Showing papers by "Amirkabir University of Technology published in 1999"

Measurement of Activity of Water in Aqueous Poly(ethylene glycol) Solutions (Effect of Excess Volume on the Flory−Huggins χ-Parameter)

Abstract: Activities of water are reported for aqueous solutions of poly(ethylene glycol) (PEG) with number average molecular weights of 300, 400, 4000, and 6000 are measured at 35, 45, 55, and 65 °C and at various concentrations from 0 to 40 wt % of PEG using vapor-pressure osmometery. A cubic equation in terms of PEG concentrations is sufficient for correlation of activities. Using measured activities, the Flory−Huggins interaction parameters have been calculated. The effect of temperature, molecular weight of PEG and its concentration, and volume change upon mixing on interaction parameter have been considered. Ignoring the volume change of mixing can lead to an average error of 2.5% with a maximum error of 5.3%.

Dynamic buckling and post-buckling of imperfect orthotropic cylindrical shells under mechanical and thermal loads, based on the three-dimensional theory of elasticity

Abstract: The three-dimensional theory of elasticity in curvilinear coordinates is employed to investigate the dynamic buckling of an imperfect orthotropic circular cylindrical shell under mechanical and thermal loads. Accurate form of the strain expressions of imperfect cylindrical shells is established through employing the general Green's strain tensor for large deformations and the equations of motion are derived in terms of the second Piola-Kirchhoff stress tensor. Then, the governing equations are properly formulated and solved by means of an efficient and relatively accurate solution procedure proposed to solve the highly nonlinear equations resulting from the above analysis. The proposed formulation is very general as it can include the influence of the initial imperfections, temperature distribution, and temperature dependency of the mechanical properties of materials, effect of various end conditions, possibility of large-deformation occurrence and application of any combination of mechanical and thermal loadings. No simplifications are done when solving the resulting equations. Furthermore, in contrast to the displacement-based layer-wise theories and the three-dimensional approaches proposed so far, the stress, force and moment boundary conditions as well as the displacement type ones, can be incorporated accurately in these formulations. Finally, a few examples of mechanical and thermal buckling of some orthotropic cylindrical shells are considered and results of the present three-dimensional elasticity approach are compared with the buckling loads predicated by the Donnell's equations, some single-layer theories, some available results of the layer-wise theory and the recently published three-dimensional approaches and the accuracy of the later methods are discussed based on the exact method presented in this paper.

A High-Order Theory for Dynamic Buckling and Postbuckling Analysis of Laminated Cylindrical Shells

Abstract: Using a high-order Reisner-Mindlin-type shear deformation theory in a power series form, the general large deformation form of the Green strain tensor for imperfect cylindrical shells is introduced. Then, based on Hamilton`s principle, the equations of motion are derived for laminated composite shells. Related constitutive equations are also proposed. In this formulation, temperature dependency of material properties is considered, too. No simplifications are made in solving the coupled nonlinear equations of motion. Finally, few examples of the well-known references are reconsidered for comparison purposes.

Effects of sodium hydroxide and calcium hydroxide on polyester fabrics

Abstract: The results of a comparison between the effects of sodium hydroxide and calcium hydroxide on poly(ethylene terephthalate) fabrics are presented. Calcium hydroxide can produce weight-loss effects similar to an aqueous solution of sodium hydroxide. The effects of some treatment variables on weight loss, fiber diameter, bending rigidity, and strength of yarns taken from fabrics are examined. The results are explained in terms of current views of polyester alkaline hydrolysis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 631–637, 1999

Dynamics of two‐phase flow in porous media: Simultaneous invasion of two fluids

Abstract: Models of two-phase flow and displacement in porous media developed so far typically involve one displacing (invader) and one displaced (defender) fluid. However, in many important applications of these phenomena at field scales, such as two-phase flow in fractured porous media, as well as in laboratory studies, require at least two invaders which also act as the defenders. The results of extensive Monte Carlo simulations of a novel model of such phenomena are reported. The porous medium is represented as a network of pore throats and pore bodies to which effective sizes are assigned that are selected from a given distribution. Both 2-D and 3-D networks are used. The simulation results indicate that the structure of the fluids` clusters is volatile, that is, it changes with the time t and length scale. Moreover, n{sub s}(S,t), the number of fluid clusters of size s, , the mean cluster size, and S(t), the saturation of the fluids all vary with t in a manner that resembles an oscillatory behavior. This behavior is caused by the dynamic breakup and recoalescence of the fluids` clusters, which is a result of simultaneous invasion of the two fluids. The flow effect of thin wetting fluids filmsmore » on the dynamics of the displacement is strong over a broad range of the capillary number. Novel dynamical scaling laws for the cluster-size distribution are obtained. Some results agree qualitatively with the experimental observations, while others provide rational explanations for some unexplained data.« less

Solvent extraction of aromatic components from lube-oil cut by N-methylpyrrolidone (NMP)

Abstract: A method has been developed for the modeling of complex hydrocarbon mixtures which is based on the accurately simulated distillation gas chromatography analysis as well as the extended method of Ruzicka et al for making the model molecules. The method has been used for modeling of the complex mixture of the lube-oil cut SAE 10 in the aromatics extraction process with the solvent N-methylpyrrolidone (NMP) from the Tehran Refinery. To carry out the liquid-liquid equilibria calculations, the van der Waals surface and volume size parameters of the model molecules and NMP as well as their interaction parameters are required which they are calculated by the Bondi's group contribution method with the NMP molecule taken as a functional group according to the approach of Rahman et al. Solvent extraction process at two temperatures of 50 and 42 °C both at 1 atm have been carried out in a batch mixer-settler and the properties of resultant phases (extract and raffinate) have been determined by the precise measuring systems using the standard methods of ASTM and the well-known Riazi's equations. Finally, the results of the equilibrium calculations have been compared with the experimental data and good agreement was found.

Pre-optimization of radiotherapy treatment planning: An artificial neural network classification aided technique

Abstract: A method has been developed which, by using the geometric information from treatment sample cases, selects from a given data set an initial treatment plan as a step for treatment plan optimization. The method uses an artificial neural network (ANN) classification technique to select a best matching plan from the `optimized' ANN database. Separate back-propagation ANN classifiers were trained using 50, 60 and 77 examples for three groups of treatment case classes (up to 21 examples from each class were used). The performance of the classifiers in selecting the correct treatment class was tested using the leave-one-out method; the networks were optimized with respect their architecture. For the three groups used in this study, successful classification fractions of 0.83, 0.98 and 0.93 were achieved by the optimized ANN classifiers. The automated response of the ANN may be used to arrive at a pre-plan where many treatment parameters may be identified and therefore a significant reduction in the steps required to arrive at the optimum plan may be achieved. Treatment planning `experience' and also results from lengthy calculations may be used for training the ANN.

Generalized coherent states for the d-dimensional Coulomb problem

Abstract: In this paper a set of generalized coherent states for the d-dimensional Coulomb problem in coordinate representation are constructed. A coordinate transformation in hyperspherical space is used that maps the d-dimensional Coulomb problem into the D-dimensional harmonic oscillator and the generalized coherent states for the d-dimensional Coulomb problem are then obtained. This exactly soluble model can provide an adequate means for a quantum coherency description of the Coulomb problem in arbitrary dimensions, specifically in the special case of the hydrogen atom, in many theoretical and applied related fields such as in coherent scattering.

Coupled Thermoelasticity of Shells of Revolution: Effect of Normal Stress and Coupling

Abstract: The coupled thermoelasticity of shells of revolution, based on second-order shell theory, is considered, and the governing equations including normal stress and strain as well as the transverse shear and rotary inertia are considered. The coupled energy equation based on the assumption of Lord and Shulman (Lord, H. W., and Shulman, Y., A Generalized Dynamical Theory of Thermoelasticity,' Journal of Mechanics and Physics of Solids, Vol. 15, No. 5, 1967, pp. 299-309) is further considered, and the total system of equations is solved by means of Galerkin finite element method. It is concluded that the inclusion of normal stress in the coupled equation is significant and for thin shells can result in a noticeable difference in shell response compared to unassumed conditions.

Monte Carlo simulation of two-phase flow in porous media: Invasion with two invaders and two defenders

Abstract: We report the results of extensive Monte Carlo simulations of a novel model of two-phase flow in porous media, recently proposed by us (Phys. Rev. Lett. 80 (1998) 3248), in which the two fluids act both as the invading as well as the defending fluids. The phenomenon is relevant to several multiphase flow problems in porous systems and, in particular, in fractured porous media. Our simulations show that the structure of the fluids’ clusters is volatile and changes with the time t and length scale. Moreover, n s , the number of clusters of size s , 〈 s 〉, the mean cluster size, and the fluids’ saturations all oscillate aperiodically with t , indicating the continuing breakup and recoalescence of the clusters. The effect of flow of thin films of the wetting fluid on the dynamics of the displacement is shown to be strong. Novel dynamical scaling laws for the cluster-size distribution are obtained. The results are in qualitative agreement with experimental observations.

Microcalcification classification in mammograms using multiwavelet features

Abstract: In this paper, a multiwavelet based feature extraction method is presented and applied to classification of microcalcification clusters in mammograms. Multiwavelet is a natural generalization to scalar wavelet in which more than one scaling function and wavelet are used to further the design degrees of freedom. We extract energy and entropy features from different channels of multiwavelet. Using a real-valued genetic algorithm (GA), the best sets of features along with their optimal weights are found. The optimal weight vector is found such that within-class scatter is minimized and between-class scatter is maximized. For evaluating the individuals in GA, we use the area under Receiver Operating Characteristic (ROC) curve criterion such that the fittest individual has the largest value of area under ROC curve and the worst has the lowest value. To obtain the ROC curve, we use KNN classifier. Several multiwavelets with different features are employed. An area of 0.91 is obtained for Chui and Lian multiwavelet. A comparative study is conducted to show that the performance of multiwavelet is generally better than the packet wavelet in the present application.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Improvement on Lennard-Jones–Devonshire theory for predicting liquid–solid phase transition

Abstract: In this paper the potential energy of the Lennard-Jones and Devonshire (LJD) model has been corrected to increase its PVT prediction abilities The correction of potential energy is done in two ways (i) taking the coordination number as a function of temperature and volume to improve the second virial prediction ability and (ii) taking pair correlation effects into account to improve the phase transition prediction ability The results of calculations indicate improvement both on PVT behavior in the above range of variation especially on the phase transition prediction ability in solid–liquid and vapor–liquid regions

Application of the continuous two impinging streams reactors in chemical absorption

Abstract: A stochastic model for the residence time distribution in continuous two impinging streams reactors with spray nozzles (CISR) has been developed based on Markov chain processes The performance capability of the CISR in chemical absorption operations has been demonstrated by a typical example of reaction between carbon dioxide and monoethanolamine

A modified dynamic non-singleton fuzzy logic system for nonlinear modeling

Abstract: This paper presents a modified version of dynamic non-singleton fuzzy logic systems (NSFLS). Mouzourise and Mendel (1997) originally introduced the NSFLS technique. This technique suffers from the lack of good convergence property. To remedy this and to improve the convergence rate of the NSFLS method, we introduce a fuzzy based algorithm. In order to show how this technique outperforms the dynamic NSFLS, gas turbine has been selected as a case study. Both methods, the NSFLS with the original learning algorithm and with the proposed technique, were applied to this problem and simulation results are very promising.

a Comparative Theoretical Analysis for a Knitted Loop Model

Abstract: The theory presented in this paper differs from previous ones in that no arbitrary loop shape is assumed. Rather a strophoid curve, that is similar to knitted fabric Loop shape, has been assumed as the basic mathematical function. Additionally, the theory is improved by adapting buckled elastic rod theory, leading to a new equation from a certain mathematical curve. This loop model is assumed to be two- dimensional initially, but is applicable to three-dimensional analysis as well. The geometry of the fabric structure is obtained from these models. The results show good agreement between the theoretical and experimental suggestions reported by other scholars.

Fingerprint classification using singular points and Fourier image

Abstract: Singular points are one of the characteristic features of fingerprint images. In this paper, a new way of finding these singular points from the directional image is proposed. The image used in this system is a 256 X 256 rectangular image from which the hexagonal image will be extracted. After producing the directional image, two other images will be constructed for the core & delta candidate points. These pair of points will be selected using a method based on Hough transform and local maximum algorithm. Based on the position and number of these points a one-byte code will be assigned to that class. By performing the Fourier image of the original picture, an eight-byte code will be assigned to the image using a 4 X 4 wedge-ring detector applied to the transformed image. These codes will be used to show the dissimilarity among similar images.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Modeling and Application of UF‐Stirred Cell Reactors in Hydrolysis of Saccharides

Abstract: Hydrolysis of sucrose by invertase as a typical example of saccharides enzymatic hydrolysis has been conducted in a UF-stirred cell reactor. A model has been derived by which the effect of some pertinent variables, such as membrane pore size, applied pressure, substrate concentration and stirring speed, on the performance capability of such systems may be predicted. A close correlation has been found between the experimental results obtained under a wide range of operating conditions and those calculated from the model.

A modified iterative fuzzy control based filter for image enhancement with multiplicative noise removal property

Abstract: In this paper we propose a modified iterative fuzzy logic control based filter acronymed by MIFCF for removing impulsive noise, smoothing additive & multiplicative Gaussian noise with preserving image edges and details. The high performance of our method especially in removing the multiplicative noise, in compared with those of recently proposed filters, is demonstrated by some experiments.