Measuring consistency in TTL-based caches

We propose a general modeling framework to evaluate the performance of cache consistency algorithms. In addition to the usual hit rate, we introduce the hit^* rate as a consistency measure, which captures the fraction of non-stale downloads from the cache. We apply these ideas to the analysis of the fixed TTL consistency algorithm in the presence of network delays. The hit and hit^* rates are evaluated when requests and updates are modeled by renewal processes. Classical results on the renewal function lead to various bounds.     

北京市危旧房改造的多目标分解模式

由于政府、居民、开发商之间复杂的博弈,北京市1990年提出的综合性危改目标遇到了很大的挑战,为解决这一问题,本文提出危旧房改造的目标分解模式,即建立一个以危改区域或危改项目为导向的危改目标实现框架,将北京市危旧房改造的多重目标进行分解,然后制定相应的分目标政策,建立相应的分目标制度,采取相应的分目标措施,最终从总体上实现危旧房改造的目标,主导目标的确定应遵循四个基本原则,最后提出几个政策建议。     

机械设备大修理与否的经济界限的确定

机械设备的大修理与更新之间存在合理的经济界限。针对传统的确定二者之界限的数学模型提出改进，确定了大修理与重置更新界限的比较原则与方法。     

首钢2号高炉的技术进步

介绍首钢2号高炉大修采用的新技术、开炉操作和投产以来的生产情况。     

A method for the efficient prioritization of infrastructure renewal projects

The infrastructure renewal program at MIT consists of a large number of projects with an estimated budget that could approach $1 billion. Infrastructure renewal at the Massachusetts Institute of Technology (MIT) is the process of evaluating and investing in the maintenance of facility systems and basic structure to preserve existing campus buildings. The selection and prioritization of projects must be addressed with a systematic method for the optimal allocation of funds and other resources. This paper presents a case study of a prioritization method utilizing multi-attribute utility theory. This method was developed at MIT's Department of Nuclear Engineering and was deployed by the Department of Facilities after appropriate modifications were implemented to address the idiosyncrasies of infrastructure renewal projects and the competing criteria and constraints that influence the judgment of the decision-makers. Such criteria include minimization of risk, optimization of economic impact, and coordination with academic policies, programs, and operations of the Institute. A brief overview of the method is presented, as well as the results of its application to the prioritization of infrastructure renewal projects. Results of workshops held at MIT with the participation of stakeholders demonstrate the feasibility of the prioritization method and the usefulness of this approach.     

Quadratic control of stochastic hybrid systems with renewal transitions

We study the quadratic control of a class of stochastic hybrid systems with linear continuous dynamics for which the lengths of time that the system stays in each mode are independent random variables with given probability distribution functions. We derive a condition for finding the optimal feedback policy that minimizes a discounted infinite horizon cost. We show that the optimal cost is the solution to a set of differential equations with unknown boundary conditions. Furthermore, we provide a recursive algorithm for computing the optimal cost and the optimal feedback policy. The applicability of our result is illustrated through a numerical example, motivated by stochastic gene regulation in biology.     

基于跳跃-扩散过程的亚式期权定价

在标的资产价格跳过程为更新过程的假设下,研究了具有浮动敲定价格的亚式期权,通过自融资交易复制将路径依赖的亚式期权定价问题转化为与路径无关的微分方程的求解问题,拓展了刘宣会的结果。     

Renewal strategies for old industrial areas in the post-industrial age—Take “Zurich-West” in Switzerland as an example

This paper introduces and analyses the renewal planning of “Zurich-West”, an old industrial area. It points out that systematic and comprehensive target orientation, extensive collaboration in argumentation and decision-making, and the design ideas of coexistence and integration are the key to its success. Considering the status quo of China’s old industrial district remodeling, the paper offers some suggestions. Supported by the National Natural Science Foundation of China (Grant No. 50878045)     

New liquid membrane technology for simultaneous extraction and stripping of copper(II) from wastewater

In this paper, a new liquid membrane technique, hollow fiber renewal liquid membrane (HFRLM), is presented, which is based on the surface renewal theory, and integrates the advantages of fiber membrane extraction, liquid film permeation and other liquid membrane processes. The results from the system of CuSO₄+D2EHPA in kerosene+HCl show that the HFRLM process is very stable. The liquid membrane is renewed constantly during the process, the direct contact of organic droplets and aqueous phase provides large mass transfer area. These effects can significantly reduce the mass transfer resistance in the lumen side. Then the mixture of feed phase and organic phase flowing through the lumen side gives a higher mass transfer rate than that of stripping phase and organic phase, because the aqueous layer diffusion of feed phase is the rate-controlling step. The overall mass transfer coefficient increases with increasing flow rates and D2EHPA concentration in the organic phase, and with decreasing initial copper concentration in the feed phase. The overall mass transfer coefficient also increases with increasing pH in the feed phase, and reaches a maximum value at pH of 4.44, then decreases. Also, there is a favorable w/o volume ratio of 20:1 to 30:1 for this process. Compared with hollow fiber supported liquid membrane and hollow fiber membrane extraction processes, HFRLM process has a high mass transfer rate. Mathematical model for the HFRLM process based on the surface renewal theory is developed. The calculated results are in good agreement with experimental results under the conditions studied.     

金昌冶炼厂铜熔炼改造工程的设计特色

通过铜陵金昌冶炼厂铜熔炼改造工程的设计,指出现代冶金工厂在工程设计中要更新观念,在满足功能且经济许可的前提下,可追求工业厂房的造型、色彩,使其美观大方;在注重节约用地的原则下,亦可以美化总图布置和厂区环境,为建立现代化工厂创造条件。