844 research outputs found
Significant Contribution of Large Particles to Optical Backscattering in the Open Ocean
The light scattering properties of oceanic particles have been suggested as an alternative index of phytoplankton biomass than chlorophyll-a concentration (chl-a), with the benefit of being less sensitive to physiological forcings (e.g., light and nutrients) that alter the intracellular pigment concentrations. The drawback of particulate scattering is that it is not unique to phytoplankton. Nevertheless, field studies have demonstrated that, to first order, the particulate beam-attenuation coefficient (c(p)) can track phytoplankton biomass. The relationship between c(p) and the particulate backscattering coefficient (b(bp)), a property retrievable from space, has not been fully evaluated, largely due to a lack of open-ocean field observations. Here, we present extensive data on inherent optical properties from the Equatorial Pacific surface waters and demonstrate a remarkable coherence in b(bp) and c(p). Coincident measurements of particle size distributions (PSDs) and optical properties of size-fractionated samples indicate that this covariance is due to both the conserved nature of the PSD and a greater contribution of phytoplankton-sized particles to b(bp) than theoretically predicted. These findings suggest that satellite-derived b(bp)could provide similar information on phytoplankton biomass in the open ocean as c(p)
Intermittency of glassy relaxation and the emergence of a non-equilibrium spontaneous measure in the aging regime
We consider heat exchange processes between non-equilibrium aging systems (in
their activated regime) and the thermal bath in contact. We discuss a scenario
where two different heat exchange processes concur in the overall heat
dissipation: a stimulated fast process determined by the temperature of the
bath and a spontaneous intermittent process determined by the fact that the
system has been prepared in a non-equilibrium state. The latter is described by
a probability distribution function (PDF) that has an exponential tail of width
given by a parameter , and satisfies a fluctuation theorem (FT)
governed by that parameter. The value of is proportional to the
so-called effective temperature, thereby providing a practical way to
experimentally measure it by analyzing the PDF of intermittent events.Comment: Latex file, 8 pages + 5 postscript figure
Visualization and spectral synthesis of rotationally distorted stars
Simple spherical, non-rotating stellar models are inadequate when describing
real stars in the limit of very fast rotation: Both the observable spectrum and
the geometrical shape of the star deviate strongly from simple models. We
attempt to approach the problem of modeling geometrically distorted, rapidly
rotating stars from a new angle: By constructing distorted geometrical models
and integrating standard stellar models with varying temperature, gravity, and
abundances, over the entire surface, we attempt a semi-empirical approach to
modeling. Here we present our methodology, and present simple examples of
applications.Comment: 7 pages, 5 figures. Contribution to GREAT-ESF Workshop on "Stellar
Atmospheres in the Gaia Era", Brussels 23-24 June 201
Molecular and morphometric variation in European populations of the articulate brachiopod <i>Terebeatulina retusa</i>
Molecular and morphometric variation within and between population samples of the articulate brachiopod <i>Terebratulina</i> spp., collected in 1985-1987 from a Norwegian fjord, sea lochs and costal sites in western Scotland, the southern English Channel (Brittany) and the western Mediterranean, were measured by the analysis of variation in the lengths of mitochondrial DNA (mtDNA) fragments produced by digestion with nine restriction endonucleases and by multivariate statistical analysis of six selected morphometric parameters. Nucleotide difference within each population sample was high. Nucleotide difference between population samples from the Scottish sites, both those that are tidally contiguous and those that appear to be geographically isolated, were not significantly different from zero. Nucleotide differences between the populations samples from Norway, Brittany, Scotland and the western Mediterranean were also very low. Morphometric analysis confirmed the absence of substantial differentiation
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