Wireless mesh networks channel reservation: modelling and delay analysis

In order to overcome the negotiation procedure bottleneck of the standard DCF in wireless mesh networks, the authors propose a new channel reservation function (CRF) that reduces the negotiation overhead of the DCF, which as a result reduces the overall transmission delay effectively without of any extra bandwidth consumption. Furthermore, the authors provide an analytical model for the proposed scheme for which the simulation results measure the amount that the new method can reduce the average total delay for both regular and fragmented mesh topologies demonstrating superiority of the new method over the classic 802.11 solution. Additionally, the authors extend the scheme to multichannel CRF upon which the proposed method can be used for multichannel applications.     

Scheduling hybrid flowshops with sequence dependent setup times to minimize makespan and maximum tardiness

This article addresses the problem of scheduling hybrid flowshops where the setup times are sequence dependent to minimize makespan and maximum tardiness. To solve such an NP-hard problem, we introduce a novel simulated annealing (SA) with a new concept, called “Migration mechanism”, and a new operator, called “Giant leap”, to bolster the competitive performance of SA through striking a compromise between the lengths of neighborhood search structures. We hybridize the SA (HSA) with a simple local search to further equip our algorithm with a new strong tool to promote the quality of final solution of our proposed SA. We employ the Taguchi method as an optimization technique to extensively tune different parameters and operators of our algorithm. Taguchi orthogonal array analysis is specifically used to pick the best parameters for the optimum design process with the least number of experiments. We established a benchmark to draw an analogy between the performance of SA with other algorithms. Two basically different objective functions, minimization of makespan and maximum tardiness, are taken into consideration to evaluate the robustness and effectiveness of the proposed HSA. Furthermore, we explore the effects of the increase in the number of jobs on the performance of our algorithm to make sure it is effective in terms of both the acceptability of the solution quality and robustness. The excellence and strength of our HSA are concluded from all the results acquired in various circumstances.     

A hybrid transformer model for determination of partial discharge location in transformer winding

Partial discharges are well known as a source for insulation degradation in power transformers. A hybrid transformer model is introduced to simulate the transformer winding transient response. Transformer structural data is used to determine the hybrid model parameters. Calculations of the hybrid transient model parameters are based on the parameters of the lumped parameter equivalent transformer model and electromagnetic rules. Modern computation techniques and optimizations are employed beside this model for PD location using the multi conductor transmission line model and also to analyze its propagation aimed at achieving (i) more reliable simulation results (ii) less computational time (iii) accurate results for a wide range of frequency. The simulation results on a 66 kV, 25 MVA fully interleaved winding are presented. The measurement results on this winding are employed to validate this model     

Polyisoprene-nanostructured carbon composite (PNCC) organic solvent vapour sensitivity and repeatability

In this paper highly structured carbon black (HSCB) dispersion method effect on polyisoprene-nanostructured carbon composite (PNCC) organic solvent vapour (OSV) sensitivity is presented. PNCC has been produced using two different HSCB dispersion techniques: (1) dry method: the HSCB dispersed in polyisoprene mixing ingredients by cold rolling and (2) wet method: the HSCB dispersed in chloroform by ultrasonic homogenizer and mixed with solution of rubber in chloroform by magnetic stirring. The sensitivity to OSV of the obtained PNCC is tested by holding the samples in vapour of toluene or ethyl acetate and measuring in situ electrical resistance, mass, and length of the sample. Obtained results indicate two mechanisms of the change of electrical resistance in PNCC. Repeatability of the response of PNCC is tested in case of toluene vapour.     

Expulsion characterization in resistance spot welding by means of a hardness mapping technique

Expulsion is an undesired event during resistance spot welding because the weld quality deteriorates. It is the ejection of molten metal from the weld nugget which usually occurs due to applying a high current for a short welding time. Expulsion has a significant impact on the final yield strength of the weld, thus the detection and characterization of expulsion events is significant for the quality assurance of resistance spot welds. In this study, hardness mapping, using a scanning hardness machine, was used as a quality assurance technique for re- sistance spot welding. Hardness tests were conducted on a resistance spot welded sample to prepare a hardness map. The test results showed good correlation between the hardness map and metallographic cross sections. The technique also provided further fundamental understand- ing of the resistance spot welding process, especially regarding the occurrence of expulsion in the nugget.     

Advanced satellite concepts for future generation VSAT networks

Advanced communication networks that use very-small-aperture terminals (VSATs) are considered. The techniques and technologies suitable for powerful satellites and system architectures for future VSAT networks are discussed. These include high effective isotropic radiated power, multiple-beam satellite antennas, and various access techniques. Examples of systems planned by the government and private industry are described     

Genetic algorithm quality of service design in resilient dense wavelength division multiplexing optical networks

The important role of quality of service (QoS) in deployment of a resilient dense wavelength division multiplexing (DWDM) backbone for global networks requires critical design-phase planning optimisation. The design issues of resilient DWDM networks for bandwidth and delay sensitive applications of dedicated path protection are addressed. A genetic algorithm (GA) model has been developed to solve the routing and wavelength assignment problem using binary variable-length chromosome encoding under two different schemes of bandwidth optimisation (BOS) and delay optimisation (DOS).The performance of the new GA-based resiliency model has been evaluated for four benchmark networks: PAN EUROPEAN, COST239, NSFNETand ARPA2. Simulation results show a superior capability and efficiency for the model to solve this complex, multi-constraint and nondeterministic polynomial-hard problem for BOS and DOS. The nonlinear nature of this process reveals a significant sensitivity for optical layer network topology on the optimum-design QoS. The results also demonstrate that the PAN EUROPEAN network shows the highest flexibility for primary path design, NSFNET for the secondary path and ARPA2 comes with the lowest design flexibility for both primary and secondary paths.     

Electrochemical assessing corrosion inhibiting effects of zinc aluminum polyphosphate (ZAPP) as a modified zinc phosphate pigment

Undesirable anti-corrosion performance of zinc phosphate pigment, the classical chromate replacement, has led researchers to take modification into account. Polyphosphate-based anti-corrosion pigments as a result of modification of zinc orthophosphate have been found to function much more efficiently. This study aimed to evaluate performance of steel samples immersed in 3.5% NaCl aqueous solution-containing zinc aluminum polyphosphate (ZAPP) pigment extract compared to those involving conventional zinc phosphate (ZP) pigment extract and also no pigment (blank) using electrochemical tests such as electrochemical impedance spectroscopy (EIS) and linear polarization (LP) as well as surface analysis. Impedance spectra and polarization curves revealed two different trends, showing the superiority of ZAPP pigment. Based on the results of scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), presence of a precipitated layer on the surface was confirmed when steel sample was immersed into the solution-containing ZAPP.     

A study on open shop scheduling to minimise total tardiness

This paper deals with open shop scheduling to minimise total tardiness. Contrary to other scheduling problems (i.e., flow and job shops), the formulation of the open shop is given far less attention in the literature. Therefore, we intend to fulfil this gap by the presentation of four different mixed integer linear programming models. We compare the models on the basis of their complexity sizes. Furthermore, we propose two metaheuristics based on genetic algorithm and variable neighbourhood search. We exhaustively explore the effect of different operators and parameters on the performance of genetic algorithm by means of Taguchi method. Two computational experiments are conducted to evaluate the models and algorithms for performance. The first one includes small-sized instances by which the models and general performance of the algorithms are examined. The second one consists of three well-known benchmarks by which we further evaluate the algorithms. The results show the effectiveness of the proposed models and algorithms.     

Application of response surface methodology for weld strength prediction in laser welding of polypropylene/clay nanocomposite

Welding as a fabrication process can be used to join materials, including composite and nanocomposites and laser welding process due to its advantages has found wide applications in this field. Its process parameters can play a significant role in determining the weld strength of laser-welded joints in polypropylene/clay nanocomposites. In this study, the effect of laser welding parameters, such as laser power, welding speed and focal position along with the clay content in a polypropylene/clay nanocomposite on weld strength were determined using response surface methodology. This methodology was applied for developing a mathematical model which can predict the main effects of the above parameters and their impacts on tensile strength of butt-welded laser joints in 2-mm thick polypropylene/clay nanocomposite sheets. The analysis of variance was performed to check the adequacy of the developed model. A comparison was also made between the predicted and actual results. The results showed that weld strength decreased when clay content was increased from 0 to 6 %, but welding speed increased from 30 to 60 mm/s. The above parameters were also optimized to achieve a high strength welded joint.