Machine learning techniques to select variable stars

In order to perform a supervised classification of variable stars, we propose and evaluate a set of six features extracted from the magnitude density of the light curves. They are used to train automatic classification systems using state-of-the-art classifiers implemented in the R statistical computing environment. We find that random forests is the most successful method to select variables

Evaluación dimensional del riesgo percibido en el barrio la dulcera, municipio de pereira

La presente investigación se realizó en el marco del proyecto “Participación de las organizaciones sociales frente a la construcción de condiciones de riesgo como conflicto ambiental en un asentamiento de la cuenca del río Consota”, financiado a través de la convocatoria interna del Centro de Investigaciones y Extensión de la Universidad Tecnológica de Pereira en el 2004 – 2005. Este artículo intenta mostrar que cada agente social tiene una propia percepción del riesgo y los desastres, lo cual se traduce no sólo en actitudes y comportamientos prácticos, sino también en las decisiones que se toman respecto a una zona de riesgo

Evaluation of bleach-sedimentation for sterilising and concentrating Mycobacterium tuberculosis in sputum specimens

RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are.Abstract Background Bleach-sedimentation may improve microscopy for diagnosing tuberculosis by sterilising sputum and concentrating Mycobacterium tuberculosis. We studied gravity bleach-sedimentation effects on safety, sensitivity, speed and reliability of smear-microscopy. Methods This blinded, controlled study used sputum specimens (n = 72) from tuberculosis patients. Bleach concentrations and exposure times required to sterilise sputum (n = 31) were determined. In the light of these results, the performance of 5 gravity bleach-sedimentation techniques that sterilise sputum specimens (n = 16) were compared. The best-performing of these bleach-sedimentation techniques involved adding 1 volume of 5% bleach to 1 volume of sputum, shaking for 10-minutes, diluting in 8 volumes distilled water and sedimenting overnight before microscopy. This technique was further evaluated by comparing numbers of visible acid-fast bacilli, slide-reading speed and reliability for triplicate smears before versus after bleach-sedimentation of sputum specimens (n = 25). Triplicate smears were made to increase precision and were stained using the Ziehl-Neelsen method. Results M. tuberculosis in sputum was successfully sterilised by adding equal volumes of 15% bleach for 1-minute, 6% for 5-minutes or 3% for 20-minutes. Bleach-sedimentation significantly decreased the number of acid-fast bacilli visualised compared with conventional smears (geometric mean of acid-fast bacilli per 100 microscopy fields 166, 95%CI 68-406, versus 346, 95%CI 139-862, respectively; p = 0.02). Bleach-sedimentation diluted paucibacillary specimens less than specimens with higher concentrations of visible acid-fast bacilli (p = 0.02). Smears made from bleach-sedimented sputum were read more rapidly than conventional smears (9.6 versus 11.2 minutes, respectively, p = 0.03). Counting conventional acid-fast bacilli had high reliability (inter-observer agreement, r = 0.991) that was significantly reduced (p = 0.03) by bleach-sedimentation (to r = 0.707) because occasional strongly positive bleach-sedimented smears were misread as negative. Conclusions Gravity bleach-sedimentation improved laboratory safety by sterilising sputum but decreased the concentration of acid-fast bacilli visible on microscopy, especially for sputum specimens containing high concentrations of M. tuberculosis. Bleach-sedimentation allowed examination of more of each specimen in the time available but decreased the inter-observer reliability with which slides were read. Thus bleach-sedimentation effects vary depending upon specimen characteristics and whether microscopy was done for a specified time, or until a specified number of microscopy fields had been read. These findings provide an explanation for the contradictory results of previous studies.Peer Reviewe

Análisis espectroscópico de las estrellas κ Draconis y T Vulpéculae

En este trabajo se presentaran los resultados preliminares de la reducción y extracción de espectros de la estrella Be κ Dra y de la cefeida T Vul, obtenidos con el espectrógrafo Boller & Chievens del observatorio astronómico San pedro Martir (Instituto de Astronomía de la UNAM, México). El proceso de reducción y extracción de los espectros se realizó usando el software IRAF (Image Reduction and Analysis Facility). Estos espectros seran utilizados para obtener la composición química de las atmosferas de estas estrellas, su tipo espectral y temperatura efectiva, como parte de un trabajo de tesis para el nivel de pregrado, iniciado recientemente. Los resultados de esta investigación serán útiles en cuanto a la determinación de variabilidad espectroscópica, al compararlos con espectros de las mismas estrellas tomadas en el pasado, existentes en bases de datos

Estudio espectroscópico de las estrellas 12 vulpécula y Cu Virgins

En este trabajo se presentan los resultados preliminares del proceso de reducción realizado por bias y flat field para los espectros de la estrella 12 Vulpécula, obtenidos por el profesor Alejandro García de la universidad de los Andes, en el observatorio San Pedro Mártir (Instituto de Astronomía, UNAM, México), y de la estrella Cu Virgins, obtenidos por la profesora Beatriz Eugenia Sabogal en el Observatorio Astrofísico Guillermo Haro (Sonora, México). Esta es una parte de un estudio espectroscópico que se realiza dentro de un trabajo de tesis para nivel de pregrado iniciado recientemente, por medio del cual se determinen diferencias espectroscópicas entre ambas estrellas, así como sus composiciones químicas

Searching for Be star candidates within large databases

Long time surveys yield many light curves among their byproducts, useful to identify candidate Be stars that can be confirmed by spectroscopic follow-ups. We present in this work different techniques we have used to find Be star candidates in the Galaxy, the Magellanic Clouds and the OGLE-IV Gaia South Ecliptic Pole Field