The Very Early Universe might not have been Radiation-Dominated     

Marcelo Samuel Berman  Rubens de Melo Marinho Jr. 《Astrophysics and Space Science》2001,278(3):367-369

The equation of state of the very early Universe and the formula for the radius, are here evaluated. It is shown that the very early classical Universe might not be radiation-dominated, although we do not exclude the existence of the radiation dominated phase for the early, but not the very early Universe. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Cosmological radiative transfer codes comparison project – I. The static density field tests     

Ilian T. Iliev  Benedetta Ciardi  Marcelo A. Alvarez  Antonella Maselli  rea Ferrara  Nickolay Y. Gnedin  Garrelt Mellema  Taishi Nakamoto  Michael L. Norman  Alexei O. Razoumov  Erik-Jan Rijkhorst  Jelle Ritzerveld  Paul R. Shapiro  Hajime Susa  Masayuki Umemura  Daniel J. Whalen 《Monthly notices of the Royal Astronomical Society》2006,371(3):1057-1086

Radiative transfer (RT) simulations are now at the forefront of numerical astrophysics. They are becoming crucial for an increasing number of astrophysical and cosmological problems; at the same time their computational cost has come within reach of currently available computational power. Further progress is retarded by the considerable number of different algorithms (including various flavours of ray tracing and moment schemes) developed, which makes the selection of the most suitable technique for a given problem a non-trivial task. Assessing the validity ranges, accuracy and performances of these schemes is the main aim of this paper, for which we have compared 11 independent RT codes on five test problems: (0) basic physics; (1) isothermal H  ii region expansion; (2) H  ii region expansion with evolving temperature; (3) I-front trapping and shadowing by a dense clump and (4) multiple sources in a cosmological density field. The outputs of these tests have been compared and differences analysed. The agreement between the various codes is satisfactory although not perfect. The main source of discrepancy appears to reside in the multifrequency treatment approach, resulting in different thicknesses of the ionized-neutral transition regions and the temperature structure. The present results and tests represent the most complete benchmark available for the development of new codes and improvement of existing ones. To further this aim all test inputs and outputs are made publicly available in digital form.  相似文献   

High-Order Spatial Simulation Using Legendre-Like Orthogonal Splines     

Ilnur Minniakhmetov  Roussos Dimitrakopoulos  Marcelo Godoy 《Mathematical Geosciences》2018,50(7):753-780

High-order sequential simulation techniques for complex non-Gaussian spatially distributed variables have been developed over the last few years. The high-order simulation approach does not require any transformation of initial data and makes no assumptions about any probability distribution function, while it introduces complex spatial relations to the simulated realizations via high-order spatial statistics. This paper presents a new extension where a conditional probability density function (cpdf) is approximated using Legendre-like orthogonal splines. The coefficients of spline approximation are estimated using high-order spatial statistics inferred from the available sample data, additionally complemented by a training image. The advantages of using orthogonal splines with respect to the previously used Legendre polynomials include their ability to better approximate a multidimensional probability density function, reproduce the high-order spatial statistics, and provide a generalization of high-order simulations using Legendre polynomials. The performance of the new method is first tested with a completely known image and compared to both the high-order simulation approach using Legendre polynomials and the conventional sequential Gaussian simulation method. Then, an application in a gold deposit demonstrates the advantages of the proposed method in terms of the reproduction of histograms, variograms, and high-order spatial statistics, including connectivity measures. The C++ course code of the high-order simulation implementation presented herein, along with an example demonstrating its utilization, are provided online as supplementary material.  相似文献   

Recent effects of tidal and hydro‐meteorological changes on coastal plains near the mouth of the Amazon River     

José Tasso Felix Guimarães  Marcelo Cancela Lisboa Cohen  Marlon Carlos França  Luiz Carlos Ruiz Pessenda  Eduardo de Jesus Souza  Afonso César Rodrigues Nogueira  Ronnie Alves 《地球表面变化过程与地形》2013,38(13):1535-1549

The goal of this work was to understand the main hydrodynamic processes acting on tidal flats of the coast of Amapá near the mouth of the Amazon River, and how they change over the short term (~ 20 years). The analysis of morphological and geobotanical units was carried out by applying processing and interpretation methods to optical and synthetic aperture radar (SAR) images, combined with data on water salinity, maximum flood height, sedimentary facies data, rainfall and river discharge. The temporal analysis of morphological and geobotanical units suggests the relative stabilization of savannah, ‘várzea’ and mangrove areas during the drier period and increasing tidal amplitude between 1987 to 1997. The wetter period and decreasing tidal amplitude between 1997 to 2008 led to an increase in the area of ‘várzea’ and lakes over savannah, and the expansion of mangroves mainly over the inundated field and tidal mud/mixed flats. Therefore, the decrease in rainfall index during the drier period is well‐correlated with the reduction of the Calçoene River discharge and jointly with increasing tidal amplitude favored the increase of migration rate of the mud bank and erosion profile along the littoral. It was followed by the increase of the Calçoene River discharge and jointly with decreasing tidal amplitude during the wetter period, favoring the development of mangroves on muddy substrates near the coastline. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Modulation of the flow structure by progressive bedforms in the Kinoshita meandering channel     

Jorge D. Abad  Christian E. Frias  Gustavo C. Buscaglia  Marcelo H. Garcia 《地球表面变化过程与地形》2013,38(13):1612-1622

An in‐house fully three‐dimensional general‐purpose finite element model is applied to solve the hydrodynamic structure in a periodic Kinoshita‐generated meandering channel. The numerical model solves the incompressible Reynolds‐averaged Navier–Stokes equations for mass and momentum, while solving the k ? ε equations for turbulence. The free surface is described by the rigid‐lid approximation (using measured water surface data) for flat (smooth‐bed) and self‐formed (rough‐bed) conditions. The model results are compared against experimental measurements in the ‘Kinoshita channel’, where three‐dimensional flow velocities and turbulence parameters were measured. This validation was carried out for the upstream‐valley meander bend orientation under smooth (flat bed) conditions. After validation, several simulations were carried out to predict the hydrodynamics in conditions where either it was not possible to perform measurements (e.g. applicability of the laboratory acoustic instruments) and to extrapolate the model to other planform configurations. For the flat smooth‐bed case, a symmetric (no skewness) planform configuration was modeled and compared to the upstream‐skewed case. For the self‐formed rough‐bed case, prediction of the hydrodynamics during the progression of bedforms was performed. It appears that the presence of bedforms on a bend has the following effects: (i) the natural secondary flow of the bend is disrupted by the presence of the bedforms, thus depending on the location of the dune, secondary flows might differ completely from the traditional orientation; (ii) an increment on both the bed and bank shear stresses is induced, having as much as 50% more fluvial erosion, and thus a potential increment on the migration rate of the bend. Implications on sediment transport and bend morphodynamics are also discussed in the paper. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

A multi-period optimization model for conjunctive surface water–ground water use via aquifer storage and recovery in Corpus Christi,Texas     

E. Annette Hernandez  Venkatesh Uddameri  Marcelo A. Arreola Jr. 《Environmental Earth Sciences》2014,71(6):2589-2604

The present study develops and evaluates a decision support system for the conjunctive management of the current surface and proposed aquifer storage and recovery (ASR) facility of the city of Corpus Christi, TX using a simulation–optimization approach. The objective of the model is to maximize water storage in the surface and subsurface storage units while meeting (1) the freshwater inflow requirements to the Corpus Christi estuary and (2) the water demands of the city and its service area. The model is parameterized using streamflow data from the U. S. Geological Survey gauging stations on the Nueces River and its tributaries as well as long-term climatic data and regional hydrogeologic information. Results indicate that a single-well field ASR facility is capable of storing approximately 925 ha-m (7,500 ac-ft) of water over a 5-year period in the Evangeline Aquifer with a total potential storage of about 2,715 ha-m (22,000 ac-ft) of water over the jurisdictional area of the Corpus Christi Aquifer Storage and Recovery Conservation District. Surplus surface water sources are seen to contribute approximately 49–96 % of the water stored in the ASR during the simulation period. The remaining storage came from either Choke Canyon Reservoir or Lake Corpus Christi, which also resulted in a slight reduction in evapotranspiration in both reservoirs. The analysis indicates that the proposed ASR system is not limited on the supply side but multiple well fields may be required to increase the storage capacity within the aquifer.  相似文献   

Estimating the Instantaneous Drag–Wind Relationship for a Horizontally Homogeneous Canopy     

Ying Pan  Marcelo Chamecki  Heidi M. Nepf 《Boundary-Layer Meteorology》2016,160(1):63-82

  相似文献   

Spatial restricted rhomboidal five-body problem and horizontal stability of its periodic solutions     

Marcelo Marchesin  Claudio Vidal 《Celestial Mechanics and Dynamical Astronomy》2013,115(3):261-279

The spatial restricted rhomboidal five-body problem, or shortly, SRRFBP, is a five body problem in which four positive masses, called the primaries, move two by two in coplanar circular motions with the center of mass fixed at the origin such that their configuration is always a rhombus, the fifth mass being negligible and not influencing the motion of the four primaries. The Hamiltonian function that governs the motion of the fifth mass is derived and has three degrees of freedom depending periodically on time. Using a synodical system of coordinates, we fix the primaries in order to eliminate the time dependence. With the help of the Hamiltonian structure, we characterize the regions of possible motion. The vertical $z$ axis is invariant and we study what we call the rhomboidal Sitnikov problem. Unlike the classical Sitnikov problem, no chaos exists and the behavior of the fifth mass is quite predictable, periodic solutions of arbitrary long periods are shown to exist and we study numerically their linear horizontal stability.  相似文献   

Airports and Environment: Proposal of Wastewater Reclamation at São Paulo International Airport     

Elaine Nolasco Ribeiro  Wilson Cabral de Sousa Jr  Marcelo de Julio  Wilfredo Urruchi Irrazabal  Marcelo Antunes Nolasco 《洁净——土壤、空气、水》2013,41(7):627-634

One way to reduce water consumption in urban areas is by using alternative sources of supply that can be provided by collecting rainwater and reusing wastewater for less restricted purposes. Thus, this study evaluated the characteristics of effluents produced by the wastewater treatment plant (WWTP) of São Paulo International Airport (SPIA), Brazil, in order to reuse it in non‐potable situations. The results achieved, indicated high efficiency in the biological system utilized by SPIA. The removal rates is equal to or >90% for most of the parameters analyzed, among them, fluoride, salinity, nitrite, nitrate, ammonium nitrogen, total nitrogen, phosphorus, sedimentable solids, turbidity, conductivity, apparent color, chemical oxygen demand, biochemical oxygen demand, total organic carbon, fecal coliforms, and oils and greases. Despite the final effluents were good enough to be launched in the local streams, they shall be submitted to a complementary treatment in order to fit some quality parameters to be reused for specific demands (landscape irrigation, toilet flushing, vehicle washing, fire fighting, and dust control).  相似文献   

The environmental impact of Aguilar mine on the heavy metal concentrations of the Yacoraite River,Jujuy Province,NW Argentina     

Alicia Kirschbaum  Jesica Murray  Emilce López  Ahinoam Equiza  Marcelo Arnosio  Geraldo Boaventura 《Environmental Earth Sciences》2012,65(2):493-504

The Yacoraite River and its tributaries run down the eastern slope of the Aguilar Range. It is one of the tributaries of the Rio Grande, located in Quebrada de Humahuaca, a UNESCO World Heritage site. The Aguilar underground mine (Pb–Ag–Zn) is located in the upper reaches of the Yacoraite River drainage basin. The aim of this work is to characterize the presence of heavy metals in water and sediments of the Yacoraite River and to identify their sources. The analysis shows the seasonal variation of heavy metals concentration in water and their relation with the World Health Organization (WHO) limits established for human consumption. The Yacoraite basin is naturally anomalous in some metals and some elements, such as As which is controlled by the chemical composition of regional lithology. During the wet season, Al, Co, Mo and Pb concentrations in water samples are higher than during the dry season; in addition, these metals are also higher than WHO limit values. High enrichment factors for Ba, Mo, Pb, Zn and Cd were found in Casa Grande stream, indicating the direct influence of the mining activities. Cd, Pb and Zn are present in the Aguilar ore minerals, such as sphalerite and galena. Sediments collected during the dry season show a drastic increase in the concentration of As, Pb, Ba, Zn, Cd and Mn. The Müller geo-accumulation index in Casa Grande indicates that it is a highly polluted stream. The concentrations of As, Pb, Ba, Zn, Cd are also high in Yacoraite River: Security Quality Guidelines indicates toxicity. A decrease in enrichment factors and geo-accumulation indices observed in sediments indicates the occurrence of precipitation/adsorption processes in the river to restore the equilibrium composition. Strict environmental controls in Aguilar Mine are necessary to avoid the uncontrolled input of toxic metals in Casa Grande stream and Yacoraite River.  相似文献