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Search Results: 1 - 10 of 18484 matches for " Ali Ghrayeb "
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On the Construction of Skew Quasi-Cyclic Codes
Taher Abualrub,Ali Ghrayeb,Nuh Aydin,Irfan Siap
Mathematics , 2008,
Abstract: In this paper we study a special type of quasi-cyclic (QC) codes called skew QC codes. This set of codes is constructed using a non-commutative ring called the skew polynomial rings $F[x;\theta ]$. After a brief description of the skew polynomial ring $F[x;\theta ]$ it is shown that skew QC codes are left submodules of the ring $R_{s}^{l}=(F[x;\theta ]/(x^{s}-1))^{l}.$ The notions of generator and parity-check polynomials are given. We also introduce the notion of similar polynomials in the ring $F[x;\theta ]$ and show that parity-check polynomials for skew QC codes are unique up to similarity. Our search results lead to the construction of several new codes with Hamming distances exceeding the Hamming distances of the previously best known linear codes with comparable parameters.
A Stochastic Geometry Based Approach to Modeling Interference Correlation in Cooperative Relay Networks
Young Jin Chun,Simon L. Cotton,Mazen O. Hasna,Ali Ghrayeb
Mathematics , 2015,
Abstract: Future wireless networks are expected to be a convergence of many diverse network technologies and architectures, such as cellular networks, wireless local area networks, sensor networks, and device to device communications. Through cooperation between dissimilar wireless devices, this new combined network topology promises to unlock ever larger data rates and provide truly ubiquitous coverage for end users, as well as enabling higher spectral efficiency. However, it also increases the risk of co-channel interference and introduces the possibility of correlation in the aggregated interference that not only impacts the communication performance, but also makes the associated mathematical analysis much more complex. To address this problem and evaluate the communication performance of cooperative relay networks, we adopt a stochastic geometry based approach by assuming that the interfering nodes are randomly distributed according to a Poisson point process (PPP). We also use a random medium access protocol to counteract the effects of interference correlation. Using this approach, we derive novel closed-form expressions for the successful transmission probability and local delay of a relay network with correlated interference. As well as this, we find the optimal transmission probability $p$ that jointly maximizes the successful transmission probability and minimizes the local delay. Finally numerical results are provided to confirm that the proposed joint optimization strategy achieves a significant performance gain compared to a conventional scheme.
On Modeling Heterogeneous Wireless Networks Using Non-Poisson Point Processes
Young Jin Chun,Mazen Omar Hasna,Ali Ghrayeb,Marco Di Renzo
Computer Science , 2015,
Abstract: Future wireless networks are required to support 1000 times higher data rate, than the current LTE standard. In order to meet the ever increasing demand, it is inevitable that, future wireless networks will have to develop seamless interconnection between multiple technologies. A manifestation of this idea is the collaboration among different types of network tiers such as macro and small cells, leading to the so-called heterogeneous networks (HetNets). Researchers have used stochastic geometry to analyze such networks and understand their real potential. Unsurprisingly, it has been revealed that interference has a detrimental effect on performance, especially if not modeled properly. Interference can be correlated in space and/or time, which has been overlooked in the past. For instance, it is normally assumed that the nodes are located completely independent of each other and follow a homogeneous Poisson point process (PPP), which is not necessarily true in real networks since the node locations are spatially dependent. In addition, the interference correlation created by correlated stochastic processes has mostly been ignored. To this end, we take a different approach in modeling the interference where we use non-PPP, as well as we study the impact of spatial and temporal correlation on the performance of HetNets. To illustrate the impact of correlation on performance, we consider three case studies from real-life scenarios. Specifically, we use massive multiple-input multiple-output (MIMO) to understand the impact of spatial correlation; we use the random medium access protocol to examine the temporal correlation; and we use cooperative relay networks to illustrate the spatial-temporal correlation. We present several numerical examples through which we demonstrate the impact of various correlation types on the performance of HetNets.
Ultrastructural Identification of the Basal-Granulated Cells in the Duodenum of Albino Rat  [PDF]
Ali Hassan A. Ali
Open Journal of Gastroenterology (OJGas) , 2014, DOI: 10.4236/ojgas.2014.47041
Abstract: The fine structure of the crypt epithelium of the duodenal mucosa in albino rats was studied to represent the types and distribution of the basal-granulated or endocrine cells. Twenty male animals were used. Perfusion-fixation was made and samples of duodenal mucosa were taken and processed to prepare epon-embedded specimens for examination by a transmission electron microscope. Cells containing membrane-bound granules were seen in the crypt epithelium. They were identified to be basal-granulated cells. Six different types of such cells were demonstrated. All of the cells were of the closed type. The possible functional significance of these closed cell types was discussed. Correlation among the distributions of such cells in the intestine of albino rat might enable the physiologists, internists and other research workers to study several biologically active peptides with well-established functions other than those which have long been investigated.
Hepatoprotective Effect of Green Tea Extract against Cyclophosphamide Induced Liver Injury in Albino Rats  [PDF]
Ali Hassan A. Ali
Forensic Medicine and Anatomy Research (FMAR) , 2018, DOI: 10.4236/fmar.2018.62002
Abstract: Background: Green tea intake is accompanied with a lower incidence of cardiovascular disease, cancer and neurodegenerative disorders; hence green tea extract has been included as dietary supplement along with other supplements and multivitamins. Aim of the Work: Studying the effect of cyclophosphamide administration on the liver of adult male albino rats and the possible protective role of green tea extract. Material and Methods: The current study was carried out on 45 adult male albino rats. They were divided into three equal groups (each included 15 rats). Group I (control group) was injected intraperitoneally with normal saline at a dosage of 0.5 mg/kg body weight twice weekly for 9 weeks. Group II was injected intraperitoneally with cyclophosphamide (CP) (150 mg/kg/day) for two weeks. Group III: rats received green tea extracts orally (50 mg/kg/day) for three weeks, and then continued for further two weeks concomitantly with intraperitoneally cyclophosphamide (CP) injected (150 mg/kg/day). Results: Rats exposed to cyclophosphamide (CP) showed several histological and histochemical changes in their liver. These changes were improved by using green tea. Conclusion: The present work showed that green tea had preventive and therapeutic effect upon livers of albino rats after they were exposed to CP.
A Primal-Dual Simplex Algorithm for Solving Linear Programming Problems with Symmetric Trapezoidal Fuzzy Numbers  [PDF]
Ali Ebrahimnejad
Applied Mathematics (AM) , 2011, DOI: 10.4236/am.2011.26089
Abstract: Two existing methods for solving a class of fuzzy linear programming (FLP) problems involving symmetric trapezoidal fuzzy numbers without converting them to crisp linear programming problems are the fuzzy primal simplex method proposed by Ganesan and Veeramani [1] and the fuzzy dual simplex method proposed by Ebrahimnejad and Nasseri [2]. The former method is not applicable when a primal basic feasible solution is not easily at hand and the later method needs to an initial dual basic feasible solution. In this paper, we develop a novel approach namely the primal-dual simplex algorithm to overcome mentioned shortcomings. A numerical example is given to illustrate the proposed approach.
Application of Linear Model Predictive Control and Input-Output Linearization to Constrained Control of 3D Cable Robots  [PDF]
Ali Ghasemi
Modern Mechanical Engineering (MME) , 2011, DOI: 10.4236/mme.2011.12009
Abstract: Cable robots are structurally the same as parallel robots but with the basic difference that cables can only pull the platform and cannot push it. This feature makes control of cable robots a lot more challenging compared to parallel robots. This paper introduces a controller for cable robots under force constraint. The controller is based on input-output linearization and linear model predictive control. Performance of input-output linearizing (IOL) controllers suffers due to constraints on input and output variables. This problem is successfully tackled by augmenting IOL controllers with linear model predictive controller (LMPC). The effecttiveness of the proposed method is illustrated by numerical simulation.
A Study on Wear Resistance, Hardness and Impact Behaviour of Carburized Fe-Based Powder Metallurgy Parts for Automotive Applications  [PDF]
Ali Emamian
Materials Sciences and Applications (MSA) , 2012, DOI: 10.4236/msa.2012.38073
Abstract: In order to study the mechanical and triboloical properties of powder metallurgy (PM) parts under different process parameters, the specimens were used in pack carburizing processes. These specimens made from industrial test pieces were carburized in a powder pack for about two to five hours at a temperature of about 850?C - 950?C. The effects of austenitization and quenching are investigated on some specimens. Also the wear tests are performed by means of a pin-on-disc tribotester using roll bearing steel as the counterface material. The results indicate that by appropriate selection of process parameters, it is possible to obtain high wear resistance along with moderate toughness. It is concluded that surface treatments increases the wear resistance and performance of PM parts in service conditions. By increasing the role of PM in industry which resulted from their ability to produce the complex shapes, high production rate, and dimension accuracy of final products, they need to be heat treated. Carburizing method was selected as a surface hardening method for PM parts. Results of wear and hardness show considerable enhancement in mechanical properties of PM parts.
Influence of Ferric and Ferrous Iron on Chemical and Bacterial Leaching of Copper Flotation Concentrates  [PDF]
Ali Ahmadi
International Journal of Nonferrous Metallurgy (IJNM) , 2012, DOI: 10.4236/ijnm.2012.13006
Abstract: The effects of ferrous and ferric iron as well as redox potential on copper and iron extraction from the copper flotation concentrate of Sarcheshmeh, Kerman, Iran, were evaluated using shake flask leaching examinations. Experiments were carried out in the presence and absence of a mixed culture of moderately thermophile microorganisms at 50?C. Chemical leaching experiments were performed in the absence and presence of 0.15 M iron (ferric added medium, ferrous added medium and a mixture medium regulated at 420 mV, Pt. vs. Ag/AgCl). In addition, bioleaching experiments were carried out in the presence and absence of 0.1 M iron (ferric and ferrous added mediua) at pulp density 10% (w/v), inoculated bacteria 20% (v/v), initial pH 1.6, nutrient medium Norris and yeast extract addition 0.02% (w/w). Abiotic leaching tests showed that the addition of iron at low solution redox potentials significantly increased the rate and extent of copper dissolution but when ferric iron was added, despite a higher initial rate of copper dissolution, leaching process stopped. Addition of both ferrous and ferric iron to the bioleaching medium levelled off the copper extraction and had an inhibitory effect which decreased the final redox potential. The monitoring of ferrous iron, ferric iron and copper extraction in leach solutions gave helpful results to understand the behaviour of iron cations during chemical and bacterial leaching processes.
Nitrification of Reactively Magnetron Sputter Deposited Ti-Cu Nano-Composite Thin Films  [PDF]
Ali Rahmati
Soft Nanoscience Letters (SNL) , 2013, DOI: 10.4236/snl.2013.31004
Abstract:

A metalloid Ti13Cu87 target was sputtered by reactive DC magnetron sputtering at various substrate temperatures in an Ar-N2 mixture ambient. The sputtered species were condensed on Si (111), glass slide and Potsssium bromide (KBr) substrates. The as-deposited films were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), optical spectrophotometry and four point probe technique. The as-deposited films present composite structure of nano-crystallite cubic anti-ReO3 structure of Ti inserted Cu3N (Ti:Cu3N) and nano-crystallite face centre cubic (fcc) structure of Cu. The titanium atoms and sequential nitrogen excess form a solid solution within the Cu3N crystal structure and accommodate in crystal lattice and vacant interstitial site, respectively. Depending on substrate temperature, unreacted N atoms interdiffuse between crystallites and their (and grain) boundaries. The films have agglomerated structure with atomic Ti:Cu ratio less than that of the original targets. A theoretical model has been developed, based on sputtering yield, to predict the atomic Ti:Cu ratio for the as-deposited films. Film thickness, refractive index and extinction coefficient are extracted from the measured transmittance spectra. The films’ resistivity is strongly depending on its microstructural features and substrate temperature.

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