Non-Linear Affine Embedding of the Dirac Field from the Multiplicity-Free SL(4,R) Unirreps

The correspondence between the linear multiplicity-free unirreps of SL(4, R) studied by Ne'eman and {\~{S}}ija{\~{c}}ki and the non-linear realizations of the affine group is worked out. The results obtained clarify the inclusion of spinorial fields in a non-linear affine gauge theory of gravitation.Comment: 13 pages, plain TeX, macros include

Factores que favorecen el aprendizaje de la estadística con proyectos

El presente estudio tiene como objetivo describir la percepción que tienen los alumnos sobre el aprendizaje de la estadística con proyectos e identificar los factores que favorecen su aprendizaje. La investigación se fundamenta en la Reforma Integral de Educación Media Superior (RIEMS en México), la cual se implementó desde 2011 a través de un enfoque por competencias

The role of translational invariance in non linear gauge theories of gravity

The internal structure of the tetrads in a Poincar\'e non linear gauge theory of gravity is considered. Minkowskian coordinates becomes dynamical degrees of freedom playing the role of Goldstone bosons of the translations. A critical length allowing a covariant expansion similar to the weak field approach is deduced, the zeroth order metric being maximally symmetric (Minkowskian in some cases).Comment: 17 pages, LaTe

Gravitational contribution to fermion masses

In the context of a nonlinear gauge theory of the Poincar\'e group, we show that covariant derivatives of Dirac fields include a coupling to the translational connections, manifesting itself in the matter action as a universal background mass contribution to fermions.Comment: revtex4, 9 pages, no figures, to be published in Eur.Phys.J.C, 200

Reaffirming the connection between the Galactic stellar warp and the Canis Major overdensity

We perform a critical re-analysis and discussion of recent results presented in the literature which interpret the CMa overdensity as the signature of an accreting dwarf galaxy or a new substructure within the Galaxy. Several issues are addressed. We show that arguments against the ``warp'' interpretation are based on an erroneous perception of the Milky Way. There is nothing anomalous with colour--magnitude diagrams on opposite sides of the average warp mid-plane being different. We witnessed the rise and fall of the blue plume population, first attributed to young stars in a disrupting dwarf galaxy and now discarded as a normal disc population. Similarly, there is nothing anomalous in the outer thin+thick disc metallicities being low (-1<[Fe/H]<-0.5), and spiral arms (as part of the thin disc) should, and do, warp. Most importantly, we show unambiguously that, contrary to previous claims, the warp produces a stellar overdensity that is distance-compatible with that observed in CMa.The CMa over-density remains fully accounted for in a first order approach by Galactic models without new substructures. Given the intrinsic uncertainties (concerning the properties of the warp, flare and disc cutoff, the role of extinction and degeneracy), minor deviations with respect to these models are not enough to support the hypothesis of an accreted dwarf galaxy or new substructure within the Milky Way disc.Comment: A&A Letter, accepted, 4 pages, 3 figure

Nonlinear gauge realization of spacetime symmetries including translations

We present a general scheme for the nonlinear gauge realizations of space-time groups on coset spaces of the groups considered. In order to show the relevance of the method for the rigorous treatment of the translations in gravitational gauge theories, we apply it in particular to the affine group. This is an illustration of the family of spacetime symmetries having the form of a semidirect product H ⊗ T, where H is the stability subgroup and T are the translations. The translational component of the connection behaves like a true tensor under H when coset realizations are involved. c Plenum Publishing CorporationPeer Reviewe

Microstructure and mechanical properties of high temperature protonic conductors fabricated by melt growth

Se han estudiado conductores protónicos de alta temperatura (CPAT) fabricados por fusión de zona flotante asistida por láser (SrCe0.9Y0.1O3-δ , SrCe0.8Y0.2O3-δ , SrZr0.9Y0.1O3-δ , SrZr0.8Y0.2O3-δ , Sr3 (Ca1.18Nb1.82)O9-δ y SrTi0.95Sc0.05O3-δ ). La caracterización microestructural se ha realizado mediante Microscopía Electrónica de Barrido y Transmisión (MEB, MET). Los materiales tienen una estructura celular, con células de anchuras entre 10-50 µm y regiones intercelulares superiores a 1 µm de espesor. El análisis de difracción indica que las células son cristalinas y que la región intercelular es amorfa. La MET revela que las células presentan múltiples defectos planares, separadas por regiones rotadas con la misma estructura cristalográfica. Las propiedades mecánicas a altas temperaturas fueron estudiadas a partir de ensayos de compresión bajo velocidad de deformación y carga constantes. Nuestros materiales resisten tensiones de 500 MPa a 700 ºC, 400 MPa a 1100 ºC y 370 MPa a 1300 ºC, observándose deformación plástica a 1100 ºC y 1300 ºC. El mejor comportamiento mecánico fue obtenido para los sistemas Sr3 (Ca1.18Nb1.82)O9- δ _ y SrZr0.9Y0.1O3-δ . Las tensiones y resistencias en fluencia de estos sistemas son mejores que las de las cerámicas policristalinas CPAT de similar estructura y composición. Después de los ensayos mecánicos, las muestras fueron estudiadas por MEB y MET. La fractura comenzó a propagarse siguiendo las regiones intercelulares. En las muestras deformadas plásticamente se detecta la actividad de dislocaciones.High temperature protonic conductors (HTPC) were successfully fabricated by melt growth using the laser heated floating zone method (SrCe0.9Y0.1O3-δ , SrCe0.8Y0.2O3-δ , SrZr0.9Y0.1O3-δ , SrZr0.8Y0.2O3-δ , Sr3 (Ca1.18Nb1.82)O9-δ and SrTi0.95Sc0.05O3-δ ). Microstructural characterization was performed by scanning and transmission electron microscopy (SEM, TEM). The materials have a cellular microstructure, with cell width ranging between 10-50 µm and intercellular regions up to 1 µm thick. The diffraction analysis indicates that the cells are crystalline, and the intercellular regions are amorphous. TEM reveals that the cells present multiple planar defects, separating rotated regions with of same crystallographic structure. The high temperature mechanical properties were studied by compression tests performed under constant strain rate and constant load. Remarkable high temperature strengths of 500 MPa at 700 o C, 400 MPa at 1100 o C and 370 MPa at 1300 o C were measured, being the plastic deformation evident at 1100 ºC and 1300 ºC. The best mechanical behavior was obtained for the systems Sr3 (Ca1.18Nb1.82)O9-δ and SrZr0.9Y0.1O3-δ . The strengths and creep resistance of these systems are better than the ones of polycrystalline HTPC ceramics of similar structure and composition. After the mechanical tests, the samples were studied by SEM and TEM. The fracture started to propagate following the intercellular regions. In the plastically deformed samples, dislocation activity was found

Hamiltonian Poincar\'e Gauge Theory of Gravitation

We develop a Hamiltonian formalism suitable to be applied to gauge theories in the presence of Gravitation, and to Gravity itself when considered as a gauge theory. It is based on a nonlinear realization of the Poincar\'e group, taken as the local spacetime group of the gravitational gauge theory, with $SO(3)$ as the classification subgroup. The Wigner--like rotation induced by the nonlinear approach singularizes out the role of time and allows to deal with ordinary $SO(3)$ vectors. We apply the general results to the Einstein--Cartan action. We study the constraints and we obtain Einstein's classical equations in the extremely simple form of time evolution equations of the coframe. As a consequence of our approach, we identify the gauge--theoretical origin of the Ashtekar variables.Comment: 38 pages, plainTe

Desarrollo de una presentación interactiva y multimedia orientada a la docencia del análisis cinemático del Movimiento Armónico Simple

Nowadays, computers suppose a great potential as complementary didactic tool to traditional means of education. For that reason, the advantage of this potential is considered by the work group, creating interactive and multimedia presentations oriented to facilitate teaching of different physics fields. In particular, the objective of this work is the design of a presentation oriented to teaching kinematical aspects of the simple harmonic movement. Given the dynamic nature of the subject, it is evident the adventages that suppose an animated presentation which it helps the student to understand the kinematical magnitudes. This tool will be very useful to the professor as complement of theoretical classes, and available to the students in the reinforcement of the knowledge.Es evidente el gran potencial que el ordenador supone como herramienta didáctica complementaria a los medios de enseñanza tradicionales. Es por ello que el grupo de trabajo se plantea el aprovechamiento de este potencial, creando presentaciones interactivas y multimedia orientadas a la docencia en los distintos campos de la física.En concreto, en este trabajo se plantea el diseño de una presentación orientada a la docencia de los aspectos cinemáticas del movimiento armónico simple. Dada la naturaleza dinámica del tema en cuestión, es evidente las ventajas que supone disponer de una presentación animada del mismo que ayude al alumno a entender la magnitudes cinemáticas implicadas, herramientas de gran utilidad para el profesor como complemento de sus clases teóricas, y disponible para alumnos de ayuda en el afianzamiento de los conocimientos

Fractional and integer stages of lithium ion-graphite systems: The role of electrostatic and elastic contributions

In the present work, we analyze the hot topic of integer and fractional stages of lithium-ion batteries by using Monte Carlo simulations. While fractional stages have been demonstrated through several experimental, simulation and theoretical measurements, in other experimental techniques, such as electrochemical ones, there is no evidence for them. In previous work, we have analyzed the thermodynamics and kinetics of lithium-ion intercalation using a potential based on empirical parameterization, where multiple stages (integer and fractional) were found and analyzed. The present simulations suggest that if we consider repulsive elastic interactions in addition to electrostatic ones, the Hamiltonian symmetry is broken and there is no evidence for fractional stages. The physical origin of these repulsive interactions is assigned to the increasing graphite layer separation during lithium-ion intercalation. In the light of these simulations, selected experimental data are revisited, validating the presented novel parameterization. The parametrization used here can be used for other kinds of intercalation compounds, such as those involving Na or K.Fil: Gavilán Arriazu, Edgardo Maximiliano. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Hümöller, Juan Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Pinto, Oscar Alejandro. Universidad Nacional de Santiago del Estero; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: De Mishima, B. A. López. Universidad Nacional de Santiago del Estero; ArgentinaFil: Leiva, Ezequiel Pedro M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Oviedo, Oscar Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin