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PubMed1999

High-temperature pulsed-field-gradient multidimensional NMR of polymers.

The application of pulsed-field-gradient (PFG) techniques has been particularly important in providing the ability to detect 2D and 3D NMR cross peaks from minor structural components in synthetic organic polymers. The lack of mobility in a large percentage of polymers leads to rapid T2 relaxation which prevents the use of pulse sequences, such as the HMBC experiment, that operate based on coherence transfer via small, long-range J couplings. High-temperature NMR increases molecular motion with corresponding line narrowing (e.g., polyethylenes are typically analyzed at 120 degrees C). However, until now, the requirement for high temperature has precluded the use of PFG methods. Here we present data from a new probe which is capable of performing high-temperature PFG coherence selection experiments at temperatures typical of those used in many polymer analyses. We illustrate the performance of this probe with PFG-HMBC spectra of a copolymer from ethylene/1-hexene/1-butene at 120 degrees C.

Magnetic Resonance Spectroscopy↗

PubMed1990

High temperature enhances cytotoxicity of mercury (HgCl2) on HeLa S3 cells.

The combined effect of mercury (HgCl2) and high temperature on the growth and synthesis of nucleic acid and protein, and on the cell cycle of HeLa S3 cells was investigated. The subsequent growth of the cells was dose-dependently inhibited by mercury at 37.2 degrees and 41.2 degrees C. The inhibitory effect of mercury on subsequent growth was enhanced at the higher temperature. IC50 values for DNA and RNA synthesis but not protein synthesis, at 41.2 degrees C, were significantly lower than those at 37.2 degrees C (P less than 0.05, P less than 0.01, respectively). Flow cytometric analysis using synchronous cells indicated the possibility of blocking of cell cycle progression in the early part of S phase by the combined treatment. These results suggest that the cytotoxicity of mercury to cell growth was enhanced at the higher temperature and that this enhancement is related to the increased inhibitory effect of mercury on DNA and RNA synthesis and on the cell cycle at high temperatures.

Cell Cycle↗

PubMed2005

Temperature alternation by an on-chip microheater to reveal enzymatic activity of beta-galactosidase at high temperatures.

A method to measure enzymatic activity at high temperatures by rapid temperature alternation of a microreactor with a microheater is proposed. On-chip microreactor and microheater were integrated on a glass plate by MEMS technology; this microheater can control the temperature of the microreactor with a response speed of 34.2 and 31.5 K/s for temperature rise and fall, respectively, with an accuracy of 3 degrees C. The enzyme, beta-galactosidase, was revealed to survive short exposure (4-s pulses) to temperatures above that which would "normally" denature them. Its activity at 60 degrees C was revealed to be approximately 4 times greater than that at room temperature. This method not only gives new kinetic information in biochemistry but also enables application in highly sensitive biosensors.

Hot Temperature↗

PubMed2002

High temperature oxidation of C2Cl4/CH4 mixtures.

Experiments on high temperature oxidation of multi-chlorinated hydrocarbons, tetrachloroethylene (C2Cl4), with hydrocarbon fuels, CH4, were performed in a 15 mm i.d. tubular flow reactor. Temperatures ranged from 700 to 850 degrees C, with the average residence time in the range from 0.3 to 1.5s. Three equivalence ratios, phi=0.87 (fuel-lean (FL)), phi=1 (stoichiometry (S)), and phi=1.3 (fuel-rich (FR)), were studied. The global Arrhenius equations for the decomposition of C(2)Cl(4) for each reactant set ratio are: k(lean)=5.77 x 10(15) exp(-30447/RT), k(stoi)=5.15 x 10(15) exp(-30421/RT), and k(rich)=6.32 x 10(14) exp(-28879/RT). The important reactions for destruction of parent C2Cl4 include: C2Cl4 --> C2Cl3 + Cl, C2Cl4 + H--> C2Cl3 + HCl and C2Cl4 + H --> C2HCl3 + Cl. The resulting reactant loss, and intermediate and final product profiles were determined. C2HCl3, C2Cl2, CO, CO2 and HCl are the major products for the reaction of C2Cl4/CH4/O2 mixtures for these three reaction systems. Minor intermediates include C2H3Cl, C2HCl, COCl2, CH3CHCl2, C2H4, C2H6, CCl2CHCH3 , trans-CHClCHCl, cis-CHClCHCl, trans-ClHC=CClCH(3), C6H6, and Cl2. The experimental data showed that as the oxygen concentration increased, the temperature needed to detect the resulting products decreased.

Environmental Pollutants↗

PubMed2005

Three-dimensionality of field-induced magnetism in a high-temperature superconductor.

Many physical properties of high-temperature superconductors are two-dimensional phenomena derived from their square-planar CuO2 building blocks. This is especially true of the magnetism from the copper ions. As mobile charge carriers enter the CuO2 layers, the antiferromagnetism of the parent insulators, where each copper spin is antiparallel to its nearest neighbours, evolves into a fluctuating state where the spins show tendencies towards magnetic order of a longer periodicity. For certain charge-carrier densities, quantum fluctuations are sufficiently suppressed to yield static long-period order, and external magnetic fields also induce such order. Here we show that, in contrast to the chemically controlled order in superconducting samples, the field-induced order in these same samples is actually three-dimensional, implying significant magnetic linkage between the CuO2 planes. The results are important because they show that there are three-dimensional magnetic couplings that survive into the superconducting state, and coexist with the crucial inter-layer couplings responsible for three-dimensional superconductivity. Both types of coupling will straighten the vortex lines, implying that we have finally established a direct link between technical superconductivity, which requires zero electrical resistance in an applied magnetic field and depends on vortex dynamics, and the underlying antiferromagnetism of the cuprates.

Copper↗

PubMed2001

Thermodynamics of the interplay between magnetism and high-temperature superconductivity.

Copper-oxide-based high-temperature superconductors have complex phase diagrams with multiple ordered phases. It even appears that the highest superconducting transition temperatures for certain cuprates are found in samples that display simultaneous onset of magnetism and superconductivity. We show here how the thermodynamics of fluid mixtures-a touchstone for chemistry as well as hard and soft condensed matter physics-accounts for this startling observation, as well as many other properties of the cuprates in the vicinity of the instability toward "striped" magnetism.

Journal Article↗

PubMed2001

Analytic models of high-temperature hohlraums.

A unified set of high-temperature-hohlraum models has been developed. For a simple hohlraum, P(S)=[A(S)+(1-alpha(W))A(W)+A(H)]sigmaT(4)(R)+(4Vsigma/c)(dT(4)(R)/dt), where P(S) is the total power radiated by the source, A(S) is the source area, A(W) is the area of the cavity wall excluding the source and holes in the wall, A(H) is the area of the holes, sigma is the Stefan-Boltzmann constant, T(R) is the radiation brightness temperature, V is the hohlraum volume, and c is the speed of light. The wall albedo alpha(W) identical with(T(W)/T(R))(4) where T(W) is the brightness temperature of area A(W). The net power radiated by the source P(N)=P(S)-A(S)sigmaT(4)(R), which suggests that for laser-driven hohlraums the conversion efficiency eta(CE) be defined as P(N)/P(Laser). The characteristic time required to change T(4)(R) in response to a change in P(N) is 4V/c[(1-alpha(W))A(W)+A(H)]. Using this model, T(R), alpha(W), and eta(CE) can be expressed in terms of quantities directly measurable in a hohlraum experiment. For a steady-state hohlraum that encloses a convex capsule, P(N)=[(1-alpha(W))A(W)+A(H)+[(1-alpha(C))A(C)(A(S)+alpha(W)A(W))/A(T)]]sigmaT(4)(RC), where alpha(C) is the capsule albedo, A(C) is the capsule area, A(T) identical with(A(S)+A(W)+A(H)), and T(RC) is the brightness temperature of the radiation that drives the capsule. According to this relation, the capsule-coupling efficiency of the baseline National Ignition Facility hohlraum is 15-23 % higher than predicted by previous analytic expressions. A model of a hohlraum that encloses a z pinch is also presented.

Journal Article↗

PubMed1996

Construction and characterization of a Yersinia enterocolitica O:8 high-temperature requirement (htrA) isogenic mutant.

The high-temperature requirement (HtrA) family of stress response proteins are induced by different environmental stress conditions in a variety of bacteria and have been shown to contribute to the pathogenicity of some of these species. In this study, the htrA gene from Yersinia enterocolitica O:8 was amplified, cloned, and sequenced. Analysis of the deduced amino acid sequence predicted that the putative HtrA homolog contains a serine protease active site and a catalytic triad characteristic of trypsin-like serine proteases, structural features characteristic of previously described HtrA proteins. In order to evaluate the biological functions of Y. enterocolitica HtrA, an isogenic mutant was constructed by a reverse-genetics PCR-based approach. Characterization of the mutant provided evidence supporting a stress response function for the Y. enterocolitica htrA gene product. In contrast to the parent strain, the mutant showed increased sensitivity to killing by H2O2, O2- and temperature stress (50 degrees C). The mutant was avirulent in the murine yersiniosis injection model and offered partial protection to mice challenged with the parent strain. Further studies with the Y. enterocolitica htrA mutant should increase our knowledge of the host-pathogen interactions which occur during Yersinia infections.

Amino Acid Sequence↗

PubMed1971

Induction of colicin 1a at high temperature.

Induction of colicin la at a high temperature (42 C) was demonstrated in a wild strain of Shigella sonnei. After transfer of the Col factor, a similar effect was observed in those recipient cells acquiring colicinogeny. The induction is suggested to be due to the presence of a thermosensitive colicin repressor. The wild-type strain segregated sensitive cells and showed heterogeneity in colicin production.

Chloroform↗

PubMed1995

Evidence for organic synthesis in high temperature aqueous media--facts and prognosis.

Hydrothermal systems are common along the active tectonic areas of the earth. Potential sites being studied for organic matter alteration and possible organic synthesis are spreading ridges, off-axis systems, back-arc activity, hot spots, volcanism, and subduction. Organic matter alteration, primarily reductive and generally from immature organic detritus, occurs in these high temperature and rapid fluid flow hydrothermal regimes. Hot circulating water (temperature range - warm to >400 degrees C) is responsible for these molecular alterations, expulsion and migration. Compounds that are obviously synthesized are minor components because they are generally masked by the pyrolysis products formed from contemporary natural organic precursors. Heterocyclic sulfur compounds have been identified in high temperature zones and hydrothermal petroleums of the Guaymas Basin vent systems. They can be interpreted as being synthesized from formaldehyde and sulfur or HS kappa- in the hydrothermal fluids. Other products from potential synthesis reactions have not yet been found in the natural systems but are expected based on known industrial processes and inferences from experimental simulation data. Various industrial processes have been reviewed and are of relevance to hydrothermal synthesis of organic compounds. The reactivity of organic compounds in hot water (200-350 degrees C) has been studied in autoclaves, and supercritical water as a medium for chemistry has also been evaluated. This high temperature aqueous organic chemistry and the strong reducing conditions of the natural systems suggest this as an important route to produce organic compounds on the primitive earth. Thus a better understanding of the potential syntheses of organic compounds in hydrothermal systems will require investigations of the chemistry of condensation, autocatalysis, catalysis and hydrolysis reactions in aqueous mineral buffered systems over a range of temperatures from warm to >400 degrees C.

Amino Acids↗

PubMed2001

High-temperature electron paramagnetic resonance in magnets with the Dzyaloshinskii-Moriya interaction.

We analyze the high-temperature electron paramagnetic resonance (EPR) absorption in a weakly anisotropic Heisenberg magnet having two distinct types of anisotropy, represented, respectively, by a symmetric term and the Dzyaloshinskii-Moriya (DM) term. Contrary to the widespread opinion that the latter is responsible for the excessive linewidth observed in the EPR spectra of many oxides, we prove that its contribution to the linewidth is only of the same level as that of the symmetric anisotropy. This gives a solution to the long-standing controversial problem of the high-temperature magnetic relaxation in quantum-spin systems with the DM interaction.

Journal Article↗

PubMed2001

Evaluation of multielement catheter-cooled interstitial ultrasound applicators for high-temperature thermal therapy.

Catheter-cooled (CC) interstitial ultrasound applicators were evaluated for their use in high-temperature coagulative thermal therapy of tissue. Studies in ex vivo beef muscle were conducted to determine the influences of applied electrical power levels (5-20 W per element), catheter flow rate (20-60 ml min(-1)), circulating water temperature (7-40 degrees C), and frequency (7-9 MHz) on temperature distribution and thermal lesion geometry. The feasibility of using multiple interstitial applicators to thermally coagulate a predetermined volume of tissue was also investigated. Results of these studies revealed that the directional shape of the thermal lesions is maintained with increasing time and power. Radial depths of the thermal lesions ranged from 10.7 +/- 0.7 mm after heating for 4 min with an applied power level of 5 W, to 16.2 +/- 1.4 mm with 20 W. The axial length of the thermal lesions is controlled tightly by the number of active transducers. A catheter flow rate of 20 to 40 ml min(-1) (52.2 +/- 5.5 kPa at 40 ml min(-1)) with 22 degrees C water was determined to provide sufficient cooling of the transducers for power levels used in this study. In vivo temperatures measured in the center of a 3-cm-diam peripheral implant of four applicators in pig thigh muscle reached 89.3 degrees C after 4 min of heating, with boundaries of coagulation clearly defined by applicator position and directivity. Conformability of heating in a clinically relevant model was demonstrated by inserting two directional CC applicators with a 2 cm separation within an in vivo canine prostate, and generating a thermal lesion measuring 3.8 cm x 2.2 cm in cross section while directing energy away from, and protecting the rectum. Maximum measured temperatures at midgland exceeded 90 degrees C within 20 min of heating. The results of this study demonstrate the utility of single or multiple CC applicators for conformal thermal coagulation and high temperature thermal therapy, with potential for clinical applications in sites such as prostate, liver, breast, or uterus.

Animals↗

PubMed1997

Comparison of the nuclear DNA stability against freezing-thawing and high temperature treatments between spermatozoa and somatic cells.

Thermostability of sperm genome against freezing-thawing and high temperature treatments was assessed by comparing the degradation patterns of genomic DNAs from epididymal sperms and somatic tissues. Golden hamster liver, kidney, epididymal sperm, and testis were frozen and thawed repeatedly, or incubated in a hot water bath. Genomic DNAs were isolated and then separated by agarose gel electrophoresis. It was revealed that the size of sperm genomic DNA was hardly changed after freezing-thawing treatment, however, the DNA sizes of the other three tissues were gradually reduced with an increasing number of freezing-thawing cycles. In contrast, high temperature treatment appears to damage not only the genomic DNAs of somatic cells but also those of spermatozoa.

Animals↗

PubMed2005

Crystal structures and topological aspects of the high-temperature phases and decomposition products of the alkali-metal oxalates M2[C2O4] (M=K, Rb, Cs).

The high-temperature phases of the alkali-metal oxalates M2[C2O4] (M = K, Rb, Cs), and their decomposition products M2[CO3] (M = K, Rb, Cs), were investigated by fast, angle-dispersive X-ray powder diffraction with an image-plate detector, and also by simultaneous differential thermal analysis (DTA)/thermogravimetric analysis (TGA)/mass spectrometry (MS) and differential scanning calorimetry (DSC) techniques. The following phases, in order of decreasing temperature, were observed and crystallographically characterized (an asterisk denotes a previously unknown modification): *alpha-K2[C2O4], *alpha-Rb2[C2O4], *alpha-Cs2[C2O4], alpha-K2[CO3], *alpha-Rb2[CO3], and *alpha-Cs2[CO3] in space group P6(3)/mmc; *beta-Rb2[C2O4], *beta-Cs2[C2O4], *beta-Rb2[CO3], and *beta-Cs2[CO3] in Pnma; gamma-Rb2[C2O4], gamma-Cs[C2O4], gamma-Rb2[CO3], and gamma-Cs2[CO3] in P2(1)/c; and delta-K2[C2O4] and delta-Rb2[C2O4] in Pbam. With respect to the centers of gravity of the oxalate and carbonate anions, respectively, the crystal structures of all known alkali-metal oxalates and carbonates belong to the AlB2 family, and adopt either the AlB2 or the Ni2In arrangement depending on the size of the cation and the temperature. Despite the different sizes and constitutions of the carbonate and oxalate anions, the high-temperature phases of the alkali-metal carbonates M2[CO3] (M = K, Rb, Cs), exhibit the same sequence of basic structures as the corresponding alkali-metal oxalates. The topological aspects and order-disorder phenomena at elevated temperature are discussed.

Carbonates↗

PubMed1996

High temperature and drought stress effects on survival of Pinus ponderosa seedlings.

We studied the effects of high temperature and drought on the survival, growth and water relations of seedlings of Pinus ponderosa (Dougl.) Lawson, one of few coniferous tree species that can successfully colonize drought-prone sites with high soil surface temperatures. Temperature profiles were measured with 0.07-mm thermocouples in a sparse ponderosa pine forest in northern Idaho. The soil surface and the adjacent 5 mm of air reached maximum temperatures exceeding 75 degrees C, well above the lethal temperature threshold for most plants. Air temperatures 50 mm above the soil surface (seedling needle height) rarely exceeded 45 degrees C. Pinus ponderosa seedlings that survived maintained basal stem temperatures as much as 15 degrees C lower than the surrounding air. The apparent threshold temperature at the seedling stem surface resulting in death was approximately 63 degrees C for less than 1 min. No correlation between seedling mortality and needle temperature was found, although some needles reached temperatures as high as 60 degrees C for periods of </= 1 min. Surviving seedlings had significantly higher stomatal conductance than seedlings that did not survive until fall. Transpiration rates, calculated from measured needle temperatures, stomatal conductance and evaporative demand, were high (up to 16.7 mmol m(-2) s(-1)), indicating that water transport through seedling stems may have acted as a heat transfer mechanism, cooling the stem below the lethal threshold temperature. Heat exchange calculations showed that rapid water flow through seedling stems can absorb sufficient energy to reduce stem temperature by 30 degrees C during peak sunlight hours.

Journal Article↗

PubMed2004

Design of 16S rRNA-targeted oligonucleotide probes for detecting cultured and uncultured archaeal lineages in high-temperature environments.

In order to facilitate the evaluation of archaeal community diversity and distribution in high-temperature environments, 14 16S rRNA oligonucleotide probes were designed. Adequate hybridization and wash conditions of the probes encompassing most known hyperthermophilic Archaea, members of the orders Thermococcales, Desulfurococcales and Sulfolobales, of the families Methanocaldococcaceae, Pyrodictiaceae and Thermoproteaceae, of the genera Archaeoglobus, Methanopyrus and Ignicoccus, and of the as yet uncultured lineages Korarchaeota, Crenarchaeota marine group I, deep-sea hydrothermal vent euryarchaeotic group 2 (DHVE 2), and deep-sea hydrothermal vent euryarchaeotic group 8 (DHVE 8) were determined by dot-blot hybridization from target and non-target reference organisms and environmental clones. The oligonucleotide probes were also used to evaluate the archaeal community composition in nine deep-sea hydrothermal vent samples. All probes, except those targeting members of Sulfolobales, Thermoproteaceae, Pyrodictiaceae and Korarchaeota, gave positive hybridization signals when hybridized against 16S rDNA amplification products obtained from hydrothermal DNA extracts. The results confirmed the widespread occurrence of Thermococcales, Desulfurococcales, Methanocaldococcaceae and Archaeoglobus in deep-sea hydrothermal vents, and extended the known ecological habitats of uncultured lineages. Despite their wide coverage, the probes were unable to resolve the archaeal communities associated with hydrothermally influenced sediments, suggesting that these samples may contain novel lineages. This suite of oligonucleotide probes may represent an efficient tool for rapid qualitative and quantitative characterization of archaeal communities. Their application would help to provide new insights in the future into the composition, distribution and abundance of Archaea in high-temperature environments.

Archaea↗

PubMed2005

Role of HSF activation for resistance to heat, cold and high-temperature knock-down.

Regulation of heat shock proteins (Hsps) by the heat shock factor (HSF) and the importance of these proteins for resistance to heat stress is well documented. Less characterized is the importance of Hsps for cold stress resistance although Hsp70 is known to be induced following long-term cold exposure in Drosophila melanogaster. In this study, a temperature-sensitive HSF mutant line was used to investigate the role of HSF activation following heat hardening, rapid cold hardening (RCH) and long-term cold acclimation (LTCA) on heat and cold resistance, and this was correlated with Hsp70 expression. In addition, the effect of HSF activation on high-temperature knock-down resistance was evaluated. We found a significantly decreased HSF activation in the mutant line as compared to a corresponding control line following heat hardening, and this was correlated with decreased heat resistance of the mutant line. However, we did not find this difference in HSF activity to be important for resistance to cold stress or high-temperature knock-down. The findings indicate that induction of stress genes regulated by HSF, such as Hsps, although occurring following LTCA, are not of major importance for cold stress resistance and neither for RCH nor high-temperature knock-down resistance in D. melanogaster.

Acclimatization↗

PubMed2006

High concentration agglomerate dynamics at high temperatures.

The dynamics of agglomerate aerosols are investigated at high solids concentrations that are typical in industrial scale manufacture of fine particles (precursor mole fraction larger than 10 mol %). In particular, formation and growth of fumed silica at such concentrations by chemical reaction, coagulation, and sintering is simulated at nonisothermal conditions and compared to limited experimental data and commercial product specifications. Using recent chemical kinetics for silica formation by SiCl4 hydrolysis and neglecting aerosol polydispersity, the evolution of the diameter of primary particles (specific surface area, SSA), hard- and soft-agglomerates, along with agglomerate effective volume fraction (volume occupied by agglomerate) is investigated. Classic Smoluchowski theory is fundamentally limited for description of soft-agglomerate Brownian coagulation at high solids concentrations. In fact, these high concentrations affect little the primary particle diameter (or SSA) but dominate the soft-agglomerate diameter, structure, and volume fraction, leading to gelation consistent with experimental data. This indicates that restructuring and fragmentation should affect product particle characteristics during high-temperature synthesis of nanostructured particles at high concentrations in aerosol flow reactors.

Journal Article↗