IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION A- SCIENCE
Year:2008 | Volume:32 | Issue:A1|Papers Count:11

In this paper, we present algebroids and crossed modules of algebroids. We also define pullback crossed module of algebroids.

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.

V. Dannon showed that spherical curves in E4 can be given by Frenet-like equations, and he then gave an integral characterization for spherical curves in E4 . In this paper, Lorentzian spherical timelike and spacelike curves in the space time R41 are shown to be given by Frenet-like equations of timelike and spacelike curves in the Euclidean space E3 and the Minkowski 3-space R31. Thus, finding an integral characterization for a Lorentzian spherical R41 -timelike and spacelike curve is identical to finding it for E3 curves and R31 -timelike and spacelike curves. In the case of E3 curves, the integral characterization coincides with Dannon’s. Let {T, N, B} be the moving Frenet frame along the curve a(s) in the Minkowski space R31. Let a(s) be a unit speed C4 -timelike (or spacelike) curve in R31 so that a'(s)=T. Then, a(s) is a Frenet curve with curvature k s) and torsion t(s) if and only if there are constant vectors a and b so that (i)T’(s)= k(s){a cos x(s)+b sin x(s)+ òs0 cos[x(s)- x(d)] T(d)k(d)dd}, T is timelike, (ii) T’(s)= k{aex+bex òs0 cosh (x(s)- x(s)- T(d)k(d)dd}, n is timelike, where x(s)+ òs0t(d)dd.

In this paper we introduce the concept of Dirac structures on (Hermiti an) 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 Ân. By using the multiplier technique and constructing an energy functional well adapted to the system, the exponential decay is proved.

On a Finsler manifold, we define conformal vector fields and their complete lifts and prove that in certain conditions they are homothetic.

Let A be a unital algebra over a field of characteristic zero. We show that every derivation from n M n (A) into its dual M n (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 a-separable topological space and O-topological group, a-first axiom, a-second axiom, and we find some relations between them with some applications in normed spaces.

Let Xn,..., X1 be a random sample from a distribution with sample mean `X and sample Variance  S2. In this paper we consider certain very general properties of the so-called "Z-scores" (Xi-`X)/S:i=1,…,n. A representation theorem is then given for Z-scores obtained from an underlying normal population, together with a theorem for their limiting distribution as the sample size tends to infinity. Finally, two applications involving grading and testing for an outlier are presented.