用于车辆传动的金属材料的疲劳试验及统计方法

　Aim　To improve the efficiency of fatigue material tests and relevant statistical treatment of test data. Methods Least square approach and other special treatments were used. Results and Conclusion The concepts of each phase in fatigue tests and statistical treatment are clarified. The method proposed leads to three important properties. Reduced number of specimens brings to the advantage of lowering test expenditures. The whole test procedure has more flexibility for there is no need to conduct many tests at the same stress level as in traditional cases.     

动态系统的自适应模糊神经网络控制

　Aim　To build an adaptive fuzzy neural controller and simulate it. Methods Fuzzy logic and back propagation(BP) algorithm are combined to utilize their advantages while avoiding the disadvantages. Results and Conclusion Simulation results of the third-order plant with disturbances and dead times show the validity of the presented controller. The presented controller can control cases that preceding controllers were unable to control.     

风险分析的尖点突变模型

　Aim　To assess simultaneously various risk states of a system. Methods Using the catastrophe and fuzzy theory, the energy and uncertainty in a system are set as two control variables and the function of the system is used as the state variable for analysis. Results and Conclusion A risk analysis model named the cusp model is presented. Various states regarding the safety of the system such as the accident state, no-accident state and miss state can be represented at will on the cusp model.     

基于DA算法的二维离散余弦逆变换的ASIC设计

　Aim　To present an ASIC design of DA-based 2-D IDCT. Methods In the design of 1-D IDCT is utilized a Chen-based fast IDCT algorithm, and multiplier accumulators based on distributed algorithm contributes in reducing the hardware amount and in enhancing the speed performance. Results and Conclusion VHDL simulation, synthesis and layout design of system are implemented. This 2-D IDCT ASIC design owns best timing performance when compared with other better designs internationally. Results of design prove to be excellent.     

极性反转瞬态电场的数值算法及应用

　Aim　To analyze the transient speciality of nonlinear, anisotropic, AC+DC coupling electric field, and to compare the withstand-voltage strength of different insulation structures. Methods The transient process of polarity reversal is analyzed, considering the anisotropic property of oil-immersed press-board, a new finite element model based on Galerkin method is presented and verified. The model developed is applied to calculate the electric field distribution in four typical winding end structures of the converter transformer. Results The whole-ring structure possesses the best insulation characteristics. Conclusion By introducing reasonable insulation components, insulation strength with the same surrounding sizes can be improved more than 30%.     

矿井通风网络分析的遗传算法

　Aim　To determine the global optimal solution for a mine ventilation network under given network topology and airway characteristics. Methods The genetic algorithm was used to find the global optimal solution of the network. Results A modified genetic algorithm is presented with its characteristics and principle. Instead of working on the conventional bit by bit operation, both the crossover and mutation operators are handled in real values by the proposed algorithms. To prevent the system from turning into a premature problem, the elitists from two groups of possible solutions are selected to reproduce the new populations. Conclusion The simulation results show that the method outperforms the conventional nonlinear programming approach whether from the viewpoint of the number of iterations required to find the optimum solutions or from the final solutions obtained.     

节理岩体弹塑性动态有限元分析

　Aim　To study the elastic-plastic dynamical constitutive relations about a jointed rock mass under explosion load and its computer simulation. Methods Stress history is taken into account and stresses will follow changes in time during a period of explosion load. According to the principle of static force balance, the corresponding nodal concentrated force is calculated and the nodal displacement is counted. The elastic-plastic dynamic finite element equations are thus obtained. Results A finite element method is given for a jointed rock mass under explosion load. Conclusion The problem of large plastic deformation for jointed rock mass on blasting was efficiently resolved through dynamic finite element analysis and the range of damages by blasting simulated, and this pushes forward the problem to engineering practice.     

燃料空气炸药近区抛散过程的研究

　Aim　To study fuel dispersion in fuel air explosive(FAE) and computational ways of fuel dispersion velocity in the near area. Methods The dispersion process of fuel in FAE was analyzed by the use of results measured with KODAK EKTAPRO EM Motion Analyzer and setting up mechanical models. Results Computational methods for fuel dispersion velocity in the acceleration stage is given and taken as a base for the study of fuel dispersion in the intermediate and the far area. Conclusion When the fuel flow velocity is higher than that of the explosion gas in the center cavity, the fuel divides with the explosion gas and its velocity of flow reaches a maximum. The acceleration stage ends at that time. The fuel dispersion velocity at this time is the initial conditions for numeral analyses of dispersion process in the intermediate and far areas.     

约束系统特性对乘员碰撞响应影响的仿真研究

　Aim　To study the influence of restraint system performance upon the occupant's response during impact, and provide a scientific base for occupant restraint system design. Methods In the light of basic theory of multibody system dynamics and impact dynamics on the basis of classical theory of impact, R-W method is adopted to construct the vehicle-occupant system model consisting of fourteen rigid bodies, thirty seven DOFs and slip joints for the simulation. A software named SVC3D(3-dimensional simulation of vehicle crash) is developed in the FORTRAN language. Results The results of simulation have a good coincidence with those of tests and the restraint system with low elongation webbing and equipped with pretensioner provides better restraint effect for the occupant. Conclusion The model of vehicle-occupant multibody system and SVC3D are suitable for use. Occupant should be belted with low elongation webbing to a certain degree and occupant restraint system should be equipped with pretensioner.     

热处理对共混物中尼龙6熔融行为的影响

　Aim　To investigate the multiple melting behavior of polyamide-6(PA-6) in polyamide-6/linear low density polyethylene blends crystallized from the crystal-amorphous state. Methods The effects of annealing temperature, annealing time, heating rate, and the step-wise annealing were measured by DSC. Results and Conclusion There exists a critical heating rate affecting the middle temperature melting peak. When annealed at the temperature close to the melting peak, the main melting peak of PA-6 shifted to a higher temperature. Within a short time, annealing time has much effect on neat PA-6 but little effect on PA-6 in the blends. Addition of PE results in a decreasing in the height of melting peak. These phenomenon show that the melting behavior of PA-6 was affected by PE, compatibilizer, as well as thermal treatment.     

Different properties of GaN-based LED grown on Si(111) and transferred onto new substrate

Nitride light-emitting diodes (LEDs) based on silicon substrate have been extensively studied[1―4]. However, it is difficult to grow high-quality nitride epilayers on Si substrate due to not only the large mismatch of lattice and thermal expansion coefficient between the epilayer and substrate, but also the SixNy will be generated during the growth process. Although it has so many obstacles to obtain satisfied GaN MQW LEDs on Si substrate, some excellent results have been achieved recen…     

Improved GaN grown on Si(111) substrate using ammonia flow modulation on SiN x mask layer by MOCVD

In this paper, 1 μm n-GaN was grown by using varied and fixed ammonia flow (NH₃) on SiN _x mask layer on Si(111) substrate using metal organic chemical vapor deposition (MOCVD). In-situ optical reflectivity traces of GaN growth show that the three- to two-dimensional process has been prolonged by using varied ammonia flow on SiN _x mask layer method compared with that grown by fixing ammonia flow. Structural and optical properties were characterized by high-resolution X-ray diffraction and photoluminescence, and compared with the sample grown by fixing ammonia flow, GaN grown using the varied ammonia flow on SiNx mask layer showed better structure and optical quality. It was assumed that the low NH₃ flow in the initial growth stage considerably increased the GaN island density on the nano-porous SiN _x layer by enhancing vertical growth. Lateral growth was significantly favored by high NH₃ flow in the subsequent step. As a result, the improved crystal and optical quality was achieved utilizing NH₃ flow modulation for GaN buffer growth on Si(111) substrate.

     

Improved GaN grown on Si(111) substrate using ammonia flow modulation on SiNx mask layer by MOCVD

In this paper, 1 μm n-GaN was grown by using varied and fixed ammonia flow (NH₃) on SiN _x mask layer on Si(111) substrate using metal organic chemical vapor deposition (MOCVD). In-situ optical reflectivity traces of GaN growth show that the three- to two-dimensional process has been prolonged by using varied ammonia flow on SiN _x mask layer method compared with that grown by fixing ammonia flow. Structural and optical properties were characterized by high-resolution X-ray diffraction and photoluminescence, and compared with the sample grown by fixing ammonia flow, GaN grown using the varied ammonia flow on SiNx mask layer showed better structure and optical quality. It was assumed that the low NH₃ flow in the initial growth stage considerably increased the GaN island density on the nano-porous SiN _x layer by enhancing vertical growth. Lateral growth was significantly favored by high NH₃ flow in the subsequent step. As a result, the improved crystal and optical quality was achieved utilizing NH₃ flow modulation for GaN buffer growth on Si(111) substrate.     

Fabrication of GaN films through reactive reconstruction of magnetron sputtered ZnO/Ga_2O_3

1　INTRODUCTIONGallium nitride (GaN) is one of the most po tential semiconductors. GaN has a direct energyband gap of 3.4 eV at room temperature and highexternal photoluminescence quantum efficiency, aswell as a high excitonic binding energy of20 meV[1]. It is an ideal material for fabrication ofultraviolet(UV)/blue/green light emitting diodes(LEDs), laser diodes(LDs), UV detectors and de vices operating in high temperature, high frequen cy and high power co…     

Wafer bonding technique used for the integration of cubic GaN/GaAs (001) with Si substrate

We successfully used the metal mediated-wafer bonding technique in transferring the as-grown cubic GaN LED structure of Si substrate. The absorbing GaAs substrate was removed by using the chemical solutions of NH4OH : H2O2=1 : 10. SEM and PL resuls show that wafer bonding technique could transfer the cubic GaN epilayers uniformly to Si without affecting the physical and optical properties of epilayers. XRD result shows that there appeared new peaks related to AgGa2 and Ni4N diffraction, indicating that the metals used as adhesive and protective layers interacted with the p-GaN layer during the long annealing process. It is just the reaction that ensures the reliability of the integration of GaN with metal and minor contact resistance on the interface.     

Fabrication of GaN films through reactive reconstruction of magnetron sputtered ZnO／Ga2O3

A simple and easily operated technique was developed to fabricate GaN films. GaN films possessing hexagonal wurtzite structure were fabricated on Si(111) substrates with ZnO buffer layers through nitriding Ga2O3 films in the tube quartz furnace. ZnO buffer layers and Ga3O3 films were deposited on Si substrates in turn by using radio frequncy magnetron sputtering system before the nitriding process. The structure and composition of GaN films were studied by X-ray diffraction, selected area electron diffraction and Fourier transform infrared spectrophotometer. The morphologies of GaN films were studied by scanning electron microscopy. The results show that ZnO buffer layer improves the crystalline quality and the surface morphology of the films relative to the films grown directly on silicon substrates. The measurement result of room-temperature photoluminescence spectrum indicates that the photoluminescence peaks locate at 365 nm and 422 nm.     

衬底效应对LiTaO3薄膜制备的影响

用溶胶凝胶法在N型硅、P型硅、石英、铂、镍衬底上制备了钽酸锂(LiTaO3)薄膜,用XRD和SEM对钽酸锂薄膜性能参数进行了表征;发现掺杂少量环氧树脂能提高钽酸锂薄膜的均匀性,改善薄膜与衬底的粘附性;研究了衬底效应与薄膜厚度的关系,薄膜厚度超过0.2 μm,Ni衬底的XRD峰值强度几乎不再出现,说明衬底对薄膜初始结晶取向有重要影响;利用不同衬底上生长钽酸锂薄膜,XRD研究结果表明:N型硅、P型硅、石英衬底上只能制备多晶钽酸锂薄膜,铂衬底上制备的钽酸锂薄膜在(012)晶向有强大的择优取向性,镍衬底上制备的钽酸锂薄膜有更好的C轴择优取向性,C轴择优取向系数可达0.082。     

基于AlGaN/GaN HEMT结构的ZnO纳米线感光栅极光电探测器

在传统的采用ZnO薄膜的AlGaN/GaN高电子迁移率晶体管(high electron mobility transistor, HEMT)光电探测器件中, 存在光吸收、光电转换效率低, 光电流小等诸多局限. 为改善上述问题, 基于AlGaN/GaN HEMT结构, 提出并成功制备了一种ZnO纳米线感光栅极光电探测器. 实验中首先通过水热法将ZnO纳米线成功制备到Si衬底材料及AlGaN/GaN HEMT衬底材料上, 并利用X射线衍射(X-ray diffraction, XRD)仪、扫描电子显微镜(scanning electron microscope, SEM)、光致发光(photo luminescence, PL)光谱仪等仪器进行了一系列测试. 结果表明, 生长在AlGaN/GaN HEMT衬底材料上的ZnO纳米线具有更低的缺陷密度、更好的结晶度和更优异的光电特性. 然后, 将ZnO纳米线成功集成到AlGaN/GaN HEMT器件的栅极上, 制备出具有ZnO纳米线感光栅极的AlGaN/GaN HEMT紫外光电探测器. 将实验中制备出的具有ZnO纳米线感光栅极的AlGaN/GaN HEMT器件与常规的AlGaN/GaN HEMT器件进行对比, 发现具有ZnO纳米线的器件在紫外波段能达到1.15×10⁴ A/W的峰值响应度, 相比常规结构的AlGaN/GaN HEMT, 峰值响应度提升约2.85倍, 并且制备的ZnO纳米线器件的响应时间和恢复时间缩短为τ_r=10 ms和τ_f=250 ms, 提高了探测器的性能.

     

Interface structure between epitaxial NiSi2 and Si

The interface structure between the Si and NiSi2 epitaxially grown on the （112） Si substrate was studied using high resolution transmission electron microscopy and computer image simulation. The results showed that the interface between Si and NiSi2 epitaxially grown on the （ 112 ） Si substrate has six different types： type A NiSi2 （111 ）/（ 111 ） Si, type A NiSi2 （001）/（001） Si, type B NiSi2 （ 111 ）/（ 111） Si, type B NiSi2 （ 112 ）/（ 1 12 ） Si, type B NiSi2 （ 271 ）/（001） Si, and type B NiSi2 （ 114 ）/（ 110 ） Si. And there are one or more different atomic structures for one type of interface.     

Structural and physical properties of permalloy thin films prepared by DC magnetron sputtering at different substrate temperature

Permalloy Ni80Fe20 films have been grown on thermal oxidized Si (111) wafers by magnetron sputtering at well-controlled substrate temperatures of 300, 500, 640 and 780 K in 0.65 Pa argon pressure. The base pressure was about 1×10-4 Pa. The deposition rate was about 5 nm/min for all the films. The structure of the films was studied using X-ray diffraction, scanning electron microscopy and atomic force microscopy. The composition of the films was analyzed using scanning Auger microprobe. The resistance and magnetoresistance of the films were measured using four-point probe technique. The results show that the content of oxygen in the films decreases gradually with raising substrate temperature. In addition, the surface morphology of the films presents notable change with the increasing of the substrate temperature; the residual gases and defects decrease and the grains have coalesced evidently, and then the grains have grown up obviously and the texture of (111) orientation develops gradually in the grow