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Fisher, John Roger. "Astronomy and patronage in Hanoverian England : the work of James Bradley, third Astronomer Royal of England." Thesis, Imperial College London, 2004. http://hdl.handle.net/10044/1/8318.
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Slagle, Judith Bailey. "The Poet and the Astronomer: Joanna Baillie’s Intersections with Sir John Herschel." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etsu-works/3216.
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Enlund, Joachim. "Utanför "vetenskapens råmärken" : Svenska astronomer och frågan om utomjordiskt liv under perioden 1880-1940." Thesis, Uppsala University, Department of History of Science and Ideas, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-113803.
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Syftet med denna uppsats är att studera hur svenska astronomer under perioden 1880-1940 närmade sig frågan om utomjordiskt liv. En stor vikt har lagts vid att se på vilket sätt som frågan om utomjordiskt liv hörde till populärvetenskapen, och hur detta påverkade det sätt som astronomerna skrev om den på. Ett vidare syfte har varit att undersöka på vilket sätt som frågan var förbunden med dåtida inomvetenskapliga och utomvetenskapliga åskådningar. I samband med detta uppmärksammas Svante Arrhenius idé om panspermi, det vill säga att livet hade kommit till jorden från yttre rymden, och hur denna idé förutsatte ett biologiskt universum. Uppsatsen avslutas med ett försök till att nyansera de utomvetenskapliga följderna av idén om ett biologiskt universum.
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Mosley, Adam John. "Bearing the heavens : astronomers, instruments and the communication of astronomy in early-modern Europe." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621908.
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de, Cruz Pérez Javier. "Implications of Dynamical Dark Energy in the expansion of the Universe and the Structure Formation." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/671792.
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En aquesta tesi s’estudien diferents models cosmològics, tots ells caracteritzats per considerar, de manera efectiva, una lleu evolució temporal de l’Energia Fosca, en contrast amb l’actual model estàndard de la cosmologia. El terme Energia Fosca s’utilitza per fer referència a una misteriosa forma d’energia que sembla impregnar tots els racons del Univers i que provoca que les galàxies s’allunyin les unes de les altres. El ritme predit d’expansió del Univers varia d’un model a un altre així com la quantitat d’estructura observada i la distribució d’aquesta.
Degut al bon moment de la cosmologia observacional tenim a la nostre disposició una gran quantitat de dades que ens permeten posar a prova els diferents models existents. Un exemple d’aquests models, seria el Running Vacuum Model (RVM), que ha estat estudiat en detall en aquesta tesi i que considera una expressió per la densitat d’energia del buit motivada en el context de les Teories Quàntiques de Camp. Un altre exemple de models cosmològics serien els anomenats models de camp escalar que suposen que l’equació d’estat de l’Energia Fosca, en el moment present, és lleugerament diferent del valor predit pel model estàndard.
No noées s’han considerat models acomodats dins del marc de la teoria de la Relativitat General, sinó que també s’han estudiat les prediccions teòriques del model presentat per Brans i Dicke al 1961 i que resulta ser el primer intent d’extensió de la teoria d’Einstein. El model de Brans i Dicke està caracteritzat pel fet que la interacció gravitatòria està no només mediada per un camp tensorial, sinó també per un camp escalar.
Les prediccions teòriques dels diferents models estudiats, tant a nivell de background com a nivell de pertorbacions, han sigut contrastades amb les mes recents dades cosmològiques revelant que l'anteriorment esmentada evolució temporal de l’Energia Fosca ajuda a rebaixar, de manera considerable, algunes de les tensions que afecten al model estàndard. La comparació teoria-observacions s’ha dut a terme mitjançant una rigorosa metodologia que involucra diferents eines estadístiques. Per tant les conclusions obtingudes al llarg d’aquesta tesi es basen en un procés robust i en un estudi detallat dels diferents models cosmològics considerants.The high quality observations performed during the last two decades, have allowed to demonstrate, with high confidence range, that the Universe is in expansion and to be more precise in accelerated expansion. In order to explain the accelerated evolution the name of dark energy was coined. It refers to a some mysterious form of diffuse energy presumably permeating all corners of the Universe as a whole. We may say that the canonical picture of our Universe defined in the framework of General Relativity, whose field equation were found by Einstein in 1917, is built upon the assumption that the observed acceleration is caused, in fact, by a rigid cosmological constant term denoted by Λ. Thanks to the aforementioned cosmological measurements, we have been able to pin down its value to an impressive level. Dark energy is not the only element, beyond the conventional baryons and photons, required by the observations since we also need large amounts of what is commonly call as dark matter. We call such an overall picture of the Universe the “concordance (or standard) cosmological model” or simply ΛCDM. Therefore, we attribute the observed accelerated expansion of the Universe to the existence of a repulsive force, exerted by the Λ term, which works against the attractive gravitational force and tends to push the clusters of galaxies apart at a speed continuously increasing with the cosmic expansion. Throughout this thesis a wide variety of models, beyond the standard model have been studied. The corresponding analyses have been carried out by studying in detail the theoretical predictions at the background and perturbation level, with the purpose of testing them with the large amount of cosmological data which we currently we have access to. The ultimate goal is to see if we can detect signals of new physics that help to alleviate some of the tensions that affect the ΛCDM. The concordance model, has remained robust and unbeaten for a long time since it is roughly consistent with a large body of cosmological data. Because of this fact, it is not reasonable to look for models with a very different behaviour than the ΛCDM, but to study models that exhibit small departures with respect to the standard model in key aspects. We have studied the Running Vacuum Models (RVM) in depth. They are characterized by having a time-evolving vacuum energy density, whose functional expression is motivated in the context of Quantum Field Theory in curved space-time. It is fundamental that its expression contains a constant term, which mimics the standard behaviour in order to first generate the transition from a decelerated to an accelerated Universe and to ensure that the fit of the structure formation data is not ruined. We have also studied the Peebles & Ratra model, which is a particularly successful scalar field model φCDM for which the potential takes the form V (φ) ∼ φ−α . The dimensionless parameter α encodes the extra degree of freedom that this model has with respect to the standard model. It is found to be small and positive, therefore V (φ) can mimic and approximate cosmological constant that is decreasing slowly with time. In the late Universe the contribution of the scalar field, φ, surfaces over the matter density, thus becoming the dominant component. Not all the models studied are motivated within a theoretical framework, since we have also considered some interesting phenomenological approaches. Last but not least, at the end of the thesis the Brans & Dicke (BD) gravity model was studied in detail. The main feature of this model is that the Newtonian constant coupling GN is replaced by a dynamical scalar field G(t) = 1/ψ(t), coupled to the curvature. As a consequence the gravitational interaction is not only mediated by the metric field, as in the General Relativity case but also for the aforementioned scalar field ψ. The obtained results clearly point out to an interesting conclusion, those models which consider an effective time-evolving dark energy are able to alleviate some of the tensions affecting the ΛCDM. Among the different tensions there are two that stand out, namely the σ8 -tension and the H0-tension.
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Kuutmann, Andrej. "Photo-evaporation of Globulettes : Numerical hydrodynamic studies of photo-evaporating low-mass globules in the Rosette Nebula." Thesis, Stockholm University, Department of Astronomy, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-8354.
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In this work, the long-term evolution of globulettes, low-mass globules found in H II regions, is studied through numerical hydrodynamic simulations. It has been proposed by Gahm et al. (2007) that these clouds may form free-floating planetary mass objects due to shock compression, caused by heating from the intense UV radiation of the central OB star cluster. To address this possibility, lifetimes are calculated for three different 3D simulated cases, similar to globulettes found in the Rosette Nebula. A plane-parallel approximation of the radiation field is used, as well as an inhomogeneous initial density distribution. The ionizing radiation will cause the globulettes to photo-evaporate, creating a rocket acceleration effect from the mass ejected on the heated side of the cloud. For a typical globulette with an initial mass of 29.5 Jupiter masses a lifetime of 50 000 yrs is estimated. This estimate is compared to the analytical models of Mellema et al. (1998) and Bertoldi and McKee (1990) which suggest longer lifetimes; the discrepancy is attributed to fragmentation of the clouds in the numerical simulation, which is not adequately described by the models. Synthesized H-alpha images and lightcurves are presented, indicating that the bright rims of small clouds are only likely to be visible in dim parts of the Rosette Nebula. The morphology of simulated clouds generally agrees with observations. While the code does not include self-gravity, the gravitational stability of the clouds is studied indirectly. It is concluded that clouds in the planetary mass range are stable against gravitational collapse, from supporting thermal pressure alone, when in pressure equilibrium with the heated ionization front. However, gravity may play a significant role during the initial shock compression.
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Brogt, E. "Pedagogical and curricular thinking of professional astronomers teaching the Hertzsprung-Russell diagram in introductory astronomy courses for non-science majors." Thesis, University of Canterbury. University Centre for Teaching and Learning, 2009. http://gradworks.umi.com/33/52/3352344.html.
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Brogt, Erik. "Pedagogical and Curricular Thinking of Professional Astronomers Teaching the Hertzsprung-Russell Diagram in Introductory Astronomy Courses for Non-Science Majors." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/195246.
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This qualitative study explores the pedagogical and curricular thinking of five professional astronomers, faculty at a university, about teaching the Hertzsprung-Russell diagram in introductory astronomy courses for non-science majors. Data sources for this study included two semi-structured interviews per participant, in which they were asked about teaching the Hertzsprung-Russell diagram, as well as about the introductory course in general. In addition, participants were asked to complete four cognitive tasks; the creation of a lesson plan, a concept map on how they would like their students to think about the Hertzsprung-Russell diagram at the end of the course, a Pathfinder network rating task, and responding to stereotypical student statements regarding the Hertzsprung-Russell diagram.The data was analyzed using a case study approach, followed by a discussion of themes that emerged from the data. Results indicate that participants had primarily affect and process goals for the course, rather than content goals. In addition, they wanted students to view the HR diagram as a part of a flow chart, where input physics (both observed and inferred properties of stars) leads to the construction of the HR diagram, which in turn is used to make inferences about stellar evolution. Participants identified several student difficulties with the HR diagram, among which interpreting a graph was the most pertinent. In several stereotypical student statements, participants responded using the exact same analogies to explain the concepts to the students. This may be indicative of some underlying pedagogical content knowledge.
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Bernal, Mera José Luis. "Cosmology on the Edge of Lambda-Cold Dark Matter." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/667707.
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Cosmology is the science that studies the Universe as whole, aiming to understand its origin, composition and evolution. During the last decades, cosmology has transitioned from a “data staved” to a “data driven” science, inaugurating what is known as precision cosmology. This huge observational effort has confirmed and fostered theoretical research, and established the standard model of cosmology: Lambda-Cold Dark Matter (LCDM).
This model successfully reproduces most of the observations. However, there are some persistent tensions between experiments that might be smoking guns of new physics beyond this model. Anyways, there is a difference between modeling and understanding, and LCDM is a phenomenological model that, for instance, does not describe the nature of the dark matter or dark energy. This thesis collects part of my research focused on pushing the limits of the standard cosmological model and its assumptions, regarding also existing tensions between experiments. New strategies to optimize the performance of future experiments are also proposed and discussed.
The largest existing tension is between the direct measurements of the Hubble constant using the distance ladder in the local Universe and the inferred value obtained from observations of the Cosmic Microwave Background when LCDM is assumed. A model independent reconstruction of the late-time expansion history of the Universe is carried out, which allows us to identify possible sources and solutions of the tension. We also introduce the concept of the low redshift standard ruler, and measure it in a model independent way. Finally, we introduce a statistical methodology to analyze several data sets in a conservative way, no matter the level of discrepancy between them, accounting for the potential presence of systematic errors.
The role of primordial black holes as candidates for dark matter is addressed in this thesis, too. Concretely, the impact of an abundant population of primordial black holes in the rest of cosmological parameters is discussed, considering also populations with extended mass distributions. In addition, massive primordial black holes might be the seeds that are needed to explain the origin of the supermassive black holes located in the center of the galaxies. We predict the contribution of a population of massive primordial black holes to the 21 cm radiation from the dark ages. This way, observations of the 21 cm intensity mapping observations of the dark ages could be used to ascertain if the seeds of the supermassive black holes are primordial.
Finally, we estimate the potential of radio-continuum galaxy surveys to constrain LCDM. These kind of experiments can survey the sky quicker than spectroscopic and optical photometric surveys and cover much larger volumes. Therefore, they will be specially powerful to constrain physics which has impact on the largest observable scales, such as primordial non Gaussianity. On the other hand, intensity mapping experiments can reach higher redshifts than galaxy surveys, but the cosmological information of this signal is coupled with astrophysics. We propose a methodology to disentangle astrophysics and optimally extract cosmological information from the intensity mapping spectrum. Thanks to this methodology, intensity mapping will constrain the expansion history of the Universe up to reionization, as shown in this thesis.El modelo estándar de cosmología, LCDM, se apoya en una cantidad ingente de observaciones extremadamente precisas, que es capaz de reproducir con gran exactitud. Sin embargo, este es un modelo fenomenológico que no es capaz de responder algunas de las preguntas fundamentales sobre el Universo, como la naturaleza de la materia oscura o la energía oscura. Además, cuando este modelo se utiliza para interpretar las observaciones, aparecen tensiones entre experimentos independientes. Estas tensiones, en el caso de no estar producidas por errores sistemáticos no tenidos en cuenta, necesitarían un modelo cosmológico diferente para ser resueltas. Esta tesis recoge trabajos publicados en revistas científicas investigando estos problemas de LCDM. Concretamente, se cubren tres temas principales: la tensión en la constante de Hubble entre las medidas directas usando la escalera de distancias y los valores inferidos a partir de las observaciones de la colaboración Planck asumiendo LCDM; el rol de los agujeros negros primordiales como semillas de los agujeros negros supermasivos, o como candidato para conformar una parte significativa de la materia oscura; y el potencial y las estrategias óptimas a aplicar en experimentos que mapean la estructura a gran escala del Universo para examinar LCDM y medir posibles desviaciones del modelo. De este modo, el trabajo aquí recogido tiene como objetivo investigar las tensiones presentes en LCDM, así como las preguntas que deja sin responder de una manera crítica y desde un punto de vista agnóstico. Además, pretende sentar las bases para futuras investigaciones en estas líneas, cuando estén disponibles nuevas y mejores observaciones, e indicar el camino para poder poner a prueba el modelo estándar de cosmología en los años venideros en regímenes en los que aún no se ha hecho ninguna medida.
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de, Val Borro Miguel. "Studies of Gas Disks in Binary Systems." Doctoral thesis, Stockholms universitet, Institutionen för astronomi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-8337.
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There are over 300 exoplanets detected through radial velocity surveys and photometric studies showing a tremendous variety of masses, compositions and orbital parameters. Understanding the way these planets formed and evolved within the circumstellar disks they were initially embedded in is a crucial issue. In the first part of this thesis we study the physical interaction between a gaseous protoplanetary disk and an embedded planet using numerical simulations. In order to trust the results from simulations it is important to compare different methods. However, the standard test problems for hydrodynamic codes differ considerably from the case of a protoplanetary disk interacting with an embedded planet. We have carried out a code comparison in which the problem of a massive planet in a protoplanetary disk was studied with various numerical schemes. We compare the surface density, potential vorticity and azimuthally averaged density profiles at several times. There is overall good agreement between our codes for Neptune and Jupiter-sized planets. We performed simulations for each planet in an inviscid disk and including physical viscosity. The surface density profiles agree within about 5% for the grid-based schemes while the particle codes have less resolution in the low density regions and weaker spiral wakes. In Paper II, we study hydrodynamical instabilities in disks with planets. Vortices are generated close to the gap in our numerical models in agreement with the linear modal analysis. The vortices exert strong perturbations on the planet as they move along the gap and can change its migration rate. In addition, disk viscosity can be modified by the presence of vortices. The last part of this thesis studies the mass transfer in symbiotic binaries and close T Tauri binary systems. Our simulations of gravitationally focused wind accretion in binary systems show the formation of stream flows and enhanced accretion rates onto the compact component.
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Faidit, Jean-Michel. "Les "amateurs de sciences" d'une province et le ciel autour du xviiieme siecle : astronomie et astronomes en languedoc. approche d'histoire des sciences." Montpellier 3, 1993. http://www.theses.fr/1993MON30041.
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Les theses sur l'histoire de l'astronomie sont rares. Afin de mieux connaitre la pratique astronomique et sa diffusion dans une epoque d'ancienne france, le cadre provincial apparait le plus approprie. On ne connait que celle de jean-marie homet sur les astronomes provencaux durat la periode cartesienne 1680-1730, les sources disponibles en archives ou dans les travaux publies imposant une periodisation elargie jusqu'en 1830 pour les astronomes de languedoc. Ces sources furent elaborees en series, permettant notamment de constituer des catalogues supports de cette etude et ouvrant la voie a des comparaisons: observatoires et instruments, observations, communications, classees par themes et ordre chronologique, completees par des notices biographiques. Le plan adopte comporte trois livres, consacres a l'approche biographique, aux oeuvres produites et au contexte dans lequel operaient ces astronomes, le creuset academique provincial plus marque par l'existence des etats de languedoc. Cette demarche a fait ressortir que ces "amateurs de sciences" appartiennent generalement aux classes privilegiees ou aisees, et qu'en depit d'une large diversite d'interet, on releve une tendance plus marquee vers la pratique observationnelle, en liaison avec un climat meridional plus favorable, ce qui permet d'expliquer une complementarite avec la capitale, encouragee par les astronomes en vus qui recherchent leur collaboration, a l'exemple de lalande a l'epoque revolutionnaire, qui fait ouvrir les portes de l'institut a plusieurs d'entre eux, et aussi une certaine dualite, la logistique de l'equipement observationnel ne suivant pas en province. Le choc de la revolution. Les transformations des institutions scientifiques, notamment une plus grande centralisation parisienne, modifient le schema de la recherche astronomique en france. L'evolution vers une professionnalisation de la pratique scientifique, et une tendance vers la mathematisation, portent en quelques annees un coup fatal a la participation de ces amateurs au progres astronomiqueTheses upon the history of astronomy are rare. To know better astronomical practical and its diffusion in an old france age, province scope appears the most appropriate. There is only jean-marie homet's thesis on astronomers in provence during the cartesian period 1680-1730, sources available in archives or in publications imposing a periodisation released till 1830 for astronomers in languedoc. These sources were organised in a way allowing to make up catalogues, backe bone of this study, and leading comparisons: observatories and instruments, observations, communications, classified by themes and chronology, completed by biographical summaries. Methods adopted have three books, devoted to biographical approach, works realised and context were operating these astronomers, specialy provincial academic crenel, more important with the existence of etats de languedoc. This approach brought out in particular that these amateurs of science generaly belong to privilegied or well-off social groups, and despite a wide various interest, we pick out a tendency more important to observational practice in relation to a more favouravle meridional climate, which allow to explain a complementarity with capital, encouraged by great astronomers who look for their collaboration like lalande at revolutionary time, who makes enter some of them to the institut, and also a certain form of duality, the observational equipment staying inferior in province. The shock of revolution, transformations of the scientific institution and a more important parisian centralisation modify astronomical research diagram in france. The evolution to professionalisation in scientifical practice and a tendancy to mathematisation, hit home in some decades a fatal braking to participation of these amateurs to astronomical progress. Possible overtures are varied: applications for
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Bellomo, Nicola. "Exploring Signatures of New Physics in Cosmology." Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/668752.
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Cosmology is the study of the origin and evolution of our Universe as a whole. Even if the theoretical framework of Cosmology was developed a century ago, with the formulation of General Relativity by Albert Einstein, it was only during the last decades that we have seen an improvement in experimental capabilities so relevant to transform Cosmology from a “data-scarce” to a “data-driven” science.
This thesis is divided in five parts. The first one is constituted by an introductory chapter which describes the standard model which we use today in Cosmology, the ΛCDM model. The main ingredients of this model are a theory of gravity that describes as the Universe evolves, in this case General Relativity; the different components existing in our Universe, namely photons, neutrinos, baryons, cold dark matter (CDM) and dark energy, described by a cosmological constant Λ; and a theory explaining the initial conditions of the Universe, which we assume to be Inflation. Even if we can describe many of these aspects in great detail, we still have several open problems in the three topics (theory of gravity, components of the Universe and initial conditions theory).
The second part is focused on the possible degeneracy between the effects that neutrinos y modified gravity theory have on cosmological observables. In the paper “Hiding neutrino masses in modified gravity cosmology” we investigated how Horndeski theory has enough freedom to reproduce a cosmological expansion as in ΛCDM and, at the same time, to boost the growth of structures at large scales. In fact this growth could hide the effects that massive neutrinos have in the matter power spectrum.
In the third part we discuss about one of the dark matter candidate, primordial black holes. In “Primordial black holes as dark matter: converting constraints from monochromatic to extended mass distributions” we show how it is possible to obtain upper limits on the abundance of primordial black holes with an extended mass distribution starting from upper limits obtained assuming a monochromatic mass distribution. We also prove that for lognormal and power-law distributions the constraints on primordial black holes abundance in the 10 solar masses window are tighter with respect to the monochromatic case. In “GW×LSS: chasing the progenitors of merging binary black holes” we explain how, correlating gravitational waves maps and galaxies maps, we can understand if the origin of the black holes that form the detected binaries is stellar or primordial.
The fourth part describes how we can obtain new probes of the first fractions of seconds of our Universe. In “Measuring the energy scale of inflation using large scale structure” we show how we can measure the energy scale of inflation through the measurement of a specific primordial non-Gaussianity signal, called “graviton exchange”. In particular we show that this primordial signal is of the same order of magnitude of the three-point function at large scale, opening the possibility of a detection. In “From primordial black holes abundance to primordial curvature power spectrum (and back)” we use the primordial black holes to put constraints on the maximum amplitude of the primordial curvature power spectrum. Specifically, we developed a procedure which connects numerical simulations of primordial black holes formation to a correct cosmological interpretation of these simulations, to a calculation of the abundance of these objects using peak theory.
The fifth part includes the summary of the results found and a discussion of those very results. Moreover we discuss about future perspectives and about how to extend these works in future scientific projects.La Cosmología es el estudio de las orígenes y evolución de nuestro Universo como un todo. Aunque bajo el lado teórico la Cosmología nació hace un siglo, se estableció como una ciencia “guiada por los datos” unicamente en las ultimas décadas. La primera de la tesis está constituida por un capítulo introductorio que describe el modelo estándar que se utiliza hoy en Cosmología, el modelo ΛCDM. La segunda parte se centra en la degeneración entre efectos de neutrinos y teorías de gravedad modificada. En “Hiding neutrino masses in modified gravity cosmology” se investigó como la teoría de Horndeski tenga suficiente libertad para reproducir una expansión como la que predice el ΛCDM y pueda incrementar el crecimiento de las estructura, escondiendo el efecto de neutrinos masivos. En la tercera parte se debate de agujeros negros primordiales. En “Primordial black holes as dark matter: converting constraints from monochromatic to extended mass distributions” se enseña como, desde los límites existentes para agujeros negros primordiales con distribución de masa monocromática, sea posible obtener límites en la abundancia de agujeros negros primordiales que tengan una distribución de masa extendida. En “GW×LSS: chasing the progenitors of merging binary black holes” se explica cómo, relacionando mapas de galaxias y mapas de ondas gravitatorias, se puede llegar a entender cuál es el origen, estelar o primordial, de los agujeros negros que forman las binarias detectadas. La cuarta parte describe como se pueda obtener nuevas pruebas sobre el Universo primigenio. En “Measuring the energy scale of inflation using large scale structure” enseñamos como se podría medir la escala energética de la Inflación mediante la medida de una señal específica de no-Gaussianidad primordial, llamada “graviton exchange”. En “From primordial black holes abundance to primordial curvature power spectrum (and back)” se utilizan los agujeros negros primordiales para poner límites en la amplitud máxima que pueda tener el espectro de potencia de la curvatura primordial. La quinta parte incluye el resumen de los resultados encontrados, una discusión de esos resultados y se debate sobre cuáles son las perspectivas futuras de estos trabajos.
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Chlench, Kathrin. "Johannes von Gmunden deutsch : der Wiener Codex 3055 : deutsche Texte des Corpus astronomicum aus dem Umkreis von Johannes von Gmunden /." Thesis, Wien : Fassbaender, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=2942867&prov=M&dok_var=1&dok_ext=htm.
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Carozzi, Tobia. "Radio waves in the ionosphere : Propagation, generation and detection." Doctoral thesis, Uppsala universitet, Institutionen för astronomi och rymdfysik, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1184.
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We discuss various topics concerning the propagation, generation, and detec-tionof high-frequency (HF) radio waves in the Earth's ionosphere. With re-gardsto propagation, we derive a full wave Hamiltonian and a polarization evo-lutionequation for electromagnetic waves in a cold, stratified magnetoplasma.With regards to generation, we will be concerned with three experiments con-ducted at the ionosphere- radio wave interaction research facilities at Sura, Rus-siaand Tromsø, Norway. These facilities operate high power HF transmittersthat can inject large amplitude electromagnetic waves into the ionosphere andexcite numerous nonlinear processes. In an experiment conducted at the Surafacility, we were able to measure the full state of polarization of stimulatedelectromagnetic emissions for the first time. It is expected that by using thetechnique developed in this experiment it will be possible to study nonlinearpolarization effects on powerful HF pump waves in magnetoplasmas in the fu-ture.In another experiment conducted at the Sura facility, the pump frequencywas swept automatically allowing rapid, high-resolution measurements of SEEdependence on pump frequency with minimal variations in ionospheric condi-tions.At the Tromsø facility we discovered by chance a highly variable, pumpinduced, HF emission that most probably emanated from pump excited spo-radicE. Regarding detection, we have proposed a set of Stokes parametersgeneralized to three dimension space; and we have used these parameters in aninvention to detect the incoming direction of electromagnetic waves of multiplefrequencies from a single point measurement.
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Triantafyllou, Nikolaos. "Primordial black holes and their implications for Inflation." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/673259.
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The standard cosmological model, ΛCDM, with the addition of an early inflationary phase, provides an accurate description of a nearly flat and homogeneous Universe, at large scales, which expands at an accelerated rate. Despite its vindication, our knowledge of the components that trigger the early formation of structures and drive the accelerated expansion of the Universe, that is, dark matter (DM) and dark energy respectively, is severely limited, given their feeble interactions with the other components of the Universe. A number of candidates from particle physics, e.g weakly interacting massive particles (WIMPs) or axions, have been proposed to constitute DM, but so far there has been no evidence to support their existence. However, the detection of a signal from the merger of a binary of black holes of stellar masses, reinvigorated the interest in an old candidate for DM, namely primordial black holes (PBHs). These black holes behave as the ones sitting at the end of stellar evolution, with the distinctive differences that they may form in significant fractions even well before the appearance of the first stars, with masses that may range from the Planck mass, to the order of MBH ∼ 1012 M. One possible formation mechanism involves perturbations originating from the fluctuations of a scalar field during inflation, that collapse after they re-enter the causal horizon in a radiation or matter domination era. The PBHs could easily form binaries in the early Universe and merge within our Hubble time, rendering them observable by the current detectors LIGO/VIRGO. The work presented in this thesis focuses on how such a population of PBHs could be utilised in order to elucidate certain spectral features of curvature perturbations characterizing the initial state of the Universe. Firstly, the effect of matter and radiation perturbations on the orbital parameter distributions of PBH binaries is studied. These perturbations are shown to provide a source of torque to the binary, particularly when their power spectrum is enhanced at the comoving scale of the binaries, leading to the suppression of the merger rate and subsequent relaxation of constraints on the PBH abundance. Secondly, the effect of primordial clustering on the distribution of orbital parameters of PBH binaries is investigated with the use of a phenomenological model of local non-Gaussianity. It is shown that due to the modal coupling of the perturbations, the merger rate and the stochastic background of gravitational waves (SBGW) sourced by merging PBH binaries, are altered. An immediate result of clustering is that the observational constraint on the abundance of PBHs in DM is relaxed considerably, allowing for significant fractions, even close to totality. Thirdly, the possibility that the SBGW from the mergers of massive PBHs could provide an explanation for the recently detected isotropic signal by the NANOGrav collaboration is considered. The presence of non-Gaussianity, sourced from a phase of constant roll, is essential in order for such massive PBHs to evade the CMB µ-distortions constraints, in which case they may have formed in small abundances, of order 0.1% with respect to DM. The present work aims to provide a more robust modelling of the observational consequences of a population of PBHs in order to gain more insight into the spectrum of primordial perturbations at small scales and therefore into the initial conditions of the early Universe.El modelo cosmológico estándar, ΛCDM, con una temprana fase de inflación, nos proporciona una descripción precisa de un Universo casi plano y homogéneo a gran escala, que se expande a un ritmo acelerado. A pesar de las evidencias observacionales, nuestro conocimiento del 95% de la energía del Universo, es decir, la materia oscura (DM) y la energía oscura, está limitado por la falta de una detección directa, debido en parte a la poca interacción, aparte de la gravitacional, que tienen con el resto de la materia. La detección de la primera señal de un sistema binario de agujeros negros, revitalizó el interés por un viejo candidato a materia oscura, los agujeros negros primordiales (PBHs). Los PBHs han recibido atención dado que se pueden formar con abundancias importantes durante el Universo temprano y con una amplia gama de posibles masas. Esta tesis se centra en su empleo para explorar el espectro de potencias de las perturbaciones de curvatura a escala pequeña. Primero, se estudia el efecto de las perturbaciones cosmológicas sobre los parámetros orbitales de los sistemas binarios de PBHs. Cuando hay una meseta de amplitud considerable en el espectro de potencia en las escalas de los sistemas binarios, la tasa de fusión se ve afectada, relajando los limites de la abundancia de PBHs. Segundo, se muestra que debido al acoplamiento modal de las perturbaciones, introducido por la presencia de no-Gaussianidad, se alteran la tasa de fusión y el resultante fondo estocástico de las ondas gravitacionales (SBGW) y que esto tambien resulta en la relajación de las restricciones de la abundancia de PBH. Tercero, se considera la posibilidad de que el SBGW proveniente de los sistemas binarios de PBHs super masivos pueda proporcionar una explicación para la señal detectada por NANOGrav. La presencia de no-Gaussianidad es esencial para que estos PBHs masivos eviten las µ-distorsiones de la CMB y se puedan haberse formado en abundancias del orden ∼ 0, 1%. Los PBHs constituyen una sonda única para explorar las condiciones iniciales del Universo y este trabajo pretende aportar un modelaje más robusto de las consecuencias observacionales de una población de PBHs.
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Camargo, Bárbara Celi Braga [UNESP]. "Estudos de estabilidade no sistema Ʋ andromedae A." Universidade Estadual Paulista (UNESP), 2015. http://hdl.handle.net/11449/124392.
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000833288.pdf: 742183 bytes, checksum: 5e7cbe805fffa4418ccfb16e5d22734c (MD5)O sistema Ʋ Andromedae foi o primeiro sistema múltiplo descoberto cujo o corpo central é pertencente a sequência principal. Apesar de ser um sistema amplamente estudado seus dados ainda possuem incertezas. A detecção dos planetas que orbitam a estrela Ʋ Andromedae A foi através do método de velocidade radial. Este método revela apenas uma faixa de possíveis valores de massas, os quais são dependentes do valor da inclinação do plano de visada. A massa do planeta Ʋ And c , por exemplo, pode variar entre 1,9 MJ e 14,57 MJ , sendo MJ a massa de Júpiter, dependendo da inclinação escolhida. Os planetas apresentam valores de excentricidade altos, o que não é explicado pela teoria de formação do sistema Solar. O quarto planeta foi previsto teoricamente em 2011, com isso, grande parte dos trabalhos realizados até agora foram considerados apenas os outros três planetas. Primeiramente realizamos uma breve revisão bibliográfica sobre as pesquisas feitas no Sistema Ʋ Andromedae, desde a descoberta do primeiro planeta em 1997 até a previsão do quarto planeta em 2011. Separamos dois modelos para os nossos estudos. Abordamos em seguida, o estudo da perturbação secular no sistema Ʋ Andromedae A, notamos que o modelo com massas grandes apresentam uma maior variação de excentricidade. Em sequência é apresentado um estudo sobre a estabilidade do quarto planeta em diversos cenários, mostrando que o modelo de massas pequenas tem uma maior faixa de estabilidade quando comparado ao modelo de massas grandes
The system Ʋ Andromedae was the first multiple system discovered whose the central body belong to the main sequence. Despite to be a widely studied system your data still have uncertainties. The detection of planets orbiting the star Ʋ Andromedae A was made using the radial velocity method. This method only give us possible values of masses, which are dependent on the value of the target plane tilt. The mass of the planet Ʋ And c, for example, can have a mass range between 1:9MJ and 14:57MJ , depending on the chosen inclination. The planets have high eccentricity values, which is not explained by the Solar System formation method. At this moment we know four planets for this system. The fourth planet was predicted theoretically in 2011, with this, the works made until now, just included three other planets. First we conducted a brief literature review on the research done about the system Ʋ Andromedae, since the discovery of the first planet in 1997 until the fourth planet in 2011. We separate two models for our studies. We approach then the study of secular perturbation in the system Ʋ Andromedae A, we note that the model with large masses have a greater variation of eccentricity. In sequence presents a study on the stability of the fourth planet in different scenarios, showing that the model of small masses have a greater range of stability when compared to the model of large masses
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Camargo, Bárbara Celi Braga. "Estudos de estabilidade no sistema Ʋ andromedae A /." Guaratinguetá, 2015. http://hdl.handle.net/11449/124392.
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Orientador: Othon Cabo WinterCoorientador: Dietmar Willian Foryta
Banca: Elbert Einstein Nehrer Macau
Banca: Rita de Cássia Domingos
Resumo: O sistema Ʋ Andromedae foi o primeiro sistema múltiplo descoberto cujo o corpo central é pertencente a sequência principal. Apesar de ser um sistema amplamente estudado seus dados ainda possuem incertezas. A detecção dos planetas que orbitam a estrela Ʋ Andromedae A foi através do método de velocidade radial. Este método revela apenas uma faixa de possíveis valores de massas, os quais são dependentes do valor da inclinação do plano de visada. A massa do planeta Ʋ And c , por exemplo, pode variar entre 1,9 MJ e 14,57 MJ , sendo MJ a massa de Júpiter, dependendo da inclinação escolhida. Os planetas apresentam valores de excentricidade altos, o que não é explicado pela teoria de formação do sistema Solar. O quarto planeta foi previsto teoricamente em 2011, com isso, grande parte dos trabalhos realizados até agora foram considerados apenas os outros três planetas. Primeiramente realizamos uma breve revisão bibliográfica sobre as pesquisas feitas no Sistema Ʋ Andromedae, desde a descoberta do primeiro planeta em 1997 até a previsão do quarto planeta em 2011. Separamos dois modelos para os nossos estudos. Abordamos em seguida, o estudo da perturbação secular no sistema Ʋ Andromedae A, notamos que o modelo com massas grandes apresentam uma maior variação de excentricidade. Em sequência é apresentado um estudo sobre a estabilidade do quarto planeta em diversos cenários, mostrando que o modelo de massas pequenas tem uma maior faixa de estabilidade quando comparado ao modelo de massas grandes
Abstract: The system Ʋ Andromedae was the first multiple system discovered whose the central body belong to the main sequence. Despite to be a widely studied system your data still have uncertainties. The detection of planets orbiting the star Ʋ Andromedae A was made using the radial velocity method. This method only give us possible values of masses, which are dependent on the value of the target plane tilt. The mass of the planet Ʋ And c, for example, can have a mass range between 1:9MJ and 14:57MJ , depending on the chosen inclination. The planets have high eccentricity values, which is not explained by the Solar System formation method. At this moment we know four planets for this system. The fourth planet was predicted theoretically in 2011, with this, the works made until now, just included three other planets. First we conducted a brief literature review on the research done about the system Ʋ Andromedae, since the discovery of the first planet in 1997 until the fourth planet in 2011. We separate two models for our studies. We approach then the study of secular perturbation in the system Ʋ Andromedae A, we note that the model with large masses have a greater variation of eccentricity. In sequence presents a study on the stability of the fourth planet in different scenarios, showing that the model of small masses have a greater range of stability when compared to the model of large masses
Mestre
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Pujol, Vallribera Arnau. "Cosmology with galaxy surveys: how galaxies trace mass at large scales." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/385515.
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Els cartografiats galàctics són una eina important per la cosmologia. No obstant això, la majoria de la matèria està en forma de matèria fosca, que no interacciona amb la llum. Per tant, les galàxies que observem des dels nostres telescopis són una petita fracció de la matèria total de l'univers. Per això és necessari entendre la connexió entre galàxies i matèria fosca per tal d'inferir la distribució de tota la matèria de l'univers a partir dels cartografiats galàctics.
Les simulacions són una eina important per a predir la formació i evolució de les estructures de matèria fosca i galàxies. Les simulacions permeten estudiar l'impacte de diferents cosmologies i models de formació de galàxies en les estructures a gran escala finals que formen les galàxies i la matèria.
A gran escala, les fluctuacions de densitat de galàxies a gran escala són proporcionals a les fluctuacions de matèria per un factor anomenat bias galàctic. Aquest factor permet inferir la distribució de matèria total a partir de la distribució de galàxies, i per tant el coneixement del bias galàctic té un impacte molt important en els nostres estudis cosmològics. Aquesta tesi doctoral està focalitzada en l'estudi del bias galàctic i el bias d'halos a grans escales.
Hi ha diferents tècniques per a estudiar el bias galàctic, en aquesta tesi ens focalitzem en dues d'elles. La primera tècnica utilitza l'anomendat Halo Occupation Distribution (HOD), que assumeix que les galàxies poblen halos de matèria fosca només segons la massa dels halos. No obstant això, aquesta hipòtesi no sempre és suficientment precisa. Utilitzem la simulació Millennium per a estudiar el bias galàctic i d'halos, la dependència en la massa del bias d'halos i els seus efectes en les prediccions del bias galàctic. Trobem que l'ocupació de galàxies en halos no depèn només de la seva massa, i assumir això causa un error en la predicció del bias galàctic. També estudiem la dependència del bias d'halos en l'ambient, i mostrem que l'ambient restringeix molt més el bias que la massa. Quan un conjunt de galàxies és seleccionat per propietats que estan correlacionades amb l'ambient, l'assumpció de que el bias d'halos només depèn de la massa falla. Mostrem que en aquests casos utilitzant la dependència en l'ambient del bias d'halos produeix una predicció del bias galàctic molt més bona.
Una altra tècnica per estudiar el bias galàctic és utilitzant Weak gravitational lensing per mesurar directament la massa en observacions. Weak lensing és el camp que estudia les distorsions lleus en les imatges de les galàxies degut a la deflexió de la llum produïda per la distribució de matèria del davant de la galàxia. Aquestes distorsions permeten inferir la distribució a gran escala de la matèria total. Desenvolupem i estudiem un nou mètode per mesurar el bias galàctic a partir de la combinació dels mapes de weak lensing i el camp de distribució de galàxies. El mètode consisteix en reconstruïr el mapa de weak lensing a partir de la distribució de les galàxies de davant del mapa. El bias és mesurat a partir de les correlacions entre el mapa de weak lensing reconstruït i el real. Testegem diferents sistemàtics del mètode i estudiem en quins règims el mètode és consistent amb altres mètodes per mesurar el bias lineal. Trobem que podem mesurar el bias galàctic utilitzant aquesta tècnica. Aquest mètode és un bon complement d'altres mètodes per mesurar el bias galàctic, perquè utilitza assumpcions diferents. Juntes, les diferents tècniques per mesurar el bias galàctic permetran restringir millor el bias galàctic i la cosmologia en els futurs cartografiats galàctics.Galaxy surveys are an important tool for cosmology. The distribution of galaxies allow us to study the formation of structures and their evolution, which are needed ingredients to study the evolution and content of the Universe. However, most of the matter is made of dark matter, which gravitates but does not interact with light. Hence, the galaxies that we observe from our telescopes only represent a small fraction of the total mass of the Universe. Because of this, we need to understand the connection between galaxies and dark matter in order to infer the total mass distribution of the Universe from galaxy surveys. Simulations are an important tool to predict the structure formation and evolution of dark matter and galaxy formation. Simulations allow us to study the impact of different cosmologies and galaxy formation models on the final large scale structures that galaxies and matter form. Simulations are also useful to calibrate our tools before applying them to real surveys. At large scales, galaxies trace the matter distribution. In particular, the galaxy density fluctuations at large scales are proportional to the underlying matter fluctuations by a factor that is called galaxy bias. This factor allows us to infer the total matter distribution from the distribution of galaxies, and hence knowledge of galaxy bias has a very important impact on our cosmological studies. This PhD thesis is focused on the study of galaxy and halo bias at large scales. There are several techniques to study galaxy bias, here we focus on two of them. The first technique is the Halo Occupation Distribution (HOD) model, that assumes that galaxies populate dark matter haloes depending only on the halo mass. With this hypothesis and a halo bias model, we can relate galaxy clustering with matter clustering and halo occupation. However, this hypothesis is not always accurate enough. We use the Millennium Simulation to study galaxy and halo bias, the halo mass dependence of halo bias, and its effects on galaxy bias prediction. We find that the halo occupation of galaxies does not only depend on mass, and assuming so causes an error in the galaxy bias predictions. We also study the environmental dependence of halo bias, and we show that environment constrains much more bias than mass. When a galaxy sample is selected by properties that are correlated with environment, the assumption that halo bias only depends on mass fails. We show that in these cases using the environmental dependence of halo bias produces a much better prediction of galaxy bias. Another technique to study galaxy bias is by using weak gravitational lensing to directly measure mass. Weak lensing is the field that studies the weak image distortions of galaxies due to the light deflections produced by the presence of a foreground mass distribution. Theses distortions can be used to infer the total mass (baryonic and dark) distribution at large scales. We develop and study a new method to measure bias from the combination of weak lensing and galaxy density fields. The method consists on reconstructing the weak lensing maps from the distribution of the foreground galaxies. Bias is then measured from the correlations between the reconstructed and real weak lensing fields. We test the different systematics of the method and the regimes where this method is consistent with other methods to measure linear bias. We find that we can measure galaxy bias using this technique. This method is a good complement to other methods to measure bias because it uses different assumptions. Together the different techniques will allow to constrain better bias and cosmology in future surveys.
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Woodard, Chelsea S. "Practical Astronomy." Thesis, University of North Texas, 2012. https://digital.library.unt.edu/ark:/67531/metadc149687/.
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This dissertation is a collection of poems preceded by a critical preface. The preface considers Anthony’s Hecht’s long poem, “The Venetian Vespers,” and the ways in which the temporally unsettled situation of the poem’s speaker parallels a problem facing narrative-meditative poets. The preface is divided into two main sections that explore divisions of this larger conflict. The first discusses the origins and effects of the speaker’s uprootedness in time, and the ways in which he tries to both combat and embrace this dislocation by temporarily losing himself in the immediacy of observing visual art. In this section I connect the dilemma of the speaker, who wishes to escape his memory by focusing outwards, to the dilemma of a representational poet who, despite his position towards the past, must necessarily confront or recollect memories and emotions in order to create authentic descriptions or characters. The second section focuses on the production and appreciation of artistic works (both visual and literary) and how the meaning, production and appreciation of beauty are inseparable from its existence within the physical limits of time. Here I discuss the significance of Hecht’s character who is surrounded with beauty yet describes himself as a person who only observes and does not create anything. Through this character, I argue that Hecht reveals a fundamental conflict that exists between artistic creation and chronological time, and that his poem embodies a particular and paradoxical view of beauty that resonates deeply with the motivations and struggles of writing poems.
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Gunnarsson, Marcus. "Gas Production in Distant Comets." Doctoral thesis, Uppsala University, The Uppsala Astronomical Observatory, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-2148.
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Molecular spectroscopy at radio wavelengths is a tool well suited for studying the composition and outgassing kinematics of cometary comae. This is particularly true for distant comets, i.e. comets at heliocentric distances greater than a few AU, where the excitation of molecules is inefficient other than for rotational energy levels. At these distances, water sublimation is inefficient, and cometary activity is dominated by outgassing of carbon monoxide.
An observing campaign is presented, where the millimeter-wave emission from CO in comet 29P/Schwassmann-Wachmann 1 has been studied in detail using the Swedish-ESO Submillimetre Telescope (SEST). Coma models have been used to analyse the spectra. The production of CO is found to have two separate sources, one releasing CO gas on the nuclear dayside, and one extended source, where CO is produced from coma material, proposed to be icy dust grains.
Radio observations of many molecules in comet C/1995 O1 (Hale-Bopp) have been carried out in a long-term international effort using several radio telescopes. An overview of the results is presented, describing the evolution of the gas production as the comet passed through the inner Solar system. Spectra recorded using the SEST, primarily of CO, for heliocentric distances from 3 to 11 AU are analysed in detail, also using coma models.
The concept of icy grains constituting the extended source discovered in comet 29P/Schwassmann-Wachmann 1 is examined by theoretical modelling of micrometre-sized ice/dust particles at 6 AU from the Sun. It is shown that that such grains can release their content of volatiles on timescales similar to that found for the extended source.
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Debom, Camila Riegel. "Representações da astronomia." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/174208.
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Nas últimas décadas diversos produtos oriundos do desenvolvimento científico têm se tornado cada vez mais presentes na vida das pessoas e em razão disso os estudantes, atualmente, têm seu acesso à informação facilitado. No entanto, o contexto escolar é visivelmente menos afetado que o restante da sociedade pelos recentes avanços tecnológicos. O modelo de escola atual brasileiro em pouco difere do modelo de escola de décadas atrás. Por outro lado, não é difícil perceber que a instituição que poderíamos nomear educação básica, de modo geral, assume um papel importante nesta mesma sociedade em relação à qual se vê descontextualizada. Neste trabalho foi investigado como o conhecimento sobre Astronomia se estabelece dentro da sociedade, supondo que diferentes grupos sociais apresentariam diferentes representações de conhecimentos relacionados tanto com Astronomia quanto com qualquer outro assunto científico. A teoria das Representações Sociais é tomada como marco teórico para uma investigação acerca desta temática, procurando estabelecer como o conhecimento de Astronomia é influenciado pelo contexto social dos indivíduos. Uma Representação Social é construída essencialmente por influência do meio social em que os sujeitos se encontram inseridos, na tentativa de transformar algo desconhecido em familiar e, nesse sentido, destaca-se o papel da mídia na abordagem de conceitos emprestados da Ciência, exercendo pressão para que os indivíduos cristalizem representações sobre tais conceitos. As representações sociais de um determinado assunto podem não ser consonantes com os conhecimentos cientificamente aceitos, pertencendo apenas ao universo consensual. Nesse sentido, foi conduzido um estudo piloto sobre Representações Sociais em um grupo de estudantes do 6º ano do Ensino Fundamental do interior de um município da região metropolitana de uma capital brasileira, utilizando-se a técnica dos mapas mentais. Adicionalmente foi desenvolvida e aplicada com os estudantes, que tinham entre 11 e 12 anos, uma estratégia didática com duração de 8 horas-aula que se apropriou de pressupostos da teoria da Aprendizagem Significativa e que tencionava permitir a aproximação das possíveis representações sociais em Astronomia apresentadas pelos estudantes daquelas aceitas pela comunidade científica e, acima de tudo, formalizando um contato científico com a Astronomia. Verificou-se que apesar de pertencerem a um grupo social relativamente bem delimitado, os estudantes apresentam poucas regularidades no que diz respeito às relações que estabelecem entre conceitos da Astronomia e outros termos. Somada à tentativa de identificação das Representações Sociais e à atividade intervencionista foram conduzidos testes de evocação de palavras com os pais dos estudantes tencionando estudar a relação entre as ideias evidenciadas pelos estudantes e seu convívio social. Outros dois estudos foram conduzidos em igualdade de condições, envolvendo estudantes de Ensino Médio, elaboração de mapas mentais, uma sequência de 14 hora-aula de Astronomia e testes de evocação de palavras. Também aplicou-se testes de evocação de palavras com os pais dos estudantes e o resultado foi coerente com o que se observou no estudo piloto. Os estudantes apresentam noções de Astronomia rasas, porém compatíveis com o conhecimento propagado pela própria educação formal. Não houve relação explícita entre Astronomia e pseudociência ou, catastrofismos. Embora rasas, as noções iniciais dos estudantes demonstraram amadurecimento após a sequência de aulas. Os testes de evocação de palavras foram determinantes em demonstrar que há regularidade entre os grupos de estudantes abordados no primeiro e no segundo estudos. Percebeu-se que a identificação destas Representações Sociais é complexa e ainda que é difícil 7 estabelecer em que medida os conhecimentos evidenciados refletem a influência da socialização ou da formação científica pobre. Assim, a identificação de Representações Sociais constitui uma temática promissora na pesquisa em ensino de Ciências pela sua relação direta com obstáculos representacionais que possam prejudicar a aprendizagem científica de conceitos e, especialmente, pela escassez de trabalhos na área.In the last few decades the products coming from scientific development had become continually more present in people daily lives and because of that the students, nowadays, have their access to information eased. However, the educational context is visibly less affected than the rest of the society by the recent technological advancements. The actual Brazilian school model is barely different of how it was decades ago. On the other hand, it’s not hard to perceive that the institution called basic education, commonly, takes an important place in this very same society, in relation to which is seen out of context. This work approaches an investigation about how the knowledge in Astronomy establishes within the society, supposing that social groups would have distinct representations of Astronomy as of any other scientific subject. The theory of social representations is the theoretical framework in the theme for a study of how Astronomy concepts are affected by the individuals social context. A Social Representation is built essentially by influence of the social environment in which the subjects are situated, trying to translate unknown things into familiar ones and, in this sense, it’s emphasized the role of media on addressing concepts borrowed from science and simultaneously exerting pressure to individuals set up representations of those concepts. Occurs that social representations on a certain subject may not be consonant with scientific knowledge, belonging exclusively to the consensual universe. In this sense, it was conducted a mapping regarding social representations of a 6th grade student group (middle school) in a countryside school of a city located in the metropolitan area of a principal city in Brazil , using the mind maps technique. Additionally, we developed and applied a didactical strategy which appropriated the meaningful learning assumptions with the students, whose we’re all 11and 12 years old, trying to provide an approximation between the representations students had shown and that scientifically accepted and, above all, formalizing a scientific contact among children and Astronomy. It was verified that although the students were inserted in a relatively well delimited social group they present few regularities in what concerns the relationship among Astronomy concepts and other terms. Added to the try on identifying students social representations and to the classroom activity, it was conducted an investigation with the students’ parents using word evocation tests in a way for understand relations between what students had shown in the mental maps and their social acquaintanceship. Two other studies were conducted on equal terms, involving high school students, mental mapping, a 14-hour sequence of Astronomy classes, and word recall tests. Word recall tests were also applied to the students' parents and the result was consistent with what was observed in the pilot study. The students present shallow Astronomy notions, but compatible with the knowledge propagated by the formal education itself. There is no explicit relation between Astronomy and pseudoscience or, catastrophisms. Although shallow, the initial notions of the students demonstrated maturity after the sequence of classes. The word evocation tests were determinant in demonstrating that there is regularity among the groups of students addressed in the first and second studies. It was noticed that to identify a social representation is a difficult task, specifically to ascertain in which way the information expressed by the students reflects influence of the social context or, more probably, a poor scientific background. Therefore, identifying social representations consists in a promising theme on the science learning research area, especially because of its direct connection with representational obstacles which can hinder the scientific learning of concepts an, particularly, by the scarcity of works in the area.
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Ringvall, Jonas, and Malin Kvist. "Jämförbarhet vs. innebörd och form." Thesis, Uppsala University, Department of Business Studies, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8988.
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Varella, Irineu Gomes. "O Sol: uma proposta de ensino." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/14/14134/tde-06082018-133254/.
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O Sol e a Lua são os astros mais acessíveis à observação quer pelas suas frequentes aparições no céu, quer pelos seus tamanhos aparentes pronunciados. Por essas razões, constituem-se em astros disponíveis ao estudo, atendendo aos cuidados necessários no caso de observações solares. Apesar disso, pouca ou nenhuma atenção é dada a eles pelos professores dos ensinos fundamental e médio deixando de utilizar observações que podem contribuir muito para o aprendizado e, ainda, despertar o interesse dos alunos pela ciência. Em particular o Sol, permite a exemplificação e a compreensão de diversos fenômenos estudados na física, na biologia, na geografia, na química assim como permite aplicações práticas da matemática geometria e trigonometria ministradas em sala de aula. Escolhemos levar aos professores e aos estudantes universitários um curso sobre astronomia e física solar abordando questões sobre o Sol algumas pouco discutidas nos livros, mesmo os de Astronomia com a finalidade de proporcionar material de aprendizado, estudo e discussão de temas da astronomia moderna. Neste curso básico, serão abordados: como se concluiu que o Sol é uma estrela; como foram determinados seus principais parâmetros físicos e astronômicos tais como a sua distância, o seu tamanho, a sua massa, sua temperatura e composição química, e sua estrutura interna; e como o Sol produz energia.The Moon and the Sun are the easiest celestial bodies to observe because their frequent appearance in the sky and their great apparent size. As a result, they are celestial bodies available to study, attending the essential cares regarding Sun observations. Nevertheless, teachers from elementary and high schools pay little or no attention to them and miss a great opportunity to use observations that might add a lot to the learning process and also to arouse students\' attention to science. The sun, specially, allows to illustrate and to understand several points that students learn in physics, biology, geography, and chemistry, and still can have practical applications in mathematics geometry and trigonometry taught in the classroom. We chose to bring to teachers and university students a course about astronomy and solar physics approaching issues of the Sun some of them very little discussed even in astronomy books for the purpose of provide learning material about modern astronomy topics. This basic course will develop: how was it concluded that the Sun is a star; how was it determined its main parameters, such as its distance, its size, its mass, its temperature and its chemical composition, and its internal structure; and how does the Sun produce energy.
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Añez, López José Ignacio. "Observational and theoretical perspective of massive star formation." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/671784.
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In this thesis, we are aimed to better understand the massive star formation process paying special attention to the role of the magnetic field. To do this, we will carry out a multi-scale analysis with a double approach, theoretical and observational.
a) The role of the magnetic field in the fragmentation process: the case of G14.225-0.506
In this first work, we study the fragmentation of an infrared dark cloud that has a filamentary structure and two hubs. We will pay special attention to the magnetic field present in the environment of the hubs and we will try to relate it to the different levels of fragmentation that these hubs present.
In order to carry out this study, we present the result of the CSO observations at 350 um, towards both hubs, North and South, in the infrared dark cloud G14.225-0.506 (from here G14.2). We also show the analysis of polarization and intensity gradient making use of the method developed by Koch et al. 2012, Koch et al. 2012b.
In the N-hub we find a magnetic field with a uniform distribution along the east-west direction.
However, in the southern hub the B-field shows a bimodal distribution. The intensity-gradient in the N-hub shows a single local minimum. In the S-hub, the intensity gradient reveals two minima reflecting the bimodal distribution of the magnetic field where each component points to each of the minima of the intensity gradient.
Analysis of the maps |delta| and Sigma_B in the N-hub indicates that, in the vicinity of the hub, gravity dominates the magnetic field. We have also estimated the intensity of the magnetic field finding higher values in the N-hub than in the S-hub. This supports the idea that the different levels of fragmentation exhibited by hubs depend on differences in magnetic field.
b) Modeling the accretion disk around the high-mass protostar GGD 27-MM1
In this second project, we descend to accretion disk scales to understand how massive stars form and evolve. In this work we have used ALMA observations at a wavelength of 1.14~mm with very high angular resolution that resolve the disk around the massive star GGD27-MM1.
Motivated by the similarity of this system to those found in low mass, we have modeled the emission of the disk using the models developed by D'Alessio et al. 2006 for low mass stars. The main objective is to investigate whether the assumptions that are valid for disks around low-mass stars could be extrapolated to the case of massive stars.
As a result we have found a very massive disk of about ~5 Msun which represents around 25 % of the stellar mass. This mass is consistent with the calculated dynamic mass. The disk has a radius of ~170 au with a 49º of inclination. We have compared the temperature and density structure obtained with our model with potential functions and show that the GGD~27--MM1 system is a potential template for future similar studies in other high-mass protostars.
Specifically, we have found a flared disk with a maximum scale height of ~13 au and a temperature profile that goes from ~150 K on the outside of the disk to ~ 1400 K on the inner edge of the disk.
Analysis of the Toomre parameter Q evaluated at the midplane temperature of the disk indicates that the disk is stable up to a radius 100 au.
This work shows that D'Alessio's models can be used as a first approximation and also obtain various observational predictions.En esta tesis, pretendemos contribuir a explicar el proceso de formación de estrellas masivas prestando especial atención al papel del campo magnético. Para ello, realizaremos un análisis multiescala con una doble aproximación, teórica y observacional. Por un lado investigaremos el proceso de acrecimiento a través de un disco de acrecimiento entorno a una estrella de alta masa. a) El papel del campo magnético en el proceso de fragmentación: el caso de G14.225-0.506 En este primer trabajo, estudiamos la fragmentación de una nube oscura infrarroja que presenta una estructura filamentaria y dos hubs. Prestaremos especial atención al campo magnético presente en el entorno de los hubs y trataremos de relacionarlo con los distintos niveles de fragmentación que presentan estos hubs. Para poder llevar a cabo este estudio presentamos el resultado de las observaciones del CSO a 350 masas solares, hacia ambos hubs, Norte y Sur, en la nube oscura infrarroja G14.225-0.506 (desde aquí G14.2). También mostramos el análisis de la polarización y gradiente de intensidad haciendo uso del método desarrollado por (Koch et al. 2012, Koch et al. 2012b). b) El modelado del disco de acrecimiento entorno a la protoestrella masiva GGD 27-MM1 En este segundo proyecto, descendemos hasta escalas de discos de acrecimiento para entender como las estrellas masivas se forman y evolucionan. En este trabajo hemos usado observaciones de ALMA a una longitud de onda de 1.14 mm con muy alta resolución angular (aproximadamente 40 mili-segundos de arco) que resuelven el disco entorno a la estrella masiva GGD27-MM1. El disco se dispone perpendicularmente al espectacular chorro de 10 pc de longitud que emana de la fuente, conocido como HH80-81. Motivados por el parecido de este sistema a los que encontramos en baja masa, hemos modelado la emisión del disco haciendo uso de los modelos desarrollados por D'Alessio et al. 2006 para estrellas de baja masa.
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Utzt, Susanne. "Astronomie und Anschaulichkeit : die Bilder der populären Astronomie des 19. Jahrhunderts /." Frankfurt am Main : Deutsch, 2004. http://www.gbv.de/dms/goettingen/390975761.pdf.
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Oliveira, Carlos Eduardo Quintanilha Vaz de. "Astronomia multimídia : a construção da exposição virtual "Astronomia : uma viagem inesquecível"." reponame:Repositório Institucional da UnB, 2010. http://repositorio.unb.br/handle/10482/6000.
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Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Biológicas, Instituto de Física, Instituto de Química, 2010.Submitted by Jaqueline Ferreira de Souza (jaquefs.braz@gmail.com) on 2010-11-08T15:31:38Z No. of bitstreams: 1 2010_CarlosEduardoQuitnanilhaVazdeOliveira.pdf: 3231952 bytes, checksum: 38f74ece811fd79674ea2a2e0ab7e3dd (MD5)
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Ensinar Astronomia é tão fascinante quanto aprender. A motivação deste trabalho acerca de novas maneiras de se ensinar a ciência mais antiga aos mais jovens. O objetivo deste trabalho é apresentar alicerces e método que fundamentaram a construção da “Exposição Virtual Astronomia: Uma viagem inesquecível”. A exposição virtual sobre Astronomia foi desenvolvida desde novembro de 2007 com a colaboração do "Projeto Astronomia para Principiantes", com o objetivo de divulgar a Astronomia, popularizando a Ciência e a Tecnologia, democratizando o conhecimento e promovendo a inclusão social por meio do acesso ao conhecimento, mediante atividades educativas apoiadas em abordagens interativas, experimentais e lúdicas. Nesse sentido, o museu virtual promove a aprendizagem para muito além da estrutura escolar tradicional. A exposição proporciona aos visitantes conhecimentos gerais sobre os componentes do Universo, tais como as galáxias, as estrelas e os sistemas planetários, além de uma seção voltada para o Sistema Solar e outra para alguns grandes nomes da Astronomia. Para reforçar os ensinamentos e atingir também pessoas que não possuem acesso à internet, foram inseridas as atividades do Gnomon, do Relógio de Sol e dos movimentos e fases da Lua, além de um jogo da memória e uma cruzadinha cujos conteúdos estão imersos na exposição virtual, as quais podem ser impressas com a finalidade de que os alunos possam desenvolvê-las fora do ambiente virtual. O Museu Virtual de Ciência e Tecnologia da Universidade de Brasília é patrocinado pelo Ministério da Ciência e Tecnologia (MCT) e pelo Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) e está acessível no site: HTTP://www.museuvirtual.unb.br. _________________________________________________________________________________ ABSTRACT
Teaching Astronomy is as fascinating as learning it. This motivation made possible this work about the new ways of teaching the oldest science to the young. The objective of this work is to present the fundamenting bases and the construction method of the Virtual Exposition “Astronomy: An Unforgettable Voyage”. The Astronomy virtual exposition wss developed since november 2007 in colaboration with the "Project Astronomy for Beginers". It was conceived to popularize and divulgate Astronomy, Space Sciences and related technologies, in order democratize knowledge through ludic didactic activities based in interactive and experimental aproaches. In this sense, the virtual museum brings learning far away beyond the traditional scholar structure. The exposition about Astronomy brings to the visitor general knowledges from components of the Universe, just as the galaxies, the stars and planetary systems, a section for the Solar System and another with a few big names of Astronomy. To improve the learning and also reach people that can´t access the internet, there are activities as the Gnomon, the Sun clock, earth motions and visual aspects of the Moon. It also has a memory and cross-word games such that the contents are inside the virtual explosition, which can be printed for using outside de virtual ambient. The exposition is being filled with a special section dedicated to the 400th aniversary of the Galileu´s observations together with others highlights of the 2009 International Astronomical Year. The Virtual Museum is sponsored by the Ministry of Science and Technology (MCT) and by the Nacional Science and Technology Development Council (CNPq). The web adress is: http://www.museuvirtual.unb.br.
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Luiz, André Amarante [UNESP]. "Formação coorbital com a terra e origem de theia." Universidade Estadual Paulista (UNESP), 2012. http://hdl.handle.net/11449/91800.
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A hipótese atualmente mais aceita da origem da Lua, é a de ela ter se formado a partir de restos gerados por uma grande colisão entre a proto-Terra e um proto-planeta de tamanho similar a Marte, conhecido como Theia. Simulações mostraram que pode-se reproduzir a falta de ferro na Lua, as massas da Terra e Lua, e o momento angular atual do sistema Terra-Lua. Para tal, a colisão deve ter ocorrido de modo peculiar. Assim sendo, foi proposto que os corpos Terra e Theia seriam coorbitais, de modo que a velocidade de impacto seria baixa. Tendo isto em vista, em nosso trabalho nos propusemos a estudar o processo de acresção de massa, como um possível mecanismo de formação de planetas coorbitais à Terra. O trabalho se divide em duas partes principais. Em um primeiro momento tentamos reproduzir o cenário da teoria descrita no primeiro parágrafo, ou seja, estudamos a possibilidade de formação de um corpo com massa D similar à de Marte e que seja coorbital com a Terra. Os presentes resultados das simulações numéricas mostram ser improvável a formação de um corpo com massa D e que seja coorbital com a Terra. Na segunda parte do trabalho estudamos a possibilidade de formação de Theia e da proto-Terra seguindo um perfil de densidades. Os resultados das simulações numéricas do modelo não levaram à formação de corpos com massas 1,0 C e 1,0 D, mas houve a formação de corpos de massa menor (t 0,6C). Isso mostrou que o modelo adotado é promissor, e então, ajustes de parâmetros e inserção de planetas similares a Júpiter e Saturno no sistema foram implementados. Os resultados dessas últimas simulações mostraram ser possível a formação da Terra e de Theia, mas com velocidades relativas de colisão 2 vezes maior do que a esperada (¤ 4km/s)
The most accepted hypothesis of the origin of the Moon, she is to have formed from debris generated by a major collision between the proto-Earth and a proto-planet of si-milar size to Mars, known as Theia. Simulations showed one can reproduce the lack of iron in the Moon, the masses of the Earth and Moon, and the angular momentum of the current Earth-Moon system. To this end, the collision must have occurred in a particular way. Therefore, it was proposed that the bodies would be sharing the same orbit, i.e., Earth and Theia would coorbitals, so that the impact velocity and impact would be low subtle. In view of this, in our work we set out to study the process of mass accretion as a possible mechanism for the formation of planets coorbitals to Earth. The work is divided into two major parts. At first we tried to reproduce the scenario of the theory described in the first paragraph, ie, we study the possibility of forming a body with mass D similar to that of Mars and the Earth is coorbital. The present results of numerical simulations show that it is unlikely the formation of a body with mass D and is coorbital with Earth. In the second part of the paper we study the possibility of formation of Theia and proto-Earth following a density profile. The results of numerical simulations of the model did not lead to the formation of bodies with masses 1.0 C e 1.0 D, but there was the formation of bodies of mass smaller (t 0.6C). This showed that the model is promising, and then, parameter settings and insertion of planets similar to Jupiter and Saturn in the system were implemented. The results of these simulations showed latest possible formation of earth and Theia, but with relative rates of collision 2 times higher than expected (¤ 4km/s)
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Souza, Alexandre Pinho dos Santos [UNESP]. "Estudo da estabilidade do anel de Jano e Epimeteu." Universidade Estadual Paulista (UNESP), 2012. http://hdl.handle.net/11449/93088.
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Em Setembro de 2006 foi descoberto um anel tênue na mesma órbita dos satélites Jano e Epimeteu. Simulações numéricas indicaram que o tempo de vida deste anel seria de poucas décadas. A partir dessa constatação foi considerado como improvável que o anel tenha sido observado pela sonda Cassini no curto período de vida do anel, veri cado pelas simula ções. Logo, faz-se necessário a existência de um mecanismo que explique a estabilidade do anel. A criação de partículas para aneis por meio de ejeções dos satélites próximos é uma possível fonte de material. Para veri car esse fato é necessário comparar resultados experimentais (fotometria) com resultados teóricos baseados no modelo de produção de partículas via colisões. A grandeza a ser comparada é o I/F que representa a intensidade de radiação captada pelo detector proveniente do alvo espalhador. Por meio da fotometria das imagens foi possível obter o valor experimental de I/F. Já, o valor do I/F teórico foi obtido por meio de um modelo que converte as distribuições de partículas em termos da grandeza profundidade óptica. Para a obtenção desses valores de profundidade óptica foram necessários resultados de simulações numéricas (com pressão de radiação solar) que indicam a relação do tempo de vida das partículas no sistema relacionado com seus respectivos tamanhos. Além da profundidade óptica, esse valor teórico depende do ângulo de transmissão e a função de fase, cujo valor foi obtido por meio do calculador Wiscombe para espalhamento Mie. Os valores de I/F teórico e experimental foram comparados e os resultados encontrados, para as considerações adotadas no trabalho, mostram que não é possível justi car a estabilidade do anel por meio de colisões...
In September of 2006 a faint ring was discovered at the same orbit of the satellites Janus and Epimetheus. Numerical simulations indicated that the lifetime of this ring would be just a few decades. Due to this veri cation it was considered improbable that the ring was detected by the Cassini spacecraft in the short period of time forseen by the simulations. Thus it is necessary to exist a mechanism that explains the stability of the ring. The creation of particles to the ring by ejections from close satellites is a possible source of material. In order to certicate this possibility it is necessary compare experimental results (photometry) with theoretical results based on a collision particles production model. The quantity to be compared is I/F, that represents the intensity of radiation that comes from the scattering object captured by the detector. Using the photometric results of the images it was possible to get the experimental value of I/F. However, the value of theorical I/F was obtained by a model that converts particles distributions in optical depth. In order to get these values of optical depth it was necessary some new results of numerical simulations (including Solar radiation pressure) that show the relation between lifetime and size of the particles in this system. Besides the optical depth, the transmission angle and the phase function, whose value is obtained by the Wiscombe calculator for Mie scattering, are required to obtain the nal value of the theoretical I/F. The values of theoretical and experimental I/F were compared and results that have been gotten under the considerations of this research indicate that it is not possible to explain the stability of this ring just by this collisions model. So the collisions do not... (Complete abstract click electronic access below)
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Souza, Alexandre Pinho dos Santos. "Estudo da estabilidade do anel de Jano e Epimeteu /." Guaratinguetá : [s.n.], 2012. http://hdl.handle.net/11449/93088.
Full textAbstract:
Orientador: Othon Cabo WinterCo orientador: Rafael Sfair
Banca: Silvia Maria Giuliatti Winter
Banca: Roberto Vieira Martins
Resumo: Em Setembro de 2006 foi descoberto um anel tênue na mesma órbita dos satélites Jano e Epimeteu. Simulações numéricas indicaram que o tempo de vida deste anel seria de poucas décadas. A partir dessa constatação foi considerado como improvável que o anel tenha sido observado pela sonda Cassini no curto período de vida do anel, veri cado pelas simula ções. Logo, faz-se necessário a existência de um mecanismo que explique a estabilidade do anel. A criação de partículas para aneis por meio de ejeções dos satélites próximos é uma possível fonte de material. Para veri car esse fato é necessário comparar resultados experimentais (fotometria) com resultados teóricos baseados no modelo de produção de partículas via colisões. A grandeza a ser comparada é o I/F que representa a intensidade de radiação captada pelo detector proveniente do alvo espalhador. Por meio da fotometria das imagens foi possível obter o valor experimental de I/F. Já, o valor do I/F teórico foi obtido por meio de um modelo que converte as distribuições de partículas em termos da grandeza profundidade óptica. Para a obtenção desses valores de profundidade óptica foram necessários resultados de simulações numéricas (com pressão de radiação solar) que indicam a relação do tempo de vida das partículas no sistema relacionado com seus respectivos tamanhos. Além da profundidade óptica, esse valor teórico depende do ângulo de transmissão e a função de fase, cujo valor foi obtido por meio do calculador Wiscombe para espalhamento Mie. Os valores de I/F teórico e experimental foram comparados e os resultados encontrados, para as considerações adotadas no trabalho, mostram que não é possível justi car a estabilidade do anel por meio de colisões... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: In September of 2006 a faint ring was discovered at the same orbit of the satellites Janus and Epimetheus. Numerical simulations indicated that the lifetime of this ring would be just a few decades. Due to this veri cation it was considered improbable that the ring was detected by the Cassini spacecraft in the short period of time forseen by the simulations. Thus it is necessary to exist a mechanism that explains the stability of the ring. The creation of particles to the ring by ejections from close satellites is a possible source of material. In order to certicate this possibility it is necessary compare experimental results (photometry) with theoretical results based on a collision particles production model. The quantity to be compared is I/F, that represents the intensity of radiation that comes from the scattering object captured by the detector. Using the photometric results of the images it was possible to get the experimental value of I/F. However, the value of theorical I/F was obtained by a model that converts particles distributions in optical depth. In order to get these values of optical depth it was necessary some new results of numerical simulations (including Solar radiation pressure) that show the relation between lifetime and size of the particles in this system. Besides the optical depth, the transmission angle and the phase function, whose value is obtained by the Wiscombe calculator for Mie scattering, are required to obtain the nal value of the theoretical I/F. The values of theoretical and experimental I/F were compared and results that have been gotten under the considerations of this research indicate that it is not possible to explain the stability of this ring just by this collisions model. So the collisions do not... (Complete abstract click electronic access below)
Mestre
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Luiz, André Amarante. "Formação coorbital com a terra e origem de theia /." Guaratinguetá : [s.n.], 2012. http://hdl.handle.net/11449/91800.
Full textAbstract:
Orientador: Othon Cabo WinterBanca: Ernesto Vieira Neto
Banca: Fernando Virgilio Roig
Resumo: A hipótese atualmente mais aceita da origem da Lua, é a de ela ter se formado a partir de restos gerados por uma grande colisão entre a proto-Terra e um proto-planeta de tamanho similar a Marte, conhecido como Theia. Simulações mostraram que pode-se reproduzir a falta de ferro na Lua, as massas da Terra e Lua, e o momento angular atual do sistema Terra-Lua. Para tal, a colisão deve ter ocorrido de modo peculiar. Assim sendo, foi proposto que os corpos Terra e Theia seriam coorbitais, de modo que a velocidade de impacto seria baixa. Tendo isto em vista, em nosso trabalho nos propusemos a estudar o processo de acresção de massa, como um possível mecanismo de formação de planetas coorbitais à Terra. O trabalho se divide em duas partes principais. Em um primeiro momento tentamos reproduzir o cenário da teoria descrita no primeiro parágrafo, ou seja, estudamos a possibilidade de formação de um corpo com massa ����D similar à de Marte e que seja coorbital com a Terra. Os presentes resultados das simulações numéricas mostram ser improvável a formação de um corpo com massa ����D e que seja coorbital com a Terra. Na segunda parte do trabalho estudamos a possibilidade de formação de Theia e da proto-Terra seguindo um perfil de densidades. Os resultados das simulações numéricas do modelo não levaram à formação de corpos com massas 1,0 ����C e 1,0 ����D, mas houve a formação de corpos de massa menor (t 0,6����C). Isso mostrou que o modelo adotado é promissor, e então, ajustes de parâmetros e inserção de planetas similares a Júpiter e Saturno no sistema foram implementados. Os resultados dessas últimas simulações mostraram ser possível a formação da Terra e de Theia, mas com velocidades relativas de colisão 2 vezes maior do que a esperada (¤ 4km/s)
Abstract: The most accepted hypothesis of the origin of the Moon, she is to have formed from debris generated by a major collision between the proto-Earth and a proto-planet of si-milar size to Mars, known as Theia. Simulations showed one can reproduce the lack of iron in the Moon, the masses of the Earth and Moon, and the angular momentum of the current Earth-Moon system. To this end, the collision must have occurred in a particular way. Therefore, it was proposed that the bodies would be sharing the same orbit, i.e., Earth and Theia would coorbitals, so that the impact velocity and impact would be low subtle. In view of this, in our work we set out to study the process of mass accretion as a possible mechanism for the formation of planets coorbitals to Earth. The work is divided into two major parts. At first we tried to reproduce the scenario of the theory described in the first paragraph, ie, we study the possibility of forming a body with mass ����D similar to that of Mars and the Earth is coorbital. The present results of numerical simulations show that it is unlikely the formation of a body with mass ����D and is coorbital with Earth. In the second part of the paper we study the possibility of formation of Theia and proto-Earth following a density profile. The results of numerical simulations of the model did not lead to the formation of bodies with masses 1.0 ����C e 1.0 ����D, but there was the formation of bodies of mass smaller (t 0.6����C). This showed that the model is promising, and then, parameter settings and insertion of planets similar to Jupiter and Saturn in the system were implemented. The results of these simulations showed latest possible formation of earth and Theia, but with relative rates of collision 2 times higher than expected (¤ 4km/s)
Mestre
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Maccarrone, Heredia Alessandro. "Microscopic analysis of rotating black holes." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/395196.
Full textAbstract:
The main objective of this thesis is to understand from a microscopic point of view some of the characteristic phenomena of rotating black holes.
The inclusion of rotation gives rise to physics that allows a more precise and detailed understanding of the microscopic string theory of black holes. In this thesis we focus on two models of particular interest: one is based on the D0-D6 system and the other on the D1-D5-P system. The former is interesting because, through its connection to M-theory, it yields a statistical-mechanics description of neutral black holes. The latter allows to have better control over the microscopic conformal field theory and yields a cleaner picture of the origin of superradiance.
We extend the microscopic analysis of extremal dyonic Kaluza-Klein (D0-D6) black holes to cover the regime of fast rotation in addition to slow rotation. Fastly rotating black holes, incontrast to slow ones, have non-zero angular velocity and possess ergospheres, so they are more similar to the Kerr black hole. The D-brane model reproduces their entropy exactly, but the mass gets renormalized from weak to strong coupling, in agreement with recent macroscopic analyses of rotating attractors.
We discuss how the microscopic model accounts for the fact that fastly rotating extremal KK black holes possess an ergosphere and exhibit superradiance while slow ones don't. In addition, we show in full generality how Myers-Perry black holes are obtained as a límit of Kaluza-Klein black holes, and discuss the slow and fast rotation regimes and superradiance in this context.
A, perhaps surprising, consequence of our analysis is that both slowly and fastly-rotating KK black holes provide microscopic accounts of the entropy formula of MP black holes, even if they correspond to rather different microscopic states. As we discuss, this does not pose any problem, since the microscopic theory always retains a memory of how the 5D black hole is embedded within Taub-NUT.
For a more detailed and quantitative study of black hole superradiance from the stringy
microscopic side, we consider the D1-D5-P system. In order to disentangle superradiance from finite-temperature effects, we consider an extremal, rotating D1-D5-P black hole that has an ergosphere and is not supersymmetric.
We explain how the microscopic dual accounts for the superradiant ergosphere of this black hole. The bound 0 < ω < mΩH on superradiant mode frequencies is argued to be a consequence of Fermi-Dirac statistics for the spin-carrying degrees of freedom in the dual CFT. We also compute the superradiant emission rates from both sides of the correspondence, and show their agreement. This is an extension of previous analyses of radiation from the D1-D5-P black holes. We generalize those results to include momentum for the bulk scalar.
It would be interesting to extend our picture for superradiance to the smooth SUGRA solitons with D1-D5-P charges which correspond to CFT states such that both sectors are in pure states. Another issue to be investigated would be the absence of fermionic superradiance emission by the previously considered systems with ergoregion.L'objectiu principal d'aquesta tesi és comprendre des d'un punt de vista microscòpic alguns dels fenòmens característics dels forats negres amb rotació. Ens centrem en forats negres amb rotació, extremals, però no supersimètrics. Aquesta mena de solucions són les més adequades per al nostre propòsit. A diferència del cas supersimètric, presenten una ergosfera i, per tant, s'hi pot produir el fenomen de la superradiància. Però, en tenir temperatura nul·la aquest fenomen no apareix “barrejat” amb la radiació de Hawking d'origen purament tèrmic. Alhora, aquestes geometries extremals també preserven el nombre de microestats en passar d'acoblament feble a acoblament fort. La primera part de la tesi, se centra en l'estudi microscòpic de l'entropia dels forats negres de Kaluza-Klein amb rotació. Aquesta família de solucions, presenta dos límits extremals: el de “rotació lenta” i el de “rotació ràpida”. Treballs anteriors ja havien aconseguit reproduir l'entropia del primer cas. Aquí, estenem aquest càlcul al límit extremal amb rotació ràpida. Alhora, mostrem que el fenomen de la superradiància es pot explicar de manera anàloga a la radiació de Hawking, en termes de dues excitacions que xoquen i provoquen l'emissió d'una corda tancada. En aquest cas, aquest mode emès té necessàriament un moment angular diferent de zero. A la segona part, ens centrem en aquesta interpretació microscòpica de la superradiància amb un tractament més quantitatiu. En aquest cas, considerem les solucions extremals no supersimètriques del sistema D1-D5-P amb rotació. A partir de la seva descripció microscòpica, aconseguim reproduir la condició de superradiància ω < mΩH i mostrem que es pot entendre com a conseqüència de l'estadística de Fermi-Dirac. També avaluem els ritmes d'emissió de superradiància des del punt de vista macroscòpic i microscòpic i analitzem si concorden.
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Ribeiro, Filipe Batista [UNESP]. "Ressonâncias planetárias spin-órbita com perturbação de terceiro corpo." Universidade Estadual Paulista (UNESP), 2015. http://hdl.handle.net/11449/138502.
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000864586.pdf: 3318763 bytes, checksum: 1aae1966dc41e12f7687a6926775e1d9 (MD5)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Neste trabalho estudaremos a dinâmica de rotação de exoplanetas perturbados pela presença de um terceiro corpo. Será dada ênfase em aplicações a exoplanetas com parâmetros físicos (e.g. raio e massa) compatíveis com uma constituição do tipo terrestre (e.g. rochosos). Numa primeira etapa a rotação do exoplaneta é perturbada apenas pelo torque da estrela central. Em seguida, o modelo é estendido para incluir a influência gravitacional de um companheiro. Exploraremos numericamente os problemas utilizando as técnicas de superfície de seção, a análise espectral e mapas dinâmicos para diferentes condições iniciais. Mostramos que, dependendo das condições iniciais e parâmetros do sistema planetário, a rotação do planeta pode ser irregular devido à perturbação do terceiro corpo. Em particular, a Super-Terra Kepler-11b pode ter seu regime de rotação na ressonância spin-órbita 1 : 1, estável no domínio no problema de dois corpos, altamente perturbada pelo planeta Kepler-11c devido à configuração orbital de ambos estarem relacionadas com uma ressonância 5 : 4 de movimentos médios. Também faremos uma introdução ao estudo dos efeitos dissipativos na rotação de exoplanetas induzidos por maré para os planetas Kepler-10b e Corot-7b. E por fim calcularemos a probabilidade de captura na ressonância spin-órbita 3 : 2 para o planeta Mercúrio
In this work we study the dynamics rotation of exoplanets disturbed by a third body. Emphasis will be placed on exoplanets with physical parameters (e.g. radius and mass) consistent with Earth's. In the first step the rotation of the exoplanet is disturbed only by the torque of the central star. Then the model is extended to include the gravitational influence of a companion. We numerically explore the problem using surface of sections, spectral analysis and dynamic maps for several initial conditions. We show that, depending on the initial conditions and parameters of the planetary system, the planet's rotation can be irregular due to the disturbance of the third body. In particular, the Super-Earth Kepler-11b can have its rotation in 1 : 1 spin-orbit resonance, stable in the problem of two bodies, highly disturbed by the planet Kepler- 11c due to orbital configuration close to the 5 : 4 mean motion resonance. We will also show an introduction of dissipative effects in the exoplanet's rotation induced by tides, applied to the planets Kepler-10b and Corot-7b. Finally we calculate the capture probability in the spin-orbit resonance 3 : 2 to Mercury
FAPESP: 2012/21611-5
FAPESP: 2014/11163-0
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Ribeiro, Filipe Batista. "Ressonâncias planetárias spin-órbita com perturbação de terceiro corpo /." Rio Claro, 2015. http://hdl.handle.net/11449/138502.
Full textAbstract:
Orientador: Nelson Callegari JuniorBanca: Tatiana Alexandrovna Michtchenko
Banca: Maria Helena Moreira Morais
Resumo: Neste trabalho estudaremos a dinâmica de rotação de exoplanetas perturbados pela presença de um terceiro corpo. Será dada ênfase em aplicações a exoplanetas com parâmetros físicos (e.g. raio e massa) compatíveis com uma constituição do tipo terrestre (e.g. rochosos). Numa primeira etapa a rotação do exoplaneta é perturbada apenas pelo torque da estrela central. Em seguida, o modelo é estendido para incluir a influência gravitacional de um companheiro. Exploraremos numericamente os problemas utilizando as técnicas de superfície de seção, a análise espectral e mapas dinâmicos para diferentes condições iniciais. Mostramos que, dependendo das condições iniciais e parâmetros do sistema planetário, a rotação do planeta pode ser irregular devido à perturbação do terceiro corpo. Em particular, a Super-Terra Kepler-11b pode ter seu regime de rotação na ressonância spin-órbita 1 : 1, estável no domínio no problema de dois corpos, altamente perturbada pelo planeta Kepler-11c devido à configuração orbital de ambos estarem relacionadas com uma ressonância 5 : 4 de movimentos médios. Também faremos uma introdução ao estudo dos efeitos dissipativos na rotação de exoplanetas induzidos por maré para os planetas Kepler-10b e Corot-7b. E por fim calcularemos a probabilidade de captura na ressonância spin-órbita 3 : 2 para o planeta Mercúrio
Abstract: In this work we study the dynamics rotation of exoplanets disturbed by a third body. Emphasis will be placed on exoplanets with physical parameters (e.g. radius and mass) consistent with Earth's. In the first step the rotation of the exoplanet is disturbed only by the torque of the central star. Then the model is extended to include the gravitational influence of a companion. We numerically explore the problem using surface of sections, spectral analysis and dynamic maps for several initial conditions. We show that, depending on the initial conditions and parameters of the planetary system, the planet's rotation can be irregular due to the disturbance of the third body. In particular, the Super-Earth Kepler-11b can have its rotation in 1 : 1 spin-orbit resonance, stable in the problem of two bodies, highly disturbed by the planet Kepler- 11c due to orbital configuration close to the 5 : 4 mean motion resonance. We will also show an introduction of dissipative effects in the exoplanet's rotation induced by tides, applied to the planets Kepler-10b and Corot-7b. Finally we calculate the capture probability in the spin-orbit resonance 3 : 2 to Mercury
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Cabanac, Rémi A. "Astronomie avec miroirs liquides." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0009/NQ36242.pdf.
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Le, Boeuffle André. "Astronomie, astrologie : lexique latin /." Paris : Picard, 1987. http://catalogue.bnf.fr/ark:/12148/cb34970568x.
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Leitz, Christian. "Studien zur ägyptischen Astronomie /." Wiesbaden : O. Harrassowitz, 1989. http://catalogue.bnf.fr/ark:/12148/cb35518525s.
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Craine, Ashton. "British amateur astronomers in the Nineteenth Century." Thesis, Open University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393186.
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Motta, Mariele Katherine Faria 1983. "The dark universe = observables and degeneracies = O universo escuro : observáveis e degenerecências." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278597.
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Orientador: Pedro Cunha de HolandaTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Gostaríamos de explorar as consequências da ausência de conhecimento prévio sobre o modelo correto para energia escura que permita interpretar as observações cosmológicas. A magnitude das distorções no espaço de redshift e da lente gravitacional fraca é determinada pela métrica na quais galáxias e luzes se propagam. Mostramos que, com observações precisas o suficiente, é possível utilizar estes dados para reconstruir a métrica no nosso cone de luz passado e portanto, o stress-anisotrópico e os potenciais gravitacionais podem ser medidos independentemente de modelo. Exploramos a degenerescência escura, ou o fato de que matéria e energia escura são indistinguíveis pois afetam o setor visível apenas através dos potenciais gravitacionais que produzem. Esta degenerescência permanece a menos que se suponha um modelo para energia escura: o bias entre galáxias e perturbações de matéria escura não pode ser determinado; e apenas quando o princípio da equivalência é assegurado, pode-se identificar a velocidade da matéria escura com a das galáxias. Mesmo com estas limitações, é possível construir testes para classes de modelos de energia escura que se baseiam em medidas em diferentes escalas e redshifts e não dependem de parametrizações ou condições iniciais. Demonstramos como se pode descartar a classe mais geral de modelos escalares-tensoriais sem precisar supor a validade do regime quasi-estático. Finalmente, discutimos como a degenerência escura se manifesta em uma análise dependente de modelo
Abstract: We would like to explore the consequences of having no prior knowledge about the correct model for dark energy that would allow us to interpret observations. The magnitude of redshift-space distortions and weak gravitational lensing is determined by the metric on which galaxies and light propagate. With precise enough observations it is then possible to use this data to reconstruct the metric on our past lightcone, therefore anisotropic stress and gravitational potentials can be measured in a model-independent way. We explore the dark degeneracy, or the fact that dark matter and dark energy are indistinguishable, for they affect the visible sector only through the gravitational potential they produce. This degeneracy remains unless a dark energy model is provided: the bias between dark matter and galaxies cannot be determined; and only when the Equivalence Principle is valid, one can identify the velocities of dark matter with that of the galaxies. In spite of these limitations, it is possible to construct tests for classes of dark energy models that are based on measurements at different scales and redshifts and do not depend on parametrizations or initial conditions. We demonstrate how one can rule out the most general class of scalar-tensor models without having to assume quasi-staticity. Finally, we discuss how the dark degeneracy manifests itself in a model-dependent analysis
Doutorado
Física
Doutora em Ciências
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Rodrigues, Marta de Souza. "A diversidade do conhecimento sobre o céu e o ensino de astronomia: propostas didáticas e potencialidades da astronomia cultural." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/81/81131/tde-21032016-141809/.
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A presente pesquisa analisou materiais e propostas didáticas sobre o tema da astronomia cultural, tendo em vista sua inserção no ensino de tópicos de Física e Ciências na educação básica. A astronomia cultural pode ser tomada como o estudo das relações entre os saberes produzidos sobre o céu e as dinâmicas socioculturais de um dado grupo. A existência de uma grande multiplicidade de culturas indica a possibilidade de inúmeras formas de se relacionar com os elementos celestes. Tal diversidade pouco ou raramente é explorada, sendo um dos objetos desta pesquisa evidenciar que as discussões desta temática podem ser potencialmente interessantes para trabalhar em sala de aula a questão do respeito à diversidade cultural, apresentando aos estudantes outras lógicas de pensamento, distintas das referências da cultura ocidental. Foram realizadas revisões bibliográficas a fim de construir um panorama da produção dos pesquisadores da área de ensino de ciências junto aos temas do multiculturalismo e da astronomia cultural. Este procedimento favoreceu o contato com materiais e propostas didáticas que foram selecionadas para comporem o conjunto de dados a ser trabalhado. Com base na metodologia da análise de conteúdo, doze documentos que abordaram a astronomia cultural de maneira articulada ao contexto da sala de aula foram analisados, investigando-se três dimensões de análise. Os questionamentos realizados se relacionam aos seguintes aspectos: principais temas abordados pelos materiais; tipos de perspectivas voltadas ao multiculturalismo e à noção de cultura; o papel de medidas legislativas, a exemplo da Lei Federal nº 11.645/08, no aumento da produção de materiais abordando a astronomia cultural. Dentre os resultados da análise, verificou-se que os temas com maior frequência estão relacionados a narrativas sobre o funcionamento do universo e aos asterismos (ou constelações) de algumas etnias indígenas, sendo pouco recorrente o trabalho aprofundado com variadas estruturas de pensamento ou outras visões de mundo distintas da cultura ocidental. Sobre a abordagem ao multiculturalismo, houve uma polarização entre um viés diferencialista, que valoriza as diferenças particulares dos grupos, e uma postura intercultural, com ênfase no diálogo. Almeja-se que o trabalho possa contribuir para evidenciar algumas das potencialidades do ensino de astronomia cultural na educação básica, ao inserir discussões voltadas a diversidade cultural a fim de formar indivíduos que estejam menos centrados nas práticas de seu próprio grupo e mais abertos ao intercâmbio entre culturas e saberes distintos.The present research examined materials and didactic proposals on the topic of cultural astronomy, with a view to their inclusion in the teaching of physics and science topics in basic education. Cultural astronomy can be taken as the study of the relationship between knowledge produced about sky and socio-cultural dynamics of a given group. The existence of a great variety of cultures indicates the possibility of numerous ways to relate to the elements of the sky. Such little diversity or is rarely explored, being one of the objects of this research show that discussions of this theme can be potentially interesting to work in the classroom the issue of respect for cultural diversity, showing other students thought logic, other than the reference of Western culture. Bibliographical reviews were carried out in order to build a panorama of the production of the researchers of science teaching with the themes of multiculturalism and cultural astronomy. This procedure favored contact with didactic materials and proposals that have been selected to compose the set of data to be worked. Based on content analysis methodology, twelve documents that addressed cultural Astronomy of articulated way to the context of the classroom were analyzed investigating three dimensions of analysis. The questions made relate to the following aspects: main themes addressed by the materials; types of prospects aimed at multiculturalism and the concept of culture; the role of legislative measures, such as the Federal Law no. 11,645, increasing production of materials addressing the cultural astronomy. One of the results of the analysis, it was found that the subjects most often are related to narratives about the workings of the universe and the asterisms (or constellations) of some indigenous ethnic groups, being little in-depth work with recurrent varied structures of thoughts or other worldviews. On the approach to multiculturalism, there\'s been a polarization between a differentialist bias, that values the differences of private groups, and an intercultural attitude. Aims that the work will help to highlight some of the potential of cultural astronomy education in basic education, to enter discussions to cultural diversity in order to train individuals who are less focused on the practices of their own group and more open to the exchange between cultures and knowledge.
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Frajuca, Carlos. "Otimização de dois Modos Mecânicos para Detectores de Ondas Gravitacionais." Universidade de São Paulo, 1996. http://www.teses.usp.br/teses/disponiveis/43/43132/tde-03122013-185914/.
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Um Detector de Ondas Gravitacionais tipo Massa-Ressonante Esférico é otimizado. Primeiramente um modelo matemático para o detector com seis transdulatores indutivos supercondutivos de dois modos é usado para simular o desempenho de tal detector. Depois disso, um conjunto completo de experimentos para melhorar os fatores de qualidade mecânico e elétrico do transdutor e dos acoplamentos entre suas partes é mostrado e os resultados, discutidos.A Spherical Resonant-Mass Detector of Gravitational Waves is optimized. First, a mathematical model for the detector with six inductive superconducting two-mode transducers is used to simulate the performance of such detector. After that, a complete set of experiments to improve the mechanical and the electrical quality factors of the materials and the transducer attachments is shown, and the results are discussed.
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Otalora, Patiño Giovanni. "Energia escura acoplada /." São Paulo, 2010. http://hdl.handle.net/11449/89570.
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Orientador: Rogério RosenfeldBanca: Alberto Vasquez Saa
Banca: Bruto Max Pimentel Escobar
Resumo: Na última década várias observações indicam que o universo está expandindo aceleradamente. Essa expansão acelerada pode ser explicada em um universo composto de 70% de energia escura e 30% de matéria (25% de matéria escura e 5% de matéria bariônica). A energia escura proporciona a pressão negativa necessária para produzir a aceleração em grandes escalas. Nesse trabalho faz-se uma revisão do modelo de um campo escalar como fonte da energia escura, conhecido genericamente como modelo de quintessência. Estuda-se o modelo de quintessência acoplada à matéria escura
Abstract: In the previous decade many observations indicate that the universe is accelerating. This rapid expansion can be explained in an universe made up of 70% of dark energy and 30% of matter (25% of dark matter and 5% of baryonic matter). The dark energy provides negative pressure to produce acceleration. In this work it is studied the model of Quintessence, a model of scalar field, as source of the dark energy. It is studied the model of Coupled Quintessence with dark matter
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Koerich, Luan Vinícius. "Dark matter in a 'Z IND. 3'-symmetry extension of the Standard model /." São Paulo, 2015. http://hdl.handle.net/11449/154727.
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Orientador: Rogério RosendeldCo-orientador: Nicolás Bernal
Banca: Ricardo D'Elia Matheus
Banca: Renata Zukanovich Funchal
Resumo: A matéria escura é responsável por cerca de 85% de toda a matéria do universo. Sabe-se que ela possui um longo tempo de vida, que é neutra e interage com a matéria comum apenas gravitacionalmente. Muitos modelos foram aventados para descrever as possíveis partículas de matéria escura, muitos deles baseados em extensões do modelo padrão para partículas elementares. Em particular, há os modelos de partículas massivas interativas por força forte, os SIMPs, que estendem o modelo padrão com um setor escalar extra contendo todas as partículas de matéria escura, cuja estabilidade é garantida por uma simetria discreta, a qual respeitam. Essa simetria também estende as possível interações entre as partículas de matéria escura para além da usual auto-aniquilação de pares e do contexto do problema de Lee-Weinberg, descrito pelas partículas massivas interagentes por força fraca, os WIMPs. Neste trabalho postulamos a existência de um setor escalar com uma simetria discreta 'Z IND. 3'; consequente de uma quebra de simetria U(1)DM global. Esta simetria permite que processos de semi-aniquilação e aniquilação 3 "SETA" 2 também ocorram, além do usual processo de auto-aniquilação. Estudaremos esses três cenários, encontrando as soluções das equações de Boltzmann e comparando suas respectivas abundâncias com o resultado observacional, para podermos avaliar nosso modelo. Começaremos por revisar importantes conceitos da cosmologia padrão e por apresentar o modelo. Então revisaremos as soluções numéricas para as equações, e apresentaremos nossos próprios resultados para soluções semi-analíticas dos processos de semianiquilação e de aniquilação 3 'SETA' 2. Concluiremos por apresentar nossos próprios resultados para a solução da equação de Boltzmann para o processo 3 'SETA' 2 usando uma seção de choque que é dependente da temperatura, calculada com o pacote CalcHEP
Abstract: Dark matter accounts for approximately 85% of all the matter in the universe. It is known to have a long lifetime, to be neutral and to interact with ordinary matter almost only gravitationally. There have been several models to suggest possible particles for the dark matter, many of them relying on extensions to the standard model of elementary particles. In particular, there are SIMP (strongly-interacting massive particles) models, which extend the standard model by an extra scalar sector containing the dark-matter particles, whose stability is provided by a discrete symmetry. This symmetry also extends the possible interactions between the dark-matter particles to beyond the usual pair annihilation and Lee-Weinberg scenario described by the WIMP (weakly-interacting massive particles) models. In our study, we postulate the existence of an extended dark sector with a 'Z IND. 3' discrete symmetry, which is the consequence of a global U(1)DM symmetry breaking. This symmetry allows the semi-annihilation and 3 'SETA' 2 annihilation processes to take place, besides the usual self-annihilation process. We will study each of these three scenarios, solving the respective Boltzmann equations and comparing the correspondent relic abundance to the observed one, in order to verify the liability of each of them. We will start by reviewing important aspects of standard cosmology and presenting our model. Then we will review the numerical solutions for the equations, and present our own results for semi-analytical solutions to the semi- and 3 'SETA' 2 annihilation processes. We will end by presenting our own results on solving the 3 'SETA' 2 Boltzmann equation for a temperature-dependent cross-section, calculated with the CalcHEP package
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Koerich, Luan Vinícius [UNESP]. "Dark matter in a 'Z IND. 3'-symmetry extension of the Standard model." Universidade Estadual Paulista (UNESP), 2015. http://hdl.handle.net/11449/154727.
Full textAbstract:
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000876019.pdf: 830419 bytes, checksum: d04b4fc0f1ac3688428cce3a07901b9e (MD5)A matéria escura é responsável por cerca de 85% de toda a matéria do universo. Sabe-se que ela possui um longo tempo de vida, que é neutra e interage com a matéria comum apenas gravitacionalmente. Muitos modelos foram aventados para descrever as possíveis partículas de matéria escura, muitos deles baseados em extensões do modelo padrão para partículas elementares. Em particular, há os modelos de partículas massivas interativas por força forte, os SIMPs, que estendem o modelo padrão com um setor escalar extra contendo todas as partículas de matéria escura, cuja estabilidade é garantida por uma simetria discreta, a qual respeitam. Essa simetria também estende as possível interações entre as partículas de matéria escura para além da usual auto-aniquilação de pares e do contexto do problema de Lee-Weinberg, descrito pelas partículas massivas interagentes por força fraca, os WIMPs. Neste trabalho postulamos a existência de um setor escalar com uma simetria discreta 'Z IND. 3'; consequente de uma quebra de simetria U(1)DM global. Esta simetria permite que processos de semi-aniquilação e aniquilação 3 SETA 2 também ocorram, além do usual processo de auto-aniquilação. Estudaremos esses três cenários, encontrando as soluções das equações de Boltzmann e comparando suas respectivas abundâncias com o resultado observacional, para podermos avaliar nosso modelo. Começaremos por revisar importantes conceitos da cosmologia padrão e por apresentar o modelo. Então revisaremos as soluções numéricas para as equações, e apresentaremos nossos próprios resultados para soluções semi-analíticas dos processos de semianiquilação e de aniquilação 3 'SETA' 2. Concluiremos por apresentar nossos próprios resultados para a solução da equação de Boltzmann para o processo 3 'SETA' 2 usando uma seção de choque que é dependente da temperatura, calculada com o pacote CalcHEP
Dark matter accounts for approximately 85% of all the matter in the universe. It is known to have a long lifetime, to be neutral and to interact with ordinary matter almost only gravitationally. There have been several models to suggest possible particles for the dark matter, many of them relying on extensions to the standard model of elementary particles. In particular, there are SIMP (strongly-interacting massive particles) models, which extend the standard model by an extra scalar sector containing the dark-matter particles, whose stability is provided by a discrete symmetry. This symmetry also extends the possible interactions between the dark-matter particles to beyond the usual pair annihilation and Lee-Weinberg scenario described by the WIMP (weakly-interacting massive particles) models. In our study, we postulate the existence of an extended dark sector with a 'Z IND. 3' discrete symmetry, which is the consequence of a global U(1)DM symmetry breaking. This symmetry allows the semi-annihilation and 3 'SETA' 2 annihilation processes to take place, besides the usual self-annihilation process. We will study each of these three scenarios, solving the respective Boltzmann equations and comparing the correspondent relic abundance to the observed one, in order to verify the liability of each of them. We will start by reviewing important aspects of standard cosmology and presenting our model. Then we will review the numerical solutions for the equations, and present our own results for semi-analytical solutions to the semi- and 3 'SETA' 2 annihilation processes. We will end by presenting our own results on solving the 3 'SETA' 2 Boltzmann equation for a temperature-dependent cross-section, calculated with the CalcHEP package
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Negrete, Regagnon Pedro. "Bispectral imaging in astronomy." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307433.
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Belokurov, Vasily. "Variability surveys in astronomy." Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401024.
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Price, Gareth James. "Microchannel plates in astronomy." Thesis, University of Leicester, 2001. http://hdl.handle.net/2381/8638.
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This thesis describes both round-pore microchannel plates (MCPs) used in energetic pho¬ton and particle detectors and their square-pore offspring, micropore optics (MPOs), used to focus x-rays. A Monte Carlo electron raytracing software package is described that is used to predict the energy and angular distribution of electrons (EDOE and ADOE) in a microchannel electron multiplier's output charge cloud, including saturated operation. The model is shown to agree with experimental evidence. The addition of a micromachined electrostatic lens to the end of a microchannel is modelled and found to have no beneficial effects upon the EDOE and ADOE of the channel. The current state of the art planar and slumped 'lobster eye' square-packed MPOs are evaluated. The best focus (5' FWHM) from a large format (61mm x 56mm), small chan¬nel (10μm side length) planar MPO is reported, together with the observation of high energy (~50keV →65keV) x-ray focusing from large (500:1) aspect ratio channels. The alignment of many small lobster eye MPOs to create a large optic for the Lobster-ISS instrument is discussed and the alignment jig constructed for this purpose is used to measure the bias angles of a Lobster specification MPO. The bias angle is found to be 4 ± 1.5'. The concept of the microchannel conic approximation to the Wolter type I and II x- ray lenses is reviewed. A radially-packed twin MPO Wolter approximation is then tested, which while of poor quality, demonstrates true Wolter II imaging with a peak gain greater than unity. Currently proposed (UK) astronomical instruments that employ MPOs are then discussed in the light of the results from the current generation of MPOs.
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Van, Tonder Vereese. "Beamforming for radio astronomy." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/96126.
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Thesis (MEng) -- Stellenbosch University, 2014.ENGLISH ABSTRACT: Beamforming is a technique used to combine signals from an array of antennas to effectively synthesize a single aperture and beam. In the Radio Astronomy community the technique is used to obtain a desirable beam pattern as well as to electronically point the beam of an array. Next generation radio telescopes such as the Square Kilometre Array (SKA) surpass current technology and will extensively make use of beamforming techniques. Various factors determine the output of a beamformer; however, given an array with a fixed configuration only the weights applied to the incoming signals affect the synthesized aperture and beam. Furthermore, the incoming data must be processed in real-time, at a rate equal to the input-output rate of the processor. Both the weighting function and the real-time implementation of beamforming, are the primary subjects of this thesis. In this thesis various deterministic weighting functions are investigated. The algorithms are implemented in a matlab program, serving as a simulation tool for investigating the techniques. The program is verified by comparing the expected theoretical outcomes to the simulated output. For the program the following functionalities are included: a steering technique, spectral weighting, Dolph-Chebychev, and the Least Square Error algorithm. Applications of these techniques is investigated and their prominence in the Radio Astronomy community is established. For the real-time beamformer implementation, the UniBoard platform configured with beamformer firmware, is investigated. This is important as the UniBoard is an excellent example of a beamformer implementation within the Radio Astronomy community. The architecture is used to emulate a linear array by implementing a python control script, where the output corresponded accurately with the expected theoretical values. The thesis also constitutes the design and implementation of a digital frequency domain beamformer on the ROACH board. This processing board is employed by the Karoo Array Telescope (KAT-7) in South Africa. This work is therefore important as it demonstrates a beamformer implementation on an architecture in use by the Radio Astronomy community. An antenna array is designed and built for the verification of the beamformer design. Results with a good degree of accuracy were obtained and where errors exist they are discussed.
AFRIKKANSE OPSOMMING: Bundelvorming is ’n tegniek waarmee die seine van ’n antenna samestelling gekombineer word om ’n enkele effektiewe stralingsvlak en stralingspatroon te sintiseer. In die Radio Astronomie gemeenskap word die tegniek gebruik om ’n gewenste stralingspatroon te sintiseer sowel as om die rigting van die patroon elektronies te beheer. Die Square Kilometre Array (SKA) is ’n toekomstige radioteleskoop en sal grootliks gebruik maak van bundelvorming tegnieke. Die uitset van bundelvormers word geaffekteer deur verskeie faktore, maar vir ’n gegewe samestelling is dit net die gewigsfunksies wat toegepas word op die inkomende seine wat die gesintiseerde patroon kan beheer. Verder moet die inkomende data verwerk word teen ’n tempo gelykstaande aan die inset-en-uitsetkoers van die verwerker. Die gewigsfunksie so wel as die implementasie van die bundelvormer is albei primêre onderwerpe van die tesis. ’n Verskeindenheid van deterministiese bundelvormingstegnieke sal ondersoek word in hierdie tesis. Die algoritmes is in ’n matlab program geïmplementeer vir simulasie doeleindes. Die program is geverifieër deur die uitset te vergelyk met die verwagte teoretiese waardes. Die program sluit die volgende funksies in: ’n rigting beheer algoritme, spektraalgewigte, Dolph-Chebychev, en die minste vierkantsfout algoritme. Hierdie tegnieke is van belang weens hul toepassing in die Radio Astronomie gemeenskap. Vir die implementasie van ’n bundelvormer is die UniBoard hardeware, geprogrameer in ’n bundelvormings modus, van gebruik gemaak. Hierdie aspek is belangrik omdat die Uni- Board ’n goeie voorbeeld van ’n geïmplementeerde bundelvormer in die Radio Astronomie gemeenskap is. Die UniBoard word gebruik om ’n lineêre samestelling te emuleer deur in python ’n beheer skrip te skryf, waar die uitset van die emuleerder akkuraat ooreenstem met die verwagte waardes. Die tesis behels ook die ontwerp en implementasie van ’n digitale frekwensiegebied bundelvormer op die ROACH platform. Hierdie verwerker word tans gebruik in die Karoo Array Telescope (KAT-7) in Suid-Afrika. Hierdie werk is dus belangrik omdat dit die implementasie van ’n bundelvormer op tegnologie wat huidiglik in die Radio Astronomie gemeenskap gebruik word demonstreer. Daarbenewens is ’n antenna samestelling ontwerp en gebou om die bundelvormer te verifieër. Die resultate is akkuraat tot ’n redelike mate. Waar daar ’n fout onstaan het word dit in die tesis bespreek.
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Harris, Robert James. "Photonic spectroscopy in astronomy." Thesis, Durham University, 2015. http://etheses.dur.ac.uk/10975/.
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This thesis investigates photonic spectroscopy and its use in astronomy. In chapter two the theory associated with both astronomical spectroscopy and photonic spectroscopy is shown. The convergence of the two in the field of astrophotonics is discussed along with existing work in the field. In chapter three models of the Integrated Photonic Spectrograph are created and compared like-for-like with existing instruments. The results suggest that the Integrated Photonic Spectrograph will be similar to existing instruments in terms of size and will require more detector pixels for a full instrument. In chapter four the modelling is extended, examining the areas where pho- tonic spectroscopy could show advatanges over conventional instrumentation. This is done by varying spectral resolution, telescope diameter, seeing and num- ber of objects sampled. The results show that the Integrated Photonic Spec- trograph will perform best when the telescope is close to the diffraction-limit, both in terms of size and number of detector pixels required. Science cases are presented for these areas. In chapter five different concepts for a redesigned Integrated Photonic Spec- trograph are presented and the advantages and disadvatanges of the variations are commented upon. The two that are chosen for development require the telescope Point Spread Function to be reformatted to a long slit. This device, which we have named the photonic-dicer is presented in chapter six. Its design, manufacture and testing is discussed both in the laboratory and on sky in conjunction with the CANARY adaptive optics system. Finally chapter seven presents our concluding remarks and discussions for future work.
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Du, Buisson Lise. "Machine learning in astronomy." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/15502.
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The search to find answers to the deepest questions we have about the Universe has fueled the collection of data for ever larger volumes of our cosmos. The field of supernova cosmology, for example, is seeing continuous development with upcoming surveys set to produce a vast amount of data that will require new statistical inference and machine learning techniques for processing and analysis. Distinguishing between real objects and artefacts is one of the first steps in any transient science pipeline and, currently, is still carried out by humans - often leading to hand scanners having to sort hundreds or thousands of images per night. This is a time-consuming activity introducing human biases that are extremely hard to characterise. To succeed in the objectives of future transient surveys, the successful substitution of human hand scanners with machine learning techniques for the purpose of this artefact-transient classification therefore represents a vital frontier. In this thesis we test various machine learning algorithms and show that many of them can match the human hand scanner performance in classifying transient difference g, r and i-band imaging data from the SDSS-II SN Survey into real objects and artefacts. Using principal component analysis and linear discriminant analysis, we construct a grand total of 56 feature sets with which to train, optimise and test a Minimum Error Classifier (MEC), a naive Bayes classifier, a k-Nearest Neighbours (kNN) algorithm, a Support Vector Machine (SVM) and the SkyNet artificial neural network.
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Utting, Muriel. "Astronomy in Western Australia." Thesis, Utting, Muriel (1993) Astronomy in Western Australia. Masters by Research thesis, Murdoch University, 1993. https://researchrepository.murdoch.edu.au/id/eprint/51548/.
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This thesis is devoted to a study of the origins and achievements of astronomers in Western Australia from 1829 to 1912. It addresses the questions about the role of astronomy in WA society, the reasons for the establishment of the Perth Observatory, and its achievements between 1896 and 1912. More widely, the thesis addresses the general question of the role of astronomy in our society and the contributions which astronomers have made to the development of Western Australia.
The first Premier of Western Australia, Sir John Forrest, persuaded his Government to build an Observatory, promising that it would house necessary services for the State, that is, timekeeping, meteorology, geodesy, tidal predictions and education services, to provide a scientific basis for society.
This service developed despite continuing opposition and interference from the Government and some sections of society. The thesis assesses the role of Lord Forrest and the Government Astronomer, W.E. Cooke, and his staff.
The thesis examines the historical context of the founding of the Observatory, the initial tasks set for it by Cooke and the extent to which these goals were achieved. Cooke's experience in establishing a modern Observatory in a fledgling society is examined in detail in order to understand the reasons for his resignation in 1912 and the nature of his achievements.
This study is intended to be both a scientific and social history of astronomy in Western Australia. It examines the scientific achievements of the Perth Observatory over its first 1 6 years in relation to its original objectives. The thesis also examines the social impact of the Observatory on WA society. The extent of its contribution is best assessed in the long-term where the benefits and costs of years of painstaking work can be more clearly understood.
This thesis is intended to provide an insight into the role of astronomy in society and the costs and benefits of major scientific institutions. By focussing on the origins and early development of astronomy in WA we can see how the interplay of political, economic and social factors influences the development of science. We can also see how long it takes for scientific projects to reach maturity and how a long-term perspective is required in order to assess their outcomes.