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Showing papers by "Amirkabir University of Technology published in 1991"


Journal ArticleDOI
TL;DR: In this article, the effect of air motion inside the solar still is studied experimentally, with a modification in the conventional design, so that air is allowed to move inside the still, using a fan.

37 citations


Journal ArticleDOI
TL;DR: In this paper, a mathematical model is used to predict the performance of the solar still using forced convection inside the still to enhance the productivity of the still and good agreement between the theoretical and experimental results is obtained.

6 citations


Journal ArticleDOI
TL;DR: In this article, the Galerkin method was used to obtain the general form of the finite-element equations of dynamic thermoelasticity in terms of stresses and temperature.
Abstract: The general, governing equations of dynamic thermoelasticity in terms of stresses are considered. Applying the approximation field to the stresses and temperature, the general form of the finite-element equations are obtained using the Galerkin method. The general traction boundary conditions are discussed. The formulations are then reduced to the one-dimensional case, and the problem of bars subjected to mechanical and thermal shocks is discussed. Assuming an isoparametric simplex element, the submatrices for the base element e are obtained and simplified. As an example, a bar of two ends free subjected to a mechanical shock at one end is considered and the plots of stress and temperature waves are obtained. The results are compared with those of the displacement formulation. While both formulations compare well, the stress formulation predicts a slightly lower value for the computed stress field that is a lower bound to the solution and offers a stiffer model.

6 citations


Journal ArticleDOI
TL;DR: In this paper, a two-step mechanism has been proposed for the oxidation of methanol to formaldehyde, accepting an oxygen molecule from the catalyst and changing the latter into a reduced form.
Abstract: Oxidation of methanol to formaldehyde, using a mixture of ferric and molybdenum oxides as catalyst, has been studied in a fixed bed integral reactor, 150 mm long, 25 mm o.d. and 10 mm i.d. The catalyst was prepared by reaction between aqueous solutions of ammonium heptamolybdate and ferric chloride. It has been shown that, under experimental conditions similar to those employed in industry, neither external nor internal diffusion had been effective in the process and isothermal conditions prevailed in both gas and solid phases. A two-step mechanism has been put forward for the oxidation of methanol. According to such a mechanism, methanol is first oxidized to formaldehyde, accepting an oxygen molecule from the catalyst and changing the latter into a reduced form. In the second step, the reduced catalyst is transformed into the original form on obtaining an oxygen molecule from the gas phase. Based on this scheme, a rate model has been derived and verified by experimental results.

5 citations


Journal ArticleDOI
TL;DR: In this paper, post-irradiation stability of 60Co-γ-ray irradiated isotactic PP has been studied at 25 and 50 kGy, and the effectiveness of 2,6-di-tert-butyl-p-cresol (BHT) and polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) at various concentrations is compared.

3 citations


Proceedings ArticleDOI
08 Jul 1991
TL;DR: In this paper, an attempt has been made to use the electromagnetic transients program (EMTP) to evaluate the effect of random pole closure of circuit breakers on phase-to-phase and phaseto-ground overvoltages in EHV lines.
Abstract: An attempt has been made to use the electromagnetic transients program (EMTP) to evaluate the effect of random pole closure of circuit breakers on phase-to-phase as well as phase-to-ground overvoltages in EHV lines. Numerical results are presented on the Iranian standard 400 kV line. >

2 citations


Proceedings ArticleDOI
31 Oct 1991
TL;DR: Results of simulating the network show the fact that reliable contraction states can be obtained for representing movement classes for both cases of two and three degree of freedom arm.
Abstract: In order to design an EMG-controlled cybernetic arm with high degree of freedom, the optimal subset of the possible muscle contraction states is to be determined for the purpose of controlling the arm. In this paper, optimal muscle contraction states have been selected using the classification error in probabilistic neural network (PNN). Results of simulating the network show the fact that reliable contraction states can be obtained for representing movement classes for both cases of two and three degree of freedom arm.

2 citations


Proceedings ArticleDOI
08 Jul 1991
TL;DR: In this paper, a highly interactive and user-friendly program called Lightning Analysis (LA) is introduced, which is capable of predicting the shielding failure, back flashover, and total lightning tripout rates for different tower design and climatic conditions.
Abstract: A highly interactive and user-friendly program called Lightning Analysis (LA) is introduced. The numerical execution is based on the two points method of J.G. Anderson (1982). LA is capable of predicting the shielding failure, back flashover, and total lightning tripout rates for different tower design and climatic conditions. LA is applied to assess the flashover (shielding failure) and back flashover across 400-kV insulators in Iran. The total tripout rates of Iranian 400-kV lines are presented. >

1 citations




Proceedings ArticleDOI
08 Jul 1991
TL;DR: In this article, an attempt has been made to evaluate lightning fifty-percent breakdown voltage (V/sub 50/) across 400 kV insulators in Iran, according to obtained keraunic levels and probabilistic results of tower footing resistances.
Abstract: The Iranian isokeraunic map developed by the authors is presented A statistical analysis of tower footing resistances of 400 kV lines in the Iranian national grid is also presented An attempt has been made to evaluate lightning fifty-percent breakdown voltage (V/sub 50/) across 400 kV insulators in Iran, according to obtained keraunic levels and probabilistic results of tower footing resistances A comparison between calculated V/sub 50/ and V/sub 50/ of presently installed insulators of 400 kV lines in the Iranian transmission system is also presented >

Proceedings ArticleDOI
11 Jun 1991
TL;DR: In this article, an extended Lyapunov theory was developed for checking the stability of nonstationary two-dimensional (2D) systems using the wave model introduced by W.A. Porter and J.L. Aravena (1984).
Abstract: An extended Lyapunov theory has been developed for checking the stability of nonstationary two-dimensional (2-D) systems. This development uses the wave model introduced by W.A. Porter and J.L. Aravena (1984). The analysis, using the Lyapunov method on the wave model, highlights the basic difficulty in stability studies for m-D systems. In utilizing the 1-D nature of the wave model, the, Lyapunov equations are time variant (TV), even for constant matrices in the Givone-Roesser model. This TV characteristic invalidates the standard necessary and sufficient conditions available for stationary, 1-D systems. However, as the study shows, it is relatively straightforward to generate necessary or sufficient conditions. >

Proceedings ArticleDOI
22 May 1991
TL;DR: A method is proposed to increase the performance of calculating the integral of absolute value (IAV) of an electromyogram signal (EMG) belonging to muscles above the elbow using a redundancy canceling technique and a criterion which leads to an optimal selection of acquisition window parameters is obtained.
Abstract: A method is proposed to increase the performance of calculating the integral of absolute value (IAV) of an electromyogram signal (EMG) belonging to muscles above the elbow using a redundancy canceling technique. A criterion which leads to an optimal selection of acquisition window parameters is obtained. Results of the simulation show that the window parameters for an EMG signal should depend on the type of feature which is to be extracted. >