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1.
The dynamic properties of a stochastic n-vector model are investigated for T < Tc in d=4−ε dimensions. Besides the non-conserved order parameter the model involves also the conserved densities of generators of the symmetry group O( n). We calculate the excitation spectra of those conserved densities and the transverse fluctuations of the order parameter to linear order in ε in the hydrodynamic region kξ1. The propagating modes have linear dispersion and quadratic damping in accordance with the phenomenological theory. The relaxing modes, however, exhibit non-hydrodynamic wavenumber dependence with a relaxation rate ω k ∞ kd/2. 相似文献
2.
The study by X-ray diffraction, calorimetry, vibrational and impedance spectroscopy of CsH(SO 4) 0.76(SeO 4) 0.24 new solid solution is presented. Crystals of this composition undergo two phase transitions at T = 333 and 408 K. The last one at 408 K is a superionic-protonic transition (SPT) related to a rapid [HS(Se)O 4−] reorientation and fast H + diffusion. A sudden jump in the conductivity plot confirms the presence of this transition. Above 408 K, this high temperature phase is characterized by high electrical conductivity (7 × 10 t-3 Ω − cm −1) and low activation energy ( Ea < 0.3 eV). 相似文献
3.
A series of polyacrylonitrile–dimethylsulfoxide–CuX 2 (X=CF 3SO 3−, Cl −, Br −), films (foils) were prepared by means of the solution cast technique. The thickness of the foils was between 0.04 and 0.09 cm and they contained 70–80 wt.% of the solvent. Conductivities of the solid electrolytes were obtained from impedance measurements. The conductivity increases with the increase of the salt content up to 8 wt.%; at higher concentrations (>8 wt.%) the conductivity is more or less stable, and reaches, in the case of Cu(CF 3SO 3) 2 and CuCl 2, the level of ca. 10 −3 Ω −1 cm −1 at room temperature. The foils based on the CuBr 2 show even higher conductivity, close to 10 −2 Ω −1 cm −1 at room temperature, a value comparable to that characteristic for liquid solutions. The temperature variation of the conductivity for all the systems studied is of the Arrhenius type. The activation energy, determined from linear plots ln σ=f( T−1), is of the order ca. 14 kJ mol −1 for the PAN/CuBr 2/DMSO and of ca. 21 kJ mol −1 for the PAN/CuCl 2/DMSO and the PAN/Cu(CF 3SO 3) 2/DMSO systems. 相似文献
4.
The results of the impedance spectroscopy measurements on eutectic samples based on zirconium oxide are presented here. Samples of CaZrO 3---ZrO 2(cubic) and MgO---ZrO 2(cubic) have been grown by a directional solidification procedure such that the different phases appear nearly oriented along the growth direction (lamellae in the system of CaZrO 3-ZrO 2(cubic) and fibers of MgO in a ZrO 2 matrix in the other system). The DC electrical conductivity has been measured by impedance spectroscopy along and across the growth axis. For CaZrO 3---ZrO 2 the coductivity is clearly anisotropic. The following values for σ T have been obtained: the conductivity at 600 °C equals 2.0 × 10 −6 Ω −1 cm −1 perpendicular to the fiber axis and 1.4 × 10 −5 Ω −1 cm −1 parallel to it and with an activation energy of 1.3 eV for σ T. For MgO---ZrO 2(cubic) the isotropic value of the conductivity at 600 °C is 10 −4 Ω −1 cm−1 with activation energy for σ T of 1.5 eV. The anisotropic conductivity in the CaZrO 3---ZrO 2 (cubic) system has been explained by a model of an ordered stacking of oxygen conducting (cubic ZrO 2) and non-conducting (CaZrO 3 or MgO) phases. 相似文献
5.
Fluorescence decay curves for 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphine tetraanion (TPPS 4−) have been measured in the absence and presence of the methylviologen dication (MV 2+) with various ionic strengths in methanol. In the presence of MV 2+ the fluorescence decays can be expressed by a double exponential function, I( t = I1exp(− t/τ 1) + I2exp(− t/τ 2). The contribution by the faster decay component to the total fluorescence signal increases with increasing MV 2+ concentration. The faster decay process is attributed to fluorescence from the excited state of a solvent-separated ion pair (SSIP) formed between TPPS 4− and MV 2+, and the slower process is attributed to fluorescence from free TPPS 4− ions in the solution. Rate constants for the quenching of fluorescence from free TPPS 4− by MV 2+ ( kq) and formation constants for the SSIP ( KSSIP) were calculated and both are found to decrease with increasing ionic strength. The decrease in kq and KSSIP values can be interpreted in terms of the shielding of electrostatic attraction between the ions. 相似文献
6.
Differential cross sections for the reactions 16O(γ, π−π+−) 16F16F to the sum of the four lowest lying states in 16F and 16N have been measured as a function of angle for pions with a kinetic energy of 30 MeV. The extracted ratios R = σ(γ, π −)/σ(γ, π +), the first ones to discrete final states as a function of angle, are in fair agreement with results obtained for the nucleon. For positive pions the energy dependence of the cross section has been measured at the angles of 45° and 90°. Distorted wave impulse approximation calculations fail to describe the energy dependence. 相似文献
7.
Two-loop radiative mechanism, when combined with an U(1) L′ symmetry generated by Le − Lμ − Lτ (= L′), is shown to provide an estimate of Δ m2/Δ m2atm ε me/ mτ, where ε measures the U(1) L′-breaking. Since Δ m2atm 3.5×10 −3 eV 2, we find that Δ m2 ε10 −6 eV 2, which will fall into the allowed region of the LOW solution to the solar neutrino problem for ε 0.1. 相似文献
8.
Angular distribution of the reaction 12C( d,τ) 11B leading to the 3/2 − ground state and the 4.44 MeV excited (5/2 − state 11B have measured at Ed = 80 MeV up to about 70° and 40°, respectively. The inclusion of second-order processes in the framework of CCBA calculations gives a good reproduction of the 3/2 − as well as of the DWBA forbidden 3/2 − angular distribution. The strong dependence of the cross section on the sign of the deformation supports a positive β 2 value for 11B. 相似文献
9.
Powder X-ray diffraction (XRD) analysis showed that the single phase perovskite-type structure of Ba 1−xLa xCe 0.90−xY 0.10+xO 3− (0
x
0.40, =0.05) could be maintained in a wide region of doping level by simultaneous partial substitution of La 3+ for Ba 2+-site and Y 3+ for Ce 4+-site in BaCeO 3. The conduction properties of these oxides were investigated using various electrochemical methods in the same concentration of oxygen vacancy ( =0.05). At high oxygen partial pressure, these oxides exhibited a mixed oxide ionic and p-type electronic conduction while at low oxygen partial pressure their conduction was almost protonic. Among these oxides, BaCe 0.90Y 0.10O 3− exhibited the highest conductivities with a value of 1.24×10 −1 S/cm in dry oxygen, and 5.65×10 −2 S/cm in wet hydrogen at 1000°C. Both of the proton and oxide ion conductivities under oxygen and under hydrogen atmospheres decreased monotonically with the increasing substitution for Ba 2+- and Ce 4+-sites. The decreases in ion conductivities appear to relate to the decreased free volume ( Vf) of crystal lattice as well as the increased distortion of lattice from ideal cubic perovskite structure. 相似文献
10.
Oxygen tracer diffusion ( D*) and surface exchange rate constant ( k*) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry (SIMS), in La 1−xSr xFe 0.8Cr 0.2O 3−δ ( x=0.2, 0.4 and 0.6). Measurements were made as a function of temperature (700–1000 °C) and oxygen partial pressure (0.21–10 −21 atm) in dry oxygen, water vapour and water vapour/hydrogen/nitrogen mixtures. At high oxygen activity, D* was found to increase with increasing temperature and Sr content. The activation energies for D* in air are 2.13 eV ( x=0.2), 1.53 eV ( x=0.4) and 1.21 eV ( x=0.6). As the oxygen activity decreases, D* increases as expected qualitatively from the increase in oxygen vacancy concentration. Under strongly reducing conditions, the measured values of D* at 1000 °C range from 10 −8 cm 2 s −1 for x=0.2 to 10 −7 cm 2 s −1 for x=0.4 and 0.6. The activation energies determined at constant H 2O/H 2 ratio are 1.21 eV ( x=0.2), 1.59 eV ( x=0.4) and 0.82 eV ( x=0.6). The surface exchange rate constant of oxygen for the H2O molecule is similar in magnitude to that for the O2 molecule and both increase with increasing Sr concentration. 相似文献
11.
A computer simulation model is used to study the density profile and flow of a miscible gaseous fluid mixture consisting of differing constituent masses ( mA= mB/3) through an open matrix. The density profile is found to decay with the height ∝exp (− mA(B)h), consistent with the barometric height law. The flux density shows a power-law increase ∝( pc− p) μ with μ2.3 at the porosity 1− p above the pore percolation threshold 1− pc. 相似文献
12.
The reactions π −p → 2π −π +p, π −p → 2π −π +π op and π −p → 2π −2π +n are analysed at 11 and 16 GeV/ c using longitudinal phase space (LPS) plots. The weighted LPS distributions for π −p → 2π −π +p is dominated by two well separated structures corresponding to single diffraction dissociation of the pion, π −p → (2π −π +)p, and of the proton, π −p → π −(π −π +p). The former is more abundant than the latter, and both are approximately constant with energy. In contrast, processes of type π −p → (2π)(πp) decrease with increasing energy. In the five-body reactions the weighted LPS distribution reveals especially at 16 GeV/c a maximum for single dissociation of the proton into 3πp, namely π−p → π−(π−π+πop); this process is likely to be diffractive. The neutron channel has a corresponding maximum displaced toward a multiperipheral configuration π−p → π−(π−2π+)n. Another strong maximum corresponds to the pion dissociation π−p → (2π−π+πo)p. This is interpreted to be an ω-exchange process because no analogous structure occurs in π−p → (2π−2π+)n. Finally, a broad structure reveals double dissociation of both incident particles; it occurs in the two channels π−p → (2π−π+)(πop) and π−p → (2π−π+)(π+n), being stronger in the latter. Further analysis of this process in terms of isospin exchange suggests that it is partially diffractive. Factorization is also discussed. An appendix gives general aspects of the LPS analysis for the asymptotic study of n-body collisions at very high energy. 相似文献
13.
Within a real-space renormalization-group framework, we approach the cubic lattice through a D = 3 diamond-like hierarchical lattice. The model is a standard, nearest-neighbor, Ising spin glass with coupling constants { Jij} distributed according to the family of continuous probability distributions Pq( Jij) ∝ 1/[1 + ( q − 1) Jij2/2 J2] 1/(q − 1) (if 1 + ( q − 1) Jij2/2 J2 > 0, and zero otherwise; q
). Such distributions, which arise naturally in the treatment, within the recently proposed nonextensive thermostatistics, of anomalous diffusion, reproduce the usual, Gaussian case, for q → 1. Moreover, they present a second moment Jij2 proportional to (5 − 3 q) −1 for q < 5/3, diverging for q ≥ 5/3, but keeping a finite width at midheight. In the limit q → 3, Pq( Jij) collapses with the abscissa, and so the width at midheight diverges. We compute the q-dependence of the spin-glass critical temperature Tc. We show numerically that Tc does not scale with Jij21/2 (contrary to the usual belief), but rather with the width at midheight of Pq( Jij). Our results suggest that Tc vanishes as −1/ q when q → −∞; furthermore, we verified that Tc diverges exponentially when q approaches 3 from below. 相似文献
14.
An alternative approach for obtaining the LiMn 2O 4 spinel phase is provided by the use of the sol-gel method in aqueous solution. The main electrochemical properties of the sol-gel LiMn 2O 4 phase are reported. In addition to chronopotentiometric and voltammetric experiments, the kinetics of the electrochemical insertion–extraction of lithium in Li xMn 2O 4 (0.25< x<1) has been investigated using ac impedance spectroscopy. The strong variation of the chemical diffusion coefficient DLi vs x, in the range 10 −8–10 −11 cm 2 s −1 ( DLi is found to be maximum for x=0.55) is critically discussed. 相似文献
15.
The time-dependence of the decay rate of initially pure K 0 into the final state (π +π −π 0) has been studied in search for the decay k S0→π +π −π 0. No evidence is found in a sample of 384 observed events. The ratio of the CP -violating K S0 amplitude and the K L0 amplitude is η +−0 = (0.13 −0.20+0.17) + i(0.17 −0.26+0.27); the ratio of the CP-conserving K S0 amplitude and the K L0 amplitude is < 0.4. The energy dependence of the K 0→π +π −π 0 matrix element is found to be a+−0 = −0.31 ± 0.03. 相似文献
16.
Data were taken at the energy 2 E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the , ω andφ production by e +e − annilations. Assuming a π +π −π 0π 0 production by the quasi two-body process e +e − → → ωπ 0 we give the correspondi ng cross section σ(e +e − → π +π −π 0π 0) = (1.1 ± 0.5) 10 −32 cm 2. Since no events with 3 and 4 charged pions have been observed σ(e +e − → π +π −π 0π −) 1.5 × 10 −33 cm 2. 相似文献
17.
The betaspectra of 12B and 12N have been measured with a NaI crystal as spectrometer. Assuming a shape correction factor 1 + aW + bW2 and b− = 1.106 × 10 −4 MeV −2, b+ = −1.397 × 10 −4 MeV −2, the spectra yield a− = (+0.91 ± 0.11) × 10 −2 MeV −1 and a+ = (−0.07 ± 0.09) × 10 −2 MeV −. the a− − a+ = (+0.98 ± 0.09) × 10 −2 MeV −1 is in agreement with the weak magnetism prediction. 相似文献
18.
A spherical harmonic moment analysis of the reactions K −p → K −π +n and K +p → K +π −Δ ++ at 13 GeV/ c demonstrates the existence of a broad K * state with mass in the vicinity of 1800 MeV and spin parity 3 −. 相似文献
19.
We present the results of a study of the exclusive reactions π + 4He → π − 4p (double charge exchange, DCE) and π + 4He → π + π − 3pn (one-pion production). The experiment was performed with the Oxford/RHEL helium bubble chamber irradiated with a 1.7 GeV/ c π + beam. A general review of DCE models is presented and experimental results at other energies are discussed in the light of these models. None of the existing theoretical models is compatible with out data at 1.7 GeV/ c. We propose a new mechanism for DCE, involving three nucleons, which reproduces the integrated as well as the differential cross sections. Some consequences for other models are also discussed. 相似文献
20.
We present here the detailed analysis of the magnetic behavior of the Co 0.53Ga 0.47 alloy, especially at temperatures above the freezing temperature Tf = 10 K. Low field static magnetization measurements were performed by using the SQUID magnetometer in the temperature range 5–65 K and magnetic fields up to 100 Oe. The temperature dependence of the field cooled susceptibility π FC( T) at T > Tf has an anomaly, which is displayed in the double change of the curvature near Ts = 24 K. The data of magnetization MFC in an external field H lie on a universal curve MFC( H/ T) at temperatures Tf < T < Ts. The plots of π -1FC( T) and non-linear magnetic susceptibility π nlFC( T-3) are linear lines in the temperature range Tf− Ts. The strong deviation of π -1FC( T) and π nlFC( T-3) from straight line, taking place at T Ts, indicates that Ts is an upper temperature limit of the classical superparamagnetic behavior with the constant cluster moment. The results suggest that such phenomena may be fairly universal for spin glasses. 相似文献
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