21,256 research outputs found
Characterizing Diffused Stellar Light in simulated galaxy clusters
[Abridged] In this paper, we carry out a detailed analysis of the performance
of two different methods to identify the diffuse stellar light in cosmological
hydrodynamical simulations of galaxy clusters. One method is based on a
dynamical analysis of the stellar component. The second method is closer to
techniques commonly employed in observational studies. Both the dynamical
method and the method based on the surface brightness limit criterion are
applied to the same set of hydrodynamical simulations for a large sample about
80 galaxy clusters.
We find significant differences between the ICL and DSC fractions computed
with the two corresponding methods, which amounts to about a factor of two for
the AGN simulations, and a factor of four for the CSF set. We also find that
the inclusion of AGN feedback boosts the DSC and ICL fractions by a factor of
1.5-2, respectively, while leaving the BCG+ICL and BCG+DSC mass fraction almost
unchanged. The sum of the BCG and DSC mass stellar mass fraction is found to
decrease from ~80 per cent in galaxy groups to ~60 per cent in rich clusters,
thus in excess of what found from observational analysis.
We identify the average surface brightness limits that yields the ICL
fraction from the SBL method close to the DSC fraction from the dynamical
method. These surface brightness limits turn out to be brighter in the CSF than
in the AGN simulations. This is consistent with the finding that AGN feedback
makes BCGs to be less massive and with shallower density profiles than in the
CSF simulations. The BCG stellar component, as identified by both methods, are
slightly older and more metal-rich than the stars in the diffuse component.Comment: 18 Pages, 15 figures. Matches to MNRAS published versio
Extensive degeneracy, Coulomb phase and magnetic monopoles in an artificial realization of the square ice model
Artificial spin ice systems have been introduced as a possible mean to
investigate frustration effects in a well-controlled manner by fabricating
lithographically-patterned two-dimensional arrangements of interacting magnetic
nanostructures. This approach offers the opportunity to visualize
unconventional states of matter, directly in real space, and triggered a wealth
of studies at the frontier between nanomagnetism, statistical thermodynamics
and condensed matter physics. Despite the strong efforts made these last ten
years to provide an artificial realization of the celebrated square ice model,
no simple geometry based on arrays of nanomagnets succeeded to capture the
macroscopically degenerate ground state manifold of the corresponding model.
Instead, in all works reported so far, square lattices of nanomagnets are
characterized by a magnetically ordered ground state consisting of local
flux-closure configurations with alternating chirality. Here, we show
experimentally and theoretically, that all the characteristics of the square
ice model can be observed if the artificial square lattice is properly
designed. The spin configurations we image after demagnetizing our arrays
reveal unambiguous signatures of an algebraic spin liquid state characterized
by the presence of pinch points in the associated magnetic structure factor.
Local excitations, i.e. classical analogues of magnetic monopoles, are found to
be free to evolve in a massively degenerated, divergence-free vacuum. We thus
provide the first lab-on-chip platform allowing the investigation of collective
phenomena, including Coulomb phases and ice-like physics.Comment: 26 pages, 10 figure
Unstructured intermediate states in single protein force experiments
Recent single-molecule force measurements on single-domain proteins have
highlighted a three-state folding mechanism where a stabilized intermediate
state (I) is observed on the folding trajectory between the stretched state and
the native state. Here we investigate on-lattice protein-like heteropolymer
models that lead to a three-state mechanism and show that force experiments can
be useful to determine the structure of I. We have mostly found that I is
composed of a core stabilized by a high number of native contacts, plus an
unstructured extended chain. The lifetime of I is shown to be sensitive to
modifications of the protein that spoil the core. We then propose three types
of modifications--point mutations, cuts, and circular permutations--aiming at:
(1) confirming the presence of the core and (2) determining its location,
within one amino acid accuracy, along the polypeptide chain. We also propose
force jump protocols aiming to probe the on/off-pathway nature of I.Comment: 10 page
Protein folding mediated by solvation: water expelling and formation of the hydrophobic core occurs after the structure collapse
The interplay between structure-search of the native structure and
desolvation in protein folding has been explored using a minimalist model.
These results support a folding mechanism where most of the structural
formation of the protein is achieved before water is expelled from the
hydrophobic core. This view integrates water expulsion effects into the funnel
energy landscape theory of protein folding. Comparisons to experimental results
are shown for the SH3 protein. After the folding transition, a near-native
intermediate with partially solvated hydrophobic core is found. This transition
is followed by a final step that cooperatively squeezes out water molecules
from the partially hydrated protein core.Comment: Proceedings of the National Academy of Science, 2002, Vol.99. 685-69
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