phase In thermodynamics, a chemically and physically uniform quantity of matter that can be separated mechanically from a nonhomogeneous mixture. It may consist of a single substance or of a mixture of substances. The three basic phases of matter are solid, liquid, and gas; other phases that are considered to exist include crystalline (see crystal), colloidal (see colloid), glass, amorphous, and plasma. The different phases of a pure sub¬ stance are related to each other in terms of temperature and pressure. For example, if the temperature of a solid is raised enough, or the pressure is reduced enough, it will become a liquid.
phase In wave motion, the fraction of the time required to complete a full cycle that a point completes after last passing through the reference position. Two periodic motions are said to be in phase when correspond¬ ing points of each reach maximum or minimum displacements at the same time. If the crests of two waves pass the same point at the same time, they are in phase for that position. If the crest of one and the trough of the other pass the same point at the same time, the phase angles differ by 180° and the waves are said to be of opposite phase. Phase differences are important in alternating electric current technology (see alternating CURRENT).
Phazania See Fezzan
pheasant Any of about 50 specie family Phasianidae (order Galli- formes), chiefly Asian but natural¬ ized elsewhere. Most species inhabit open woodlands and brushy fields.
All have a hoarse call. The feet and lower legs are unfeathered. Females are inconspicuous. Most males are strikingly coloured and have one or more leg spurs, and some have a fleshy facial ornament. Males some¬ times fight to the death for a harem of hens. Male ring-necked or com¬ mon pheasants {Phcisianus colchi- cus), 35 in. (90 cm) long, have a
streaming tail, coppery breast, purplish green neck, and ear tufts; they are widespread in the northern U.S. Japanese green pheasants (P versicolor ) call in concert when an earthquake is imminent.
Pheidias See Phidias
phenol Vfe-.nol, 'fe-.nolV Any of a class of organic compounds with a hydroxyl group (-OH; see functional group) attached to a carbon atom in a ring of an aromatic compound. The simplest one, carbolic acid (C 6 H 5 OH), is also called phenol; its most important reaction is with formaldehyde, with which it forms widely used polymers called phenol-formaldehyde (phe¬ nolic) resins. Phenols are similar to alcohols but form stronger hydrogen bonds (see bonding), so they dissolve more readily in water and boil at higher temperatures. They may be colourless liquids or white solids; many have a sharp, spicy odour. Some are found in essential oils. Phenols with higher molecular weights and phenol derivatives have supplanted phenol itself as industrial antiseptics (germicidal cleaners). See also Leo Baekeland.
phenol See carbolic acid
phenomenalism View that statements about material objects are reducible to statements about actual and possible sensations, or sense-data. According to phenomenalists, a material object is not a mysterious some¬ thing “behind” the appearances presented in sensation. If it were, the material world would be unknowable; indeed, the term matter is unintel¬ ligible unless it somehow can be defined by reference to sensations. In speaking about a material object, then, reference must be made to a very large system of possible sense-data, only some of which (if any) are ever actualized. Thus the statement “There is a fire in the next room” would be analyzed as a series of hypothetical statements such as “If one were to enter the next room with one’s eyes open, one would see a bright light of a yellowish orange colour.” Some philosophers have objected that it is difficult to remove all references to material objects from the hypotheti¬ cal statements to which material-object talk is supposedly reducible. See also George Berkeley.
phenomenology Philosophical discipline originated by Edmund Hus¬ serl. Husserl developed the phenomenological method to make possible “a descriptive account of the essential structures of the directly given.” Phenomenology emphasizes the immediacy of experience, the attempt to isolate it and set it off from all assumptions of existence or causal influ¬ ence and lay bare its essential structure. Phenomenology restricts the phi¬ losopher’s attention to the pure data of consciousness, uncontaminated by metaphysical theories or scientific assumptions. Husserl’s concept of the life-world—as the individual’s personal world as directly experienced— expressed this same idea of immediacy. With the appearance of the Annual for Philosophical and Phenomenological Research (1913-30), under Husserl’s editorship, his personal philosophizing flowered into an inter¬ national movement. Its most notable adherents were Max Scheler and Mar¬ tin Heidegger.
phenotype Vfe-n9-,tlp\ All the observable characteristics of an organ¬ ism, such as shape, size, colour, and behaviour, that result from the inter¬ action of its genotype (total genetic makeup) with the environment. The phenotype may change throughout the life of an individual because of environmental changes and the changes associated with aging. Different environments can influence the development of inherited traits (e.g., size is affected by available food supply) and can alter expression by similar genotypes (e.g., twins brought up in dissimilar families may mature dif¬ ferently). Furthermore, not all inherited possibilities in the genotype are expressed in the phenotype, because some are the result of inactive, reces¬ sive, or inhibited genes. See also variation.
phenylalanine V.fe-ffl-'a-b-.nen, ,fe-n 3 l-'a-b- l nen\ One of the essen¬ tial amino acids, present in many common proteins, especially hemoglobin. It is used in medicine and nutrition and as one of the two amino acids making up aspartame. Persons with phenylketonuria do not metabolize phe¬ nylalanine properly and must adhere to a diet free of it.
phenylketonuria \ 1 fe-n 3 l- I ke-t 3 n- , ur-e-o\ (PKU) or phenylpyru- vic oligophrenia \ l fe-n 3 l-pI- l rii-vik- l al-i-go- , fre-ne-3\ Inability to nor¬ mally metabolize phenylalanine, the accumulation of which interferes with normal childhood development. Central nervous system effects include mental retardation and seizures (see epilepsy), with behavioral signs seen at four to six months of age. Abnormal metabolism also leads to low mela¬ nin levels, with light hair, eye, and skin colour. Tests detect this recessive genetic disorder (see congenital disorder; recessiveness) in two-thirds of the 1 in 10,000 newborns born with high levels of phenylalanine. Keeping
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1486 I pheromone ► Philip
phenylalanine out of the diet (by total avoidance of meat, dairy, and high- protein foods and aspartame) until adolescence permits normal develop¬ ment. Protein is supplied in a phenylalanine-free formula. Pregnant women with PKU must resume the diet to prevent severe damage to the unborn child.
pheromone \'fer-3- l mon\ Any chemical compound secreted by an organism in minute amounts to elicit a particular reaction from other organ¬ isms of the same species. Pheromones are widespread among insects and vertebrates (except birds) and are present in some fungi, slime molds, and algae. The chemicals may be secreted by special glands or incorporated into other substances (e.g., urine), shed freely, or deposited in selected loca¬ tions. Pheromones are used to bring creatures together (e.g., in termite, bee, and ant colonies), lead them to food (e.g., in scent trails laid by ants), signal danger (e.g., when released by wounded fish to alert others), attract a mate and elicit sexual behaviour (numerous examples, possibly including humans), and influence sexual development (in many mammals and certain insects). Alarm pheromones often last a shorter time and travel a shorter distance than other types. In vertebrates, chemical stimuli often influence parent-young responses. Sex-attractant pheromones are used in certain products to lure and trap unwanted or harmful insects.