98 research outputs found

    Understanding Galaxy Formation and Evolution

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    The old dream of integrating into one the study of micro and macrocosmos is now a reality. Cosmology, astrophysics, and particle physics intersect in a scenario (but still not a theory) of cosmic structure formation and evolution called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to explain the origin of galaxies. In these lecture notes, I first present a review of the main galaxy properties, highlighting the questions that any theory of galaxy formation should explain. Then, the cosmological framework and the main aspects of primordial perturbation generation and evolution are pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation, presenting a review on LCDM halo assembling and properties, and on the main candidates for non-baryonic dark matter. It is shown how the nature of elemental particles can influence on the features of galaxies and their systems. Finally, the complex processes of baryon dissipation inside the non-linearly evolving CDM halos, formation of disks and spheroids, and transformation of gas into stars are briefly described, remarking on the possibility of a few driving factors and parameters able to explain the main body of galaxy properties. A summary and a discussion of some of the issues and open problems of the LCDM paradigm are given in the final part of these notes.Comment: 50 pages, 10 low-resolution figures (for normal-resolution, DOWNLOAD THE PAPER (PDF, 1.9 Mb) FROM http://www.astroscu.unam.mx/~avila/avila.pdf). Lectures given at the IV Mexican School of Astrophysics, July 18-25, 2005 (submitted to the Editors on March 15, 2006

    Toward an internally consistent astronomical distance scale

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    Accurate astronomical distance determination is crucial for all fields in astrophysics, from Galactic to cosmological scales. Despite, or perhaps because of, significant efforts to determine accurate distances, using a wide range of methods, tracers, and techniques, an internally consistent astronomical distance framework has not yet been established. We review current efforts to homogenize the Local Group's distance framework, with particular emphasis on the potential of RR Lyrae stars as distance indicators, and attempt to extend this in an internally consistent manner to cosmological distances. Calibration based on Type Ia supernovae and distance determinations based on gravitational lensing represent particularly promising approaches. We provide a positive outlook to improvements to the status quo expected from future surveys, missions, and facilities. Astronomical distance determination has clearly reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press (chapter 8 of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Age

    On the spin distributions of Λ\LambdaCDM haloes

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    We used merger trees realizations, predicted by the extended Press-Schechter theory, in order to study the growth of angular momentum of dark matter haloes. Our results showed that: 1) The spin parameter λâ€Č\lambda' resulting from the above method, is an increasing function of the present day mass of the halo. The mean value of λâ€Č\lambda' varies from 0.0343 to 0.0484 for haloes with present day masses in the range of 109h−1M⊙ 10^9\mathrm{h}^{-1}M_{\odot} to 1014h−1M⊙10^{14}\mathrm{h}^{-1}M_{\odot}. 2)The distribution of λâ€Č\lambda' is close to a log-normal, but, as it is already found in the results of N-body simulations, the match is not satisfactory at the tails of the distribution. A new analytical formula that approximates the results much more satisfactorily is presented. 3) The distribution of the values of λâ€Č\lambda' depends only weakly on the redshift. 4) The spin parameter of an halo depends on the number of recent major mergers. Specifically the spin parameter is an increasing function of this number.Comment: 10 pages, 8 figure

    Testing dark energy beyond the cosmological constant barrier

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    Although well motivated from theoretical arguments, the cosmological constant \emph{barrier}, i.e., the imposition that the equation-of-state parameter of dark energy (ωx≡px/ρx\omega_x \equiv p_x/\rho_x) is ≄−1\geq -1, seems to introduce bias in the parameter determination from statistical analyses of observational data. In this regard, \emph{phantom} dark energy or \emph{superquintessence} has been proposed in which the usual imposition ω≄−1\omega \geq -1 is relaxed. Here, we study possible observational limits to the \emph{phantom} behavior of the dark energy from recent distance estimates of galaxy clusters obtained from interferometric measurements of the Sunyaev-Zel'dovich effect/X-ray observations, Type Ia supernova data and CMB measurements. We find that there is much \emph{observationally} acceptable parameter space beyond the Λ\Lambda \emph{barrier}, thus opening the possibility of existence of more exotic forms of energy in the Universe.Comment: 5 pages, 5 figures, to appear in Phys. Rev.

    A method for comparing multiple imputation techniques: A case study on the U.S. national COVID cohort collaborative

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    Healthcare datasets obtained from Electronic Health Records have proven to be extremely useful for assessing associations between patients’ predictors and outcomes of interest. However, these datasets often suffer from missing values in a high proportion of cases, whose removal may introduce severe bias. Several multiple imputation algorithms have been proposed to attempt to recover the missing information under an assumed missingness mechanism. Each algorithm presents strengths and weaknesses, and there is currently no consensus on which multiple imputation algorithm works best in a given scenario. Furthermore, the selection of each algorithm's parameters and data-related modeling choices are also both crucial and challenging. In this paper we propose a novel framework to numerically evaluate strategies for handling missing data in the context of statistical analysis, with a particular focus on multiple imputation techniques. We demonstrate the feasibility of our approach on a large cohort of type-2 diabetes patients provided by the National COVID Cohort Collaborative (N3C) Enclave, where we explored the influence of various patient characteristics on outcomes related to COVID-19. Our analysis included classic multiple imputation techniques as well as simple complete-case Inverse Probability Weighted models. Extensive experiments show that our approach can effectively highlight the most promising and performant missing-data handling strategy for our case study. Moreover, our methodology allowed a better understanding of the behavior of the different models and of how it changed as we modified their parameters. Our method is general and can be applied to different research fields and on datasets containing heterogeneous types

    Deliberação online em consultas pĂșblicas? O caso da assembleia legislativa de Minas Gerais

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    Este artigo busca analisar uma consulta pĂșblica online sobre reforma polĂ­tica promovida em 2011 pela Assembleia Legislativa de Minas Gerais. Embasado pela teoria deliberacionista, o estudo de 752 posts guiou-se pela discussĂŁo de seis tĂłpicos: (1) inclusividade; (2) provimento de razĂ”es; (3) reciprocidade; (4) respeito mĂștuo; (5) orientação para o bem comum; e (6) articulação entre arenas. Os resultados indicam: (1) uma sobrerepresentação de participantes masculinos e oriundos da RegiĂŁo Metropolitana de Belo Horizonte, embora nĂŁo tenha havido concentração de posts em alguns comentadores; (2) o predomĂ­nio de posts on topic e que apresentam justificativas para as posiçÔes advogadas; (3) Ă­ndices muito baixos de reciprocidade entre posts e de uso de marcadores de interatividade; (4) graus muito elevados de respeito; (5) diferentes formas de ligação das justificativas a ideias de bem comum; (6) o baixo impacto decisĂłrio e a conexĂŁo com outras arenas da esfera pĂșblica, destacando-se a relação com uma matĂ©ria publicada em jornal de grande circulação. Os achados sĂŁo ambivalentes para os defensores da deliberação, indicando baixa probabilidade de deliberação interna ao fĂłrum, mas algum potencial deliberativo quando se adotam lentes mais amplas. Os cruzamentos entre variĂĄveis sugerem que as pessoas tendem a prover mais justificativas em discussĂ”es mais controversas, embora tendam a dialogar menos nesses casos. Assim, a hipĂłtese da preferĂȘncia por conversas entre like-minded encontra respaldo nos dados analisados

    Thermal Evolution and Magnetic Field Generation in Terrestrial Planets and Satellites

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    Bio-analytical Assay Methods used in Therapeutic Drug Monitoring of Antiretroviral Drugs-A Review

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