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401.
Carlos Marín-Lechado Jesús Galindo-Zaldívar Luís Roberto Rodríguez-Fernández Antonio Pedrera 《Pure and Applied Geophysics》2007,164(1):1-21
The boundary between the Alboran Sea and Betic Cordillera is a good example of a fold related mountain front in the Internal
Zone of an alpine mountain range. Since the late Miocene, NNW-SSE convergence between the Eurasian and African plates has
produced shortening and related orthogonal extension. To improve the characterisation of the geometry of the deep structure
in the region and to establish the recent tectonic evolution of the mountain front, well logs and newly acquired geophysical
data (multichannel reflection seismic and gravimetric surveys) have been interpreted and integrated with available surface
data. The most marked tectonic structure corresponds to large antiforms and synforms of ENE-WSW trend which are related to
mountain ranges and basins, respectively. The fold belt continues toward the northern continental shelf of the Alboran Sea.
The fold vergence is generally northwards and its amplitude decreases progressively towards SSE, until disappearring in a
sharp boundary where the reflectors are undeformed. The deep geometry suggests that fold growth started during upper Tortonian
times and continued its activity up to Pliocene or even Quaternary times. The NNW-SSE compression produces crustal thickening
and a regional and progressive southwards emersion. The location of main present-day deformation fronts in the Internal Zones
contrasts with classical models where the deformation progresses towards the frontal part of External Zones of cordilleras.
In addition, this fold-related deformation mountain front has features different from fault related fronts, as it does not
show a sharp boundary, and folds that determine rectilinear mountain boundaries decrease progressively in amplitude or in
wavelength up to undeformed areas. 相似文献
402.
Paula Teves-Costa Carlos S. Oliveira M. Luisa Senos 《Soil Dynamics and Earthquake Engineering》2007,27(11):986-999
During the Mw=6.9 January 1, 1980 earthquake in the Azores, the damage distribution in the town of Angra do Heroísmo, in Terceira Island, had a non-homogeneous spatial character. In order to understand the observed pattern of damage a microtremor survey was carried out, using ambient vibrations, and the data were analysed with the J-Sesame software, following the H/V Nakamura methodology. The results are in good agreement with the surface geology and they show a good correlation with the observed damages. Two building surveys were performed, in 1980 on damage evaluation and in 2000 on characterization of few building parameters. With all these elements (surface geology type, soil peak frequency, building type, number of stories and damage level) for 2111 buildings it was possible to perform several interparameter analysis, which enabled the identification of indicators that could be used to improve the damage estimation for future events. 相似文献
403.
Neural network based daily precipitation generator (NNGEN-P) 总被引:1,自引:0,他引:1
Jean-Philippe Boulanger Fernando Martinez Olga Penalba Enrique Carlos Segura 《Climate Dynamics》2007,28(2-3):307-324
Daily weather generators are used in many applications and risk analyses. The present paper explores the potential of neural network architectures to design daily weather generator models. Focusing this first paper on precipitation, we design a collection of neural networks (multi-layer perceptrons in the present case), which are trained so as to approximate the empirical cumulative distribution (CDF) function for the occurrence of wet and dry spells and for the precipitation amounts. This approach contributes to correct some of the biases of the usual two-step weather generator models. As compared to a rainfall occurrence Markov model, NNGEN-P represents fairly well the mean and standard deviation of the number of wet days per month, and it significantly improves the simulation of the longest dry and wet periods. Then, we compared NNGEN-P to three parametric distribution functions usually applied to fit rainfall cumulative distribution functions (Gamma, Weibull and double-exponential). A data set of 19 Argentine stations was used. Also, data corresponding to stations in the United States, in Europe and in the Tropics were included to confirm the results. One of the advantages of NNGEN-P is that it is non-parametric. Unlike other parametric function, which adapt to certain types of climate regimes, NNGEN-P is fully adaptive to the observed cumulative distribution functions, which, on some occasions, may present complex shapes. On-going works will soon produce an extended version of NNGEN to temperature and radiation. 相似文献
404.
Carlos Roberto de Souza Filho Alfredo Rossetto Nunes Emilson Pereira Leite Lena Virgínia Soares Monteiro Roberto Perez Xavier 《Surveys in Geophysics》2007,28(5-6):377-405
The Serra Leste region, located in the northeast portion of Carajás Mineral Province (PA), hosts important chrome-PGE, Au–Pd–Pt,
Cu–Mo–Au, iron, and manganese deposits and occurrences related to different geological settings. We present a regional prospective
model with focus on PGE mineralizations based on airborne geophysics (magnetometry, gamma-ray spectrometry and time domain
electromagnetometry) and geological data. Geological and geophysics data analysis indicate a plausible correspondence between
areas with meta-mafic–ultramafic rocks and low values in gamma spectrometry, mainly for the thorium channel. The meta-ultramafic
units of the complexes, the main host rock of the PGE mineralization, are well defined by analytic signal from the anomalous
magnetic field and by the apparent conductance anomalies derived from the GEOTEM system. The combination of the derivative
products with updated geological data of the Serra Leste region and PGE-Luanga deposit enable to establish a regional prospective
model for PGE and the identification of new targets within the studied area. 相似文献
405.
da Rosa CE de Souza MS Yunes JS Proença LA Nery LE Monserrat JM 《Marine pollution bulletin》2005,50(9):956-964
In January of 2003, a cyanobacterial bloom in the Patos' Lagoon (Southern Brazil) (32 degrees 05'S-52 degrees 12'W) was observed. Water samples were taken to identify the composition and abundance of the bloom, as well as the occurrence of toxins. The effects of this occurrence on the estuarine worm Laeonereis acuta (Polychaeta, Nereididae) was also evaluated. Predominance of cyanobacteria, particularly Anabaena trichomes ( approximately 2.5.10(6) individuals per liter) was observed, and low concentrations of microcystins and anticholinesterasic toxins were detected. Augmented levels of lipid hydroperoxides (LPO) and glutathione-S-transferase activity, and lowering of total protein content were also observed in organisms collected during the bloom event. Although non-toxic, the cyanobacterial bloom could augment the cycle of hyper-oxygenation and hypoxia in the water. During hyperoxia, L. acuta, an oxyconformer, should consume more oxygen, thus augmenting the rate of reactive oxygen species generation. A repeated cycle of hyper-oxygenation and hypoxia would finally induce oxidative stress, as evidenced by the high levels of LPO and glutathione-S-transferase activity. 相似文献
406.
Carlos Garza-Gonzlez Antoni Camprubí Eduardo Gonzlez-Partida Germn Arriaga-García Fernando Rosique-Naranjo 《Journal of Geochemical Exploration》2006,89(1-3):124
The Tiámaro deposit in Michoacán state has been dated as Lower Cretaceous (Valanginian), though most of the porphyry deposits in central Mexico were dated or have an attributed Eocene–Oligocene age. The host rocks belong to a volcanoplutonic complex overlain by red conglomerates. These rocks were intruded by pre-Valanginian plutonic and hypabissal rocks. Propylitic, phyllic, and argillic alteration assemblages developed, and their superimposition draws the evolution of the deposit. Stage I is represented by propylitic assemblages, stage II contains the main ore forming stockworks and both phyllic and argillic assemblages, and stage III contains late carbonatization assemblages. The obtained temperatures and salinities from inclusion fluids are low for a porphyry-type deposit, but we interpret that the known part of the deposit represents the shallow portion of a bigger deposit. The evolution of mineralizing fluids draws a dilution trend of brines from “porphyry-like” to “epithermal-like” stages. The richest ore zone is roughly located between the 300 and 350 °C isotherms, though unnoticed resources may occur at depth. 相似文献
407.
Paulo Cesar Abreu César S. B. Costa Carlos Bemvenuti Clarisse Odebrecht Wilhelm Graneli Alexandre M. Anesio 《Estuaries and Coasts》2006,29(2):277-285
Stable isotopes ratios (δ13C and δ15N) were measured in primary producers and consumers of two bays with contrasting eutrophic conditions in the Patos Lagoon
estuary, southern Brazil: the Justino bay, a more pristine ecosystem, and the Mangueira bay, a heavily polluted region that
receives the Rio Grande city sewage and effluencts of several industries. δ13C values of organisms collected in both subsystems were not different, but δ15N values had significant statistical differences, ca. 3.5‰ higher in the Mangueira bay. It is likely that primary producers
and consumers in this subsystem are greatly influenced by higher nitrogen input due to domestic and industrial sewages. The
stable isotope analysis also corroborated several trophic interactions previously established by gut content analysis, and
due to its higher sensitivity, it was possible to better determine the contributions of different primary producers and detrital
fractions to the consumers' diets. It was confirmed that plant detritus represents the main food source for most organisms.
The stable isotope analysis also demonstrated that detritivorous benthic organisms in the same habitat have distinct diet
compositions, with differential consumption of C3 and C4 plants. This technique showed that some consumers that eat detritus
do not have in their stable isotopic signature any relationship with that of plants. It is likely that these consumers assimilate
their carbon and nitrogen from other sources like microalgae or microorganisms that colonize decaying plants. 相似文献
408.
Will J. Percival Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Stephen Moody Peder Norberg John A. Peacock Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2001,327(4):1297-1306
The 2dF Galaxy Redshift Survey has now measured in excess of 160 000 galaxy redshifts. This paper presents the power spectrum of the galaxy distribution, calculated using a direct Fourier transform based technique. We argue that, within the k -space region , the shape of this spectrum should be close to that of the linear density perturbations convolved with the window function of the survey. This window function and its convolving effect on the power spectrum estimate are analysed in detail. By convolving model spectra, we are able to fit the power-spectrum data and provide a measure of the matter content of the Universe. Our results show that models containing baryon oscillations are mildly preferred over featureless power spectra. Analysis of the data yields 68 per cent confidence limits on the total matter density times the Hubble parameter , and the baryon fraction , assuming scale-invariant primordial fluctuations. 相似文献
409.
410.
To test the various theories of the dissolution time of binary systems, we have performed a series of numerical experiments. The present simulations represent a number of binaries subject to perturbations by passing field stars. Various masses and velocities of the field stars were used to exhibit their effects on the dissolution time. Because of simplicity, the pair considered consisted of a primary of one solar mass plus a secondary of negligible mass.The computations gave, among other things, the evolution in time of the energies and excentricities of the secondary components. We found from these results the need to redefine the concept of time of dissolution to represent more realistically the rate of loss of secondary components. The dissolution times found from the present computations do not agree with any of the existing theories, neither in the general behavior nor in actual numerical values. The times of dissolution found in the present calculations are between a factor of two and a factor of fifteen longer than predicted by existing theories. 相似文献