Cyclic Temperature Changes Research Articles

加熱・冷却にともなう大島花こう岩のＡＥと熱膨張

AE and thermal expansion of both stressed and unstressed Oshima granite were investigated. The samples were subjected to slow cyclic temperature change (0.5K/min) between 290K and 370K or between 210K and 290K. A large number of AE events occurred only during the first cycle both heating and cooling. Under unstressed conditions, the thermal expansion coefficient became highly temperature dependent when the occurrence of AE events was observed. When the rock was subjected to thermal cycling under uniaxial stress conditions, the thermal expansion coefficient in the axial (loading) direction became temperature independent, while that in the circumferential direction was unchanged. The reactivation of the AE events was observed during the first heating after the removal of stress. These observations suggest that microcracks are produced by the mismatch of thermal expansion of individual mineral grains and cause the temperature dependency of the thermal expansion coefficient of Oshima granite. The anisotropy of thermal expansion observed when the samples were uniaxially compressed, is explained by the closure of microcracks perpen-dicular to the axial direction.

Thermosynthesis by biomembranes: Energy gain from cyclic temperature changes

A theoretical mechanism is described allowing biomembranes to convert heat into electrical energy during temperature cycling (thermosynthesis). Necessary conditions for thermosynthesis are a temperature dependent electrical capacity and a conductivity as low as that of artificial lipid bilayers. Temperature cycling, and consequently thermosynthesis, can take place in leaves during cyclic transpiration and in organisms in natural waters that are carried along by convection currents. Electrogenic ATPases can convert the electrical energy gained by thermosynthesis into ATP if their activity and stoichiometry are properly regulated. The power of thermosynthesis is discussed and its possible value compared with the power of respiration. Environments where thermosynthesis may occur are listed. Thermosynthesis is a plausible energy source for the first living organisms.

低温で熱サイクルをうける含水岩石の熱膨張について

Thermal expansions of several saturated rocks were measured under a cyclic temperature change between 110K and 300K at a slow rate. The following changes due to water saturation were observed in thermal expansion; suppression of thermal cracking, hysteresis in thermal expansion, and an increase within thermal expansion coefficient. These changes were explained by freezing of pore water within cracks and the difference in temperature between freezing and melting of pore water. When the ice forms in the crack pore of granitic rocks, it bonds the surfaces of each crack to impede crack extension. The residual strain and the temperature at which thermal cracking initiated, therefore, decreased in these rocks. The temperature difference between freezing and melting is probably caused by supercooled water and a capillary force acting on the pore water. The hysteresis therefore appeared in the thermal expansion of nongranitic rocks which showed no hysteresis in the dry condition. These rocks exhibited no residual strain in the wet condition as well as in the dry condition except for the tuff in which a large amount of residual strain was observed after the first cycle.

低温で熱サイクルをうける乾燥岩石の熱膨張について

Thermal expansions of 11 dry rocks were investigated. These rocks were subjected to slow cyclic temperature change (0.5K/min) between 110K and 300K. They were divided into 2 groups according to their thermal expension behavior; existence of a hysteresis in the thermal expansion and a residual strain after the thermal cycling. (1) Nongranitic rocks (sedimentary and volcanic rocks) showed neither residual strain nor hysteresis. (2) Granitic rocks and Akiyoshi marble showed the residual strain and the hysteresis. Thermal expansion coefficient of the marble was negative at almost all temperatures. The difference in the thermal expansion between these groups was explained by the thermal cracking and the cracks in the rocks. Thermal cracking which is the cause of the residual strain can be produced by the mismatch of thermal expansion among the mineral grains. Cracks are responsible for the hysteresis by frictional sliding at crack surfaces and partial crushing of asperities. Decreasing temperature cannot provide the local strain sufficient to produce the cracking in the nongranitic rocks which consist of small grains and glassy matrix. On the contrary, the granitic rocks contain large grains and a large amont of quartz that shows larger expansion than other minerals. Akiyoshi marble is the aggregation of polycrystalline calcite that expands anisotropically. Themal cracking is therefore produced in these rocks during the first cooling stage.

Ability of the composite 50 Ti-47 Ni-3 Cu to transform heat energy into mechanical work upon cyclic temperature change

Ability of the composite 50 Ti-47 Ni-3 Cu to transform heat energy into mechanical work upon cyclic temperature change

Body Temperature Regulation in Red-Tailed Hawks and Great Horned Owls: Responses to Air Temperature and Food Deprivation

-Core body temperatures of Red-tailed Hawks (Buteojamaicensis) and Great Homed Owls (Bubo virginianus) were monitored by telemetry at intervals throughout the winter and summer. The mean body temperature of the hawks over a 24-h period was 41.1PC, compared to 39.50C for the owls. Body temperature of both species fluctuated daily in association with periods of activity and rest. In the hawks, however, the difference between active and inactive body temperature increased in cold weather and in response to food deprivation because the birds maintained a lower nocturnal (inactive) body temperature. Hawks that were fasted in the winter kept their body temperatures 3.20C lower at night than during the day, which may result in a substantial savings of energy for this species at night. Body temperatures of Great Homed Owls were not influenced by cold, but were lower during inactive periods in response to food deprivation. Thus, owls may also reduce metabolic expenses during periods of food shortage by physiological adjustments. Most birds exhibit cyclical daily changes in body temperature (Tb), with highest temperatures occurring when they are active and lowest when they are inactive (see Dawson and Hudson 1970, Calder and King 1974 for reviews). A 1-30C difference in Tb between the active and inactive phases of the daily cycle may be augmented by cold exposure or food deprivation, and is especially apparent in small species (<50 g), which are incapable of subsisting on their energy reserves for more than two to three days (Calder and King 1974, Chaplin 1976, Biebach 1977, Ketterson and King 1977, Bucher and Worthington 1982). Birds of prey typically feed irregularly and may have to endure long periods of fasting during the winter when low temperatures and snow cover diminish or obscure the activity of their prey. Despite the energetic advantage gained by reducing Tb while inactive or fasting, daily fluctuations in Tb rarely exceed 1-20C in several species of owls (Coulombe 1970, Siegfried et al. 1975, Gessaman 1978), even when they are fasted to 75% of their initial body mass (Ligon 1969). Daily cycles in Tb, specifically in response to cold and/or fasting, have been reported for only a few falconiforms, and the manner in which the birds respond is still unclear. For example, Heath (1962) and Hatch (1970) disagreed as to the stability of Tb of the Turkey Vulture (Carthartes aura) when it is fasted or cold-stressed. However, the Tb of the Black Vulture (Coragyps atratus) is very labile and highly dependent on air temperature (Larochelle et al. 1982). Is such lability characteristic of falconiforms, and are the metabolic adjustments of these birds to winter therefore different from those of owls, their nocturnal counterparts? In this study, we compared the thermoregulatory responses of Red-tailed Hawks (Buteo jamaicensis) and Great Homed Owls (Bubo virginianus) to changes in air temperature and weight loss as a test of their metabolic adaptations to winter conditions. These two species are similar in size and in their utilization of habitat and prey (Craighead and Craighead 1956, Orians and Kuhlman 1956, Hagar 1957, Korshgen and Stuart 1972, McInvaille and Keith 1974, Petersen 1979, and Jaksic 1982). Their geographic ranges overlap throughout most of the United States year-round (Bent 1937, Robbins et al. 1983); even their home ranges overlap greatly in some localities (Craighead and Craighead 1956, Petersen 1979). In fact, the most notable ecological difference between them is the period of the day when they are active. Since these two species, representing different orders, are so similar ecologically, we wondered if their metabolic responses to such typical winter stresses as cold exposure and food limitation were also similar.

Harper‐Dorn Creep: An artifact of low‐amplitude temperature cycling?

Harper‐Dorn (HD) creep may be produced by inadvertent low‐amplitude temperature cycling that is inevitable during high‐temperature creep tests. A cyclic temperature change causes a cyclic change in the equilibrium point defect concentration. In turn, a cyclic chemical force on dislocations that produces climb motion is created because the actual point defect concentration can never exactly equal the instantaneous equilibrium value. A cyclic ±1 K can produce a maximum chemical stress of ±5 MPa. When the period of the cycling is neither very large nor very small and the chemical stress is larger than the applied mechanical stress, it, rather than the mechanical stress, determines the dislocation density. In this case, the dislocation density is independent of the applied stress. Therefore, the creep rate is proportional to the applied stress and is independent of grain size, the characteristics of HD creep. If this explanation of HD creep is correct, this type of creep will not occur in the earth's mantle and will not serve as a mechanism for Newtonian mantle viscosity.

Leaf Temperature and Transpiration of Rice Plants in Relation to Short-Wave Radiation and Wind Speed

Leaf temperature and transpiration amount of rice plants were measured in a steady environment in a laboratory and in field situations. The plants set in Wagner pots were used. Experiments were carried out at the tillering and booting stages, and on the date of maturity. Measured leaf temperatures and transpiration rates were analyzed in connection with incident short-wave radiation on a leaf and wind speed measured simultaneously.Instantaneous supplying and turning-off of steady artificial light caused cyclic changes in leaf temperature and transpiration. Leaf temperature dropped in feeble illumination compared with the steady temperature in the preceeding dark.On the date of maturity, a rice plant leaf was warmer than the air, even in feeble light. Then, the leaf-air temperature difference and transpiration rate showed approximately linear increases with short-wave radiation intensity. On the same date, an increase in wind speed produced a decrease in leaf-air temperature difference, i.e., leaf temperature dropped, and an increase in transpiration rate. The rates of both changes in leaf temperature and transpiration rate were fairly large in a range of wind speed below about 1m/s.For rice plants growing favorably from the tillering stage through the booting stage, the leaves were considerably cooler than the air, even in an intense light and/or solar radiation. The leaf temperature showed the lowest value at short-wave radiations between 0.15 and 0.20ly/min, at above which the leaf temperature rised with an increase in short-wave radiation until it approached the air temperature. Transpiration rate of rice plants increased rapidly with an increase in short-wave radiation ranging below 0.2 or 0.3ly/min, at above which the increase in transpiration rate slowed.The relationships between leaf temperature and/or transpiration rate and wind speed and/or incident short-wave radiation (solar radiation) which were obtained experimentally, supported the relationships evaluated after solving the heat budget equation of a plant leaf. Further, it was suggested that the transpiration amount of rice plants might be estimated by solving a heat budget equation using a horizontal leaf temperature.

The surface content of asialoglycoprotein receptors on isolated hepatocytes is reversibly modulated by changes in temperature.

We have investigated the effect of temperature on the content of surface asialoglycoprotein receptors on isolated rat hepatocytes. Receptor was determined by measuring the specific binding of 125I- or [3H] asialo-orosomucoid at 0 degrees C. As reported previously, the receptor number/cell increases 2-3-fold within 30-60 min when freshly isolated cells are warmed from 0-37 degrees C (Weigel, P. H. (1980) J. Biol. Chem. 255, 6111-6120). This increase in receptor number is not inhibited by cycloheximide and also occurs on cells which have first been treated with EDTA to expose a population of cryptic receptors on the cell surface. The rate and extent of the receptor number increase on the cell surface are proportional to the temperature above about 17 degrees C. If cells are first equilibrated at 37 degrees C and then transferred to a lower temperature, the surface receptor number decreases at a rate and to an extent dependent on the temperature. The surface receptor number can be modulated up and down by successive temperature change cycles between 25 and 37 degrees C. In this temperature range, the number of surface receptors/cell is dependent on the final temperature but independent of the pathway to that temperature and is, therefore, a function of state with respect to temperature. The results demonstrate that temperature changes reversibly modulate the number of receptors on the hepatocyte surface. We conclude that, in the absence of ligand, surface receptors can either recycle or can be reversibly internalized or sequestered to prevent access to ligand. The results may also explain why different laboratories have reported a wide range of values for the number of receptors per hepatocyte.

Reduction in heat resistance of metals with a cyclic change in temperature

Let us consider the kinetics of oxidation of a metal under isothermal conditions (temperature T, time t) and with a cyclic change in temperature. We will assume that under cyclic temperature conditions oxidation occurs only at the maximum temperature, equal to the temperature of isothermal oxidation. We will designate the number of temperature change cycles during the time of oxidation t Z as N and the time of oxidation during a single cycle as t i. The acceleration of oxidation with a cyclically changing temperature is related to the periodic failure of the oxide film on the metal, which normally fulfills a protective function. This process is influenced by varioUs factors, such as the level of the maximum cycle temperature, the amplitude of the temperature change, the structure and mechanical properties of the oxide film, its thickness and adhesion to the surface of the metal, the formation of a zone of internal oxidation, etc. [i-3], Taking into consideration the role of these factors in the kinetics Q~ oxidation is still impractical, Therefore, we will assume that at each change in temperature there is complete failure and removal from the surface of the metal of the oxide film, as the result of which oxidation in the next cycle occurs the same as in the preceding one. In other words, oxidation with a cyclic change in temDerture is a successive multiple repetition of the oxidation in the first cycle of the process. Consequently, the maximum possible specific loss of weight of metal in cyclic oxidation qN max is equal to (qi is the specific loss of weight of metal in a single oxidation cvcle~. Nqi

Microleakage of selected composite restorative resins

Five selected composite restorative resins were used to restore Class V preparations in extracted human maxillary canine teeth. In addition, a low-viscosity bonding resin was used in conjunction with one of the restorative resins. Microleakage, at both the incisal and cervical margins of the restorations, was assessed by means of a radioisotope after the restored teeth had been subjected to 2500 cyclic temperature changes at 5° and 55°, respectively. Incisal microleakage was not significantly different but severe microleakage was recorded at the cervical margins of the restorations.

Cyclic thermal transformations in caesium graphite

Various physical properties can yield novel information about effects of texture of a graphite, on the detailed course of any thermal transformation of a graphite intercalate, when it is subjected to cyclic changes of temperature including a lambda peak. Using a DSC calorimeter with an imposed temperature change of 10 K min−1, we have found a novel transformation in caesium graphite CsC8 around 250 K. We show here that fine details appear to be sensitive to the texture of the graphite used.

Microleakage of conventional and microfilled composite restorative resins

Microfilled composite resins have been introduced in clinical dentistry because of the difficulty in finishing conventional composite resins satisfactorily. Owing to the difference in coefficients of thermal expansion of the two resin systems, the objective of this in vitro study was to evaluate microleakage of a conventional and a microfilled composite resin. Class V cavities with butt cavosurface margins were prepared in the middle third of the facial surfaces of the crowns of 80 noncarious human premolar teeth; they were acid etched within the preparations only. Forty preparations were restored with Concise composite and forty with Silar microfilled resin. Ten teeth from each group were subjected to cyclic temperature changes between 5 and 55 degrees C for 1000, 2500, or 5000 cycles, respectively, and ten teeth from each group were not cycled (controls). After suitable preparation, the teeth were immersed in 45Ca solution for 18 h and contact radiographs were prepared. Microleakage was scored 0-3 at both the cervical and occlusal margins of the restorations. Microleakage was significantly greater at the cervical margins than at the occlusal margins. Differences within occlusal and cervical microleakages among the two resins were not significant.

Evaluating the durability of power-plant parts under variable operating conditions

1. Cyclic change in stresses and temperatures in power-plant elements operated with frequent startups and shutdowns may lead to softening (reduction in the heat resistance) of the material. In connection with this, parameter D in the formula for summation of damages from creep and low-cycle fatigue (1) may be substantially less than unity even when the damage from fatigue is nearly zero. 2. The softening of the steel with a cyclic change in stress and temperature is connected with an intensification of structural changes which occur under creep conditions. 3. To refine methods of determining the lifetime of power-plant elements under the combined influence of creep and low-cycle fatigue, it is necessary to conduct further studies to determine the region and conditions of the reduction in heat resistance due to cyclic loading.

Crystallization of amorphous Al-Cu films

Quench-condensed (- 160°C) Al-Cu films in the composition range from 19% to 50% Cu were heated to room temperature and annealed up to 300°C. The temperature dependence of the resistivity and the temperature coefficient of the resistivity were observed during various cycles of temperature changes. The films are amorphous at the condensation temperature. Phase transitions which occur as the temperature is increased initiate sharp decreases in the resistance. Investigations of the film structure and composition were carried out with an electron microscope (transmission electron microscopy, electron diffraction, scanning transmission electron microscopy and X-ray microanalysis). The results could be clearly related to the phase transitions as observed via the resistance changes during annealing. For film compositions below 37.4% Cu the phase transition is determined by a eutectic crystallization into two phases. For larger copper contents, an intermediate single- phase state is produced first during the transition by polymorphous crystallization and is succeeded by a multiphase stable state.

Polymer/concrete composites—A review

AbstractThe development of polymer/concrete composites is directed at both improved and new construction materials by combining the ancient technology of hydraulic‐cement‐concrete with the modern technology of polymers. The need for such materials has always existed since the traditional construction material portland‐cement‐concrete (PCC) suffers the drawbacks 4 little or no resistance to chemical attack; rapid deterioration under freeze/thaw conditions due to cyclic temperature changes; low tensile, shear and bond strengths; and inherent micro‐structural menaces (voids, shrinkage‐cracks, capillaries) which, individually or in combination with each other, shorten the service life of the structures.

Effect of solvent power on the adsorption of polystyrene onto a metal surface

AbstractThe adsorption of linear polystyrenes from cyclohexane solutions onto a chrome plate of 35 (the theta temperature), 40, and 45°C was studied by ellipsometry. The adsorbance decreases with increasing temperature, while the extension of the adsorbed polymer layer increases. The adsorbance is almost independent of the molecular weight at these temperatures. The slope of a double logarithmic plot of extension versus molecular weight is 0.5 at the theta temperature, whereas at the higher temperatures the slope is a little larger. Both the adsorbance and the extension of the adsorbed layer change reversibly over a cycle of temperature change, indicating that a reversible conformational change has occurred. The expansion factor αt of the adsorbed layer is compared with the theoretical predictions of Hoeve and of Jones and Richmond. The expansion factor αt according to Hoeve's theory, was smaller than the measured value, whereas the expansion calculated by the Jones–Richmond theory is much larger than the measured value. It is concluded that the tail portions of adsorbed chains predominantly govern the extension of the adsorbed layer.

The Effects of Fluctuating Temperature, Salinity, and Aerial Exposure Upon Larval Release in Balanus Balanoides and Elminius Modestus

Intertidal estuarine barnacles suffer cyclic changes in salinity and temperature, the latter being most marked and often quite abrupt at the time of tidal immersion and emersion.

The influence of nitrogen on the oxidation resistance of low alloy steels

Experiments in simulated boiler flue gas have shown that the oxidation resistance of mild steel is increased by up to two orders of magnitude by a surface nitriding treatment. Oxidation resistance was determined under isothermal conditions and during cyclic changes of temperature and oxygen potential. The oxide scale has a fine grain size, is extremely adherent and is therefore protective. A nitrided surface layer is produced by gas-metal equilibration with NH 3 : H 2 gas mixtures under conditions to form austenite (y) at nitriding temperature. On cooling to room temperature, martensite (a') is formed with retained austenite, the relative proportions of which depend on cooling rate. During oxidation at 420 °C, martensite and austenite in the immediate surface layer temper within a few minutes to form ferrite (a) containing a fine dispersion of y'-Fe 4 N platelets ca . 50 nm in diameter. X-ray analysis at increasing depth from the surface of nitrided mild steel shows that tempering of the a' + y structure to a + y'-Fe 4 N is accelerated at the free surface of the alloy relative to the remainder of the nitrided layer, and results in formation of incoherent nitride precipitates on the surface. The nitride particles act as nucleation sites for oxide formation, and electron microscopy shows that the oxide nuclei are of the same order of size as the nitride particles.

Service of refractory concretes in the lining of steel-teeming ladles

An investigation of the temperature and slag regimes of concrete linings has shown that one half of the lining's thickness, the one on the metal melt side, is subjected to severe cyclical changes in temperature, whereas the other half operates under steady thermal conditions throughout the furnace campaign. It has been established that cooling of the lining with water sharply reduces the temperature of the contact layer of the lining, i. e., it leads to thermal shock with accompanying crack formation. The durability of the lining is largely determined by the correspondence of the chemical nature of the lining material with the chemical composition of the slags. Under the influence of converter slag with a basicity of 3,1–4.5, the rate of transfer of SiO2 from the acid lining to the slag increases by 2–3 times in comparison that observed for slag with a basicity of 2.5–3.35. This in tarn leads to more intense decrease in the basicity of the ladle slag, enhancing its fluidity and causing intense wear of the lining in the lower sector of the ladle. The results of industrial tests showed that the most agressive effect on an acid lining is exerted by fluid slags with a basicity of 2.1–2.7. Slags of lower basicity are more viscous and closer in chemical composition to that of the lining. Slags of higher basicity have a higher viscosity and their penetrative power is therefore less.