18 research outputs found
Do clusters contain a large population of dwarf galaxies?
We analyze systematic effects in the determination of the galaxy luminosity
function in clusters using a deep mock catalogue constructed from a numerical
simulation of a hierarchical universe. The results indicate a strong tendency
to derive a rising faint end (\alpha \lsim -1.5) in clusters selected in two
dimensions, using a galaxy catalogue constructed with a universal flat
luminosity function with . This is due to the projection
effects inherent in catalogues of clusters constructed using 2 dimensional
data. Many of the clusters found in 2d have no significant 3d counterparts, and
most suffer from massive background contamination that cannot be corrected for
by subtracting random offset fields. The luminosity function of high surface
brightness galaxies in the field and within small groups follows a Schechter
function with a fairly flat faint end slope, with
to -1.2. On the contrary, observational studies of clusters
constructed using Abell, EDCC and APM catalogues are systematically found to
have steeper luminosity functions with to -2.0. This may be
attributed to projection effects rather than a dominant population of high
surface brightness dwarf galaxies (M\gsim M^*+2) in clusters. It should be
straighforward to confirm our results by measuring redshifts of these faint
cluster galaxies.Comment: 23 pages, 7 Postscript figures TeX, accepted for publication in the
Astrophysical Journal, e-mail:[email protected]
http://iate.oac.uncor.edu/cv.htm
Evaluating the effect of mutations and ligand binding on transthyretin homotetramer dynamics
<div><p>Native transthyretin (TTR) homotetramer dissociation is the first step of the fibrils formation process in amyloid disease. A large number of specific point mutations that destabilize TTR quaternary structure have shown pro-amyloidogenic effects. Besides, several compounds have been proposed as drugs in the therapy of TTR amyloidosis due to their TTR tetramer binding affinities, and therefore, contribution to its integrity. In the present paper we have explored key positions sustaining TTR tetramer dynamical stability. We have identified positions whose mutations alter the most the TTR tetramer equilibrium dynamics based on normal mode analysis and their response to local perturbations. We have found that these positions are mostly localized at ÎČ-strands E and F and EF-loop. The monomer-monomer interface is pointed out as one of the most vulnerable regions to mutations that lead to significant changes in the TTR-tetramer equilibrium dynamics and, therefore, induces TTR amyloidosis. Besides, we have found that mutations on residues localized at the dimer-dimer interface and/or at the T4 hormone binding site destabilize the tetramer more than the average. Finally, we were able to compare several compounds according to their effect on vibrations associated to the ligand binding. Our ligand comparison is discussed and analyzed in terms of parameters and measurements associated to TTR-ligand binding affinities and the stabilization of its native state.</p></div