Analytical analysis of applying packet fragmentation mechanism on IEEE 802.11b DCF network in non ideal channel with infinite load conditions

The analytical modeling and performance analysis of the 802.11 network in all its various extensions (802.11b, 802.11a, 802.11g, 802.11e, 802.11n, etc.) have already been widely explored over the past years. However, the packet fragmentation mechanism (PFM), which is proposed by the IEEE work group to reduce the impact of bit error rate (BER) on the packet error rate (PER), has not been considered in the analytical models proposed in the literature. Yet, the PFM constitutes a key parameter to achieve the best performances of 802.11 networks. In this paper, we extend the Bianchi’s Markov chain model with the PFM and the PER. Then, we analyze the performance improvement level achieved with the PFM in an IEEE 802.11 network under the impact of BER and packet length. The proposed analysis has been applied on the basic access method of 802.11b network in saturated traffic conditions. So, we have analyzed the throughput and the mean response time of the 802.11 network. The obtained theoretical results are validated by simulation.     

A Brief Survey of our Contribution to Stable Carbene Chemistry

This personal account summarizes our work, beginning with the discovery of the first stable carbene in 1988 up until the recent isolation of mesoionic carbenes. It explains why we have moved our focus from acyclic to cyclic carbenes, and shows that these stable species are not limited to the role of ligand for transition metals, but that they are also powerful agents for the activation of small molecules, and for the stabilization of highly reactive diamagnetic and paramagnetic species.     

Work stealing with private integer–vector–matrix data structure for multi‐core branch‐and‐bound algorithms

In this paper, the focus is put on multi‐core branch‐and‐bound algorithms for solving large‐scale permutation‐based optimization problems. We investigate five work stealing (WS) strategies with a new data structure called integer–vector–matrix (IVM). In these strategies, each thread has a private IVM allowing the local management of a set of subproblems enumerated using a factorial system. The WS strategies differ in the way the victim thread is selected and the granularity of stolen work units (intervals of factoradics). To assess the efficiency of the private IVM‐based WS approach, the five WS strategies have been extensively experimented on the flowshop scheduling permutation problem and compared with their conventional linked‐list‐based counterparts. The obtained results demonstrate that the IVM‐based WS outperforms the linked‐list‐based one in terms of CPU time, memory usage and number of performed WS operations. Copyright © 2016 John Wiley & Sons, Ltd.     

Study of microstructure, phases and microhardness of metallic coatings deposited by flame thermal spray

The recharging technique by thermal spraying offers the opportunity of renovating the worn surface parts of a machine element to give it again a new technical life despite its previous degradation in service. This process has consequently interesting economic impacts. In order to improve the adherence between 100Cr6 steel deposits and the substrate material (left worn crankshafts), company SNC ATRA of Béjaïa uses at present a composite formed by (100Cr6 steel/molybdenum bond coat of 0.2 mm thick/crankshaft substrate). As a matter of fact, it is shown in the present work that the molybdenum bond coat is not appropriate since, for the 0.2 mm thickness, lateral cracks are observed in the middle of the bond coat. On the other hand, our experiment is that a deposit of 100Cr6 steel projected directly on the substrate seems more promising since no gaps or cracks were detected at the “deposit/substrate” interface of this two-material composite. Lastly, phase analysis using X-ray diffraction confirmed that during spraying process, a stable -phase (bcc) of 100Cr6 wire was transformed to a new phase of γ-phase (fcc). The coatings exhibited the higher microhardness which would contribute to increase wear resistance.     

Modeling and performance evaluation of the IEEE 802.15.4e LLDN mechanism designed for industrial applications in WSNs

The IEEE 802.15.4 standard has been introduced for low latency and low energy consumption in wireless sensor networks. To better support the requirements of industrial applications, where the use of this standard is limited, the low latency deterministic network (LLDN) mechanism of the IEEE 802.15.4e amendment has been proposed. In this paper, we develop a three dimensional Markov chain model for the IEEE 802.15.4e LLDN mechanism. Then, we estimate the stationary probability distribution of this chain in order to derive theoretical expressions of some performance metrics, as the reliability, energy consumption, throughput, delay and jitter. After that, we conduct a comparative study between the IEEE 802.15.4e LLDN and the IEEE 802.15.4 slotted carrier sense multiple access with collision avoidance (CSMA/CA). Numerical results show that the deterministic behavior of the LLDN mechanism significantly reduces the collision probability providing best performances in terms of reliability, energy consumption, throughput and delay compared to the IEEE 802.15.4 slotted CSMA/CA. Finally, the accuracy of our theoretical analysis is validated by Monte Carlo simulations.     

Determination of the combustion properties of natural gases by pseudo-constituents

This paper presents a methodology for a rapid determination of important natural gas combustion properties (lower heating value, Wobbe index and the stoichiometric air-fuel ratio) using easily detectable physical properties. It is possible to determine natural gas composition by measuring two physical properties and using specific ternary diagrams (CH₄-C₂H₆-C₃H₈ and CH₄-C₂H₆-N₂). The first part of the work deals with the selection of two physical properties from a group comprising thermal conductivity, refraction index, and speed of sound. Then, in the second part, a sensor using the best couple of physical property is used to determine the ternary pseudo-constituents of the gas mixture. The model and the sensor are applied to specific situations such as the online determination of LHV. The error on the combustion properties of natural gas is less than 1% over the gases considered in the present study and over about 20 typical gases supplied over Europe. The effect of small errors in the measurement of physical properties has also been highlighted.     

Performances comparison of pulse-pair and 2-step prediction algorithms for the doppler spectrum estimation

In this work we use real data provided by terminal pulse Doppler radar (WSR-88D) echoes to estimate the windshear hazards disastrous for the aircraft takeoffs and landings. Briefly two different methods are used to estimate the received Doppler moments. The second central moment which is the variance of the wind speed is called width or shear. A first method is in the time domain and also called pulse-pair, while the second is in the frequency domain. The main aim of this study is a performances comparison of results provided by the two mentioned methods and assumes that the power spectrums of the received signals are approached with the Gaussian shape.