Fold boudins : what is that?

The hypothesis proposed in this work is related with the genesis and evolution, in HT simple shear zones, of a new conceptual structure designed by fold boudin. The field evidences, achieved in the scope of a methodology to analyze the kinematics of shearband boudins (Pamplona & Rodrigues, 2011), are the basis to show how folds evolute until reach a shearband boudin final state. The critical mass factor (Mc) is the responsible for that mechanism. This parameter, which is now being introduced, is controlled by the hickness (t). The systematic analyses of shearband oudins geometry point to the hypothesis that the development of this structure is precluded by a folding phase, according to the following path evolution in HT shear zones shearband boudins: fold => fold boudin => shearband boudin.Fundação para a Ciência e a Tecnologia (FCT

Geoscout

A crusta terrestre é a camada mais externa, menos espessa e, também, a menos densa das que constituem a Terra. As tensões geradas nos níveis superiores da estrutura terrestre podem gerar episódios sísmicos de consequências, por vezes, dramáticas. A prevenção destes fenómenos (caóticos) tem-se revelado falível, visto não existirem sinais de aviso com tempo suficiente para a evacuação das regiões onde ocorrem, ou não existirem sinais de todo. No sentido de se poder contribuir para melhorar a previsão destes fenómenos, apresenta-se aqui uma proposta de um sistema de monitorização para regiões suscetíveis a sismos, deslizamentos de terra e queda de blocos. Denominado GEOSCOUT (GEOlogical Sound Continuous OUTput), este sistema consiste num sensor piezoeléctrico ligado a um computador para a deteção acústica de vibrações no solo numa vasta gama de frequências, operando em regime contínuo. A caracterização dos padrões de emissões acústicas de um dado local permitirá assinalar a ocorrência de anomalias que poderão corresponder a fenómenos transientes, alterações estruturais, ou à ativação/reativação de falhas.Direcção Regional de Ciência, Tecnologia e Comunicações do Governo Regional dos Açores (Refª M3.2.2/I/039/2011

Kinematic interpretation of shearband boudins : new parameters and ratios useful in HT simple shear zones

Shearband boudins (asymmetric boudins showing slip along the inter-boudin surface, which is synthetic with respect to the bulk shear sense) are ubiquitous and well-exposed in HT simple shear zones. The present work aims to extend the methodology of analysis of shearband boudins developed by Goscombe and Passchier (2003). Such shearband boudins represent complex objects that require an adequate methodology for unambiguous kinematic interpretation. We propose new geometric parameters (Bbs, B-t, c’, D’, d, ψ’) in order to describe and identify, with confidence, the kinematics of boudinage in this particular geological framework. The key-observation for kinematic interpretation in simple shear regimes is the boudin axis (Lb) that is commonly present, excluding the necessity to identify the regional stretching lineation (Lx) in the metasedimentary matrix. In monoclinic HT simple shear zones, this approach involves the use of a local displacement plane (Sx), which is always normal to the boudin axis (Lb).Partial funding to JP was provided by the Centro de Investigacao GeolUgica, Ordenamento e Valorizacao de Recursos that is supported by the Pluriannual program of the Fundacao para a Cilncia e a Tecnologia, funded by the European Union (FEDER program) and the national budget of the Portuguese Republic. Very insightful and helpful reviews were done by C. Fernandez (University of Huelva) and two reviewers, for which we are grateful. We want to acknowledge to T. Valente (University of Minho) for her suggestions that helped to simplify the manuscript structure and to A. McCaig (University of Leeds) for his final comments and English revision that significantly improved this manuscript

Supersymmetric Higgs pair discovery prospects at hadron colliders

We study the potential of hadron colliders in the search for the pair production of neutral Higgs bosons in the framework of the Minimal Supersymmetric Standard Model. Using analytical expressions for the relevant amplitudes, we perform a detailed signal and background analysis, working out efficient kinematical cuts for the extraction of the signal. The important role of squark loop contributions to the signal is emphasised. If the signal is sufficiently enhanced by these contributions, it could even be observable at the next run of the upgraded Tevatron collider in the near future. At the LHC the pair production of light and heavy Higgs bosons might be detectable simultaneously.Comment: 5 pages, hep99, 6 figures; Presented at the International Europhysics Conference on High Energy Physics, Tampere, Finland, 15-21 July 199

Lito e tectono-estratigrafia da Unidade do Minho Central e Ocidental: uma proposta de reclassificação

A revisão cartográfica do sector correspondente à unidade parautóctone designada por Minho Central e Ocidental, permitiu identificar novas unidades: autóctones (formação Sobrado); parautóctones (unidades de Torre-Amonde e Vilar de Mouros) e alóctones (Unidades de Vila Mou-Covas e Arga). São propostas correlações destas unidades com outros sectores da Zona Galiza – Trás-os-Montes, nomeadamente, Celorico de Basto, Vila Pouca de Aguiar e Macedo de Cavaleiros.New geological mapping of the parauthocthonous unit of “Minho Central e Ocidental”, allowed the identification of some new units: autochthonous (Sobrado formation); parauthocthonous (TorreAmonde and Vilar de Mouros units) and allochthonous units (Vila Mou-Covas, Arga). Some correlations are established with other sector of Galiza - Trás-os-Montes Zone, namely, Celorico de Basto, Vila Pouca de Aguiar and Macedo de Cavaleiros sectors.(undefined

Landslides risk evaluation: proposal of a methodology

Este trabalho apresenta uma abordagem metodológica simples para a avaliação e cartografia de zonas susceptíveis à ocorrência de movimentos de massa. Assume-se assim como um contributo para o ordenamento do território, nomeadamente, ao nível do planeamento urbanístico e rodoviário, na medida em que gera instrumentos que podem evitar, ou pelo menos minorar, a ocorrência de acidentes com danos materiais e humanos.This work aims to present a simple methodological approach for the assessment and mapping of areas susceptible to the occurrence of landslides. Thus, it represents a contribution to land management, in particular regarding urban and road planning, in that it generates management tools appropriate to avoid or mitigate the occurrence of accidents with material and human damage.(undefined

Power spectra of the natural input to the visual system

AbstractThe efficient coding hypothesis posits that sensory systems are adapted to the regularities of their signal input so as to reduce redundancy in the resulting representations. It is therefore important to characterize the regularities of natural signals to gain insight into the processing of natural stimuli. While measurements of statistical regularity in vision have focused on photographic images of natural environments it has been much less investigated, how the specific imaging process embodied by the organism’s eye induces statistical dependencies on the natural input to the visual system. This has allowed using the convenient assumption that natural image data are homogeneous across the visual field. Here we give up on this assumption and show how the imaging process in a human model eye influences the local statistics of the natural input to the visual system across the entire visual field. Artificial scenes with three-dimensional edge elements were generated and the influence of the imaging projection onto the back of a spherical model eye were quantified. These distributions show a strong radial influence of the imaging process on the resulting edge statistics with increasing eccentricity from the model fovea. This influence is further quantified through computation of the second order intensity statistics as a function of eccentricity from the center of projection using samples from the dead leaves image model. Using data from a naturalistic virtual environment, which allows generation of correctly projected images onto the model eye across the entire field of view, we quantified the second order dependencies as function of the position in the visual field using a new generalized parameterization of the power spectra. Finally, we compared this analysis with a commonly used natural image database, the van Hateren database, and show good agreement within the small field of view available in these photographic images. We conclude by providing a detailed quantitative analysis of the second order statistical dependencies of the natural input to the visual system across the visual field and demonstrating the importance of considering the influence of the sensory system on the statistical regularities of the input to the visual system

Sobre as possíveis fontes das pedras do Mosteiro de Salzedas (Tarouca - Portugal)

O Mosteiro e Igreja de Salzedas situam-se sobre o Granito de Penodono-Salzedas-Alvite, que neste local se apresenta muito meteorizado e fracturado. A utilização de elementos petrográficos permitiu discriminar diferentes tipos de granitos nestes monumentos e, com informações topográficas e históricas, propor possíveis relações com pedreiras próximas.Fundação para a Ciência e a Tecnologia (FCT

Statistical procedures applied to floods in the Douro river basin

The aim was to study flood event triggers. To this end, flood occurrence data were collected and stored, as well as hydro-meteorological variables for the Douro River basin. The Douro River and its tributaries have very steep longitudinal profiles in some sections, and consequently sudden rises in water levels are observed after heavy precipitation. The data treatment and analysis begins with a univariate study of the different variables. Several statistical procedures are used, in order to understand the possible relationship of each of the observed factors with the occurrence of floods, either individually or globally. This is done using Fisher's exact tests, chi-square tests, logistic regression models, and random forests explaining the flood phenomenon, adjusted on the basis of available data. In the logistic regression model, there is a need to use the categorized predictors because their empirical distributions exhibit very sharp positive skewness, with many outliers. In this model, the important predictors are monthly-accumulated precipitation (mm) and monthly surface discharge (dam3). The model has a specificity of over 90% but sensitivity of only 33.3%, which is not surprising given the complexity of the phenomenon under analysis. The discriminatory ability of the logistic regression model, measured by the area under the ROC curve, AUC, is 76.8% and is therefore acceptable. The random forest algorithm is used with the uncategorized variables, since it does not depend on their distributions. With the same predictors, specificity higher than 99% and a sensitivity of only 60% is obtained with this procedure, indicating an excellent performance taking into account the complexity of the phenomenon and the fact that only two predictors are being used

Folding as a precursor of asymmetric boudinage in shear zones affecting migmatitic terranes

The folding laws control the process responsible for the genesis and the initial morphological evolution of shearband boudins. In this model, the generation of boudins begins with folding of tabular competent veins of different thickness immersed in a less competent matrix. Veins thicker than a given critical value form initial asymmetric open folds that evolve by asymmetric antithetical rotation and later by an internal mass redistribution with translation along the interface vein-matrix. On the other side, the veins thinner than the critical value follow the folding process until it culminates with the coalescence and stacking of the folds. By this mechanism the critical thickness is reached and these bodies are prone to suffer a new phase of boudinage similar to that followed by the originally thicker veins. Therefore, all deformed tabular veins, embedded in a ductile matrix, converge to classical shearband boudin morphology, independently from their original thickness.La génesis y evolución morfológica inicial de los "boudins” de tipo “shearband" están controlados por mecanismos de plegamiento. En este modelo, el "boudinage" comienza con el plegamiento de cuerpos tabulares (venas) de diferentes espesores, inmersos en una matriz menos competente. Las venas más gruesas exceden un espesor crítico que determina la formación inicial de un pliegue abierto. Posteriormente evoluciona por rotación antitética en relación con la cinemática de la zona de cizalla y por traslación de masa a lo largo de la interfase vena-matriz,conduciendo a la morfología clásica de un "shearband boudin”. Por su parte, los cuerpos comparativamente más delgados continúan plegándose hasta que se produce la unión y apilamiento de los flancos de los pliegues (“stacked-folds”). Mediante este proceso se alcanza el espesor crítico necesario para que se desarrolle una nueva fase de "boudinage" similar a la seguida por las venas gruesas