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61.
Manal El Tanab Walaa Hamouda Yasmine Fahmy 《Wireless Communications and Mobile Computing》2016,16(15):2212-2224
Cognitive radio networks have emerged to improve the utilization of the scarce spectrum. In this paper, we propose a distributed resource allocation algorithm that allocates resources opportunistically to the secondary users in a multiple‐input multiple‐output environment. In order to reduce the complexity and cost, antenna selection schemes are employed to allow the secondary communication using a single radio frequency chain. The proposed algorithm is proved theoretically and using simulations, to give a performance very close to that of a centralized one with lower delay and overhead. Furthermore, we introduce two techniques for the proposed algorithm based on the allowable data rates referred to as limited and maximum rates. We derive closed‐form expression for the consumed power and tight upper bounds for the average throughput achieved by each technique. A comparison between the proposed techniques is also provided. Both simulations and analytical results show that the proposed algorithm achieves high throughput with low complexity. Moreover, the results show that the tightness of the bounds improves with the diversity order. Finally, the proposed techniques are compared with two suggested random schemes to investigate their effectiveness. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
62.
Arafa M. S. Meshref Walaa A. Moselhy Nour El-Houda Y. Hassan 《Sensing and Instrumentation for Food Quality and Safety》2014,8(4):381-388
Milk and dairy products are an important food in the human diet. The present investigation was carried out to determine concentrations of lead, cadmium, zinc, copper and iron in milk and dairy products and evaluate the potential health risks of metals to humans via consumption of milk and dairy products. A total of 77 samples of milk and dairy products (22 raw milk, 20 kareish cheese, 21 butter and 14 rice pudding) were collected from farms, individual farmers and dairy shops in Beni-Suef governorate, Egypt. Pb, Cd, Zn, Cu and Fe concentrations in milk and dairy products ranged from 0.044–0.751, 0.008–0.179, 0.888–18.316, 0.002–1.692 and 1.3208–45.6198 ppm respectively. Pb concentration in all samples exceeded the maximum permissible limit (0.02 mg/kg) established by codex standard. Pd and Cd intake through milk and dairy products consumption were 1.27 and 0.33 μg/kg bw/day, which represent 35.3 and 39.8 % of the tolerable daily intake. Dairy products are poor sources of iron, copper and zinc, and milk contributes little to the total iron and zinc intake. Target hazard quotient values of less than 1 indicate a relative absence of health risks associated with the consumption of milk and dairy products. 相似文献
63.
M. K. Habibi M. Paramsothy A. M. S. Hamouda M. Gupta 《Journal of Materials Science》2011,46(13):4588-4597
Uniaxial compressive properties of hybrid Mg/Al–CNT nano-composites are studied in the present paper. Hybrid nano-composites
were fabricated using powder metallurgy route followed by microwave assisted rapid sintering technique and hot extrusion.
The hybrid Mg/Al–CNT nano-composites exhibited slightly smaller grain sizes compared to monolithic Mg and reasonable hybrid
Al–CNT nano-particle distribution up to Al content of 1.00 wt%. Compared to pure Mg, the Mg/Al–CNT nano-composites exhibited
higher compressive yield strength (0.2% CYS), ultimate compressive strength (UCS) and work of fracture (WOF) (up to +36%,
+76%, +36%) compared to pure Mg but failure strain was compromised. Inclusive of crystallographic texture changes, the effect
of hybrid Al–CNT nano-particle integration on the enhancement of compressive properties of Mg is investigated in this paper. 相似文献
64.
Yao Y Ji L Lin Z Li Y Alcoutlabi M Hamouda H Zhang X 《ACS applied materials & interfaces》2011,3(9):3732-3737
A novel type of hybrid membrane was fabricated by incorporating sulfonated polystyrene (S-PS) electrospun fibers into Nafion for the application in proton exchange membrane fuel cells. With the introduction of S-PS fiber mats, a large amount of sulfonic acid groups in Nafion aggregated onto the interfaces between S-PS fibers and the ionomer matrix, forming continuous pathways for facile proton transport. The resultant hybrid membranes had higher proton conductivities than that of recast Nafion, and the conductivities were controlled by selectively adjusting the fiber diameters. Consequently, hybrid membranes fabricated by ionomers, such as Nafion, incorporated with ionic-conducting nanofibers established a promising strategy for the rational design of high-performance proton exchange membranes. 相似文献
65.
66.
The general theory of factorial analysis of continuous correspondance (FACC) is used to investigate the binary case of a continuous
probability measure defined as:T(xm,y)=ay
n
+b, (x,y)ɛD&nɛN=0, elsewhere
Wheren≥0,a andb are the parameters of this distribution. While the DomainD is a variable trapezoidal inscribed in the unit square. The trapezoid depends on two parameters α and β.
This problem is solved. As special cases of our problem we obtaine a complete solution fot two of them which correspondt to
a particular form of the correlation matrix in the discrete case. 相似文献
67.
Experimental quasi-static crushing tests and finite element analysis have been carried out for unidirectional filament wound laminated cotton/epoxy tubes. The work focuses on three main factors, which considerably affect the axial collapse load of unidirectional natural composite tubes. These factors are structural geometry, fibre diameter and fibre orientation. Cotton/epoxy tubes with different diameters (50, 70, 90, 110 and 130 mm) were examined and tested. The fibre orientation angles were 80 and 90°. The initial geometric imperfections are measured using the computerised Mistral coordinate measuring machine. The numerical prediction was obtained using commercially available finite element software. A limited agreement between the experimental and computational results was obtained. For all structures considered classical axial collapse eigenvalues were computed. The initial failure crush load computed from the finite element simulation model has been compared with the experiments. 相似文献
68.
Similar to the univariate CUSUM chart, a multivariate CUSUM (MCUSUM) chart can be designed to detect a particular size of the mean shift optimally based on the scheme of a sequential likelihood ratio test for the noncentrality parameter. However, in multivariate case, the probability ratio of a sequential test is intractable mathematically and the test statistic based on the ratio does not have a closed form expression which makes it impractical for real application. We drive an approximate log-likelihood ratio and propose a multivariate statistical process control chart based on a sequential χ2 test to detect a change in the noncentrality parameter. The statistical properties of the proposed test statistic are explored. The average runs length (ARL) performance of the proposed charts is compared with other MCUSUM charts for process mean monitoring. The experimental results reveal that the proposed charts achieve superior, both zero-state and steady-state, ARL performance over a wide range of mean shifts, especially when the dimension of measurements is large. 相似文献
69.
Md Ershadul AlamSamson Han Quy Bau NguyenAbdel Magid Salem Hamouda Manoj Gupta 《Journal of Alloys and Compounds》2011,509(34):8522-8529
In the present study, 1 and 2 wt.% of aluminum were successfully incorporated into magnesium based AZ31 alloy to develop new AZ41 and AZ51 alloys using the technique of disintegrated melt deposition. AZ41-Al2O3 and AZ51-Al2O3 nanocomposites were also successfully synthesized through the simultaneous addition of aluminum (1 and 2 wt.%, respectively) and 1.5 vol.% nano-sized alumina into AZ31 magnesium following same route. Alloy and composite samples were then subsequently hot extruded at 400 °C and characterized. Microstructural characterization studies revealed equiaxed grain structure, reasonably uniform distribution of particulate and intermetallics in the matrix and minimal porosity. Physical properties characterization revealed that addition of both aluminum and nano-sized alumina reduced the coefficient of thermal expansion of monolithic AZ31. The presence of both Al and nano-sized Al2O3 particles also assisted in improving overall mechanical properties including microhardness, engineering and specific tensile strengths, ductility and work of fracture. The results suggest that these alloys and nanocomposites have significant potential in diverse engineering applications when compared to magnesium AZ31 alloy. 相似文献
70.
Hend A. Elbarbary Ahlam F. Hamouda 《Sensing and Instrumentation for Food Quality and Safety》2013,7(4):194-198
The aim of this study was to determine the content of lead, cadmium, aluminum, copper and mercury during Feta cheese manufacturing by using atomic absorption spectrometer. Results revealed that lead and mercury concentrations were higher after curdling and in fresh cheese after salting than other elements. Cadmium was detected at low concentrations in raw milk, pasteurized milk, after curdling and fresh cheese (0.053, 0.10, 0.20 and 0.24 mg/kg, respectively). Aluminum concentration did not change seriously during different steps of cheese manufacturing. On the other hand, the concentration of copper increased from 2.83 ± 0.97 mg/kg in raw milk to 3.25 ± 1.06 mg/kg in fresh cheese. It was concluded that the curdling and cheese after salting are the major technological steps that affect the concentration of some heavy metals rather than heat treatment. 相似文献