Polydispersity Effects in the Dynamics and Stability of Bubbling Flows

The occurrence of swarms of small bubbles in a variety of industrial systems enhances their performance. However, the effects that size polydispersity may produce on the stability of kinematic waves, the gain factor, mean bubble velocity, kinematic and dynamic wave velocities is, to our knowledge, not yet well established. We found that size polydispersity enhances the stability of a bubble column by a factor of about 23% as a function of frequency and for a particular type of bubble column. In this way our model predicts effects that might be verified experimentally but this, however, remain to be assessed. Our results reinforce the point of view advocated in this work in the sense that a description of a bubble column based on the concept of randomness of a bubble cloud and average properties of the fluid motion, may be a useful approach that has not been exploited in engineering systems.Comment: 11 pages, 2 figures, presented at the 3rd NEXT-SigmaPhi International Conference, 13-18 August, 2005, Kolymbari, Cret

Long-Range Order and Dynamic Structure Factor of a Nematic under a Thermal Gradient

We use a fluctuating hydrodynamic approach to calculate the orientation fluctuations correlation functions of a thermotropic nematic liquid crystal in a nonequilibrium state induced by a stationay heat flux. Since in this nonequilibrium stationary state the hydrodynamic fluctuations evolve on three widely separated times scales, we use a time-scale perturbation procedure in order to partially diagonalize the hydrodynamic matrix. The wave number and frequency dependence of these orientation correlation functions is evaluated and their explicit functional form on position is also calculated analytically in and out of equilibrium. We show that for both states these correlactions are long-ranged. This result shows that indeed, even in equilibrium there is long-range orientational order in the nematic, consistently with the well known properties of these systems.We also calculate the dynamic structure of the fluid in both states for a geometry consistent with light scattering experiments experiments. We find that as with isotropic simple fluids, the external temperature gradient introduces an asymmetry in the spectrum shifting its maximum by an amount proportional to the magnitude of the gradient. This effect may be of the order of 7 per cent. Also, the width at half height may decrease by a factor of about 10 per cent. Since to our knowledge there are no experimental results available in the literature to compare with, the predictions of our model calculation remains to be assessed.Comment: 11 pages, 3 figures, presented at the 3rd NEXT-SigmaPhi International Conference (13-18 August 2005, Kolymbari CRETE

Examining the structure of ideas of reference in clinical and community samples

Aims: This study addresses the psychometric properties of a Spanish validation of the REF scale of ideas of reference (IRs) in detecting and following at-risk mental states and psychosis. Methods: A total of 9447 participants were distributed in three groups: 676 patients with various diagnoses-154 with psychotic disorders, 6291 youths aged 11 to 20, and 2480 adult participants aged 21 to 84. Results: Youths had higher scores than adults on IRs, observing a progressive decrease and stabilization in the twenties. Exploratory factor analysis provided a structure for the overall IRs score, with five first-order dimensions and one second-order dimension. Confirmatory factor analysis supported the structure with excellent fit. The REF scale was invariant across sex and samples. The internal consistency of the complete scale was excellent and acceptable across the five first-order factors. Strong relationships were found with the positive dimension of the community assessment of psychic experience-42, as well as with aberrant salience. Low and moderate relationships were found with public self-consciousness, anxiety, and depression. Youths and patients diagnosed with schizophrenia and other psychotic disorders had a high mean IRs frequency. Male sex, greater age (among the adults), and the "causal explanations", "Songs, newspapers, books" and laughing and commenting" REF subscales showed predictive power in the diagnostic categories of schizophrenia and other psychotic disorders

Equation of state of hard oblate ellipsoids by replica exchange Monte Carlo

We implemented the replica exchange Monte Carlo technique to produce the equation of state of hard 1:5 aspect-ratio oblate ellipsoids for a wide density range. For this purpose, we considered the analytical approximation of the overlap distance given by Bern and Pechukas and the exact numerical solution given by Perram and Wertheim. For both cases we capture the expected isotropic-nematic transition at low densities and a nematic-crystal transition at larger densities. For the exact case, these transitions occur at the volume fraction 0.341, and in the interval $0.584-0.605$, respectively.Comment: 4 pages, 2 figure

Computationally efficient min-max MPC

2005 IFAC 16th Triennial World Congress, Prague, Czech RepublicMin-Max MPC (MMMPC) controllers (Campo and Morari, 1987) suffer from a great computational burden that is often circumvented by using upper bounds of the worst possible case of a performance index. These upper bounds are usually computed by means of LMI techniques. In this paper a more efficient approach is shown. This paper proposes a computationally efficient MMMPC control strategy in which the worst case cost is approximated by an upper bound which can be easily computed using simple matrix operations. This implies that the algorithm can be coded easily even in non mathematical oriented programming languages such as those found in industrial embedded control hardware. Simulation examples are given in the paper

El polen de Poaceae en la atmósfera de Lugo y su relación con los parámetros meteorológicos (1999-2001)

. El polen de Poaceae en la atmósfera de Lugo y su relación con los parámetros meteorológicos (1999-2001). Se han estudiado las concentraciones de polen de Poaceae presente en la atmósfera de la ciudad de Lugo durante 3 años (1999-2001). Para ello se ha utilizado un captador volumétrico tipo Hirst, modelo Lanzoni VPPS-2000. El polen de Poaceae es el más abundante y su porcentaje frente al total de polen anual es de un 38-40%. La cantidad total de polen anual es de 8.400 granos como resultado de la media de los tres años de estudio, con un período de polinización durante los meses de Junio y Julio. A lo largo del día los máximos de concentración tienen lugar durante la tarde. Se ha realizado un análisis de correlación con los principales parámetros meteorológicos, siendo la temperatura máxima la variable que presentó el coeficiente más elevado. La suma acumulada de la temperatura máxima y la regresión múltiple integrando la temperatura máxima y las concentraciones de polen del día anterior como estimadores, resultaron métodos válidos y complementarios para realizar la predicción del inicio del periodo de polinización y de las concentraciones medias diarias que se alcanzan durante el periodo de polinización principal respectivament

Explosive Disintegration of a Massive Young Stellar System in Orion

Young massive stars in the center of crowded star clusters are expected to undergo close dynamical encounters that could lead to energetic, explosive events. However, there has so far never been clear observational evidence of such a remarkable phenomenon. We here report new interferometric observations made with the Submillimeter Array (SMA) that indicate the well known enigmatic wide-angle outflow located in the Orion BN/KL star-forming region to have been produced by such a violent explosion during the disruption of a massive young stellar system, and that this was caused by a close dynamical interaction about 500 years ago. This outflow thus belongs to a totally different family of molecular flows which is not related to the classical bipolar flows that are generated by stars during their formation process. Our molecular data allow us to create a 3D view of the debris flow and to link this directly to the well known Orion H$_2$ "fingers" farther outComment: Accepted by ApJ Letters The 3D movie can be found in: ftp://ftp.mpifr-bonn.mpg.de/outgoing/lzapata/movie.gi

A new proof of the higher-order superintegrability of a noncentral oscillator with inversely quadratic nonlinearities

The superintegrability of a rational harmonic oscillator (non-central harmonic oscillator with rational ratio of frequencies) with non-linear "centrifugal" terms is studied. In the first part, the system is directly studied in the Euclidean plane; the existence of higher-order superintegrability (integrals of motion of higher order than 2 in the momenta) is proved by introducing a deformation in the quadratic complex equation of the linear system. The constants of motion of the nonlinear system are explicitly obtained. In the second part, the inverse problem is analyzed in the general case of $n$ degrees of freedom; starting with a general Hamiltonian $H$, and introducing appropriate conditions for obtaining superintegrability, the particular "centrifugal" nonlinearities are obtained.Comment: 16 page