38,160 research outputs found
Unconventional critical activated scaling of two-dimensional quantum spin-glasses
We study the critical behavior of two-dimensional short-range quantum spin
glasses by numerical simulations. Using a parallel tempering algorithm, we
calculate the Binder cumulant for the Ising spin glass in a transverse magnetic
field with two different short-range bond distributions, the bimodal and the
Gaussian ones. Through an exhaustive finite-size scaling analysis, we show that
the universality class does not depend on the exact form of the bond
distribution but, most important, that the quantum critical behavior is
governed by an infinite randomness fixed point.Comment: 6 pages, 6 figure
On the kinematic evolution of young local associations and the Sco-Cen complex
Context: Over the last decade, several groups of young (mainly low-mass)
stars have been discovered in the solar neighbourhood (closer than ~100 pc),
thanks to cross-correlation between X-ray, optical spectroscopy and kinematic
data. These young local associations -- including an important fraction whose
members are Hipparcos stars -- offer insights into the star formation process
in low-density environments, shed light on the substellar domain, and could
have played an important role in the recent history of the local interstellar
medium. Aims: To study the kinematic evolution of young local associations and
their relation to other young stellar groups and structures in the local
interstellar medium, thus casting new light on recent star formation processes
in the solar neighbourhood. Methods: We compiled the data published in the
literature for young local associations. Using a realistic Galactic potential
we integrated the orbits for these associations and the Sco-Cen complex back in
time. Results: Combining these data with the spatial structure of the Local
Bubble and the spiral structure of the Galaxy, we propose a recent history of
star formation in the solar neighbourhood. We suggest that both the Sco-Cen
complex and young local associations originated as a result of the impact of
the inner spiral arm shock wave against a giant molecular cloud. The core of
the giant molecular cloud formed the Sco-Cen complex, and some small cloudlets
in a halo around the giant molecular cloud formed young local associations
several million years later. We also propose a supernova in young local
associations a few million years ago as the most likely candidate to have
reheated the Local Bubble to its present temperature.Comment: 27 pages, 13 figures, 14 tables. Accepted for publication in
Astronomy & Astrophysic
Puzzles in quarkonium hadronic transitions with two pion emission
The anomalously large rates of some hadronic transitions from quarkonium are
studied using QCD multipole expansion (QCDME) in the framework of a constituent
quark model which has been successful in describing hadronic phenomenology. The
hybrid intermediate states needed in the QCDME method are calculated in a
natural extension of our constituent quark model based on the Quark Confining
String (QCS) scheme. Some of the anomalies are explained due to the presence of
an hybrid state with a mass near the mass of the decaying resonance whereas
other are justified by the presence of molecular components in the wave
function. Some unexpected results are pointed out.Comment: Conference proceedings of the XI Quark Confinement and the Hadron
Spectrum (CONFINEMENT XI). Saint Petersburg (Russia) from 8 to 12 September
201
Retinoic acid as a modulator of T cell immunity
Indexación: Scopus. DOAJ.Vitamin A, a generic designation for an array of organic molecules that includes retinal, retinol and retinoic acid, is an essential nutrient needed in a wide array of aspects including the proper functioning of the visual system, maintenance of cell function and differentiation, epithelial surface integrity, erythrocyte production, reproduction, and normal immune function. Vitamin A deficiency is one of the most common micronutrient deficiencies worldwide and is associated with defects in adaptive immunity. Reports from epidemiological studies, clinical trials and experimental studies have clearly demonstrated that vitamin A plays a central role in immunity and that its deficiency is the cause of broad immune alterations including decreased humoral and cellular responses, inadequate immune regulation, weak response to vaccines and poor lymphoid organ development. In this review, we will examine the role of vitamin A in immunity and focus on several aspects of T cell biology such as T helper cell differentiation, function and homing, as well as lymphoid organ development. Further, we will provide an overview of the effects of vitamin A deficiency in the adaptive immune responses and how retinoic acid, through its effect on T cells can fine-tune the balance between tolerance and immunity.http://www.mdpi.com/2072-6643/8/6/34
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