RESEARCH JOURNAL OF UNIVERSITY OF ISFAHAN "SCIENCE"
Year:2007 | Volume:26 | Issue:4 (PHYSICS, MATHEMATICS AND STATISTICS)|Papers Count:5

In embedding method, the classical solution of partial differential equations is rarely considered for solving the optimal control problems. Applying the classical solution to obtain the optimal inner control for physical systems governed by an inhomogeneous linear wave equation with initial, final and terminal conditions, is the aim of this paper. First, the classical solution is determined. Then, by a metamorphosis, the problem is changed by one in which a linear functional to be minimized on a set of positive Radon measures.The property of the optimal measure causes to identify it as a solution of a finite linear programming problem by two steps of approximation. Therefore, the optimal control is obtained as a piecewise constant function. Moreover, the advantages of this method is explained by numerical examples and comparing the results.

In this paper, we extend some moment inequalities for partial sums of negative dependence (ND) random variables. Based on these inequalities, some useful inequalities are obtained.

We report details of calculation of the lattice thermal conductivity in wurtzite GaN in the wide temperature range of 5-300 K. Our analysis shows that on the basis of the Debye specific heat model, this material has a characteristic temperature of 616 K. This quantity affects the probability of phonon-phonon umklapp (u) scattering process at temperatures above 150 K. At lower temperatures, dislocations and ionised impurities becoming the dominant mechanisms for phonons scattering, respectively. Although the peak conductivity (kmax) in a sample reported by Jezowski et al [9] has the highest reported value (17 W.cm-1K-1), it is expected that by reduction both in the density of dislocations and ionised impurities by an amount of one order of magnitude this peak value will be increased by a factor of 10.

In this research, the effect of current density, the time of anodisation and HF concentration on optical properties of silicon wafers have been considered.A monocrystal p-type  substrate with crystalline direction (100) with resistivity of 1.4-2.6Wcm current densities of 10-20 mA/cm2 and anodisation time in range of 1800-3600 sec. were used.Spectroscopy of some of wafers with Carry 500 spectrometer have been also done. Experimental results showed that  the existene of porosity make reasonable changes in optical absorption of wafers.

Seismic waves are nonstationary signals because their frequency contents are changed when they propagate through layers of different elastic properties. Hydrocarbon reservoirs and fault zone are two major sources of attenuating high frequency components of a seismic wave. Dropping of higher frequency components of a seismic wave while passing through a hydrocarbon reservoir appears as low frequency shadow zone on a seismic section.In this study, we used instantaneous spectral attributes of real seismic data in time-frequency domain in order to trace the existence of hydrocarbon reservoir and fault zone in the study area. For this purpose, we used short time Fourier transform and continuous wavelet transform. In order to reduce the run time, the instantaneous frequency was calculated directly from scalograms.