Static and dynamic properties of XY systems with extended defects in cubic anisotropic crystallines

Static and dynamic critical behavior ofXY systems in cubic anisotropic crystallines, with extended defects (or quenched nonmagnetic impurities) strongly correlated along _d -dimensional space and randomly distributed ind – _d dimensions, were studied. These extended defects make the systems coordinate anisotropic, resulting in unique critical behavior due to competition between the cubic anisotropy and the coordinate anisotropy. The systems were analyzed by an ^1/2 (4 – d) type of expansion with double expansion parameters based on a renormalization-group (RG) approach. Critical exponents were calculated near the second-order phase transition point and the behavior of the first-order transition was evaluated near the tricritical point.     

Modeling of anisotropic spheres in extended teleparallel theory with matter coupling

This work is devoted to investigate the structures of compact stars by using spherically static symmetric space-time in the background of $f(\tau ,T)$ gravity, where $\tau$ represents the torsion scalar and $T$ represents the trace of the energy momentum tensor. We develop the field equations by using the concept of quintessence to discuss the motion by using anisotropic fluid distribution with a spherically symmetric metric. We use the convention of junction conditions to evaluate the unknown parameters used in the study of the compact stars. In this study we use the available data of three different compact objects $4U1608-52,$ $CenX-3$ and $EXO1785-240$. We discuss the physical and analytical existence of compact stars by satisfying some standard properties of compact stars like the behavior of the energy density, quintessence density, radial and tangential pressures, anisotropy, to elaborate the anisotropic nature of the star. We discuss the sound speeds and casuality conditions to show the stability of the system. Equilibrium of the star is justified by the TOV equation. Red-shift function, compactness, and mass function states the physical existence of the star. It is examined that all these parameters show the viability and stability of the model used in the effects of $f(\tau ,T)$ gravity.     

Diffusion-induced oscillations of extended defects

From a simple model for the driven motion of a planar interface under the influence of a diffusion field we derive a damped nonlinear oscillator equation for the interface position. Inside an unstable regime, where the damping term is negative, we find limit-cycle solutions, describing an oscillatory propagation of the interface. In the case of a growing solidification front this offers a transparent scenario for the formation of solute bands in binary alloys and, taking into account the Mullins-Sekerka instability, of banded structures.     

等离子体辅助甲烷聚合物制备及分析

在氢气和甲烷环境下,利用辉光等离子体放电制备了聚合物。该聚合物的外观特征为白色、略发黄、柔软、丝状,易碎为粉末状。聚合物中含有–CH3,–CH2,C–O,–C=C–,–OH等官能团且不存在单质形态的碳。有机溶剂溶解分析发现,常温下该聚合物在各种有机溶剂中的溶解性极小、小于0.1mg.ml^-1,几乎不溶于甲苯中,在不同有机溶剂中的溶解度大小依次为,S丙酮>S三氯甲烷>S乙醇>S环己醇>S甲苯。低温等离子体的离化率越高、中性气体被极化时的极化半径越大、环境温度越低以及介电常数越小,聚合物的生成能力越强。     

Transmission through chiral twist defects in anisotropic periodic structures

A long-lived photonic state is observed in measurements of microwave transmission through a helical stack of anisotropic overhead transparencies with various twist defects in the center of the structure. Once account is taken of absorption and of the angular spread of the source, computer simulations of transmission through a polarized localized state are in agreement with measurements. Unlike for isotropic one-dimensional bandgaps, the intensity of the localized mode is not modulated in space on a wavelength scale.     

Ground states of the one-dimensional anisotropic extended hubbard model

We investigate a one-dimensional half-filled electron system with on-site and spin-dependent nearest-neighbor-site Coulomb interactions. Non-Tomonaga-Luttinger-type scatterings bring about Gaussian and hidden SU(2) Berezinskii-Kosterlitz-Thouless transitions in the charge and spin parts. We accurately determine these critical points using the level-spectroscopy method. The boundaries deviate from those given by bosonization prediction with the increase of interactions. In particular, in the easy-plain anisotropy region, we find a crossing point of transition lines in the charge and spin parts, which is a multicritical point of four phases. We also check consistencies among excitation levels.     

On the role of interaction of implanted atoms with extended defects

The process of implanted atom gas release from a crystal into microcracks arising under implantation and annealing has been theoretically studied. The rate of heat exchange with a substrate has been shown to affect the microcrack growth.     

From compact point defects to extended structures in silicon

We show that in contrast to the 1d Frenkel-Kontorova (FK) chain known to obey the Fourier law of heat conduction and several 2d models which show logarithmic dependence of conductivity on system size, a scalar 2d FK lattice with commensurate structure exhibits anomalous heat conduction, whose thermal conductivity displays a power law behavior. The dependence of thermal gradient on bulk temperature and noise correlation is critically analyzed. A dynamical contribution to conductivity when the system attains a nonequilibrium steady state of thermal conduction has been identified.     

Cathodoluminescence study of extended defects in hydrothermal ZnO crystals

Understanding the luminescence of ZnO is very important for some applications. In spite of the many studies carried out, there are still some points concerning the origin of some of the luminescence emissions in ZnO crystals that require additional study; in particular, the role of extended defects remains to be a matter of controversy. We present here a cathodoluminescence analysis of the defects generated by Vickers indentation in hydrothermal HTT crystals. Special emphasis was paid to the luminescence band peaking around 3.3 eV. The origin of this band is a matter of controversy, since it has been related to different causes, extended defects being one of the candidates for this emission. The CL images were acquired around crystal defects. It is observed that the 3.3 eV emission is enhanced around the crystal defects; though it is also observed, but weaker, out of the defect regions, which suggests that there exist two luminescence emissions peaking very close to 3.3 eV. The two emissions, one related to structural defects and the other to the LO phonon replica of the free excitonic band, appear very close each other and their relative intensity should determine the shape of the spectrum.     

Elastic displacement field of point defects in anisotropic cubic crystals

The elastic displacement field of point defects in cubic crystals is calculated for weak anisotropy by second order perturbation theory and by a variational procedure. The results are compared with numerical calculations for Cu. Further analytical approximations are given for the volume change in an infinite crystal and for the interaction energy of two point defects.     

Defect equilibria for extended point defects,with application to nonstoichiometric ceria

The dependence of electronic conductivity and composition of ceria on oxygen pressure is described by equilibrium equations for a material containing oxygen vacancies, divacancies, cerium interstitials and polarons, where these defects are considered to include distorted zones of material. The analyses takes the extension of simple “point defects” into proper account, whereas earlier analyses have not. It is concluded that available data can be explained by polarons in equilibrium with isolated oxygen vacancies, but not with divacancies or interstitial cerium ions.     

The phase diagram of the extended anisotropic ferromagnetic-antiferromagnetic Heisenberg chain

By using Density Matrix Renormalization Group (DMRG) technique we study the phase diagram of 1D extended anisotropic Heisenberg model with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions. We analyze the static correlation functions for the spin operators both in- and out-of-plane and classify the zero-temperature phases by the range of their correlations. On clusters of 64, 100, 200, 300 sites with open boundary conditions we isolate the boundary effects and make finite-size scaling of our results. Apart from the ferromagnetic phase, we identify two gapless spin-fluid phases and two ones with massive excitations. Based on our phase diagram and on estimates for the coupling constants known from literature, we classify the ground states of several edge-sharing materials.     

各向异性焊缝缺陷超声阵列全聚焦成像方法

针对奥氏体不锈钢焊接构件安全评价需要,对各向异性结构中超声波传播特性进行了研究,利用射线追踪法确定了各向异性介质中声波传播路径。在传统全聚焦成像基础上,发展了一种用于各向异性焊缝中缺陷检测的超声阵列全聚焦成像方法。通过数值仿真和实验,研究了介质材质对超声阵列成像的影响,结果表明,发展的全聚焦成像方法可以很好实现各向异性焊缝中缺陷检测,缺陷定位更准确。项目研究工作为奥氏体不锈钢焊缝检测提供了可行的技术方案.     

A quantum dissipative system in an anisotropic non-linear absorbing environment

A canonical quantization scheme is represented for a quantum system interacting with a non-linear absorbing environment. The environment is taken anisotropic and the main system is coupled to its environment through some coupling tensors of various ranks. The non-linear response equation of the environment against the motion of the main system is obtained. The non-linear Langevin-Schrödinger equation is concluded as the macroscopic equation of motion of the dissipative system. The effect of non-linearity of the environment is investigated on the spontaneous emission of an initially excited two-level atom imbedded in such an environment.     

Influence of extended defects on gold diffusion in plastically deformed silicon

The effect of defects formed in dislocation trails behind dislocations on the gold diffusion has been investigated by the deep level transient spectroscopy (DLTS) and electron beam induced current (EBIC) methods. It is found that the gold concentration in the deformed samples is two orders of magnitude higher than that in the defect-free crystal. Estimations show that the concentration of electrically active gold obtained from the DLTS data is at least ten times higher than the value, which might be expected for the dislocations themselves. A strong increase in the recombination activity of dislocation trails after gold diffusion is found from EBIC measurements, which probably is related with gettering properties of defects formed in the dislocation trails.