Amplification of gravitational waves in scalar-tensor accelerating lambda-Universes     

Marcelo Samuel Berman 《Astrophysics and Space Science》2010,325(2):283-286

After reviewing the scalar-tensor lambda-accelerating power-law solutions by Berman (Astrophys. Space Sci. 323:103, 2009a), we obtain solutions for the amplification of gravitational waves in the models. The solutions consider a perfect gas equation of state, with cosmic pressure proportional to the energy density, the proportionality constant being smaller than −2/3.  相似文献   

Influence of ENSO and the South Atlantic Ocean on climate predictability over Southeastern South America   总被引：1，自引：0，他引：1  

Marcelo Barreiro 《Climate Dynamics》2010,35(7-8):1493-1508

We perform a systematic study of the predictability of surface air temperature and precipitation in Southeastern South America (SESA) using ensembles of AGCM simulations, focusing on the role of the South Atlantic and its interaction with the El Niño-Southern Oscillation (ENSO). It is found that the interannual predictability of climate over SESA is strongly tied to ENSO showing high predictability during the seasons and periods when there is ENSO influence. The most robust ENSO signal during the whole period of study (1949–2006) is during spring when warm events tend to increase the precipitation over Southeastern South America. Moreover, the predictability shows large inter-decadal changes: for the period 1949–1977, the surface temperature shows high predictability during late fall and early winter. On the other hand, for the period 1978–2006, the temperature shows (low) predictability only during winter, while the precipitation shows not only high predictability in spring but also in fall. Furthermore, it is found that the Atlantic does not directly affect the climate over SESA. However, the experiments where air–sea coupling is allowed in the south Atlantic suggest that this ocean can act as a moderator of the ENSO influence. During warm ENSO events the ocean off Brazil and Uruguay tends to warm up through changes in the atmospheric heat fluxes, altering the atmospheric anomalies and the predictability of climate over SESA. The main effect of the air–sea coupling is to strengthen the surface temperature anomalies over SESA; changes in precipitation are more subtle. We further found that the thermodynamic coupling can increase or decrease the predictability. For example, the air–sea coupling significantly increases the skill of the model in simulating the surface air temperature anomalies for most seasons during period 1949–1977, but tends to decrease the skill in late fall during period 1978–2006. This decrease in skill during late fall in 1978–2006 is found to be due to a wrong simulation of the remote ENSO signal that is further intensified by the local air–sea coupling in the south Atlantic. Thus, our results suggest that climate models used for seasonal prediction should simulate correctly not only the remote ENSO signal, but also the local air–sea thermodynamic coupling.  相似文献   

Influence of cattle grazing on population density and species richness of granivorous birds (Emberizidae) in the arid plain of the Monte, Argentina     

Jorge Marcelo Gonnet 《Journal of Arid Environments》2001,48(4):569

Cattle grazing is an important disturbance in the Monte plain, reducing grass biomass and rates of fruit setting. Grass seeds are the most important food for granivorous birds (Emberizidae) during winter. The objective of this study was to test whether granivorous bird populations (Emberizidae), grass seed production, and vegetation structure differed at sites with different intensities of grazing. Emberizid density and species richness were higher in the ungrazed site than in the two grazed paddocks. Seed abundance was also higher in ungrazed vs. grazed sites. Woody vegetation, that serve as safe nest sites, did not differ among treatments. Granivorous bird populations seemed to be affected by cattle grazing; however, the main mechanisms of this process remain unknown.  相似文献   

Crustal structure of the Ribeira fold belt, SE Brazil, derived from receiver functions     

George Sand Frana  Marcelo Assumpo 《Journal of South American Earth Sciences》2004,16(8):522

Crustal thicknesses previously estimated by [J. Geophys. Res. 107 (2002) 2] in SE Brazil varied from 47 km in the middle of the Paraná basin to approximately 35 km in the Ribeira fold belt. We study the crustal structure of the Ribeira belt in more detail by identifying the Ps Moho converted phase and its multiple reflection PpPms, as well as using waveform modeling of receiver functions. We use phase-weighted slant stacking to identify the Ps and PpPms arrival times, which provides the v_P/v_S beneath each station. In inverting the receiver functions, we use average crustal velocities and initial models obtained from a deep seismic refraction line, as well as data from a timed quarry blast. The crustal thickness ranges 34–42 km with a thinning trend toward the coast. Crustal thickness correlates with elevation, indicating approximate regional Airy isostasy. Along the Serra do Mar coastal range, the average crustal Poisson ratio is about 0.25. The southern part of the Mantiqueira range has a higher Poisson ratio of 0.28. Stations near the São Francisco craton have a lower Poisson ratio of 0.23.  相似文献   

Threshold for particle entrainment into suspension     

Yarko NiÑo  Fabian Lopez†  Marcelo Garcia‡ 《Sedimentology》2003,50(2):247-263

ABSTRACT Laboratory observations regarding the limit conditions for particle entrainment into suspension are presented. A high‐speed video system was used to investigate conditions for the entrainment of sediment particles and glass beads lying over a smooth boundary as well as over a rough bed. The results extend experimental conditions of previous studies towards finer particle sizes. A criterion for the limit of entrainment into suspension is proposed which is a function of the ratio between the flow shear velocity and particle settling velocity. Observations indicate that particles totally immersed within the viscous sublayer can be entrained into suspension by the flow, which contradicts the conclusions of previous researchers. A theoretical analysis of the entrainment process within the viscous sublayer, based on force–balance considerations, is used to show that this phenomenon is related to turbulent flow events of high instantaneous values of the Reynolds stress, in agreement with previous observations. In the case of experiments with a rough bed, a hiding effect was observed, which tends to preclude the entrainment of particles finer than the roughness elements. This implies that, as the ratio between particle and roughness element sizes becomes smaller, progressively higher bed shear stresses are required to entrain particles into suspension. On the other hand, an overexposure effect was also observed, which indicates that a particle moving on a smooth bed is more prone to be entrained than the same particle moving on a bed formed by identical particles.  相似文献   

Sequence stratigraphic distribution of diagenetic alterations in coal-bearing, paralic sandstones: evidence from the Rio Bonito Formation (early Permian), southern Brazil   总被引：6，自引：0，他引：6  

J. Marcelo Ketzer  Michael Holz†  S. Morad  I. S. Al-Aasm‡ 《Sedimentology》2003,50(5):855-877

Abstract Linking siliciclastic diagenesis to sequence stratigraphy allows a better understanding of the parameters controlling the spatial and temporal distribution of diagenetic alterations, and hence of reservoir quality. A study of the coal-bearing, alluvial, deltaic, estuarine and shallow-marine sandstones of the Rio Bonito Formation, early Permian, Paraná Basin (southern Brazil), reveals that the distribution of diagenetic alterations and of related reservoir quality evolution can be constrained within a sequence stratigraphic framework. Calcite, dolomite, siderite, kaolinite and pyrite cementation is consistently linked to sequence and parasequence boundaries, transgressive and maximum flooding surfaces and is systematically distributed within lowstand, transgressive and highstand systems tracts. Diagenesis of coal layers at parasequence boundaries has promoted the formation of stratabound calcite (detectable in resistivity wire line logs), concretionary pyrite and kaolinite and of silicate grain dissolution in sandstones located above and below these boundaries, particularly in the transgressive systems tract. Meteoric water diagenesis caused grain dissolution and the formation of kaolinite in sandstones below sequence boundaries and in lowstand systems tract sandstones. Carbonate bioclasts and low sedimentation rates in lag deposits at parasequence boundaries, transgressive and maximum flooding surfaces favoured the formation of grain-rimming siderite. The results of this study are relevant to the exploration of coal-bed methane and other coal-bearing reservoirs, where it is crucial to unravel and predict the distribution and quality of reservoirs and compartments.  相似文献   

An operational forecasting system for physical processes in the Santos-Sao Vicente-Bertioga Estuarine System,Southeast Brazil     

Costa  Carine G. R.  Leite  José Roberto B.  Castro  Belmiro M.  Blumberg  Alan F.  Georgas  Nickitas  Dottori  Marcelo  Jordi  Antoni 《Ocean Dynamics》2020,70(2):257-271

Ocean Dynamics - We describe the design, implementation, and performance of a fully automated Santos Operational Forecasting System (SOFS), built to monitor and predict short-term (< 3 days)...  相似文献   

Groundwater Level Prediction/Forecasting and Assessment of Uncertainty Using SGS and ARIMA Models: A Case Study in the Bauru Aquifer System (Brazil)     

Takafuji  Eduardo Henrique de Moraes  Rocha  Marcelo Monteiro da  Manzione  Rodrigo Lilla 《Natural Resources Research》2019,28(2):487-503

Natural Resources Research - Best water management practices should involve the prediction of the availability of groundwater resources. To predict/forecast and consequently manage these water...  相似文献   

Distribution of whitemouth croaker (Micropogonias furnieri, Desmarest 1823) larvae in the Río de la Plata estuarine front     

Mara S. Braverman  E. Marcelo Acha  Domingo A. Gagliardini  Martín Rivarossa   《Estuarine, Coastal and Shelf Science》2009,82(4):557-565

Whitemouth croaker (Micropogonias furnieri) larvae obtained and hydrographic data collected in the Rio de la Plata estuary (35°S–56°W) between 1987 and 2000 were used to explore the early life stages spatial and temporal distribution patterns and their relation to oceanographic features. The spatial distribution, restricted to a band in the inner part of the estuary, coincided with the bottom salinity front and the maximum turbidity zone (MTZ, turbidity front). Larvae were present during the warmest months (October through May) within a range of 14–24.5 °C temperature and 0.9–33 salinity. A vertically stratified sampling performed in the region where the largest abundance was found (December 2005 and March 2006) was used to test the hypothesis that larvae retention occurs in the bottom salinity front.The vertically stratified sampling showed larvae throughout the water column with high predominance in the river–estuary transition zone. A positive correlation between abundance and the bottom salinity horizontal gradient was found. The size analysis showed that the largest individuals (>10 mm SL), probably undergoing the settlement process, inhabited near the bottom and that the smallest (<10 mm SL) were present in the whole water column. Length distribution along the front showed no trend.Results support the estuarine retention hypothesis of previous studies on whitemouth croaker gravid females, eggs distribution and outcomes from a numerical simulation model. Retention in the salinity front/MTZ would allow larvae to benefit from food accumulation in the region, the high turbidity level provide shelter against predators and retention in the estuary secure closeness to the main nursery ground.  相似文献   

Behavior of the fresh- and saline-water phases in an urban area in Western Buenos Aires Province, Argentina     

Luis Vives  Marcelo Varni  Eduardo Usunoff 《Hydrogeology Journal》2005,13(2):426-435

Given the particular hydrogeological setting at Salliqueló County, Western Buenos Aires Province, Argentina, this paper places attention on the lens that supplies fresh water to its capital, Salliqueló. This lens constitutes the most important fresh-water reservoir in the county. It overlies saline waters, and is recharged through high-permeability sandy sediments at a rate that exceeds by far the actual water demand. Restrictions in exploitation are not limited by the total requirement but rather by the flows extracted from individual wells that may generate up-coning of saline waters, with a resulting overall deterioration in quality of the pumped water. The variations in the position of the interface between saline and fresh waters, as related to the change in extraction rates, were obtained by means of a simulation of the flow of two fluids of different densities. Finally, based on the general hydrogeological characterization and on the simulation results, various methods for the management of these fresh-water resources are proposed, such as the deactivation of urban supply wells, the monitoring of the saline interface position, and the establishment of a protection perimeter for the water-supply wells.

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Resumen Enmarcado dentro de las características hidrogeológicas generales del partido de Salliqueló, oeste de la provincia de Buenos Aires, Argentina, este trabajo se centra en la lente que abastece de agua dulce a Salliqueló, la capital del partido. Esta lente constituye la reserva de agua dulce más importante del partido, se ubica sobre aguas salinas y es recargada a través de sedimentos arenosos de alta permeabilidad a una tasa que excede grandemente los requerimientos de la población. Sin embargo, las restricciones en la explotación no están dadas por las demandas totales sino por las extracciones en perforaciones individuales, que pueden generar ascensos de agua salina con el consiguiente deterioro en la calidad del agua extraída. Las variaciones de la posición de la interfase respecto de los cambios en la explotación fueron obtenidas por medio de la simulación del flujo de dos fluidos de diferente densidad. Finalmente, con base en la caracterización hidrogeológica general y en los resultados de la simulación, se proponen varias medidas para la protección del recurso hídrico, tales como: la desactivación de los pozos de abastecimiento en el ámbito urbano, el control de la posición de la interfase salina y la definición de perímetros de protección de los pozos de abastecimiento, entre otras.

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Résumé Etant donné les particularités hydrogéologiques de la région de Salliqueló, ouest de la province de Buenos Aires, Argentine, cet article traite de la lentille deau douce alimentant en eau potable la capitale, Salliqueló. Cette lentille constitue la réserve la plus importante deau douce de la région. Elle se superpose aux eaux salées et est rechargée via les sédiments sableux et perméables, à un taux dépassant largement la demande actuelle en eau. Les restrictions dans lexploitation ne sont pas limitées par la demande totale mais par les débits extraits des forages privés, qui pourraient générer des rabattements induisant des arrivées deaux salées, arrivées qui peuvent dégrader la ressource pompée. Les variations de la position de linterface eau douce–eau salée, en relation avec les taux dexploitation, ont été obtenues en simulant lécoulement de deux fluides de différentes densités. Finalement, sur base dune caractérisation hydrogéologique et des résultats de la simulation, des méthodes variées pour la gestion de la ressource en eau douce sont proposées, entre autre, la désactivation de pompages urbains, suivi de linterface eau douce–eau salée, et la mise en place de zones de protections des captages deau souterraine.

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