“Biaxiality Effect” on the Energy Dissipated by Elastoplastic Base-Isolators

A plane elastic-plastic solid body presenting kinematic hardening is used to simulate a pair of dampers at the base of a rigid structure and determine the energy dissipation under conditions of assigned, homogeneous cyclic loading. The well-known von Mises theory of plasticity is applied with the aim of obtaining analytical solutions to the problem. Such solutions are arrived at by first calculating the Odqvist parameter, which yields dimensionless relations that depend on the external loads and mechanical properties of the material. The results, in terms of dissipated energy, are given for the case of a sinusoidal process, represented with the help of dimensionless parameters useful for engineering applications.     

卫星包装箱的随机隔振优化分析

用钢丝绳隔振器将卫星包装箱支承在运输车上,将卫星与车辆简化为二自由度体系,优化分析了在随机路面上行驶时使包装箱响应最小之隔振参数,对实测得到的钢丝绳减振器的非线性迟滞性能作了描述,提出了统计线性化分析的方法。     

Isolation of single yeast cells by optical trapping

Individual yeast cells can be successfully isolated and recultured on plates with a new isolation method making use of optical trapping with infrared laser light. The cells can be selected on morphological criteria by high resolution microscopy. The isolation device is constructed from two coverslips separated by spacers, in which selected cells are transferred to a plastic capillary, using the optical trap. To test the procedure, selection experiments were done with a mixture of two Saccharomyces cerevisiae strains, distinguishable both in fluorescence microscopy and on agar plates. These experiments showed that only selected cells were isolated, and close to 100% of the isolated stationary-phase cells formed colonies on agar plates, indicating a high recovery. A lower recovery was obtained with exponential-phase cells, possibly because of a higher sensitivity to laser irradiation. Applications for this method may include the isolation of mutants with altered morphology and the isolation of subpopulations of yeast cultures, for their separate investigation or for the initiation of pure cultures.     

高速列车浮式地板振动响应有限元分析

针对采用试验方法开发高速列车浮式地板耗时耗力,且试验规模小,不能反映整车的振动效果的问题,基于有限元法进行高速列车振动响应分析.对三明治夹芯理论、蜂窝板理论和等效板理论进行比较,确定采用等效板理论数值模拟某浮式地板中的蜂窝板;利用橡胶材料的超弹性理论拟合橡胶材料参数;建立完整模型模拟实际工况下浮式地板的振动响应,得到浮式地板的隔振效果.结果表明此浮式地板的隔振效果约为90%,满足设计要求.     

不同土性地基考虑 ＳＳＩ效应的隔震结构地震响应分析

为探究不同土性地基的ＳＳＩ效应对层间隔震结构影响机理与动力响应规律,选取一个典型层间隔震结构,对其简化并制作缩尺模型,采用振动台试验的方法,分别在硬土、软土这两种地基上单向输入4条地震波来研究模型的动力响应。结果表明:土体具有明显的放大效应,随着地基土由硬变软,隔震结构周期延长倍数降低。隔震结构在硬土地基上能发挥较好的减震效果,而软土地基上减震效果明显减弱。软土地基上塔楼的动力响应较硬土地基增大,塔楼容易成为薄弱部位,其抗震设计应重点关注。     

煤矿井下采掘设备隔爆兼本安型电气控制箱的本安设计

针对煤矿井下采掘设备防爆兼本安型电气控制箱内本安电路与非本安电路并存、非本安电路的能量可能会窜入本安电路而影响本安电路防爆及本安性能的问题,从结构设计和电气隔离两方面介绍了煤矿井下采掘设备隔爆兼本安型电气控制箱的本安设计方法,给出了电气间隙、爬电距离、绝缘及耐压、接线端子、本安布线、电源变压器、本安隔离栅印制板等结构布置方法以及RS485通信隔离电路、模拟量隔离电路、压频变换电路、电阻信号隔离电路、开关量隔离电路、继电器隔离电路等电气隔离措施。应用表明,采用该方法设计的煤矿井下采掘设备隔爆兼本安型电气控制箱安全可靠,维护简便,能够满足煤矿井下的防爆要求。     

断层破裂过程对减隔震桥梁地震反应的影响

为了研究断层破裂过程对减隔震桥梁地震反应的影响,提出利用相位特性模拟方向性效应的改进随机格林函数法. 以1994年美国北岭地震的断层条件为例,通过与实际地震记录对比验证模拟方法的有效性;应用改进的随机格林函数法模拟相同震中距离的4组地震动时程作为输入条件,比较断层破裂过程对相同震中距离、不同方位的减隔震桥梁地震反应影响. 结果表明,利用持时包络曲线与相位差分分布的相似性可以方便模拟随机格林函数的地震动加速度时程;在相同震中距离条件下,断层破裂方向的观测点地震动以及对应位置的桥梁结构地震反应明显大于非破裂方向位置的观测点;当破裂方向上地震动时程不具有脉冲特性时,断层周围的减隔震桥梁地震反应主要受地震动强度的影响,桥梁方位的影响不明显.     

光电隔离技术在PLC上的应用

光电耦合技术主要是为了解决模拟电路和数字电路的集成、交叉应用时的相互干扰问题,同时具有信号整形、降低误操作等功能。本文就光电隔离抗干扰技术的特性在PLC的接口、功率驱动、远距离传送、过零检测电路中的应用做了介绍。     

火焰原子吸收光谱法测定电缆绝缘护套中的铅

提出了用空气—乙炔原子吸收光谱法测定电缆绝缘护套中的铅含量。铅在0.00~11.00μg.ml-1(r=0.9991)范围内有良好的线性关系。本法的RSD≤3.17%,回收率在97.2%~103.2%之间。     

Guidelines for facilitating the development of learning communities in online courses

Online learning has grown exponentially in recent years; however, dropout problem remains challenging for some online programmes. The dropout problem can be attributed to a number of reasons, with a lack of interaction between learners and the instructor constituting one of the main reasons. The lack of interaction also leads to learners' feeling of isolation. Learning communities can provide learners with an environment conducive to increased interactions and alleviate their feeling of isolation. Unfortunately, there are no clear rules that instructors can follow to help learners create learning communities. In this paper, we propose guidelines for online instructors to facilitate the development of learning communities in online courses. We first review the definition of a learning community, importance of a learning community and factors affecting the development of a learning community. Afterwards, based on a review of the existing guidelines and other relevant literature, we propose guidelines for facilitating the development of learning communities in online courses.