IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION A- SCIENCE
Year:2007 | Volume:31 | Issue:A4|Papers Count:12

In direct torque control, the selection of an applied voltage vector is based on the measured parameters at the beginning of the sampling period. The delay between the measurement and the application of the voltage vector is the origin of an extra torque ripple. In this paper, a new predictive controller is proposed for compensating this delay and reducing the torque ripple. The stator current is measured twice in each sampling period and its expected value at the end of the period is predicted according to a linear extrapolation algorithm. Therefore, none of the machine parameters are used in the prediction, and consequently, the algorithm is quite robust against machine parameter variations. The calculation of the electromagnetic torque is performed using the predicted value of the stator current. Therefore, the selection of the voltage vector is more realistic and prevents extra torque ripple. This controller is quite suitable for high power drives where the sampling frequency is low, and there is enough time for the extra measurements. Simulation and experimental results which confirm the ability of this method to considerably reduce the torque ripple are presented.

The aim of this paper is to introduce and study a new concept of strong double (As)D - convergence sequences with respect to an Orlicz function, and some properties of the resulting sequence spaces were also examined. In addition, we define the (As)D -statistical convergence and establish some connections between the spaces of strong double (As)D -convergence sequences and the space of double (As)D -statistical convergence.  

In this paper, we introduce a Satisfaction Function (SF) to compare interval values on the basis of Tseng and Klein’s idea. The SF estimates the degree to which arithmetic comparisons between two interval values are satisfied. Then, we define two other functions called Lower and Upper SF based on the SF. We apply these functions in order to present a new interpretation of inequality constraints with interval coefficients in an interval linear programming problem. This problem is as an extension of the classical linear programming problem to an inexact environment. On the basis of definitions of the SF, the lower and upper SF and their properties, we reduce the inequality constraints with interval coefficients in their satisfactory crisp equivalent forms and define a satisfactory solution to the problem. Finally, a numerical example is given and its results are compared with other approaches.

In this work we deal with the coefficients of ½A(eit ) ½2 , where A is in a class of polynomials having Unimodular coefficients. We first present a technique that calculates lower bounds for particular autocorrelations and then in a more general case we present an upper bound for their maximal order.

In order to improve the performance of a newly developed radiochromic film, GIC-79, some dosimetric characteristics of this film have been studied based on relevant standard practice. The present study describes some parameters that may affect the dosimeter response before, during, and after irradiation. The effect of absorbed dose rate on dosimeter response was determined by irradiating dosimeters at low absorbed dose rates with gamma rays. Calibration irradiations of dosimeters were performed with both gamma rays and also electrons to determine the effect of large difference absorbed dose rates on dosimeter response. In addition, post irradiation stability was obtained and also the temperature and humidity effects on the dosimeter response during the storage time prior to irradiation and post irradiation have been investigated.

In this paper we consider some (a, b)- metrics such as generalized Kropina, Matsumoto and F=(a+b)2/a metrics, and obtain necessary and sufficient conditions for them to be Einstein metrics when b is a constant Killing form. Then we prove with this assumption that the mentioned Einstein metrics must be Riemannian or Ricci flat.

In this study, absorption of high frequency radio waves in the ionospheric plasma have been investigated. The wave equation was obtained in terms of ionospheric parameters. The numerical values of the absorption have been calculated for 4 MHz, 4.5 MHz and 5 MHz waves. The necessary parameters for calculation have been obtained using an International Reference Ionosphere (IRI) Model. The altitudinal, diurnal, seasonal and the variations of absorption with frequency have been examined. The calculations show that the highest absorption occurs in the D-region. The absorption is higher in summer than in other seasons and is maximum at daylight. In addition, absorption decreases with the increase of frequency.

The main objective of this paper is to find the necessary and sufficient condition of a given Finsler metric to be Einstein in order to classify the Einstein Finsler metrics on a compact manifold. The considered Einstein Finsler metric in the study describes all different kinds of Einstein metrics which are point wise projective to the given one. This study has resulted in the following theorem that needs the proof of three prepositions. Let F be a Finsler metric tric (n >2) projectively related to an Einstein non-protectively flat Finsler metric F- , then F is Einstein if and only if F = l F- where l is a constant. A Schur type lemma is also proved.

In this paper the concept of Homothetic Dual Exponential Motions in D3 is discussed and their velocities obtained. Due to the way in which the matter is presented, the paper gives some formula and facts about dual exponential motions which are not generally known.

In this letter we have proposed a new regularization scheme to deal with the divergent integrals occurring in the quantum mechanical problem of calculating the bound state energy of the delta-function potential in two and three dimensions. Based on the Schwinger parameterization technique we argue that there are no infinities even in D dimensions. In this way we were able to compare our proposal with the Schwinger regularization approch.

We prove that every R-quadratic metric of scalar flag curvature with a dimension greater than two is of constant flag curvature. Then we show that generalized Douglas-Weyl metrics contain R-quadratic metrics as a special case, but the class of R-quadratic metric is not closed under projective transformations.