88 research outputs found
Theoretical and experimental activities on opacities for a good interpretation of seismic stellar probes
Opacity calculations are basic ingredients of stellar modelling. They play a
crucial role in the interpretation of acoustic modes detected by SoHO, COROT
and KEPLER. In this review we present our activities on both theoretical and
experimental sides. We show new calculations of opacity spectra and comparisons
between eight groups who produce opacity spectra calculations in the domain
where experiments are scheduled. Real differences are noticed with real
astrophysical consequences when one extends helioseismology to cluster studies
of different compositions. Two cases are considered presently: (1) the solar
radiative zone and (2) the beta Cephei envelops. We describe how our
experiments are performed and new preliminary results on nickel obtained in the
campaign 2010 at LULI 2000 at Polytechnique.Comment: 6 pages, 4 figures, invited talk at SOHO2
Radiative properties of stellar plasmas and open challenges
The lifetime of solar-like stars, the envelope structure of more massive
stars, and stellar acoustic frequencies largely depend on the radiative
properties of the stellar plasma. Up to now, these complex quantities have been
estimated only theoretically. The development of the powerful tools of helio-
and astero- seismology has made it possible to gain insights on the interiors
of stars. Consequently, increased emphasis is now placed on knowledge of the
monochromatic opacity coefficients. Here we review how these radiative
properties play a role, and where they are most important. We then concentrate
specifically on the envelopes of Cephei variable stars. We discuss the
dispersion of eight different theoretical estimates of the monochromatic
opacity spectrum and the challenges we need to face to check these calculations
experimentally.Comment: 6 pages, 5 figures, in press (conference HEDLA 2010
SYNTHESIS OF MONODISPERSE Au, Pt, Pd, Ru AND Ir NANOPARTICLES IN ETHYLENE GLYCOL
Abstract-Au, Pt, Pd, Ru and Ir nanoparticles with a narrow size distribution have been synthesized by chemical reduction of their corresponding metal species in ethylene glycol. In all cases, the average particle size was found to be smaller than 10 nm. Particle size was mainly controlled by varying the initial total metal concentration, the reaction temperature, and the concentration of PVP. With the exception of Ir, metal particle agglomeration and sintering was prevented by the addition of PVP, a well known protective agent that also aids particle dispersion
Temperature effects on kinetics of paralytic shellfish toxin elimination in Atlantic surfclams,Spisula solidissima
Surfclams,Spisula solidissima, pose a particular health risk for human consumption as they are characterized by accumulation of extremely high levels of toxins associated with paralytic shellfish poisoning (PSP), slow toxin elimination and an extremely high post-ingestive capacity for toxin bioconversion. Surfclam populations experience a wide range of temperatures along the NW Atlantic continental shelf, and are undergoing range contraction that has been attributed to global warming. In this study the influence of temperature (5, 12 and 21 C) on detoxification kinetics of individual PSP toxins in two tissue compartments of juvenile surfclams
(∼35 mm shell length) was determined under controlled laboratory conditions, over prolonged (2.4 months) depuration. Clams were toxified with a representative regional Gulf of Maine isolate of the dinoflagellate
Alexandrium fundyense of known toxin profile, allowing tracking of changes in toxin composition and calculated toxicity in surfclam tissues. The visceral mass detoxified at all temperatures, although toxin loss rate increased with increasing temperature. In contrast, total toxin content and calculated toxicities in other tissues remained constant or even increased during depuration, suggesting a physiological or biochemical toxin-retention mechanism in this tissue pool and temperature-independent detoxification. In vivo toxin compositional changes in surfclam tissues found in this study provide evidence of specific toxin conversion pathways,involving both reductive and decarbamoylation pathways. We conclude that such toxin biotransformations, especially in non-visceral tissues, may introduce a discrepancy in describing kinetics of total toxicity (in saxitoxin equivalents [STXeq]) of S. solidissima over prolonged detoxification. Nevertheless, use of total toxicity values generated by routine regulatory monitoring based upon mouse bioassays or calculated from chemical analytical determination of molar toxin concentrations is adequate for
first-order modeling of toxin kinetics in this species. Furthermore, the differential detoxification response of viscera and other tissues in relation to temperature emphasizes the need for two-compartment modeling
to describe the fate of PSP toxins in this species. Finally, key parameters were identified that may prove
useful in hindcasting the timing of toxic blooms or new toxin input in deep offshore waters where routine monitoring of toxic phytoplankton is impractical
X-ray emission spectroscopy of well-characterised non-LTE plasmas
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