32 research outputs found
La desigualdad de Penrose luminosa y la versión para capas delgadas en Minkowski
No full text[ES]El objetivo de esta tesis doctoral es estudiar la desigualdad de Penrose en el caso luminoso, es decir,
aquellos casos en que la superficie atrapada genera un cono de luz pasado que se extiende de manera regular hasta infinito pasado luminoso. La desigualdad de Penrose en este caso involucra la demonimada masa de Bondi del espacio-tiempo. Este contexto tiene interés, además de por ser el más sencillo compatible con un proceso de colapso realista, porque incluye como caso particular la construcción originalmente propuesta por Penrose y que consiste en una capa delgada de materia que se propaga a la velocidad de la luz en el espacio-tiempo de Minkowski. En este caso la desigualdad de Penrose se convierte en una desigualdad geométrica para superficies espaciales convexas (más precisamente "espacio-temporalmente convexas") en el espacio-tiempo de Minkowski. Esta situación particular, pero de especial interés, es objeto de estudio pormenorizado en esta tesis doctoral. La desigualdad de Penrose en ese caso se denomina "desigualdad de Penrose para capas"
Asymptotic behaviour of spacetimes with positive cosmological constant
No full textTesis por compendio de publicaciones[EN] In this thesis we study the asymptotic Cauchy problem of general relativity with positive
cosmological constant in arbitrary (n + 1)-dimensions. Our aim is to provide geometric
characterizations of Kerr-de Sitter and related spacetimes by means of their initial data
at conformally flat (n-dimensional) I . In our setting, the conformal Killing vector fields
(CKVFs) of I become very relevant because of their relation with the symmetries of
the spacetime.
In the first part of the thesis, we study the CKVFs ξ of conformally flat n-metrics γ,
as well as their equivalence classes [ξ] up to conformal transformations of γ. We do
that by analyzing in detail SkewEnd(M1,n+1), the skew-symmetric endomorphisms of
the Minkowski space M1,n+1. The cases n = 2, 3 are worked out in special detail. A
canonical form that fits every element in SkewEnd(M1,n+1) is obtained along with several
applications. Of relevance for the study of asymptotic data is that it gives a canonical
form for CKVFs which allows us to determine the conformal classes [ξ] and study the
quotient topology associated to these clases. In addition, the canonical form for CKVFs
is applied to the n = 3 case to obtain a set of coordinates adapted to an arbitrary
CKVF. With these coordinates we provide the set of asymptotic data which generate
all conformally extendable spacetimes solving the (Λ > 0)-vacuum field equations and
admitting two commuting symmetries, one of which axial. From this, a characterization
of Kerr-de Sitter and related spacetimes follows. Our study provides in principle a
good arena to test definitions of mass and angular momentum for positive cosmological
constant.
In the second part of this thesis we focus in the asymptotic Cauchy problem in arbitrary
dimensions. For this we use the Fefferman-Graham formalism. We carry out an study of
the asymptotic initial data in this picture and extend an existing geometric characteri-
zation of them, in the conformally flat I case, to arbitrary signature and cosmological
constant. We discuss the validity of this geometric characterization of data beyond
the conformally flat I case. We provide a KID equation for asymptotic analytic data
(which comprise Kerr-de Sitter). This equation being satisfyied by the data amounts to
the existence of a Killing vector field in the corresponding spacetime. With the above
results in hand we provide a geometric characterization of Kerr-de Sitter by means of
its asymptotic initial data, which happen to be determined by the conformally flat class
of metrics [γ] and one particular conformal class of CKVFs [ξ] of [γ]. These data admit
a generalization, keeping [γ] conformally flat, by allowing [ξ] to be an arbitrary confor-
mal class. This extends the so-called Kerr-de Sitter-like class with conformally flat I ,
defined in previous works in four spacetime dimensions, to arbitrary dimensions. We
study this class and prove that the corresponding spacetimes are contained in the set
of (Λ > 0)-vacuum Kerr-Schild spacetimes, which share (conformally flat) I with their
background metric (de Sitter). We name these Kerr-Schild-de Sitter spacetimes. The
proof largely relies on our study of the space of classes of CKVFs and in particular on
the properties of its quotient topology. In addition, we prove the converse inclusion,
providing a full characterization of the Kerr-de Sitter-like class as the Kerr-Schild-de
Sitter spacetimes
Trapped surfaces in spacetimes with symmetries and applications to uniqueness theorems
No full text[ES] El objetivo de esta tesis es, precisamente, estudiar las propiedades de las superficies atrapadas en espacio-tiempos con simetrías y su posible relación con la teoría de los agujeros negros. Aunque es modesto este objetivo también es amplio. Nos centraremos en un aspecto de esta posible equivalencia, es decir, que la singularidad de la estática de los teoremas de agujeros negros se extienden a espacio-tiempos estáticos que contienen MOTS. El principal resultado de estos estados de la tesis, en esta cuestión, tiene una respuesta afirmativa, bajo condiciones adecuadas sobre el espacio-tiempo. Para resolver esta cuestión habrá que analizar en profundidad las propiedades de MOTS y superficies atrapadas débilmente en el exterior en espacio-tiempos con simetrías y, esto producirá una serie de resultados que son, con suerte, de interés independiente.[EN] The aim of this thesis is precisely to study the properties of trapped surfaces
in spacetimes with symmetries and their possible relation with the theory of black
holes. Even this more modest goal is vast. We will concentrate on one aspect of this
possible equivalence, namely whether the static black hole uniqueness theorems
extend to static spacetimes containing MOTS. The main result of this thesis states
that this question has an affirmative answer, under suitable conditions on the
spacetime. To solve this question we will have to analyze in depth the properties
of MOTS and weakly outer trapped surfaces in spacetimes with symmetries, and
this will produce a number of results which are, hopefully, of independent interest
Gravitational Waves and first detection in LIGO.
No full textTrabajo de fin de Grado. Grado en Física. Curso académico 2021-2022.[ES]El presente Trabajo de Fin de Grado (TFG) constituye el recorrido histórico de la radiación gra vitatoria, abordado desde un punto de vista teórico y práctico.
Las ondas gravitaciones (GW) nacen teóricamente con la relatividad general (GR) y las soluciones
en forma de ondas a las ecuaciones de campo de Einstein (EFE) en el marco de la teoría linealizada,
basada en una perturbación espacio-temporal hµν sobre una métrica base g¯µν, propuestas hace unos
100 años, poco después de la publicación de la GR. Analizaremos cómo se emiten estas ondas, los
efectos que tienen y sus características, en especial la energía que emiten curvando el espacio-tiempo
para lo que desarrollaremos una expresión en función de parámetros observables como la frecuencia
del tensor energía momento T
GW
µν .
A continuación, hablaremos sobre la primera observación indirecta de la emisión de GW realizada
por Hulse y Taylor usando un púlsar binario en la década de 1970, y de fuentes astronómicas viables
para la detección directa de radiación gravitatoria. Para ambos casos desarrollaremos los cálculos teó ricos que nos llevan a la emisión de ondas gravitacionales.
El trabajo sigue con una descripción de los proyectos LIGO y Virgo de interferómetros láser para
la detección de GW, que comienzan a construirse en 1990 y son operativos desde 2015.
Por último, comentaremos las observaciones más destacadas realizadas por los detectores y su im portancia tanto en la exploración del universo como en la determinación de la constante de Hubble
H0, complementando el estudio realizado con telescopios tradicionales.[EN]This Final Degree Project (TFG) is a historical overview of gravitational radiation, approached
from a theoretical and practical point of view.
Gravitational waves are theoretically born with general relativity (GR) and the wave solutions to
the Einstein field equations (EFE) in the framework of the linearized theory, based on a space-time
perturbation hµν on a base metric g¯µν, proposed about 100 years ago, shortly after the publication
of GR. We will analyse how these waves are emitted, the effects they have and their characteristics,
especially the energy they emit by curving space-time, for which we will develop an expression of the
stress-energy tensor T
GW
µν as a function of observable parameters such as the frequency .
We will then discuss the first indirect observation of GW emission by Hulse and Taylor using a
binary pulsar in the 1970s, and viable astronomical sources for the direct detection of gravitational
radiation. For both cases we will develop the theoretical calculations that lead to the emission of gra vitational waves.
The work continues with a description of the LIGO and Virgo laser interferometer projects for GW
detection, which started construction in 1990 and have been operational since 2015.
Finally, we will discuss the most outstanding observations made by the detectors and their impor tance both in the exploration of the universe and in the determination of the Hubble constant H0,
complementing traditional telescopes
Geometry of abstract null hypersurfaces and matching of spacetimes
No full text[EN] The purpose of this thesis is two-fold. As already mentioned, we are firstly interested
in the geometry of null hypersurfaces. In this context
the formalism of hypersurface data becomes a powerful mathematical framework.
Our second aim (and actually the starting point of the thesis) is the study of the
problem of matching two completely general spacetimes across a null hypersurface,
which we address in Chapters 7, 8, 9.
Concerning the part of the thesis where we expand the formalism of hypersurface
data, the motivations described above have lead us to study how to characterize
curvature information at the abstract level. Also, they have allowed
us to understand how the data is affected by the existence of a privileged vector
field. In particular, this has permitted that we construct abstract notions
of Killing horizons of order zero and one which do not require of any ambient
space and which generalize the concepts of non-expanding, (weakly) isolated and
Killing horizons. Finally, we have been able to derive an equation, called generalized
master equation, that governs the geometry of null hypersurfaces with an extra null
tangent vector field. The analysis of this equation reveals properties
about the surface gravity of such vector and about homothetic Killing horizons
and Killing horizons of order zero and one. Moreover, it allows us to recover, as
particular cases, the well-known near horizon equation of isolated horizons as well
as the so-called master equation of multiple Killing horizons.
The problem of matching two spacetimes across a null hypersurface constitutes
the second part of the thesis. In a spacetime context and by requiring a simple
topology of the boundaries, we have been able to encode the whole matching
information in a function and a diffeomorphism between the set of null generators
of both matching hypersurfaces. We have also derived explicit expressions for the
matter-energy content of the shell. Finally, we have exploited the formalism of
hypersurface data to address the problem of matching in a completely abstract
context and without requiring topological restrictions upon the boundaries. This
approach, as we will see, has many advantages that will be discussed later
Lightlike Geodesics and Shadows of Black Holes
No full textTrabajo de fin de Grado. Grado en Física. Curso académico 2022-2023.[ES]En este trabajo se estudian las propiedades de la geometr´ıa de Kerr y las trayecto rias de geod´esicas luminosas en la cercan´ıa del agujero negro. Mediante el an´alisis de las
geod´esicas luminosas, describimos la regi´on de fotones atrapados, sus propiedades y ha llamos unas expresiones para representar la sombra de un agujero negro anal´ıticamente.
Sirvi´endonos de esta representaci´on, analizamos c´omo var´ıa la forma de la sombra en fun ci´on de diversos par´ametros.
En la segunda parte del trabajo, se describen los detalles de un c´odigo desarrollado
en Python con el que se representan las im´agenes de distintos agujeros negros. Mediante
dichas im´agenes, se analizan los resultados num´ericos para las sombras de agujeros ne gros de Kerr con distintos par´ametros. Adem´as, describimos el comportamiento ca´otico
de las geod´esicas luminosas cerca del borde de la sombra y representaremos im´agenes para
m´etricas diferentes a la de Kerr.[EN]In this work we study the properties of the Kerr geometry and the trajectories of
lightlike geodesics in the vicinity of the black hole. By analyzing the lightlike geodesics,
we describe the trapped photon region, its properties and find expressions to represent
the shadow of a black hole analytically. Using this representation, we analyze how the
shape of the shadow varies as a function of various parameters.
In the second part of the work, we describe the details of a code we have written in
Python to represent the images of different black holes. Using these images, numerical
results for Kerr black hole shadows with different parameters are analyzed. In addition,
we will describe the chaotic behavior of lightlike geodesics near the edge of the shadow
and represent images for metrics other than Kerr
Actividades de difusión y promoción para el nuevo Máster Universitario en Física y Matemáticas
No full textMemoria ID-0225. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2015-2016
Implementing citizen science activities for climate action: the I-CHANGE Day
No full textThe H2020 I-CHANGE project (Individual Change of HAbits Needed for Green European transition) aims to actively engage citizens in tackling climate change through citizen science practices. To this end, I-CHANGE has collaborated with citizens and stakeholders across eight Living Labs (LLs) situated in seven countries representing diverse geographical and climatic regions. This paper presents the I-CHANGE Day, an event organized simultaneously in the eight LLs, with the aim of collecting and analyzing data on air pollution and meteorological variables through citizen science and raise public awareness on climate change and individual adaptation measures. The paper details the methodology adopted to facilitate the citizens' participation and the implementation of the proposed activities in contrasting social and environmental settings, and the outcomes of these various citizen science activities. The two main activities implemented in the present case study were air pollution monitoring using Smart Citizen Kits (SCKs) and comparing personal temperature and humidity perception with observations acquired through MeteoTrackers sensors. The results show significant community involvement and provide useful insights for enhancing the effectiveness of international citizen science initiatives. They also highlight the importance of a co-creative process to capture different objectives and capabilities of LLs. Across all LLs, the activities presented engaged groups ranging from 8 to 60 citizens, who demonstrated high levels of interest and effectively acquired the skills to operate the low-cost sensors. This study further aims to facilitate the replication of the proposed campaign across other LLs in other areas of the globe.Funding
The author(s) declare that financial support was received for the research and/or publication of this article. This project, I-CHANGE (2022–2025) has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101037193.
Acknowledgments
This study was conducted as part of the I-CHANGE project (2022–2024, EC grant agreement 101037193). We thank all participants and institutions involved in the project and Living Labs for their contributions to data collection and analysis. We are very grateful to all the staff from the I-CHANGE Living Labs teams for their role in implementing the LL activities, and to Juan Quintero Marín (University College Dublin) for his contribution to this paper. We would also like to acknowledge the key role played by all stakeholders who engaged in the initiative and made the organization of the I-CHANGE Day possible: AMS Institute (Amsterdam, the Netherlands), Civic Centre Verdum (Ajuntament de Barcelona, Spain), Bike Library (Dublin, Ireland),
Genoa Amateur Bikers’ Association (Genoa, Italy), the sociocultural non-profit organization Avansa Limburg (Hasselt, Belgium), the Botanical Garden of Jerusalem (Jerusalem, Israel), the Paglayiri Market and Cité An Market (Ouagadougou, Burkina
Faso), as well as Laura Ceraldi, Josep María Perelló, Marc Gasulla, Jordi Cherta, Carles Mesa, and Marcos Lloret from the Jesuïtes Educació Foundation
Actualización de material de laboratorio para la impartación de la asignación de física de 1er. curso del nuevo grado en Física
No full textMemoria ID-0040. Ayudas de la Universidad de Salamanca para la Innovación Docente, curso 2008-2009.El presente proyecto se enmarca en la puesta en marcha y posterior desarrollo del futuro Grado en Física por la Universidad de Salamanca que se pretendía comenzar a impartir en el próximo curso 2009/2010. A la fecha actual este nuevo título ya ha recibido la verificación de ANECA por lo que parece que será una realidad su impartición en el próximo curso académico. Este nuevo título transformará la actual Licenciatura en Física e integrará dichos estudios en el nuevo marco del Espacio Europeo de Educación Superior (EEES)
Image_4_Multi-System Adaptation to Confinement During the 180-Day Controlled Ecological Life Support System (CELSS) Experiment.jpeg
No full textConfinement experiments are essential to prepare long-term space exploration. The 180-day Chinese CELSS (Controlled Ecological Life Support System) study is unique in its design, including a closed-loop system and mid-mission simulation of Mars-like day–night cycle of 24 h 40 min for 36 days (days 72–108). Our aim was to study physiological and psychological consequences of this confinement in four healthy volunteers (one female). CELSS platform consisted of six interconnected modules including four greenhouses. Life support systems were controlled automatically. Body composition, fluid compartments, metabolic state, heart, large vessels, endothelial function, and muscle tone were studied using biological, functional, and/or morphological measurements. Behavioral activities were studied by ethological monitoring; psychological state was assessed by questionnaires. Body weight decreased by ∼2 kg mostly due to lean mass loss. Plasma volume and volume-regulating hormones were mostly stable. Carotid intima-media thickness (IMT) increased by 10–15%. Endothelium-dependent vasodilation decreased. Masseter tone increased by 6–14% suggesting stress, whereas paravertebral muscle tone diminished by 10 ± 6%. Behavioral flow reflecting global activity decreased 1.5- to 2-fold after the first month. Psychological questionnaires revealed decrease in hostility and negative emotions but increase in emotional adaptation suggesting boredom and monotony. One subject was clearly different with lower fitness, higher levels of stress and anxiety, and somatic signs as back pain, peak in masseter tone, increased blood cortisol and C-reactive protein. Comparison of CELSS experiment with Mars500 confinement program suggests the need for countermeasures to prevent increased IMT and endothelial deconditioning. Daily activity in greenhouse could act as countermeasure against psycho-physiological deconditioning.</p
