9,666 research outputs found
Observational constraints on dark matter-dark energy scattering cross section
In this letter, we report precise and robust observational constraints on
dark matter-dark energy scattering cross section, using the latest data from
cosmic microwave background (CMB) Planck temperature and polarization, baryon
acoustic oscillations (BAO) measurements and weak gravitational lensing data
from Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). The scattering
scenario consists of a pure momentum exchange between the dark components, and
we find at 95\% CL from the joint analysis
(CMB + BAO + CFHTLenS), for typical dark matter particle mass of the order 1-10
. We notice that the scattering among the dark components may
influence the growth of large scale structure in the Universe, leaving the
background cosmology unaltered.Comment: 6 pages, 4 figures, 1 table, Minor changes/additions, Matches the
version published in EPJ
Comparison between the Logotropic and CDM models at the cosmological scale
We perform a detailed comparison between the Logotropic model [P.H. Chavanis,
Eur. Phys. J. Plus 130 (2015) 130] and the CDM model. These two models
behave similarly at large (cosmological) scales up to the present. Differences
will appear only in the far future, in about , when the
Logotropic Universe becomes phantom while the CDM Universe enters in
the de Sitter era. However, the Logotropic model differs from the CDM
model at small (galactic) scales, where the latter encounters serious problems.
Having a nonvanishing pressure, the Logotropic model can solve the cusp problem
and the missing satellite problem of the CDM model. In addition, it
leads to dark matter halos with a constant surface density , and can explain its observed value
without adjustable parameter. This makes the logotropic model rather unique
among all the models attempting to unify dark matter and dark energy. In this
paper, we compare the Logotropic and CDM models at the cosmological
scale where they are very close to each other in order to determine
quantitatively how much they differ. This comparison is facilitated by the fact
that these models depend on only two parameters, the Hubble constant and
the present fraction of dark matter . Using the latest
observational data from Planck 2015+Lensing+BAO+JLA+HST, we find that the best
fit values of and are and for the Logotropic model,
and and for the CDM model. The difference between the two models
appears at the percent level.Comment: 37 pages, 14 figures; New appendix and references adde
Structure of the twin-arginine signal-binding protein DmsD from Escherichia coli
The translocation of folded proteins via the twin-arginine translocation (Tat) pathway is regulated to prevent the futile export of inactive substrate. DmsD is part of a class of cytoplasmic chaperones that play a role in preventing certain redox proteins from premature transport. DmsD from Escherichia coli has been crystallized in space group P4_12_12, with unit-cell parameters a = b = 97.45, c = 210.04 Å, in the presence of a small peptide. The structure has been solved by molecular replacement to a resolution of 2.4 Å and refined to an R factor of 19.4%. There are four molecules in the asymmetric unit that may mimic a higher order structure in vivo. There appears to be density for the peptide in a predicted binding pocket, which lends support to its role as the signal-recognition surface for this class of proteins
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