缺失数据下非线性均值方差模型的参数估计

文章在响应变量随机缺失下研究非线性均值方差模型的参数估计问题.基于回归插补和随机回归插补两种缺失插补方法以及结合Gauss-Newton迭代计算算法给出该模型中未知参数的极大似然估计.并通过对两个随机模拟例子实际例子的研究分析,结果都表明了所提出的模型与统计方法具有可行性和实用性.     

An Institutional Analysis of the Multi-layered Characteristics of Social Organizations in China

The actual state of affairs of Chinese social organizations and the latest theoretical findings on the subject indicate that independence and autonomy are concepts that are interrelated but not fundamentally interchangeable; their actual organizational relationship is complex and varied. Exploration of the relationship between the two concepts is a necessary step in the construction and improvement of a rule-based interpretation of the characteristics of Chinese social organizations. Combining resource dependence theory with the institutional logics perspective enables us to analyze the multiple mechanisms influencing the relationship between independence and autonomy at the organizational level and to test for these mechanisms using a mixed methods research design. Our empirical findings indicate that social organizations gain greater autonomy when they have greater independence from government resources and when they strongly identify, structurally and behaviorally, with classical third sector theory. Organizations’ behavioral identification can regulate the relationship between independence and autonomy. Further case studies support the value of the above findings. This shows that other mechanisms can often replace, offset or constrain the effects of resource dependence. In the real world, no single fixed theory can cover the independence-autonomy relationship.     

Building Supply Chain Resilience through Virtual Stockpile Pooling

Stockpiling inventory is an essential strategy for building supply chain resilience. It enables firms to continue operating while finding a solution to an unexpected event that causes a supply disruption or demand surge. While extremely valuable when actually deployed, stockpiles incur large holding costs and usually provide no benefits until such a time. To help to reduce this cost, this study presents a new approach for managing stockpiles. We show that if leveraged intelligently, stockpiles can also help an organization better meet its own regular demand by enabling a type of virtual pooling we call virtual stockpile pooling (VSP). The idea of VSP is to first integrate the stockpile into several locations’ regular inventory buffers and then dynamically reallocate the stockpile among these locations in reaction to the demand realizations to achieve a kind of virtual transshipment. To study how to execute VSP and determine when it can provide the most value, we formulate a stylized multi‐location stochastic inventory model and solve for the optimal stockpile allocation and inventory order policies. We show that VSP can provide significant cost savings: in some cases nearly the full holding cost of the stockpile (i.e., VSP effectively maintains the stockpile for free), in other cases nearly the savings of traditional physical inventory pooling. Last, our results prescribe implementing VSP with many locations for large stockpiles, but only a few locations for small stockpiles.     

Distributionally Robust Optimization of Two‐Stage Lot‐Sizing Problems

This paper studies two‐stage lot‐sizing problems with uncertain demand, where lost sales, backlogging and no backlogging are all considered. To handle the ambiguity in the probability distribution of demand, distributionally robust models are established only based on mean‐covariance information about the distribution. Based on shortest path reformulations of lot‐sizing problems, we prove that robust solutions can be obtained by solving mixed 0‐1 conic quadratic programs (CQPs) with mean‐risk objective functions. An exact parametric optimization method is proposed by further reformulating the mixed 0‐1 CQPs as single‐parameter quadratic shortest path problems. Rather than enumerating all potential values of the parameter, which may be the super‐polynomial in the number of decision variables, we propose a branch‐and‐bound‐based interval search method to find the optimal parameter value. Polynomial time algorithms for parametric subproblems with both uncorrelated and partially correlated demand distributions are proposed. Computational results show that the proposed models greatly reduce the system cost variation at the cost of a relative smaller increase in expected system cost, and the proposed parametric optimization method is much more efficient than the CPLEX solver.     

Equilibrium Joining Strategies and Optimal Control of a Make‐to‐Stock Queue

We consider a make‐to‐stock, finite‐capacity production system with setup cost and delay‐sensitive customers. To balance the setup and inventory related costs, the production manager adopts a two‐critical‐number control policy, where the production starts when the number of waiting customers reaches a certain level and shuts down when a certain quantity of inventory has accumulated. Once the production is set up, the unit production time follows an exponential distribution. Potential customers arrive according to a Poisson process. Customers are strategic, i.e., they make decisions on whether to stay for the product or to leave without purchase based on their utility values, which depend on the production manager's control decisions. We formulate the problem as a Stackelberg game between the production manager and the customers, where the former is the game leader. We first derive the equilibrium customer purchasing strategy and system performance. We then formulate the expected cost rate function for the production system and present a search algorithm for obtaining the optimal values of the two control variables. We further analyze the characteristics of the optimal solution numerically and compare them with the situation where the customers are non‐strategic.     

农村计划生育社会保障机制建设的探讨——以江苏省溧阳市为例

本文结合江苏溧阳市计划生育社会保障机制建设的主要做法及面临的困境与挑战,提出了计划生育社会保障机制发展的基本思路与对策:必须整合计划生育社会保障制度的基本内容、突出计划生育社会保障制度的重点;计划生育社会保障机制必须更好地融合到社会保障体系中去,实现计划生育社会保障机制的良性循环。     

论我国养老保险的筹资模式

如何选择最佳的筹资方式是依托社会保障体系化解我国人口老龄化压力的关键所在。作为最基本的养老金筹资方式,现收现付制与个人帐户制的特征与对经济的影响不同,但并不能简单地由此分出两者谁优谁劣,不是由现收现付制完全转为个人帐户制所有问题就会迎刃而解。未来我国养老保险筹资方式的上佳选择是建立多支柱、多层次的社会保障体系。在此前提下,现收现付制与个人帐户制相互协调,共同存在较之相互替代更有助于缓解不可避免的养老金支付困难。     

中国的独生子女与独生子女户

近几十年来 ,中国的“独生子女”与“独生子女户”成为与计划生育政策有关的一代特殊人口与一类特别家庭。对二者界定的不同标准造成了对其规模估计的分歧和深入研究的困难。根据 2 0 0 0年第五次人口普查数据 ,估算出我国现有独生子女数量约为 90 0 0万 ,其中城市独生子女的数量远远高于农村。独生子女之间彼此婚配 ,有可能会形成广受关注的“四二一”家庭。研究显示 ,大城市中独生子女间的婚配概率似乎更高一些 ,但对于全国并不具有普遍意义。由于严格意义的“四二一”家庭的出现取决于多种因素 ,其大规模出现的可能性并不大。对“独生子女”以及“独生子女户”的关注 ,主要来源于对“独生子女”养老能力的质疑和对“独生子女户”养老需求获取满足的前景的担忧。国家目前正在通过“农村部分计划生育家庭奖励扶助制度”等措施帮助“独生子女户”逐步消除后顾之忧     

流行病学转变--人口变化的流行病学理论的形成和发展

本文主要综述了流行病学转变理论的形成和发展,重点介绍了流行病学转变理论的四个基本概念,流行病学转变与人口和社会变化之间的关系,流行病学转变的机理,流行病学转变的影响因素及其在转变中的作用.