24,406 research outputs found
Bottom-loading dilution refrigerator with ultra-high vacuum deposition capability
A Kelvinox 400 dilution refrigerator with the ability to load samples onto
the mixing chamber from the bottom of the cryostat has been combined with an
ultrahigh-vacuum (UHV) deposition chamber equipped with molecular beam sources.
The liquid helium cooled sample transfer mechanism is used in a manner that
allows films to be grown on substrates which are kept at temperatures of order
8K with chamber pressures in the 10^-9 to 10^-10 Torr range. This system
facilitates the growth of quench-condensed ultrathin films which must always be
kept below ~ 12K in a UHV environment during and after growth. Measurements can
be made on the films down to millikelvin temperatures and in magnetic fields up
to 15 T.Comment: 10 pages text, 1figur
Accurate Determination of Conformational Transitions in Oligomeric Membrane Proteins
The structural dynamics governing collective motions in oligomeric membrane proteins play key roles in vital biomolecular processes at cellular membranes. In this study, we present a structural refinement approach that combines solid-state NMR experiments and molecular simulations to accurately describe concerted conformational transitions identifying the overall structural, dynamical, and topological states of oligomeric membrane proteins. The accuracy of the structural ensembles generated with this method is shown to reach the statistical error limit, and is further demonstrated by correctly reproducing orthogonal NMR data. We demonstrate the accuracy of this approach by characterising the pentameric state of phospholamban, a key player in the regulation of calcium uptake in the sarcoplasmic reticulum, and by probing its dynamical activation upon phosphorylation. Our results underline the importance of using an ensemble approach to characterise the conformational transitions that are often responsible for the biological function of oligomeric membrane protein states
On minimal affinizations of representations of quantum groups
In this paper we study minimal affinizations of representations of quantum
groups (generalizations of Kirillov-Reshetikhin modules of quantum affine
algebras introduced by Chari). We prove that all minimal affinizations in types
A, B, G are special in the sense of monomials. Although this property is not
satisfied in general, we also prove an analog property for a large class of
minimal affinization in types C, D, F. As an application, the Frenkel-Mukhin
algorithm works for these modules. For minimal affinizations of type A, B we
prove the thin property (the l-weight spaces are of dimension 1) and a
conjecture of Nakai-Nakanishi (already known for type A). The proof of the
special property is extended uniformly for more general quantum affinizations
of quantum Kac-Moody algebras.Comment: 38 pages; references and additional results added. Accepted for
publication in Communications in Mathematical Physic
Extended T-systems
We use the theory of q-characters to establish a number of short exact
sequences in the category of finite-dimensional representations of the quantum
affine groups of types A and B. That allows us to introduce a set of 3-term
recurrence relations which contains the celebrated T-system as a special case.Comment: 36 pages, latex; v2: version to appear in Selecta Mathematic
Clone size distributions in networks of genetic similarity
We build networks of genetic similarity in which the nodes are organisms
sampled from biological populations. The procedure is illustrated by
constructing networks from genetic data of a marine clonal plant. An important
feature in the networks is the presence of clone subgraphs, i.e. sets of
organisms with identical genotype forming clones. As a first step to understand
the dynamics that has shaped these networks, we point up a relationship between
a particular degree distribution and the clone size distribution in the
populations. We construct a dynamical model for the population dynamics,
focussing on the dynamics of the clones, and solve it for the required
distributions. Scale free and exponentially decaying forms are obtained
depending on parameter values, the first type being obtained when clonal growth
is the dominant process. Average distributions are dominated by the power law
behavior presented by the fastest replicating populations.Comment: 17 pages, 4 figures. One figure improved and other minor changes. To
appear in Physica
Rubidium and zirconium abundances in massive Galactic asymptotic giant branch stars revisited
Luminous Galactic OH/IR stars have been identified as massive (>4-5 M_s) AGB
stars experiencing HBB and Li production. Their Rb abundances and [Rb/Zr]
ratios derived from hydrostatic model atmospheres, are significantly higher
than predictions from AGB nucleosynthesis models, posing a problem to our
understanding of AGB evolution and nucleosynthesis. We report new Rb and Zr
abundances in the full sample of massive Galactic AGB stars, previously studied
with hydrostatic models, by using more realistic extended model atmospheres. We
use a modified version of the spectral synthesis code Turbospectrum and
consider the presence of a circumstellar envelope and radial wind. The Rb and
Zr abundances are determined from the 7800 A Rb I resonant line and the 6474 A
ZrO bandhead, respectively, and we explore the sensitivity of the derived
abundances to variations of the stellar (Teff) and wind (M_loss, beta and vexp)
parameters in the extended models. The Rb and Zr abundances derived from the
best spectral fits are compared with the most recent AGB nucleosynthesis
theoretical models. The new Rb abundances are much lower (even 1-2 dex) than
those derived with the hydrostatic models, while the Zr abundances are similar.
The Rb I line profile and Rb abundance are very sensitive to the M_loss rate
but much less sensitive to variations of the wind velocity-law and the
vexp(OH). We confirm the earlier preliminary results based on a smaller sample
of massive O-rich AGB stars, that the use of extended atmosphere models can
solve the discrepancy between the AGB nucleosynthesis theoretical models and
the observations of Galactic massive AGB stars. The Rb abundances, however, are
still strongly dependent of the M_loss, which is unknown in these AGB stars.
Accurate M_loss rates in these massive Galactic AGB stars are needed in order
to break the models degeneracy and get reliable Rb abundances in these stars.Comment: Accepted for publication in A&A, 14 pages, 12 figures, 4 table
HERA-B Framework for Online Calibration and Alignment
This paper describes the architecture and implementation of the HERA-B
framework for online calibration and alignment. At HERA-B the performance of
all trigger levels, including the online reconstruction, strongly depends on
using the appropriate calibration and alignment constants, which might change
during data taking. A system to monitor, recompute and distribute those
constants to online processes has been integrated in the data acquisition and
trigger systems.Comment: Submitted to NIM A. 4 figures, 15 page
Isolated elliptical galaxies in the local Universe
We have studied a sample of 89 very isolated, elliptical galaxies at z < 0.08
and compared their properties with elliptical galaxies located in a
high-density environment such as the Coma supercluster. Our aim is to probe the
role of environment on the morphological transformation and quenching of
elliptical galaxies as a function of mass. In addition, we elucidate the nature
of a particular set of blue and star-forming isolated ellipticals identified
here. We study physical properties of ellipticals such as color, specific star
formation rate, galaxy size, and stellar age, as a function of stellar mass and
environment based on SDSS data. We analyze the blue star-forming isolated
ellipticals in more detail, through photometric characterization using GALFIT,
and infer their star formation history using STARLIGHT. Among the isolated
ellipticals ~ 20% are blue, 8% are star forming, and ~ 10% are recently
quenched, while among the Coma ellipticals ~ 8% are blue and just <= 1% are
star forming or recently quenched. There are four isolated galaxies (~ 4.5%)
that are blue and star forming at the same time. These galaxies, with masses
between 7 x 10^9 and 2 x 10^10 h-2 M_sun, are also the youngest galaxies with
light-weighted stellar ages <= 1 Gyr and exhibit bluer colors toward the galaxy
center. Around 30-60% of their present-day luminosity, but only < 5% of their
present-day mass, is due to star formation in the last 1 Gyr. The processes of
morphological transformation and quenching seem to be in general independent of
environment since most of elliptical galaxies are 'red and dead', although the
transition to the red sequence should be faster for isolated ellipticals. In
some cases, the isolated environment seems to propitiate the rejuvenation of
ellipticals by recent (< 1 Gyr) cold gas accretion.Comment: 23 pages, 15 figures (16 pages and 9 figures without appendices).
A&A, in pres
Meta-analysis of a very low proportion through adjusted wald confidence intervals
In this paper we will discuss the meta-analysis of one low proportion. It is well known, that there are
several methods to perform the meta-analysis of one proportion, based on a linear combination of
proportions or transformed proportions. However, in the context of a linear combination of binomial
proportions has been proposed some approximate estimators with some improvements on low
proportion estimation. In this paper we will show, with a simple adaptation, the possible contribution
of several approximate adjusted Wald confidence intervals (CIs) for the meta-analysis of proportions. In
the context of low proportions, a simulation study scenario is carried out to compare these CIs amongst
themselves and with other available methods with respect to bias and coverage probabilities, using the
fixed effect or the random-effects model. Pointing our interest in rare events (analogous for the abundant
events) and taking into account the prevalence estimation of the Methicillin-resistant Staphylococcus
aureus with mecc gene, we discuss the choice of the meta-analysis methods on this low proportion. The
default meta-analysis methods of meta-analysis software programs are not always the best choice, in
particular to the meta-analysis of one low proportion, where the methods including the adjusted Wald
can outperform.publishe
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