Understanding dark matter halos with tidal caustics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 181-188).The products of interactions between galaxies with a high mass ratio and low orbital angular momentum are studied. The interactions scatter the material from the smaller galaxy into structures with distinctive dynamics and morphology, including high local densities and a simple density profile related to properties of the participating galaxies. The role of the larger galaxy's tides in creating these structures and their relation to a well-studied class of mathematical objects motivates us to name them "tidal caustics". We study the densities achievable in tidal caustics for a typical merger of this type using an example from the Andromeda galaxy to determine whether they are sufficient to produce a detectable gamma-ray signal from self-interactions in the dark matter component, for likely particle models of dark matter. We find that the expected signal is an order of magnitude too low to be detected with current instruments. We also study the constraints that can be placed on the properties of the participating galaxies by observing the surface brightness profiles of the tidal caustics. We find that the local gravity and gravity gradient of the larger galaxy, and the energy spread and initial phase space density of the smaller galaxy, can be jointly constrained by fitting this profile. The constraints are degenerate but model-independent. We find that measurements of multiple caustics and the velocity of the material in each caustic along the line of sight give information about the orbital angular momentum and the deviations from spherical symmetry in the larger galaxy, though this information is somewhat model-dependent. We discuss the main technical difficulty in fitting the surface brightness profile: determining the inclination angle of the caustic. We demonstrate that a simple model can successfully recover the necessary parameters for some cases, and that a simple modification to this model will improve its success rate.by Robyn Ellyn Sanderson.Ph.D

Epistemology of Experimental Gravity - Scientific Rationality

The evolution of gravitational tests from an epistemological perspective framed in the concept of rational reconstruction of Imre Lakatos, based on his methodology of research programmes. Unlike other works on the same subject, the evaluated period is very extensive, starting with Newton's natural philosophy and up to the quantum gravity theories of today. In order to explain in a more rational way the complex evolution of the gravity concept of the last century, I propose a natural extension of the methodology of the research programmes of Lakatos that I then use during the paper. I believe that this approach offers a new perspective on how evolved over time the concept of gravity and the methods of testing each theory of gravity, through observations and experiments. I argue, based on the methodology of the research programmes and the studies of scientists and philosophers, that the current theories of quantum gravity are degenerative, due to the lack of experimental evidence over a long period of time and of self-immunization against the possibility of falsification. Moreover, a methodological current is being developed that assigns a secondary, unimportant role to verification through observations and/or experiments. For this reason, it will not be possible to have a complete theory of quantum gravity in its current form, which to include to the limit the general relativity, since physical theories have always been adjusted, during their evolution, based on observational or experimental tests, and verified by the predictions made. Also, contrary to a widespread opinion and current active programs regarding the unification of all the fundamental forces of physics in a single final theory, based on string theory, I argue that this unification is generally unlikely, and it is not possible anyway for a unification to be developed based on current theories of quantum gravity, including string theory. In addition, I support the views of some scientists and philosophers that currently too much resources are being consumed on the idea of developing quantum gravity theories, and in particular string theory, to include general relativity and to unify gravity with other forces, as long as science does not impose such research programs. DOI: 10.13140/RG.2.2.35350.7072

Third International Conference on Inverse Design Concepts and Optimization in Engineering Sciences (ICIDES-3)

Papers from the Third International Conference on Inverse Design Concepts and Optimization in Engineering Sciences (ICIDES) are presented. The papers discuss current research in the general field of inverse, semi-inverse, and direct design and optimization in engineering sciences. The rapid growth of this relatively new field is due to the availability of faster and larger computing machines

Pictorial space in relationship to beliefs and cognitive structures : the Ixion room, the Bardi chapel, the Nymphéas

Ma recherche consiste à examiner l'espace pictural de trois œuvres provenant de trois périodes distinctes de l'histoire de l'art afin de démontrer que l'art participe, d'une part, d'un modèle culturel spécifique et, d'autre part, de données perceptivo-spatiales universellement partagées qui relient entre eux des individus soumis à des expériences historiquement très distinctes. Le corpus se compose de la salle dédiée à Ixion datant de la fin de l'empire romain, vers le premier siècle après Jésus-Christ; des fresques de Giotto exécutées pour la chapelle Bardi au début du XIVe siècle, donc à la fin du Moyen-Âge et au début de la Renaissance; et des Nymphéas de Monet, œuvre commencée à la fin du XIXe et terminée au début du XXe siècle. La méthodologie utilisée dans la présente thèse pourrait être qualifiée d'analyse multiple niveau des éléments suivants de la perception : 1) les catégories de croyances de premier ordre, ou croyances primaires, qui sont sous-jacentes à toutes les autres croyances et jouent un rôle important dans la production de toutes les œuvres d'art. Les croyances primaires comprennent les croyances physiologiques et perceptuelles, et la sous-catégorie des croyances multi-sensorielles; 2) les catégories de croyances de second ordre ou croyances conceptuelles; les croyances philosophiques, spirituelles et religieuses, les croyances scientifiques (relativement au système optique), les croyances mathématiques et les croyances médicales (relativement au corps humain) sont des croyances conceptuelles. Les croyances conceptuelles peuvent englober un domaine de la connaissance, ce qui est le cas pour les cinq croyances qui servent ici d'arrière-plan à l'analyse des trois œuvres d'art choisies. J'avance que la production et la réception des œuvres d'art, et dans ce cas particulier de l'espace pictural, supposent non seulement un rapport multi-sensoriel, mais qu'elles sont également liées à l'acquisition de croyances qui influent sur la formation et la réception des représentations de l'espace pictural qui s'opèrent conjointement avec la navigation du corps humain dans l'espace du réel. Les représentations étudiées ici ont été intentionnellement choisies parce qu'elles étreignent de façon manifeste la structure architecturale qui les soutient, et à cause de leur intégration dans cette structure de soutien aux fins d'étendre la dimension spatiale et les processus par lesquels nous nous situons dans cette dimension. La présente thèse vise à démontrer que perception et conception sont, dans un sens, le miroir l'une de l'autre, un miroir qui existe chez l'artiste et chez le spectateur. C'est la base même de leur cohérence, ou commensurabilité, et le moyen par lequel la signification que nous pouvons attribuer à une œuvre donnée réussit à nous convaincre de son autorité. J'ai cherché à démontrer que la représentation de l'espace pictural n'est pas une simple affaire de conventions, ni une histoire quelconque de progrès, et certainement pas une question de style. Elle repose en fait sur les croyances, ces fragiles mais tenaces éléments qui s'associent à l'occasion à ce que nous considérons comme un savoir convaincant. L'artiste et le spectateur fusionnent sur l'axe de la croyance, et un acte de persuasion devient un acte d'interprétation.\ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : histoire de l'art, peinture, espace pictural, perception, conception, croyances

PSA 2018

These preprints were automatically compiled into a PDF from the collection of papers deposited in PhilSci-Archive in conjunction with the PSA 2018

Proceedings of the ECCOMAS Thematic Conference on Multibody Dynamics 2015

This volume contains the full papers accepted for presentation at the ECCOMAS Thematic Conference on Multibody Dynamics 2015 held in the Barcelona School of Industrial Engineering, Universitat Politècnica de Catalunya, on June 29 - July 2, 2015. The ECCOMAS Thematic Conference on Multibody Dynamics is an international meeting held once every two years in a European country. Continuing the very successful series of past conferences that have been organized in Lisbon (2003), Madrid (2005), Milan (2007), Warsaw (2009), Brussels (2011) and Zagreb (2013); this edition will once again serve as a meeting point for the international researchers, scientists and experts from academia, research laboratories and industry working in the area of multibody dynamics. Applications are related to many fields of contemporary engineering, such as vehicle and railway systems, aeronautical and space vehicles, robotic manipulators, mechatronic and autonomous systems, smart structures, biomechanical systems and nanotechnologies. The topics of the conference include, but are not restricted to: ● Formulations and Numerical Methods ● Efficient Methods and Real-Time Applications ● Flexible Multibody Dynamics ● Contact Dynamics and Constraints ● Multiphysics and Coupled Problems ● Control and Optimization ● Software Development and Computer Technology ● Aerospace and Maritime Applications ● Biomechanics ● Railroad Vehicle Dynamics ● Road Vehicle Dynamics ● Robotics ● Benchmark ProblemsPostprint (published version