مجله ایرانی علوم و تکنولوژی-ب
سال:1381 | دوره:27 | شماره:ب-1 |تعداد مقالات:21

In this paper a numerical procedure is presented based on the method of least squares (MLS) to synthesize a stepline transformer to match two complex impedances over a frequency bandwith for a specified line length. First, the input impedance of a stepline terminated in a load impedance is obtained using the transmission matrices of the line sections and junction discontinuity impedances. Then, an error function is constructed as the sum of the magnitude squared of the difference between the input impedance of the stepline and the generator impedance over discrete frequencies in the desired bandwidth. The error function is then minimized with respect to the stepline characteristic impedances and also separately with respect to the stepline length. This numerical procedure serves as an effective tool for the design of transformers of complex impedances with specified lengths and frequency bandwidths and its implementation reveals uncommon and interesting transformer shapes which best realize matching conditions in the least square sense.

This paper describes a new method and several views for a minimally dependent set of measurements in the power systems observability studies. The minimal measurement sets are important schemes for state estimation analysis. The presented approach is based on a novel observability method named RCD, which does not use an initial measurement set. The total number and each combination of measurements in a search-tree construction are discussed. Owing to the large number of cases, the results are shown for 3-bus and a 6-bus power network.

Artificial neural networks with their inherent parallelism have been shown to perform well in many image processing applications. In this paper, a new self-organizing approach for the recovery of gray level images degraded by additive noise based on embedding the diffusion equation in a neural network (without using a priori knowledge about the image point spread function, noise or original image) is described which enhances and restores gray levels of degraded images and is for application in low-level processing. Two learning features have been proposed which would be effective in the practical implementation of such a network. The recovery procedure needs some parameter estimation such as different error goals. While the required computation is not excessive, the procedure does not require too many iterations and convergence is very fast. In addition, through the simulation the new network showed that it has superior ability to give a better quality result with a minimum of the sum of the squared error.

The paper presents a simple yet powerful fuzzy logic based static VAR compensator (FLSVC) applied to an industrial power system consisting of three phase induction motors and static loads. In the proposed fuzzy logic controller (FLC), the speed and acceleration variations of a specific machine are taken as the inputs. To demonstrate the effectiveness and capabilities of the employed FLSVC, some extensive and comparative non-linear time domain digital simulation tests are performed. The results show that over a wide range of operating conditions and disturbances, the FLSVC remarkably improves the voltage profile and the overall dynamic performance.

Self-propagating high temperature synthesis (SHS) is one variety of combustion, in which, as a result of a fast reaction, the valuable condensed products are formed. Although the reactants in (SHS) may be in various states of solid, liquid or gas, the products after cooling should be in solid state. Molybdenite concentrate from Sarchechme mines (South-east of Iran) with the composition of mainly: 41.5% S, 2.8% Fe, 1.3% Cu and 47.7% Mo by weight was used as a source of molybdenum. It was mixed with different concentration of aluminum, pressed to a briquette of 25.4 mm. in diameter and ignited by use of a microwave oven. Depending on the conditions, different modes of combustion of the briquettes were observed. The product of the reaction was leached with dilute hydrocholoric acid, and was tested for sulfur, aluminum and molybdenum. The respective effects of aluminum powder size, pellet density and power input to the pellet before ignition on the final product were investigated; in some samples the sulfur was reduced to less than 1%.

The water transfer behavior of cation exchange selemion CMV and anion exchange selemion AMV and DMV membranes (Asahi Glass Co., Japan), has been studied in the vanadium redox cell, as was the water transfer across cation exchange Nafion 117 membrane (E.I. Du Pont, U.S.A.) and a composite membrane which was prepared by crosslinking Daramic (a microporous separator, W.R. Grace, USA) with divinylbenzene (DVB) followed by sulfonation [1,2]. The earlier water transport studies of a variety of commercial ion exchange membranes and non-ionic separators in the vanadium redox cell have shown that the net water transport through anion exchange membranes and non-ionic separators in the vanadium redox cell is from the positive half cell (+ve) to the negative half cell (-ve), while for cation exchange membranes, the net water transport is in the opposite direction. It was found that for cation exchange membranes, the hydrogen ion concentration gradient causes the osmotic water transfer rather than the vanadium ions which make only a minor contribution, while for anion exchange membranes, the sulphate ion concentration gradient is responsible for the osmotic pressure effect.

Using the concepts of partial segregation theory, the effects of temperature and density on the Lennard-Jones parameters are evaluated and then a new relation is derived for the second Virial coefficient. The comparison made with the reported values for the second Virial coefficient substantiates the effectiveness of the proposed new relation based on aggregating fluid concepts.

The effect of solid boundary under a surface-mounted ribbon on particle collection efficiency was studied. The turbulent fluid velocity was obtained by solving the Navier-Stokes equation based on k-ه turbulence model. The trajectory model was adopted to obtain the information on the particle phase trajectories. The equation of particle motion included inertial, viscous drag and gravity forces. To check the validity of numerical results, target efficiency of particles over the free-stream ribbon with respect to Stokes number was compared with the same experimental data. It was observed that the agreement between these is excellent. For the surface-mounted ribbon, the target efficiency in the range of small Stokes numbers is larger than that for the free-stream ribbon, but for larger Stokes number is smaller. The Stokes and gravity numbers were introduced to interprete the effect of gravity and inertial impaction on particle deposition at the back and front of the surface-mounted ribbon. The dominant deposition mechanism (inertial impaction, gravity force) over the surfacemounted ribbon depends on Stokes and gravity numbers.

Biodegradation of petroleum hydrocarbons in salt medium (SM) containing sea water by Pseudomanas sp. was investigated. Different oil hydrocarbons such as n-decane, benzene, naphthalene, paraffin, paraffin + vaseline, paraffin + kerosene, and fuel oil were used as carbon sources. Cell growth (OD) and COD were measured for evaluation of oil biodegradability. The effect of inorganic and organic nitrogen sources on COD removal revealed a 95% and 75% reduction of COD for inorganic and organic nitrogen sources, respectively.

–In this paper, the effect of random eccentricity, mass and stiffness parameter on the dynamic characteristics of structure and story shear and torsional response has been comprehensively examined. Numerical results are obtained for a five-story torsional building excited by random excitation with various damping ratio and frequency parameter values using both approaches of response calculations – a more accurate complex mode and an approximate normal mode have been used. The results show that the introduction of eccentricity in a direction introduces torsional moments in the system and reduces the direct story shear. For a safe design, eccentricity should be neglected in the calculations for shear, and a value of 0.05 of radius of gyration for calculation of torsional moment should be considered, even if a structure is intended to be symmetrical.

Simply supported reinforced concrete deep beams occur as transfer girders, foundation walls in tall buildings, offshore gravity type structures, dams, bridges and many other structures. This is expected because the columns and other members cannot restrain deformations at the ends of the beam. In this paper, results of tests performed, in the Building and Housing Research Center, on eighteen simply supported deep beams are reported. The beams were loaded from the top mid-center. From experimental results, three modes of failure were observed, namely; (1) flexural, (2) shear and (3) bearing. The transition of reinforced concrete beams from ordinary-beam behavior to deep-beam behavior is imprecise for design purposes. Therefore a simple method based on truss analogy is used to analyze the results. This method has been used previously to analyze reinforced concrete deep beams with fixed ends. The method takes into account the strength of concrete and reinforcement. The analysis is capable of predicting the ultimate strength and to some extent the modes of failure. The predicted load and modes of failure for beams with shear failure, compared well with experimental results.