resin Vre-z 3 n\ Any natural or synthetic organic compound consisting of a noncrystalline (amorphous) solid or viscous liquid substance or mix¬ ture. Natural resins are usually transparent or translucent yellow to brown and can melt and burn. Most are exuded from trees, especially pines and firs (see conifer), when the bark is injured or stripped. The fluid secretion usually dries out and hardens into a material that can be worked. Natural resins have been used in perfumes and medicines (e.g., balsams), in paints and varnishes (e.g., turpentine and shellac, the latter derived from the secretion of an insect), and in decorative ware (e.g., amber, Oriental lac¬ quer). Synthetic resins are all plastics; the term resin, though still used in the modem industry, dates from the years when synthetics began to replace natural resins. Thermoplastic resins are plastics such as polyeth¬ ylene that can be shaped repeatedly on reheating, whereas thermosetting resins are plastics such as epoxy that set permanently and cannot be reshaped.
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1610 I resistance ► Reston
resistance Opposition that a material or electrical circuit offers to the flow of electric current. It is the property of a circuit that transforms elec¬ trical energy into heat energy as it opposes the flow of current. The resis¬ tance R, the electromotive force or voltage V, and the current I are related by Ohm's law. The resistance of an electrical conductor generally increases with increasing temperature and is utilized in devices such as lamps and heaters. The ohm (Q) is the common unit of electrical resis¬ tance; one ohm is equal to one volt (see electromotive force) per ampere.
Resistance or Underground Clandestine groups opposed to Nazi rule in German-occupied Europe in World War II. The groups included civilians who worked secretly against the occupation and armed bands of partisans or guerrilla fighters. Resistance activities ranged from assisting the escape of Jews and Allied airmen shot down over enemy territory to committing sabotage, ambushing German patrols, and sending intelligence information to the Allies. Resistance groups were not always unified; in some countries, rival groups divided along communist and noncommunist lines. However, in France the clandestine National Council of the Resis¬ tance coordinated all French groups, which gave support to the Normandy Campaign and participated in the August 1944 uprising that helped liberate Paris. Resistance groups in other northern European countries also under¬ took military actions to help the Allied forces in 1944^15.
resistivity Electrical resistance of a conductor of unit cross-sectional area and unit length. The resistivity of a conductor depends on its com¬ position and its temperature. As a characteristic property of each mate¬ rial, resistivity is useful in comparing various materials on the basis of their ability to conduct electric current. As temperature increases, the resis¬ tivity of a metallic conductor usually increases and that of a semiconduc¬ tor usually decreases.
Resnais \ro-'na\, Alain (b. June 3, director. After studying at the French cinema school IDHEC, he made short films on the visual arts (Van Gogh [1948]) and documentaries (Night and Fog [1956]). His first fea¬ ture film, Hiroshima mon amour (1959), created a sensation with its alternation between past and present and is considered one of the earliest and best films of the New Wave. He continued his exploration of the complex themes of time and memory in Last Year at Marienbad (1961).
His later films include Muriel (1963), Stavisky (1974), My Ameri¬ can Uncle (1980), Love unto Death (1984), I Want to Go Home (1989),
Smoking/No Smoking (1993), and
J Same Old Song (1997).
H resonance In physics, the rela¬
tively large selective response of an
tm object or a system that vibrates in
y step with an externally applied vibration. Acoustical resonance is the vibra¬
tion induced in a string of a given pitch when a note of the same pitch is produced nearby, in the sound box of an instrument such as a guitar, or in the mouth or nasal cavity when speaking. Mechanical resonance, such as that produced in a bridge by wind or by marching soldiers, can even¬ tually produce wide swings great enough to cause the bridge’s destruc¬ tion. Resonance in frequency-sensitive electrical circuits makes it possible for certain communication devices to accept signals of some frequencies while rejecting others. Magnetic resonance occurs when electrons or atomic nuclei respond to the application of magnetic fields by emitting or absorbing electromagnetic radiation. See also nuclear magnetic resonance.
Respighi \re-'spe-ge\, Ottorino (b. July 9, 1879, Bologna, Italy—d. April 18, 1936, Rome) Italian composer. After musical studies in Bolo¬ gna (1891-1901), he played viola in a Russian orchestra and studied with Nikolay Rimsky-Korsakov, from whom he learned much about orchestra¬ tion. His best-known works are the colourful tone poems The Fountains of Rome (1916) and The Pines of Rome (1924). Interested in early music, he also produced works such as Gli uccelli (1927), based on works by Jean-Philippe Rameau, and La Boutique fantasque, based on works by Gio¬ acchino Rossini.
respiration Process of taking in air for oxygen and releasing it to dis¬ pose of carbon dioxide. The amount of air inhaled and exhaled in an aver¬ age human breath (tidal volume) is about one-eighth the amount that can be inhaled after exhaling as much as possible (vital capacity). Nerve cen¬ tres in the brain regulate the movements of muscles of respiration (dia¬ phragm and chest wall muscles). Blood in the pulmonary circulation brings carbon dioxide from the tissues to be exhaled and takes up oxygen from the air in the pulmonary alveoli to carry it to the heart and the rest of the body. Because the body stores almost no oxygen, interruption of respiration—by asphyxiation, drowning, or chest muscle paralysis —for more than a few minutes can cause death. Disorders affecting respiration include allergy, asthma, bronchitis, emphysema, pneumonia, and tuberculosis. See also respiratory system; respiratory therapy.
respiratory distress syndrome or hyaline membrane dis¬ ease Common complication in newborns, especially after premature birth. Symptoms include very laboured breathing, bluish skin tinge, and low blood oxygen levels. Insufficient surfactant in the pulmonary alveoli raises surface tension, hampering lung expansion. The alveoli collapse (see atelectasis), and a “glassy” (hyaline) membrane develops in the alveolar ducts. Once the leading cause of death in premature infants, the syndrome is now usually treated for a few days with a mechanical ventilator (see respiratory therapy), with no aftereffects. An adult respiratory distress syn¬ drome (ARDS) can follow lung injury.
respiratory system Organ system involved in respiration. In humans, the diaphragm and, to a lesser extent, the muscles between the ribs gen¬ erate a pumping action, moving air in and out of the lungs through a sys¬ tem of pipes (conducting airways), divided into upper and lower airway systems. The upper airway system comprises the nasal cavity (see nose), siNUSes, and pharynx; the lower airway system consists of the larynx, tra¬ chea, bronchi, bronchioles, and alveolar ducts (see pulmonary alveolus). The blood and cardiovascular system can be considered elements of a working respiratory system. See also thoracic cavity. See illustration on opposite page.
respiratory therapy Medical profession concerned with assisting the respiratory function of individuals who have severe lung disorders. Prac¬ tices include suctioning to clear secretions from the airway, use of aero¬ sol mists (sometimes medicated) or gases to ease breathing, and tilting the body and chest percussion to promote drainage. A respiratory thera¬ pist also manages mechanical ventilation, a process in which a machine generates a controlled flow of a gas mixture into the airway of a patient who cannot breathe efficiently.