Explanation of Temperature-Dependent Resistivity of Sm-Doped Cuprates by Electron–Phonon Scattering

The resistivity of electron-doped cuprate Sm_1.85Ce_0.15CuO_{4 –} is theoretically analyzed within the framework of electron–phonon i.e., Bloch–Gruneisen (BG) model of resistivity. Characteristic temperatures as the Debye temperature and the Einstein temperature were first derived from an overlap repulsive potential. The optical phonons of the oxygen-breathing mode yield a relatively larger contribution to the resistivity compared to the contribution of acoustic phonons above 220 K. While to that, below this temperature, acoustic phonon is a major cause of resistivity. Estimated contribution to resistivity by considering both phonons i.e., _ac (acoustic phonons) and _op (optical phonons), along with the zero limited resistivity, when subtracted from single crystal data, infers a quadratic temperature dependence over most of the temperature range (25 T 300). Power temperature dependence of _diff.{=[ _exp. – ( ₀ + _e-ph(= _ac + _op))]} points the contribution of electron–electron inelastic scattering. The present analysis allows us to infer that the single crystal experimental data is well approximated within the framework of BG electron–phonon model of resistivity. Further calculations of superconducting transition temperature and isotope effect exponent from Kresin's strong coupling theory indicates that the electron–phonon interaction plays an important role in the attractive pairing mechanism.     

Influence of Multiple‐Scattering Processes on the Laser Probing of Biological Tissues

Theoretical aspects of multiplescattering processes in laser probing of biological tissues have been considered. The method of digital dynamic specklephotography has been described. The results of experimental studies of the nearsurface blood flow and stressedstrained states in a pinstructure–toothroot model are presented.     

Calculation of Scattering Parameters for Ultracold K–Cs Elastic Collisions

A theoretical study of elastic scattering properties in a mixture of ³⁹K and ¹³³Cs atoms at cold and ultracold temperatures is reported in this paper. Based on the new constructed accurate singlet X ¹∑⁺ and triplet a ³∑⁺ states interatomic potentials for ³⁹K¹³³Cs mixture, the interspecies s-wave scattering lengths and the p-wave scattering volumes are calculated by the variable phase method and the semiclassical method, respectively. Good agreement between two methods is obtained. The mass dependence of the scattering data by considering all isotopomers is explored, and the numbers of bound states supported by the molecular potentials for each isotopomer are also calculated.     

Study of the Characteristics of Scattering of Electromagnetic Waves from Complex‐Shaped Bodies by the Method of Auxiliary Sources

The problem of diffraction of a plane wave on sphere–cone–sphere and cone–sphere bodies by the method of auxiliary sources is solved. According to this method, diffraction fields may be presented in the form of vector wave potentials with densities distributed over the auxiliary surface drawn inside the scattering body. Comparison of theoretical and experimental results is made.     

Scattering of waves by a soft–hard half-plane between isorefractive medium

The scattering of plane waves by a soft–hard half-plane residing between isorefractive medium is studied. The scattered geometrical optics fields are obtained by subtracting the initial geometrical optics fields from the total geometrical optics waves. The diffracted fields are determined by considering the structure of the scattered geometrical optics waves. The uniform expressions for the diffracted fields are derived. The behaviour of the total waves is investigated numerically.     

Stochastic Modeling of Impurity Motion and Scattering in the Mechanics of Turbulent Gas‐Dispersed Flows

Issues associated with the development and realization of stochastic models of the impurity particle motion and scattering in a turbulent flow are considered. The proposed model is used to calculate turbulent flows of a lowconcentration gas suspension in channels and jets. We compare the results of the calculations obtained from the viewpoint of different models and the results of numerical simulation with the data in which the influence of turbulent pulsations on the particle motion was ignored.     

Diffusion Modes of an Equimolar Methane–Ethane Mixture from Dynamic Light Scattering

The hydrodynamic diffusion modes of an equimolar methane–ethane mixture have been investigated by dynamic light scattering. Measurements were performed over a wide temperature range between the plait critical point at 263.55 K and 310 K along the critical isochore. Two relaxation modes have been observed which are commonly associated with pure mass diffusion and pure thermal diffusion, but in near-critical binary fluid mixtures—according to recent theory—may alternatively be interpreted as two effective diffusivities resulting from a coupling between mass and thermal diffusion. Diffusivity values for the slow mode were obtained with typical standard deviations of 1% over the whole temperature range, whereas the low amplitude of the fast mode only allowed values of this component with a large measurement uncertainty. The results are discussed in connection with literature data available for the thermophysical properties of this binary fluid mixture and regarding the various possibilities of theoretical interpretation.     

Thermal Conductivity of a Molecular Crystal with Rotational Degrees of Freedom: Orientational Defect Scattering

Measurements of thermal conductivity of solid methane-deuteromethane solutions at equilibrium vapor pressure in the temperature range 1.2÷20 K are reported. The obtained dependences of thermal conductivity on temperature and concentration can be explained qualitatively assuming that the dominant mechanism of phonon scattering is connected with the interaction of phonons with the rotational motion of the molecules in all of the three orientational phases of the CH₄-CD₄ system. The contribution of the orientational defect scattering to the thermal conductivity is discussed in frame of the model of local changes in the moments of inertia of molecules.      

Light Scattering Study of Aqueous Poly(Vinyl)pyrrolidone–Fullerene C70 Solutions

Abstract

It was shown by static and dynamic light scattering that poly(vinyl)pyrrolidone (PVP) molecules form large intermolecular complexes (clusters) with C₇₀ in aqueous solutions. The molecular weights and dimensions of PVP–C₇₀ clusters increase both with the increase of fullerene content and the molecular weight of the matrix PVP. However, two different diffusion coefficients were detected by dynamic light scattering. The slow mode was explained as diffusion of large PVP–C₇₀ clusters. The fast mode represents free PVP molecules in solution. Dimensions of clusters revealed in aqueous PVP–C₇₀ solutions are less than that for PVP–C₆₀ by factor of 2.5–3.     

Kinetics of the Temperature Fields in a Light‐Scattering Layer Heated by a Radiant Flux

The process of heating and cooling down of a lightscattering and absorbing planeparallel layer irradiated by a light pulse is discussed. Results are obtained by solving numerically the differential equations of radiation transfer and heat conduction. By the method of finitedifference approximation of space derivatives the problem is reduced to a system of ordinary differential equations with respect to time for the temperature at each point of the layer. Results of calculations for different durations and powers of pulses and different optical and thermophysical parameters of the medium are reported. A comparison is made of the characteristics of temperature processes in the layer on the source side of incidence of a light pulse and on the opposite side.     

Growth Kinetics of Nanocrystals and Nanorods by Employing Small-angle X-ray Scattering （SAXS） and Other Techniques

In this article, we report the results of our detailed investigations of the growth kinetics of zero-dimensional nanocrystals as well as one-dimensional nanorods by the combined use of small angel X-ray scattering （SAXS）, transmission electron microscopy （TEM） along with other physical techniques. The study includes growth kinetics of gold nanocrystals formed by the reduction of HAuCl4 by tetrakis（hydroxymethyl） phosphonium chloride in aqueous solution, of CdSe nanocrystals formed by the reaction of cadmium stearate and selenium under solvothermal conditions, and of ZnO nanorods formed by the reaction of zinc acetate with sodium hydroxide under solvothermal conditions in the absence and presence of capping agents. The growth of gold nanocrystals does not follow the diffusion-limited Ostwald ripening, and instead follows a Sigmoidal rate curve. The heat change associated with the growth determined by isothermal titration calorimetry is about 10 kcal·mol^-1 per I nm increase in the diameter of the nanocrystals. In the case of CdSe nanocrystals also, the growth mechanism deviates from diffusion-limited growth and follows a combined model containing both diffusion and surface reaction terms. Our study of the growth kinetics of uncapped and poly（vinyl pyrollidone） （PVP）-capped ZnO nanorods has yielded interesting insights. We observe small nanocrystals next to the ZnO nanorods after a lapse of time in addition to periodic focusing and defocusing of the width of the length distribution. These observations lend support to the diffusion-limited growth model for the growth of uncapped ZnO nanorods. Accordingly, the time dependence on the length of uncapped nanorods follows the L3 law as required for diffusion-limited Ostwald ripening. The PVP-capped nanorods, however, show a time dependence, which is best described by a combination of diffusion （L^3） and surface reaction （L^2） terms.     

Neutron and Raman Scattering Studies of Hgba2CuO4+δ

The HgBa₂CuO₄₊ sample was characterized by Neutron diffraction and magnetic measurements. Both of the measurements indicate a high purity of the sample. Raman measurement was performed on a HgBa₂CuO₄₊ compound of T_c = 96 K. The apical oxygen vibration at 592 cm^–1 was found to show (a) an above T_c anomaly, and (b) frequency hardening and linewidth broadening below the superconducting phase transition. The latter is attributed to the coupling of the phonon to the electronic excitation and related to the opening of the superconducting gap below the phonon frequency.     

Fabry–Perot Cavity Control for Tunable Raman Scattering

The Fabry–Perot (FP) resonator is an intuitive and versatile optical structure owing to its uniqueness in light-matter interactions, yielding resonance with a wide range of wavelengths as it couples with photonic materials encapsulated in a dielectric cavity. Leveraging the FP resonator for molecular detection, a simple geometry of the metal-dielectric-metal structure is demonstrated to allow tuning of the enhancement factors (EFs) of surface-enhanced Raman scattering (SERS). The optimum near-field EF from randomly dispersed gold nano-gaps and dynamic modulation of the far-field SERS EF by varying the optical resonance of the FP etalon are systematically investigated by performing computational and experimental analyses. The proposed strategy of combining plasmonic nanostructures with FP etalons clearly reveals wavelength matching of FP resonance to excitation and scattering wavelengths plays a key role in determining the magnitude of the SERS EF. Finally, the optimum near-field generating optical structure with controlled dielectric cavity is suggested for a tunable SERS platform, and its dynamic SERS switching performance is confirmed by demonstrating information encryption through liquid immersion.     

Scattering and Heat Exchange of Disperse Impurity Particles in Turbulent Nonisothermal Gas and Low‐Temperature Plasma Jets

This paper considers issues connected with the simulation of the motion and heat exchange of disperse impurity particles in nonisothermal gas and lowtemperature plasma jets under the action of turbulent pulsations of the carrier flow. The influence of the outflow conditions, the initial parameters of the phases, and the conditions of particle injection into a jet flow on the laws of impurity scattering and heat exchange are investigated. The results of the numerical calculations are compared with the data obtained without taking into account the influence of turbulent pulsations on the particle motion.     

Mechanism of Inelastic Phonon Scattering on the Quadrupolar o–H2 Impurity in p–H2 Matrix

A quantum–mechanical problem on inelastic phonon scattering by a quadrupolar pair defect is discussed. As an example of the physical system, where this mechanism is of great concern, the solution of o–H ₂ molecules in p–H ₂ matrix is considered. The effective relaxation time _p of a phonon collision with a pair defect as a function of the phonon frequency is calculated. Due to intrinsic degrees of freedom, pair defects give rise to the resonance phonon scattering above a certain temperature T ₀ , which for o–H ₂ —p–H ₂ mixtures is approximately 6 ÷ 7 K.     

Scattering of Electromagnetic Waves by a Reflector Antenna with Feed Containing a Nonlinear Metal–Dielectric–Metal Contact

We have studied scattering of electromagnetic waves by a reflector antenna with feed containing a metal–dielectric–metal contact with nonlinear voltage–current characteristic. We propose and evaluate the effectiveness of ways to eliminate stray radiation.     

D''yakonov–Perel'' Spin Relaxation Controlled by Electron–Electron Scattering

The D'yakonov–Perel' mechanism of spin relaxation is connected with the spin splitting of the electron dispersion curve in crystals lacking a center of symmetry. In a two-dimensional noncentrosymmetric system, e.g. quantum well or heterojunction, the spin splitting is a linear function of k, at least for small values of k. We demonstrate that the spin relaxation time _s due to the spin splitting is controlled not only by momentum relaxation processes as widely accepted but also by electron–electron collisions which have no effect on the electron mobility. In order to calculate the time _s taking into account the electron–electron scattering, we have solved the two-dimensional kinetic equation for the electron spin density matrix. The result has been compared with that obtained assuming the momentum scattering to occur due to elastic scattering of electrons by ionized impurities. We have also extended the quasi-elastic approximation to describe the electron–electron collision integral for a spin-polarized three-dimensional electron gas.     

D'yakonov–Perel' Spin Relaxation Controlled by Electron–Electron Scattering

The D'yakonov–Perel' mechanism of spin relaxation is connected with the spin splitting of the electron dispersion curve in crystals lacking a center of symmetry. In a two-dimensional noncentrosymmetric system, e.g. quantum well or heterojunction, the spin splitting is a linear function of k, at least for small values of k. We demonstrate that the spin relaxation time τ_s due to the spin splitting is controlled not only by momentum relaxation processes as widely accepted but also by electron–electron collisions which have no effect on the electron mobility. In order to calculate the time τ_s taking into account the electron–electron scattering, we have solved the two-dimensional kinetic equation for the electron spin density matrix. The result has been compared with that obtained assuming the momentum scattering to occur due to elastic scattering of electrons by ionized impurities. We have also extended the quasi-elastic approximation to describe the electron–electron collision integral for a spin-polarized three-dimensional electron gas.     

Revealing Precipitate Development During Hot Rolling and Cooling of a Ti–Nb Micro-Alloyed High Strength Low-Alloy Steel through X-Ray Scattering

High-energy synchrotron X-ray small-angle scattering (SAXS) is used to study the precipitate development during hot rolling and cooling of a commercial Ti–Nb micro-alloyed, high-strength, low-alloy (HSLA) steel. To study precipitation during hot rolling conditions, Gleeble and dilatometer trials are made. Samples are then studied at room temperature using SAXS in conjunction with transmission electron microscopy (TEM). TEM is used to determine the morphology and composition of the precipitates, whilst both TEM and SAXS are used to study the particle sizes. One major advantage with high-energy SAXS is the ability to make measurements after a minimum of sample preparation and in transmission geometry, as opposed to just at prepared surfaces, plus the possibility to determine volume fractions of the precipitates. The measurements show that after deformation at high temperature, particle coarsening occurs and the volume fraction of precipitates increases after holding for 20 s at 900 °C which confirms strain-induced precipitation at finishing rolling conditions. The measurements show that holding at 600 or 650 °C for one hour gives a larger volume fraction of nanosized particles. Coiling simulations with slow cooling from 600 to 470 °C show coarsening of particles and an increase in the volume fraction of the smaller particles compared to holding at a constant temperature.     

Static Ferromagnetic Modulation Revealed by Neutron Scattering in La1−xCaxMnO3

Mn perovskites La_1?x Ca _x MnO₃ (0≤x0.1) have been studied by small angle neutron scattering (SANS) and “elastic” neutron scattering (ESANS). At low temperature, both experiments reveal a broad modulation centered at the same q _m whatever the q direction. This scattering pattern is typical of a liquid-like distribution of similar magnetic droplets, or large magnetic polarons.