Inverse Temperature Dependence Research Articles

Support for radiolabeling of a glycine recognition domain on the N-methyl-D-aspartate receptor ionophore complex by 5,7-[3H]dichlorokynurenate in rat brain.

Pretreatment with Triton X-100 more than doubled the binding of radiolabeled 5,7-dichlorokynurenic acid (DCKA), a proposed antagonist at a glycine (Gly) recognition domain on the N-methyl-D-aspartate (NMDA) receptor ionophore complex, in rat brain synaptic membranes. The binding exhibited an inverse temperature dependency, reversibility, and saturability, the binding sites consisting of a single component with a high affinity (27.5 nM) and a relatively low density (2.87 pmol/mg of protein). The binding of both [3H]DCKA and [3H]Gly was similarly displaced by numerous putative agonists and antagonists at the Gly domain in a concentration-dependent manner at a concentration range of 100 nM to 0.1 mM. Among the 24 putative ligands tested, DCKA was the second most potent displacer of the binding of both radioligands with no intrinsic affinity for the binding of [3H]kainic acid and alpha-amino-3-hydroxy-5- [3H]methylisoxazole-4-propionic acid (AMPA) to the non-NMDA receptors. In contrast, the other proposed potent Gly antagonist, 5,7-dinitroquinoxaline-2,3-dione, was active in displacing the binding of [3H]glutamic ([3H]Glu) and D,L-(E)-2-amino-4-[3H]propyl-5-phosphono-3-pentenoic acids to the NMDA recognition domain with a relatively high affinity for the non-NMDA receptors. In addition, the proposed antagonist at the AMPA-sensitive receptor, 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline, not only displaced weakly the binding of both [3H]-Gly and [3H]DCKA, but also inhibited the binding of (+)-5-[3H]methyl-10,11- dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine ([3H]MK-801) to an ion channel associated with the NMDA-sensitive receptor in the presence of added Glu alone in a manner sensitive to antagonism by further added Gly. Clear correlations were seen between potencies of the displacers to displace [3H]DCKA binding and [3H]Gly binding, in addition to between the potencies to displace [3H]-DCKA or [3H]Gly binding and to potentiate or inhibit [3H]MK-801 binding. All quinoxalines tested were invariably more potent displacers of [3H]DCKA binding than [3H]Gly binding, whereas kynurenines were similarly effective in displacing the binding of both [3H]Gly and [3H]DCKA. These results undoubtedly give support to the proposal that [3H]DCKA is one useful radioligand available in terms of its high selectivity and affinity for the Gly domain in the brain. Possible multiplicity of the Gly domain is suggested by the differential pharmacological profiles between the binding of [3H]Gly and [3H]DCKA.

Diffusivity and Solubility of Hydrogen in Grain-Refined Aluminum

Diffusion coefficients and solubilities of hydrogen in grain-refined aluminum have been measured by a vacuum hot extraction method. Four samples with different grain sizes are prepared by melting, addition of Ti and B, casting, remelting and unidirectional solidification. Grain-refined samples contain some small particles in the matrix. The hydrogen diffusivity follows an Arrhenius type linearity on an inverse temperature dependence at 573 to 873 K. The diffusivity is not influenced by the small particles in the matrix, and depends only on the grain size. We have confirmed a propriety of the «Grain Boundary Cross Effect » relating to both of a fast diffusion along grain boundaries and of a suppressed diffusion by a hydrogen trapping at nodes or junctions of grain boundaries

Tunneling transfer of an electron in oxidation of the HS? ion by an I 3 ? complex in aqueous solution

Methods of chemical kinetics have been used in a study of the mechanism of hydrogen sulfide oxidation by iodine. It has been shown that the stage of electron transfer from HS− to the I3/− complex proceeds through a tunneling mechanism. A proposed “twinkling” model of the reaction mechanism provides an explanation for the observed experimental facts: the dependence of the rate constant on the acidity, viscosity, and ionic strength of the solution; the inverse temperature dependence of the reaction rate constant; the dependence of the reaction rate constant on the concentrations of iodide ion and maleic acid, which are not involved directly in the reaction.

Topological excitations vs intergranular phase ? coherence in a HTSC Y0.5Sm0.5Ba2Cu3O7 ceramics

This paper reports a detailed study of the electrical transport properties of good quality superconducting Y0.5Sm0.5Ba2Cu3O7 ceramic samples. Analyses of the dependence of resistance on temperature, the relations current-voltage and the magnetoresistance allows to identify:a) the mean field critical temperature (TCO=93.73±0.01 K);b) a power law behaviorV∼≅Iα atT<TCO. The α exponent jumps abruptly from 1 to 3, at a certain temperatureTC=93.276±0.005 K;c) an exponential inverse root-square temperature dependence of the resistivity in theTC−TCO temperature range. These features, typically observed when topological excitations sets in two dimensional systems, can also be interpreted as a signature of a percolation process and a transition towards intergranular phase coherence. We analyze and discuss the relevance of both models to account for the experimental data.

複合電析膜加熱法によるＮｉ‐Ａｌ合金膜の組織と硬度

Electrodeposited composites of Ni-metallic Al particles about 9μm in diameter have been successfully prepared in the form of flat, 400μm-thick films ranging in composition from 0 to 28.3at% Al. The films were then heated at 800°C for 3h. The structures and hardness of the resultant films were then studied by X-ray diffraction, X-ray microanalysis, and measurement of Vickers hardness from room temperature to 750°C. It was found that the matrix and the particles reacted readily to form stable phases: the Ni-5at% Al alloy was a single-phase alloy of fcc solid solution; the Ni-16 and 17at% Al alloys were dual phase alloys of fcc solid solution and Ni3Al; the Ni-25at% Al alloy was a single phase alloy of Ni3Al; and the Ni-28.3at% Al alloy was a dual phase alloy of Ni3Al and NiAl. All the alloys contained small Al2O3 particles, which were found initially to be consist of hydroxide films covering metallic Al particles. The room-temperature hardness of the alloys increased with the Al content. Hot hardness measurement of Ni-60vol% Ni3Al alloy showed an inverse temperature dependence of hardness, which is characteristic of the Ni3Al phase.

Dynamic equilibria between subcomponents of CĪ, the first component of human complement

Clr̄ and Cls̄, the serine protease components of activated Cl, form a tetramer in the presence of Ca 2+. The stability of this tetramer is sufficient that its association with the third component, Clq, has been successfully treated as a reversible bimolecular equilibrium reaction [Siegel and Schumaker, Molec. Immun. 20, 53–66 (1983)]. We have used the fluorescence anisotropy ( A) of fluorescein-labeled Cls̄ (s ∗) to monitor assembly and subcomponent exchange in 0.15 mol/1 NaCl, 0.001 mol/l Ca 2+ 0.02 mol/l Tris, pH 7.4. Addition of q to r 2s 2 ∗ causes a small but measurable Δ A of 0.01–0.02. The response is too fast to measure at 37° but can be readily followed at 4° where t 1 2 = 0.6 min when [q] = [r̄ 2s̄ 2 ∗] = 0.5 μmol/l. The increase in A can be readily reversed by dilution or by addition of unlabeled Cls̄. Slow incremental addition of q to a solution of r̄ 2s̄ 2 ∗ produces a dose-dependent Δ A from which stoichiometry and dissociation constants can be derived. Measurements of K d as a function of temperature establish an inverse temperature dependence with Δ H = − 15 kcal/mol and a value of K d = 0.031 μmol/l at 37° († G = + 11, T† S = − 26 kcal/mol). Thus, the assembly process appears to be entropy-driven presumably due to the exclusion of structured water from protein-protein interfaces in the complex.

Identification and characterization of specific binding sites of [ 3H]spermidine in synaptic membranes of rat brain

Synaptic membranes of rat brain contained specific binding sites of [ 3H]spermidine (SPD) that exhibited an inverse temperature dependency, structure selectivity, reversibility, saturability, low affinity and high density with an uneven distribution profile. The affinities were not significantly different from each other in the rodent brain, while the highest density was found in the medulla-pons among the central structures examined with progressively lower densities in the midbrain, striatum, cerebellum, hypothalamus, hippocampus and cerebral cortex. The binding was insensitive to digestion by various proteases and glycosidases but sensitive to potentiation by phospholipases. A clear correlation was seen between the abilities of several natural and synthetic polyamines to displace [ 3H]SPD binding and to potentiate [ 3H] (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine binding to open cation channels associated with an N- methyl- d-aspartate (NMDA)-sensitive subclass of brain excitatory amino acid receptors. Treatment of brain membranes with deoxycholic acid resulted in a significant solubilization of [ 3H]SPD binding sites. Furthermore, [ 3H]SPD markedly associated with the acidic phospholipid phosphatidylserine irrespective of the presence of synaptic membranes in a manner sensitive to inhibition by a variety of calmodulin antagonists. These results suggest that endogenous polyamines may play a stimulatory role in neuronal responses mediated by the NMDA receptor ionophore complex through an interaction between their positive charges and negative charges of membranous phosphatidylserine in rat brain.

High-temperature deformation characteristics of Ti-15at.% Al alloy

The deformation characteristics of Ti-15 at.% Al alloy have been investigated by compression tests in the temperature range 873 to 1273 K (0.44 to 0.64T m) and by extensive transmission electron microscopy. Two types of deformation patterns were identified depending on the temperature: at lower temperatures below about 1073 K, the yield stress of the sample showed inverse temperature dependence, and serrations were found on the flow curves, whereas the normal dependences of the yield stress on temperature and strain rate were found at higher temperatures above about 1073 K. Corresponding dislocation substructures were composed of coarse bands of localized slip at 1023 K, and of rather uniformly distributed dislocations at 1123 K, and sub-boundaries as well as free dislocations at 1273 K. The main operating mechanisms in these temperature regimes were assumed to be the co-operative movement of numerous dislocations under the condition of the dynamic strain ageing, viscous glide of dislocations and dynamic recovery, respectively.

Magnetization and magnetic resonance studies of ultrafine Ho 3Fe 5O 12 and Yb 3Fe 5O 12

Ultrafine particles of Ho 3Fe 5O 12 and Yb 3Fe 5O 12 garnet materials from 1.0 to 35 nm crystalline in size are prepared by thermal decomposition of citrate precursors. The crystallites in the 1.0 to 1.5 nm size range exist in the disordered state as aggregates and exhibit superparamagnetism, whereas 10 to 35 nm crystallites are monoliths. The observed higher M s-values and T c-values of 1.0 to 1.5 nm crystallites are attributed to the weakening of the anisotropic R c 3+O 2Fe d 3+ coupling in the disordered state which allows the Fe sublattice magnetization to dominate. The g eff-values of > 2.0 in resonance studies and their inverse temperature dependence are the result of the low Ho 3+ and Yb 3+ sublattice magnetization, the presence of an internal magnetic field produced by interparticle dipolar interactions and the distortion of Fe 3+ sites in the garnet structure. The 10 to 35 nm crystallites have larger g eff-values, as compared to single crystal or polycrystalline garnets due to the dipolar interactions; the temperature dependence of g eff-values is comparable to the polycrystalline materials. The resonance line broadening in 1.0 to 1.5 nm crystallites is dominated by dipolar broadening Δ H dp whereas in 10 to 35 nm crystallites anisotropy broadening Δ H a and intrinsic broadening Δ H i are predominant.

Photodissociation of F 2 in crystalline krypton: effect of molecule—lattice prealignment

Photodissociation studies of F 2 isolated in crystalline krypton are reported. At an excess energy of 1.16 eV, the dissociation quantum yield is 12%. The quantum yield reaches unity for excess energies above 2.5 eV. At 4 K, dissociation probabilities are higher than at 12 K. This inverse temperature dependence is ascribed to prealignment of the molecule along a reaction cone of the cage.

Observation of a strong inverse temperature dependence for the opacity of atmospheric water vapor in the MM continuum near 280 GHz

Using atmospheric opacity measurements made at 278 GHz (9.3 cm−1) at McMurdo Station, Antarctica during the austral springs of 1986 and 1987, combined with measurements of water vapor profile and total column density from near-simultaneous balloon flights, we have determined the attenuation per mm of precipitable water vapor (pwv) at this frequency. Our data were taken at significantly lower temperatures than other measurements in the literature for which accompanying water vapor pressure and temperature data are available. The results show a strong inverse dependence with temperature: measured opacity per mm of pwv is roughly a factor of two times greater at −35°C than at −10°C and three times greater than measurements at the same wavelength at +25°C reported by Zammit and Ade. We briefly review various theories proposed to explain excess absorption in continuum regions. Our lowtemperature measurements demonstrate a significantly greater inverse temperature dependence than embodied in several formulations, theoretical or empirical, proposed to represent mm-wave attenuation as a function of temperature and water vapor. The present results are qualitatively similar to observations of strong inverse temperature dependence in the near IR, but if attributed to water vapor dimer formation, imply a greater binding energy for the dimer than generally proposed by others. There is some independent evidence for a local anomaly in temperature dependence as a function of frequency near 280 GHz. It remains to be established whether our own results are strongly frequency dependent or apply generally to the mm-wave continuum.

Temperature dependence of intrinsic stress in Fe, Si, and AlN prepared by ion beam sputtering

The intrinsic stress in ion beam sputtered Fe, Si, and AlN films was investigated as a function of deposition temperature. At low deposition temperature (300 K) the intrinsic stress is high and compressive for all materials investigated. With increasing deposition temperature the stress initially decreases gradually followed by a rapid drop for Td &amp;gt;Tm /3. The initial slope of the stress variation with temperature appears to be material dependent, being steepest for iron and shallowest for AlN with silicon falling in between. Unlike AlN and Si, Fe converts from compressive to tensile stress at Td /Tm =0.25, where Tm is the absolute melting temperature. The inverse temperature dependence of the intrinsic stress is explained in terms of the grain growth and annealing of a strained microstructure models. Applying the forward-sputtering model [which relates the intrinsic stress to the elastic energy/mole, EM/(1−ν)D, where E is Young’s modulus of elasticity, D the mass density, M the atomic mass, and ν Poisson’s ratio] it is shown that the temperature dependence of the material properties do not contribute significantly to the intrinsic stress variation with temperature.

Adsorption of non-ionic surfactants from aqueous solutions on graphite: adsorption isotherms and calorimetric enthalpies of displacement for C 8E 4 and related compounds

Adsorption isotherms and the enthalpies of displacement of solvent by solute have been determined for the non-ionic surfactant tetraethylene glycol octyl ether (C 8E 4) from aqueous solution on graphitized carbon black (Vulcan 3G). Strong (effectively irreversible) adsorption up to a surface concentration corresponding to a close-packed monolayer of molecules oriented parallel to the surface was observed in the entire temperature range (293–328 K). Further adsorption at higher bulk concentrations increases with temperature and pronounced multilayer adsorption occurs as the lower consolute phase boundary of the surfactant solution is approached. Endothermic differential enthalpies of displacement are found for this regime, in accordance with the inverse temperature dependence of the adsorption. A similar (but less pronounced) behaviour of the adsorption enthalpies is found also for aqueous solutions of lower C n E m compounds.

A note on the coefficient of viscosity of pure molten 2,4,6-trinitrotoluene (TNT)

The viscosity of pure molten TNT has been investigated over the temperature range 82.0°–95.4°C. The temperature dependence of viscosity was found to be best represented by a relation of the typeη = A e B/T whereA = 0.000541,B = 3570,η is the viscosity in mPa s andT is the temperature in Kelvin. Earlier work, which suggests an inverse temperature dependence of the flow activation energy, is shown to include an error in the published equation for the temperature dependence of the viscosity of molten TNT.

Effect of variation of temperature on second-derivative fluorescence spectra. Part I. Spectral changes and uncorrected temperature coefficients

The effects of variation of temperature in the range 5–45 °C on the zero-order and second-derivative excitation and emission fluorescence spectra of ten compounds have been investigated. Both the zero-order fluorescence intensities and their second-derivative amplitudes decrease linearly with increasing temperature. When the spectral measurements are not subject to interference from Raman or Rayleigh-Tyndall scattered light, the temperature coefficients of the second-derivative amplitudes are similar to or only slightly greater than those of the zero-order fluorescence intensities. Raman scatter bands of water and their second-derivative amplitudes show a small inverse temperature dependence and Rayleigh-Tyndall scatter bands and their second-derivative amplitudes show a positive temperature dependence. Raman and Rayleigh-Tyndall scatter interferences in spectral measurements result in erroneously low temperature coefficients.

The control of spontaneous ignition under rapid compression

Evolution of the spontaneous ignition of n-butane is investigated under conditions of varying heat dissipation rates, controlled through the intensity of gas motion generated during mechanical compression of the reactants in a cylinder. As the heat dissipation rate is enhanced the minimum compressed gas temperature required for ignition is also raised, from 700 to 870 K in the present conditions. This increase is linked to the initial rate of cooling in the post compression period before significant chemical heat release begins to take place. At this threshold for reaction the common factor is the prevailing gas temperature, which at its minimum during a marginally supercritical ignition delay, is about 600 K. Heat release rates just balance dissipation rates here, permitting the evolution of “low temperature” degenerate chain branching. Moreover, the end-of-compression temperatures within which an inverse temperature dependence of the ignition delay is observed increase when the heat dissipation rate is raised. This feature is also rationalised in terms of the prevailing post-compression gas temperature, consistently in the range 660–725 K. The heat release rates derived from experimental results exhibit a negative temperature coefficient in this range and are the origin of the complex, overall time dependence. Some contrasts due to the much lower reactivity of isobutane are also presented.

The bifurcated hydrogen-bond model of water and amorphous ice

The existence of bifurcated hydrogen bonds (BHB) between three molecules as a major feature of the structure of liquid water was postulated recently to account for the remarkable effect of temperature on the O–H stretching bands in the Raman spectra. As a corollary, there should be two kinds of H⋅⋅⋅O distances in water: one, 1.85 Å, for the well-known linear bonds (LHB), prevalent in cold water, the other, 2.3 Å, for the weaker BHB. This is evident in the neutron diffraction studies of heavy water, which reveal important structural changes with temperature. For instance, the atom pair correlation functions, both in the first-order difference, and the isochoric temperature derivative methods, show two peaks at 1.8 and 2.3 Å, with inverse temperature dependence similar to that of the Raman bands at 3220 (LHB) and 3420 cm−1 (BHB). In the BHB the nearest-neighbor O⋅⋅⋅O distances are the same as in the LHB, but the apex angle is much smaller than the tetrahedral, between 95° and 100°. This allows slightly shorter second neighbor O⋅⋅⋅O distances, and a closer packing of the molecules. The increased average coordination of the H and O atoms creates an imbalance in the stoichiometry of hydrogen bonding. As a result, a few percent of the water molecules are left with one ‘‘free,’’ i.e., nonhydrogen-bonded OH group (NHB). The energy of the BHB is estimated at 2.5 kcal mol−1, i.e., half that of the LHB, and its proportion in the liquid, at nearly 30% at 0 °C. Amorphous ice prepared from the vapor may also contain BHB according to x-ray and neutron diffraction data. The BHB appears as a common feature of hydroxylic compounds; e.g., hydrogen peroxide, alcohols, etc.

Origin of Paramagnetic Defect in Single Crystal and Ceramic B4C

ABSTRACTWe compare electron spin resonance (ESR) spectra of B4C samples made by three methods. The samples are 1) two ceramics made by hot-pressing boron and carbon powders, 2) a polycrystal made by carbothermic reduction, and 3) a single crystal grown from a palladium metal melt. All samples show remarkably similar spectra between 2 and 100 K. In particular, all samples show a single Lorentzian absorption, a linewidth that decreases with increasing temperature, and an inverse temperature dependence of the integrated intensity. The integrated intensity of the paramagnetic spin signal corresponds to a density of 2×1019/cm2 localized spins. Having a single crystal sample enables us to meaningfully measure the angular dependence of the ESR linewidth. This angular dependence is consistent with the paramagetic centers being unpaired electrons centered on the central carbon atoms of positively charged C-C-C intericosahedral chains. These chains appear to replace 0.5 % of the positively charged C-B-C intericosahedral chains which occur in B4C.

The temperature dependence of the yellow glow from active nitrogen

A discharge flow/shock tube has been used to investigate the change in emission, in the temperature range 300–1200 K, for the ν= 6, 10, 11 and 12 levels of N2(B3Πg) in discharged nitrogen. For each level the emission decreased with temperature and empirical equations are given to describe the behaviour. The results are interpreted qualitatively in terms of the Thrush mechanism modified to include the N2(W3Δu) state. The general decrease is attributed to the fall in the third-order recombination rate constant; the detailed differences between levels are correlated with the varying energy spacings between the vibrational levels of the N2(B3Πg) and N2(W3Δu) states. A second peak in the emission traces, attributed to the early arrival of the contact surface, is observed at much longer times than those during which the main measurements are made. It is observable only because of the inverse temperature dependence of the emission and so our experimental methods offer a unique way of studying contact surface and boundary layer processes.

Nuclear magnetic resonance study of the heavy-fermion system URu 2Si 2

Nuclear magnetic resonance (NMR) and relaxation studies on 29Si have been carried out on the heavy Fermion system URu 2Si 2. Above the Kondo temperature of about 60 K, the nuclear relaxation time T 1 is nearly temperature independent, which is consistent with the occurrence of fluctuations of localized U moments. Below about 60 K T 1 is inversely proportional to temperature suggesting that the system behaves like a Fermi liquid. A sharp increase in T 1 occurs below 17 K which is probably associated with the opening of an energy gap at the Fermi surface due to the formation of a spin density wave state. Below about 10 K, T 1 reacquires the inverse temperature dependence observed in the 17 K ∼ 60 K temperature range.