Validation of soft bottom benthic habitats identified by single-beam acoustics     

Freitas R  Sampaio L  Oliveira J  Rodrigues AM  Quintino V 《Marine pollution bulletin》2006,53(1-4):72-79

Acoustic diversity charts were produced for a Portuguese soft bottom mid-shelf area, depth from 30 to 90 m, using a single-beam echo sounder coupled to the acoustic systems QTC VIEW Series IV and V. A similar acoustic pattern was identified by both systems, which, after ground-truth interpretation based in available sediment and biological data, established a preliminary spatial distribution model of the benthic habitats in this coastal area. However, some of the acoustic areas were interpreted using one or very few sediment and benthic samples. A specific validation survey was conducted a posteriori, in which the positioning of the sediment and benthic community sampling sites was based on the acoustic diversity previously identified. The results clearly confirm the benthic habitats distribution model suggested by the acoustic method, indicating a high potential for the use of such approach in the identification and mapping of large-scale soft bottom coastal shelf habitat diversity.  相似文献   

A case study of the direct radiative effect of biomass burning aerosols on precipitation in the Eastern Amazon     

E.P. Vendrasco  P.L. Silva Dias  E.D. Freitas   《Atmospheric Research》2009,94(3):409

Numerical experiments with the Brazilian additions to the Regional Atmospheric Modeling System were performed with two nested grids (50 and 10 km horizontal resolution, respectively) with and without the effect of biomass burning for 8 different situations for 96 h integrations. Only the direct radiative effect of aerosols is considered. The results were analyzed in large areas encompassing the BR163 road (one of the main areas of deforestation in the Amazon), mainly where most of the burning takes place. The precipitation change due to the direct radiative impact of biomass burning is generally negative (i.e., there is a decrease of precipitation). However, there are a few cases with a positive impact. Two opposite forcing mechanisms were explored: (a) the thermodynamic forcing that is generally negative in the sense that the aerosol tends to stabilize the lower atmosphere and (b) the dynamic impact associated with the low level horizontal pressure gradients produced by the aerosol plumes. In order to understand the non-linear relationship between the two effects, experiments were performed with 4-fold emissions. In these cases, the dynamic effect overcomes the stabilization produced by the radiative forcing and precipitation increase is observed in comparison with the control experiment. This study suggests that, in general, the biomass burning radiative forcing decreases the precipitation. However, very large concentrations of aerosols may lead to an increase of precipitation due to the dynamical forcing associated with the horizontal pressure gradients.  相似文献   

The branch-cut quantum gravity with a self-coupling inflation scalar field: The wave function of the Universe     

Fridolin Weber  Peter O. Hess  Benno Bodmann  José de Freitas Pacheco  Dimiter Hadjimichef  Marcelo Netz-Marzola  Geovane Naysinger  Moisés Razeira  César A. Zen Vasconcellos 《Astronomische Nachrichten》2024,345(2-3):e230148

This paper focuses on the implications of a commutative formulation that integrates branch-cutting cosmology, the Wheeler–DeWitt equation, and Hořava–Lifshitz quantum gravity. Building on a mini-superspace structure, we explore the impact of an inflaton-type scalar field on the wave function of the Universe. Specifically analyzing the dynamical solutions of branch-cut gravity within a mini-superspace framework, we emphasize the scalar field's influence on the evolution of the evolution of the wave function of the Universe. Our research unveils a helix-like function that characterizes a topologically foliated spacetime structure. The starting point is the Hořava–Lifshitz action, which depends on the scalar curvature of the branched Universe and its derivatives, with running coupling constants denoted as $g_i$. The corresponding wave equations are derived and are resolved. The commutative quantum gravity approach preserves the diffeomorphism property of General Relativity, maintaining compatibility with the Arnowitt–Deser–Misner formalism. Additionally, we delve into a mini-superspace of variables, incorporating scalar-inflaton fields and exploring inflationary models, particularly chaotic and nonchaotic scenarios. We obtained solutions for the wave equations without recurring to numerical approximations.  相似文献   

The branch-cut quantum gravity with a self-coupling inflation scalar field: Dynamical equations     

Fridolin Weber  Peter O. Hess  Benno Bodmann  José de Freitas Pacheco  Dimiter Hadjimichef  Marcelo Marzola  Geovane Naysinger  Moisés Razeira  César A. Zen Vasconcellos 《Astronomische Nachrichten》2024,345(2-3):e230152

This article focuses on the implications of the recently developed commutative formulation based on branch-cutting cosmology, the Wheeler–DeWitt equation, and Hořava–Lifshitz quantum gravity. Assuming a mini-superspace of variables, we explore the impact of an inflaton-type scalar field $\varphi (t)$ on the dynamical equations that describe the trajectories evolution of the scale factor of the Universe, characterized by the dimensionless helix-like function ${\ln }^{-1}[\beta (t)]$. This scale factor characterizes a Riemannian foliated spacetime that topologically overcomes the big bang and big crunch singularities. Taking the Hořava–Lifshitz action as our starting point, which depends on the scalar curvature of the branched Universe and its derivatives, with running coupling constants denoted as $g_i$, the commutative quantum gravity approach preserves the diffeomorphism property of General Relativity, maintaining compatibility with the Arnowitt–Deser–Misner formalism. We investigate both chaotic and nonchaotic inflationary scenarios, demonstrating the sensitivity of the branch-cut Universe's dynamics to initial conditions and parameterizations of primordial matter content. The results suggest a continuous connection of Riemann surfaces, overcoming primordial singularities and exhibiting diverse evolutionary behaviors, from big crunch to moderate acceleration.  相似文献   

Noncommutative branch-cut quantum gravity with a self-coupling inflaton scalar field: The wave function of the Universe     

Peter O. Hess  Fridolin Weber  Benno Bodmann  José de Freitas Pacheco  Dimiter Hadjimichef  Marcelo Netz-Marzola  Geovane Naysinger  Moisés Razeira  César A. Zen Vasconcellos 《Astronomische Nachrichten》2024,345(2-3):e230162

This article focuses on the implications of a noncommutative formulation of branch-cut quantum gravity. Based on a mini-superspace structure that obeys the noncommutative Poisson algebra, combined with the Wheeler–DeWitt equation and Hořava–Lifshitz quantum gravity, we explore the impact of a scalar field of the inflaton-type in the evolution of the Universe's wave function. Taking as a starting point the Hořava–Lifshitz action, which depends on the scalar curvature of the branched Universe and its derivatives, the corresponding wave equations are derived and solved. The noncommutative quantum gravity approach adopted preserves the diffeomorphism property of General Relativity, maintaining compatibility with the Arnowitt–Deser–Misner Formalism. In this work we delve deeper into a mini-superspace of noncommutative variables, incorporating scalar inflaton fields and exploring inflationary models, particularly chaotic and nonchaotic scenarios. We obtained solutions to the wave equations without resorting to numerical approximations. The results indicate that the noncommutative algebraic space captures low and high spacetime scales, driving the exponential acceleration of the Universe.  相似文献   

Modern sedimentation processes in a wave-dominated coastal embayment: Espírito Santo Bay,southeast Brazil     

Alex Cardoso Bastos  Daphnne Moraes Costa Moscon  Dannilo Carmo  José Antonio Baptista Neto  Valéria da Silva Quaresma 《Geo-Marine Letters》2015,35(1):23-36

  相似文献   

Changes in extreme daily rainfall for São Paulo, Brazil     

Maria A. F. Silva Dias  Juliana Dias  Leila M. V. Carvalho  Edmilson D. Freitas  Pedro L. Silva Dias 《Climatic change》2013,116(3-4):705-722

Significant positive trends are found in the evolution of daily rainfall extremes in the city of São Paulo (Brazil) from 1933 to 2010. Climatic indices including ENSO, PDO, NAO and the sea surface temperature at the coast near São Paulo explain 85 % of the increasing frequency of extremes during the dry season. During the wet season the climatic indices and the local sea surface temperature explain a smaller fraction of the total variance when compared to the dry season indicating that other factors such as the growth of the urban heat island and the role of air pollution in cloud microphysics need to be taken into account to explain the observed trends over the almost eight decades.  相似文献   

Boulder deposition during major tsunami events     

Pedro J. M. Costa  César Andrade  Maria C. Freitas  Maria A. Oliveira  Carlos M. da Silva  Rachid Omira  Rui Taborda  Maria A. Baptista  Alastair G. Dawson 《地球表面变化过程与地形》2011,36(15):2054-2068

A remarkable accumulation of marine boulders located above the present spring tide level has occurred in two coastal lowlands of the Algarve (Portugal). The size‐interval of the particles studied here is seldom reported in the literature in association with extreme events of coastal inundation, thus making this study of relevance to many other coasts worldwide. The spreads of boulders extend several hundred meters inland and well beyond the present landward limit of storm activity. The marine origin of the boulders is demonstrated by well‐developed macro‐bioerosion sculpturing and in situ skeletal remains of endolithic shallow marine bivalves. The good state preservation of the fossils within the boulders indicates that abrasion during transport and redeposition was not significant. We envisage boulder deposition as having taken place during the Lisbon tsunami of ad 1755 through the simultaneous landward entrainment of coarse particles from nearshore followed by rapid shoreward suspended‐dominated transport and non‐graded redeposition that excluded significant sorting by weight or boulder dimensions. We use numerical hydrodynamic modeling of tsunami (and storm) waves to test the observational data on boulder dimensions (density, size, distribution) on the most likely processes of sediment deposition. This work demonstrates the effectiveness of the study of boulder deposits in tsunami reconstruction. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Experimentally gained parameters,decisive for rock fall analysis   总被引：5，自引：0，他引：5  

A. Azzoni  M. H. de Freitas 《Rock Mechanics and Rock Engineering》1995,28(2):111-124

Summary This paper presents the methodology adopted for assessing experimental parameters relevant to computer rockfall analyses and describes the data gathered from several in situ rockfall tests carried out by ISMES and ENEL CRIS during recent years.Through the calculation of block velocities during their fall from and onto slopes of various geometry, and the measurement of the run-out distances, heights of bounce and the geometric characteristics of blocks, the following experimental parameters were studied: Restitution Coefficient, Rolling Friction Coefficient, dispersion of trajectories, effect of block geometry on its fall, and efficiency of a ditch, at the bottom of a slope, for arresting fallen blocks.  相似文献   

Evolution of the phase-space density of dark matter haloes and mixing effects in merger events     

Sébastien Peirani  Fabrice Durier  José A. de Freitas Pacheco 《Monthly notices of the Royal Astronomical Society》2006,367(3):1011-1016

Cosmological N -body simulations were performed to study the evolution of the phase-space density   Q =ρ/σ³  of dark matter haloes. No significant differences in the scale relations   Q ∝σ^−2.1  or   Q ∝ M ^−0.82  are seen for the 'cold' or 'warm' dark matter models. The follow-up of individual haloes from   z = 10  up to the present time indicate the existence of two main evolutionary phases: an early and fast one  (10 > z > 6.5)  , in which Q decreases on the average by a factor of 40 as a consequence of the randomization of bulk motions, and a late and long one  (6.5 > z ≥ 0)  , in which Q decreases by a factor of 20 because of mixing induced by merger events. The study of these haloes has also evidenced that rapid and positive variations of the velocity dispersion, induced by merger episodes, are related to a fast decrease of the phase-space density Q .  相似文献