92 research outputs found
Mixing and coherent structures in two-dimensional viscous flows
We introduce a dynamical description based on a probability density
of the vorticity in two-dimensional viscous flows
such that the average vorticity evolves according to the Navier-Stokes
equations. A time-dependent mixing index is defined and the class of
probability densities that maximizes this index is studied. The time dependence
of the Lagrange multipliers can be chosen in such a way that the masses
m(\sigma,t):=\intdxdy \phi(\sigma,x,y,t) associated with each vorticity value
are conserved. When the masses are conserved then 1) the
mixing index satisfies an H-theorem and 2) the mixing index is the
time-dependent analogue of the entropy employed in the statistical mechanical
theory of inviscid 2D flows [Miller, Weichman & Cross, Phys. Rev. A \textbf{45}
(1992); Robert & Sommeria, Phys. Rev. Lett. \textbf{69}, 2776 (1992)]. Within
this framework we also show how to reconstruct the probability density of the
quasi-stationary coherent structures from the experimentally determined
vorticity-stream function relations and we provide a connection between this
probability density and an appropriate initial distribution
Coarse-grained distributions and superstatistics
We show an interesting connexion between the coarse-grained distribution
function arising in the theory of violent relaxation for collisionless stellar
systems (Lynden-Bell 1967) and the notion of superstatistics introduced
recently by Beck & Cohen (2003). We also discuss the analogies and differences
between the statistical equilibrium state of a multi-components
self-gravitating system and the metaequilibrium state of a collisionless
stellar system. Finally, we stress the important distinction between mixing
entropies, generalized entropies, H-functions, generalized mixing entropies and
relative entropies
Clone wars:asexual reproduction dominates in the invasive range of Tubastraea spp. (Anthozoa: Scleractinia) in the South-Atlantic Ocean
Although the invasive azooxanthellate corals Tubastraea coccinea and T. tagusensis are spreading quickly and outcompeting native species in the Atlantic Ocean, there is little information regarding the genetic structure and path of introduction for these species. Here we present the first data on genetic diversity and clonal structure from these two species using a new set of microsatellite markers. High proportions of clones were observed, indicating that asexual reproduction has a major role in the local population dynamics and, therefore, represents one of the main reasons for the invasion success. Although no significant population structure was found, results suggest the occurrence of multiple invasions for T. coccinea and also that both species are being transported along the coast by vectors such as oil platforms and monobouys, spreading these invasive species. In addition to the description of novel microsatellite markers, this study sheds new light into the invasive process of Tubastraea.Coordenacao de Aperfeicoamento de Pessoal de Nivel SuperiorFundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de JaneiroConselho Nacional de Desenvolvimento Cientifico e TecnologicoFundacao de Amparo a Pesquisa do Estado de Sao PauloNSF-OA (National Science Foundation)Univ Fed Rio de Janeiro, Dept Zool, Rio De Janeiro, BrazilUniv Hawaii Manoa, Hawaii Inst Marine Biol, Sch Ocean & Earth Sci & Technol, Kaneohe, HI USACoral Sol Res Technol Dev & Innovat Network, Rio De Janeiro, BrazilUniv Fed Rio de Janeiro, Inst Microbiol Paulo Goes, Rio De Janeiro, BrazilUniv Estado Rio de Janeiro, Dept Ecol, Rio De Janeiro, BrazilUniv Fed Sao Paulo, Dept Ciencias Mar, Santos, BrazilUniv Sao Paulo, Ctr Biol Marinha, Sao Sebastiao, BrazilUniv Fed Sao Paulo, Dept Ciencias Mar, Santos, BrazilCAPES: 1137/2010FAPERJ: E26/010.003031/2014FAPERJ: E26/201.286/2014CNPq: 305330/2010-1FAPESP: 2014/01332-0Web of Scienc
Detailed predictions of climate induced changes in the thermal and flow regimes in mountain streams of the Iberian Peninsula
The present study aimed at predicting the effects of climate change on the thermal and flow regime in the Iberian Peninsula, refining the resolution of previous studies. For this purpose, the study encompassed 28 sites at eight different mountain rivers and streams in the central part of the Iberian Peninsula (Spain). The daily flow was modelled using different daily, monthly and quarterly lags of the historical precipitation and temperature time series. These precipitation-runoff models were developed by means of M5 model trees. On the other hand water temperature was modelled at similar time scale by means of nonlinear regression from dedicated site-specific data. The developed models were used to simulate the temperature and flow regime under two Representative Concentration Pathway (RCPs) climate change scenarios (RCP 4.5 and RCP 8.5) until the end of the present century by considering nine different GCMs, which were pertinently downscaled
Stream flow regime, temperature and climate change: the loss of fish habitat
This study is aimed at forecasting the changes in the suitability of brown trout habitat (Salmo trutta L.), caused by alterations in the stream temperature and the flow regime under climate change scenarios. The stream temperature and instantaneous flow in several streams in Central Spain were modelled from daily temperature and precipitation data. Logistic models were used for stream temperature modelling whereas M5? model trees were used to develop the precipitation-runoff models. These models were utilized to simulate the running flows under the climate change scenarios RCP4.5 and RCP8.5 (5thIPCC). The resulting forecasts suggested a different response of the stream temperature to the atmospheric warming in accordance with the geologic nature of basins. At the same time, significant decreases in summer flow and increases in the frequency of zero-flow events were predicted. In the future, significant declines in summer flow could exacerbate the negative impact on trout populations of increased water temperature by reducing both the suitable spatial habitat and the warming resistance of the water mass
Performance of the double multilayer monochromator on the NSLS wiggler beam line X25
A tunable, double multilayer x-ray monochromator has recently been implemented on the National Synchrotron Light Source (NSLS) X25 wiggler beam line. It is based on a parallel pair of tungsten-boron-carbide multilayer films grown on silicon substrates and purchased from Osmic, Inc. of Troy, Michigan, USA. It acts as an optional alternative to the conventional double silicon crystal monochromator, and uses the same alignment mechanism. Two other NSLS beam lines also have had this kind of monochromator installed recently, following the lead of the NSLS X20C IBM/MIT beam line which has used a double multilayer monochromator for several years. Owing to the 100 times broader bandwidth of a multilayer x-ray monochromator, compared with a silicon monochromator, the multilayer monochromator has the obvious advantage of delivering 100 times the flux of a silicon monochromator, and thereby makes more efficient use of the continuous synchrotron radiation spectrum, yet preserves the narrow collimation of the incident synchrotron beam. In particular, multilayer x-ray bandwidths, on the order of 1%, are well-matched to x-ray undulator linewidths. Performance results for the X25 multilayer monochromator are presented, comparing it with the silicon monochromator. Of note is its short- and long-term performance as an x-ray monochromator delivering the brightness of the wiggler source in the presence of the high-power white beam. Detailed measurements of its spatial beam profile and wavelength dispersion have been made, and it is shown how its resolution could be improved when desired. Finally, its peculiar, anisotropic resolution function in reciprocal space, and its bearing upon x-ray crystallography and scattering experiments, will be discussed, and highlighted by the results of a protein crystallography experiment. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87844/2/71_1.pd
Cadmium Exposure and Neurodevelopmental Outcomes in U.S. Children
Background: Low-level environmental cadmium exposure in children may be associated with adverse neurodevelopmental outcomes
Cartografia e diplomacia: usos geopolíticos da informação toponímica (1750-1850)
O artigo explora dimensões geopolíticas da toponímia, registradas em documentos cartográficos, desde as reformas empreendidas pelo consulado pombalino em meados do século XVIII, até às primeiras décadas do século XIX, em meio ao processo de afirmação do Estado imperial pós-colonial.This paper explores the geopolitical dimensions of toponymy as registered in cartographic documents dating from the reforms pushed through by the consulate of Marquis of Pombal in the mid 18th century to the early decades of the 19th century, as the post-colonial imperial State established itself
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