Analyzing priority queues with 3 classes using tree-like processes

In this paper we demonstrate how tree-like processes can be used to analyze a general class of priority queues with three service classes, creating a new methodology to study priority queues. The key result is that the operation of a 3-class priority queue can be mimicked by means of an alternate system that is composed of a single stack and queue. The evolution of this alternate system is reduced to a tree-like Markov process, the solution of which is realized through matrix analytic methods. The main performance measures, i.e., the queue length distributions and loss rates, are obtained from the steady state of the tree-like process through a censoring argument. The strength of our approach is demonstrated via a series of numerical examples. AMS Subject Classifications Primary—60K25; Secondary—60M20, 90B22     

Analysis of a simple Markovian re-entrant line with infinite supply of work under the LBFS policy

We consider a two machine 3 step re-entrant line, with an infinite supply of work. The service discipline is last buffer first served. Processing times are independent exponentially distributed. We analyze this system, obtaining steady state behavior and sample path properties. AMS Subject Classifications 60K25 · 90B22 I. Adan and G. Weiss: Research supported in part by Network of Excellence Euro-NGI. G. Weiss: Research supported in part by Israel Science Foundation Grant 249/02.     

Strong approximations for priority queues; head-of-the-line-first discipline

In this paper, we obtain strong approximation theorems for a single server queue withr priority classes of customers and a head-of-the-line-first discipline. By using priority queues of preemptive-resume discipline as modified systems, we prove strong approximation theorems for the number of customers of each priority in the system at timet, the number of customers of each priority that have departed in the interval [0,t], the work load in service time of each priority class facing the server at timet, and the accumulated time in [0,t] during which there are neither customers of a given priority class nor customers of priority higher than that in the system.Research supported by the National Natural Science Foundation of China.     

Comparison of statistical procedures in analytic hierarchy process using a ranking test

Several statistical procedures for estimation of the priority parameters in the setup of the Analytic Hierarchy Process (AHP) exist in the literature. The purpose of this article is to make appropriate comparisons of such statistical methods. Pairwise comparison matrices are simulated using different statistical distributions of the error part used in the procedures. Priority parameters are estimated for each simulated pairwise comparison matrix using the method suggested. Standard nonparametric statistical procedures are applied to check whether the order of the priority estimates is consistent with that of their parameter values irrespective of the choice of particular statistical procedure. Statistical procedures based on the reciprocal matrices are also compared with the eigenvalue method.     

Performance evaluation of nonlinear optimization methods via pairwise comparison and fuzzy numbers

In this paper we extend the deterministic performance evaluation of nonlinear optimization methods: we carry out a pairwise comparison using fuzzy estimates of the performance ratios to obtain fuzzy final scores of the methods under consideration. The key instrument is the concept of fuzzy numbers with triangular membership functions. The algebraic operations on them are simple extensions of the operations on real numbers; they are exact in the parameters (lower, modal, and upper values), not necessarily exact in the shape of the membership function. We illustrate the fuzzy performance evaluation by the ranking and rating of five methods (geometric programming and four general methods) for solving geometric-programming problems, using the results of recent computational studies. Some general methods appear to be leading, an outcome which is not only due to their performance under subjective criteria like domain of applications and conceptual simplicity of use; they also score higher under more objective criteria like robustness and efficiency.     

On the single server retrial queue with priority customers

We consider anM ₂/G ₂/1 type queueing system which serves two types of calls. In the case of blocking the first type customers can be queued whereas the second type customers must leave the service area but return after some random period of time to try their luck again. This model is a natural generalization of the classicM ₂/G ₂/1 priority queue with the head-of-theline priority discipline and the classicM/G/1 retrial queue. We carry out an extensive analysis of the system, including existence of the stationary regime, embedded Markov chain, stochastic decomposition, limit theorems under high and low rates of retrials and heavy traffic analysis.Visiting from: Department of Probability, Mechanics and Mathematics, Moscow State University, Moscow 119899, Russia.     

CCD测量系统实现及其实时性讨论

针对一个具体的CCD测量系统,就其软硬件的构成及其之间的关系进行了详细的阐述和讨论.对系统至关重要的实时性问题,以WindowsNT操作系统为基础,深入分析了造成系统实时性下降的原因,并提出了一些已被验证有效的改善措施.     

Comparison of On-Column and Splitless Injections for the Capillary Gc Quantitation of Organics Extracted from Landfill Leachatesl

Abstract

An extensive study of the organic components of the leachate from the University of Connecticut landfill has been carried out. A modification of EPA Method 625 for base/neutral extractable organics was used to obtain both the gas chromatographic profiles and the mass spectrometric identification of the organics in groundwater samples from six test wells and several private wells in the vicinity of the landfill. A characteristic fingerprint representing a number of components was consistently found in the analysis of the landfill leachate but not in the drinking water of the private residences located on an adjoining road. Gas chromatographic parameters for optimum qualitative and quantitative analysis of field samples were determined using an acetone solution of the model leachate sample. It was confirmed that the on-column injection mode resulted in greater flame ionization detector (FID) response and more reproducible peak areas than the splitless mode. The major variable in obtaining reproducible data was the field sampling at the landfill, not the solvent reduction step or the injection mode used to introduce the sample into the gas chromatograph.     

The impact of breakdowns disciplines and repeated attempts on performances of Small Cell Networks

This paper aims at presenting an approach to study performance and reliability of Small Cell Networks, taking into account the retrial phenomenon, the finite number of customers (mobiles) served in a cell and the random breakdowns of the base station channels. We consider the classical disciplines namely, active and dependent breakdowns and moreover we propose new breakdowns disciplines, in which we give to the interrupted customers due to a channel failure, a higher priority compared to other customers. To this end, we use the Generalized Stochastic Petri Nets (GSPNs) model as a support. However, one of the major drawbacks of this high-level formalism in performance evaluation of large networks is the state space explosion problem which increases when considering repeated calls and multiple unreliable channels. Hence, the novelty of this investigation is the presentation, for the different breakdowns disciplines with and without priority, of an approach which allows a direct computing of the infinitesimal generator describing the customers behavior and the channels allocation in as small cell, neither generating nor storing the reachability set. In addition, we develop the formulas of the main stationary performance and reliability indices, as a function of the network parameters, the stationary probabilities and independently of the reachability set markings. Through numerical examples, we discuss the effect of retrials, breakdowns disciplines and the priority on performances.     

OBS网络中一种基于优先级和门限的偏射路由算法

为了解决偏射算法在偏射控制上的问题,提出了一种基于优先级和门限的偏射路由算法.该算法采用丢弃少量偏射的高优先级分割突发数据包来保证偏射路由上低优先级非偏射突发数据包的QoS.当冲突发生时,分割偏射优先级低的突发数据包,从而保护高优先级突发数据包|在偏射路由上,通过启用偏射检测函数来判断是允许偏射的分割突发数据包抢占资源或是丢弃偏射的分割突发数据包.仿真结果表明,虽然该算法增加了少量的端到端的传输时延,但这种算法可以很好地控制偏射突发对网络偏射路由上正常流量的影响,并且能够有效地降低整个网络的丢包率,很好地保护高优先级突发数据包的完整性.故这种方法能够有效地提高OBS网络的性能.