Mean-field approximation for the potts model of a diluted magnet in the external field

The Potts model of a diluted magnet with an arbitrary number of states placed in the external field has been considered. Phase transitions of this model have been studied in the mean-field approximation, the dependence of the critical temperature on the external field and the density of magnetic atoms has been found, and the magnetic susceptibility has been calculated. An improved mean-field technique has been proposed, which provides more accurate account of the effects associated with nonmagnetic dilution. The influence of dilution on the first-order phase transition curve and the magnetization jump at the phase transition has been studied by this technique.     

Visualization of the photorefractive grating in BSO

A technique based on self-imaging at finite conjugates has been experimentally demonstrated for visualization of laser-induced photorefractive gratings in BSO. A simple model theory has been used to provide the correct rules of geometrical optics of self-imaging. A novel technique has been used for photoinducing the periodic structure. An application has been made to determine the harmonic components of the nonsinusoidal refractive index modulation in the BSO for a grating period of 10 m and for external DC voltages of 6.0 and 3.0 kV. The technique is directly applicable to the visualization and study of laser-induced gratings (LIG) in thin nonlinear optical media.     

Atomic Absorption Spectrophotometry with the Absorption Tube Technique

A device to increase the sensitivity of the atomic absorption spectrophotometric measurement by elongating the absorption path length has originally been developed by Fuwa and Vallee and the present authors called it “absorption tube technique”. Although the technique has been fully described in comparison with the flame photometry, and the behavior of the elements and the reactions in the tube were investigated for several elements, application of a newly designed ring burner to this technique and the detailed examination of the operating conditions have never beer, published.     

Complete elimination of the beam hardening effect in quantitative absorption tomography using polychromatic x-rays with single-component specimens

Absorption tomography has been a unique technique for 3D imaging in many scientific research and applications. However, the use of polychromatic x-ray sources for quantitative tomography has been limited due to the well-known beam hardening effect. In this article, we will describe the theoretical details of a new technique for quantitative tomography using polychromatic x-rays. The technique incorporates the full spectral information of the incident beam into the tomographic reconstruction process. Consequently, beam-hardening effects are eliminated and the result is quantitative. We will also demonstrate the technique experimentally using a single-component specimen. This technique promises great opportunities for laboratory-based x-ray sources to be used in quantitative applications.     

激光诱导击穿光谱技术分析土壤中的Cr和Sr

采用波长1 064 nm的调Q脉冲Nd:YAG激光器和多通道小型光纤光栅光谱仪,建立了一套激光诱导击穿光谱分析装置.记录了系列土壤标准样品的激光诱导等离子体发射光谱,详细研究了重金属原子Cr和Sr的特征辐射谱线信号强度、标准偏差与数据采样方式以及采样平均次数的关系,首次采用300个激光脉冲轰击样品表面同一点,并取其中最大光谱信号后的200次激光轰击等离子体发射光谱的平均值进行分析的取样平均方式,发现能较好地把对重金属Cr和Sr浓度分析测量的相对标准偏差(RSD)分别减小到9.02%和10.5%,并得到了定量分析Cr和Sr等金属的定标曲线,对Cr和Sr元素的检测灵敏度分别为25.3和15.2 μg·g-1,优于目前国内外报道的结果.研究表明我们的采用的数据采集、分析定标方法对提高了LIBS技术在土壤中金属检测检测灵敏度和精密度具有很好的应用价值.     

A photonic scheme for the generation of dual linear chirp microwave waveform based on the external modulation technique and its airborne application

Due to high frequency and large time bandwidth product; photonic generation and processing of arbitrary microwave waveforms has been an interesting topic in recent time. Here, a relatively new photonic technique has been proposed for the generation of a dual linear chirp microwave waveform in Ku-band. In this method two single drive Mach–Zehnder Modulators are cascaded at minimum transmission point and in push–pull mode. Theoretical analysis and simulation are developed by giving a complete mathematical model. As the result of this methodology, a dual linear chirp microwave waveform in Ku-band with relatively large bandwidth is generated. Comparative analysis is done in the present cascading technique with dual parallel Mach–Zehnder Modulator (DPMZM) technique. Range-Doppler coupling of the radar system has been investigated with the help of an ambiguity function diagram of the generated waveform. Results have analyzed through MATLAB simulation and verified by experimental results.     

离子探测法在钠分子光谱研究中的应用

本文首次实现了钠分子体系中离子探测脉冲激光光谱,研究了钠分子电离限附近的高里德堡态,获得了高灵敏度和高增益的光谱,拓宽了分子光谱研究领域。本     

Argonne国家实验室ECR离子源在固体材料离子束流产生方面的研究进展

Development work with solid materials at the Argonne National Laboratory ECR ion sources has been focused on two areas-introduction of materials with low vapour pressures,and increasing the beam intensities of heavy beams(i.e.-lead and uranium).An induction oven,with a demonstrated operating temperature extending to 2000℃,has been utilized to produce a Ti-50 beam with an intensity of 5.5eμA (12 ).In addition,a refinement of the sputter technique has been employed which has resulted in a 42% improvement in lead beam intensities.Details of the induction oven as well as the refined sputter technique will be presented.     

The application of homodyne spectroscopy to the study of low-frequency microturbulence in the TEXT tokamak

Summary The wave propagation direction of microturbulence in a tokamak plasma has been accurately measured by application of a new homodyne spectroscopy technique. This method has been used in conjunction with a collective far-infrared laser scattering experiment on TEXT. The low-frequency density fluctuations are observed to propagate primarily in the electron diamagnetic drift direction, however, the broadband spectra also possess an appreciable level of fluctuations traveling in the ion drift direction. Application of the homodyne spectroscopy technique represents an inexpensive and easily implemented alternative to the more technically demanding heterodyne schemes available in the far-infrared.     

The transfer of ultrasonic energy in the diffraction technique for crack sizing

During the past five years a programme of work has been carried out at the Harwell NDT Centre concerned with the use of scattered or diffracted ultrasound in the sizing of defects. The progress made in this direction and some of the possible lines of further research have been indicated in other papers.^1–3 This diffraction technique has been evaluated on a number of fatigue cracked specimens and it has been found that accuracies in crack sizing consistently better than $\text{1}\text{2}$ mm have been achieved. The technique is thus thought to be on the verge of application to practical ndt problems.The basis of the sizing technique is the recognition and subsequent timing of various discrete ultrasonic pulses, as will be outlined later. The scope of the technique thus depends on these signals remaining both well separated and large enough to be resolved in a wide range of examination geometries. The purpose of the present paper is to consider the mechanisms by which two of the ultrasonic pulses of importance in the diffraction technique are produced. In this connection the current theoretical situation is reviewed and this is compared, where appropriate, with experimental measurements taken during the period of this work.     

Strict Kinetic Treatment of the Electron Response to Spatial Field Disturbances in Nonequilibrium Plasmas

In generalization of former approaches for the simplified solution of the inhomogeneous electron Boltzmann equation a higher order solution technique has been developed. This technique is based on a multi-term expansion of the electron velocity distribution function and allows a strict study of the electron kinetics in plasmas acted upon by space-dependent electric fields. This solution technique is used to investigate the response of the plasma electrons to spatially limited disturbances of the electric field in weakly ionized plasmas of helium and mercury. By solving the kinetic equation with increasing order of the multi-term expansion the convergent solution of the kinetic problem and thus the strict spatial behaviour of the velocity distribution and of significant macroscopic properties of the electrons has been determined and analysed. Furthermore, the impact of higher order terms of the expansion has been revealed and the falsification of the velocity distribution and of related macroscopic properties has been evaluated when instead of the multi-term solution the simpler two-term solution of the kinetic equation is used.     

A new technique to measure the differential XAFS spectrum

A new technique has been developed for direct measurement of the differential X-ray absorption fine structure(XAFS) spectrum by the energy-modulation method. To acquire the energy-oscillating incident X-ray beam, a piezoelectric actuator is used to control the double-crystal monochromator. A logarithmic converter circuit and a lock-in amplifier are used to extract the modulated signals. The normal and differential XAFS spectra of the Mn K-edge of Li2 Mn O3 have been collected. The X-ray-absorption near-edge-structure(XANES) spectra verify that the signal-to-noise ratio has been greatly improved by the new technique, and the extended X-ray absorption fine structure(EXAFS) spectra demonstrate that this new technique can efficiently enhance the signals of the backscattering atoms.     

Fractional models of cosmic ray acceleration in the Galaxy

Possible formulations of the problem of the acceleration of cosmic rays in the interstellar galactic medium with fractional differential equations have been considered. The applied technique has been physically justified. A Fermi result has been generalized to the case of the acceleration of particles in shock waves in the supernovae remnants fractally distributed in the Galaxy.     

Identification of dynamic characteristics of nonlinear joint based on the optimum equivalent linear frequency response function

Identification of dynamic characteristics of local nonlinearities has been aimed in this paper. The spirit of the identification method is established on Optimum Equivalent Linear Frequency response function (OELF). Dynamic behavior of nonlinear elements in system is extracted from OELF using two different techniques. The first technique is “Direct Identification Method” (DIM) in which no pre-assumed model is considered for the nonlinearity's behavior and the second technique is “Model based Identification Method” (MIM). The second technique is introduced with two different formulations, in order to take into account the practical limits due to the inaccessibility of nonlinearity location and/or indeterminability of degree of freedom. Dynamic characteristics of common nonlinearity mechanisms like cubic stiffness, pure slip, and stick-slip have been identified using the proposed technique and it has been shown that, although the proposed identification technique is simple, it does not require any sophisticated measurement hardwares and techniques, as required by most of the identification methods proposed so far. Also, the relation of this technique to harmonic balance method is discussed.     

Use of the LM-OSL technique for the detection of partial bleaching in quartz

We present a study of the sensitivity to light (ease-of-bleaching) of the trapped charge in sedimentary quartz grains using an optically stimulated luminescence (OSL) technique in which the intensity of the stimulation light is linearly increased during the measurement period. The technique is known as linear modulation OSL (LM-OSL). In controlled laboratory conditions, this technique has been employed to study the ease-of-bleaching of the trapped charge in quartz by comparing the OSL curves of quartz aliquots which have been either: (1) fully bleached, followed by a laboratory dose of β-irradiation, or (2) partially bleached, followed by the laboratory β-dose. The ratio of the OSL signals due to the β-dose from the partly and fully bleached aliquots is illustrated to be a potential indicator of the degree of optical resetting of the OSL signal in dating material. The key parameter governing the ease-of-bleaching is the photoionization cross-section of the trap involved. The concept is also demonstrated in a model study from which very good agreement with the experimental observations has been found. Potential applications of the technique to dating are discussed.     

A time-differential measurement of the hyperfine structure of the 6.13 MeV state in highly ionized 16O atoms

A time-differential technique has been developed which makes possible the observation of time dependent effects produced by hyperfine interactions in highly ionized atoms during recoil into vacuum. Theoretical and experimental considerations of the technique are discussed and a value for |g_I| of 0.55 ± 0.03 has been obtained for the 6.13 MeV (3^?) state of ¹⁶O.     

Variation of the gas components of a TEA CO2 laser during its lifetime

An in situ mass-spectrometric sampling technique has been developed for lifetime studies of TEA CO₂ lasers. Using the new technique, an analysis of the gas components of a TEA CO₂ laser during its lifetime has been performed. The results show that the laser output pulse energy was strongly influenced by the oxygen concentration inside the device.     

贵金属Au冷却过程中结构及能量变化的分子动力学计算机模拟

通过分子动力学方法,研究了不同冷速下贵金属Ａｕ在温度２０００～３００Ｋ的冷却过程中微观结构的变化特点,结果发现,冷却速度对Ａｕ的微观结构产生重要影响,采用偶关联函数和键对分析技术对原子局域团簇结果者分析,并考察了冷却过程中原子势能随温度的变化,比较了Ａｕ的微观结构转变与能量变化的对应关系,从能量转化的角度对冷却过程中Ａｕ的结构变化进行了说明。     

Search of self-organized criticality processes in magnetically confined plasmas: hints from the reversed field pinch configuration

In order to test the self-organized criticality (SOC) paradigm in transport processes, a novel technique has been applied for the first time to plasmas confined in reversed field pinch configuration. This technique consists of an analysis of the probability distribution function of the times between bursts in density fluctuations measured by microwave reflectometry and electrostatic probes. The same analysis has also been applied to intermittent events sorted out from the Gaussian background. In both cases, the experimental results disagree with the predictions for a SOC system.     

Probing the ground state properties of iron-based superconducting pnictides and related systems by muon-spin spectroscopy

In this short review, we attempt to give a comprehensive discussion of studies performed to date by muon-spin spectroscopy (more precisely the relaxation and rotation technique, also know as μSR) on the recently discovered layered iron-based superconductors. On one side, μSR has been used to characterize the magnetic state of different families of layered iron-based systems. Similarly the subtle interplay of the magnetic state and the structural transition present in some families has been investigated. We will also discuss the information provided by this technique on the interaction between the magnetic state and the superconducting phase. Finally the μSR technique has been used to investigate the magnetic penetration depth of the superconducting ground state. The study of its absolute value, temperature and magnetic field dependence provides crucial tests for investigating possible unconventional superconducting states in such systems.