Neural network modelling of planform geometry of headland-bay beaches     

G. Iglesias  I. Lpez  A. Castro  R. Carballo 《Geomorphology》2009,103(4):577-587

The shoreline of beaches in the lee of coastal salients or man-made structures, usually known as headland-bay beaches, has a distinctive curvature; wave fronts curve as a result of wave diffraction at the headland and in turn cause the shoreline to bend. The ensuing curved planform is of great interest both as a peculiar landform and in the context of engineering projects in which it is necessary to predict how a coastal structure will affect the sandy shoreline in its lee. A number of empirical models have been put forward, each based on a specific equation. A novel approach, based on the application of artificial neural networks, is presented in this work. Unlike the conventional method, no particular equation of the planform is embedded in the model. Instead, it is the model itself that learns about the problem from a series of examples of headland-bay beaches (the training set) and thereafter applies this self-acquired knowledge to other cases (the test set) for validation. Twenty-three headland-bay beaches from around the world were selected, of which sixteen and seven make up the training and test sets, respectively. As there is no well-developed theory for deciding upon the most convenient neural network architecture to deal with a particular data set, an experimental study was conducted in which ten different architectures with one and two hidden neuron layers and five training algorithms – 50 different options combining network architecture and training algorithm – were compared. Each of these options was implemented, trained and tested in order to find the best-performing approach for modelling the planform of headland-bay beaches. Finally, the selected neural network model was compared with a state-of-the-art planform model and was shown to outperform it.  相似文献   

The response of the Sao Paulo Continental Shelf, Brazil, to synoptic winds     

Marcelo Dottori  Belmiro Mendes Castro 《Ocean Dynamics》2009,59(4):603-614

The response of the Sao Paulo Continental Shelf (SPCS) to synoptic wind forcing has been analyzed. Two different methods are used for this purpose, one based on hydrographic data, bottom topography, and geographical characteristics, and a second on analyzing currentmeter data directly and using empirical orthogonal functions. Both methods show similar results for an essentially barotropic shelf. The SPCS response in the subinertial frequency band appears to be trapped on the continental shelf. Numerical experiments have also been carried out showing results that qualitatively agree with the observations, including the velocity component parallel to the coastline. Supported by CAPES.  相似文献   

A Search for Warm Neutral Gas Associated with the Giant HII Region NGC 604     

A.I. Gómez de Castro  L. Sanz  J. Beckman 《Astrophysics and Space Science》2000,272(1-3):15-22

The characteristics of the halo gas and its interaction with the galactic disk in spiral galaxies are poorly known; this is particularly true for the warm neutral gas associated with HVCs and galactic chimneys. The detection of absorption features such as the NaI D or the CaII (H,K)lines is instrumental to study its detailed physical properties but requires very long integration times. In this work very deep optical spectra of NGC 604, the brightest giant HII region among the nearby spirals, are presented. The detection of two absorption components at LSR velocities -255 km/s and −20 km/s respectively, is reported; the first component is associated with the HII region. The inferred line width after deconvolution is 155 km/s; this large width is produced by the blending of the multiple absorption components produced by the diverse sources of internal motion (expanding shells and general turbulence). The radial velocity of the CaII absorption is slightly larger than the measured in the HII emission lines suggesting a possible flow of gas into the halo above the young star cluster. The large ratio x = W _λ (NaID_2)/W _λ (CaIIK) = 0.7indicates the probable presence of shocks which release Ca from the dust grains into the gas phase. The lower velocity component most likely trace galactic gas. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The far-UV spectrum of T Tauri stars – I. The relevance of the IUE Newly Extracted Spectra     

N. Huélamo  M. Franqueira  A. I. Gómez de Castro 《Monthly notices of the Royal Astronomical Society》2000,312(4):833-842

The far-UV spectrum of the T Tauri stars (TTSs) provides important clues about the structure of the stellar atmospheres, winds and accretion shocks. The IUE ( International Ultraviolet Explorer ) Final Archive contains the most complete data base for such studies. A new extraction system, the IUE Newly Extracted Spectra ( ines ), has been developed to overcome the disadvantages of the extraction system used in the IUE Final Archive, the Signal Weighted Extraction Technique ( swet ). We have compared the ines spectra of the whole sample of TTSs in the far-UV range (1200–2000 Å) with the swet low-resolution spectra available in the IUE Final Archive. Although in most of the cases there is a good agreement between both samples, an important enhancement of the ines line fluxes with respect to the swet line fluxes is reported for particular spectra. The line fluxes are enhanced by as much as a factor of ∼2.5 in some objects, which is significant for variability studies of TTSs because the variations of the UV lines are typically of this order. The emission-measure distributions built to study the atmospheres of these stars are based on the UV emission line fluxes, so the new system is susceptible to introduce changes in these models. Moreover, the non-linear enhancement of the ines line fluxes produces variations in diagnostic line ratios usually taken as temperature and density tracers in late-type stars. These line ratios can vary by as much as a factor of 3 when the ines data are compared with the swet , with the subsequent variation of the physical parameters derived from them.  相似文献   

On the use of logistic regression for stellar classification     

Leire Beitia-Antero  Javier Yáñez  Ana I. Gómez de Castro 《Experimental Astronomy》2018,45(3):379-395

We are totally immersed in the Big Data era and reliable algorithms and methods for data classification are instrumental for astronomical research. Random Forest and Support Vector Machines algorithms have become popular over the last few years and they are widely used for different stellar classification problems. In this article, we explore an alternative supervised classification method scarcely exploited in astronomy, Logistic Regression, that has been applied successfully in other scientific areas, particularly biostatistics. We have applied this method in order to derive membership probabilities for potential T Tauri star candidates from ultraviolet-infrared colour-colour diagrams.  相似文献   

All-sky ultraviolet surveys: the needs and the means     

Ana I. Gómez de Castro  Noah Brosch  Boris Shustov 《Astrophysics and Space Science》2018,363(10):201

This is a crucial time in the history of astronomy with major all-sky surveying work being carried out in all spectral bands, as well as in astrometry. The results of this activity are advancing all fields of astrophysical research, from the investigation of exo-planetary systems to the study of the chemical evolution of the Universe. Full sky surveys are available from the radio domain to X-ray wavelengths but not in the ultraviolet range (UV). While large UV missions are currently under discussion within the astrophysical community and at the major Space Agencies, the efficient use of resources requires preparatory work that can fill the UV surveying gap. This article summarizes the research and on-going activities in this field.  相似文献   

Spectral Trends of Solar Bursts at Sub-THz Frequencies     

L. O. T. Fernandes  P. Kaufmann  E. Correia  C. G. Giménez de Castro  A. S. Kudaka  A. Marun  P. Pereyra  J.-P. Raulin  A. B. M. Valio 《Solar physics》2017,292(1):21

Previous sub-THz studies were derived from single-event observations. We here analyze for the first time spectral trends for a larger collection of sub-THz bursts. The collection consists of a set of 16 moderate to small impulsive solar radio bursts observed at 0.2 and 0.4 THz by the Solar Submillimeter-wave Telescope (SST) in 2012?–?2014 at El Leoncito, in the Argentinean Andes. The peak burst spectra included data from new solar patrol radio telescopes (45 and 90 GHz), and were completed with microwave data obtained by the Radio Solar Telescope Network, when available. We critically evaluate errors and uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission, and introduce a new method to obtain a uniform flux scale criterion for all events. The sub-THz bursts were searched during reported GOES soft X-ray events of class C or larger, for periods common to SST observations. Seven out of 16 events exhibit spectral maxima in the range 5?–?40 GHz with fluxes decaying at sub-THz frequencies (three of them associated to GOES class X, and four to class M). Nine out of 16 events exhibited the sub-THz spectral component. In five of these events, the sub-THz emission fluxes increased with a separate frequency from that of the microwave spectral component (two classified as X and three as M), and four events have only been detected at sub-THz frequencies (three classified as M and one as C). The results suggest that the THz component might be present throughout, with the minimum turnover frequency increasing as a function of the energy of the emitting electrons. The peculiar nature of many sub-THz burst events requires further investigations of bursts that are examined from SST observations alone to better understand these phenomena.  相似文献   

TPH and PAH concentrations in the subsoil of polyduct segments, oil pipeline pumping stations, and right-of-way pipelines from Central Mexico     

Rosario Iturbe  Alejandrina Castro  Guillermina Perez  Carlos Flores  Luis G. Torres 《Environmental Geology》2008,55(8):1785-1795

For the year 1996, 366 incidents related with clandestine poaching of oil-products were reported in Mexico, 159 in 1997, and 240 in 1998. For the year 2003 (the most recently reported figure), there were 136 events. Petroleos Mexicanos (PEMEX), very concerned with the environmental agenda, has developed programs oriented to diminish contamination levels in all of its oil facilities. This work was aimed at characterizing zones around polyduct segments, pipelines, pumping stations, and right-of-way pipelines located in the center of Mexico. The TPH contaminated sites were, in decreasing order, polyduct km 39 + 150 > polyduct km 25 + 020 > Zoquital > Tepetitlan > Catalina > Venta Prieta > Ceiba. Most of the sampled points showed the presence of more than one of the 16 PAHs considered by USEPA as priority pollutants. Except point TEPE 2A, where no PAHs were detected, all the sampled points showed values from low to medium concentrations; however, values found at the sites did not exceed the limits according to the Mexican or the American legislation. The place with the largest contaminated area corresponded to the polyduct km 39 + 150, with 130 m² and 260 m³ to be treated. The least contaminated area was that around the JUAN 4 point at Juandho station, with 20 m² and 22 m³ of contaminated soil. The total area to be treated is about 230 m² and 497 m³.  相似文献   

Determination of S-wave energy release of earthquakes in the region of Friuli, Italy     

Raúl R. Castro  Francesca Pacor  Carmine Petrungaro 《Geophysical Journal International》1997,128(2):399-408

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Simulation of a long-lived meso-β scale convective system over the mediterranean coast of spain. Part I: Numerical predictability     

C. Fernández  M. A. Gaertner  C. Gallardo  M. Castro 《Meteorology and Atmospheric Physics》1995,56(3-4):157-179

Summary An unusually long-lived (33 hours), devastating (local maximum rainfall rate over 800 mm/24 hr) meso--scale (diameter smaller than 200 km) convective system that occurred over the Mediterranean coast of Spain has been simulated reasonably well by means of a regional numerical model. Several runs of the model including parameterized convection and boundary conditions of varying degrees of complexity have been performed. In most of these experiments, the main characteristics of the event, namely its, stationarity and duration, are captured. The direct relationship between the Lagrangian lifetime of a meteorological system and its degree of deturministic predictability seems to be corroborated by the results: It appears that the meso--scale forcing that preceded and favoured the MCS was especially well predictable, and once initiated, the simulated MCS seems to have several feedback mechanisms helping to extend its life. Results are encouraging, because they reveal that it might be possible to predict very severe episodes of small MCSs such as the one shown here sufficiently in advance.With 15 Figures  相似文献