共查询到20条相似文献，搜索用时 46 毫秒
1.
Freeze avoidance in a mammal: body temperatures below 0 degree C in an Arctic hibernator 总被引：1，自引：0，他引：1
B M Barnes 《Science (New York, N.Y.)》1989,244(4912):1593-1595
Hibernating arctic ground squirrels, Spermophilus parryii, were able to adopt and spontaneously arouse from core body temperatures as low as -2.9 degrees C without freezing. Abdominal body temperatures of ground squirrels hibernating in outdoor burrows were recorded with temperature-sensitive radiotransmitter implants. Body temperatures and soil temperatures at hibernaculum depth reached average minima during February of -1.9 degrees and -6 degrees C, respectively. Laboratory-housed ground squirrels hibernating in ambient temperatures of -4.3 degrees C maintained above 0 degree C thoracic temperatures but decreased colonic temperatures to as low as -1.3 degrees C. Plasma sampled from animals with below 0 degree C body temperatures had normal solute concentrations and showed no evidence of containing antifreeze molecules. 相似文献
2.
Arctic sculpins of the genus Myoxocephalus adapted to water at 5 degrees C escaped from warm water at 20 degrees , 16 degrees , and 12 degrees C when their deep-body temperatures increased from an initial 5 degrees C to about 8 degrees C. Heating parts of the forebrain with water at 25 degrees C circulating through a pair of thermodes astraddle rostral parts of the forebrain shortened the time spent in the warm water and lessened the incease in deep-body temperature before exit from the warm water. Cooling the forebrain to about -1 degrees C caused a large increase in the body temperature and sometimes suppressed the escape from the warm water. 相似文献
3.
Limits of microbial existence: temperature and pH 总被引：10，自引：0，他引：10
A microscopic survey made to detect the presence of bacteria in hot springs of varying temperature and pH characteristics revealed that in neutral and alkaline hot springs bacteria are found at temperatures up to the boiling point of water (92 degrees to 100 degrees C, depending on the altitude). In hot springs of increasing acidity the upper temperature limit at which bacteria are found decreases; at pH 2 to 3 the upper temperature limit is 75 degrees to 80 degrees C. Bacteria have thus been able to evolve with the ability to grow at either high temperature or high acidity, but not at both high temperature and high acidity. These results suggest that there are physicochemical limitations of the environment beyond which life is impossible. 相似文献
4.
E C Crawford 《Science (New York, N.Y.)》1972,177(47):431-433
Panting in Sauromalus obesus is effective enough to keep deep body temperature (T(C)) and brain temperature (T(B)) below an ambient temperature of 45 degrees C for extended periods of time and has a greater cooling effect on the brain than on the remainder of the body. Six animals maintained T(C) and T(B) 0.9 degrees C (+/- 0.08 standard error) and 2.7 degrees C (+/- 0.2 standard error) respectively lower than the ambient temperature of 45 degrees C. It is possible that intracranial vascular shunts play a role in cranial cooling during panting. 相似文献
5.
A shear press has been used to determine the mechanical behavior of serpentinized dunite and forsterite at normal pressures to 50 kilobars, temperatures to 900 degrees C; and strain rates from 10(-1) to 10(-4) per second. The shear strength of dunite, containing less than 5 percent by volume of serpentine, is reduced by at least 30 percent as the temperature is raised from 300 degrees to 520 degrees C. Abundant kink bands develop at normal pressures above 35 kilobars at 27 degrees C and at lower pressures as the temperature is increased. 相似文献
6.
Thermoregulation in endothermic insects 总被引：2，自引：0，他引：2
B Heinrich 《Science (New York, N.Y.)》1974,185(153):747-756
On the basis of body weight, most flying insects have higher rates of metabolism, and hence heat production, than other animals. However, rapid rates of cooling because of small body size in most cases precludes appreciable endothermy. The body temperature of small flies in flight is probably close to ambient temperature, and that of flying butterflies and locusts is 5 degrees to 10 degrees C above ambient temperature. Many moths and bumblebees are insulated with scales and hair, and their metabolism during flight can cause the temperature of the flight muscles to increase 20 degrees to 30 degrees C above ambient temperature. Curiously, those insects which (because of size, insulation) retain the most heat in the thorax during flight, also require the highest muscle temperature in order to maintain sufficient power output to continue flight. The minimum muscle temperature for flight varies widely between different species, while the maximum temperature varies over the relatively narrow range of 40 degrees to 45 degrees C. As a consequence, those insects that necessarily generate high muscle temperatures during flight must maintain their thoracic temperature within a relatively narrow range during flight. Active heat loss from the thorax to the abdomen prevents overheating of the flight motor and allows some large moths to be active over a wide range of ambient temperatures. Bumblebees similarly transfer heat from the flight musculature into the abdomen while incubating their brood by abdominal contact. Many of the larger insects would remain grounded if they did not actively increase the temperature of their flight muscles prior to flight. Male tettigoniid grasshoppers elevate their thoracic temperature prior to singing. In addition, some of the social Hymenoptera activate the "flight" muscles specifically to produce heat not only prior to flight but also during nest temperature regulation. During this "shivering" the "flight" muscles are often activated in patterns different from those during flight. The muscles contract primarily against each other rather than on the wings. However, the rate of heat production during shivering and flight is primarily a function of the action potential frequency rather than of the patterns of activation. Thermoregulation is a key factor in the energetics of foraging of some of the flower-visiting insects. The higher their muscle temperature the more flowers they can visit per unit time. When food supplies are ample, bees may invest relatively large amounts of energy for thermoregulation. While shivering to maintain high body temperatures during the short intervals they are perched on flowers (as well as while in the nest), bumblebees often expend energy at rates similar to the rates of energy expenditure in flight. Unlike vertebrates, which usually regulate their body temperature at specific set points, the body temperature of insects is labile. It often appears to be maintained near the lower temperature at which the muscles are able to perform the function at hand. The insects' thermal adaptations may not differ as much from those of vertebrates as previously supposed when size, anatomy, and energy requirements are taken into account. 相似文献
7.
Electrical heat sources implanted in the abdominal cavities of sheep were heated to give initial temperatures of 42 degrees and 45 degrees C at the surfaces of the heaters. During 18 days of constant heating, a vascularized connective-tissue envelope encapsulated the heat sources, and the temperatures at the surfaces of the heaters declined 0.8 degrees and 1.8 degrees C, respectively. The degree of vascularization and the magnitude of the decrease in the surface temperature appeared to be related to the proximity of the tissue's initial temperature to 45 degrees C, a temperature ordinarily considered detrimental to cell structure. The vascularization thus appears to be adaptive. 相似文献
8.
The preferred body temperature was determined for several groups of Sceloporus occidentalis previously acclimated to several constant temperature levels. Acclimation to a high temperature (35 degrees C) resulted in the selection of a lowered mean preferred body temperature, whereas acclimation to lower temperatures (12 degrees C and 25 degrees C) produced no change in the preferred body temperature. 相似文献
9.
汪开英 《浙江大学学报(农业与生命科学版)》2003,29(6):675-678
采用先进的DSI动物生理无线遥测系统和动物环境自动检测系统研究了华东地区夏季高温高湿条件与育成猪体温调节的相关性,结果表明,猪舍环境温湿度指标THI对猪的体温变化影响极显著(P=0.0001),猪舍环境温湿度指标THI能充分反映猪舍环境的优劣及对猪热调节的影响,发现当温湿度指标THI高于28时育成猪将出现体温升高等明显的热应激反应. 相似文献
10.
Elevation in brain temperature during paradoxical sleep 总被引：4，自引：0，他引：4
During ordinary sleep, the temperature of the rabbit brain tended to drop, but during paradoxical sleep it rose sharply 0.1 degrees to 0.4 degrees C, a greater elevation than was observed during arousal. Changes in body temperature generally did not parallel the alterations in brain temperature. Shifts of direct-current potential in the brain are basically independent of the changes in brain temperature. 相似文献
11.
The West Indian hummingbird, Eulampis jugularis, maintained its body temperature in torpor at 18 degrees to 20 degrees C over an ambient temperature range of 2.5 degrees to 18 degrees C. At ambient below 18 degrees C oxygen consumption during torpor increased linearly with decreasing temperature. Thermal conductances were the same for resting and torpid Eulampis regulating their body temperatures at 40 degrees and 18 degrees C, respectively. 相似文献
12.
The currently known upper temperature limit for growth of organisms, shared by a number of archaebacteria, is 110 degrees C. However, among the sulfate-reducing bacteria, growth temperatures of greater than 100 degrees C have not been found. A search for high-temperature activity of sulfate-reducing bacteria was done in hot deep-sea sediments at the hydrothermal vents of the Guaymas Basin tectonic spreading center in the Gulf of California. Radiotracer studies revealed that sulfate reduction can occur at temperatures up to 110 degrees C, with an optimum rate at 103 degrees to 106 degrees C. This observation expands the upper temperature limit of this process in deep-ocean sediments by 20 degrees C and indicates the existence of an unknown group of hyperthermophilic bacteria with a potential importance for the biogeochemistry of sulfur above 100 degrees C. 相似文献
13.
温度和叶表化学物质对松杨栅锈菌夏孢子萌发的影响 总被引：1，自引：0，他引：1
松杨栅锈菌夏孢子萌发适宜温度范围为10～24℃,最适温度20℃左右。供试的2菌株对温度有不同的依赖性。TH菌株温度适应性范围较宽,GL菌株较窄。在最适温度范围内,供试的2个菌株呈现相同的萌发动力学模式,萌发最大速率出现在4～12h,温度越高,最大萌发速率出现时间越晚,并随时间的延长,萌发速率逐渐减小。在5、30℃,萌发速率有2～3个峰值,第1峰值最大,第2、第3峰值逐渐减小或消失。26℃下峰值呈现过渡型状态,有1个较小的次高峰。供试的2菌株,TH的萌发速率较GL稍高并在出现时间上略前。最适萌发条件下,石油醚、乙醚、乙酸乙酯、正丁醇、水的卜氏杨和毛白杨提取物对松杨栅锈菌夏孢子萌发有不同的影响。毛白杨所有提取物在接种12h内,均抑制夏孢子的萌发,而卜氏杨乙醚提取物则促进夏孢子萌发,其余则抑制夏孢子萌发。所有水提取物在接种12h均表现为抑制作用。接种12～24h,2种杨树叶片正丁醇萃取物对夏孢子萌发速率均有一定程度的促进作用。 相似文献
14.
测定了5种温度(14 、17、 20、 24和29℃)下,白条锦蛇的耗氧量及耗氧率.结果表明:在这5种温度条件下,白条锦蛇的耗氧量均随体质量的增加而明显增大,而白条锦蛇的耗氧率则刚好相反,随体质量的增加耗氧率反而减小; 另外,白条锦蛇的耗氧量、耗氧率与温度均呈显著的线性回归关系.在14～29℃白条锦蛇的耗氧量、耗氧率均随温度升高而增加,并得出耗氧量x0与温度t的一元线性回归方程:x0=-25.25+3.51t,耗氧率Q0与温度t的一元线性回归方程Q0=-230.25+27.14t.白条锦蛇的耗氧率与温度的变化关系,说明白条锦蛇的新陈代谢率随环境温度改变而改变,在14～29℃白条锦蛇的新陈代谢随环境温度升高而加快. 相似文献
15.
Poudel B Hao Q Ma Y Lan Y Minnich A Yu B Yan X Wang D Muto A Vashaee D Chen X Liu J Dresselhaus MS Chen G Ren Z 《Science (New York, N.Y.)》2008,320(5876):634-638
The dimensionless thermoelectric figure of merit (ZT) in bismuth antimony telluride (BiSbTe) bulk alloys has remained around 1 for more than 50 years. We show that a peak ZT of 1.4 at 100 degrees C can be achieved in a p-type nanocrystalline BiSbTe bulk alloy. These nanocrystalline bulk materials were made by hot pressing nanopowders that were ball-milled from crystalline ingots under inert conditions. Electrical transport measurements, coupled with microstructure studies and modeling, show that the ZT improvement is the result of low thermal conductivity caused by the increased phonon scattering by grain boundaries and defects. More importantly, ZT is about 1.2 at room temperature and 0.8 at 250 degrees C, which makes these materials useful for cooling and power generation. Cooling devices that use these materials have produced high-temperature differences of 86 degrees , 106 degrees , and 119 degrees C with hot-side temperatures set at 50 degrees, 100 degrees, and 150 degrees C, respectively. This discovery sets the stage for use of a new nanocomposite approach in developing high-performance low-cost bulk thermoelectric materials. 相似文献
16.
California scorpionfish, Scorpaena guttata, were implanted with a pair of thermodes which straddled the anterior brainstem. When the fish were in water of about 20 degrees C, warming the thermodes to temperatures above 20 degrees C caused a proportional increase in the ventilatory minute volume. Cooling the thermodes below 20 degrees C caused a proportional decrease in the ventilatory minute volume. It is concluded that the anterior brainstem temperature provides an important input to the respiratory control center in teleost fish. 相似文献
17.
Smith WK 《Science (New York, N.Y.)》1978,201(4356):614-616
Surface temperatures of perennial plants in the Sonoran Desert of California ranged from 20 degrees C above air temperature to over 18 degrees C below air temperature during rapid growth periods following rain. Desert cactus with large photosynthetic stem surfaces had the highest temperatures and lowest transpiration rates. Perennial plants with relatively small leaves had moderate transpiration rates and leaf temperatures close to air temperature. Desert perennials with relatively large leaves had leaf temperatures well below air temperature along with the greatest accompanying transpiration rates of over 20 micrograms per square centimeter per second, but also had correspondingly low temperatures for maximum photosynthesis. The low leaf temperatures measured for these large-leafed species are an exception to the more common pattern for desert plants whereby a smaller leaf size prevents overheating and leads to reductions in transpiration and increased water-use efficiency. The contribution of a larger leaf size to a lower leaf temperature, and thus higher rate of photosynthesis for these large-leafed species, may represent an adaptive pattern previously unrecognized for desert plants. 相似文献
18.
At varying environmental temperatures, measurements of body temperatures and gas exchange of a female Indian python (Python molurus bivittatus) show that during the brooding period this animal can regulate its body temperature by physiological means analogous to those in endotherms. Ambient temperatures below 33 degrees C result in spasmodic contractions of the body musculature with a consequent increase in metabolism and body temperature. 相似文献
19.
The kinetics of the Fe(2+)-Mg, order-disorder phenomenon in a highly ordered natural anthophyllite have been determined over the temperature range from 400 degrees to 720 degrees C at a pressure of 2 kilobars. At temperatures of 600 degrees C and above, equilibrium is attained by disordering as well as ordering reactions. The intracrystalline exchange is defined by a standard Gibbs free energy of 4247 +/- 54 calories per formula unit. Rate studies at 550 degrees and 500 degrees C show that equilibrium is attained by ordering but not by disordering within the same time scale and that the exchange reaction is characterized by an activation energy of approximately 55 kilocalories per formula unit. An equilibration temperature for the natural anthophyllite of 270 degrees C is determined from the termination of the ordering process owing to excessively slow reaction kinetics after approximately 10(7) years. From the rate constants of the exchange process, for different crystallization temperatures, the apparent equilibration temperature of 270 degrees C defines a maximum linear cooling rate for the rock of 1 x 10(4) degrees C per year. 相似文献
20.
J L Griffin 《Science (New York, N.Y.)》1972,178(63):869-870
Within tested strains of the genera Naegleria and Acanthamoeba the ability to grow at high temperatures seems directly related to virulence, with nonvirulent strains unable to grow at normal or elevated body temperatures. Outside these genera, nonvirulent Hartmannella and Tetramitus do grow at elevated temperatures, which suggests a barrier to pathogenicity other than temperature sensitivity. The high optimal temperature of pathogenic Naegleria apparently explains previous difficulty in obtaining isolates from the aquatic environment. 相似文献