均恒强磁场在材料科学中的应用

均恒强磁场在材料科学中应用的研究正处于起步阶段 ,已经进行了广泛的探索性实验研究和理论研究 ,发现了大量有重大理论价值和应用前景的强磁现象。本文主要综述强磁场在材料科学中取向和控制流体流动的研究现状 ,并且探讨了存在的问题以及今后的发展方向     

平行板反应离子刻蚀系统均匀磁场的数值计算

在平行板反应离子刻蚀系统的圆筒形腔体的侧壁上绕上电流线圈后,系统中的磁场强度和均匀性都可进行调节。本文根据螺线管线圈内部磁场的分布规律,通过数值计算的方法在该系统中获得均匀的磁场。     

船用高速发电机基波磁场下机座电磁振动

以船用高速同步发电机为对象进行电磁振动特性分析。用有限元法计算空载下电机基波气隙磁场引起的径向电磁力波在机座机脚处垂向振动加速度。通过对不同机座安装方式、材料刚度及结构阻尼的振动仿真对比,分析影响振动加速度主因及有限元模型简化处理对计算结果影响。用三维谐波场及瞬态场有限元法计算机脚振动加速度,用电动机运行法测试发电机空载下机座机脚振动加速度。结果表明,仿真与试验结果基本一致,机座及机脚振动受机座安装方式影响较大,定子振幅受材料弹性模量响应较大,在弹性安装/自由状态下机座形变分布主要受结构阻尼影响。该结果可为船用高速电机减振降噪设计、研究提供依据及参考。     

Ordered state of one-dimensional antiferromagnetic superconductors in the presence of a homogeneous magnetic field

Assuming a one-dimensional electron band and examining the free energy difference F (=F _S–F _N) for an antiferromagnetic superconductor in the presence of a homogeneous magnetic field H₀, it is shown that (i) for temperatureT=0, the spatially varying order parameter _Q (having the same period as the antiferromagnetic fieldH _Q) and the BCS order parameter coexist when |–H _QH ₀<+H _Q (here, the pairing coupling constant for _Q is assumed small), and (ii) forT near the second-order phase transition temperature the coexistence of _Q and is always realized whenH ₀0.Work supported in part by a grant from the Natural Sciences and Engineering Research Council of Canada.On leave of absence from Physics Department, Tohoku University, Sendai, Japan.     

Ti-based amorphous alloys with a wide supercooled liquid region

Ti-Cu-Ni-Co quaternary amorphous alloys produce by melt spinning were found to have a wide supercooled liquid region before crystallization, though no glass transition was observed in Ti-Cu binary amorphous alloys. The largest temperature interval of the supercooled liquid region (ΔT_x) is as large as 90 K for Ti₅₀Cu₂₅Ni₂₀Co₅.There is a tendency for ΔT_x to increase with an increase in storage modulus and with a decrease in loss modulus. It is therefore presumed that the increase in ΔT_x for the multicomponent amorphous alloy is due to the suppression of crystallization for the supercooled liquid resulting from the increase in viscosity.     

Topology optimization of a magnetic field in a three-dimensional finite region

This article describes the method of magnetic field topology optimization in an axisymmetric three-dimensional finite region. It is assumed that the region of interest is surrounded by a cylindrical solenoid with an electrical current. The solenoid’s inner and outer surfaces are built-up by rotating plane Bezier curves around the symmetry axis. As a global minimizer a genetic algorithm method is used. Optimal configurations are provided under given constraints.     

Microwave generation features in a vircator with an inhomogeneous magnetic field in the interaction region

A vircator with an inhomogeneous external magnetic field superimposed onto the cathode-anode-virtual cathode potential well was studied by methods of computer modeling. It is shown that the application of such additional field allows a significant (almost fivefold) increase in the microwave generation efficiency, which is explained by the gyrotron effect development.     

Reflectance spectra of a 6H-SiC single crystal placed in a strong homogeneous magnetic field

We have made a theoretical study of the external reflection coefficients of a uniaxial anisotropic SiC (6H polytype) single crystal exposed to a strong homogeneous magnetic field (in the cases of Faraday and Voigt configurations). For the first time, in the external reflection spectra of a 6H-SiC single crystal, regions of the appearance of new oscillations due to the action of a strong homogeneous magnetic field have been revealed. The interrelationship between the phonons and plasmons in a 6H-SiC single crystal exposed to a strong homogeneous magnetic field has been studied.     

Generation of remote homogeneous magnetic fields

This paper presents a magnetic efficiency model for comparing efficiencies of various magnets for magnetic resonance imaging. It demonstrates that monohedral magnets, magnets with sources on one side, can generate remote saddle points in the field profile relatively efficiently. These magnets may be modeled by a minimum of two magnetic dipoles. The paper examines the field profile and magnetic dipole efficiency for the two-dipole model in detail, and develops some fundamental properties of homogeneous magnetic fields     

Coating and filling of carbon nanotubes with homogeneous magnetic nanoparticles

Magnetic multi-walled carbon nanotube (MWCNT) composites were obtained by decoration of metal oxide nanoparticles on or in carbon nanotubes. The method involved the dispersion of the carbon nanotubes in iron pentacarbonyl Fe(CO)₅ followed by vacuum thermolysis and subsequent oxidation. The magnetic iron oxide particle deposition was always homogeneous and could be controlled selectively on the outer, inner, or both surfaces of MWCNTs by using different MWCNTs. Since the hollow channels remained intact, these MWCNT based composites could find special applications in cellular delivery systems.     

Loss-induced phase-sensitive spatial light modulator with a wide field of view

We investigate the feasibility of achieving practical phase modulation by changing only the absorption of the device. We present a spatial light modulator that consists of a three-mirror cavity with lossy slabs inserted between the mirrors. When only the absorption of these slabs is changed, this device can have a gradual change in phase, but no intensity modulation. Theoretical analysis by the use of numbers appropriate to multiple quantum wells shows that the total phase-tuning range can be as large as 2π with an absorption coefficient change of less than 9000 cm(-1); the length of each multiple-quantum-well slab is ~ 1.5 μm. This gives an expected 16° field of view with the nanosecond speed typical of semiconductors.     

高磁感宽温区线性磁温度补偿合金研究

主要研究了FeNi系合金材料的磁温度补偿特性,分析了不同微量合金元素对磁性能的影响.并探讨了不同冷加工度、不同时效温度及不同磁场下合金的磁补偿性能.获得了线性度好、性能稳定可靠的新型磁温度补偿合金材料.典型磁性能为B20℃=0.824T、dB/dt=(-0.005～-0.003)T/℃,B值线性误差为±0.05T(-40～+80℃、H=7960A/m).     

An undulator with a composite magnetic field

A new type of undulator greatly improved in tunability as compared with a usual undulator, is proposed. The undulator has a composite magnetic field which is a linear superposition of two sinusoidally varying fields with different spatial periods. The wavelength can be changed by varying the field strength of the longer-period component while keeping that of the shorter-period component at the highest possible value. Numerical calculations of the spectral brightness were carried out. The proper ratios between the two spatial periods were found to be 3:1, 5:1 and 7:1.     

Transient magnetic field of a strip line with a magnetic keeper

The transient magnetic field of a strip line in a memory device with a finite conductivity ground plane and a finite permeability magnetic keeper is studied. The driving source consists of a line current or a uniform current sheet. The waveform of the current is assumed to be piecewise linear. Laplace and Fourier transform methods are used to obtain the field.     

“Pretreatment” of a homogeneous fuel-air mixture with an electric field

Results are shown of a study concerning the effect which treating a homogeneous fuel-air mixture with an electric field has on the velocity V of the flame travel through it. Data are presented pertaining to the flame front velocity V and the flame front shape as functions of the electric field intensity E, the field application time t, and the time interval between field removal and subsequent ignition.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 2, pp. 204–207, August, 1973.     

Equilibrium near and far electromagnetic field structures at a flat boundary of the half-space filled with a homogeneous dielectric (magnetic) medium

The most general expression for the density of electromagnetic field modes at a flat interface between a semi-infinite homogeneous dielectric (magnetic) medium and vacuum is obtained. The medium is characterized by the frequency-dependent dielectric permittivity and magnetic permeability.     

Two-point optical resolution with homogeneous,evanescent and self field: Resolution criterion in near field imaging

Abstract

The radiative and non-radiative electromagnetic field of a quantum particle is studied. An optical resolution criterion is proposed in terms of the two-point resolution. Resolution of optical microscopes is limited either by homogeneous diffraction (conventional microscopes) or by evanescent diffraction (near-field microscopes). The evanescent diffraction limit is a function of the wavelength and the observation distance (a portion of the wavelength), which may be circumvented by measuring the non-radiative field, namely the self field in the quantum range of the objects. The resolution then becomes a function of the object size, and is no longer limited by the wavelength of light used. The two-level hydrogen atom is taken as an example.     

Calculation of eddy-current-induced magnetic fields in vacuuminterrupters with axial magnetic field contacts

The variation of the nonsteady magnetic-induction field of axially symmetric contact arrangements in space and time is calculated by using a finite-element program system. The influence of individual design elements on the induction field is analyzed and the effectiveness of measures for suppressing eddy current is represented. The delaying and damping effect of the eddy currents on the magnetic field increases from the outside towards the axis of symmetry. This changes the radial field distribution for the duration of the arc and the zone of maximum induction travels towards the inside. When the contacts are open, the radial component predominates over the axial induction field in the vicinity of the contact edge. The azimuthal inherent magnetic field of the arc is free of eddy currents and dominates in the outer arc region, particularly in the phase of current increase