Iranian Journal of science and Technology (A: Siences)
Volume:32 Issue: 1, Winter 2008

The efficiency of induction motors decreases at light loads. Efficiency optimizer control systems adjust the motor flux value to achieve the best efficiency in a wide range of load variations. Reduced flux operation has some other benefits such as power factor improvement and torque ripple reduction. The latter is an important issue in a direct torque controlled induction motor drive. In this paper, the effect of flux reference value on the torque ripple of a direct torque controlled induction motor is analyzed. The effect of flux value on torque ripple in a wide range of speed variations is investigated. Simulation and the experimental results presented justify the validity of the theoretical analysis about torque ripple.

Here, the concept of electric capacity on Finsler spaces is introduced and the fundamental conformal invariant property is proved, i.e. the capacity of a compact set on a connected non-compact Finsler manifold is conformal invariant. This work enables mathematicians and theoretical physicists to become more familiar with the global Finsler geometry and one of its new applications.

In this paper we introduce the concept of Dirac structures on (Hermitian) modules and vector bundles and deduce some of their properties. Among other things we prove that there is a one to one correspondence between the set of all Dirac structures on a (Hermitian) module and the group of all automorphisms of the module. This correspondence enables us to represent Dirac structures on (Hermitian) modules and on vector bundles in a very suitable form and define induced Dirac structures in a natural way.

We study the exponential decay of global solution for an n-dimensional thermo-elasticity system in a bounded domain of Rn. By using the multiplier technique and constructing an energy functional well adapted to the system, the exponential decay is proved.

Let be a unital algebra over a field of characteristic zero. We show that every derivation from Mn (A) into its dual Mn (A)* is the sum of an inner derivation and a derivation induced by a derivation from A into A*.

We introduce some new concepts of topological spaces which say α-separable topological space and O-topological group, α-first axiom, α-second axiom, and we find some relations between them with some applications in normed spaces.