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Jamasb S.,Hamedan University of Technology
Surface Engineering and Applied Electrochemistry | Year: 2017

The instability of the dc operating point in the pH-sensitive ion-selective field effect transistors (ISFETs) has been ascribed to a chemical ageing at the electrolyte–insulator. This instability, commonly referred to as a drift, is believed to involve formation of a chemically-modified insulator surface layer as a result of hydration of the insulator material. A kinetic model for hydration of the amorphous insulator material is presented. The kinetics of hydration is limited by the hopping and/or trap-limited transport mechanism known as dispersive transport, the key characteristic of which is a power-law time dependence of the diffusion coefficient. The power-law time dependence of the diffusion coefficient will be shown to lead to a stretchedexponential decay in the form exp[–(t/τ)β] for the excess density of sites or traps occupied by the hydrating chemical species undergoing dispersive diffusion, where τ is the time constant associated with a structural relaxation and β is the dispersion parameter satisfying 0 < β < 1. The kinetics associated with a hydration reaction limited by the dispersive diffusion has been shown to lead to a hydrated layer thickness exhibiting a time dependence in the form {1–exp[–(t/τ)β]}. The first order rate equation describing the kinetics of the hydration reaction is characterized by the time-dependent rate coefficient. © 2017, Allerton Press, Inc.

Vaseghi M.,Hamedan University of Technology | Vaseghi M.,Pohang University of Science and Technology | Kim H.S.,Pohang University of Science and Technology
Materials and Design | Year: 2012

In this paper static and dynamic strain ageing behavior in Al-Mg-Si alloys related to equal channel angular pressing (ECAP) was investigated. In order to examine the combined plastic deformation, solution treatment and ageing effects on strengthening characteristics, experimental results of ageing without ECAP, pre-ECAP ageing, post-ECAP ageing and dynamic ageing inside of ECAP die were compared. In particular, the effects of ageing temperature, ageing time, strain rate in ECAP, and sequence of heat treatment and ECAP on Vickers hardness were discussed. To achieve a higher hardness, an optimum ageing cycle combined with ECAP process is presented based on the results of current study. By employing the proposed schedule the hardness value was increased from 86 HV (as-solution treatment) to 138 HV (peak hardness of the current schedule). © 2011 Elsevier Ltd.

Rezaeivala M.,Hamedan University of Technology | Keypour H.,Bu - Ali Sina University
Coordination Chemistry Reviews | Year: 2014

In this paper, there is an attempt to review the developments in the design and synthesis of pyridine containing [1+1] and [2+2] macrocyclic Schiff base ligands, formed by condensations of 2,6-diacylpyridine or 2,6-diformylpyridine and appropriate polyamines, which utilize the templating capability of different metal ions to direct the synthetic pathway. The reduction of the cyclic Schiff bases to their related amine derivatives is also considered since this leads to more flexible ligands capable of structural elaboration through donor groups. Attention is mainly paid to the synthetic and structural aspects of the resulting metal complexes, particularly to the role of the coordination preferences of the different metal ions in directing the synthesis totally or preferentially toward mono-, di- or poly-nuclear entities. The preparation of functionalized ligands, containing pendant arms, capable of promoting rapid complexation and decomplexation and their use in selective metal ion transportation and separation are also paid attention to. Furthermore, a summary of the new approach of these compounds such as mechanically interlocked molecules, catalytic properties and cofactors and artificial metalloenzymes is reviewed. © 2014 Elsevier B.V.

Afkhami A.,Bu - Ali Sina University | Ghaedi H.,Bu - Ali Sina University | Madrakian T.,Bu - Ali Sina University | Rezaeivala M.,Hamedan University of Technology
Electrochimica Acta | Year: 2013

A new chemically modified electrode was constructed for rapid, simple, accurate, selective and highly sensitive simultaneous determination of lead and cadmium using square wave anodic stripping voltammetry (SWASV). The electrode was prepared by incorporation of new synthesized Schiff base and multi-walled carbon nanotubes (MWCNT) in carbon paste electrode. The limit of detection was found to be 0.25 ng mL-1 and 0.74 ng mL-1 for Pb 2+ and Cd2+, respectively. The stability constants of the complexes of the ligand with several metal cations in ethanol medium were determined. The effects of different cations and anions on the simultaneous determination of metal ions were studied and it was found that the electrode is highly selective. The proposed chemically modified electrode was used for the determination of lead and cadmium in several foodstuffs and water samples. © 2012 Elsevier Ltd. All Rights Reserved.

Najafi M.,Hamedan University of Technology | Yousefi Y.,Bu - Ali Sina University | Rafati A.A.,Bu - Ali Sina University
Separation and Purification Technology | Year: 2012

Amino functionalized silica gel (NH 2-SG) and amino functionalized silica nano hollow sphere (NH 2-SNHS) with rather monodispers shape and size were prepared and characterized by X-ray differaction, scanning electron microscopy (SEM), FT-IR, thermogravimetery, and N 2 adsorption-desorption techniques. The synthesized nano particles were employed as a Cd 2+, Ni 2+, and Pb 2+ adsorbent from aqueous solutions at room temperature. Adsorption performances of three different adsorbents prepared by functionalization of commercial silica gel (NH 2-SG), silica nano hollow sphere (NH 2-SNHS), and a non functionalized silica nano hollow sphere (SNHS) have been compared. Heavy metal adsorption process has been thoroughly studied from both kinetic and equilibrium points of view for all adsorbents. The adsorption isotherms were analyzed using the seven different isotherm models and correlation coefficients were determined for each isotherm. It was found that the Langmuir-Freundlich (Sips) isotherm showed better correlation with the experimental data than other isotherms. The adsorption kinetics was tested for the pseudo-first order, pseudo-second order and Elovich kinetic models at different experimental conditions. The kinetic data show that the process is very fast and the reactions follow pseudo-second-order kinetic models for amino functionalized adsorbents. Also, the maximum adsorption values for Cd 2+, Ni 2+, and Pb 2+ under the experimental conditions were determined for all adsorbents. © 2011 Elsevier B.V. All rights reserved.

Moradi M.H.,Bu - Ali Sina University | Hajinazari M.,Bu - Ali Sina University | Jamasb S.,Hamedan University of Technology | Paripour M.,Hamedan University of Technology
Energy | Year: 2013

An optimization method, which considers the Combined Heat and Power (CHP) model under uncertainty, has been developed to determine the optimal capacities for the CHP and boiler such that thermal and electrical energy demands can be satisfied with high cost efficiency. The proposed method offers an energy management system (EMS) strategy which employs the fuzzy set theory to account for the uncertainties associated with electrical and thermal energy demands as well as those associated with natural gas and electrical power prices in order to determine the optimum ranges for boiler and CHP capacities which maximize an objective function based on the net present value (NPV). The reduction in operational strategy expenses arising from the monetary cost of the credit attainable by air pollution reduction is also taken into account in evaluation of the objective function. The optimal range for boiler and CHP capacities and the resulting projection for the range of optimal value of the objective function are derived using a hybrid optimization method involving the particle swarm optimization (PSO) and the linear programming algorithms. The viability of the proposed method is demonstrated by analyzing the decision to construct a CHP system for a typical hospital. © 2012 Elsevier Ltd.

The influence of drying temperature, T on the surface structure of polyaniline (PANI) nanostructured films dried at temperatures less than the glass transition temperature, Tg and between Tg and melting temperature, Tm was investigated by atomic force microscopy (AFM) and ZeScope optical profilometry. The expected power law behavior associated with surface roughness over small length scales was confirmed at different drying temperatures. To correlate the value of the film thickness determined based on AFM with that obtained from ZeScope measurements, a model of height correcting factor is introduced. The variation in saturated roughness of the PANI film was determined to follow a power law model in the range of T < Tg, with a saturated roughness exponent of 4.48 ± 0.4. The structure of the PANI film has been investigated based on molecular dynamics simulation. The applicability of power law model was confirmed by simulations, based on which the saturated roughness exponent was determined to be 4.90 ± 0.5. © 2014 Elsevier B.V.

Bahramian A.,Hamedan University of Technology
Industrial and Engineering Chemistry Research | Year: 2013

Coral-like TiO2 nanostructured films were chemically synthesized through the sol-gel method for fabrication of dye-sensitized solar cell (DSSC). The influence of experimental parameters such as precursor hydrolysis rate, reaction time, type and concentration of acid, and annealing temperature was studied through analysis of the surface structure of the films. The coral-like TiO2 film has excellent light scattering property and a mesoporous structure with fairly large specific surface area of 164 m2 g-1. The resulting DSSC, which consists of a dense, coral-like TiO2 nanostructured film and the dye N719 in an electrolyte, shows a better performance as compared to a fabricated DSSC by using commonly used TiO2. A photocurrent value of approximately 16.1 mA cm-2, a fill factor of 77.6%, and a conversion efficiency of 9.4% were obtained. The low cost and the possibility of controlling the morphology of the prepared film make this method an interesting candidate for use in fabricating photovoltaic devices. © 2013 American Chemical Society.

Effects of the deposition process parameters on the thickness of TiO 2 nanostructured film were simulated using the molecular dynamics (MD) approach and modeled by the artificial neural network (ANN) and regression method. Accordingly, TiO2 nanostructured film was prepared experimentally with the sol-gel dip-coating method. Structural instabilities can be expected, due to short- and/or long-range intermolecular forces, leading to the surface inhomogeneities. In the MD simulation, the Morse potential function was used for the inter-atomic interactions, and equations of motion for atoms were solved by Verlet algorithm. The effect of the withdrawal velocity, drying temperature and number of deposited layers were studied in order to characterize the film thickness. The results of MD simulations are reasonably consistent with atomic force microscopy, scanning electron microscopy and Dektak surface profiler. Finally, the outputs from experimental data were analyzed by using the ANN in order to investigate the effects of deposition process parameters on the film thickness. In this case, various architectures have been checked using 75% of experimental data for training of the ANN. Among the various architectures, feed-forward back-propagation network with trainer training algorithm was found as the best architecture. Based on the R-squared value, the ANN is better than the regression model in predicting the film thickness. The statistical analysis for those results was then used to verify the fitness of the complex process model. Based on the results, this modeling methodology can explain the characteristics of the TiO2 nanostructured thin film and growth mechanism varying with process conditions. © 2013 John Wiley & Sons, Ltd.

Delavari H.,Hamedan University of Technology | Baleanu D.,Romanian Space Science Institute | Sadati J.,Babol Noshirvani University of Technology
Nonlinear Dynamics | Year: 2012

In this paper stability analysis of fractional-order nonlinear systems is studied. An extension of Lyapunov direct method for fractional-order systems using Bihari's and Bellman-Gronwall's inequality and a proof of comparison theorem for fractional-order systems are proposed. © 2011 Springer Science+Business Media B.V.

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