Canonical Formulation of Gravitational Teleparallelism in 2+1 Dimensions in Schwinger's Time Gauge

We consider the most general class of teleparallel gravitational {}{}theories quadratic in the torsion tensor, in three space-time dimensions, and carry out a detailed investigation of its Hamiltonian formulation in Schwinger's time gauge. This general class is given by a family of three-parameter theories. A consistent implementation of the Legendre transform reduces the original theory to a one-parameter family of theories. By calculating Poisson brackets we show explicitly that the constraints of the theory constitute a first-class set. Therefore the resulting theory is well defined with regard to time evolution. The structure of the Hamiltonian theory rules out the existence of the Newtonian limit.Comment: 17 pages, Latex file, no figures; a numerical coefficient has been corrected and a different result is achieve

Black Holes in 2+1 Teleparallel Theories of Gravity

We apply the Hamiltonian formulation of teleparallel theories of gravity in 2+1 dimensions to a circularly symmetric geometry. We find a family of one-parameter black hole solutions. The BTZ solution fixes the unique free parameter of the theory. The resulting field equations coincide with the teleparallel equivalent of Einstein's three-dimensional equations. We calculate the gravitational energy of the black holes by means of the simple expression that arises in the Hamiltonian formulation and conclude that the resulting value is identical to that calculated by means of the Brown-York method.Comment: 20 pages, Latex file, no figure

Ab initio calculation of the dynamical properties of PPP and PPV

In this work, we have calculated the vibrational modes and frequencies of the crystalline PPP (in both the Pbam and Pnnm symmetries) and PPV (in the P21/c symmetry). Our results are in good agreement with the available experimental data. Also, we have calculated the temperature dependence of their specific heats at constant volume, and of their vibrational entropies. Based on our results, at high temperatures, the PPP is more stable in the Pnnm structure than in the Pbam one.Comment: 5 pages, 7 figures, accepted for publication in Braz. J. Phys., special number, Proceedings of BWSP-12, 12th Brazilian Workshop on Semiconductor Physic

Preliminary results of aerial infrared surveys at Pisgah Crater, California

In-flight tests of airborne infrared scanners, and comparison with field reflectance dat

Orality as critique of history: reading the "Poema de Mío Cid"

This study involves an inquiry into notions of reading, the relationship between orality and literacy, and theory of history, all with regard to Poema de Mío Cid criticism. It deals in particular with the responses to traditional criticism mounted by two important recent studies, those by María Eugenia Lacarra (1980) and Joseph Duggan (1989). Both studies question various of the basic lineaments of traditional criticism but at the same time, paradoxically, can be seen to reinscribe in different ways that criticism's central historico-referential gesture. The conclusion arrived at by means of examination of that phenomenon is that the PMC is in fact "narrated" by the literary-critical activity produced around it and that such narration is carried outthrough regress to certain dominant tendencies in modern historical narration. The study concludes with the proposed reading of a PMC fragment in which the text's resistance to interpretation by recourse to historical referentiality is demonstrated.El presente estudio indaga acerca de las nociones de lectura, de la relación entre lo oral-lo letrado y de la teoría de la historia, todas con respecto a la crítica del Poema de Mío Cid. En particular, nos ocupamos de las respuestas que ofrecen a la crítica tradicional dos recientes estudios importantes, los de María Eugenia Lacarra (1980) y Joseph Duggan (1989). Ambos textos cuestionan varios cle los lineamientos básicos de la crítica tradicional, mientras que, paradójicamente, reinscriben en maneras diversas la faceta histórico-referencial central de dicha crítica. Mediante nuestra indagación cle este fenómeno, llegamos a la conclusión de que el PMC es de hecho "narrado" por la actividad crítico-literaria generada a su alrededor, y que dicha narración se lleva a cabo mediante un "retorno" a ciertas tendencias dominantes de la narración histórica moderna. Nuestro estudio se cierrra con una propuesta de lectura de un fragmento clel PMC en la que se muestra la resistencia del texto a ser interpretado por los medios de referencialidad histórica

Quantum theory of spectral diffusion induced electron spin decoherence

A quantum cluster expansion method is developed for the problem of localized electron spin decoherence due to dipolar fluctuations of lattice nuclear spins. At the lowest order it provides a microscopic explanation for the Lorentzian diffusion of Hahn echoes without resorting to any phenomenological Markovian assumption. Our numerical results show remarkable agreement with recent electron spin echo experiments in phosphorus doped silicon.Comment: 5 pages, 1 figur

Graviton resonances on two-field thick branes

This work presents new results about the graviton massive spectrum in two-field thick branes. Analyzing the massive spectra with a relative probability method we have firstly showed the presence of resonance structures and obtained a connection between the thickness of the defect and the lifetimes of such resonances. We obtain another interesting results considering the degenerate Bloch brane solutions. In these thick brane models, we have the emergence of a splitting effect controlled by a degeneracy parameter. When the degeneracy constant tends to a critical value, we have found massive resonances to the gravitational field indicating the existence of modes highly coupled to the brane. We also discussed the influence of the brane splitting effect over the resonance lifetimes.Comment: 15 pages, 8 figure