1,887 research outputs found
Chemo-dynamical Evolution of the ISM in Galaxies
Chemo-dynamical models have been introduced in the late eighties and are a
generally accepted tool for understanding galaxy evolution. They have been
successfully applied to one-dimensional problems, e.g. the evolution of
non-rotating galaxies, and two-dimensional problems, e.g. the evolution of disk
galaxies. Recently, also three-dimensional chemo-dynamical models have become
available. In these models the dynamics of different components, i.e. dark
matter, stars and a multi-phase interstellar medium, are treated in a
self-consistent way and several processes allow for an exchange of matter,
energy and momentum between the components or different gas phases. Some
results of chemo-dynamical models and their comparison with observations of
chemical abundances or star formation histories will be reviewed.Comment: 10 Pages, 5 Figures, to appear in "From Observations to
Self-Consistent Modelling of the ISM in Galaxies", 2003, eds M. Avillez et a
Early evolution of Tidal Dwarf Galaxies
Our aim is to study the evolution of tidal dwarf galaxies. The first step is
to understand whether a model galaxy without Dark Matter can sustain the
feedback of the ongoing star formation. We present tests of the evolution of
models in which star formation efficiency, temperature threshold, initial
distribution of gas and infall are varied. We conclude that it is feasible to
keep a fraction of gas bound for several hundreds of Myr and that the
development of galactic winds does not necessarily stop continuous star
formation.Comment: 2 pages, 1 figure, to appear in the Proceedings of the CRAL
conference "Chemodynamics: from first stars to local galaxies", Lyon, France,
10-14 July 200
Physical Processes in Star-Gas Systems
First we present a recently developed 3D chemodynamical code for galaxy
evolution from the K**2 collaboration. It follows the evolution of all
components of a galaxy such as dark matter, stars, molecular clouds and diffuse
interstellar matter (ISM). Dark matter and stars are treated as collisionless
N-body systems. The ISM is numerically described by a smoothed particle
hydrodynamics (SPH) approach for the diffuse (hot) gas and a sticky particle
scheme for the (cool) molecular clouds. Physical processs such as star
formation, stellar death or condensation and evaporation processes of clouds
interacting with the ISM are described locally. An example application of the
model to a star forming dwarf galaxy will be shown for comparison with other
codes. Secondly we will discuss new kinds of exotic chemodynamical processes,
as they occur in dense gas-star systems in galactic nuclei, such as
non-standard ``drag''-force interactions, destructive and gas producing stellar
collisions. Their implementation in 1D dynamical models of galactic nuclei is
presented. Future prospects to generalize these to 3D are work in progress and
will be discussed.Comment: 4 pages, 4 figures, "The 5th Workshop on Galactic Chemodynamics" -
Swinburne University (9-11 July 2003). To be published in the Publications of
the Astronomical Society of Australia in 2004 (B.K. Gibson and D. Kawata,
eds.). Accepted version, minor changes relative to origina
Tuning the scattering length with an optically induced Feshbach resonance
We demonstrate optical tuning of the scattering length in a Bose-Einstein
condensate as predicted by Fedichev {\em et al.} [Phys. Rev. Lett. {\bf 77},
2913 (1996)]. In our experiment atoms in a Rb condensate are exposed to
laser light which is tuned close to the transition frequency to an excited
molecular state. By controlling the power and detuning of the laser beam we can
change the atomic scattering length over a wide range. In view of laser-driven
atomic losses we use Bragg spectroscopy as a fast method to measure the
scattering length of the atoms.Comment: submitted to PRL, 5 pages, 5 figure
THE PROLIFERATIVE AND ANAMNESTIC ANTIBODY RESPONSE OF RABBIT LYMPHOID CELLS IN VITRO : II. REQUIREMENT FOR ADHERENT AND NONADHERENT CELLS OF THE RESPONSES TO PARTICULATE ANTIGENS IN SPLEEN CELL CULTURES
Both primary and secondary responses to sheep erythrocytes and to Brucella abortus antigen have been obtained in cultures of dispersed rabbit spleen cells. Removal of adherent cells by repeated incubation of spleen cells on absorbent cotton diminished the ability of the spleen cell suspensions to give secondary as well as primary responses in vitro. When comparing cultures made in dishes and in tubes, the loss of responsiveness after incubation on cotton was much more evident in the dish cultures. It was concluded that the cell-to-cell interaction needed for immune responses to particulate antigens in vitro was more readily interfered with when the cells were spread over a larger surface area. The proliferative response to antigen, as measured by uptake of 3H-thymidine in tube cultures of the sensitive spleen cells, appeared particularly resistant to the depletion effect of adherent cell removal. Dispersed spleen cells from sensitized mice gave a secondary response to sheep erythrocytes. This response was readily abolished by one incubation on absorbent cotton when the cells were cultured in dishes
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