Al Ain, United Arab Emirates
Al Ain, United Arab Emirates

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Khaleel A.,UAEU | Nawaz M.,UAEU | Al-Hadrami S.,UAEU | Greish Y.,UAEU | Saeed T.,FHMS
Microporous and Mesoporous Materials | Year: 2013

Transition-metal-doped γ-alumina with various dopant concentrations was prepared by straightforward template-free sol-gel method. The presence of dopant metal ions, generally, enhanced the gel formation and their behavior was dependent on the nature of the metal ion and its concentration. Certain ions, especially Fe3+, resulted in rapid formation of a transparent gel upon hydrolysis. The prepared doped γ-alumina powders weakly crystalline at low dopant ion concentrations, 2%, and became completely amorphous at a concentration of 10%. The morphology of the particles was also dependent on the dopant concentration. While dopant concentration of 2% resulted in nano-particles with significant amount of inter-particle mesopores, 10% concentration led to significant aggregation into larger particles. The prepared doped γ-Al2O3 as well as the undoped γ-Al2O3 showed high surface areas and pore volumes which were largely dependent on the nature of the dopant metal ions and on their concentrations. While composites with low dopant concentration, 2%, exhibited surface areas and pore volumes comparable to those of undoped γ-alumina, a considerable decrease was associated with higher concentrations. The changes in textural properties were referred to the evident enhanced sintering associated with high dopant concentrations. © 2012 Elsevier Inc. All rights reserved.

Janajreh I.,Masdar Institute of Science and Technology | Su L.,Masdar Institute of Science and Technology | Alan F.,UAEU
Renewable Energy | Year: 2013

Annual wind data at Masdar City (24.4202° N, 54.6132° E) has been recorded in attempt to assess wind energy potential. Thereby, accurate wind energy production can be assessed for a given region. The vertical wind profile is inferred and was appropriately fitted with power law profile. The spectrum of the temporal data is obtained which exhibits turbulent type. Investigation of high resolution temporal records also emphasized the turbulence, non-periodicity, and intermittency of the wind data. Consequently, frequency-scale wavelet decomposition is carried out, and intermittency of the data is identified. The measured wind capacity categorized Masdar City as poor wind region. It is followed by fitting the measured wind data with the maximum likelihood Weibull distribution. The power curves of two sizes of horizontal axis wind turbines (HAWTs) are coupled with the Weibull distribution. The annual energy production was found to be 3307.08 MWh and 28.73 MWh at the height of 50 m for the large and small turbine, respectively. Considering the turbine efficiency and the return on the investment for the current case study, results are in favor of small size HAWT deployment, i.e. 3.5 KW Windspot, over the larger size. © 2012.

Khaleel A.,UAEU | Shehadi I.,University of Sharjah | Al-Marzouqi A.,UAEU
Fuel Processing Technology | Year: 2011

Mesoporous γ-alumina, mp-γ-Al2O3, possessing surface area around 385 m2/g and total pore volume of 2.0 cm3/g was prepared via template-free sol-gel synthesis. The catalytic activity of the prepared alumina for the conversion of chloromethane to dimethyl ether, DME, in the presence of water or methanol was studied in the temperature range of 170-450 °C employing FTIR spectroscopy. In the absence of water and methanol, the fresh surface of mp-γ-Al2O 3 showed 100% conversion of chloromethane to DME at temperatures between 250 and 350 °C. However, rapid deactivation of the catalyst resulted in a sharp decrease in the conversion to < 5% within a few minutes of reaction. The catalytic activity was noticeably enhanced by adding water vapor to the gas feed resulting in higher conversions to DME and methanol. The catalytic activity and DME selectivity were further enhanced in the presence of methanol instead of water. In the temperature range of 200-300 °C, complete conversions were obtained at the beginning of reactions before they declined to values between 31 and 45% depending on the reaction temperature. It was proposed that the surface hydroxyl groups are the active sites where chloromethane molecules dissociatively adsorb forming adsorbed methoxy ion intermediates. The adsorption of molecular methanol regenerates the surface hydroxyl groups and enhances the formation of adsorbed methoxy ions on the surface which react further with chloromethane or methanol molecules to produce more DME. © 2011 Elsevier B.V.

Hajji M.A.,UAEU | Allan F.M.,UAEU
AIP Conference Proceedings | Year: 2012

Homotopy analysis method (HAM) has been employed recently by many authors to solve nonlinear problems, in particular nonlinear initial and boundary values problems. Such nonlinear problems are usually derived from physical problems such as fluid mechanics; heat transfer, boundary layer equations and many others. In the suggested work we will extend the use of the HAM to solve a certain class of boundary value problems. Focus will be on multi-layer boundary problems. Examples of these kind of problems include fluid flow through multi-layer porous media. © 2012 American Institute of Physics.

Allan F.M.,UAEU | Hajji M.A.,UAEU
AIP Conference Proceedings | Year: 2012

The present article discusses the characteristics of Newtonian water-base-Copper nano-fluid flowing over an infinite flat plate moving with a constant velocity in the direction of the flow. The non-classical similarity transformation is employed to transform the Navier-Stokes equation into a nonlinear ordinary differential equation with specific boundary conditions. The Homptopy analysis method (HAM) is employed to solve the resulting nonlinear differential equation to study the effects of the nanoparticle volume fraction and wall velocity on the flow velocity profile, the boundary layer thickness and the local skin friction coefficient. The existence and non-uniqueness of the solution as a function of the wall velocity will be also discussed. © 2012 American Institute of Physics.

Powders of xerogel γ-Al2O3 doped with various concentrations of Cr3+ and Cu2+ (M/M + Al molar fraction = 0.75-10%) were prepared via a sol-gel method. Cr3+ and Cu 2+ precursors (acetylacetonate, nitrate or chloride) were added to 0.12 M 2-propanol solution of aluminum tri-sec-butoxide (ASB) and hydrolysis was performed using a H2O/ASB molar ratio of 4.7. The effect of the dopant precursor on structural, textural and morphological properties was studied. Employing acac precursors resulted in unique properties after calcination at 500 °C including high surface areas, as high as 455 m 2/g, homogeneous mesopores, 3-12 nm, and amorphous powders (5-10 nm particles in diameter). On the other hand, the acac precursor enhanced the resistance to sintering mainly at higher metal loads (10%) and elevated temperature (800 °C). Nevertheless, the solids issued from nitrate and chloride precursors exhibited lower surface areas at high metal loads, and lower resistance to sintering. © 2013 Elsevier Ltd.

Santagati P.,UAEU | Beiu V.,UAEU
Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering, LNICST | Year: 2014

The aim of this paper is to investigate how the length of communication links could affect the reliability during operations, by analysing how the Johnson-Nyquist (thermal) noise on the links affects the probability of failure (defined as the probability of switching) of devices/switches scaled to the limit like, e. g., ion channels but also nanoscale CMOS transistors. To this end, we will consider classical CMOS circuits, and base our analysis on statistical considerations. In particular, our aim is to look for the existence of an optimum wire/link length in this context, which would maximize the reliability of the simplest system formed by a communication link (wire) driving a switch (transistor or ion channel). © Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2014.

El-Maaddawy T.A.,UAEU | Sherif E.-S.I.,Al Wasl Al Jadeed Consultants AWAJ
Journal of Composites for Construction | Year: 2014

This paper aims to investigate the structural response of concrete corbels reinforced internally with steel rebars and externally with carbon fiber-reinforced polymer (CFRP) composite sheets. Nine specimens were constructed and tested. Test parameters included the amount of internal longitudinal steel rebars and configuration of the external composite sheets. Nine two-dimensional finite-element (FE) models were developed, assuming a perfect bond between the CFRP and concrete. Three additional FE models were developed in which an interfacial bond stress-slip model was adopted between the diagonal CFRP reinforcement and the concrete. The external CFRP composite reinforcement resulted in up to 40% increase in the load capacity. The contribution of the external CFRP reinforcement to the load capacity decreased with an increased amount of internal steel rebars. The addition of primary longitudinal CFRP sheets in a direction parallel to the primary steel rebars reduced the steel strains and increased the yield and ultimate loads. The inclusion of secondary CFRP longitudinal reinforcement at the midheight of the corbels did not result in additional strength gain. The diagonal CFRP reinforcement restricted growth and widening of the shear cracks, and hence, increased the gain in the load capacity. The numerical load capacity was in the range of 10% error band. The numerical crack pattern, deflection response, and steel and CFRP strain responses were in good agreement with those measured experimentally. The integration of the interfacial bond stress-slip model in the FE analysis between the diagonal CFRP reinforcement and concrete resulted in more conservative/accurate predictions for the structural response. © 2013 American Society of Civil Engineers.

Khaleel A.,UAEU | Al-Marzouqi A.,UAEU
Materials Letters | Year: 2012

Aerogel chromium-iron mixed oxide with equimolar amounts of both metals was prepared by a sol-gel method using nitrate salts of both metals. Propylene oxide was used as an efficient gelation promoter and supercritical CO 2 was employed for solvent extraction from the gel. The calcined mixed oxide showed significantly higher surface areas, larger pore volume, and enhanced thermal stability as compared with its xerogel counterpart and the corresponding single-metal oxides. Textural properties were compared at various calcination temperatures and unique textural properties were observed after calcinations at 350 °C. © 2011 Elsevier B.V. All rights reserved.

Khaleel A.,UAEU | Shehadi I.,University of Sharjah | Al-Marzouqi A.,UAEU
Materials Letters | Year: 2012

Ti-doped alumina with unique textural properties was prepared via sol-gel method using alkoxide precursors in toluene and 2-propanol without an acid catalyst. The composites possessed high surface areas, 400-430 m 2/g and large pore volumes, as high as 2.68 cm 3/g, after calcinations at 500 °C. The composites also retained high surface areas and large pore volumes after calcinations at elevated temperatures. The textural properties of the composites were dependent on the composition, the solvent and the presence of an acid catalyst. © 2011 Elsevier B.V. All rights reserved.

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