critical temperature


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Related to critical temperature: critical volume, triple point

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 symptomatic hypothermia.
absolute temperature (T) that reckoned from absolute zero (−273.15°C), expressed on an 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 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 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.
References in periodicals archive ?
At the critical temperature [T.sub.c] (~100 K), [X.sub.Cu], [X.sub.Au] are very near unit and we can take [X.sub.Cu] = [X.sub.Au] = 1.
Table 1: The surface tension [sigma] at 298.15 K and its temperature coefficient [([partial derivative][sigma]/[partial derivative]T).sub.p]; the molar masses M and the density coefficients of [rho] = a - b (t/[degrees]C) of deep eutectic solvents; and the derived critical temperatures: [T.sup.E.sub.c] according to (3), [T.sup.G.sub.c] according to (4), [T.sup.M.sub.c] from Mirza et al.
S4 critical temperature ([T.sub.c-S4]), residual stresses ([[sigma].sub.[theta]]), and adhesive fracture energy for 110/11 skinned PE100 pipes.
"Critical temperature and performance of refrigerants, application to chillers." Proceedings of 2015-International Congress on Refrigeration.
For the simply supported steel beam with different geometric parameters of cracks, the variations of the critical temperatures are shown in Figure 8.
Due to the fact, that the critical temperatures of the tested LPG fuels differ significantly, the rail pressure drop is expected to occur at different fuel temperatures during the investigated warm-up phases.
A new observation from this work shows that for a given size pipe, there appears to be a unique correlation between critical temperature and critical pressure, independent of resin type.
The critical temperature increases monotonically as the modulus ratio or/and layer number increase.
The data presented in 3.1, and in particular in Figure 5, clearly show the stepwise intensification of ultrafine particle emission at the critical temperature [T.sub.u].The existence of such critical temperatures for car brake materials was mentioned earlier.
However, heat transfer from the brakes combined with the high ambient temperature and the heat generated by the high-speed taxi events caused the tires to reach a critical temperature. Tire explosions fractured hydraulic lines and the ensuing fire caused extensive damage to the landing gear and wheelwell.
Polarized-light microscopy allows researchers to visualize critical temperature. It also allows them to determine if their sample is crystalline or partially crystalline based on the birefringence of anisotropic crystals within the frozen matrix.
-- For STI's cryocooler design, protecting STI's unique capabilities for efficiently and reliably cooling HTS circuits to the critical temperature (77 Kelvin) needed for the superconducting properties of the materials to be utilized from the U.S.

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