Current Issue : January - March Volume : 2012 Issue Number : 1 Articles : 6 Articles
We analyze a previous paper by S. T. Mohyud-Din and M. A. Noor (2007) and show the mistakes in it. Then, we demonstrate a more efficient method for solving fourth-order boundary value problems....
This paper studies a perishable inventory model, which assumes that each perishable item has finite lifetime, and only one item is consumed each time. The lifetimes of perishable items are independent random variables with the general distribution and so are the consumption internal. Under this assumption, by using backward equations and limit distribution of Markov skeleton processes, this paper obtains the existence conditions and the explicit expression of the limit distribution of the inventory level of perishable inventory model....
We study the general solution of equation kB,cux fx, where k B,c is the ultrahyper-bolic Bessel operator iterated k-times and is defined by k B,c= [1/c2(Bx1 Bx2 �· �· �· Bxp) - (Bxp1 �· �· �· Bxpq)] k, p q n, n is the dimension of Rn {x : x=( x1, x2, . . . , xn), x > 0}, . . . , xn >0}, Bxi ?2/?x2i (2vi/xi)(?/?xi), 2vi = 2�Ÿi 1, �Ÿi > -1/2, xi > 0( i = 1, 2, . . . , n), f(x) is a givengeneralized function, u(x) is an unknown generalized function, k is a nonnegative integer, c is a positive constant, and x ? Rn....
We consider the problem of the optimization of the functioning of a pumped-storage hydroplant. The problem can be mathematically formulated as an optimal control problem, and when the considered hydromodel is of the fixed-head type, an added complication arises: the solution is of the bangsingular-bang type. In this paper, we propose a simple and efficient optimization algorithm to find the solution....
The influence of switching frequency on the low-frequency oscillation in the voltage-controlled buck-boost converter is studied in this paper. Firstly, the mathematical model of this system is derived. And then, a glimpse at the influence of switching frequency on the low-frequency oscillation in this system by MATLAB/Simulink is given. The improved averaged model of the system is established, and the corresponding theoretical analysis is presented. It is found that the switching frequency has an important influence on the low-frequency oscillation in the system, that is, the low-frequency oscillation is easy to occur when the switching frequency is low. Finally, the effectiveness of the improved averaged model and the theoretical analysis are confirmed by circuit experiment....
Identification, prediction, and control of a system are engineering subjects, regardless of the nature of the system. Here, the temporal evolution of the number of individuals with dengue fever weekly recorded in the city of Rio de Janeiro, Brazil, during 2007, is used to identify SIS susceptible-infective-susceptible and SIR susceptible-infective-removed models formulated in terms of cellular automaton CA. In the identification process, a genetic algorithm GA is utilized to find the probabilities of the state transition S ? I able of reproducing in the CA lattice the historical series of 2007. These probabilities depend on the number of infective neighbors. Time-varying and non-time-varying probabilities, three different sizes of lattices, and two kinds of coupling topology among the cells are taken into consideration. Then, these epidemiological models built by combining CA and GA are employed for predicting the cases of sick persons in 2008. Such models can be useful for forecasting and controlling the spreading of this infectious disease....
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