共查询到19条相似文献，搜索用时 468 毫秒
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Yi-cong GAO Yi-xiong FENG Jian-rong TAN 《浙江大学学报(A卷英文版)》2014,15(11):862-872
研究目的：为复杂机械产品提供满足整机可靠性指标和维护成本指标的预防性维护方案多准则规划方法。创新要点：1.分析了检查、维修、更换等对复杂机械产品零部件工作寿命变化的作用机理;2.提出了复杂机械产品预防性维护多准则规划方法。研究方法：1.基于非完美维修理论,建立不同模式下零件间工作寿命模型,定义维修效能因子,表征检查、维修、更换对零件寿命的影响;2.通过求解获得复杂机械产品指定时间区间的预防性维护方案,根据零部件工作寿命,采取维修和更换等预防性维护措施,减少零部件故障的发生。重要结论：零部件的预防性维护次数与其故障因子相关;机械产品尤其是复杂机械产品实施定期预防性维护能够减少或消除故障的发生。 相似文献
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研究了两个不同型部件一个修理工组成温贮备可修系统.假定两部件故障之后均不能"修复如新"且部件1具有优先使用权,部件2温贮备故障之后可以"修复如新".利用几过程、更新报酬理论,以部件1维修次数为更换策略,给出了系统经过长期运行单位时间内平均损失具体表达式.最后,通过数值实例对所结果进行仿真模拟,验了最优更换策略存在性. 相似文献
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针对多设备串联系统考虑基于寿命为中心,采用机会维修策略,分析了系统的维修费用组成和系统的利用率。在此基础上,满足系统利用率的条件下,以设备寿命的限值作为可靠性的约束,以有限区间[0,T]内维修总费用最小化为目标,建立了多设备串联系统预防性维修优化模型。最后,采用遗传算法,以某球团生产线为背景,对模型进行有效验证。 相似文献
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以多部件系统为研究对象,为提高系统可用度,考虑非等周期检测和不完全维修,建立基于可用度的维修优化模型.引入役龄回退因子描述部件不完全维修效果,提出非等检测周期的建模方法.将系统不可用状态划分为3个相互独立的事件,分析和计算每个事件下的系统不可用度.在分析不可用状态与非等检测周期之间关系的基础上,建立不完全维修条件下的维修优化模型,以优化系统的期望可用度.以某风力机的变速箱、发电机和主轴3个核心部件的维修优化为案例,比较非等周期检测维修模型和等周期检测维修模型的优化结果.结果表明,提出的基于可用度的非等检测周期维修模型能够实时更新风力机系统的维修计划,实现维修活动优化,有效地提高系统可用度 相似文献
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对有两个不同型部件和一个修理工的温贮备可修系统进行研究。假定两部件的工作故障修理均服从几何过程,利用预防性维修和马尔可夫更新过程获得了系统平均成本率的精确表达式,并得到使得系统平均成本率最小的方法。 相似文献
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研究了两同型部件组成的可修冷备系统,在假定故障部件不能"修复如新"的条件下.在假定部件寿命分布和维修分布均为指数分布时,我们利用几何过程和补充变量法求得了系统的一些可靠性指标. 相似文献
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王莉君 《安徽教育学院学报》2014,(3)
为评估在线修复对仪表系统误跳车的影响,提出了基于马尔科夫(Markov)模型二取一仪表系统误跳车计算模型。通过对二取一(1oo2)系统各种状态的可用性分析,在对在线维修对误跳车的影响进行深入分析的基础上,提出了一种误跳车的新定义。分析表明,在线维修在提高系统可用性的同时,也对误跳车产生明显的影响。数值分析表明,对1oo2系统而言,在线维修对于降低仪表系统的误跳车具有促进作用。而在不进行维修或不可维修的前提下,危险失效对误跳车的影响十分复杂。在某些情况下,危险失效不进行维修有助于降低误跳车,但却会降低仪表系统的可用性。而当危险故障率大于安全故障率时,随着危险故障率的增加,误跳车会增加。此外,共因失效可降低误跳车,但对误跳车的影响很小。 相似文献
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研究了服务台可修排队系统的最优更换策略,假定服务台不能“修复如新”,利用几何过程,以初服务的顾客数N为其更新策略,选择最优的N^*,使得系统工期运行单位时间内的期望效益达到最大,并求出了系统经长期运行单位时间内期望效益的明显表达式,最后还对结果进行了讨论。 相似文献
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段悦兰 《黄冈职业技术学院学报》2012,14(5):75-77
计算企业计划利润完成情况是加强企业管理、实现目标管理、评价工作业绩的重要手段。一般情况下,计划利润完成率的计算方法是直接用利润完成数除以利润计划数。但是,由于企业的发展是一个长期的过程,企业在一定时期、一定阶段利润为负值是一种正常现象。计划利润为负数是现实存在的客观问题。计算计划利润是负值时的计划完成率,不能简单采用利润完成数除以利润计划数的方法。结合金商贸易集团股份公司的内部考核指标完成情况,探讨计划利润为负值情况下,计划利润完成率计算的理论依据和实际应用。 相似文献
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《Journal of educational and psychological consultation》2013,23(1):47-57
The value and relevance of Alpert's (1977) guidelines for school consultants are reconsidered after 1 1/2 decades of significant societal changes that have resulted in calls for educational reform and restructuring. The debate over the Regular Education Initiative-its underlying assumptions, its proposed methods, and aims-is discussed as an illustration of the necessity for an informed and realistic approach to planned change. Recent additions to the literature on planned change are considered, particularly those pertaining to specific methods and strategies necessary for successful implementation. The importance of institutionalization as the terminal stage of a planned change is also discussed. Finally, the potential impact of the educational reform movement on the role of the school psychologist is addressed. 相似文献
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The transition from school to university can prove problematic for a number of academic and social reasons and first-year attrition rates are high. Research suggests that first-year students need help adjusting to a new phase of learning in a larger community of practice and that a student’s decision to leave represents a negative combination of multiple integration variables. One practice that may help to reduce stress and subsequently assist in lowering first-year attrition rates is a peer pentoring (PM) scheme. Within the Centre for Biomedical Sciences Education (CBMSE) at Queen’s University Belfast (QUB) a PM scheme was designed to engage new students in informal supportive relationships with more experienced students. Qualitative reports indicate that the scheme provided an avenue for new students to reappraise their previous expectations of university and develop a sense of identity within their course. An added benefit from this PM scheme was that it also allowed older students to gain transferrable employment-related skills in communication, teamwork and organisational expertise. In 2009–10, 9.1% of Biomedical Science (BMS) students, studying at QUB, did not return to the second year of their degree; however, following implementation of a PM scheme in 2011–12, figures show a reduction of first-year attrition to 3%. While such improvement is characteristic of many transition initiatives, not just those associated with PM, it is likely that implementation of PM is intrinsically linked to student retention within a course. 相似文献
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This article explores heterogeneity as fundamental to learning. Inspired by Bakhtin's notion of heteroglossia, a design team consisting of an experienced classroom teacher and 2 researchers investigated how a class of 3rd and 4th graders came to understand disciplinary points of view on heat, heat transfer, and the particulate nature of matter. Through a series of planned and unplanned encounters, official versions of the Second Law of Thermodynamics and the particulate view of matter were juxtaposed with varied domains of experience of heat transfer and phase change in water. We analyze the children's discourse to examine how they populated these phenomena with meaning and what they learned in the process. We conclude by describing key principles and a conundrum that emerged from this research. 相似文献
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We compare the optimal operating cost of the two bicriterion policies, 〈p,T〉 and 〈p,N〉, for an M/G/1 queueing system with second optional service, in which the length of the vacation period is randomly controlled either by the number of arrivals during the idle period or by a timer. After all the customers are served in the queue exhaustively, the server immediately takes a vacation and may operate 〈p,T〉 policy or 〈p,N〉 policy. For the two bicriterion policies, the total average cost function per unit time is developed to search the optimal stationary operating policies at a minimum cost. Based upon the optimal cost the explicit forms for joint optimum threshold values of （p,T） and （p,N） are obtained. 相似文献
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David Haycock 《British Journal of Sociology of Education》2010,31(3):291-305
One key aspect of the growing policy emphasis on educational inclusion in England has been the tendency for physical education (PE) to be used as an important vehicle of social policy targeted at promoting the inclusion of young disabled people and those with special educational needs in mainstream schools. Drawing on aspects of figurational sociology, the central objective of this study is to examine the extent to which PE teachers have been able to achieve the government’s inclusion policy goals articulated in the 2000 National Curriculum for Physical Education (NCPE) for England. The findings indicate that using the NCPE as a means to pursue the government’s educational inclusion policy goals has had unplanned outcomes that have the effect of undermining the extent to which the government is able to use inclusion to make a greater contribution to the promotion of young people’s experiences of PE. It is also argued that these outcomes that no‐one had planned or intended may, for some of the groups involved, be seen as undesirable consequences that emanate from teachers’ attempts to manage the contradictory pressures brought about by pursuing the priorities of government. 相似文献
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作为衡量空气质量的重要指标,准确预测PM2.5浓度变化尤为重要。提出Prophet和长短期记忆（LSTM）相结合的组合预测模型（Prophet-LSTM）。在模型构建过程中,首先利用Prophet模型的可分解方法,将PM2.5日值浓度序列分解成趋势、周期和随机波动分量|然后对趋势和周期分量建立Prophet模型,对随机波动分量建立LSTM模型|最后将各分量的预测值集成得到PM2.5浓度的预测值。以郑州市PM2.5日值浓度数据为例进行实证分析,结果表明,该组合预测模型相较对比模型能够更好地预测PM2.5日值浓度的变化趋势。 相似文献
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This paper presents a model of the process of implementation of school change. The model has been developed from observation of and interaction with planned changes in a large number of schools, and traces the process through eight stages, from the initial climate for change to full field trials of innovative programs. At each of these stages the contribution of any of a number of components is discussed: the social context in which change occurs, organizational considerations, the role of evaluation, the development of innovative programs, and the role of the teacher, principal, administrator, and academic. The model is presented as a conceptual framework from which implementation strategies may be, and are being, derived for use in implementation of change in the schools. 相似文献