User cooperation to mitigate the jamming in OFDMA networks

In this paper, jamming and anti-jamming in a time slotted orthogonal frequency division multiple access (OFDMA) are investigated. The users of the network cooperate to mitigate the jamming effect. Interactions among the network users and the jammer are modeled by a mixed integer non-cooperative generalized game which is a NP-hard problem. To relax the problem, a new algorithm is proposed based on channel state information (CSI) to determine the transmission channels and the partners of users in the network. To solve the proposed game, an optimization problem is solved for each player considering the best response of the other player. Another generalized game is proposed to model the cooperation among users of the network. The latter game is transformed to an equivalent Quasi Variational Inequality (QVI). Then, a new gradient based algorithm is proposed by utilizing the Karush-Kuhn-Tucker (KKT) conditions to find the solution of the equivalent QVI. Then, solving the latter game and substituting the best related response, the solution of the former generalized game is also obtained. The convergence of the proposed algorithms, and the uniqueness related to the solution of the both generalized games are proven. Finally, the simulation results confirm the effectiveness of the proposed approach.

     

Fabrication of sensitive glutamate biosensor based on vertically aligned CNT nanoelectrode array and investigating the effect of CNTs density on the electrode performance

In this report, the fabrication of vertically aligned carbon nanotube nanoelectrode array (VACNT-NEA) by photolithography method is presented. Electrochemical impedance spectroscopy as well as cyclic voltammetry was performed to characterize the arrays with respect to different diffusion regimes. The fabricated array illustrated sigmoidal cyclic voltammogram with steady state current dominated by radial diffusion. The fabricated VACNT-NEA and high density VACNTs were employed as electrochemical glutamate biosensors. Glutamate dehydrogenase is covalently attached to the tip of CNTs. The voltammetric biosensor, based on high density VACNTs, exhibits a sensitivity of 0.976 mA mM(-1) cm(-2) in the range of 0.1-20 μM and 0.182 mA mM(-1) cm(-2) in the range of 20-300 μM glutamate with a low detection limit of 57 nM. Using the fabricated VACNT-NEA, the sensitivity increases approximately to a value of 2.2 Am M(-1) cm(-2) in the range of 0.01 to 20 μM and to 0.1 A mM(-1) cm(-2) in the range of 20-300 μM glutamate. Using this electrode, a record of low detection limit of 10 nM was achieved for glutamate. The results prove the efficacy of the fabricated NEA for low cost and highly sensitive enzymatic biosensor with high sensitivity well suited for voltammetric detection of a wide range of clinically important biomarkers.     

Clinical and bacteriologic impact of rifabutin prophylaxis for Mycobacterium avium complex infection in patients with human immunodeficiency virus infection

Carcinoma of the oesophagus is the seventh most common malignancy worldwide. It is a disease with a poor prognosis; more than half of the patients present with surgically irresectable tumours. For such patients, palliative therapy is directed towards the relief of dysphagia. Expandable metallic stents have recently been developed for use in the oesophagus. These have the advantage of being introduced through small diameter delivery catheters. Once released, they can expand to as much as 25 mm in diameter, potentially allowing patients to consume a normal diet. The current designs of metallic stents include the Strecker stent, the Wallstent endoprosthesis, and the Gianturco-Rosch stent. The Strecker is an uncovered stent while the other two are covered on the outside of the stent with plastic to prevent tumour ingrowth. A review of the literature indicates that deployment of these stents is associated with a high technical success rate. Improvement in swallowing function is seen in 83% to 100% of these patients. The overall complication rates are low. However, covered stents are prone to migration while uncovered stents are vulnerable to tumour ingrowth. Further improvements in design promise to expand the role of these endoprostheses in the management of oesophageal carcinoma.     

Structural,magnetic and elastic properties of Mn0.3−xMgxCu0.2Zn0.5Fe3O4 nanoparticles

In this paper, Mn_0.3?xMg_xCu_0.2Zn_0.5Fe₃O₄ (x?=?0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30) nanoparticles were prepared by the nitrate-citrate technique at low temperature. The structural, microstructural, magnetic and elastic properties of the samples were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy, Transmission electron microscopy, field emission-scanning electron microscopy and vibrating-sample magnetometer at room temperature. Rietveld refinement of the XRD patterns indicated the formation of the single phase cubic spinel structure (space group Fd-3m) without any detectable impurity phase in all the samples that also was confirmed by FTIR studies. The lattice parameter is found to increase non-monotonically with an increase in Mg ion concentration. Also, the bond lengths and bond angles (A and B sites) of the studied ferrites were calculated by the refining of the XRD data. The values of the crystallite size decrease with increasing micro-strain (and conversely) and both of them reach extremum at x?=?0.15. The low remanence and coercivity values confirmed the formation of the superparamagnetic ferrites nanoparticles. The saturation magnetization of the samples gradually grows with Mg substitution and reach extremum at x?=?0.15. Variation of saturation magnetization with Mg content can be mainly attributed to change of cation distribution, and Yafet-Kittel angle occurred between magnetic moments on B-site in the samples. The values of Young's modulus, Debye temperature, bulk modulus, rigidity modulus of the samples were determined by the values of elastic constant and wave velocities obtained from the force constants. The improvement of the elastic properties of sample x?=?0.05 could be explained regarding the smaller values of the lattice parameter (a), the bond length and angle and the smaller crystallite size.     

Gasification of wastes: The impact of the feedstock type and co-gasification on the formation of volatiles and char

A gasification pilot plant was built up in order to investigate the influence of both feedstock type and co-gasification on the distribution and composition of the products. The results showed that at the same process condition, different feedstocks could result in different product yields. For instance, the highest gas yield was obtained from tire gasification, while the lowest one belonged to weed gasification. The characterization of the products showed the presence of different components and functionalities in the samples produced. In addition, the co-gasification of the feedstocks resulted in the products with different specifications than single feeding, proving the existence of different reaction pathways. This means that feedstocks and their derivatives could interact with each other and resulted in nonproportional yields and composition for the char, tar, and gaseous products in comparison with the products from the gasification of the single feedstocks. As an example, the tar from co-gasification had a lower content of acids but a higher content of amines and amides. This confirmed that co-gasification influenced the reaction network significantly, impacting the formation of gases, tar, and char, originated from the cross-interaction among the reaction intermediates derived from the pyrolysis/gasification of the various feedstocks.     

Study of Structural,Electrical and Optical Properties of (200)-Oriented CdTe Thin Films Depending on the Post-deposition Low Temperature

Cadmium telluride nanoparticles (CdTe NPs) have been synthesized by a sonochemical technique, deposited on glass and quartz glass at 100°C and 2.7?×?10^?6 kPa and then studied by analyzing the x-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–Vis), current–voltage test (I–V) and scanning electron microscopy (SEM). The XRD results indicated the formation of a strong preferential (200) orientation of CdTe with a cubic zinc-blende structure on both substrates. In order to show the effect of heating on the structure and optical properties of the prepared thin films, they were annealed at temperatures of 50°C, 70°C and 100°C for 1 h. It was found that the grain size in this orientation increases with the increase of the temperature. In addition, the obtained optical band gap energies by UV–Vis measurements were in the range of 1.46–1.53 eV. The electrical properties of the prepared films were observed to increase with annealing using I–V measurements. The thin films were also found to be uniform with a small particle size, as revealed by SEM.

     

Fuzzy Bayesian system reliability assessment based on prior two‐parameter exponential distribution under different loss functions

The fuzzy Bayesian system reliability assessment based on prior two‐parameter exponential distribution under squared error symmetric loss function and precautionary asymmetric loss function is proposed in this paper. In order to apply the Bayesian approach, the fuzzy parameters are assumed as fuzzy random variables with fuzzy prior distributions. Because the goal of the paper is to obtain fuzzy Bayes point estimators of system reliability assessment, prior distributions of location‐scale family has been changed to scale family with change variable. On the other hand, also the computational procedures to evaluate the membership degree of any given Bayes point estimate of system reliability have been provided. In order to achieve this purpose, we transform the original problem into a non‐linear programming problem. This non‐linear programming problem is then divided into four sub‐problems for the purpose of simplifying computation. Finally, the sub‐problems can be solved by using any commercial optimizers, e.g. GAMS or LINGO. Copyright © 2010 John Wiley & Sons, Ltd.