6,822 research outputs found
New Constraints on the Star Formation History of the Star Cluster NGC 1856
We use the Wide Field Camera 3 onboard the Hubble Space Telescope to obtain
deep, high-resolution photometry of the young (age ~ 300 Myr) star cluster
NGC1856 in the Large Magellanic Cloud. We compare the observed colour-magnitude
diagram (CMD), after having applied a correction for differential reddening,
with Monte Carlo simulations of simple stellar populations (SSPs) of various
ages. We find that the main sequence turn-off (MSTO) region is wider than that
derived from the simulation of a single SSP. Using constraints based on the
distribution of stars in the MSTO region and the red clump, we find that the
CMD is best reproduced using a combination of two different SSPs with ages
separated by 80 Myr (0.30 and 0.38 Gyr, respectively). However, we can not
formally exclude that the width of the MSTO could be due to a range of stellar
rotation velocities if the efficiency of rotational mixing is higher than
typically assumed. Using a King-model fit to the surface number density profile
in conjunction with dynamical evolution models, we determine the evolution of
cluster mass and escape velocity from an age of 10 Myr to the present age,
taking into account the possible effects of primordial mass segregation. We
find that the cluster has an escape velocity Vesc ~ 17 km/s at an age of 10
Myr, and it remains high enough during a period of ~ 100 Myr to retain material
ejected by slow winds of first-generation stars. Our results are consistent
with the presence of an age spread in NGC1856, in contradiction to the results
of Bastian & Silva-Villa (2013).Comment: 17 pages, 14 figures. Re-submitted to MNRAS after addressing all the
comments by the refere
Comparing indirect encodings by evolutionary attractor analysis in the trait space of modular robots
In evolutionary robotics, the representation of the robot is of primary importance. Often indirect encodings are used, whereby a complex developmental process grows a body and a brain from a genotype. In this work, we aim at improving the interpretability of robot morphologies and behaviours resulting from indirect encoding. We develop and use a methodology that focuses on the analysis of evolutionary attractors, represented in what we call the trait space: Using trait descriptors defined in the literature, we define morphological and behavioural Cartesian planes where we project the phenotype of the final population. In our experiments we show that, using this analysis method, we are able to better discern the effect of encodings that differ only in minor details
Constraining Modified Gravity with Euclid
Future proposed satellite missions as Euclid can offer the opportunity to
test general relativity on cosmic scales through mapping of the galaxy weak
lensing signal. In this paper we forecast the ability of these experiments to
constrain modified gravity scenarios as those predicted by scalar-tensor and
theories. We found that Euclid will improve constraints expected from
the PLANCK satellite on these modified gravity models by two orders of
magnitude. We discuss parameter degeneracies and the possible biases introduced
by modified gravity
Irreversible thermodynamics of open chemical networks I: Emergent cycles and broken conservation laws
In this and a companion paper we outline a general framework for the
thermodynamic description of open chemical reaction networks, with special
regard to metabolic networks regulating cellular physiology and biochemical
functions. We first introduce closed networks "in a box", whose thermodynamics
is subjected to strict physical constraints: the mass-action law, elementarity
of processes, and detailed balance. We further digress on the role of solvents
and on the seemingly unacknowledged property of network independence of free
energy landscapes. We then open the system by assuming that the concentrations
of certain substrate species (the chemostats) are fixed, whether because
promptly regulated by the environment via contact with reservoirs, or because
nearly constant in a time window. As a result, the system is driven out of
equilibrium. A rich algebraic and topological structure ensues in the network
of internal species: Emergent irreversible cycles are associated to
nonvanishing affinities, whose symmetries are dictated by the breakage of
conservation laws. These central results are resumed in the relation between the number of fundamental affinities , that of broken
conservation laws and the number of chemostats . We decompose the
steady state entropy production rate in terms of fundamental fluxes and
affinities in the spirit of Schnakenberg's theory of network thermodynamics,
paving the way for the forthcoming treatment of the linear regime, of
efficiency and tight coupling, of free energy transduction and of thermodynamic
constraints for network reconstruction.Comment: 18 page
Role of fetal MRI in the evaluation of isolated and non-isolated corpus callosum dysgenesis: results of a cross-sectional study
PURPOSE:
The aims of this study were to characterize isolated and non-isolated forms of corpus callosum dysgenesis (CCD) at fetal magnetic resonance imaging (MRI) and to identify early predictors of associated anomalies.
METHODS:
We retrospectively analyzed 104 fetuses with CCD undergoing MRI between 2006 and 2016. Corpus callosum, cavum septi pellucidi, biometry, presence of ventriculomegaly, gyration anomalies, cranio-encephalic abnormalities and body malformations were evaluated. Results of genetic tests were also recorded.
RESULTS:
At MRI, isolated CCD was 26.9%, the rest being associated to other abnormalities. In the isolated group, median gestational age at MRI was lower in complete agenesis than in hypoplasia (22 vs 28 weeks). In the group with additional findings, cortical dysplasia was the most frequently associated feature (P = 0.008), with a more frequent occurrence in complete agenesis (70%) versus other forms; mesial frontal lobes were more often involved than other cortical regions (P = 0.006), with polymicrogyria as the most frequent cortical malformation (40%). Multivariate analysis confirmed the association between complete agenesis and cortical dysplasia (odds ratio = 7.29, 95% confidence interval 1.51-35.21).
CONCLUSIONS:
CCD is often complicated by other intra-cranial and extra-cranial findings (cortical dysplasias as the most prevalent) that significantly affect the postnatal prognosis. The present study showed CCD with associated anomalies as more frequent than isolated (73.1%). In isolated forms, severe ventriculomegaly was a reliable herald of future appearance of associated features
Finite dimensional corrections to mean field in a short-range p-spin glassy model
In this work we discuss a short range version of the -spin model. The
model is provided with a parameter that allows to control the crossover with
the mean field behaviour. We detect a discrepancy between the perturbative
approach and numerical simulation. We attribute it to non-perturbative effects
due to the finite probability that each particular realization of the disorder
allows for the formation of regions where the system is less frustrated and
locally freezes at a higher temperature.Comment: 18 pages, 5 figures, submitted to Phys Rev
Financial instability from local market measures
We study the emergence of instabilities in a stylized model of a financial
market, when different market actors calculate prices according to different
(local) market measures. We derive typical properties for ensembles of large
random markets using techniques borrowed from statistical mechanics of
disordered systems. We show that, depending on the number of financial
instruments available and on the heterogeneity of local measures, the market
moves from an arbitrage-free phase to an unstable one, where the complexity of
the market - as measured by the diversity of financial instruments - increases,
and arbitrage opportunities arise. A sharp transition separates the two phases.
Focusing on two different classes of local measures inspired by real markets
strategies, we are able to analytically compute the critical lines,
corroborating our findings with numerical simulations.Comment: 17 pages, 4 figure
Phase diagram of the lattice Wess-Zumino model from rigorous lower bounds on the energy
We study the lattice N=1 Wess-Zumino model in two dimensions and we construct
a sequence of exact lower bounds on its ground state energy
density , converging to in the limit . The bounds
can be computed numerically on a finite lattice with sites and
can be exploited to discuss dynamical symmetry breaking. The transition point
is determined and compared with recent results based on large-scale Green
Function Monte Carlo simulations with good agreement.Comment: 32 pages, 12 figure
Realistic Simulations of the Galactic Polarized Foreground: Consequences for 21-cm Reionization Detection Experiments
Experiments designed to measure the redshifted 21~cm line from the Epoch of
Reionization (EoR) are challenged by strong astrophysical foreground
contamination, ionospheric distortions, complex instrumental response and other
different types of noise (e.g. radio frequency interference). The astrophysical
foregrounds are dominated by diffuse synchrotron emission from our Galaxy. Here
we present a simulation of the Galactic emission used as a foreground module
for the LOFAR- EoR key science project end-to-end simulations. The simulation
produces total and polarized intensity over maps of
the Galactic synchrotron and free-free emission, including all observed
characteristics of the emission: spatial fluctuations of amplitude and spectral
index of the synchrotron emission, together with Faraday rotation effects. The
importance of these simulations arise from the fact that the Galactic polarized
emission could behave in a manner similar to the EoR signal along the frequency
direction. As a consequence, an improper instrumental calibration will give
rise to leakages of the polarized to the total signal and mask the desired EoR
signal. In this paper we address this for the first time through realistic
simulations.Comment: 14 pages, 8 figures, published in MNRA
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