Showing papers by "King Fahd University of Petroleum and Minerals published in 1992"

Efficiency and inefficiency in thinly traded stock markets: Kuwait and Saudi Arabia

Abstract: This study examines stock returns in Saudi Arabia and Kuwait over the period 1985–1989. The Kuwaiti market is similar to other thinly traded markets in the proportion of individual stocks exhibiting statistically significant autocorrelations and price change runs. In contrast, all 35 Saudi stocks show a significant departure from the random walk. The mean Saudi autocorrelation coefficient of −0.471 is opposite in sign and is huge in magnitude in comparison to autocorrelations reported in other stock market studies. Institutional factors contributing to market inefficiency include illiquidity, market fragmentation, trading and reporting delays, and the absence of official market makers.

The flow over a backward-facing step under controlled perturbation: laminar separation

Abstract: The flow over a backward-facing step with laminar separation was investigated experimentally under controlled perturbation for a Reynolds number of 11000, based on a step height h and a free-stream velocity UO. The reattaching shear layer was found to have two distinct modes of instability: the ‘shear layer mode’ of instability at Stθ ≈ 0.012 (Stθ ≡ fθ/UO, θ being the momentum thickness at separation and f the natural roll-up frequency of the shear layer); and the ‘step mode’ of instability at Sth ≈ 0.185 (Sth ≡ fh/U0). The shear layer instability frequency reduced to the step mode one via one or more stages of a vortex merging process. The perturbation increased the shear layer growth rate and the turbulence intensity and decreased the reattachment length compared to the unperturbed flow. Cross-stream measurements of the amplitudes of the perturbed frequency and its harmonics suggested the splitting of the shear layer. Flow visualization confirmed the shear layer splitting and showed the existence of a low-frequency flapping of the shear layer.

Multiresolution Hough transform-an efficient method of detecting patterns in images

Abstract: A new multiresolution coarse-to-fine search algorithm for efficient computation of the Hough transform is proposed. The algorithm uses multiresolution images and parameter arrays. Logarithmic range reduction is proposed to achieve faster convergence. Discretization errors are taken into consideration when accumulating the parameter array. This permits the use of a very simple peak detection algorithm. Comparative results using three peak detection methods are presented. Tests on synthetic and real-world images show that the parameters converge rapidly toward the true value. The errors in rho and theta , as well as the computation time, are much lower than those obtained by other methods. Since the multiresolution Hough transform (MHT) uses a simple peak detection algorithm, the computation time will be significantly lower than other algorithms if the time for peak detection is also taken into account. The algorithm can be generalized for patterns with any number of parameters. >

Fast and flexible architectures for RNS arithmetic decoding

Abstract: An implementation of a fast and flexible residue decoder for residue-number-system (RNS)-based architectures is proposed. The decoder is based on the Chinese remainder theorem. It decodes a set of residues to its equivalent representation in weighted binary number system. This decoder is flexible since the decoded data can be selected to be either unsigned magnitude or 2's complement binary number. Two different architectures are analyzed; the first one is based on using carry-save adders, while the other is based on utilizing modulo adders. The implementation of both architectures is modular and is based on simple cells, which leads to efficient VLSI realization. The proposed decoder is fast; it has a time complexity of theta (log N), where N is the number of moduli. >

Grounded capacitor current-mode oscillator using single current follower

Abstract: A new configuration for realizing a current-mode oscillator using single positive current-follower is presented. The circuit uses three grounded capacitors and three resistors. The feasibility of obtaining a quadrature oscillator is investigated. >

Basement Tectonics of Saudi Arabia as Related to Oil Field Structures

Abstract: All the oil fields of Saudi Arabia are of the structural type and they all lie in the northeastern part of the country, including the Saudi offshore portion of the Persian Gulf.

Factors affecting a contractor's mark-up size decision in Saudi Arabia

Abstract: Deciding upon the right mark-up to add to an estimate is not an easy task for a contractor. The mark-up must be small enough to ensure a good chance of winning the contract, yet big enough to realize a reasonable profit. The determination of the proper mark-up size entails the evaluation of numerous factors. This study presents 37 factors, with their relative importance to contractors operating in Saudi Arabia, underlying the mark-up size decision. The size of contract and availability of required cash, not competition, labour availability and profitability, are the most important factors that affect mark-up size decision.

Experimental investigations of the vortex flow on delta wings at high incidence

Abstract: It is reported in the literature that strongly asymmetric vortex flow occurs on the lee side of slender delta wings at high incidence, similar to that observed on slender cones, and a boundary is given for the onset of asymmetry vs wing aspect ratio. To study this phenomenon, dye flow-visualization tests were carried out on two slender, sharp-edged delta wings of aspect ratio A = 0.56 and 0.28 up to high incidences in a water tunnel. Another wing with A = 0.56 was studied in a wind tunnel, using a smoke flow-visualization technique. Reynolds numbers based on the root chord in the water tunnel and wind tunnel were Rec — 3.4 x 10 4 and 1.32 x 10 s, respectively. No strongly asymmetric vortex flow was observed in our tests before vortex breakdown occurred on the wing. Subsequent evaluation of flow observations reported elsewhere did not reveal strongly asymmetric vortex flow on slender wings of various planforms. One delta wing reported to exhibit strongly asymmetric vortex configurations; on closer study, it probably had near its apex the shape of something like a thick, elliptic cone, rather than that of a flat, thin delta wing. Theoretical results for inviscid flow past slender cones at incidence strongly suggest that on a thin delta wing no strongly asymmetric vortex flow occurs of the type found on slender, circular, or thick elliptic cones.

Modeling the fate and transport of Al-Ahmadi oil spill

Abstract: Over the period January-May 1991 Iraqi forces, occupying the state of Kuwait, caused a massive amount of oil to be released in the waters of the Arabian Gulf. The volume of oil released may have been as large as 6 × 106 bbls. Most of the oil was released at or near Mina Al-Ahmadi in southern Kuwait. Two mathematical models, GULFSLIK II and OILPOL, were used to simulate the fate and transport of oil spilled at Al-Ahmadi. The oil spill trajectory model GULFSLIK II was used in an operational real time mode to predict the surface trajectory of oil spills at various locations. The real time trajectory analysis was used to support tactical spill response. Short term precictions were made using 7-d wind forecasts. Long term predictions were made using monthly wind averages. Comparisons between predicted trajectories and actual sightings show that GULFSLIK II is reasonably accurate. The oil spill fate and transport model, OILPOL, was applied to compute surface and subsurface distribution of oil, and analyze the fate of the spilled oil. An oil spill size of 4 × 106 bbls was assumed. OILPOLL results were used to support damage assessment studies and environmental impact statements. The distribution of oil on the surface and subsurface layers were obtained daily for a period of 80 d. Oil concentration at strategic locations in the Gulf were also computed. Surface oil distribution as predicted by OILPOL was compared with sighting data. The results show excellent agreement.

Interference between short- and long-distance contributions to b-->sl+l-

Abstract: In this Brief Report we present a simple argument to fix the relative sign of the interference between the short-distance and the resonance amplitudes for the decay $b\ensuremath{\rightarrow}{\mathrm{sl}}^{+}{l}^{\ensuremath{-}}$. Our result agrees with the sign found from independent considerations by O'Donnell and Tung [Phys. Rev. D 43 R2067 (1991)].

Thematic mapping of subtidal coastal habitats in the western Arabian Gulf using Landsat TM data— Abu Ali Bay, Saudi Arabia

Abstract: Landsat-5 data provide information related to bathymetry and bottom type variations as registered by three water-penetrating bands. In this study, band 1 and band 2 data were used for mapping of subtidal coastal habitats in the Abu Ali Bay, Gulf Coast of Saudi Arabia. The method used here is based on eigenvector rotation of the two bands to enhance bottom type variations. The eigenvector rotation reduced the effect of water depth variations on bottom types. The results are presented as a colour-coded image showing five major habitats in Abu Ali Bay.

Flow injection spectrophotometric determination of the antibiotic ciprofloxacin in drug formulations.

Abstract: A flow injection spectrophotometric method for the assay of ciprofloxacin was developed. The method was based on the chelation of iron(III) with the drug in 0.023 mol dm–3 sulfuric acid solution in a 72 cm long coil and the brown–red complex produced was monitored at 447 nm. The super modified simplex computer program was employed for the optimization of the system and chemical parameters with respect to throughput and sensitivity as a measure of system performance. A working range for ciprofloxacin determination of 50–500 ppm for a 110 mm3 sample size with an optimum of 250 samples per hour was achieved with a relative standard deviation of less than 0.92%. The method was successfully applied to the determination of ciprofloxacin in drug formulations.

Design — Construction interface problems in Saudi Arabia

Abstract: During the last decade the construction industry in Saudi Arabia employed 15% of the total labour force and used 19% of energy consumed in the country. Abdulmohsen Al‐Hammad and Sadi Assaf discuss the results of a survey which identified the interface problems in design and construction, and document the lessons to be learned from that boom period

Thermal stability of a platinum aluminide coating on nickel-based superalloys

Abstract: An investigation was carried out to determine the thermal stability of a platinum aluminide coating on the directionally solidified alloy MAR M 002 and its single-crystal version alloy, SRR 99, at 800, 1000 and 1100°C. The morphology, structure and microchemical composition of the coating were characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. In the as-deposited condition, the coating was found to consist of two layers. Most of the platinum was concentrated in the outer coating layer which consisted of a fine dispersion of PtAl2 in a matrix of β-(Ni, Pt)Al containing other elements in solid solution, such as cobalt and chromium. The inner coating layer was relatively free of platinum and consisted essentially of β-NiAl. Exposure at 800°C was found to have no significant effect on the structure and composition of the coating on each alloy. At temperatures ⩾1000°C, however, PtAl2 became thermodynamically unstable and significant interdiffusion occurred between the coating and alloy substrate. After exposure at 1000°C, the components of the outer coating layer were NiAl and Ni3Al. However, after exposure at 1100°C, the outer coating layer consisted only of Ni3Al. Also, after exposure at both temperatures, the composition of the outer coating layer approached that of the inner layer due to interdiffusion. Although the coating on both alloys exhibited similar structural stability at all temperatures investigated, the coating on alloy MAR M 002 was found to develop a more protective scale. This behaviour was correlated with differences in alloy substrate composition particularly rare-earth elements such as hafnium.

High-temperature oxidation behavior of a Ni-Cr-Al-Fe-Y alloy

Abstract: A study was conducted to examine the isothermal oxidation behavior of a wrought Ni-Cr-Al-Fe-Y alloy in air at temperatures in the range of 950–1150°C. Oxidation kinetics were determined from weight-change measurements. Analytical electron microscopy, scanning electron microscopy, and x-ray diffraction were used to characterize the morphology, structure, and composition of the oxide scale. Overall oxidation of the alloy was found to follow parabolic kinetics. Under steady-state conditions, the oxidation reaction appeared to be controlled by diffusional transport in an adherent Y-modified α-Al2O3 scale with an activation energy of about 400 KJ/mol. Yttrium was found to preferentially segregate to grain boundaries of α-Al2O3 which maintained a fine columnar grain structure about 0.05–0.2 μm in size. Based upon the results obtained, it was suggested that the role of Y was to promote the formation of a thin layer of α-Al2O3 with improved mechanical strength.

Aspects of seagrass ecology along the western Arabian Gulf coast

Abstract: Results of semi-quantitative observations and quantitative sampling of seagrasses at coastal and offshore sites along the western Arabian Gulf are presented. Overall seagrass cover (all species together) shows significant positive correlation with latitude, but not with salinity, temperature or depth. The same pattern is shown by Halodule uninervis (Forsk.) Aschers., the dominant species. Mean seagrass biomass ranged from 53–235 g m-2 (dry weight). These values are comparable with biomass estimates from regions in which environmental conditions are generally less extreme than in the Gulf. Seagrass biomass is significantly negatively correlated with depth and sediment grain size. No significant correlation is apparent between seagrass biomass and factors such as season, salinity, or concentrations of nutrients and heavy metals measured. It is pointed out that any correlations observed are not necessarily taken to imply causality.

Bounds on net delays for VLSI circuits

Abstract: The problem of finding net delay bounds for all the nets of VLSI circuits is formulated. A polynomial-time algorithm, IMP, is presented to solve this problem efficiently. Some basic properties of this algorithm are investigated, and proofs are provided. A modification of this algorithm to further improve its time efficiency, is also proposed. Applications of net delay bound algorithm are provided. >

Azimuthally uniform surface-plasma modes in thin metallic cylindrical shells

Abstract: The pure transverse-magnetic (TM)-polarized surface-plasma bound modes of a thin metallic right circular cylindrical shell imbedded in dielectric materials are studied. Two modes are generally found to be supported by the structure. They are analogous to the two modes of the corresponding planar structure of a thin metallic film bound by dielectrics. One of the modes is shown to have sufficiently small loss to make it of potential application in fiber optics. The transcendental equation of the modes generalizes that of the planar geometry by having the cylinder radius as a parameter. The equation is solved exactly in the complex domain for all cases considered. >

Improved approximate analytical solution for generalised diode equation

Abstract: A mathematical function for representing the generalised normalised diode equation is presented. This function, being simple, accurate and, more importantly, continuous, provides solutions for the generalised normalised diode equation which are in excellent agreement with numerical calculations

Simplex-optimized and flow injection spectrophotometric assay of tetracycline antibiotics in drug formulations

Abstract: The modified simplex method was applied to the selection of the proper experimental conditions for the flow injection spectrophotometric determination of tetracycline, chlortetracycline, oxytetracycline and demeclocycline. In the method a 157 mm3 sample volume was injected, for all the compounds, into the carrier stream of iron(III) of concentrations 554, 626, 701 and 447 ppm flowing at rates of 3.72, 4.37, 3.72 and 3.72 cm3 min–1, thus passing through a reaction coil of length 55, 85, 45 and 45 cm for the respective compounds, all in 0.001 mol dm–3 sulfuric acid as an over-all reaction medium. A high sampling frequency of the order of at least 170 h–1 was attained for all the compounds. A high precision with a relative standard deviation of less than 0.9%(n= 5) was also obtained. The accuracy was found to be high as the Student t-values were calculated to be less than the theoretical values when the results were compared with those obtained by the conventional spectrophotometric method. There were no interferences from excipients in dosage forms when the method was applied to pharmaceutical preparations.

Mechanism of carburization of high-temperature alloys

Abstract: An investigation of the mechanism of gaseous carburization in a reducing environment was conducted for selected Fe- and Ni-base alloys. Carburization kinetics were measured as functions of temperature in the range 870–980 °C. Scanning electron microscopy, analytical electron microscopy and X-ray diffractometry were employed for microstructural characterization and microchemical analysis. Changes in mechanical strength produced by carburization were determined from microhardness and tensile property measurements. Kinetic studies indicated that the carburization reaction followed a parabolic rate law. Depending upon the nature of surface scale formed in the presence of a carburizing environment, the rate-determining step of the reaction varied from C diffusion into the alloy in the presence of a carbide scale to that in the presence of an oxide scale. Under reducing carburizing conditions, alloys inherently protected by Cr2O3-base scale were found to develop a surface carbide scale which allowed C to penetrate into the alloy with relative ease and, thus, the carburization kinetics was accelerated. In contrast, an alloy capable of forming Al2O3 developed and maintained a protective surface oxide scale which acted as an effective barrier to C diffusion into the alloy. Degradation of mechanical strength due to precipitation of carbides in the alloy was correlated with the rate of attack and consequently the nature of the surface scale.