Discrete-time queues with discretionary priorities

In this paper, we consider a discrete-time two-class discretionary priority queueing model with generally distributed service times and per slot i.i.d. structured inputs in which preemptions are allowed only when the elapsed service time of a lower-class customer being served does not exceed a certain threshold. As the preemption mode of the discretionary priority discipline, we consider the Preemptive Resume, Preemptive Repeat Different, and Preemptive Repeat Identical modes. We derive the Probability Generating Functions (PGFs) and first moments of queue lengths of each class in this model for all the three preemption modes in a unified manner. The obtained results include all the previous works on discrete-time priority queueing models with general service times and structured inputs as their special cases. A numerical example shows that, using the discretionary priority discipline, we can more subtly adjust the system performances than is possible using either the pure non-preemptive or the preemptive priority disciplines.     

Optimal policies for inventory systems with discretionary sales, random yield and lost sales

We determine replenishment and sales decisions jointly for an inventory system with random demand, lost sales and random yield. Demands in consecutive periods are independent random variables and their distributions are known. We incorporate discretionary sales, when inventory may be set aside to satisfy future demand even if some present demand may be lost. Our objective is to minimize the total discounted cost over the problem horizon by choosing an optimal replenishment and discretionary sales policy. We obtain the structure of the optimal replenishment and discretionary sales policy and show that the optimal policy for finite horizon problem converges to that of the infinite horizon problem. Moreover, we compare the optimal policy under random yield with that under certain yield, and show that the optimal order quantity （sales quantity） under random yield is more （less） than that under certain yield.     

Linux环境下访问控制列表机制的设计与实现

访问控制列表ACL(Access Control Last)是一种细粒度的自主访问控制DAC(Discretionary Access Control)技术。在Linux内核中基于框架模式设计并实现了ACL安全子系统,不仅能够为用户提供更灵活的自主访问控制,同时还与Linux内核中现有的基于文件权限位的DAC功能最大程度地兼容,避免了因引入ACL可能带来的系统兼容性问题。同时还实现了符合POSIX 1003．2c标准的API及命令行工具,便于进行安全管理和安全开发。     

我国上市公司应计质量现状研究

以我国深市和沪市上市公司1992~2006共15年的数据为样本,用修正的DD模型,计算了我国1997~2005年的应计质量AQ值,通过分析发现:我国上市公司应计质量在2002年是一个拐点,也就是说,在2002年之前,上市公司应计质量呈现下降趋势,而在2002年之后,上市公司应计质量在逐步提高.     

9AC访问控制策略的研究

自主访问控制（DAc）模型是根据自主访问控制策略建立的一种模型,允许合法用户以用户或用户组的身份访问策略规定的客体,同时阻止非授权用户访问客体。这种技术通常应用于一些实际的单安全级的系统中,在web系统的安全访问控制中有一定的优势,也存在一些弊端。     

中国上市公司宣布配股信息前后的盈余管理

上市公司为了取得股权再融资的资格,在配股以前存在强烈向上的盈余管理动机.通过对242例中国A股上市公司宣布配股信息前后的盈余管理的实证研究,发现中国配股企业在宣布配股信息前两年和宣布配股信息当年存在远高于成熟证券市场和其他新兴证券市场的盈余管理行为,而在宣布配股后第2年和第3年,配股企业没有进行盈余管理,同时还发现信用交易是配股企业盈余管理的重要工具.     

上市公司应计项目盈余管理与所得税关系研究

经营性应计利润项目的盈余管理与公司所得税税负成显著负相关关系,而高估应计收入与低估应计成本的盈余管理与公司所得税税务间有较弱的正相关关系。换言之,上市公司对经营性应计利润项目的操纵可以减少一定的所得税成本,当上市公司高估应计收入、低估应计成本时,则需要承担一定的所得税成本。     

The impossibility of convex constant returns-to-scale production technologies with exogenously fixed factors

The extensions to the variable (VRS) and the constant (CRS) returns-to-scale models developed by Banker and Morey are considered among the main approaches to the incorporation of exogenously fixed factors in models of data envelopment analysis (DEA). Recently, Syrjänen showed that the Banker and Morey CRS technology is not convex. Taking into account that its subset VRS technology is explicitly assumed convex, this observation leads to difficulties with explaining the fundamental production assumptions of the CRS extension. Motivated by the example of Syrjänen, the contribution of this paper is twofold. First, we show that the nonconvex Banker and Morey CRS technology is nevertheless a suitable reference technology for the assessment of scale efficiency. Second, we ask if a convex technology could be constructed that would “correct” the nonconvexity of the CRS technology of Banker and Morey. The answer to this is negative: one consequence of assuming both convexity and ray unboundness with fixed exogenous factors is that we can always “mix-and-match” discretionary and nondiscretionary factors taken from different units, arriving at totally unrealistic production plans. This demonstrates that generally there exists no meaningful convex CRS technology with exogenously fixed factors that can be used in its own right, apart from its use as a reference technology in the measurement of scale efficiency.     

Optimal investment,consumption and timing of annuity purchase under a preference change

In this paper, we study the optimal investment and consumption strategies for a retired individual who has the opportunity of choosing a discretionary stopping time to purchase an annuity. We assume that the individual receives a fixed annuity income and changes his/her preference after paying a fixed cost for annuitization. By using the martingale method and the variational inequality method, we tackle this problem and obtain the optimal strategies and the value function explicitly for the case of constant force of mortality and constant relative risk aversion (CRRA) utility function.