2,819 research outputs found
Quantum Hall Effect and Semimetallic Behavior of Dual-Gated ABA-Stacked Trilayer Graphene
The electronic structure of multilayer graphenes depends strongly on the
number of layers as well as the stacking order. Here we explore the electronic
transport of purely ABA-stacked trilayer graphenes in a dual-gated field-effect
device configuration. We find that both the zero-magnetic-field transport and
the quantum Hall effect at high magnetic fields are distinctly different from
the monolayer and bilayer graphenes, and that they show electron-hole
asymmetries that are strongly suggestive of a semimetallic band overlap. When
the ABA trilayers are subjected to an electric field perpendicular to the
sheet, Landau level splittings due to a lifting of the valley degeneracy are
clearly observed.Comment: 5 figure
New Velocity Distribution in the Context of the Eddington Theory
Exotic dark matter together with the vacuum energy (associated with the
cosmological constant) seem to dominate the Universe. Thus its direct detection
is central to particle physics and cosmology. Supersymmetry provides a natural
dark matter candidate, the lightest supersymmetric particle (LSP). One
essential ingredient in obtaining the direct detection rates is the density and
velocity distribution of the LSP. The detection rate is proportional to this
density in our vicinity. Furthermore, since this rate is expected to be very
low, one should explore the two characteristic signatures of the process,
namely the modulation effect, i.e. the dependence of the event rate on the
Earth's motion and the correlation of the directional rate with the motion of
the sun. Both of these crucially depend on the LSP velocity distribution. In
the present paper we study simultaneously density profiles and velocity
distributions based on the Eddington theory.Comment: 40 LaTex pages, 19 figures and one table. The previous version was
expanded to include new numerical solutions to Poisson's equation. Sheduled
to appear in vol. 588, ApJ, May 1, 300
A Puzzling Merger in A3266: the Hydrodynamic Picture from XMM-Newton
Using the mosaic of nine XMM-Newton observations, we study the hydrodynamic
state of the merging cluster of galaxies Abell 3266. The high quality of the
spectroscopic data and large field of view of XMM-Netwon allow us to determine
the thermodynamic conditions of the intracluster medium on scales of order of
50 kpc. A high quality entropy map reveals the presence of an extended region
of low entropy gas, running from the primary cluster core toward the northeast
along the nominal merger axis. The mass of the low entropy gas amounts to
approximately 2e13 solar masses, which is comparable to the baryonic mass of
the core of a rich cluster. We test the possibility that the origin of the
observed low entropy gas is either related to the disruption a preexisting
cooling core in Abell 3266 or to the stripping of gas from an infalling
subcluster companion. We find that both the radial pressure and entropy
profiles as well as the iron abundance of Abell 3266 do not resemble those in
other known cooling core clusters (Abell 478). Thus we conclude that the low
entropy region is subcluster gas in the process of being stripped off from its
dark matter halo. In this scenario the subcluster would be falling onto the
core of A3266 from the foreground. This would also help interpret the observed
high velocity dispersion of the galaxies in the cluster center, provided that
the mass of the subcluster is at most a tenth of the mass of the main cluster.Comment: 6 pages, ApJ sub
Symbolic Algorithms for Language Equivalence and Kleene Algebra with Tests
We first propose algorithms for checking language equivalence of finite
automata over a large alphabet. We use symbolic automata, where the transition
function is compactly represented using a (multi-terminal) binary decision
diagrams (BDD). The key idea consists in computing a bisimulation by exploring
reachable pairs symbolically, so as to avoid redundancies. This idea can be
combined with already existing optimisations, and we show in particular a nice
integration with the disjoint sets forest data-structure from Hopcroft and
Karp's standard algorithm. Then we consider Kleene algebra with tests (KAT), an
algebraic theory that can be used for verification in various domains ranging
from compiler optimisation to network programming analysis. This theory is
decidable by reduction to language equivalence of automata on guarded strings,
a particular kind of automata that have exponentially large alphabets. We
propose several methods allowing to construct symbolic automata out of KAT
expressions, based either on Brzozowski's derivatives or standard automata
constructions. All in all, this results in efficient algorithms for deciding
equivalence of KAT expressions
Physical activity and the risk of gestational diabetes mellitus: a systematic review and dose-response meta-analysis of epidemiological studies
Physical activity has been inconsistently associated with risk of gestational diabetes mellitus in epidemiological studies, and questions remain about the strength and shape of the dose-response relationship between the two. We therefore conducted a systematic review and meta-analysis of cohort studies and randomized trials on physical activity and gestational diabetes mellitus. PubMed, Embase and Ovid databases were searched for cohort studies, and randomized controlled trials of physical activity and risk of gestational diabetes mellitus, up to August 5th 2015. Summary relative risks (RRs) were estimated using a random effects model. Twenty-five studies (26 publications) were included. For total physical activity the summary RR for high versus low activity was 0.62 (95 % CI 0.41-0.94, I(2) = 0 %, n = 4) before pregnancy, and 0.66 (95 % CI 0.36-1.21, I(2) = 0 %, n = 3) during pregnancy. For leisure-time physical activity the respective summary RRs for high versus low activity was 0.78 (95 % CI 0.61-1.00, I(2) = 47 %, n = 8) before pregnancy, and it was 0.80 (95 % CI 0.64-1.00, I(2) = 17 %, n = 17) during pregnancy. The summary RR for pre-pregnancy activity was 0.70 (95 % CI 0.49-1.01, I(2) = 72.6 %, n = 3) per increment of 5 h/week and for activity during pregnancy was 0.98 (95 % CI 0.87-1.09, I(2) = 0 %, n = 3) per 5 h/week. There was evidence of a nonlinear association between physical activity before pregnancy and the risk of gestational diabetes mellitus, pnonlinearity = 0.005, with a slightly steeper association at lower levels of activity although further reductions in risk were observed up to 10 h/week. There was also evidence of nonlinearity for physical activity in early pregnancy, pnonlinearity = 0.008, with no further reduction in risk above 8 h/week. There was some indication of inverse associations between walking (before and during pregnancy) and vigorous activity (before pregnancy) and the risk of gestational diabetes mellitus. This meta-analysis suggests that there is a significant inverse association between physical activity before pregnancy and in early pregnancy and the risk of gestational diabetes mellitus. Further studies are needed to clarify the association between specific types and intensities of activity and gestational diabetes mellitus
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