Stability of scheduled message communication over degraded broadcast channels

We develop a multi-class discrete-time processor-sharing queueing model for scheduled message communication over a discrete memoryless degraded broadcast channel. The framework we consider here models both the random message arrivals and the subsequent reliable communication by suitably combining techniques from queueing theory and information theory. Requests for message transmissions are assumed to arrive according to i.i.d. arrival processes. Then, (i) we derive an outer bound to the stability region of message arrival rate vectors achievable by the class of stationary scheduling policies, (ii) we show for any message arrival rate vector that satisfies the outer bound, that there exists a stationary "state-independent" policy that results in a stable system for the corresponding message arrival processes, and (iii) under an asymptotic regime, we show that the stability region of information arrival rate vectors is the information-theoretic capacity region of a degraded broadcast channel.

Probing top-gated field effect transistor of reduced graphene oxide monolayer made by dielectrophoresis

We demonstrate a top-gated field effect transistor made of a reduced graphene oxide (RGO) monolayer (graphene) by dielectrophoresis. The Raman spectrum of RGO flakes of typical size of 5 mu m x 5 mu m shows a single 2D band at 2687 cm(-1), characteristic of single-layer graphene.The two-probe current-voltage measurements of RGO flakes, deposited in between the patterned electrodes with a gap of 2.5 mu m using ac dielectrophoresis, show ohmic behavior with a resistance of similar to 37 k Omega. The temperature dependence of the resistance (R) of RGO measured between 305 K and 393 K yields a temperature coefficient of resistance [dR/dT]/R similar to -9.5 x 10(-4)/K, the same as that of mechanically exfoliated single-layer graphene. The field-effect transistor action was obtained by electrochemical top-gating using a solid polymer electrolyte (PEO + LiClO4) and Pt wire. The ambipolar nature of graphene flakes is observed up to a doping level of similar to 6 x 10(12)/cm(2) and carrier mobility of similar to 50 cm(2)/V s. The source-drain current characteristics show a tendency of current saturation at high source-drain voltage which is analyzed quantitatively by a diffusive transport model. (C) 2010 Elsevier Ltd. All rights reserved.

Structure and dynamics of benzene in one-dimensional channels

Molecular dynamics investigation of benzene in one-dimensional channel systems A1PO(4)-5, VPI-5, and carbon nanotube is reported. The results suggest that, in all the three host systems, the plane of benzene is almost perpendicular to the channel axis when the molecule is near the center of the channel and the plane of benzene is parallel to the channel axis when the molecule is near the wall of the channel. The density distribution of benzene as a function of channel length, z and the radial distance, r, from the channel axis is also different in the three host structures. Anisotropy in translational diffusion coefficient, calculated in body-fixed frame of benzene, suggests that benzene prefers to move with its plane parallel to the direction of motion in A1PO(4)-5 and VPI-5 whereas in carbon nanotube the motion occurs predominantly with the plane of the benzene perpendicular to the direction of motion.;Anisotropy associated with the rotational motion is seen to alter significantly in confinement as compared to liquid benzene. In A1PO(4)-5, the rotational anisotropy is reversed as compared to liquid benzene thereby suggesting that anisotropy arising out of molecular geometry can be reduced. Reorientational correlation times for C-6 and C-2 axes Of benzene are reported. Apart from the inertial decay of reorientational correlation function due to free, rotation, two other distinct regimes of decay are observed in narrower channels (AIPO(4)-5 and carbon nanotube): (i) an initial fast decay (0.5-2 ps) and (ii) a slower decay (>2 ps) of reorientational correlation function where C-6 decays slower than C-2 Similar to what is observed in liquid benzene. In the initial fast decay, it is seen that the decay for C-6 is faster than C-2 which is in contrast to what is observed in liquid benzene or for benzene confined in VPI-5.

Selective para metalation of unprotected 3-methoxy and 3,5-dimethoxy benzoic acids with n-butyl lithium-potassium tert-butoxide (LIC-KOR): synthesis of 3,5-dimethoxy-4-methyl benzoic acid

The potassium salt of 3-methoxy and 3,5-dimethoxy benzoic acids undergoes deprotonation at the position para to the carboxylate group selectively when treated with LIC-KOR in THF at -78 degrees C and it has been extended to the synthesis of 3,5-dimethoxy-4-methyl benzoic acid. (C) 2000 Elsevier Science Ltd. All rights reserved.

Constellation Constrained Capacity of Two-user Broadcast Channels

Capacity region for two-user Gaussian Broadcast Channels (GBC) is well known with the optimal input being Gaussian. In this paper we explore the capacity region for GBC when the users' symbols are taken from finite complex alphabets (like M-QAM, M-PSK). When the alphabets for both the users are the same we show that rotation of one of the alphabets enlarges the capacity region. We arrive at an optimal angle of rotation by simulation. The effect of rotation on the capacity region at different SNRs is also studied using simulation results. Using the setup of Fading Broadcast Channel (FBC) given by [Li and Goldsmith, 2001], we study the ergodic capacity region with inputs from finite complex alphabets. It is seen that, using the procedure for optimum power allocation obtained in [Li and Goldsmith, 2001] for Gaussian inputs, to allocate power to symbols from finite complex alphabets, relative rotation between the alphabets does not improve the capacity region. Simulation results for a modified heuristic power allocation procedure for finite-constellation case, show that Constellation Constrained capacity region enlarges with rotation.

Information Theoretic Results for Three-User Cognitive Channels

In this paper, we introduce the three-user cognitive radio channels with asymmetric transmitter cooperation, and derive achievable rate regions under several scenarios depending on the type of cooperation and decoding capability at the receivers. Two of the most natural cooperation mechanisms for the three-user channel are considered here: cumulative message sharing (CMS) and primary-only message sharing (PMS). In addition to the message sharing mechanism, the achievable rate region is critically dependent on the decoding capability at the receivers. Here, we consider two scenarios for the decoding capability, and derive an achievable rate region for each one of them by employing a combination of superposition and Gel'fand-Pinsker coding techniques. Finally, to provide a numerical example, we consider the Gaussian channel model to plot the rate regions. In terms of achievable rates, CMS turns out to be a better scheme than PMS. However, the practical aspects of implementing such message-sharing schemes remain to be investigated.

A Reactive Tabu Search Based Equalizer for Severely Delay-Spread UWB MIMO-ISI Channels

We propose a novel equalizer for ultrawideband (UWB) multiple-input multiple-output (MIMO) channels characterized by severe delay spreads. The proposed equalizer is based on reactive tabu search (RTS), which is a heuristic originally designed to obtain approximate solutions to combinatorial optimization problems. The proposed RTS equalizer is shown to perform increasingly better for increasing number of multipath components (MPC), and achieve near maximum likelihood (ML) performance for large number of MPCs at a much less complexity than that of the ML detector. The proposed RTS equalizer is shown to perform close to within 0.4 dB of single-input multiple-output AWGN performance at 10(-3) uncoded BER on a severely delay-spread UWB MIMO channel with 48 equal-energy MPCs.

A.C. electrical conductivity of pure and doped potassium perchlorate

A.C. electrical conductivity of potassium perchlorate (KP) has been measured in the temperature range 25�325°C at frequencies ranging from 50�500 Hz using an automated technique. The results are interpreted in terms of a novel mechanism involving Schottky defects in the anion sublattice and Frenkel defects in the cation sublattice. Theconductivity behavior of KP is compared with literature data on similar low-symmetry systems containing polyatomic ions.

System effects in double‐channel gated‐integrator‐based deep‐level transient spectroscopy

The effects of the two sampling gate positions, and their widths and the integrator response times on the position, height, and shape of the peaks obtained in a double‐channel gated‐integrator‐based deep‐level transient spectroscopy (DLTS) system are evaluated. The best compromise between the sensitivity and the resolution of the DLTS system is shown to be obtained when the ratio of the two sampling gate positions is about 20. An integrator response time of about 100 ms is shown to be suitable for practical values of emission time constants and heating rates generally used.

Optimal Receive Antenna Selection in Time-Varying Fading Channels with Practical Training Constraints

Hardware constraints, which motivate receive antenna selection, also require that various antenna elements at the receiver be sounded sequentially to obtain estimates required for selecting the `best' antenna and for coherently demodulating data thereafter. Consequently, the channel state information at different antennas is outdated by different amounts and corrupted by noise. We show that, for this reason, simply selecting the antenna with the highest estimated channel gain is not optimum. Rather, a preferable strategy is to linearly weight the channel estimates of different antennas differently, depending on the training scheme. We derive closed-form expressions for the symbol error probability (SEP) of AS for MPSK and MQAM in time-varying Rayleigh fading channels for arbitrary selection weights, and validate them with simulations. We then characterize explicitly the optimal selection weights that minimize the SEP. We also consider packet reception, in which multiple symbols of a packet are received by the same antenna. New suboptimal, but computationally efficient weighted selection schemes are proposed for reducing the packet error rate. The benefits of weighted selection are also demonstrated using a practical channel code used in third generation cellular systems. Our results show that optimal weighted selection yields a significant performance gain over conventional unweighted selection.

Thermodynamic Stability of Potassium-beta-Alumina

The activity of K sub 2 O in a mixture of alpha -alumina and potassium beta -alumina has been determined using a solid state galvanic cell in the temperature range 600-1000K. The cell is written such that the right hand electrode is positive. The solid electrolyte consisted of a dispersion of alpha -alumina ( approx 15 vol.%) in a matrix of K beta -alumina. The emf of the cell was found to be reversible and to vary linearly with temperature. From the emf and auxiliary data on In sub 2 O sub 3 and K sub 2 O from the literature, the activity of K sub 2 O in the two-phase mixture is obtained. The standard free energy of formation of K beta -alumina from component oxides is given. Graphs.

Effect of trimethylammonium perchlorate on the decomposition and combustion of potassium perchlorate and potassium perchlorate-polyurethane propellants

Addition of trimethylammonium perchlorate to potassium perchlorate (KP) catalyzes its thermal decomposition. However, although the additive sensitises KP-PU propellant decomposition, its combustion is desensitised. The observed effects have been explained in terms of the role played by the early formation of potassium chloride.