可持续的中国城乡居民养老保险体系数学模型

本文从我国现行养老金政策出发,利用灰关联分析得到养老金收支的影响因素的排序,建立中国城乡居民养老金收支模型.然后利用Logistic人口预测模型估计出不同替代率下2013-2035未来23年我国养老金缺口,并利用仿真方法算出保证我国养老保险体系的可持续性的替代率的合理区间为50%-70%.进一步分析影响替代率各因素的灵敏性,并考虑延迟退休、做实个人账户以及市场化投资等因素对模型进行改进.最后以养老金替代率为切入点,对退休年龄等模型参数的调整和有关措施进行了分析与评价.     

人体硬组织替代材料的研究进展

硬组织（骨、牙等）损伤或病变是临床上常见的事件，如果损伤或病变严重到无法进行药物治疗的程度，需要采取硬组织替代材料进行修复或置换。文章对人体硬组织替代材料的类型、力学性能及生物学性能等方面进行了综述，并指出了硬组织替代材料的发展方向。     

Stochastic Comparison of Age-Dependent Block Replacement Policies

The age-dependent block replacement policy is a modified block replacement policy with an age limit for preventive replacements. Under this policy, any failed component is repaired, but only the components whose ages exceed a fixed age limit are replaced preventively at the scheduled maintenance times. Using the compensator method, we compare stochastically the failure counting processes of the age-dependent block replacement policies with different parameters, and show that the age-dependent block replacement policy, although cost effective, leads to more failures than the age and block replacement policies. AMS 2000 Subject Classification 60K10     

基于截断δ-冲击模型的不完全维修更换策略

本文在截断δ-冲击模型的基础上,考虑了因系统劣化而导致的冲击失效门限值与维修时间的变化,扩充失效状态,从而提出一种新的截断δ-冲击模型。以最小费用为目标,稳态可用度为约束条件,建立N型更换策略的不完全维修更换策略模型,并给出三种常用冲击到达间隔分布的期望寿命。最后通过算例验证模型的有效性,并对参数进行灵敏度分析。     

再生碎石混凝土力学性能试验研究

针对再生粗骨料为碎石的再生混凝土,设计了99个试件,分别进行立方体抗压强度、棱柱体抗压强度、抗折强度、弹性模量和泊松比等力学性能的试验。本文研究了再生混凝土的强度指标、变形性能、损伤过程、能量耗散等特征,分析了骨料取代率对其各性能指标的影响;基于试验数据,得出各强度性能指标的换算关系;分别采用分段式本构关系模型和损伤本构关系模型对再生混凝土的应力-应变本构关系进行研究,并提出相应的本构方程。研究结果表明:与天然骨料混凝土相比,再生混凝土的各项强度指标均略为增大,但变形性能和耗能性能降低,应力-应变全曲线下降段更为陡峭;随着取代率的增大,弹性模量呈先减小后增大的变化趋势,泊松比无明显变化,与天然混凝土接近;其损伤发展过程加快,应变在ε=(3~5)×10-3时最为迅速。分段式本构方程和损伤本构方程的计算结果与试验值均能较好地吻合。     

A replacement model for an additive damage model with restoration

A system existing in a random environment receives shocks at random points of time. Each shock causes a random amount of damage which accumulates over time. A breakdown can occur only upon the occurrence of a shock according to a known failure probability function. Upon failure the system is replaced by a new identical one with a given cost. When the system is replaced before failure, a smaller cost is incurred. Thus, there is an incentive to attempt to replace the system before failure. The damage process is controlled by means of a maintenance policy which causes the accumulated damage to decrease at a known restoration rate. We introduce sufficient conditions under which an optimal replacement policy which minimizes the total expected discounted cost is a control limit policy. The relationship between the undiscounted case and the discounted case is examined. Finally, an example is given illustrating computational procedures.     

一种可供选择的随机化调查方法

本文提出了一种新的随机化调查方法,Warner(1965)和Horvitz,Simmons(1967)随机化回答方法是本文方法的特殊情形.这一方法比Warner(1965)方法和Mangat(1990)方法更有效. 当考虑存在不真实回答时,在一定的条件下并且不损失对个体保护度和不增加调查成本的前提下,提出的方法优于Simmons(1967)方法和Sarjinder Singh(2000)方法.对简单随机不放回抽样,在总体非敏感属性个体比例未知的情况下,给出了两个子样本容量的最优配置.     

Repair-replace strategies for two-dimensional warranty policies

For repairable items sold with free replacement warranty, the actions available to the manufacturer to rectify failures under warranty are to

1. (1) repair the failed item or

2. (2) replace it with a new one.

A proper repair-replace strategy can reduce the expected cost of servicing the warranty. In this paper, we study repair-replace strategies for items sold with a two-dimensional free replacement warranty.     

A general replacement model

Summary Replacement models deal with the problem of finding the optimal random time for a preventive replacement of a technical system. A large class of such models has been considered in the literature recently. In this paper a unifying approach to the replacement problem is given regarding it as an optimal stopping problem. The generalization allows to weaken a necessary monotonicity condition and to consider different information levels. Measuring information in this context leads to discussing the problem in general terms of stochastic process theory. An example shows how to get explicit solutions and how the information level influences the optimal replacement policy.

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Zusammenfassung Ersetzungsmodelle beschreiben im Rahmen der Zuverlässigkeitstheorie das Problem, einen optimalen Zeitpunkt für die vorbeugende Ersetzung eines technischen Systems festzulegen. Eine große Vielfalt solcher Modelle ist in letzter Zeit in der Literatur zu finden. Ziel dieser Arbeit ist es, einen einheitlichen Zugang zu dem Ersetzungsproblem anzugeben, indem dieses Problem als Problem des optimalen Stoppens aufgefaßt wird. Die Verallgemeinerung vorhandener Modelle erlaubt es, eine notwendige Monotoniebedingung abzuschwächen und unterschiedliche Informationsniveaus zu betrachten. An einem Beispiel wird gezeigt, wie sich explizite Lösungen des Ersetzungsproblems gewinnen lassen und wie sich das Informationsniveau auf die optimale Ersetzungsstrategie auswirkt.

     

Assessment of the Effectiveness of Rehabilitation after Total Knee Replacement Surgery Using Sample Entropy and Classical Measures of Body Balance

Exercises in virtual reality (VR) have recently become a popular form of rehabilitation and are reported to be more effective than a standard rehabilitation protocol alone. The aim of this study was to assess the efficacy of adjunct VR training in improving postural control in patients after total knee replacement surgery (TKR). Forty-two patients within 7–14 days of TKR were enrolled and divided into a VR group and a control group (C). The C group underwent standard postoperative rehabilitation. The VR group additionally attended twelve 30-min exercise sessions using the Virtual Balance Clinic prototype system. Balance was assessed on the AMTI plate in bipedal standing with and without visual feedback before and after the four-week rehabilitation. Linear measures and sample entropy of CoP data were analyzed. After four weeks of rehabilitation, a significant reduction in parameters in the sagittal plane and ellipse area was noted while the eyes remained open. Regression analysis showed that sample entropy depended on sex, body weight, visual feedback and age. Based on the sample entropy results, it was concluded that the complexity of the body reaction had not improved. The standing-with-eyes-closed test activates automatic balance mechanisms and offers better possibilities as a diagnostic tool.