Spin transfer torque and tunneling magnetoresistance dependences on finite bias voltages and insulator barrier energy

We investigate the dependence of perpendicular and parallel spin transfer torque (STT) and tunneling magnetoresistance (TMR) on the insulator barrier energy of the magnetic tunnel junction (MTJ). We employed the single orbit tight binding model combined with the Keldysh non-equilibrium Green's function method in order to calculate the perpendicular and parallel STT and the TMR in the MTJ with finite bias voltages. The dependences of the STT and TMR on the insulator barrier energy are calculated for semi-infinite half metallic ferromagnetic electrodes. We find a perfect linear relation between the parallel STT and the tunneling current for a wide range of insulator barrier energy. Furthermore, the TMR also depends on the insulator barrier energy, contradicting Julliere's simple model.     

X-ray and Magnetoresistance Measurements of Electrodeposited Cu-Co Granular Films

Granular CoxCu1-x alloy films were prepared by electrodeposition at room temperature directly onto semiconducting Si substrate. X-ray diffraction (XRD) revealed that the as-deposited films formed single phase metastable fcc alloy structure. The fcc lattice parameter αwas found to decrease linearly with increasing Co concentration x in the studied range. The giant magnetoresistance (GMR) of the films was improved after annealing. Pure Co fcc diffraction peaks were observed in the diffractogram of the annealed sample, indicating phase separation occurred upon annealing. The optimal annealing temperature was 450℃. The maximum of magnetoresistance (MR) ratio 8.21% was obtained for the Co20Cu80 thin film after annealing at 450℃for 1 h. The saturation field decreased upon annealing in the MR curves of Co20Cu80 film.     

Co_xAg_(100-x)颗粒膜的巨磁电阻效应及其物理机制研究

用超高真空电子束蒸发沉积方法制备了ＣｏｘＡｇ１００－ｘ颗粒并研究了其中的巨磁电阻（ＧＭＲ）效应。实验结果表明：１５ｋＯｅ外磁场下，玻璃衬底上制备态Ｃｏ３９Ａｇ６１颗粒膜室温ＧＭＲ效应值高达２０２％，并随氮气中退火温度上升而单调减小；颗粒膜的电阻与其磁化强度直接相关，可用四次多项式偶函数来描述。     

Effect of annealing on diamond-like carbon characteristics by electron spin resonance spectral analysis

We have examined the effect of annealing on physicochemical properties of the diamond-like carbon (DLC) films to produce higher quality films by the electron spin resonance spectral analyses of the immobilized dangling-bond sites (DBS), since amount of DBS reflects the characteristics of DLC films. On heat treatment of DLC deposited from ethylene monomer under anaerobic condition, the DBS decay was clearly shown, as the temperature raised. The decay described by second-order kinetics indicated that the recombination reaction of DBS progressed on heat treatment, suggesting that annealing treatment would accelerate the carbon-carbon covalent bonding network to produce harder films. In fact, the resulted DLC film derived from ethylene monomer showed non-existence of any type of oxygen atom based on X-ray photoelectron spectrum measurement, and water contact angle measurement showed higher hydrophobic surface of the DLC films.     

Effect of Co Ion Implantation on GMR of [NiFeCo(10 nm)/Ag(10 nm)] ×20Multilayer Film

The composition, phase structure and microstructure of the discontinuous multilayer film [NiFeCo(10 nm)/Ag(10 nm)]×20 were investigated after Co ion implantation and annealing at 280, 320, 360 and 400℃, respectively.GMR (giant magnetoresistance) ratio of the film with/without Co ion implantation was measured. The results showed that Co ion implantation decreased the granule size of the annealed multilayer film, and increased Hc value and GM R ratio of the multilayer film. After annealing at 360℃, the multilayer film [NiFeCo(10 nm)/Ag(10 nm)] ×20with/without Co ion implantation both exhibited the highest GMR ratio of 12.4%/11% under 79.6 kA/m of applied saturation magnetic field.     

Effect of Co Ion Implantation on GMR of [NiFeCo(10 nm)/Ag(10 nm)]×20 Multilayer Film

The composition, phase structure and microstructure of the discontinuous multilayer film [NiFeCo(10 nm)/ Ag(10 nm)]×20 were investigated after Co ion implantation and annealing at 280, 320, 360 and 400℃, respectively. GMR (giant magnetoresistance) ratio of the film with/without Co ion implantation was measured. The results showed that Co ion implantation decreased the granule size of the annealed multilayer film, and increased Hc value and GMR ratio of the multilayer film. After annealing at 360℃, the multilayer film [NiFeCo(10 nm)/Ag(10 nm)]×20 with/without Co ion implantation both exhibited the highest GMR ratio of 12.4%/11% under 79.6 kA/m of applied saturation magnetic field.     

Optical rotation and electron spin resonance of an electro-optically active polythiophene

A chiroptical polythiophene, is synthesized by electrolytic polymerization in a cholesteric liquid crystal electrolyte solution. The polymer displays a fingerprint texture similar to that of the cholesteric electrolyte solution. Upon electrochemical doping, the polymer displays optical rotation at wavelengths corresponding to the doping band observable in the absorption spectra. The formation of polarons on the main-chain is confirmed by electron spin resonance measurements. The results demonstrate the intermolecular chirality of polarons in this π-conjugated polymer, indicating continuum delocalized polarons are in a three-dimensional helical environment.     

Speed controller design of direct torque control system for induction motors by using adaptive supervisory Fuzzy-CMAC

A model-free approach was used to develop an adaptive supervisory Fuzzy-cerebellar model articulation controller (ASFCMAC) for a direct torque control system for an induction motor without shaft encoder. The two parts of the ASFCMAC are a supervisory controller for limiting tracking error to a bounded range and a Fuzzy-cerebellar model articulation controller subsystem for learning and approximating system dynamics. The ASFCMAC parameters are tuned according to adaptive rules derived from Lyapunov stability theory. Simulations and experimental comparisons with adaptive Fuzzy-cerebellar model articulation controller, adaptive cerebellar model articulation controller, fuzzy logic control, and proportional–integral control show that the proposed ASFCMAC has a superior root mean square error in operation over a wide range of speeds.     

A spin wave resonance study on reentrant Au77Fe23 films

Thin films prepared by both flash and slow evaporation of the bulk Au₇₇Fe₂₃ alloy have been studied by electron spin resonance (ESR) technique at the temperature range between 77–300 K. A series of spin wave resonance (SWR) peaks were observed at all temperatures when the external de magnetic field is applied along the directions lying in a small angular interval with respect to the film normal. The classical spin wave model has been used to analyze the experimental data. The magnetic parameters, such as exchange stiffness constant, the effective bulk and the surface anisotropy energy parameters of the system have been derived as a function of temperature. While the easy plane surface anisotropy almost remains constant, considerable increments were found in the exchange parameter, the magnetization and the linewidth with decreasing temperature. The SWR linewidths for the films obtained by slow evaporation at higher substrate temperatures are noticeably smaller compared to those of the film prepared by flash evaporation technique.     

制动力矩波动引起方向盘抖动的传递途径试验研究

通过制动抖动整车道路再现试验和dynamo试验台的制动器台架试验研究，确定了制动器制动力矩的低频波动（BTV）向方向盘传递的主要路径，并考察了传递路径中各个零部件对制动抖动的吸收与放大，为寻求传递途径的衰减控制措施奠定了良好的基础。研究表明，制动力矩波动传递的主要过程是制动力矩经过轮胎地面耦合作用，经过悬架系统传递到转向横拉杆并最终传递到方向盘，制动抖动在传递过程中整体衰减，但是在局部存在放大现象，机械结构上的放大对抖动的传递有很大的影响。     

Evidence of energy transfer among Nd ions in Nd:YAG driven by a mixture of exchange and multipolar interactions

The non-radiative energy transfer between Nd ions in Nd:YAG is investigated through high time-resolution fluorescence measurements of the level of Nd. Our experimental data suggests that a strong short-range interaction, i.e., exchange interaction, contributes to the energy transfer process between Nd ions at early times. In addition to it, our Monte Carlo simulations predict a multipolar mixture of interactions, that is, dipole–dipole, dipole–quadrupole, quadrupole–quadrupole and exchange interactions. This result is compared with a similar measurement and analysis for the Nd, Er, Cr:YAG luminescent system previously reported.     

缝合夹层结构复合材料树脂传递模塑成型工艺充模仿真

对复合材料与金属经缝合连接形成的夹层结构板的树脂传递模塑成型（RTM）工艺进行了充模模拟研究。首先通过实验和数值计算的方法,分别获得缝合夹层结构织物和芯层孔洞的渗透率;随后,建立能够反映缝孔内流动情况的二维和三维简化模型,进行RTM充模仿真,讨论不同工艺参数对成型流动的影响;最后通过成型实验验证工艺的可行性。缝线与孔洞直径之比为0.3~0.8时,孔洞渗透率随缝线直径的增大而减小,预制体织物渗透率与孔洞渗透率相差两个数量级;缝孔内容易产生缺陷,没有缺陷的区域随着注射压力的增加、孔洞密度和芯层厚度的减小而增大,在芯层表面沿每排孔洞单向开槽能够改善树脂在孔洞内的浸润;线注射时,树脂整体流动情况优于点注射,而点注射时,将进胶口设置在一角,能够减少表面干斑。     

基于复转矩系数法研究并网双馈风电场引发电力系统次同步振荡问题综述

风能作为一种可持续的清洁能源,近年来在我国得到迅猛的发展。双馈感应型风力发电机（doubly-fed induction generator,DFIG）具有灵活的控制特性,得到了广泛的应用,但由于其结构的特殊性,并网双馈风电场容易引发次同步振荡问题。该文首先介绍了并网双馈风电场引发电力系统次同步振荡（sub-synchronous oscillation,SSO）的机制。其次,对基于复转矩系数法的3类SSO问题的研究情况进行了系统性综述,并讨论了复转矩系数法的推广形式及其适用领域。最后,基于风力发电的前景和复转矩系数法的特性,对今后的研究方向进行了展望。     

An experimental investigation of class A surface finish of composites made by the resin transfer molding process

Achievement of high class surface finish is important to the high volume automotive industry when using the resin transfer molding (RTM) process for exterior body panels. Chemical cure shrinkage of the polyester resins has a direct impact on the surface finish of RTM molded components. Therefore, resins with low profile additives (LPA) are used to reduce cure shrinkage and improve surface quality of the composite parts. However, little is known about the behaviour of low profile resins during RTM manufacturing and their ultimate effects on the surface quality of molded plaques. In this work, the effects of controlled material and processing parameters on the pressure variations, process cycle times and ultimately on the surface quality of RTM molded components were investigated. Taguchi experimental design techniques were employed to design test matrices and an optimization analysis was performed. Test panels were manufactured using a flat plate steel mold mounted on a press. Pressure sensors were inserted in the mold cavity to monitor pressure variations during different stages of cure and at various locations in the mold cavity. It was found that a critical amount of LPA (10%) was required to push the material against the mold cavity and to compensate for the resin cure shrinkage. A significant increase in pressure was observed during the later stages of resin cure due to the LPA expansion. The pressure increase had a significant effect on the surface roughness of the test samples with higher pressures resulting in better surface finish. A cure gradient was observed for low pressure injections which significantly reduced the maximum pressure levels.     

Effect of microwave irradiation on carbon fiber/epoxy resin composite fabricated by vacuum assisted resin transfer molding

The effects of microwave irradiation for resin-curing of carbon fiber/epoxy resin composite (CFRTS), which was fabricated by vacuum-assisted resin transfer molding (VARTM) method, were investigated at 2.45 GHz frequency. The mechanical properties of CFRTS cured by microwave irradiation for 20 min at 120 °C were similar as compared to the conventional oven for 300 min at 120 °C. Moreover, the CFRTS irradiated by microwave had better adherence property between fiber and resin as compared to conventional oven at same resin-curing time. From the relation between resin-curing and mechanical property, it was found that the curing rate of microwave-irradiated CFRTS was 15 times faster as compared to conventional heating. Furthermore, the activation energies for resin-curing reaction on conventional- and microwave-cured CFRTS were estimated to be 2.7 and 1.3 × 10⁴ J/mol, respectively. The resin-curing reaction in CFRTS prepared by VARTM method was significantly promoted by microwave irradiation at short time.     

Three-dimensional process cycle simulation of composite parts manufactured by resin transfer molding

A process cycle of resin transfer molding (RTM) consists of two sequential stages, i.e. filling and curing stages. These two stages are interrelated in non-isothermal processes so that the curing stage is dominated by the resin flow as well as temperature and conversion distributions during the filling stage. Therefore, it is necessary to take into account both filling and curing stages to analyze the process cycle accurately. In this paper, a full three-dimensional process cycle simulation of RTM is performed. Full three-dimensional analysis is necessary for thick parts or parts having complex shape. A computer code is developed based on the control volume/finite element method (CV/FEM). The resulting computer code can provide information regarding flow progression and pressure field during mold filling; and temperature distribution and degree of cure distribution for a process cycle. The computer code can also be used for process cycle simulation of composite structures with complex geometry and with various molding strategies including switching injection strategy, multiple gate injection strategy and variable mold wall temperature. Numerical examples provided in the present work show the capabilities of the computer code in analyzing the process cycle.