Determination of the rate constant for the OH(X2Pi) + OH(X()Pi) --> O(3P) + H2O reaction over the temperature range 293-373 K

The rate constant for the reaction OH(X2Pi) + OH(X2Pi) --> O(3P) + H2O has been measured over the temperature range 293-373 K and pressure range 2.6-7.8 Torr in both Ne and Ar bath gases. The OH radical was created by 193 nm laser photolysis of N2O to produce O(1D) atoms that reacted rapidly with H2O to produce the OH radical. The OH radical was detected by quantitative time-resolved near-infrared absorption spectroscopy using Lambda-doublet resolved rotational transitions of the first overtone of OH(2,0) near 1.47 microm. The temporal concentration profiles of OH were simulated using a kinetic model, and rate constants were determined by minimizing the sum of the squares of residuals between the experimental profiles and the model calculations. At 293 K the rate constant for the title reaction was found to be (2.7 +/- 0.9) x 10(-12) cm(3) molecule(-1) s(-1), where the uncertainty includes an estimate of both random and systematic errors at the 95% confidence level. The rate constant was measured at 347 and 373 K and found to decrease with increasing temperature.     

Kinetic study on catalytic gasification of a modified sludge fuel

A new type of mixture fuel, sludge-oil-coal agglomerate (SOCA), was catalytically gasified with steam in a thermobalance reactor under atmospheric pressure. All the four catalysts studied (KeCO3, CaO, NiO and Fe2O3) were found capable of enhancing the steam gasification rate and significantly increasing the conversion of carbon. The ranking of catalytic activity was found to be K2CO3 >> CaO > NiO > Fe2O3. A modified volumetric-reaction model in the literature was used to describe the conversion behavior of the steam gasification studied by evaluating the kinetic parameters. Expressions of the apparent gasification rates for SOCA were presented for the design of catalytic gasification processes.     

Coexistence of filamentary and homogeneous resistive switching in graded WOx thin films

Reversible clockwise and counter‐clockwise resistive switching in a Pt/graded WO_x /W stack is reported. Two stable switching modes with opposite switching polarity and different electrical characteristics are found to coexist in the same memory cell. Clockwise switching shows filamentary characteristics that lead to relatively faster switching with excellent retention at high temperature. Counter‐clockwise switching exhibits homogeneous conduction with slower switching and moderate retention. The field‐induced switching reversal might be due to inhomogeneous expansion of W during thermal oxidation. Our results provide a clue to modulate the switching type in Pt/WO_x /W memory cells. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Performance of Reservation in Call Admission Control Schemes for Code-Division Multiple Access Systems with Nonuniform Traffic Distribution Among Cells

In this paper, we propose the reservation type call admission control (CAC) scheme to resolve the intercell unbalanced traffic problem. Differently from a conventional CAC scheme where the system resource is fully allocated to the local users in the home cell, the proposed CAC scheme reserves a small portion of the system resource for new calls occurring in the neighboring cells instead of fully allowing the local users in the home cell to occupy the system resource. As a result, the proposed CAC scheme improves the overall call blocking probability when the traffic is nonuniformly distributed among cells. More specifically, the proposed CAC scheme improves the overall call blocking probability by 15% when one cell has 67% more traffic than its surrounding cells.     

Experimental study on variation of acoustical resonance frequency of duct with orifice depending on periodic motion

Recently, a linear compressor has been actively developed to improve the energy efficiency of home appliances, such as refrigerators. Unlike a reciprocating compressor, the suction part of a linear compressor is periodically moving. Therefore, the suction valve and the muffler constituting the suction part are periodically moving. However, up to now, there has been no research into the characteristics of the sound propagation in a periodically moving acoustic system. Thus, in this study, characteristics of sound propagation in a periodically moving acoustic system were investigated for the first time. Among a variety of acoustic filters used in a suction muffler, the change in the orifice impedance has been observed because this change is considered to be easily affected by periodically moving. Due to difficulty in measuring the orifice impedance in a periodically moving acoustic system, the change in the orifice impedance was predicted from the change in the input impedance of the suction muffler that included orifice. The experiments were carried out while changing the diameter and the pattern of orifice as well as length of the duct. As a result of experiments, the impedance of periodically moving orifice was changed depending on diameter, pattern of orifice and frequency band. Therefore, if periodically moving orifice was used to design a suction muffler in linear compressor or acoustic system, the change in the orifice impedance should be taken into consideration.     

BER minimization for dual‐polarized wireless systems with polarization‐domain rotation

We consider the problem of bit error rate (BER) degradation because of the power gain imbalance between horizontal (H)‐polarization and vertical (V)‐polarization components in an orthogonal dual‐polarization transmission system. To alleviate the aforementioned BER degradation problem, we propose a non‐orthogonal polarization‐domain rotation scheme where the axes of H‐polarization and V‐polarization components are rotated with different angles at the transmitter and de‐rotated at the receiver. In addition, in order to assess the effectiveness of the polarization‐domain rotation scheme, we derive the closed‐form BER expression under a practical dual‐polarized channel model, which is represented by cross‐polarization ratio and co‐polarization ratio (CPR). We also derive the approximated BER expressions for the two asymptotic values of CPR: balanced CPR and infinite CPR. With the derived BER expressions, we find the optimal rotation angles that jointly minimize the BER. According to the numerical results, it is shown that about 3dB E_b/N₀ gain is obtained at the BER of 10^?4 and the CPR of 10dB by the polarization‐domain rotation scheme with optimal rotation angles compared with the conventional orthogonal dual‐polarization transmission. Copyright © 2015 John Wiley & Sons, Ltd.     

A myopic mobile sink migration strategy for maximizing lifetime of wireless sensor networks

Network lifetime maximization is challenging particularly for large-scale wireless sensor networks. The sensor nodes near the sink node tend to suffer high energy consumption due to heavy traffic relay operations, becoming vulnerable to energy depletion. The rationale of the sink mobility approach is that as the sink node moves around, such risk of energy depletion at some nodes can be alleviated. In this paper, we first obtain the optimal mobile sink sojourning pattern by solving a linear programming model and then we mathematically analyze why the optimal solution exhibits such sojourning pattern. We use the insights from this analysis to design a simple practical heuristic algorithm for sink mobility, which utilizes only local information. Our heuristic is very different from the existing algorithms which often use the traffic volume as the main decision factor, in that we consider the variance of residual energy of neighboring sensor nodes. The simulation results show that our scheme achieves near-optimal network lifetime even with the relatively low moving speed of the mobile sink.     

Analysis of charge conduction mechanisms in nitrided SiO2 Film on 4H SiC

Seven different thicknesses (2-20 nm) of nitrided SiO₂ on n-type 4H-SiC have been employed to investigate the charge conduction mechanism through these oxides. Several potential mechanisms have been identified. The mechanisms are depending on electric field and oxide thickness. A relationship plot among these three parameters has been established.