Showing papers by "Amirkabir University of Technology published in 2001"

Modification of polysiloxane polymers for biomedical applications: a review

Abstract: This paper reviews methods of modifying polydimethylsiloxane (PDMS) polymers to improve their properties for biomedical applications. The modification methods are discussed under three different categories: bulk, surface and other modification techniques. Surface modification techniques include physical and chemical techniques to modify polymer surfaces. Bulk modification techniques include blending, copolymerization, interpenetrating polymer networks (IPNs) and functionalization. The third category includes less common modification techniques. © 2001 Society of Chemical Industry

Interior-Point Method for Reservoir Operation with Stochastic Inflows

Abstract: A new method is proposed for long-term reservoir operation planning with stochastic inflows. In particular, the problem is formulated as a two-stage stochastic linear program with simple recourse. The stochastic inflows are approximated by multiple inflow scenarios, leading to a very large deterministic model which is hard to solve using conventional optimization methods. This paper presents an efficient interior-point optimization algorithm for solving the resulting deterministic problem. It is also shown how exploiting the problem structure enhances the performance of the algorithm. Application to regulation of the Great Lakes system shows that the proposed approach can handle the stochasticity of the inflows as well as the nonlinearity of the operating conditions in a real-world reservoir system.

Study on morphology of ternary polymer blends. I. Effects of melt viscosity and interfacial interaction

Abstract: The morphology of some ternary blends was investigated. In all of the blends polypropylene, as the major phase, was blended with two different minor phases, ethylene–propylene–diene terpolymer (EPDM) or ethylene–propylene–rubber (EPR) as the first minor phase and high-density polyethylene (HDPE) or polystyrene (PS) as the second minor phase. All the blends were investigated in a constant composition of 70/15/15 wt %. Theoretical models predict that the dispersed phase of a multiphase polymer blend will either form an encapsulation-type phase morphology or phases will remain separately dispersed, depending on which morphology has the lower free energy or positive spreading coefficient. Interfacial interaction between phases was found to play a significant role in determining the type of morphology of these blend systems. A core–shell-type morphology for HDPE encapsulated by rubber was obtained for PP/rubber/PE ternary blends, whereas PP/rubber/PS blends showed a separately dispersed type of morphology. These results were found to be in good agreement with the theoretical predictions. Steady-state torque for each component was used to study the effect of melt viscosity ratio on the morphology of the blends. It was found that the torque ratios affect only the size of the dispersed phases and have no appreciable influence on the type of morphology. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1129–1137, 2001

Mechanism of morphology development in dynamically cured EPDM/PP TPEs. I. Effects of state of cure

Abstract: Attempts were made to follow and correlate morphological development with the crosslinking density, or state of cure (SOC), and the surface tension (γ) of the rubber phase in dynamically cured thermoplastic elastomers (TPEs) based on ethylene propylene diene rubber and polypropylene (PP) with 60/40 (w/w) ratios. Samples were taken from a hot running mixer without interruption and quickly quenched in liquid nitrogen both before and after the onset of vulcanization at various SOCs to carry out this process. The quick cooling of the samples prevented the coalescence and agglomeration of the dispersed rubber particles. A two-phase morphology with the rubber particles dispersed throughout the PP matrix was observed for the uncured but frozen samples, whereas unfrozen blend samples showed a particulate cocontinuous morphology in the uncured state. An increase in the mixing torque with the SOC was observed after the addition of a curing system. This was understood to be caused by the increase in the rubber crosslinking density and also by the enhancement of the interfacial adhesion between the cured rubber phase and the PP matrix, leading to the better wetting of the two phases. Above a certain crosslinking density (SOC), γ of the rubber particles decreased through elastic shrinkage. This phenomenon, together with the breakdown of the agglomerate structure formed by the cured rubber particles, led to a decrease in the mixing torque after a maximum was passed and, finally, to a defined morphology. Based on the obtained results, a four-stage model is proposed to describe the microstructural development in dynamically vulcanized TPEs. Dynamic mechanical thermal analysis and differential scanning calorimetry results are also used to support the model. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2531–2544, 2001

Neural network based face recognition with moment invariants

Abstract: This paper introduced an experimental evolution of the effectiveness of utilizing various moments as pattern features in human face technology. In this paper, we apply pseudo Zernike moments (PZM) for recognition of human faces in two-dimensional images, and we compare their performance with other type of moments. The moments that we have used are Zernike moments (ZM), pseudo Zernike moments (PZM) and Legendre moments (LM). We have used shape information for human face localization, also we have used a radial basis function (RBF) neural network as a classifier for this application. The performance of classification is dependent on the moment order as well as the type of moment invariant, but the classification error rate was below %10 in all cases. Simulation results on the face database of Olivetti Research Laboratory (ORL) indicate that high order degree pseudo Zernike moments contain very useful information about face recognition process, while low order degree moments contain information about face expression.

Broken bar detection in induction motor via wavelet transformation

Abstract: This paper presents a novel approach for the detection of broken rotor bars in induction motors based on the wavelet transformation Multiresolution signal decomposition based on wavelet transform or wavelet packet provides a set of decomposed signals in independent frequency bands, which contain independent dynamic information due to the orthogonality of wavelet functions Also wavelet transforms and wavelet packets in tandem with some signal processing methods, such as autoregressive spectrum, energy monitoring, fractal dimension, etc, can produce desirable results for the condition monitoring and fault diagnosis of induction motors In the proposed method, broken bar detection is based on the decomposition of the stator currents, where wavelet coefficients of these signals have been extracted Comparing these extracted coefficients is used for diagnosing the healthy machine from faulty machine Experimental results are presented for healthy machines and machines with two, three, four and five broken bars in their rotor Deviation of wavelet coefficients in healthy mode from faulty modes depicts the number of broken bars in the rotor cage Simulation and experimental results show the effectiveness of the proposed method for broken rotor bar detection in squirrel cage induction motors

Probabilistic design of systems with general distributions of parameters

Abstract: This paper presents a new method for finding optimal solutions of systems with design parameters which are random variables distributed with various general and possibly non-symmetrical distributions. A double-bounded density function is used to approximate the distributions. Specifications may require tracking constraints in time domain and stability conditions in frequency domain. Using sensitivity information, the proposed method first finds a linearized feasible region. Afterwards it attempts to place a tolerance box of the design parameters such that the region with higher yield lies in the feasible region. The yield is estimated by the joint cumulative density function over a portion of the tolerance box contained in the feasible region. Optimal designs are found for a fourth-order servomechanism and actual yields are evaluated by Monte-Carlo simulation. Copyright © 2001 John Wiley & Sons, Ltd.

Real-time estimation of vehicle state and tire-road friction forces

Abstract: An approach to estimate vehicle state and tire road friction forces using an extended Kalman filter (EKF) is presented. A numerically stable algorithm is used to implement the EKF. This approach does not require knowledge of the tire model and road friction coefficient. This is an advantage, because although many tire models have been developed so far, there is still a significant difference between these models and the real behavior of the tire-road interface. The main advantages of the proposed method are numerical stability, computational efficiency and to use vehicle mounted sensors. The effectiveness of the presented method is confirmed by simulation of a lane-change and an ABS braking maneuver for a full vehicle. In these simulations, a seven DOF vehicle model, a Pacejka tire model and a nonlinear model for a hydraulic brake system are used. The results show that the EKF has good performance in presence of significant sensor noise in both scenarios.

Novel Type of Impinging Streams Contactor for Liquid−Liquid Extraction

Abstract: An experimental study was conducted on liquid-liquid extraction of succinic acid by means of normal butanol from its aqueous solution (BSW), iodine from its aqueous solution by means of kerosene (KIW), and acetic acid by means of distilled water from kerosene (WAK) in a novel type of contactor based on an impinging streams technique. This high-intensity jet contactor provides significant improvement over the conventional extractor because of the impingement of high-velocity feed streams upon one another in a relatively small contactor volume, resulting in a high-turbulent mixing of two phases. As a result of both the impinging process and shear forces exerted on the phases, the overall volumetric (capacity) mass-transfer coefficients, K L a, of up to 15, 23, and 26 min -1 have been obtained for BSW, KIW, and WAK, respectively. The order of magnitudes of the latter coefficients are higher than typical values obtained by conventional extractors. In addition, the effects of the upper disk speed, solution flow rate, disk diameter, distance between disks and the enhancing effect of impinging streams have been investigated. These experimental results verify the capability of the new contactor in liquid-liquid extraction.

Kinetic Study of Zinc Oxide Reduction by Methane

Abstract: Zinc oxide reduction by methane can be an alternative method for zinc production Methane is more reactive than coke (the common reducing agent), thus, the operating temperature can be considerably decreased Therefore, this method can omit or simplify the troublesome splash zinc condenser of the usual processes Moreover, the gaseous products of this method can be used as synthesis gas for the petrochemical industries In this work, the kinetics of zinc oxide reduction with methane was studied by thermogravimetry, and simultaneous and online gas analysis Then by applying a suitable model, kinetic parameters were determined These parameters are essential for the design of pilot or industrial plants

A new strategy for traction control in turning via engine modeling

Abstract: The driving stability is affected by driven wheel slip, which can be controlled by the driven wheel torque. In a vehicle powered by an internal combustion engine, the torque can be controlled by an engine management system. The sliding mode algorithm is the mechanism behind the design of the traction control system (TCS). The longitudinal slip is controlled by the position of the throttle valve. The vehicle model used has seven degrees of freedom and a two-state engine model, i.e., the mass of air in the intake manifold and the engine speed. Time-delay transport is considered in the engine model used. A nonlinear tire model for combined slip is used for tire force computation. Due to the nonlinear dynamic of the tire, vehicle, and engine, the control method of sliding mode is used for its robustness. A controller is designed based on the dynamic surface control, for which two first-order surfaces are defined. The effectiveness of the controller is demonstrated with simulation results for different maneuvers. Results show that for different road conditions, the acceleration performance, directional stability, and steerability of a vehicle equipped with TCS is improved. The reason is that the slip is controlled by keeping it in a desired range.

In vitro studies of platelet adhesion on laser-treated polyethylene terephthalate surface.

Abstract: In order to improve blood compatibility, the surfaces of polyethylene terephthalate (PET) were treated using CO2 pulsed and KrF excimer lasers. The physico-chemical characterization of the laser-treated PET surfaces was carried out through attenuated total reflectance infrared spectroscopy and contact-angle measurements. The hemocompatibility of the laser-irradiated PET films was examined in vitro to evaluate their capability of inducing platelet adhesion in comparison with unmodified PET. The number of adhered platelets was determined by lactate dehydrogenase (LDH) activity measurement. Platelet adhesion on the untreated PET was relatively high compared to the laser-treated samples. Laser irradiation of PET surface reduced the number of adherent platelets and prevented platelet spreading on the surface. Reduction of platelet adhesion was attributed to the change in morphology, chemical structure, and crystallinity of the PET surface due to laser irradiation with various numbers of pulses. The morphology of adhered platelets on the PET surfaces was investigated by scanning electron microscopy (SEM). The SEM observations were consistent with the results obtained from LDH activity measurement. © 2000 John Wiley & Sons, Inc. J Biomed Mater 54: 540–546, 2001

Study on morphology of ternary polymer blends. II. Effect of composition

Abstract: The composition effect on morphology of polypropylene/ethylene–propylene–diene terpolymer/polyethylene (PP/EPDM/PE) and polypropylene/ethylene–propylene–diene terpolymer/polystyrene (PP/EPDM/PS) ternary blends has been investigated. In all of the blends, polypropylene as the major phase was blended with two minor phases, that is, EPDM and PE or PS. From morphological studies using the SEM technique a core–shell morphology for PP/EPDM/PE and separated dispersed morphology for PP/EPDM/PS were observed. These results were found to be in agreement with the theoretical predictions. The composition of components affected only the size of dispersed phases and had no appreciable effect on the type of morphology. The size of each dispersed phase, whether it forms core or shell or disperses separately in matrix, can be related directly to its composition in the blend. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1138–1146, 2001

Dynamic Crack Analysis Under Coupled Thermoelastic Assumption

Abstract: A boundary element method using Laplace transform in time domain is developed for the analysis of fracture mechanic under coupled thermoelastic assumption. The transient coupled thermoelastic field is solved without need for domain discretization. The singular behavior of the temperature and displacement fields in the vicinity of the crack tip is modeled by quarter-point elements. Thermal dynamic stress intensity factors for mode I are evaluated from computed nodal values, using the well-known displacement and traction formulas. The accuracy of the method is investigated through comparison of the results with the available data in literature. The conditions where the inertia term plays an important role is discussed and variations of the dynamic stress intensity factor is investigated.

Electromagnetic field distributions around conducting slabs, produced by eddy-current probes with arbitrary shape current-carrying excitation loops

Abstract: The theoretical prediction of eddy-current probe output signals for various nondestructive testing (NDT) applications usually involves solution of the electromagnetic field due to a current-carrying excitation loop in the vicinity of a flawless conductor. The paper presents a general theory for the time-harmonic magnetic field distribution produced by an arbitrary shape current-carrying excitation loop around a linear, isotropic, homogeneous conducting slab. In this theory the authors develop a Fourier-integral-based model for computing the magnetic field distributions, which greatly simplifies the computation procedure. The main feature of the model is its ability to analyse two- and three-dimensional excitation geometry, with a similar degree of computation burden. This feature stems from the fact that in this model, knowledge of the field distribution at the place of the conductor surface in free space suffices to compute the field in the presence of the conductor. To demonstrate the accuracy of the model, the authors consider two special cases of an infinite straight wire and an elliptical loop exciter. The comparison of the results with those obtained using the conventional algorithms in the literature validates the model introduced in the paper. To show the generality of the model, the authors also present results associated with a solenoid exciter with a three-dimensional geometry for which no analytical solution is available in the literature.