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El-Mossalamy E.H.,King Abdelaziz University | Mahmoud W.E.,King Abdelaziz University | Al-Owais A.,King Saud University | Arafa H.M.,University of Tabuk
Chemistry and Technology of Fuels and Oils | Year: 2011

The dielectric parameters of polyvinyl alcohol containing 0-0.8 wt. % vanadium pentoxide are studied in the temperature range 20-150 °C at different frequencies: the dielectric constant, dielectric losses, and tangent of the angle of dielectric losses. Cole-Cole plots are used to determine the static dielectric constant and the dielectric constant at infinitely high frequency. The relaxation time is determined at different frequencies as a function of the tangent of the angle of dielectric losses versus the temperature. It is found that the relaxation properties follow the Arrhenius equation, the activation energy decreases with the vanadium pentoxide content in polyvinyl alcohol. An investigation of the dielectric relaxation as a function of temperature at constant frequency revealed two types of relaxation processes: dipole-segmented motion (α-relaxation) and side-chain dipole group motion (β-relaxation). The ac conductivity in the system polyvinyl alcohol - vanadium pentoxide is explained on the basis of the correlated barrier hopping model. © 2011 Springer Science+Business Media, Inc. Source


Ng J.,University of Alberta | Dubljevic S.,University of Alberta | Aksikas I.,King Abdelaziz University
Proceedings of the American Control Conference | Year: 2012

There are many industrial and biological reaction-diffusion systems which exhibit time-varying features where certain parameters of the system change during the process. The underlying transport-phenomena are often modelled using parabolic partial differential equations (PDEs) with time-varying coefficients which describe the dynamics of the process. Often it is of interest to control this dynamical behaviour such as the regulation of temperature or concentration, and one approach is the use of infinite-dimensional systems theory to represent the PDE models, with time-varying process parameters, as abstract nonautonomous evolution equations on appropriately defined function spaces. In contrast to timeinvariant control problems, the theory for controllability and observability for time-varying systems is less well established. In this work, we consider some pertinent aspects regarding the controllability and observability of nonautonomous infinite-dimensional systems. An example is considered for which the conditions for exact, null, and approximate controllability and observability are verified, and some observations regarding the influence of time-varying input and measurement operators are provided. © 2012 AACC American Automatic Control Council). Source


Ahmed M.,King Abdelaziz University | Ahmed M.,Minia University | El-Sayed N.Z.,Minia University | Ibrahim H.,Minia University | Abdelhady K.,Minia University
Turkish Journal of Physics | Year: 2012

The dynamics of AlGaAs laser diodes under analog intensity modulation are characterized and the associated intensity noise is evaluated. The study is based on numerical solution of the stochastic rate equations of semiconductor lasers. Based on the shape of the modulated laser signal, the modulation dynamics are classified into eight distinct types. Four types are characterized by continuous periodic signals, and three types have periodic pulsing signals. These signals happen to have period doubling or superposed by sub-peaks from the relaxation oscillations of the laser. The last type is chaos, in which the signal is irregular and non-uniform. The noise results show that the relative intensity noise is closest to the quantum level under weak modulation where the laser signal is sinusoidal. LF-RIN is pronounced when the laser emits irregular spike-like pulses under low-frequency strong modulation. The chaotic dynamics dominate the region of strong with modulation frequencies around the relaxation frequency of the laser. © TÜBİTAK. Source


Habib H.S.,King Abdelaziz University
Journal of Pediatric Neurology | Year: 2013

Moyamoya disease is a progressive vascular disease associated with steno-occlusion of the terminal portions of the internal carotid arteries and with several congenital and acquired conditions, including ischemic stroke in young children. This case report describes the discovery of an unusual association between moyamoya disease and type 1 diabetes mellitus in a 9-year-old child presenting with stroke-associated diabetic ketoacidosis. Discovery of this case highlights the importance of considering stroke as well as cerebral edema, the more likely etiology, in the differential diagnosis of neurological deterioration in children with diabetic ketoacidosis, as well as considering moyamoya syndrome in the diagnosis of diabetic children presenting with stroke. © 2013 - IOS Press and the authors. All rights reserved. Source


Ouassila L.,University Mentour | Hassan M.A.,University Mentour | Ahmed Z.,University Mentour | Yacine K.,King Abdelaziz University | Thierry C.,Laboratoire des science Du Genie Chimique
Energy Procedia | Year: 2012

In the present work a new configuration of absorption refrigeration machine based on phase separation has been studied. The main objective is to investigate the performance of this machine, using a number of binary systems (refrigerant absorbent) showing a partial miscibility and having a low critical solution temperature. A computer code has been developed for the calculation of the coefficient of performance (COP) of the machine as well as to study the influence of the operating conditions on this parameter, testing a binary mixture made of methyl diethyl amine (MDEA) as refrigerant and water as absorbent. The obtained results confirm the feasibility of this new cycle which can be regarded as a good alternative to classical cycle with no phase separation. The use of the computer code can be extended to test different working fluids for this machine, for an optimisation of the COP. © 2012 Published by Elsevier Ltd. Source

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