JOURNAL OF SCIENCE (KHARAZMI UNIVERSITY)
Year:2002 | Volume:2 | Issue:1-2|Papers Count:8

To prove the famous Cohen factorization theorem, even in Banach algebras, having a bounded approximate identity has special importance. In extending the Cohen's theorem to topological algebras, we not only use an approximate identity, but some more powerful boundedness is also needed. Here we recall an open problem about uniformly bounded approximate identities on complete metrizable LMC algebras, and try to answer it.      

Determinati9n of approximate solution to ordinary or partial differential equations and integral equations, after discretization, leads to solving system of linear equations. Some of these equations are ill-conditioned and we have to use special methods to obtain a satisfactory approximation. In this paper instead of solving the system AX=B having known bounds on the components of the vector X, it is shows that approximate solution could be found by solving the following optimization problem: Min.    ║ AX-B ║   S. t. :     │xi│ ≤ δi ,     i=1,…,n It is shown that this problem in well-conditioned and gives a satisfactory approximate solution to the original problem. Numerical examples are also provided to demonstrate the method.      

In this paper the concept of location and scale measure and definitions regarding partial ordering for comparing distributions will be presented and examined. By using order of k convex, stochastic and dispersion ordering relations are presented. It will be proved that familiar measures such as mean and standard deviation are location and scale measures respectively. We present function of distribution entropy, which is scale measure, and this itself is an interesting relationship between entropy and variance of univariate distributions.      

An important problem in spatial data analysis is variogram modeling to specify the correlation structure of data. Usually the values of a variogram estimator at different lags are used for variogram modeling. Since the number of lags affects the accuracy of the model fitted to the variogram estimates, finding an optimal value for the number of lags plays an important role in variogram modeling. In this paper a simulation study is carried out to find the optimal value of the number of lags for data generated from a Gaussian random field. The result has been used in a real practical example to fit an exponential variogram model to the variogram estimates. Then, the variogram is used in kriging to predict tuberculosis disease incidence rates in some cities of Iran.    

More recently the muon transfer rate from deuterium and tritium to helium isotopes is determined. It seems that one important parameter in not having quite good agreement between experimental and theoretical values of cycling rate could be this transes which infact are not considered in previous theoretical calculations (due to unavalibity ). In this research we have determined the muon cycling rate in µdd and µdt fusion systems while muon transfer from hydrogen isotopes to helium isotopes (3 He, He) are included. It is shown that despite having high transfer rates but there is no considerable changes in muon cycling rate and the calculated cycling rates have considerable variation for D-D and D-T systems in comparison with experimental values.      

Spectroscopic measurements in the range of 10 kHz to MHz at different temperatures are reported for Au/CIMgPc/Au thin film sandwich devices. The ac conductivity is found to vary with the angular frequency ω as ωn where the index n≈ 1at high frequencies indicating the predominance of a hopping conduction mechanism in this material at low temperatures and high excitation frequencies. The variation of activation energy is studied as a function of temperature and frequency. The capacitance data are analysed within the framework of the Goswami model [10].      

In this paper with use of a fluid model for plasma, the influence of trapped particles on the expansion of a semibounded plasma into the vaccum in presence of strong electromagnetic field is studied. It is shown that as the velocity of plasma boundary decreases the velocity of the wavefront increases in comparison with the case without trapping.      

Ferroelectrie films have been studied by an Ising model in a transverse field within the mean-field approximation. We consider an N-layer film of simple cubic symmetry with nearest- neighbor exchange in which the exchange strength and transverse field are assumed in the Ns surface layers to be different from the bulk values, and we derive and illustrate expressions for the phase diagrams and polarization profile. In ferroelectric films, Curie temperature can be shifted to either lower and higher temperature compared with the corresponding bulk value. If the surface exchange strength is strong enough, there is still a phase transition to ferroelectricity even when the transverse field is larger than the bulk critical value. In surface-enhanced film with Ns≥2 the maximum in the order parameter profile occurs in the layers next to the outermost surface layer.