Ravshan Ashurov

Ravshan Ashurov
National University of Uzbekistan · Department of differential equations

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101
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516
Citations
Citations since 2016
54 Research Items
410 Citations
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120

Publications

Publications (101)
Article
Initial boundary value problems with a time-nonlocal condition for a subdiffusion equation with the Riemann-Liouville time-fractional derivatives are considered. The elliptical part of the equation is the Laplace operator, defined in an arbitrary N−dimensional domain Ω with a sufficiently smooth boundary ∂Ω. The existence and uniqueness of the solu...
Preprint
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The Schr\"odinger equation $i \partial_t^\rho u(x,t)-u_{xx}(x,t) = p(t)q(x) + f(x,t)$ ( $0<t\leq T, \, 0<\rho<1$), with the Riemann-Liouville derivative is considered. An inverse problem is investigated in which, along with $u(x,t)$, also a time-dependent factor $p(t)$ of the source function is unknown. To solve this inverse problem, we take the ad...
Article
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The nonlocal boundary value problem, dtρu(t)+Au(t)=f(t) (0<ρ<1, 0<t≤T), u(ξ)=αu(0)+φ (α is a constant and 0<ξ≤T), in an arbitrary separable Hilbert space H with the strongly positive selfadjoint operator A, is considered. The operator dt on the left hand side of the equation expresses either the Caputo derivative or the Riemann–Liouville derivative...
Preprint
The nonlocal boundary value problem, dtρu(t)+Au(t)=f(t) (0<ρ<1, 0<t≤T), u(ξ)=αu(0)+φ (α is a constant and 0<ξ≤T), in an arbitrary separable Hilbert space H with the strongly positive selfadjoint operator A, is considered. The operator dt on the left hand side of the equation expresses either the Caputo derivative or the Riemann-Liouville derivative...
Article
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The nonlocal boundary value problem, d ρ t u(t) + Au(t) = f (t) (0 < ρ < 1, 0 < t ≤ T), u(ξ) = αu(0) + φ (α is a constant and 0 < ξ ≤ T), in an arbitrary separable Hilbert space H with the strongly positive selfadjoint operator A, is considered. The operator dt on the left hand side of the equation expresses either the Caputo derivative or the Riem...
Article
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In this paper we consider an inverse problem for simultaneously determining the order of the Riemann-Liouville time fractional derivative and a source function in subdiffusion equations. Using the classical Fourier method, we prove the uniqueness and the existence theorem for this inverse problem.
Preprint
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It is well known that Luzin's conjecture has a positive solution for one-dimensional trigonometric Fourier series, but in the multidimensional case it has not yet found its confirmation for spherical partial sums of multiple Fourier series. Historically, progress in solving Luzin's hypothesis has been achieved by considering simpler problems. In th...
Preprint
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The inverse problem of determining the order of the fractional Riemann- Liouville derivative with respect to time in the subdi_usion equation with an arbitrary positive self-adjoint operator having a discrete spectrum is considered. Using the classical Fourier method it is proved, that the value of the norm jju(t)jj of the solution at a_xed time in...
Preprint
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As it is known various dynamical processes can be modeled through the systems of time-fractional order pseudo-differential equations. In the modeling process one frequently faces with determining the adequate orders of time-fractional derivatives in the sense of Riemann-Liouville or Caputo. This problem is qualified as an inverse problem. The right...
Preprint
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An initial-boundary value problem for a time-fractional subdiffusion equation with the Riemann-Liouville derivatives on N-dimensional torus is considered. The uniqueness and existence of the classical solution of the posed problem are proved by the classical Fourier method. Sufficient conditions for the initial function and for the right-hand side...
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The backward problem for subdiffusion equation with the fractional Riemann-Liouville time-derivative of order ? 2 (0; 1) and an arbitrary positive self-adjoint operator A is considered. This problem is ill-posed in the sense of Hadamard due to the lack of stability of the solution. Nevertheless, we will show that if we consider sufficiently smooth...
Article
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We deal with boundary value problems for equations with the ∂y 2 operator ∂ 2 − A (x, D), where A (x, D) is a nonnegative elliptic differential operator and with boundary operators depending on a positive real parameter ρ. In particular, boundary conditions can be given through the one-sided Marchaud, Gru¨nwald-Letnikov or Liouville-Weyl fractional...
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The paper investigates the inverse problem of determining the order of the fractional derivative in the sense of Gerasimov-Caputo in the wave equation with an arbitrary positive self-adjoint operator A with a discrete spectrum. It is proved by the classical Fourier method that the value of the projection of the solution on some eigenfunction at a fi...
Preprint
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In this work, an analogue of the Tricomi problem for equations of mixed type with a fractional derivative is investigated. In one part of the domain, the considered equation is a subdiffusion equation with a fractional derivative of order ? 2 (0; 1) in the sense of Riemann-Liouville, and in the other it is a wave equation. Assuming the parameter ?...
Preprint
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In this paper the inverse problem of determining the fractional orders in mixed-type equations is considered. In one part of the domain the considered equation is the subdiffusion equation with a fractional derivative in the sense of Gerasimov-Caputo of the order 0<a<1 , and in the other part - a wave equation with a fractional derivative of the or...
Article
An initial-boundary value problem for a time-fractional subdiffusion equation with an arbitrary order elliptic differential operator is considered. Uniqueness and existence of the classical solution of the posed problem are proved by the classical Fourier method. Sufficient conditions for the initial function and for the right-hand side of the equa...
Article
In this paper we consider of a multidimensional loaded mixed type equation of the second order with some seminonlocal conditions on the coefficients. The existence and uniqueness of solution of the seminonlocal boundary value problem of second kind is proved in the Sobolev space (Formula presented.). In proof of the theorems are used the methods of...
Article
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This paper is devoted to the general theory of linear systems of fractional order pseudo-differential equations. Single fractional order differential and pseudo-differential equations are studied by many authors and several monographs and handbooks have been published devoted to its theory and applications. However, the state of systems of fraction...
Article
В работе изучается сходимость почти всюду сферических частичных сумм кратных рядов Фурье функций из классов Соболева. Доказано, что сходимость почти всюду будет иметь место при тех же условиях на порядок гладкости разлагаемой функции, что и при кратных интегралов Фурье, что установлено в известной работе Карбери и Сория (1988). Наши рассуждения во...
Article
В работе исследована обратная задача по определению порядка дробной производной в смысле Герасимова-Капуто в волновом уравнении с произвольным положительным самосопряженным оператором $A$, имеющий дискретный спектр. Классическим методом Фурье доказано, что значение проекции решения на некоторую собственную функцию в фиксированный момент времени одн...
Article
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The identification of the right order of the equation in applied fractional modeling plays an important role. In this paper we consider an inverse problem for determining the order of time fractional derivative in a subdiffusion equation with an arbitrary second order elliptic differential operator. We prove that the additional information about th...
Article
Full-text available
An inverse problem for determining the order of the Caputo time-fractional derivative in a subdiffusion equation with an arbitrary positive self-adjoint operator A with discrete spectrum is considered. By the Fourier method it is proved that the value of {\|Au(t)\|} , where {u(t)} is the solution of the forward problem, at a fixed time instance rec...
Preprint
Full-text available
An initial-boundary value problem for a subdiffusion equation with an elliptic operator A(D) in R^n is considered. Uniqueness and existence theorems for a solution of this problem are proved by the Fourier method. Considering the order of the Caputo time-fractional derivative as an unknown parameter, the corresponding inverse problem of determining...
Preprint
An initial-boundary value problem for a time-fractional subdiffusion equation with an arbitrary order elliptic differential operator is considered. Uniqueness and existence of the classical solution of the posed problem are proved by the classical Fourier method. Sufficient conditions for the initial function and for the right-hand side of the equa...
Preprint
Full-text available
The identification of the right order of the equation in applied fractional modeling plays an important role. In this paper we consider an inverse problem for determining the order of time fractional derivative in a subdiffusion equation with an arbitrary second order elliptic differential operator. We prove that the additional information about th...
Preprint
Let $S_\lambda F(x)$ be the spherical partial sums of the multiple Fourier series of function $F\in L_2(\mathbb{T}^N)$. We prove almost-everywhere convergence $S_\lambda F(x)\rightarrow F(x)$ for functions in Sobolev spaces $H_p^a(\mathbb{T}^N)$ provided $1< p \leq 2$ and $a> (N-1)(\frac{1}{p}-\frac{1}{2})$. For multiple Fourier integrals this is w...
Preprint
It is well known, that Luzin's conjecture has a positive solution for one dimensional trigonometric Fourier series and it is still open for the spherical partial sums $S_\lambda f(x)$, $f\in L_2(\mathbb{T}^N)$, of multiple Fourier series, while it has the solution for square and rectangular partial sums. Historically progress with solving Luzin's c...
Article
Full-text available
In this paper the generalized localization principle for the spherical partial sums of the multiple Fourier series in the \(L_2\)-class is proved, that is, if \(f\in L_2({\mathbb {T}}^N)\) and \(f=0\) on an open set \(\Omega \subset {\mathbb {T}}^N\), then it is shown that the spherical partial sums of this function converge to zero almost-everywhe...
Article
In this paper the generalized localization principle for the spherical partial sums of the multiple Fourier series in the L2-class is proved, that is, if f L2 (ТN) and f = 0 on an open set ТN then it is shown that the spherical partial sums of this function converge to zero almost - everywhere on . It has been previously known that the generalized...
Article
Spherically symmetric continuous wavelet decompositions are considered, and the notion of Riesz means is introduced for them. Generalized localization is proved for the decompositions under study in Lp classes without any restrictions on the wavelets. Further, generalized localization is studied for the Riesz means of wavelet decompositions of dist...
Article
In this paper, we study the well-posedness of a linear inverse problem for a mixed-type second-order multidimensional equation of the first kind. We prove the unique solvability of this problem in a certain function class with the help of “ε-regularization”, a priori estimates, and successive approximation methods.
Preprint
In this paper it is proposed a very simple method for estimating the maximal operator in $L_1$. Using this method one can considerably improve the existing theorems on convergence almost-everywhere of eigenfunction expansions of an arbitrary elliptic differential operators with a point spectrum. In particular, it is obtained a new result on converg...
Preprint
Full-text available
In this paper the generalized localization principle for the spherical partial sums of the multiple Fourier series in the $L_2$ - class is proved, that is, if $f\in L_2(T^N)$ and $f=0$ on an open set $\Omega \subset T^N$, then it is shown that the spherical partial sums of this function converge to zero almost - everywhere on $\Omega$. It has been...
Article
We study the well-posedness of a linear inverse problem for a multidimensional mixed-type equation including the classical equations of elliptic, hyperbolic, and parabolic types as special cases. For this problem, using the “ε-regularization,” a priori estimate, and successive approximationmethods, we prove the existence and uniqueness theorems for...
Article
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В работе рассматриваются сферически симметричные непрерывные всплеск-разложения и вводится для них понятие средних Рисса. В классах $L_p$ без каких-либо ограничений на всплески, доказана справедливость обобщенной локализации для рассматриваемых разложений. Далее обобщенная локализация изучена для средних Рисса всплеск-разложений распределений из со...
Article
We obtain sufficient conditions for the Riesz means of spectral expansions converge to the function to be expanded.
Article
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One of the effective methods to find explicit solutions of differential equations is the method based on the operator representation of solutions. The essence of this method is to construct a series, whose members are the relevant iteration operators acting to some classes of sufficiently smooth functions. This method is widely used in the works of...
Article
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In this article, the capability of discrete wavelet transform (DWT) to discriminate tree species with different ages using airborne hyperspectral remote sensing is investigated. The performance of DWT is compared against commonly used traditional methods, i.e. original reflectance and first and second derivatives. The hyperspectral data are obtaine...
Article
Full-text available
In this article, the capability of discrete wavelet transform (DWT) to discriminate tree species with different ages using airborne hyperspectral remote sensing is investigated. The performance of DWT is compared against commonly used traditional methods, i.e. original reflectance and first and second derivatives. The hyperspectral data are obtaine...
Article
Full-text available
Discriminating tropical rainforest tree species is still a challenging task due to a variety of species with high spectral similarity and due to very limited studies conducted in this area. We are investigating the effect of discrete wavelet transform (DWT) on enhancing discrimination of tropical rainforest tree species. For this purpose, airborne...
Article
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In this work we investigate the Neumann boundary value problem in the unit ball for a non-homogeneous biharmonic equation. It is well known, that even for the Poisson equation this problem does not have a solution for an arbitrary smooth right hand side and boundary functions; it follows from the Green formula, that these given functions should sat...
Article
Full-text available
The processing of remotely sensed data includes compression, noise reduction, classification, feature extraction, change detection and any improvement associated with the problems at hand. In the literature, wavelet methods have been widely used for analysing remote sensing images and signals. The second-generation of wavelets, which is designed ba...
Article
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In this work the Neumann boundary value problem for a non-homogeneous polyharmonic equation is studied in a unit ball. Necessary and sufficient conditions for solvability of this problem are found. To do this we first reduce the Neumann problem to the Dirichlet problem for a different non-homogeneous polyharmonic equation and then use the Green fun...
Article
Almost-everywhere convergence of wavelet transforms of Lp -functions under minimal conditions on wavelets was proved by Rao et al. in 1994. However, results on convergence almost everywhere do not provide any information regarding the exceptional set (of Lebesgue measure zero), where convergence does not hold. We prove that if a wavelet ψ satisfies...
Article
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We study the behavior of Fourier integrals summed by the symbols of elliptic operators and pointwise convergence of Fourier inversion. We consider generalized localization principle which in classical L p spaces was investigated by Sjölin (1983), Carbery and Soria (1988, 1997) and Alimov (1993). Proceeding these studies, in this paper, we establi...
Conference Paper
Detection and mapping the impervious surface accurately is one of the important tasks in urban remote sensing. In this study, airborne hyperspectral data and Worldview-2 image were used to classify urban area .The main goal of this study are to compare the hyperspectral data and worldview 2 images and shows the potential of worldview 2 images for d...
Article
Cities are centers of human activity and more than half of the world's population live in metropolitan areas. Urban areas are characterized by a large variety of artificial and natural surface materials influencing ecological, climatic and energetic conditions. With advent of new sensors in remote sensing fields that capture the data in high spatia...
Article
The partial integrals of the N-fold Fourier integrals connected with elliptic polynomials (not necessarily homogeneous; principal part of which has a strictly convex level surface) are considered. It is proved that if a + s > (N - 1)/2 and ap = N then the Riesz means of the nonnegative order s of the N-fold Fourier integrals of continuous finite fu...
Article
Wavelet analysis is a universal and promising tool with very rich mathematical content and great potential for applications in various scientific fields, in particular, in signal (image) processing and the theory of differential equations. On the other hand distributions are widely used in these fields. And to apply wavelet analysis in these areas...
Article
The almost everywhere convergence of wavelets transforms of L p-functions under minimal conditions on wavelets is well known. But this result does not provide any information about the exceptional set (of Lebesgue measure zero), where convergence does not hold. In this paper, under slightly stronger conditions on wavelets, we prove convergence of w...
Article
We consider spectral expansions of functions from Nikol’skii classes H p a (ℝ N ), related to selfadjoint extensions of elliptic differential operators A(D) of order m in ℝ N . We construct a continuous function from Nikol’skii class with pa<N, such that the Riesz means of spectral expansion of which diverge at the origin. This result demonstrates...
Article
The partial integrals of the N-fold Fourier integrals connected with elliptic polynomials (with a strictly convex level surface) are considered. It is proved that if a + s > (N -1)/2 and ap = N, then the Riesz means of the nonnegative order s of the N-fold Fourier integrals of continuous finite functions from the Sobolev spaces Wpa (R ) converge un...
Article
It is well-known that only a single condition (called the admissibility condition) is sufficient for L2-convergence of multiple continuous wavelet transforms (MCWT). However known results suggest that to guarantee the pointwise convergence of MCWT for Lp-functions wavelets should vanish quite rapidly at infinity. In this article, we consider the cl...
Article
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In this paper we consider an initial-value problem for diffusion equation in three dimensional Euclidean space. The initial value is a piecewise smooth function. To solve this problem we apply Fourier transform method and since Fourier integrals of a piecewise smooth function do not converge everywhere, we make use of Riesz summation method.
Article
It is well known, that if N ≥ 3, then spherical partial sums of N-fold Fourier integrals (eigenfunction expansions of Laplace operator) of the characteristic function of the unit ball diverge at the origin. Note, here level surface of Laplace operator and the surface of discontinuity of the considered piecewise smooth function are both spheres. It...
Article
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In this paper we investigate almost-everywhere convergence properties of the Bochner–Riesz means of N-fold Fourier integrals under summation over domains bounded by the level surfaces of the elliptic polynomials. It is proved that if the order of the Bochner–Riesz means s⩾(N−1)(1/p−1/2), then the Bochner–Riesz means of a function f∈Lp(RN), 1⩽p⩽2 co...
Article
When n>2 it is well known that the spherical partial sums of n-fold Fourier integrals of a characteristic function of the ball D={x:|x|2<1} do not converge at the origin. In the mathematical literature this result is called “the Pinsky phenomenon”. In 1993 Pinsky established necessary and sufficient conditions for a piecewise smooth function, suppo...
Article
When n>2 it is well known that the spherical partial sums of n-fold Fourier integrals of the characteristic function of a ball diverge at the origin, because of the jump at the boundary of the ball. The relation between convergence properties of spherical partial sums and geometry of discontinuities of the function being expanded was investigated i...
Article
The theory of linear ordinary quasi-differential operators has been considered in Lebesgue locally integrable spaces on a single interval of the real line. Such spaces are not Banach spaces but can be considered as complete, locally convex, linear topological spaces where the topology is derived from a countable family of semi-norms. The first conj...
Article
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In this study we consider further analysis on the classification problem of linear second order partial differential equations with non-constant coefficients. The equations are produced by using convolution with odd or even functions. It is shown that the patent of classification of new equations is similar to the classification of the original equ...
Article
The eigenfunction expansions of an integer power of the Schrödinger operator in an arbitrary two-dimensional domain are considered. The convergence of the corresponding expansions of piecewise smooth functions is proved. When the dimension of the domain is greater than two, then it is well known that this result is not valid any more.
Article
For piecewise smooth functions of n variables, we prove the uniform Riesz summability of order s > (n − 3)/2 of their spectral expansions associated with an arbitrary elliptic operator with constant coefficients. For s = (n − 3)/2, the corresponding Riesz means are bounded.
Article
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We consider two forms of eigenfunction expansions associated with an arbitrary elliptic differential operator with constant coefficients and order m, that is the multiple Fourier series and integrals. For the multiple Fourier integrals, we prove the convergence of the Riesz means of order s > (N − 3)/2 of piecewise smooth functions of N ≥ 2 variabl...
Article
In the N-cube T N ={x∈ℝ N :-π≤x j ≤π}, consider the homogeneous elliptic differential operator an arbitrary order m A(D)=∑ |α|=m a α D α with constant coefficients. The operator is defined for functions from C ∞ (ℝ N ) that are 2π-periodic with respect to each argument. As is known, this operator is essentially self-adjoint (see, e.g., [Sh. A. Alim...
Article
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We show that spectral resolutions of differential vector-operators may be represented as a specific direct sum integral operator with a kernel written in terms of generalized vector-operator eigenfunctions. Then we prove that a generalized eigenfunction measurable with respect to the spectral parameter may be decomposed using a set of analytical de...
Article
In the present paper, we prove the uniform convergence and convergence in mean of the Riesz means of eigenfunction expansions associated with the Schrodinger operator with a singular po- tential satisfying the Stummel condition. This is the widest class of potentials suitable for the analysis of uniform convergence of eigenfunction expansions, sinc...
Article
The theory of ordinary linear quasi-differential expressions and operators has been extensively developed in integrable-square Hilbert spaces. There is also an extensive theory of ordinary linear differential expressions and operators in integrable-p Banach spaces. However, the basic definition of linear quasi-differential expressions involves Lebe...
Article
The basic objects of study in this article are functions of several variables which are periodic in each of these variables. We may assume (this assumption is not very restrictive) that the corresponding periods are the same and equal to 2π.

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Project
In this paper we consider an inverse problem for simultaneously determining the order of the Riemann-Liouville time fractional derivative and a source function in subdiffusion equations. Using the classical Fourier method, we prove the uniqueness and the existence theorem for this inverse problem.
Project
solve linear and nonlinear partial differential equations by integrals transforms