In this paper, we investigate and characterize the effects of multi-channel and rendezvous protocols on the connectivity of dynamic spectrum access networks using percolation theory. In particular, we focus on the scenario where the secondary nodes have plenty of vacant channels to choose from a phenomenon which we define as channel abundance. To cope with the existence of multi-channel, we use two types of rendezvous protocols: naive ones which do not guarantee a common channel and advanced ones which do. We show that, with more channel abundance, even with the use of either type of rendezvous protocols, it becomes difficult for two nodes to agree on a common channel, thereby, potentially remaining invisible to each other. We model this invisibility as a Poisson thinning process and show that invisibility is even more pronounced with channel abundance. Following the disk graph model, we represent the multiple channels as parallel edges in a graph and build a multi-layered graph (MLG) in R2. In order to study the connectivity, we show how percolation occurs in the MLG by coupling it with a typical discrete percolation. Using a Boolean model and the MLG, we study both cases of primaries' absence and presence. For both cases, we define and characterize connectivity of the secondary network in terms of the available number of channels, deployment densities, number of simultaneous transmissions per node, and communication range. When primary users are absent, we derive the critical number of channels which maintains supercriticality of the secondary network. When primary users are present, we characterize and analyze the connectivity for all the regions: channel abundance, optimal, and channel deprivation. For each region we show the requirement and the outcome of using either type of rendezvous techniques. Moreover, we find the tradeoff between deployment-density versus rendezvous probability which results in a connected network. Our results can be used to decide on the goodness of any channel rendezvous algorithm by computing the expected resultant connectivity. They also provide a guideline for achieving connectivity using minimal resources.
This study seeks to answer urgent questions about the role of new media that have emerged recently, such as the Internet and social networking sites and information services through mobile and others to increase awareness among young people, especially university students. during a field study that took place on a sample of students in the Department of Media at the University of Petra Kingdom of Jordan during the second semester in 2013 in the study the researcher finds increased attention and follow-up by young people for many of the world events and regional and local communities through exposure to a number of new media; in the forefront of the Internet and increase the level of awareness and interests young people do many of the eve
... Show MoreAbstract Iraq has an important place in the regional and international balance, and the competition among countries has increased in rapprochement with Iraq, not only for its geography or its privileged location, but because it has many other components that make regional and international countries want to strengthen their relations with it (Regional and international powers). In addition to that, Iraq has become increasingly important for these international and regional powers after its victory over the terrorist organization (ISIS), which proved an important fact that Iraq represents the most important pillars in the international balance.
Polyacrylonitrile:Polypyrole (PAN:PPy) undoped and doped with graphene Nano composites were synthesized using casting methods. Optical properties were utilized to describe the effect of composite ratio PAN/PPy as well as doping with Nanoscale graphene on the energy gap and the optical constants. PAN/PPy undoped and doped with Nanoscale graphene was used to detect gas nitrogen dioxide. In this article, the effect of mixing PAN with PPy at different weight ratios without addition and with the addition of 2% nanoscale graphene to the previous mixture on gas sensing performance on a large scale is explored. The results showed that doping with graphene enhanced the performance of gas sensing properties. Moreover, the article whic
... Show MoreThis work contains synthesis and characterization of new compounds [I-VIII], starting from compound [I] which was prepared through the reaction of chloroacetyl chloride with hydrazine hydrate and then cyclized the product with chloroacetic acid using phosphorous oxychloride to give 2,5-bis(chloromethyl)-1,3,4-oxadiazole compound [II], then the later compound [II] reacted with 4-hydroxy benzaldehyde to form compound [III]. The compound thiazolidine 2,4-dione [IV] was prepared from the reaction of chloroacetic acid with thiourea. Subsequently compound [III] reacted with compound [IV] to get [V] compound. Then the later compound was reacted with n-alkyl bromide (with several carbon atoms n= 4,5,6,8 ) to give compounds [VI]n. compound
... Show MoreAnaemia is one of the most important problems of malnutrition in the world, especially in countries developing and anemia is associated inextricably important public health and HIV and morbidity and reduced mental capacity This study aims to determine the incidence of anemia for the period 1999-2000 among healthy adults outwardly and its relationship with some variablesjob related study sample included 200 male and 200 Antymn but the cities of Baghdad and Baquba reviewers for central labs
The preparation, spectroscopic characterisation of complexes derived from the mixed ligands with CdII, ZnII and CoII metal ions with Schiff base, Dithiocarbamates (DTCs) and 8-Hydroxyquinoline are reported. The compounds that prepared have been defined via; chloride content, F.T-IR, UV-Vis 1H-NMR spectroscopy and C.H.N.S, as well as conductance and magnetic susceptibility.All data which collected from such methods specified complexes with 6 coordinates in solution and solid states. The biologicalactivity that is related to all the prepared compounds which were screened for their antimicrobial activitiesagainst (G+ and (G- )). The data that collected from biological activity indicate that complexes will have extra activity against such teste
... Show MoreComplexes from the ligand (2-hydroxy benzaldine)-4-aminoantipyrine with some transition metal ions V(l?),Cr(lll),Fe(lll) and Co(ll) were prepared in the presence of the co-ligand 1,10-phenanthroline in alcoholic medium. These compounds were characterized by the available techniques: FT-IR ,UV-Visible ,magnetic susceptibility, Flame atomic absorption technique as well as elemental analysis and conductivity mesurments .From these spectral studies, a square pyramidal structure proposed for V(IV) complex and an octahedral geometry for Cr(III),Fe(III) and Co(II) complexes. The biological activity of the ligands and their complexes were evaluated by a gar plate diffusion technique against three human pathogenic bacterial strains: Pseudomonas ae
... Show MoreThe study is about Maxwell , three dimensions of non – Newtonian fluid. Method of th Homotopy applied to analysis mass transfer and heat with thermophoresis effects. (Sc), Impact of therrmophoretic (𝜏), magnetic (M), Biot (γ), radiation (Rd),Schmidt Prandtle (Pr) parameters and ratio parameter(β) on concentration, temperature are offered in the paper.
The collected premiums and the compensations paid are among the main variables that have a prominent role in determining the level of financial solvency of insurance companies, as the higher the financial solvency of the insurance company, the more attractive it is to the target audience to acquire the company's insurance services.
Hence the importance of the issue of the solvency of insurance companies, as it is one of the critical matters on which the effectiveness of the insurance company and its continuation in the labor market depend.
In this research, we try to clarify the role of collected premiums and compensations paid in determining the level of operational solvency of t
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