37 research outputs found
Decoding machine learning benchmarks
Despite the availability of benchmark machine learning (ML) repositories
(e.g., UCI, OpenML), there is no standard evaluation strategy yet capable of
pointing out which is the best set of datasets to serve as gold standard to
test different ML algorithms. In recent studies, Item Response Theory (IRT) has
emerged as a new approach to elucidate what should be a good ML benchmark. This
work applied IRT to explore the well-known OpenML-CC18 benchmark to identify
how suitable it is on the evaluation of classifiers. Several classifiers
ranging from classical to ensembles ones were evaluated using IRT models, which
could simultaneously estimate dataset difficulty and classifiers' ability. The
Glicko-2 rating system was applied on the top of IRT to summarize the innate
ability and aptitude of classifiers. It was observed that not all datasets from
OpenML-CC18 are really useful to evaluate classifiers. Most datasets evaluated
in this work (84%) contain easy instances in general (e.g., around 10% of
difficult instances only). Also, 80% of the instances in half of this benchmark
are very discriminating ones, which can be of great use for pairwise algorithm
comparison, but not useful to push classifiers abilities. This paper presents
this new evaluation methodology based on IRT as well as the tool decodIRT,
developed to guide IRT estimation over ML benchmarks.Comment: Paper published at the BRACIS 2020 conference, 15 pages, 4 figure
Distance determination to 12 Type II-P Supernovae using the Expanding Photosphere Method
We use early-time photometry and spectroscopy of 12 Type II plateau
supernovae (SNe IIP) to derive their distances using the expanding photosphere
method (EPM). We perform this study using two sets of Type II supernova (SN II)
atmosphere models, three filter subsets (, , ), and
two methods for the host-galaxy extinction, which leads to 12 Hubble diagrams.
We find that systematic differences in the atmosphere models lead to 50%
differences in the EPM distances and to a value of between 52 and
101 . Using the filter subset we obtain the
lowest dispersion in the Hubble diagram, { mag}. We
also apply the EPM analysis to the well-observed SN IIP 1999em. With the
filter subset we derive a distance ranging from 9.3 0.5 Mpc to
13.9 1.4 Mpc depending on the atmosphere model employed.Comment: Accepted for publication in the Astrophysical Journa
Single-lens mass measurement in the high-magnification microlensing event Gaia19bld located in the Galactic disc
This work was supported from the Polish NCN grants: Preludium No. 2017/25/N/ST9/01253, Harmonia No. 2018/30/M/ST9/00311, MNiSW grant DIR/WK/2018/12, Daina No. 2017/27/L/ST9/03221, and by the Research Council of Lithuania, grant No. S-LL-19-2. The OGLE project has received funding from the NCN grant MAESTRO 2014/14/A/ST9/00121 to AU. We acknowledge the European Commissionâs H2020 OPTICON grant No. 730890. YT acknowledges the support of DFG priority program SPP 1992 âExploring the Diversity of Extrasolar Planetsâ (WA 1047/11-1). EB and RS gratefully acknowledge support from NASA grant 80NSSC19K0291. Work by AG was supported by JPL grant 1500811. Work by JCY was supported by JPL grant 1571564. SJF thanks Telescope Live for access to their telescope network. NN acknowledges the support of Data Science Research Center, Chiang Mai University. FOE acknowledges the support from the FONDECYT grant nr. 1201223. MK acknowledges the support from the NCN grant No. 2017/27/B/ST9/02727.Context. Microlensing provides a unique opportunity to detect non-luminous objects. In the rare cases that the Einstein radius ΞE and microlensing parallax ÏE can be measured, it is possible to determine the mass of the lens. With technological advances in both ground- and space-based observatories, astrometric and interferometric measurements are becoming viable, which can lead to the more routine determination of ΞE and, if the microlensing parallax is also measured, the mass of the lens. Aims. We present the photometric analysis of Gaia19bld, a high-magnification (A approximate to 60) microlensing event located in the southern Galactic plane, which exhibited finite source and microlensing parallax effects. Due to a prompt detection by the Gaia satellite and the very high brightness of I = 9.05 mag at the peak, it was possible to collect a complete and unique set of multi-channel follow-up observations, which allowed us to determine all parameters vital for the characterisation of the lens and the source in the microlensing event. Methods. Gaia19bld was discovered by the Gaia satellite and was subsequently intensively followed up with a network of ground-based observatories and the Spitzer Space Telescope. We collected multiple high-resolution spectra with Very Large Telescope (VLT)/X-shooter to characterise the source star. The event was also observed with VLT Interferometer (VLTI)/PIONIER during the peak. Here we focus on the photometric observations and model the light curve composed of data from Gaia, Spitzer, and multiple optical, ground-based observatories. We find the best-fitting solution with parallax and finite source effects. We derived the limit on the luminosity of the lens based on the blended light model and spectroscopic distance. Results. We compute the mass of the lens to be 1.13 ± 0.03 Mâ and derive its distance to be 5.52-0.64+0.35 kpc. The lens is likely a main sequence star, however its true nature has yet to be verified by future high-resolution observations. Our results are consistent with interferometric measurements of the angular Einstein radius, emphasising that interferometry can be a new channel for determining the masses of objects that would otherwise remain undetectable, including stellar-mass black holes.Publisher PDFPeer reviewe
Single-lens mass measurement in the high-magnification microlensing event Gaia 19bld located in the Galactic disc
CONTEXT: Microlensing provides a unique opportunity to detect non-luminous objects. In the rare cases that the Einstein radius Ξ_{E} and microlensing parallax Ï_{E} can be measured, it is possible to determine the mass of the lens. With technological advances in both ground- and space-based observatories, astrometric and interferometric measurements are becoming viable, which can lead to the more routine determination of Ξ_{E} and, if the microlensing parallax is also measured, the mass of the lens. AIMS: We present the photometric analysis of Gaia19bld, a high-magnification (Aâââ60) microlensing event located in the southern Galactic plane, which exhibited finite source and microlensing parallax effects. Due to a prompt detection by the Gaia satellite and the very high brightness of Iâ=â9.05 mag at the peak, it was possible to collect a complete and unique set of multi-channel follow-up observations, which allowed us to determine all parameters vital for the characterisation of the lens and the source in the microlensing event. METHODS: Gaia19bld was discovered by the Gaia satellite and was subsequently intensively followed up with a network of ground-based observatories and the Spitzer Space Telescope. We collected multiple high-resolution spectra with Very Large Telescope (VLT)/X-shooter to characterise the source star. The event was also observed with VLT Interferometer (VLTI)/PIONIER during the peak. Here we focus on the photometric observations and model the light curve composed of data from Gaia, Spitzer, and multiple optical, ground-based observatories. We find the best-fitting solution with parallax and finite source effects. We derived the limit on the luminosity of the lens based on the blended light model and spectroscopic distance. RESULTS: We compute the mass of the lens to be 1.13â
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0.03âM_{â} and derive its distance to be 5.52_{â0.64}^{+0.35} kpc. The lens is likely a main sequence star, however its true nature has yet to be verified by future high-resolution observations. Our results are consistent with interferometric measurements of the angular Einstein radius, emphasising that interferometry can be a new channel for determining the masses of objects that would otherwise remain undetectable, including stellar-mass black holes
The mammals of Angola
Scientific investigations on the mammals of Angola started over 150 years
ago, but information remains scarce and scattered, with only one recent published
account. Here we provide a synthesis of the mammals of Angola based on a thorough
survey of primary and grey literature, as well as recent unpublished records. We present
a short history of mammal research, and provide brief information on each species
known to occur in the country. Particular attention is given to endemic and near endemic
species. We also provide a zoogeographic outline and information on the conservation
of Angolan mammals. We found confirmed records for 291 native species, most of
which from the orders Rodentia (85), Chiroptera (73), Carnivora (39), and
Cetartiodactyla (33). There is a large number of endemic and near endemic species,
most of which are rodents or bats. The large diversity of species is favoured by the wide range of habitats with contrasting environmental conditions, while endemism tends to
be associated with unique physiographic settings such as the Angolan Escarpment. The
mammal fauna of Angola includes 2 Critically Endangered, 2 Endangered, 11
Vulnerable, and 14 Near-Threatened species at the global scale. There are also 12 data
deficient species, most of which are endemics or near endemics to the countryinfo:eu-repo/semantics/publishedVersio
Models of environmental effects on anion polarizability
This paper deals with three different approaches to the representation of environmental effects on anion polarizability in cubic crystals of the stoichiometry MX, where M is an alkali metal and X is a halogen. Ab initio embedded cluster calculations of the variation in anion polarizability with pressure in a fixed crystal type are presented and compared with experiment. The results are then used in a scaled ab initio model used to predict further values for the pressure dependence of the in-crystal anion polarizability. This scaled model is compared with a fully empirical 'universal' model due to Batana et al. based on polarizability change with ionic radius [1997, Molec. Phys., 92, 1029]. The assumptions of the two models differ substantially and the central purpose of this paper is to contrast these differences and highlight their consequences for prediction. Although the empirical model typically overestimates the experimental pressure derivatives, and the ab initio calculations somewhat underestimate them, it is shown that the assumption of incompressible cations in the scaled ab initio-derived model has a firmer physical basis than the empirical picture in which all ions are compressible. © 1999 Taylor and Francis Ltd