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PubMed1998

High-Temperature In Situ Straining Experiments in the High-Voltage Electron Microscope.

: Design rules are described here for high-temperature straining stages for transmission electron microscopy. Temperatures above 1000 degreesC can be attained by electron bombardment of the specimen grips. Thermal equilibrium can be reached in a short time by carrying off the heat by water cooling. Some applications of this stage are described. Ferroelastic deformation was observed at 1150 degreesC in t' and partially stabilized zirconia, which changes the microstructure for successive dislocation plasticity. In the oxide-dispersion-strengthened alloy INCOLOY MA 956, dislocations are impeded by oxide particles and move smoothly between the particles. At high temperatures, both the resting and traveling times control the average dislocation velocity. In MoSi2 single crystals of a soft orientation, dislocations with 1/2<111> Burgers vectors are created in localized sources and move on {110} planes in a viscous manner. The dislocations in Al-Pd-Mn single quasicrystals are oriented in preferred crystallographic directions and move in a viscous way as well. On the basis of in situ observations, conclusions are drawn for interpreting macroscopic deformation behavior at high temperatures.

Journal Article↗
PubMed2004

Incipient order in the t-J model at high temperatures.

We analyze the high-temperature behavior of the susceptibilities towards a number of possible ordered states in the t-J-V model using the high-temperature series expansion. From all diagrams with up to ten edges, reliable results are obtained down to temperatures of order J, or (with some optimism) to J/2. In the unphysical regime, t J, these susceptibilities are small and decreasing with decreasing temperature; this suggests that the t-J model does not support high-temperature superconductivity. We also find modest evidence of a tendency toward nematic and d-density wave orders.

Journal Article↗
PubMed2003

Biodegradation of aliphatic and aromatic hydrocarbons at high temperatures.

In this paper, the high temperature (65-75 degrees C) biodegradation of aliphatic and aromatic hydrocarbons is investigated and kinetic parameters are derived. The shift of the physico-chemical system properties with rising temperature will be discussed in detail. For example, the solubility of naphthalene is increased by a factor of about ten if the temperature is increased from 20 to 75 degrees C. This effect is essential to increase the bioavailability of sparingly soluble hydrocarbons. It is also demonstrated in experiments that very high oxygen transfer rates can be obtained at high temperatures in the presence of hydrocarbons. It is shown that efficient phenol biodegradation is essential for high temperature hydrocarbon degradation because some microorganisms tend to transform phenols into polyphenols which are very inhibitory for microbial growth. A defined mixed culture adapted to phenol converted more than 90% of a mixture of phenol, hexadecane and pyreno and a very high maximal growth rate of 0.19 h(-1) was determined. A yield coefficient Y(X/S) of about 0.8 g (biomass)/g (hydrocarbons) was calculated in this experiment. In a separate experiment the influence of the hydrocarbon droplet size on the biodegradation is investigated at 70 degrees C using a newly isolated Thermus sp. In this case, the growth on a hexadecane/pyrene mixture was described by a model based on the Monod equation and the corresponding kinetic parameters are derived. A mixed culture was used for the bioremediation of soil in a slurry reactor. The initial contamination of 11 g/kg was lowered to about 2 g in a reactor inoculated by an immobilized culture of extreme thermophilic microorganisms, while 9 g/kg remained in a sterile control.

Biodegradation, Environmental↗
PubMed1988

High-resolution electron microscopic investigation of supported platinum particles reduced at high temperatures.

High-resolution electron microscopy has been used to characterize the platinum particles supported on TiO2 or ZnO. After reduction at elevated temperatures, the metallic particles display a regular, faceted shape, and several superstructures, Pt3 Ti(C), Pt3 Ti(H), PtTi, and PtZn, have been found. These results, which may involve strong metal-support interaction, have been confirmed by optical diffraction and image simulation.

Hot Temperature↗
PubMed2004

Approaches for the coating of capillary columns with highly phenylated stationary phases for high-temperature GC.

Two highly phenylated tetramethyl-p-silphenylene-diphenylsiloxane copolymers were coated on fused silica capillary columns and used as stationary phases in GC. The copolymers offered new insights into the coating process and column preparation due to their physicochemical properties. The fused silica capillary surface had to be pretreated in various ways to achieve a homogeneous film and a well deactivated surface: etching with ammonium bifluoride; leaching with sodium hydroxide and hydrochloric acid; silylation with tetraphenyldimethyldisilazane and triphenylsilylamine. Droplet formation was observed on tetraphenyldimethyldisilazane silylated surfaces leading to capillary columns with low separation efficiency. The topology of inhomogeneous films was investigated by light microscopy, scanning electron microscopy, and Auger electron spectroscopy. It became apparent that the stationary phase did not form droplets but islands, which are connected by a wetting layer according to the Stranski-Krastanov growth mode. Both copolymers are potential stationary phases for high-temperature GC with promising properties. They offer a higher overall polarity than 75% phenyl, 25% methyl-polysiloxanes in combination with increased thermal stability and reduced bleed levels.

Journal Article↗
PubMed1995

The origin of life--did it occur at high temperatures?

A high-temperature origin of life has been proposed, largely for the reason that the hyperthermophiles are claimed to be the last common ancestor of modern organisms. Even if they are the oldest extant organisms, which is in dispute, their existence can say nothing about the temperatures of the origin of life, the RNA world, and organisms preceding the hyperthermophiles. There is no geological evidence for the physical setting of the origin of life because there are no unmetamorphosed rocks from that period. Prebiotic chemistry points to a low-temperature origin because most biochemicals decompose rather rapidly at temperatures of 100 degrees C (e.g., half-lives are 73 min for ribose, 21 days for cytosine, and 204 days for adenine). Hyperthermophiles may appear at the base of some phylogenetic trees because they outcompeted the mesophiles when they adapted to lower temperatures, possibly due to enhanced production of heat-shock proteins.

Biological Evolution↗
PubMed2002

Analysis of artificial fireplace logs by high temperature gas chromatography.

High temperature gas chromatography is used to analyze the wax of artificial fireplace logs (firelogs). Firelogs from several different manufacturers are studied and compared. This study shows that the wax within a single firelog is homogeneous and that the wax is also uniform throughout a multi-firelog package. Different brands are shown to have different wax compositions. Firelogs of the same brand, but purchased in different locations, also have different wax compositions. With this information it may be possible to associate an unknown firelog sample to a known sample, but a definitive statement of the origin cannot be made.

Journal Article↗
PubMed1997

Automated control and monitoring of thermal processing using high temperature, short time pasteurization.

High temperature, short time pasteurization was used to evaluate a computer-based system for controlling the pasteurization process, acquiring data, and monitoring records. Software was used for the control of hot water temperature, flow rate through the centrifugal timing pump, and diversion of under-processed product. Three types of control strategies were conducted: single loop, cascade, and multivariable. The single loop control strategy showed the most rapid responses to temperature changes, but the temperature response curve was slowest to return to its set point. The cascade control strategy showed slower recoveries to temperature changes, but the temperature response curve was smoother. The multivariable control strategy responded slightly faster than the cascade control strategy, and the temperature response curve was slightly smoother than the cascade control strategy. The multivariable control strategy was able to control the flow diversion valve by the use of a lethality controller. The data acquisition system, used to monitor the data obtained from the high temperature, short-time pasteurization system, was within +/- 0.1 degree C of the temperature recorded by the safety thermal limit recorder. Reliability was determined by examining the changes in the position of the flow diversion valve to identify process deviations and by comparing the changes to the event marker on circular charts. The data acquisition system was an effective alternative for monitoring the completeness of data.

Animals↗
PubMed1994

Possible role of tissue-bound calcium ions in citrate-mediated high-temperature antigen retrieval.

High-temperature preheating of sections in the presence of a salt (e.g., citrate) or a protein denaturant (e.g., urea) solution has been shown recently to provide a reliable alternative to tissue proteolysis for antigen retrieval from formaldehyde-fixed, paraffin-embedded tissues. However, the underlying mechanism of action of this form of pretreatment remains highly speculative. In this study, we show that calcium chelating agents such EDTA and EGTA are more effective than citrate in the retrieval of a citrate-sensitive nuclear antigen, Ki-67. Also, sodium carbonate and another calcium precipitating agent are both able to effect antigen retrieval at high temperatures. The overall data therefore suggest that either the chelation or the precipitation of tissue-bound calcium ions, and perhaps also other divalent metal cations, is a critical step in salt-mediated antigen retrieval. As a corollary, it is suggested that tight complexing of calcium ions or other divalent metal cations with proteins during formaldehyde tissue fixation is responsible for the masking of certain antigens.

Antigens↗
PubMed1992

Interaction between the Adh and alpha Gpdh loci in Drosophila melanogaster: adult survival at high temperature.

The role of high temperature resistance in the world-wide cline of Adh and alpha Gpdh allele frequencies of Drosophila melanogaster was investigated. Experimental strains were used with different combinations of Adh and alpha Gpdh alleles but with similar genetic background. The survival time of adult males, reared at different pre-adult temperatures, was measured at 35 degrees C. To investigate the relationship between survival and protein content, triglycerides content and ADH and alpha GPDH enzyme activity, the latter characters were measured before and after 12 h exposure to 35 degrees C. Three-way ANOVA of survival at 35 degrees C showed significant effects of rearing temperature and Adh genotype, interaction between Adh and alpha Gpdh, interaction between Adh and rearing temperature and interaction between Adh, alpha Gpdh and rearing temperature, alpha GPDH enzyme activity did not change significantly. Although protein content, triglycerides content and ADH enzyme activity decreased significantly at 35 degrees C, no correlation was observed between survival and these traits. It is concluded that the world-wide cline of Adh and alpha Gpdh allele frequencies cannot simply be explained by the genotypic differences in resistance to high temperature of adult Drosophila melanogaster.

Alcohol Dehydrogenase↗
PubMed1999

Ceramic fibers for matrix composites in high-temperature engine applications

High-temperature engine applications have been limited by the performance of metal alloys and carbide fiber composites at elevated temperatures. Random inorganic networks composed of silicon, boron, nitrogen, and carbon represent a novel class of ceramics with outstanding durability at elevated temperatures. SiBN(3)C was synthesized by pyrolysis of a preceramic N-methylpolyborosilazane made from the single-source precursor Cl(3)Si-NH-BCl(2). The polymer can be processed to a green fiber by melt-spinning, which then undergoes an intermediate curing step and successive pyrolysis. The ceramic fibers, which are presently produced on a semitechnical scale, combine several desired properties relevant for an application in fiber-reinforced ceramic composites: thermal stability, mechanical strength, high-temperature creep resistivity, low density, and stability against oxidation or molten silicon.

Journal Article↗
PubMed1988

Plants and high temperature stress.

The effect of high temperature on higher plants is primarily on photosynthetic functions. The heat tolerance limit of leaves of higher plants coincides with (and appears to be determined by) the thermal sensitivity of primary photochemical reactions occurring in the thylakoid membrane system. Tolerance limits vary between genotypes, but are also subject to acclimation. Long-term acclimations can be superimposed upon fast adaptive adjustment of the thermal stability, occurring in the time range of a few hours. Light causes an increase in tolerance to heat, and this stabilization is related to the light-induced proton gradient. In addition to irreversible effects, high temperature may also cause large, reversible effects on the rate of photosynthesis. We report here some studies of photosynthetic gas exchange and chlorophyll fluorescence, designed to examine the energetic balance between photosynthetic carbon metabolism and light reactions during steady state photosynthesis with leaves of cotton plants at different temperatures. At temperatures exceeding the optimum for assimilation, but well below the tolerance limit, the feedback control of light reactions by carbon metabolism declines, as additional dissipative processes become important. Energy dissipated by photorespiration can exceed that consumed by CO2 assimilation, and a reversible, temperature-induced non-photochemical 'quenching' process, related to 'spillover' of excitation energy to photosystem 1, decreases the efficiency of photosystem 2 with increasing temperature. However, despite the overall decline in the 'potential quantum efficiency', our analysis indicates that CO2 assimilation may be limited, in part, at high temperature by an imbalance in the regulation of the carbon metabolism, which is reflected in a 'down-regulation' of the ribulose-1,5-bisphosphate carboxylase/oxygenase.

Adaptation, Physiological↗
PubMed2002

Interaction between drought and chronic high temperature during kernel filling in wheat in a controlled environment.

Wheat plants (Triticum aestivum L. 'Lyallpur'), limited to a single culm, were grown at day/night temperatures of either 18/13 degrees C (moderate temperature), or 27/22 degrees C (chronic high temperature) from the time of anthesis. Plants were either non-droughted or subjected to two post-anthesis water stresses by withholding water from plants grown in different volumes of potting mix. In selected plants the demand for assimilates by the ear was reduced by removal of all but the five central spikelets. In non-droughted plants, it was confirmed that shading following anthesis (source limitation) reduced kernel dry weight at maturity, with a compensating increase in the dry weight of the remaining kernels when the total number of kernels was reduced (small sink). Reducing kernel number did not alter the effect of high temperature following anthesis on the dry weight of the remaining kernels at maturity, but reducing the number of kernels did result in a greater dry weight of the remaining kernels of droughted plants. However, the relationship between the response to drought and kernel number was confounded by a reduction in the extent of water stress associated with kernel removal. Data on the effect of water stress on kernel dry weight at maturity of plants with either the full complement or reduced numbers of kernels, and subjected to low and high temperatures following anthesis, indicate that the effect of drought on kernel dry weight may be reduced, in both absolute and relative terms, rather than enhanced, at high temperature. It is suggested that where high temperature and drought occur concurrently after anthesis there may be a degree of drought escape associated with chronic high temperature due to the reduction in the duration of kernel filling, even though the rate of water use may be enhanced by high temperature.

Acclimatization↗
PubMed1991

In vitro intracanal temperatures produced by low- and high-temperature thermoplasticized injectable Gutta-percha.

An in vitro computerized temperature measurement system was developed to measure intracanal temperatures produced by different heated gutta-percha obturation techniques. The temperatures produced by low- and high-temperature thermoplasticized injectable gutta-percha systems were recorded and compared in this investigation. The mean intrachamber temperature of the Obtura syringe was 178.68 degrees C. The mean temperature of the Ultrafil heater was 93.06 degrees C. The mean temperature of the extruded gutta-percha was 137.81 degrees C from the Obtura syringe and 62.88 degrees C from the Ultrafil cannule. The intracanal temperature of the gutta-percha recorded for both systems showed that the gutta-percha cools rapidly after injection into the canal.

Gutta-Percha↗
PubMed2002

High-temperature controlled atmosphere for post-harvest control of Indian meal moth (Lepidoptera: Pyralidae) on preserved flowers.

High carbon dioxide atmospheres combined with high temperature were effective for controlling Indian meal moth, Plodia interpunctella (Hübner) pupae. Pupae were exposed to atmospheres of 60, 80, or 98% carbon dioxide (CO2) in nitrogen (N2), or 60 or 80% CO2 in air at temperatures of 26.7 degrees C or 32.2 degrees C and 60% RH. Controlled atmosphere treatments at 32.2 degrees C controlled pupae faster than the same treatments at the lower temperature. At both temperatures high CO2 concentration treatments combined with nitrogen killed pupae faster than high CO2 concentration treatments combined with air. Exposure to 80% carbon dioxide mixed with nitrogen was the most effective treatment causing 100% mortality in 12 h at 32.2 degrees C and 93.3% mortality in 18 h at 26.6 degrees C. High-temperature controlled atmosphere treatments had no adverse effects on quality of two preserved floral products, Limonium sinuatum (L.) and Gypsophila elegans (Bieb.), tested for 12, 18, and 24 h according to industry standards.

Animals↗
PubMed2005

Differences in in vitro pollen germination and pollen tube growth of cotton cultivars in response to high temperature.

UNLABELLED BACKGROUND AND AIMS: High-temperature environments with >30 degrees C during flowering reduce boll retention and yield in cotton. Therefore, identification of cotton cultivars with high-temperature tolerance would be beneficial in both current and future climates. * METHODS: Response to temperature (10-45 degrees C at 5 degrees C intervals) of pollen germination and pollen tube growth was quantified, and their relationship to cell membrane thermostability was studied in 12 cultivars. A principal component analysis was carried out to classify the genotypes for temperature tolerance. * KEY RESULTS: Pollen germination and pollen tube length of the cultivars ranged from 20 to 60 % and 411 to 903 microm, respectively. A modified bilinear model best described the response to temperature of pollen germination and pollen tube length. Cultivar variation existed for cardinal temperatures (T(min), T(opt) and T(max)) of pollen germination percentage and pollen tube growth. Mean cardinal temperatures calculated from the bilinear model for the 12 cultivars were 15.0, 31.8 and 43.3 degrees C for pollen germination and 11.9, 28.6 and 42.9 degrees C for pollen tube length. No significant correlations were found between pollen parameters and leaf membrane thermostability. Cultivars were classified into four groups based on principal component analysis. * CONCLUSIONS: Based on principal component analysis, it is concluded that higher pollen germination percentages and longer pollen tubes under optimum conditions and with optimum temperatures above 32 degrees C for pollen germination would indicate tolerance to high temperature.

Cell Membrane↗
PubMedDate not supplied

Liberation of hydrogen cyanide and hydrogen chloride during high-temperature dispersion of CS riot control agent.

High temperature dispersion (greater than 700 degrees C) of the riot control agent orthochlorobenzylidenemalononitrile (CS) has previously been shown to produce a number of organic thermal degradation products through rearrangements and loss of cyano and chlorine substituents present on the parent CS compound. Until now the possibility that HCN and HCl might also be air contaminants produced during high temperature CS dispersion has not been examined. Air samples were collected to detect HCN and HCl as air contaminants released during high-temperature CS dispersion indoors. Sampling and analysis based on National Institute of Occupational Safety and Health methods 7904 and 6010 for HCN, and 7903 for HCl, showed evidence that both compounds were present in air samples collected. A reassessment of human health risks associated with exposure to CS riot control agent dispersed at high temperature should be conducted, and should consider the full range of contaminants produced during the dispersion process.

Environmental Exposure↗