Synthesis of 9-Arylhexahydroacridine-1,8-diones Using Phosphate Fertilizers as Heterogeneous Catalysts

Russian Journal of Organic Chemistry - A new strategy has been proposed for the synthesis of 9-arylhexahydroacridine-1,8-diones by three-component condensation of aromatic aldehydes with...     

Geometrical inverse matrix approximation for least-squares problems and acceleration strategies

Numerical Algorithms - We extend the geometrical inverse approximation approach to the linear least-squares scenario. For that, we focus on the minimization of $1-\cos \limits (X(A^{T}A),I)$ ,...     

Nonlinear hybrid procedures and fixed point iterations

Let (x_n) and (?_n) be two vector sequences converging to a common limit. First, we shall define nonlinear hybrid procedures which consist of constructing a new vector sequence (y_n) with better convergence properties than (x_n) and (?_n). Then, this procedure is used for accelerating the convergence of a given sequence and applied to the construction of fixed point methods. New methods are derived. Finally, the connection between fixed point iterations and methods for the numerical integration of differential equations is also exploited. Numerical results are given.     

Dual path surface reconstruction in the H/Ni (110) system

Reconstruction of a Ni (110) surface under the influence of adsorbed hydrogen atoms can proceed in two different ways: Below 180 K a 2×1 lattice-gas structure with θ_H = 1.0 transforms cooperatively into a two-dimensional 1×2 structure by additional uptake of hydrogen up to θ_H = 1.5. At higher temperatures, activated local transformation into a more stable one-dimensional structure starts already at low coverages.     

An implicit preconditioning strategy for large-scale generalized Sylvester equations

Large-scale generalized Sylvester equations appear in several important applications. Although the involved operator is linear, solving them requires specialized techniques. Different numerical methods have been designed to solve them, including direct factorization methods suitable for small size problems, and Krylov-type iterative methods for large-scale problems. For these iterative schemes, preconditioning is always a difficult task that deserves to be addressed. We present and analyze an implicit preconditioning strategy specially designed for solving generalized Sylvester equations that uses a preconditioned residual direction at every iteration. The advantage is that the preconditioned direction is built implicitly, avoiding the explicit knowledge of the given matrices. Only the effect of the matrix-vector product with the given matrices is required. We present encouraging numerical experiments for a set of different problems coming from several applications.     

Multiparameter Schemes for Evolutionary Equations

Multiparameter extensions (MP) of (linear and nonlinear) descent methods have been proposed for the solution of finite dimensional time independent problems; these new methods are based on a different treatment of several blocks of components of the solution, basically via the substitution of a scalar relaxation by a (suitable) matricial relaxation. Similarly, the Nonlinear Galerkin Method (NLG), that stems from the dynamical system theory, propose to apply distinct temporal integration schemes to different sets of data scales when solving dissipative PDEs. In this paper, the algebraic similarity of Richardson iteration and Forward-Euler time integration is extended to new grounds through the expansion of the realm of MP methods to the field of the numerical integration of dissipative PDEs. The separation of the structures is realized by the utilization of hierarchical preconditioners in finite differences, which are conjugated to a MP temporal integration steeming from NLG theory. Numerical examples of fluid dynamics problems show the improved temporal stability of these new methods as compared to the classical ones.     

Incremental unknowns for solving nonlinear eigenvalue problems: New multiresolution methods

In this article, we present several numerical multilevel schemes for the solution of nonlinear eigenvalue problems. Using the Incremental Unknowns, we construct some generalization of the Marder and Weitzner method, which is well suited for the calculation of unstable solutions. The new methods that we present are based on a different treatment of the several structures appearing with the utilization of the hierarchical preconditioner. We illustrate the efficiency of the new methods with the calculation of unstable solutions of a reaction diffusion problem. © 1995 John Wiley & Sons, Inc.     

Existence,uniqueness, and numerical simulations of Föppl‐von Kármán equations for simply supported plate

In this paper, we consider the Föppl‐von Kàrmàn equations in the case of a simply supported thin plate. We introduce a nonlinear Gauss‐Seidel fixed point scheme which allows to obtain a constructive proof of the existence and the uniqueness, when a small nonzero source term is considered. Numerical simulations are given using finite elements approximation. We point out the important role of a parameter which allows to select situations in which a buckling phenomena is observed numerically.     

Hydrogen desorption from Ni sites on (110) CuNi surfaces

Hydrogen adsorption on Ni-rich (110) CuNi alloy surfaces has been studied by means of thermal desorption spectroscopy. After adsorption near room temperature the hydrogen desorption spectra exhibit a coverage dependence similar to that known from pure (110)Ni. Besides a slightly composition dependent desorption energy the alloy surfaces behave like a (110)Ni surface diluted by practically inert Cu. These results are compared to those reported by Yu Ling and Spicer.