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1.
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. 相似文献
2.
3.
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. 相似文献
4.
《Automatica》2014,50(11):2822-2834
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. 相似文献
5.
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。 相似文献
6.
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) 相似文献
7.
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. 相似文献
8.
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。 相似文献
9.
针对设备在实际运行和执行任务时经常涉及到维修、更新报废等管理活动缺乏定量模型支撑的问题,提出了利用典型部件的预测寿命和非典型部件的历史寿命对设备系统级的健康状态进行综合评估的方法,建立了一种以状态指标为决策序列的动态规划更新决策方法;该方法能综合考虑维修费用和更新费用,确定最优更新决策,降低保障费用,有效地提高了设备的经济效益;最后经过案例分析证明了该方法的有效性,对于提高设备的保障能力和经济效益提供了理论支撑和方法指导. 相似文献
10.
城市发展更新的加快,使我国历史文化名城遭受不同程度的破坏。通过比较国内外有关的实践经验,作者认为应将历史街区作为保护的重点。并力图探索一条如何在传统与现代,整治与保护以及资金短缺等矛盾中实施保护的切实可行之路。 相似文献