Rudiments of Holography

An elementary introduction to Maldacena's AdS/CFT correspondence is given, with some emphasis in the Fefferman-Graham construction. This is based on lectures given by one of us (E.A.) at the Universidad Autonoma de Madrid.Comment: 60 pages, additional misprints corrected, references adde

Estudio polínico de la turbera del Cueto de la Avellanosa, Polaciones (Cantabria)

[Resumen] El presente trabajo trata del estudio poIínico de una turbera en el Cueto de la Avellanosa, Polaciones (Cantabria). Incluye un diagrama polinico con las especies arbóreas y no arbóreas correspondiente a los 3,4 metros del perfil de la turbera; lo que supone el tratamiento de 34 nuestras de turba que han sido estudiadas desde el punto de vista micropaleontol6gico o paleopolínico. También fueron datadas 3 muestras mediante el 14C. y la edad obtenida xwestra que la turba se formó entre los 6.020 años B.P. y los 1.100 años B.P. El inicio de la turbera se produce durante la transición entre el Boreal y el Atlántico, y tanto estos dos periodos como el Subboreal y Subatlántico aparecen bien definidos en el Palinograma. El conjunto del espectro polinico muestra que la turba se generó bajo condiciones más frias que otros depósitos de turba estudiados en la región Cantábrica o zona Norte.[Abstract] This paper describes the palinological study carried out in a peat deposit in Polaciones (Cantabria, Spain). A 3,4 m profile was obtained and 34 samples were studied. 14C. ages were also determined. The data obtained shows that the peat was formed between 6.020 years B.P. and 1.100 years B.P. starting during the transition between the Boreal and Atlantic, the Subboreal and Subatlantic periods appear well defined in the diagrams. On the whole, the polinic assemblege shows the the peat was formed under colder conditions than other peat deposits studied in the Cantabrian regio

Spanish Spelt Wheat: From an Endangered Genetic Resource to a Trendy Crop

Spelt wheat (Triticum aestivum L. ssp. spelta Thell.) is an ancient wheat that was widely cultivated in the past. This species derived from a cross between emmer wheat (T. turgidum spp. dicoccum Schrank em. Thell.) and Aegilops tauschii Coss. Its main origin was in the Fertile Crescent (Near East), with a secondary center of origin in Europe due to a second hybridization event between emmer and hexaploid wheat. This species has been neglected in most of Europe; however, the desire for more natural foods has driven a revival in interest. Iberian spelt is classified as a geographical group differing to the rest of European spelt. In this review, the particularities, genetic diversity and current situation of Spanish spelt, mainly for quality traits, are discussed

Comments on noncommutative gravity

We study the possibility of obtaining noncommutative gravity dynamics from string theory in the Seiberg-Witten limit. We find that the resulting low-energy theory contains more interaction terms than those proposed in noncommutative deformations of gravity. The role of twisted diffeomorphisms in string theory is studied and it is found that they are not standard physical symmetries. It is argued that this might be the reason why twisted diffeomorphisms are not preserved by string theory in the low energy limit. Twisted gauge transformations are also discussed.Comment: 37 pages. Typos corrected. Final version to appear in Nuclear Physics

Riemannian Geometry of Noncommutative Surfaces

A Riemannian geometry of noncommutative n-dimensional surfaces is developed as a first step towards the construction of a consistent noncommutative gravitational theory. Historically, as well, Riemannian geometry was recognized to be the underlying structure of Einstein's theory of general relativity and led to further developments of the latter. The notions of metric and connections on such noncommutative surfaces are introduced and it is shown that the connections are metric-compatible, giving rise to the corresponding Riemann curvature. The latter also satisfies the noncommutative analogue of the first and second Bianchi identities. As examples, noncommutative analogues of the sphere, torus and hyperboloid are studied in detail. The problem of covariance under appropriately defined general coordinate transformations is also discussed and commented on as compared with other treatments.Comment: 28 pages, some clarifications, examples and references added, version to appear in J. Math. Phy

Nuclear shape dependence of Gamow-Teller distributions in neutron-deficient Pb isotopes

We study Gamow-Teller strength distributions in the neutron-deficient even isotopes (184-194)Pb in a search for signatures of deformation. The microscopic formalism used is based on a deformed quasiparticle random phase approximation (QRPA) approach, which involves a self-consistent quasiparticle deformed Skyrme Hartree-Fock (HF) basis and residual spin-isospin forces in both the particle-hole and particle-particle channels. By analyzing the sensitivity of the Gamow-Teller strength distributions to the various ingredients in the formalism, we conclude that the beta-decay of these isotopes could be a useful tool to look for fingerprints of nuclear deformation.Comment: 20 pages, 11 figures. To be published in Physical Review

Breaking a chaos-noise-based secure communication scheme

This paper studies the security of a secure communication scheme based on two discrete-time intermittently-chaotic systems synchronized via a common random driving signal. Some security defects of the scheme are revealed: 1) the key space can be remarkably reduced; 2) the decryption is insensitive to the mismatch of the secret key; 3) the key-generation process is insecure against known/chosen-plaintext attacks. The first two defects mean that the scheme is not secure enough against brute-force attacks, and the third one means that an attacker can easily break the cryptosystem by approximately estimating the secret key once he has a chance to access a fragment of the generated keystream. Yet it remains to be clarified if intermittent chaos could be used for designing secure chaotic cryptosystems.Comment: RevTeX4, 11 pages, 15 figure

Screening of charged spheroidal colloidal particles

We study the effective screened electrostatic potential created by a spheroidal colloidal particle immersed in an electrolyte, within the mean field approximation, using Poisson--Botzmann equation in its linear and nonlinear forms, and also beyond the mean field by means of Monte Carlo computer simulation. The anisotropic shape of the particle has a strong effect on the screened potential, even at large distances (compared to the Debye length) from it. To quantify this anisotropy effect, we focus our study on the dependence of the potential on the position of the observation point with respect with the orientation of the spheroidal particle. For several different boundary conditions (constant potential, or constant surface charge) we find that, at large distance, the potential is higher in the direction of the large axis of the spheroidal particle

El Origen de las lexias "de toda broza", "a toda broza": un caso de contaminación

The two phrases quoted are exceedingly common in Castilian literary texts of the sixteenth and seventeenth centuries, including the popular Guzmán de Alfarache. Hence the attempts, albeit unsatisfactory, at semantic and etymological explanation by lexicographers in these periods. Having conducted a detailed analysis of both the literary and lexicographical types of testimony, I propose that the irrelevance of the latter and the vagueness of the former are due to lack of awareness that the two phrases are hybrid derivatives of similar cognate ones in which the head noun was not broza but boça, a term from the lexical field of weaponry, which in the fourteenth and fifteenth centuries passed from Italian into French, Catalan and Spanish, and referred to a test to which the principal pieces of armour were subjected to check their strength.Las dos unidades fraseológicas citadas tienen un alto índice de frecuencia en textos literarios castellanos de los siglos XVI y XVII, alguno tan difundido como el Guzmán de Alfarache. De ahí los intentos, si bien insatisfactorios, de explicación semántica y etimológica por los lexicógrafos de dichos siglos. Tras un análisis detallado de ambos tipos de testimonios, los literarios y los lexicográficos, se propone aquí que la vaguedad de aquellos y la no pertinencia de éstos deriva del hecho de que se ignoraba que ambas frases son sucesoras, por cruce paronímico, de otras similares en las que el núcleo nominal no es broza sino boça, término del lenguaje de la armería, que del italiano pasó en los siglos XIV y XV al francés, catalán y castellano, y designaba un tipo de prueba de resistencia a que se sometía a las principales piezas de la armadura

El Origen de las lexias "de toda broza", "a toda broza": un caso de contaminación

Las dos unidades fraseológicas citadas tienen un alto índice de frecuencia en textos literarios castellanos de los siglos XVI y XVII, alguno tan difundido como el Guzmán de Alfarache. De ahí los intentos, si bien insatisfactorios, de explicación semántica y etimológica por los lexicógrafos de dichos siglos. Tras un análisis detallado de ambos tipos de testimonios, los literarios y los lexicográficos, se propone aquí que la vaguedad de aquellos y la no pertinencia de éstos deriva del hecho de que se ignoraba que ambas frases son sucesoras, por cruce paronímico, de otras similares en las que el núcleo nominal no es broza sino boça, término del lenguaje de la armería, que del italiano pasó en los siglos XIV y XV al francés, catalán y castellano, y designaba un tipo de prueba de resistencia a que se sometía a las principales piezas de la armadura.The two phrases quoted are exceedingly common in Castilian literary texts of the sixteenth and seventeenth centuries, including the popular Guzmán de Alfarache. Hence the attempts, albeit unsatisfactory, at semantic and etymological explanation by lexicographers in these periods. Having conducted a detailed analysis of both the literary and lexicographical types of testimony, I propose that the irrelevance of the latter and the vagueness of the former are due to lack of awareness that the two phrases are hybrid derivatives of similar cognate ones in which the head noun was not broza but boça, a term from the lexical field of weaponry, which in the fourteenth and fifteenth centuries passed from Italian into French, Catalan and Spanish, and referred to a test to which the principal pieces of armour were subjected to check their strength