1,953 research outputs found
The Dirac theory of constraints, the Gotay-Nester theory and Poisson geometry
The Dirac theory of constraints has been widely studied and applied very successfully by physicists since the original works by Dirac and by Bergmann. From a mathematical standpoint, several aspects of the theory have been exposed rigorously afterwards by many authors. However, many questions related to, for instance, singular or infinite dimensional cases remain open. The work of Gotay and Nester presents a mathematical generalization in terms of presymplectic geometry, which introduces a dual point of view. We present a study of the Dirac theory of constraints emphasizing the duality between the Poisson-algebraic and the geometric points of view, related respectively to the work of Dirac and of Gotay and Nester, under strong regularity conditions. We deal with some questions insufficiently treated in the literature: a study of uniqueness of solution; avoiding almost completely the use of coordinates; the role of the Pontryagin bundle. We also show how one can globalize some results usually treated locally in the literature. For instance, we introduce the globalnotion of second class submanifoldas being tangent to a second class subbundle. A general study of global results for Dirac and Gotay-Nester theories remains an open question in this theory.La TeorÃa de ligaduras deDirac, lateorÃa de Gotay-Nester y geometrÃa dePoissin. La teorÃa de Dirac ha sido ampliamente estudiada y aplicada muy exitosamente por los fÃsicos desde los trabajos originales de Dirac y de Bergmann. Desde un punto de vista matemático, varios aspectos de la teorÃa han sido expuestos rigurosamente por varios autores. Sin embargo, aún quedan abiertas varias preguntas relacionadas, por ejemplo, con casos singulares o infinito-dimensionales. El trabajo de Gotay y Nester presenta una generalización matemática en términos de la geometrÃa presimpléctica, lo cual introduce un punto de vista dual. Presentamos un estudio de la teorÃa de ligaduras de Dirac enfatizando la dualidad entre los puntos de vista de las álgebras de Poisson y de la geometrÃa presimpléctica, relacionados respectivamente con los trabajos de Dirac y de Gotay-Nester, bajo condiciones de regularidad fuertes. Abordamos algunas cuestiones insuficientemente tratadas en la literatura: un estudio de la unicidad de solución; evitar casi completamente el uso de coordenadas; el rol del fibrado de Pontryagin. También mostramos cómo se pueden globalizar algunos resultados usualmente tratados localmente en la literatura. Por ejemplo, introducimos la noción globalde subvariedad de segunda clasecomo variedad tangente a un subfibrado de segunda clase. Un estudio general de resultados globales para las teorÃas de Dirac y de Gotay-Nester sigue siendo una pregunta abierta en esta teorÃa.Fil: Cendra, Hernan. Universidad Nacional del Sur. Departamento de Matemática; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca; ArgentinaFil: Etchechoury, MarÃa del Rosario. Universidad Nacional de La Plata; ArgentinaFil: Ferraro, Sebastián José. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca. Instituto de Matemática BahÃa Blanca. Universidad Nacional del Sur. Departamento de Matemática. Instituto de Matemática BahÃa Blanca; Argentin
Economic Effects of Global Warming under Stock Growth Uncertainty: The European Sardine Fishery
Global warming of the oceans is expected to alter the environmental conditions that determine the growth of a fishery resource. Most climate change studies are based on models and scenarios that focus on economic growth, or they concentrate on simulating the potential losses or cost to fisheries due to climate change. However, analysis that addresses model optimization problems
to better understand of the complex dynamics of climate change and marine ecosystems is still lacking. In this paper a simple algorithm to compute transitional dynamics in order to quantify the effect of climate change on the European sardine fishery is presented. The model results indicate that global warming will not necessarily lead to a monotonic decrease in the expected biomass levels. Our results show that if the resource is exploited optimally then in the short run, increases in the surface temperature of the fishery ground are compatible with higher expected biomass and economic profit.Financial aid from the European Commission (MYFISH, FP7-KBBE-2011-5,
nº 289257), the Spanish Ministry of Science and Innovation (ECO2009-14697-C02-02) and the Spanish
Ministry of Economy and Competitiveness (ECO2012-39098-C06-01 and ECO2012-35820) is gratefully
acknowledged. The first draft of the paper was written while Jose MarÃa Da Rocha was visiting Institut
d'Anà lisi Econòmica-CSIC, and the hospitality extended by its members is gratefully acknowledged.
Sebastián Villasante acknowledges the financial support of the Latin American and Caribbean
20
Environmental Economic Program, the Swedish International Cooperation Development Agency, the
International Development Research Center, and the Pedro Barrié de La Maza Foundation. The author is
also grateful to the Beijer International Institute of Ecological Economics (The Royal Swedish Academy
of Sciences, Sweden) for awarding him the Karl-Göran Mäler Scholarship
Análisis crÃtico de la renta básica: costes e incentivos. Aplicación al caso español
This paper estimates the costs of basic income and analyses its incentives to conclude that there is an inverse relationship between them. The more unconditional the basic income is, the less incentive problems will arise, but it will be more costly. We approximate its costs to the case of Spain, both using a macroeconomic approach and one with micro data. The high cost of the universal basic income implementation requires to limit the number of recipients by income or labour status and, therefore, labour supply and human capital incentive problems could be materialized. Implications for inequality are also discussed.Este trabajo estima los costes de la renta básica y analiza los problemas de incentivos que puede generar, para concluir que existe una relación inversa entre ambos. Cuanto más incondicional es la renta básica menos problemas de incentivos provoca, pero más costosa es desde un punto de vista financiero. Se estima, para el caso español, su posible coste utilizando tanto un enfoque macroeconómico como uno con micro datos. El elevado coste de aplicar la renta básica universal hace necesario limitar el número de perceptores para que sea posible su implementación, pero esto podrÃa provocar importantes problemas de incentivos a la oferta de trabajo y a la acumulación de capital humano. También se discuten las posibles implicaciones en materia de desigualdad.Instituto Complutense de Análisis EconómicoFac. de Ciencias Económicas y EmpresarialesTRUEpu
Infrared thermograms applied to near-field testing
Electromagnetic fields close to radiant structures can be measured quickly using an infrared camera. Examples of induced fields by wire antennas over a detection screen at distances shorter than one wavelength are presented. The measured thermograms agree with simulations that take into account heat propagation on the detection screen.Peer ReviewedPostprint (published version
Using a 3DOF Parallel Robot and a Spherical Bat to hit a Ping-Pong Ball
Playing the game of Ping-Pong is a challenge to human abilities since it requires developing skills, such as fast reaction capabilities, precision of movement and high speed mental responses. These processes include the utilization of seven DOF of the human arm, and translational movements through the legs, torso, and other extremities of the body, which are used for developing different game strategies or simply imposing movements that affect the ball such as spinning movements. Computationally, Ping-Pong requires a huge quantity of joints and visual information to be processed and analysed, something which really represents a challenge for a robot. In addition, in order for a robot to develop the task mechanically, it requires a large and dexterous workspace, and good dynamic capacities. Although there are commercial robots that are able to play Ping-Pong, the game is still an open task, where there are problems to be solved and simplified. All robotic Ping-Pong players cited in the bibliography used at least four DOF to hit the ball. In this paper, a spherical bat mounted on a 3-DOF parallel robot is proposed. The spherical bat is used to drive the trajectory of a Ping-Pong ball.Fil: Trasloheros, Alberto. Universidad Aeronáutica de Querétaro; MéxicoFil: Sebastián, José MarÃa. Universidad Politécnica de Madrid; España. Consejo Superior de Investigaciones CientÃficas; EspañaFil: Torrijos, Jesús. Consejo Superior de Investigaciones CientÃficas; España. Universidad Politécnica de Madrid; EspañaFil: Carelli Albarracin, Ricardo Oscar. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - San Juan. Instituto de Automática. Universidad Nacional de San Juan. Facultad de IngenierÃa. Instituto de Automática; ArgentinaFil: Roberti, Flavio. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - San Juan. Instituto de Automática. Universidad Nacional de San Juan. Facultad de IngenierÃa. Instituto de Automática; Argentin
Cannibalism in Telmatobius rubigo (Anura: Telmatobiidae) and comments on seasonal variation of diet
In the present study, we report a case of cannibalism in T. rubigo and analyze the seasonal variation of the diet. Finally, we discussed the implications of our registers for the ecology and conservation of this threatened aquatic Andean frog.Fil: Gastón, MarÃa Soledad. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; ArgentinaFil: Salica, MarÃa José. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; ArgentinaFil: Akmentins, Mauricio Sebastián. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; Argentin
Sección Especial sobre Visión por Computador y Modelado 3D
[ES] La presente sección especial está compuesta por seis trabajos que abordan tanto novedosos algoritmos como relevantes aplicaciones. Es necesario destacar que la visión 3D se encuentra en un momento de importante desarrollo, ya que la aparición de nuevos equipos (cámaras ToF, escáneres láseres…) está permitiendo el planteamiento y la resolución de nuevos problemas. Por otro
lado, la creación de modelos 3D es una fase fundamental para la resolución de estos problemas. Además de las ya tradicionales aplicaciones industriales, destacan las aportaciones en el guiado y modelado de sistemas autónomos, su interacción con humanos o el reconocimiento y modelado de objetos en entornos complejos.Sebastián, JM. (2012). Sección Especial sobre Visión por Computador y Modelado 3D. Revista Iberoamericana de Automática e Informática industrial. 9(4):417-418. https://doi.org/10.1016/j.riai.2012.09.015OJS4174189
DesafÃos de las tecnologÃas emergentes y la alfabetización digital
En esta lÃnea de investigación se busca mejorar la calidad de la educación y la formación docente para la enseñanza de las ciencias. Para ello se continúa estudiando las posibilidades de las tecnologÃas informáticas para definir metodologÃas de enseñanza interactiva y elaborar lineamientos que aporten al diseño de aplicaciones interactivas basadas en entornos virtuales - como videojuegos, simulaciones, y nuevas tecnologÃas como la Televisión Digital Interactiva (TVDi) e Interfaces Cerebro- Computador (ICC)
Fluctuations and Instabilities of Ferromagnetic Domain Wall pairs in an External Magnetic Field
Soliton excitations and their stability in anisotropic quasi-1D ferromagnets
are analyzed analytically. In the presence of an external magnetic field, the
lowest lying topological excitations are shown to be either soliton-soliton or
soliton-antisoliton pairs. In ferromagnetic samples of macro- or mesoscopic
size, these configurations correspond to twisted or untwisted pairs of Bloch
walls. It is shown that the fluctuations around these configurations are
governed by the same set of operators. The soliton-antisoliton pair has exactly
one unstable mode and thus represents a critical nucleus for thermally
activated magnetization reversal in effectively one-dimensional systems. The
soliton-soliton pair is stable for small external fields but becomes unstable
for large magnetic fields. From the detailed expression of this instability
threshold and an analysis of nonlocal demagnetizing effects it is shown that
the relative chirality of domain walls can be detected experimentally in thin
ferromagnetic films. The static properties of the present model are equivalent
to those of a nonlinear sigma-model with anisotropies. In the limit of large
hard-axis anisotropy the model reduces to a double sine-Gordon model.Comment: 15 pages RevTex 3.0 (twocolumn), 9 figures available on request, to
appear in Phys Rev B, Dec (1994
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