Quantum transport in a time-dependent random potential with a finite correlation time

Using an earlier density matrix formalism in momentum space we study the motion of a particle in a time-dependent random potential with a finite correlation time τ, for 0 < t ? τ. Within this domain we consider two subdomains bounded by kinetic time scales (t _c ² = 2m? ^-1 c ², c ² = σ ², ξ ², σξ, with 2σ the width of an initial wavepacket and the correlation length of the gaussian potential fluctuations), where we obtain power law scaling laws for the effect of the random potential in the mean squared displacement 〈x ²〉 and in the mean kinetic energy 〈E _kin〉. At short times, ? min (t _σ ², 1/2t _ξ ²), 〈x ²〉 and 〈E _kin〉 scale classically as t ⁴ and t ², respectively. At intermediate times, t _σξ ? t ? 2t _σ ² and 1/2t _ξ ² ? t ? t _σξ, these quantities scale quantum mechanically as t ^3/2 and as √t, respectively. These results lie in the perspective of recent studies of the existence of (fractional) power law behavior of 〈x ²〉 and 〈E _kin〉 at intermediate times. We also briefly discuss the scaling laws for 〈x ²〉 and 〈E _kin〉 at short times in the case of spatially uncorrelated potential.     

Quantitative Mössbauer analysis

The quantitative analysis of Mössbauer data, as in the measurement of Fe³⁺/Fe²⁺ concentration, has not been possible because of the different mean square velocities 〈x²〉 of Mössbauer nuclei at chemically different sites. A method is now described which, based on Mössbauer data at several temperatures, permits the comparison of absorption areas at 〈x²〉=0.     

Deep inelastic neutrino interactions in the bubble chamber skat at 2–30 GeV

Data on inclusive deep inelastic neutrino interactions at 2–30 GeV are presented. Distributions in x, y and 〈Q²〉 dependence on neutrino energy are compared with quark-parton model predictions. The 〈Q²〉 dependence on energy has the form: 〈Q²〉 = (0.2 ± 0.1) + (0.25 ± 0.02) E_v.     

An SO(10) model with 54 + 126 + 10 higgs

We find an absolute minimum of an SO(10) symmetric potential with SU(3) × U(1) invariance. By fixing the higher scales M_R(〈126〉) ? M_x(〈54〉), the model is consistent with the experimental knowledge about matter stability and the value of sin²θ_w. We determine the spectrum of scalar particles and show that their tree-diagram contributions to nucleon decay amplitudes are proportional to 1/M_x².     

Cosmic ray results on the A dependence of multiplicity and angular distributions in proton nuclear interactions above 100 GeV

A calorimeter-spark chamber system was used to collect data on several hundred proton-nucleus interactions above 100 GeV using targets of C, Al, Fe, Sn and Pb. The average charged prong multiplicity is found to depend on atomic mass number as 〈n_c〉 = 〈n_c〉(p-p)A^x where x = 0.129 ± 0.004, with the dominant increase in multiplicity occuring in the backward (p-p c.m.) hemisphere. The value of x shows no significant energy dependence.     

Estimation of parameters ofK-meson structure functions

On the basis of multiparton recombination model with the use of the Kuti-Weisskopf parametrization there have been analyzed the available experimental data on inclusive spectra of the vector and tensor mesons in the reactionsK ^± p→MX (M=?, φ,K(890),K(1430)) in the kaon fragmentation region at high energies (32–110GeV/c) with the aim to extract the parameters of theK-meson structure functions. For the suppression factor of the kaon strange sea the valueλ = 0.18±0.01 is obtained. The kaon longitudinal momentum fractions carried away by nonstrange and strange valence quarks and sea partons respectively are 〈x _N ^V 〉=0.17, 〈x _S ^V 〉=0.30 and 〈x ^S 〉=0.53.     

Self-consistent Gaussian model of nonperturbative QCD vacuum

We show that the minimal Gaussian model of nonlocal vacuum quark and quark-gluon condensates in QCD violates the transverse character of the correlator of two vector currents. We suggest the improved Gaussian model of the nonperturbative QCD vacuum, which respects QCD equations of motion and minimizes the revealed gauge-invariance breakdown. We obtain the refined values of pion distribution amplitude (DA) conformal moments 〈ξ^2N 〉_π (N = 1, ..., 5) using the improved QCD vacuum model, including the inverse moment 〈x ^?1〉_π, being inaccessible if one uses the standard QCD SR. We construct the allowed region for Gegenbauer coefficients a ₂ and a ₄ of the pion DA for two values of the QCD vacuum nonlocality parameter, λ _q ² = 0.4 and 0.5 GeV².     

Correlation between band structure and hydride formation in dilute palladium alloys

Data on the free energy change ΔG, following solution of hydrogen in dilute Pd-alloys Pd_1?xM_x have been reviewed for different concentrations of M (M = Au, Ag, Pt, Ir, Rh, V, Cu, Ni, Pb, Sn and Ti) in both the α and β phases. The dependence of ΔG values upon the nature of the substituents (transition metals) is consistently explained within the framework of a metal-hydrogen bonding mechanism in the hydrides. For the β-hydride the ΔG values can be calculated on the basis of the equation ΔG = ΔG_pd + a(T)(〈?^M_LB〉 ? 〈?^Pd_LB〉)x, where $\text{ΔG}{}_{\mathrm{<mtext>Pd</mtext>}}\text{= ? 0.0489}\text{eV}\text{H}$ atom and is the free energy change of solution of hydrogen in pure Pd, a(T) = 0.194 at T = 298 K, 〈?^m_LB〉 and 〈?^pd_LB〉 are the average energies of the lowest band of the pure constituents ($\text{〈?}{}^{\mathrm{<mtext>Pd</mtext>}}{}_{\mathrm{<mtext>LB</mtext>}}\text{〉 = ?9.15}\text{eV}\text{atom}$). The stability of the palladium-hydrogen bond in dilute Pd-alloys depends on the value of 〈?^M_LB〉; for substituents having lower 〈?^M_LB〉 values than Pd the bond will strengthen, while for those having higher 〈?^M_LB〉 values it will weaken. This behaviour agrees well with the general trend of the stability of the stoichiometric hydrides predicted by Gelatt, Ehrenreich and Weiss using band structure results.     

Exponents for the excluded volume problem as derived by the dynamic renormalization group method

By regarding the contour length L of a polymer chain as “time”, we derive the mean-square end-to-end distance 〈x²〉 for the polymer chain with excluded volume by means of the dynamic renormalization group. The result to first order in ? = 4 ? d (d is the dimension of the space) is $\text{〈x}{}^2\text{〉 =}\text{const}\text{× L}{}^{\mathrm{<mtext>1+?</mtext><mtext>8</mtext>}}$.     

Mass generation in the O(3) non-linear σ model

We study the two-point function of the azimuthal angle, G^(φ)(x) = 〈e^iφ(x)e^?iφ(0)〉_inst [φ = arg (q¹ + iq²), where q^a is a three-component unit vector field], in the dense instanton gas approximation for the two-dimensional O(3) non-linear σ model. We find that G^(φ) (x) decreases exponentially as |x| → ∞. This suggests that the dense instanton gas may generate a mass gap in the O(3) non-linear σ model. The physical mechanism of this mass generation is also discussed.     

Exact Results for Conditional Means of a Passive Scalar in Certain Statistically Homogeneous Flows

For a passive scalar T(r, t) randomly advected by a statistically homogeneous flow, the probability density function (pdf) of its fluctuation can in general be expressed in terms of two conditional means: 〈?² T|T〉 and 〈|?T|²|T〉. We find that in some special cases, either one of the two conditional means can be obtained explicitly from the equation of motion. In the cases when there is no external source and that the normalized fluctuation reaches a steady state or when a steady state results from a negative damping, 〈?² T|T〉=?(〈|?T|²〉/〈T ²〉)T. The linearity of the conditional mean in these cases follows directly from the fact that the advection equation of a passive scalar is linear. On the other hand, when the scalar is supported by a homogeneous white-in-time external source, 〈|?T|²|T〉=〈|?T|²〉.     

Finite-temperature perturbation theory for the random directed polymer problem

We study the random directed polymer problem—the short-scale behavior of an elastic string (or polymer) in one transverse dimension subject to a disorder potential and finite temperature fluctuations. We are interested in the polymer short-scale wandering expressed through the displacement correlator 〈[δu(X)]²〉, with δu(X) being the difference in the displacements at two points separated by a distance X. While this object can be calculated at short scales using the perturbation theory in higher dimensions d > 2, this approach becomes ill-defined and the problem turns out to be nonperturbative in the lower dimensions and for an infinite-length polymer. In order to make progress, we redefine the task and analyze the wandering of a string of a finite length L. At zero temperature, we find that the displacement fluctuations 〈[δu(X)]²〉 ∝ LX ² depend on L and scale with the square of the segment length X, which differs from a straightforward Larkin-type scaling. The result is best understood in terms of a typical squared angle 〈α²〉 ∝ L, where α = ? _x u, from which the displacement scaling for the segment X follows naturally, 〈[δu(X)]²〉 ∝ 〈α²〉 X ². At high temperatures, thermal fluctuations smear the disorder potential and the lowest-order results for disorder-induced fluctuations in both the displacement field and the angle vanish in the thermodynamic limit L → ∞. The calculation up to the second order allows us to identify the regime of validity of the perturbative approach and provides a finite expression for the displacement correlator, albeit depending on the boundary conditions and the location relative to the boundaries.     

Measurement of the ratios of deep inelastic muon-nucleus cross sections on various nuclei compared to deuterium

Results are presented on the ratios of the deep inelastic muon-nucleus cross sections for carbon, copper and tin nuclei to those measured on deuterium. The data confirm that the structure functions of the nucleon measured in nuclei are different from those measured on quasi-free nucleons in deuterium. The kinematic range of the data is such that 〈Q²〉 ∼ 5 GeV² at x ∼ 0.03, increasing to 〈Q²〉 ∼ 35 GeV² for x ∼ 0.65. The measured cross section ratios are less than unity for x ≲ 0.05 and for 0.25 ≲ x < 0.7. The decrease of the ratio below unity for low x becomes larger as A increases as might be expected from nuclear shadowing. However, this occurs at relatively large values of Q² (∼ 5 GeV²) indicating that such shadowing is of patrionic origin.     

Estimating the Enantiomorphic Excess in Polycrystalline Metal Samples with a B20-Type Structure

The degree of enantiomorphic excess (average chirality 〈Γ〉)in bulk polycrystalline Fe_1–xCo_xSi samples with a cobalt concentration of x = 0.10, 0.15, 0.20, 0.25, 0.30, and 0.50 is studied. Polycrystals are synthesized by melting the initial high-purity components. Surface examination of the samples showed that they are composed of acicular coaxially oriented crystallites with an average volume of ~2 mm³. The magnetic chirality γ, which is directly related to the crystallographic chirality Γ as γ =–Γ, is measured using small-angle polarized neutron diffraction. It is established that the average chirality of polycrystals 〈γ〉 is independent of the Co concentration within the statistical precision of the number of crystallites in the samples used in the experiment. The chirality of individual polycrystallites is distinct from zero and sometimes reaches 10–20%, being determined by the total number of crystallites in a sample (~100). The measurement error of the average chirality 〈γ〉 is determined by neutron scattering statistics and does not exceed 1%.     

Anomalous hyperfine field and orbital moment of cobalt in RCo2; R = Pr,Nd, Sm,Gd, Tb,Dy, Ho,Er and Tm

⁵⁹Co spin echo NMR spectra in the magnetically ordered phase of the MgCu₂ type RCo₂ compounds (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm) have been observed. For the RCo₂ with the easy direction of magnetication parallel to the 〈011〉 or 〈111〉 direction, the ⁵⁹Co hyperfine fields at two magnetically inequivalent Co sites are found to be antiparallel, revealing a large anisotropy in the ⁵⁹Co hyperfine field. The results are discussed in terms of a large and anisotropic orbital moment of Co. The transferred hyperfine field due to rare earth spins is estimated from well resolved satellite lines observed in Tb_1?xY_xCo₂. The nuclear quadrupole splitting in the magnetically ordered phase is found to be always larger than that in the paramagnetic phase.     

Investigation of thermal sensitivity and radiation resistance of SiOx〈Ti〉 metal-dielectric films

In this investigation the composite SiO_x〈Ti〉 films were prepared by the thermal evaporation of a mixture of silicon oxide (SiO₂) and Тi powders. The optical transmission of the films in the IR spectral range and their temperature-sensitive properties are studied. By varying the contents of the metal in vaporizer and time of evaporation it is possible to obtain SiO_x〈Ti〉 layers with resistance (for monopixel of 0.8 × 1 mm) from tens kOhms to MOhms and a value of the temperature coefficient of resistance (TCR) is equal to −2.22% K⁻¹. IR spectrum of SiO_x〈Ti〉 film is characterized by a broad absorption band in the range of 8–12 μm which is associated with the Si–O–Si stretching mode.Investigations of the effect of gamma irradiation on SiO_x〈Ti〉 films have shown that their temperature-sensitive properties, in particular TCR does not change up to a dose of 10⁶ Gy.These results suggest that SiO_x〈Ti〉 films can be used as materials for production of radiation-resistant thermosensitive detectors operated in radiation fields of γ-radiation and combining functions of IR-absorption and formation of an electric signal.     

Determination of Lamb–Mössbauer factors and lattice dynamics in some nitroprusside single crystals

Mössbauer spectra have been recorded for sodium, guanidinium, barium and lithium nitroprussides single crystal cuts. The temperature dependence of the Lamb–Mössbauer fraction f, respectively, the mean-square nuclear displacement 〈x ²〉 and the mean-square (of the total) velocity of the iron nucleus 〈v ²〉 were analyzed on the basis of the Debye and Einstein lattice-vibration models. The characteristic temperatures of the two models, θ _D and θ _E, fitted to 〈x ²〉 are considerably lower than those fitted to 〈v ²〉. This effect seems to be typical for the iron complexes and was explained with the presence of low and high frequencies in the phonon vibration spectra and of low-temperature anharmonicity. The Lamb–Mössbauer fraction at 77 K in all principal crystal directions of sodium, guanidinium and barium nitroprussides has been determined. These values will be used for more precise studies of the population and the properties of the light-induced molecular states of the nitrosyl [Fe(CN)₅NO]^2? anion.     

Impurity lattice dynamics of Fe in Cr from precision Mössbauer fraction measurements

Precision 〈x²〉-values and their anharmonicity been measured for ⁵⁷Fe in Cr between 80 K and 600 K. At 294 K. $\text{? = 0.798 ± 0.005}$. A theoretical analysis based upon Cr neutron scattering data yields 0.8 for the impurity/host force constant ratio.     

Low-temperature plasticity and lattice dynamics of solid parahydrogen with an isotopic impurity

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.