New study of the abnormal behavior of the low temperature dependence of the current in inhomogeneous Schottky diode

In this study, we show clearly why unexpected observations have been reported in the current–voltage curves of Schottky diodes, containing barrier inhomogeneities generated by using the analytical results based on a Gaussian distribution model of barrier heights. The Chand's calculations have shown that the current (saturation current) at low temperatures may exceed the current (saturation current) at high temperatures when the effective barrier height is calculated from an appropriate integral with integration limits −∞ and +∞. In this new study, we show that the method followed by Chand to remove these anomalies is not accurate enough. We prove that the origin of these anomalies stems from the nature of a proper function f(φ) that moves to the negative barrier heights and takes large value of the integral at low temperatures than at high temperatures when it has large standard deviation (σ) and the discrepancies are not due to the integration limits as Chand concluded. In order to obtain results consistent with the thermionic emission–diffusion theory, the standard deviation must have lower values. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of Cloisite® 30B on the Diffusion of Irganox 1076 in HDPE

The diffusion of a thermal stabilizer, Irganox 1076, is studied both in pure high‐density polyethylene (HDPE) and HDPE matrix filled with 1 wt% of Cloisite® 30B. The diffusion experiments are carried out by using the Roe method formed by a stack of several polymer films of 120 ± 01 μm in thickness. In this study, a simple method is used to measure the diffusion coefficient, with the aid of Fourier Transform InfraRed spectroscopy without any extraction or refining steps in the analysis. The diffusion coefficient (D_p) of both materials are obtained in the temperature range 80–100°C using the second Fick's law. By applying the Arrhenius equation to the calculated D_p coefficients, an estimation of activation energies of the diffusion process is also achieved. The results indicate that the diffusion coefficient of Irganox 1076 in HDPE has been decreased by adding 1% of Cloisite® 30B.     

An efficient QoS routing algorithm for solving MCP in ad hoc networks

Providing guaranteed quality of service (QoS) in wireless networks is a key issue for deploying multimedia applications. To support such a QoS, an arduous problem concerning how to find a feasible end to end path to satisfy multiple QoS constraints should be studied. In general, multi-constrained path selection, with or without optimization, is an NP-complete problem that cannot be exactly solved in polynomial time. Approximation algorithms and heuristics with polynomial and pseudo-polynomial time complexities are often used to deal with this problem. However, existing solutions suffer either from excessive computational complexities that cannot be used for multimedia applications in ad hoc networks characterized by mobility and performance constraints (e.g., limited energy, wireless medium, etc.). Recently a promising heuristic algorithm H_MCOP using a non linear Lagrange relaxation path functions has demonstrated an improvement in its success rate and in finding feasible paths. However, the H_MCOP is not suitable for ad hoc networks and has not exploited the full capability that a Lagrange relaxation could offer. In this paper, we propose an efficient multi-constrained path heuristic called E_MCP, which exploits efficiently the Lagrange relaxation and enhances the path search process to be adequate to mobile ad hoc networks. Using extensive simulations on random mobile network with correlated and uncorrelated link weights, we show that the same level of computational complexity, E_MCP can achieve a higher success ratio of finding feasible paths.     

Glyceraldehyde-3-phosphate dehydrogenase from Tetrahymena pyriformis: enzyme purification and characterization of a gapC gene with primitive eukaryotic features

The characteristics of acetate-free biofiltration (AFB) are now well documented in patients with chronic renal failure: hemodynamic tolerance, correction of acid-base imbalance, buffer-free dialysate (without acetate) and absence of backfiltration. This hemodialysis technique can be beneficial to patients with acute renal failure (ARF). In our intensive care unit, we prospectively studied 29 patients with isolated ARF or ARF associated with failure of other organs. All eligible patients were randomly assigned to undergo dialysis with bicarbonate hemodialysis (BH) or with (AFB). All used the same high flux biocompatible dialysis membranes. Effectiveness and hemodynamic tolerance of hemodialysis sessions and evolution of patients were analyzed. Correction of metabolic disorders, although better in the AFB group was not statistically different from that in the BH group. Re-equilibration of acid-base balance was also similar, with or without mechanical ventilation. Heparin consumption was significantly higher in the AFB group, with no effect on haemorrhagic complications. Analysis of hypo- and hypertensive episodes, defined as arterial pressure (AP) variations 20% greater than initial pressure, showed no difference in terms of number or degree of AP variation. However, weight loss and the rate of ultrafiltration led to a higher hypotensive risk in the BH group (p < 0.05). Finally, the clinical course and prognosis was similar in both groups. In summary, AFB may be considered as effective a hemodialysis technique as BH in patients with ARF. Weight loss was better tolerated in the AFB group and can be a favorable factor considering the deleterious effect of overhydration in patients admitted to an intensive care unit. This study invites a comparison of longer dialysis session of AFB therapy and continuous hemodiafiltration.     

Raman spectroscopic study of the ternary system Sb2S3-As2S3-Tl2S

Raman spectroscopy has been used to study the local structure in glassy compositions of the ternary system As₂S₃-Sb₂S₃-Tl₂S. The evolution of the positions and shapes of the bands observed is attributed to modifications in the environment of arsenic and antimony corresponding to structural changes as the composition is varied.     

An efficient heterogeneous key management approach for secure multicast communications in ad hoc networks

In a mobile wireless ad hoc network, mobile nodes cooperate to form a network without using any infrastructure such as access points or base stations. Instead, the mobile nodes forward packets for each other, allowing communication among nodes outside wireless transmission range. As the use of wireless networks increases, security in this domain becomes a very real concern. One fundamental aspect of providing confidentiality and authentication is key distribution. While public-key encryption has provided these properties historically, ad hoc networks are resource constrained and benefit from symmetric key encryption. In this paper, we propose a new key management mechanism to support secure group multicast communications in ad hoc networks. The scheme proposes a dynamic construction of hierarchical clusters based on a novel density function adapted to frequent topology changes. The presented mechanism ensures a fast and efficient key management with respect to the sequential 1 to n multicast service.     

TBSA: Threshold-Based Simulation Accuracy Method for Fast Analog DC Fault Simulation

Starting from a good solution approximation has proved to be very efficient to reduce CPU time required by DC simulation of analog circuits. In order to obtain an additional speedup in DC fault simulation, this paper proposes a new criterion to end the Newton-Raphson (NR) iterative algorithm before convergence. In the case where an initial solution approximation is used, the analysis of the NR algorithm behavior until convergence is presented and a threshold-based simulation accuracy (TBSA) method is then proposed. TBSA stops the iterations when the solution at current NR iteration is enough accurate to immediately classify the fault. According to the detection thresholds, a CPU time/accuracy tradeoff is achieved without altering the fault classification results. The proposed method has been validated on 12 MOS and BJT benchmark circuits considering DC fault simulation under process parameter variations. TBSA is compared to two existing methods which are: standard simulation until convergence method which is accurate but requires a large CPU time, and single NR iteration method which is very fast but without any control over the accuracy. All the compared methods reuse the fault-free circuit results as initial solution for each faulty circuit simulation. It is shown that TBSA requires an intermediate number of NR iterations while achieving correct fault classification, especially for parametric faults which take advantage of using a more accurate initial solution.     

Integrated production quality and condition-based maintenance optimisation for a stochastically deteriorating manufacturing system

This paper investigates the problem of optimally integrating production quality and condition-based maintenance in a stochastically deteriorating single- product, single-machine production system. Inspections are periodically performed on the system to assess its actual degradation status. The system is considered to be in ‘fail mode’ whenever its degradation level exceeds a predetermined threshold. The proportion of non-conforming items, those that are produced during the time interval where the degradation is beyond the specification threshold, are replaced either via overtime production or spot market purchases. To optimise preventive maintenance costs and at the same time reduce production of non-conforming items, the degradation of the system must be optimally monitored so that preventive maintenance is carried out at appropriate time intervals. In this paper, an integrated optimisation model is developed to determine the optimal inspection cycle and the degradation threshold level, beyond which preventive maintenance should be carried out, while minimising the sum of inspection and maintenance costs, in addition to the production of non-conforming items and inventory costs. An expression for the total expected cost rate over an infinite time horizon is developed and solution method for the resulting model is discussed. Numerical experiments are provided to illustrate the proposed approach.     

Prediction of reliability analysis of composite tubular structure under hygro-thermo-mechanical loading

The present paper focuses on reliability prediction of composite structure under hygro-thermo-mechanical loading, conditioned by Tsai-Wu failure criterion, where the Monte–Carlo method is used to estimate the failure probability(Pf). This model was developed in two steps: first, the development of a deterministic model, based on an analytical and numerical approach, and then, a probabilistic computation. Using the hoop stress for each ply, a sensitivity analysis was performed for random design variables, such as materials properties, geometry, manufacturing, and loading, on composite cylindrical structure reliability. The probabilistic results show the very high increase of failure probability when all parameters are considered.