Three types of Gabbros in the Toledo Complex

[Resumen] En este trabajo se describen tres tipos de rocas gabroideas que afloran en el CompIejo de Toledo, atendiendo principalmente a aspectos petrográficos, geoquímicos y a su comparación con otros tipos de rocas básicas hercínicas. El primero de estos grupos está constituido por gabros olivínicos y piroxénicos, denominados tipo La Bastida, que generalmente están en relación con granitoides calcoalcalinos (granitos de Argés), y que varían desde melanoritas olivínicas hasta gabronoritas, observándose en ocasiones un ligero bandeado ígneo. Geoquímicamente presentan una afinidad calcoalcalina normal y definen secuencias en diagramas geoquímicos que pueden explicarse mediante procesos de cristalización fraccionada con acumulaci6n de olivino en los términos más básicos de la serie. Son rocas con caracteres petrológicos y geoquímicos similares a los de rocas básicas de tipo cortlandítico descritas en otros sectores del Hercínico Ibérico (Gredos, Costero-Catalana). Existe un segundo grupo de rocas básicas constituido por gabros anfib61icos, denominados tipo Toledo, que se encuentran, al igual que en el caso anterior, relacionados desde un punto de vista espacio-temporal con la serie de granitoides de Argés. Petrográficamente varían desde gabros (próximos a dioritas) a cuarzogabros anfib6licos, con plagioclasa, anfíbol y biotita como fases fundamentales.Desde un punto de vista geoquímico este grupo presenta características muy contrastadas con respecto a los otros dos grupos gabroideos. pestacan sus altos contenidos en Ti02(1.6-2.2 %), Al20 3 (16-20%), P20 S (0:32-0.88%) ysobre todo en álcalis (Na20+K20 entre 4.7 y 6.3% para un rango de SiG2 de 47-53%). Son también notables sus altos contenidos en Ba y Sr, así como sus bajas relaciones ZrIP20 S• Por estas características se le asigna a este grupo una afinidad de tipo shoshonítico. Son rocas con caracteres geoquímicos en parte similares a los de tipos vaugneríticoshercínicos. Por último, aflora en el Complejo un tercer grupo de gabros, fundamentalmente anfib6licos, aunque también se encuentran variedades anfib61ico-piroxénicas, que aflora exclusivamente en la esquina sureste del mismo y que se ha denominado gabros tipo Villanueva. No están en relaci6n con los granitoides de Argés como ocurría con los otros dos grupos gabroideos. Por el contrario, estas rocas son intrusivas en mármoles dolomíticos preordovícicos en los que provocan un intenso metamorfismo de contacto. petrográficamente se trata de gabros s. s. con plagioclasa, anfíbol, clinopiroxeno y biotita como fases funtamentales. Geoquímicamente presentan características de una serie calcoalcalina, de caracteres similares a los de gabros afines de la Sierra de Guadarrama.[Abstract] The present work deals with petrographical and geochemical aspects of three groups of basics rock that outcrops in the Toledo complexo The relation of these three groups with other hercynian basic rock is also argued. The first group consists of olivine and pyroxene gabbtos (La Bastida type) that usually occurs related to calcalkaline granitoids. Geochemically this group have calcalkaline affinity and its variation trends can be explained by a crystal fractionation mechanism. The chemical characteristics ofLa Bastida gahbros ressembles those of other hercynian zones. The second group of basic rocks consists of amphibole gabbros (Toledo type), that, as La Bastida type, is spatially and age related with calcalkaline granites. Geochemically this group present a shoshonitic affinity because of its high alkalies and associated elements content, and it is chemically similar to sorne variscan vaugneritic rocks. Finally, there is a group of gabbros (Villanueva type) intruded in paleozoic marbIes and unrelated to calcalkaline granites. 1t has calcalkaline affinity, ressembling to the Sierra de Guadarrama gabbro

On the propagation speed of evanescent modes

The group-velocity of evanescent waves (in undersized waveguides, for instance) was theoretically predicted, and has been experimentally verified, to be Superluminal (v_g > c). By contrast, it is known that the precursor speed in vacuum cannot be larger than c. In this paper, by computer simulations based on Maxwell equations only, we show the existence of both phenomena. In other words, we verify the actual possibility of Superluminal group velocities, without violating the so-called (naive) Einstein causality. (Subject classes: General physics, Classical physics, Optics, Special Relativity; PACS nos.: 73.40Gk, 03.80+z, 03.65Bz; Keywords: evanescent waves; tunnelling photons; Hartman effect; group velocity; Superluminal waves; precursors; transient waves; front velocity; Maxwell equations; electromagnetic waves; computer simulations; Special Relativity; Extended Relativity).Comment: plain LaTeX file (14 pages), plus 15 figures in .jp

Alignment transition in a nematic liquid crystal due to field-induced breaking of anchoring

We report on the alignment transition of a nematic liquid crystal from initially homeotropic to quasi-planar due to field-induced anchoring breaking. The initial homeotropic alignment is achieved by Langmuir-Blodgett monolayers. In this geometry the anchoring strength can be evaluated by the Frederiks transition technique. Applying an electric field above a certain threshold provokes turbulent states denoted DSM1 and DSM2. While DSM1 does not affect the anchoring, DSM2 breaks the coupling between the surface and the liquid crystal: switching off the field from a DSM2 state does not immediately restore the homeotropic alignment. Instead, we obtain a quasi-planar metastable alignment. The cell thickness dependence for the transition is related to theComment: 7 pages, LaTeX2e article, 4 figures, 7 EPS files, added references, accepted for publication in Europhysics Letter

SO(4,C)-covariant Ashtekar-Barbero gravity and the Immirzi parameter

An so(4,C)-covariant hamiltonian formulation of a family of generalized Hilbert-Palatini actions depending on a parameter (the so called Immirzi parameter) is developed. It encompasses the Ashtekar-Barbero gravity which serves as a basis of quantum loop gravity. Dirac quantization of this system is constructed. Next we study dependence of the quantum system on the Immirzi parameter. The path integral quantization shows no dependence on it. A way to modify the loop approach in the accordance with the formalism developed here is briefly outlined.Comment: 14 pages, LATEX; minor changes; misprints corrected; commutator of two secondary second class constraints correcte

BF Actions for the Husain-Kuchar Model

We show that the Husain-Kuchar model can be described in the framework of BF theories. This is a first step towards its quantization by standard perturbative QFT techniques or the spin-foam formalism introduced in the space-time description of General Relativity and other diff-invariant theories. The actions that we will consider are similar to the ones describing the BF-Yang-Mills model and some mass generating mechanisms for gauge fields. We will also discuss the role of diffeomorphisms in the new formulations that we propose.Comment: 21 pages (in DIN A4 format), minor typos corrected; to appear in Phys. Rev.

Numerical study of surface-induced reorientation and smectic layering in a nematic liquid crystal

Surface-induced profiles of both nematic and smectic order parameters in a nematic liquid crystal, ranging from an orienting substrate to "infinity", were evaluated numerically on base of an extended Landau theory. In order to obtain a smooth behavior of the solutions at "infinity" a boundary energy functional was derived by linearizing the Landau energy around its equilibrium solutions. We find that the intrinsic wave number of the smectic structure, which plays the role of a coupling between nematic and smectic order, strongly influences the director reorientation. Whereas the smectic order is rapidly decaying when moving away from the surface, the uniaxial nematic order parameter shows an oscillatory behavior close to the substrate, accompanied by a non-zero local biaxiality.Comment: LaTeX, 17 pages, with 4 postscript figure

Remarks on the Reduced Phase Space of (2+1)-Dimensional Gravity on a Torus in the Ashtekar Formulation

We examine the reduced phase space of the Barbero-Varadarajan solutions of the Ashtekar formulation of (2+1)-dimensional general relativity on a torus. We show that it is a finite-dimensional space due to existence of an infinite dimensional residual gauge invariance which reduces the infinite-dimensional space of solutions to a finite-dimensional space of gauge-inequivalent solutions. This is in agreement with general arguments which imply that the number of physical degrees of freedom for (2+1)-dimensional Ashtekar gravity on a torus is finite.Comment: 13 pages, Latex. More details have been included and the expression for the finite residual gauge transformations has been worked ou