicholas I. Photius added to the conflict by refusing to restore dioceses earlier transferred from the Roman to the Byzantine church. Angry that Nicholas would not recognize him, Photius excommunicated the pope (867), thus beginning the Photian Schism. Pho¬ tius was deposed the same year but restored in 877 after his successor died. He and Pope John VIII agreed to return Bulgaria to the Roman church but to allow Greek bishops to remain.
Photo-Realism Late 20th-century painting style based on photogra¬ phy, in which realistic scenes are rendered in meticulous detail. An off¬ shoot of Pop art, it became a trend in U.S. painting in the 1970s among artists fascinated by camera images. Though photographs had been used by 19th-century painters such as Eugene Delacroix as substitutes for real¬ ity, the Photo-Realists relied on the photograph itself, replicating it in large-scale detail as the reality on which to base an acrylic painting. Its subjects often included reflecting surfaces (chrome-plated diners, motor¬ cycles, glass-fronted buildings, etc.). Its awesome technical precision, brilliant colour schemes, and visual complexity earned the style wide popularity. Its most notable practitioners were Chuck Close, Don Eddy, Richard Estes, and Audrey Flack.
Photo-Secession Group of U.S. photographers influenced by the Pic- torialist movement. Founded in 1902 by Alfred Stieglitz, the Photo- Secession sought recognition of photography as an art to be judged on its own terms. It was akin to such groups as the Linked Ring in London, and its name reflected that of the Sezession movement in Austria and Germany. The group regularly showed its work at the Little Galleries of the Photo- Secession, also known as “291” (its address on Fifth Avenue in New York City), a gallery run by Stieglitz. While Stieglitz did not believe in retouch¬ ing or manipulating negatives or prints, others of the group, such as Edward Steichen, were adherents of the impressionistic soft-focus school and the new techniques. By 1910 many members of the group left due to different aesthetic visions. The record of the Photo-Secession is contained in the quarterly Camera Work (1903-17).