AMIRKABIR
Year:2006 | Volume:16 | Issue:63-E|Papers Count:10

In this paper we present a method for computing the Hilbert function and regularity of projective monomial curves. This method is based on ordering of the numerical semigroup associated to the generating set of the curve. We introduce a certain subset of the numerical semigroup associated to a projective monomial curve, which is served as an important base for it. One of the advantages of using this method is that it is independent from the computation of a minimal graded free resolution of the graded coordinate rings of these curves that needs the computation of syzygy modules of the defining ideal. In addition, this method is useful for systematic search for certain projective monomial curves with desired properties.

In this paper, the renewal process, for the homogeneous and non-homogeneous Poisson process as well as Kijima models, are reviewed. Given the distribution function of time of the successive repair time's form, the corresponding cost function is defined. Then, using the failure function the optimal time of repair is achieved.

This paper solves the problem of performance calculation for a set of n machines, which are bi-directionally patrolled by one operative worker or robot. The time taken to walk from one machine to the next and inspect and service them is assumed to be a constant, and also the machines are equally spaced installed on the floor of factory. It is supposed when the operator reaches to a stopped machine he spends an additional constant repair time cutting it in order before proceeding to the next machines, and also, the operator gets random cycles as a new repair policy proposed in this paper. It is assumed that the machines breakdown occur randomly with poisson distribution. We have formulated a performance rate for each machine in both homogenous and heterogeneous cases and notify numerical results. We approved that the new repair policy leads to an increase in the performance rate of the machines.

Transient analysis of power network for insulation coordination is essential in both design and utility engineering fields. Accuracy modeling of equipment behavior in network simulation can effect on this study: Transformers are one of important equipment which has been developed in simulation software recently.Transformer manufacturers use detailed model for insulation coordination of windings, while terminal model of transformer is interested for utility engineers in simulation of global network analysis. Order reduced model of detailed model can be used in this purpose.In this paper, transformer detailed model is used as a start point to achievement of accurate order reduced model. A number of order reduction methods have been applied to reference model and appropriate algorithm has been selected considering of simulation limits. Result model can be used in power network simulation simultaneously with other equipment easily. This model shows transient properties of network analysis as well as detailed model.

The symmetric curvature and associated curvatures of a vector bundle E with connection Ñ on a manifold M with connection Ñ were introduced. It is well-known that a total space of semi-Riemannian vector bundle over a semi-Riemannian manifold can be made into a semi-Riemannian manifold. In this case, the relation between curvatures of the Levi-Civita connections of E and M was studied. Here, the relation between symmetric curvatures of the Levi-Civita connections and their associated curvatures of E and M is studied.

In this paper by combining the concepts of ultrafilters and multiplicative means in a nice way we find a good tool for dealing with the Stone -Č ech compactification of infinite discrete semigroups.

In the present paper, a rate-based model has been developed for the simulation of H2S and CO2 absorption column using alkanolamine solutions. The model adopts the film theory and assumes that thermodynamic equilibrium exist only for H2S species. The most difficulty and time consuming part in the mathematical solution of this model is determination of CO2 and H2S concentration in liquid film. In this research we overcame this difficulty by linear equation and matrix solution. The simulation results have been validated using available plant data. It has been found that there is a good agreement between the models computed results and plant data (Khangiran MEA and Ahvaz-1 DEA gas refinery, Iran).

An analytical solution is presented for the steady state and purely tangential flow of a nonlinear viscoelastic fluid obeying the constitutive FENE-P model in a concentric annulus with inner cylinder rotation. The effect of fluid elasticity (Weissenberg number), the extensibility parameter of the model (L2 ) and aspect ratio on the velocity profile and production of friction factor and Reynolds number (¦¢Re) are investigated. The results show the strong effect of viscoelastic parameters on the velocity profile. The results also show that ¦¢Re decreases with increasing fluid elasticity and radius ratio.

The tension of warp and weft yams plays an important role in weaving process, such as yam breakage rate and weaving efficiency. They also influence the physical properties of fabric. To investigate the effect bf weft yarn tension in an air - jet loom, five fabric samples were woven from 32/2 Ne polyester – viscose warp and weft yam with five different weft yam tension levels (with average of 30, 35, 40, 45 and 50 cN). Then, they were measured and analyzed for weft and warp density and crimp, the strength and elongation at warp and weft direction, weight, thickness, drape, and abrasion resistance. Statistical analysis revealed that there is a linear relationship between weft yarn tension and investigated fabric physical properties with high correlation.