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41.
Large‐scale fading (LSF) between interacting nodes is a fundamental element in radio communications, responsible for weakening the propagation, and thus worsening the service quality. Given the importance of channel‐losses in general, and the inevitability of random spatial geometry in real‐life wireless networks, it was then natural to merge these two paradigms together in order to obtain an improved stochastical model for the LSF indicator. Therefore, in exact closed‐form notation, we generically derived the LSF distribution between a prepositioned reference base‐station and an arbitrary node for a multi‐cellular random network model. In fact, we provided an explicit and definitive formulation that considered at once: the lattice profile, the users' random geometry, the effect of the far‐field phenomenon, the path‐loss behavior, and the stochastic impact of channel scatters. The veracity and accuracy of the theoretical analysis were also confirmed through Monte Carlo simulations. 相似文献
42.
Determining the Main Factors in Declining the Urmia Lake Level by Using System Dynamics Modeling 总被引:4,自引:2,他引:4
Urmia Lake in Iran is the second largest saline lake in the world. This ecosystem is the home for different species. Due to
various socio-economical and ecological criteria, Urmia Lake has important role in the Northwestern part of the country but
it has faced many problems in recent years. Because of droughts, overuse of surface water resources and dam constructions,
water level has decreased in such a way that one quarter of the lake has changed to saline area in the last 10 years. The
purpose of this research is to determine the main factors which reduce the lake’s water level. To this end, a simulation model,
based on system dynamics method, is developed for the Urmia Lake basin to estimate the lake’s level. After successful verification
of the model, results show that (among the proposed factors) changes in inflows due to the climate change and overuse of surface
water resources is the main factor for 65% of the effect, constructing four dams is responsible for 25% of the problem, and
less precipitation on lake has 10% effect on decreasing the lake’s level in the recent years. In the future, the model also
can be used by managers as a decision support system to find the effects of building new dams or other infrastructures. 相似文献
43.
Yousef A. Mubarak 《应用聚合物科学杂志》2011,122(4):2228-2243
This article highlights the melt crystallization behavior of different grades of isotactic polypropylene (iPP) using a hot‐stage polarizing optical microscopy. iPP samples were heated up at a heating rate of 10°C/min passing the melting temperature and then kept for 3 min at a temperature range of 175–200°C before they cooled rapidly at 40°C/min to crystallize isothermally at a range of 130–145°C. It has been found that the temperature at which the samples were kept has a strong effect on the crystallization mode; for samples heated up and kept at temperatures below 190°C, the crystallization started with thin and long rods or nodules, which grew in the circumferential direction only while their lengths remain unchanged as the time passed. The shape of the nodules can be straight, circular, branched, or entangled, and they can grow parallel to each other or they can be crossed or in a random way. This phenomenon disappeared completely for samples melted and kept at temperatures above 195°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
44.
H. M. Ali A. M. Ramadan M. A. Yousef 《Polymer-Plastics Technology and Engineering》2013,52(1-2):61-71
Commercial hydroxyethyl cellulose (HEC) was cyanoethylated with acrylonitrile in nonaqueous medium in the presence of sodium hydroxide under a variety of conditions. Variables studied included the amount of acrylonitrile and the reaction temperature. The reaction was proved by NMR and its extent was measured by determining the nitrogen content. The physical properties of the obtained derivatives—i.e., the electric properties and the apparent viscosity at various rates of shear—were investigated. It was found that the extent of reaction was increased by increasing the amount of acrylonitrile as well as the reaction temperature. The products were water soluble and their apparent viscosity increased with increasing nitrogen content. The same holds true for the dielectric constant and dielectric loss. 相似文献
45.
Magda A Akl Ayman M Atta Abd El-Fatah M Yousef Mohamed I Alaa 《Polymer International》2013,62(12):1667-1677
Stabilized and dispersed superparamagnetic porous nanogels based on sodium acrylate (AA‐Na) and acrylamide (AM) in a surfactant‐free aqueous system were synthesized via solution polymerization at room temperature. The formation of magnetite nanoparticles was confirmed and their properties characterized using Fourier transform infrared spectroscopy. Extensive characterization of the magnetic polymer particles using transmission electron microscopy (TEM), dynamic light scattering and zeta potential measurements revealed that Fe3O4 nanoparticles were incorporated into the shells of poly(AM/AA‐Na). The average particle size was 5–8 nm as determined from TEM. AM/AA‐Na nanoparticles with a diameter of about 11 nm were effectively assembled onto the negatively charged surface of the as‐synthesized Fe3O4 nanoparticles via electrostatic interaction. Crosslinked magnetite nanocomposites were prepared by in situ development of surface‐modified magnetite nanoparticles in an AM/AA‐Na hydrogel. Scanning electron microscopy was used to study the surface morphology of the prepared composites. The morphology, phase composition and crystallinity of the prepared nanocomposites were characterized. Atomic force microscopy and argon adsorption–desorption measurements of Fe3O4.AM/AA indicated that the architecture of the polymer network can be a hollow porous sphere or a solid phase, depending on the AA‐Na content. © 2013 Society of Chemical Industry 相似文献
46.
Mono and disubstituted 2,3-dihydroquinazolin-4(1H)-ones were obtained in good yields via a one-pot, three component reaction of isatoic anhydride and aromatic aldehydes with ammonium acetate or primary amines in the presence of perchlorated zirconia (HClO4/ZrO2) nano particles as an efficient solid acid catalyst under solvent-free conditions. Simple workup and reusability of the catalyst are advantages of this method. 相似文献
47.
R. Nirmala Hak Yong Kim R. Navamathavan Chaun Yi Jeong Jin Won Kyungsoo Jeon Ayman Yousef R. Afeesh Mohamed El-Newehy 《Ceramics International》2012,38(6):4533-4540
SnO2 doped TiO2 electropsun nanofiber photocatalysts were successfully prepared by means of electrospinning process. The surface morphology, structure and optical properties of the resultant products were characterized by field-emission electron microscopy (FE-SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, photoluminescence (PL) and cathodoluminescence (CL) techniques. The utilized physiochemical analyses indicated that the introduced SnO2 doped TiO2 nanofibers have a smooth surface and uniform diameters along their lengths. The photocatalytic performance of the composite nanofibers was tested for degradation of methylene blue (MB) and methyl orange (MO) dye solution under ultraviolet (UV) irradiation. Under the UV irradiation, the photocatalytic reaction rate in case of utilizing SnO2-doped TiO2 nanofibers was rapidly increased than that of the pristine TiO2 nanofibers. Overall, this study demonstrates cheap, stable and effective material for photocatalytic degradation at room temperature. 相似文献
48.
Yousef Jahani 《Polymer Engineering and Science》2007,47(12):2041-2048
The effect of epoxy resin on mechanical and Rheological properties, and moisture absorption of wood flour polypropylene composites (WPCs) were investigated. The reactive mixing of epoxy resin with 30, and 40 wt% wood flour and polypropylene (PP) was carried out in twin screw extruder with a special screw elements arrangement. PP grafted maleic anhydrides (MPP) were used as coupling agent to improve the interfacial interactions of wood flour, epoxy resin, and PP. The tensile strength of composites decreased, and elastic modulus and moisture absorption increased with increasing epoxy resin content. The complex viscosity η* increased with increasing epoxy resin content of composites, and a synergistic effect in increasing the η* was observed at 3 wt% resin. The epoxy resin modified wood‐PP composites that chemically coupled by MPP showed minimum water absorption with highest elastic modulus. The experimental oscillation rheologyical data were used to drive a model to predict the flow behavior of WPCs, in a wide range of frequencies. POLYM. ENG. SCI., 47:2041–2048, 2007. © 2007 Society of Plastics Engineers 相似文献
49.
Rapid quantitative method for total brominated vegetable oil in soft drinks using ion chromatography
Yousef AA Abbas AB Badawi BSh Al-Jowhar WY Zain EA El-Mufti SA 《Food additives & contaminants. Part A, Chemistry, analysis, control, exposure & risk assessment》2012,29(8):1239-1243
A simple, quantitative and rapid method for total brominated vegetable oil (BVO) using ion chromatography (IC) with suppressed conductivity detection was developed and successfully applied to soft drinks with results expressed as inorganic bromide anion. The procedure involves extraction of BVO with diethyl ether and treatment with zinc dust in a solution of acetic acid, giving recoveries ranging between 92.5 and 98.5%. The calibration curves obtained were linear with correlation coefficients (r (2)) of 0.998, a coefficient of variation (CV) of less than 5% and limit of detection (LOD) and limit of quantification (LOQ) of 250 and 750?μg?l(-1), respectively. The method was successfully applied to the determination of BVO in several commercial soft drinks which were found to contain BVO in the range 1.8-14.510?mg?l(-1). The method has less sources of error compared to previously published methods. 相似文献
50.
Synthesis,characterization, rheological and thermal behavior of metallocene ethylene − norbornene copolymers with low norbornene content using pentafluorophenol modified methylaluminoxane
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Ethylene ? norbornene copolymers were synthesized using rac‐ethylene bis(indenyl) zirconium dichloride/pentafluorophenol modified methylaluminoxane. First, the effect of using a modifier in combination with a low ratio of Al/Zr on the catalyst activity and co‐monomer incorporation was studied. The results of copolymerization reveal a 20% co‐monomer incorporation improvement and a rise of activity by 2‐fold in the presence of the modifier. Rheological measurements show a higher molecular weight in copolymers synthesized using modified methylaluminoxane. The alternative and dyad block microstructures of copolymers become possible in the case of a norbornene content of more than 14 mol%. Second, the effect of co‐monomer content on the rheological and thermal behavior of the synthesized copolymers was investigated. The results of the rheological study indicate a lower molecular weight in samples containing a higher norbornene content. Dynamic mechanical thermal analysis confirms the influence of different microstructures on the glass transition temperature. The crystal structure of copolymers having a higher molecular weight is emphasized using wide angle X‐ray scattering and DSC even with a greater incorporation of norbornene. © 2015 Society of Chemical Industry 相似文献