When, what and how image transformation techniques should be used to reduce error in Particle Image Velocimetry data?

© 2019 Elsevier Ltd Particle Image Velocimetry is commonly used to compute velocity fields in several areas including fluid mechanics, hydraulics and geophysics. However, acquired images often contain deformations caused either by camera lenses or placement. In this work the most popular digital transformation methods used to remove/reduce these deformations are benchmarked and suggestions tailoring specific transformations to different types of deformations are made. This article also shows the reduction of the error associated to the first and second order statistics, in the case of two-dimensional Particle Image Velocimetry, when the transformation techniques are applied to the computed velocity fields, and not the raw images, a common option in available commercial software

Advances in interior point methods and column generation

In this thesis we study how to efficiently combine the column generation technique (CG) and interior point methods (IPMs) for solving the relaxation of a selection of integer programming problems. In order to obtain an efficient method a change in the column generation technique and a new reoptimization strategy for a primal-dual interior point method are proposed. It is well-known that the standard column generation technique suffers from unstable behaviour due to the use of optimal dual solutions that are extreme points of the restricted master problem (RMP). This unstable behaviour slows down column generation so variations of the standard technique which rely on interior points of the dual feasible set of the RMP have been proposed in the literature. Among these techniques, there is the primal-dual column generation method (PDCGM) which relies on sub-optimal and well-centred dual solutions. This technique dynamically adjusts the column generation tolerance as the method approaches optimality. Also, it relies on the notion of the symmetric neighbourhood of the central path so sub-optimal and well-centred solutions are obtained. We provide a thorough theoretical analysis that guarantees the convergence of the primal-dual approach even though sub-optimal solutions are used in the course of the algorithm. Additionally, we present a comprehensive computational study of the solution of linear relaxed formulations obtained after applying the Dantzig-Wolfe decomposition principle to the cutting stock problem (CSP), the vehicle routing problem with time windows (VRPTW), and the capacitated lot sizing problem with setup times (CLSPST). We compare the performance of the PDCGM with the standard column generation method (SCGM) and the analytic centre cutting planning method (ACCPM). Overall, the PDCGM achieves the best performance when compared to the SCGM and the ACCPM when solving challenging instances from a column generation perspective. One important characteristic of this column generation strategy is that no speci c tuning is necessary and the algorithm poses the same level of difficulty as standard column generation method. The natural stabilization available in the PDCGM due to the use of sub-optimal well-centred interior point solutions is a very attractive feature of this method. Moreover, the larger the instance, the better is the relative performance of the PDCGM in terms of column generation iterations and CPU time. The second part of this thesis is concerned with the development of a new warmstarting strategy for the PDCGM. It is well known that taking advantage of the previously solved RMP could lead to important savings in solving the modified RMP. However, this is still an open question for applications arising in an integer optimization context and the PDCGM. Despite the current warmstarting strategy in the PDCGM working well in practice, it does not guarantee full feasibility restorations nor considers the quality of the warmstarted iterate after new columns are added. The main motivation of the design of the new warmstarting strategy presented in this thesis is to close this theoretical gap. Under suitable assumptions, the warmstarting procedure proposed in this thesis restores primal and dual feasibilities after the addition of new columns in one step. The direction is determined so that the modi cation of small components at a particular solution is not large. Additionally, the strategy enables control over the new duality gap by considering an expanded symmetric neighbourhood of the central path. As observed from our computational experiments solving CSP and VRPTW, one can conclude that the warmstarting strategies for the PDCGM are useful when dense columns are added to the RMP (CSP), since they consistently reduce the CPU time and also the number of iterations required to solve the RMPs on average. On the other hand, when sparse columns are added (VRPTW), the coldstart used by the interior point solver HOPDM becomes very efficient so warmstarting does not make the task of solving the RMPs any easier

Rubén Darío y su aproximación al mundo oriental y árabe

A study of the presence of Oriental and particularly Arabic culture in Rubén Darío’s works leads to a consideration of important matters such as the books which were part of the poet’s cultural formation and his permanent desire for innovative language. For this reason, Darío uses texts on the Orient written by French authors, and is also inspired by historical texts and timeless works such as The Arabian Nights. He realises that by modifying the content and style dominant in Spanish poetry of his time, and by giving prominence to autonomous images, he can give his writing its function.Para un estudio del tema de lo oriental y en especial de la presencia árabe en la obra de Rubén Darío, hay que abordar puntos fundamentales como la formación cultural del nicaragüense a través de sus primeras lecturas y, más tarde, su intención permanente de innovar el lenguaje. Para lograr este objetivo se sirvió de textos sobre el Oriente escritos por franceses, y también encontró inspiración en textos históricos y en obras duraderas en el tiempo como Las mil y una noches. Se dio cuenta de que modificando contenido y estilo usados hasta ese momento en la poesía española, y ensalzando imágenes dueñas de su propia acción, él puede llegar a darle una función al verbo

A source time reversal method for seismicity induced by mining

In this work, we present a modified Time-Reversal Mirror (TRM) Method, called Source Time Reversal (STR), to find the spatial distribution of a seismic source induced by mining activity. This methodology is based on a known full description of the temporal dependence of the source, the Duhamel's principle, and the time-reverse property of the wave equation. We also provide an error estimate of the reconstruction when the measurements are acquired over the entire boundary, and we show experimentally the influence of measuring on a subdomain of the boundary. Numerical results indicate that the methodology is able to recover continuous and discontinuous sources, and it remains stable for partial boundary measurements

A Rapid, Empirical Method for Detection and Estimation of Outlier Frames in Particle Imaging Velocimetry Data using Proper Orthogonal Decomposition

This paper develops a method for detection and removal of outlier images from digital Particle Image Velocimetry data using Proper Orthogonal De-composition (POD). The outlier is isolated in the leading POD modes, removed and a replacement value re-estimated. The method is used to estimate and replace whole images within the sequence. This is particularly useful, if a single PIV image is suddenly heavily contaminated with background noise, or to estimate a dropped frame within a sequence. The technique is tested on a synthetic dataset that permits the effective acquisition frequency to be varied systematically, before application to flow field frames obtained from a large-eddy simulation. As expected, outlier re-estimation becomes more difficult when the integral time scale for the flow is long relative to the sampling period. However, the method provides a systematic improvement in predicting frames compared to interpolating from neighbouring(1) frames

Representando el espacio: experiencias de movilidad cotidiana a partir de la confección de mapas en La Araucanía, Chile

El presente artículo entrega una síntesis de diversas experiencias de representación social y visual respecto al papel del ferrocarril como medio de transporte utilizado cotidianamente en las actividades desarrolladas por algunos habitantes de La Araucanía. A partir de una metodología cualitativa, fue posible simbolizar las experiencias de viaje de los usuarios del ferrocarril, explorando en la connotación social que tiene un medio de transporte público respecto a la organización de las rutinas que son desarrolladas en los lugares de frecuentación cotidiana. Al momento de analizar los mapas elaborados por los sujetos de estudio, se identificaron espacios altamente significativos respecto al entorno, los cuales representan diversas dinámicas de movilidad a partir de los tiempos de viaje, lugares de tránsito y rutinas cotidianas

Prevalencia y susceptibilidad a antimicrobianos de Mycoplasma hominis y Ureaplasma spp. en flujos vaginales de un grupo de mujeres atendidas en el consultorio de salud “José Dionisio Astaburuaga” de Talca

64 p.Desde su descubrimiento en 1898, los micoplasmas han ido aumentando su importancia en la investigación clínica, debido a que se relacionan con enfermedades agudas y crónicas, en particular Mycoplasma hominis y Ureaplasma sp. responsables de una serie de patologías del tracto urogenital, pudiendo favorecer el desarrollo de vaginosis bacteriana, enfermedad inflamatoria pélvica, uretritis, cervicitis y cistitis, entre otros. La información existente en cuanto a la prevalencia de este tipo de microorganismos y su susceptibilidad a antibióticos es escasa. El objetivo de la presente investigación fue determinar la prevalencia y susceptibilidad a antimicrobianos de Mycoplasma hominis y Ureaplasma sp. aislados de flujos vaginales de un grupo de mujeres atendidas en el consultorio de salud “José Dionisio Astaburuaga” de la ciudad de Talca, Chile. Se realizó un estudio en una población de 92 mujeres sin límite de edad, atendidas en el servicio de ginecología y obstetricia del consultorio en cuestión. Los criterios de inclusión utilizados fueron: ser sexualmente activas y presentar inflamación en el cérvix (cervicitis). Las muestras fueron procesadas a través del kit IST 2 de BioMeriux. De las 92 mujeres participantes del estudio, solo 64 cumplieron con los criterios de inclusión, siendo la prevalencia total de infección por alguno o ambos microorganismos de 76,6%, presentando mayor frecuencia el aislamiento de Ureaplasma sp. Las edades de las pacientes fluctuaron entre los 15 y los 63 años de edad, presentándose una mayor frecuencia de infección entre los 20 y 24 años. En cuanto a la sensibilidad frente a antibióticos, todas las cepas de Mycoplasma hominis y Ureaplasma sp. aisladas de forma independiente fueron sensibles a doxiciclina, tetraciclina y pristinamicina, con una elevada resistencia frente a ciprofloxacino y eritromicina. Por otra parte, en aquellos cultivos mixtos, se presentó una resistencia absoluta o intermedia frente a todos los antibióticos incluidos en este estudio. Algunas pacientes, presentaron una co- infección de Mycoplasma hominis y/o Ureaplasma sp. con otros tipos de microorganismos como Gardnerella vaginalis, Cándida albicans y Trichomonas vaginalis. En Chile, se ha reportado una frecuencia de aislamiento de Mycoplasma hominis de un 26% y de un 52% de Ureaplasma urealyticum, valores inferiores a los resultados de este estudio (34,4% y 71,9% respectivamente), la susceptibilidad a antimicrobianos mostrada por los micoplasmas fue similar a otros estudios realizados en Chile