Performance Analysis of an ATM Buffered Switch Transmitting Two-Class Traffic over Unreliable Channels

In this article we analyze the performance of a space division output buffered switch operating in an ATM multimedia environment as follows. Fixed size packets arrive onto the switch inputs in each time slot. These packets are of two classes. Class-1 packets, representing real time communications, are sensitive to delay but insensitive to loss. Class-2 packets, representing nonreal time communications, are insensitive to delay but sensitive to loss. The switch transmits these two-class packets over communications channels which are unreliable. That is, the packets could be lost before reaching the other end.To respond to the class-1 delay sensitivity, the switch gives class-1 packets higher service priority over class-2 packets. And to respond to the class-2 loss sensitivity, the switch requires an acknowledgment for each class-2 packet it transmits. It is this latter response that is the major contribution of the article. In particular, it gives rise to two service times, rather than one as has usually been considered in the published literature.For the purpose of the analysis, the switch is modelled as a priority, discrete time, batch arrival, single server queueing system, with infinite buffer and two service times: one deterministic for class-1 and one geometric for class-2. Three performance measures are analyzed: occupancy, unfinished work, and waiting time.     

Schrödinger Equation for An Extended Electron

A new quantum mechanical wave equation describing the dynamics of an extended electron is derived via Bohmian mechanics. The solution to this equation is found through a wave packet approach which establishes a direct correlation between a classical variable with a quantum variable describing the dynamics of the center of mass and the width of the electron wave packet. The approach presented in this paper gives a comparatively clearer picture than approaches using elaborative manipulation of infinite series of operators. It is shown that the new Schrödinger equation is free of any runaway solutions or any acausal responses.     

Multiple and sequential charge transfer interactions occurring in situ: A redox reaction of thiazolidine-2-thione with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

Interaction of thiazolidine-2-thione (T2T) as an electron donor with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an electron π-acceptor has been studied. Electronic absorption spectra of the system T2T-DDQ in several organic solvents of different polarities have been measured. A charge transfer (CT) complexation has occurred between T2T and DDQ. This CT interaction has led to a redox reaction in which T2T has been oxidized to the corresponding dehydrogenated T2T (T2T-2H), meanwhile DDQ has been fully reduced to the corresponding hydroquinone (DDQH2). However, the two new species, resulting in situ, have been interacted, whereas a CT complex having the formula (T2T-2H·DDQH2) has occurred. IR, 1H NMR and mass spectra were used for ascertaining the structural formula of the synthesized CT complex. Formation constants (KCT), molar absorption coefficients (?CT) and thermodynamic properties of this CT interaction in various organic solvents were determined and discussed. The obtained KCT and ?CT values have indicated that T2T-2H is a weak CT donor, whereas the formed CT complex has a low stability and it is classified as a contact-type CT complex.     

Synthesis and Antitumor Activity of New Substituted Mercapto‐1,2,4‐Triazine Derivatives,Their Thioglycosides,and Acyclic Thioglycoside Analogs

New 1,2,4‐triazine and their derived thioglycoside derivatives were synthesized from 5,6‐diphenyl‐1,2,4‐triazine‐3‐thiol. Furthermore, the corresponding acyclic thioglycoside analogs were synthesized from the corresponding mercapto derivatives and acyclic oxygenated alkyl halides. The newly synthesized compounds were evaluated for their antitumor activity and some of them showed high inhibition activities.     

Nickel(II) complexes of 2-aminoacetophenone N(4)-substituted thiosemicarbazones

Mononuclear nickel(II) complexes with 2-aminoacetophenone thiosemicarbazones and three N(4)-substituted thiosemicarbazones have been prepared in EtOH solution and characterized by physical and spectral methods. I.r. and electronic spectra of the thiosemicarbazones and their complexes, along with physical properties of the complexes, have been obtained. The 2-aminoacetophenone thiosemicarbazones coordinate both as neutral and anionic ligands via the thiosemicarbazone moiety's azomethine nitrogen and thione/thiolato sulfur [on loss of the N(2) hydrogen].     

A FINITE DIFFERENCE SCHEME FOR THE GENERALIZED NONLINEAR SCHRDINGER EQUATION WITH VARIABLE COEFFICIENTS

1. Generalized Nonlinear Schrsdinger EquationThe Schr6dinger equation has been extensively used in physics research, particularlyin the modeling of nonlinear dispersion waves [8]. Numerical methods for solving theSchr6dinger equation have been discussed in the literature. In this article, we considera generalized nonlinear Schr6dinger equation with variable coefficientsi: ~ g(A(x)Z) iF(t)u B(x) lulp~' u = 0, iZ ~ ~l, P > 1, (1)where u(x, 0) ~ of (x). The coefficients A(x), F(t) and, …     

Multi‐carrier platform for wireless communications. Part 1: High‐performance,high‐throughput TDMA and DS‐CDMA via multi‐carrier implementations

Multi‐carrier technologies in general, and OFDM and MC‐CDMA in particular, are quickly becoming an integral part of the wireless landscape. In this first of a two‐part survey, the authors present the innovative transmit/receive multi‐carrier implementation of TDMA and DS‐CDMA systems. Specifically, at the transmit side, the pulse shape (in TDMA) and the chip shape (in DS‐CDMA) corresponds to a linear combining of in‐phase harmonics (called a CI signal). At the receiver side, traditional time‐domain processing (equalization in TDMA and RAKE reception in DS‐CDMA) is replaced by innovative frequency based processing. Here, receivers decompose pulse (or chip) shapes into carrier subcomponents and recombine these in a manner achieving both high frequency diversity gain and low MAI. The resulting system outperforms traditional TDMA and DS‐CDMA systems by 10–14 dB at typical BERs, and, by application of pseudo‐orthogonal pulse shapes (chip shapes), is able to double system throughput while maintaining performance gains of up to 8 dB. Copyright © 2002 John Wiley & Sons, Ltd.