芯片封装焊球连接疲劳寿命预测分析--能量法和有效应变法之比较

研究了目前常用的两种芯片封装焊球连接的寿命预测方法一能量法和有效应变法。对焊球连接的材料本构关系进行了对比分析，并利用FORTRAN语言编制了相应的材料本构模型子程序，将其与有限元仿真工具ANSYS耦合，实现了将焊球连接的材料本构模型用户子程序导入到ANSYS的材料库。在此基础上模拟了三维芯片叠层球栅阵列尺寸封装的焊球结构，在热循环条件下(-40～ 125℃的工作状态，并分别利用能量法和有效应变法对焊球连接的寿命预测进行了比较分析，最后对两种方法作出了评价。     

OPTIMUM GROWTH AND REPRODUCTION SCHEDULES FOR FOREST TREES

A control theory optimization of iteroparous life histories indicates that if growth and reproduction are nonlinear functions of energy allocations, graded allocations of energy to potential reproduction can be optimal.     

各向异性损伤力学在螺纹疲劳寿命预估中的应用

引用损伤力学方法研究金属构件疲劳问题。在微结构力学模型基础上建立轴对称的各向异性疲劳损伤本构关系,通过有限元-附加力解法编制考虑各向异性损伤的有限元程序。应用引入门槛条件的损伤演化方程,并以损伤划分步长预估了构件疲劳裂纹形成与扩展寿命。用这一方法预估30CrMnSiNi2Aφ5和φ8螺栓全寿命。结果表明,理论S-N曲线与试验S-N曲线吻合良好并且门槛条件对修正低应力下疲劳寿命有很好的效果。本方法所需机时较少,可用于工程实际构件的高周疲劳寿命预估及抗疲劳优化设计。     

A High‐Voltage and Ultralong‐Life Sodium Full Cell for Stationary Energy Storage

Recently, there has been great interest in developing advanced sodium‐ion batteries for large‐scale application. Most efforts have concentrated on the search for high‐performance electrode materials only in sodium half‐cells. Research on sodium full cells for practical application has encountered many problems, such as insufficient cycles with rapid capacity decay, low safety, and low operating voltage. Herein, we present a layered P2‐Na_0.66Ni_0.17Co_0.17Ti_0.66O₂, as both an anode (ca. 0.69 V versus Na⁺/Na) and as a high‐voltage cathode (ca. 3.74 V versus Na⁺/Na). The full cell based on this bipolar electrode exhibits well‐defined voltage plateaus near 3.10 V, which is the highest average voltage in the symmetric cells. It also shows the longest cycle life (75.9 % capacity retention after 1000 cycles) in all sodium full cells, a usable capacity of 92 mAh g^?1, and superior rate capability (65 mAh g^?1 at a high rate of 2C).     

基于网络媒体信息的传染病传播模型及其仿真研究

当一种突发传染病开始流行时,政府、媒体会以各种形式告知民众,有防范意识的民众将采取一定的防范措施来降低感染率.考虑面对一种突发传染病,将易感群体划分为具有防范意识和不具有防范意识两种群体,利用生命周期理论,分析网络媒体信息报道对传染病传播的影响,以此为依据建立一种改进的传染病传播模型(MSI).利用网络大数据得到对传染病有防范意识群体的观测值信息,利用神经网络技术对模型MSI的参数进行反演.然后对模型MSI数值仿真得到传染病传播过程,提出了相应的控制措施.     

Analysis of survivorship life insurance portfolios with stochastic rates of return

A general portfolio of survivorship life insurance contracts is studied in a stochastic rate of return environment with a dependent mortality model. Two methods are used to derive the first two moments of the prospective loss random variable. The first one is based on the individual loss random variables while the second one studies annual stochastic cash flows. The distribution function of the present value of future losses at a given valuation time is derived. For illustrative purposes, an AR(1) process is used to model the stochastic rates of return, and the future lifetimes of a couple are assumed to follow a copula model. The effects of the mortality dependence, the portfolio size and the policy type, as well as the impact of investment strategies on the riskiness of portfolios of survivorship life insurance policies are analyzed by means of moments and probability distributions.     

Unit-linked life insurance policies: Optimal hedging in partially observable market models

In this paper we investigate the hedging problem of a unit-linked life insurance contract via the local risk-minimization approach, when the insurer has a restricted information on the market. In particular, we consider an endowment insurance contract, that is a combination of a term insurance policy and a pure endowment, whose final value depends on the trend of a stock market where the premia the policyholder pays are invested. To allow for mutual dependence between the financial and the insurance markets, we use the progressive enlargement of filtration approach. We assume that the stock price process dynamics depends on an exogenous unobservable stochastic factor that also influences the mortality rate of the policyholder. We characterize the optimal hedging strategy in terms of the integrand in the Galtchouk–Kunita–Watanabe decomposition of the insurance claim with respect to the minimal martingale measure and the available information flow. We provide an explicit formula by means of predictable projection of the corresponding hedging strategy under full information with respect to the natural filtration of the risky asset price and the minimal martingale measure. Finally, we discuss applications in a Markovian setting via filtering.     

吊车荷载作用下钢结构吊车梁的疲劳可靠寿命评估

从Miner累积损伤的定义出发，视累积损伤为随机过程，临界损伤为随机变量，基于疲劳动态可靠性理论，提出了在役钢结构吊车梁疲劳剩余寿命的可靠寿命评估法。之后与现行《钢结构检测评定与加固技术规程》(YB9257-96)中安全期限寿命评估法进行了分析比较，说明了安全寿命评估方法的概率意义。算例分析结果表明，本文提出的可靠寿命评估方法更加合理。     

T300/648迭层板接头挤压疲劳损伤参数的选择与测定

本文对碳纤维增强复合材料迭层板(C.F.R.P)接头在不同环境条件下的挤压疲劳损伤扩展进行了实验研究.并根据“剩余强度,剩余刚度”理论和“疲劳模量”概念,讨论了接头的刚度下降和强度变化.由此提出了“损伤参数”D的定义和测量方法;并对损伤试件,进行了X射线检测分析,验证了累积损伤的扩展.     

耐磨环氧胶粘涂层冲蚀磨损特性的研究

本文对气固冲蚀和浆体冲蚀条件下耐磨环氧胶粘涂层的磨损特性进行了研究。结果表明,这种涂层的冲蚀磨损是由粘结剂的磨损和抗磨填料的磨损所组成;填料粒度和磨料粒度都对涂层的气固冲蚀磨损有影响,但在给定的试验条件下,填料粒度对涂层的浆体冲蚀磨损影响甚微。文章指出,耐磨环氧胶粘涂层在气固冲蚀和浆体冲蚀下的磨损机理相似,但磨损规律却有所不同;耐磨环氧胶粘涂层尤其适用于浆体冲蚀的场合,可以明显地提高机械过流部件的使用寿命。