critical temperature

[′krid·ə·kəl ′tem·prə·chər] (agriculture) The temperature below which a plant cannot grow. (physical chemistry) The temperature of the liquid-vapor critical point, that is, the temperature above which the substance has no liquid-vapor transition. Symbolized T_c.

Critical Temperature

(1) The temperature of a substance in its critical state. For single substances the critical temperature is defined as the temperature at which the physical properties of the liquid and the vapor in equilibrium become identical. At the critical temperature the density of the saturated vapor and the liquid become identical, the interface between them disappears, and the heat of vaporization becomes zero. The critical temperature is one of the constants of a substance. (For the value of the critical temperature T_c for some substances, see.)

In binary systems (for example, propane-isopentane) the fluid-vapor equilibrium has no single critical temperature but rather a spatial critical curve for which the terminal points are the critical temperatures of the pure components.

(2) The temperature in fluid mixtures having components of limited solubility at which the mutual solubility becomes unlimited; it is called the critical solution temperature.

(3) The transition temperature of a number of conductors into the superconducting state. It has been measured for a large number of metals, alloys, and chemical compounds. In pure metals the lowest critical temperature occurs in titanium (0.37°K) and the highest in technetium (11.2°K). A very high value has been found in the compound Nb₃Ge (T_c ≈ 23°K).

critical temperature

1. The temperature at which a steel structure cannot carry the service load for which it was designed because of softening of the steel that occurs when it is heated significantly. 2. Same as self-ignition temperature.

critical temperature

i. The temperature inside the cylinder of a reciprocating engine that will cause the fuel to explode rather than burn evenly when it is ignited.
ii. The temperature at which the internal structure of a metal takes on a crystalline form.

critical temperature

temperature

[tem´per-ah-chur] the degree of sensible heat or cold, expressed in terms of a specific scale. See Table of Temperature Equivalents in the Appendices. Body temperature is measured by a clinical thermometer and represents a balance between the heat produced by the body and the heat it loses. Though heat production and heat loss vary with circumstances, the body regulates them, keeping a remarkably constant temperature. An abnormal rise in body temperature is called fever.
Normal Body Temperature. Body temperature is usually measured by a thermometer placed in the mouth, the rectum, or the auditory canal (for tympanic membrane temperature). The normal oral temperature is 37° Celsius (98.6° Fahrenheit); rectally, it is 37.3° Celsius (99.2° Fahrenheit). The tympanic membrane temperature is a direct reflection of the body's core temperature. These values are based on a statistical average. Normal temperature varies somewhat from person to person and at different times in each person. It is usually slightly higher in the evening than in the morning and is also somewhat higher during and immediately after eating, exercise, or emotional excitement. Temperature in infants and young children tends to vary somewhat more than in adults.Temperature Regulation. To maintain a constant temperature, the body must be able to respond to changes in the temperature of its surroundings. When the outside temperature drops, nerve endings near the skin surface sense the change and communicate it to the hypothalamus. Certain cells of the hypothalamus then signal for an increase in the body's heat production. This heat is conducted to the blood and distributed throughout the body. At the same time, the body acts to conserve its heat. The arterioles constrict so that less blood will flow near the body's surface. The skin becomes pale and cold. Sometimes it takes on a bluish color, the result of a color change in the blood, which occurs when the blood, flowing slowly, gives off more of its oxygen than usual. Another signal from the brain stimulates muscular activity, which releases heat. Shivering is a form of this activity—a muscular reflex that produces heat.

When the outside temperature goes up, the body's cooling system is ordered into action. Sweat is released from sweat glands beneath the skin, and as it evaporates, the skin is cooled. Heat is also eliminated by the evaporation of moisture in the lungs. This process is accelerated by panting.
An important regulator of body heat is the peripheral capillary system. The vessels of this system form a network just under the skin. When these vessels dilate, they allow more warm blood from the interior of the body to flow through them, where it is cooled by the surrounding air.Abnormal Body Temperature. Abnormal temperatures occur when the body's temperature-regulating system is upset by disease or other physical disturbances. fever usually accompanies infection and other disease processes. In most cases when the oral temperature is 37.8°C (100°F) or over, fever is present. Temperatures of 40°C (104°F) or over are common in serious illnesses, although occasionally very high fever accompanies an illness that causes little concern. Temperatures as high as 41.7°C (107°F) or higher sometimes accompany diseases in critical stages. Subnormal temperatures, below 35.6°C (96°F) occur in cases of collapse; see also hypothermia" >symptomatic hypothermia.absolute temperature (T) that reckoned from absolute zero (−273.15°C), expressed on an scale" >absolute scale.basal body temperature (BBT) the temperature of the body under conditions of absolute rest; it has a slight sustained rise during the luteal phase of the cycle" >menstrual cycle and can be used as an indirect indicator of when ovulation has occurred.body temperature the temperature of the body of a human or animal; see temperature.core temperature the temperature of structures deep within the body, as opposed to peripheral temperature such as that of the skin.critical temperature that below which a gas may be converted to a liquid by increased pressure.normal temperature the body temperature usually registered by a healthy person, averaging 37°C (98.6°F).risk for imbalanced body temperature a nursing diagnosis accepted by the North American Nursing Diagnosis Association, defined as a state in which an individual is at risk of failure to maintain body temperature within the normal range.subnormal temperature temperature below the normal. See also hypothermia" >symptomatic hypothermia.

crit·i·cal tem·per·a·ture

the temperature of a gas above which it is no longer possible by use of any pressure, however great, to convert it into a liquid.

crit·i·cal tem·per·a·ture

(krit'i-kăl tem'pĕr-ă-chŭr) The temperature of a gas above which it is no longer possible by use of any pressure, however great, to convert it into a liquid.

单词	critical temperature
释义	critical temperature critical temperature n.1. The temperature above which a gas cannot be liquefied, regardless of the pressure applied.2. The temperature at which a material becomes a superconductor.3. The temperature at which a property of a material, such as its magnetism, changes. critical temperature n (General Physics) the temperature of a substance in its critical state. A gas can only be liquefied by pressure alone at temperatures below its critical temperature critical temperature critical temperature [′krid·ə·kəl ′tem·prə·chər] (agriculture) The temperature below which a plant cannot grow. (physical chemistry) The temperature of the liquid-vapor critical point, that is, the temperature above which the substance has no liquid-vapor transition. Symbolized T_c. Critical Temperature (1) The temperature of a substance in its critical state. For single substances the critical temperature is defined as the temperature at which the physical properties of the liquid and the vapor in equilibrium become identical. At the critical temperature the density of the saturated vapor and the liquid become identical, the interface between them disappears, and the heat of vaporization becomes zero. The critical temperature is one of the constants of a substance. (For the value of the critical temperature T_c for some substances, see.) In binary systems (for example, propane-isopentane) the fluid-vapor equilibrium has no single critical temperature but rather a spatial critical curve for which the terminal points are the critical temperatures of the pure components. (2) The temperature in fluid mixtures having components of limited solubility at which the mutual solubility becomes unlimited; it is called the critical solution temperature. (3) The transition temperature of a number of conductors into the superconducting state. It has been measured for a large number of metals, alloys, and chemical compounds. In pure metals the lowest critical temperature occurs in titanium (0.37°K) and the highest in technetium (11.2°K). A very high value has been found in the compound Nb₃Ge (T_c ≈ 23°K). critical temperature 1. The temperature at which a steel structure cannot carry the service load for which it was designed because of softening of the steel that occurs when it is heated significantly. 2. Same as self-ignition temperature. critical temperature i. The temperature inside the cylinder of a reciprocating engine that will cause the fuel to explode rather than burn evenly when it is ignited. ii. The temperature at which the internal structure of a metal takes on a crystalline form. critical temperature temperature [tem´per-ah-chur] the degree of sensible heat or cold, expressed in terms of a specific scale. See Table of Temperature Equivalents in the Appendices. Body temperature is measured by a clinical thermometer and represents a balance between the heat produced by the body and the heat it loses. Though heat production and heat loss vary with circumstances, the body regulates them, keeping a remarkably constant temperature. An abnormal rise in body temperature is called fever. Normal Body Temperature. Body temperature is usually measured by a thermometer placed in the mouth, the rectum, or the auditory canal (for tympanic membrane temperature). The normal oral temperature is 37° Celsius (98.6° Fahrenheit); rectally, it is 37.3° Celsius (99.2° Fahrenheit). The tympanic membrane temperature is a direct reflection of the body's core temperature. These values are based on a statistical average. Normal temperature varies somewhat from person to person and at different times in each person. It is usually slightly higher in the evening than in the morning and is also somewhat higher during and immediately after eating, exercise, or emotional excitement. Temperature in infants and young children tends to vary somewhat more than in adults.Temperature Regulation. To maintain a constant temperature, the body must be able to respond to changes in the temperature of its surroundings. When the outside temperature drops, nerve endings near the skin surface sense the change and communicate it to the hypothalamus. Certain cells of the hypothalamus then signal for an increase in the body's heat production. This heat is conducted to the blood and distributed throughout the body. At the same time, the body acts to conserve its heat. The arterioles constrict so that less blood will flow near the body's surface. The skin becomes pale and cold. Sometimes it takes on a bluish color, the result of a color change in the blood, which occurs when the blood, flowing slowly, gives off more of its oxygen than usual. Another signal from the brain stimulates muscular activity, which releases heat. Shivering is a form of this activity—a muscular reflex that produces heat. When the outside temperature goes up, the body's cooling system is ordered into action. Sweat is released from sweat glands beneath the skin, and as it evaporates, the skin is cooled. Heat is also eliminated by the evaporation of moisture in the lungs. This process is accelerated by panting. An important regulator of body heat is the peripheral capillary system. The vessels of this system form a network just under the skin. When these vessels dilate, they allow more warm blood from the interior of the body to flow through them, where it is cooled by the surrounding air.Abnormal Body Temperature. Abnormal temperatures occur when the body's temperature-regulating system is upset by disease or other physical disturbances. fever usually accompanies infection and other disease processes. In most cases when the oral temperature is 37.8°C (100°F) or over, fever is present. Temperatures of 40°C (104°F) or over are common in serious illnesses, although occasionally very high fever accompanies an illness that causes little concern. Temperatures as high as 41.7°C (107°F) or higher sometimes accompany diseases in critical stages. Subnormal temperatures, below 35.6°C (96°F) occur in cases of collapse; see also hypothermia" >symptomatic hypothermia.absolute temperature (T) that reckoned from absolute zero (−273.15°C), expressed on an scale" >absolute scale.basal body temperature (BBT) the temperature of the body under conditions of absolute rest; it has a slight sustained rise during the luteal phase of the cycle" >menstrual cycle and can be used as an indirect indicator of when ovulation has occurred.body temperature the temperature of the body of a human or animal; see temperature.core temperature the temperature of structures deep within the body, as opposed to peripheral temperature such as that of the skin.critical temperature that below which a gas may be converted to a liquid by increased pressure.normal temperature the body temperature usually registered by a healthy person, averaging 37°C (98.6°F).risk for imbalanced body temperature a nursing diagnosis accepted by the North American Nursing Diagnosis Association, defined as a state in which an individual is at risk of failure to maintain body temperature within the normal range.subnormal temperature temperature below the normal. See also hypothermia" >symptomatic hypothermia. crit·i·cal tem·per·a·ture the temperature of a gas above which it is no longer possible by use of any pressure, however great, to convert it into a liquid. crit·i·cal tem·per·a·ture (krit'i-kăl tem'pĕr-ă-chŭr) The temperature of a gas above which it is no longer possible by use of any pressure, however great, to convert it into a liquid. FinancialSeecriticalAcronymsSeetake careThesaurusSeetemperature
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