排序方式: 共有39条查询结果,搜索用时 31 毫秒
31.
The novel helerocycles 5-methyl-1,3,2-benzodithiazoles (7) were prepared in 30–50% yields from toluene-3,4-dithiol (6) and appropriate primary amines in the presence of 2 equivalents of triethylamine under high-dilution conditions. These compounds, which exhibit one reversible oxidation potential around +0.90 V vs. SCE, serve as a model study in the quest of synthesizing a new donor, the “boron-nitrogen” analog of tetrathiafulvalene (BNTTF). 相似文献
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Donatella Donatelli 《Journal of Differential Equations》2008,245(5):1356-1385
A model for the dynamics of gaseous stars is introduced and formulated by the Navier-Stokes-Poisson system for compressible, reacting gases. The combined quasineutral and inviscid limit of the Navier-Stokes-Poisson system in the torus Tn is investigated. The convergence of the Navier-Stokes-Poisson system to the incompressible Euler equations is proven for the global weak solution and for the case of general initial data. 相似文献
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Marco Donatelli Claudio Estatico Stefano Serra-Capizzano 《Journal of Computational and Applied Mathematics》2007
In this paper we are concerned with deblurring problems in the case of multiple images coming from the Large Binocular Telescope (an important example of telescope of interferometric type). For this problem, we are interested in checking the role of the boundary conditions in the quality of the reconstructed image. In particular, we will consider reflective and anti-reflective boundary conditions and the re-blurring idea. The results of the proposed combinations are quite satisfactory when compared with classical Dirichlet or periodic boundary conditions, especially when increasing the number of images acquired by the LBT. This behavior is confirmed by a wide numerical experimentation. 相似文献
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Donatella Donatelli Pierangelo Marcati 《Transactions of the American Mathematical Society》2004,356(5):2093-2121
In this paper we investigate the diffusive zero-relaxation limit of the following multi-D semilinear hyperbolic system in pseudodifferential form:
We analyze the singular convergence, as , in the case which leads to a limit system of parabolic type. The analysis is carried out by using the following steps:
We analyze the singular convergence, as , in the case which leads to a limit system of parabolic type. The analysis is carried out by using the following steps:
- (i)
- We single out algebraic ``structure conditions' on the full system, motivated by formal asymptotics, by some examples of discrete velocity models in kinetic theories.
- (ii)
- We deduce ``energy estimates ', uniformly in , by assuming the existence of a symmetrizer having the so-called block structure and by assuming ``dissipativity conditions' on .
- (iii)
- We assume a Kawashima type condition and perform the convergence analysis by using generalizations of compensated compactness due to Tartar and Gérard.
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Preconditioned HSS method for large multilevel block Toeplitz linear systems via the notion of matrix‐valued symbol 下载免费PDF全文
Marco Donatelli Carlo Garoni Mariarosa Mazza Stefano Serra‐Capizzano Debora Sesana 《Numerical Linear Algebra with Applications》2016,23(1):83-119
We perform a spectral analysis of the preconditioned Hermitian/skew‐Hermitian splitting (PHSS) method applied to multilevel block Toeplitz linear systems in which the coefficient matrix Tn(f) is associated with a Lebesgue integrable matrix‐valued function f. When the preconditioner is chosen as a Hermitian positive definite multilevel block Toeplitz matrix Tn(g), the resulting sequence of PHSS iteration matrices Mn belongs to the generalized locally Toeplitz class. In this case, we are able to compute the symbol ?(f,g) describing the asymptotic eigenvalue distribution of Mnwhen n→∞ and the matrix size diverges. By minimizing the infinity norm of the spectral radius of the symbol ?(f,g), we are also able to identify effective PHSS preconditioners Tn(g) for the matrix Tn(f). A number of numerical experiments are presented and commented, showing that the theoretical results are confirmed and that the spectral analysis leads to efficient PHSS methods. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Mariarosa Mazza Marco Donatelli Carla Manni Hendrik Speleers 《Numerical Linear Algebra with Applications》2023,30(1):e2462
In this work, we focus on a fractional differential equation in Riesz form discretized by a polynomial B-spline collocation method. For an arbitrary polynomial degree , we show that the resulting coefficient matrices possess a Toeplitz-like structure. We investigate their spectral properties via their symbol and we prove that, like for second order differential problems, the given matrices are ill-conditioned both in the low and high frequencies for large . More precisely, in the fractional scenario the symbol vanishes at 0 with order , the fractional derivative order that ranges from 1 to 2, and it decays exponentially to zero at for increasing at a rate that becomes faster as approaches 1. This translates into a mitigated conditioning in the low frequencies and into a deterioration in the high frequencies when compared to second order problems. Furthermore, the derivation of the symbol reveals another similarity of our problem with a classical diffusion problem. Since the entries of the coefficient matrices are defined as evaluations of fractional derivatives of the B-spline basis at the collocation points, we are able to express the central entries of the coefficient matrix as inner products of two fractional derivatives of cardinal B-splines. Finally, we perform a numerical study of the approximation behavior of polynomial B-spline collocation. This study suggests that, in line with nonfractional diffusion problems, the approximation order for smooth solutions in the fractional case is for even , and for odd . 相似文献
39.
Marco Donatelli 《PAMM》2011,11(1):745-746
Local Fourier analysis (LFA) is a classical tool for proving convergence theorems for multigrid methods (MGMs). Analogously, the symbols of the involved matrices are studied to prove convergence results for MGMs for Toeplitz matrices. We show that in the case of elliptic partial differential equations (PDEs) with constant coefficients, the two different approaches lead to an equivalent optimality condition. We argue that the analysis for Toeplitz matrices is an algebraic generalization of the LFA which allows to deal not only with differential problems but also, e.g., with integral problems. A class of grid transfer operators related to the B-spline's refinement equation is discussed as well. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献