Browsing by Author "Bravo, M."

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    Delfin plus plus : A Delaunay based algorithm for finding 3D polyhedral voids in galaxy surveys
    (2023) Guidotti, V.; Alonso, R.; Bravo, M.; Hitschfeld, N.; Marinello, G.; Hervias, C.; Campusano, L. E.
    Delfin++ (Delaunay Edge Void Finder) is a simple and time-efficient algorithm, with a single input variable, designed to find cosmological voids within a 3-dimensional distribution of galaxies by characterizing them as polyhedral regions from a Delaunay tessellation. Two density metrics are defined and used to search for density minima and construct polyhedra that represent the underdense zones. A density threshold is used to define the limit above which a galaxy will not be considered part of a void. This threshold is commonly defined as 0.2n over bar , where n over bar is the mean point density of the sample, whereas the values used in this work range from 0.2n over bar to 0.33n over bar . The algorithm is applied to artificial data, with different density contrasts, as well as to galaxy data from SDSS DR10. The detected voids are compared with voids that have been produced through the application of VIDE. Our algorithm detects roundish underdense regions in the galaxy samples, with differences and overlaps compared to the VIDE algorithm's results. Closer agreement is revealed when the edge length density metric is used over large galaxy samples, allowing for the detection of up to 90% of the largest VIDE voids. We measure ellipticities of Delfin++ detected voids and find that their distribution is shifted towards smaller values in comparison with VIDE's distribution, and with predictions from an analytical model. The voids found with Delfin++ are not intended to generate a catalog, but rather represent a proof of concept of a simpler algorithm or with fewer rules for further calibration and future production of a final catalog. Delfin++ performance tests suggest that enhanced characterization of voids can be achieved through (i) choice of other density threshold values, and (ii) early recognition and rejection of deformed polyhedra induced by missing data.& COPY; 2023 Elsevier B.V. All rights reserved.
  • Thumbnail Image
    Item
    Maximal isometric muscle strength values obtained By hand-held dynamometry in children between 6 and 15 years of age
    (2017) Bravo, M.; Banados, P.; Domínguez de Landa, María Angélica; Muñoz Avendaño, Karin Trinidad; Escobar Henríquez, Raúl
  • Thumbnail Image
    Item
    Overestimation of abortion in Colombia and other Latin American countries
    (2012) Koch, E.; Bravo, M.; Gatica, S.; Stecher, J. F.; Aracena, P.; Valenzuela, S.; Ahlers, I.
    Recently, the Guttmacher Institute estimated a number of 400,400 clandestine abortions for Colombia. Because of the strong implications that such brief could have in different areas of interest, a full revision of the methodology of estimation was performed. The methodology used by the Guttmacher Institute was as follows: first, the authors estimated the losses from spontaneous and induced abortions from the opinion of 289 subjects who work in an equal number of Colombian health institutions through the opinion survey entitled "Health Facilities Survey". Subsequently, an expansive multiplier (x3, x4, x5, etc.) was applied to the numbers obtained by this survey that also emerges from a subjective opinion of another 102 respondents of the "Health Professional Survey" selected by convenience. There is no objective data based on real vital events, the whole estimate is based on imagining/numbers underlying mere opinions. Even as public opinion survey, the sampling technique introduced serious selection bias in the gathering of information. Valid epidemiological methods using standardized rates, choosing the paradigmatic cases of Chile and Spain as standard populations, it was observed that Guttmacher Institute methodology overestimates more than 9 times the complications due to induced abortion in hospital discharges and more than 18 times the total number of induced abortions. In other Latin American countries where the same methodology was applied including Argentina, Brazil, Chile, Mexico, Peru, Guatemala, and Dominican Republic, the number of induced abortions was also largely overestimated. These results call for caution with this type of reports that alarm public opinion.
  • Thumbnail Image
    Item
    Synthesis of citrophilus mealybug sex pheromone using chrysanthemol extracted from Pyrethrum (Tanacetum cinerariifolium)
    (2019) Bergmann, J.; Tapia, J.; Bravo, M.; Zaviezo Palacios, Tania; Flores, M. F.