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991.
The nonlinear dynamic
problems of three dimensional flexible multibody systems are investigated. The elastic
deformation fields of flexible space beams are decomposed into axial deformation and
bending deformation, and described by each exact vibration modes in the body coordinate
systems. The constrainted nonlinear dynamic equations are derived by using Lagrange
multiplier method. A numerical procedure for solving the resulting differential algebraic
equations is presented based on Newmark direct integration method combined with the
modified Newton-Raphson iterative method. Numerical results verify the effectiveness of
the proposed method. 相似文献
992.
In modern four-stroke automotive engine technology, variable valve timing and lift control offer potential benefits for making
a high-performance engine. In this paper, a novel design named dual-mode electrohydraulic fully variable valve train (EHFVVT)
for both engine intake and exhaust valves is introduced. The system is mainly controlled by either proportional flow control
valves or proportional pressure relief valves, and hence two different families of valve displacement patterns can be achieved.
The construction of the mathematical model of the valve train system and its dynamic analysis are also presented in this paper.
Experimental and simulation results show that the dual-mode electrohydraulic variable valve train can achieve fully variable
valve timing and lift control, and has the potential to eliminate the traditional throttle valve in the gasoline engines.
With the proposed system, the engine performance at various speeds and loads will be significantly improved. 相似文献
993.
目的分析原发性小血管炎患者多系统的临床表现和肾脏病理特点。方法选取我院1996年1月至2007年8月间明确诊断的原发性小血管炎患者共78例,患者均有肾脏损害,并行肾活检,总结分析患者的临床病理资料。结果78例中15例胞浆型抗中性粒细胞胞浆抗体(cANCA)阳性,均识别蛋白酶3(PR3);62例环核型抗中性粒细胞胞浆抗体(PANCA)阳性,均识别髓过氧化物酶(MPO)。临床表现呈多器官受累:不规则发热;浮肿、血尿、蛋白尿、肾功能减退;咳嗽、咯血、胸痛、肺部浸润;鼻塞伴有脓性分泌物;关节肿痛等。肾活检可见小血管壁节段性纤维素样坏死,新月体多见。免疫荧光无免疫球蛋白或微量免疫球蛋白及补体C3沉积。治疗采用糖皮质激素联用细胞毒药物或吗替麦考酚酯,部分患者同时给予透析治疗,治疗有效率达85.9%。结论原发性小血管炎并不少见,且以显微镜下型多血管炎居多;患者以中老年为主;ANCA检测有助于早期诊断及复发判断;及时治疗可逆转。 相似文献
994.
目的研究KCNE2蛋白在自发性高血压大鼠(SHR)心脏不同部位的分布和表达差异,及鼠龄对其表达水平的影响。方法提取幼龄和高龄SHR心肌不同部位(心室、室隔膜和心房)组织的膜蛋白,利用Western印迹技术和图象分析方法,比较KCNE2蛋白在样品之间免疫强度差异。结果SHR心肌不同部位组织中均有KCNE2蛋白的分布;同龄大鼠心肌不同部位组织中KCNE2蛋白的表达均无显著性差异;但在高龄大鼠的右心室和室隔膜组织中,KCNE2蛋白的表达显著高于其在幼龄大鼠相同组织中的表达。结论KCNE2蛋白在SHR心脏不同部位均有分布;在高龄大鼠右心室和室隔膜组织中,KCNE2蛋白的表达水平均高于其在幼龄大鼠同一组织中的表达。 相似文献
995.
列车空气制动均衡速度的局部稳定性 总被引:1,自引:1,他引:0
为了研究空气制动工况下列车均衡速度的稳定性,分析了列车均衡速度与单位合力函数单调性的关系.当单位合力函数单调递减时,列车均衡速度稳定,否则,其均衡速度不稳定.因此,在空气制动工况下,单位合力函数在部分速度区间单调递减,均衡速度存在局部稳定性,并采用二分法计算了均衡速度稳定的速度区间.以SS4型机车牵引中磷闸瓦空货车为例,列车运行限速和制动初速度为100 km/h,其临界速度为53.5 km/h,当列车速度为53.5~100 km/h时,空气制动下均衡速度是稳定的. 相似文献
996.
目的探讨绝经后妇女女性生理因素与腰椎、髋部骨密度的关系。方法对西安市城区281名绝经后妇女进行了女性生理因素的流行病学调查,并测定了腰椎、髋部骨密度。结果相关分析显示年龄、绝经年限、生育活产子女数和骨密度均呈显著负相关(P<0.01),而行经年限、身高、体重及体重指数(BMI)和骨密度均呈显著正相关(P<0.01)。比较骨质疏松组、骨量减少组和骨量正常组,年龄、绝经年限、生育活产子女数等,骨质疏松组明显高于骨量减少组和正常组(P<0.05);而平均每次月经持续天数、行经年限、身高、体重、BMI等,骨质疏松组明显低于骨量减少组和正常组(P<0.05)。结论西安市城区绝经后妇女的年龄、行经年限、绝经年限、生育活产子女数、身高、体重和BMI等与其腰椎和髋部的骨密度有明显的相关性。 相似文献
997.
Explaining obesity with urban form: a cautionary tale 总被引:1,自引:0,他引:1
Tudor D. Bodea Laurie A. Garrow Michael D. Meyer Catherine L. Ross 《Transportation》2008,35(2):179-199
In recent years, there has been a dramatic increase in studies exploring associations between the built environment and obesity.
Many studies have found that built environment characteristics, such as high-density land developments, mixed-land uses, and
connected street networks, are associated with lower rates of obesity. However, depending on the research field and the researcher,
how one specifies the experimental model and how sociodemographic characteristics of the population are defined and included
in the model has led to different policy conclusions and implications. This is not a surprising observation; however, it is
one that does seem to have been lost in current discussions. This article highlights several data-processing, model-specification,
and model-estimation factors that should be comprehensively considered in studies of the built environment and obesity. Empirical
results based on data from Atlanta, GA, USA, illustrate that the association between the built environment and obesity is
sensitive to how age, income, and educational attainment are included in the model. Also, a detailed examination of land-use-mix
measures shows that it is difficult to create this measure and that results are sensitive to the treatment of missing values.
Models that distinguish between overweight and obese individuals are shown to provide richer insights into the associations
among obesity, built environment, and sociodemographic characteristics for the Atlanta area. The article concludes by offering
modeling recommendations for future studies.
Tudor D. Bodea is a doctoral student in the School of Civil and Environmental Engineering at the Georgia Institute of Technology. His doctoral work examines the integration of customer-choice models into optimization algorithms for travel-industry applications. Laurie A. Garrow is an assistant professor in the School and Civil and Environmental Engineering at the Georgia Institute of Technology. Her research addresses the development and application of advanced models of travel demand that integrate discrete choice, econometric, and market research methods to enhance understanding of travel behavior. Michael D. Meyer is professor in the School of Civil and Environmental Engineering and Director of the Georgia Transportation Institute at the Georgia Institute of Technology. He has written over 160 technical articles and has authored or coauthored numerous texts on transportation systems, planning, and policy, including a college textbook. In 2006, he was the chairman of the Transportation Research Board Executive Committee. Catherine L. Ross is Harry West professor in the City and Regional Planning Program and Director of the Center for Quality Growth and Regional Development at the Georgia Institute of Technology. She has published extensively in the fields of urban planning, transportation planning, and public participation. She is the coauthor of The Inner City: Urban Poverty and Economic Development in the next Century. 相似文献
Laurie A. GarrowEmail: |
Tudor D. Bodea is a doctoral student in the School of Civil and Environmental Engineering at the Georgia Institute of Technology. His doctoral work examines the integration of customer-choice models into optimization algorithms for travel-industry applications. Laurie A. Garrow is an assistant professor in the School and Civil and Environmental Engineering at the Georgia Institute of Technology. Her research addresses the development and application of advanced models of travel demand that integrate discrete choice, econometric, and market research methods to enhance understanding of travel behavior. Michael D. Meyer is professor in the School of Civil and Environmental Engineering and Director of the Georgia Transportation Institute at the Georgia Institute of Technology. He has written over 160 technical articles and has authored or coauthored numerous texts on transportation systems, planning, and policy, including a college textbook. In 2006, he was the chairman of the Transportation Research Board Executive Committee. Catherine L. Ross is Harry West professor in the City and Regional Planning Program and Director of the Center for Quality Growth and Regional Development at the Georgia Institute of Technology. She has published extensively in the fields of urban planning, transportation planning, and public participation. She is the coauthor of The Inner City: Urban Poverty and Economic Development in the next Century. 相似文献
998.
999.
Transportation - Suburban development in the US is widely criticized for its contribution to automobile dependence and its consequences. Not surprisingly, then, a return to more urban-style... 相似文献
1000.
对梯形动铁式交流焊机的优化目标进行了探讨,在此基础上建立了动铁式交流焊机优化设计的数学模型,编制了计算机优化设计软件,利用该软件对焊机进行了优化设计,结果表明:利用该软件所设计的交流焊机具有较低的制造成本和较高的综合性能 相似文献