Showing papers by "University of Bahrain published in 1993"

Heavy metals in street and house dust in Bahrain

Abstract: A total of 106 street and household dusts have been sampled throughout Bahrain and analyzed for Pb, Zn, Cd, Ni and Cr using the atomic absorption spectrophotometric method. The sampling sites were divided into seven categories, including the control site. Results showed that dust samples contained significant levels of the metals studied compared with the control values. The mean values for Pb, Zn, Cd, Ni and Cr in street dust were 697.2, 151.8, 72.0, 125.6 and 144.4 μg g−1 respectively, whereas for household dust they were 360.0, 64.4, 37.0, 110.2 and 144.7 μg g−1. These values suggest that motor vehicles form a major source of these metals in dust samples. The values of heavy metals in dust samples in this study were compared with values found in other investigations in various countries. With respect to Ni, elevated concentration could be attributed to smoke from the burning of Kuwait oil fields. Also correlations between metal levels in dust samples for all the metals were investigated. Our results show that heavy metal levels in various sites in Bahrain are similar, which indicate that Bahrain can be considered as one big urban center with high population and traffic density.

Embedding of cycles in arrangement graphs

Abstract: Arrangement graphs have been proposed as an attractive interconnection topology for large multiprocessor systems. The authors study these graphs by proving the existence of Hamiltonian cycles in any arrangement graph. They also prove that an arrangement graph contains cycles of all lengths ranging between 3 and the size of the graph. They show that an arrangement graph can be decomposed into node disjoint cycles in many different ways. >

Embedding Grids, Hypercubes, and Trees in Arrangement Graphs

Abstract: The use of a new topology, called the arrangement graph, as a viable interconnection scheme for parallel and distributed systems, has been recently proposed and examined. The arrangement graphs represent a rich class of generalized star graphs with many attractive properties, In this paper we obtain (1) unit expansion embeddings of a variety of multi-dimensional grids, (2) dilation 1, 2, 3, and 4 embeddings of hypercubes and (3) hierarchical and greedy spanning trees to support broadcasting and personalized communication in arrangement graphs.

Using symbolic execution and data flow criteria to aid test data selection

Abstract: The utilization is described of a data flow path selection criterion in a symbolic execution system. The system automatically generates a subset of program paths according to a certain control flow criterion. This subset is called the ZOT-subset, since it requires paths that traverse loops zero, one and two times. Experience indicates that traversing this subset of program paths is enough to cover most control flow and data flow components of the program. The problem with the ZOT-subset is that it might contain, for large programs, a large number of paths. The number of paths in this subset can be reduced by concentrating on executable paths that cover vital components of programs such as data flow components. This object is achieved by employing a data flow path selection criterion in the system. The system symbolically executes the paths of the ZOT-subset, and creates a system of branch conditions for each one. The user determines infeasible paths by checking the consistency of each system of conditions. The system selects feasible paths from the ZOT-subset that cover the data flow criterion. Solving the systems of conditions of the selected paths provides the user with test data to fulfil the given data flow criterion.

REACTIONS OF ISOPROPYLISOCYANIDE AND t-BUTYLISOCYANIDE WITH COBALT(II) PERCHLORATE AND TETRAFLUOROBORATE

Abstract: Reaction of isopropylisocyanide with CoX2·6H2O (X = ClO4, BF4) in EtOH produced [Co2(CNCHMe2)10X4 · 5H2O, and reaction of t-butylisocyanide, produced [Co(CNCMe3)4H2O]X2·nH2O. The complexes were characterized by IR, electronic spectra, magnetic susceptibility, and molar conductivity. CNCHMe2 complexes are diamagnetic in the solid state and one-electron paramagnetic in solution; this and other data are consistent with dimerization in the solid and dissociation in solution. CNCMe3 complexes are one-electron paramagnetic in the solid and solution states, this being consistent with a monomeric structure.

Acrylamide as an inducer of metabolic activation system (S9) in rats.

Abstract: The S9 fraction was prepared from rats i.p. injected with a single dose of 75 mg/kg acrylamide. The efficiency of the acrylamide induction procedure was verified on Salmonella mutagenicity testing (TA98 and TA100) using a number of known mutagens. These mutagens are aflatoxin B 1 , benzo[α]pyrene, 2-acetylaminofluorene and sodium azide. The activity of the mutagen is measured in terms of histidine revertant numbers which were found to be almost proportional to the concentration of acrylamide-induced S9. The maximum activation of the mutagens (except sodium azide) was recorded using around 50 μl of S9 per plate. The efficiency of our prepared S9 fraction as a metabolic activator for some known mutagens is comparable to that of standard S9. On the basis of our results, acrylamide-induced S9 demonstrated considerable increase in the activation of the tested compounds. Accordingly, acrylamide could be used as an additional procedure for the induction of rat hepatic enzymes (S9).

Solar spectrum distribution and optical depth of Bahrain's sky

Abstract: The solar spectrum of wavelength 350–800 nm has been measured for the four seasons. The intensity of the solar radiation in W m-2 nm-1 has been calculated and used to estimate the monochromatic optical depth of Bahrain's sky. It was found that the optical depth (i.e., extinction coefficient,k) is least in winter and highest in summer. Comparison of the hourly variation of the optical depth between Bahrain's atmosphere and that of Dhahran (Saudi Arabia) shows that the abundance of small size particles in the former is more than in the latter. This causes more extinction effect in Bahrain than in Dhahran, especially in the wavelengths 350–525 nm. The relation betweenk andλ for each season in Bahrain is in the formk =Aλ n , whereA is a constant andn is a negative integer, is reported in this study.

THE INFLUENCE OF Pb, Ni AND V DOPING ON THE CHARACTERISTICS OF HIGH-TcBi-Si-Ca-Cu-O SUPERCONDUCTORS

Abstract: We report on the studies of ac susceptibility, ultrasonic attenuation, superconductivity and some calorimetric measurements on Pb-doped for Bi-site as well as Ni and V substitution for Cu in Bi-Sr-Ca-Cu-O superconductors. It was confirmed that the Bi(Pb)-based glass ceramics (i.e. crystallized glasses) exhibit superconductivity with Tc above 105 K higher than Bi(Ni) with Tc 68 K and Bi(V)-based glasses with Tc 40K. X-ray diffraction analysis revealed that the structure of these materials is Bi-2223 type with a=4.067 A and C=30.768 A. It was found from the temperature dependence of ac complex susceptibility that the coupling nature at grain boundaries of superconducting crystals in the samples obtained was weak, and was improved by increasing the annealing time. Data are discussed for varying Tc of different substituents. Our results on the ultrasonic attenuation revealed a series of relaxation peaks with low activation enthalpies which indicate that electronic defects may be the cause for the relaxation processes.

Studies on the bacterial activity of cobalt(iii) complexes. part iii. cobalt(iii) carboxylate complexes

Abstract: Cobalt(III) complexes of the type [Co(en)2(chel)]X.nH2O where en = ethylenediamine, chel = phthalato = C6H4CO2)2- 2, maleato = (O2CCH = CHCO2)2-, succinato = (O2CCH2CH2CO2)2-, homophthalato = (O2CC6H4(CH2)CO2)2-, citraconato = (O2CC(CH3) = CHCO2)2-, itaconato = (CH2 = C(CO2)CH2CO2)2-, X = NO− 3, Br−, (O2CC6H4CO2H)−, (O2CHC = CHCO2H)−, (O2C(CH2)2CO2H)−, (O2CC6H4(CH2)CO2H)−, (O2CHC = C(CH2)-CO2H)−, and (O2C-CH2−C(= CH2)-CO2H)−, [Co(en)2(malonato)]X.2H2O (where malonato = (O2CCH2CO2)2-, X = Cl−, Br−, and NO− 3) and [Co(en)2CO3]Cl.2H2O have been investigated for their bacterial activity against Escherichia coli B growing on EMB agar and in minimal glucose media both in lag and log phases. Among the most active are where chel = phthalato and homophthalato. The effects are distinct from those known for compounds of Pt, e.g., cis−[Pt(NH3)2Cl2] and rhodium, e.g., trans−[Rh(C5H5N)4, Cl2].6H2O. Antagonisms are reported.

Liquid-liquid extraction and spectrophotometric determination of uranium with n-phenyl-3-styrylacrylohydroxamic acid (PSAHA)

Abstract: A rapid, selective and sensitive liquid-liquid extraction and spectrophotometric method for the separation and microgram determination of uranium using PSAHA is described. Uranium is extracted with PSAHA into chloroform at pH 6.0–6.8. The U-PSAHA chelate is orange red in color having maximum absorbance at 410 nm and molar absorptivity 1.2·104l·mol−1·cm−1. The system obeys Beer's Law in the range of 1.2 to 22.00 ppm of uranium. The uranium is determined in sea water and rock samples.

Film-thickness effects on the optical and electrical properties of Cu-GeO2 thin cermet films

Abstract: The effect of film thickness on the optical and electrical properties of Cu-30 wt % GeO2-70 wt % thin cermet films prepared by electron-beam deposition at about 10−3 Pa and at a substrate temperature of 300 K is reported. The ultraviolet, visible and direct current (d.c.) conductivity results are analysed with the aim of determining the optical band gap,E opt, the width of the band tails,E e, and the d.c. thermal activation energy,E a. It was found that the optical energy gap increases with increasing thickness and that the absorption was due to indirect transitions ink-space. The general feature of the absorption edge remains similar for both unannealed and annealed films, but annealing has the effect of decreasingE opt. The d.c. conductivity results show thatE a decreases with increasing thickness. From a knowledge ofE opt andE a, a probable model of the electronic band structure in Cu-GeO2 thin films has been suggested.

Optimum control strategies for transient as well as oscillatory instability of power systems

Abstract: A coordinated dynamic braking strategy and excitation control for arresting the first swing instability as well as subsequent oscillations in a power system is proposed. Comparison is made between braking resistor, resistor-reactor and resistor-capacitor strategies with and without excitation control. The control strategies are obtained in terms of system states and other measurable quantities. Assumptions that the reference machine is large and that it is not equipped with dynamic braking lead to a simpler control strategy. The excitation strategy can also be significantly simplified by relaxing the constraints on the rotor angle. Computer simulation of a multimachine power system shows that a coordinated application of braking resistor-capacitor and excitation strategies controls the transients effectively. >

Subject relationship between articles determined by co-occurrence of keywords in citing and cited titles

Abstract: It is assumed that a paper which cites an earlier document shares a subject relationship with that particular document. In order to determine if this assumption is valid, a study was conducted by analysing 1000 articles from the Science Citation Index k and Social Sciences Citation Inde®. These articles were selected in ten different disciplines by using a purposive sampling technique. Various Spearman's Correlation Coefficient tests were computed to find out if a subject relationship existed between the Articles which have the same keywords in their titles (Parent Articles and Related Records). Through the analysis the hypothesis has been veri fied showing that there is a relationship between the articles which are citing the same references. This was determined by co-occurrences of the same keywords among the shared refer ences. However, there are some unique differences in the science and the social science disciplines that exist in these two databases.

Synthesis Of Monosubstituted Pentakis(2, 6-Diethylphenyliso-Cyanide)Cobalt(I) Complexes With Bidentate Tertiary Phosphine Ligands. Ii. Bimetallic Complexes

Abstract: Reaction of bidentate tertiary phosphines with excess [Co(CNR)5]BF4, or reaction of [Co(CNR)4L-L]BF4 with excess [Co(CNR)5]BF4, leads to bimetallic complexes of the form, [(RNC)4CoL-LCo(CNR)4](BF4)2, R = 2,6-Et2C6H3, L-L = p-Ph2PC6H4PPh2, Ph2PC═CPPh2, Me2PCH2CH2PMe2, Ph2PCH2CH2PPh2, Ph2PCH2CH2CH2PPh2. Comparison of the v(− N═C) IR patterns, electronic spectra, and molar conductivity values of these bimetallic complexes with data for other Co(I)-organoisocyanide complexes indicates that the two -Co(CNR)4 moieties are almost totally independent of each other. Recorded λmax values are the same as for the [Co(CNR)4L-L]BF4 complexes, but the ∊ values, although very large, are less than double. ΛM values in acetone, and probably also in CH2Cl2, are better interpreted as twice the normal conductivity for 1:1 electrolytes than conductivity for 2:1 electrolytes.

The Pedagogical Needs of Low Achievers.

Abstract: Expose sur le probleme de l'echec et des sous-performances dans l'apprentissage des langues etrangeres. Probleme associe a une absence de motivation et a une attitude de rejet plutot qu'a un manque d'aptitude. Proposition de suggestions susceptibles d'aider les enseignants a supprimer certains obstacles frequents lors du processus d'apprentissage.

Determination of ground conductivity in Bahrain by the ground-wave attenuation method

Abstract: The authors discusses the measurement of equivalent ground conductivity, which plays an important role in ground-wave radio transmission. The author concludes that the humidity (moisture content) of soils is a major factor in determining the conductivity values. Measurements of conductivity as a function of moisture content show very low values for dried samples, compared with moistened ones. There is no significant diurnal or seasonal variation. The author believes this is due to the fact that Bahrain is a sand dominated country, and sand is moisture-regain sensitive. >

Measurement of capacitance using identical oscillators

Abstract: A novel method for the measurement of (extremely small) capacitances is presented. Two oscillators are used, both operate at the same frequency; but the insertion of an unknown capacitor in the circuit changes the frequency of one of the oscillators while the other is used as the reference. This resultant change in the frequency has a linear relationship with the unknown capacitance. The use of identical oscillators makes the readout circuitry much simpler and results in significant hardware savings. A meter for the 99 pF range with l00 fF resolution and a worst case accuracy of better than 2% was constructed to verify the validity of the principle. However a resolution in the sub-femtofarad region is highly feasible, which makes the method suitable for transducer applications. With a choice of waveform generators available, the method is simple to implement with only a few off-the-shelf components and gives an above average performance.