共查询到20条相似文献，搜索用时 46 毫秒
1.
Graham JB 《Science (New York, N.Y.)》1971,172(3985):861-863
Species of Pacific shallow-water fish are more tolerant of low temperatures than Atlantic species are. At high temperatures Atlantic species are more tolerant than Pacific species. For species pairs of Bathygobius differences in the tolerance of low temperatures are small and can be removed by acclimation to 23 degrees C. Differences in the tolerance to low temperature in transisthmian species of Apogon, however, are large and persist after acclimation to 23 degrees C. Some Pacific species adapt to the cooler temperatures of their habitat through increasing their rates of oxygen consumption at ambient temperatures or decreasing the dependence of oxygen uptake rate on temperature, or both. 相似文献
2.
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
3.
Heinrich B 《Science (New York, N.Y.)》1979,205(4412):1269-1271
At high ambient temperatures, honeybees regulate head teriperature by evaporative cooling of regurgitated honeycrop contents. Thoracic temperature is secondarily stabilized as heat flows from thorax to head by means of passive conduction and physiological facilitation resulting from accelerated blood flow. The mechanism permits flight at the extraordinarily high ambient temperature of 46 degrees C without overheating the head and thorax despite prodigious amounts of heat produced as a by-product of flight metabolism. In contrast, at low ambient temperatures, thoracic rather than head temperature is regulated; no liquid is regurgitated, and the head is heated passively by conduction both in flight and while stationary. 相似文献
4.
5.
DC and RF Superconducting QUantum Interference Devices (SQUIDs) fabricated from low transition temperature (T(c)) superconductors and operated at liquid (4)He temperatures are routinely used as ultrasensitive detectors in many applications, for example, as magnetometers, magnetic gradiometers, voltmeters, and motion detectors. SQUIDs fabricated from high T(c) superconductors such as YBa(2)Cu(3)O(7) and operated in liquid nitrogen at 77 K offer a greater convenience in operation at the expense of a poorer noise performance, particularly at low frequencies. The resolution of SQUID-based magnetometers is compared with that of other types of magnetometers operatng at ambient temperatures. 相似文献
6.
Oyster herpes-type virus 总被引：10，自引：0，他引：10
A herpes-type virus infection, the first to be found in an invertebrate animal, is reported in the oyster Crassostrea virginica. Intranuclear herpes-type viral inclusions were more prevalent in the oyster at elevated water temperatures of 28 degrees to 30 degrees C than at normal ambient temperatures of 18 degrees to 20 degrees C. The inclusions were associated with a lethal disease at the elevated temperatures. 相似文献
7.
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
8.
Assessing the energy costs of development in extreme environments is important for understanding how organisms can exist at the margins of the biosphere. Macromolecular turnover rates of RNA and protein were measured at -1.5 degrees C during early development of an Antarctic sea urchin. Contrary to expectations of low synthesis with low metabolism at low temperatures, protein and RNA synthesis rates exhibited temperature compensation and were equivalent to rates in temperate sea urchin embryos. High protein metabolism with a low metabolic rate is energetically possible in this Antarctic sea urchin because the energy cost of protein turnover, 0.45 joules per milligram of protein, is 1/25th the values reported for other animals. 相似文献
9.
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
10.
Precision isothermal solution calorimetry was used to determine the standard-state enthalpy of formation of a number of phases in the Y-Ba-Cu-O system. An analysis of the data indicates that YBa(2)Cu(4)O(8) is thermodynamically metastable under ambient conditions. Taken together with the results from previous investigations, these data show that all of the superconducting compounds in the Y-Ba-Cu-O system are thermodynamically metastable at low temperatures. 相似文献
11.
Heinrich B 《Science (New York, N.Y.)》1972,175(4018):185-187
Bombus vagans forages for nectar at 5 degrees C in shade and at 31 degrees C in sunshine. The production of heat while the bumblebee is on flowers, at ambient temperatures below 24 degrees C, helps to maintain a thoracic temperature that is near the minimum for flight between flowers. However, at ambient temperatures above 24 degrees C the thoracic temperature is no longer regulated at 32 degrees to 33 degrees C and rises. 相似文献
12.
贮藏温度对柑橘果肉中柠檬苦素和柚皮苷含量变化的影响 总被引：1，自引：1，他引：0
将国庆1号和国庆3号温州蜜柑的成熟果实分别贮藏在4℃和常温下,利用高效液相色谱法检测贮藏过程中果肉主要苦味物质的含量变化。结果表明:2个品种的成熟果肉中检测不到诺米林,采后0d柚皮苷含量为柠檬苦素的10倍以上;在4℃和常温贮藏时,柠檬苦素和柚皮苷含量总体上均呈增加的趋势,有一定波动,但冷库贮藏时变化较剧烈;国庆1号受低温影响较大,使其在几个时期的2种苦味物质含量发生了显著变化;4℃低温贮藏利于苦味物质的增加,柠檬苦素尤甚,而贮后0～20d是其敏感时期。 相似文献
13.
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
14.
家蚕体温与环境温度差异动态变化 总被引：1，自引：0，他引：1
在不同的环境温度下测定五龄幼虫体温与环境温度之差,发现环境温度小于30℃时,蚕体温高于环境温度。环境温度越低,差数越大;但环境温度低于20℃时,差数反而缩小。当环境大于30℃时,蚕体温低于环境温度,温度越高,差效越大。各环境温度下幼虫体温与其之差的绝对值随五龄天数的增加而减少。因此认为家蚕具有一定的体温主动调节能力和一生理适温点(供试品种在30℃左右)。这种调节能力龄初和龄中较强,龄末最弱,测定家蚕品种的生理适温点,可作为确定其饲育适温的重要参考指标。 相似文献
15.
Selected captive lobsters have been successfully mated at the Massachusetts Lobster Hatchery. Progeny raised in warm seawater grew at least four times as fast as lobsters grown at ambient ocean temperatures. These studies demonstrate that lobsters will reach sexual maturity (a weight of about 454 grams) in less than 2 years, compared to 8 years at ambient temperatures in Canadian waters. A further reduction in this time has been achieved by phenotypic selection for fast-growing lobsters. Our initial success in accelerating growth and in mating selected parents suggests that lobster farming may be possible. 相似文献
16.
The radiation dose detected by microthermoluminescent dosimeters attached to pocket mice,Perognathus formosus, indicated the amount of time these animals were active on the surface of the ground. Radiation was from anelevated, partially shielded source in the center of the 8-hectareenclosure. The rodents are almost entirely inactive in midwinter but spend 30 to 40 percent of their time above ground in the summer months. Periods of activity increase gradually through the spring. These results support laboratory findings that members of this genus undergo periods of torpor in response to low ambient temperatures or food shortage. That this adaptation may enhance survival is indicated by the longevity of marked individuals of a related species. 相似文献
17.
Milliman JD 《Science (New York, N.Y.)》1966,153(3739):994-997
Recrystallized planktonic limestones from two guyots in the North Atlantic are in oxygen-isotopic equilibrium with their present ambient waters, suggesting submarine lithifica tion and recrystallization. The early stages of submarine lithification of carbonates may involve precipitation of, and replacement by, magnesium-rich calcite; with time this may invert to magnesium-poor calcite. This type of lithification probably requires very low rates of sediment accumulation. 相似文献
18.
【目的】通过测定环境低温诱发AS发生发展过程中缺氧诱导因子-1α表达的动态变化,初步探讨HIF-1α与AS发生发展之间的关系。【方法】100只商品代肉公雏,15d时随机分为常温对照组(22~24℃)和低温组(9~11℃)。各组在22、29、36和43d随机选取6只鸡,测定mPAP、AHI和心、肺组织中HIF-1αmRNA的表达量,试验结束后统计腹水发生率。【结果】低温组AS发生率(22%)显著高于对照组(4%)(P0.05);低温组肉鸡mPAP和AHI显著或极显著高于对照组(P0.05,P0.01);低温组肉鸡心脏HIF-1αmRNA表达量显著或极显著(P0.05,P0.01)增加;肺脏HIF-1αmRNA表达量类似于同时间点的心脏。【结论】低温诱发AS发生过程中,肉鸡心脏和肺脏HIF-1α表达量明显增加,可能参与肉鸡AS的发生发展。 相似文献
19.
选取设计6个处理组,每组6个水平,每个水平6只蛋鸭。分别添加VC 0、200、800 mg.kg-1,温度(2±1)℃或(18±1)℃,试验期为6、12周龄金定蛋鸭216只,设两个温度水平,研究了环境温度和VC(维生素C)对后备蛋鸭免疫器官发育及抗氧化的影响。结果表明,低温对胸腺指数影响显著(P0.05),VC对脾脏指数和法氏囊指数影响不显著(P0.05),但随着VC添加量的提高,脾脏指数和法氏囊指数有上升趋势。低温和维生素C的交互作用对胸腺指数影响显著(P0.05)。低温和维生素C对血清一氧化氮(NO)、维生素C影响显著(P0.05),对GSH-PX的影响不显著(P0.05)。由此可知,寒冷应激影响后备蛋鸭体内VC的合成,但日粮中添加VC 200 mg.kg-1时,可提高血液VC的水平,对低温应激组胸腺、脾脏和法氏囊的萎缩有缓解的趋势。 相似文献
20.
Recent studies have implied that (Mg, Fe)SiO(3)-perovskite, a likely dominant mineral phase in the lower mantle, may have a high melting temperature. The implications of these findings for the dynamics of the lower mantle were investigated with the use of numerical convection models. The results showed that low homologous temperatures (0.3 to 0.5) would prevail in the modeled lower mantle, regardless of the effective Rayleigh number and internal heating rates. High-temperature ductile creep is possible under relatively cold conditions. In models with low rates of internal heating, local maxima of viscosity developed in the mid-lower mantle that were similar to those obtained from inversion of geoid, topography, and plate velocities. 相似文献