Selecting a Doctoral Programme Using the Analytic Hierarchy Process — The Importance of Perspective

This paper discusses the application of the analytic hierarchy process (AHP) to the selection of a doctoral programme. The first section of this paper includes a brief discussion of the AHP. In the next section, we describe a hierarchy for selecting a doctoral programme that includes the perspective or career objective of the decision-maker as what we call a pseudo-level. This is followed by an illustration of the hierarchy in a case study with MBA students contemplating a doctoral programme. Finally, we discuss the results and highlight the importance of perspective as a discrete criterion that should not be included as another level of the hierarchy in the usual way.     

Loss profiles: A quality of service measure in mobile computing

With rapid technological advances being made in the area of wireless communications it is expected that, in the near future,mobile users will be able to access a wide variety of services that will be made available over future high-speed networks. The quality of these services in the high-speed network domain can be specified in terms of several QOS parameters. In this paper we identify a new QOS parameter for the mobile environment, calledloss profiles, that ensuresgraceful degradation of service (for applications that can tolerate loss) in situations where user demands exceed the network's capacity to satisfy them. A new transport sub-layer is proposed that efficiently implements this new QOS parameter. We also show how this protocol can be easily incorporated into existing proposals for high-speed network transport layer protocols and into the MPEG-2 Transport System.This work was supported by the NSF under grant number NCR-9410357.     

Stochastic behaviour of a two-unit redundant system with switchover time

There is a two-unit standby redundant system. Standby is kept in cold state. Whenever one unit is operating and the other is in the waiting standby state, switching is initiated on the latter after a random time. If the operative unit fails before the time to initiate switching action on the waiting standby unit, the system fails and the failed unit immediately undergoes repair type 2 along with the switching. However, if the operative unit fails when the other unit is as standby (after switchover), the failed unit undergoes repair type 1 and the unit as standby takes over the operation. All the distributions are arbitrary except failure-time, which is exponential.The system is defined with the help of states which generate a pseudo semi-Markov process. Abundant use of results from the theory of SMP has been made to obtain a large number of parameters which measure reliability characteristics of the system viz. MTSF, steady-state availability, expected number of visits to a state, conditional transition probabilities, first passage time distributions, expected profit rate, etc. Numerical examples are included to illustrate the results.     

Optimal Control of Some Simple Deterministic Epidemic Models

Using control variables such as the level of medicare programme effort and the level of inoculation programme effort, three simple mathematical models of epidemics are transformed into optimal control problems. These are multi-state problems with the state variables as numbers of infectives and susceptibles and with the objective function being minimization of the total present value of the social or economic costs of infectives and medical controls. The problems are analysed with the framework of the maximum principle to obtain or, at least, partially characterize the optimal policies over time.     

Software reliability of programs with network structure

The aim of this paper is to present the reliability expression of programs/packages with general network structure, which is not sequential, branch or parallel in logic flow of the concerned algorithm. The reliability expression for logic flow (R_L) of an example program of a general network structure (whose segments are listed in Appendix 1) is discussed and thereby overall reliability expression for the entire program which can be built in several different ways is derived. Such evaluations help increase the probability of programs having complex structure to be executed without errors on the computer system. The problem is obviously of great interest to programmers/system analysts while designing the flow system, debugging or testing the program.     

Designing reliable communication networks in a planned failure environment

A very important issue in many network applications is to provide protection against planned failures. In this paper we first define the concept of a planned failure and then analyze the cost implications in the design of a network for survivability (i.e. protection against planned failure), as against designing a network against random failures. We suggest a simple and systematic approach for designing survivable communication networks and also discuss briefly the consequences of availability of partial knowledge only.     

Capacity Consideration in Reliability Analysis of Communication Systems

This paper presents a simple method for deriving a symbolic reliability expression of some practical systems such as a communication system having fixed channel capacities of its links, a power distribution system having limited power ratings of its power lines, a transport system which might not allow traffic more than a particular value, or a chemical system in which oil or gas flow through pipes is permissible only up to some safe limits. A system is good if and only if it is possible to transmit successfully the required capacity from source node to the sink node. This paper defines a group as a set of branches such that success of these branches ensures system success, as defined above. All such groups are obtained from a knowledge of the minimal paths of the system graph. The method is computerized and implemented on DEC-20 computer. Two examples are considered and their solutions presented to illustrate the technique.