家用电器接触电流测量浅析

泄漏电流是考核家用电器产品安全性能的主要指标之一,是评价家电产品绝缘性能的重要参数.家电产品接触电流的测量,首先要正确理解和掌握家用电器标准中"接触电流"的概念、测量方法,同时还需要掌握相关的基础标准、引用标准以及IECEE的OD指导文件要求,明确加权接触电流测试设备的相关要求.从标准要求、测试设备、试验方法等几个方面...     

引领飞机飞向备降场安全着陆有关问题研究

安全是所有飞行活动正常进行的根本,是飞行的生命线。在特殊情况下,如何引领飞机在备降场安全降落,是摆在航空人面前的一个现实问题。深入分析造成飞机被迫降停的原因,对如何选择合理的备降场进行针对性分析,总结出选择备降机场所遵循的原则,并提出正确引领飞机飞向备降场的方案,这对在特殊情况下引领飞机飞向备降场,安全着陆,指导飞行实践,提供一定的借鉴作用,具有积极的现实意义。     

双燃料发动机气缸压力变动研究

为了准确测量发动机气缸压力、分析燃烧过程,开发了一套可同时测量多缸汽油机各缸示功图的高速数据采集系统,最多同时采集16路信号,最大采样频率1MHz.应用本数据采集系统对化油器发动机改造的双燃料发动机进行了测试.每个气缸测量了至少50循环的压力数据,用倒拖最大压力的平均值为评价标准比较了各缸的进气量差异.同时,分别连续测量了各个气缸燃烧汽油和CNG时的燃烧压力.最后,用最大燃烧压力的平均值和变动系数比较了各缸的燃烧变动.实验结果表明,实验用发动机的各缸进气和燃烧状况存在明显差异,而燃用CNG时最大燃烧压力的变动系数小于燃用汽油时的数据.     

跟踪机动目标的一种新方法的研究

本文提出了跟踪三维空中机动目标的一种新方法,在这种方法中,未知的目标加速度被认为是具有非零均值、时间相关的随机过程并将它的概率密度函数假定为截断正态型。借助于切比雪夫(Chebyshev)不等式来确定目标随机加速度的均值和方差之间的关系。理论分析和仿真结果表明,由作者们提出的模型和算法去跟踪恒加速目标时稳态偏差为零,从而消除了R.A.Singer方法在跟踪恒加速度目标时所存在的稳态偏差。给出了计算机仿真结果。截断正态概率密度模型和自适应算法适合于跟踪高度机动目标并且易于实现。     

小湾坝址场地对地震动影响的研究

河谷两岸地震地面运动的差异对于建造在深山峡谷、基底延伸很长、各点高差很大的复杂空间结构的高拱坝地震反应和抗震安全有极为重要的影响，可导致两岸坝肩形成抗震薄弱部位。本文采用显式有限元法结合人工透射边界，对小湾河段左岸孤立半岛地形对坝址河谷地震动的影响作了初步分析探讨，半岛地形引起的河谷两岸地震动频谱分量和动位移的差异，在大坝抗震安全性的评估中应予考虑。     

带垫座拱坝的静动力分析

本文采用有限元法进行了九甸峡带垫座拱坝的静动力分析 ,着重讨论了垫座对坝体反应的影响 ,垫座合理尺寸的确定。分析结果表明 :垫座的设置对坝体的静动位移影响较小 ,坝体的静动应力虽在分布上稍有不同 ,但也无实质性变化。对九甸峡这类地质条件有缺陷的拱坝坝基 ,可以采用加垫座的工程措施进行处理。     

Recombinant bone morphogenetic protein (BMP)-2 regulates costochondral growth plate chondrocytes and induces expression of BMP-2 and BMP-4 in a cell maturation-dependent manner

This study examined the effect of recombinant human bone morphogenetic protein-2 on several parameters of growth, differentiation, and matrix synthesis and on the endogenous production of mRNA of bone morphogenetic proteins 2 and 4 by growth plate chondrocytes in culture. Chondrocytes from resting and growth zones were obtained from rat costochondral cartilage and cultured for 24 or 48 hours in medium containing 0.05-100 ng/ml recombinant human bone morphogenetic protein-2 and 10% fetal bovine serum. Incorporation of [3H]thymidine, cell number, alkaline phosphatase specific activity, incorporation of [3H]proline into collagenase-digestible protein and noncollagenase-digestible protein, and incorporation of [35S]sulfate were assayed as indicators of cell proliferation, differentiation, and extracellular matrix synthesis. mRNA levels for bone morphogenetic proteins 2 and 4 were determined by Northern blot analysis. Recombinant human bone morphogenetic protein-2 increased the incorporation of [3H]thymidine by quiescent resting-zone and growth-zone cells in a similar manner, whereas it had a differential effect on nonquiescent cultures. At 24 and 48 hours, 12.5-100 ng/ml recombinant human bone morphogenetic protein-2 caused a dose-dependent increase in cell number and DNA synthesis in resting-zone chondrocytes. No effect was seen in growth-zone cells. Recombinant human bone morphogenetic protein-2 stimulated alkaline phosphatase specific activity in resting-zone chondrocytes in a bimodal manner, causing significant increases between 0.2 and 0.8 ng/ml and again between 25 and 100 ng/ml. In contrast, alkaline phosphatase specific activity in growth-zone chondrocytes was significantly increased only between 12.5 and 100 ng/ml. Recombinant human bone morphogenetic protein-2 increased the production of both collagenase-digestible protein and noncollagenase-digestible protein by resting-zone and growth-zone cells, but incorporation of [35S]sulfate was unaffected. Administration of recombinant human bone morphogenetic protein-2 also increased incorporation of [3H]uridine in both resting-zone and growth-zone chondrocytes; these cells produced mRNA for bone morphogenetic proteins 2 and 4. Bone morphogenetic protein-2 mRNA levels in both resting-zone and growth-zone chondrocytes increased in the presence of recombinant human bone morphogenetic protein-2; however, bone morphogenetic protein-4 mRNA levels in growth-zone cells decreased under its influence, and those in resting-zone cells were upregulated only with a dose of 10 ng/ml. This indicates that recombinant human bone morphogenetic protein-2 regulates chondrocyte proliferation, differentiation, and matrix production, and the effects are dependent on the stage of cell maturation. Resting-zone chondrocytes were more sensitive, suggesting that they are targeted by bone morphogenetic protein-2 and that this growth factor may have autocrine effects on these cells.     

合成甲基叔戊基醚的化学平衡研究

合成甲基叔戊基醚的化学平衡研究是在测量平衡常数的基础上进行的，由平衡常数推算出反应的ΔＨ°和ΔＳ°。反应以甲基叔戊基醚分解的方式进行，以酸性树脂为催化剂，压力控制在１．０ＭＰａ，在４０—９０℃范围内，由试验测得３个反应的标准焓变和熵变分别为：ΔＨ°１＝－３４．９±１．４ｋＪ／ｍｏｌ，ΔＨ°２＝－２８．１±１．１ｋＪ／ｍｏｌ，ΔＨ°３＝－６．９５±１．１ｋＪ／ｍｏｌ；ΔＳ°１＝－７５．５９±３．９Ｊ／（ｍｏｌ·Ｋ），ΔＳ°２＝－７４．８±３．４Ｊ／（ｍｏｌ·Ｋ），ΔＳ°３＝－１．１６±３．１Ｊ／（ｍｏｌ·Ｋ）     

Portable autonomous walk calibration for 4-legged robots

In the present paper we describe an efficient and portable optimization method for calibrating the walk parameters of a quadruped robot, and its contribution for the robot control and localization. The locomotion of a legged robot presents not only the problem of maximizing the speed, but also the problem of obtaining a precise speed response, and achieving an acceptable odometry information. In this study we use a simulated annealing algorithm for calibrating different parametric sets for different speed ranges, with the goal of avoiding discontinuities. The results are applied to the robot AIBO in the RoboCup domain. Moreover, we outline the relevance of calibration to the control, showing the improvement obtained in odometry and, as a consequence, in robot localization.     

Achieving stress-constrained topological design via length scale control

A new suite of computational procedures for stress-constrained continuum topology optimization is presented. In contrast to common approaches for imposing stress constraints, herein it is proposed to limit the maximum stress by controlling the length scale of the optimized design. Several procedures are formulated based on the treatment of the filter radius as a design variable. This enables to automatically manipulate the minimum length scale such that stresses are constrained to the allowable value, while the optimization is driven to minimizing compliance under a volume constraint – without any direct constraints on stresses. Numerical experiments are presented that incorporate the following : 1) Global control over the filter radius that leads to a uniform minimum length scale throughout the design; 2) Spatial variation of the filter radius that leads to local manipulation of the minimum length according to stress concentrations; and 3) Combinations of the two above. The optimized designs provide high-quality trade-offs between compliance, stress and volume. From a computational perspective, the proposed procedures are efficient and simple to implement: essentially, stress-constrained topology optimization is posed as a minimum compliance problem with additional treatment of the length scale.