A “Discretization” Technique for the Solution of ODEs II

A functional analytic technique was recently presented for finding discrete equivalent counterparts of initial value problems of ODEs and obtaining their real analytic solutions. In the current paper, this technique is extended to boundary value problems of ODEs and to the complex solutions of ODEs. In order to demonstrate this technique, it is applied to the classic Blasius problem of fluid mechanics. Apart from its real solution, its complex solution is also studied. The obtained results indicate that the complex Blasius function exhibits an oscillatory behavior and strengthen a conjecture regarding its singularities in the complex plane.     

A “discretization” technique for the solution of ODEs

A functional-analytic technique was developed in the past for the establishment of unique solutions of ODEs in H₂(D) and H₁(D) and of difference equations in ?₂ and ?₁. This technique is based on two isomorphisms between the involved spaces. In this paper, the two isomorphisms are combined in order to find discrete equivalent counterparts of ODEs, so as to obtain eventually the solution of the ODEs under consideration. As an application, the Duffing equation and the Lorenz system are studied. The results are compared with numerical ones obtained using the 4th order Runge-Kutta method. The advantages of the present method are that, it is accurate, the only errors involved are the round-off errors, it does not depend on the grid used and the obtained solution is proved to be unique.     

Global existence, singularities and ill-posedness for a nonlocal flux

In this paper we study a one-dimensional model equation with a nonlocal flux given by the Hilbert transform that is related with the complex inviscid Burgers equation. This equation arises in different contexts to characterize nonlocal and nonlinear behaviors. We show global existence, local existence, blow-up in finite time and ill-posedness depending on the sign of the initial data for classical solutions.     

Algebraic independence of logarithmic singularities of some complex functions

We show that algebraic independence of some complex functions of one variable over regular functions implies their algebraic independence over a larger ring, containing complex powers of regular functions. Based on this we obtain a generalization of a special case of the theorem of Kaczorowski and Perelli on functional independence of logarithms of functions in the Selberg class. As an application we state a new result on oscillations of arithmetical functions.     

RECOVERING SINGULARITIES FROM BACKSCATTERING IN TWO DIMENSIONS

We have shown that in two dimensions the leading singularities of the quantum mechanical scattering potential are determined by the backscattering data. We assume that the short range potential belongs to a suitable weighted Sobolev space, and by estimating the iterative terms in the Born-expansion we are able to show, that for example for Heaviside-type singularities across a smooth hypersurface, both the location and the size of the jump are recovered from backscattering.

The main part of the proof consists in getting sharp enough estimates for the first non-linear Born-term. These estimates are proven using a recent characterization of W ^1,p -functions due to P. Hajlasz, and a modification of the classical Triebel's Maximal Inequality.     

Logistic型方程周期解和概周期解的存在性

In this paper, we study the Logistic type equation x= a（t）x -b（t）x^2＋ e（t）. Under the assumptions that e（t） is small enough and a（t）, b（t） are contained in some positive intervals, we prove that this equation has a positive bounded solution which is stable. Moreover, this solution is a periodic solution if a（t）, b（t） and e（t） are periodic functions, and this solution is an almost periodic solution if a（t）, b（t） and e（t） are almost periodic functions.     

Periodic solutions of a logistic type population model with harvesting

We consider a bifurcation problem arising from population biology

     

Multimodal admittance method in waveguides and singularity behavior at high frequencies

This work presents a multimodal method for the propagation in a waveguide with varying height and its relation to trapped modes or quasi-trapped modes. The coupled mode equations are obtained by projecting the Helmholtz equation on the local transverse modes. To solve this problem we integrate the Riccati equation governing the admittance matrix (Dirichlet-to-Neumann operator). For many propagating modes, i.e. at high frequencies, the numerical integration of the Riccati equation shows that the rule is that this matrix has quasi-singularities associated to quasi-trapped modes.     

二阶复微分方程的亚纯元素解及代数元素解

研究了一类二阶亚纯系数复微分方程的亚纯元素解及代数元素解的存在性问题,得到了几个有关解的存在性定理.     

关于指数率Logistic方程在无限柱体内的波前解的存在性

与一维空间中研究连接两个常数的波前解的存在性不同的是,本文建立了在多维无限长的柱体内连接两个曲面的单调行波解的存在性.相应的模型是一种具有指数率的Logistic方程.所用的方法是一种改进了的单调性方法.本文的研究结果对自然界中波的实际传播行为给出了有益的启示.     

ON A PERIODIC DELAY LOGISTIC TYPE POPULATION MODEL

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Fundamental solutions for a class of non-elliptic homogeneous differential operators

We compute temperate fundamental solutions of homogeneous differential operators with real-principal type symbols. Via analytic continuation of meromorphic distributions, fundamental solutions for these non-elliptic operators can be constructed in terms of radial averages and invariant distributions on the unit sphere.     

Minimal initial data for potential Navier-Stokes singularities

Assuming some initial data lead to a singularity for the 3d Navier-Stokes equations, we show that there are also initial data with the minimal -norm which will produce a singularity.     

Numerical Methods to Solve the Complex Symmetric Stabilizing Solution of the Complex Matrix Equation $X+A^TX^{−1}A=Q$

When the matrices $A$ and $Q$ have special structure, the structure-preservingalgorithm was used to compute the stabilizing solution of the complex matrix equation $X+A^TX^{-1}A=Q.$ In this paper, we study the numerical methods to solve the complexsymmetric stabilizing solution of the general matrix equation $X+A^TX^{-1}A=Q.$ Wenot only establish the global convergence for the methods under an assumption, butalso show the feasibility and effectiveness of them by numerical experiments.     

Positive solutions for logistic type quasilinear elliptic equations on R

In this paper, we consider positive solutions of the logistic type p-Laplacian equation −Δ_pu=a(x)|u|^p−2u−b(x)|u|^q−1u, xR^N (N2). We show that under rather general conditions on a(x) and b(x) for large |x|, the behavior of the positive solutions for large |x| can be determined. This is then used to show that there is a unique positive solution. Our results improve the corresponding ones in J. London Math. Soc. (2) 64 (2001) 107–124 and J. Anal. Math., in press.     

Desingularization of quasi-excellent schemes in characteristic zero

Grothendieck proved in EGA IV that if any integral scheme of finite type over a locally noetherian scheme X admits a desingularization, then X is quasi-excellent, and conjectured that the converse is probably true. We prove this conjecture for noetherian schemes of characteristic zero. Namely, starting with the resolution of singularities for algebraic varieties of characteristic zero, we prove the resolution of singularities for noetherian quasi-excellent Q-schemes.     

On the dynamics of a strongly singular parabolic equation

In this paper we study the semiflow defined by a semilinear parabolic equation, in which both the diffusion and the reaction term present strong order of singularity at the origin. We justify the existence of a global branch of nontrivial equilibrium solutions for subcritical nonlinearities. The approach, based on the critical Caffarelli–Kohn–Nirenberg inequality, follows the arguments of  and .     

Singularities of the solution of the laplacian in domains with circular edges

In this paper we generalize the results from [4] to special domains with curved edges. For general elliptic boundary value problems the behavior of the solutions near arbitrary, smooth edges is analyzed by Maz'ja and Rossmann [3]. First following Dauge [1] we derive a regularity theorem for the solution of the Dirichlet problem of the Laplacian with a decomposition into edge singularities of nontensor product form. In this case the regularity of the remainder term in the decomposition corresponds to the one in the two-dimensional case [2]. Following [4] we obtain a refined decomposition where all singularity terms are of tensor product form. We illustrate our results with several examples.