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Showing papers by "Amirkabir University of Technology published in 1997"


Journal ArticleDOI
TL;DR: A comprehensive review of all published research in nondestructive evaluation (NDE) performed with the superconducting quantum interference device (SQUID) magnetometer since the first work was reported in the mid-1980s is presented in this article.
Abstract: We attempt a comprehensive review of all published research in nondestructive evaluation (NDE) performed with the superconducting quantum interference device (SQUID) magnetometer since the first work was reported in the mid-1980s The SQUID is the most sensitive detector of magnetic flux known The energy sensitivity of the SQUID may make it the most sensitive detector of any kind The research on SQUIDs for NDE is based on the promise of that sensitivity and on the various other desirable properties developed for SQUID instrumentation in biomagnetism and other fields The sensitivity of SQUID instruments down to very low frequencies allows them to function as eddy-current sensors with unparalleled depth resolution, and to image the static magnetization of paramagnetic materials and the flow of near-dc corrosion currents The wide dynamic range of the SQUID makes it possible to image defects in steel structures and to measure the magnetomechanical behaviour of ferromagnetic materials with high sensitivity In the last decade SQUID instrumentation designed specifically for NDE has appeared and improved the spatial resolution of most work to roughly 1 mm, with promise of another order of magnitude improvement within the next five years Algorithms for flaw detection and image deconvolution have begun to flourish With many talented, industrious people in the field, the future of SQUID NDE looks bright, provided the crucial first niche can be found

141 citations


Journal ArticleDOI
TL;DR: In this article, the effects of cations on the yields of char, tar, light oils, and total gases from rapid pyrolysis of beech wood were studied.

133 citations


Proceedings ArticleDOI
02 Jul 1997
TL;DR: An experimental evaluation of the effectiveness of utilizing various moments as pattern features in recognition of the handwritten Farsi characters, and the pseudo Zernike moments of order 5 had the best performance among all the moment invariants.
Abstract: This paper introduces an experimental evaluation of the effectiveness of utilizing various moments as pattern features in recognition of the handwritten Farsi characters. The moments that have been used are Zernike moments, pseudo Zernike moments, and Legendre moments. We have used an unsupervised neural network (ART2) for this application, so that the clusters are formed only based on inherent properties of pattern features. The performance of classification is dependent on the moment order as well as the type of the moment invariant, but the classification error rate was below 10% in all cases. The pseudo Zernike moments of order 5 had the best performance among all the moment invariants. Its error rate and discrimination factor were 3.06% and 96.92% respectively.

66 citations


Journal ArticleDOI
01 Jul 1997-Zeolites
TL;DR: In this article, the synthesis of ZSM-5 using 1,6-hexanediol as a structure-directing agent has been studied in a vigorously stirred system at 152, 160, and 170°C.

60 citations


Journal ArticleDOI
TL;DR: In this paper, the antiplane deformation of an isotropic wedge with finite radius is studied and the solution of governing differential equations is accomplished by means of finite Mellin transforms.

41 citations


Journal ArticleDOI
TL;DR: The results suggest that pentylenetetrazol-kindling is accompanied by enhanced excitability and a reduction of paired-pulse inhibition in hippocampal CA1, and may be interpreted as an adaptive process to cope with subsequent seizures.

34 citations


Proceedings ArticleDOI
02 Dec 1997
TL;DR: This method is capable of verifying simple and skilled forgeries with a good performance and is based on signature shape descriptors such as the skeleton, upper and lower envelopes, and the high pressure region of the signatures.
Abstract: This paper presents an off-line signature verification system. The verification is based on signature shape descriptors such as the skeleton, upper and lower envelopes, and the high pressure region of the signatures. Multiple multilayer perceptron neural network modules cooperating in taking a verification decision via a fuzzy integral voter are used. This method is capable of verifying simple and skilled forgeries with a good performance.

31 citations


Journal ArticleDOI
01 Nov 1997-Fuel
TL;DR: In this article, the dynamics of formation of asphalt and asphaltene aggregates are studied, and three different characteristics of the aggregates and their time evolution are compared, namely their precipitation, small-angle scattering, and molecular weight distributions.

30 citations


Journal ArticleDOI
TL;DR: In this article, the authors derived nonlinear equilibrium and stability equations of thin cylindrical shells under axial compression, external pressure, or external fluid pressure, which are applicable to shells without length limitation as the rotations and transverse shears are included in the derivations.
Abstract: Based on the concept of secant and tangent modulus, the nonlinear equilibrium and stability equations of thin cylindrical shells under axial compression, external pressure, or external fluid pressure are derived. The resulting equations are applicable to shells without length limitation as the rotations and transverse shears are included in the derivations. The reduction factors for plastic and creep buckling are then obtained. A procedure for determining secant and tangent modulus in the very general case of elastic, plastic, or creep stress in the presence of temperature gradient is proposed. Then, using Donnell`s nonlinear theory of shells, the effect of initial imperfection on the strength of the elastic shell is discussed. The foregoing results are extended to plastic and creep buckling of cylindrical shells of arbitrary length and temperature gradient. Some design curves are proposed using the obtained equations. Finally, the present results are compared with available results in the literature and the accuracy of the method is examined.

27 citations


Journal ArticleDOI
TL;DR: In this paper, a stochastic model was developed to predict the residence time distribution in continuous two impinging streams reactors with spray nozzles (CISR), and the reaction between carbon dioxide and monoethanolamine was chosen as an example of gas-liquid reactions to demonstrate the performance capability of the CISR in chemical absorption operations.
Abstract: A stochastic model was developed to predict the residence time distribution in continuous two impinging streams reactors with spray nozzles (CISR). The reaction between carbon dioxide and monoethanolamine was chosen as an example of gas–liquid reactions to demonstrate the performance capability of the CISR in chemical absorption operations. © 1997 SCI.

26 citations


Proceedings ArticleDOI
02 Dec 1997
TL;DR: A new method for calculating the TDS and t (operating time of O/C relays) based on a neural network and fuzzy logic is used and the calculation speed as well as the accuracy is increased.
Abstract: For coordination of O/C relays, it is necessary to model the relay characteristics and calculate the time dial setting (TDS) of the relays. The O/C relays' characteristics are normally modeled by a polynomial using a curve fitting technique. A new method for calculating the TDS and t (operating time of O/C relays) based on a neural network and fuzzy logic is used. In this method, fuzzy logic uses the same information as the neural network. Also the variation of t with the TDS is not assumed linear, therefore t is calculated with a high accuracy. In addition, in the method used for determination of the TDS, we do not need to use numerical analysis and mathematical equations, so the calculation speed as well as the accuracy is increased.

Journal ArticleDOI
TL;DR: In this article, the authors presented extensive new experimental data for the amount of precipitated asphalt and asphaltene aggregates formed with crude oil and various solvents, and their molecular weight distributions.
Abstract: We present extensive new experimental data for the amount of precipitated asphalt and asphaltene aggregates formed with crude oil and various solvents, and their molecular weight (MW) distributions. A new scaling equation is proposed for predicting the onset and amount of the precipitates, somewhat similar to those encountered in aggregation and gelation phenomena. The scaling function takes on a very simple form, and its predictions are in very good agreement with the available data. We also present an analysis of small-angle X-ray and neutron scattering data to delineate the structure of the asphalt and asphaltene aggregates. Our analysis suggests that the asphalt and asphaltene aggregates are fractal structures with well-defined fractal properties. We identify the mechanisms that give rise to such fractal aggregates, based on which we propose a new analytical form for the MW distribution of the asphalt and asphaltene aggregates which provides accurate predictions for our data.

Journal ArticleDOI
TL;DR: In this paper, structural and mechanical properties of core-spun yarns produced with a 2.2 tex monofilament core and a cotton wrap on a modified ring spinning frame are discussed and compared with the equivalent 100% cotton ring-spuns yarns.
Abstract: The spinning of core-spun yarn on the ring frame is a technique used to upgrade the cotton yarn properties. In a core-spun yarn, a filament is covered by a staple fibre. In the current paper the structural and mechanical properties of core-spun yarns produced with a 2.2 tex monofilament core and a cotton wrap on a modified ring spinning frame are discussed and compared with the equivalent 100% cotton ring-spun yarns. The tracer fibre technique which was used showed that there is no significant difference between the internal structure of the core- and ring-spun yarns. The investigation of twist and pretension of filament on the core-spun yarns showed that, in some cases, the optimum structural and mechanical properties of core-spun yarns could be achieved compared with the equivalent ring-spun yarn.

Proceedings ArticleDOI
13 Jul 1997
TL;DR: In this article, the authors used segmentation, desegmentation and multiport network theory to predict the antenna characteristics such as resonant frequency, input impedance, scattering parameters, and radiation patterns.
Abstract: Dual linear polarization with low cross polarization and high isolation has previously been reported using a cross shaped microstrip patch antenna. Here, by slightly deforming the shape of the patch, the bandwidth of the cross shaped structure is increased from 1.7 percent to 4.2 percent and the changes had minimal effect on radiation properties of the antenna. Segmentation, desegmentation and multiport network theory were used to predict the antenna characteristics such as resonant frequency, input impedance, scattering parameters, and radiation patterns of the antenna. Experimental results are in good agreement with theoretical calculations.

Journal ArticleDOI
TL;DR: In this article, a new discretely stiffened circular plate theory is presented in outline, and the governing plate equations are solved using a finite-difference implementation of the dynamic relaxation (DR) algorithm.

Journal ArticleDOI
TL;DR: A spectral method of solving the controlled Duffing oscillator is presented, based upon constructing the Mth degree interpolation polynomials, using Chebyshevs nodes, to approximate the state and the control vectors.


Journal ArticleDOI
TL;DR: In this paper, a new approximating formula is presented to compute the path critical index and activity critical index for the PERT network with any structure, which is highly efficient and has excellent results compared to Elmaghraby and Dodin's approach.

Journal ArticleDOI
TL;DR: In this paper, the influence of electron trapping on the propagation of an electrosound wave is investigated, and it is shown that on the stage of modulational instability the trapped particles prevent the spatial localization of the HF field.
Abstract: The influence of electron trapping on the propagation of an electrosound wave is investigated. It is shown, that on the stage of modulational instability the trapped particles prevent the spatial localization of the HF field. Under certain conditions the trapped particles destroy the stationary soliton. For nonstationary envelope waves the nonlinearity, connected with trapped particles, leads to a Korteveg-de Vries equation.

Journal ArticleDOI
TL;DR: In this article, a method for selective harmonic elimination in pulsewidth modulated (PWM) inverter waveforms by the use of piecewise constant orthogonal functions is presented, which reduces the number of combinations for the case where more than one angle is allowed to vary within a given interval.

Proceedings ArticleDOI
13 Jul 1997
TL;DR: In this paper, a new method for the analysis of arbitrary shaped multilayered printed antennas is presented, which is also applicable to numerous other radiation and scattering problems and is based on the surface equivalence principle and Green's functions of homogeneous space.
Abstract: A new method for the analysis of arbitrary shaped multilayered printed antennas is presented. It is also applicable to numerous other radiation and scattering problems. Admittance matrices of the differential surface elements of homogeneous and isotropic sections are computed using the surface equivalence principle and Green's functions of homogeneous space. Then, using multiple network theory, the overall characteristic of the composite antenna is derived. In this method, we do not need the Green's functions of composite materials and the calculation of Sommerfeld-type integrals. Additionally, all the field parameters are represented in terms of surface parameters, and the singularity of the source elements is analytically removed.

Proceedings ArticleDOI
02 Dec 1997
TL;DR: An experimental evaluation of the effectiveness of utilizing orthogonal moments such as Zernike moments, pseudo Zernikes moments, and Legendre moments in recognition of the handwritten Farsi numerals.
Abstract: Moments and functions of moments have been utilized as pattern features in various applications to achieve invariant recognition of two-dimensional image patterns. This paper introduces an experimental evaluation of the effectiveness of utilizing orthogonal moments such as Zernike moments, pseudo Zernike moments, and Legendre moments in recognition of the handwritten Farsi numerals. We used evolution strategies (ESs) for clustering of handwritten Farsi numerals, so that the clusters are formed only based on the inherent properties of the pattern features. Considering the fact that the classification is unsupervised, the error rate is about 5% for moments of orders higher than 5. The pseudo Zernike moments of order of 5 have the best performance among all the moment invariants.

Journal ArticleDOI
TL;DR: In this paper, the machine interference problem is solved where a team of operatives look after two separate groups of machines and repair times are assumed to have a negative exponential distribution, and the service discipline is of service in random order (SIRO) form.

Journal ArticleDOI
TL;DR: In this article, the authors investigated invariant cross-sections for production of k ∗− and K ∗0, in the fragmentation region of the proton, in p - p and γ - p reactions, giving a direct and unambiguous probe to the symmetry breaking of the nucleon sea.

Proceedings ArticleDOI
09 Nov 1997
TL;DR: In this paper, a new viewing theory (surface viewing theory) on position sensing is described, which removes this limitation by shortening the heights and broadening the widths of the readout channels (cathode strips).
Abstract: A study of a new viewing theory (surface viewing theory) on position sensing is described. The viewing that the infinite height cathode strips is based on it (linear viewing theory), limits the width of the readout channel to a severe narrow strip. Therefore, the number of channels for long length position sensing increases. The surface viewing theory, removes this limitation by shortening the heights and broadening the widths of the readout channels (cathode strips). In the surface viewing theory since the surface of the affected area is used for position determination, it is possible to broader sensing area comparing with the cathode strip, Preliminary designs and experiments show that the optimum sensing area (OPSA) based on the surface viewing theory decreases at least 10 times in number of the readout channels without any degradation in linearity comparing with the single cathode strip. Increasing the signal to noise ratio in sake of a better resolution is possible with vertical cascading of the OPSA. Two type combinations of the OPSA result in extended OPSAs that correspond to suitable patterns long length position sensitive detectors.

Proceedings ArticleDOI
02 Dec 1997
TL;DR: The gradient partan algorithm for learning the neural networks is modified by using two different learning rates, one for gradient search and the other for accelerating through parallel tangent, respectively, and the dynamic self-adaptation of the learning rate is used to improve the performance.
Abstract: In gradient based learning algorithms, momentum usually has an improving effect on convergence rate and reduces zigzagging phenomena but sometimes it causes the convergence rate to decrease. The parallel tangent (partan) gradient is used as a deflecting method to improve the convergence. In this paper, we modify the gradient partan algorithm for learning the neural networks by using two different learning rates, one for gradient search and the other for accelerating through parallel tangent, respectively. Moreover, the dynamic self-adaptation of the learning rate is used to improve the performance. In dynamic self adaptation, each learning rate is adapted locally to the cost function landscape and the previous learning rate. Finally we test the proposed algorithm, called the accelerated partan on various problems such as xor and encoders. We compare the results with those of dynamic self adaptation of learning rate and momentum.

Book ChapterDOI
01 Jan 1997
TL;DR: In this article, a simple analytical solution along with a numerical finite element method for designing of moderately thick filament over-wrapped metallic cylindrical pressure vessels is presented. But the method is not suitable for high-pressure gases and liquids.
Abstract: Modern composites, using continuous fibres in a resin matrix, are important candidate materials in the engineering of energy-efficient structures In many applications, fibre/matrix materials are lighter, stronger and possibly cost effect when compared with traditional materials like metals Many high-strength composite products are fabricated using the filament winding process In this process, bands of resin-impregnated fibre are wound over a cylindrical mandrel using a computer controlled fibre placement machine Filament-wound tubular structures, more specificly pressure vessels, offer significant weight saving over conventional all metallic ones for containment of high-pressure gases and liquids The subject of this study is to provide a simple analytical solution along with a numerical finite element method for designing of moderately thick filament over-wrapped metallic cylindrical pressure vessels

Proceedings ArticleDOI
09 Jun 1997
TL;DR: This approach uses a stochastic automata learning rule for selection of the best coefficient in each step of the learning phase to give faster convergence than the conventional and adaptive learning rate backpropagation rules.
Abstract: In this paper an approach for selection of convergence coefficient in a backpropagation learning rule is presented. This approach uses a stochastic automata learning rule for selection of the best coefficient in each step of the learning phase. This approach is applied to a nonlinear function approximation problem. Simulation results show that it gives faster convergence than the conventional and adaptive learning rate backpropagation rules.

Proceedings ArticleDOI
09 Sep 1997
TL;DR: The aim of this paper is the development of a fault tolerant parallel processing system on an Ethernet LAN with IBM PC workstations with two fault tolerance approaches used: Watchdog timer and periodic signal transmission.
Abstract: Workstations of a computer network can be used to implement a parallel processing system. In this method the existing network equipment can be used without any extra hardware cost for parallel processing. The aim of this paper is the development of a fault tolerant parallel processing system on an Ethernet LAN with IBM PC workstations. One of the application of the above system is in medical image processing in a Picture Archiving and Communication System (PACS), to be used in the hospitals. For example, if a group of ultrasound images are produced in a medical examination, a noise rejection filter program must be applied on all of the images. In this system, the client has a number of input files and executable ones. Each of the server workstations must load one of these input files and its related executable one. Then, it executes the loaded task and prepares the output file for the client. This system must be fault tolerant, because if a server crashes or is turned off by its user or an infinite loop error occurs, and so on, the client must detect the fault and prevent the system failure. If a software or hardware error is detected, the uncompleted task will be put on a wait state to be loaded by another server. The number of clients or servers is arbitrary and variable during the operation of the system. We have compared two fault tolerance approaches that can be used to design the above system: Watchdog timer and periodic signal transmission. Then, the Watchdog timer was selected in conjunction with a fault counting approach to be used in the parallel processing system. A shared data structure file in the file server's disk is used for communication between clients and servers. Each client uses this file for management of its tasks and monitoring of the operation progress. Finally, the experimental results of the system are presented.

Book ChapterDOI
01 Jan 1997
TL;DR: Aalami et al. as discussed by the authors investigated the elastic large deflection response of steel plates with the trend towards the use of thinner steel plates as a means of achieving material economy.
Abstract: Steel plates may be regarded as the building blocks of many structures used in engineering applications. Because of their practical importance numerous investigations into their structural behaviour have been undertaken. The earliest investigations were concerned with elastic small deformation response. Interest in the elastic large deflection response of steel plates grew with the trend towards the use of thinner plates as a means of achieving material economy. A useful summary of elastic large deflection data for design is given in (Aalami et al., 1979).