Performance of Transmit Antenna Selection and Maximal-Ratio Combining in Dual Hop Amplify-and-Forward Relay Network over Nakagami-m Fading Channels

In this paper, we study end-to-end performance of transmit antenna selection (TAS) and maximal ratio combining (MRC) in dual hop amplify-and-forward relay network in flat and asymmetric Nakagami-m fading channels. In the network, source and destination communicate by the help of single relay and source-destination link is not available. Source and destination are equipped with multiple antennas, and relay is equipped with single antenna. TAS and MRC are used for transmission at the source and reception at the destination, respectively. The relay simply amplifies and forwards the signal sent by the source to the destination by using channel state information (CSI) based gain or fixed gain. By considering relay location, for CSI based and fixed relay gains, we derive closed-form cumulative distribution function, moments and moment generating function of end-to-end signal-to-noise ratio, and closed-form symbol error probability expression. Moreover, asymptotical outage probability and symbol error probability expressions are also derived for both CSI based and fixed gains to obtain diversity order of the network. Analytical results are validated by the Monte Carlo simulations. Results show that diversity order is minimum of products of fading parameter and number of antennas at the end in each hop. In addition, for optimum performance the relay must be closer to the source when the diversity order of the first hop is smaller than or equal to that of the second hop.     

Resistive switching behavior of a CeO2 based ReRAM cell incorporated with Si buffer layer

We propose a novel resistive switching device with a W/CeO₂/Si/TiN structure by incorporating a very thin Si buffer layer in the interface, the memory performance of this device such as forming voltage, operation power, and window and endurance characteristics were found to be remarkably improved compared with the performance of the device without the Si layer. This improvement was attributed to the formation of Ce-silicate and thus proper introduction of oxygen vacancies at the interface. The gradual reset process of the W/CeO₂/Si/TiN device under sweeping voltage was quantitatively analyzed by parallel conductive filaments model. Our results provide a guideline for the operation voltage control for further optimizing device performance and give new insights into the gradual reset process.     

Cooperation-based resource allocation and call admission for?wireless network operators

The increasing number of radio access technologies and the availability of multi-radio devices boost the need for novel resource allocation schemes in cellular networks. This paper uses a cooperative game theoretic approach for resource allocation at the network level, while utilizing simultaneous use of available radio interfaces at the device level. We model resource allocation management using the well known bankruptcy model and apply Kalai-Smorodinsky bargaining solution method to find a distribution rule, based on which we propose resource allocation and call admission control schemes. Performance analysis of our allocation and control schemes demonstrates significant improvements over previous approaches in terms of utilization of the available bandwidth and the number of call drops. We also study the performance of proposed approach for different operator policies.     

APPLICATION OF OPTIMAL CONTROL THEORY IN PIPE INSULATION

Optimum insulation thickness of a pipe subjected to convective heat transfer that minimizes the heat loss is studied using the control theory approach and steepest descent method. As a constraint to the problem, the amount of insulation material is assumed to be fixed. A circular pipe through which fluid is transported from one end to the other is considered. Variations of the bulk temperature of the fluid as well as the temperatures of the outer surface of the insulation are evaluated. It is shown that obtaining an optimal thickness variation of insulation that minimizes the heat losses to the ambient using control theory can be done in a systematic manner. The method can be extended easily to more complex and nonlinear problems.     

BOUNDARY ELEMENT SOLUTIONS FOR FREE BOUNDARY CONVECTION-DIFFUSION PROBLEMS

The boundary element technique is used to solve the steady state convection-diffusion problem with constant velocity in a two-dimensional domain with a free interface. These problems arise in a number of important heat transfer applications involving melting or solidification, such as bulk crystal growth in Bridgman furnaces. The boundary element approach reduces the dimension of the problem, thereby improving the computational efficiency, and is particularly well suited to free-surface problems in which the position and shape of the solid-liquid interface are of primary importance. Results are presented for a case study problem representing solidification in a two-dimensional, rectangular configuration.     

Experimental investigation for optimization of design parameters in a rectangular duct with plate-fins heat exchanger by Taguchi method

This study presents the determination of optimum values of the design parameters in a heat exchanger with a rectangular duct by using Taguchi method. The heat exchanger has plate-fins containing periodically interrupted diverging and converging channel flow domains. The experimental investigation for the established heat exchanger involves short rectangular fins attached in 8 × 8 arrays to a surface having various inclination angles. The effects of the six design parameters such as the ratio of the duct channel width to height, the ratio of the winglets length to the duct channel length, inclination angles of winglets, Reynolds number, flow velocity and pressure drop are investigated. In the Taguchi experimental design method, Nusselt number and friction factor are considered as performance parameters. An L₂₅ (5⁶) orthogonal array is chosen as an experimental plan for the design parameters. The analysis of Taguchi method conducted with an optimization process to reach minimum pressure drop (friction factor) and maximum heat transfer (Nusselt number) for the designed heat exchanger. Experimental results validated the suitability of the proposed approach.     

Analytical solutions Zakharov–Kuznetsov equations

In this paper, we apply Homotopy Analysis Method (HAM) to find appropriate solutions for the Zakharov–Kuznetsov equations with fully nonlinear dispersion which are of utmost importance in applied and engineering sciences. Numerical results re-confirm the reliability of the proposed algorithm (HAM).     

A process targeting model for a product with two dependent quality characteristics using 100% inspection

The purpose of this paper is to develop a process targeting model for a product with two quality characteristics produced by two processes in series. The first quality characteristic is determined by the setting of the first process, whereas the second quality characteristic depends on the setting of the two processes. The quality of the product is controlled by a 100% inspection plan, and inspection is assumed to be error free. The objective of the model is to determine the optimal target for both processes that maximizes the profit. A realistic case study has been used to demonstrate the utility of the model. The results have shown that the model results improve the profit per lot and aid the factory in conducting cost/benefit analysis for reducing the variances of the two processes. In addition, sensitivity analysis has been performed to study the effect of different parameters on the expected profit and optimal processes means. It has been shown that the results of the model are sensitive to the variances of the two processes, selling prices, and rework costs.     

Integrated supply chain risk management via operational methods and financial instruments

Supply chain risk management (SCRM) is an emerging field that generally lacks integrative approaches across different disciplines. This study contributes to narrowing this gap by developing an integrated approach to SCRM using operational methods and financial instruments. We study a supply chain composed of an aluminium can supplier, a brewery and a distributor. The supply chain is exposed to aluminium price fluctuation and beer demand uncertainty. A stochastic optimisation model is developed for managing operational and financial risks along the supply chain. Using this model as a base, we compare the performance of an integrated risk management model (under which operational and financial risk management decisions are made simultaneously) to a sequential model (under which the financial risk management decisions are made after the operational risk management decisions are finalised). Through simulation-based optimisation and using experimental designs and statistical analyses, we analyse the performance of the two models in minimising the expected total opportunity cost of the supply chain. We examine the supply chain performance as a function of three factors, each at three levels: risk aversion, demand variability and aluminium price volatility. We find that the integrated model outperforms the sequential model in most but not in all cases. Furthermore, while the results indicate that the supply chain improves its performance by being less risk averse, there exists a threshold beyond which accepting a higher risk level is not justified. Managerial insights are provided for various business scenarios experimented with.     

Synthesis of C60-Furfural Adduct

Abstract

Diels-Alder cycloaddition of furfural to C₆₀ in toluene has been realised. UV-VIS, FTIR and ¹H-NMR investigations suggest that the conjugated structure of furfural was changed into a non-conjugated structure in the product.