8,562 research outputs found
Investigating the Use of Geometric Semantic Operators in Vectorial Genetic Programming
Azzali, I., Vanneschi, L., & Giacobini, M. (2020). Investigating the Use of Geometric Semantic Operators in Vectorial Genetic Programming. In T. Hu, N. Lourenço, E. Medvet, & F. Divina (Eds.), Genetic Programming - 23rd European Conference, EuroGP 2020, Held as Part of EvoStar 2020, Proceedings (pp. 52-67). (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); Vol. 12101 LNCS). Springer. https://doi.org/10.1007/978-3-030-44094-7_4 ------- This work was partially supported by FCT, Portugal through funding of LASIGE Research Unit (UID/CEC/00408/2019), and projects PREDICT (PTDC/CCI-IF/29877/2017), BINDER (PTDC/CCI-INF/29168/2017), GADgET (DSAIPA/DS/0022/2018) and AICE (DSAIPA/DS/0113/2019).Vectorial Genetic Programming (VE_GP) is a new GP approach for panel data forecasting. Besides permitting the use of vectors as terminal symbols to represent time series and including aggregation functions to extract time series features, it introduces the possibility of evolving the window of aggregation. The local aggregation of data allows the identification of meaningful patterns overcoming the drawback of considering always the previous history of a series of data. In this work, we investigate the use of geometric semantic operators (GSOs) in VE_GP, comparing its performance with traditional GP with GSOs. Experiments are conducted on two real panel data forecasting problems, one allowing the aggregation on moving windows, one not. Results show that classical VE_GP is the best approach in both cases in terms of predictive accuracy, suggesting that GSOs are not able to evolve efficiently individuals when time series are involved. We discuss the possible reasons of this behaviour, to understand how we could design valuable GSOs for time series in the future.authorsversionpublishe
New ATLAS9 And MARCS Model Atmosphere Grids for the Apache Point Observatory Galactic Evolution Experiment (APOGEE)
We present a new grid of model photospheres for the SDSS-III/APOGEE survey of
stellar populations of the Galaxy, calculated using the ATLAS9 and MARCS codes.
New opacity distribution functions were generated to calculate ATLAS9 model
photospheres. MARCS models were calculated based on opacity sampling
techniques. The metallicity ([M/H]) spans from -5 to 1.5 for ATLAS and -2.5 to
0.5 for MARCS models. There are three main differences with respect to previous
ATLAS9 model grids: a new corrected H2O linelist, a wide range of carbon
([C/M]) and alpha element [alpha/M] variations, and solar reference abundances
from Asplund et al. 2005. The added range of varying carbon and alpha element
abundances also extends the previously calculated MARCS model grids. Altogether
1980 chemical compositions were used for the ATLAS9 grid, and 175 for the MARCS
grid. Over 808 thousand ATLAS9 models were computed spanning temperatures from
3500K to 30000K and log g from 0 to 5, where larger temperatures only have high
gravities. The MARCS models span from 3500K to 5500K, and log g from 0 to 5.
All model atmospheres are publically available online.Comment: 8 pages, 6 figures, 5 tables, accepted for publication in The
Astronomical Journa
The psychosocial impact of assistive device scale: Italian validation in a cohort of nonambulant people with neuromotor disorders
The importance of adaptive seating system on body structure and function is widely accepted, but its impact on psychosocial aspects needs more consideration by health professionals. This article describes the Italian validation of the Psychosocial Impact of Assistive Device Scale (IT-PIADS) for non-ambulant people with neuromotor disorders. Once agreement has been given by the original authors, the scale was translated and adapted to the Italian culture. The IT-PIADS was administered to different wheelchairs users with heterogeneous diagnosis. The internal consistency and test-retest reliability were examined. Its concurrent validity was evaluated with the Italian version of the WheelCon-M-SF. The IT-PIADS was administered to 87 subjects. Cronbach's α was 0.92 (p < 0.05), and the testretest reliability (ICC) for competence, adaptability and self-esteem subscales were 0.96, 0.90, 0.93 respectively. The Pearson correlation coefficient of the IT-PIADS with the WheelCon-M-I-SF scores showed significant data for competence and adaptability subscales. Psychosocial perception on assistive devices can be reliably measure. The IT-PIADS showed good psychometric properties and it is possible to confirm its validity for clinical and research purposes. Nevertheless, before using this measure with greater confidence, further psychometric properties tests of the IT-PIADS are recommended
About the linearity of the color-magnitude relation of early-type galaxies in the Virgo cluster
We revisit the color-magnitude relation (CMR) of the Virgo cluster early-type
galaxies in order to explore its alleged non-linearity. To this aim, we
reanalyze the relation already published from data obtained within the ACS
Virgo Cluster Survey of the Hubble Space Telescope, and perform our own
photometry and analysis of the images of the 100 early-type galaxies observed
as part of this survey. In addition, we compare our results with those reported
in the literature from data of the Sloan Digital Sky Survey. We have found that
when the brightest galaxies and untypical systems are excluded from the sample,
a linear relation arises in agreement with what is observed in other groups and
clusters. The central regions of the brightest galaxies also follow this
relation. In addition, we notice that Virgo contains at least four compact
elliptical galaxies besides the well known object VCC 1297 (NGC 4486B). Their
locations in the -luminosity diagram define a different trend to that
followed by normal early-type dwarf galaxies, setting an upper limit in
effective surface brightness and a lower limit in effective radius for their
luminosities. Based on the distribution of different galaxy sub-samples in the
color-magnitude and -luminosity diagrams we draw some conclusions on
their formation and the history of their evolution.Comment: 21 pages, 4 figures, 2 tables. Accepted for publication in Ap
Theoretical stellar models for old galactic clusters
We present new evolutionary stellar models suitable for old Population I
clusters, discussing both the consequences of the most recent improvements in
the input physics and the effect of element diffusion within the stellar
structures. Theoretical cluster isochrones are presented, covering the range of
ages from 1 to 9 Gyr for the four selected choices on the metallicity Z= 0.007,
0.010, 0.015 and 0.020. Theoretical uncertainties on the efficiency of
superadiabatic convection are discussed in some details. Isochrone fitting to
the CM diagrams of the two well observed galactic clusters NGC2420 and M67
indicates that a mixing length parameter alpha = 1.9 appears adequate for
reproducing the observed color of cool giant stars. The problems in matching
theoretical preditions to the observed slope of MS stars are discussed.Comment: 7 pages, 14 postscript figures, accepted for publication on MNRA
On the properties of the interstellar medium in extremely metal-poor blue compact dwarf galaxies: GMOS-IFU spectroscopy and SDSS photometry of the double-knot galaxy HS 2236+1344
The main goal of this study is to carry out a spatially resolved
investigation of the warm interstellar medium (ISM) in the extremely metal-poor
Blue Compact Dwarf (BCD) galaxy HS 2236+1344. Special emphasis is laid on the
analysis of the spatial distribution of chemical abundances, emission-line
ratios and kinematics of the ISM, and to the recent star-forming activity in
this galaxy. This study is based on optical integral field unit spectroscopy
data from Gemini Multi-Object Spectrograph at the Gemini North telescope and
archival Sloan Digital Sky Survey images. The data were obtained in two
different positions across the galaxy, obtaining a total 4 arcsec X 8 arcsec
field which encompasses most of its ISM. Emission-line maps and broad-band
images obtained in this study indicate that HS 2236+1344 hosts three Giant HII
regions. Our data also reveal some faint curved features in the BCD periphery
that might be due to tidal perturbations or expanding ionized-gas shells. The
ISM velocity field shows systematic gradients along the major axis of the BCD,
with its south-eastern and north-western half differing by ~80 km/s in their
recessional velocity. The Ha and Hb equivalent width distribution in the
central part of HS 2236+1344 is consistent with a very young (~3 Myr) burst.
Our surface photometry analysis indicates that the ongoing starburst provides
~50% of the total optical emission, similar to other BCDs. It also reveals an
underlying lower-surface brightness component with moderately red colors, which
suggest that the galaxy has undergone previous star formation. We derive an
integrated oxygen abundance of 12+log(O/H)=7.53\pm0.06 and a nitrogen-to-oxygen
ratio of log(N/O)=-1.57\pm0.19. Our results are consistent, within the
uncertainties, with a homogeneous distribution of oxygen and nitrogen within
the ISM of the galaxy. (abridged)Comment: 15 pages, 16 figures, accepted for publication in A&
Analysis of thermomechanical fatigue of unidirectional titanium metal matrix composites
Thermomechanical fatigue (TMF) data was generated for a Ti-15V-3Cr-3Al-3Sn (Ti-15-3) material reinforced with SCS-6 silicon carbide fibers for both in-phase and out-of-phase thermomechanical cycling. Significant differences in failure mechanisms and fatigue life were noted for in-phase and out-of-phase testing. The purpose of the research is to apply a micromechanical model to the analysis of the data. The analysis predicts the stresses in the fiber and the matrix during the thermal and mechanical cycling by calculating both the thermal and mechanical stresses and their rate-dependent behavior. The rate-dependent behavior of the matrix was characterized and was used to calculate the constituent stresses in the composite. The predicted 0 degree fiber stress range was used to explain the composite failure. It was found that for a given condition, temperature, loading frequency, and time at temperature, the 0 degree fiber stress range may control the fatigue life of the unidirectional composite
Integrated Light 2MASS IR Photometry of Galactic Globular Clusters
We have mosaiced 2MASS images to derive surface brightness profiles in JHK
for 104 Galactic globular clusters. We fit these with King profiles, and show
that the core radii are identical to within the errors for each of these IR
colors, and are identical to the core radii at V in essentially all cases. We
derive integrated light colors V-J, V-H, V-K_s, J-H and J-K_s for these
globular clusters. Each color shows a reasonably tight relation between the
dereddened colors and metallicity. Fits to these are given for each color. The
IR--IR colors have very small errors due largely to the all-sky photometric
calibration of the 2MASS survey, while the V-IR colors have substantially
larger uncertainties. We find fairly good agreement with measurements of
integrated light colors for a smaller sample of Galactic globular clusters by
Aaronson, Malkan & Kleinmann from 1977. Our results provide a calibration for
the integrated light of distant single burst old stellar populations from very
low to Solar metallicities. A comparison of our dereddened measured colors with
predictions from several models of the integrated light of single burst old
populations shows good agreement in the low metallicity domain for V-K_s
colors, but an offset at a fixed [Fe/H] of ~0.1 mag in J-K_s, which we ascribe
to photometric system transformation issues. Some of the models fail to
reproduce the behavior of the integrated light colors of the Galactic globular
clusters near Solar metallicity.Comment: Accepted for publication in the A
The Distance of the First Overtone RR Lyrae Variables in the MACHO LMC Database: A New Method to Correct for the Effects of Crowding
Previous studies have indicated that many of the RR Lyrae variables in the
LMC have properties similar to the ones in the Galactic globular cluster M3.
Assuming that the M3 RR Lyrae variables follow the same relationships among
period, temperature, amplitude and Fourier phase parameter phi31 as their LMC
counterparts, we have used the M3 phi31-logP relation to identify the M3-like
unevolved first overtone RR Lyrae variables in 16 fields near the LMC bar. The
temperatures of these variables were calculated from the M3 logP-logTe relation
so that the extinction could be derived for each star separately. Since blended
stars have lower amplitudes for a given period, the period amplitude relation
should be a useful tool for identifying which stars are affected by crowding.
We find that the low amplitude stars are brighter. We remove them from the
sample and derive an LMC distance modulus 18.49+/-0.11.Comment: 30 pages, 7 figures, accepted for publication in the Astronomical
Journa
- …