Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Temperature environment”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed2002

Development of the line-focus-beam ultrasonic material characterization system.

A line-focus-beam ultrasonic material characterization (LFB-UMC) system has been developed to evaluate large diameter crystals and wafers currently used in electronic devices. The system enables highly accurate detection of slight changes in the physical and chemical properties in and among specimens. Material characterization proceeds by measuring the propagation characteristics, viz., phase velocity and attenuation, of Rayleigh-type leaky surface acoustic waves (LSAWs) excited on the water-loaded specimen surface. The measurement accuracy depends mainly upon the translation accuracy of the mechanical stages used in the system and the stability of the temperature environment. New precision mechanical translation stages have been developed, and the mechanical system, including the ultrasonic device and the specimen, has been installed in a temperature-controlled chamber to reduce thermal convection and conduction at the specimen. A method for precisely measuring temperature and longitudinal velocity in the water couplant has been developed, and a measurement procedure for precisely measuring the LSAW velocities has been completed, achieving greater relative accuracy to better than +/- 0.002% at any single chosen point and +/- 0.004% for two-dimensional measurements over a scanning area of a 200-mm diameter silicon single-crystal substrate. The system was developed to address various problems arising in science and industry associated with the development of materials and device fabrication processes.

Journal Article↗
PubMed2003

Magnesium and phosphorus distribution in the avian eggshell.

Magnesium and phosphorus are major inorganic constituents of the avian eggshell. The Mg/Ca ratio has been used as a palaeothermometer in a range of calcite biominerals. Eggshells provide the opportunity to examine the Mg/Ca ratio of a calcite biomineral produced in a constant temperature environment. Mg distribution is not constant throughout the shell, decreasing from nucleation until after fusion of the mammillary caps and then increasing to termination. This indicates that temperature of deposition is not the only factor controlling the Mg content of this biomineral system. There is a greater increase in magnesium concentration in the outer region of eggshells from older birds. The variation in magnesium concentration does not appear to correlate with organic content. Phosphorus occurs in the outer quarter of the eggshell and rises to termination and is therefore not confined to cuticular vesicles.

Animals↗
PubMed1982

A low x-ray background low temperature specimen stage for biological microanalysis in the TEM.

The side entry specimen stage described in this paper is a development of a specimen stage for use at room temperature in the JEOL JEM 100 and 200 series transmission electron microscopes. The earlier specimen stage was designed to ensure that the extraneous instrumental contribution to thin specimen X-ray spectra is both small and quantifiable. As well as having a low X-ray background the new stage will also maintain the specimen at temperatures sufficiently low (down to 100 K) to minimize the loss of organic material due to electron irradiation. A new anticontaminator which provides a clean low temperature environment for the specimen stage is also described.

Cold Temperature↗
PubMed1992

Epinephrine and norepinephrine release from bullfrog gastrointestinal sympathetic postganglionic endings at a high ambient temperature.

The influence of a high ambient temperature on sympathetic neurotransmitter release in bullfrogs was studied. Gastrointestinal vascular perfusates were collected before and after splanchnic nerve stimulation, and their content of epinephrine and norepinephrine was determined. A marked increase in epinephrine and norepinephrine release was observed following stimulation at 29-32 degrees C, indicating that epinephrine and norepinephrine may both act as adrenergic transmitters in a high-temperature environment.

Animals↗
PubMed2002

Insects and low temperatures: from molecular biology to distributions and abundance.

Insects are the most diverse fauna on earth, with different species occupying a range of terrestrial and aquatic habitats from the tropics to the poles. Species inhabiting extreme low-temperature environments must either tolerate or avoid freezing to survive. While much is now known about the synthesis, biochemistry and function of the main groups of cryoprotectants involved in the seasonal processes of acclimatization and winter cold hardiness (ice-nucleating agents, polyols and antifreeze proteins), studies on the structural biology of these compounds have been more limited. The recent discovery of rapid cold-hardening, ice-interface desiccation and the daily resetting of critical thermal thresholds affecting mortality and mobility have emphasized the role of temperature as the most important abiotic factor, acting through physiological processes to determine ecological outcomes. These relationships are seen in key areas such as species responses to climate warming, forecasting systems for pest outbreaks and the establishment potential of alien species in new environments.

Acclimatization↗
PubMed1997

Environmental stress and the expression of genetic variation.

We have started to test the effects of environmental extremes on the expression of genetic variation for traits likely to be under selection in natural populations. We have shown that field heritability may be high for stress response traits in contrast to morphological traits, which tend to show lower levels of heritable variation in nature compared with the laboratory. Selection for increased stress resistance can lead to a number of other evolutionary changes, and these may underlie trade-offs between favourable and stressful environments. Temperature extremes can have a marked influence on the heritability of life history traits. Heritabilities for fecundity can be high when parental flies are reared at low temperatures and under field conditions. The expression of genetic variation for development time is somewhat more complex when temperature extremes are considered. Populations at species margins may be ideal for studying the effects of environmental stress on evolution.

Animals↗
PubMed1976

Thermal adaptation in yeast: growth temperatures, membrane lipid, and cytochrome composition of psychrophilic, mesophilic, and thermophilic yeasts.

The temperature limits of growth of a number of yeast species were examined, and on this basis the organisms were classified into different thermal categories. The following species were examined: Leucosporidium frigidum and Leucosporidium nivalis, psychrophilic, temperature limits of growth, -2 to 20 degrees C; Canadian lipolytica mesophilic, temperature limits of growth, 5 to 35 degrees Candida parapsilosis and Saccharomyces telluris, thermotolerant, temperature limits of growth, 8 to 42 degrees C; Torulopsis bovina and Candida slooffi, thermophilic, temperature limits of growth, 25 to 45 degrees C and 28 to 45 degrees C, respectively. The membrane lipid and cytochrome composition of mitochrondrial fractions isolated from these yeasts were compared. There was a direct correlation between the growth temperature and the degree of membrane of lipid unsaturation; the lower the temperature, the greater the degree of lipid unsaturation. The membrane lipid composition of the thermophilic yeasts were distinguished by the high percentage (30 to 40%) of saturated fatty acid, as compared with the mesophilic and psychrophilic yeasts. The latter contained approximately 90% unsaturated fatty acid, 55% of which was linolenic acid, C alpha-18:3. Changes in phospholipid composition in relation to temperature were also noted. The respiratory-deficient thermophile, C. slooffi, was characterized by the absence of cardiolipin (sensitivity 0.1 mug of phosphorus) and cytochrome aa3. The absence of conventional mitochondrial structures in this thermophilic microorganism is tentatively suggested although low concentrations of cytochromes b, c, and c1 were detected by low-temperature spectroscopy. On the other hand, the respiratory-competent thermophile, T. bovina, was characterized by a high cardiolipin (25% of the total phospholipid) and cytochrome aa3 content (1 nmol/mg of mitochrondrial protein). Low-temperature spectra showed the presence of one b-type cytochrome in the thermophilic yeasts, two b-type cytochromes in the mesophilic yeasts, and three b-type cytochromes in the psychrophilic yeasts. It was concluded that a knowledge of the properties of the biological membrane is fundamental to an understanding of the ability of a microorganism to grow and reproduce in different temperature environments.

Adaptation, Physiological↗
PubMed1998

Estimation of thermal sensation during varied air temperature conditions.

Seven male students were exposed to four varied air temperature environments: hot (37 degrees C) to neutral (27 degrees C) (HN), neutral to hot (NH), cool (17 degrees C) to neutral (CN), and neutral to cool (NC). The air temperature was maintained at the first condition for 20 min, then was changed to the second condition after 15 min and was held there for 20 min. Each subject wore a T-shirt, briefs, trunks, and socks. Each sat on a chair and was continuously evaluated for thermal sensation, thermal comfort, and air velocity sensation. Some physiological and thermal parameters were also measured every 5 s during the experiment. The correlation between thermal sensation and skin temperature at 15 sites was found to be poor. The subjects felt much warmer during the rising phase of the air temperature (CN, NH) than during the descending phase (HN, NC) at a given mean skin temperature. However, thermal sensation at the same heat flux or at the same value of the difference between skin and air temperature (delta(Tsk - Ta)) was not so different among the four experimental conditions, and the correlation between thermal sensation and heat flux or delta(Tsk - Ta) was fairly good. The multiple regression equation of the thermal sensation (TS) on 15 sites of skin temperature (Tsk; degrees C) was calculated and the coefficient of determination (R*2) was found to be 0.656. Higher coefficients of determination were found in the equations of thermal sensation for the heat flux (H; kcal.m-2.h-1) at the right and left thighs of the subjects and on delta(Tsk - Ta) (degrees C) at 4 sites. They were as follows: TS = 2.04 - 0.016 Hright - 0.036 Hleft; R*2 = 0.717, TS = 1.649 + 0.013 delta(Tsk - Ta)UpperArm - 0.036 delta(Tsk - Ta)Chest - 0.223 delta(Tsk - Ta)Thigh-0.083 delta(Tsk - Ta)LowerLeg; R*2 = 0.752, respectively.

Adult↗
PubMed2004

Cold acclimation induced genes of trifoliate orange (Poncirus trifoliata).

Commercial citrus varieties are sensitive to low temperature. Poncirus trifoliata is a close relative of Citrus species and has been widely used as a cold-hardy rootstock for citrus production in low-temperature environments. mRNA differential display-reverse transcription (DDRT)-PCR and quantitative relative-RT-PCR were used to study gene expression of P. trifoliata under a gradual cold-acclimation temperature regime. Eight up-regulated cDNA fragments were isolated and sequenced. These fragments showed high similarities at the amino acid level to the following genes with known functions: betaine/proline transporter, water channel protein, aldo-keto reductase, early light-induced protein, nitrate transporter, tetratricopeptide-repeat protein, F-box protein, and ribosomal protein L15. These cold-acclimation up-regulated genes in P. trifoliata are also regulated by osmotic and photo-oxidative signals in other plants.

Acclimatization↗
PubMed1975

Ascorbic acid changes in cultured rabbit lenses after microwave irradiation.

Whole body exposure of rabbits to microwave radiation causes a decrease in ascorbic acid in the lens. In our study, rabbit lenses maintained in culture medium (37 degrees C) were exposed to either pulsed or continuous wave S-band radiation for 10-15 min at power densities between 0 and 200 mW/cm-2. Total ascorbic acid was measured in selected lenses 1-3 days after irradiation. The temperature of the culture medium was measured during irradiation. Matched control lenses were exposed to similar time-temperature environments, but without microwave irradiation. Ascorbic acid decreased significantly in lenses exposed to microwave radiation. No differences were found, however, between irradiated and control lenses subjected to identical time-temperature conditions. At a given average power density, the time-temperature variation was independent of modulation. A decrease in ascorbic acid is apparently a direct thermal effect of microwave radiation in rabbit lens culture.

Animals↗
PubMed2005

Effective factors in thermostability of thermophilic proteins.

Thermostability of proteins in general and especially thermophilic proteins has been subject of a wide variety of studies based on theoretical and experimental investigation. Thermostability seems to be a property obtained through many minor structural modifications rather than certain amino acids substitution. In comparison with its mesophile homologue in a thermostable protein, usually a number of amino acids are exchanged. A wide variety of theoretical studies are based on comparative investigation of thermophilic proteins characteristics with their mesophilic counterparts in order to reveal their sequences, structural differences and consequently, to relate these observed differences to the thermostability properties. In this work we have compared a dataset of thermophilic proteins with their mesophilic homologues and furthermore, a mesophilic proteins dataset was also compared with its mesophilic homologue. This strategy enabled us first, to eliminate noise or background differences from signals and moreover, the important factors which were related to the thermostability were recognized too. Our results reveal that thermophilic and mesophilic proteins have both similar polar and nonpolar contribution to the surface area and compactness. On the other hand, salt bridges and main chain hydrogen bonds show an increase in the majority of thermophilic proteins in comparison to their mesophilic homologues. In addition, in thermophilic proteins hydrophobic residues are significantly more frequent, while polar residues are less. These findings indicate that thermostable proteins through evolution adopt several different strategies to withstand high temperature environments.

Adaptation, Physiological↗
PubMed1998

Cation diffusion in calcite: determining closure temperatures and the thermal history for the Allan Hills 84001 meteorite.

The presence of zoned Fe, Mg, Ca, and Mn in the carbonate phases associated with the cracks and inclusions of the Allan Hills (ALH) 84001 meteorite provides evidence for constraining the thermal history of the meteorite. Using self- and tracer-diffusion coefficients obtained from laboratory experiments on natural calcite, cooling rates are calculated for various temperatures and diffusion distances to assist in the evaluation of the compositional zoning associated with the carbonate phases in ALH 84001. The closure temperature model provides the average temperature below which compositional zoning will be preserved for a given cooling rate, that is, the temperature at which diffusion will be ineffective in homogenizing the phase. The validity of various theories for the formation of the carbonate globules may be examined, therefore, in view of the diffusion-limited kinetic constraints. Experiments using a thin film-mineral diffusion couple and ion microprobe for depth profiling analysis were performed for the temperature range of 550-800 degrees C to determine self- and tracer-diffusion coefficients for Ca and Mg and in calcite. The resulting activation energies for Ca (Ea(Ca) = 271 +/- 80 kJ/mol) and for Mg (Ea(Mg) = 284 +/- 74 kJ/mol) were used then to calculate a series of cooling rate, grain size, and closure temperature curves. The data indicate, for example, that by the diffusion of Mg in calcite, a 10 micrometers compositional zone would be completely homogenized at a temperature of 300 degrees C for cooling rates <100 K/Ma. These data provide no constraint on formation models that propose a low-temperature fluid precipitation mechanism; however, they indicate that the carbonate globules were not exposed to a high-temperature environment for long time scales following formation.

Calcium↗
PubMed2006

Characterization and quantitation of a tertiary mixture of salts by Raman spectroscopy in simulated hydrothermal vent fluid.

This article will demonstrate that Raman spectroscopy can be a useful tool for monitoring the chemical composition of hydrothermal vent fluids in the deep ocean. Hydrothermal vent systems are difficult to study because they are commonly found at depths greater than 1000 m under high pressure (200-300 bar) and venting fluid temperatures are up to 400 degrees C. Our goal in this study was to investigate the use of Raman spectroscopy to characterize and quantitate three Raman-active salts that are among the many chemical building blocks of deep ocean vent chemistry. This paper presents initial sampling and calibration studies as part of a multiphase project to design, develop, and deploy a submersible deep sea Raman instrument for in situ analysis of hydrothermal vent systems. Raman spectra were collected from designed sets of seawater solutions of carbonate, sulfate, and nitrate under different physical conditions of temperature and pressure. The role of multivariate analysis techniques to preprocess the spectral signals and to develop optimal calibration models to accurately estimate the concentrations of a set of mixtures of simulated seawater are discussed. The effects that the high-pressure and high-temperature environment have upon the Raman spectra of the analytes were also systematically studied. Information gained from these lab experiments is being used to determine design criteria and performance attributes for a deployable deep sea Raman instrument to study hydrothermal vent systems in situ.

Calibration↗
PubMed1982

Choroidal blood flow II. Reflexive control in the monkey.

Temperature measurements were taken from (1) the retina-choroid in the macula, (2) the scleral surface, or (3) the bulbar conjunctiva of the cynomolgus monkey, while the fellow eye was exposed to a moderate-intensity light source. Light stimulation produced an increase in tissue temperature in the non-light-stimulated eye. The increase in tissue temperature presumably results from a reflexive increase in choroidal blood flow. Hydrogen washout measurements of blood flow in the retina-choroid confirmed this increase in flow. This active mechanism, along with the passive ability of the choroidal circulation to dissipate light-generated heat, may be an important physiologic safeguard in helping to maintain a stable temperature environment for the outer retinal layers in the macula.

Animals↗
PubMed2005

Effect of temperature and insecticide stresses on Aedes aegypti larvae and their influence on the susceptibility of mosquitoes to dengue-2 virus.

Two major factors, higher temperatures and the application of insecticides, can drastically alter the genetic structure of a vector mosquito population. Due to these two stresses, the majority of the population gets wiped out, but the ones that withstand the stress and survive are likely to pass on survivability, and have an altered physiology. Our study shows that exposures to higher temperatures and DDT during the larval stage affects their susceptibility as adult mosquitoes to the DEN-2 virus. The overall transcription and translation status of heat shock protein (Hsp70) in virus high- and low-susceptible was the same as that in other batches. In the case of a DDT-resistant (R-7) strain two bands were obtained during RT-PCRs after heat shock. These two alleles were obtained only with HY-1 in which R-7 males were used for the crosses, suggesting that the second allele is probably male sex linked. The higher expression of Hsp70 may provide DDT-resistant strains a better chance of survival high temperature environments, particularly in homozygotes and hybrids. It was also interesting to note that these strains have a significantly lower susceptibility to the virus. Wide-spread DDT-resistance and a rise in temperature above the average temperature during summer may result in a population with a low susceptibility to the virus. Several families of heat shock proteins are known to be expressed in mosquitoes, and may have a cumulative role in determining susceptibility to the virus, which itself is governed by several genes.

Animals↗
PubMed2006

Alteration of foot temperature in diabetic neuropathy: is it another piece of puzzle?

Poor glycaemic control and the duration of diabetes mellitus are known to accelerate development and progression of neuropathy. Diabetic co-morbidities: hypertension and hyperlipidaemia, have been postulated to associate with development of neuropathy. A diabetic foot with low temperature and frequent exposure to low temperature environment has recently been hypothesized to be at higher risk to develop early neuropathy. This cross-sectional study is undertaken to identify risk factors for diabetic neuropathy and the association between foot temperature and development of diabetic neuropathy by using simple clinical examination in the outpatient setting. From April 18, to April 30, 2005, universal sampling method was used to select 134 diabetic patients (type 1 or type 2 for >1 year) with peripheral neuropathy. Excluded are those with chronic alcoholism, drug-induced neuropathy, dietary history of vitamin B deficiency and family history of porphyria and hereditary sensorimotor neuropathy. The patient's duration of diabetes, glycaemic control status and the presence of co-morbids: hypertension and hyperlipidemia, were recorded. The temperature of the foot was measured by using thermo buddy. Of 134 patients representing Malaysian ethnic distribution with an equal number of males and females, 20.1% were in the age group of 61 to 65 years and, 85.1% and 67.9% belonged to lower socioeconomic and educational groups respectively. Associations between diabetic neuropathy and glycaemic control (p = 0.018) and duration of diabetes (p < 0.05) were significant. However, hypertension, hyperlipidaemia and low foot temperature were not significantly associated with development of diabetic neuropathy. Poor glycaemic control is significantly associated with diabetic neuropathy. Foot temperature alteration is merely an effect of autonomic neuropathy with a cold foot is attributed to co-existing peripheral arterial disease.

Adult↗
PubMed1997

Pressure-enhanced activity and stability of a hyperthermophilic protease from a deep-sea methanogen.

We describe the properties of a hyperthermophilic, barophilic protease from Methanococcus jannaschii, an extremely thermophilic deep-sea methanogen. This enzyme is the first protease to be isolated from an organism adapted to a high-pressure-high-temperature environment. The partially purified enzyme has a molecular mass of 29 kDa and a narrow substrate specificity with strong preference for leucine at the P1 site of polypeptide substrates. Enzyme activity increased up to 116(deg)C and was measured up to 130(deg)C, one of the highest temperatures reported for the function of any enzyme. In addition, enzyme activity and thermostability increased with pressure: raising the pressure to 500 atm increased the reaction rate at 125(deg)C 3.4-fold and the thermostability 2.7-fold. Spin labeling of the active-site serine revealed that the active-site geometry of the M. jannaschii protease is not grossly different from that of several mesophilic proteases; however, the active-site structure may be relatively rigid at moderate temperatures. The barophilic and thermophilic behavior of the enzyme is consistent with the barophilic growth of M. jannaschii observed previously (J. F. Miller et al., Appl. Environ. Microbiol. 54:3039-3042, 1988).

Journal Article↗
PubMed2005

Development and validation of a dynamic vapor sorption-fast gas chromatography-flame ionization detection method for rapid analysis of volatile release from glassy matrices.

Historically, saturated salt solutions in desiccators have been used to investigate the effects of increasing relative humidity and temperature on the volatile retention efficiency of amorphous glasses. Obtaining data using desiccators is a static process that gives the researcher discrete data points with which to draw conclusions. Dynamic vapor sorption (DVS; SMS, London, U.K.) is a humidification system that creates specific relative humidity and temperature environments within a chamber that contains the material being investigated. This study had two specific aims: (1) to develop a DVS-fast GC-FID method that dynamically evaluates the effects of humidification and temperature increases on volatile release from amorphous carbohydrate glasses and (2) to evaluate the validity of the DVS-fast GC-FID method. Artificial cherry Durarome (Firmenich, Plainsboro, NJ) was used as the model system. The DVS-fast GC-FID method proved to be an innovative, accurate, and precise technique that can be used to conduct humidification/temperature-volatile release studies.

Benzaldehydes↗