Application of the $$\bar\partial$$ -dressing method to a $$(2+1)$$ -dimensional equation

Theoretical and Mathematical Physics - A remarkable method for investigating solutions of nonlinear soliton equation is the $$\bar\partial$$ -dressing method. Although there are other methods that...     

Pointwise estimates for relative fundamental solutions of heat equations in $${\mathbb{R} \times \mathbb{C}}$$

Let be a subharmonic, nonharmonic polynomial and a parameter. Define , a closed, densely defined operator on . If and , we solve the heat equations , u(0,z) = f(z) and , . We write the solutions via heat semigroups and show that the solutions can be written as integrals against distributional kernels. We prove that the kernels are C ^∞ off of the diagonal {(s, z, w) : s = 0 and z = w} and find pointwise bounds for the kernels and their derivatives.      

Approximation of $$\bar \omega $$ -integrals of continuous functions defined on the real axis by Fourier operators

We obtain asymptotic formulas for the deviations of Fourier operators on the classes of continuous functions and in the uniform metric. We also establish asymptotic laws of decrease of functionals characterizing the problem of the simultaneous approximation of -integrals of continuous functions by Fourier operators in the uniform metric.Translated from Ukrainskyi Matematychnyi Zhurnal, Vol. 56, No. 5, pp. 663–676, May, 2004.     

Equivalence of regularity for the Bergman projection and the\bar \partial-neumann operator

A necessary and sufficient condition for regularity of the -Neumann operator on (0,q)-forms in a smooth bounded pseudoconvex domain in Cⁿ is that the orthogonal projections onto -closed forms of degrees (0,q−1), (0,q), and (0,q+1) all be regular. The first author partially supported by NSF Grant DMS-8701038     

Global analytic hypoellipticity of the\bar \partial-Neumann problem on circular domains

In this paper we show that if \(D \subseteq \mathbb{C}^n ,n \geqq 2\) , is a smooth bounded pseudoconvex circular domain with real analytic defining functionr(z) such that \(\sum\limits_{k = 1}^n {z_k \frac{{\partial r}}{{\partial z_k }}} \ne 0\) for allz near the boundary, then the solutionu to the \(\bar \partial\) -Neumann problem, $$square u = (\bar \partial \bar \partial * + \bar \partial *\bar \partial )u = f,$$ is real analytic up to the boundary, if the given formf is real analytic up to the boundary. In particular, if \(D \subseteq \mathbb{C}^n ,n \geqq 2\) , is a smooth bounded complete Reinhardt pseudoconvex domain with real analytic boundary. Then ? is analytic hypoelliptic.     

Microlocalisation et estimations pour\bar \partial _b dans quelques hypersurfaces pseudoconvexes

Résume Nous étudions des estimations précises pour sur des hypersurfaces dont la matrice de Levi dans une base a une certaine forme. En particulier, nous donnons, par la méthode de microlocalisation, une démonstration très simple des estimations dites maximales lorsque les valeurs propres sont comparables. Nous obtenons en fait une précision supplémentaire (inégalité 3.17) qui permet de considérer des cas plus généraux. Finalement, de telles estimations, on déduit des estimations sous elliptiques optimales pour .

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Summary We study precise estimates for on hypersurfaces the Levi matrix of which has certain form. In particular, we give and simple proof of the so-called maximal estimates, using the microlocal analysis. In fact, we obtain a refined version (inequality 3.17), which permits the study of more general cases. Finally, from such estimates, we deduce optimal subelliptic estimates for .

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Oblatum 3-IX-1990     

Miura-type transformations of nonlinear partial differential equations integrable by the\bar \partial-problem methodmethod

A new method is suggested for constructing Miura-type transformations for systems of nonlinear equations of mathematical physics integrable by the -problem method using a generalized normalization function in the -problem. Examples of these transformations for the Kadomtsev-Petviashvili equation are considered. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 119, No. 1, pp. 47–54, April, 1999.     

Fibred multilinks and singularities $${f \overline g}$$

In this article we extend Milnor’s fibration theorem to the case of functions of the form with f, g holomorphic, defined on a complex analytic (possibly singular) germ (X, 0). We further refine this fibration theorem by looking not only at the link of , but also at its multi-link structure, which is more subtle. We mostly focus on the case when X has complex dimension two. Our main result (Theorem 4.4) gives in this case the equivalence of the following three statements:

The \bar \partial -Neumann operator and commutators of the Bergman projection and multiplication operators

We prove that compactness of the canonical solution operator to restricted to (0, 1)-forms with holomorphic coefficients is equivalent to compactness of the commutator defined on the whole L _(0,1)²(Ω), where is the multiplication by and is the orthogonal projection of L _(0,1)²(Ω) to the subspace of (0, 1) forms with holomorphic coefficients. Further we derive a formula for the -Neumann operator restricted to (0, 1) forms with holomorphic coefficients expressed by commutators of the Bergman projection and the multiplications operators by z and . Partially supported by the FWF grant P19147-N13.     

q-Pseudoconvexity and Regularity at the Boundary for Solutions of the \bar \partial -problem

For a domain of we introduce a fairly general and intrinsic condition of weak q-pseudoconvexity, and prove, in Theorem 4, solvability of the -complex for forms with -coefficients in degree . All domains whose boundary have a constant number of negative Levi eigenvalues are easily recognized to fulfill our condition of q-pseudoconvexity; thus we regain the result of Michel (with a simplified proof). Our method deeply relies on the L ²-estimates by Hörmander (with some variants). The main point of our proof is that our estimates (both in weightened-L ² and in Sobolev norms) are sufficiently accurate to permit us to exploit the technique by Dufresnoy for regularity up to the boundary.     

A division problem for\bar \partial _b - CLOSED forms

LetG ₁,…,G_m be bounded holomorphic functions in a strictly pseudoconvex domainD such that . We prove that for each (0,q)-form ϕ inL ^p(∂D), 1<p<∞, there are formsu ₁, …,u _m inL ^p(∂D) such that ΣG _ju_j=ϕ. This generalizes previous results forq=0. The proof consists in delicate estimates of integral representation formulas of solutions and relies on a certainT1 theorem due to Christ and Journé. For (0,n−1)-forms there is a simpler proof that also gives the result forp=∞. Restricted to one variable this is precisely the corona theorem. The author was partially supported by the Swedish Natural Research Council.     

Boundary regularity for the\bar \partial _b - Neumann problem, part 1problem, part 1

We establish sharp regularity and Fredholm theorems for the operator on domains satisfying some nongeneric geometric conditions. We use these domains to construct explicit examples of bad behavior of the Kohn Laplacian: It is not always hypoelliptic up to the boundary, its partial inverse is not compact and it is not globally subelliptic.     

Approximation of classesC_\infty ^{\bar \psi } by zygmund sumsby zygmund sums

We consider the approximation of functions of the classes of by Zygmund sums. In papticular, we present asymptotic equalities for the quantities under various conditions imposed on functions ψ₁(·) and ψ₂(·). Institute of Mathematics, Ukrainian Academy of Sciences, Kiev. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 52, No. 6, pp. 856–860, June, 2000.     

A note on the kernel of the\bar \partial -Neumann operator on strongly pseudo-convex domains

In this paper, we discuss the relations between a special Heisenberg coordinate system and a normalized Levi metric on strongly pseudo-convex domains in Cⁿ and see how they are related to the -Neumann operator.Work supported by MSRI, Berkeley, California.     

The limits in\bar d of multi-step Markov chainsof multi-step Markov chains

The of the class of multi-step Markov chains is shown to consist of all direct products of Bernoulli processes with processes of rational pure point spectrum. The class of processes that are approached in by their canonical multi-step Markov approximations is also studied. It is found to be strictly smaller than the former class, dense in it, and characterized within it by a certain (noninvariant) property of its rotation factors.     

Computing the Minkowski Sum of Prisms

Within this paper we study the Minkowski sum of prisms (“Cephoids”) in a finite dimensional vector space. For a vector with positive components we write and denote by the associated prism. We provide a representation of a finite sum of prisms in terms of inequalities. Dedicated to the 65th birthday of Alexander Rubinov.     

Multiple Fourier Sums on Sets of \bar \psi-Differentiable Functions (Low Smoothness)

We investigate the behavior of deviations of rectangular partial Fourier sums on sets of -differentiable functions of many variables.     

Non-subelliptic estimates for the tangential Cauchy–Riemann system

We prove non-subelliptic estimates for the tangential Cauchy-Riemann system over a weakly “q-pseudoconvex” higher codimensional submanifold M of $\mathbb{C}^{n}We prove non-subelliptic estimates for the tangential Cauchy-Riemann system over a weakly “q-pseudoconvex” higher codimensional submanifold M of . Let us point out that our hypotheses do not suffice to guarantee subelliptic estimates, in general. Even more: hypoellipticity of the tangential C-R system is not in question (as shows the example by Kohn of (Trans AMS 181:273–292,1973) in case of a Levi-flat hypersurface). However our estimates suffice for existence of smooth solutions to the inhomogeneous C-R equations in certain degree. The main ingredients in our proofs are the weighted L ² estimates by H?rmander (Acta Math 113:89–152,1965) and Kohn (Trans AMS 181:273–292,1973) of Sect. 2 and the tangential -Neumann operator by Kohn of Sect 4; for this latter we also refer to the book (Adv Math AMS Int Press 19,2001). As for the notion of q pseudoconvexity we follow closely Zampieri (Compositio Math 121:155–162,2000). The main technical result, Theorem 2.1, is a version for “perturbed” q-pseudoconvex domains of a similar result by Ahn (Global boundary regularity of the -equation on q-pseudoconvex domains, Preprint, 2003) who generalizes in turn Chen-Shaw (Adv Math AMS Int Press 19, 2001).To Prof. Giovanni Zacher in his 80th birthday.     

有限群的$\Phi$-$\tau$-可补子群

假设$\tau$是一个子群算子, $H$是有限群$G$的一个$p$-子群. 令 $\bar{G}=G/H_{G}$且$\bar{H}=H/H_{G}$, 如果$\bar{G}$有一个次正规子群$\bar{T}$ 和一个包含于$\bar{H}$ 的$\tau$-子群$\bar{S}$满足$\bar{G}=\bar{H}\bar{T}$且$\bar{H}\cap\bar{T}\leq \bar{S}\Phi(\bar{H})$, 就称$H$是$G$的一个$\Phi$-$\tau$- 可补子群. 文章通过讨论群$G$的准素数子群的$\Phi$-$\tau$-可补性给出了超循环嵌入和$p$-幂零性的一些新的特征.     

Semiclassical $$\bar \partial $$ -Method: Generating Equations for Dispersionless Integrable Hierarchies

We use the semiclassical -dressing method to derive compact generating equations for dispersionless hierarchies. The considered illustrative examples are the dispersionless Kadomtsev–Petviashvili and two-dimensional Toda lattice hierarchies.