Removal of ammonia by immobilizaed Nitrosomonas europaea in a biotrickling filter packed with polyurethane foam

[Abstract] A chemolithoautrotrophic microorganism Nitrosomonas europaea has been utilized to remove gaseous ammonia in a biotrickling filter packed with polyurethane foam. The optimal pH for removing was 7.5 and the biological removal efficiency was zero at pH 6.5. Empty bed residence time of 150, 100, 50, 25, 20, 11 and 5 seconds were tested; the removal efficiency was of 100% in all range for a constant load of 8 gN.m-3.h-1. The critical elimination capacity was 270 gN.m-3.h-1 while the nitrite concentration was below of 100 mM (EBRT of 11 second, pH 7.5-7.6). Therefore, these results demonstrate that is possible to reach a high removal of ammonia using polyurethane foam, as solid support for Nitrosomonas europaea, and a biotrickling filter system

Building initial models of rotating white dwarfs with SPH

A general procedure to build self-gravitational, rotating equilibrium structures with the Smoothed Particle Hydrodynamics (SPH) technique does not exist. In particular, obtaining stable rotating configurations for white dwarf (WD) stars is currently a major drawback of many astrophysical simulations. Rotating WDs with low internal temperatures are connected with both, explosive and implosive scenarios such as type Ia supernova explosions or neutron stars formation. Simulations of these events with SPH codes demand stable enough particle configurations as initial models. In this work we have developed and tested a relaxation method to obtain equilibrium configurations of rotating WDs. This method is straightforward and takes advantage of the excellent mass and angular momentum conservation properties of the SPH technique. Although we focus on rigid rotation and its potential applications to several Type Ia supernova scenarios, we also show that our proposal is also able to provide good initial models in differential rotation, which has the potential to benefit many other types of simulations where rotation plays a capital role, like disk evolution and stellar formation.Peer ReviewedPostprint (published version

Application of piecewise-linear switched-capacitor circuits for random number generation

An unconventional application of switched-capacitor (SC) circuits is discussed. A systematic method for the design of piecewise-linear (PL) parasitic-insensitive SC chaotic discrete maps is given. A simple circuit which generates a random one-bit digital sequence is reported. Simulation results show that the random behavior is not significantly altered by large (about 5%) variations in the values of the design parameters, which makes monolithic implementation feasible. Simulation results and layout for a 2- mu m double-metal CMOS prototype are included

Relajación de problemas de control en los coeficientes con un funcional dependiendo del gradiente

Se considera un problema de diseño ´optimo consistente en mezclar dos materiales (eléctricos o térmicos) anisótropos de tal forma que se inimice un funcional coste dependiente del gradiente de la función estado. En general, este tipo de problemas no admite solución, lo que obliga a introducir una formulación relajada. Mostramos en este trabajo como esta relajación puede ser obtenida usando materiales compuestos, construidos por homogeneización, y realizando una determinada extensión del funcional coste a estos nuevos materiales. Esta extensión admite una representación integral. Nuestros resultados contienen en particular los obtenidos por otros autores en el caso de materiales isótropos

Relaxation of a control problem in the coefficients with a functional of quadratic growth in the gradient

We study an optimal design problem consisting in mixing two anisotropic (electric or thermal) materials in order to minimize a functional depending on the gradient of the state. It is known that this type of problem has no solution in general, and then it is necessary to introduce a relaxed formulation. Here we prove that this relaxation is obtained by using composite materials, is constructed by homogenization, and takes a particular extension of the cost functional to these new materials. We obtain an integral representation of this relaxed cost functional. Besides, we show that our results contain some previous results obtained by other authors for isotropic materials.Ministerio de Educación y CienciaJunta de Andalucí

Homogenization of very thin elastic reticulated structures

This work is devoted to the homogenization of the anisotropic, linearized elasticity system posed on thin reticulated structures involving several parameters. We show that the result depends on the relative size of the parameters. In every case, we obtain a limit problem where both the microscopic and macroscopic scales appear together. From this problem, we get an asymptotic development which gives an approximation in L2 of the displacements and the linearized strain tensor.Ministerio de Ciencia y Tecnologí

Optimality conditions for nonconvex multistate control problems in the coefficients

The purpose of this paper is to attain some optimality conditions for the identification of a diffusion matrix (material) under several restrictions. Assuming that the set of such diffusion matrices is closed for the H-convergence, we give a method to obtain admissible directions which applies to a not-necessarily convex control set. Our results permit obtaining the diffusion matrix from the state functions.Dirección General de Investigación (Ministerio de Ciencia y Tecnología)Junta de Andalucí

Smoothed particle hydrodynamics: checking a tensor approach to calculating gradients

Postprint (published version

Homogenization and corrector for the wave equation with discontinuous coefficients in time

In this paper we analyze the homogenization of the wave equation with bounded variation coefficients in time, generalizing the classical result, which assumes Lipschitz-continuity. We start showing a general existence and uniqueness result for a general sort of hyperbolic equations. Then, we obtain our homogenization result comparing the solution of a sequence of wave equations to the solution of a sequence of elliptic ones. We conclude the paper making an analysis of the corrector. Firstly, we obtain a corrector result assuming that the derivative of the coefficients in the time variable is equicontinuous. This result was known for non-time dependent coefficients. After, we show, with a counterexample, that the regularity hypothesis for the corrector theorem is optimal in the sense that it does not hold if the time derivative of the coefficients is just bounded

A corrector for a wave problem with periodic coefficients in a 1D bounded domain

We consider a wave problem posed in a bounded open interval of R, where the coefficients, the initial conditions and the right-hand side are highly oscillating, periodic in the space variable and almost periodic in the time one. Our purpose is to find not only the corresponding limit equation but a corrector, i.e. a strong approximation in the H1 topology, which for the wave equation is known to be non-local. In a previous paper we have studied this problem in the whole RN, here we consider the case of a bounded domain in dimension one. Thus the novelty in this paper is the analysis of the boundary conditions.Ministerio de Economía y Competitivida