Fast Algorithms for Generating Discrete Random Variates With Changing Distributions

One of the most fundamental and frequently used operations in the process of simulating a stochastic discrete event system is the generation of a nonuniform discrete random variate. The simplest form of this operation can be stated as follows: Generate a random variable X which is distributed over the integers 1,2,...,n such that P(X = i) = pi. A more difficult problem is to generate X when the pi\u27s change with time. For this case, there is a well-known algorithm which takes O(log n) time to generate each variate. Recently Fox [4] presented an algorithm that takes an expected o(log n) time to generate each variate under assumptions restricting the way the pi\u27s can change. In this paper we present algorithm for discrete random variate generation that take an expected O(1) time to generate each variate. Furthermore, our assumptions on how the pi\u27s change are less restrictive than those of Fox. The algorithms are quite simple and can be fine-tuned to suit a wide variety of application. The application to the simulation of queueing networks is discussed in some detail

I Know Where You are and What You are Sharing: Exploiting P2P Communications to Invade Users' Privacy

In this paper, we show how to exploit real-time communication applications to determine the IP address of a targeted user. We focus our study on Skype, although other real-time communication applications may have similar privacy issues. We first design a scheme that calls an identified targeted user inconspicuously to find his IP address, which can be done even if he is behind a NAT. By calling the user periodically, we can then observe the mobility of the user. We show how to scale the scheme to observe the mobility patterns of tens of thousands of users. We also consider the linkability threat, in which the identified user is linked to his Internet usage. We illustrate this threat by combining Skype and BitTorrent to show that it is possible to determine the file-sharing usage of identified users. We devise a scheme based on the identification field of the IP datagrams to verify with high accuracy whether the identified user is participating in specific torrents. We conclude that any Internet user can leverage Skype, and potentially other real-time communication systems, to observe the mobility and file-sharing usage of tens of millions of identified users.Comment: This is the authors' version of the ACM/USENIX Internet Measurement Conference (IMC) 2011 pape

Corporate social responsibility:reviewed, rated, revised

Purpose: Critical literature review of CSR research in both general management and hospitality management literature. Discusses trends,commonalities, and inconsistencies to better understand the state of contemporary scholarship, and calls for a context-specific conceptual engagement with the phenomenon.Design/Methodology/Approach: Systematic literature review, noting and critiquing a general tendency towards measurement of financial and other internal benefit impacts.Findings: Hospitality management is well-positioned to evaluate the opportunities and challenges of CSR, yet research has uncritically adopted the instrumental emphasis on assessing processes, perceptions, and private profitability from the general management literature, without engaging on a contextually-specific and/or theoretical level.Research limitations: CSR research is abundant and therefore difficult to summarise in one article.The primarily Anglo-American and Asian contextual bias is reflected in this review.Practical implications: Consistently inconsistent results challenge the portability of financial impact studies.Studies are needed to re-evaluate the concept of CSR as it pertains to hospitality, and measure the effectiveness of CSR activities relative to context and resource availability.Social implications: Further research into the scope of CSR in hospitality management, with an emphasis on recuperating social value, would lead to widespread positive social implications.Originality/value: This critical review offers a new perspective on CSR in the hospitality literature and industry, calling for a reconsideration of the concept in context, and formulates a working definition

Efficient Simulation of Large-Scale Loss Networks

Recently Rajasekaran and Ross [1] presented an algorithm that takes an expected 0(1) time to generate a nonuniform discrete random variate. In this paper we discuss how this algorithm can be employed in the efficient simulation of large-scale telephone networks. In a simulation based upon a standard event-list approach, the generation of a new event in the systems take 0(log n) time. With this new algorithm, event generation becomes an 0(1) process, and simulation times for large networks can be reduced

Percentile objective criteria in limiting average Markov Control Problems

Infinite horizon Markov Control Problems, or Markov Decision Processes (MDP's, for short), have been extensively studied since the 1950's. One of the most commonly considered versions is the so-called "limiting average reward" model. In this model the controller aims to maximize the expected value of the limit-average ("long-run average") of an infinite stream of single-stage rewards or outputs. There are now a number of good algorithms for computing optimal deterministic policies in the limiting average MDP's. In this paper we adopt the point of view that there are many natural situations where the controller is interested in finding a policy that will achieve a sufficiently high long-run average reward, that is, a target level with a sufficiently high probability, that is, a percentile

Optimal priority assignment with constraint

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