Performance analysis of opportunistic nonregenerative relaying

Opportunistic relaying in cooperative communication depends on careful relay selection. However, the traditional centralized method used for opportunistic amplify‐and‐forward protocols requires precise measurements of channel state information at the destination. In this paper, we adopt the max–min criterion as a relay selection framework for opportunistic amplify‐and‐forward cooperative communications, which was exhaustively used for the decode‐and‐forward protocol, and offer an accurate performance analysis based on exact statistics of the local signal‐to‐noise ratios of the best relay. Furthermore, we evaluate the asymptotical performance and deduce the diversity order of our proposed scheme. Finally, we validate our analysis by showing that performance simulation results coincide with our analytical results over Rayleigh fading channels, and we compare the max–min relay selection with their centralized channel state information‐based and partial relay selection counterparts. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance analysis of an opportunistic multi‐user cognitive network with multiple primary users

Consider a multi‐user underlay cognitive network where multiple cognitive users concurrently share the spectrum with a primary network with multiple users. The channel between the secondary network is assumed to have independent but not identical Nakagami‐m fading. The interference channel between the secondary users (SUs) and the primary users is assumed to have Rayleigh fading. A power allocation based on the instantaneous channel state information is derived when a peak interference power constraint is imposed on the secondary network in addition to the limited peak transmit power of each SU. The uplink scenario is considered where a single SU is selected for transmission. This opportunistic selection depends on the transmission channel power gain and the interference channel power gain as well as the power allocation policy adopted at the users. Exact closed form expressions for the moment‐generating function, outage performance, symbol error rate performance, and the ergodic capacity are derived. Numerical results corroborate the derived analytical results. The performance is also studied in the asymptotic regimes, and the generalized diversity gain of this scheduling scheme is derived. It is shown that when the interference channel is deeply faded and the peak transmit power constraint is relaxed, the scheduling scheme achieves full diversity and that increasing the number of primary users does not impact the diversity order. Copyright © 2014 John Wiley & Sons, Ltd.     

Modelling an insulated gate bipolar transistor using bond graph techniques

Simulators in power electronics are less developed than in other electronic fields. The main modelling methods are between the numerical simulation of semiconductor device equations that hardly simulate circuits, and equivalent circuit models that show poor accuracy. We propose the application of the bond graph techniques to model modular power semiconductor devices. Furthermore, the IGBT is a new power device which combines a bipolar transistor with a MOSFET transistor. We develop a new IGBT bond graph model. The bond graph techniques give us good primary simulation results. We present in this paper the principle and the results of this modelling method.     

Chemical Modification of Guaran Gum. Part 3: Carboxymethylation in non-Aqueous Medium

Guar gum was isolated from the seeds and subjected to modification via non-aqueous carboxymethylation. Highly substituted carboxymethyl guaran derivatives could be obtained via repeating the reaction four times, where a product of degree of substitution (D.S.) 2.07 was obtained indicating that the free hydroxyl groups of both glucose and mannose (which form the main constituents of guaran) can react with monochloro acetic acid. The modification increases the solubility of the gum in cold water, and increases the stability of its pastes to microorganisms. Pastes of these derivatives are characterized by non-Newtonian pseudoplastic behaviour regardless of their D.S. or the measuring temperature, while their apparent viscosity decreases by increasing the D.S. and/or the measuring temperature.     

Cold compaction of polyether-etherketone and nickel powder blends

This study deals with the cold compaction of polyether-etherketone (PEEK) and nickel powder blends. Four different types of PEEK powders which are commercially available from Imperial Chemical Industries (ICI) were utilized for this investigation. These PEEK powders included fine and coarse size powders of a low viscosity grade (150PF and 150P) and similar powders of a high viscosity grade (450PF and 450P). Each of the four different PEEK powders were blended with about 10 vol?% nickel powder (Novamet) using a dry mixing technique. These PEEK/nickel powder blends were then successfully compacted at room temperature. Green strengths as high as 39.5 MPa and 26.3 MPa were measured on nickel filled 150 grade and 450 grade compacts, respectively. The higher strength values of the nickel filled compacts compared to their respective unfilled ones were attributed to a higher degree of mechanical interlocking and plastic deformation, which was induced in the polymer particles during compaction by the hard nickel filler. These composites also exhibited lower viscoelastic recoveries than their respective unfilled compacts. Electrical resistivities as low as 0.06 ohm-cm were achieved by compacting 150P/nickel powder blends. This resistivity value agreed well with the calculated value predicted from the literature.     

Kinetic and Quality Study of Mushroom Drying under Microwave and Vacuum

Abstract

The aim of this work is to model the drying kinetics of mushrooms under several operational conditions, to evaluate the effective diffusivity coefficient of moisture removing by a drying model and inverse calculus method in finite differences and to study the effect on the final quality of dehydrated mushrooms. Different ways of microwave vacuum drying were compared to freeze-drying. Results show that a decrement of the applied pressure produces a certain increase in the drying rate together with a lower moisture in the dehydrated product at the end. Temperature control inside the sample helps to ensure a better quality in the dehydrated product, than when controlled at the surface. Diffusivity coefficients show a correspondence with product temperature during drying. The microwave dried samples obtained with moderate power and temperature control of product shown an important degree of quality similar to that obtained by freeze-drying.     

High-Performance Work Systems and Organizational Performance in Emerging Economies: Evidence from MNEs in Turkey

This study examines the association between the usage of high-performance work systems (HPWS) by subsidiaries of multinational enterprises (MNEs) in Turkey and employee and subsidiary level outcomes. The study is based on a survey of 148 MNE subsidiaries operating in Turkey. The results show that the usage of HPWS has a significant positive impact on employee effectiveness. However, their impact on employee skills and development, and organizational financial performance are far less clear. Our findings highlight the extent to which HWPS need to be adapted to take account of context-specific institutional realities.     

Encapsulation of nano Disperse Red 60 via modified miniemulsion polymerization. I. Preparation and characterization

Nanocolorant, nano Disperse Red 60, was successfully prepared via modified miniemulsion polymerization process. Transmission electron microscopy was employed to determine the droplet and particle sizes. The effects of the speed and the time of homogenization, the surfactant nature and its amount, the presence of dye, the initiator nature, and the presence of a crosslinker on the morphology and particle size of nanocolorant were studied. UV–vis absorption spectra of nanocolorant with respect to the commercial corresponding dye showed a hypsochromic shift confirming the decrease in particle size. Fourier transform infrared spectra proved the chemical composition of nanocolorant particles assisting the incorporation of the dye within the polystyrene particles. The monomer conversion, surface tension, and apparent sedimentation stability also were measured. The relative electrical conductivity of the suspension was used for determining the polymerization mechanism. The kinetic polymerization was investigated using a pseudofirst-order and it is found that the rate constant of polymerization equals 0.01358 min⁻¹. Zeta potential measurements were employed for miniemulsion which showed that it has good stability at all range of pH. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

HIx system thermodynamic model for hydrogen production by the Sulfur–Iodine cycle

The HI_x ternary system (H₂O–HI–I₂) is the latent source of hydrogen for the Sulfur–Iodine thermo-chemical cycle. After analysis of the literature data and models, a homogeneous approach with the Peng–Robinson equation of state used for both the vapor and liquid phase fugacity calculations is proposed for the first time to describe the phase equilibrium of this system. The MHV2 mixing rule is used, with UNIQUAC activity coefficient model combined with of hydrogen iodide solvation by water. This approach is theoretically consistent for HI_x separation processes operating above HI critical temperature. Model estimation is done on selected literature vapor–liquid, liquid–liquid, vapor–liquid–liquid and solid–liquid equilibrium data for the ternary system and the three binaries subsystems. Validation is done on the remaining literature data. Results agree well with the published data, but more experimental effort is needed to improve modeling of the HI_x system.