Numerical studies on new techniques for gravitational wave extraction and binary black hole simulations

This dissertation presents numerical studies of gravitational waves produced by black holes in two scenarios: perturbations of a single black hole, and the collision of a binary pair. Their detection plays a crucial roll in further testing General Relativity and opens a whole new field of observational astronomy. First, a technique called Cauchy--perturbative matching is revisited in one dimension through the use of new numerical methods, such as high order finite difference operators, constraint-preserving boundary conditions and, most important, a multi-domain decomposition (also referred to as multi-patch, or multi-block approach). These methods are then used to numerically solve the fully non-linear three-dimensional Einstein vacuum equations representing a non-rotating distorted black hole. In combination with a generalization of the Regge-Wheeler-Zerilli formalism, we quantify the effect of the background choice in the wave extraction techniques. It is found that a systematic error is introduced at finite distances. Furthermore, such error is found to be larger than those due to numerical discretization. Subsequently, the first simulations ever of binary black holes with a finite-difference multi-domain approach are presented. The case is one in which the black holes orbit for about twelve cycles before merging. The salient features of this multi-domain approach are: i) the complexity of the problem scales linearly with the size of the computational domain, ii) excellent scaling, in both weak and strong senses, for several thousand processors. As a next step, binary black hole simulations from inspiral to merger and ringdown are performed using a new technique, turduckening, and a standard finite difference, adaptive mesh-refinement code. The computed gravitational waveforms are compared to those obtained through evolution of the same exact initial configuration but with a pseudo-spectral collocation code. Both the gravitational waves extracted at finite locations and their extrapolated values to null infinity are compared. Finally, a numerical study of generic second order perturbations of Schwarzschild black holes is presented using a new gauge invariant high order perturbative formalism. A study of the self-coupling of first order modes and the resulting radiated energy, in particular its dependence on the type of initial perturbation, is detailed

Risk factor assessment to anticipate performance in the National Developmental Screening Test in children from a disadvantaged area

Introducción. Detectar menores en riesgo de no pasar la Prueba Nacional de Pesquisa del Desarrollo, combinando prevalencias de sospechosos de padecer trastornos inaparentes del desarrollo (STID) y factores de riesgo (FR) asociados, permitiría ahorrar recursos. Objetivos. 1. Estimar la prevalencia de STID. 2. Identificar FR asociados. 3. Evaluar tres métodos, desarrollados a partir de los FR hallados, para proponer un procedimiento prepesquisa. Materiales y métodos. Se administró la Prueba Nacional de Pesquisa del Desarrollo a 60 menores, de entre 2 y 4 años, de un área socioeconómicamente desfavorecida de Puerto Madryn, elegidos de modo aleatorio. Se evaluaron 24 variables biológicas y socioambientales para identificar posibles FR mediante los enfoques bivariado y multivariado. La probabilidad de no pasar la pesquisa se estimó de la siguiente manera: 1. construyendo un modelo multivariado de regresión logística; 2. relacionando el número de FR presentes en cada menor con el porcentaje de quienes no pasaron la prueba; 3. integrando los métodos anteriores. Resultados. La prevalencia de STID fue 55,0% (IC 95%: 42,4%-67,6%). Mediante el enfoque bivariado, se identificaron preliminarmente seis FR. Tres de ellos, instrucción materna, número de controles en salud y puntajes Z-talla/edad, más edad materna, fueron incluidos en el modelo de regresión logística con mayor poder explicativo. El tercero de los métodos evaluados presentó las mayores sensibilidad y especificidad (85% y 79%, respectivamente). Conclusiones. La prevalencia estimada de STID fue cuatro veces superior a la del estándar nacional. Se identificaron siete FR. La integración del análisis del efecto acumulativo de los FR y un modelo multivariado proveen una sólida base para el desarrollo de un procedimiento prepesquisa sensible, específico y práctico en zonas desfavorecidas socioeconómicamente.Introduction. Identifying children at risk of failing the National Developmental Screening Test by combining prevalences of children suspected of having inapparent developmental disorders (IDDs) and associated risk factors (RFs) would allow to save resources. Objectives.1. To estimate the prevalence of children suspected of having IDDs. 2. To identify associated RFs. 3. To assess three methods developed based on observed RFs and propose a pre-screening procedure. Materials and Methods. The National Developmental Screening Test was administered to 60 randomly selected children aged between 2 and 4 years old from a socioeconomically disadvantaged area from Puerto Madryn. Twenty-four biological and socioenvironmental outcome measures were assessed in order to identify potential RFs using bivariate and multivariate analyses. The likelihood of failing the screening test was estimated as follows: 1. a multivariate logistic regression model was developed; 2. a relationship was established between the number of RFs present in each child and the percentage of children who failed the test; 3. these two methods were combined. Results. The prevalence of children suspected of having IDDs was 55.0% (95% confidence interval: 42.4%-67.6%). Six RFs were initially identified using the bivariate approach. Three of them (maternal education, number of health checkups and Z scores for height-for-age, and maternal age) were included in the logistic regression model, which has a greater explanatory power. The third method included in the assessment showed greater sensitivity and specificity (85% and 79%, respectively). Conclusions. The estimated prevalence of children suspected of having IDDs was four times higher than the national standards. Seven RFs were identified. Combining the analysis of risk factor accumulation and a multivariate model provides a firm basis for developing a sensitive, specific and practical pre-screening procedure for socioeconomically disadvantaged areas.Fil: Montes, Alejandro. Hospital Provincial Dr. Andrés Isola; ArgentinaFil: Pazos, Gustavo Enrique. Universidad Nacional de la Patagonia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin

Orbiting binary black hole evolutions with a multipatch high order finite-difference approach

We present numerical simulations of orbiting black holes for around twelve cycles, using a high-order multipatch approach. Unlike some other approaches, the computational speed scales almost perfectly for thousands of processors. Multipatch methods are an alternative to AMR (adaptive mesh refinement), with benefits of simplicity and better scaling for improving the resolution in the wave zone. The results presented here pave the way for multipatch evolutions of black hole-neutron star and neutron star-neutron star binaries, where high resolution grids are needed to resolve details of the matter flow

Simulación del flujo de viento sobre el territorio de Guatemala utilizando un modelo climático regional

Se presenta un análisis de de circulación del viento en la vecindad de la superficie terrestre, para una región centrada alrededor de Guatemala. Para tal fin se utilizó el modelo climático regional (RegCM), con el caul se simuló la dinámica atmosférica sobre dicha región durante todo el 2016. El propósito del estudio es obtener la variación de mesoescala (decenas de kilómetros) del campo de velocidad del viento. Se puede observar que a medida que la resolución se incrementa se obtiene una representación más precisa de los detalles y características de la topografía del terreno, la cual influye en los patrones de circulación del viento a escalas de pocos kilómetros. Con una resolución fina de 2 km es posible observar zonas de flujo intenso de viento sobre la superficie; como en Palín, Escuintla. También se logra ver la presencia de patrones de circulación diurna que son producto del ciclo diario de calentamiento del terreno debido al sol y el consecuente enfriamiento durante la noche. Este es el primer reporte de una línea de estudio en donde se planea analizar las características climáticas propias de la región guatemalteca

DoME: A Deterministic Technique for Equation Development and Symbolic Regression

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] Based on a solid mathematical background, this paper proposes a method for Symbolic Regression that enables the extraction of mathematical expressions from a dataset. Contrary to other approaches, such as Genetic Programming, the proposed method is deterministic and, consequently, does not require the creation of a population of initial solutions. Instead, a simple expression is grown until it fits the data. This method has been compared with four well-known Symbolic Regression techniques with a large number of datasets. As a result, on average, the proposed method returns better performance than the other techniques, with the advantage of returning mathematical expressions that can be easily used by different systems. Additionally, this method makes it possible to establish a threshold at the complexity of the expressions generated, i.e., the system can return mathematical expressions that are easily analyzed by the user, as opposed to other techniques that return very large expressions.This study is partially supported by Instituto de Salud Carlos III, grant number PI17/01826 (Collaborative Project in Genomic Data Integration (CICLOGEN) funded by the Instituto de Salud Carlos III from the Spanish National Plan for Scientific and Technical Research and Innovation 2013–2016 and the European Regional Development Funds (FEDER)—“A way to build Europe”. It was also partially supported by different grants and projects from the Xunta de Galicia [ED431D 2017/23; ED431D 2017/16; ED431G/01; ED431C 2018/49; IN845D-2020/03]. The authors thank the CyTED, Spain and each National Organism for Science and Technology for funding the IBEROBDIA project (P918PTE0409). In this regard, Spain specifically thanks the Ministry of Economy and Competitiveness for the financial support for this project through the State Program of I+D+I Oriented to the Challenges of Society 2017–2020 (International Joint Programming 2018), project (PCI2018-093284). Funding for open access charge: Universidade da Coruña/CISUGXunta de Galicia; ED431D 2017/23Xunta de Galicia; ED431D 2017/16Xunta de Galicia; ED431G/01Xunta de Galicia; ED431C 2018/49Xunta de Galicia; IN845D-2020/0