IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION A- SCIENCE
Year:2006 | Volume:30 | Issue:A3|Papers Count:14

We prove that the set of homotopy classes of the paths in a topological ring is a topological ring object (called topological ring-groupoid). Let p:X~→Xbe a covering map and let X~ be a topological ring. We define a category UTRCov(X) of coverings of X in which both X and X~ have universal coverings, and a category UTRGdCov( p1X ) of coverings of topological ring-groupoid π1X , in which X and R~0 =X~ have universal coverings, and then prove the equivalence of these categories. We also prove that the topological ring structure of a topological ring-groupoid lifts to a universal topological covering groupoid.

The aim of the present paper is the investigation of some problems which can be reduced to the Goursat problem for a third order equation. Some results and theorems are given concerning the existence and uniqunce for solving the suggested problem.

Let (M,g) be a compact immersed hypersurface of (Rn+1,<,>), l1 the first nonzero eigenvalue, a the mean curvature, P the support function, A the shape operator, vol(M) the volume of M, and S the scalar curvature of M. In this paper, we established some eigenvalue inequalities and proved the above.1/n òM \\A\\2 P2DV ³ </span></p>M  a2 P2 dV. 2 òM a2 P2 dV ³ 1/n (n-1) òM sp2 dV.If the scalar curvature S and the first nonzero eigenvalue l1 staisfy S= l1 (N-1), than òM [a2 - l1/n] p2 dv³ 0, 4) Suppose that the Ricci curvature of M is bounded below by a positive constant k. ThusòM a2 P2 dV ³ k/n(n-1) òM \\ gradf\\ dv+vol(M). 5) Suppose that the Ricci curvature is bounded and the scalar curvature satisfy S= l1(n− 1) and L=k- 2S>0 is a constant. Thusvol (M) ³ kl1 /L òM\\ Y \\ a pdv – 2S/L òM a2 P2 Dv.

We give the concept of ‘braiding’ for 2-groupoids, and we show that this structure is equivalent to braided regular, crossed modules.

In this paper the concepts of fuzzifying b- irresolute functions and fuzzifying b- compact spaces are characterized in terms of fuzzifying b- open sets and some of their properties are discussed.

In this paper, two new Hamilton operators are defined and the algebra of dual split quaternions is developed using these operators. It is shown that finite screw motions in Minkowski 3-space can be expressed by dual-number r (3×3) matrices in dual Lorentzian space. Moreover, by means of Hamilton operators, screw motion is obtained in 3-dimensional Minkowski space R31.

In this study, the stability problem of a circular orthotropic cylindrical shell under the effect of an axial compression varying with a power function of time is considered. At first, the modified Donnell type dynamic stability and compatibility equations are obtained using Love’s shell theory. Applying the Galerkin method and Rayleigh-Ritz variational techniques to these equations and taking the large values of loading parameters into consideration, analytics are obtained for critical parameter values. The results show that critical parameters are affected by loading parameters variations, ratio of the Young’s moduli variations, radius to thickness variations and the power of time in the axial compression expression variations. Comparing results with those in the literature validates the present analysis.

A reconnaissance study has been made on the distribution of 238U, 232Th, 40K, 137Cs and geochemical features in soil and sediment samples at various locations on the coast of Bushehr in the Persian Gulf. In this study a gamma-ray spectrometer based on a High Purity Germanium detector and a PC based MCA and X-ray fluorescence (XRF) method were used. Estimation of the measured radionuclide content have been made for the absorbed dose rate of gamma radiation. The Activity concentration (A), the equivalent radium (Req), and the external hazard index (Hex) which resulted from the natural radionuclides in soil and sediment are also calculated. The base-line data of radionuclides and heavy metals in view of the commissioning of nuclear and non-nuclear industries for the coast of Bushehr, which does not yet exist, was obtained.Activity concentration levels due to radionuclides were measured in 50 soil and sediment samples collected from this region. The measurement was performed with respect to their gamma radioactivity for a counting time of 24 hour intervals. From the accumulated spectra, activity concentration were determined for 40K (range from 108 to 520 Bq Kg-1), 137Cs (from 6 to 40 Bq Kg-1), 238U (from 12 to 75 Bq Kg-1) and 232Th (from 8 to 33 Bq Kg-1) with the lowest limit detection (LLD) of, respectively, 68, 3.2, 4.3 and 4.3 Bq Kg-1. The dose rate from ambient air at the soil ranges was between 14 to 44 nGy h-1 with an average of 30.56±7.86 nGy h-1.

In this experimental work the pressure induced phase transformation of silicon and Germanium has been studied. It was shown that at a particular value of applied pressure, (Pt), depending on the sample temperature, the electrical resistance of the specimen falls off to a metallic state. The main goal of this study was to find out how the phase transformation pressure, Pt, for a p-type silicon varies with the sample temperature. The results show that, the value of Pt  decreases linearly as the temperature of the sample increases. Meanwhile, other related results including the rate of resistance change in accordance with applied pressure on the sample at different temperatures (~270-350K), both for the semiconductor and the metallic state of the specimen were determined. In another effort, the amount of Pt for an n-type germanium, but only at room temperature, was also determined.

In this paper, we use a third degree B-spline function to construct an approximate solution for third order linear and nonlinear boundary value problems coupled with the least square method. Several examples are given to illustrate the efficiency of the proposed technique.

The problem of finding the minimum cost multi-commodity flow in an undirected and complete network is studied when the link costs are piecewise linear and convex. The arc-path model and overflow model are presented to formulate the problem. The results suggest that the new overflow model outperforms the classical arc-path model for this problem. The classical revised simplex, Frank and Wolf and a heuristic method are compared for the problem.

In a finite stationary Markov chain, transition probabilities may depend on some explanatory variables. A similar problem has been considered here. The corresponding posteriors are derived and inferences are done using these posteriors. Finally, the procedure is illustrated with a real example.

In this paper, we extend some famous maximal inequalities and obtain strong laws of large numbers for arbitrary random variables by use of these inequalities and martingale techniques.

In this paper, we establish some results on the existence of at least three weak solutions for a Dirichlet problem involving p-Laplacian using a variational approach.