Solute-solvent interactions in surfactant adsorption: Part I. The influence of the polar head

This study deals with the variation of the interfacial tension of mercury aqueous solutions with potential and concentrations for solutions of butanol. butyric acid, butyramide and butyl monoether glycol. The results obtained have been analysed using an isotherm proposed by Bennes leading to values for the energy of adsorption corrected for the influence of the solute-solvent interactions in solution.A correlation has been revealed been to exist between the corrected energy of adsorption, the hydrophobicity coefficient and the dipole moment of the molecule which are all parameters related to the nature of the hydrophilic grouping.These result serve to show how the adsorption on mercury can be used to approach the problem of interactions between molecules in surfactant solutions.     

Packet-error probability analysis for FH-CDMA unslotted packet networks

This letter is concerned with the interference analysis in time-unslotted frequency-hopping code-division multiple-access packet networks with error control coding. We derive, under the conditional independence assumption, a new exact closed-form expression for the packet error probability of a reference packet in the presence of other K interfering packets. In contrast to the previously known results, the computational complexity of the new result is independent of K. We also develop a new tight upper bound on packet error probability relying on mapping the unslotted system into an equivalent slotted one experiencing the same level of short-term average interference. The accuracy of the proposed approximation is demonstrated by some numerical examples and is shown to be tighter than the previously used results.     

Interference characterization in the unlicensed band

We consider performance of a wireless communication receiver in the presence of a field of continuous wave (CW) interferers that are randomly distributed according to a Poisson process in space and frequency domain in the unlicensed band. From our theoretical model, we derive an accurate analytical expression for average bit error rate (BER). Judging from our results for a strong desired signal, when the user density grows up to ten times its value for a given signal to noise ratio (SNR), BER performance falls by 9.09% and 8.51 % for BPSK and DPSK respectively.     

Analysis of nonblocking ATM switches with multiple input queues

An analytical model for the performance analysis of a multiple input queued asynchronous transfer mode (ATM) switch is presented. The interconnection network of the ATM switch is internally nonblocking and each input port maintains a separate queue of cells for each output port. The switch uses parallel iterative matching (PIM) to find the maximal matching between the input and output ports of the switch. A closed-form solution for the maximum throughput of the switch under saturated conditions is derived. It is found that the maximum throughput of the switch exceeds 99% with just four iterations of the PIM algorithm. Using the tagged input queue approach, an analytical model for evaluating the switch performance under an independent identically distributed Bernoulli traffic with the cell destinations uniformly distributed over all output ports is developed. The switch throughput, mean cell delay, and cell loss probability are computed from the analytical model. The accuracy of the analytical model is verified using simulation     

On the Spectral Efficiency of VSG CDMA in Nakagami and Rician Fading

This paper presents new analytical expressions for the spectral efficiency of variable spreading gain code division multiple access (VSG CDMA) networks in a Nakagami and Rician fading environments. These are used to gain insight into the impact of fading and background noise on the optimal transmit powers. Numerical results for a dual class and 5-class system, reveal that the spectral efficiency is optimized at higher signal-to-noise ratio levels when each user is retaining the same bit energy. However, at lower levels of the signal-to-noise-ratio, the spectral efficiency would be optimized when a larger amount of energy is allocated to the classes of higher data rate, as compared to the lower rate classes     

Semi-blind amplify-and-forward in two-way relaying networks

This paper addresses the analysis of a two-way semi-blind amplify-and-forward (AF) relay network, in which the relay node requires partial instantaneous channel state information (CSI) to amplify the received signals. First, we derive the expression of end-to-end signal-to-noise ratio in dual-hop transmissions over independent and not necessarily identically distributed Rayleigh fading channels. Based on the opportunistic AF selection relaying, we define bounds of some metrics such as average sum-rate and outage probability. Furthermore, we provide exact and approximate expressions for the average symbol error rate. The obtained results show that the performance of the proposed system decreases slightly while the processing complexity is reduced significantly compared to those of CSI-assisted AF relay schemes. In order to prove the exactness of the proposed analysis, a selection of numerical results is provided.     

VAD Based on Kernel Smoothed Function of EGARCH Models

An algorithm for a voice activity detector (VAD) is proposed. It is based on the exponential generalized autoregressive conditional heteroscedasticity (EGARCH) filter for generalized hyperbolic (GH), Gaussian random variables, adaptive threshold values and autocorrelation coefficients. EGARCH models are a new variation of GARCH models used especially in economic time series. A speech signal is assumed to have a GH because GH has heavier tails than the Gaussian distribution (GD) covering other heavy tailed distributions like hyperbolic, skewed $t$ , variance gamma (VG), inverse Gaussian (NIG), Cauchy, Student’s $t$ and Laplace distributions. The distribution of noise signal is assumed to be uncorrelated (white noise), but in general, that is not necessary. In the proposed method, heteroscedasticity is modeled by EGARCH. A kernel smoothed function of conditional variances and autocorrelations generate the soft detection vector. Finally, hard detection is the result of comparing the soft detection vector with an adaptive threshold value. The simulation results show that the proposed VAD is able to operate down to $-5$  dB.     

Multimedia-MAC protocol: its performance analysis and applications for WDM networks

The design of the medium-access control (MAC) protocol is the most crucial aspect for high-speed and high-performance local and metropolitan area networks, since the decisions made at this level determine the major functional characteristics of these networks. Most of the MAC protocols proposed in the literature are not suitable for multimedia applications, since they have been designed with one generic traffic type in mind. As a result, they perform quite well for the traffic types they have been designed for, but poorly for other traffic streams with different characteristics. In this paper, we propose an integrated MAC protocol called the Multimedia-MAC (M-MAC), which integrates different MAC protocols into a hybrid protocol in a shared-medium network to efficiently accommodate various types of multimedia traffic streams with different characteristics and quality-of-service demands, namely, a constant-bit-rate traffic, bursty traffic (say, variable-bit-rate traffic), and emergency messages (say, control messages). We have developed a mathematical framework for the analysis and performance evaluation of our M-MAC protocol, which involves a queueing system with vacation. We have applied our M-MAC design approach to a wavelength-division multiplexing network, and evaluated its performance under various traffic conditions.     

Computer and network security risk management: theory,challenges, and countermeasures

The need to secure information systems and networked infrastructures is now commonplace in most enterprises. The use of novel communication technologies has became a crucial factor that can considerably improve or affect productivity. This is essentially due to the importance of the information transmitted across communication networks and stored in servers. As a consequence, strong ties are being built between security and the enterprise business activity. Risk management, which is the discipline that deals with this aspect, integrates a litany of architectures, techniques, and models that are described in this paper. A global view is proposed to the reader through a presentation of the research activity that has been directed towards this field. Copyright © 2005 John Wiley & Sons, Ltd.