微量调速阀抗污染机理研究

本文分析和证明了微量调速阀在实现2-100ml/min 的微量控制时,其压力补偿器的结构性自动抗污染机理和阀具有的综合抗污染性能、其抗污染的机理和性能对设计和研究低污染敏感度的液压元件有实际的指导意义.     

虚拟仪器在1553B总线通信系统中的应用

现代航空通信系统大多建立MIL－STD－1553B多路传输数据总线通信网络基础上，应用于1553B总线通信系统中的虚拟仪器技术实时监控／回放总线信息，分析故障原因，协助验证总线设计。本文就虚拟仪器在1553B总线通信系统中的应用进行了初步探讨。     

A method to extract mobility degradation and total seriesresistance of fully-depleted SOI MOSFETs

Free-carrier mobility degradation in the channel and drain/source series resistance are two important parameters limiting the performance of MOS devices. In this paper, we present a method to extract these parameters from the drain current versus gate voltage characteristics of fully-depleted (FD) SOI MOSFETs operating in the saturation region. This method is developed based on an integration function which reduces errors associated with the extraction procedure and on the DC characteristics of MOS devices having several different channel lengths. Simulation results and measured data of FD SOI MOSFETs are used to test and verify the method developed     

The hemodynamics in intracranial aneurysm ruptured region with active contrast leakage during computed tomography angiography

Precise locations of rupture region under contrast agent leakage of five ruptured cerebral artery aneurysms during computed tomography angiography, which is to our knowledge for the first time, were successfully identified among 101 patients. These, together with numerical simulations based on the reconstructed aneurysmal models, were used to analyze hemodynamic parameters of aneurysms under different cardiac cyclic flow rates. For side wall type aneurysms, different inlet flow rates have mild influences on the shear stresses distributions. On the other hand, for branch type aneurysms, the predicted wall shear stress (WSS) correlates strongly with the increase of inlet vessel velocity. The mean and time averaged WSSes at rupture regions are found to be lower than those over the surface of the aneurysms. Also, the levels of the oscillatory shear index (OSI) are higher than the reported threshold value, supporting the assertion that high OSI correlates with rupture of the aneurysm. However, the present results also indicate that OSI level at the rupture region is relatively lower.     

Design of Self-Tuning PID Power System Stabilizers for Synchronous Generators

A new technique for the excitation control of a synchronous generator is presented in this paper. The proposed technique employs a self-tuning proportional-integral-derivative (PID) power system stabilizer in order to improve the dynamic performance of a synchronous machine under a wide range of operating condition. Digital simulation of a synchronous machine subject to a major disturbance of a three phase fault under different operating conditions is performed to demonstrate the effectiveness of the proposed controller. It is found that the self-tuning PID stabilizer can enhance both the transient stability and the dynamic performance of the synchronous machine.     

Heat transfer in a smooth-walled reciprocating anti-gravity open thermosyphon

This paper describes an experimental investigation of heat transfer in a smooth-walled reciprocating anti-gravity open thermosyphon with relevance to the ‘shaker’ cooling system for the pistons of marine propulsive diesel engines. A selection of experimental results illustrates the interactive effects of inertial, reciprocating and buoyancy forces on heat transfer. It is demonstrated that the gravitational and reciprocating buoyancy effects, respectively, improve heat transfer in the static and reciprocating anti-gravity open thermosyphon. The individual pulsating force effect impairs heat transfer in the axial region with 5 hydraulic diameter length measured from the entrance of thermosyphon (region I). In the vicinity of sealed end of reciprocating thermosyphon with one hydraulic diameter from the sealed surface (region II), the individual pulsating force effect improves heat transfer at low pulsating number range, over which range a subsequent heat transfer reduction in this axial region is followed. The synergistic effects of inertial force, reciprocating force and buoyancy interaction in the reciprocating anti-gravity open thermosyphon could, respectively, impede or improve the regional heat transfers in the axial regions I and II from the static references of zero-buoyancy. A set of empirical correlations, which is physically consistent, was developed that permits the individual and interactive effects of inertial, reciprocating and buoyancy forces on heat transfer to be evaluated.     

气相二氧化硅生产现状及其在涂料中的应用

介绍了气相二氧化硅国内外生产状况,根据气相二氧化硅在涂料方面的应用特点及主 要技术关键的分析,提出了建议。     

Comparison of Cartesian grid configurations for application of the finite-difference time-domain method to electromagnetic scattering by dielectric particles

Two grid configurations can be employed to implement the finite-difference time-domain (FDTD) technique in a Cartesian system. One configuration defines the electric and magnetic field components at the cell edges and cell-face centers, respectively, whereas the other reverses these definitions. These two grid configurations differ in terms of implication on the electromagnetic boundary conditions if the scatterer in the FDTD computation is a dielectric particle. The permittivity has an abrupt transition at the cell interface if the dielectric properties of two adjacent cells are not identical. Similarly, the discontinuity of permittivity is also observed at the edges of neighboring cells that are different in terms of their dielectric constants. We present two FDTD schemes for light scattering by dielectric particles to overcome the above-mentioned discontinuity on the basis of the electromagnetic boundary conditions for the two Cartesian grid configurations. We also present an empirical approach to accelerate the convergence of the discrete Fourier transform to obtain the field values in the frequency domain. As a new application of the FDTD method, we investigate the scattering properties of multibranched bullet-rosette ice crystals at both visible and thermal infrared wavelengths.     

A land surface process/radiobrightness model with coupled heat andmoisture transport in soil

Heat and moisture transport in soil are coupled processes that jointly determine temperature and moisture profiles. The authors present a physically based, one-dimensional (1D), coupled heat and moisture transport hydrology (1-DH) model for bare, unfrozen, moist soils subject to insolation, radiant heating and cooling, and sensible and latent heat exchanges with the atmosphere. A 60-day simulation is conducted to study the effect of dry-down on soil temperature and moisture distributions in summer for bare soil in the Midwest United States. Given a typical initial moisture content of 38% by volume, the authors find that temperature differences between the water transport and no water transport cases exhibit a diurnal oscillation with a slowly increasing amplitude, but never exceed 4.4 K for the 60-day period. However, moisture content of the surface decreases significantly with time for the water transport case and becomes only about 21% at the end of the same period. The 1-DH model is linked to a radiobrightness (1-DH/R) model as a potential means for soil moisture inversion. The model shows that radiobrightness thermal inertia (RTI) correlates with soil moisture if the two radiobrightnesses are taken from times near the thermal extremes, e.g., 2 a.m. and 2 p.m., and that RTI appears temperature-dependent at the ending stages of the drydown simulations where soils are dry and their moisture contents vary slowly. Near times of thermal crossover, the RTI technique is insensitive to soil moisture     

中铝瓷球的应用研究

本文以长石、粘土、矾土等天然矿物原料,采用可塑法成型工艺,研究了配方与烧结温度、瓷球密度、外观颜色的关系,研制成功了成本低、密度大、外观质量较好的中铝瓷球的较佳配方,并解决了瓷球生产中的关键工艺技术问题。