Towards an Ashtekar formalism in eight dimensions

We investigate the possibility of extending the Ashtekar theory to eight dimensions. Our approach relies on two notions: the octonionic structure and the MacDowell-Mansouri formalism generalized to a spacetime of signature 1+7. The key mathematical tool for our construction is the self-dual (antiself-dual) four-rank fully antisymmetric octonionic tensor. Our results may be of particular interest in connection with a possible formulation of M-theory via matroid theory.Comment: 15 pages, Latex, minor changes, to appear in Class. Quantum Gra

Quimismo de un sedimento clástico formador de esmectita y sus implicaciones en la transformación esmectita-ilita

3 páginas, 1 figura.-- Trabajo presentado en la XX Reunion de la Sociedad Española de Mineralogía, La Coruña (2000).Prior to the development of "in-situ" analysis techniques, data on the chemical composition of minerals was derived exclusively from whole rocks using monomineral samples or from assemblages in which the separation of minerals was possible. Therefore, knowledge concerning the real composition of smectites in soils and sediments was significantly delayed, and it was assumed that the typical smectite composition was that of materials in which they were the only phase or easily separated. Recently, Analytical Electron Microscopy (AEM) analyses have demonstrated that smectites forming sediments or sedimentary rocks can also be analysed in spite of their small size and their defective nature. Smectites play an important role in the geological cycle. They are the basic material for the smectiteillite transformation during the diagenesis of sedimentary materials giving rise to illitebearing sedimentary rocks.Financial support was supplied by Research Project nº PB96-1383 of the Spanish Ministry of Education and Research Group RNM-0179 of the Junta de Andalucía.Peer reviewe

Quimismo de un sedimento clástico formador de esmectita y sus implicaciones en la transformación esmectita-ilita

3 páginas, 1 figura.-- Trabajo presentado en la XX Reunion de la Sociedad Española de Mineralogía, La Coruña (2000).Prior to the development of "in-situ" analysis techniques, data on the chemical composition of minerals was derived exclusively from whole rocks using monomineral samples or from assemblages in which the separation of minerals was possible. Therefore, knowledge concerning the real composition of smectites in soils and sediments was significantly delayed, and it was assumed that the typical smectite composition was that of materials in which they were the only phase or easily separated. Recently, Analytical Electron Microscopy (AEM) analyses have demonstrated that smectites forming sediments or sedimentary rocks can also be analysed in spite of their small size and their defective nature. Smectites play an important role in the geological cycle. They are the basic material for the smectiteillite transformation during the diagenesis of sedimentary materials giving rise to illitebearing sedimentary rocks.Financial support was supplied by Research Project nº PB96-1383 of the Spanish Ministry of Education and Research Group RNM-0179 of the Junta de Andalucía.Peer reviewe

Influence of the Ground-State Topology on the Domain-Wall Energy in the Edwards-Anderson +/- J Spin Glass Model

We study the phase stability of the Edwards-Anderson spin-glass model by analyzing the domain-wall energy. For the bimodal distribution of bonds, a topological analysis of the ground state allows us to separate the system into two regions: the backbone and its environment. We find that the distributions of domain-wall energies are very different in these two regions for the three dimensional (3D) case. Although the backbone turns out to have a very high phase stability, the combined effect of these excitations and correlations produces the low global stability displayed by the system as a whole. On the other hand, in two dimensions (2D) we find that the surface of the excitations avoids the backbone. Our results confirm that a narrow connection exists between the phase stability of the system and the internal structure of the ground-state. In addition, for both 3D and 2D we are able to obtain the fractal dimension of the domain wall by direct means.Comment: 4 pages, 3 figures. Accepted for publication in Rapid Communications of Phys. Rev.

Wind loads analysis at the anchorages of the Talavera de la Reina cable stayed bridge

This paper describes wind tunnel tests performed on wind tunnel models of the Talavera de la Reina cable stayed bridge. The work describes the aeroelastic model construction and it is focused on the evaluation and analysis of the mean and peak wind loads at the tower foundation and the cable anchorages since these data can be very useful by the bridge manufacturer as a support for the bridge design. The work is part of a complete wind tunnel study carried out to analyze the aeroelastic stability of the bridge

A Practical Example for Model-Driven Web Requirements

The number of approaches for Web environments has grown very fast in the last years: HDM, OOHDM, and WSDM were among the first, and now a large number can be found in the literature. With the definition of MDA (Model- Driven Architecture) and the acceptance of MDE (Model-Driven Engineering) techniques in this environment, some groups are working in the use of metamodels and transformations to make their approaches more powerful. UWE (UMLBased Web Engineering) or OOWS (Object-Oriented Web Solutions) are only some examples. However, there are few real experiences with Web Engineering in the enterprise environment, and very few real applications of metamodels and MDE techniques. In this chapter the practical experience of a Web Engineering approach, NDT, in a big project developed in Andalusia is presented. Besides, it shows the usability of metamodels in real environments

A Practical Environment to Apply Model-Driven Web Engineering

The application of a model-driven paradigm in the development of Web Systems has yielded very good research results. Several research groups are defining metamodels, transformations, and tools which offer a suitable environment, known as model-driven Web engineering (MDWE). However, there are very few practical experiences in real Web system developments using real development teams. This chapter presents a practical environment of MDWE based on the use of NDT (navigational development techniques) and Java Web systems, and it provides a practical evaluation of its application within a real project: specialized Diraya.Ministerio de Educación y Ciencia TIN2007-67843-C06-03Ministerio de Educación y Ciencia TIN2007-30391-

ExoplANNET: A deep learning algorithm to detect and identify planetary signals in radial velocity data

The detection of exoplanets with the radial velocity method consists in detecting variations of the stellar velocity caused by an unseen sub-stellar companion. Instrumental errors, irregular time sampling, and different noise sources originating in the intrinsic variability of the star can hinder the interpretation of the data, and even lead to spurious detections. In recent times, work began to emerge in the field of extrasolar planets that use Machine Learning algorithms, some with results that exceed those obtained with the traditional techniques in the field. We seek to explore the scope of the neural networks in the radial velocity method, in particular for exoplanet detection in the presence of correlated noise of stellar origin. In this work, a neural network is proposed to replace the computation of the significance of the signal detected with the radial velocity method and to classify it as of planetary origin or not. The algorithm is trained using synthetic data of systems with and without planetary companions. We injected realistic correlated noise in the simulations, based on previous studies of the behaviour of stellar activity. The performance of the network is compared to the traditional method based on null hypothesis significance testing. The network achieves 28 % fewer false positives. The improvement is observed mainly in the detection of small-amplitude signals associated with low-mass planets. In addition, its execution time is five orders of magnitude faster than the traditional method. The superior performance exhibited by the algorithm has only been tested on simulated radial velocity data so far. Although in principle it should be straightforward to adapt it for use in real time series, its performance has to be tested thoroughly. Future work should permit evaluating its potential for adoption as a valuable tool for exoplanet detection.Comment: Accepted for publication; Corrected typos; Added section 6.1 with a robustness analysis of the method; Added section 6.2 with tests on a real time series; Added section 6.3 with a more detailed analysis of the caution of the network around activity periods; Added other tested models to the appendi

Hydrogen atom as an eigenvalue problem in 3D spaces of constant curvature and minimal length

An old result of A.F. Stevenson [Phys. Rev.} 59, 842 (1941)] concerning the Kepler-Coulomb quantum problem on the three-dimensional (3D) hypersphere is considered from the perspective of the radial Schr\"odinger equations on 3D spaces of any (either positive, zero or negative) constant curvature. Further to Stevenson, we show in detail how to get the hypergeometric wavefunction for the hydrogen atom case. Finally, we make a comparison between the ``space curvature" effects and minimal length effects for the hydrogen spectrumComment: 6 pages, v