Charge and spin order on the triangular lattice: NaxCoO2 at x=0.5

The nature of electronic states due to strong correlation and geometric frustration on the triangular lattice is investigated in connection to the unconventional insulating state of NaxCoO2 at x=0.5. We study an extended Hubbard model using a spatially unrestricted Gutzwiller approximation. We find a new class of charge and spin ordered states at x=1/3 and x=0.5 where antiferromagnetic (AFM) frustration is alleviated via weak charge inhomogeneity. At x=0.5, we show that the square root of 3a x 2a off-plane Na dopant order induces weak square root of 3a x 1a charge order in the Co layer. The symmetry breaking enables successive square root of 3a x 1a AFM and 2a x 2a charge- or spin-ordering transitions at low temperatures. The Fermi surface is truncated by the 2a x 2a hexagonal zone boundary into small electron and hole pockets. We study the phase structure and compare to recent experiments.     

中性介质中I-对鲁米诺电化学发光的增敏作用及机理研究

在中性鲁米诺电化学发光体系研究的基础上, 对中性介质中I-对鲁米诺电化学发光的增敏作用进行了研究, 结果表明, 在选定的条件下, 碘离子显著增强鲁米诺的电化学发光, 可以灵敏地对I-进行检测, 线性范围为3.8×10-7～2.2×10-6 mol·L-1, 检测下限达到4.0×10-8 mol·L-1. 该反应过程为涉及自由基的过程, 碘离子在电化学氧化过程中生成自由基, 并经过能量转移提高鲁米诺自由基的生成和激发, 提高电化学发光的量子效率, 从而起到增敏作用.     

First-order transition from a Kondo insulator to a ferromagnetic metal in single crystalline FeSi(1-x)Ge(x)

The phase diagram of FeSi(1-x)Ge(x), obtained from magnetic, thermal, and transport measurements on single crystals, shows a discontinuous transition from Kondo insulator to ferromagnetic metal with x at a critical concentration, x(c) approximately 0.25. The gap of the insulating phase strongly decreases with x. The specific heat gamma coefficient appears to track the density of states of a Kondo insulator. The phase diagram is consistent with an insulator-metal transition induced by a reduction of the hybridization with x in conjunction with disorder on the Si/Ge ligand site.     

First-principles study on the effect of Hf content onmartensitic transformation temperatureof TiNiHf alloy

In this paper a first-principles study of the electronic structure and stability of B2 TiDFT TiNiHf 电子结构 马氏体转化温度 平面波DFT, TiNiHf, electronic structure, martensitic transformation temperatureProject supported by the National Natural Science Foundation of China (Grant No 50471018).3/3/2006 12:00:00 AM6/7/2006 12:00:00 AMIn this paper a first-principles study of the electronic structure and stability of B2 Ti1-xNiHfx （x = 0.2, 0.4, 0.6） and B19′ Ti1-xNiHfx（x = 0, 0.5） alloys is presented. The calculations are performed by the plane-wave pseudopotential method in the framework of the density functional theory with the generalized gradient approximation. This paper calculates the lattice parameters, density of states, charge density, and heats of formation. The results show that the electronic structure and stability of B2 Ti1-xNiHfx change gradually with Hf content. However, Hf content has little effect on the electronic structure and stability of B19′ Ti1-xNiHfx. The mechanism of the effect of Hf content on martensitic transformation temperature of TiNiHf alloys is studied from the electronic structure.     

Tuning the plasmon energy of palladium-hydrogen systems by varying the hydrogen concentration

First-principles calculations are performed to obtain the dielectric function and loss spectra of bulk PdH(x). Hydrogen concentrations between x = 0 and 1 are considered. The calculated spectra are dominated by a broad peak that redshifts in energy with x. The obtained bulk dielectric function is employed to compute the loss spectra of PdH(x) spherical nanoparticles as a function of x. The dominant plasmon peak in the spherical nanoparticle is lowered in energy with respect to the bulk case. However, the dependence of the resonance energy on the hydrogen concentration is roughly similar to that in bulk.     

Cation Radii and Oxygen Deficiency Effects on the Structural,Magnetic, and Electrical Properties in La 1− x Sr x MnO 3−δ □ δ Manganites ( x = 0.2-0.5 and δ = 0.1)

The series of non-stochiometric strontium substituted lanthanium manganites La 1 m x Sr x MnO 3 m i i ( i = 0.1, x = 0.2-0.5) has been studied and show the effect of oxygen deficiency on the structural transition, magnetic and electrical properties of these compounds. Polycrystalline samples La 1 m x Sr x MnO 3 m i i were synthesised by a new method at atmospheric pressure. In this series of manganites, the Mn 4+ content is systematically decreased due to increase in the non-stoichiometry. X-ray diffraction analysis shows a phase transition from orthorhombic to rhombohedral systems for 0.2 h x h 0.5. The material is ferromagnetic for 0.3 h x h 0.5 and antiferromagnetic for x = 0.2. The Curie temperature T C increases with increasing x . The resistivity as a function of temperature shows that samples with x = 0.3 and ferromagnetic metal between T CF and T P becomes ferromagnetic insulators below T CF where charge-ordering seems to appear.     

The conceptual analysis (CA) method in theories of microchannels: Application to quantum theory. Part I. Fundamental concepts

A method is proposed that should facilitate the construction of theories of submicroscopic particles (denoted as theories of microchannels) in a way similar to the use of group-theoretical methods. The conceptual analysis (CA) method is based on the analysis of the basic concepts of a theory; it permits a determination of necessary conditions imposed on the mathematical apparatus (of the theory) which then appear as a mathematical representation of the structures obtained in a formal scheme of a theory. A pertinent conceptual analysis leads to a new definition (relativization) of the concept empirical implication. The approach may be characterized as realistic and operational. The application of the CA method is illustrated on the example of quantum theory. In Part I the algebraic structure of a partially ordered, up-ward directed, bounded set is deduced from the rudimentary concepts. In Parts II and III, we shall deduce the Hilbert-space structure (well established in quantum mechanics) from postulates on some essential idealizations accepted in the theory. Whereas Part II is concerned with the idealizations of existing quantum theories based on the Hilbert-space formalism, Part I may be considered as a general basis for a wider class of theories.Dedicated to Prof. G. Ludwig on the occasion of his 60th birthday.     

Scaling properties of adsorption energies for hydrogen-containing molecules on transition-metal surfaces

Density functional theory calculations are presented for CHx, x=0,1,2,3, NHx, x=0,1,2, OHx, x=0,1, and SHx, x=0,1 adsorption on a range of close-packed and stepped transition-metal surfaces. We find that the adsorption energy of any of the molecules considered scales approximately with the adsorption energy of the central, C, N, O, or S atom, the scaling constant depending only on x. A model is proposed to understand this behavior. The scaling model is developed into a general framework for estimating the reaction energies for hydrogenation and dehydrogenation reactions.     

Spacer layer thickness fluctuation scattering in a modulation-doped Al_xGa_1-xAs/GaAs/Al_xGa_1-xAs quantum well

We theoretically study the influence of spacer layer thickness fluctuation(SLTF) on the mobility of a twodimensional electron gas(2DEG) in the modulation-doped Al x Ga 1 x As/GaAs/Al x Ga 1 x As quantum well.The dependence of the mobility limited by SLTF scattering on spacer layer thickness and donor density are obtained.The results show that SLTF scattering is an important scattering mechanism for the quantum well structure with a thick well layer.     

Magnetic phase separation in La1-xSrxCoO3 by 59Co nuclear magnetic resonance

59Co NMR measurements on La1-xSrxCoO3 reported here establish unequivocally, for the first time, the coexistence of ferromagnetic regions, spin-glass regions, and hole-poor low spin regions at all x values from 0.1 to 0.5. A zero external field NMR spectrum, which is assigned to the ferromagnetic regions, has a spectral shape that is nearly x independent at 1.9 K, as are the relaxation times, T1 and T2. The integrated spectral area increases rapidly with x up to x = 0.2 and then decreases slightly for larger x. In a field of 9.97 T, a narrow NMR line is observed at 102 MHz, identical to that found in x = 0 samples in previous work. The integrated intensity of this spectrum decreases rapidly with increasing x, and is ascribed to hole-poor low spin regions. Beneath this spectrum, a third broad line, with a peak at 100 MHz, is assigned to a spin- or cluster-glass-like phase.     

流动注射化学发光测定盐酸丙卡特罗

发现盐酸丙卡特罗(Procaterol hydrochloride)在硫酸介质 中能与铈(Ⅳ)和罗丹明B产生微弱的化学发光,而在该体系中加入盐酸和表面活性剂CTMAB,能显著增强化学发光的强度。探索了该化学发光体系最佳的反应条件,初步提出了该体系的反应机理,据此建立了流动注射化学发光测定盐酸丙卡特罗的新方法,线性响应范围为2×10-8g·mL-1～1×10-6g·mL-1,检出限为6×10-9g·mL-1; 对2.0×10-7g·mL-1盐酸丙卡特罗连续11次平行测定的相对标准偏差为1.6％,该方法用于测定盐酸丙卡特罗片剂并与标准方法(中国药典法)比较,结果令人满意。     

Phase Manipulation between c(4 x 2) and p(2 x 2) on the Si(100) surface at 4.2 K

Phase manipulation between c(4x2) and p(2x2) on the Si(100) surface has been demonstrated at 4.2 K for the first time using a low-temperature scanning tunneling microscope. We have discovered that it is possible to change the c(4x2) surface into the p(2x2) surface, artificially, through a flip-flop motion of the buckling dimers by using a sample bias voltage control. Also, scanning at a negative bias voltage or applying a pulse voltage can restore the c(4x2) surface. The STM images as a function of bias voltage and tunneling current reveal the interesting dynamics of the buckling dimers on the long debated surface. Our results will show that energetic tunneling electrons are most likely responsible for the observed phase transition from c(4x2) to p(2x2).     

流动注射电化学发光分析法测定注射液中的硫酸庆大霉素

基于硫酸庆大霉素对鲁米诺在铂电极上弱的电氧化发光信号的强增敏作用与流动注射技术的结合,建立了一种测定硫酸庆大霉素的电化学发光分析新方法。该法测定硫酸庆大霉素的检出限为8.0×10-10 g·mL-1,线性范围为1.2×10-9～4.0×10-6 g·mL-1,相对标准偏差为2.0%(n =11)。该法简单、快速、灵敏,已成功地用于注射液中硫酸庆大霉素的测定。     

测定双嘧达莫的化学发光新方法

提出了双嘧达莫与高锰酸钾和罗丹明B的化学发光新体系,并发现表面活性剂吐温-80可显著增强该体系的化学发光,据此建立了流动注射化学发光测定双嘧达莫的新方法。该方法选择性好,灵敏度高,线性范围宽,双嘧达莫在5.0×10-8～5.0×10-5g·mL-1范围内与发光信号呈线性关系,检出限1.7×10-8g·mL-1, RSD为1.1%(n=11, c_s=1.0×10-6g·mL-1双嘧达莫浓度)。     

基于标准互相关函数的图像分辨率自动标定方法

理想规则图像特征经标准互相关函数匹配后,相似函数C*(x)可用确定的解析式Z(x)表达.但是对于含噪声图像,相似函数C(x)较之C*(x)发生了变化,但存在"零相似不变性".将此原理应与于显微视觉中图像物面分辨率的在线标定,推导了矩形图像特征的一维相似函数解析式Z(x);求解C(x)=0作为Z(x)的近似,并给出了具体标定算法;通过仿真图像实验,给出标定算法的正确度在0.1～0.2 pixel;最后,将标定算法应用于可连续变焦的微对准装配系统,实测算法的精密度可达为0.08 pixel.实验结果表明,基于"零相似不变性"的标定算法是具有实用性的亚像素标定方法.～290nm波长激发下,310～390nm范围内产生荧光光谱,峰位波长在350nm,最佳激励波长为250nm;采用垂直偏振片(起偏角为0°)起偏照射样品,发现偏振荧光峰位不变,荧光峰强度随检偏角的增大而呈明显的线性递减关系.由实验数据计算得到荧光偏振度为0.783,表明分子具有一定确定取向;另外,分析认为酸性橙Ⅱ产生荧光,是由于分子中含有苯环和萘环结构吸收紫外光能量,以及氮键在光子作用下形成顺式异构体的激发单线态后,两者发射的光子所致.整个结果对酸性橙Ⅱ在食品中的违禁使用检测、特性表征、以及分子规律的更深入研究,有一定的参考价值.     

Average shape of a fluctuation: universality in excursions of stochastic processes

We study the average shape of a fluctuation of a time series x(t), which is the average value (T) before x(t) first returns at time T to its initial value x(0). For large classes of stochastic processes, we find that a scaling law of the form (T) = T(alpha)f(t/T) is obeyed. The scaling function f(s) is, to a large extent, independent of the details of the single increment distribution, while it encodes relevant statistical information on the presence and nature of temporal correlations in the process. We discuss the relevance of these results for Barkhausen noise in magnetic systems.     

Planar waveguide‐resonator: a new device for x‐ray optics

Systematic investigations of the width dependence on the x‐ray beam propagation mechanism for a narrow extended slit formed by two plane dielectric plates are presented. It is shown that the mechanism of a multiple consecutive total reflection for Cu Kα radiation dominates in a slit width range s ≥ 3 µm. At the same time the manner of Cu Kα radiation propagation for super‐narrow slits s ≤ 0.1 µm is very different from the multiple total reflection mechanism. The x‐ray beam intensity proves to be constant for all this range of magnitude. This gives grounds to expect that the super‐narrow slit area is characterized by a specific type of mechanism of x‐ray beam propagation: waveguide‐resonance. A simple model for the waveguide‐resonance propagation mechanism based on the formation of a uniform x‐ray standing wave interference field in the total space of a narrow extended slit was developed. The design of a new x‐ray optical device, namely a planar x‐ray waveguide‐resonator, is proposed based on the waveguide‐resonance mechanism. Some properties of the composite planar x‐ray waveguide‐resonator are discussed. It is shown that under specific conditions the composite waveguide can demonstrate a partial tunneling effect of the x‐ray beam. The main applications of the new technique are discussed. Copyright © 2004 John Wiley & Sons, Ltd.     

Space-time-wave number-frequency Z(x, t, k, f) analysis of SAW generation on fluid filled cylindrical shells

A new 4D space-time-wave number-frequency representation Z(x,t,k,f) is introduced. The Z(x,t,k,f) representation is used for processing 2D space-time signal collection issued from wave propagation along a 1D medium. This representation is an extension along the time dimension of the space-wave number-frequency representation. The Z(x,t,k,f) representation is obtained by short time-space 2D Fourier transforming the space-time collection. The Z(x,t,k,f) representation allows the characterization transient aspects of wave generation and propagation in both space and time dimensions. The Z(x,t,k,f) representation is used to experimentally investigate Lamb wave generation and propagation around a cylindrical shell (relative thickness is equal to 0.03) surrounded by water and excited by a pulse (0.1 micros duration with 1-5 MHz transducers). Three kinds of fluids have been used inside the shell: air, water, propanol. In all the cases, the Z(x,t,k,f) analysis clearly identify the reflected field on the insonified side of the shell and it allows the measurement of the local reflection coefficients R(x,t,k,f). The generation and the propagation of Lamb waves are also quantified. For the liquid filled shells, the multiple internal reflections are revealed by Z(x,t,k,f) analysis: the local transmission coefficients T(x,t,k,f) are also measured. When local matching conditions allows Lamb wave generation, the multiple regeneration of Lamb wave is observed. Based on these results, a link is establish toward the theoretical results obtained by steady state approach and Sommerfeld-Watson transform.     

化学发光法测定左氧氟沙星

利用左氧氟沙星对碱性luminol H2 O2 化学发光体系具有强的增敏作用 ,建立了一种测定左氧氟沙星的新方法。方法的线性范围为 5 5 3× 10 - 1 1 ～ 2 2 1× 10 - 8mol·L- 1 ,检测限 (3σ)为 1 38× 10 - 1 1 mol·L- 1 ,RSD为2 5 6 % (n=9)。该法用于胶囊的测定 ,结果满意。