8,015 research outputs found
N-body Efimov states from two-particle noise
The ground state energies of universal N-body clusters tied to Efimov
trimers, for N even, are shown to be encapsulated in the statistical
distribution of two particles interacting with a background auxiliary field at
large Euclidean time when the interaction is tuned to the unitary point.
Numerical evidence that this distribution is log-normal is presented, allowing
one to predict the ground-state energies of the N-body system.Comment: Extended discussion of results; published versio
A Tidally-Disrupted Asteroid Around the White Dwarf G29-38
The infrared excess around the white dwarf G29-38 can be explained by
emission from an opaque flat ring of dust with an inner radius 0.14 of the
radius of the Sun and an outer radius approximately equal to the Sun's. This
ring lies within the Roche region of the white dwarf where an asteroid could
have been tidally destroyed, producing a system reminiscent of Saturn's rings.
Accretion onto the white dwarf from this circumstellar dust can explain the
observed calcium abundance in the atmosphere of G29-38. Either as a bombardment
by a series of asteroids or because of one large disruption, the total amount
of matter accreted onto the white dwarf may have been comparable to the total
mass of asteroids in the Solar System, or, equivalently, about 1% of the mass
in the asteroid belt around the main sequence star zeta Lep.Comment: ApJ Letters, in pres
Mechanisms of vascular smooth muscle contraction and the basis for pharmacologic treatment of smooth muscle disorders
The smooth muscle cell directly drives the contraction of the vascular wall and hence regulates the size of the blood vessel lumen. We review here the current understanding of the molecular mechanisms by which agonists, therapeutics, and diseases regulate contractility of the vascular smooth muscle cell and we place this within the context of whole body function. We also discuss the implications for personalized medicine and highlight specific potential target molecules that may provide opportunities for the future development of new therapeutics to regulate vascular function.Accepted manuscrip
Local ecosystem feedbacks and critical transitions in the climate
Global and regional climate models, such as those used in IPCC assessments, are the best tools available for climate predictions. Such models typically account for large-scale land-atmosphere feedbacks. However, these models omit local vegetationenvironment 5 feedbacks that are crucial for critical transitions in ecosystems. Here, we reveal the hypothesis that, if the balance of feedbacks is positive at all scales, local vegetation-environment feedbacks may trigger a cascade of amplifying effects, propagating from local to large scale, possibly leading to critical transitions in the largescale climate. We call for linking local ecosystem feedbacks with large-scale land10 atmosphere feedbacks in global and regional climate models in order to yield climate predictions that we are more confident about
Critical behavior of repulsive linear -mers on triangular lattices
Monte Carlo (MC) simulations and finite-size scaling analysis have been
carried out to study the critical behavior in a submonolayer two-dimensional
gas of repulsive linear -mers on a triangular lattice at coverage
. A low-temperature ordered phase, characterized by a repetition of
alternating files of adsorbed -mers separated by adjacent empty sites,
is separated from the disordered state by a order-disorder phase transition
occurring at a finite critical temperature, . The MC technique was
combined with the recently reported Free Energy Minimization Criterion Approach
(FEMCA), [F. Rom\'a et al., Phys. Rev. B, 68, 205407, (2003)], to predict the
dependence of the critical temperature of the order-disorder transformation.
The dependence on of the transition temperature, , observed in MC
is in qualitative agreement with FEMCA. In addition, an accurate determination
of the critical exponents has been obtained for adsorbate sizes ranging between
and . For , the results reveal that the system does not belong
to the universality class of the two-dimensional Potts model with (,
monomers). Based on symmetry concepts, we suggested that the behavior observed
for and 3 could be generalized to include larger particle sizes ().Comment: 17 pages, 13 figure
Amplitude dependent frequency, desynchronization, and stabilization in noisy metapopulation dynamics
The enigmatic stability of population oscillations within ecological systems
is analyzed. The underlying mechanism is presented in the framework of two
interacting species free to migrate between two spatial patches. It is shown
that that the combined effects of migration and noise cannot account for the
stabilization. The missing ingredient is the dependence of the oscillations'
frequency upon their amplitude; with that, noise-induced differences between
patches are amplified due to the frequency gradient. Migration among
desynchronized regions then stabilizes a "soft" limit cycle in the vicinity of
the homogenous manifold. A simple model of diffusively coupled oscillators
allows the derivation of quantitative results, like the functional dependence
of the desynchronization upon diffusion strength and frequency differences. The
oscillations' amplitude is shown to be (almost) noise independent. The results
are compared with a numerical integration of the marginally stable
Lotka-Volterra equations. An unstable system is extinction-prone for small
noise, but stabilizes at larger noise intensity
- …