56,340 research outputs found
The SOS Platform: Designing, Tuning and Statistically Benchmarking Optimisation Algorithms
open access articleWe present Stochastic Optimisation Software (SOS), a Java platform facilitating the algorithmic design process and the evaluation of metaheuristic optimisation algorithms. SOS reduces the burden of coding miscellaneous methods for dealing with several bothersome and time-demanding tasks such as parameter tuning, implementation of comparison algorithms and testbed problems, collecting and processing data to display results, measuring algorithmic overhead, etc. SOS provides numerous off-the-shelf methods including: (1) customised implementations of statistical tests, such as the Wilcoxon rank-sum test and the HolmāBonferroni procedure, for comparing the performances of optimisation algorithms and automatically generating result tables in PDF and formats; (2) the implementation of an original advanced statistical routine for accurately comparing couples of stochastic optimisation algorithms; (3) the implementation of a novel testbed suite for continuous optimisation, derived from the IEEE CEC 2014 benchmark, allowing for controlled activation of the rotation on each testbed function. Moreover, we briefly comment on the current state of the literature in stochastic optimisation and highlight similarities shared by modern metaheuristics inspired by nature. We argue that the vast majority of these algorithms are simply a reformulation of the same methods and that metaheuristics for optimisation should be simply treated as stochastic processes with less emphasis on the inspiring metaphor behind them
Geodesic Transport Barriers in Jupiter's Atmosphere: A Video-Based Analysis
Jupiter's zonal jets and Great Red Spot are well known from still images. Yet
the planet's atmosphere is highly unsteady, which suggests that the actual
material transport barriers delineating its main features should be
time-dependent. Rare video footages of Jupiter's clouds provide an opportunity
to verify this expectation from optically reconstructed velocity fields.
Available videos, however, provide short-time and temporally aperiodic velocity
fields that defy classical dynamical systems analyses focused on asymptotic
features. To this end, we use here the recent theory of geodesic transport
barriers to uncover finite-time mixing barriers in the wind field extracted
from a video captured by NASA's Cassini space mission. More broadly, the
approach described here provides a systematic and frame-invariant way to
extract dynamic coherent structures from time-resolved remote observations of
unsteady continua
Detecting Differential Rotation and Starspot Evolution on the M dwarf GJ 1243 with Kepler
We present an analysis of the starspots on the active M4 dwarf GJ 1243, using
four years of time series photometry from Kepler. A rapid day rotation period is measured due to the 2.2\%
starspot-induced flux modulations in the light curve. We first use a light
curve modeling approach, using a Monte Carlo Markov Chain sampler to solve for
the longitudes and radii of the two spots within 5-day windows of data. Within
each window of time the starspots are assumed to be unchanging. Only a weak
constraint on the starspot latitudes can be implied from our modeling. The
primary spot is found to be very stable over many years. A secondary spot
feature is present in three portions of the light curve, decays on 100-500 day
timescales, and moves in longitude over time. We interpret this longitude
shearing as the signature of differential rotation. Using our models we measure
an average shear between the starspots of 0.0047 rad day, which
corresponds to a differential rotation rate of
rad day. We also fit this starspot phase evolution using a series of
bivariate Gaussian functions, which provides a consistent shear measurement.
This is among the slowest differential rotation shear measurements yet measured
for a star in this temperature regime, and provides an important constraint for
dynamo models of low mass stars.Comment: 13 pages, 7 figures, ApJ Accepte
Freeze-drying modeling and monitoring using a new neuro-evolutive technique
This paper is focused on the design of a black-box model for the process of freeze-drying of pharmaceuticals. A new methodology based on a self-adaptive differential evolution scheme is combined with a back-propagation algorithm, as local search method, for the simultaneous structural and parametric optimization of the model represented by a neural network. Using the model of the freeze-drying process, both the temperature and the residual ice content in the product vs. time can be determine off-line, given the values of the operating conditions (the temperature of the heating shelf and the pressure in the drying chamber). This makes possible to understand if the maximum temperature allowed by the product is trespassed and when the sublimation drying is complete, thus providing a valuable tool for recipe design and optimization. Besides, the black box model can be applied to monitor the freeze-drying process: in this case, the measurement of product temperature is used as input variable of the neural network in order to provide in-line estimation of the state of the product (temperature and residual amount of ice). Various examples are presented and discussed, thus pointing out the strength of the too
On the relation between sSFR and metallicity
In this paper we present an exact general analytic expression
linking the gas metallicity Z to the specific
star formation rate (sSFR), that validates and extends the approximate relation
put forward by Lilly et al. (2013, L13), where is the yield per stellar
generation, is the instantaneous ratio between inflow and star
formation rate expressed as a function of the sSFR, and is the integral of
the past enrichment history, respectively. We then demonstrate that the
instantaneous metallicity of a self-regulating system, such that its sSFR
decreases with decreasing redshift, can be well approximated by the first term
on the right-hand side in the above formula, which provides an upper bound to
the metallicity. The metallicity is well approximated also by the L13 ideal
regulator case, which provides a lower bound to the actual metallicity. We
compare these approximate analytic formulae to numerical results and infer a
discrepancy <0.1 dex in a range of metallicities and almost three orders of
magnitude in the sSFR. We explore the consequences of the L13 model on the
mass-weighted metallicity in the stellar component of the galaxies. We find
that the stellar average metallicity lags 0.1-0.2 dex behind the gas-phase
metallicity relation, in agreement with the data. (abridged)Comment: 14 pages, 6 figures, MNRAS accepte
Simulations of turbulent convection in rotating young solar-like stars: Differential rotation and meridional circulation
We present the results of three-dimensional simulations of the deep
convective envelope of a young (10 Myr) one-solar-mass star, obtained with the
Anelastic Spherical Harmonic code. Since young stars are known to be faster
rotators than their main sequence counterparts, we have systematically studied
the impact of the stellar rotation speed, by considering stars spinning up to
five times as fast as the Sun. The aim of these nonlinear models is to
understand the complex interactions between convection and rotation. We discuss
the influence of the turbulence level and of the rotation rate on the intensity
and the topology of the mean flows. For all of the computed models, we find a
solar-type superficial differential rotation, with an equatorial acceleration,
and meridional circulation that exhibits a multicellular structure. Even if the
differential rotation contrast decreases only marginally for high rotation
rates, the meridional circulation intensity clearly weakens according to our
simulations. We have also shown that, for Taylor numbers above a certain
threshold (Ta>10^9), the convection can develop a vacillating behavior. Since
simulations with high turbulence levels and rotation rates exhibit strongly
cylindrical internal rotation profiles, we have considered the influence of
baroclinic effects at the base of the convective envelope of these young Suns,
to see whether such effect can modify the otherwise near cylindrical profiles
to produce more conical, solar-like profiles.Comment: 32 pages, 18 figures, 2 tables, to appear in Ap
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