超声振动车削参数对切削力的影响

为了探究超声振动车削（UVT）过程中刀具振动频率、振幅和切削速度3个参数对切削力的影响,课题组通过建立有限元模型,对高强度铝合金超声振动车削和普通车削（CT）过程进行了对比研究。首先,研究了切削区域的Mises应力分布的变化;其次,对切削区域温度和微观切屑形态进行了分析,从微观层面揭示UVT方法降低切削力和切削温度的机理;最后,分别研究了刀具振动频率、振幅和切削速度对UVT平均切削力的影响。研究表明：超声振动车削的有限元仿真结果与“刀具 工件接触比理论”一致;在一定的范围内,增大刀具振动频率或振幅以及降低切削速度的方法可以有效降低切削力。文中的研究显示合理的选择超声振动车削工艺参数可以降低切削力,改善高强度铝合金的制造工艺。     

胎压监测装置中橡胶材料本构模型的确定及力学研究

针对汽车胎压监测装置在装配和运转过程中,存在橡胶元件易损坏的问题,采用有限元法研究了元件与轮毂过盈量对橡胶材料所受应力、应变的影响。利用虚功方程确定了橡胶Mooney Rivlin模型的应力 应变方程,通过单轴拉伸试验得出橡胶材料模型参数,建立了胎压监测装置的有限元模型。分析结果表明当过盈量为0.4 mm时既能保证装配质量又能减小运转过程中橡胶所受的应力,从而延长其使用寿命。     

仿生鳍形状与运动模式对推进性能的影响

为探究仿生鳍形状与其运动模式间的内在关系,采用非耦合隐式求解器求解非定常不可压缩NAVIER STOKES方程和连续性方程。分析相同运动学参数和面积时,菱形、正方形、长方形和三角形4种形状仿生鳍在波动和摆动2种运动模式下产生的推进力大小;从压力分布、涡街结构等方面给出差异存在的原因,并找出鳍面形状和推进模式之间的内在联系。结果显示：相同运动学参数和鳍面形状时,不同推进模式产生的推进力存在较大差异;同样,相同运动学参数和推进模式时,鳍面形状对推进力也有较大影响。该研究为仿鱼推进器选择合适的鳍面形状和匹配的推进模式以实现较优推进性能提供参考。     

Measuring the complexity of generalized linear hierarchical models

Measuring a statistical model's complexity is important for model criticism and comparison. However, it is unclear how to do this for hierarchical models due to uncertainty about how to count the random effects. The authors develop a complexity measure for generalized linear hierarchical models based on linear model theory. They demonstrate the new measure for binomial and Poisson observables modeled using various hierarchical structures, including a longitudinal model and an areal‐data model having both spatial clustering and pure heterogeneity random effects. They compare their new measure to a Bayesian index of model complexity, the effective number p_D of parameters (Spiegelhalter, Best, Carlin & van der Linde 2002); the comparisons are made in the binomial and Poisson cases via simulation and two real data examples. The two measures are usually close, but differ markedly in some instances where p_D is arguably inappropriate. Finally, the authors show how the new measure can be used to approach the difficult task of specifying prior distributions for variance components, and in the process cast further doubt on the commonly‐used vague inverse gamma prior.     

On Nonparametric Maximum Likelihood Estimations of Multivariate Distribution Function Based on Interval-Censored Data

This article considers the nonparametric maximum likelihood estimator (NPMLE) of a joint distribution function when the multivariate failure times of interest are interval-censored. With different types of interval censoring mechanism, the NPMLE's of the multivariate distribution function are studied and the strong consistency for the NPMLEs is obtained in terms of a self-consistency equation. Furthermore, the convergence rate of the estimator is given, which depends on the types of interval censoring mechanism.     

具有奇(偶)条件的波动方程混合问题的行波解

利用定义广义奇(偶)函数及其性质,给出了在各种边界条件下,定义在有限区间上的具有奇(偶)外部激励条件的波动方程的混合问题解的有限形式,并指出了在此条件下,与定义在无限区间上的初值问题一样具有行波解.     

Pathways between education and health: a causal modelling approach

Summary.  The association of poor education and poor health has been consistently observed in many studies and in various countries. Thus far, studies examining the mechanisms underlying this association have looked at only a limited set of potential pathways. This study simultaneously examines six distinctive pathways, which have been hypothesized to link education and health and found support from previous studies. A causal analysis of education and health was performed using structural equation models. Data were used from six phases of the National Child Development Study, which is based on following up an initial sample of 17416 children who were born in 1958. The association between education and health appears to be explained by a combination of mechanisms: adolescent health and adult health behaviours for men and women, adult social class among men and parental social class among women. We conclude that improvements in population educational attainment may not automatically lead to improvements in population health, and that health policies for improving health and reducing health inequalities need to target specific causal pathways.     

Marginal and association regression models for longitudinal binary data with drop‐outs: A likelihood‐based approach

Longitudinal data often contain missing observations, and it is in general difficult to justify particular missing data mechanisms, whether random or not, that may be hard to distinguish. The authors describe a likelihood‐based approach to estimating both the mean response and association parameters for longitudinal binary data with drop‐outs. They specify marginal and dependence structures as regression models which link the responses to the covariates. They illustrate their approach using a data set from the Waterloo Smoking Prevention Project They also report the results of simulation studies carried out to assess the performance of their technique under various circumstances.     

Are there causal relationships between the dimensions of the Maslach Burnout Inventory? A review and two longitudinal tests

Arising from interest concerning the possibility of causal relationships among the three components of the Maslach Burnout Inventory, several process models have been proposed for the development of burnout. The present paper first reviews the evidence in favour of the three most influential of these (Leiter and Maslach's model (1988); Golembiewski, Boudreau, Munzenrider, & Luo's (1996) phase model; and Lee and Ashforth's model (1993)). These three models, and our own model (which integrates of two of them, and includes feedback effects of depersonalization on emotional exhaustion) are then compared with each other using structural equation modelling, drawing on longitudinal data from two Dutch samples (total N=1185). The review revealed that none of the seven previous studies on this issue provided any convincing support for any particular causal order proposed so far. In contrast, our own study showed that high levels of exhaustion were associated with high levels of depersonalization over time across both samples. Further, higher levels of depersonalization led to higher levels of emotional exhaustion and lower levels of personal accomplishment. To our knowledge, the present research is the first to provide reliable longitudinal evidence for the conceptualization of burnout as a developmental process, although the effects are not large enough to be of practical use in the recognition of burnout.     

企业内员工知识共享的实证研究

将知识特性以及员工知识共享的意愿作为分析影响员工知识共享的2个因素,以此建立一个概念框架;运用结构方程模型方法,结合对115家中国企业所作的调查研究数据,从实证的角度研究这些因素对企业内部员工知识共享的影响.研究结果表明,知识的隐含性和分散性与企业员工知识共享之间存在显著负相关关系,员工对未来合作的预期、知识的价值与企业员工知识共享之间存在显著正相关的关系.最后,讨论了研究结果的管理含义及进一步研究方向.