Freeze avoidance in a mammal: body temperatures below 0 degree C in an Arctic hibernator

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.     

Freezing resistance in polar fishes

Arctic and antarctic fishes, living in contact with sea ice at -1.9 degrees C, have plasma equilibrium freezing points near -1.2 degrees C which are dependent on salt concentrations. These supercooled fishes have plasma protein concentrations much higher than other polar animals have, and the proteins impede ice propagation at temperatures down to -2 degrees C. Plasma protein concentration increases as environmental water temperature decreases.     

Metastable Superheated Ice in Liquid-Water Inclusions under High Negative Pressure

In some microscopic inclusions (consisting of aqueous liquid and vapor) in minerals, freezing eliminates the vapor phase because of greater volume occupied by the resulting ice. When vapor fails to nucleate again on partial melting, the resulting negative pressure (hydrostatic tension) inside the inclusions permits the existence of ice I crystals under reversible, metastable equilibrium, at temperatures as high as +6.5 degrees C and negative pressures possibly exceeding 1000 bars.     

Atmosphere of Mars: Mariner IV Models Compared

Three classes of models for the atmosphere of Mars differ in identifying the main ionospheric layer measured by Mariner IV as being analogous to a terrestrial F(2), F(1), or E layer. At an altitude of several hundred kilometers, the relative atmospheric mass densities for these models (in the order named) are approximately 1, 10(2), and 10(4), and the temperatures are roughly 100 degrees , 200 degrees , and 400 degrees K. Theory and observation are in best agreement for an F, s model, for which photodissociation of CO(2), and diffusive separation result in an atomic-oxygen upper atmosphere, with O(+) being the principal ion in the isothermal topside of the ionosphere. The mesopause temperature minimum would be at or below the freezing point of CO(2), and dry ice particles would be expected to form. However, an F(1) model, with molecular ions in a mixed and warmer upper atmosphere, might result if photodissociation and diffusive separation are markedly less than would be expected from analogy with Earth's upper atmosphere. The E model proposed by Chamberlain and McElroy appears very unlikely; it is not compatible with the measured ionization profile unless rather unlikely assumptions are made about the values, and changes with height, of the effective recombination coefficient and the average ion mass. Moreover our theoretical heat-budget computations for the atmospheric region probed by Mariner IV indicate markedly lower temperatures and temperature gradients than were obtained for the E model.     

Evidence that nitric acid increases relative humidity in low-temperature cirrus clouds

In situ measurements of the relative humidity with respect to ice (RHi) and of nitric acid (HNO3) were made in both natural and contrail cirrus clouds in the upper troposphere. At temperatures lower than 202 kelvin, RHi values show a sharp increase to average values of over 130% in both cloud types. These enhanced RHi values are attributed to the presence of a new class of HNO3-containing ice particles (Delta-ice). We propose that surface HNO3 molecules prevent the ice/vapor system from reaching equilibrium by a mechanism similar to that of freezing point depression by antifreeze proteins. Delta-ice represents a new link between global climate and natural and anthropogenic nitrogen oxide emissions. Including Delta-ice in climate models will alter simulated cirrus properties and the distribution of upper tropospheric water vapor.     

How Does a Raindrop Grow?: Precipitation in natural clouds may develop from ice crystals or from large hygroscopic aerosols

On the basis of presently available data, combined with present-day knowledge of the physics and chemistry of cloud particle development, it is possible to make the following generalizations about the mode of precipitation in natural clouds. 1) The all-water mechanism begins to operate as soon as a parcel of cloud air is formed and continues to operate throughout the life of the cloud. The ice-crystal mechanism, on the other hand, can begin to operate only after the top of the cloud has reached levels where ice nuclei can be effective (about -15 degrees C). Some clouds never reach this height; any precipitation from them must be through the all-water mechanism. In cold climates and at high levels in the atmosphere, the cloud bases may be very close to this critical temperature. In the tropics, approximately 25,000 feet separate the bases of low clouds from the natural ice level. 2) The number of large hygroscopic nuclei in maritime air over tropical oceans is entirely adequate to rain-out any cloud with a base below about 10,000 feet, provided the cloud duration and cloud depth is sufficient for the precipitation process to operate. Extensive trajectories over land will decrease the number of sea-salt particles, both because of sedimentation and removal in rain. Measurements show an order-of-magnitude decrease in the number of large particles as maritime air moves from the Gulf of Mexico to the vicinity of St. Louis, during the summer months. Measurements in Arizona and New Mexico show even smaller chloride concentrations, presumably because of the long overland trajectories required in reaching these areas. The maritime particles lost in overland trajectories apparently are more than replaced by particles of land origin. The latter are usually of mixed composition and are less favorable for the formation of outsized solution droplets. 3) Ice nuclei, required for the formation of ice crystals and for droplet freezing, are rather rare at temperatures higher than about -10 degrees C. This, of course, accounts for the fact that natural clouds undergo extensive undercooling. Because of the scarcity of suitable nuclei, precipitation through the ice phase usually is not found in clouds warmer than about -15 degrees to -20 degrees C. Natural cirrus clouds might provide ice nuclei for precipitation at somewhat higher temperatures, but this possibility has not been extensively studied. 4) Precipitation in tropical clouds invariably first develops through the all-water mechanism; points discussed in paragraphs 1, 2, and 3 above all work toward this end. Tropical clouds which reach to heights above about 25,000 feet also develop precipitation through snow pellets. The data for mid-latitude clouds are conflicting. Some measurements suggest that summer clouds in the central United States and in the semiarid Southwest develop rain largely through the all-water process; existing theories support such a suggestion. However, flight measurements indicate that there is considerably more ice and snow in the clouds than can be accounted for by present theory; as a consequence, one must be careful in ruling out the ice mechanism in these areas. It appears to me, however, that the ice particles in these clouds are best accounted for through the hypothesis of freezing of drops which have grown to fairly large size through diffusion of vapor. Thus, the ice would be only incidental to the precipitation development. Winter clouds in the central United States and almost all of the clouds of northern United States and Canada appear to precipitate largely through the ice-crystal mechanism. The relatively cold cloud bases and the continental sources of air masses in these regions appear to retard the warm-rain mechanism to the point where the ice mechanism dominates. But here again, a great deal of research must be completed before a firm conclusion can be drawn (18).     

Glycoproteins as biological antifreeze agents in antarctic fishes

The blood serums of Antarctic fishes freeze at -2 degrees C, which is approximately 1 degrees C below the melting points of their serums. This thermal hysteresis is due to the influence of serum glycoproteins. The temperatures of freezing and melting of aqueous solutions of the purified glycoproteins suggest that this thermal hysteresis results from the adsorption of the glycoprotein molecule onto the surface of ice crystals.     

不同冻结温度对山药片营养品质的影响

[目的]研究不同冻结温度对山药片营养品质变化的影响,为速冻山药产品的加工提供理论指导。[方法]将山药片分别在不同速冻温度(-20、-25、-30、-35℃)下进行速冻,研究速冻前后山药细胞结构、质构、维生素C含量和失水率的变化。[结果]不同冻结温度对山药片细胞破坏程度不同。-20和-25℃冻结的山药片,其细胞内形成的冰晶较大,破坏了细胞的结构,解冻后细胞形态受破坏;-35℃冻结的山药,冻结速度较快,形成的冰晶小,对细胞结构的破坏较小。解冻后产品不仅硬度损失少,而且维生素C的损失以及失水率都最小,营养品质变化也最少。[结论]-30℃速冻是冻结山药片较适宜的温度。     

Historical trends in lake and river ice cover in the northern hemisphere

Freeze and breakup dates of ice on lakes and rivers provide consistent evidence of later freezing and earlier breakup around the Northern Hemisphere from 1846 to 1995. Over these 150 years, changes in freeze dates averaged 5.8 days per 100 years later, and changes in breakup dates averaged 6.5 days per 100 years earlier; these translate to increasing air temperatures of about 1.2 degrees C per 100 years. Interannual variability in both freeze and breakup dates has increased since 1950. A few longer time series reveal reduced ice cover (a warming trend) beginning as early as the 16th century, with increasing rates of change after about 1850.     

紫彩血蛤低温保活技术研究

[目的]研究紫彩血蛤在低温条件下的保活效果。[方法]以紫彩血蛤为原料,测定了它的冻结曲线并对其在生态冰温区域内和冰块堆积条件下以及不同冷藏温度和湿度下的保活效果进行了比较。[结果]紫彩血蛤的生态冰温区大致在0~-2℃。随着温度的升高,紫彩血蛤的存活率逐渐降低,存活率最高的组为冰温保藏组(-1.5~-0.5℃),在保活10 d后其存活率依然达99%。淡水冰堆积组和4~6℃组保活效果较好,在保活7 d后,两者的存活率均达99%,而且总体表现接近。湿度对紫彩血蛤保活效果有一定的影响,呈正相关性,相对湿度越高越有利于蛤体的存活。[结论]该研究为紫彩血蛤的实际生产应用提供了理论依据。     

THE TRIPLE POINT OF WATER

(1) A common error in text-books on physical chemistry is pointed out. It is hoped that the correct value for the triple point temperature, +.0098 degrees C, will be given in new books and in succeeding editions of the books surveyed above. (2) Inconsistencies in the vapor pressure values for ice and for liquid water near 0 degrees C are pointed out. (3) The equilibrium vapor pressures for ice and liquid water under two different sets of equilibrium conditions are compared with the triple point pressure.     

Surface tension measurements of surface freezing in liquid normal alkanes

Surface tension measurements reveal surface freezing in liquid n-alkanes. A solid monolayer of molecules is found to exist up to 30 degrees C above the bulk freezing point. This surface phase exists only for carbon numbers 14 n 相似文献   

Freezing tolerance in an adult insect

The adult carabid beetle Pterostichus brevicornis tolerates freezing under natural conditions. Laboratory tests confirm that winter beetles tolerate temperatures below -35 degrees C, whereas summer beetles die if frozen at -6.6 degrees C. Winter beetles can be cooled to about -10 degrees C before freezing, and they thaw near -3.5 degrees C. Summer beetles thaw at -0.7 degrees C. To avoid freezing damage even in winter beetles, cooling rates must be near 20 degrees C per hour or less.     

Liquids at large negative pressures: water at the homogeneous nucleation limit

An isochoric cooling method for obtaining unprecedented tensions on liquids was used to determine the homogeneous nucleation limit for stretching of water at a variety of water densities. At densities in the range 0.55 to 0.68 gram per milliliter (g/ml), the data agree with the homogeneous nucleation temperatures measured by Skripov for superheated water at positive pressures. At densities between 0.68 and 0.93 g/ml, cavitation occurred only at negative pressures (that is, under tension). The cavitation tensions measured were in excellent agreement with those predicted by Fisher's 1948 vapor nucleation theory. A maximum tension of 140 megapascals (=1400 bars) was reached at 42 degrees C, which lies on an extrapolation of the line of isobaric density maxima. At higher densities, cavitation of droplets that survived heterogeneous nucleation failed to occur at all unless provoked, at much lower temperatures, by freezing. This observation confirms the existence of a density maximum at 42 degrees C and -140 megapascals and hence greatly strengthens the basis for Speedy's conjecture of a reentrant spinodal for water.     

Ross ice shelf sea temperatures

Two temperature profiles recorded by a sensitive bathythermograph at the Ross Ice Shelf Project site (82 degrees 22.5'S, 168 degrees 37.5'W) are presented. From the shape of the profiles it is concluded that an inflow of water at intermediate depths provides a source of heat to drive a regime in which ice is melted from the interface at a depth of 360 meters. Melting maintains the temperature of a thick layer under the ice at about -2.14 degrees C, close to the ambient freezing temperature. A very well mixed layer about 35 meters thick was found at the seabed.     

Artificial cloud formation in the atmosphere

An artificial cloud in the cloudless atmosphere at a temperature below 0 degrees C was formed by introducing pellets of Dry Ice into air containing more water vapor than would be present at the saturation point with respect to ice. Such clouds could be utilized to establish radiative equilibrium between ground and air so as to inhibit the cooling of selective arctic surface regions under clear skies.     

Interparticle collisions driven by ultrasound

Ultrasound has become an important synthetic tool in liquid-solid chemical reactions, but the origins of the observed enhancements remained unknown. The effects of high-intensity ultrasound on solid-liquid slurries were examined. Turbulent flow and shock waves produced by acoustic cavitation were found to drive metal particles together at sufficiently high velocities to induce melting upon collision. A series of transition-metal powders were used to probe the maximum temperatures and speeds reached during such interparticle collisions. Metal particles that were irradiated in hydrocarbon liquids with ultrasound underwent collisions at roughly half the speed of sound and generated localized effective temperatures between 2600 degrees C and 3400 degrees C at the point of impact for particles with an average diameter of approximately 10 microns.     

Limits of microbial existence: temperature and pH

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.     

Carbon dioxide hydrate and floods on Mars

Ground ice on Mars probably consists largely of carbon dioxide hydrate, CO(2) . 6H(2)O. This hydrate dissociates upon release of pressure at temperatures between 0 degrees and 10 degrees C. The heat capacity of the ground would be sufficient to produce up to 4 percent (by volume) of water at a rate equal to that at which it can be drained away. Catastrophic dissociation of carbon dioxide hydrate during some past epoch when the near surface temperature was in this range would have produced chaotic terrain and flood channels.     

鞍山市一次冻雨天气过程分析

利用MICAPS和鞍山站实况资料,对2010年2月24日鞍山出现的罕见冻雨天气进行分析。结果表明,当地面气温在0℃以下,地面到850 hPa甚至到700 hPa有逆温层,从高空到地面为冷-暖-冷的温度层结结构,且存在一定厚度的冰晶融化层时,鞍山市出现冻雨天气。