A 3D analytical modeling of tri-gate tunneling field-effect transistors

In this paper, a three-dimensional (3D) analytical solution of the electrostatic potential is derived for the tri-gate tunneling field-effect transistors (TG TFETs) based on the perimeter-weighted-sum approach. The model is derived by separating the device into a symmetric and an asymmetric double-gate (DG) TFETs and then solving the 2D Poisson’s equation for these structures. The subthreshold tunneling current expression is extracted by numerical integrating the band-to-band tunneling generation rate over the volume of the device. It is shown that the potential distributions, the electric field profile, and the tunneling current predicted by the analytical model are in close agreement with the 3D device simulation results without the need of fitting parameters. Additionally, the dependence of the tunneling current on the device parameters in terms of the gate oxide thickness, gate dielectric constant, channel length, and applied drain bias is investigated and also demonstrated its agreement with the device simulations.     

Poly (α-methylstyrene-styrene-acrylonitrile) as a heat deflection additive for PVC: Physical and rheological properties

Poly(α-methylstyrene-styrene-acrylonitrile) (AMSAN) is an additive used to improve the heat deflection temperature of PVC. The effect of its addition on the HDT of a typical injection molding formulation is studied. Other physical properties like impact strength, yield strength, modulus of elasticity, and viscosity are also reported. It is shown that HDT and impact strength are decoupleable based on the amount of AMSAN and impact modifier in the formulation. Calculation of the required percentage of heat distortion additive and impact modifier for a typical injection molding application are demonstrated.     

Investigation on hydrophilicity of micro-arc oxidized TiO2 nano/micro-porous layers

Titania porous layers with a rough surface were synthesized via micro-arc oxidation (MAO) and the effect of the applied voltage and electrolyte concentration on surface structure, and chemical composition of the layers was studied. Morphological and topographical investigations, performed by SEM and AFM, revealed that pore size and surface roughness of the layers increased with the applied voltage and the electrolyte concentration. Based on the XRD and XPS results, the grown layers consisted of anatase and rutile phases with varying fractions depending on growth conditions. It was found that anatase/rutile relative content reached its maximum value at medium applied voltages or electrolyte concentrations. Finally, hydrophilicity of the grown layers was determined using a water contact angle apparatus, and a correlation between measured contact angles and MAO-parameters was suggested. It was observed that the layers synthesized under the applied voltage of 400 V in the electrolytes with a concentration of 10 g l⁻¹ exhibited the highest hydrophilicity.     

Application of genetic algorithm in computing the tradeoffs between power consumption versus delay in digital integrated circuit design

This paper presents a novel methodology to obtain the entire power consumption versus delay tradeoff curve for the critical paths of a combinational logic circuit in a very efficient way using the genetic algorithm (GA). In order to evaluate the proposed algorithm the most representative set of two-level and multi-level networks from the MCNC91 benchmark suite were processed. The required computational effort, measured in terms of CPU time, is several times better for the proposed GA optimization technique than liner programming (LP) technique. On the other hand, the optimal design points obtained by the GA and LP techniques are very close to each other to within 0.3%.     

Critical heat flux of nanofluids inside a single microchannel: Experiments and correlations

This study investigated experimentally the CHF phenomena of aqueous-based alumina nanofluids in single microchannels, and assessed the validity of a number of microchannel based CHF correlations using experimental nanofluids data. While usual approaches for CHF enhancement are through the modification of different tube surfaces or employing different inserts, this work showed that CHF in microchannels could be enhanced significantly by the inclusion of small concentrations of nanoparticles. The CHF value was found to increase with increase of mass flux, initial subcooling and alumina nanoparticle concentrations. The maximum subcooled CHF enhancement occurred at the lowest mass flux and highest alumina concentration within the experimental range. In addition, the Lee and Mudawar correlation was modified to predict the critical heat flux of water and nanofluids. The new model was examined by experimental data and 24% and 30% mean absolute error were observed for water and alumina nanofluid respectively.     

Modeling and fuzzy control of the engine coolant conditioning system in an IC engine test bed

Mechanical and thermodynamical performance of internal combustion engines is significantly affected by the engine working temperature. In an engine test bed, the internal combustion engines are tested in different operating conditions using a dynamometer. It is required that the engine temperature be controlled precisely, particularly in transient states. This precise control can be achieved by an engine coolant conditioning system mainly consisting of a heat exchanger, a control valve, and a controller. In this study, constitutive equations of the system are derived first. These differential equations show the second-order nonlinear time-varying dynamics of the system. The model is validated with the experimental data providing satisfactory results. After presenting the dynamic equations of the system, a fuzzy controller is designed based on our prior knowledge of the system. The fuzzy rules and the membership functions are derived by a trial and error and heuristic method. Because of the nonlinear nature of the system the fuzzy rules are set to satisfy the requirements of the temperature control for different operating conditions of the engine. The performance of the fuzzy controller is compared with a PI one for different transient conditions. The results of the simulation show the better performance of the fuzzy controller. The main advantages of the fuzzy controller are the shorter settling time, smaller overshoot, and improved performance especially in the transient states of the system.     

Effects of preparation conditions on the morphology and gas permeation properties of polyethylene (PE) and ethylene vinyl acetate (EVA) films

In this study, the effect of film preparation conditions on the gas permeation properties of polyethylene (PE) and ethylene vinyl acetate (EVA) films (containing 18 and 28 wt% vinyl acetate) was investigated. Film blowing and phase inversion methods were applied in the production of PE and EVA films, respectively. The permeation of pure oxygen and carbon dioxide gases was measured at room temperature. The results indicated that with the increase of PE film thickness, permeability and solubility of O₂ and CO₂ in these films decreased; but the diffusivities of gases through PE films increased. In addition, in the case of EVA copolymers, by increasing the content of vinyl acetate, the permeability of CO₂ increased. The rate of increase in CO₂ permeability was different for samples having different preparation conditions. For example, the samples prepared using chloroform as the solvent instead of THF, showed lower CO₂ permeability. Also, the morphological studying of film structure indicated that the higher CO₂ permeability for the samples made from THF solvent is due to the existing of higher porosity in the under layer polymer area. Also scanning electron microscopy (SEM) micrographs showed that with the usage of phase inversion method, there will be a thin dense layer near to the glass substrate.     

Potassium hydroxide catalyst supported on palm shell activated carbon for transesterification of palm oil

In this study, potassium hydroxide catalyst supported on palm shell activated carbon was developed for transesterification of palm oil. The Central Composite Design (CCD) of the Response Surface Methodology (RSM) was employed to investigate the effects of reaction temperature, catalyst loading and methanol to oil molar ratio on the production of biodiesel using activated carbon supported catalyst. The highest yield was obtained at 64.1 °C reaction temperature, 30.3 wt.% catalyst loading and 24:1 methanol to oil molar ratio. The physical and chemical properties of the produced biodiesel met the standard specifications. This study proves that activated carbon supported potassium hydroxide is an effective catalyst for transesterification of palm oil.     

Buckling behavior improvement of steel plate shear wall systems

To improve buckling stability and to prevent early elastic buckling of infill plates, vertical and horizontal plate stiffeners are designed for steel plate shear wall (SPSW) systems. Furthermore, effective design of stiffeners for SPSW systems results in improved structural behavior, such as increase of stiffness, capacity and energy absorption. In this paper, the effect of stiffeners is studied on SPSW structural behavior and consequently a rational method is proposed to determine the minimum required moment of inertia for stiffeners resulting in local buckling mode of the infill plate. The proposed requirement is then compared to results obtained from tests previously conducted, as well as those gained from finite element (FE) analyses performed for this study. Copyright © 2007 John Wiley & Sons, Ltd.