Identical Temperature Dependence Research Articles

Heating nuclear matter with GeV 3He beams

Abstract The heating curve for hot nuclei formed in the 4.8 GeV 3He+natAg, 197Au reactions has been derived from reconstructed excitation-energy distributions and temperatures based on 2,3H/3,4He isotope ratios. Intranuclear-cascade predictions over-estimate the excitation-energy distributions for hot thermal-like residues, but are in general agreement with the data when contributions from preequilibrium emission are included. Both targets exhibit nearly an identical temperature vs. excitation energy dependence. The heating curve initially increases rapidly, undergoes a slope change near E ∗ /A = 2–3 MeV, and then follows a gradual monotonic increase up to E ∗ /A = 10 MeV. The results are in qualitative agreement with predictions of EES and SMM multifragmentation models.

Substitutional carbon in germanium

Carbon impurities implanted into single-crystalline germanium are studied with infrared absorption spectroscopy and ion channeling. After implantation of $^{12}\mathrm{C}^{+}$ at room temperature and subsequent annealing at 350 \ifmmode^\circ\else\textdegree\fi{}C, a sharp infrared absorption line is observed at 531 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. When $^{12}\mathrm{C}^{+}$ is substituted by $^{13}\mathrm{C}^{+}$, the line shifts down in frequency to 512 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and co-implantation of $^{12}\mathrm{C}^{+}$ and $^{13}\mathrm{C}^{+}$ does not give rise to additional lines. Therefore, the 531-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ line represents a local vibrational mode of a defect containing a single carbon atom. Channeling measurements are carried out around the 〈100〉, 〈110〉, and 〈111〉 axes in $^{12}\mathrm{C}^{+}$-implanted samples annealed at 450 \ifmmode^\circ\else\textdegree\fi{}C. The analysis of the data shows that 31\ifmmode\pm\else\textpm\fi{}3 % of the carbon atoms are located at substitutional sites, while the remaining carbon atoms appear to be located randomly. The population of the substitutional site and the intensity of the 531-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ mode have identical temperature dependencies. It is concluded that the 531-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ mode is the three-dimensional ${\mathrm{T}}_{2}$ stretch mode of substitutional carbon. The effective charge of the mode is determined to be (3.4\ifmmode\pm\else\textpm\fi{}0.5)e.mAb initio local density functional cluster theory is applied to calculate the structure and the local vibrational modes of substitutional carbon in germanium. The calculated frequencies and isotope shifts for the ${\mathrm{T}}_{2}$ stretch mode are in good agreement with the observations.

Vortices in a thin-film superconductor with a spherical geometry

We report results from Monte Carlo simulations of a thin film superconductor in a spherical geometry within the lowest Landau level approximation. We observe the absence of a phase transition to a low temperature vortex solid phase with these boundary conditions; the system remains in the vortex liquid phase for all accessible temperatures. The correlation lengths are measured for phase coherence and density modulation. Both lengths display identical temperature dependences, with an asymptotic scaling form consistent with a continuous zero temperature transition. This contrasts with the first order freezing transition which is seen in the alternative quasi-periodic boundary conditions. The high temperature perturbation theory and the ground states of the spherical system suggest that the thermodynamic limit of the spherical geometry is the same as that on the flat plane. We discuss the advantages and drawbacks of simulations with different geometries, and compare with current experimental conclusions. The effect of having a large scale inhomogeneity in the applied field is also considered.

Studies of single crystalline UBe13 below 1 K using a capacitive magnetometer

Measurements of the magnetic force and magnetic torque acting upon a high quality single crystal of UBe13 have been made with a Si cantilever capacitive magnetometer from 1.2 K to about 40 mK in a field of 10 T. The torque is found to approach low temperature saturation likeT 2; an identical temperature dependence is observed for the magnetic force and hence the susceptibility. While this temperature dependence of the susceptibility is consistent with a Fermi liquid ground state for UBe13 it also suggests, for this particular experiment, a dominant presence of magnetic torque in the magnetic force data.

Effect of proximity coupling of chains and planes on the penetration-depth anisotropy in YBa2Cu3O7.

We calculate the penetration depth $\lambda$ in the $a$, $b$ and $c$ directions for a simple model of YBa$_2$Cu$_3$O$_7$. In this model there are two layers---representing a CuO$_2$ plane and a CuO chain---per unit cell. There is a BCS--like pairing (both $s$ wave and $d$ wave are considered) interaction localised in the CuO$_2$ planes. The CuO chains become superconducting at temperatures lower than $T_c$ because of their proximity to the planes, and there is an induced gap in the chains. Since the temperature dependence of the penetration depth in the $b$ direction (along the chains) is sensitive to the size of the induced gap, the difference between the shapes of the penetration depth curves in the $a$ and $b$ directions reveals a great deal about the nature of the condensate in the chains. We find that in our proximity model there are always regions of the chain Fermi surface on which the induced gap is much smaller than $T_c$, so that the temperature dependence of $\lambda_b$ is always different than that of $\lambda_a$. Experimental observations of the of the $ab$ anisotropy show nearly identical temperature dependences. The main result of our paper, then, is that a simple proximity model in which the pairing interaction is localized to the planes, and the planes are coherently coupled to the chains cannot account for the superfluid on the chains.

Room temperature light emitting silicon diodes fabricated by erbium ion implantation

In this work we report the fabrication and characteristics of light emitting erbium-doped Si diodes operating at room temperature (RT). These devices were prepared by multiple high energy Er implantation in the active region of a p +-n + Si diode. Oxygen or fluorine implantation in the Er-doped region was also performed in order to properly modify the Er 3+ chemical surrounding. Electroluminescence (EL) at 1.54 μm and at RT has been observed under both forward and reverse bias conditions with the maximum intensity under reverse bias. The temperature dependence of the luminescence revealed that forward-bias EL decreases by about a factor of 30 on going from 100 K to 300 K. An identical temperature dependence is observed in photoluminescence (PL) suggesting that similar excitation mechanisms are responsible for PL and forward-bias EL. In contrast, reverse-bias EL presents a very weak temperature dependence, with a decrease by only a factor of 4 from 100 K to 300 K. These data are reported and possible excitation mechanisms are discussed.

Intermodulation in the oscillatory magnetoresistance of a two-dimensional electron gas.

The oscillatory magnetoresistance wave form of a 2-D electron gas shows multiple structures when two subbands are populated. In addition to high-field oscillations at a frequency equal to the sum of the two frequencies corresponding to the concentrations of the subbands, and to a superposition at intermediate fields, we observed oscillations at the difference frequency at low fields and higher temperatures. The field range at which the frequency difference is observed increases with increasing temperature. The crossover from superposition to frequency difference is accompanied by a beat. Similar beats, whose field location shows identical temperature dependence, can be observed in data obtained by other groups on different structures. The various components of the wave form can be attributed to different phase relations between the diagonal and off-diagonal elements of the conductivity tensor. It is shown how the intermodulation term, when inserted into the extended oscillatory equation, can give rise to all three structures.

Cu and O NMR studies of the magnetic properties of YBa2Cu3O6.63 (Tc=62 K).

The microscopic magnetic properties of the ${\mathrm{CuO}}_{2}$ planes in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.63}$ (${\mathit{T}}_{\mathit{c}}$=62 K) have been investigated in Cu and O NMR experiments. Unlike the fully oxygenated Y-Ba-Cu-${\mathrm{O}}_{7}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\simeq}90 K), the various components of the Cu and O Knight-shift tensors show strong but identical temperature dependences in the normal state. This supports the picture that there is only one spin component in the ${\mathrm{CuO}}_{2}$ planes. The spin susceptibility deduced from Knight-shift results shows significant reduction with decreasing temperature in the normal state. The temperature dependences of the nuclear-spin-relaxation rates (1/${\mathit{T}}_{1}$) are very different for the Cu and the O sites. 1/(${\mathit{T}}_{1}$T) at the O sites is nearly proportional to the spin susceptibility. 1/(${\mathit{T}}_{1}$T) at the Cu sites shows a broad peak around 150 K. We discuss these relaxation behaviors based on a model of the dynamical spin susceptibility proposed by Millis, Monien, and Pines.

17O NMR study of YBa2Cu3O7−δ

We present our 17O NMR experimental results in a magnetically aligned powder sample of YBa2Cu3O7−δ (Tc = 93K). The sign of the anisotropic Knight shift shows that the spin density resides mainly on the pσ orbitals at the planar O(2,3) and bridging O(4) sites. About 30 % of the total spin susceptibility is attributed to the oxygen 2pσ states. The Knight shift at the O(2,3) sites decrease more rapidly than that at the chain O(1) sites, indicating a larger gap in the planes. The nuclear relaxation rate at the O(2,3) sites shows linear-T (Korriga) behavior above Tc, in contrast to the much weaker temperature dependence at the planar Cu(2) sites. However, these two rates show identical temperature dependence below about 110 K, indicating that an important change in the spin dynamics takes place above Tc.

Hydrogen-1 nuclear magnetic resonance of the nitrogenase iron protein (Cp2) from Clostridium pasteurianum.

Proton NMR spectra (250 MHz) of the nitrogenase iron protein from Clostridium pasteurianum (Cp2) were found to display 9 or 10 paramagnetically shifted resonances in the 15-50 ppm range. The most shifted resonances belonged to two approximately equal subsets having temperature dependences of opposite sign. The latter occurrence is consistent with the interaction of the corresponding protons with an antiferromagnetically coupled metal center. The number of proton resonances of Cp2, their positions, and their temperature dependences were similar to those observed in spectra of (4Fe-4S)+ ferredoxins, particularly those of the latter that contain a single tetranuclear cluster, such as the ferredoxin from Bacillus stearothermophilus. The effects of several adenine nucleotides on the paramagnetically shifted proton resonances of Cp2 have been investigated. Whereas MgAMP had no effect at all, MgADP and MgATP were found to induce different modifications, which in both cases involved approximately half only of the shifted proton resonances. These data suggest that nucleotide binding affects mainly one part of the iron-sulfur cluster. A remarkable feature of the spectra of Cp2 in the presence of MgATP is the grouping of the shifted proton resonances in sets of two or four having identical chemical shifts and temperature dependences. A nearly perfect 2-fold symmetry is thus suggested for the arrangement of the cysteine protons around the active site. These observations lend support to the proposal that the (4Fe-4S) cluster is held symmetrically between the two identical subunits and are consistent with the existence of two MgATP binding sites on nitrogenase iron proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

ANISOTROPY OF THE FARADAY ROTATION IN PRASEODYMIUM GALLIUM GARNET SINGLE CRYSTALS

Faraday Rotation (FR) measurements performed on single crystals Praseodymium Gallium Garnet (PrGaG) at 0.6328 and 1.15 micron wavelengths are reported in a continuous magnetic field up to 20 kOe which was parallel to the three main crystallographic directions, over the temperature range 6-300 K. On the same samples, the magnetic properties are investigated. At 0.6328 micron wavelength, the Verdet constant V is found anisotropic : below 130 K, [100] corresponds to the weakest rotation. No anisotropic behaviour is observed at 1.15 micron wavelength. The reciprocal Verdet constants (V) and the inverse of the magnetic susceptibility (x) are found rigourously proportional to the temperature. The ratio V/ appears temperature independent in agreement with the model of Van Vleck and Hebb above about 80 K. These results are briefly discussed in terms of strongly and weaky allowed electric dipole transitions. In paramagnetic materials, it has been admitted since the historical work of Van Vleck and Hebb (1) that the Verdet constant and the magnetic susceptibility should exhibit identical temperature dependences. Although a lot of work has been devoted to this subject, some essential features remain unclear to this day due to the absence of precise experimental data in a large domain of temperature. Furthermore very few results concerning the anisotropic character of the Faraday Rotation have been reported and, to our knowledge, the properties of the erbium iron garnet (2) and of the ytterbium gallium garnet (3) have been investigated only. In this last crystal, it has heen observed the singular fact that when the magnetic properties are rigorously isotropic the Verdet constaut is anisotropic

Patterns of sarcomere activation, temperature dependence, and effect of ryanodine in chemically skinned cardiac fibers.

Functionally skinned and electrochemically shunted myocytes were prepared by perfusing rat hearts with collagenase in order to obtain a technically improved measurement of sarcomere dynamics and to evaluate the role of sarcoplasmic reticulum in situ with respect to contractile activation. In the presence of micromolar calcium, the myocytes exhibited phasic and propagated contraction waves beginning at one end and proceeding along the myocyte. Beating rates, the propagation velocity of the activation wave, and single sarcomere shortening and relaxation velocities were obtained by manual or automated analysis of 16-mm film recorded at 170 frames/s from a camera attached to a microscope that was equipped with a temperature-controlled stage. In parallel experiments, calcium accumulation by the sarcoplasmic reticulum of the myocytes in situ was measured by direct isotopic tracer methods. The frequency (10-38 min-1) of spontaneous contractions, the velocity (1.9-7.4 microns . s-1) of sarcomere shortening, and the velocity (1.7-6.8 microns . s-1) of sarcomere relaxation displayed identical temperature dependences (Q10 = 2.2), which are similar to that of the calcium pump of sarcoplasmic reticulum and are consistent with a rate limit imposed by enzyme-catalyzed mechanisms on all these parameters. On the other hand, the velocity (77-159 microns . s-1) of sequential sarcomere activation displayed a lower temperature dependence (Q10 = 1.5), which is consistent with a diffusion-limited and self-propagating release of calcium from one sarcomere to the other. The phasic contractile activity of the dissociated myocytes was inhibited by 10(-8)-10(6) M ryanodine (and not by myolemmal calcium blockers) under conditions in which calcium accumulation by sarcoplasmic reticulum in situ was demonstrated to proceed optimally. The effect of ryanodine is attributed to an interaction of this drug with sarcotubular structures, producing inhibition of calcium release from the sarcoplasmic reticulum. The consequent lack of sarcomere activation underlines the role of sarcoplasmic reticulum uptake and release in the phasic contractile activation of the electrochemically shunted myocytes.

Reaction of lecithin:cholesterol acyltransferase with micellar complexes of apolipoprotein A-I and phosphatidylcholine, containing variable amounts of cholesterol.

In a continued investigation of lecithin:cholesterol acyltransferase reaction with micellar, discoidal complexes of phosphatidylcholine (PC) . cholesterol . apolipoprotein A-I (apo-A-I), we prepared well defined complexes with variable free cholesterol contents and examined their reactivity with purified enzyme. The complexes, prepared by the sodium cholate dialysis method, were fractionated into "small" and "large" classes by gel filtration of the reaction mixtures through a Bio-Gel A-5m column. The small complexes had egg-PC/cholesterol/apo-A-I molar ratios from 68:14:1 to 80:1:1, discoidal shapes with diameters around 114 (+/- 13) A and widths of 42 A by electron microscopy, and Stokes radii from 47 to 49 A corresponding to molecular weights near 2 X 10(5). The corresponding properties of the large complexes, isolated from samples with higher cholesterol contents, were egg-PC/cholesterol/apo-A-I molar ratios from 84:26:1 to 96:17:1, diameters of 161 (+/- 20) A, widths of 43 A, Stokes radii around 80 A, and estimated molecular weights in the vicinity of 5 X 10(5). Both types of complexes, when adjusted to equal apo-A-I concentrations, gave essentially identical initial reaction velocities with purified lecithin:cholesterol acyltransferase over a wide range of cholesterol concentrations (from 2 X 10(-7) to 4 X 10(-4) M), PC/cholesterol molar ratios (from 3:1 to 12:1), and quite different lipid fluidity conditions as detected by diphenylhexatriene fluorescence polarization. When complexes were adjusted to a constant cholesterol concentration, the initial velocities of the lecithin:cholesterol acyltransferase reaction followed Michaelis-Menten kinetics relative to the apo-A-I concentrations. Arrhenius plots of initial reaction rates for various complexes with variable cholesterol content and fluidity, measured at constant apo-A-I concentrations, gave identical temperature dependences with an average activation energy of 18.0 kcal/mol. These results strongly suggest that the cholesterol esterification on high density lipoprotein particles does not depend on their unesterified-cholesterol contents, PC/unesterified-cholesterol molar ratios, nor on the fluidity of their lipid domains.

Comparison of the dispersion parameters from time-of-flight and photo-induced midgap absorption measurements on sputtered a-Si:H

We present the results of a combined study of photo-induced midgap absorption and time-of-flight measurements on samples of a-Si:H prepared by the sputtering process. The samples were characterized by a low density of states at the Fermi level and activated band transport. Both time-of-flight and induced absorption decay measurements reveal identical temperature dependence of the dispersion parameter with a transition from dispersive to non-dispersive statistics near 300 K.

Effects of CNS temperature on generation and transmission of temperature signals in homeotherms. A common concept for mammalian and avian thermoregulation.

Neurophysiological studies on avian hypothalamic thermosensitivity have presented evidence for a higher Q10 of cold than of warm signal transmission in the CNS of birds. An identical temperature dependence of central cold and warm signal transmission in mammals is suggested by considerations on the phylogeny of temperature regulation. By taking into account the experimental evidence for the existence of thermosensory afferents in the CNS of mammals and birds, being differently developed in the various sections of the neural axis and exerting quantitatively different influences on the various thermoregulatory effectors, a common concept of homeothermic thermoregulation is proposed resting on the same basic assumptions for mammals and birds. The great diversity of negative as well as positive feedback effects of CNS temperature displacements on homeothermic thermoregulation, which is particularly expressed in avian autonomic and behavioral thermoregulation and, further, certain pathophysiological conditions of disturbed thermoregulation could be accounted for by assuming quantitatively different contributions of the central thermosensory inputs of thermoregulatory effector control, but maintaining the Q10 values of hypothalamic warn and cold signal transmission constant. The proposed model, while basically additive in its mathematical design, meets a number of properties described by multiplicative models of thermoregulation. In additionally generalizes these models of predicting that changes of hypothalamic temperature modify the sensitivities with which any thermoregulatory effector responds to any thermosensory input.

Substituent Effects in Heterogeneous Catalysis. VII. Temperature Independence of the Relative Rates in Metal-catalyzed Hydrogenation of Cyclohexanone and Its 2-Alkyl Derivatives

Abstract The rates of hydrogenation of cyclohexanone and its 2-alkyl derivatives have been measured using decalin as the solvent in a temperature range of −5 to 68 °C over Ru/Al2O3, Rh/Al2O3, and Pt/Al2O3 catalysts. As predicted previously, 2-methyl-, 2-ethyl-, and 2-propylcyclohexanone have exhibited nearly identical temperature dependencies in adsorption and hydrogenation, while cyclohexanone and 2-isopropylcyclohexanone had quite different dependencies.

The identity of the acid and alkaline phosphatases of human seminal plasma.

Examination of human seminal plasma showed that there was no p-nitrophenylphosphatase activity maximum at alkaline pH values. A constant ratio of enzyme activities in 8 split ejaculates, identical temperature dependence and copurification through a three-step purification procedure led us to conclude that the alkaline phosphatase in human semen is identical to acid phosphatase.

The temperature dependence of network forces in rubber‐like materials

AbstractIn the simplest model of rubber‐like materials only two kinds of forces are assumed: network forces with identical temperature dependence, and liquid forces which. are isotropic. For this simple model the relation between the temperature dependence of the network forces and that of the observed elastic force is calculated. When the elastic equation of the network is of the classical one term type, the well‐known equation of Flory, Ciferri and Hoeve is found without using assumptions about the physical meaning of the front factor in the elastic equation. When the elastic equation of the network is of the Mooney‐Rivlin type with two terms, the difference between the temperature dependence of the observed forces and of the network forces is found to depend on the ratio of the coefficients in the Mooney‐Rivlin equation and on the elongation. The effect of the internal pressure is to add a factor to this term. The conclusion is that detailed knowledge about the network forces is needed in order to establish the value of the correction term for thermal expansion in the equation for the temperature dependence of the elastic force in the material.

Transport properties of dynamically disordered chains and applications to TTF-TCNQ and related compounds

A model for the high-temperature transport properties of one-dimensional conductors with very narrow bands and strong electron-phonon couplings is discussed. It is argued that electronic states can be viewed as effectively localised over some characteristic time scale and that the conductivity is due to dynamic rearrangement of the localisation region. For a series of charge-transfer complexes like tetrathiofulvalene-tetracyanoquinodimethane (TTF-TCNQ) it is argued that a consistent interpretation of the almost identical temperature dependences of the high-temperature conductivities and yet apparently totally dissimilar temperature dependences of the thermopowers is possible if one regards both the donor and the acceptor stacks as conducting. In particular, for TTF-TCNQ where most of the relevant parameters are known, quantitative calculations of the magnitudes and the temperature dependences of the conductivity and the thermopower are presented. The results are in excellent agreement with the observed values.

Ultrasonic Properties of Pure and Ag-Doped Amorphous Chalcogenides (As2S3, As2Se3)

The lattice (elastic and relaxation) properties of the amorphous chalcogenides, mainly on pure and Ag-doped As 2 S 3 , have been studied by measuring ultrasonic velocities and attenuations. The observed drastic increase (5∼10%) of the velocity with a small amount (1 at.%) of doped Ag in As 2 S 3 has been attributed to its anomalous behaviors of the density, the anharmonicity and the bulk modulus due to the doping. The experimental temperature dependences of shear wave attenuation α s ( T ) and of high-frequency electrical conductivity σ( T ) in As 2 S 3 are both well represented by exp (- E h / k t ) with approximately the same activation energy E h ∼0.1 eV. The mechanism of the phonon-assisted hopping of As–S dipoles (activated by thermal phonons) has been shown to explain the identical temperature dependence for α s ( T ) and σ( T ). Thus, these are the two manifestations, the mechanical relaxation (α) and the dielectric relaxation (σ), of the same origin, i.e., due to the hopping of ions, perhaps mainl...