Eigenfrequencies of a tube bundle immersed in a fluid

In this paper we study a simplified version of a mathematical model that describes the eigenfrequencies and eigenmotions of a coupled system consisting of a set of tubes (or a tube bundle) immersed in an incompressible perfect fluid. The fluid is assumed to be contained in a rectangular cavity, and the tubes are assumed to be identical, and periodically distributed in the cavity. The mathematical model that governs this physical problem is an elliptic differential eigenvalue problem consisting of the Laplace equation with a nonlocal boundary condition on the holes, and a homogeneous Neumann boundary condition on the boundary of the cavity. In the simplified model that we study in this paper, the Neumann condition is replaced by a periodic boundary condition. Our goal in studying this simple version is to derive some basic properties of the problem that could serve as a guide to envisage similar properties for the original model. In practical situations, this kind of problem needs to be solved for tube bundles containing a very large number of tubes. Then the numerical analysis of these problems is in practice very expensive. Several approaches to overcome this difficulty have been proposed in the last years using homogenization techniques. Alternatively, we propose in this paper an approach that consists in obtaining an explicit decomposition of the problem into a finite family of subproblems, which can be easily solved numerically. Our study is based on a generalized notion of periodic function, and on a decomposition theorem for periodic functions that we introduce in the paper. Our results rely on the theory of almost periodic functions, and they provide a simple numerical method for obtaining approximations of all the eigenvalues of the problem for any number of tubes in the cavity. We also discuss a numerical example.     

The Distributional Hankel Transform of δ(k)(m2×P

In this note we give a sense to certain kinds of n-dimensional distributional Hankel transforms of the Dirac measure δ^(k)(m² + P). The most important result is the interchange formula between the product and the convolution of the Hankel transform of δ^(k)(m² + P).     

Amazonian lignocellulosic materials-V

A plate-agar technique for fungal screening was applied to evaluate the xylanolytic activities of 18Penicillium janthinellum and 10Aspergillus sydowi species from the Amazon region. In order to compare these genera with those of other regions, oneAspergillus sp., one P.janthinellum, and 12 unknown genera from the southern region of Chile were studied. From these fungi strain,A. sydowi (56 strain) (25.2 IU/mL),P. janthinellum (671 strain) (47.3 IU/mL) from Amazonia,P. janthinellum (X4Z2 strain) (9.5 IU/mL), and anAspergillus sp. (X2M1 strain) (33.3 IU/mL) from the southern region of Chile were identified.     

On the conformal geometry of transverse Riemann–Lorentz manifolds

Physical reasons suggested in [J.B. Hartle, S.W. Hawking, Wave function of the universe, Phys. Rev. D41 (1990) 1815–1834] for the Quantum Gravity Problem lead us to study type-changing metrics on a manifold. The most interesting cases are Transverse Riemann–Lorentz Manifolds. Here we study the conformal geometry of such manifolds.     

On the product of distributions with coincident point singularities

In this paper we generalize the result obtained by Gonzáles Domínguez, Scarfiello and Fisher (A. Gonzáles Domínguez and R. Scarfiello, Rev. Un. Mat. Argentina, Volumen de Homenaje a Beppo Levi (1956) 58–67; B. Fisher, Proc. Cambridge Philos. Soc. 72 (1972) 201–204). This result can be used in quantum field theory for the evaluation of products of propagators of the fields. With this new result we obtain the product . As a physical example, we evaluate the selfenergy Green function of a massless scalar field.     

Efficient polymers in conjunction with membranes to remove As(V) generated in situ by electrocatalytic oxidation

Electrochemistry and ultrafiltration membrane methods (electro‐oxidation and liquid phase polymer based retention technique LPR, respectively) were coupled to remove As(III) inorganic species from aqueous solutions. Our main objective was to achieve an efficient extraction of arsenic species by associating a polymer‐assisted liquid phase retention procedure, based on the As(V) adsorption properties of cationic water‐soluble polymers, with the electrocatalytic oxidation process of As(III) into its more easily removable analog As(V). The exhaustive oxidation of As(III)–As(V) was readily performed in high yield at iridium oxide film modified carbon felt electrodes in the presence of different water‐soluble poly(quaternary ammonium) salts acting also as supporting electrolyte. The progress of the macro‐scale oxidation of As(III)–As(V) was followed using iridium oxide film modified glassy carbon electrodes. Finally, a study on arsenic retention by LPR‐technique performed on fully oxidized solutions of arsenic, showing that complete (100%) retention of the arsenic could be achieved using a 20:1 polyammonium:As(III) mole ratio. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of spatial competition on the diversity of a quasispecies

The diversity harbored by populations of RNA viruses results from high mutation rates, as well as from the characteristics of the environment where they evolve. By means of a simple model for structured quasispecies, we quantify how competition for space among phenotypic types shapes their distribution at the mutation-selection equilibrium. We introduce a general framework to treat this problem and relate mutation rate and competition strength to the quasispecies composition. For diffusion limited competition, diversity typically increases and the asymptotic growth rate of the population diminishes as diffusion decreases. Limited mobility confers a relative advantage to worse competitors. The stationary state is characterized by an over-production of viral particles. Empirical data allow an estimation of mutation rates compatible with the diversity observed in viral populations infecting cellular monolayers.     

Tailoring the electroactive area of carbon screen-printed electrodes by simple activation steps towards rutin determination

Journal of Solid State Electrochemistry - Screen-printed electrodes (SPEs) have the advantage of being considered electrochemical cells that can be implemented in portable sensor applications. With...