Hybrid method for computing demagnetizing fields

A hybrid finite-element-boundary integral method is proposed for computing demagnetizing field. For a three-dimensional (3-D) mesh with N nodes in the magnetic region, the method requires storage O( N^4/3), and no nodes outside the magnetic region need to be considered. The method is suitable for nonlinear calculations, can be adapted to handle curved boundaries, and is especially convenient when the magnetic region consists of several parts whose relative positions are variable     

Novel technique for the measurement of demagnetizing fields in longitudinal recording

The maximum losses occurring at very short wavelengths, due to demagnetization in γFe2O3tape, have been calculated to be rather small (4.5 dB and 8 dB for magnetic and non-magnetic head reproduction, respectively) and they are therefore difficult to measure in the face of the relatively large and indeterminate spacing loss. A method is described for testing a particular tape in free space which avoids the difficulty. Essentially, a determination of the incremental remanent susceptibility of the tape is made. Because the remanence curve is so highly nonlinear, this susceptibility is uniquely associated with the demagnetizing field within the tape. Whereas the demagnetizing fields thus found agree with theory for wavelengths greater than 1 mil, they decrease, contrary to expectations, at the shorter wavelengths.     

Effects of magnetic fields on flexible disk drive performance

The read/write heads in flexible disk drives operate in the presence of AC and DC magnetic fields generated by solenoids, motors, recording head erase structures, circuit board components, and external sources such as CRT flyback transformers present in "smart terminals and word processors. Time varying magnetic fields induce signal on the read/write coil and introduce interference. This interfering signal increases the error rate and can cause "extra bits". Steady state fields cause shifts in the location of transitions, which also translates into higher error rates. The benefits derived from various shield configurations in and external to the flexible disk drive are presented.     

Analog memory devices based on NDRO toroidal cores

Discussed are the main aspects of operation, physics, design, and application of toroidal cores as nondestructive read-out analog memory elements. The analog memory element and switch are the basic components of the analog memory device of the open-loop type (i.e., without negative feedback). The toroidal core has been shown, both theoretically and experimentally, to exhibit linear read-write characteristics in pulse remagnetization. Diode switches are the most preferable for writing analog information. Analysis of the output and read circuits required to determine the optimal value for the read circuit resistance is given. The complex studies carried out resulted in a simple analog memory device with ± 3 percent error and the write time of 0.3μs. Ways to improve these parameters are described.     

传输斜移对同步并行光传输系统性能的影响

针对一个具体的链路模型,通过计算机仿真分析了传输斜移对同步并行光传输系统性能的影响.光纤中的信号分析在频域中通过快速傅立叶变换(fast fourier transform,FFT)进行.分别计算了单信道误码率以及没有传输斜移和有传输斜移时并行信道总的误码率.计算结果表明,在噪声不是影响系统性能的主要因素时,传输斜移是决定并行光传输系统最大同步传输速率和传输距离的一个重要因素.     

Analysis of an exchange-coupled NDRO magnetic thin-film memory element

An analysis of a pair of exchange-coupled magnetic thin films is outlined. The previous formulation of Goto et al. ensures that the first variation of the magnetic free energy is zero. In the present paper, an expression for the second variation of the energy is presented. Evaluation of this expression determines the stability of solutions to the coupled-film equations derived by Goto et al. In this way, magnetization curves and critical field plots are obtained exactly (i.e., the equations are not approximated) for pairs of exchange-coupled magnetic thin films. These results enable evaluation of coupled films as nondestructive readout (NDRO) memory elements.     

Diagonal dominance and S.O.R. performance with skew nets

Alternative finite difference formulations for elliptic equations on skew nets are investigated for suitability for rapid convergence of S.O.R. iterations. In dealing with the differential equation directly, diagonal dominance is a key property for convergence theorems. Mixed derivatives boundary conditions threatens this property, but formulas are presented which protect it as long as the net skewness is not too severe. Test calculations are reported showing convergence for these formulas to be as good as that of optimal S.O.R. theory, whereas other more direct formulas give a very inferior performance.     

Seismic performance and prediction equations of sandwich beam-column joints subjected to skew cyclic loads

To study the seismic performance of sandwich beam-column joints constructed with high strength concrete column and normal strength concrete floor system and joint regions, four specimens with different column to beam concrete strength ratios (α) were tested under skew cyclic loads. The performance indices of the specimens including the failure mode, ductility, energy dissipation were compared and analyzed. The results show that the failure modes of the sandwich joints are in form of joint shear failure after yielding of the beam, while the ductility coefficient is found to be greater than 3.0. Compared to the joints with low concrete strength ratios α, the specimen with a high concrete strength ratio α features larger deformation at the joint. Based on the softened strut-and-tie model, a set of shear strength prediction equations for the sandwich beam-column joint, taking into account the effects of the concrete strength ratio α, floor slabs and plastic region of beams, is proposed. Comparison of the present tests against the published literature confirms that the shear strength of the sandwich joints can be well predicted by the proposed model.     

Surface magnetic charge distributions and demagnetizing factors ofcircular cylinders

A circular cylinder in which a relative permeability is finite and constant is considered. The surface magnetic charge distributions and the demagnetizing factors are calculated numerically by the surface magnetic charge simulation method and are shown for various cases of different aspect ratios of length to diameter and different relative permeabilities. The results are used to obtain the ballistic demagnetizing factors and to compare them with other available data     

非均匀退磁场对NiFe薄膜AMR元件性能的影响

采用磁控溅射制备了NiFe各向异性磁电阻(AMR)薄膜,经过光学曝光及离子刻蚀将NiFe薄膜制成了宽度w=20μm、厚度t=20nm、长度l=2.5mm的AMR元件.测量了NiFe元件的磁电阻效应.考虑沿宽度方向退磁场的非均匀性,计算了磁电阻比率.结果表明,理论和实验符合.     

微型斜超声波电机的研究

提出一种新型微超声波电机——斜齿型微超声波电机。它是利用压电材料的逆压电效应，将交流电信号转变成定子表面超声频率的机械纵向振动，借助于定子表面的斜齿与转子的相互压紧，使斜齿端面质点产生椭圆运动，实现转子单方向旋转运动，该电机的驱动力矩较大、反向自锁力矩大、结构简单。文中将定子斜齿与转子接触分为三个阶段——接触黏着阶段、接触滑移阶段和分离阶段，建立定子斜齿与转子耦合的非线性动力学模型，并对其进行仿真研究，分析电机的瞬态响应特性及主要结构参数对电机机械特性的影响；最后，研制了尺寸为乃10的斜齿型微型超声波电机，经过实验表明，电机的堵转力矩可达10mN·m以上，空载转速达到840r／min以上，连续运转性能良好。     

Simulation of a NDRO memory cell with very small excess current Josephson junctions

The dynamic behaviour of a single flux quantum NDRO interferometer cell with two very small excess current Josephson junctions is simulated for a clamping impedance parallel to the interferometer inductance. A proper design of the clamping impedance yields the required NDRO and written operations at large damping parameters β > 1000 of the Josephson junctions. Since large damping parameters are required for logic circuits the proposed NDRO memory cell and logic circuits can now be implemented with the same fabrication process.     

Buckling of thick skew plates

The paper considers the elastic buckling of thick skew plates. Up to now, very little work has been done on this subject and the paper aspires to fill this gap. Based on the principle of stationary total potential energy and the recently developed pb-2 Rayleigh-Ritz method as a solution procedure, buckling solutions for skew plates of various aspect ratios, skew angles and boundary conditions are determined. The tabulation of these results, not available thus far, should be useful to designers and researchers who may use them as benchmark values to test the validity and convergence of their numerical techniques and softwares for thick plate analysis.     

多场耦合作用下流变液悬浮性态仿真与分析

仿真分析了磁场和剪切场作用下双分散、单分散磁流变液的微观结构演化,从4个方面考察了磁流变液悬浮性态：微观结构相变,链长分布,聚合结构各向异性和悬浮粒子运动涨落。结果表明,在磁场作用下,场强幅值越高,相态迁移的时间越短、簇-墙相越明显;在低磁场时,双分散悬浮较单分散悬浮容易形成长链,而在中、高磁场时,单分散悬浮却较双分散悬浮容易形成长链;磁极粒子具有智能特性,在无剪切场作用下总是寻找最易形成墙的方向排列成簇,而在稳态剪切作用下沿流场方向形成通长墙相以抑制流场的输运;外加磁场有助于减小悬浮粒子的运动涨落,但在剪切场的引导作用下,磁场强度的变化对悬浮粒子运动涨落无明显影响。     

Buckling of simply-supported skew plates

The difficulties associated with the solution of the skew plate buckling problem are described, and the work of other writers is summarized. By solving a numerical example, the relative advantages of two proposed refinements to the finite element displacement method are demonstrated: A technique of boundary condition relaxation appears justified and gives favourable results compared with conventional boundary condition specification. A mesh grading technique, which is simple to apply, results in a marked improvement in convergence to a solution.     

Effects of weak electric fields on the activity of neurons and neuronal networks

Electric fields applied to brain tissue will affect cellular properties. They will hyperpolarise the ends of cells closest to the positive part of the field, and depolarise ends closest to the negative. In the case of neurons this affects excitability. How these changes in transmembrane potential are distributed depends on the length constant of the neuron, and on its geometry; if the neuron is electrically compact, the change in transmembrane potential becomes an almost linear function of distance in the direction of the field. Neurons from the mammalian hippocampus, maintained in tissue slices in vitro, are significantly affected by fields of around 1-5 V m(-1).     

The performance of thin film superconducting bolometers in magnetic fields

Thin films of pure superconducting metals and alloys can be used as rapid response bolometers over a wide temperature range if a small magnetic field is applied. The characteristics of various films are discussed together with a brief consideration of methods of use.