Performance of Low Earth Orbit Satellite Systems with Coding

The effect of block, convolutional and Turbo coding on the probability of error and the capacity are investigated for CDMA Low Earth Orbit (LEO) Satellite systems. The model employed assumes a contaminated Gaussian traffic model to be more compatible with different population areas. The conventional Gaussian distribution can be considered as a special case.     

A framework for the characterization and verification of embedded phase-locked loops

With the increasing use of phase-locked loops (PLLs) embedded in FPGAs, ASICs, and system-on-chip (SOC), there is a growing need for methods to verify their operation. This paper describes a general and organized list that includes tests for lock, jitter, stability, and modulation response. The list is offered as a guide to the verification and testing of an embedded PLL. For that reason, it is presented in such a way as to allow the reader to determine the extent to which the verification will be carried out. The tests are covered from the easiest to the most complicated to perform, with the amount of information gathered increasing along with the complexity of the test.     

A new alternative method to evaluate the J-integral in the case of elastomers

This study concerns the fracture of rubbers. The objective is to verify the validity of the J-integral expression we proposed for such materials (Aït Hocine et al., 2002). In this expression, the parameter J is represented as a multiplicative form of a geometrical η^* (or η) factor and elastic work per unit area as it has been already done in the Linear Elastic Fracture Mechanics (LEFM) (Turner, 1973). The whole problem rests in the fact that the factor η^* (or η) is unknown whereas in LEFM, expressions of η_el factors are available for several kinds of specimen geometry. Thus, in this work, an experimental and a numerical analysis have been achieved and we have shown, for both the studied materials and the considered specimens, that these unknown factors could be replaced by those issued from the LEFM or from the work of Kim and Joe (1989) on rubber-like materials. The results obtained confirm the validity of our model representing a single specimen method of an experimental evaluation of the elastomers fracture energy.     

Stability and calibration of platinum/palladium thermocouples following heat treatment

In this paper we describe the changes in the thermo EMF of Pt/Pd thermocouples in the temperature range from 0 to 1100 °C following a series of heat treatment at 960 °C. The magnitudes of the changes in EMF, the short and long term stability of the thermocouple were estimated, experimental results are presented. For the calibration of the thermocouple we have employed a reference polynomial function given in the literature [Metrologia 35 (1998) 761] for Pt/Pd thermocouples based on the International Temperature Scale of 1990 (ITS-90).     

Influence of state of stress on mixed mode stable crack growth through D16AT aluminium alloy

The stable crack growth through three-point bend (TPB) and stiffened and unstiffened compact tension (CT) specimens of D16AT aluminium alloy has been studied both theoretically and experimentally. The specimen thickness is 8 mm. The variation of load with crack opening displacement, the extent of stable crack growth, the cumulative plastically deformed zone and crack edge profiles have been obtained experimentally. These are also predicted theoretically under the assumption of either a state of plane stress or plane strain using a finite element scheme and the COA criterion. Generally, the experimental results agree well with the predictions based on the plane stress condition. There appears to be no significant variation in size of the experimental cumulative plastic zone across the specimen thickness, thereby indicating that the constraint on the plastic zone does not develop near the mid-thickness region.     

A Dempster–Shafer Based Tit-for-Tat Strategy to Regulate the Cooperation in VANET Using QoS-OLSR Protocol

In this paper, we address the problem of cooperation among vehicles in VANET using QoS-OLSR protocol in the presence of selfish nodes. QoS-OLSR is a proactive protocol that considers the Quality of Service (QoS) of the nodes while electing the cluster-heads and selecting the Multi-Point Relay (MPRs) nodes. Cluster-heads and MPRs might misbehave on the roads by over-speeding or under-speeding. Classical and generous Tit-for-Tats are proposed to analyze the interaction among vehicles. However, both strategies are not able to enforce the cooperation due the fact that they (1) count on individual watchdogs monitoring, (2) rely on the node-to-node cooperation decision, (3) and ignore the high mobility and packet collisions. Therefore, we propose a Dempster–Shafer based Tit-for-Tat strategy that is able to improve the decision and regulate the cooperation in the vehicular network. This is done by (1) launching a cooperative watchdogs monitoring, (2) correlating the observations of the different watchdogs using Dempster–Shafer theory, and (3) propagating the decisions among clusters. Thereafter, we compare the Dempster–Shafer based strategy with several strategies derived from the original Tit-for-Tat. Simulation results prove that the Dempster–Shafer based strategy is able to maintain the survivability of the vehicular network in the presence of high mobility and packet collisions with minimal time and overhead.     

The effect of nanographite addition on the physical properties of poly(vinylidene fluoride)/hydroxypropyl cellulose blend

In this study, polymeric films of poly(vinylidene fluoride) (PVDF)/hydroxypropyl cellulose (HPC) blend filled with various graphite-nanoparticles (GNP) contents were prepared via solvent-mixing technique. The compatibility between PVDF and HPC polymers was studied. The variations in structure, dielectric and thermal properties were investigated over the frequency range (20 Hz–3 MHz) and temperature range (20–110 °C). The X-ray diffraction and differential scanning calorimetry results reveal that the crystallinity of PVDF was affected by the presence of HPC and GNP. The dielectric results reveal that the great enhancement of dielectric constant ( \(\upvarepsilon^{{\prime }}\) ) and ac conductivity (σ_ac) were observed. The dielectric properties were explained in terms of the dielectric polarization mechanism. Both HPC and GNP additions enhance the \(\upvarepsilon^{{\prime }}\) of PVDF due to the formation of β-phase polymorph and the interface effect between the GNP and blend matrix. The improvement of the thermal stability was observed due to the regular arrangement of the side chains. The easy processing, high dielectric constant, low tangent loss and high thermal stability of the composites make the composites attractive for practical applications in embedded capacitors.     

Mesure de coefficients de convection par méthode impulsionnelle—influence de la perturbation de la couche limiteMeasurement of the convective heat coefficients by the pulsed method—influence of the boundary-layer perturbation

We present here some elements in order to improve the non-destructive procedures for the measurement of the local heat transfer coefficient between a plate uniformly heated and an air-flow. We use the pulsed photothermal method which consists of analysing the transient temperature on the front face of a wall, initially subjected to a convective flow, after a sudden deposit of luminous energy. For the examination of the experimental thermograms, two models are used: in the first one the heat coefficient is assumed to remain constant during the pulsed experiment, and we take into account its variation in time in the second one. The temporal variation law of the heat transfer coefficient used in the second model is obtained by extension of the differential method to the unsteady laminar boundary-layer due to a finite duration excitation. We compare the results of the two models in transient state with those given in steady state by multi-layered heat flux sensor.     

Accurate surface potential determination in Schottky diodes by use of correlated current and capacitance voltage measurements. Application to n–InP

Based on current voltage (I-V_g) and capacitance voltage (C-V_g) measurements, a reliable procedure is proposed to determine the effective surface potential V_d.V_g/ in Schottky diodes. In the framework of thermionic emission, our analysis includes both the effect of the series resistance and the ideality factor, even voltage dependent. This technique is applied to n-type indium phosphide (n-InP) Schottky diodes with and without an interfacial layer and allows us to provide an interpretation of the observed peak on the C-V_g measurements. The study clearly shows that the depletion width and the flat band barrier height deduced from C-V_g, which are important parameters directly related to the surface potential in the semiconductor, should be estimated within our approach to obtain more reliable information.     

Denitrogenation of carbazole by a novel strain Bacillus Clausii BS1 isolated from Egyptian Coke

In this study, an effective enrichment technique was applied to isolate different bacterial strains with capabilities to denitrogenate carbazole (CAR), as a model compound for nitrogenous polyaromatic hydrocarbons (NPAHs). Twenty-four different CAR-denitrogenating bacterial strains were isolated from mineral coke samples. From all, a Gram +ve bacterial isolate designated BS1 showed a higher biodenitrogenation (BDN) efficiency relevant to the well-known biodenitrogenating bacterium strain Pseudomonas resinovorans CA10, recording 77.15 and 60.66% removal of 1000 ppm CAR with the production of 119.79 and 102.43 ppm anthranilic acid, and 121.19 and 90.33 ppm catechol, as by-products, respectively. BS1 was identified by 16S rDNA gene sequence analysis to be Bacillus clausii BS1 (NCBI GenBank Accession no. KF985981) with a similarity of 99.14%. The CAR-BDN pathway was also elucidated using high-performance liquid chromatography (HPLC) and gas chromatography mass spectrometry analysis (GC/MS), which proved further metabolism of catechol to muconic acid.