Multiple scattering of matter waves: an analytic model of the refractive index for atomic and molecular gases

We present an analytic model of the refractive index for matter waves propagating through atomic or molecular gases. The model, which combines a WKB treatment of the long range attraction with the Fraunhofer model treatment of the short range repulsion, furnishes a refractive index in compelling agreement with recent experiments of Jacquey et al. [Phys. Rev. Lett. 98, 240405 (2007)] on Li atom matter waves passing through dilute noble gases. We show that the diffractive contribution, which arises from scattering by a two dimensional "hard core" of the potential, is essential for obtaining a correct imaginary part of the refractive index.Comment: 5 pages, 1 figure, 2 table

An analytic model of rotationally inelastic collisions of polar molecules in electric fields

We present an analytic model of thermal state-to-state rotationally inelastic collisions of polar molecules in electric fields. The model is based on the Fraunhofer scattering of matter waves and requires Legendre moments characterizing the "shape" of the target in the body-fixed frame as its input. The electric field orients the target in the space-fixed frame and thereby effects a striking alteration of the dynamical observables: both the phase and amplitude of the oscillations in the partial differential cross sections undergo characteristic field-dependent changes that transgress into the partial integral cross sections. As the cross sections can be evaluated for a field applied parallel or perpendicular to the relative velocity, the model also offers predictions about steric asymmetry. We exemplify the field-dependent quantum collision dynamics with the behavior of the Ne-OCS($^{1}\Sigma$) and Ar-NO($^2\Pi$) systems. A comparison with the close-coupling calculations available for the latter system [Chem. Phys. Lett. \textbf{313}, 491 (1999)] demonstrates the model's ability to qualitatively explain the field dependence of all the scattering features observed

The nonlinear time-dependent response of isotactic polypropylene

Tensile creep tests, tensile relaxation tests and a tensile test with a constant rate of strain are performed on injection-molded isotactic polypropylene at room temperature in the vicinity of the yield point. A constitutive model is derived for the time-dependent behavior of semi-crystalline polymers. A polymer is treated as an equivalent network of chains bridged by permanent junctions. The network is modelled as an ensemble of passive meso-regions (with affine nodes) and active meso-domains (where junctions slip with respect to their positions in the bulk medium with various rates). The distribution of activation energies for sliding in active meso-regions is described by a random energy model. Adjustable parameters in the stress--strain relations are found by fitting experimental data. It is demonstrated that the concentration of active meso-domains monotonically grows with strain, whereas the average potential energy for sliding of junctions and the standard deviation of activation energies suffer substantial drops at the yield point. With reference to the concept of dual population of crystalline lamellae, these changes in material parameters are attributed to transition from breakage of subsidiary (thin) lamellae in the sub-yield region to fragmentation of primary (thick) lamellae in the post-yield region of deformation.Comment: 29 pages, 12 figure

Fourth Order Algorithms for Solving the Multivariable Langevin Equation and the Kramers Equation

We develop a fourth order simulation algorithm for solving the stochastic Langevin equation. The method consists of identifying solvable operators in the Fokker-Planck equation, factorizing the evolution operator for small time steps to fourth order and implementing the factorization process numerically. A key contribution of this work is to show how certain double commutators in the factorization process can be simulated in practice. The method is general, applicable to the multivariable case, and systematic, with known procedures for doing fourth order factorizations. The fourth order convergence of the resulting algorithm allowed very large time steps to be used. In simulating the Brownian dynamics of 121 Yukawa particles in two dimensions, the converged result of a first order algorithm can be obtained by using time steps 50 times as large. To further demostrate the versatility of our method, we derive two new classes of fourth order algorithms for solving the simpler Kramers equation without requiring the derivative of the force. The convergence of many fourth order algorithms for solving this equation are compared.Comment: 19 pages, 2 figure

Kinetic equations for thermal degradation of polymers

Kinetic equations are analyzed for thermal degradation of polymers. The governing relations are based on the fragmentation-annihilation concept. Explicit solutions to these equations are derived in two particular cases of interest. For arbitrary values of adjustable parameters, the evolution of the number-average and mass-average molecular weights of polymers is analyzed numerically. Good agreement is demonstrated between the results of numerical simulation and experimental data. It is revealed that the model can correctly predict observations in thermo-gravimetric tests when its parameters are determined by matching experimental data for the decrease in molecular weight with exposure time

Wave-induced loss of ultra-relativistic electrons in the Van Allen radiation belts.

The dipole configuration of the Earth's magnetic field allows for the trapping of highly energetic particles, which form the radiation belts. Although significant advances have been made in understanding the acceleration mechanisms in the radiation belts, the loss processes remain poorly understood. Unique observations on 17 January 2013 provide detailed information throughout the belts on the energy spectrum and pitch angle (angle between the velocity of a particle and the magnetic field) distribution of electrons up to ultra-relativistic energies. Here we show that although relativistic electrons are enhanced, ultra-relativistic electrons become depleted and distributions of particles show very clear telltale signatures of electromagnetic ion cyclotron wave-induced loss. Comparisons between observations and modelling of the evolution of the electron flux and pitch angle show that electromagnetic ion cyclotron waves provide the dominant loss mechanism at ultra-relativistic energies and produce a profound dropout of the ultra-relativistic radiation belt fluxes

Short-range oscillators in power-series picture

A class of short-range potentials on the line is considered as an asymptotically vanishing phenomenological alternative to the popular confining polynomials. We propose a method which parallels the analytic Hill-Taylor description of anharmonic oscillators and represents all our Jost solutions non-numerically, in terms of certain infinite hypergeometric-like series. In this way the well known solvable Rosen-Morse and scarf models are generalized.Comment: 23 pages, latex, submitted to J. Phys. A: Math. Ge

Optical and photoelectrical properties of CdSxSe1–x films produced by screen-printing technology

In this paper the optical and photoelectrical properties of CdSxSe1–x films prepared using the screenprinting and sintering technique, were studied. CdCl2 was used both as a sintering flux and as a doping agent. CuCl was also used as a doping agent. The temperatures and times of preparation varied in the range of 500–600 °С and 5–60 min, respectively. The as-prepared films were characterized by the scanning electron microscopy, micro-probe X-Ray analysis, photoluminescence and photoconductance methods. Our investigations have shown that photoresponse of the CdSxSe1–x films prepared by a screenprinting method can be suitable for the production of large-area photosensitive devices

Debating capabilities of biochemical markers of liver function in patients with alcoholic liver cirrhosis

Introduction. The diagnosis of alcohol-related liver disease is limited by the lack of a tool to reliably identify whether the present deterioration in the patient’s condition is due to alcohol consumption or other causes.Purpose. to conduct a comparative assessment of the clinical and diagnostic significance of liver function biochemical indicators (AST, ALT, GGT, ALP) and their calculated derivatives (AST/ALT, GGT/ALP, GGT/GGTn, ALP/ALPn) as markers of alcohol consumption in patients with alcoholic liver cirrhosis.Material and methods. The observational study included 112 men over 18 years of age with alcohol-related liver cirrhosis. The patients were assessed the severity of liver cirrhosis according to the Child-Pugh scale, performed general and biochemical blood tests, coagulation test, assessment of the fact of alcohol consumption by the level of phosphatidylethanol. An analysis was made of the relationship between alcohol consumption and changes in laboratory parameters of liver function, with the determination of their sensitivity and specificity.Results. Patients with Child-Pugh B cirrhosis who consumed alcohol on phosphatidylethanol had higher levels of plasma albumin, GGT, and lower values of creatinine, direct and total bilirubin, urea, and aPTT compared with patients who did not drink alcohol (p < 0.05). Alcohol-drinking patients with class C cirrhosis have higher ALT levels compared with abstinent patients with the same severity of cirrhosis (p < 0.05). The relationship between the fact of alcohol consumption, determined by the level of phosphatidylethanol, and the ratio of GGT of patients to the normal GGT value, as well as between the ratio of GGT to alkaline phosphatase and the degree of increase in GGT, turned out to be statistically significant. To assess the fact of alcohol consumption, the level of serum GGT > 65 IU/ l (75.5%) has the highest sensitivity, the highest specificity is the ratio of the patient’s GGT to the normal value of GGT > 2 (82.9%).Conclusion. Compared with the known 100% sensitivity and > 92% specificity of Peth as a alcohol biomarker, among the biochemical indicators of liver function and their calculated derivatives, GGT > 65 IU/l have the greatest sensitivity or specificity (respectively, 75.5% and 65%) and GGTnorm. > 2 (37.7% and 82.9%, respectively), which makes it possible to use the totality of these parameters as an indicator of the continued impact on the patient of the main etiological factor of alcohol-related liver cirrhosis in the routine practice of most medical organizations of the Russian Federation