Showing papers by "Iran University of Science and Technology published in 1997"

A logarithmic conformal field theory solution for two-dimensional magnetohydrodynamics in the presence of the Alf'ven effect

Abstract: When the Alf'ven effect is present in magnetohydrodynamics one is naturally led to consider conformal field theories, which have logarithmic terms in their correlation functions. We discuss the implications of such logarithmic terms and find a logarithmic conformal field theory with central charge c = − (209/7), within the border of the minimal series, which satisfies all the constraints. The energy spectrum is found to be E(k) ~ k−(13/7)log {(k)}.

An inverse problem for a nonlinear diffusion equation

Abstract: The determination of an unknown diffusion coefficient in a nonlinear diffusion equation from overspecified data measured at the boundary will be considered. We also design a new method for identifying mesh points and seek a member of admissible coefficients which minimize a given error functional.

Logarithmic Operators in Conformal Field Theory and The W∞-algebra

Abstract: It is shown explicitly that the correlation functions of conformal field theories (CFT) with the logarithmic operators are invariant under the differential realization of Borel subalgebra of -algebra. This algebra is constructed by tensor-operator algebra of differential representation of ordinary . This method allows us to write differential equations which can be used to find general expression for three- and four-point correlation functions possessing logarithmic operators. The operator product expansion (OPE) coefficients of general logarithmic CFT are given up to third level.

Mechanical Properties of M7 High Speed Cast Steel Modified with Niobium

Abstract: Some parts of W and V in a high speed M7 steel were replaced by Nb to improve the mechanical properties. Microstructure and mechanical properties of as-cast and heat treated samples of this modified steel were investigated by both light microscope and electron microscope coupled with an EDX analyser. Various heat cycles were applied in order to optimize the mechanical properties of this cast steel. The properties were compared with those of a standard cast and a wrought M7 and a wrought M2 high speed steels for better understanding of the effects of alloy modification. It was shown that high temperature hardness and cutting performance of the modified cast steel in a properly heat treated condition are about 95 and 70% of those of a standard wrought M7 and a wrought M2 steel, respectively.

Stabilization of Coastal Slopes by Anchored Geosynthetic Systems

Abstract: Coastal slopes are subjected to destabilizing forces from wave action, current scour, and exfiltrating ground water. As such, they are vulnerable to both surficial erosion and shallow sliding failure because of their low shear strength near the surface. One way of increasing the stability of these slopes is to increase the confining stress on the ground surface by means of an anchored geosynthetic system (AGS). This approach is less visually and physically intrusive than traditional “hard armor” methods, which in many instances are prohibited in environmentally sensitive areas such as coastal sand dunes. Theoretical relationships for determining required AGS loads and anchorage lengths are presented that can be used to evaluate stability for different soil conditions and seepage directions. Some important variables affecting AGS performance such as failure depth, surface configuration, anchor orientation, and seepage influence on near-surface stability are also described. The theoretical predictions were examined by conducting laboratory stability tests on saturated sand slopes, which were stabilized by an anchored geosynthetic netting and subjected to parallel seepage and tractive surface stresses. Good agreement was observed between predicted and actual anchor loads at failure.

Domain decomposition for finite element analysis

Abstract: An efficient algorithm is developed for automatic partitioning of unstructured meshes for the parallel solution of problems in the finite element method. The algorithm partitions a domain into subdomains with approximately equal loads and good aspect ratios, while the interface nodes are confined to the smallest possible.

Control of multilevel-inverters for active power filters using a fuzzy space-vector method

Abstract: Nonlinear loads have destructive effects in power systems. Active filters have been used as a solution to this problem. The main prohibitive factor in this method is the cost of high-speed and high-current switching devices. In this paper, by proposing a new formula, it is shown that using multilevel inverters in active power filters can decrease the switching frequency while sustaining the same specific performance. A fuzzy space-vector method is also developed for controlling a three-phase multilevel active filter. The simulation results confirm the suitable performance of the filter using this control method.

DIPC: A System Software Solution for Distributed Programming.

Abstract: Distributed Inter-Process Communication (DIPC) provides the programmers of the Linux operating system with distributed programming facilities, including Distributed Shared Memory (DSM). It works by making UNIX System V IPC mechanisms (shared memory, message queues and semaphores) network transparent, thus integrating neatly with the rest of the system. The underlying network protocol used is TCP/IP. DIPC is targeted to work on WANs (Wide Area Networks) and in heterogeneous environments.

Full Coverage Discrete Hole Film Cooling: Investigation of the Effect of Variable Density Ratio (Part II)

Abstract: Experimental results of the corrective film heat transfer coefficient at the hot gas-side of the wall for full coverage discrete hole film cooling are presented for a range of practical geometries. The results are reported for various hot gas mainstream-to-coolant temperature (density) ratios, in the realistic range of 1.0–3.2. For combustor wall and turbine blades film cooling applications, the corrective film heat transfer coefficient was influenced significantly by the design parameters. It decreased with an increase in the number of holes per unit wall surface area, over the range of 4306–26910 m−2 and with an increase in the hole size, in the range of 1.0–2.2 mm, due to the improvement in film cooling. This was supported by the overall cooling effectiveness results, as reported previously (Bazdidi-Tehrani and Andrews 1994). A comparison between the two approaches for the prediction of the convective film heat transfer coefficient was made. It showed that the higher wall overall heat transfer, obtained using the present measurements of the wall overall heat transfer coefficient, resulted in a considerably higher film heat transfer coefficient than that predicted using the summation of the hole approach surface correlation of Sparrow (1982) and the internal hole correlation of Mills (1962). The variation of the mainstream-to-coolant temperature ratio did not establish consistent trends for various configurations and its effect on the film cooling performance was shown to be small.Copyright © 1997 by ASME

New operational amplifier using a positive feedback

Abstract: A very high gain bipolar op amp was designed using controlled positive feedback. The circuit has a theoretical voltage gain of 160 dB and unity gain-bandwidth of 3.3 MHz. Despite using positive feedback, the op amp is compensated and a slew rate of 1 V//spl mu/s is achieved.

High-resolution spectroscopy of methanol-D 3 : assignments and predictions of optically pumped far-infrared laser lines

Abstract: The results of high-resolution Fourier-transform infrared and far-infrared spectroscopic studies have been applied to the analysis and prediction of optically pumped far-infrared laser emission for 11 transition systems of the CD3OH isotopomer of methanol. The assignments are supported by the formation of closed transition combination loops that confirm the spectroscopic assignments and yield calculated far-infrared laser wave numbers to the spectroscopic accuracy of order ±0.0005 cm-1. This represents a substantial improvement over customary wavelength measurements. Four of the systems involve the strong asymmetry mixing known to occur between K=0 and K=2E1 levels, which is discussed and partially analyzed. Several inconsistencies are noted between previous proposed assignments in the literature, which were based primarily on calculated energies and infrared wave numbers, and our new spectroscopic data.

A novel experimental setup for Atlas II robot using Visual Basic

Abstract: Considering the rapid development in using PCs and advance computer graphics, simulation and control of robots and graphical representation and prediction of the programmed movement seems essential. On these bases, by using the Visual Basic programming language and under the MS Windows graphical operating system, a software has been developed that simulates the Atlas II robot movement. Three experiments are designed-system acquaintance, direct kinematics and inverse kinematics-for using this software in the robotics lab. Also three observing aspects for showing direct kinematics, inverse kinematics and point-to-point movement are covered in this package. This package with a little change in the source program can be used for any robot in order to show and simulate its movement program for any educational or industrial purposes.

Discretisation of continuous-time control systems with guaranteed stability [comment with reply]

Abstract: The commenters refer to the paper by Markazi et al. (IEE Proc. Control Theory Appl. Vol.142, No.4 (1995)) and point out that when they simulated the step response for the three digital controllers and found, using both MATLAB and Program CC, that the results were similar to those given in the paper. However, on further investigation they found that the closed loop system was not asymptotically stable due to the presence of poles on and outside the unit circle. Thus it is concluded that the results given by the authors are clearly unstable and the validity of the paper must be questioned. In reply, Markazi et al. acknowledge that the issues of numerical stability and responses to a disturbance need to be clarified.

A competitive learning algorithm for non-zero memory codebook design in encoding of CT sequences

Abstract: The implementation of artificial neural networks (ANN) in various aspects is increasing day by day. One of the major applications is image compression. Here an algorithm has been developed for use in the encoding of computed tomography (CT) image sequences. The method is based on application of an ANN distributed system which classifies all possible m/spl times/m (here 4/spl times/4) blocks into a smaller number well distinct classes of vectors. In an extension of the Kohonen self organising net called the frequency sensitive competitive learning (FSCL) algorithm, the required time for obtaining an ignorable error will depend on both the distortion and the number of iterations which, are more or less equal for all units. The application of an ANN to vector quantisation (VQ) stems from the concept that in the usual methods the error between each input pattern and the pattern of the codebook (word), is calculated without regarding the weight of each pixel value in the entire pattern. A proper ANN exploits this concept in an efficient classification of various patterns in an image and/or sequence of images. This significantly decreases the artefact, such as the blocking effect which normally appears in ordinary VQ reconstructed images at a low bit rate. In the case of sequences, interframes correlation is exploited in the provision of a common codebook for highly correlated frames. Further, the redundancy is decreased by optimal decomposition of the sequence into the most correlated subsequences.

Preparation of Fine Mullite Powders with High Surface Area by Agglomeration Control of Alkoxide-derived Precursor Sol

Abstract: Ultra-fine mullite precursor powders were prepared by the hydrolysis of molecular-designed Al, Si-complex alkoxide. The surface areas of the resulting mullite powders derived from sol-gel route varied depending upon the aging and/or drying condition. This was due to the different agglomeration states of their primary particles, which precipitated by the hydrolysis of the precursor solutions. A thin electrical double layer was formed on the primary particles of the solvents with low dielectric constants, and then primary particles agglomerated into coarse secondary agglomerates, leading to mullite powders with high surface areas even after high-temperature calcination. A thick electrical double layer on the primary particles resulted in the uniform packing, which formed relatively dense secondary agglomerates during drying. This resulted in the lower surface areas when solvents with high dielectric constants were used during aging. This agglomeration behavior was confirmed by pore-size distributions and the observation of SEM of the mullite powders.

Application of neural networks to the segmentation of MRI: comparison of different networks

Abstract: In this paper a comparative study of the application of four neural networks (NN) for the segmentation of magneticresonance images (MRI) of brain, is proposed. The segmentation of MRJ images enable one to present tissues of the samecategory with an equal gray level (or color) resulting in a more clear image for future diagnosis and treatments. Results ofusing three supervised networks, i.e. multi-layered perceptron (MLP), probabilistic neural network (PNN) and radial basisfunctions (RBF) and one unsupervised network, i.e. adaptive resonance theory 2 (ART2) will be reported.Keywords: Segmentation, MRJ, Neural networks, Multi-layered perceptron, Probabilistic neural network,Radial basis functions, Adaptive resonance theory 2

A window-based image processing approach for measuring traffic movements at junctions

Abstract: Road traffic data collection and analysis is extensively required by the traffic engineers for traffic control and management. Image processing techniques with wide area sensing and analysis capabilities have several advantages over the conventional point based sensors, like magnetic loops etc. So far, many different algorithms have been proposed for measuring simple traffic parameters, but less attention has been paid to measure complex traffic parameters such as traffic movements at junctions (TMJ). In this paper, we described a low-cost image processing approach for measuring the TMJ parameters in real-time. An effective edge detection technique is used to detect the vehicles and to measure the TMJ parameters in real-time.

Combining Subset Selection and Parameter Constraints in Model Updating

Abstract: Model updating often produces sets of equations whose solution are ill-conditioned and extra information must be used to produce a well-conditioned estimation problem. One possibility is to change all the parameters, but to introduce extra constraints, for example by taking the minimum norm solution. This paper takes a different approach, by considering only a subset of the parameters to be in error. The critical decision is then the choice of parameters to include in the subset. The methods of subset selection are outlined and extended to the selection of groups of parameters. The incorporation of side constraints is considered and demonstrated using an experimental example.