Tabuk, Saudi Arabia
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Aly W.I.A.,University of Tabuk | Aly W.I.A.,Helwan University
Energy Conversion and Management | Year: 2014

A computational fluid dynamics (CFD) study has been carried out to study the heat transfer and pressure drop characteristics of water-based Al 2O3 nanofluid flowing inside coiled tube-in-tube heat exchangers. The 3D realizable k-ε turbulent model with enhanced wall treatment was used. Temperature dependent thermophysical properties of nanofluid and water were used and heat exchangers were analyzed considering conjugate heat transfer from hot fluid in the inner-coiled tube to cold fluid in the annulus region. The overall performance of the tested heat exchangers was assessed based on the thermo-hydrodynamic performance index. Design parameters were in the range of; nanoparticles volume concentrations 0.5%, 1.0% and 2.0%, coil diameters 0.18, 0.24 and 0.30 m, inner tube and annulus sides flow rates from 2 to 5 LPM and 10 to 25 LPM, respectively. Nanofluid flows inside inner tube side or annular side. The results obtained showed a different behavior depending on the parameter selected for the comparison with the base fluid. Moreover, when compared at the same Re or Dn, the heat transfer coefficient increases by increasing the coil diameter and nanoparticles volume concentration. Also, the friction factor increases with the increase in curvature ratio and pressure drop penalty is negligible with increasing the nanoparticles volume concentration. Conventional correlations for predicting average heat transfer and friction factor in turbulent flow regime such as Gnielinski correlation and Mishra and Gupta correlation, respectively, for helical tubes are also valid for the tested nanofluids which suggests that nanofluids behave like a homogeneous fluid. © 2013 Elsevier Ltd. All rights reserved.


Parsegian A.,Medical University of South Carolina | See R.E.,Medical University of South Carolina | See R.E.,University of Tabuk
Neuropsychopharmacology | Year: 2014

Methamphetamine (meth) addicts often exhibit enduring cognitive and neural deficits that likely contribute to persistent drug seeking and the high rates of relapse. These deficits may be related to changes in the prefrontal cortex (PFC) and its glutamatergic projections to the nucleus accumbens (NAc). Here, we performed in vivo microdialysis in the PFC and NAc in rats following either meth self-administration or yoked-saline control histories to assess baseline glutamate (GLU) levels, or reinstatement-evoked GLU and dopamine (DA) efflux in both regions simultaneously under cue-induced, meth-primed, or combined cues+meth reinstatement conditions. Our results show that meth self-administration (1) reduced basal GLU levels in both the dmPFC and NAc, (2) concurrently increased dmPFC and NAc GLU efflux during reinstatement, and (3) increased DA efflux in the dmPFC, but not in the NAc, under all reinstatement conditions when compared with yoked-saline controls. These data demonstrate for the first time that a history of psychostimulant self-administration alters GLU homeostasis not only in the NAc, but also in the dmPFC, its primary GLU projection source. Furthermore, combined cues+meth-primed reinstatement conditions produced the most pronounced increases in mPFC and NAc extracellular GLU, suggesting that the cue and meth prime conditions are additive in promoting reinstatement. Finally, increased efflux of DA in the dmPFC, but not in the NAc, across reinstatement conditions suggests that DA release in the dmPFC may be an important mediator of drug seeking initiated by multiple relapse triggers.


Elgala H.,Jacobs Engineering | Mesleh R.,University of Tabuk | Haas H.,University of Edinburgh
IEEE Communications Magazine | Year: 2011

In recent years, interest in optical wireless (OW) as a promising complementary technology for RF technology has gained new momentum fueled by significant deployments in solid state lighting technology. This article aims at reviewing and summarizing recent advancements in OW communication, with the main focus on indoor deployment scenarios. This includes a discussion of challenges, potential applications, state of the art, and prospects. Related issues covered in this article are duplex transmission, multiple access, MAC protocols, and link capacity improvements. © 2011 IEEE.


Fourier transform infrared (FTIR) spectrum dielectric constant, ε', loss tangent, tan(δ), electric modulus, M*, and ac conductivity, σ ac, of pure polyvinyl alcohol (PVA) as well as La-, Gd-, and Er-PVA doped samples have been carried out. The dielectric properties have been studied in the temperature and frequency ranges; 300-450 K and 1 kHz-4 MHz, respectively. FTIR measurements reveal that La 3+, Gd 3+, and Er 3+ ions form complex configuration within PVA structure. Two relaxation processes, namely, ρ and α were observed in pure PVA sample. The first process is due to the interfacial or Maxwell-Wagner-Sillers polarization. The second one is related to the micro-Brownian motion of the main chains. For doped PVA samples, α-relaxation process splits into α a and α c. This splitting is due to the segmental motion in the amorphous (α a) and crystalline (α c) phases of PVA matrix. Electric modulus analysis was discussed to understand the mechanism of the electrical transport process. The behavior of ac conductivity for all PVA samples indicates that the conduction mechanism is correlated barrier hopping. © 2012 American Institute of Physics.


Sadiq M.,University of Tabuk
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

The elegant predictions of loop quantum gravity are obscured by the free Immirzi parameter (. γ). Dreyer (2003), considering the asymptotic quasinormal modes spectrum of a black hole, proposed that γ may be fixed by letting the j=. 1 transitions of spin networks as the dominant processes contributing to the black hole area, as opposed to the expected j=. 1/2 transitions. This suggested that the gauge group of the theory might be SO(3) rather than SU(2). Corichi (2003), maintaining SU(2) as the underlying gauge group, and invoking the principle of local fermion-number conservation, reported the same value of γ for j=. 1 processes as obtained by Dreyer. In this note, preserving the SU(2) structure of the theory, and considering j=. 1 transitions as the dominant processes, we point out that the value of γ is in fact twice the value reported by these authors. We arrive at this result by assuming the asymptotic quasinormal modes themselves as dynamical systems obeying SU(2) symmetry. © 2015 The Author.


Mansour H.E.,University of Tabuk | Dillon T.,Curtin University Australia
IEEE Transactions on Services Computing | Year: 2011

In this paper, we propose a service-oriented reliability model that dynamically calculates the reliability of composite web services with rollback recovery based on the real-time reliabilities of the atomic web services of the composition. Our model is a hybrid reliability model based on both path-based and state-based models. Many reliability models assume that failure or error arrival times are exponentially distributed. This is inappropriate for web services as error arrival times are dependent on the operating state including workload of servers where the web service resides. In this manuscript, we modify our previous model (for software based on the Doubly Stochastic Model and Renewal Processes) to evaluate the reliability of atomic web services. In order to fix our idea, we developed the case of one simple web service which contains two states, i.e., idle and active states. In real-world applications, where web services could contain quite a large number of atomic services, the calculus as well as the computing complexity increases greatly. To limit our computing efforts and calculus, we chose the bounded set techniques that we apply using the previously developed stochastic model. As a first type of system combination, we proposed to study a scheme based on combining web services into parallel and serial configurations with centralized coordination. In this case, the broker has an acceptance testing mechanism that examines the results returned from a particular web service. If it was acceptable, then the computation continues to the next web service. Otherwise, it involves rollback and invokes another web service already specified by a checkpoint algorithm. Finally, the acceptance test is conducted using the broker. The broker can be considered as a single point of failure. To increase the reliability of the broker introduced in our systems and mask out errors at the broker level, we suggest a modified general scheme based on Triple modular redundancy and N-version programming. To imitate a real scenario where errors could happen at any stage of our application and improve the quality of Service QoS of the proposed model, we introduce fault-tolerance techniques using an adaption of the recovery block technique. © 2011 IEEE.


Asad J.H.,University of Tabuk
Journal of Statistical Physics | Year: 2013

The equivalent resistance between the origin and the lattice site (2n,0,0), in an infinite Face Centered Cubic (FCC) network consisting from identical resistors each of resistance R, has been evaluated analytically and numerically. The asymptotic behavior of the equivalent resistance has been also investigated. Finally, some numerical values for the equivalent resistance are presented. © 2013 Springer Science+Business Media New York.


Ebaid A.E.,University of Tabuk
Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences | Year: 2010

Many problems in applied mathematics and engineering are usually formulated as singular two-point boundary value problems. A well-known fact is that the exact solutions in closed form of such problems were not obtained in many cases. In this paper, the exact solutions for a class of nonlinear singular two-point boundary value problems are obtained to the first time by using Adomian decomposition method. © 2010 Verlag der Zeitschrift für Naturforschung, Tübingen.


El Minshawy O.,University of Tabuk
Saudi journal of kidney diseases and transplantation : an official publication of the Saudi Center for Organ Transplantation, Saudi Arabia | Year: 2014

The purpose of this study was to determine the prevalence, etiology and risk factors of treated end-stage renal disease (ESRD) in the region of Tabuk, Saudi Arabia. We studied 460 renal replacement therapy patients through a review of medical records and patient interviews and obtained patient demographics, family history, risk factors for ESRD, environmental exposure to toxins, work conditions, social history and causes of death. The estimated prevalence of treated ESRD was 460 per million populations (PMP); 350 (76%) were treated by hemodialysis, 30 (7%) by peritoneal dialysis and 80 (17%) by kidney transplantation. The mean age was 48 ± 17 years, body mass index was 25 ± 2 kg/m 2 and the male vs. female ratio was 64% vs. 36%. Most patients (55%) were living in rural areas. Etiology of the ESRD was unknown in 33%, hypertension in 24%, chronic glomerulonephritis in 8%, obstructive uropathy in 3.5%, analgesic nephropathy in 5%, Bilhaziasis in 0.5%, chronic pyelonephritis in 2% and diabetic nephropathy in 18%. Other causes such as gouty nephropathy, collagen diseases, toxemia of pregnancy and lupus nephritis constituted 6% of the cases. We conclude that the epidemiology of the treated ESRD in Tabuk area is similar to that in Egypt, but very different from that in the United States.


Ebaid A.,University of Tabuk
Computers and Mathematics with Applications | Year: 2014

In applied science, the exact solution (when available) for any physical model is of great importance. Such exact solution not only leads to the correct physical interpretation, but also very useful in validating the approximate analytical or numerical methods. However, the exact solution is not always available for the reason that many authors resort to the approximate solutions by using any of the analytical or the numerical methods. To ensure the accuracy of these approximate solutions, the convergence issue should be addressed, otherwise, such approximate solutions inevitably lead to incorrect interpretations for the considered model. Recently, several peristaltic flow problems have been solved via the homotopy perturbation method, which is an approximate analytical method. One of these problems is selected in this paper to show that the solutions obtained by the homotopy perturbation method were inaccurate, especially, when compared with the exact solutions provided currently and also when compared with a well known accurate numerical method. The comparisons reveal that great remarkable differences have been detected between the exact current results and those approximately obtained in the literatures for the temperature distribution and the nano-particle concentration. Hence, many similar problems that have been approximately solved by using the homotopy perturbation method should be re-investigated by taking the convergence issue into consideration, otherwise, the published results were really incorrect. © 2014 Elsevier Ltd. All rights reserved.

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