巩膜压陷法在玻璃体视网膜手术中的应用

巩膜压陷法是指玻璃体视网膜显微手术中用手术器械压凹巩膜进行眼内的检查和操作。最早由Ｌｅｗｉｓ［１，２］介绍用于切除晶状体囊膜和处理前段增生性玻璃体视网膜病变（ａｎｔｅｒｉｏｒｐｒｏ－ｌｉｆｅｒａｔｉｖｅｖｉｔｒｅｏｒｅｔｉｎｏｐａｔｈｙ，ａＰＶＲ）。...

外伤性晶体脱位的治疗(附5例报告)

外伤性晶体脱位的治疗一直是眼科医生视为困难的有争论的问题。在手术与保守,摘晶体或保留晶体之间总有争议。主张保守治疗者常证明晶体脱位尚有好的视力及眼对脱位晶体耐受性好,可维持多年,处理应十分谨慎。主张手术者则认为脱位晶体可引起其他并发症,导致失明,尽管有时摘出相当困难,仍主张应早期摘出。通过复习文献及实践,我们对手术适应症;术式的选择;

FE analysis of extrusion defect and optimization of metal flow in porthole die for complex hollow aluminium profile

To solve the defects of bottom concave appearing in the extrusion experiments of complex hollow aluminium profiles,a 3D finite element model for simulating steady-state porthole die extrusion process was established based on HyperXtrude software using Arbitrary Lagrangian–Eulerian(ALE)algorithm.The velocity distribution on the cross-section of the extrudate at the die exit and pressure distribution at different heights in the welding chamber were quantitatively analyzed.To obtain an uniformity of metal flow velocity at the die exit,the porthole die structure was optimized by adding baffle plates.After optimization,maximum displacement in the Y direction at the bottom of profile decreases from 1.1 to 0.15 mm,and the concave defects are remarkably improved.The research method provides an effective guidance for improving extrusion defects and optimizing the metal flow of complex hollow aluminium profiles during porthole die extrusion.

Prediction of central bursting defects in rod extrusion process with upper bound analysis method

The prediction of central bursting defects in the rod extrusion process through conical dies using the upper bound analysisis investigated. A kinematically admissible velocity field, including the radial and angular velocity components, is proposed. A newcriterion is presented to predict the occurrence of the central bursting defects. Parameter bobt, which represents the risk probability ofcracking, is proposed. It is calculated using the shape of the boundary at the entrance by minimizing the total power dissipationduring the extrusion process. When bobt is equal to or greater than bcr, central bursting occurs. Furthermore, the quantitativerelationships between central bursting defects and process parameters （semi die angle, reduction in area and frictional factor） arestudied. The results show that the central bursting defects are affected primarily by the reduction in area and the friction factor. Thepresented criterion is verified by comparing with the FEM simulation data and the results of the published paper.

Discrete element analysis on press and fracture mechanism of propellant grain

To analyze fracture mechanism of propellant grain and study the mechanical properties of propellant grain, the press and fracture processes of propellant grain with and without initial defects are modeled using the discrete element method. On the basis of the appropriate constitutive relationships, the discrete element model of the propellant grain was established. Compared with experimental measurements, the micro-parameters of the bonded-particle model of the propellant grain under unconfined uniaxial compression tests were calibrated. The propellant grains without initial defects, with initial surface defects, and with initial internal defects were studied numerically through a series of unconfined uniaxial compression tests. Results show that the established discrete element model is an efficient tool to study the press and fracture processes of the propellant grain. The fracture process of the propellant grain without initial defects can be divided into the elastic deformation phase, crack initiation phase, crack stable propagation phase, and crack unstable propagation phase. The fracture mechanism of this grain is the global shear failure along the direction of the maximum shear stress. Initial defects have significant effects on both the fracture mechanism and peak strength of the propellant grain. The major fracture mechanism of the propellant grain with initial surface defects is local shear failure, whereas that of the propellant grain with initial internal defects is global tensile failure. Both defects weaken the peak strengths of the propellant grain. Therefore, the carrying and filling process of the propellant grain needs to minimize initial defects as far as possible.

Research on Ground Movement Laws for Strip Mining Under Thick Alluvium

With the discrete element method, the simulation and analysis of a series of numerical models were made. This research revealed ground movement laws for strip mining under thick alluvium and gave calculation formulae for the maximum ground subsidence and horizontal movement as a function of basement rock thickness and mining width, thus providing sound evidence for future strip mining under thick alluvium.

软质泡沫聚合材料硬度特性数值测定系统

硬度是一个衡量材料性能的重要物理量,是体现材料弹性、塑性、强度和韧性等力学性能的综合指标。主要从硬件及软件上讨论了针对软质泡沫聚合材料硬度的数字测试系统。该系统应用了STC12系列带A/D转换的单片机,高精度压力传感器以及可控电机,来保证测试的稳定性和高精度。实践证明,该系统满足GB/T 10807-2006/ISO 2439:1997要求,可广泛用于在国家标准要求的A法、B法、C法下对标准尺寸的海绵、泡沫等试样的硬度进行准确的测试。