37,118 research outputs found
Supernovae Types Ia/II and Intracluster Medium Enrichment
We re-examine the respective roles played by supernovae (SNe) Types Ia and II
in enriching the intracluster medium (ICM) of galaxy clusters, in light of the
recent downward shift of the ASCA abundance ratios of alpha-elements to iron
favoured by Ishimaru & Arimoto (1997, PASJ, 49, 1). Because of this shift,
Ishimaru & Arimoto conclude that >50% of the ICM iron must have originated from
within Type Ia SNe progenitors. A point not appreciated in their study, nor in
most previous analyses, is the crucial dependence of such a conclusion upon the
adopted massive star physics. Employing several alternative Type II SN yield
compilations, we demonstrate how uncertainties in the treatment of convection
and mass-loss can radically alter our perception of the relative importance of
Type Ia and II SNe as ICM polluters. If mass-loss of the form favoured by
Maeder (1992, A&A, 264, 105) or convection of the form favoured by Arnett
(1996, Supernovae and Nucleosynthesis) is assumed, the effect upon the oxygen
yields would lead us to conclude that Type Ia SNe play no part in polluting the
ICM, in contradiction with Ishimaru & Arimoto. Apparent dichotomies still exist
(e.g. the mean ICM neon-to-iron ratio implies a 100% Type II Fe origin, while
the mean sulphur ratio indicates a 100% Type Ia origin) that cannot be
reconciled with the currently available yield tables.Comment: 6 pages (incl 1 PostScript figure), LaTeX, also available at
http://msowww.anu.edu.au/~gibson/publications.html, MNRAS, in pres
Expanding the toolbox for nanoparticle trapping and spectroscopy with holographic optical tweezers
We have developed a workstation based on holographic tweezers to optically trap, move and characterize metal nanoparticles. Our advanced darkfield imaging system allows us to simultaneously image and take spectra of single trapped metal nanoparticles. We take advantage of the beamshaping abilities of the spatial light modulator and correct for aberrations of the trapping optics. We monitor the improvement of the optical trap with video-based nanoparticle tracking. Furthermore we theoretically assess the capabilities and limitations of video-based tracking for nanoparticle position detection, in particular with respect to acquisition frequencies below the corner frequency
Microbial Load Monitor
The Microbial Load Monitor (MLM) is an automated and computerized system for detection and identification of microorganisms. Additionally, the system is designed to enumerate and provide antimicrobic susceptibility profiles for medically significant bacteria. The system is designed to accomplish these tasks in a time of 13 hours or less versus the traditional time of 24 hours for negatives and 72 hours or more for positives usually required for standard microbiological analysis. The MLM concept differs from other methods of microbial detection in that the system is designed to accept raw untreated clinical samples and to selectively identify each group or species that may be present in a polymicrobic sample
Free-flight measurements of dynamic stability derivatives of a blunted 120 deg cone in helium at Mach number 15.4
Free flight measurements of dynamic stability derivatives of blunted 120 deg cone in helium compared to unmodified Newtonian theory prediction
The [?/Fe] ratios of very metal-poor stars within the integrated galactic initial mass function theory
The aim of this paper is to quantify the amplitude of the predicted plateau in [α/Fe] ratios associated with the most metal-poor stars of a galaxy. We assume that the initial mass function (IMF) in galaxies is steeper if the star formation rate (SFR) is low – as per the integrated galactic initial mass function (IGIMF) theory. A variant of the theory, in which the IGIMF depends upon the metallicity of the parent galaxy, is also considered. The IGIMF theory predicts low [α/Fe] plateaus in dwarf galaxies, characterized by small SFRs. The [α/Fe] plateau is up to 0.7 dex lower than the corresponding plateau of the Milky Way. For a universal IMF one should expect instead that the [α/Fe] plateau is the same for all the galaxies, irrespective of their masses or SFRs. Assuming a strong dependence of the IMF on the metallicity of the parent galaxy, dwarf galaxies can show values of the [α/Fe] plateau similar to those of the Milky Way, and almost independent of the SFR. The [Mg/Fe] ratios of the most metal-poor stars in dwarf galaxies satellites of the Milky Way can be reproduced either if we consider metallicity-dependent IMFs or if the early SFRs of these galaxies were larger than we presently think. Present and future observations of dwarf galaxies can help disentangle between these different IGIMF formulations
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