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.
Hanafy T.A.,University of Tabuk
Journal of Applied Physics | Year: 2012
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.
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.
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.