共查询到20条相似文献，搜索用时 212 毫秒
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汤海霞 《西安文理学院学报》2018,(3)
举升机同步机构设计使得举升机比较液压平稳,在同步机构的基础上设计补油回路和机械锁回路,使得举升机的安全系数得到大大的提高.液压举升机在作业过程中出现故障,首先要对过滤网、电磁阀、调速阀、液压泵等元件进行检查,检查是否有堵塞和损坏的现象.举升机最重要的就是维护,它关系到汽车维修工的安全.在保养时重点是减少液压系统污染来源,定期更换液压油,避免粗暴、冲击载荷和超载.随着汽车维修行业的迅速发展,汽车液压举升机的维护和保养非常重要,是汽车维修时的安全保障.通过对液压举升机工作原理的分析,研究举升机举不起来和降不下去等故障原因.分析举升机液压系统污染来源和污染带来的危害,研究液压举升机日常维护和保养的方法.另外,介绍了延长举升机寿命和安全作业的方法. 相似文献
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为研究多种随机因素对一类两部件串联系统预防性维修决策的影响,提出一种拟周期预防性维修策略优化模型．假设预防性维修对部件1为完整修,对部件2为保养,预防性活动在实施区间内根据动态计划随机进行;意外更换和预防性更换的竞争结果决定系统的更换,当部件2发生严重故障时引发系统的意外更换,当预防性维修次数达到设定的阈值Ⅳ时实施预防性更换．通过建模和优化分析,给出了最优预防性维修实施区间和最佳维修次数的求解算法,并通过数值案例对模型的优化过程和参数的敏感性做了说明．分析结果表明,在满足实际生产需求的前提下,尽可能地缩短实施区间能提高系统的平均运行时间和降低系统的长期运行成本率． 相似文献
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邓正义 《辽宁科技学院学报》2017,19(5)
WK-10 B型电铲支座在工作过程中故障频发,且使用寿命较短,维修或者更换的成本高.为了提高其使用寿命,从材料和结构两方面,提出一系列改进措施.实践证明,改进效果较好,支座寿命显著提高. 相似文献
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张荐青 《中国远程教育(综合版)》1986,(1)
目前录象机在电视大学已成为主要的教学工具之一,由于它的机械结构精密、电路系统复杂,故如能正确地使用、维护和检修,无疑会延长录象机的使用寿命、提高电教工作能量。为此,本栏将连续介绍录象机的使用与维修知识。共计六讲:第一讲,录象机的基本结构;第二讲,磁头与磁带的正确使用与维护;第三讲,走带系统的故障及维修;第四讲,信号系统的故障及维修;第五讲,伺服系统的故障及维修;第六讲,录象机的正确连接与使用。为了便于说明问题,在每讲中都介绍一些基本概念和术语。 相似文献
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20世纪初期,工程机械维修一般都是在发生故障以后才进行的,即事后维修.它的最大优点是充分地利用了零部件或系统部件的寿命,但事后维修是非计划性维修,浪费了较多的剩余修理,同时还存在一定的缺陷和不足. 相似文献
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The multi-pass scheduling method is a key issue in die-less spinning for determining the quality of the final products, including their shape deviations and wall thicknesses, and has drawn increasing interest in recent studies devoted to trying to improve the accuracy of the formed parts. In this paper, two main parameters, roller path profiles and deformation allocations in each pass, are considered in newly proposed multi-pass scheduling and optimizing methods in die-less spinning. Four processing methods with different roller path profiles and with three deformation allocation methods are proposed for investigating the influence of scheduling parameters on product qualities. The ‘similar geometry principle for restraining shape deviation’ and the ‘small curvature principle for maintaining wall thickness’ are presented for optimal design of roller path profiles; in addition, the ‘uniform allocation principle for maintaining wall thickness’ and the ‘large deformation principle for restraining shape deviation’ are brought forward as suggestions for deformation allocations. Based on these principles, a scheduling method denoted by RF+(FP & EHS) is presented to improve the comprehensive quality of a product of die-less spinning. 相似文献
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研究非惯性系中单面约束力学系统的微分变分原理。得到了具有单面完整和单面Chetaev型非完整约束的力学系统的D’Alembert原理、Jourdain原理和Gauss原理。给出了非惯性系中单面约束系统带乘子形式的各类运动方程。 相似文献
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Principles of Integrated Instruction for Engagement in Reading 总被引：1，自引：0，他引：1
John T. Guthrie Kathleen E. Cox Emily Anderson Kelly Harris Susan Mazzoni Leslie Rach 《Educational Psychology Review》1998,10(2):177-199
Our purpose in this article is to propose a set of design principles to serve as a structural framework for enhancing engagement in reading. We provide a rationale for our emphasis on engagement, which we believe is an important aim of reading instruction. We discuss the sources of the proposed design principles. These design principles consist of a set of features of the classroom context including: conceptual themes, real-world interactions, self-direction, interesting texts, social collaboration, self-expression, cognitive strategy instruction, time for engaged reading, and coherence. We present empirical support from the educational psychology literature for each principle. For illustration, we provide a brief depiction of each principle functioning within a framework of Concept-Oriented Reading Instruction (CORI). We emphasize that each principle is dependent on several others, and we describe how the functioning of each principle is contingent on the occurrence of several affiliated principles in the vignettes of CORI. 相似文献
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走入新世纪的美国小学数学的原则和标准述评 总被引：1，自引：0，他引：1
美国国家数学教师协会在其《学校数学的原则和标准 :讨论稿》(1998)中制定了小学数学的公平原则、课程原则、教学原则、学习原则、评价原则和技术原则。并制定了内容标准和过程标准。这些原则和标准带着先进的观念走入新世纪 ,对我国制定数学课程标准具有一定的启发意义。 相似文献
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Symmetry breaking phenomena exist in many mechanical products. Based on an analysis of the variation in physical features in several design examples, mechanical symmetry breaking concept systems that consist of general requirements, working principles, and cross-scale mechanical structures are established from the macro to micro levels and in both machine assembly and the design of parts. The connection between symmetry breaking and product requirements is systematically studied. Eight design principles using symmetry breaking to achieve mechanical functions, performance, and constraints are proposed. The method and process of applying symmetry breaking in mechanical concept design are described. These principles, method, and process are then used in the concept design of a gear chain. With symmetry breaking characters, the transmission stability of the newly innovated gear chain is greatly improved, compared with traditional ones. 相似文献
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Michael D. Coyne Edward J. Kame'enui Deborah C. Simmons 《Learning disabilities research & practice》2001,16(2):62-73
This paper addresses two sets of organizing principles to guide prevention and intervention in beginning reading: (a) the complexity in our alphabetic writing system, and (b) the complexity in our schools. The first set is related to instructional design, while the second set is related to a schoolwide model. Prevention and intervention efforts in beginning reading for students with learning disabilities must attend to 2 systems, our complex alphabetic writing system and our equally complex schools. In this article, we present 2 sets of organizing principles to guide prevention and intervention in beginning reading drawn from the substantial body of converging research evidence accumulated over the past 40 years. The first set consists of 6 instructional design principles focused on teaching reading in our alphabetic writing system. These principles include big ideas, mediated scaffolding, conspicuous strategies, strategic integration, primed background knowledge, and judicious review. The second set includes organizational principles designed to anchor effective reading practices at the school‐building level. These principles are structured around 3 interrelated areas: (1) the schoolwide establishment of long‐term reading goals and intermediate performance benchmarks, (2) the early identification and frequent monitoring of students experiencing reading difficulties, and (3) the development of coordinated and differentiated instructional interventions for the full range of learners. 相似文献
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A method is proposed to monitor and control Hopf bifurcations in multi-machine power systems using the information from wide area measurement systems （WAMSs）. The power method （PM） is adopted to compute the pair of conjugate eigenvalues with the algebraically largest real part and the corresponding eigenvectors of the Jacobian matrix of a power system. The distance between the current equilibrium point and the Hopf bifurcation set can be monitored dynamically by computing the pair of conjugate eigenvalues. When the current equilibrium point is close to the Hopf bifurcation set, the approximate normal vector to the Hopf bifurcation set is computed and used as a direction to regulate control parameters to avoid a Hopf bifurcation in the power system described by differential algebraic equations （DAEs）. The validity of the proposed method is demonstrated by regulating the reactive power loads in a 14-bus power system. 相似文献
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何吉欢 《上海大学学报(英文版)》1997,(1)
lintroductionIn1954,byso-calledtry-and-el.l.ormethodHull]deducedtheHu-Washizupl'inciple,whichplaysan.importantroleinthehistoryofvariation.In1964,ChienlZIsystematicallydiscussedtheLagrangemultipliermethod.Withthemethod,hesuccessfullydeducedHu-Washizuprinci… 相似文献
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Jihuan He Ph. D. 《上海大学学报(英文版)》1997,1(1):36-41
The paper has proved that Hellinger-Reissner and Hu-Washizu variational principles are but equivalent principles in elasticity
by following three ways: 1) Lagrange multiplier method. The paper points out that only a new independent variable can be introduced
when one constraint equation has been eliminated by one Lagrange multiplier, which must be expressed as a function of the
original variable(s) and/or the new introduced variable after identification. In using Lagrange multiplier method to deduce
Hu-Washizu principle from the minimum potential energy principle, which has only one kind of independent variable namely displacement,
by eliminating the constraint equations of stress-displacement relations, one can only obtain a principle with two kinds of
variables namely displacement and stress; 2) involutory transformation, with such method Hu-Washizu variational principle
can be deduce directly from the Hellinger-Reissner variational principle under the same variational constraints of stress-strain
relation, and vice verse; 3)semi-inverse method, by which both of the above variational principles can be deduced from the
minimum potential energy principle with the same variational constraints. So the three kinds of variational functions in Hu-Washizu
variational principle are not independent to each other, the stress-strain relationships are still its constraint conditions. 相似文献
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贺少锋 《河南师范大学学报(哲学社会科学版)》2006,33(3):74-77
公司设立过程中,股东或设立人可能因各种原因对公司法规定的设立事项或程序进行规避或违反,对此,英美法系国家一般采取瑕疵设立原则承认主义,而大陆法系国家法律一般规定的有设立无效或撤销设立登记制度。我国应借鉴两大法系的优点,结合我国实际,确立以公司设立形式判断为主要原则、以公司设立无效为补充的制度体系,并就设立无效公司的认定程序、公司行为的效力等问题加以规定,从而解决目前司法实践中的问题和困惑。 相似文献