A New Design of Magnetic Fluid Seal for Liquids

Direct contract between the sealed liquid and the magnetic fluid in a dynamic system under magnetic field may lead to an unstable interface, consequently, break down the seal. Aiming at this problem, a new magnetic fluid seal （MFS） was developed. In this new MFS, a soft iron bushing with high permeability was introduced on the shaft and nonferrous shields were installed beside the bushing and the pole pieces. The parameters of the bushing and the shields were optimized in a seal simulation facility. The results show that the bushing with a thickness of 7 mm and shields with a width of 8 mm are best for sealing a shaft 20 mm in diameter. The MFS designed based on the optimum parameters shows good performance and long life span for sealing lubricating oil.     

Influences of polishing on return loss of optical fiber connectors

With Al2O3 and SiO2 as polishing medium, under different polishing conditions, e.g. with different polishing pressure, polishing time and polishing fluid, the influences of polishing treatment on the return loss of optical fiber connectors were investigated. The return loss of optical fiber connectors is 32-38 dB before polishing. The resuits show that dry polishing(i, e. no polishing fluid) with Al2O3 has less influence on return loss of optical fiber connectors, while dry polishing with SiO2 reduces return loss to about 20dB because of the end-face of optical fiber contaminated. The wet polishing(i, e. using distilled water as polishing fluid) with Al2O3 or SiO2 can increase return loss to 45-50dB, but wet polishing with Al2O3 may produce optical fiber undercut depth of 80-140nm. Wet polishing with SiO2 should be preferentially selected for optical fiber connectors and polishing time should be controlled within 20-30s.     

浅析篮球运动防守中假动作的运用

随着篮球技战术的发展，要求个人防守更具实效性和针对性，篮球比赛防守中假动作的运用增强了个人防守的能力，使防守更具攻击性和实效性。     

提高认识,深化改革,努力提高毕业生就业竞争力

从专业发展的战略高度教育，让教师认识到毕业生就业工作的重要意义，通过深化专业教学改革，大力实施产学合作教育，积极探索对学生综合素质培养工作，从而提高人才培养质量，提高毕业生就业竞争力。     

基于KQML的协同CAD系统的通讯模型及冲突解决

设计基于KQML的代理的通讯模型，提出了基于多代理的协同设计系统中冲突解决方法，并给出其过程框架，详细说明了基于实例的推理的决策过程。     

Rheological behavior of continuous roll casting process of aluminum alloy

The rheological behavior of aluminum alloy and its influencing factors in physical simulation of continuous roll casting process were studied by using a Gleeble-1500 thermal-mechanical simulation tester with a set of special clamp system. The relationships between the flow stress and the strain rate in the deformation process of simulating roll casting experiment were obtained. The results show that four different characteristic stages exist in the temperature range of the whole rheological process. The first occurs when the temperature is higher than 600℃, which belongs to the creep deformation stage; the second occurs when the temperature lies in the range of 500 - 600℃, and it can be regarded as the high temperature and low stress level deformation stage; the third occurs when the temperature decreases to the range of 300 - 500℃, it is considered to be the middle stress level deformation stage; the last occurs when the temperature is less than 300℃ and the strain rate is less than 1.00 s^-1 , it belongs to middle stress level deformation stage. But when the strain rate is larger than 1.00 s^-1, it belongs to the high stress level deformation stage. And the relative constitutive models suitable for the four different stages of continuous roll casting process were established through multivariate linear regression analysis of the experimental data.     

Parameters Relevant to Bubble Detachment when Gas-injecting into Polymer Melt Flow Field

The bubble deformation processes were reported when gas was injected into polymer melt flow field in another paper, the experiments showed that the deformation was severely affected by the volume of the bubble, and in turn, for the different bubbles, several different deformation processes were presented during their movement along the flow channel. In addition, we could find that the magnitude of the bubble volume was dependent upon the pressure difference of the gas injection pressure and the melt pressure, In this paper, more experimental conditions were changed to investigate the parameters relevant to the detachment of bubbles from the injection nozzle. The experimental results show that the pressure difference, the melt flow velocity as well as the melt pressure were all critical for the purameters, such as the bubble detachment time, the maximum bubble diometers and the magnitude of the bubble volume. The morphology changes of bubble were very large when the flow field was abruptly changed, and the situations were more complicated.     

Microstructure and wear resistance of electro-thermal explosion sprayed stellite coating used for remanufacturing

Electro-thermal explosion directional spraying was used to prepare the stellite coating on substrate of the AISI 1045 steel. The morphologies of cross-section and worn scar, porosity, distribution of elements, micro-hardness and wear resistance of the coating were determined by means of SEM, EDAX, micro-hardness tester and sliding wear tester. Because of the compact construction, good bonding and high hardness, the coating is characterized by good wear resistance. The results show that the mainly failure mode of the stellite coating is micro-plowing. Foundation item: Project(2003AA331130) supported by Hi-tech Research and Development Program of China; Project(50235030) supported by the National Natural Science Foundation of China     

The electrode/sample contact effects on the dielectric properties of the CaCu3Ti4O12 ceramic

In this paper, the contact effects at the electrode/sample interfaces on the dielectric properties of the CaCu₃Ti₄O₁₂ (CCTO) ceramic were studied. The experimental results provide clear evidence that the colossal dielectric constant in CCTO is related to the ceramic itself; however, it may also partly originated from the electrode/sample contact effects which depends on the surface resistivity of the sample. When the surface resistivity of the ceramic is as high as 1.2 × 10⁸ Ω cm, no obvious mobile space charges can be observed, and the dielectric properties of the sample is inert to the different metal electrodes and various sample thicknesses, indicating the colossal dielectric constant (near 2000 at 10 kHz) at room temperature is due to the true properties of the ceramic itself. However, after the surface resistivity is lowered to 3.1 × 10⁷ Ω cm through post-annealing the sample in N₂ atmosphere at 750 °C, obvious mobile space charges can be observed, and the dielectric properties of the sample become sensitive to the different types of contacts. The dielectric constant of the sample with Pt electrode shows a significant enhancement (up to 5000 at 10 kHz), comparing with that of the sample with Ag electrode. Clearly, in this case, the extrinsic contact contributes partly to the colossal dielectric constant of CCTO ceramic.     

Influence of thermal annealing on optical properties and structure of aluminium oxide thin films by filtered cathodic vacuum arc

Optical and structural properties of aluminium oxide thin films are investigated in the annealing temperature range of 200–900 °C. The changes in optical properties and film structure show the great dependence on the temperature. For the film annealed at low temperatures (from 200 °C to 600 °C), the film optical properties, such as transmittance and optical constants, could be improved by thermal annealing with amorphous structure and smooth surface. However, for the film annealed at higher temperature (e.g. 900 °C), the poor performance of optical properties indicates undesirable application for precise use in optics due to significant changes in both structure and surface roughness. At optimum annealing temperature of 600 °C, the transmittance could reach as high as that of substrate and the film possesses better optical constants (refractive index was 1.73 and extinction coefficient was ∼10⁻⁴ at 550 nm) with remaining amorphous structure and smooth surface.