E. V. Akulich, A. V. Lebedev
The article presents the procedure of the index calculation for the elements of the algebra generated by one dimensional singular integral operators with discontinuous oscillating coefficients.
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In the first part, we obtain sharp results for L^2 boundedness of strongly singular operators on the Heisenberg group. We also define the oscillating convolution operators on the Heisenberg group and study their boundedness properties. In the second part, we obtain the boundedness on Hardy spaces.
Recently V. Kokilashvili, N. Samko, and S. Samko have proved a sufficient condition for the boundedness of the Cauchy singular integral operator on variable Lebesgue spaces with radial oscillating weights over Carleson curves. This condition is formulated in terms of Matuszewska-Orlicz indices of weights. We prove a partial converse of their result.
Suppose $α$ is an orientation preserving diffeomorphism (shift) of $\mR_+=(0,\infty)$ onto itself with the only fixed points $0$ and $\infty$. We establish sufficient conditions for the Fredholmness of the singular integral operator \[ (aI-bW_α)P_++(cI-dW_α)P_- \] acting on $L^p(\mR_+)$ with $1<p<\infty$, where $P_\pm=(I\pm S)/2$, $S$ is the Cauchy singular integral operator, and $W_αf=f\circα$ is the shift operator, under the assumptions that the coefficients $a,b,c,d$ and the derivative $α'$ of the shift are bounded and continuous on $\mR_+$ and may admit discontinuities of slowly oscillatin…
We investigate the boundedness of oscillating singular integrals on Lie groups of polynomial growth in order to extend the classical oscillating conditions due to Fefferman and Stein for the boundedness of oscillating convolution operators. Kernel criteria are presented in terms of a fixed sub-Riemannian structure on the group induced by a sub-Laplacian associated to a Hörmander system of vector fields. In the case where the group is graded, kernel criteria are presented in terms of the Fourier analysis associated to an arbitrary Rockland operator.
In [24, Theorem 2'] Charles Fefferman has proved the weak (1,1) boundedness for a class of oscillating singular integrals that includes the oscillating spectral multipliers of the Euclidean Laplacian $Δ,$ namely, operators of the form \begin{equation} T_θ(-Δ):= (1-Δ)^{-\frac{nθ}{4}}e^{i (1-Δ)^{\fracθ{2}}},\,0\leq θ<1. \end{equation} The aim of this work is to extend Fefferman's result to oscillating singular integrals on any arbitrary compact Lie group. Applications to oscillating spectral multipliers of the Laplace-Beltrami operator are also considered. The proof of our main theorem illustrat…
Oscillating singular integral operators on graded Lie groups revisited
本文将 Fefferman–Stein 的振荡奇异积分理论推广至任意分次李群，借助 Rockland 算子的无穷小表示刻画核及其群 Fourier 变换的判据。
Suppose $α$ is an orientation-preserving diffeomorphism (shift) of $\mR_+=(0,\infty)$ onto itself with the only fixed points $0$ and $\infty$. In \cite{KKLsufficiency} we found sufficient conditions for the Fredholmness of the singular integral operator with shift \[ (aI-bW_α)P_++(cI-dW_α)P_- \] acting on $L^p(\mR_+)$ with $1<p<\infty$, where $P_\pm=(I\pm S)/2$, $S$ is the Cauchy singular integral operator, and $W_αf=f\circα$ is the shift operator, under the assumptions that the coefficients $a,b,c,d$ and the derivative $α'$ of the shift are bounded and continuous on $\mR_+$ and may admit disc…
We prove a Fredholm criterion for operators in the Banach algebra of singular integral operators with matrix piecewise continuous coefficients acting on a variable Lebesgue space with a radial oscillating weight over a logarithmic Carleson curve. The local spectra of these operators are massive and have a shape of spiralic horns depending on the value of the variable exponent, the spirality indices of the curve, and the Matuszewska-Orlicz indices of the weight at each point. These results extend (partially) the results of A. Böttcher, Yu. Karlovich, and V. Rabinovich for standard Lebesgue spac…
Let $α,β$ be orientation-preserving diffeomorphism (shifts) of $\mathbb{R}_+=(0,\infty)$ onto itself with the only fixed points $0$ and $\infty$ and $U_α,U_β$ be the isometric shift operators on $L^p(\mathbb{R}_+)$ given by $U_αf=(α')^{1/p}(f\circα)$, $U_βf=(β')^{1/p}(f\circβ)$, and $P_2^\pm=(I\pm S_2)/2$ where \[ (S_2 f)(t):=\frac{1}{πi}\int\limits_0^\infty \left(\frac{t}τ\right)^{1/2-1/p}\frac{f(τ)}{τ-t}\,dτ, \quad t\in\mathbb{R}_+, \] is the weighted Cauchy singular integral operator. We prove that if $α',β'$ and $c,d$ are continuous on $\mathbb{R}_+$ and slowly oscillating at $0$ and $\inf…
Let $α,β$ be orientation-preserving homeomorphisms of $[0,\infty]$ onto itself, which have only two fixed points at $0$ and $\infty$, and whose restrictions to $\mathbb{R}_+=(0,\infty)$ are diffeomorphisms, and let $U_α,U_β$ be the corresponding isometric shift operators on the space $L^p(\mathbb{R}_+)$ given by $U_μf=(μ')^{1/p}(f\circμ)$ for $μ\in\{α,β\}$. We prove sufficient conditions for the right and left Fredholmness on $L^p(\mathbb{R}_+)$ of singular integral operators of the form $A_+P_γ^++A_-P_γ^-$, where $P_γ^\pm=(I\pm S_γ)/2$, $S_γ$ is a weighted Cauchy singular integral operator, $…
Let $α$ and $β$ be orientation-preserving diffeomorphisms (shifts) of $\mathbb{R}_+=(0,\infty)$ onto itself with the only fixed points $0$ and $\infty$, where the derivatives $α'$ and $β'$ may have discontinuities of slowly oscillating type at $0$ and $\infty$. For $p\in(1,\infty)$, we consider the weighted shift operators $U_α$ and $U_β$ given on the Lebesgue space $L^p(\mathbb{R}_+)$ by $U_αf=(α')^{1/p}(f\circα)$ and $U_βf= (β')^{1/p}(f\circβ)$. For $i,j\in\mathbb{Z}$ we study the simplest weighted singular integral operators with two shifts $A_{ij}=U_α^i P_γ^++U_β^j P_γ^-$ on $L^p(\mathbb{R…
Modelling of singularities given by discontinuous functions or distributions by means of generalized functions has proved useful in many problems posed by physical phenomena. We introduce in a systematic way generalized functions of Colombeau that model such singularities. Moreover, we evaluate some products of singularity-modelling generalized functions whenever the result admits an associated distribution
Making use of the weighted Mourre theory developed in [GJ1], we show the limiting absorption principle for Schr{ö}dinger operators with perturbed oscillating potential on appropriate energy intervals. We focus on a certain class of oscillating potentials (larger than the one in [GJ2]) that was already studied in [BD, MU, ReT1, ReT2]. We allow long-range and short-range components and local singularities in the perturbation. We improve known results, the main novelty being the presence of a long-range perturbation. A subclass of the considered potentials actually cannot be treated by the usual …
We study existence and uniqueness of distributional solutions to the differential equation of the Euler-Bernoulli rod with discontinuous coefficients and right-hand side. Upon checking the validity of a solution the occurring products of singular coefficients with the distributional solution have no obvious meaning. When interpreted on the most general level of the so-called hierarchy of distributional products, it turns out that existence of a solution forces a minimum regularity to hold. Curiously, the choice of the distributional product concept is thus incompatible with the possibility of …
Modelling of singularities given by discontinuous functions or distributions by means of generalized functions has proved useful in many problems posed by physical phenomena. We introduce in a systematic way generalized functions of Colombeau that model singularities given by distributions with singular point support. Moreover, we evaluate various products of such generalized models whenever the results admit associated distributions. The results obtained follow the idea of a well-known result of Jan Mikusinski on balancing of singular distributional products.
In the smooth scattering theory framework, we consider a pair of self-adjoint operators $H_0$, $H$ and discuss the spectral projections of these operators corresponding to the interval $(-\infty,λ)$. The purpose of the paper is to study the spectral properties of the difference $D(λ)$ of these spectral projections. We completely describe the absolutely continuous spectrum of the operator $D(λ)$ in terms of the eigenvalues of the scattering matrix $S(λ)$ for the operators $H_{0}$ and $H$. We also prove that the singular continuous spectrum of the operator $D(λ)$ is empty.
Vibration modes of the Euler-Bernoulli beam equation with singularities
本研究针对含不连续奇异系数的含时Euler-Bernoulli梁方程，推广Hörmander分布乘积得到其在Schwartz分布空间的显式表述，证明解的相关性质，分析不同边界下梁特征频率与抗弯刚度奇点的关联并与现有结果对比。
In this work we extend the $L^1$-Björk-Sjölin theory of strongly singular convolution operators to arbitrary graded Lie groups. Our criteria are presented in terms of the oscillating Hörmander condition due to Björk and Sjölin of the kernel of the operator, and the decay of its group Fourier transform is measured in terms of the infinitesimal representation of an arbitrary Rockland operator. The historical result by Björk and Sjölin is re-obtained in the case of the Euclidean space.
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