SIMPLE TECHNIQUES FOR DETERMINING THE SMALL-SIGNAL EQUIVALENT CIRCUIT OF MESFET’s

Simple techniques for determining the broadband small signal equivalent circuit (SSEC) of MESFETs are presented in this paper. The intrinsic elements are calculated using two-dimensional method from the Y parameters, which are obtained from the Fourier analysis of the device transient response to voltage-step perturbations at the drain and gate electrodes. Whereas, the parasitic external elements are determined by simple approximations used in transmission line modeling. In addition, a new technique is also proposed to determine the source and drain series resistances. A comparison of the SSEC of three different MESFETs technologies shows that the MESFETs on GaN and 4H-SiC are suitable for high power applications. The method used to determine the intrinsic elements is validated with simulated data obtained by Monte Carlo method.     

Instrumental neutron activation analysis of mass fractions of toxic metals in plastic

It is very challenging to decompose a plastic product for the purpose of analysis of hazardous elements contained. To circumvent such technical problem, it is imperative that an analyst employ a nondestructive analytical method free of any pretreatments. The analytical results of the concentrations of toxic metals such as Cd and Cr in polypropylene for seven samples at two different levels were obtained using the instrumental neutron activation analysis. This work was intended ultimately to establish certified reference materials (CRMs) of these metals in the polypropylene, traceable to the SI. The uncertainties associated with the analytical procedures were estimated in accordance with the ISO guideline. The results were subsequently validated by a comparison with those for CRM-680 and −681 of the Bureau Communautaire de Reference (BCR), which demonstrated acceptable agreement within their uncertainty ranges.     

Well-posedness of a multidimensional free boundary problem modelling the growth of nonnecrotic tumors

In this paper we study a free boundary problem modelling the growth of nonnecrotic tumors. The main trait of this free boundary problem is that it is essentially multidimensional, so that its well-posedness is hard to establish by using the usual methods in the classical theory of free boundary problems. In this paper we use the functional analysis method based on the theory of analytic semigroups to prove that this problem has a unique local solution in suitable function spaces. Continuous dependence of the solution on the initial data and regularities of the solution can also be easily obtained by using the argument of this paper.     

Theory and Application of Characteristic Finite Element Domain Decomposition Procedures for Coupled System of Dynamics of Fluids in Porous Media

For a coupled system of multiplayer dynamics of fluids in porous media,the characteristic finiteelement domain decomposition procedures applicable to parallel arithmetic are put forward.Techniques suchas calculus of variations,domain decomposition,characteristic method,negative norm estimate,energy methodand the theory of prior estimates are adopted.Optimal order estimates in L~2 norm are derived for the error inthe approximate solution.     

Numerical comparison of methods for solving second-order ordinary initial value problems

In this paper, we apply Adomian decomposition method (shortly, ADM) to develop a fast and accurate algorithm of a special second-order ordinary initial value problems. The ADM does not require discretization and consequently of massive computations. This paper is particularly concerned with the ADM and the results obtained are compared with previously known results using the Quintic C²-spline integration methods. The numerical results demonstrate that the ADM is relatively accurate and easily implemented.     

Algorithms for finding proper essential surfaces in 3-manifolds

In this paper, we present an algorithm which, for a given compact orientable irreducible boundary irreducible 3-manifold M, verifies whether M contains an essential orientable surface (possibly, with boundary), whose genus is at most N. The algorithm is based on Haken’s theory of normal surfaces, and on a trick suggested by Jaco and consisting in estimating the mean length of boundary curves in an unknown essential surface of a given genus in the given manifold.     

Integral representations of nonnegative solutions for parabolic equations and elliptic Martin boundaries

We consider nonnegative solutions of a parabolic equation in a cylinder D×(0,T), where D is a noncompact domain of a Riemannian manifold. Under the assumption [IU] (i.e., the associated heat kernel is intrinsically ultracontractive), we establish an integral representation theorem: any nonnegative solution is represented uniquely by an integral on (D×{0})∪(M_∂D×[0,T)), where M_∂D is the Martin boundary of D for the associated elliptic operator. We apply it in a unified way to several concrete examples to explicitly represent nonnegative solutions. We also show that [IU] implies the condition [SP] (i.e., the constant function 1 is a small perturbation of the elliptic operator on D).     

半正二阶三点边值问题的解和正解

考察了非线性二阶三点边值问题的n个解和正解的存在性,其中允许非线性项有一个负的下界并且n是一个任意的自然数．主要结论表明该问题可以具有n个解或者正解,只要非线性项在某些有界集上的“高度”是适当的．     

Corner view on the crown domain

In this paper we raise a question about the boundary of the crown domain of a Riemannian symmetric space X. In case X is of Hermitian type we give an affirmative answer.     

Polynomial expansion of basis sets: Alternatives to fully optimized exponents

Alternatives based on polynomial expansions of gaussian basis set exponents are introduced and evaluated. The formulas presented here outperform methods based upon the even-tempered formula or combinations of it. They closely match the performance of other methods based upon larger polynomial expansions of the logarithm of the exponents using the same or one less parameter per orbital angular symmetry.