Experimental creation of chainlike beams and investigation of their structure

The effect of the Gaussian beam width on the focusing properties of the chainlike Gaussian beam formed upon diffraction of laser radiation on a binary amplitude mask is studied. It is found that a decrease in the Gaussian beam width increases the sizes of focal spots and the focus depth, decreases the intensity in the focuses, and does not affect the focus position.     

Prevailing effects of interference or diffraction by multiple apertures

The effects of interference and diffraction produced by a bidimensional structure composed of multiple and identical apertures are studied. Such effects are competitive during the propagation, that is, in some planes the interference effects are more visible, while in others prevail the diffraction ones. Using the number of Fresnel zones, the spatial domains where the interference or diffraction effects prevail are defined and parameterized. Simulation and experimental results are further introduced to verify the proposed method.     

Disposable Graphite Foil Based Electrodes and Their Application in Pharmaceutical Analysis

This paper explores a new source of graphite for working electrodes, which presents advantages such as low electrical resistance, good flexibility, favorable mechanical performance, versatility to design electrodes in almost any size and very low cost. The new electrodes were investigated in batch electrochemical cells as associated with flow injection analysis systems. Cyclic voltammetry, stripping voltammetry, and amperometry associated with flow injection analysis techniques were applied for the determination of ascorbic acid, zinc and paracetamol in pharmaceutical formulations, respectively. Well‐established analytical methods were applied for comparison purposes. The results herein demonstrate the potential of graphite foils as working electrodes in different electroanalytical methods, offering the possibility of producing disposable sensors for routine applications.     

On the efficiency and quality of numerical solutions in CFD problems using the interface strip preconditioner for domain decomposition methods

In this paper, some pathologies found for simple tests solved by means of preconditioned full iterative schemes are presented. According to these results (Sections 4 and 5), the accuracy deterioration observed should be considered as a warning for the final application given to these solutions. Even though it is well known that full iterative solvers are not the best selection for comparison, they were chosen because they are widely used by the computational fluid dynamic (CFD) community for a diversity of complex fluid dynamics applications. FEM simulated solutions are compared with analytical solutions or measured data for problems that have been considered as ‘benchmarks’ in the CFD literature. For this purpose, the study of the solution obtained via parallelized iterative methods that have been extensively used (e.g. conjugate gradients (CG), GMRes global iteration and its variants, ‘overlapping’ and ‘non‐overlapping’ additive Schwarz domain decomposition schemes) in CFD computations and those obtained with the new interface strip preconditioner (J. Comput. Meth. Sci. Engng 2003; Int. J. Numer. Meth. Engng 2005; 62 (13):1873–1894) for the Schur complement method is carried out. The idea is to present the new solver as an alternative to obtain more accurate and faster solutions in the context of monolithic and non‐monolithic schemes applied to a internal/external viscous compressible/incompressible flows around bodies of complex shapes. Therefore, the target of this work is to show how the reliability of CFD codes is affected by the solver selection and why domain decomposition methods should be viewed not only as a more efficient strategy, but also to guarantee the solution quality. Copyright © 2006 John Wiley & Sons, Ltd.     

Lupeol

The title compound [systematic name: 3β‐lup‐20(29)‐en‐3‐ol], C₃₀H₅₀O, was isolated from the leaves of Garcinia brasiliensis (common name: bacupari; a member of the Guttiferae family) and has been shown to have many useful medicinal and biological properties. The lupeol molecule consists of four six‐membered rings (adopting chair conformations) and one five‐membered ring (with an envelope conformation), all fused in trans fashion. Lupeol is isomorphic with the pentacyclic triterpene 3β,30‐dihydroxylup‐20(29)‐ene, which differs from lupeol due to the presence of an additional hydroxy group. The crystal packing is stabilized by van der Waals interactions and intermolecular O—H...O hydrogen bonds, giving rise to an infinite helical chain along the c axis.     

Markovian networks in labour markets

In labour theory, equilibrium is described in terms of mean variables, which is limited and can be misleading. In this article, we model the labour market as a closed Markovian network and find the steady state distribution of unemployment and advertised vacancies. We determine the stochastic equilibrium distribution for two different types of matching functions and allow for both unemployed and on the job search. In general cases, where probabilities cannot be analytically computed, we find restrictions that must hold for all matching processes. Our modelling is applicable to most economic markets with frictions.     

Two variational approaches for domain decomposition problems solved by SGBEM with nonconforming discretizations

Two original approaches for the solution of elastic boundary value problems with domain decomposition (DDBVP) using the symmetric Galerkin boundary element method (SGBEM) are presented. Each approach is based on a variational principle, a difference between them consisting in the treatment of the coupling conditions which connect the solutions through an interface. The computer codes developed are able to deal with curved interfaces in a domain decomposition problem discretized by nonmatching meshes of linear elements along the interfaces. The effectiveness of the methods is documented by a numerically solved example. The text was submitted by the authors in English.     

Gradient Estimates for the Ground State¶Schrödinger Eigenfunction and Applications

Let Ω be a planar convex domain which is symmetric with respect to each coordinate axes. In this paper we give a simple and very short proof, based on the maximum principle, of the sharp lower bound for the spectral gap of the Dirichlet Laplacian in Ω. Received: 21 May 2001 / Accepted: 29 June 2001     

Information encryption through dyadic permutations

Dyadic displacements of an image can be interpreted as a special type of permutations of its pixel addresses. Owing to this property, they can be used to encrypt the information contained in the pictures without information loss or damage. The information recovery can be performed successfully by using dyadic correlations.