Temperature-dependent Processes Research Articles

Excitation Spectra of Photoluminescence Bands in Cd1–xMnx Te

The excitation spectra of photoluminescence bands B (2.0 eV), C (1.2 eV), and D (1.4 to 1.6 eV) are investigated at 5 and 78 K in Cd1–xMnxTe single crystals for 0.40 ≦ x ≦ 0.70. The data for the B-band are interpreted in terms of the model of Mn2+ intra-ion d–d transitions. The disagreement of some experimental results with this model is discussed. The photoluminescence band C, in contrast to B, is excited by several different temperature-dependent processes. The models based on the common excitation mechanism for the B and C photoluminescence bands are shown to be insufficient to interpret the experimental results. [Russian Text Ignored].

Temperature and viscosity effects on fluorescence in 9-t-butylanthracene

Temperature and viscosity effects on the fluorescence in 9-t-butylanthracene (TBA) have been investigated over a wide temperature range (77–365 K) by measuring fluorescence lifetimes with the time-correlated single-photon counting technique. In non-viscous solvents such as isopentane, ethanol and EPA τƒ increases from ca. 0.2 ns at room temperature to a maximum value of 15.9 ns at ca. 123 K, but the fluorescence decays always remain single exponential. The activation energies and frequency factors associated with temperature-dependent radiationless processes are calculated to be ca. 21 kJ mol–1 and 1013 s–1, respectively. On the other hand, τf values in highly viscous solvents such as glycerol and poly(methyl methacrylate)(PMMA) are already rather long at room temperature (4–10 ns), and the fluorescence decays are not single exponential but are analysed as double or triple exponential. A detailed analysis of the multiple exponentials yields 7.8 ± 1.2 kJ mol–1 and (2.8 ± 0.1)× 109 s–1 as the activation energy and frequency factor, respectively, for the radiationless process from S1 in PMMA. A large difference in the frequency factors between the non-viscous solvents and in PMMA implies the existence of two different temperature-dependent radiationless processes from S1. Very fast [graphic omitted] internal conversion is thought to be dominant in non-viscous solvents. However, in PMMA this internal conversion is totally suppressed and instead decay via an intermediate X, which may finally lead to 9-t-butyl-9,10-(Dewar anthracene), is proposed to be competitive with fluorescence, thus making the fluorescence decay double exponential.

On the Recruitment of O-Group Plaice in the North Sea

(i) Variability in North Sea plaice recruitment seems to be generated mainly during the egg stage. (ii) Density-dependent mortality processes, if they apply, are likely to operate in the early post-larval stage in the nurseries. However, the data do not exclude the possiblity that such processes are lacking or insignificant in juvenile plaice. (iii) An inverse relationship between length and abundance, observed in O-group plaice, appears to be generated by temperature-dependent processes in the egg stage, affecting the rate of egg development and egg mortality. (iv) Recruitment fluctuations in North Sea plaice are probably mainly generated by between-year temperature differences experienced during the egg stage. Variations in egg production by the adult stock might also affect recruitment, but in the range of stock sizes considered the effect seems less important.

Inhibition of agonist-induced degradation of muscarinic cholinergic receptor by quinacrine and tetracaine—possible involvement of phospholipase A 2 in receptor degradation

Muscarinic cholinergic receptors (mAChR) are degraded on the addition of agonists through energy- and temperature-dependent processes, probably with clustering and endocytosis. Pretreatment of guinea-pig vas deferens with 0.5 mM quinacrine or 5 mM tetracaine, phospholipase A 2 (PLase A 2) inhibitors, inhibited the ACh-induced degradation of mAChR in the smooth muscle and kept mAChR on the surface membrane, while cocaine and procaine were not effective. On pretreatment with quinacrine or tetracaine the PLase A 2 activity in the smooth muscle decreased continuously during culture without change in the contractile response of the tissue. Pretreatment with cocaine and procaine which had no significant effect on the down regulation of mAChR did not inhibit PLase A 2 activity. However, activation of PLase A 2 by long-term culture of the muscle with ACh and formation of endogenous inhibitor of PLase A 2 were not observed under our experimental conditions. The participation of PLase A 2 in the agonist-induced degradation of mAChR is discussed in the light of these findings.

In vitro maturation and fertilization of bovine oocytes are temperature-dependent processes.

Effects of temperature on bovine sperm acrosome reaction, oocyte maturation, hyaluronic acid production by cumulus cells and in vitro fertilization were studied. Viability and a true acrosome reaction of bovine spermatozoa were impaired at 40 degrees C. Temperatures lower than 35 degrees C did not enhance the acrosome reaction. However, viability between 30 degrees C-38 degrees C was not altered after 22 h of incubation. The optimal temperature for the acrosome reaction was 38 degrees C. Labeled glucosamine incorporation into glycosaminoglycans was not different among temperatures of 35 degrees C, 37 degrees C or 39 degrees C, whereas 41 degrees C caused a significant reduction (P less than 0.02). Temperatures ranging between 35 degrees C-39 degrees C had no deleterious effects on resumption and completion of meiosis, but at 41 degrees C the frequency of oocytes that progressed to Metaphase II was significantly reduced (P less than 0.0001). Ova matured at 39 degrees C had significantly higher rates of fertilization than at 35 degrees C, 37 degrees C, or 41 degrees C. Killed spermatozoa (control) had no effect on ovum activation at 39 degrees C. From these results it was concluded that events occurring prior to and during fertilization are temperature sensitive.

Interactions between a Lizard and Its Thermal Environment: Implications for Sprint Performance and Space Utilization in the Lizard Uta Stansburiana

At the end of their breeding season, male side-blotched lizards, Uta stansburiana, from western Colorado decreased their home range to a size not different from that of females. Both males and females showed a high degree of overlap in home ranges, not found in populations previ- ously studied in Texas. Uta's sprint speed was dependent on body temperature, with maximum sprint speed occurring at body temperatures between 35? and 38cC, with lower speeds at higher and lower tem- peratures. An energy budget model was used to predict the range of body temperatures (and thus sprint speeds) available to lizards in four microhabitats within each animal's home range. Predicted body temperatures were converted to a space-time index. The distribution of the space-time index in each microhabitat was used to predict the spatial and temporal distributions of lizards. Predicted distri- butions accurately reflected the measured distributions of lizards in the morning and late afternoon, but did not reflect the measured distributions during midday. These inconsistencies are thought to be the result of lizard responses to other temperature-dependent processes, such as evaporative water loss.

Dielectric properties of microemulsions and of their liquid crystalline mesophases

Isotropic w/o microemulsions as well as the liquid crystalline (LC) phase that develops in the former upon water addition, were investigated as a function of increasing water concentration, mass fraction, in the interval 0.024-0.8. We measured: the complex permettivity in the frequency range 16Hz–50MHz; concentration dependence of both ϵ′ and ϵ′ at the different frequencies; the thermally stimulated dialectric polarization release (TSD); and the electro-optical behavior. The different structures that develop in isotropic microemulsions as water is added, were analyzed. An accurate description of the temperature-dependent relaxation processes occuring both in the isotropic state and in the LC phase of these systems was obtained and their activation energy and relaxation time calculated. Two different structures, of lyotropic nature, respectively of cylindrical and lamellar type, were identified; their concentration range of existence and temperature domain were determined. The concentration regions where the transition occurs from an isotropic microemulsion to an LC mesophase (0.3–0.48) and from the first to the second lyotropic LC structure (0.580-0.605) were also investigated.

Huntington's disease: Glutamate and aspartate metabolism in blood platelets

The metabolism of two excitatory amino acids, glutamate and aspartate, was determined in human blood platelets because of their hypothetical involvement in the etiology of the heritable neurodegenerative disorder, Huntington's disease (HD). The specific activities of the two acids and their amides, glutamine and asparagine, constitute markers for the efficiency of the enzymatic cascades originating from [ 3H]acetate and [ 14C]glucose, respectively. Results demonstrate that both precursors are converted by temperature-dependent processes, thus indicating the presence, in platelets, of all glycolytic and tricarboxylic acid cycle enzymes necessary for the biosynthesis of glutamate and aspartate. No differences between normal and HD platelets were found in any of the specific activities investigated. A genetic defect in any of these enzymes is therefore not like to underlie HD neuropathology.

Vitrification of high-level wastes: A review of the computer thermal analyses for storage canisters

CANIST, a two-dimensional ( r and θ) computer program that solves the unsteady-state, heat-conduction equation, was used to model the thermal behavior of canisters filled with waste glass. CANIST has been found to be a valuable analytical tool for predicting the temperature profile of a waste storage canister as a function of several variables, including the diameter of the canister, the placement of internal fins, the heat generation rate of the waste glass, and the thermophysical properties of the canister and the waste glass. Thus, temperature-dependent processes that may affect the integrity of the glass/canister unit, for example cracking, can be investigated using an analytical approach.

Temperature dependence of morphological response of glioblasts to glia maturation factor.

Glioblasts respond to glia maturation factor (GMF) by outgrowth of cell processes. This morphological response takes place at 37 degrees C but not at 23 degrees C, suggesting the involvement of temperature-dependent chemical processes in the mechanism of action of GMF. The morphological response of glioblasts to GMF is correlated with the rearrangement of microtubules but not with any net change in tubulin content of the cells.

The case for Auger recombination in In1−xGaxAsyP1−y

The possible Auger recombination mechanisms in direct-gap semiconductors are investigated. These include band-to-band processes, phonon-assisted processes, and Auger recombination via shallow traps. The band-to-band Auger rates are calculated including Fermi statistics, nonparabolic bands, and screening effects both for n-type and p-type semiconductors. The nonparabolicity is calculated using the Kane-band model. The band-to-band Auger processes are characterized by a strong temperature dependence, the Auger rate decreasing rapidly with decreasing temperature. The phonon-assisted and the trap processes do not exhibit such a strong temperature dependence. This is because the additional momentum conservation for the four-particle states in band-to-band processes gives rise to a ’’threshold energy’’ for the process. For the same reason, the band-to-band Auger rate decreases rapidly with increasing band gap. In large-band-gap semiconductors the weakly temperature-dependent phonon-assisted processes are expected to dominate. The Auger recombination rate via shallow-trap levels increases with increasing trap depth. A numerical computation is carried out for the quaternary alloy In1−xGaxAsyP1−y. We find that the calculated Auger rate is significant enough to account for the observed temperature dependence of threshold current of 1.3- and 1.55-μm InGaAsP-InP double heterostructure lasers.

Gene regulation of shell banding in a land snail from Israel

The Israeli land snail, Xeropicta vestalis, offers a particularly clear example of gene regulation in relation to natural selection, in that within each population the appropriate phenotype is generated only at the correct part of the animals life cycle, and a contrasting phenotype develops when the forces of natural selection change. In the mountains of Jerusalem, where the winter is cold, the shells are dark. Westwards, towards the coastal plain where the winter is warmer, the shells gradually become paler. As dark shells absorb more radiation than pale ones, this clinal variation in morph frequencies can be explained in thermal terms. (Banded shells are also more cryptic than non-banded shells, so that in the mountains visual selection by predators may be an additional force which favours dark shells.) Xeropicta vestalis is an annual, semelparous species: the snails hatch in winter, become mature within one year, reproduce, and then die. In the coastal plain the snails are active throughout most of the year, and they have a long period in which to grow to reach adult size. In the mountains and hills, on the other hand, the snails are active for only a very short period. They spend most of their lives as small snails, in a state of aestivation. Xeropicta vestalis must be dark in mountains because when it finally awakens, it must very rapidly and hastily reach reproduction size. A dark shell, by speeding up temperature-dependent processes in this critical stage, assists the snail to mature rapidly. Shell darkness varies with age: in the mountains and hills the shells are moderately dark when they hatch, but become darker whilst growing in early winter. In the coastal plain also, the snails are moderately dark when they hatch; but here they become paler, whilst growing in winter and spring. In both cases, each snail is darker in the colder months and paler in the hot ones. A strategy of gene regulation of shell colour is thus favoured when the subsequent forces of the environment are very contrasting in their direction, very severe—yet also very predictable.

Receptor-activated and energy-dependent decrease of muscarinic cholinergic receptors in guinea-pig vas deferens

Organ cultures of guinea-pig vasa deferentia were used for studying both the decrease in muscarinic cholinergic receptor (mAChR) concentration induced by muscarinic agonists and the simultaneous decrease in contraction to ACh. After a lag period the decrease followed first-order kinetics and was completely blockd by atropine. The decrease was dependent not only on the extent of occupation of mAChR by ACh, but was also related to the efficacy of agonists as deduced from the contractions. Moreover the amount of mAChR was not affected by other contractile agents, norepinephrine and high K + even under conditions in which mAChR was occupied by atropine or pilocarpine. These findings indicate that the decrease in the amount of mAChR mediated by muscarinic receptors in vas deferens was due to the extent of both receptor occupation and receptor activation by agonists. Furthermore it was shown that the decrease involved energy- and temperature-dependent processes and that cyclic nucleotides did not regulate the quantitative level of mAChR.

Fluorescence quantum yield of oxazine and carbazine laser dyes

The structural features responsible for radiationless deactivation in Oxazine and Carbazine dyes are determined by measurement of the fluorescence quantum yield in various solvents and at different temperatures. A distinction can be made between temperature-independent radiationless processes involving H-vibrations and temperature-dependent processes which have their origin in a lack of rigidity of the molecular skeleton.

Intercellular recognition: quantitation of initial binding events.

The hypothesis that intercellular adhesion can be subdivided into two separable phenomena--an initial recognition event and a subsequent stabilization--is supported by the use of a cell binding assay that provides a quantitative measure of intercellular binding strengths. Radioactive single cells are brought into contact with cell monolayers at 4 degrees C in sealed compartments. The compartments are inverted and a centrifugal force is then applied to dislodge the probe cells from the monolayers. By varying the speed of centrifugation, the force maintaining associations between embryonic chicken neural retina cells was determined to be on the order of 10(-5) dyne. Topographic specificities of single neural retina cells for retinal monolayers from various regions of the retina were detected with this assay and corresponded to those observed in more traditional assays at 37 degrees C. Also observed were two time- and temperature-dependent stabilization processes in which the force required for dislodgment increased. One of the stabilization processes was sensitive to dinitrophenol and was inactive at 4 degrees C; the second was still active in metabolically blocked cells. The metabolic-dependent process resulted in interactions at least 13 times as strong as the initial binding. The metabolic-independent process resulted in about a 2-fold increase in binding strength and had a temperature dependence similar to that of membrane diffusional phenomena.

Temperature-dependent relaxation processes and optical properties of microemulsion mesomorphic structures

The interaction between a 33 V/cm, 0.5 Hz electric field and the liquid crystalline (LC) phase of a w/o microemulsion was studied as a function of increasing water concentration (C, mass fraction), by means of the thermally stimulated depolarization method (TSD) and electrical-anisotropy measurements. The angular dependence of the transmitted-light intensityrs. The input angle of the light electric vector was also investigated. A comparison was made between the optical and electro-optical anisotropy studies, the TSD results and the behaviour,vs. concentration, of both the real (e′) and the imaginary (e″) part of the relative complex perimttivity, at two main representative frequencies. On the basis of the experimental evidence, two different LC mesophases, of lyotropic nature, were identified and their concentration range of existence and temperature domain determined. A complete analysis of the TSD spectra associated with the two LC mesophases was performed. The activation energy and the relaxation time of the many different relaxation processes that characterize the microemulsion system at any given concentration in the interval 0.35<C<0.7 were evaluated by following the Bucci and Fieschi method.

Spurious conformational transitions in proteins?

Temperature-dependent dynamic processes in biological macromolecules can produce sharp and reversible transitions in spectroscopic properties that might be misinterpreted as evidence for thermally induced conformational changes. This provides a rational explanation for the paradoxical case of D-amino acid oxidase [D-amino-acid:oxygen oxidoreductase (deaminating), EC 1.4.3.3], for which a sharp fluorescence transition at 14 degrees C, not observed by sensitive calorimetry [Sturtevant, J. M. & Mateo, P. L. (1978) Proc. Natl. Acad. Sci. USA 75, 2584-2587], could be due to a dynamic quenching process of large activation energy, rather than a change in conformational state of the protein. Similar interpretations may be valid in other systems studied by experimental techniques that depend, directly or indirectly, on molecular relaxation processes.

Temperature-dependent absorption processes in the XeF laser

Temperature-dependent absorption processes in neon/xenon/NF3 mixtures are reported. In pure neon plasmas there are two types of absorption present; a broad but weak band of absorption is observed, which increases with increasing temperature, and a strong narrow band of absorption is observed around 351 nm. Moderate heating reduces this absorption. Improved performance of the XeF laser at elevated temperature is primarily due to reduced absorption in the laser medium at 351 nm.

Test-Tube Pyrolysis--Simple Technique for Identifying Yield and Maturity of Source Rocks: ABSTRACT

When small samples (i.e., well cuttings) of kerogen-rich rock are pyrolyzed in a test tube placed over a propane torch, oil-like material may be generated and condense as a brown residue around the walls of the tube. This simple technique may be used to identify source rocks capable of generating liquid oil. The artificial test-tube-generating process is believed to be similar to that associated with natural time- and temperature-dependent processes accompanying rock burial in depositional basins. The relative amount of oily residue pyrolytically generated in a test tube is therefore a semi-quantitative measure of the natural oil-generating capacity of the rock. Source rocks which have been subjected to advanced stages of thermal maturation are not capable of generating l quid hydrocarbons and therefore End_Page 496------------------------------ do not yield oily pyrolysis residues. The disappearance of pyrolysis residues from rock samples representing deep-burial and high-temperature histories relative to those which yield good residues at shallower depths and lower temperatures may be utilized to determine the depth of the oil-generating to gas-condensate-generating maturity threshold. The technique has been utilized to map source-rock distributions and maturity thresholds in the Pennsylvanian of the western Anadarko basin. End_of_Article - Last_Page 497------------

Activation of fracture mechanisms

The method of analyzing the activation of fracture mechanisms under the influence of generalized forces is described, leading to a generalized approach to the problem of time- and temperature-dependent fracture processes. The analysis of complex fracture mechanisms of the type necessary for the simultaneous fracture of two phases is discussed. Fracture processes are described in terms of a network of events that can occur both sequentially and simultaneously.