An extension problem for the CR fractional Laplacian

We show that the conformally invariant fractional powers of the sub-Laplacian on the Heisenberg group are given in terms of the scattering operator for an extension problem to the Siegel upper halfspace. Remarkably, this extension problem is different from the one studied, among others, by Caffarelli and Silvestre. We also prove an energy identity that yields a sharp trace Sobolev embedding.     

Nonlinear fractional integro-differential Langevin equation involving two fractional orders with three-point multi-term fractional integral boundary conditions

In this article, we study a nonlinear fractional integro-differential Langevin equation involving two fractional orders with three-point multi-term fractional integral boundary conditions. By using fixed point theorems and Leray-Schauder degree theory, some new existence results are obtained. Two examples illustrate our results.     

Bi-Lipschitz extension from boundaries of certain hyperbolic spaces

Tukia and Väisälä showed that every quasi-conformal map of ${\mathbb{R}^n}$ extends to a quasi-conformal self-map of ${\mathbb{R}^{n+1}}$ . The restriction of the extended map to the upper half-space ${\mathbb{R}^n \times \mathbb{R}_+}$ is, in fact, bi-Lipschitz with respect to the hyperbolic metric. More generally, every simply connected homogeneous negatively curved manifold decomposes as ${M = N \rtimes \mathbb{R}_+}$ where N is a nilpotent group with a metric on which ${\mathbb{R}_+}$ acts by dilations. We show that under some assumptions on N, every quasi-symmetry of N extends to a bi-Lipschitz map of M. The result applies to a wide class of manifolds M including non-compact rank one symmetric spaces and certain manifolds that do not admit co-compact group actions. Although M must be Gromov hyperbolic, its curvature need not be strictly negative.     

A Nagata-like theorem for certain function spaces

Let X be a space, and let A be a zero-dimensional topological ring. In this paper we will consider a few natural questions that arise when studying the space C _p (X, A), the ring of continuous functions from X to A, endowed with the topology of pointwise convergence. It will be shown that the zero-dimensionality of the codomain plays a vital role in this study. An upper and lower bound will be determined for the density of C _p (X, A) using the density of A and the weight of X. The character of C _p (X, A) will be computed, thus characterizing when C _p (X, A) is metrizable. Lastly, we will consider the topological dual space of C _p (X, A) and use it to prove a Nagata-like theorem.     

Multipliers on certain function spaces

Si generalizza un teorema di deLeeuw per moltiplicatiri su spazi di Lorentz e spazi con norme miste.

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Dedicated to my dear teacher, Professor Guido Weiss, for his 65 birthday     

The nonlocal Cauchy problem for nonlinear fractional integrodifferential equations in Banach spaces

In this paper we prove the existence of solutions of certain kinds of nonlinear fractional integrodifferential equations in Banach spaces. Further, Cauchy problems with nonlocal initial conditions are discussed for the aforementioned fractional integrodifferential equations. At the end, an example is presented.     

Continuity and differentiability for weighted Sobolev spaces

Our aim in this paper is to discuss continuity and differentiability of functions in weighted Sobolev spaces in the limiting case of Sobolev's imbedding theorem.

     

Domain representability of certain function spaces

Let Cp(X) be the space of all continuous real-valued functions on a space X, with the topology of pointwise convergence. In this paper we show that Cp(X) is not domain representable unless X is discrete for a class of spaces that includes all pseudo-radial spaces and all generalized ordered spaces. This is a first step toward our conjecture that if X is completely regular, then Cp(X) is domain representable if and only if X is discrete. In addition, we show that if X is completely regular and pseudonormal, then in the function space Cp(X), Oxtoby's pseudocompleteness, strong Choquet completeness, and weak Choquet completeness are all equivalent to the statement “every countable subset of X is closed”.     

具有逐项分数阶导数的微分方程边值问题解的存在性

研究了一类具有逐项分数阶导数的微分方程边值问题.对参数的各种取值情况进行了全面的分析,运用Banach压缩映射原理和Schauder不动点定理,得到并证明了边值问题解的存在性定理.最后,给出了两个例子来证明结论有效.     

Surjectivity of differential operators and the division problem in certain function and distribution spaces

We give an overview on surjectivity conditions for partial differential operators and operators defined by multiplication with polynomials on certain function and distribution spaces of Laurent Schwartz. We complement the classical results by treating the surjectivity of operators on the space of slowly increasing functions and on the space of rapidly decreasing distributions, respectively.     

A study of nonlinear Langevin equation involving two fractional orders in different intervals

This paper studies a nonlinear Langevin equation involving two fractional orders α∈(0,1] and β∈(1,2] with three-point boundary conditions. The contraction mapping principle and Krasnoselskii’s fixed point theorem are applied to prove the existence of solutions for the problem. The existence results for a three-point third-order nonlocal boundary value problem of nonlinear ordinary differential equations follow as a special case of our results. Some illustrative examples are also discussed.     

The Stepanov differentiability theorem in metric measure spaces

We extend Cheeger’s theorem on differentiability of Lipschitz functions in metric measure spaces to the class of functions satisfying Stepanov’s condition. As a consequence, we obtain the analogue of Calderon’s differentiability theorem of Sobolev functions in metric measure spaces satisfying a Poincaré inequality. Communicated by Steven Krantz     

Multiplicity results for a Kirchhoff singular problem involving the fractional p-Laplacian

The aim of this paper is to study the multiplicity of solutions for a Kirchhoff singular problem involving the fractional p-Laplacian operator. Using the concentration compactness principle and Ekeland"s variational principle, we obtain two positive weak solutions.     

Diameters of certain sets in function spaces

The precise values of the diameters (according to A. N. Kolmogorov) of the class H _C in the space C[a, b] and lower bounds for the diameters of the class H _p in the spaceL_p(0, 2) (1p), for any modulus of continuity(), are obtained. The latter bounds give the exact values of the odd-numbered diameters of the class and the exact order of decay of the diameters of the class H ₁ .Translated from Matematicheskie Zametki, Vol. 13, No. 5, pp. 637–646, May, 1973.In conclusion, the author wishes to thank A. L. Garkavi, A. V. Efimov, and S. B. stechkin for their help.     

The differentiability of nonlinear semigroups in uniformly convex spaces

LetT(t) be a semigroup on a subset of Banach spaceX. T(t) is generated by a product integral of the resolventJ _λ of an accretive operatorA. IfX is a Hilbert space, it is known that forx in the domain ofA, ‖J _t x−T(t)x‖=o(t) ast decreases to zero. We show this is true whenX is uniformly convex, and deduce some consequences.