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1.
The retardation coefficient, K R = k l/k s, for a homogeneous reaction in the bulk of a crystal was calculated within the framework of the free-volume model of unimolecular reactions in the solid phase in the approximation of an isotropic continuum. The key parameters entering into the working formula, more specifically, the additional activation volume for the solid phase and the compressibility coefficient, were estimated using semiempirical methods. The calculated values of K R range from several units to several thousand units, an interval that encompasses all the experimental values of this quantity. Low values of K R are indicative of reactions in the bulk of the crystal lattice. In addition, reactions on defects can occur, being predominant at K R > 100. In all cases, the calculated values of K R give an upper estimate of the degree of retardation, above which no experimental values have been obtained.  相似文献   

2.
The interaction of an electromagnetic E wave with a thin metal film placed between two dielectric media is calculated in the case of different specular reflectances q1 and q2 for the reflection of electrons from the surface of the thin metal layer, in the case of variations in the values of dielectric permittivities ε1 and ε2 of the media, and in the case of different values of angle of incidence θ of the electromagnetic wave. The behavior of reflection coefficient R, transmission coefficient T, and absorption coefficient A in relation to the frequency of the external field is analyzed.  相似文献   

3.
We present the results of the study of the energy correlators K2(n) and K3(n) and their ratio R3(n) as a function of the hadron multiplicity at the LHC. The PYTHIA generator has been used. PYTHIA predicts that R3(n) is not dependent on multiplicity. K2(n), K3(n), and the R3(n) ratio can be studied at ATLAS.  相似文献   

4.
Hysterestic behavior of the magnetoresistance of granular HTSCs and its interaction with the magnetic hysteresis are studied by measuring magnetoresistance R(H) and critical current I c(H) of composites formed by HTSC Y0.75Lu0.25Ba2Cu3O7 and CuO. A network of Josephson junctions is formed in such composites, in which the nonsuperconducting component plays the role of barriers between HTSC grains. Hysteretic dependences R(H) of magnetoresistance are studied in a wide range of transport current density j and are analyzed in the framework of the two-level model of a granular superconductor, in which dissipation takes place in the Josephson medium and the magnetic flux can be pinned both in grains and in the Josephson medium. The interrelation between the hysteresis of critical current I c(H) and the evolution of the hysterestic dependence R(H) of the magnetoresistance upon transport current variation is demonstrated experimentally. The effect of the magnetic past history on the hysteretic behavior of R(H) and the emergence of a segment with a negative magnetoresistance are analyzed. It is shown for the first time that the R(H) dependences are characterized by a parameter that is independent of the transport current, viz., the width of the R(H) hysteresis loop.  相似文献   

5.
The isothermal magnetization of the Bi1 – xHo x FeO3 (x = 0?0.2) multiferroic has been studied at a hydrostatic pressure up to 9 GPa in the range of room temperatures. A new anomaly at PC ≈ 3.81 GPa related to intermediate phases between the structural transition R3cPnma has been found against the background of the pressure-induced antiferromagnetic ordering in BiFeO3 (BFO) at P ≈ 2.59 GPa. It is established that the ferromagnetic behavior under pressure depends on the Ho impurity concentration: PC decreases at 0.05 ≤ x ≤ 0.1 because of the decrease in R3c bond lengths in the structure, and the stabilization of ferromagnetism is implemented at 0.1 ≤ x ≤ 0.2 probably because of the coexistence of the R3c and Pnma phases. The results of studies indicate that, in Bi1 – xHo x FeO3 with x = 0.2, the transition pressure PC = 3.7 GPa exceeds the values for BFO doped with other 4f elements (Eu, Y, Sm) in the region R3cPnma of the transition.  相似文献   

6.
TheK-conversion coefficient of the 321 keVE1 transition in Hf177 has been measured by means of an iron free double focusing beta-ray spectrometer, using the internalexternal conversion method. The result obtained for α K (321)=0.162±0.016 is in disagreement with the theoretical values for pureE1 transition (α K =0.0154) calculated bySliv andBand. The large anomaly observed in theK-conversion process of the inhibitedE1 transition is compatible with a largeM2 admixture or, more probable with the presence of penetration matrix elements.  相似文献   

7.
We have analyzed the transport regimes and the asymptotic forms of the impurity concentration in a randomly inhomogeneous fractal medium in the case when an impurity source is surrounded by a weakly permeable degrading barrier. The systematization of transport regimes depends on the relation between the time t 0 of emergence of impurity from the barrier and time t * corresponding to the beginning of degradation. For t 0 < t *, degradation processes are immaterial. In the opposite situation, when t 0 > t *, the results on time intervals t < t * can be formally reduced to the problem with a stationary barrier. The characteristics of regimes with t * < t < t 0 depend on the scenario of barrier degradation. For an exponentially fast scenario, the interval t * < t < t 0 is very narrow, and the transport regime occurring over time intervals t < t * passes almost jumpwise to the regime of the problem without a barrier. In the slow power-law scenario, the transport over long time interval t * < t < t 0 occurs in a new regime, which is faster as compared to the problem with a stationary barrier, but slower than in the problem without a barrier. The asymptotic form of the concentration at large distances from the source over time intervals t < t 0 has two steps, while for t > t 0, it has only one step. The more remote step for t < t 0 and the single step for t > t 0 coincide with the asymptotic form in the problem without a barrier.  相似文献   

8.
We investigate whether it is possible to dynamically generate from classical transport theory the observed surprising Rout ≈ Rside in Au+Au at \(\sqrt s = 130A\) GeV at RHIC [1,2]. We obtained covariant solutions to the Boltzmann transport equation via the MPC technique [3], for a wide range of partonic initial conditions and opacities. We demonstrate that there exist transport solutions that yield a freezeout distribution with R out < R side for K ? 1.5 GeV. These solutions correspond to continuous evaporation-like freezeout, where the emission duration is comparable to the source size. Naively this would mean R out > R side. Nevertheless, our sources exhibit R out < R side because they are narrower in the‘out’ than in the‘side’ direction and, in addition, a positive x out-t correlation develops reducing R out further.  相似文献   

9.
Based on a solution of the Navier-Stokes equations for the inertial range of fully developed turbulence, a statistical theory is developed to determine the Lagrangian structure functions K n (τ). Over times τ shorter than the large-scale correlation time τc, they obey scaling relations of the form K n (τ) ∞ \(\tau ^{\zeta _n } \). Analytical expressions are derived for ζ n . A detailed comparison between the theory and the experimental results presented in [1] demonstrates complete quantitative agreement. A new concept is introduced in turbulence theory: the correlation R n (τ) between tracer-particle positions on a Lagrangian trajectory. It is shown that the position correlation functions R n exhibit universal scaling behavior for n > 3.  相似文献   

10.
The Hall coefficient and the electrical resistivity of liquid alloys has been measured with an ac current — ac magnetic field method. The experimental Hall coefficients are in agreement with the values given by the free-electron model. If for alloys of the Ag-In type the Fermi wave numbers 2k F deduced from the experimental Hall coefficients agree with the wave numbersK p of the first maximum of the partial or total correlation functionsa AB ora(K), negative temperature coefficients and a maximum of the electrical resistivity are observed for the corresponding concentrations. For alloys of the In-Sn type,K p is allways smaller than 2k F, and these alloys do not show any anomalies of the electrical resistivity. The behavior of the electrical resistivity can be explained using the formula for liquid alloys due toFaber andZiman.  相似文献   

11.
The Hall coefficient R H , resistivity ρ, and Seebeck coefficient S of the CeAl2 compound with fast electron density fluctuations were studied in a wide temperature range (from 1.8 to 300 K). Detailed measurements of the angular dependences R H (? T, H≤70 kOe) were performed to determine contributions to the anomalous Hall effect and study the behavior of the anomalous magnetic R H am and main R H a components of the Hall signal of this compound with strong electron correlation. The special features of the behavior of the anomalous magnetic component R H am were used to analyze the complex magnetic phase diagram H-T determined by magnetic ordering in the presence of strong spin fluctuations. An analysis of changes in the main contribution R H a (H, T) to the Hall effect made it possible to determine the complex activation behavior of this anomalous component in the CeAl2 intermetallic compound. The results led us to conclude that taking into account spin-polaron effects was necessary and that the Kondo lattice and skew-scattering models were of very limited applicability as methods for describing the low-temperature transport of charge carriers in cerium-based intermetallic compounds. The effective masses and localization radii of manybody states in the CeAl2 matrix were estimated to be (55–90)m0 and 6–10 Å, respectively. The behaviors of the parameters R H , S, and ρ were jointly analyzed. The results allowed us to consistently describe the transport coefficients of CeAl2.  相似文献   

12.
The results of measurements of the vertical component of electric field at a radio path with the permafrost at a frequency of 255 kHz have been interpreted. An analysis of the results has shown that the considered radio path exhibits the properties of a two-part impedance surface, i.e., it consists of two sections. At a distance of 70 km from a radiation source and at a frequency of 255 kHz of the electromagnetic wave, the field decreases with the distance R according to the power law as R-1.5 and a power index takes an intermediate value between the power indices for decreasing the field in free space R-2 and for the decrease in the field above an ideal conducting surface R-1. With further propagation at a distance of 70–220 km, the field shows the specific behavior of a surface electromagnetic wave.  相似文献   

13.
We present a systematic study of the impurity scattering effect induced by Pd dopants in the superconductor SrPt3P. Using a solid-state reaction method, we fabricated the Pd-doped superconductor Sr(Pt1?x Pd x )3P.We found that the residual resistivity ρ 0 increases quickly with Pd doping, whereas the residual resistance ratio (RRR) displays a dramatic reduction. In addition, both the nonlinear field-dependent behavior of the Hall resistivity ρ xy and the strong temperature dependence of the Hall coefficient R H at low temperature are suppressed by Pd doping. All the experimental results can be explained by an increase in scattering by impurities induced by doping. Our results suggest that the Pt position is very crucial to the carrier conduction in the present system.  相似文献   

14.
Attenuation of the Rayleigh waves propagating along an irregular surface of an empty borehole is investigated. This problem generalizes the problem on the attenuation of Rayleigh waves by an irregular boundary of a half-space. The technique used to evaluate the attenuation coefficient is based on the perturbation method and the mean field method. As a result, an expression is obtained that relates the partial attenuation coefficients of the surface Rayleigh wave to the scattering by the irregular surface of an empty borehole into the bulk longitudinal and transverse waves (the RP and RS processes) and into the surface Rayleigh waves (the RR processes). The frequency-dependent behavior of the partial attenuation coefficients is analyzed for different correlation functions of irregularities.  相似文献   

15.
K-shell X-ray fluorescence parameters of low Z elements cobalt, nickel, copper, and zinc have been measured employing a simple method. These elemental targets were excited by using 32.86 keV barium K X-ray photons from a weak 137Cs γ-ray source, and the emitted K-shell X-rays from these targets were detected using a low-energy high-purity germanium X-ray detector spectrometer. The results are compared with the standard theoretical, semi-empirical, fitted values and with the others’ experimental values.  相似文献   

16.
The hysteresis of magnetoresistance R(H) and relaxation of the remanent resistance R rem with time after magnetic field treatment of HTSC (Y-Ba-Cu-O) + CuO composites are studied. Such a composite constitutes a network of Josephson junctions wherein the nonsuperconducting component (CuO) forms Josephson barriers between HTSC grains. By comparing the experimental R rem(t) and R(H) dependences, it is shown that the relaxation of the remanent resistance is caused by the decreased magnetic field in the intergrain medium due to relaxation of magnetization. The reason is uncovered for the differences between the published values of pinning potentials determined by measuring the relaxation of magnetization or resistance and fitting them by the Anderson law.  相似文献   

17.
We report on structural, magnetic, conductivity, and thermodynamic studies of FeSe0.5Te0.5 single crystals grown by self-flux and Bridgman methods. The lowest values of the susceptibility in thenormal state, the highest transition temperature T c of 14.4 K, and the largest heat-capacity anomaly at T c were obtained for pure (oxygen-free) samples. The criticalcurrent density j c of 8.6 × 104A/cm2 (at 2 K) achieved in pure samples is attributed to intrinsic inhomogeneity due to disorder at the anion sites. The samples containing an impurity phase of Fe3O4 show increased j c up to2.3 × 105A/cm2 due to additional pinning centers. The upper critical field\(H_{c2}\)of ~500 kOe is estimated from the resistivity studyin magnetic fields parallel to the c-axis using a criterion of a 50%drop of the normal state resistivity R n . The anisotropy ofthe upper critical fieldγ H c2 =H ab c2/H c2 c reaches a value ~6 at\(T\longrightarrow T_c\). Extremely low values of the residualSommerfeld coefficient \(\gamma_r\) of about 1 mJ/mol K2,compared to the normal state Sommerfeld coefficient γ n = 25mJ/mol K2 for pure samples indicate a high volume fraction of thesuperconducting phase (up to 97%). The electronic contribution to the specific heat in thesuperconducting state is well described within a single-band BCS model with a temperature dependent gapΔ(0 K) = 27(1) K. A broad cusp-like anomaly in the electronic specific heat observed at low temperatures in samples with suppressed bulk superconductivity is ascribed to a splitting of the ground state of the Fe2+ ions at the 2c sites. This contribution is fully suppressed in the ordered state in samples with bulk superconductivity.  相似文献   

18.
The possibility of the study of ferromagnetic correlations caused by d-metal impurities in nonmagnetic matrices is discussed. The polarization and magnetic-nuclear interference obtained by analyzing the small-angle scattering of polarized neutrons in a CuZn(20) alloy with Ni impurity (1 at %) are reported. It has been shown that Ni is clustered in the CuZn matrix with the characteristic correlation radius in the range 100 Å < R c < 5000 Å depending on the thermal processing of the samples. The cross correlation function determining magnetic-nuclear interference is satisfactorily approximated by the exponential exp(?r/R c), where r is the distance. It has been found that the nonmagnetic matrix CuZn(20) with an almost uniform distribution of 1% Ni impurity has metamagnetic properties in the field H ≈ 0.5 T at room temperature.  相似文献   

19.
The dynamics of charge carriers in doped graphene, i.e., graphene with a gap in the energy spectrum depending on the substrate, in the presence of a Coulomb impurity with charge Z is considered within the effective two-dimensional Dirac equation. The wave functions of carriers with conserved angular momentum J = M + 1/2 are determined for a Coulomb potential modified at small distances. This case, just as any two-dimensional physical system, admits both integer and half-integer quantization of the orbital angular momentum in plane, M = 0, ±1, ±2, …. For J = 0, ±1/2, ±1, critical values of the effective charge Zcr(J, n) are calculated for which a level with angular momentum J and radial quantum numbers n = 0 and n = 1 reaches the upper boundary of the valence band. For Z < Zcr (J, n = 0), the energy of a level is presented as a function of charge Z for the lowest values of orbital angular momentum M, the level with J = 0 being the first to descend to the band edge. For Z>Zcr (J, n = 0), scattering phases are calculated as a function of hole energy for several values of supercriticality, as well as the positions ε0 and widths γ of quasistationary states as a function of supercriticality. The values of ε0* and width γ* are pointed out for which quasidiscrete levels may show up as Breit–Wigner resonances in the scattering of holes by a supercritical impurity. Since the phases are real, the partial scattering matrix is unitary, so that the radial Dirac equation is consistent even for Z > Zcr. In this single-particle approximation, there is no spontaneous creation of electron–hole pairs, and the impurity charge cannot be screened by this mechanism.  相似文献   

20.
The low-temperature plasticity of solid polycrystalline parahydrogen doped with an isotopic impurity (deuterium) is studied. The dependences of the rate of steady-state creep in p-H2 on the impurity concentration and stress are obtained. The deformation of p-H2 is described with inclusion of the zero-point mean-square displacements 〈x2〉 of particles making up a crystal. The calculated and experimental values of 〈x2〉 are compared for two possible isotope molecules (HD and D2) at three stress levels. A correlation between the 〈x2〉 values and an increase in the force constants of a p-H2 crystal doped with the isotopic impurity is established. An increase in the mean-square displacements of p-H2 with the tensile load is discussed. Deformation-induced purification of a p-H2 crystal from the isotopic impurity is suggested to occur.  相似文献   

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