مجله بین المللی علوم مهندسی(انگلیسی)
سال:1385 | دوره: | شماره: |تعداد مقالات:9

In this paper, we study an inverse problem in the case when the unknown terms are time-dependent diffusivity coefficient and radiation term on the boundary.Unknown terms are determined from two known over specified conditions.The uniqueness of the solution of the inverse problem will be discussed. Finally, some examples will be given.

A simple example in fluid dynamics is presented to show the important role of the law of increase of entropy in the dynamics. In a stationary 3-D viscous flow with negligible thermal conduction, the Lyapunov method is employed to obtain the fluid velocity "without" solving the equation of motion. This flow which is given around the point of maximum entropy consists of some closed orbits lying simultaneously on both surfaces of constant entropy and spherical surfaces centered at that point. Also the flow near to this stable point must be incompressible and non-viscous.

A square matrix over F with non-negative integral trace is called a quasi-permutation matrix over F. Let G be a finite linear group of degree n, that is, a finite group of authomorphisms of an n-dimensional complex vector space or, equivalently, a finite group of non-singular matrices of order n with complex coefficients. We shall say that G is a quasi-permutation group if the trace of every element of G is a non-negative rational integer. Thus a permutation group of degree n has a representation as a quasi-permutation group of degree n. In this paper we calculate the kernel and Galois groups for the irreducible characters of the group GL (3,q). These help us to obtain the permutation and quasi-permutation representations of the group GL (3,q).

Variable mesh finite difference method of fifth order have been derived for solution of singular two point boundary value problem, which reduces to the method of order six, for uniform mesh case. These methods are self starting and are exact for u=r-1. The convergence of the sixth order method is discussed. The absolute error, for solution of four problems, two linear and two nonlinear are listed to show the accurate and effectiveness of the present method.

In conventional PERT analyses, using beta distribution as underlying distribution for activity durations, the mean and variance of activity durations are estimated using optimistic, pessimistic, and probable estimates given by an expert. In order to improve these estimates, various methods have been proposed. In this paper, we propose a new model, whose estimate of the mean of activity durations is more accurate than original PERT estimates and its modifications. In addition, the proposed method does not rely on any assumptions on beta parameters.

The exponentially weighted moving average (EWMA) and double EWMA are two basic control charts in the sensitive manufacturing process such as semiconductor manufacturing. Optimal value for the weight parameters of these control charts are important for evaluation of their performance. In this paper we have used multi criteria decision making (MCDM) and goal programming (GP) models to reduce bias and standard deviation of statistics of EWMA and double EWMA control charts based on decision maker openion. The proposed model as a Engineering Process Control (EPC) tools can be used for optimal adjastment of sensitive process.

This paper presents an integrated production and inventory model. Our multi-echelon model includes the maximization of production while it minimizes the cost of production, inventory holding and setup operations. The model consists of two main parts, the primary and finishing operations. The primary operation corresponds to purchasing of raw material and the finishing operation is for preparation of finished product. Demand is influenced by price elasticity and the cost of purchasing raw material is also affected by demand. The resulted model, therefore, is highly nonlinear and non-convex. Geometric Programming (GP) is used to locate the global solution of the proposed model. We analyze the solution in different cases in order to study the behaviour of the model and for each case, a numerical examples is used to demonstrate the implementation of our analysis.

Determining a production scheduling and limited resource allocation in production scheduling problems plays an important and effective role in manufacturing organizations since correct determination of the production schedule and limited resource allocation leads to capital stack avoidance, losses reduction, machine idleness reduction or elimination and better use of them, supplying the customers orders and demands in time, and providing materials and parts. The objective of production scheduling is to allocate limited resources to perform a set of competitor's activities. Having a proper production schedule significantly increases the performance and provides access to organizational goals. In this paper, job-shop production scheduling problems with limited resource allocation in each stage and minimizing the total weighted tardiness have been studied and die production scheduling have been determined through a combinational algorithm of critical path and limited resource allocation methods. Finally, effectiveness of the proposed algorithm in comparison to other methods has been verified through several instances.

This paper reformulates the unified robust model and reveals the relationship between uncertainty sets using norm bodies and their corresponding robust counterparts defined by dual norms. It shows how to apply a unified robust modeling approach to portfolio selection. It is shown how the robust model of an uncertain portfolio selection can be adjusted according to the decision maker's utility function and the uncertainty of the return parameters. The model can be tuned by choosing an appropriate norm body and the radius of the uncertainty region. Simulation experiments have been carried out using 10000 samples of the return parameters for various lp-norm solutions. The computational results provide some general guidelines as how to choose a suitable Ip -norm in the unified robust model according to the degree of risk aversion of an investor. In addition, when the uncertainty is large, the investor personality does not play an important role and l¥ norm is the choice.