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At least 55 records · Page 3Linked to original sources
PubMed2004

On the origin of high-temperature ferromagnetism in the low-temperature-processed Mn-Zn-O system.

The recent discovery of ferromagnetism above room temperature in low-temperature-processed MnO(2)-ZnO has generated significant interest. Using suitably designed bulk and thin-film studies, we demonstrate that the ferromagnetism in this system originates in a metastable phase rather than by carrier-induced interaction between separated Mn atoms in ZnO. The ferromagnetism persists up to approximately 980 K, and further heating transforms the metastable phase and kills the ferromagnetism. By studying the interface diffusion and reaction between thin-film bilayers of Mn and Zn oxides, we show that a uniform solution of Mn in ZnO does not form under low-temperature processing. Instead, a metastable ferromagnetic phase develops by Zn diffusion into the Mn oxide. Direct low-temperature film growth of Zn-incorporated Mn oxide by pulsed laser deposition shows ferromagnetism at low Zn concentration for an optimum oxygen growth pressure. Our results strongly suggest that the observed ferromagnetic phase is oxygen-vacancy-stabilized Mn(2-x)Zn(x)O(3-delta.).

Magnetics↗
PubMed2006

The temperature-dependence of rapid low temperature reactions: experiment, understanding and prediction.

Despite the success of the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) method in measuring rate coefficients for neutral-neutral reactions of radicals down close to the very low temperatures prevalent in dense interstellar clouds (ISCs), there are still many reactions of potential importance in the chemistry of these objects for which there have been no measurements of low temperature rate coefficients. One important class of reactions is that between atomic and molecular free radicals and unsaturated hydrocarbons; that is, alkynes and alkenes. Based on semi-empirical arguments and correlations of 'room temperature' rate coefficients, k(298 K), for reactions of this type with the difference between the ionisation energy of the alkyne/alkene and the electron affinity of the radical, we suggest which reactions between the radicals, C(3P), O(3P), N(4S), CH, C2H and CN, and carbon chain molecules (Cn) and cyanopolyynes (HC2nCN and NCC2nCN) are likely to be fast at the temperature of dense ISCs. These reactions and rate coefficients have been incorporated into a purely gas-phase model (osu2005) of ISC chemistry. The results of these calculations are presented and discussed.

Journal Article↗
PubMed2004

[Effect of long-term suboptimal temperature and short-term low temperature under low light density on cucumber growth and its photosynthesis].

The study on the effects of long-term suboptimal temperature (T1) and short-term low temperature (T2) under low light density on cucumber seedling's growth and its photosynthesis showed that the growth speed, photosynthetic rate (Pn), carboxylation efficiency (CE), apparent quantum yield (AQY) and actual quantum yield of P(S II) electron transport (phi(PS II)) all declined remarkably, and the photochemical efficiency of PS II (Fnu/Fm) also decreased to some extent. The decreasing extents of Pn, CE and AQY of T1 were less than those of T2, while the recovery rate of T1 was slower than that of T2. The Fnu/Fm and phi(PS II) of T1 declined to less extent and resiled quickly, while those of T2 decreased to larger extent and recovered slowly. The contents of chlorophyll a, chlorophyll b and carotenoid of T1 increased remarkably after being treated, while those of T2 decreased evidently. The Chl a/b of both T1 and T2 declined remarkably. With recovery time going, the pigment of T1 declined under most conditions, while that of T2 increased gradually. Three days later, the pigment content of T1 and T2 were both higher than control. The Chl a/b had no significant change during the recovery period, and was still obviously lower than control.

Cucumis sativus↗
PubMed1999

Effect of low temperature on microbial growth: lowered affinity for substrates limits growth at low temperature.

The effect of environmental temperature on the affinity of microorganisms for substrates is discussed in relation to measurements of affinity by either K(s) values or specific affinity (a(A)). It can be shown for psychrophiles, mesophiles and thermophiles that when a(A) is used as the measure of affinity, affinity decreases consistently as temperature drops below the optimum temperature for growth. This effect may be because of stiffening of the lipids of the membrane below the temperature optimum, leading to decreased efficiency of transport proteins embedded in the membrane. The lower temperature limit for growth is, therefore, that temperature at which an organism is no longer able to supply the maintenance requirement of the growth rate-limiting nutrient because of loss of affinity for that substrate. This linking of temperature and affinity for substrates taken up by active transport (a temperature-modulated substrate affinity model) includes uptake of both organic and inorganic substrates. This effect of decreased substrate affinity at low temperature may have profound implications on the availability of substrates in the natural environment as environmental temperatures change. At temperatures below their optimum for growth microorganisms will become increasingly unable to sequester substrates from their environment because of lowered affinity, exacerbating the anyway near-starvation conditions in many natural environments.

Journal Article↗
PubMed1976

Identification of PCB's in the presence of DDT-type compounds using low temperature luminescence.

Low temperature (77 degrees K) luminescence spectra of polychlorinated biphenyls (PCB's), DDT-type compounds and mixtures suggest a simplified method for identification and quantitation of aromatic pesticides with minimal prior sample treatment. Spectral differences allow identification of PCB's in the presence of DDT and the converse. Approximate detection limits, possible interferences and suggestions for further work are discussed

Cyclohexanes↗
PubMed1983

Characterization of the glucocorticoid receptor translocated to the nucleus in intact AtT-20 mouse pituitary tumor cells at low temperatures.

Although low temperatures retard the nuclear translocation of glucocorticoid-receptor complexes, they do not completely inhibit it. To gain insight into the mechanism of nuclear translocation, we determined the Stokes radius and surface charge density of the receptors bound to the nucleus at 0 C and compared them with the values obtained from standard preparations of activated and unactivated glucocorticoid receptors. Specifically, intact, viable AtT-20 cells were incubated at 0 C for 3 h with 10 nM tritiated triamcinolone acetonide and the nuclear receptor extracted with 0.3 M KCl/20 mM sodium molybdate. These nuclear receptors were found to elute from an Agarose A 1.5 m column with a Stokes radius identical to that of an "activated" receptor (6.4 nm) but eluted from a DEAE column at the same position as an "unactivated" species (0.17 M KCl). From these results we hypothesize that the change in receptor structure that leads to nuclear binding is a multistep process, and although the change in molecular size may be a prerequisite for nuclear binding, the change in surface charge is not.

Animals↗
PubMed1981

[Functional and structural changes of E. coli membranes induced by low temperature freezing].

Low temperature freezing of E. coli cells causes a fall in endogenous respiration and stimulation of respiration by the non-penetrant substrate NADH. This decrease is not due to disturbances in the function of electron transport chain, since the dehydrogenase and oxidase activities and cytochrome content in the membranes of intact and frozen cells are practically the same. Frozen E. coli cells are incapable of ATP synthesis by artificial proton motive force, although the ATPase activity of isolated membranes is not changed. The disturbances in the penetrability barrier of protons after freezing can be revealed from changes in pH of cell suspensions after rapid acidification. It is assumed that the cell penetrability barrier undergoes alterations causing a loss of respiration substrates and, probably, oxidative phosphorylation uncoupling. A correlation between constant damages of the membrane penetrability barrier and cell survival was established. Using spin labelling of different localization, the changes in the state of membrane surface at the intact hydrophobic lipid zone were demonstrated. It was found that freezing does not induce lipid peroxidation.

Adenosine Triphosphatases↗
PubMed2004

Changes in the thermal dissipation and the electron flow in the water-water cycle in rice grown under conditions of physiologically low temperature.

Effects of low temperature on chlorophyll (Chl) fluorescence, gas exchange rate, the amounts of xanthophyll cycle pigments (Xp) and the activities of several antioxidant enzymes were examined in the 8th leaf of two rice (Oryza sativa L.) cultivars (japonica and indica types) and rbcS antisense rice. All plants were grown hydroponically at 25/20 degrees C (day/night), and then exposed to 20/17 degrees C (day/night) after full expansion of the 8th leaf, or exposed to either 20/17 degrees C or 15/13 degrees C (day/night) during the expansion of the 8th leaf. All plants exposed to low temperatures showed a decrease in CO(2) assimilation rate without photoinhibition, and increases in the fraction of thermal dissipation in PSII, and in the electron flux through the water-water cycle (WWC) were observed. Although the increase of thermal dissipation was associated with increases in the ratio of carotenoids to Chl, the ratio of Xp to carotenoids and the de-epoxidation state of Xp, the increase of the electron flux of WWC was not accompanied by an increase in the activities of antioxidant enzymes. Such photoprotective responses did not differ between during and after full expansion of the leaf, and did not differ among the three genotypes. Quantitative analyses on the dissipation of excess light energy showed that thermal dissipation makes a larger contribution than WWC. Thus, although low temperature led to a decrease in CO(2) assimilation, rice potentially coped with the excess light energy by increasing the thermal dissipation and the electron flux of WWC under low temperature irrespective of leaf development and genotypes.

Antioxidants↗
PubMed1972

Ultrahigh-temperature activation of a low-temperature Bacillus subtilis spore germination system.

Exposure of Bacillus subtilis A spores to 115 to 125 C for several seconds activated a low-temperature germination system that remained dormant after a heat treatment that activated the normal l-alanine- and glucose-stimulated germination systems. The low-temperature germination system was characterized by an optimum temperature lower than that of the l-alanine or glucose germination systems (30 C versus 45 C), germination in the absence of exogenous germination stimulants, and the capacity for heat-induced deactivation and subsequent reactivation. The rates of activation at 115 to 125 C were exponential and were not influenced by a previous heat treatment that activated the l-alanine- or glucose-stimulated germination systems. Although activation of the low-temperature germination system was accompanied by suppression of l-alanine-stimulated germination, it did not appear to be a modification of the l-alanine germination system.

Alanine↗
PubMed2025

The SlWRKY39-SlZF61 module synergistically regulates SlGSTU42 to enhance low-temperature tolerance in tomato.

Low-temperature stress affects plant growth, and WRKY transcription factors alleviate such damage by regulating downstream genes. This study found that tomato SlWRKY39 significantly responds to low temperatures: its overexpression enhances seedling low-temperature tolerance by promoting ROS scavenging, while knockout exacerbates ROS accumulation and increases sensitivity to low temperatures. Transcriptome analysis indicated induction of glutathione metabolic pathway genes in slwrky39 plants under low-temperature stress. Y1H, EMSA, and Dual-LUC experiments confirmed that SlWRKY39 specifically binds to and activates the SlGSTU42 promoter; silencing SlGSTU42 attenuated the low-temperature tolerance conferred by SlWRKY39 overexpression, verifying that SlWRKY39 improves low-temperature tolerance via direct regulation of SlGSTU42. Additionally, SlZF61 interacts with SlWRKY39, enhancing its regulatory effect on SlGSTU42. SlZF61 overexpression strengthens low-temperature tolerance, while knockout increases sensitivity to low temperatures. In summary, under low-temperature stress, SlWRKY39 and SlZF61 are upregulated expression in tomato; SlWRKY39 binds to the SlGSTU42 promoter, and SlZF61 interacts with SlWRKY39 to form a protein complex, enhancing this binding. They synergistically activate SlGSTU42 transcription, thereby improving seedling low-temperature tolerance by scavenging ROS. This coordinated regulatory mechanism provides a new theoretical basis and practical insights for enhancing tomato low-temperature tolerance and ensuring stable production under low-temperature stress conditions.

Solanum lycopersicum↗