Mustafa M. Alidrisi

The reliability of a dynamic warm standby redundant system of n components with imperfect switching

Abstract A recursive formula is obtained for the reliability of a dynamic warm standby redundant system of n components with imperfect switching and constant failure rates. The formula is obtained using success modes analysis and is verfied for some known special cases.

A simulation approach for computing systems reliability

Abstract The basis of the concept of reliability is that a given component has a certain stress-resisting capacity; if the stress induced by the operating conditions exceeds this capacity, failure results. Most of the published results in this area are based upon analytical modelling of stress and strength, using various probability distributions, and then trying to find an exact expression for system reliability, which can be very difficult to obtain sometimes. The approach used in this paper is very simple and uses simulation techniques to repeatedly generate stress and strength of a system by the computer, using a random number generator and methods such as the inverse transformation technique. The advantage of this approach is that it can be used for any stress-strength distribution functions. Finally, numerical results obtained from using this approach are compared with results obtained using the analytical methods for various strength-stress distribution functions, such as exponential, normal, log normal, gamma and Weibull. Results show the viability of the simulation approach.

Evaluation of noise stresses in Jeddah industrial estate

Abstract This paper reports the detailed field study carried out to asses the noise stresses in Jeddah Industrial Estate in Saudi Arabia. The study was carried out over a period of two years and covered a total of 78 factories producing food, chemical, plastic, metal, paper and other types of products. A global analysis is provided to obtain a clear picture of the magnitude of the noise stresses prevailing in the area. The report is concluded with some suggestions to improve the situation.

Linear programming model for the optimal control of a queueing network

Up to a decade ago, most research in queueing was concerned with descriptive aspects, i.e. mathematical characteristics and structure such as steady-state queue length probability distributions, waiting time distributions, average queue length, and busy and idle periods analysis. However, in real life the operator of a queueing system is also concerned with design and control. The operator wants to maximize his profit or minimize his costs. For this reason, optimization problems in queueing have received much attention during the past few years. In this paper, a queueing system with two service stations is considered. Arrivals to each station from outside follow a Poisson process. The service time at each station is an exponentially distributed random variable with mean depending on the state of the system, defined as the number of customers at each station at time t. A customer served at either of the stations leaves the system or goes to the other station with specified probabilities. A linear programmi...

Cell cycle kinetics analysis of Hela cells exposed to aphidicolin: Computer simulation

A computer simulation model was developed and used to analyze the inhibitory effect of aphidicolin on the proliferation of Hela cells. Simulation results were compared with actual experimental results [Pedrali-Noy et al. (1980) Nuc. Acid Res. 8, 377] and were found to be in good agreement. Also, the simulation showed that aphidicolin caused cells to be accumulated at the G1/S boundary and that recruitment and synchrony occurred.

Regression models for estimating survival of patients with non-Hodgkin's Lymphoma

Abstract The life-table method is used for estimating the survivorship of 989 patients treated for non-Hodgkins Lymphoma at King Faisal Specialist Hospital and Research Center in Riyadh, Saudi Arabia. Estimates of various survival measures and their standard errors are obtained. Then, four common probability distributions namely; the exponential, Weibull, Gompertz, and the linear hazard are used to estimate the survivorship function, hazard function and the probability density function. Comparison between the log-likelihood values for the estimated data is also made to choose the best fitting model.

Optimal control of the service rate of an exponential queuing network using Markov decision theory

An exponential queuing network of two service stations is considered. The service rate at each station can either be fast or slow. A policy in which the service rate to be used at each station is specified as a function of the state of the system is investigated in order to minimize a given objective cost function. Howards policy space algorithm is used to characterize the form of the optimal policy. Results show that the optimal policy is a simply connected one and of montone structure.

Appraisal of work hazards and safety in the industrial estate of Jeddah

An environmental study for the appraisal of work hazards and safety in Jeddah Industrial Estate (JIE), Saudi Arabia has been conducted. The study is based upon a representative (stratified random) sample of 44 enterprises, including 52 plants and employing 5830 workers.Nearly 2/3 of the workers have heat exposure, orginating from climatic heat and heat dissipated from industrial operations, while exposure to noise is slightly less, and is attributed to noisy operations and machinery and to lack of meticulous maintenance; both exposures are mild in most of the plants and moderate in some. Mild exposures to nonionizing radiations (UV and IR) and to deficient illumination occur in 25% and 19.2% of the plants studied. Respiratory exposure to chemical agents (organic and inorganic dusts, metal fumes, gases and vapours — including asphyxiants, irritants, liver and nervous system offenders and acid and alkali mists) occurs in 75% of the plants, particularly in the medium-size enterprises plants; however, is mainly mild with a few moderate and severe exposures. Skin absorption contributes to absorption of chemical agents in 29% of the plants, and direct skin contact to chemicals (particularly to lubricating oils) occurs in 81% of the plants.Meanwhile, only eight plants, out of the 32 plants where controls for physical hazards are required (51.2%), apply engineering controls, and even in a few of these plants the efficiency of the control measures has been rated ‘bad’. A few of them provide personal protective equipment, and even no maintenance to this equipment is provided.The level of safety is better in the large plants than in the small and medium-size plants; the safety score is the best in the recently established plants, while is the worst in the plastic industry, which is relatively old. The appraisal of fire protection is better than that of the safety, due to efficient supervision of the General Directorate of Civil Defense (GDCD). However, most of the safety problems are managerial and are preventable.First aid is present in all enterprises, as required by the Saudi Labor Laws; however, an in-plant medical service is present in 75% of the large enterprises, in 31.6% of the medium-size and in only 17.6% of the small enterprises. Also, satisfactory medical, accidents and absenteeism records exist in only 15.9% of the enterprises; safety supervision exists in 27.3, and safety education exists in 91% of them, while no environmental monitoring is carried out in any enterprise. Sanitation facilities exist in satisfactory numbers in most of the enterprises; however, their maintenance is poor in most of them, due to lack of hygienic supervision. All enterprises dispose of their liquid wastes into the JIE sewerage system without any treatment, while the solid wastes are collected by the city authorities in 56.8% of them; both wastes are anticipated to cause environmental pollution problems.

Heat stress assessment in the industrial facilities (A case study)

Abstract Heat stress assessment in the work place is of vital importance for the well‐being of industrial workers and consequently the optimum performance of the industrial facilities. A methodology for determining the heat stress in a large number of factories is presented. The Wet Bulb Globe Temperature (WBGT) index was adapted in this study. Detailed strategy is given for proper and efficient assessment. The data were carefully analyzed in the light of set international standards and the degree of compliance of the facilities surveyed. Furthermore other factors such as the type of industry, air‐conditioning and outdoor conditions which affect the indoor situation, were also investiated.

Cell growth simulation (CGS): the design philosophy

Cell Growth Simulation (CGS) is a software package that simulates the growth of cell cultures, and the effects of different types of agents on the cell populations in vitro. It is a stochastic simulation system based on the cell cycle kinetics. Experiments involving DNA synthesis blocking, mitosis inhibition, labelling and cell kill can be simulated by imitating agents such as thymidine, aphidicoline, hydroxyurea, vincristine, vinblistine, colcemid and others. The model to be simulated is described by the user according to his theoretical convictions, The system provides numerous facilities to help the user describe an experiment and examine the simulation results. A menu driven interactive scheme is used to communicate with the user. CGS has a modular structure and its general structure, design philosophy and capabilities are presented. The system has been developed through the cooperation of industrial engineering, cell biology, medical oncology and computer programming disciplines. It is implemented on...