STUDY OF ELECTRONIC SPECTRA IN INHOMOGENEOUS DISORDERED CHAINS BY RENORMALIZATION-GROUP BLOCK-DECIMATION METHOD

we have generalized the renormalization-group block-decimation method to study the spectra of the inhomogeneous disordered binary alloy chains. The numerical results for the densities of states in periodically modulated disordered chains are obtained.     

Dielectric spectra of disordered ferroelectric systems: Polycrystals and composites

The dielectric spectra of heterogeneous systems that have very large dielectric constants and exhibit the Maxwell-Wagner relaxation are analyzed. The spectra of the disordered systems are found to be of a non-Debye type, and attempts to fit them using either the Cole-Cole or Davidson-Cole equations sometimes fail to produce satisfactory results. Experimental spectra of disordered systems are proved to be close to the spectra obtained by computer simulation of statistical mixtures and ferroelectric ceramics. A new formula is suggested to describe the dielectric relaxation in polycrystalline and composite materials, and reasons for the non-Debye nature of the dielectric spectra are examined.     

一维二元非对角关联无序体系交流跳跃电导特性

在单电子紧束缚无序模型基础上，建立了一维二元非对角关联无序体系电子跳跃输运交流电导模型，并推导了其交流电导公式，通过计算其交流电导率，探讨了格点能量无序度、格点原子组分、非对角关联及温度、外场对体系交流跳跃电导的影响.计算结果表明，一维二元非对角关联无序体系的交流电导率随格点能量无序度的增大而减小.同时，体系中两种原子的组分的变化实际代表着体系成分无序程度的变化，因而对其交流电导率的影响很大，表现为随A类原子含量p的增加而先减小后增大.当引入非对角关联时，体系出现退局域化现象，电子波函数由局 关键词： 二元无序体系 交流跳跃电导 格点能量无序度 非对角关联     

Practical aspects of running the WIEN2k code for electron spectroscopy

The Wien2k code is widely used for the calculation of electron energy loss spectra. Low loss spectra can be calculated with the OPTIC package while core loss spectra are calculated with the TELNES program. A new version, TELNES.2, takes into account the effects of relativity for anisotropic materials. In this paper we discuss the effects of different parameters used for the self-consistent calculation of the electron density on the obtained spectra. We give an overview of possibilities for the calculation of complicated systems requiring a super-cell, like defects or disordered systems. We discuss the problem of the core hole and of the calculation of orientation-sensitive spectra and give an overview of results already published.     

Electric hyperfine interactions in ferromagnetic binary alloys above the curie temperature

In the frame of an unscreened point charge model we calculated all possible electric field gradients for first neighbor atom arrangements in disordered binary fcc alloys. With these values and a distribution of isomer shifts we fit experimental spectra of nearly disordered alloys.     

Ionic motion in materials with disordered structures

The dynamics of mobile ions in materials with disordered structures constitute a challengingly complicated many-particle process. Time-resolved information on the dynamics is obtained from spectra of the complex ionic conductivity, which span more than 17 decades on the frequency scale. Ionic crystals with structural disorder as well as ion-conducting glasses, melts and polymers are found to display similar characteristics of their complex conductivity spectra. The features observed in the spectra led us to formulate a set of simple rules for the ion dynamics. The rules may be written as rate equations, forming the so-called MIGRATION concept. The acronym stands for MIsmatch Generated Relaxation for the Accommodation and Transport of IONs. Ionic movements that remain localised are described by a modified version of the MIGRATION concept, which accounts for the NCL (Nearly Constant Loss) behaviour. In general, all aspects of the experimental conductivity spectra of disordered ionic materials are well reproduced by model spectra comprising MIGRATION-type, NCL-type and vibrational components.     

Study of optical response in disordered alloys using the generalized recursion in augmented space: Application to ferromagnetic FeCo alloy

We propose and briefly describe the generalized recursion in augmented space using a minimal TB-LMTO basis set for the calculation of configuration averaged current response functions in disordered binary alloys. Since disorder in the current terms is off-diagonal and non-separable, single-site mean-field approaches are unable to deal with it without further approximations. The augmented space approach is ideally suited for such situations and the generalized recursion proposed by Viswanath and Müller provides a fast and accurate O(N) technique for the actual calculations of the configuration averaged susceptibilities. We have applied the method to the disordered FeCo alloy. The results agree reasonably well with available experimental data on ordered versions of both the alloy systems, with extra broadening due to disorder induced lifetime effects.     

Statistical analysis of spectra of single impurity molecules and dynamics of disordered solids: I. Distributions of linewidths,moments, and cumulants

A review of recent results of studying the low-temperature dynamics of a disordered solid-state medium that were obtained by the method of single molecule spectroscopy (SMS) is presented. The studies were carried out with the use of the new approach of the statistical analysis of a large number of spectra of single molecules embedded into a medium under study as a microscopic spectral probe. The measurements were performed in the range 2–7 K. The use of SMS allowed us to avoid the information losses connected with the averaging over an ensemble of impurity molecules that is inherent in conventional spectral methods. For the example of the system studied (amorphous polyisobutylene doped with molecules of tetra-tert-butylterrylene), it was shown experimentally that, at low temperatures, the spectra of single impurity molecules in disordered media obey the Levy statistics. New microscopic information on the interaction of two-level systems and quasi-local low-frequency vibrational modes of the matrix with impurity molecules in a disordered medium was obtained.     

Random lasing in strongly disordered medium

Using the time-dependent theory, we calculate the random-laser emission spectra in a two-dimensional strongly disordered medium. The calculation results show that in low dimensional systems, such as thin- film disordered media and planar waveguides, the larger the difference of the refractive indices between the scattering and background media, the smaller the lasing threshold. We also reveal the existence of multi-mode survival and mode competition. We experimentally obtain the emission spectra of a dye solution with Al particles doped at different pumping energies, and the experimental results agree well with the calculated ones.     

多元无序合金相干势近似的图形分析

本文将处理二元无序合金电子性质的平均单粒子和双粒子格林函数的图形分析推广到多元无序合金。在单格点近似下,如果我们自洽地处理累积量中的多次占有修正,则从图形分析得到的平均单粒子和双粒子格林函数与相干势近似的结果相一致。 关键词：     

Renormalization group decimation technique for disordered binary harmonic chains

The density of states of disordered binary harmonic chains is calculated using the Renormalization Group Decimation Technique on the displacements of the masses from their equilibrium positions. The results are compared with numerical simulation data and with those obtained with the current method of Gonçalves da Silva and Koiller. The advantage of our procedure over the other methods is discussed.     

基于Isomap算法的恒星光谱离群点挖掘

如何从已分类的海量光谱中发现被错分的光谱一直是天文数据处理专家重点研究的问题,探讨的Isomap算法在该问题方面有很好的表现。通过Isomap算法与主成分分析方法(PCA)算法的实验结果对比发现：(1)PCA将具有不同特征的光谱投影到邻近的区域,而Isomap算法却可以将具有相似特征的光谱投影到邻近区域,而将具有不同特征的光谱投影到相距较远的区域;(2)Isomap算法给出的大部分离群点较易判断,且是具有很高科学价值的双星;而PCA给出的离群点难以判断,科学价值不高。因此,在光谱离群点发掘上Isomap算法比PCA有明显优势。由于使用的数据为SDSS最新发布的M型的九种光谱次型的光谱,因而Isomap算法能够快速发现被斯隆数字巡天数据处理流程(SDSS pipeline)错分的光谱,可帮助有效提高现有光谱分类算法的准确率。更进一步,由于被SDSS pipeline错分的光谱大部分是双星,因而Isomap算法还可以进一步帮助我们发现有很高科学研究价值的双星,提高双星的发现效率。虽然实验显示Isomap算法对信噪比变化较为敏感,在具有较低信噪比的光谱上表现较差,但由于信噪比低的光谱的光谱型难以判断,因而该缺点并不影响Isomap算法的在光谱发掘上的应用。     

Observational Results of Stellar Speckle Interferometric Spectroscopy

Stellar speckle spectroscopy is a speckle interferometric method enabling us to separate point by point spectra on a stellar object with a diffraction-limited spatial resolution of a telescope. We describe observational results obtained with our system for speckle spectroscopy. Data of two binary stars, of which separations are closer than seeing disc, were taken and processed by cross-correlation method. In each object, spectral images of two component stars around the Hα line (656.3 nm) were spatially resolved with nearly diffraction-limited resolution. The separated spectra of ADS940 reveal different spectral types of the component stars. These results demonstrate the ability of the speckle spectroscopic method.Presented at the International Commission of Optics Topical Meeting, Kyoto, 1994.     

Luminescence and gain spectroscopy of disordered CdS1−x Se x under high excitation

The absorption-, reflection-, and luminescence spectra of CdS_1–x Se _x are measured under low excitation. The luminescence under high excitation is also observed. For the first time, the gain spectra of disordered crystals are investigated with the excite- and probebeam technique to get a better understanding of the high density electron-hole pair system in this type of materials. We compare the results with those obtained in pure CdS and CdSe.     

Critical ultrasonic attenuation in a disordered binary alloy

The expression for ultrasonic attenuation in a binary alloy (annealed disordered) system has been obtained solving the Green function equation of motion and performing configurational averaging. Its typical dependence on the configurational fluctuation correlation is seen to lead to a non-divergent behaviour in the ultrasonic attenuation near the order-disorder transition point, where the correlations diverge. The results compare well with the experimental observations on β-brass.     

The soft X-ray spectra of concentrated binary alloys

The soft X-ray spectra of Al-Mg alloys are discussed within a simple model. Reasonable agreement with experiment is obtained. The results explain the main features of the spectra of any binary alloy with non-zero valence difference. Elementary consequences are discussed.     

无序二元合金（NixCu1-x）表面CO吸附及对表面偏析的影响

根据计算机编程构造出了存在和不存在表面偏析的无序二元合金Ni_xCu_1-x（x=0.4）的原子集团模型，然后按覆盖度θ=0.5，构造出了CO表面吸附的模型 ，应用Recursion方法计算了CO在（Ni_xCu_1-x）（存在偏析和不存在偏析时）合金表面不同位置（顶位和芯位）吸附的电子结构 .由此得出：1)CO在顶位吸附时较稳定；2)CO吸附使合金表面态密度峰降低，带宽加宽，使d轨道的局域性变弱；3)CO的吸附抑制了Cu 关键词： 化学吸附 表面偏析 Recursion方法 态密度     

Density of states of vibrations in a disordered chain

We study the local density of vibrational states of a disordered binary chain using a renormalization approach suitable for the alloy problem. We include isotopic and spring constant disorder. Short range order effects in the alloy are taken into account in the pair approximation. We present some numerical results for the case of spring constant disorder and discuss their relevance for the interpretation of neutron scattering experiments in some metallic amorphous systems.     

71Ga NMR of reference GaIV, GaV, and GaVI compounds by MAS and QPASS, extension of gallium/aluminum NMR parameter correlation

We report new measurements of NMR parameters for 71Ga in gallium bearing oxide reference compounds, ranging from perfectly ordered systems to disordered crystalline structures and their aluminate counterparts. Static, MAS, and QPASS spectra are obtained at magnetic fields ranging from 7.0 to 18.8 T. With these results we enhance the previously established correlation between isotropic chemical shifts of 71Ga and 27Al and propose a correlation between gallium and aluminum electric field gradients (EFG). This correlation shows that the EFG at 71Ga sites are generally three times greater than those at equivalent 27Al sites.