劳特布尔（Lauterbur，Panl C，1929-）美国化学家（Chemist，America）

核磁共振成像（NMRI）是利用物体在非均匀磁场中不同点处的场强不同，因而在不同点上产生不同的核磁共振频率，共振吸收线的频率分布就对应于共振核的空间分布，藉助于计算机，便可以重建原来的图像。和CT相比，NMRI的优点：一是没有有害的辐射，人体在磁场中不会受到伤害：二是能够对多种病变进行早期诊断。因为病变首先引起人体组织的化学变化，到一定程度才引起形态变化，CT只能检查出组织的形态变化，而NMRI则能发现组织的化学变化。     

再谈气垫导轨上变力问题的实验

作者在《大学物理》1990年第12期上《在气垫导轨上有关变力问题的实验》中提出了一种验证力学中变力规律的实验方法。但在实验装置上还遗留一个缺陷,由于金属链自重的影响,金属链在导轨上的一段呈弧形,且随着链子的增长,弧度随之变大。这既给实验结果带来一定的误差,又使     

Soliton Collision in a Ferromagnetic Spin Chain Driven by a Magnetic Field

By employing an inverse-scattering transformation, the exact solution of an N-soliton train in the spin chain with a time-dependent magnetic field is derived. As a special case the one-soliton solution (N = 1) exhibits explicitly the spin precession around the magnetic field and periodic shape-variation induced by the time varying field as well. In terms of the general solution, inelastic two-soliton collision is analysed. The inelastic collision, by which we mean the soliton shape-change before and after collision, appears generally due to the time varying field.     

Effect of Magnetic Field and Equilibrium Flow on Rayleigh-Taylor Instability

We investigate the effect of a finite equilibrium flow and magnetic field on the Rayleigh-Taylor instability. It is found that the equilibrium flow only makes a frequency shift of perturbation and the growth rate of the Rayleigh-Taylor instability remains unchanged. However, the magnetic field can change the growth rate and, in particular,a very strong magnetic field suppresses the growth rate.     

气垫转盘测转动惯量时空气粘滞阻力矩的影响

气垫转盘测转动惯量时空气粘滞阻力矩的影响徐军（承德石油高等专科学校０６７０００）一、引言气垫转盘测刚体的转动惯量，厂家提供的测量原理及设备条件，均未考虑空气粘滞阻力矩的影响．测量仪器如图１．其中１为动盘，２为定盘，３为气轴，４为砝码，５为挡光片，６为...     

A Unified Model of Magnetic Extraction of Spin Energy from a Black Hole

A unified model of magnetic extraction of spin energy from a black hole in discussed based on the theory of black hole magnetosphere.The magnetic extracting power is expressed by a unified formula,which is applicable to bloth the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process.The strength and characteristics of the BZ power and the MC power are compared in detail.In addition,the impedance matching condition for the BZ power is extended to the more general case.     

Electro-Magnetic Control of Vortex Shedding Behind a Circular Cylinder

Both open- and closed-loop control algorithms have been developed for suppressing of vortex shedding behind a circular cylinder in an electrically low-conducting fluid. For the open-loop control, the localized Lorentz forces are generated parallel to the cylinder surface, which have the accelerated effect to the fluid. Furthermore, two closed-loop control methods have been derived from the equations of motion capable of determining at all times the intensity of the Lorentz force to control the vortex shedding of a cylinder.     

Bianchi Type-Ⅲ String Cosmological Model With Bulk Viscosity and Magnetic Field

The Bianchi type-Ⅲ cosmological model for a cloud string in the presence of bulk viscosity and magnetic field are presented. To obtain the determinate model it is assumed that there is an equation of state ρ = kA and the scalar of expansion is proportional to the shear scalar θ ∝ σ, which leads to a relation between metric potentials B = mC^n. The physical and geometric aspects of the model are also discussed. The model describes a shearing non-rotating continuously expanding universe with a big-bang start. In the absence of magnetic field, it reduces to the string model with bulk viscosity that was previously given in the literature.     

斜向静磁场中光导波模式转换与衍射理论

应用经典场论和耦合模理论计算了斜向静磁场作用下，磁性薄膜波导中静磁波与导波光的相互作用.计算结果表明，与垂直静磁场情形相比，斜向静磁场时的相匹配条件有所变化，由于磁性薄膜波导中法拉第磁光效应增强等因素，导波光的Bragg衍射效率得以显著增加.这有利于应用YIG等低损耗磁性薄膜做成高衍射效率的磁光波导器件，亦有利于降低Bi∶YIG等高比法拉第旋转的磁光薄膜波导器件的体积和损耗.此外，理论指出的在斜向静磁场条件下所具有的一些磁光特性与实验结果亦符合得很好. 关键词：