Enhanced optical oxygen sensing using a newly synthesized ruthenium complex together with oxygen carriers

In this article, an emission based, simple and fast method is proposed for the determination of gaseous oxygen. A newly synthesized fluorophore, dichloro-{2,6-bis[1-(4-dimethylamino-phenylimino) ethyl]pyridine}ruthenium(II) has been used for oxygen sensing together with oxygen carrier perfluorochemicals (PFCs) in silicon matrix. It should be noted that the solubility of oxygen in fluorocarbons is about three to ten times large as that observed in the parent hydrocarbons or in water, respectively. Employed PFCs are chemically and biochemically inert, have high dissolution capacities for oxygen, and, once doped into sensing film, considerably enhance the response of sensing agent.     

Studying an overload system using rotation

1. IntroductionThe motivation of writing this paper was from calculating the blocking probability foran overloaded finite system. Our numerical experiments suggested that this probability canbe approximated efficiently by rotating the transition matrix by 180". Some preliminaryresults were obtained and can be found in [11 and [2]. Rotating the transition matrix definesa new Markov chain, which is often called the dual process in the literature, for example,[3--7]. For a finite Markov chain, …     

Optimal control and sensitivity analysis of SIV→HIV dynamics with effects of infected immigrants in sub‐Saharan Africa

Regional migration has become an underlying factor in the spread of HIV transmission. In addition, immigrants with HIV status has contributed with high‐risk of sexually transmitted infection to its “destination” communities and promotes dissemination of HIV. Efforts to address HIV/AIDS among conflict‐affected populations should be properly addressed to eliminate potential role of the spread of the disease and risk of exposure to HIV. Motivated from this situation, HIV‐infected immigrants factor to HIV/SIV transmission link will be investigated in this research and examine its potential effect using optimal control method. Nonlinear deterministic mathematical model is used which is a multiple host model comprising of humans and chimpanzees. Some basic properties of the model such as invariant region and positivity of the solutions will be examined. The local stability of the disease‐free equilibrium was examined by computing the basic reproduction number, and it was found to be locally asymptotically stable when ?₀<1 and unstable otherwise. Sensitivity analysis was conducted to determine the parameters that help most in the spread of the virus. Pontryagin's maximum principle is used to obtain the optimality conditions for controlling the disease spread. Numerical simulation was conducted to obtain the analytical results. The results shows that combination of public health awareness, treatment, and culling help in controlling the HIV disease spread.     

Discrete time queues and matrix-analytic methods

This is an expository paper dealing with discrete time analysis of queues using matrix-analytic methods (MAM). Discrete time analysis queues has always been popular with engineers who are very keen on obtaining numerical values out of their analyses for the sake of experimentation and design. As telecommunication systems are based more on digital technology these days than analog the need to use discrete time analysis for queues has become more important. Besides, we find that several queues which are difficult to analyse by the continuous time approach are sometimes easier to analyse using discrete time method. Of course, there are some queueing problems which are easier to analyse using continuous time approach instead of discrete time. We discuss, in this paper, both the advantages and disadvantages of discrete time analysis. The paper focusses on setting up several queueing systems as discrete time quasi-birth-and-death processes and then shows how to use matrix-geometric method (MGM), a class of MAM, to analyse the problems. We point out that there are other methods for analysing such queues but MGM provides a much simpler approach for setting up the problems in order to obtain semi-explicit results for computational tractability. We also point out some of the shortcomings of MGM. The paper mainly focusses on the Geo/Geo/1, PH/PH/1, GI/G/1 and GI/G/1/K systems and some of the related problems, including vacation models with time-limited visits.     

Entrywise perturbation theory for diagonally dominant M-matrices with applications

Summary. This paper introduces a new perspective on the study of computational problems related to diagonally dominant M-matrices by establishing some new entrywise perturbation results. If a diagonally dominant M-matrix is perturbed in a way that each off-diagonal entry and its row sums (i.e. the quantities of diagonal dominance) have small relative errors, we show that its determinant, cofactors, each entry of the inverse and the smallest eigenvalue all have small relative errors. The error bounds are given and they do not depend on any condition number. Applying this result to the studies of electrical circuits and tail probabilities of a queue whose embedded Markov chains is of GI/M/1 type, we discuss the relative sensitivity of the operating speed of circuits and of the percentile of the queue length, respectively. Received January 17, 2000 / Published online June 7, 2001