Characteristic analysis of scattering field in two-layer media by Green's function

The problem of three-dimensional(3D) acoustic scattering in a complex medium has aroused considerable interest of researchers for many years. An ultrasonic scattered field calculating technique is proposed to study the scattering echo from strongly scattered materials in a two-layer medium in this work. Firstly, with the high frequency stationary phase method,the Green's function of two-layer fluid media is derived. And then based on the idea of integral equation discretization,the Green's function method is extended to two-layer fluid media to derive the scattering field expression of defects in a complex medium. With this method, the scattering field of 3D defect in a two-layer medium is calculated and the characteristics of received echoes are studied. The results show that this method is able to solve the scattering P wave field of 3D defect with arbitrary shape at any scattering intensity in two-layer media. Considering the circumstance of waterimmersion ultrasonic non-destructive test(NDT), the scattering sound field characteristics of different types of defects are analyzed by simulation, which will help to optimize the detection scheme and corresponding imaging method in practice so as to improve the detection quality.

An Improved Preisach Distribution Function Identification Method Considering the Reversible Magnetization

This paper presents an identification method of the scalar Preisach model to consider the effect of reversible magnetization in the process of distribution function identification.By reconsidering the identification process by stripping the influence of reversible components from the measurement data,the Preisach distribution function is identified by the pure irreversible components.In this way,the simulation accuracy of both limiting hysteresis loops and the inner internal symmetrical small hysteresis loop is ensured.Furthermore,through a discrete Preisach plane with a hybrid discretization method,the irreversible magnetic flux density components are computed more efficiently through the improved Preisach model.Finally,the proposed method results are compared with the traditional method and the traditional method considering reversible magnetization and validated by the laboratory test for the B30P105 electrical steel by Epstein frame.

Finite Volume Time Domain with the Green Function Method for Electromagnetic Scattering in Schwarzschild Spacetime

The finite volume time domain(FVTD) algorithm and Green function algorithm are extended to Schwarzschild spacetime for numerical simulation of electromagnetic scattering. The FVTD method in Schwarzschild spacetime is developed by filling the flat spacetime with an equivalent medium. The Green function in Schwarzschild spacetime is acquired by solving initial value problems. Both the FVTD code and the Green function code are validated by numerical results. Scattering in Schwarzschild spacetime is simulated with these methods.

Configuration of propagator method for calculation of electron velocity distribution function in gas under crossed electric and magnetic fields

This paper presents a self-contained description on the configuration of propagator method(PM)to calculate the electron velocity distribution function(EVDF) of electron swarms in gases under DC electric and magnetic fields crossed at a right angle. Velocity space is divided into cells with respect to three polar coordinates v,θ and f. The number of electrons in each cell is stored in three-dimensional arrays. The changes of electron velocity due to acceleration by the electric and magnetic fields and scattering by gas molecules are treated as intercellular electron transfers on the basis of the Boltzmann equation and are represented using operators called the propagators or Green’s functions. The collision propagator, assuming isotropic scattering, is basically unchanged from conventional PMs performed under electric fields without magnetic fields. On the other hand, the acceleration propagator is customized for rotational acceleration under the action of the Lorentz force. The acceleration propagator specific to the present cell configuration is analytically derived. The mean electron energy and average electron velocity vector in a model gas and SF6 were derived from the EVDF as a demonstration of the PM under the Hall deflection and they were in a fine agreement with those obtained by Monte Carlo simulations. A strategy for fast relaxation is discussed, and extension of the PM for the EVDF under AC electric and DC/AC magnetic fields is outlined as well.

Lattice Green's Function for Infinite Square Lattice in the Second Nearest-Neighbour Interaction Approximation

In dealing with the square lattice model,we replace the traditionally needed Born-Von Karmann periodic boundary condition with additional Hamiltonian terms to make up a ring lattice.In doing so,the lattice Green's function of an infinite square lattice in the second nearest-neighbour interaction approximation can be derived by means of the matrix Green's function method.It is shown that the density of states may change when the second nearest-neighbour interaction is turned on.

NEW TYPE OF DUAL BEM AND GREEN'S-FUNCTION-LIBRARY STRATEGY FOR FRACTURE ANALYSIS IN COMPLEX STRUCTURES

A new type of dual boundary integral equations(DBIE)is presented first,through which,a smaller system of equations needs to be solved in fracture analysis.Then a non-conforming crack tip element in two-dimensional problems is proposed.The exact formula for the hypersingular integral over the non-con- forming crack tip element is given next.By virtue of Green's-function-library strategy,a series of stress in- tensity factors(SIF)of different crack orientations,locations and/or sizes in a complicated structure can be obtained easily and efficiently.Finally,several examples of fracture analysis in two dimensions are given to demonstrate the accuracy and efficiency of the method proposed.

The relativistic density functional investigations on geometries,electronic and magnetic properties of Ir_n (n=1-13) clusters

The Ira （n=1-13） clusters are studied using the relativistic density functional method with generalized gradient approximation. A series of low-lying structures with different spin multiplicities have been considered. It is found that all the lowest-energy Ira （n=4-13） geometries prefer non-compact structures rather than compact structure growth pattern. And the cube structure is a very stable cell for the lowest-energy Ira （n 〉 8） clusters. The second-order difference of energy, the vertical ionization potentials, the electron affinities and the atomic average magnetic moments for the lowest-energy Ira geometries all show odd even alternative behaviours.

Time Slice Analysis Method Based on OTCA Used in fMRI Weak Signal Function Extraction

The original temporal clustering analysis (OTCA) is an effective technique for obtaining brain activation maps when the timing and location of the activation are completely unknown, but its deficiency of sensitivity is exposed in processing brain activation signal which is relatively weak. The time slice analysis method based on OTCA is proposed considering the weakness of the functional magnetic resonance imaging (fMRI) signal of the rat model. By dividing the stimulation period into several time slices and analyzing each slice to detect the activated pixels respectively after the background removal, the sensitivity is significantly improved. The inhibitory response in the hypothalamus after glucose loading is detected successfully with this method in the experiment on rat. Combined with the OTCA method, the time slice analysis method based on OTCA is effective on detecting when, where and which type of response will happen after stimulation, even if the fMRI signal is weak.

Computing Radial Distortion of Projector Magnetic Lenses by Analytical Method

The radial distortion of projector magnetic lenses with field distributions in the form of inverse law has been theoretically studied using analytical method. The radial distortion coefficient can be expressed explicitly in term of Bessel function of fraction order Therefore, analytical formulae for radial distortion coefficient of each projector magnetic lenses in this article have derived to computation these coefficients. Also, the dimensionless quality factors for radial distortion are calculated to estimate the performance of image in electron microscope. The results of calculations show that the increasing of order of multipole （n） leads to increase the radial distortion coefficient.

Chaotic Motion Analysis for a Coupled Magnetic-Flow-Mechanical Model of the Rectangular Conductive Thin Plate

The chaotic motion behavior of the rectangular conductive thin plate that is simply supported on four sides by airflow andmechanical external excitation in a magnetic field is studied.According to Kirchhoff’s thin plate theory,considering geometric nonlinearity and using the principle of virtualwork,the nonlinearmotion partial differential equation of the rectangular conductive thin plate is deduced.Using the separate variable method and Galerkin’s method,the system motion partial differential equation is converted into the general equation of the Duffing equation;the Hamilton system is introduced,and the Melnikov function is used to analyze the Hamilton system,and obtain the critical surface for the existence of chaos.The bifurcation diagram,phase portrait,time history response and Poincarémap of the vibration system are obtained by numerical simulation,and the correctness is demonstrated.The results showthatwhen the ratio of external excitation amplitude to damping coefficient is higher than the critical surface,the system will enter chaotic state.The chaotic motion of the rectangular conductive thin plate is affected by different magnetic field distributions and airflow.

比率低频振幅技术在延年九转法治疗慢性疲劳综合征伴焦虑抑郁中的应用价值

目的比较延年九转法与认知行为治疗后,慢性疲劳综合征(chronic fatigue syndrome,CFS)伴焦虑与抑郁症状患者的大脑静息态下功能MRI(functional MRI,fMRI)比率低频振幅(fractional amplitude of low-frequency fluctuations,fALFF)的脑区差异改变情况。材料与方法将30例CFS患者随机分为延年九转法组和认知行为组,治疗12周后进行fMRI检测,采用Pearson相关分析探索fALFF变化与焦虑抑郁量表(Hospital Anxiety and Depression Scale,HADS)的线性相关性。结果与认知行为组相比,延年九转法组fALFF减弱的脑区有左侧梭状回、左侧枕上回、左侧角回;增强的脑区有右侧颞中回。焦虑症状分值与梭状回(r=0.525,P=0.044)和枕上回(r=0.559,P=0.030)的fALFF平均值呈正相关,抑郁症状分值与梭状回(r=0.542,P=0.037)的fALFF平均值呈正相关(P<0.05)。结论延年九转法可能通过梭状回、枕上回、角回、颞中回神经活动水平强弱客观反映CFS患者焦虑与抑郁症状。

考虑不对称饱和的电机径向电磁力解析建模

由于内置式永磁同步电机磁饱和特性的存在,使得解析分析电机运行过程中定子所受的径向电磁力缺乏系统有效的方法,不利于在前期设计开发阶段进行电机电磁振动和噪声的抑制。针对内置式永磁同步电机转子不对称磁饱和的问题提出了一种电磁力的解析计算模型。通过将绕组函数法与等效磁路法相结合,推导了考虑电磁饱和情况下的电机磁动势。利用卡特系数计算了电机的等效气隙磁导。通过磁势乘磁导法建立气隙磁场模型,并结合Maxwell应力方程最终建立了电机径向电磁力的解析模型。最终通过有限元法验证了该模型的准确性。该模型能够反应电磁力与电机各结构参数的关系,有利于在设计阶段快速改进电机结构来抑制电机电磁振动和噪声。

舰艇磁性对抗能力综合评估模型

为精确评估舰艇对抗磁性水雷的能力,本文提出了一种基于层次分析法和模糊综合评价法的舰艇磁性对抗能力评估模型。基于层次分析法建立了舰艇磁性处理与磁性水雷对抗能力评估指标体系,通过专家打分法求得指标权重,利用多级模糊综合评价法进行综合对抗评估,其中隶属度函数采用正态分布函数,模糊综合算子采用乘加、加权平均型算子。采用多物理场仿真和磁性船模在磁性处理前后分别进行对抗能力评估。研究表明:磁性处理前后舰艇对抗磁性水雷的评估分值分数分别提升了35.65分和21.58分。评估结果验证了所建模型的合理性和有效性。

基于fMRI的角刺法联合经筋排刺法治疗难治性周围性面瘫临床观察

目的探究基于功能性磁共振成像(fMRI)的角刺法联合经筋排刺法治疗难治性周围性面瘫的临床效果。方法随机将76例难治性周围性面瘫患者分为对照组和观察组,每组38例,分别给予常规针刺、基于fMRI的角刺法联合经筋排刺法治疗,持续4周,比较2组面神经功能(Sunnybrook)评分、面神经麻痹症状评分以及面部肌电图指标,计算愈显率。结果观察组治疗后Sunnybrook评分高于对照组(P<0.05),面神经麻痹症状评分低于对照组(P<0.05),面部肌电图瞬目反射潜伏期和面神经传导潜伏期、波幅参数优于对照组(P<0.05),愈显率高于对照组(P<0.05)。结论基于fMRI的角刺法联合经筋排刺法能够有效恢复难治性周围性面瘫患者面神经功能,改善临床症状,临床疗效优越。

Review: Progress in the Preparation of Iron Based Magnetic Nanoparticles for Biomedical Applications

With unique physical properties, chemical properties, and biological effects, magnetic nanomaterials are important functional materials in many fields. In the past decades, iron based magnetic nanomaterials have attracted much attention in the biomedicine field due to their superior magnetic properties and great potential in biomedical applications. In particular, magnetic iron oxide nanoparticles(MIONPs) have been playing a crucial role in the biomedicine field because of their diagnostic and therapeutic functions. Meanwhile, MIONPs are benign, low toxic, biocompatible, and biodegradable, so they are the only inorganic magnetic nanomaterials approved by the U.S. Food and Drug Administration(FDA) for clinical use at present. In this review, we mainly introduce the progress in the preparation of iron based magnetic nanomaterials for biomedical applications, including pure iron nanoparticles, iron-based alloy nanoparticles, and MIONPs, with a focus on MIONPs. Also, we summarize the preparation methods of MIONPs and point out the importance of their developments.

An improved boundary element method for modelling a self-reacting point absorber wave energy converter

A numerical model based on a boundary element method (BEM) is developed to predict the performance of two-body selfreacting floating-point absorber (SRFPA) wave energy systems that operate predominantly in heave.The key numerical issues in applying the BEM are systematically discussed.In particular,some improvements and simplifications in the numerical scheme are developed to evaluate the free surface Green's function,which is a main element of difficulty in the BEM.For a locked SRFPA system,the present method is compared with the existing experiment and the Reynolds-averaged NavierStokes (RANS)-based method,where it is shown that the inviscid assumption leads to substantial over-prediction of the heave response.For the unlocked SRFPA model we study in this paper,the additional viscous damping primarily induced by flow separation and vortex shedding,is modelled as a quadratic drag force,which is proportional to the square of body velocity.The inclusion of viscous drag in present method significantly improves the prediction of the heave responses and the power absorption performance of the SRFPA system,obtaining results excellent agreement with experimental data and the RANS simulation results over a broad range of incident wave periods,except near resonance in larger wave height scenarios.It is found that the wave overtopping and the re-entering impact of out-of-water floating body are observed more frequently in larger waves,where these non-linear effects are the dominant damping sources and could significantly reduce the power output and the motion responses of the SRFPA system.

Ultra-high-field magnetic resonance:Why and when?

This paper briefly summarizes the development of magnetic resonance imaging and spectroscopy in medicine.Aspects of magnetic resonancephysics and-technology relevant at ultra-high magnetic fields as well as current limitations are highlighted.Based on the first promising studies,potential clinical applications at 7 Tesla are suggested.Other aims are to stimulate awareness of the potential of ultra-high field magnetic resonance and to stimulate active participation in much needed basic or clinical research at 7 Tesla or higher.

Effect of Gd doping on the magnetism and work function of Fe_(1-x)Gd_x/Fe(001)

The magnetism and work function Ф of Fe1-xGdx/Fe （001） films have been investigated using first-principles methods based on the density functional theory. The calculated results reveal that Gd doping on the Fe （001） surface would greatly affect the geometrical structure of the system. The restruction of the surface atoms leads to the transition of magnetic coupling between Gd and Fe atoms from ferromagnetic （FM） for 0.5 ≤x ≤ 0.75 to antiferromagnetic （AFM） for x = 1.0. For Fe1-xGdx/Fe （001） （x = 0.25, 0.5, 0.75, 1.0）, the charge transfer from Gd to Fe leads to a positive dipole formed on the surface, which is responsible for the decrease of the work function. Moreover, it is found that the magnetic moments of Fe and Gd on the surface layer can be strongly influenced by Gd doping. The changes of the work function and magnetism for Fe1-xGdx/Fe （001） can be explained by the electron transfer, the magnetic coupling interaction between Gd and Fe atoms, and the complex surface restruction. Our work strongly suggests that the doping of the metal with a low work function is a promising way for modulating the work function of the magnetic metal gate.

Thermodynamic properties of Heisenberg magnetic systems

In this paper, we present a comprehensive investigation of the effects of the transverse correlation function （TCF） on the thermodynamic properties of Heisenberg antiferromagnetic （AFM） and ferromagnetic （FM） systems with cubic lattices. The TCF of an FM system is positive and increases with temperature, while that of an AFM system is negative and decreases with temperature. The TCF lowers internal energy, entropy and specific heat. It always raises the free energy of an FM system but raises that of an AFM system only above a specific temperature when the spin quantum number is S 〉 1. Comparisons between the effects of the TCFs on the FM and AFM systems are made where possible.

Quantum Theory for Interfacial Roughness and Angle Dependence of Giant Magnetoresistance in Magnetic Multilayers

The giant magnetoresistance (GMR) in magnetic multilayers with current in the plane of the layers is studied by using the quantum-statistical Green's function approach, in which the effects of the interfacial roughness and magnetization configuration on the GMR are included. It is shown that the maximal GMR first increases and then decreases with increasing interfacial roughness, exhibiting a peak at an optimum value of interfacial roughness. An approximately linear dependence of GMR on is obtained, where is the angle between magnetizations of the two successive ferromagnetic layers. Furthermore, the maximal GMR is found to increase with increasing the number of bilayers.