用1／f噪声表征MOSFET的负温偏不稳定性

负温偏不稳定性是ＭＯＳ顺件最重要的可靠问题之一。本文实验上发现ＭＯＳＦＥＴ的Ａ／ｆ噪声与其负温偏不稳定性相关，初始１／ｆ噪声谱密度正比于负温偏应力下的跨导退化量。     

Instabilities generated by friction in a pad–disc system during the braking process

This paper presents a numerical and experimental study of a pad–disc tribometer. The explicit dynamic finite element software PLAST 3 in 3-D is used to simulate the behaviour of the two bodies involved. Coulomb's friction law is used at the contact surface with a constant coefficient. For this application, temporal simulations show that separation occurs between surfaces, proof of instabilities. This unstable state is characterized by a stick–slip–separation wave. We show that instabilities describe a periodic shock phenomenon at the contact interface. Consequently, the acceleration spectrum recorded on the surface of the pad reveals periodicity in the frequency domain. It shows also that, in this case, the vibrations responsible for the instability are localized in the pad. The mode responsible for squealing can be obtained by a modal analysis of the pad–disc system by assuming that the interface is stuck. We highlight the importance of the pad Poisson's ratio in the occurrence of this unstable state. A numerical/experimental comparison has been performed and the fundamental frequency of squeal obtained experimentally and its magnitude agree with those calculated numerically with PLAST 3.     

Instability analysis in pressurized three-layered fiber-reinforced anisotropic rubber tubes in torsion

Instability analysis of the large deformation of three-layered fiber-reinforced anisotropic rubber tubes subjected to an inner pressure combined with torsion and axial stretch is examined within the framework of finite elasticity. Based on a fiber-reinforced incompressible hyper-elastic material model, the relation between the principal stretch and the inner pressure, torsion and axial stretch is obtained. It is shown that there exists a critical thickness for the tubes. For a thin-walled tube which is thinner than the critical thickness, the tube under-goes a uniform stable inflation when the inner pressure is small. However, the tube may under-go a strikingly non-uniform deformation when the inner pressure is larger than a certain critical value. One portion of the tube may become highly distended as a bubble and it is proved that this deformation is unstable. While a thick-walled tube which is thicker than the critical thickness, always under-goes a uniform inflation. The critical thickness of the tube to take unstable deformation is given based on the deformation curve and its slope. Furthermore, the effect of axial stretch, torsion and the distribution angle or the strength of the fiber on the deformation and the stress of the tube are discussed.     

Instability of beams with reduced beam section moment connections emphasizing the effect of column panel zone ductility

Column panel zone (PZ) ductility significantly affects the failure mode of beams with reduced beam section (RBS) moment connections. Even though good hysteretic behaviour is expected in connections with strong PZs, their flexural strength considerably deteriorates due to beam instability. In contrast, weak PZs are prone to high shear deformation, resulting in brittle fracture of connections. This study aims to question the provisions specified in the codes for the design of PZs. To this end, a numerical analysis was conducted on a series of subassemblies with various PZ properties. Use of lower deep sections is another major concern. It is indicated in this study that partial shear yielding in PZs can improve the hysteretic response of specimens by avoiding premature instability in beams. The results show that the PZ ultimate shear strength commonly prescribed in the design codes does not extend to an adequate safety margin. Furthermore, a new parameter is expressed for controlling an RBS beam as regards instability. This parameter is able to appropriately model the behaviour of RBS beams. The results are generally in good agreement with the existing experimental data.     

Stability of ferrofluid flow between concentric rotating cylinders with an axial magnetic field

A linear stability analysis for the ferrofluid flow between two concentric rotating cylinders in the presence of an axial magnetic field is implemented in this study. Both of the wide-gap and small-gap cases are considered and the governing equations with respect to three-dimensional disturbances including axisymmetric and non-axisymmetric modes are derived and solved by a direct numerical procedure. A parametric study covering wide ranges of ?, the volume fraction of colloidal particles; ξ, the strength of axial magnetic field; μ, the ratio of angular velocity of the outer cylinder to that of the inner cylinder; and ε, the ratio of radius of the inner cylinder to that of the outer cylinder, is conducted. Results show that the stability characteristics depend heavily on these factors. It is found that the increases of ? and ξ, and decrease of ε tend to stabilize the basic flow for an assigned value of μ. The variations of the onset mode with these parameters are discussed in detail. An example for the practical application of present results is given to help the understanding of stability behaviour of this flow.     

虚拟板材冲压皱曲特性试验

利用非线性有限元软件系统的数值模拟运算功能，对冲压板材皱曲特性试验（YBT）的试样、夹具和载荷进行数字化虚拟，并对试验过程和试验结果进行运算和讨论。     

HgCdTe光导芯片室温电阻率不稳定问题探讨

集中讨论 MCT 光导芯片电阻率随时间变化的问题。研究结果表明:MCT芯片中 Hg 原子的逐渐逸出导致了材料组分即 x 值随时间变化,这是芯片室温电阻率变化的主要原因;另外,在某些条件下(如加温),芯片表面可形成高浓度的 n 型载流子薄层,也将引起芯片的室温电阻率的变化。     

Experimental study on drop formation in liquid-liquid fluidized bed

Drop formation in liquid-liquid fluidized bed was investigated experimentally. The normal water was injected via a fine-capillary spray nozzle into the co-flowing No. 25 transformer oil with jet directed upwards in a vertical fluidized bed. Experiments under a wide variety of conditions were conducted to investigate the instability dynamics of the jet, the size and size distribution of the drops. Details of drop formation, drop flow patterns and jet evolution were monitored in real-time by an ultra-high-speed digital CCD (charge couple device) camera. The Rosin-Rammler model was applied to characterize experimental drop size distributions. Final results demonstrate that drop formation in liquid-liquid system takes place on three absolutely different developing regimes: bubbling, laminar jetting and turbulent jetting, depending on the relative Reynolds number between the two phases. For different flow domains, dynamics of drop formation change significantly, involving mechanism of jet breakup, jet length pulsation, mean size and uniformity of the drops. The jet length fluctuates with time in variable and random amplitudes for a specified set of operated parameters. Good agreement is shown between the drop size and the Rosin-Rammler distribution function with the minimum correlation coefficient 0.9199. The mean drop diameter decreases all along with increasing jet flow rate. Especially after the relative Reynolds number exceeds a certain value about 3.5×10⁴, the jet disrupts intensely into multiple small drops with a diameter mainly ranging from 1.0 to and a more and more uniform size distribution. The turbulent jetting regime of drop formation is the most preferable to the dynamic ice slurry making system.     

层次分析法在斜坡失稳灾害预测评估中的应用

着重介绍了斜坡失稳灾害预测评估的层次分析法,对影响斜坡稳定性的各因素进行了深入分析,确定了判别因子,并结合工程实际情况,制定了因子量化原则。