Operations research/management science in the Arab world: historical development

This study aims to review the related literature on operations research (OR)/management science (MS) in the Arab world published during the last three decades. Owing to the nature of this study, an extensive survey of the related literature was conducted and inferences were drawn. The inferences drawn from the literature survey on OR/MS in the Arab world were first, there is a paucity of published real‐world applications of OR/MS. Second, there is a lack of published survey‐type studies in most Arab countries, except in Jordan, Lebanon, Palestine, Syria, and the United Arab Emirates. Third, the majority of published works on OR/MS were of a conceptual nature. A few papers concerned with OR/MS in the Arab world were published during the 1980s, with a special emphasis on conceptual issues rather than on applied or survey‐type studies. The 1990s witnessed an increased number of publications on both survey‐type and conceptual studies. Since 2000, the number of publications has increased substantially, mainly through conceptual studies. This study has a number of implications for both practitioners and researchers. Practitioners will be made aware of the applications of OR/MS in the Arab world and the type of problems that have been addressed. This, in turn, might motivate the decision makers and the managers to adopt OR/MS approaches in solving their organizations' problems. As a result, this might increase the usage of OR/MS in this part of the world. Researchers will be able to identify the OR/MS research areas that need more attention in the Arab world. The study mainly covers the studies that are written in English and indexed in non‐Arabic databases. Although the Arabic works were not surveyed exhaustively, the author reviewed and included some available OR/MS works written in Arabic. This study is considered as the first work of its type in surveying the scholarly publications pertaining to OR/MS in the Arab world since the 1980s.     

An analytical simulator for deploying IP telephony

Deploying IP telephony or voice over IP (VoIP) is a major and challenging task. This paper describes an analytical design and planning simulator to assess the readiness of existing IP networks for the deployment of VoIP. The analytical simulator utilizes techniques used for network flows and queuing network analysis to compute two key performance bounds for VoIP: delay and bandwidth. The simulator is GUI‐based and has an interface with drag‐and‐drop features to easily construct any generic network topology. The simulator has an engine that automates and implements the analytical techniques. The engine determines the number of VoIP calls that can be sustained by the constructed network while satisfying VoIP QoS requirements and leaving adequate capacity for future growth. As a case study, the paper illustrates how the simulator can be utilized to assess the readiness to deploy VoIP for a typical network of a small enterprise. We have made the analytical simulator publicly available in order to improve and ease the process of VoIP deployment. Copyright © 2008 John Wiley & Sons, Ltd.     

Statistical models for spot welding of commercial aluminium sheets

The present paper reports experimental investigations on the spot welding of commercial aluminium sheets. Experiments were carried out to study the influence of spot welding parameters (welding current, welding time, electrode force and sheet thickness) on the strength of spot welded aluminum sheets with commercial purity. Experiments were planned on the basis of response surface methodology (RSM) technique. The mathematical models (failure load and nugget area) correlating process parameters and their interactions with response parameters have been established. These models have been used in selecting the optimum process parameters for obtaining the desired spot welding quality at the least possible consumed power.     

Practical Considerations for Recursive DFT Implementation in Numerical Relays

In this paper, practical considerations for recursive Discrete Fourier Transform (DFT) implementation in numerical relays are presented. The DFT filter instabilities which would produce accumulated errors are emphasized. The aspects ruling error accumulation of the estimated magnitude and phase are highlighted. Novel solutions directed for the elimination of error accumulation are proposed and intensively tested. Digital signal processing (DSP) board based test set-up is utilized for the experimental verification. The paper results are valuable for the protection engineers particularly those concerned with the development and implementation of numerical relays     

Watershed characteristics, land use and fabric: The application of remote sensing and geographical information systems

Integrated watershed assessment, especially relying on remote sensing (RS), is a newly established procedure in developing countries. It is proving to be a major component in river‐basin environmental management. The recurrence of environmental problems in the Akkar El Kabir River watershed, as well as the lack of proper data on sources and sinks of pollutants, and the extent of human interference, led to the current study. Advanced geoinformation tools, such as RS and geographical information systems (GIS), prove to be a valuable asset in securing data on the fabric of the Akkar watershed in relation to its natural setting and anthropic interference. This is particularly true in the current study as the river constitutes the boundary between Lebanon and Syria. Remote sensing captures the watershed characteristics and land use on both sides without constraints. The natural fabric includes geology, drainage, hydrogeology, forest and soil. The anthropic fabric includes settlements, utilities, roads, agriculture and land use. If it were not for geoinformation techniques, the task of securing such data would be difficult. Also, these techniques show the impact of malpractices from excessive human interference that result in degradation of land and water quality. Changes in the watershed, such as environmental deterioration, are observed as water pollution, soil erosion, forest decline and socioeconomic imbalance. Obviously, this is the outcome of malpractices in a multisectorial system. A major challenge for RS and GIS is to quantify, model and predict, if possible, the extent of these changes. Remote sensing inherently captures the impact of interaction between nature and human beings. Detection of change is a major indicator that RS can contribute to the evaluation of the state of the environment. The application of it on this watershed reveals that significant changes have occurred over the last 10–15 years, most of which are anthropic.     

Investigating Morphology and Stability of Fac‐tris (2‐phenylpyridyl)iridium(III) Films for OLEDs

Stable film morphology is critical for long‐term high performance organic light‐emitting diodes (OLEDs). Neutron reflectometry (NR) is used to study the out‐of‐plane structure of blended thin films and multilayer structures comprising evaporated small molecules. It is found that as‐prepared blended films of fac‐tris(2‐phenylpyridyl)iridium(III) [Ir(ppy)₃] in 4,4′‐bis(N‐carbazolyl)biphenyl (CBP) are uniformly mixed, but the occurrence of phase separation upon thermal annealing is dependent on the blend ratio. Films comprised of the ratio of 6 wt% of Ir(ppy)₃ in CBP typically used in OLEDs are found to phase separate with moderate heating while a higher weight percent mixture (12 wt%) is found to be stable. Furthermore, it is found that thermal annealing of a multilayer film comprised of typical layers found in efficient devices ([tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA)/Ir(ppy)₃:CBP/bathocuproine (BCP)]) causes the BCP layer to become mixed with the emissive blend layer, whereas the TCTA interface remains unchanged. This significant structural change causes no appreciable difference in the photo­luminescence of the stack although such a change would have a dramatic effect on the charge transport through the device, leading to changes in performance. These results demonstrate the effect of thermal stress on the delicate interplay between the chemical composition and morphology of OLED films.     

The choice of probing sites by Bracon hebetor Say (Hymenoptera: Braconidae) foraging for Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

A direct behavioral assay was conducted to investigate the preferred habitat for host searching by the parasitoid Bracon hebetor (Hymenoptera: Braconidae). The effects of mating, feeding and post-emergence experience on female parasitoid choices of searching sites were also examined. B. hebetor appears to be directed to the habitat of its host through chemical cues originating from the host larvae, frass and adults. These cues elicit a series of directed responses by the female. Generally, the data showed that flour containing 30-day-old larvae was preferred by B. hebetor females. This was followed by the flour containing the frass, then the adult host, and finally the flour containing 10-day-old larvae. It appears that cues produced by young larvae were the weakest whereas cues produced by older ones were the strongest. Feeding seemed to be important in the location of the proper searching site. Although the cues were normally learned by the immature stages of the parasitoid, and were subsequently manifested in their responses as adults, adult experience increased the ability of the parasitoid to locate the suitable habitat for searching.     

Effect of tool bit insert-holder assembly on dimensional accuracy and geometrical tolerances of machined workpieces

Different techniques are normally used for assembling insert-holders of metal cutting tools. For instance, mechanical clamping, brazing and adhesive bonding are common techniques for assembling metal cutting tools insert-holders. The present work addresses the impact of the assembly technique on the dimensional accuracy and geometrical tolerances of machined workpieces.Extensive cutting tests conducted on mild steel specimens using different insert holder assembly techniques, revealed that bonded assembly ranked ahead in preserving dimensional accuracy and geometrical tolerances, when compared with mechanical clamped and brazed assemblies.     

A new control technique for active power filters using a combinedgenetic algorithm/conventional analysis

In this paper, the computational problems associated with the optimization techniques used to evaluate the switching patterns for controlling variable-characteristics active power filters are presented and critically analyzed. Genetic algorithms (GAs) are introduced in this paper to generate a fast and accurate initial starting point in the highly nonlinear optimization space of mathematical optimization techniques. GAs tend to speed up the initialization process by a factor of 13. A combined GA/conventional technique is also proposed and implemented to reduce the associated computational burden associated with the control and, consequently, increasing the speed of response of this class of active filters. Comparisons of these techniques are discussed and presented in conjunction with simulation and practical results for the filter operation     

Transient response of optoelectronic integrated bistable device

In this paper, the transient response of an optical bistable device with optically controlled set and reset functions is analyzed. The device is made from a vertical integration of two heterojunction phototransistors (HPTs) and a laser diode (LD). One of the HPTs (HPT-A) is integrated just above the active layer of the LD and is utilized in the set operation, while the other HPT (HPT-B) is used to achieve the reset operation. The effect of the various device parameters on the set and reset operations is outlined. Finally, expressions for the rise time during the setting, and fall time during the resetting conditions are derived