In this paper, the onset voltage of negative corona is theoretically predicted for point-cup gaps positioned in air. The method of calculation is based on the criterion developed for the formation of repetitive negative corona Trichel pulses. Field distributions are determined through charge simulation method coupled with least-square error method for optimal charge distribution and accurate field computation. Different gap dimensions are studied. Accurate distributions, not only for the potential but also for the electric field have been obtained throughout the entire interelectrode space. Negative onset voltage of corona is calculated at different gap dimensions and different air pressures.. The values of calculated onset voltages agreed well with those measured experimentally within 5 %.

Models of HVDC ionized fields have, traditionally, been based on deterministic approaches, i.e. the exposure variables are defined as single-point estimates. Alternatively, the present work acknowledges the probabilistic nature of these variables and caters for their inherent uncertainties. Randomness in the exposure variables; such as the ambient field intensity and current density, the wind speed, and the object dimensions, is identified and accounted for. A general probabilistic model of exposure, in which the exposure variables are presented in the form of probability distributions, is presented. The model is employed to derive basic exposure severity indices that can be used to quantify the impact of exposure to ionized fields under HVDC lines.

The electronic transmission through a one-dimensional (1D) monomode wave-guide made of asymmetric loops pasted together with segments of finite length is investigated. Existence of gaps (where the propagation of electrons is forbidden) in the band structure is reported. These gaps originate both from the periodicity of the system and the resonance states of the loops. The width of these band gaps depends on the geometrical parameters of the structure and may be drastically increased in a tandem geometry made of several successive asymmetric serial loops structures (ASLSs) which differ by their geometrical characteristics. These ASLSs may have potential applications as ultra-wide-band filters.

In the frame of the long-wavelength Heisenberg model, the magnonic bandgaps and the selective transmission in a serial loop structure, made of loops pasted together with segments of finite length, are investigated theoretically. The loops and the segments are assumed to be one-dimensional ferromagnetic materials. Using a Green function method, we obtained closed-form expressions for the band structure and the transmission coefficients for an arbitrary value of the number N of loops in the serial loop structure. It was found that the gaps originated from the periodicity of the system. The width of these forbidden bands depends on the structural and compositional parameters. We also present analytical and numerical results for the transmission coefficient through a defective geometry where the length of one finite branch has been modified. It was demonstrated that the presence of this defect in the structure can give rise to localized states inside the gaps. We show especially that these localized states are very sensitive to the size of the loops and to the periodicity as well as to the length and the location of the defect branch.

Four commercial non-ionic surfactant compounds, namely tween 80, 60, 40 and 20, were tested as inhibitors for corrosion of nickel in 1.0 M H2SO4 solution. Weight loss measurements, potentiostatic polarization and cyclic voltammetry techniques were used in this study. It was found that all the four used compounds act as good inhibitors for acid corrosion of nickel. The inhibition efficiencies obtained by the three techniques were almost the same, and increase with increasing the hydrocarbon chain length, the presence of a double bond in the chemical structure of the surfactant and with increasing the surfactant concentration. The polarization studies show that tween compounds act as mixed inhibitors. The inhibition action of these surfactants is interpreted in view of their adsorption on the metal surface making a barrier to mass and charge transfer. It was found that the adsorption of only tween 20 and 40 follows Langmuir adsorption isotherm. The values of free energy of adsorption for them were calculated. It was found that the adsorption process is spontaneous and increases, for different surfactants, in the same direction as inhibition efficiency. The cyclic voltammetry shows that there is only one anodic peak corresponding to the dissolution reaction of nickel electrode. The current of this dissolution peak was used also for corrosion rate measurements and in evaluation of inhibition efficiencies of the used compounds.

The paper presents a model for the interaction between humans and ELF magnetic fields generated by power lines. Electric current densities induced due to 50 Hz magnetic fields in a human model placed in a close proximity of 500 kV lines are presented and analyzed. The specific absorption rate (SAR), is investigated for various human model locations under the power lines. Also examined in this work is the case of live line maintenance workers, where they may be located near the central and the outermost phase conductors. The induced current density and SAR are computed and discussed.

Electric field intensity and ion current density at the ground level of HVDC power lines are significant electrical environment parameters in relation to biological effects. These quantities, largely, depend on the line geometry and meteorological conditions. In. order to make a reliable predetermination of the electric field intensity and ion current density, the paper presents detailed numerical assessment of these quantities on a full scale line.. The governing equations are solved using an iterative algorithm. Factors influencing the ionized field quantities, namely, the wind speed, the line sag, the conductor surface gradient, are accounted for both individually and collectively and the interactions between them is established. Results and discussion are presented.

Guar gum was tested as corrosion inhibitor for carbon steel in 1 M H2SO4 solution using weight loss and Tafel polarization techniques. The results showed that the inhibition efficiency increases with the increasing of the guar gum concentration, which act as an inhibitor of the mixed type. The inhibition action of guar gum was discussed in terms of its horizontal adsorption on the metal surface. The adsorption follows Langmuir adsorption isotherm. The effect of the presence of chloride ion in pitting corrosion was analyzed by the potentiodynamic anodic polarization technique. The pitting corrosion potential changes with the concentration of Cl- ion according to a sigmoid S-shaped curve. This behaviour was explained on the basis of the formation of passivatable, active and continuously propagated pits.

A magnonic chain of cells consisting of a serial loop structure with dangling resonators (SLS-DRs) is designed to obtain possibly large stop bands. Contrary to all known systems of this kind, a spectral gap of nonzero width occurs here even with a single cell. General expressions for the dispersion relation and for the transmission coefficient are given for all serial systems of this kind within the framework of the long-wavelength Heisenberg ferromagnetic model. The width of the stop bands is very sensitive to the number of resonators and may be drastically increased in a tandem geometry made of several successive SLS-DRs which differ by their geometrical characteristics. These SLS-DRs may have potential applications in spin injection into devices.

The acoustic band structures and transmissions through a one-dimensional (I D) monomode waveguide made of asymmetric slender tube loops pasted together with slender tubes of finite length are investigated theoretically. These monomode circuits may exhibit large stop bands where the propagation of acoustic waves is forbidden. These stop bands (gaps) originate both from the periodicity of the system and the resonant modes of the loops. The width of these bandgaps depends on the geometrical parameters of the structure and may be drastically increased in a tandem geometry made of several successive asymmetric serial loop structures (ASLSs) which differ in their geometrical characteristics. These ASLSs may have potential applications as ultra-wideband filters.

We consider, in the frame of the long-wavelength Heisenberg model, the effect of a pinning field on the spin wave band gaps and transmission spectra of one-dimensional comb-like structures. Using a Green's function method, we obtained closed-form expressions for the band structure and the transmission coefficients for an arbitrary value of the number N of sites (N'of resonators) in the comb-like structure. We report the opening-up of stop bands inside the pass-bands due to the effect of the pinning field at the ends of the resonators of the comb. These structures, composed of one-dimensional ferromagnetic materials, may exhibit large gaps where the propagation of spin waves is forbidden. The width and frequency position of these gaps depends on the strength of the pinning field.

We present a simple multiplexing structure made of two discrete plasmon wires coupled by two metal nanoclusters. We show that this simple nanosystem can transfer one plasmon wavelength from one wire to the other. Closed-form relations between the transmission coefficients and the nanocluster distances are given to optimize the desired directional plasmon ejection.

Simple multiplexing phonon structures are presented. Such structures can be deposited on a surface with current ultra-high vacuum technologies. In the atomic domain they are supposed to be made out of two parallel mono-atomic chains of atoms and of a simple coupling device made out of two other atoms interacting together and with the two chains. We show analytically that these simple structures can transfer with selectivity and directivity one phonon from one chain to the other, leaving neighbor phonons unaffected. We give closed-form relations enabling to obtain the values of the relevant physical parameters for this multiplexing phenomenon to happen at a chosen wavelength. Finally, we illustrate this general theory by an application.

A system of equations of motion for the Green functions in layered antiferromagnets such as La2CuO4 and YBa2Cu3O6 has been treated by an "equal access" decoupling scheme. The correlation functions are fully equivalent in this scheme in contrast with the ordinary random-phase approximation (RPA). The method provides a new insight into the nature of the RPA treatment of the localized spin dynamics in magnets. Explicit self-consistent expression for the sublattice magnetization in a perpendicular field is given. The dependence of the sublattice magnetization on a perpendicular magnetic field is studied. High temperature tails of the in-plane sublattice magnetization have been found to result from a nonlinear coupling of the perpendicular magnetic field with the antiferromagnetic order parameter.

Thermal gradients may develop between the upper and lower surfaces of bridge decks in severe hot or cold weathers during the lifetime of any bridge. Temperature gradients over a bridge cross section vary with time and depend on many variables. If thermal expansion or contraction due to these thermal gradients is restrained; then high stresses are produced which can be of the same order as dead and live loads. If these gradients are too severe and are not taken into consideration during the design phase; then severe cracking may occur which can lead to early deterioration of bridge decks. The present work alms at studying the effect of thermal gradients between upper and lower surfaces of bridge decks on the behavior of these decks. Bridges having different cross sections, different supporting conditions in substructures and different thicknesses of the wearing surfaces have been studied; to evaluate their effect on the straining actions resulting from thermal loading. The results of the present work have indicated that a significant increase in straining actions resulting from thermal gradients takes place. Also, it has been revealed that the effect of thermal gradients on voided slab bridges is more pronounced than box girder bridges. Moreover, the thickness of the wearing surface had a significant effect on the straining actions resulting from thermal loading. Thus, thermal gradients should always be taken into account during the design phases of bridges; to insure the safety and integrity of these structures.

This paper describes theoretical and experimental investigations of the effect of an electrode coating on the onset voltage of a corona on negatively stressed electrodes. Dielectric-coated hemispherically-capped rod-to-plane gaps positioned in air are investigated. The onset voltage is calculated based on the self-recurring single electron avalanche developed in the investigated gap. Accurate calculation of the electric field in the vicinity of a coated rod and its correlation to the field values near a bare rod of the same radius are obtained using the charge simulation method. The calculated field values are utilized in evaluating the onset voltage of the corona. Also, laboratory measurements of the onset voltage on bare and coated electrodes are carried out. The effects of varying the field nonuniformity, the coating thickness and its permittivity on the onset voltage values are investigated. The results show that coating the electrodes with a dielectric material is effective in increasing the onset voltage of the corona on its surface. The calculated onset voltage values for coated and bare electrodes agree satisfactorily with those measured experimentally.

The reaction of 5-vinylsalicylidene-2-aminomethyl-pyridine (VSAPH) with Cu(II) resulted in a yellow-red Cu(II) polymer complex with very low magnetic moment at room temperature, while reaction with Co(II) produced a diamagnetic octahedral Co(III) polymer complex. NiCl2 gave a paramagnetic octahedral polymer complex, while the rest are diamagnetic with square planar and tetrahedral geometries.

This study represents an experimental and computational investigation of the aerodynamic and heat transfer characteristics of two interfering low-rise buildings. The two buildings situated in line are similar with a slanted roof. The investigated parameters include the gap between the two buildings, the roof angle, and the wind speed (Reynolds number). The solar radiation absorbed by the roof and conducted into the building that appears as a cooling load is also studied. Heat flow through such roofs is found to be sensitive to number of factors, including, wind speed, roof angle and surface to air temperature difference. The experimental results demonstrated pressure distributions on the different walls and roofs of the two buildings. Also, the drag force on the two buildings is measured for different interfering cases. The corresponding numerical results were obtained using the computational finite element procedure (ANSYS 9.0 for two-dimensional model and Fluent 6.12 for three dimensional model) that uses the standard k- Hmodel. Computational results include velocity vectors, distributions of turbulence kinetic energy, and temperature gradients as well as the pressure distribution. Certain consideration was paid to the difference in aerodynamic characteristics between a single building and two interfering buildings. Comparison between the numerical and experimental results showed a good agreement in terms of gross feature of mean flow for all cases examined, although some detailed differences were observed.

The inhibitive action of the extract of Ficus nitida leaves toward general and pitting corrosion of C-steel, nickel and zinc in different aqueous media was investigated. Weight loss measurements, potentiostatic and potentiodynamic polarization techniques were used in this study. It was found that the presence of ficus extract in the corrosive media (acidic, neutral or alkaline) decreases the corrosion rates of the three tested metals. The inhibition efficiency increases as the extract concentration is increased. The inhibition efficiency depends on the type of corroded metal and on the corrosive solution. It was also found that the presence of ficus extract in the chloride containing solution shifts the pitting potentials of the tested metals toward the noble direction. The inhibitive action of ficus extract is discussed in view of adsorption of its components, the poly aromatic compounds, friedelin, epifriedelanol and nitidol, on the metal surface. It was found that such adsorption follows Langmuir adsorption isotherm. The calculated values of the free energy of adsorption indicated that the adsorption process is spontaneous.

The effect of supply reactance on the performance of a three-phase induction motor fed from a non-ideal single-phase supply, using a capacitor phase converter, is investigated. Equations for predicting the performance of the motor are derived, with the effect of the single-phase supply reactance taken into consideration. Star-and delta-connected motors are considered in deriving the performance equations. Computed results for the motor-performance characteristics obtained when the motor is fed from a non-ideal single-phase supply are compared with those obtained when the motor is fed from a non-ideal three-phase balanced supply having the same supply reactance as that of the single-phase supply.

In this paper a closed-form solution of the performance of a three-phase voltage-source, six-step inverter feeding a three-phase static inductive bond is presented. Analytical expressions for the steady-state currents of the system are derived from which the performance of the system can be investigated. Explicit formulae for the current ratings of the switching elements, whether thyristors, transistors or diodes used in the system are derived.

This paper describes the switching operations and the accompanied overvoltages produced on composite feeders, when a circuit breaker closes at the peak of the applied voltage. Transformer and line-cable feeders are considered. The studies have covered the energisation of both systems from sources ranging from the purely resistive to the purely inductive. The means of reducing such overvoltages, such as pre-insertion resistor, surge arrester, shunt compensation, and combinations of them, are also included and the effect of system parameters and factors, such as circuit-breaker position, source inductance, type of source, transmission-line-length, effect of arrester position for different values of source inductance and cable-side and line-side energisation, on initial voltage applied and accompanied overvoltages are covered. The results which are obtained, are summarized in tables and graphic forms, followed by a general conclusion.

The thermal performance of heat exchangers that are essential units in power plants can be substantially improved by a number of augmentation techniques. The entropy generation and exergy destruction rate due to the flow friction and heat transfer across temperature differences were proposed numerically to evaluate the benefits of utilisation of these techniques. Enhanced tubes with either dimples or spiral corrugations that are isothermally heated were investigated. The combination of spirally corrugated tubes with twisted tape inserts was also presented. In general, dimpled and spirally corrugated tubes and the combination of spirally corrugated tubes with a twisted tape substantially increase the percentage of temperature raise ratio and decrease the percentage of exergy destruction rate relative to smooth tubes. Increasing both the additional heat transfer area due to dimpling, and ridge height of corrugation increases the percentage of temperature raise ratio and decreases the exergy destruction rate. Also, the combination of corrugated tubes with twisted tapes is attractive as an augmentation technique based on exergy analysis, especially at low twisted tape length to inner tube diameter ratio, and high ridge height of corrugation for high Reynolds number.

In wire EDM, better exclusion of debris from the machined kerf is very important to obtain a stable machining performance. The purpose of this study is to investigate the fluid flow in the kerf and better jet flushing conditions of working fluid from the nozzles. The flow field and the debris motion in the kerf were analyzed by computational fluid dynamics (CFD) simulation, comparing with the observation by high-speed video camera. The influence of flow rate of working fluid from nozzles and the nozzle standoff distance on flow field in the kerf and debris particle motion were discussed. (C) 2009 CIRP.

In this paper, a novel approach based on Stochastic Particle Swarm optimization (SPSO), with dominant eigenvalue shift for designing robust decentralized load frequency control system for interconnected power system is presented. A proportional - integral - derivative (PID) controller is considered to exemplify the optimum parameter search. To demonstrate the robustness of the obtained controller, a two-area non reheat thermal system, equipped with such optimized tuned controller, is tested under different operating conditions and parameter changes. The optimal PID parameters search is formulated as an optimization problem with a standard eigenvalue objective function. Its effectiveness is shown through comparison with the well-known conventional integral controller. The eigenvalue-based performance index is considered. The simulation results demonstrate the enhancement in the dynamic response of the two area power system.

Mobile agent is a process that can transport its state from one environment to another, with its data intact, and be capable of performing appropriately in the new environment. Fault tolerance support of mobile agent execution is essential for achieving a high and reliable performance for the computing process executed by the agent in distributed systems. Most of existing mobile agent systems considers checkpointing or replication as a mechanism in achieving the fault tolerant property. In this paper we present new protocol which employs the benefits gained from combing both mechanisms to achieve reliable mobile agent execution. Our approach uses group communication services to avail different essential issues such as agent's synchronization to facilitate the implementation the protocol. The proposed approach is dynamic in the sense that it allows a flexible membership mechanism to join or leave a mobile agent groups used in achieving the reliable execution.

The design of a model-free fuzzy power system stabilizer (PSS) lacks systematic stability analysis and performance guarantees. This paper provides a step towards the design of a model-based fuzzy PSS that guarantees not only stability but also performance specifications of power systems. A new practical and simple design based on static output feedback is proposed. The design guarantees robust pole-clustering in an acceptable region in the complex plane for a wide range of operating conditions. A power system design model is approximated by a set of Takagi-Sugeno (T-S) fuzzy models to account for nonlinearities, uncertainties and large scale power systems. The proposed PSS design is based on parallel distributed compensation (PDC). Sufficient design conditions are derived as linear matrix inequalities (LMI). The design procedure leads to a tractable convex optimization problem in terms of the stabilizer gain matrix. Simulations results of both single-machine and multi-machine power systems confirm the effectiveness of the proposed PSS design. (c) 2008 Elsevier Ltd. All rights reserved.

The present study investigated experimentally the heat transfer from a heat source simulating an electronic chip mounted on a printed circuit board placed downstream of a guide fence on the lower wall of the flow passage with two different aspect ratios (H/W = 0.3 and 1). The channel height to the heat source height ratios (H/B) are of 10 and 3. The effect of the guide fence height (b) and the spacing between the guide fence and the heat source (S) were investigated. The guide fence was orientated such that guide fence extension point was varied from the midpoint of the front face of the heat source to the endpoint of the side face at 5000

Free convection heat transfer from the inside surface of a horizontal elliptic tube of different axis ratios and different orientation angles with a uniformly heated surface is investigated experimentally. The axis ratio is changed from 1.5 to 3.5 and the orientation angle is changed from 0 degrees to 90 degrees with steps of 15 degrees. The experiments covered a range of Rayleigh numbers (Ra) from 6.5 x 10(5) to 1.13 x 10(8). The local and average heat transfer coefficients and Nusselt number (Nu) are estimated for different axis ratios and different orientation angles at different Rayleigh numbers. The results showed that the surface temperature increases with the increase in axial distance from both ends until a maximum value at the middle of the elliptic tube at a constant heat flux. The surface temperature decreases with the increase in the axis ratio or the orientation angle; consequently the local Nu increase with the increase in the axis ratio or the orientation angle at the same axial distance and Ra. The average Nu increases with the increase in the axis ratio or the orientation angle at the same Ra. The results obtained are correlated by dimensionless groups and with the available data of the horizontal elliptic tube. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3207799]

An experimental investigation has been conducted to clarify heat transfer characteristics and entropy generation for individual elliptic tubes with longitudinal fins. The investigated geometrical parameters included the placement of the fins at the front of the tube, at the rear of the tube and at the front and rear of the tube. The experiments have been carried out on the different cases of electrically heated elliptic tubes which are separately installed in a square tunnel. The surface temperature at different cases of elliptic tubes, have been measured. The testing fluid was air and the Reynolds number ranged from about 4.75 x 10(3) to 3.96 x 10(4). The analysis of the entropy generation is based on the principle of minimizing the rate of total entropy generation that includes the generation of entropy due to heat transfer and friction forces are presented. The results indicate that the fin position on the elliptic tube has an effect on the results of heat transfer coefficient, friction factor and irreversibility ratio. The correlations of average Nusselt number, friction factor and irreversibility ratio with Re are presented. (C) 2009 Elsevier Ltd. All rights reserved.

This paper proposes a closed-loop control strategy to operate an off-the-shelf single-phase induction motor (IM) as a symmetrical two-phase IM. The proposed control strategy employs the SFC technique to independently control the stator currents of both the main and auxiliary windings, and make them follow a pre-defined sinusoidal waveform. Simulation and experimental results show that the proposed 'scheme is successful in operating the conventional single-phase IM as a symmetrical two-phase IM with fast dynamic and transient responses. In addition, the proposed control system achieves cost-effectiveness in both initial and running costs.

Integration of aerial images and lidar data compensate for the individual weaknesses of each data set when used alone, thus providing more accurate classification of terrain cover, such as buildings, roads and green areas, and advancing the potential for automation of large scale digital mapping and GIS database compilation. This paper presents work on the development of automatic feature extraction from multispectral aerial images and lidar data. A total of 22 feature attributes have been generated from the aerial image and the lidar data which contribute to the detection of the features. The attributes include those derived from the Grey Level Co-occurrence Matrix (GLCM), Normalized Difference Vegetation Indices (NDVI), and standard deviation of elevations and slope. A Self-Organizing Map (SOM) was used for fusing the aerial image, lidar data and the generated attributes for building detection. The classified images were then processed through a series of image processing techniques to separate the detected buildings. Results show that the proposed method can extract buildings accurately. Compared with a building reference map, 95.5 percent of the buildings were detected with a completeness and correctness of 83 percent and 80 percent respectively for buildings around 100m(2) in area; these measures increased to 96 percent and 99 percent respectively for buildings around 1100m(2) in area. Further, the contributions of lidar and the individual attributes to the quality of the classification results were evaluated.

Whereas the efficiency of traditional cutting processes is limited by the mechanical properties of the processed material and the complexity of the workpiece geometry, electrical discharge machining (EDM) being a thermal erosion process, is subject to no such constraints. The lack of correlations between the cutting rate, the surface finish and the physical material parameters of this process made it difficult to use. This paper highlights the development of a comprehensive mathematical model for correlating the interactive and higher order influences of various electrical discharge machining parameters through response surface methodology (RSM), utilizing relevant experimental data as obtained through experimentation. The adequacy of the above the proposed models have been tested through the analysis of variance (ANOVA). Optimal combination of these parameters was obtained for achieving controlled EDM of the workpieces. (C) 2009 Elsevier Inc. All rights reserved.

This paper presents a study on the fresh and hardened characteristics of lightweight aggregate concrete incorporating self compacting agent (LWSCC). Self-compacting agent (SCA) (a polycarboxylic-based superplasticiser in combination with a viscosity-modifying admixture) and locally produced lightweight aggregate (LWA) produced from expanded clay type were utilised. Various LWSCC mixes made with different mix proportions, namely dosage of self-compacting agent, water/cement ratio, LWA/sand ratio and normal-weight aggregate as a partial replacement of LWA, were prepared. The initial slump flow, rate of slump flow loss and air content were then performed to assess the fresh properties of LWSCC. Twenty-eight-day compressive strength, ultrasonic pulse velocity, porosity and density were determined for investigating the hardened properties of LWSCC. The results reveal that, by using locally produced materials, it is possible to manufacture a structural LWA concrete with low density and high self-consolidating characteristics (flowability, deformability and stability). Both fresh and hardened characteristics of LWSCC are mainly controlled by dosage of an SCA, where the flowability, self-compactability, strength, homogeneity LWSCC can be enhanced with increasing SCA content up to certain dosage of SCA (approximate to 0.80), at which all these characteristics would start to decline with increasing SCA content. However LWSCC loses its fresh parameters rapidly with increasing the dosage of SCA and lightweight aggregate/sand ratio. The results also showed that the compressive strength, homogeneity and porosity of LWSCC could be significantly improved by reducing the ratio of w/c and LWA/sand ratio, and utilising normal-weight aggregate in LWSCC mixes.

Smart Grid (SG) technology aims at bringing the world's aging electric grids into the twenty first century. To this end, the current power grids require to be overlayed with a robust communications system. Home Area Network (HAN) is an important part of the SG communications framework through which the end-users are able to communicate with the electricity provider. In a HAN, there is typically a smart-meter and a number of electric appliances. Most of the proposals to-date have agreed upon using IEEE 802.15.4 wireless technology dubbed as ZigBee for the HAN communications amongst the smart meter and the various electric appliances. Although ZigBee provides few security features, the technology still suffers from a number of security vulnerabilities, particularly in case of SG HAN. In this paper, we describe a HANIdentifier (HANId) conflict attack against ZigBee for HAN communications and demonstrate the impact of the attack on SG communications through computer simulations. Finally, we also envision an appropriate framework to prevent the attack.

This article proposes a novel application of adjustable-speed one-phase induction motors in air conditioners powered by photovoltaic arrays. Employing the slip-frequency control scheme, an off-the-shelf one-phase induction motor is operated as an unsymmetrical two-phase induction motor. Maintaining certain control conditions, the unsymmetrical two-phase induction motor is made to behave like a symmetrical two-phase induction motor. This has the advantage of increasing the motor efficiency and reducing the torque pulsations inherent to unsymmetrical two-phase induction motors. The proposed control scheme reduces both initial and running costs of the proposed photovoltaic system. Initial cost is cut down by reducing the required size of the photovoltaic array through (i) limiting the motor current during both transient and dynamic phases of operation, (ii) extracting maximum power from the photovoltaic array under various climate conditions by operating the photovoltaic array on the maximum power line, and (iii) dispensing with the need for specially designed two-phase induction motors. Reduction in the running cost of the photovoltaic system is achieved by enhancing the motor efficiency through eliminating the backward component of the air gap flux. The article outlines a procedure for sizing the photovoltaic arrays. Simulation results of the system behavior during transient and dynamic phases confirm the capability of the proposed scheme.

The current-voltage characteristics of the photovoltaic module are highly non-linear and depend, among other factors, on solar insolation level and on the module surface temperature. At a fixed value of insolation level to which the module is subjected, the terminal voltage decreases non-linearly as the load current increases. Most previous research in this area depends on non-linear mathematical equations elating the module voltage with its current. Therefore, numerical methods of analysis are required to determine the performance of a system in which a photovoltaic module, or array, is an element. It is known that most operating points in such systems lie in the range between the no-load voltage and the maximum power point voltage of the photovoltaic module. In this article, an approach is presented to obtain approximate closed-form analytical expressions for the current-voltage characteristics of any photovoltaic array in the range from no-load condition up to the maximum power point condition. The photovoltaic arrays when feeding loads, such as DC motors, without using tedious voltage characteristics obtained analytically are compared with corresponding exact characteristics, with very close agreement obtained. To validate the proposed closed-form analytical expressions of the current-voltage characteristics of the photovoltaic array when feeding DC motors, the torque speed characteristics of different types of DC motors are obtained analytically and compared with the corresponding exact characteristics. The different between the approximate and exact characteristics is very small.

Composites of AA6063 Al alloy reinforced with SiC particles (SiC(p)) were prepared by the vortex method. Hot extrusion was carried out for the as cast composites with a reduction in area of 25%. Tensile and creep behavior of as-cast and extruded composites were studied at elevated temperatures. Tensile tests carried out at room temperature showed that for the as-cast composites, the addition of SiC(p) up to 10% by weight improves the strength but reduces ductility. Further addition of SiC(p) reduces the strength and ductility of the composites. At 150 and 300 degrees C the matrix alloy exhibits higher strength than the composites. Extrusion generally raised the strength of the composites at both room and elevated temperatures. Time rupture creep tests carried out at 300 degrees C showed that the composites exhibit higher creep resistance as compared to the matrix alloy except at relatively low stresses where the matrix has a better creep resistance. Extrusion improved the resistance of composites to creep rupture.

The current Internet framework is, no longer, able to support the heterogeneous networking technologies, mobile devices, increased number of users, and also the high user requirements for sophisticated services and applications. As a consequence, researchers envision the "future Internet" whereby all these issues may be effectively addressed. The future Internet architecture, amongst many components, is expected to comprise Peer-to-Peer (P2P) Video on Demand (VoD) streaming technologies. Since the conventional streaming techniques over P2P frameworks have a number of shortcomings, design issues pertaining to the P2P VoD schemes need to be seriously reconsidered. In this paper, we envision a scheme to effectively provide a VoD using P2P-based mesh overlay networks that may be part of the future Internet. Our scheme also comprises domain-based localization and congestion awareness strategies for the selection of the most appropriate peers. Empirical results have demonstrated the effectiveness of this scheme in terms of scalability and capability to reduce the startup latency and total link cost, and to also ensure a sustainable playback rate that is crucial for providing VoD services over the future Internet.

Photoacoustic (PA) technique has been applied to measure the effective thermal diffusivity (alpha(eff)) of hydrating cement pastes with a varying water to -cement ratio (w/c) and for variable duration (d) of hydration. Four samples with w/c = 0.3, 0.4, 0.5 and o.6 were prepared. The frequency variation of the PA signal for each sample was recorded at the begining (0 d), as well as one week and one month of hydration. The effective thermal effusivity (e(eff)) was obtained by measuring the variation of the signal with modulation frequency and the corresponding values of the effective thermal conductivity (k(eff)) were calculated. The results for kat. show a decrease at higher w/c (0.6), no change for other samples has been observed. The thickness of the duplex film of Ca(OH)(2) and C-S-H formed on the surface of the samples of w/c = 0.5 were determined using the effective layer model in the 0 d and after one month of hydration; a remarkable increase was observed in the last case.

This article presents a cost-effective variable frequency drive for starting and operating large three-phase squirrel cage induction motors. The proposed drive employs the constant V/F control scheme, which regulates the rotor frequency such that it is always kept below a predetermined value. This has the effect of drastically reducing the motor shaft torque oscillations and significantly limiting the maximum value of the motor line current. In addition to its simplicity and hence cost-effectiveness, the proposed scheme is shown to be capable of (i) reducing the shaft torque oscillations to approximately 22% of that of the direct on-line start of the large motor, and (ii) limiting the motor line current to approximately 36% of that of the direct on-line start value.

The replacement of Portland cement by dealuminated calcined kaolin, the waste obtained from the extraction of aluminum in the alum factories, also by samples treated with lime solution, is investigated. The chemical and mineralogical compositions of the samples are measured. Their pozzolanic reactivity and their surface areas are determined. The effect of up to 20% cement replacement on the setting time, the flowability behavior of the mortars, and the strength are tested and compared to OPC and OPC-silica fumes mixes. It is found that the surface area and the pozzolanic reactivity of the dealuminated kaolin are larger than that of silica fumes. The as received sample accelerates the setting time of OPC; while the lime-treated samples act as retarder. The initial flowability of the OPC mortars is slightly affected by the as received sample but reduces strongly in the presence of the lime-treated one and silica fumes. The flowability is strongly lost with time under all conditions. The 56d-compressive and tensile strengths of the mortars improve with 5 and 10% replacement.

As natural resources are becoming limited and energy price dramatically increased, energy utilization with efficient systems is required to be used in desalination technologies. Freezing is a well known technique for water desalination. In the present paper, a new proposed system depends on optimization of utilizing the heat flow of heat pump system to increase the whole system efficiency is introduced. The suggested system overcomes a lot of disadvantages of traditional freezing methods of desalination like ice handling, special compressor types, etc. In the suggested system, the ice washing and melting process occur at the same place of formation by reversing refrigerant flow through the vapor compression cycle so there is no need for ice handing mechanical systems. A detailed description of the system and thermal analysis are represented with simple cost analysis. Cost comparing with other methods gives a promising lower cost for the suggested system with respect to other systems. (C) 2009 Elsevier B.V. All rights reserved.

In the present investigation, the microstructure and mechanical characteristics of dissimilar A319 and A356 cast Al alloys plates joined by friction stir welding (FSW) were evaluated. The effect of tool rotational and welding speeds as well as the post-weld heat treatment (PWHT) on such properties was investigated. Post-weld heat treatment was carried out at a solutionising temperature of 540 degrees C for 12 h followed by aging at 155 degrees C for 6 h. For the as welded specimens, the welded zone (WZ) exhibited higher hardness values when compared with the A319 and A356 parent alloys. The peak hardness at the WZ was found to increase by increasing the tool rotational speed and/or reducing the welding speed. In contrast, the post-weld heat treated (PWHTed) specimens exhibited lower hardness values at the WZ than the parent alloys. For PWHTed specimens, the peak hardness at the WZ was found to decrease by increasing the tool rotational speed and/or reducing the welding speed. Tensile tests results demonstrate that, for the as welded specimens, the tensile fracture took place on A356 side where the hardness was minimal. While for PWHTed specimens, the fracture took place at the WZ. Increasing the tool rotational speed reducing both tensile and yield strengths, but increases the ductility of the joint.

A comparative study was made of the fracture behavior of austenitic and duplex stainless steel weldments at cryogenic temperatures by impact testing. The investigated materials were two austenitic (304L and 316L) and one duplex (2505) stainless steel weldments. Shielded metal arc welding (SMAW) and tungsten inert gas welding (TIG) were employed as joining techniques. Instrumented impact testing was performed between room and liquid nitrogen (-196 degrees C) test temperatures. The results showed a slight decrease in the impact energy of the 304L and 316L base metals with decreasing test temperature. However, their corresponding SMAW and TIC weld metals displayed much greater drop in their impact energy values. A remarkable decrease (higher than 95%) was observed for the duplex stainless steel base and weld metals impact energy with apparent ductile to brittle transition behavior. Examination of fracture surface of tested specimens revealed complete ductile fracture morphology for the austenitic base and weld metals characterized by wide and narrow deep and shallow dimples. On the contrary, the duplex stainless steel base and weld metals fracture surface displayed complete brittle fracture morphology with extended large and small stepped cleavage facets. The ductile and brittle fracture behavior of both austenitic and duplex stainless steels was supplemented by the instrumented load-time traces. The distinct variation in the behavior of the two stainless steel categories was discussed in light of the main parameters that control the deformation mechanisms of stainless steels at low temperatures; stacking fault energy, strain induced martensite transformation and delta ferrite phase deformation. (C) 2010 Elsevier Ltd. All rights reserved.

We study, in the frame of the discrete dipole approximation, the magnons propagation through a simple multiplexing device made of chains of magnetic nanoparticles along which a small chains (called a resonators) is attached. We show that this simple structure can transfer with selectivity one magnon frequency from one chain to the other, leaving neighbour magnonic frequencies unaffected. With an appropriate choice of the geometrical (or magnetic) parameters of the structure, it is possible to control the desired magnon ejection. A general analytical expression for the transmission coefficient is given for various structures of this kind within the framework of the Green's function method. The amplitude, the phase, and the phase time of the transmission are discussed as a function of frequency. These results may opens new perspectives for constructing, more efficient and more compact, magnonic devices such as narrow-frequency microwave multiplexers.

In the present article, the effect of friction stir processing (FSP) on the microstructural and mechanical characteristics of A390 hypereutectic Al-Si alloy was studied. The effect of tool rotational speed omega, traverse speed upsilon and the number of passes on such characteristics was investigated. The results showed that FSP significantly improved the microstructural characteristics of A390 Al alloy by reducing the structural defects found in the as cast alloy such as porosity and the size of alpha-Al primary grains as well as the size of the primary Si particles. The size of Si particulates was found to be reduced by reducing the tool rotational speed, increasing tool traverse speed and increasing the number of FSP passes.

In the present study, the effect of aging heat treatment at 650, 750, and 850 degrees C on the impact toughness of 316L austenitic stainless steel, 2205 duplex stainless steel and their weldments has been investigated. Welding process was conducted using the TIG (tungsten inert gas) welding technique. Instrumented impact testing, at room temperature, was employed to determine the effect of aging treatment on the impact properties of investigated materials. Aging treatment resulted in degradation in the impact toughness as demonstrated by the reduction in the impact fracture energy and deformation parameters (strain hardening capacity, fracture deflection, and crack initiation and propagation energy). The degree of embrittlement was more noticeable in duplex stainless steel parent and weld-metal than in 316L stainless steel and became greater with the increase of aging temperature. The degradation in impact toughness was discussed in relation to the observed precipitation of the intermetallic sigma phase in the microstructure of the stainless steel weldments and the corresponding fracture surface morphology.

An experimental study is conducted to investigate the local heat flow at a solid-liquid-vapor contact line. A vertical channel of 600 mu m width is built using two parallel flat plates; a 10 mu m thick stainless steel heating foil forms a part of one of the flat plates. A liquid-vapor meniscus is formed between the plates due to capillary forces. In this study the fluid HFE7100 is evaporated inside the channel under steady state conditions. Two-dimensional microscale temperature fields at the back side of the heating foil are observed with a infrared camera with a spatial resolution of 14.8 mu m x 14.8 mu m. An in situ calibration procedure is applied. The measured local wall temperature difference between the contact line area and the bulk liquid is up to 12 K. The liquid front undergoes a slow oscillatory motion which can be attributed to the instability of evaporating 3-phase contact line. The local heat fluxes from the heater to the evaporating meniscus are calculated from the measured wall temperatures using an energy balance for each pixel element. The local heat fluxes at the contact line area are found to be about 5.4-6.5 times higher than the mean input heat fluxes at the foil. (C) 2010 Elsevier Inc. All rights reserved.

This article proposes a new scheme to drive an air conditioner powered by photovoltaic (PV) arrays. The main objective is to reduce the cost of the system, which is a major concern in PV applications. This is achieved by reducing both the initial and running costs of the PV system. Initial cost is cut down by reducing the required size of the PV array through (i) limiting the motor current during both startup and dynamic phases of operation, and (ii) extracting maximum power from the PV array under various metrological conditions by operating the PV array on the maximum power line. Reduction in the running cost of the PV system is achieved by controlling the motor speed such that its slip is kept at a small value at various operating conditions, ensuring highly efficient operation of the system. This article outlines a procedure for sizing the photovoltaic array. Also, the article presents a control strategy that achieves acceptable levels of the motor current with good dynamic response. Simulation results of the system behavior during transient and dynamic phases confirm the capability of the proposed scheme.

Smart homes have enjoyed increasing popularity in recent years. In order for them to further expand their market share, users need to be able to fully control devices. Policies are one way for users to achieve such flexible control of devices. However, user policies often tend to interact in unwanted ways leading to unexpected behavior of devices. This paper describes the design of a run-time policy interaction management module (PIMM) that serves as manager for detecting and resolving interactions between user policies in KNX-based smart homes. This module extends the traditional KNX networking system with the ability to manage policy interactions. The module operates in the run-time S-mode of the KNX network and works as part of the Engineering Tool Software (ETS) used to configure and control the operation of the KNX network in smart homes. The proposed module serves as the first of its kind that can be implemented inside the KNX networking system to detect and resolve unwanted policies interactions.

This study assesses the performance of three classification trees (CT) models (entropy, gain ratio and gini) for building detection by the fusion of airborne laser scanner data and multispectral aerial images. Data from four study areas with different sensors and scene characteristics were used to assess the performance of the models. The process of performance evaluation is based on four criteria: model validation and testing, classification accuracies, relative importance of input variables, as well as transferability of CT derived from one data set to another. The LiDAR point clouds were filtered to generate a digital terrain model (DTM) based on the orthogonal polynomials, and then a digital surface model (DSM) and the normalized digital surface model (nDSM) were generated. A set of 26 uncorrelated feature attributes were derived from the original aerial images, LiDAR intensity image, DSM and nDSM. Finally, the three CT models were used to classify buildings, trees, roads and ground from aerial images, LiDAR data and the generated attributes, with the most accurate average classifications of 95% being achieved. The entropy splitting algorithm proved to be a preferable algorithm for building detection from aerial images and LiDAR data.

Panelized systems are prefabricated components that are brought to a construction site and assembled into the finished structure. Traditional constructions are often subjected to termite attack, mold buildups and have poor penetration resistance against wind-borne debris. To overcome these problems, a new type of composite structural insulated panel (CSIP) was developed and is analyzed in this study for structural floor applications. The concept of the panel is based on the theory of sandwich construction. The proposed composite panel is made of low cost orthotropic thermoplastic glass/polypropylene (glass-PP) laminate as a facesheet and expanded polystyrene foam (EPS) as a core. Full scale experimental testing was conducted to study the flexural behavior of the CSIP floor member. CSIP floor panels failed due to facesheet/core debonding. Analytical modeling was further presented to predict the interfacial tensile stress at the core/facesheet interface, critical wrinkling stress, flexural strength and deflections for structural CSIP floor panels. The experimental results were validated using the proposed models and were in good agreement. (C) Koninklijke Brill NV, Leiden, 2011

Navigation of autonomous mobile robots in unpredictable and dynamic environments is restricted by uncertainty, complexity, and unreliability issues of robots and their environments. In this context a navigation system for an autonomous mobile robot using intelligent fuzzy logic technique will be presented. Fuzzy logic control is able to emulate human experience about how best to control a system without needing accurate model equations, and can handle any perturbation in the system. A hierarchical behavior based control strategy has been devised in which four different reactive behaviors are combined by means of a fuzzy supervisor. For testing and validation, many simulations have been proposed which focus on: moving towards static or movable goal; escaping from local minima whenever it's detected; and traversing a cluttered environment with unknown static and dynamic obstacles.

This paper presents a new type of composites structural insulated panels (CSIPs) for structural wall applications. The proposed composite panel is made of low-cost thermoplastic orthotropic glass/poly-propylene (glass-PP) laminate as a facesheet and expanded polystyrene foam (EPS) as a core with very high facesheet/core moduli ratio. The proposed CSIP walls are intended to overcome problems of traditional Structural Insulated Panels (SIPs) such as termite attack, mold buildups and poor penetration resistance against wind borne debris. This paper investigates the behavior of CSIPs under concentric and eccentric loading. CSIPs specimens failed by global buckling mode in which no debonding was observed. The eccentric specimens failed at load 35% lower than that of the concentric ones. Global buckling formulas for concentric and eccentric loading were presented and validated using the experimental results and were in a good agreement. An equivalent stiffness formula was also developed for sandwich wall under in-plane loading considering the shear deformations effect of the core. Design study for CSIP walls is also presented to help in designing this new type of composite panels. (C) 2010 Elsevier Ltd. All rights reserved.

The forced convection from outside surfaces of helical coiled tubes is studied experimentally with a constant wall heat flux. Ten helical coiled-tubes of different parameters with a range of diameter ratio (D/d(o)) ranged from 7.086 to 16.142 and pitch ratio (P/d(o)) ranged from 1.81 to 3.205 are employed in the present study. The experiments are performed in an open-circuit airflow wind tunnel system operated in suction mode. The experiments covered a range of Reynolds number (Re) of 6.6 x 10(2) to 2.3 x 10(3). The experimental results indicated that these parameters (D/d(o) and P/d(o)) have important effects on the average heat transfer coefficient. The average Nusselt number (Nu(m)) increases with the increase of D/d(o) at constant Re and P/d(o). Also, Nu(m) increases with the increase of P/d(o) at constant Re and D/d(o). A considerable agreement between the present experimental data and previous work is achieved. The average Nusselt numbers is correlated with Re, D/d(o) and P/d(o). (C) 2010 Elsevier Ltd. All rights reserved.

This investigation is aimed at studying the heat transfer characteristics and pressure drop for turbulent airflow in a sudden expansion pipe equipped with propeller type swirl generator or spiral spring with several pitch ratios. The investigation is performed for the Reynolds number ranging from 7500 to 18,500 under a uniform heat flux condition. The experiments are also undertaken for three locations for the propeller fan (N = 15 blades and blade angle of 65 degrees) and three pitch ratios for the spiral spring (P/D = 10, 15 and 20). The influences of using the propeller rotating freely and inserted spiral spring on heat transfer enhancement and pressure drop are reported. In the experiments, the swirl generator and spiral spring are used to create a swirl in the tube flow. Mean and relative mean Nusselt numbers are determined and compared with those obtained from other similar cases. The experimental results indicate that the tube with the propeller inserts provides considerable improvement of the heat transfer rate over the plain tube around 1.69 times for X/H = 5. While for the tube with the spiral spring inserts, an improvement of the heat transfer rate over the plain tube around 1.37 times for P/d = 20. Thus, because of strong swirl or rotating flow, the propeller location and the spiral spring pitch become influential on the heat transfer enhancement. The increase in pressure drop using the propeller is found to be three times and for spiral spring 1.5 times over the plain tube. Correlations for mean Nusselt number, fan location and spiral spring pitch are provided. (C) 2010 Elsevier Inc. All rights reserved.

Experimental and numerical studies were carried out to investigate forced convection heat transfer and flow features around the downstream elliptic cylinder in four staggered cylinders in cross flow. The elliptic cylinders examined had an axis ratio (b/c) of 1:2, and they were arranged with zero angle of attack to the upstream flow. The present heat transfer measurements were obtained by heating only the downstream elliptic cylinder (test cylinder) under the condition of constant heat flux. The testing fluid was air and the Reynolds number based on the major axis length (c) was ranged from 4,000 to 45,570. The tested longitudinal spacing ratio (S(x)/c) and the transversal spacing ratio (S(y)/b) were in the ranges of 1.5 a parts per thousand currency sign S(x)/c a parts per thousand currency sign 4.0 and 1.5 a parts per thousand currency sign S(y)/b a parts per thousand currency sign 4.0, respectively. The air flow pattern and temperature fields around the four staggered elliptic cylinders were predicted by using CFD software package. Also, a flow visualization study was made to show the flow features around the elliptic cylinders. It was observed that Nu(m) of the downstream elliptic cylinder in four staggered cylinders was higher than that of three in-line cylinders for all tested spacing ratios and Reynolds numbers except for Re = 4,000. It was clear that, at lower Reynolds number values (Re < 14,100), the average Nusselt number of the downstream elliptic cylinder in three staggered arrangement was higher than that of the downstream cylinder in four staggered arrangement for all tested spacing ratios. On the other hand, at Re > 14,100, the tested elliptic cylinder in four staggered arrangement had the higher values of the average Nusselt number. Moreover, in four staggered arrangement, the maximum average Nusselt number enhancement ratio (average Nusselt number of the tested downstream cylinder/average Nusselt number of a single elliptic cylinder) was found to be about 2.0, and was obtained for spacing ratios of S(x)/c = 2.5, S(y)/b = 2.5 and at Re = 32,000. Finally, the average Nusselt number of the tested cylinder in four staggered arrangement was correlated in terms of Reynolds number and cylinder spacing ratios.

Experimental investigation of heat transfer and friction factor characteristics of elliptic tubes with different twist ratios (Y) and pitch ratios (S) has been conducted under laminar flow condition. All data are obtained using cold water flowing in the tube side and hot water flowing in the annuli side of the heat exchanger. The experiments covered a range of Reynolds numbers, 5.7 x 10(2)

Three dimensional (3D) mapping has been used widely in the spatial industry as a powerful technique for rendering artificial objects and their surrounding topography. However, an accurate and effective 3D modelling of complex features e. g. feature rich buildings and trees, is still challenging. The aim of this study is to develop an efficient framework to obtain a high-accuracy 3D model of urban buildings using Airborne Laser Scanning (ALS) data and aerial ortho-imagery. First, building outlines and a digital surface model are extracted from ALS data. Aerial ortho-imagery is then integrated to improve the accuracy of building outlines. Digital photos of building facades are patched to the 3D model for texture mapping. The accuracy analysis is conducted by assessing the heights and outlines of extracted features. As far as the authors know, this is the first accuracy evaluation of constructed 3D models. The digital surface model (DSM) shows vertical errors of less than 12 cm. Building heights are less accurate than the DSM, with errors of less than 22 cm. This difference is explained in the paper. In order to examine the building model more closely, the buildings are classified into three categories: simple rectangular objects, complex polygons, and curved outlines. The horizontal accuracy of the three categories ranges from 42 to 64 cm in Easting (1 sigma) and 16 to 48 cm in Northing (1 sigma). The results show that the horizontal coordinates of simple rectangular buildings are more accurate than those of complex polygons or circular-shape buildings. Mean errors and root mean square errors for each category are presented in the paper.

Feature Interaction is a problem mostly considered in the telecommunications domain. Many solutions for detecting interactions between telephony features have been reported. In this paper, we investigate the feature interaction problem beyond the traditional telecommunications domain and look at interactions between policies in other domains. We propose the use of semi-formal methods for detecting interactions between policies in the smart homes domain. The novelty of this research is threefold: firstly, a six step semi-formal approach, called IRIS (Identifying Requirements Interactions using Semi-formal methods), for detecting interactions is presented. A major component within IRIS, which is an interaction taxonomy, is also presented. Secondly, we extend the scope of the problem of feature interactions beyond telecommunication features and investigate interactions between policies in the smart homes domain. Thirdly, in order to show how IRIS is used to detect interactions between policies, a case study of the smart homes domain is conducted. A complete description of the results obtained is also provided. Our approach was successfully applied to the smart homes domain and was able to discover 83 interactions among 35 user policies using only 525 pairwise comparisons as opposed to 630 a human expert would have to do. These results support the paper's main claim of being able to use the semiformal approach IRIS to detect interactions between policies. Furthermore, these results are to date the most complete publication of interactions between policies in the smart homes domain. (c) 2007 Elsevier B.V

Forced convection heat transfer and pressure drop characteristics of air flow inside a horizontal semi-circular duct are investigated experimentally. The experiments are carried out on a semi-circular duct of 23 mm inner radius, 2 mm thickness, and 2,000 mm length within a range of Reynolds number (8,242

In this study, the artificial neural network (ANN) approach is used to predict the wear rate of Al/Al2O3 metal matrix composites (MMCs). The Al/Al2O3 MMCs were fabricated using the conventional powder metallurgy route. Different ANN structures were used to develop models for prediction and optimization of the wear rates of the Al/Al2O3 composites under dry sliding conditions. The effects of the volume fraction of Al2O3 particulates, density, and hardness of the Al/Al2O3 composites, as well as the applied pressure, sliding speed, and test temperature on the wear rates were evaluated using the ANN models. The results showed that the developed multilayer perceptron ANN model can be effectively used to predict the wear rates of Al/Al2O3 MMCs. The generalized radial basis function showed lower prediction performance.

Most of the structural elements in a steel structure are subjected to bending moment and axial force simultaneously. In some elements, one of the two components is relatively small compared to the other. Yet, the smaller component cannot be ignored due to the interactive behavior of the two components. Therefore, it is not adequate to design the beam-column element as a beam or a column by ignoring one of the two load components even if the ignored component is relatively small. Most of the design codes use empirical interaction equations that are based on semi-experimental semi-analytical results. Most of the design formulae adopted by the design codes do not explicitly account for the geometrical imperfection. This research aims at investigating the buckling behavior of steel beam-column elements for the sake of developing an analytical model to calculate their ultimate resistance under axial compression and bending moment. The analytical model will be based on Perry-type formulation, and it will account for the effect of initial imperfection. The model will be validated by comparing its results with those obtained by the Finite Element Non-Linear Elasto-Plastic analysis using ANSYS 5.4 program. Finally, a simple but rational design method based on the model, will be introduced. This method can be applied using a simple mathematical expression or charts and tables. The results of the developed design method will be compared with the design method of the international codes of practice for design of steel structures. On light of these comparisons, design recommendations are introduced. (C) 2011 Elsevier Ltd. All rights reserved.

This paper proposes a closed-loop control strategy to operate an unsymmetrical two-phase induction motor (1M) as a symmetrical 2-phase motor using Fuzzy Logic (FL) control. The unsymmetrical two-phase 1M is realized using an off-the-shelf single phase 1M. The proposed control strategy employs constant air-gap flux control technique to independently control the stator currents of both the main and auxiliary windings of the two-phase unsymmetrical motor and make them follow a predefined sinusoidal waveform. Experimental results show that the proposed FL controller scheme is successful in operating the unsymmetrical two-phase 1M as a symmetrical 2-phase motor with fast dynamic and transient response. Notably, the proposed control scheme achieves reduction in the inherent torque oscillations of the two-phase unsymmetrical 1M, rendering its behavior similar to its symmetrical counterpart.

SF6 gas insulated switchgear plays an important role in electric power networks all over the world due to its merits as compared to traditional air insulated switchgear. According to a numerous studies, it appears very difficult that any pure gas can bring a solution to the issue of desirable insulation ability and low environmental impact, so the mixtures composed of a strongly electronegative gases with high dielectric strength such as SF6 and ordinary gases (N-2, CO2, or Air) are used to reduce the gas price and liquefaction temperature. From this point of view, various types of gas mixtures such as(5%SF6+5%CO2+90%Air), (5%SF6+40%CO2+55%Air),(5%SF6+80%CO2+15%Air),(5%SF6+5%N-2+90%Air),(5%SF6+40%N-2+55%Air) and (5%SF6+80%N-2+15%Air) are used inside compressed gas devices to give a higher dielectric strength with lower cost and lower environmental impact. In this paper, the Finite Elements Method (FEM) is used to evaluate the electric field distribution on and around multi-contaminating filamentary wire particles. The effect of two contaminating particles which one of them is rested at ground plate and other is hovering inside the gap on the electric field values are studied. The effect of three contaminating particles which are rested at ground plate on the electric field values are also studied. The effect of gas pressure, SF6 gas concentration in mixture, gap spacing and height between particles on the breakdown voltage calculations are also studied.

This numerical study investigates the steady state natural convection of light and heavy water entering a vessel from the left and leaving on the right. The cavity consists of a matrix of cylindrical heated rods as in light and heavy water reactors. The aim of the study is to describe the effects of water inlet velocity on the flow and thermal fields in presence of such heated obstacle. The investigations are conducted for different values of rods temperatures. From the numerical results, it is evident that the flow pattern and temperature fields are significantly dependent on the water inlet velocity and rods temperature.

A recently developed method to synthesize metal/semiconductor Ag/CdSe core/shell hybrid nanocomposite has been used. Seed of silver nanoparticles was prepared by reduction of silver acetylacetonate organometallic complex using alkyl amine. Different shell thicknesses have been grown, directly on the Ag core, by the organometallic pyrolysis method. Absorption spectroscopy, photoacoustic spectroscopy, High Resolution Transmission Electron Microscopy (HRTEM), emission spectroscopy, and Raman spectroscopy were used to characterize the Ag/CdSe core/shell samples. The effect of Ag plasmon core on the optical properties of CdSe shell is discussed in the weak exciton-plasmon coupling regime. Emission, absorption, and Raman spectra are employed to determine the Huang-Rhys parameter which is found to show that the exciton-phonon is in the weak coupling regime. (C) 2012 Elsevier B.V. All rights reserved.

This paper investigates the structural behavior of a new type of Composite Structural Insulated Panels (CSIPs) for load-bearing wall applications. The proposed composite panel is made of low cost orthotropic thermoplastic glass/polypropylene (glass-PP) laminate as a facesheet and Expanded Polystyrene Foam (EPS) as a core. The proposed CSIP wall is intended to overcome problems of the traditional Structural Insulated Panels (SIPs). These problems include termite attack, disintegration due to flood water, mold buildups and poor penetration resistance against wind borne debris. Full scale experimental testing for three CSIP panels was conducted to study the behavior of CSIP walls under eccentric load. Further, pull off strength tests were conducted to determine the bonding strength between the glass-PP facesheet and EPS foam core. Facesheet/core debolnding was observed to be the general mode of failure. This study provides also analytical models to predict the interfacial tensile stress at the core/facesheet interface, critical wrinkling stress and deflections fori a structural CSIP wall member. In addition, finite element modeling was also conducted using ANSYS Software in order to model the response of CSIPs walls under in-plane loading. Experimental results were validated using the proposed analytical models and FE modeling, and were observed to be in good agreement. Furthermore, a parametric FE study was conducted to investigate the influence of key design Parameters on the behavior of CSIPs. The study showed that span-to-depth ratio and core density have a significant effect on the structural performance of CSIP wall panels. (C) 2012 Elsevier Ltd. All rights reserved.

This paper proposes a new blind, robust image watermarking for copyright protection and ownership verification in the DCT domain, The owner information is in the form of a logo image. Two different watermarking systems are considered. The first one is based on the principle of spread spectrum communication, in which we propose an adaptive direct sequence spread spectrum DSSS embedding, and a correlation based decoding. The second one is based on Spread Transform (ST) which is a hybrid combination between spread spectrum and a quantization watermarking scheme called Scalar Costa Scheme (SCS). We describe how to incorporate a perceptual model, based on Watson's perceptual model, into the frameworks. The proposed systems are tested using different standard test images and the performance is evaluated under JPEG compression and compared to each other and to other watermarking schemes. Experimental Results show that the proposed systems have good imperceptibility and higher robustness to JPEG image compression.

PA-FTIR is applied in virto to study the effects of diabetes induced on the lens and retina tissues of rabits within periods up to three monthes after diabetes induction. The results indicate the disappearance of IR bands ( 1100 1700 cm(-1)), the range corresponding to protein bands.

The optical absorption properties of as prepared CdSe quantum rods (QRs) are measured by the photoacoustic (PA) method. CdSe QRs were fabricated by the chemical solution deposition (CD) technique. Decreasing the rod size (width and length) that is determined by scanning tunneling microscope (STM), causes blue-shift of the PA spectra that can be clearly observed. The exciton energy of the CdSe QRs as estimated using the effective mass approximation (EMA) model and the dimensions determined by STM shows a reasonable agreement with that predicted by the PA measurements. The exciton energies calculated by EMA model show deviations from the experimental data for samples having smaller diameters. The thermal diffusivity of samples of different sizes shows an increase by at least an order of magnitude than the bulk value.

We report on the optical absorption properties of as prepared CdSe quantum dots (QDs) measured by the photoacoustic (PA) method. CdSe QDs were fabricated by the chemical solution deposition (CD) technique. With increasing growing time, the redshift of the PA spectra can be clearly observed and optical absorption in the visible region due to CdSe Q-dots is demonstrated. The average diameters of the CdSe QDs for each growth time interval is estimated using the effective mass approximation giving diameters ranging from 2.6 nm to 3.4 nm. These values are comparable to those obtained by scanning tunnelling microscope (STM). Thus, PA spectroscopy is useful to obtain the QDs sizes as grown and with no further preparation. In addition, PA measurements provide also the thermal diffusivity of samples of different sizes which in this case show an increase by at least an order of magnitude than the bulk value.

An experimental investigation is carried out to study heat transfer characteristics of a rotating triangular thermosyphon, using R-134a refrigerant as the working fluid. The tested thermosyphon is an equilateral triangular tube made from copper material of 11 mm triangular length, 2 mm thickness, and a total length of 1,500 mm. The length of the evaporator section is 600 mm, adiabatic section is 300 mm, and condenser section is 600 mm. The effects of the rotational speed, filling ratio, and the evaporator heat flux on each of the evaporator heat transfer coefficient, h(e), condenser heat transfer coefficient, h(c), and the overall effective thermal conductance, C-t are studied. Experiments are performed with a vertical position of thermosyphon within heat flux ranges from 11 to 23 W/m(2) for the three selected filling ratios of 10, 30 and 50 % of the evaporator section volume. The results indicated that the maximum values of the tested heat transfer parameters of the rotational equilateral triangular thermosyphon are obtained at the filling ratio of 30 %. Also, it is found that the heat transfer coefficient of the condensation is increased with increasing the rotational speed. The tested heat transfer parameters of the thermosyphon are correlated as a function of the evaporator heat flux and angular velocity.

As Natural resources are becoming limited and energy price dramatically increased, energy utilization with efficient systems is essentially required to be used in desalination technologies. The use of solar energy in desalination processes is one of the most promising applications of renewable energies. The primary focus on desalination by solar energy is suitable for use in remote areas. A proposed desalination system uses solar radiation, which concentrated by parabolic dish to heat up the working fluid in a closed space. Then the generated pressure in this space used to push salt water into RO module. Daily production rate of fresh water quantity for suggested system compaied with other solar techniques is a promising rate for each m(2) of solar radiation collecting surface. The production rate for one operation cycle could reach to 1800 L/cycle of fresh water at low water salinity (Brackish water with 5000 ppm) and 55 L/cycle at highest water, salinity (sea water salinity with 42,000 ppm). The required energy needed to produce 1 kg of fresh water is also promising even when in case of using another type of energy, also operating cycle has ability of repetition according to salinity concentration through sunny hour. (C) 2012 Elsevier Ltd. All rights reserved.

The dry sliding wear performance of hypereutectic A390 Al-Si alloy reinforced with graphite particulates (Gr(p)) was investigated. Composites containing 4 and 8 wt% of Gr(p) were produced by rheocasting technique followed by squeeze casting. Pins of the materials were rubbed against a 316 stainless steel disc using pin-on-ring type apparatus under various loads and speeds. It has been observed that both wear rate and the coefficient of friction of the composites decreased considerably with Gr(p) additions. The A390/Gr(p) composites exhibited higher wear resistance than those obtained for the monolithic A390 alloy. The formation of the hard tribo-layer on the surface of the composites assisted in increasing the wear resistance of these materials. It is believed that the reduction of the friction coefficient is attributed the presence of the graphite layers within the tribo-layer.

In the present investigation, the effect of the friction stir processing (FSP) on the microstructural, mechanical and tribological characteristics of as-cast A413 aluminum alloy was studied. The influence of the tool rotational and traverse speeds on such characteristics was evaluated. The results revealed that FSP has significantly improved the microstructure of the A413 Al alloy by eliminating structural defects such as porosity and Si segregation. The size of the Si particulates as well as the alpha-Al grains increases with increasing tool rotational speed and/or decreasing the tool traverse speed. The FSPed zones exhibited better mechanical properties as well as dry sliding wear resistance than the as-cast base alloy. (C) 2012 Elsevier B.V. All rights reserved.

A thermal-hydraulic model has been developed to simulate loss of the ultimate heat sink in a typical material testing reactor (MTR). The model involves three interactively coupled sub-models for reactor core, heat exchanger and cooling tower. The model is validated against PARET code for steady-state operation and verified by the reactor operation records for transients. Then, the model is used to simulate the thermal-hydraulic behavior of the reactor under a loss of the ultimate heat sink event. The simulation is performed for two operation regimes: regime I representing 11 MW power and three cooling tower cells operated, and regime II representing 22 MW power and six cooling tower cells operated. In regime I, the simulation is performed for 1,2 and 3 cooling tower cells failed while in regime II, it is performed for 1, 2, 3, 4, 5 and 6 cooling tower cells failed. The simulation is performed under protected conditions where the safety action called power reduction is triggered by reactor protection system to decrease the reactor power by 20% when the coolant inlet temperature to the core reaches 43 degrees C and scram is triggered if the core inlet temperature reaches 44 degrees C. The model results are analyzed and discussed. (C) 2012 Elsevier Ltd. All rights reserved.

In the electrical discharge machining (EDM) process, thin tool-electrodes are constantly gaining much importance due to the growing demand for manufactured parts with more functional characteristics and with small geometrical dimensions for applications in many work fields. This article highlights the utilization of the EDM process using multi-thin tool-electrodes with diameters of 0.3, 0.5 and 1.0 mm and different lateral spaces (3.0 to 0.8 mm). This machining technology requires using more than one tool-electrode in the same time for fabrication of microholes with high process performance and productivity. One of the principal aims of the experimental investigations of this article is to determine the minimum lateral spacing required between tool-electrodes for reducing process costs under acceptable conditions related to the surface of the machined workpiece. Tool-electrode wear and material removal rate are investigated as result of these experiments under adjustment of different process parameters. The beneficial effects of this machining process are also highlighted. The first experimental results of EDM with multi-thin tool-electrodes indicate some technical and economical advantages as a machining process.

A novel combination of genetic algorithms (GAs) and the charge simulation method (CSM) is proposed for enhancing the computation precision of electric fields associated with plate-type electrostatic separators; a new recycling technology of electrical and electronics waste. An algorithm is developed to, automatically, arrive at optimal arrangement of the simulating charges and their locations in order to eliminate dependency on user judgment and experience. Accurate results for electric field computation, compared with earlier published techniques, are realised for several design parameters of the separator. Experiments carried out for determination of detachment fields of small metallic particles (steel spheres of radius 0.501 mm) confirmed validity of the numerical simulation. The present work shows that the coupled GA-CSM algorithm can be an efficient and flexible design tool for accurate field computation of electrostatic separation equipment.

Heat and fluid flow characteristics for sinusoidal smooth pipes with different wavelength and amplitude have been investigated experimentally. The effects of the dimensionless wavelength (a/d(i)) and the amplitude (b/d(i)) on the thermal performance of a sinusoidal pipe inside a straight pipe heat exchanger are investigated. The experiments employed one straight smooth pipe, five sinusoidal smooth pipes at different a/d(i) and three sinusoidal smooth pipes at different b/d(i). The Reynolds number ranged from 8.8 x 10(3) to 2.8 x 10(4), and the Prandtl number ranged from 4.53 to 5.85. The range of the dimensionless wavelength (b/d(i)) is from 18.52 to 55.55, and the dimensionless amplitude (a/d(i)) range is from 4 to 13.6. The results showed that the heat transfers in sinusoidal pipes are increased in all cases of a/d(i) and b/d(i) above those of the straight pipe. Also, the friction factor(f) in the sinusoidal pipes is increased in all cases of a/d(i) and b/d(i) above that of the straight pipe. The dimensionless exergy loss (e) decreases with the increase of b/d(i), but in the case of a/d(i), the maximum of e is attained at a/d(i) = 6.22 and the minimum is attained at a/d(i) = 13.6. Correlations of Nu and f as a function of Re, b/d(i) and a/d(i) are presented. Also, a correlation of e as a function of Re, b/d(i) and a/d(i) is given. (c) 2007 Elsevier Ltd. All rights reserved.

Experimental investigation of free convection heat transfer from the inside surface of vertical and inclined elliptic tubes of different axis ratios, different orientation angles and different inclination angles with a uniformly heated surface are presented. The axis ratio is changed from 1.5 to 3.5, the inclination angle is changed from 15 degrees to 75 degrees and the orientation angle is changed from 0 degrees to 90 degrees. The experiments covered a range of Rayleigh number, Ra from 6.85 x 10(5) to 1.3 x 10(8). The local and average heat transfer coefficients and Nusselt numbers arc estimated for different axis ratios and different orientation angles at different Rayleigh numbers. The experimental results showed that the axis ratio has a significant effect on the local and average heat transfer coefficients. The local Nusselt number (Nu) increases with the increase of axial distance from the lower end of the elliptic tube until a maximum value is reached near the top of the elliptic tube, and then, the Nit gradually decreases. Also, the local Nit increases with the increase of alpha, phi and AR at the same axial distance. The average Nit increases with the increase of orientation angle, inclination angle and axis ratio (AR) at a constant Ra. Correlations of the average Nusselt number for free convection inside vertical and inclined elliptic tubes with the orientation angles (a), inclination angles (phi) and axis ratios (AR) are presented. (c) 2007 Elsevier Ltd. All rights reserved.

Degradation of structural material because of floodwater is one of the major damaging effects during flooding events. As a result, thousands of homes in coastal states, especially those that are constructed from wood-based materials, have been destroyed after each severe hurricane. This paper evaluates the performance a new type of composite structural insulated panel (CSIP) after exposure to floodwater. The proposed composite panel is made of low-cost orthotropic thermoplastic glass/polypropylene laminate as the facesheet and expanded polystyrene foam as the core. The proposed CSIP panel is intended to overcome problems of traditional structural insulated panels, especially those resulting from strength degradation. An extensive experimental program was conducted to investigate the flexural strength degradation of CSIPs after exposure to floodwater for various periods of time. The residual flexural strength following full submergence of CSIPs in simulated floodwater was evaluated using a four-point loading test. Furthermore, the experimental results were validated using new analytical models and were observed to be in good agreement. Insignificant strength degradation was recorded by CSIPs, and therefore they demonstrated the potential for their use in sustainable building structures against flood hazards.

In the present investigation, surface modification of A390 hypereutectic cast Al-Si alloys using friction stir processing (FSP) was conducted. The effect of the tool rotational and traverse speeds as well as the number of passes on the microstructural, mechanical and tribological characteristics of the modified surfaces was investigated. The results showed that FSP significantly improved the microstructure of the as-cast A390 Al-Si alloy by eliminating the porosity and refining both the alpha-Al grains and the Si particulates. The as-cast A390 alloy exhibited mean size and aspect ratio of Si particulates of about 59 +/- 24 mu m and 3.56 +/- 1.9, respectively. FSP significantly reduced both the mean size and aspect ratio of the Si particulates. The mean size of the Si particles increases with increasing the tool rotational and/or reducing the tool traverse speeds, but reduced by increasing the number of passes. Samples of friction stir (FS) processed at 1200 rpm, 20 mm/min and three passes exhibited the minimum mean size (4.39 +/- 1.9 mu m) and aspect ratio (1.18 +/- 0.4) of the Si particulates. The FS-processed regions exhibited less scattered and higher hardness values than the as-cast A390 alloy. The as-cast A390 alloy exhibited highly scattered hardness values between 62.5 and 94.6 VHN. Samples FS-processed at 1200 rpm, 20 mm/min and three passes exhibited the maximum hardness values between 114.66 and 119.34 VHN. The mean hardness of the stirred zones increases with increasing the tool traverse speed and the number of passes, while decreases with increasing the tool rotational speed. The FS-processed samples exhibited lower wear rates and coefficient of frictions than the as-cast A390 alloy. Both the wear rates and the coefficient of frictions were found to be reduced by reducing the tool rotational speed and/or increasing the tool traverse speed. Increasing the number of passes reduces the wear rate as well as the coefficient of friction. (C) 2013 Elsevier B.V. All rights reserved.

This paper presents the derivation of a new boundary element formulation for plate bending problems. The Reissner's plate bending theory is employed. Unlike the conventional direct or indirect formulations, the proposed integral equation is based on minimizing the relevant energy functional. In doing so, variational methods are used. A collocation based series, similar to the one used in the indirect discrete boundary element method (BEM), is used to remove domain integrals. Hence, a fully boundary integral equation is formulated. The main advantage of the proposed formulation is production of a symmetric stiffness matrix similar to that obtained in the finite element method. Numerical examples are presented to demonstrate the accuracy and the validity of the proposed formulation.

The low-velocity impact response of plain autoclaved aerated concrete (AAC) and carbon fiber reinforced polymer (CFRP)/AAC sandwich panels has been investigated. The structural sandwich panels composed of CFRP/AAC combinations have shown excellent characteristics in terms of high strength and high stiffness-weight ratios. In addition to having adequate flexural and shear properties, the behavior of CFRP/AAC sandwich panels needs to be investigated when subjected to impact loading. During service, the structural members in building structures are subject to impact loading that varies from object-caused impacts, blasts due to explosions, and high-velocity impact of debris during tornados, hurricanes, and storms. Low-velocity impact (LVI) testing serves as a means to quantify the allowable impact energy the structure can withstand, and to assess the typical failure modes encountered during this type of loading. The objectives of this paper are: to study the response of plain AAC and CFRP/AAC sandwich structures to low-velocity impact and to assess the damage performance of the panels; to study the effect of CFRP laminates on the impact response of CFRP/AAC panels; and to study the effect of the processing method (hand lay-up versus vacuum assisted resin transfer molding) and panels' stiffness on the impact response of hybrid panels. Impact testing was conducted using an Instron drop-tower testing machine. Experimental results showed a significant influence of CFRP laminates on energy absorption and peak loads of CFRP/AAC panels. A theoretical analysis was conducted to predict the energy absorbed by CFRP/AAC sandwich panels using the energy balance model. Results found were in good accordance with the experimental data.

Time diversity is achieved in direct sequence spread spectrum by receiving different faded delayed copies of the transmitted symbols from different uncorrelated channel paths when the transmission signal bandwidth is greater than the coherence bandwidth of the channel. In this paper, a new time diversity scheme is proposed for spread spectrum systems. It is called code-time diversity. In this new scheme, N spreading codes are used to transmit one data symbol over N successive symbols interval. The diversity order in the proposed scheme equals to the number of the used spreading codes N multiplied by the number of the uncorrelated paths of the channel L. The paper represents the transmitted signal model. Two demodulators structures will be proposed based on the received signal models from Rayleigh flat and frequency selective fading channels. Probability of error in the proposed diversity scheme is also calculated for the same two fading channels. Finally, simulation results are represented and compared with that of maximal ration combiner (MRC) and multiple-input and multiple-output (MIMO) systems.

Video-based automatic incident detection (AID) systems are increasingly being used in intelligent transportation systems (ITS). Video-based AID is a promising method of incident detection. However, the accuracy of video-based AID is heavily affected by environmental factors such as shadows, snow, rain, and glare. This paper presents a review of the different work done in the literature to detect outdoor environmental factors, namely, static shadows, snow, rain, and glare. Once these environmental conditions are detected, they can be compensated for, and hence, the accuracy of alarms detected by video-based AID systems will be enhanced. Based on the presented review, this paper will highlight potential research directions to address gaps that currently exist in detecting outdoor environmental conditions. This will lead to an overall enhancement in the reliability of video-based AID systems and, hence, pave the road for more usage of these systems in the future. Last, this paper suggests new contributions in the form of new suggested algorithmic ideas to detect environmental factors that affect AID systems accuracy.

This paper extended the concept of the technique for order preference by similarity to ideal solution (TOPSIS) to develop a methodology for solving multi-level non-linear multi-objective decision-making (MLN-MODM) problems of maximization-type. Also, two new interactive algorithms are presented for the proposed TOPSIS approach for solving these types of mathematical programming problems. The first proposed interactive TOPSIS algorithm includes the membership functions of the decision variables for each level except the lower level of the multi-level problem. These satisfactory decisions are evaluated separately by solving the corresponding single-level MODM problems. The second proposed interactive TOPSIS algorithm lexicographically solves the MODM problems of the MLN-MOLP problem by taking into consideration the decisions of the MODM problems for the upper levels. To demonstrate the proposed algorithms, a numerical example is solved and compared the solutions of proposed algorithms with the solution of the interactive algorithm of Osman et al. (2003)141. Also, an example of an application is presented to clarify the applicability of the proposed TOPSIS algorithms in solving real world multi-level multi-objective decision-making problems. (C) 2013 Elsevier Inc. All rights reserved.

The aim of this paper is to study the effect of friction stir processing (FSP) on electrical conductivity and corrosion resistance of AA6063-T6 Al alloy. Also, the microstructural and mechanical characteristics were examined. Different samples were structured by employing a constant feed rate M of 120 mm/min and different rotating speeds (omega) of 250, 315, 400, 500, 630, and 800 r/min. The results showed that FSP significantly refines the microstructure of the AA6063-T6 Al alloy. Increasing the rotational speed increases the grain size in the centres of stirred zones (SZ). The FSP significantly increases the electrical conductivity of the alloy. The highest electrical conductivities were observed at the centres of the SZ for the alloys processed with varying rotational speeds between 315 and 500 r/min. Increasing the rotational speed above this range tends to reduce the electrical conductivity, but it is still higher than the base material. In contrast, the corrosion resistance was found to decrease due to FSP of the AA6063-T6 aluminium alloy. It has been found that, increasing the rotational speed decreases the corrosion resistance of the SZ in 1 M HCl solution.

Manufacturing of WC-Co composites using the electroless precipitation method at different sintering temperatures of 1100, 1250, 1 350 and 1 500 degrees C was successfully achieved. The chemical composition of the investigated materials was 90 wt.% WC with 10 wt.% Co, and 80 wt.% WC with 20 wt.% Co. The specific density, densification, and Vickers microhardness measurements were found to increase with increased sintering temperature for both the WC-Co compositions. The composites of tungsten carbide with 10 wt.% Co had a higher specific density and Vickers microhardness measurements than those for the composites of tungsten carbide with 20 wt.% Co. Composites with WC-10 wt.% Co had better wear resistance. The stress-strain and transverse rupture strength increased monotonically with the increase in sintering temperatures, agreeing with the material hardness and wear resistance behavior. Fractographical scanning electron microscopy analysis of the fracture surface demonstrated a rough characteristic conical shape failure in the direction of the maximum shear stress. A proposed mechanism for the formation of the conical fracture surface under compression testing is presented.

The core cooling of upward flow MTR pool type Research Reactor (RR) at the later stage of pump coast down is experimentally handled to clarify the effect of some operating parameters on RR core cooling. Therefore, a test rig is designed and built to simulate the core cooling loop at this stage. The core is simulated as two vertical channels, electrically heated, and extended between upper and lower plenums. Two elevated tanks filled with water are connected to the two plenums. The first one constitutes a left branch, connected to the lower plenum, and is electrically heated to simulate the core return pipe. The second one constitutes the right branch, connected to the upper plenum, and is cooled by refrigerant circuit to simulate the reactor pool. Channel coolant and wall temperatures at different power and branch temperatures are measured, registered and analyzed. The results show that at this stage of core cooling two cooling loops are established; an internal circulation loop between the channels dominated by the difference in channel's power and an external circulation loop between the branches dominated by the temperature difference between branches. Also, there is a double inversion in core flow, upward-downward-upward flow. This double inversion increases largely the channel's wall temperature. Complementary safety analysis to evaluate this phenomenon must be performed.

Cerebellar model articulation controller neural networks is one of the computational intelligence tools that can be applied for modeling, classification, and control. Proportional velocity controller is a servo-type controller, which is commonly applied to motion control systems. This paper presents a novel combination of cerebellar model articulation controller neural networks and optimal proportional velocity controller. A simple mathematical model for applying and studying cerebellar model articulation controller is introduced, and a study of its parameters is presented individually. The effect of parameters variation on cerebellar model articulation controller performance is identified. Learning algorithms highly affect the cerebellar model articulation controller behavior even when the parameters are optimized, and proper selection of the learning scheme must be taken under consideration. Three different learning algorithms are studied for evaluating transient and steady-state cerebellar model articulation controller responses. The results showed that the change of cerebellar model articulation controller generalization size and scale of the control signal has a marked effect on the performance of cerebellar model articulation controller. Furthermore, the constant learning rate algorithm gives the best overall performance.

Cerebellar model articulation controller neural networks is one of the computational intelligence tools that can be applied for modeling, classification, and control. Proportional velocity controller is a servo-type controller, which is commonly applied to motion control systems. This paper presents a novel combination of cerebellar model articulation controller neural networks and optimal proportional velocity controller. A simple mathematical model for applying and studying cerebellar model articulation controller is introduced, and a study of its parameters is presented individually. The effect of parameters variation on cerebellar model articulation controller performance is identified. Learning algorithms highly affect the cerebellar model articulation controller behavior even when the parameters are optimized, and proper selection of the learning scheme must be taken under consideration. Three different learning algorithms are studied for evaluating transient and steady-state cerebellar model articulation controller responses. The results showed that the change of cerebellar model articulation controller generalization size and scale of the control signal has a marked effect on the performance of cerebellar model articulation controller. Furthermore, the constant learning rate algorithm gives the best overall performance.

The thermophysical properties of EBT2 films exposed to different doses of x-ray were investigated. The doses ranged from 2 to 818 cGy. The films were irradiated by a Varian linear accelerator using a 6 MV photon beam. The thermal conductivity (k) was obtained by measuring the thermal diffusivity (alpha) and thermal effusivity (e) using the photoacoustic (PA) technique. The alpha, e, and k values clearly indicated their dependence on the dose from 0 to 818 cGy. The results demonstrate that the PA technique can detect variations in the thermal diffusivity at doses as low as approximately 3 cGy. The thermal conductivity for the film exposed to 818 cGy of radiation increased by a factor of approximately 3.70 compared to the non-exposed film. The PAspectroscopic technique displayed good reproducibility, with a relative standard deviation of less than 5%.

The present work is a description of a proposed system for seawater desalination. The suggested system operates basically the same as the MSF system operates but uses high pressurized saturated water. The system operating pressure through all stages of the system and the final stage pressure are higher than atmospheric pressure. The system is simple and easy to construct. No need for high operation maintenance or high technical stuff in operation. No need for vacuum pumps because it operates at pressure higher than atmospheric pressure which also makes the system starts to operate fast and easy. The seawater could be with any quality or grade even brackish water could be used so no need for seawater pretreatment. The system could also be run by solar energy through replacing heat exchanger with a solar collector according to operating pressure and assigned saturated temperature. Energy consumption and production cost are promising even if system uses electricity as heat source. (C) 2014 Elsevier B.V. All rights reserved.

The aim of the present work was to study the possibility of joining two dissimilar cast Al-Si alloys, typically, A319 and A413 using friction stir welding. Both of the mechanical and microstructural characteristics of dissimilar A319 and A413 cast aluminum friction stir welded joints were studied. The effect of both tool rotational and welding speeds on the mechanical and microstructural characteristics was investigated. The results showed that sound joints between the A319 and A413 plates were successfully obtained. The average size of the Si particles increases with increasing the tool rotational speed and/or decreasing the welding speed. The average size of alpha-Al grains increases with increasing the tool rotational speed and/or decreasing the welding speed. At the center of stirred zone, the Si particles were found to be uniformly distributed at low welding or high rotational speeds in comparison with at higher welding or lower rotational speeds. The hardness of the welded region was higher than the hardness range of A413 base alloy, but it is approximately located within the hardness range of A319 base alloy. The average hardness of the welded regions increases with increasing the welding speed and/or reducing the tool rotational speed. The tensile tests results showed that the welded joints have better tensile properties than the base alloys. All of the tensile specimens were fractured outside the welded regions at the A413 base metal placed at the advancing side.

In the present study, a novel indirect solar cooker with outdoor elliptical cross section, wickless heat pipes, flat-plate solar collector and integrated indoor PCM thermal storage and cooking unit is designed, constructed and tested under actual meteorological conditions of Giza, Egypt. Two plane reflectors are used to enhance the insolation falling on the cooker's collector, while magnesium nitrate hexahydrate (T-m = 89 degrees C, latent heat of fusion 134 kJ/kg) is used as the PCM inside the indoor cooking unit of the cooker. It is found that the average daily enhancement in the solar radiation incident on the collector surface by the south and north facing reflectors is about 24%. Different experiments have been performed on the solar cooker without load and with different loads at different loading times to study the possibility of benefit from the virtues of the elliptical cross section wickless heat pipes and PCMs in indirect solar cookers to cook food at noon and evening and to keep food warm at night and in early morning. The results indicate that the present solar cooker can be used successfully for cooking different kinds of meals at noon, afternoon and evening times, while it can be used for heating or keeping meals hot at night and early morning. (C) 2008 Elsevier Ltd. All rights reserved.

The paper presents the measurement and computation of the corona onset voltages, electric field and ion current density profiles of a new "Tri-electrode system" intended for electrostatic separation applications. Unlike the well-known "dual cylinder-wire electrode system", the new system utilizes an extra adjustable wire in order to provide the means for a more efficient ion charging current; necessary for separation of different granular mixtures. An experimental setup is constructed to model the present multi-electrode arrangement. The measurements are carried out for wire diameters between 0.3-1.0 mu m and for different geometrical parameters. Without resorting to the commonly used Deutch's assumption, a computational scheme is developed to solve the corona equations and to compute the associated ionized field quantities of the system. Mapping of the ion flow field patterns demonstrates the impact of this assumption on the solution's accuracy. The computed results were found to be in good agreement with experiments. The configuration offers a more efficient charging process and separation in comparison with earlier separators' designs.

This paper proposes a simple and effective evolutionary computation-based technique to estimate the equivalent circuit parameters of a single-phase transformer from its nameplate data without the need to conduct any experimental measurements. Two techniques, namely: particle swarm optimization and genetic algorithm are employed to track nameplate data by minimizing certain objective functions. The effectiveness of the proposed technique is examined through its application for three single-phase transformers of different ratings. The results show that evolutionary computation techniques can precisely identify transformer equivalent circuit parameters. The proposed technique can be extended to estimate the parameters of a three-phase power transformer from its nameplate data without taking the transformer out of service to carry out any experimental testing.

The performance of alloyed CdS0.33Se0.67 quantum dots-sensitized solar cells (QDSSCs) is studied. Fluorine doped Tin Oxide (FTO) substrates were coated with 20nm-diameter TiO2 nanoparticles (NPs). Presynthesized CdS0.33Se0.67 quantum dots (QDs) (radius 3.1 nm) were deposited onto TiO2 nanoparticles (NPs) using direct adsorption (DA) method, by dipping for different times at ambient conditions. The FTO counter electrodes were coated with platinum, while the electrolyte containing I-/I-3(-) redox species was sand-wiched between the two electrodes. The characteristic parameters of the assembled QDSSCs were measured at different dipping times, under AM 1.5 sun illuminations. The maximum values of short circuit current density (J(sc)) and conversion efficiency (II) are 1.115 mA/cm(2) and 0.25% respectively, corresponding 6h dipping time. Furthermore, the J(sc) increases linearly with increasing the intensities of the sun light which indicates the linear response of the assembled cells.

This paper extended the concept of the technique for order preference by similarity to ideal solution (TOPSIS) to develop a methodology for solving multi-level non-linear multi-objective decision-making (MLN-MODM) problems of maximization-type. Also, two new interactive algorithms are presented for the proposed TOPSIS approach for solving these types of mathematical programming problems. The first proposed interactive TOPSIS algorithm includes the membership functions of the decision variables for each level except the lower level of the multi-level problem. These satisfactory decisions are evaluated separately by solving the corresponding single-level MODM problems. The second proposed interactive TOPSIS algorithm lexicographically solves the MODM problems of the MLN-MOLP problem by taking into consideration the decisions of the MODM problems for the upper levels. To demonstrate the proposed algorithms, a numerical example is solved and compared the solutions of proposed algorithms with the solution of the interactive algorithm of Osman et al. (2003)141. Also, an example of an application is presented to clarify the applicability of the proposed TOPSIS algorithms in solving real world multi-level multi-objective decision-making problems. (C) 2013 Elsevier Inc. All rights reserved.

In the present investigation, friction stir spot welding on annealed aluminum alloy AA5754 sheets was performed. The influences of the tool rotational speed and tool stirring (dwell) time on the weld structure and static strength of welds were evaluated. The results revealed that the width of the completely metallurgical-bonded region increases with the increasing tool rotational speed and/or the dwell time up to certain levels. Increasing such parameters beyond these levels slightly reduces the width of the bonding region. The stirred zone exhibited higher microhardness than that of the base material. The tensile-shear force was found to increase with the increasing tool rotational speed and/or dwell time up to a certain level (9s). Higher tool rotational speeds and/or prolonged dwell times slightly reduce(s) the tensile-shear force.