Thermomechanical simulation of an industrial quenching process applied to a centrifugal pump impeller

En este trabajo se estudia el comportamiento termomecánico durante el tratamiento térmico de templado de un rodete de una bomba centrífuga fabricada en fundición blanca. El análisis se realiza mediante una formulación termomecánica acoplada discretizada mediante el método de elementos finitos. La respuesta del material se describe por medio de un modelo termoplástico que incorpora efectos de cambio de fase. En particular, se presenta el proceso de templado desde la austenización hasta el enfriamiento del rodete con la finalidad de evaluar la ocurrencia de falla en la pieza al final del proceso. Para la determinación del daño mecánico se comparan 3 criterios diferentes escritos en función de las tensiones y de las deformaciones plásticas desarrolladas durante el proceso. El estudio se enfoca en 2 tipos de configuración de rodetes, con 4 y 5 álabes, donde la primera de ellas experimenta fractura en el proceso industrial de producción. Los resultados numéricos obtenidos en este trabajo confirman que la metodología propuesta permite predecir de manera realista las posibilidades de falla para los 2 casos analizados.The thermomechanical behaviour during the quenching process of a centrifugal pump impeller made of white iron is studied in this work. The analysis is carried out using a coupled thermomechanical formulation that is discretized within the context of the finite element method. The material response is described by means of a thermoplastic model that includes phase-change effects. In particular, a heat treatment consisting in cooling from the austenizing temperature is presented with the aim of assessing the failure occurrence of the part at the end of the process. Three different criteria written in terms of the stresses and plastic deformations developed during the cooling stage are specifically compared to evaluate the final mechanical damage. The study is focused on two impeller configurations, with 4 and 5 blades, where fracture occurs in the former during its industrial production. The numerical results obtained in this work for these two cases confirm that the proposed methodology realistically predicts their failure possibilities.Peer Reviewe

Capacitance Measurements for Subcell Characterization in Multijunction Solar Cells.

On this paper we present an alternative way to analyze de electronic properties of each subcell from the complete device. By illuminating the cell with light sources which energy is near one of the subcell bandgaps, it is possible to “erase” the presence of such subcell on the CV curve. The main advantages of this technique are that it is not destructive, it can be measured on the complete cell so can be easily implemented as a diagnostic technique for controlling electronic deviations

Spectral properties of a generalized chGUE

We consider a generalized chiral Gaussian Unitary Ensemble (chGUE) based on a weak confining potential. We study the spectral correlations close to the origin in the thermodynamic limit. We show that for eigenvalues separated up to the mean level spacing the spectral correlations coincide with those of chGUE. Beyond this point, the spectrum is described by an oscillating number variance centered around a constant value. We argue that the origin of such a rigid spectrum is due to the breakdown of the translational invariance of the spectral kernel in the bulk of the spectrum. Finally, we compare our results with the ones obtained from a critical chGUE recently reported in the literature. We conclude that our generalized chGUE does not belong to the same class of universality as the above mentioned model.Comment: 12 pages, 3 figure

Scintillator-based diagnostic for fast ion loss measurements on DIII-D

A new scintillator-based fast ion loss detector has been installed on DIII-D with the time response 100 kHz needed to study energetic ion losses induced by Alfvén eigenmodes and other MHD instabilities. Based on the design used on ASDEX Upgrade, the diagnostic measures the pitch angle and gyroradius of ion losses based on the position of the ions striking the two-dimensional scintillator. For fast time response measurements, a beam splitter and fiberoptics couple a portion of the scintillator light to a photomultiplier. Reverse orbit following techniques trace the lost ions to their possible origin within the plasma. Initial DIII-D results showing prompt losses and energetic ion loss due to MHD instabilities are discussed. © 2010 American Institute of Physics.U.S. Department of Energy DE-FC02-04ER54698, SC-G903402, DE-FG03-94ER5427

Estimación del coeficiente de dispersión longitudinal en ríos de la región central de Argentina utilizando ADCP

RESUMENEl coeficiente de dispersión longitudinal (D) es un parámetro fundamental requerido para predecir el transporte de contaminantes en un curso fluvial. La determinación experimental de D mediante técnicas convencionales como, por ejemplo, ensayo de trazadores, requieren una gran inversión en planificación, personal técnico y análisis posterior, y los resultados son únicamente válidos para las condiciones de flujo presentes en el momento de realizar la medición. En los ríos de la zona central de Argentina, los cuales presentan una gran variabilidad estacional de caudales, se hace muy costosa la determinación de este coeficiente D con ensayo de trazadores, ya que se deberían evaluar un amplio rango de condiciones de flujo existentes. Debido a esto, se utilizan fórmulas empíricas, desarrolladas por diversos autores, que permiten estimar el coeficiente de dispersión longitudinal de acuerdo con parámetros hidráulicos globales (profundidad, velocidad media del flujo, ancho del río, etc.). Sin embargo, estas expresiones presentan una gran variación en sus resultados y solo funcionan adecuadamente en ríos con características similares a los que fueron ajustadas. Es por ello que, en este trabajo, se estima, de manera alternativa, el coeficiente D mediante una caracterización hidrodinámica detallada, realizada en sistema fluvial con un perfilador de corriente acústico Doppler (ADCP). Se adoptó, como sistema fluvial de estudio, el río Carcarañá que escurre por la región central de Argentina (provincias de Córdoba y Santa Fe). A partir de las estimaciones realizadas, se evalúa D en los principales tributarios del sistema fluvial y se comparan los resultados con los obtenidos de la aplicación de las formulas empíricas y con ábacos desarrollados sobre la base de valores reportados para diferentes ríos del mundo.ABSTRACTThe Longitudinal dispersion coefficient (D) is a fundamental parameter required to predict the transport of pollutants in rivers. The experimental determinations of D by conventional techniques, such as tracers test, require a large investment in planning, staff and subsequent analysis, and the results are only valid for the flow conditions present during the test. Using tracers test to estimate D is very expensive in rivers of central region of Argentina which have a large seasonal variability of flow discharges (with maximum values one or two orders of magnitude larger than the mean values), as tracers test should be performed for a wide range of flow conditions. Thus, water quality modelers use empirical formulas developed by various authors estimating the longitudinal dispersion coefficient based on global hydraulic parameters (mean flow depth and velocity, river width, etc.). However, these formulas show large scatter in the results and only perform properly in rivers with similar characteristics that were calibrated. On that basis, an alternative estimation of the coefficient of longitudinal dispersion is performed in this paper through a detailed experimental hydrodynamic characterization performed in a fluvial system with an Acoustic Doppler Current Profiler (ADCP). The Carcarañá River, flowing through the Cordoba and Santa Fe provinces in Argentina, has been selected as a study system. The results of this paper include the values o longitudinal dispersion coefficients in different streams of the analyzed fluvial system which are the compared with values estimated using empirical formulas and plots developed using data from different river systems around the world

Alineación frontal de la rodilla. Concepto y determinación de la posición neutra en el vivo

Se estudiaron 28 rodillas asintomáticas con objeto de confirmar en el vivo la existencia de movilidad mediolateral, tomando como posición neutra aquella en la que el contacto articular se produce simultáneamente en ambos compartimentos. Hemos observado, que la interlínea articular en posición neutra es sensiblemente mas amplia en el compartimento lateral, en proporción de 1,3 a 1 respecto del medial. Se estudió la rodilla en diversas actitudes posturales durante la estación bípeda, hallando que al colocar la extremidad inferior en adducción de la cadera la altura de la interlínea aumenta significativamente en el compartimento lateral, alcanzando una proporción de 1,9 a 1 respecto del medial. Es decir, que en distintas actitudes fisiológicas, la amplitud de la interlínea articular de la rodilla y por tanto el ángulo fémorotibial, son variables, lo cual es compatible con la hipótesis del «Contacto articular alternativo». Creemos que la existencia de cierta movilidad mediolateral fisiológica en la rodilla, puede tener trascendencia en el diseño de la geometría frontal de las prótesis, así como en la realización de las técnicas radiográficas y su valoración

General Relativity as an Attractor in Scalar-Tensor Stochastic Inflation

Quantum fluctuations of scalar fields during inflation could determine the very large-scale structure of the universe. In the case of general scalar-tensor gravity theories these fluctuations lead to the diffusion of fundamental constants like the Planck mass and the effective Brans--Dicke parameter, $\omega$. In the particular case of Brans--Dicke gravity, where $\omega$ is constant, this leads to runaway solutions with infinitely large values of the Planck mass. However, in a theory with variable $\omega$ we find stationary probability distributions with a finite value of the Planck mass peaked at exponentially large values of $\omega$ after inflation. We conclude that general relativity is an attractor during the quantum diffusion of the fields.Comment: LaTeX (with RevTex) 11 pages, 2 uuencoded figures appended, also available on WWW via http://star.maps.susx.ac.uk/index.htm

Real-time phase-shift detection of the surface plasmon resonance

We investigate a method to directly measure the phase of a laser beam reflected from a metallic film after excitation of surface plasmon polaritons. This method permits real time access to the phase information, it increases the possible speed of data acquisition, and it may thus prove useful for increasing the sensitivity of surface plasmon based sensors