28,469 research outputs found
Exploring Io's atmospheric composition with APEX: first measurement of 34SO2 and tentative detection of KCl
The composition of Io's tenuous atmosphere is poorly constrained. Only the
major species SO2 and a handful of minor species have been positively
identified, but a variety of other molecular species should be present, based
on thermochemical equilibrium models of volcanic gas chemistry and the
composition of Io's environment. This paper focuses on the spectral search for
expected yet undetected molecular species (KCl, SiO, S2O) and isotopes (34SO2).
We analyze a disk-averaged spectrum of a potentially line-rich spectral window
around 345 GHz, obtained in 2010 at the APEX-12m antenna (Atacama Pathfinder
EXperiment). Using different models assuming either extended atmospheric
distributions or a purely volcanically-sustained atmosphere, we tentatively
measure the KCl relative abundance with respect to SO2 and derive a range of
4x10^{-4}-8x10^{-3}. We do not detect SiO or S2O and present new upper limits
on their abundances. We also present the first measurement of the 34S/32S
isotopic ratio in gas phase on Io, which appears to be twice as high as the
Earth and ISM reference values. Strong lines of SO2 and SO are also analyzed to
check for longitudinal variations of column density and relative abundance. Our
models show that, based on their predicted relative abundance with respect to
SO2 in volcanic plumes, both the tentative KCl detection and SiO upper limit
are compatible with a purely volcanic origin for these species.Comment: Accepted for publication in ApJ. 11 pages, 4 figure
The Bak-Sneppen Model on Scale-Free Networks
We investigate by numerical simulations and analytical calculations the
Bak-Sneppen model for biological evolution in scale-free networks. By using
large scale numerical simulations, we study the avalanche size distribution and
the activity time behavior at nodes with different connectivities. We argue the
absence of a critical barrier and its associated critical behavior for infinite
size systems. These findings are supported by a single site mean-field analytic
treatment of the model.Comment: 5 pages and 3 eps figures. Final version appeared in Europhys. Let
Phase Space Reduction for Star-Products: An Explicit Construction for CP^n
We derive a closed formula for a star-product on complex projective space and
on the domain using a completely elementary
construction: Starting from the standard star-product of Wick type on and performing a quantum analogue of Marsden-Weinstein
reduction, we can give an easy algebraic description of this star-product.
Moreover, going over to a modified star-product on ,
obtained by an equivalence transformation, this description can be even further
simplified, allowing the explicit computation of a closed formula for the
star-product on \CP^n which can easily transferred to the domain
.Comment: LaTeX, 17 page
Preferência de consumidores de maçã cv. Fuji minimamente processada e tratada com substâncias coadjuvantes.
Are stealth scalar fields stable?
Non-gravitating (stealth) scalar fields associated with Minkowski space in
scalar-tensor gravity are examined. Analytical solutions for both non-minimally
coupled scalar field theory and for Brans-Dicke gravity are studied and their
stability with respect to tensor perturbations is assessed using a covariant
and gauge-invariant formalism developed for alternative gravity. For
Brans-Dicke solutions, the stability with respect to homogeneous perturbations
is also studied. There are regions of parameter space corresponding to
stability and other regions corresponding to instability.Comment: 10 pages, 1 table, no figures, to appear in Phys. Rev,
Accurate Noise Projection for Reduced Stochastic Epidemic Models
We consider a stochastic Susceptible-Exposed-Infected-Recovered (SEIR)
epidemiological model. Through the use of a normal form coordinate transform,
we are able to analytically derive the stochastic center manifold along with
the associated, reduced set of stochastic evolution equations. The
transformation correctly projects both the dynamics and the noise onto the
center manifold. Therefore, the solution of this reduced stochastic dynamical
system yields excellent agreement, both in amplitude and phase, with the
solution of the original stochastic system for a temporal scale that is orders
of magnitude longer than the typical relaxation time. This new method allows
for improved time series prediction of the number of infectious cases when
modeling the spread of disease in a population. Numerical solutions of the
fluctuations of the SEIR model are considered in the infinite population limit
using a Langevin equation approach, as well as in a finite population simulated
as a Markov process.Comment: 38 pages, 10 figures, new title, Final revision to appear in Chao
Charged-current inclusive neutrino cross sections in the SuperScaling model including quasielastic, pion production and meson-exchange contributions
Charged current inclusive neutrino-nucleus cross sections are evaluated using
the superscaling model for quasielastic scattering and its extension to the
pion production region. The contribution of two-particle-two-hole vector
meson-exchange current excitations is also considered within a fully
relativistic model tested against electron scattering data. The results are
compared with the inclusive neutrino-nucleus data from the T2K and SciBooNE
experiments. For experiments where GeV, the
three mechanisms considered in this work provide good agreement with the data.
However, when the neutrino energy is larger, effects from beyond the
also appear to be playing a role. The results show that processes induced by
two-body currents play a minor role at the kinematics considered.Comment: 10 pages, 7 figure
Fluctuating epidemics on adaptive networks
A model for epidemics on an adaptive network is considered. Nodes follow an
SIRS (susceptible-infective-recovered-susceptible) pattern. Connections are
rewired to break links from non-infected nodes to infected nodes and are
reformed to connect to other non-infected nodes, as the nodes that are not
infected try to avoid the infection. Monte Carlo simulation and numerical
solution of a mean field model are employed. The introduction of rewiring
affects both the network structure and the epidemic dynamics. Degree
distributions are altered, and the average distance from a node to the nearest
infective increases. The rewiring leads to regions of bistability where either
an endemic or a disease-free steady state can exist. Fluctuations around the
endemic state and the lifetime of the endemic state are considered. The
fluctuations are found to exhibit power law behavior.Comment: Submitted to Phys Rev
Comprehensive study of Leon-Queretaro area
There are no author-identified significant results in this report
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