Analysis and optimisation of the HIPERLAN Channel Access Contention Scheme

This paper analyses the HIPERLAN channel access mechanism. Both a purely mathematical and a simulation model are built in order to evaluate the two successive phases of the contention scheme. Several optimisations, based on the choice of parametric values, are proposed, evaluated and compared.     

Reliability‐based estimation of the survival of Listeria monocytogenes in chorizos

Reliability analysis is especially important when critical decisions are to be made involving potentially severe adverse consequences such as foodborne illness. Owing to uncertainty associated with the parameters controlling survival of Listeria monocytogenes in chorizo (a Mexican‐style sausage), the time needed to reduce the count by a certain number (n) of logs (t_nD) is probabilistic. In this paper the first‐order second‐moment (FOSM) method based on Taylor series expansion is used to derive the expected value and standard deviation of t_nD as function of the operating conditions (random variables) affecting survival, namely initial water activity (a_w0) of the sausage batter, storage temperature (T) and airflow velocity (F), along with their uncertainties characterised by their means and coefficients of variation. For any given n the derived t_nD probability distribution enables one to determine an estimate of t_nD for any desired level of reliability or confidence level, such as 50% (median value), 95%, 99%, etc. Among the conclusions drawn were: (i) the variability associated with T and F has a minor effect on estimating uncertainty in t_nD, whereas the reliability of t_nD estimation is greatly influenced by the uncertainty in a_w0; and (ii) the uncertainty in a_w0 has the greatest impact when a_w0 of the sausage formulation exceeds 0.90. The approach used and discussed in this paper can be applied to any survival/inactivation study to incorporate the effect of uncertainty in the various extrinsic and intrinsic parameters on the survival kinetics of the pathogen in a food system under evaluation. Copyright © 2006 Society of Chemical Industry     

Analytical general results for handoff dwell time distribution in wireless networks

1 Introduction The calling dwell time characteristic is critical for the user network planning and deployment, e.g., global system for mobile communications (GSM), as well as the next generation wireless multimedia networks, such as, the currently standar…     

Conditions for the Acceptance of Deontic Conditionals.

Recent psychological research has investigated how people assess the probability of an indicative conditional. Most people give the conditional probability of q given p as the probability of if p then q. Asking about the probability of an indicative conditional, one is in effect asking about its acceptability. But on what basis are deontic conditionals judged to be acceptable or unacceptable? Using a decision theoretic analysis, we argue that a deontic conditional, of the form if p then must q or if p then may q, will be judged acceptable to the extent that the p & q possibility is preferred to the p & not-q possibility. Two experiments are reported in which this prediction was upheld. There was also evidence that the pragmatic suitability of permission rules is partly determined by evaluations of the not-p & q possibility. Implications of these results for theories of deontic reasoning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A new approach for sequential experimental design for model discrimination

Model discrimination procedures are useful tools for selection of the best mathematical models to be used to represent a specific chemical process. The present paper presents and discusses a new sequential discrimination procedure, which makes use of model probabilities and concentrates the efforts on models with higher probabilities. Model probabilities are determined based on simple statistical arguments. Four numerical examples illustrate the application of the proposed discrimination procedure. The obtained results indicate that the new procedure is able to discriminate kinetic models with fewer experiments when compared to other procedures and also indicates when model discrimination is not possible and, thus, when the sequential design must be halted. Furthermore, the speed of the proposed discrimination procedure can be controlled by tuning a design parameter which reflects the analyst's mood (confidence) towards the discrimination problem and allows for increase or decrease of the number of experiments required for model discrimination during the sequential procedure.     

Almost k-wise independence versus k-wise independence

We say that a distribution over {0,1}ⁿ is (ε,k)-wise independent if its restriction to every k coordinates results in a distribution that is ε-close to the uniform distribution. A natural question regarding (ε,k)-wise independent distributions is how close they are to some k-wise independent distribution. We show that there exist (ε,k)-wise independent distributions whose statistical distance is at least n^O(k)·ε from any k-wise independent distribution. In addition, we show that for any (ε,k)-wise independent distribution there exists some k-wise independent distribution, whose statistical distance is n^O(k)·ε.     

Probabilistic cell modelling of cleavage fracture

Various aspects on probabilistic modelling of cleavage fracture are discussed. The investigation involves consideration of a unit cell with an explicitly modelled void. The results from this model are compared with results for the case when the void content is accounted for in the sense of a Gurson-Tvergaard law. It is found that explicit modelling of the void can give substantially different results for the fracture probability. The effect depends on the exponent in the assumed Weibull distribution, the threshold stress, the constraint conditions and the hardening of the material. This revised version was published online in August 2006 with corrections to the Cover Date.     

Optimal search for signals in a multichannel system: Arbitrary initial distribution in state space merging scheme

Markovian and semi-Markovian random processes are used to analyze the problem of optimal search for signals in a multichannel communication system with arbitrarily distributed random outputs. The search efficiency factor is found in explicit form based on state space merging, and a mathematical programming problem is set up to find a numerical suboptimal solution. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 144–150, May–June 2007.     

马尔可夫链在产品可靠性预测中的应用

事物未来的状态仅仅受事物现状的影响，而与过去的状态无关，也就是具有马尔可夫性。用马尔可夫链的理论与方法，对具有马尔可夫性产品的可靠性进行预测，既为产品的可靠性设计和产品售后服务的经济性分析提供了参考，也为马尔可夫模型的实际应用拓广了范围。通过实例说明在数学软件的帮助下这种预测方法的简单可行性。     

N_2/Fe(100)相互作用的动力学研究

用准经典轨迹法对N2－Fe（100）系统进行了研究，分析了氮分子在Fe（100）面上的直接散射和离解性吸附等过程中的能量传递和重新分配，阐明了表面催化的机理。作为准经典轨迹法更为深入的应用，研究了主要LEPS势参数和势特性对初始离解吸附几率（S0）的影响，得出了S0随势特性变化的规律。