106,005 research outputs found
The stellar populations of massive galaxies in the local Universe
I present a brief review of the stellar population properties of massive
galaxies, focusing on early-type galaxies in particular, with emphasis on
recent results from the ATLAS3D Survey. I discuss the occurrence of young
stellar ages, cold gas, and ongoing star formation in early-type galaxies, the
presence of which gives important clues to the evolutionary path of these
galaxies. Consideration of empirical star formation histories gives a
meaningful picture of galaxy stellar population properties, and allows accurate
comparison of mass estimates from populations and dynamics. This has recently
provided strong evidence of a non-universal IMF, as supported by other recent
evidences. Spatially-resolved studies of stellar populations are also crucial
to connect distinct components within galaxies to spatial structures seen in
other wavelengths or parameters. Stellar populations in the faint outer
envelopes of early-type galaxies are a formidable frontier for observers, but
promise to put constraints on the ratio of accreted stellar mass versus that
formed 'in situ' - a key feature of recent galaxy formation models. Galaxy
environment appears to play a key role in controlling the stellar population
properties of low mass galaxies. Simulations remind us, however, that current
day galaxies are the product of a complex assembly and environment history,
which gives rise to the trends we see. This has strong implications for our
interpretation of environmental trends.Comment: 10 pages, 4 figures, LaTeX. Invited talk for the IAU Symposium 295
"The Intriguing Life of Massive Galaxies". To appear in Proc. of the XXVIII
IAU General Assembly, Beijing, China, August 2012, eds. D. Thomas, A.
Pasquali; I. Ferreras. Cambridge University Pres
Generation and Breakup of Worthington Jets After Cavity Collapse
Helped by the careful analysis of their experimental data, Worthington (1897)
described roughly the mechanism underlying the formation of high-speed jets
ejected after the impact of an axisymmetric solid on a liquid-air interface. In
this work we combine detailed boundary-integral simulations with analytical
modeling to describe the formation and break-up of such Worthington jets in two
common physical systems: the impact of a circular disc on a liquid surface and
the release of air bubbles from an underwater nozzle. We first show that the
jet base dynamics can be predicted for both systems using our earlier model in
Gekle, Gordillo, van der Meer and Lohse. Phys. Rev. Lett. 102 (2009).
Nevertheless, our main point here is to present a model which allows us to
accurately predict the shape of the entire jet. Good agreement with numerics
and some experimental data is found. Moreover, we find that, contrarily to the
capillary breakup of liquid cylinders in vacuum studied by Rayleigh, the
breakup of stretched liquid jets at high values of both Weber and Reynolds
numbers is not triggered by the growth of perturbations coming from an external
source of noise. Instead, the jet breaks up due to the capillary deceleration
of the liquid at the tip which produces a corrugation to the jet shape. This
perturbation, which is self-induced by the flow, will grow in time promoted by
a capillary mechanism. We are able to predict the exact shape evolution of
Worthington jets ejected after the impact of a solid object - including the
size of small droplets ejected from the tip due to a surface-tension driven
instability - using as the single input parameters the minimum radius of the
cavity and the flow field before the jet emerges
Information Surfaces in Systems Biology and Applications to Engineering Sustainable Agriculture
Systems biology of plants offers myriad opportunities and many challenges in
modeling. A number of technical challenges stem from paucity of computational
methods for discovery of the most fundamental properties of complex dynamical
systems. In systems engineering, eigen-mode analysis have proved to be a
powerful approach. Following this philosophy, we introduce a new theory that
has the benefits of eigen-mode analysis, while it allows investigation of
complex dynamics prior to estimation of optimal scales and resolutions.
Information Surfaces organizes the many intricate relationships among
"eigen-modes" of gene networks at multiple scales and via an adaptable
multi-resolution analytic approach that permits discovery of the appropriate
scale and resolution for discovery of functions of genes in the model plant
Arabidopsis. Applications are many, and some pertain developments of crops that
sustainable agriculture requires.Comment: 24 Pages, DoCEIS 1
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