Analysis of the characteristics of time-resolved signals for transient radiative transfer in scattering participating media

Transient radiative transfer (TRT) in one-dimensional (1-D) homogeneous and inhomogeneous media with ultra-short pulse laser irradiated is investigated by means of the finite volume method (FVM) in the present research. Comparing with the steady radiative transfer (SRT), the extra time-resolved information can be obtained in TRT. Meanwhile, the propagation speed of short-pulse laser and the geometric thickness of the media should be considered in the simulation of TRT problem besides the optical thickness. A new nondimensional number ζ=ct_p/L is presented. For the homogeneous media, the temporal signals would overlap one another with different combinations of the pulse duration and the thickness of the media with the same ζ. Furthermore, in two-layer media, the influence of the scattering albedo, optical thickness and the geometric thickness of the participating media on ‘dual-peak’ are studied thoroughly. The improved expression of the ‘local minimum’ in the ‘dual-peak’ and the interface location of the multi-layer media are provided.     

Antiferromagnetic order and phase transitions in GdS as studied with X-ray resonance-exchange scattering

We report on X-ray resonance exchange and neutron scattering of metallic GdS. At the L_II and L _III absorption edges of Gd, resonance enhancements of more than two orders of magnitude over the non-resonant magnetic scattering are observed. Polarisation analysis proves that these enhancements are due to dipolar transitions from the 2p to the 5d states. The branching ratio between the L_II and L _III edges of 2.5 suggests a polarisation of the 5d electrons in the ground state. The antiferromagnetic order is of type II in the fcc lattice. Single crystal diffraction of hot neutrons suggests that the spin direction lies within the (111) planes with a value for the sublattice magnetisation of 6.51(3) . The critical exponent for the sublattice magnetisation has a value of β = 0.38(2) in agreement with a pure Heisenberg model. Above T _N, a sharp component persists in the critical diffuse scattering. Lattice distortions give indications for two additional low-temperature phase transitions at about 49 K and 32 K. We argue that these transitions are not connected to spin reorientations and discuss the possible influence of fourth-order exchange interactions. Received 19 November 1999 and Received in final form 12 December 2000     

Observation of transient adsorption or skipping motion in small angle ion-surface scattering

Transient adsorption or skipping motion of silicon ions scattered under specular conditions from a Cu(111) surface is reported. The phenomena is identified on the basis of the observation of discrete energy loss peaks in the scattered positive and negative ion kinetic energy distributions, together with their behaviour upon variation of the crystal azimuth, incidence angle of the beam to the surface, and scattering angular distributions. Up to five reflections in a binding potential were seen. We propose that the beam is trapped following an energy loss, by electron-hole pair or plasmon excitation, which exceeds the incident beam energy component normal to the surface. The results lend strong support to the thesis that ion beam techniques can probe the family of potential surfaces upon which adsorption and reaction, at thermal energies, proceed.     

Visualization of aggregation process of dispersed water droplets and the effect of aggregation on secondary atomization of emulsified fuel droplets

The effect of aggregation of dispersed water droplets on secondary atomization of emulsified fuel droplets in a heating process was investigated. Secondary atomization was observed using a single droplet experiment in which a water-in-oil (W/O) emulsified fuel droplet prepared using colored water was heated by a halogen heater. The initial diameter of dispersed water droplets before heating was controlled, and the change in the diameter of dispersed water droplets was measured by image analysis. As a result, the aggregation process of dispersed water droplets in the heating process was successfully visualized. The dispersed water droplet diameter increased with an increase in W/O emulsified fuel droplet temperature. The occurrence probability of micro-explosion increased with an increase in the dispersed water droplet diameter in emulsified fuel droplets. It is suggested that the occurrence probability of micro-explosion can be increased by accelerating the aggregation and coalescence of dispersed water droplets below 430 K, which is the average temperature of the starting point of puffing.     

Absolute intensity and phase of the resonant X-ray scattering from a germanium crystal

The 222 and 600 reflections near the germanium absorption K edge were studied on the Kurchatov synchrotron radiation source. The energy spectrum of the 222 reflection is caused by the interference of the weak nonresonant and purely resonant contributions to the tensor atomic factor, whereas the 600 reflection is purely resonant. The energy dependence of the magnitude and phase of the resonant contribution to the scattering amplitude was determined from a change in the interference pattern. The numerical simulation of the energy spectra of reflections with the inclusion of the dipole-quadrupole and thermally induced contributions shows that the latter is dominant at room temperature. Original Russian Text ? E.Kh. Mukhamedzhanov, M.M. Borisov, A.N. Morkovin, A.A. Antonenko, A.P. Oreshko, E.N. Ovchinnikova, V.E. Dmitrienko, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 12, pp. 896–900.     

Absolute intensity and phase of the resonant X-ray scattering from a germanium crystal

The 222 and 600 reflections near the germanium absorption K edge were studied on the Kurchatov synchrotron radiation source. The energy spectrum of the 222 reflection is caused by the interference of the weak nonresonant and purely resonant contributions to the tensor atomic factor, whereas the 600 reflection is purely resonant. The energy dependence of the magnitude and phase of the resonant contribution to the scattering amplitude was determined from a change in the interference pattern. The numerical simulation of the energy spectra of reflections with the inclusion of the dipole-quadrupole and thermally induced contributions shows that the latter is dominant at room temperature.     

X-ray scattering and theα-α′ phase transition in coherent metal-hydrogen systems

Metallic singlet ground state systems have often anomalous elastic properties which result from the coupling of the phonons to the crystal field energy levels of the rare earth ions. It is shown that structural and magnetic phase transitions should occur in the same way in those systems. They are caused by a sufficiently strong electron-ion interaction. While the orbital part of this interaction is responsible for possible structural phase transitions, the spin dependent part is responsible for magnetic phase transitions. This is demonstrated in detail by considering as an example the aspherical Coulomb charge scattering and the isotropic exchange interaction. We calculate the sound velocity, the sound attenuation and the excitations in the presence of the aspherical Coulomb charge scattering. Furthermore we discuss the mutual coupling of structural and magnetic phase transitions. This includes a consideration of other types of coupling than aspherical Coulomb scattering and isotropic exchange.     

Theory of defect states in the two-dimensional planar rotator model with long-range interaction

The interaction law for defect states of the vortex-pair type in the planar rotator model with long-range interaction $\text{1}\text{r}{}^{\mathrm{\alpha }}$ and 2?α?4, is derived. It is shown that the constituents of a vortex-pair do not interact via a log r law as it is the case for the short-range interaction but are more tightly bound. Furthermore the concept of the state of excitation of a vortex-pair is developed. The consequences of this theory for the character of the phase transition in these models is discussed.     

In-situ monitoring of EuTiO_3 and SrTiO_3 film growth using time-resolved X-ray scattering during pulsed-laser deposition

Time-resolved X-ray scattering was employed to in-situ monitor the epitaxial growth process of the thin films and multilayers of EuTiO3 and SrTiO3 during pulsed laser deposition. The temporal intensity oscillations of the reflected X-rays at auti-Bragg position and the transient processes following the flux pulses were observed. The temporal intensity oscillations were used to control the film thickness, and the reflectivity along the crystal truncation rod was used to measure both the film thickness and the surface/interface roughness. The primary features of the X-ray intensity oscillations were reproduced via simulating the experimental data using diffusive rate equation model. Several mechanisms of determining the X-ray intensity features were discerned.     

Anisotropy of critical X-ray scattering in the vicinity of smectic B-nematic phase transition in EPPCB

The high-resolution X-ray scattering has been used to study the anisotropy of the density correlation function in the vicinity of S_B-N phase transition in the recently developed material EPPCB. The effective critical exponents estimated in the temperature interval 10^?4 <t< 10^?2 (t = T/T_C ? 1) are: γ = 1.34 ± 0.09, ν_⊥ = 0.56 ± 0.08, ν_| = 0.70 ± 0.06 and fulfill, within experimental errors, the relation γ = ν_⊥ + ν_|.The novel feature is that the iso-intensity contours in the scattering plane containing the direction normal to the smectic layers have been found to be of four-winged shaped. A phenomenological (mean-field) theoretical approach explaining this shape in terms of the independence of fluctuations in the longitudinal (perpendicular to the smectic layers) and transversal (in the smectic planes) directions has been proposed.     

Evaporation of droplets in the two-dimensional Ginzburg–Landau equation

We consider the problem of coarsening in two dimensions for the real (scalar) Ginzburg–Landau equation. This equation has exactly two stable stationary solutions, the constant functions +1 and −1. We assume most of the initial condition is in the “−1” phase with islands of “+1” phase. We use invariant manifold techniques to prove that the boundary of a circular island moves according to Allen–Cahn curvature motion law. We give a criterion for non-interaction of two arbitrary interfaces and a criterion for merging of two nearby interfaces.     

Deduction of the temperature-dependent structure of the four-layer intermediate smectic phase using resonant X-ray scattering

A binary mixture of an antiferroelectric liquid-crystal material containing a selenium atom and a highly chiral dopant is investigated using resonant X-ray scattering. This mixture exhibits a remarkably wide four-layer intermediate smectic phase, the structure of which is investigated over a temperature range of 16K. Analysis of the resonant X-ray scattering data allows accurate measurement of both the helicoidal pitch and the distortion angle as a function of temperature. The former decreases rapidly as the SmC ^* phase is approached, whilst the latter remains constant over the temperature range studied at 8^°±3^° . We also observe that the senses of the helicoidal pitch and the unit cell of the repeating four-layer structure are opposite in this mixture and that there is no pitch inversion over the temperature range studied.     

Diffuse X-ray scattering from a calomel crystal near the temperature of the structural phase transition

X-ray scattering from a calomel crystal near the temperature of a structural phase transition is analyzed theoretically. It is shown that the diffuse lines of the x-ray diffraction, which correspond to both the X points and Z point of the Brillouin zone, are formed in the high-temperature phase. The latter lines result from the scattering by the beats of fluctuations of two components of the order parameter. Such lines were previously observed experimentally, but the nature of the lines corresponding to the Z point remained unclear. It is shown that the Z line at the point (5, 0, 0) should be an order of magnitude stronger than the observed Z line at the point (4, 3, 0).     

Structure of the amorphous phase of pyrolisates of lanthanum diphthalocyanine according to X-ray scattering data

Data on X-ray diffraction in lanthanum diphthalocyanine pyrolysates synthesized at temperatures of 800–1800°С demonstrate the formation of an amorphous carbon phase with embedded lanthanum atoms. Low-temperature pyrolysis (800–900°С) creates layered carbon structures. Due to annealing at 1000°С, carbon integrates into globules whose number of atoms is m ~ 100. Such structures with gyration radii of R _g ~ 0.4–0.5 nm on the order of the precursor molecule size are synthesized in the temperature range of 1000–1800°С, and are stable in terms of size and mass. In this case, their density approaches that of graphite.     

利用基于自动复形技术的二维光子晶体模型设计宽角度宽波长偏振分束器

基于自动复形技术，在148—152μm的近红外波段设计了可以实现全角度偏振分束（TM模透过，TE模反射）的波状膜层二维光子晶体结构.从能带角度解释了全角度偏振分束的原理.波状膜层倾角θ和a-Si单层膜厚T分别可以在38°—49°和014—015μm的范围内变动，不影响全角度的偏振特性.对波状膜层进行了变形，针对波长128—1 31μm设计了宽角度偏振分束的箭羽型二维光子晶体结构.对比两种结构的能带，阐明了二 维光子晶体偏振分束器光线入射角范围的拓宽与能带结构变化的关系.能带计算全部采用平 面波展开算法. 关键词： 偏振分束 平面波展开 完全禁带     

On the theory of slow-particle scattering in the two-dimensional case

A solution to the problem of elastic scattering of low-energy particles on a “weak” potential U is given. An expression for the amplitude of s-wave scattering is found in this approximation, and it is shown that, for U < 0, it has a pole at the energy E ₀ of the corresponding loosely bound state. An explicit expression in terms of the potential U is obtained for the preexponential factor, which refines the known order-of-magnitude estimate for E ₀.     

Quantum phase transition in the two-dimensional XY model with single-ion anisotropy

In this paper we study the quantum phase transition and low temperature behavior in a square lattice quantum two-dimensional XY model with single-ion anisotropy and spin S=1. Starting with the Villain representation, a Landau-Ginzburg expression is written. The large D phase is studied using the bond operator formalism.