59 research outputs found
From regular black holes to horizonless objects: quasi-normal modes, instabilities and spectroscopy
We study gravitational and test-field perturbations for the two possible
families of spherically symmetric black-hole mimickers that smoothly
interpolate between regular black holes and horizonless compact objects
accordingly to the value of a regularization parameter. One family can be
described by the Bardeen-like metrics, and the other by the Simpson-Visser
metric. We compute the spectrum of quasi-normal modes (QNMs) of these
spacetimes enlightening a common misunderstanding regarding this computation
present in the recent literature. In both families, we observe long-living
modes for values of the regularization parameter corresponding to ultracompact,
horizonless configurations. Such modes appear to be associated with the
presence of a stable photon sphere and are indicative of potential non-linear
instabilities. In general, the QNM spectra of both families display deviations
from the standard spectrum of GR singular BHs. In order to address the future
detectability of such deviations in the gravitational-wave ringdown signal, we
perform a preliminary study, finding that third generation ground-based
detectors might be sensible to macroscopic values of the regularization
parameter
METAPHOR: Probability density estimation for machine learning based photometric redshifts
We present METAPHOR (Machine-learning Estimation Tool for Accurate
PHOtometric Redshifts), a method able to provide a reliable PDF for photometric
galaxy redshifts estimated through empirical techniques. METAPHOR is a modular
workflow, mainly based on the MLPQNA neural network as internal engine to
derive photometric galaxy redshifts, but giving the possibility to easily
replace MLPQNA with any other method to predict photo-z's and their PDF. We
present here the results about a validation test of the workflow on the
galaxies from SDSS-DR9, showing also the universality of the method by
replacing MLPQNA with KNN and Random Forest models. The validation test include
also a comparison with the PDF's derived from a traditional SED template
fitting method (Le Phare).Comment: proceedings of the International Astronomical Union, IAU-325
symposium, Cambridge University pres
Probability density estimation of photometric redshifts based on machine learning
Photometric redshifts (photo-z's) provide an alternative way to estimate the
distances of large samples of galaxies and are therefore crucial to a large
variety of cosmological problems. Among the various methods proposed over the
years, supervised machine learning (ML) methods capable to interpolate the
knowledge gained by means of spectroscopical data have proven to be very
effective. METAPHOR (Machine-learning Estimation Tool for Accurate PHOtometric
Redshifts) is a novel method designed to provide a reliable PDF (Probability
density Function) of the error distribution of photometric redshifts predicted
by ML methods. The method is implemented as a modular workflow, whose internal
engine for photo-z estimation makes use of the MLPQNA neural network (Multi
Layer Perceptron with Quasi Newton learning rule), with the possibility to
easily replace the specific machine learning model chosen to predict photo-z's.
After a short description of the software, we present a summary of results on
public galaxy data (Sloan Digital Sky Survey - Data Release 9) and a comparison
with a completely different method based on Spectral Energy Distribution (SED)
template fitting.Comment: 2016 IEEE Symposium Series on Computational Intelligence, SSCI 2016
784995
Stable Rotating Regular Black Holes
We present a rotating regular black hole whose inner horizon has zero surface
gravity for any value of the spin parameter, and is therefore stable against
mass inflation. Our metric is built by combining two successful strategies for
regularizing singularities, i.e. by replacing the mass parameter with a
function of and by introducing a conformal factor. The mass function
controls the properties of the inner horizon, whose displacement away from the
Kerr geometry's inner horizon is quantified in terms of a parameter ; while
the conformal factor regularizes the singularity in a way that is parametrized
by the dimensionful quantity . The resulting line element not only avoids
the stability issues that are common to regular black hole models endowed with
inner horizons, but is also free of problematic properties of the Kerr
geometry, such as the existence of closed timelike curves. While the proposed
metric has all the phenomenological relevant features of singular rotating
black holes -- such as ergospheres, light ring and innermost stable circular
orbit -- showing a remarkable similarity to a Kerr black hole in its exterior,
it allows nonetheless sizable deviations, especially for large values of the
spin parameter . In this sense, the proposed rotating "inner-degenarate"
regular black hole solution is not only amenable to further theoretical
investigations but most of all can represent a viable geometry to contrast to
the Kerr one in future phenomenological tests.Comment: 12 pages; formatting matched to submitted versio
DAMEWARE - Data Mining & Exploration Web Application Resource
Astronomy is undergoing through a methodological revolution triggered by an
unprecedented wealth of complex and accurate data. DAMEWARE (DAta Mining &
Exploration Web Application and REsource) is a general purpose, Web-based,
Virtual Observatory compliant, distributed data mining framework specialized in
massive data sets exploration with machine learning methods. We present the
DAMEWARE (DAta Mining & Exploration Web Application REsource) which allows the
scientific community to perform data mining and exploratory experiments on
massive data sets, by using a simple web browser. DAMEWARE offers several tools
which can be seen as working environments where to choose data analysis
functionalities such as clustering, classification, regression, feature
extraction etc., together with models and algorithms.Comment: User Manual of the DAMEWARE Web Application, 51 page
Statistical analysis of probability density functions for photometric redshifts through the KiDS-ESO-DR3 galaxies
Despite the high accuracy of photometric redshifts (zphot) derived using
Machine Learning (ML) methods, the quantification of errors through reliable
and accurate Probability Density Functions (PDFs) is still an open problem.
First, because it is difficult to accurately assess the contribution from
different sources of errors, namely internal to the method itself and from the
photometric features defining the available parameter space. Second, because
the problem of defining a robust statistical method, always able to quantify
and qualify the PDF estimation validity, is still an open issue. We present a
comparison among PDFs obtained using three different methods on the same data
set: two ML techniques, METAPHOR (Machine-learning Estimation Tool for Accurate
PHOtometric Redshifts) and ANNz2, plus the spectral energy distribution
template fitting method, BPZ. The photometric data were extracted from the KiDS
(Kilo Degree Survey) ESO Data Release 3, while the spectroscopy was obtained
from the GAMA (Galaxy and Mass Assembly) Data Release 2. The statistical
evaluation of both individual and stacked PDFs was done through quantitative
and qualitative estimators, including a dummy PDF, useful to verify whether
different statistical estimators can correctly assess PDF quality. We conclude
that, in order to quantify the reliability and accuracy of any zphot PDF
method, a combined set of statistical estimators is required.Comment: Accepted for publication by MNRAS, 20 pages, 14 figure
METAPHOR: a machine-learning-based method for the probability density estimation of photometric redshifts
A variety of fundamental astrophysical science topics require the determination of very accurate photometric redshifts (photo-z). A wide plethora of methods have been developed, based either on template models fitting or on empirical explorations of the photometric parameter space. Machine-learning-based techniques are not explicitly dependent on the physical priors and able to produce accurate photo-z estimations within the photometric ranges derived from the spectroscopic training set. These estimates, however, are not easy to characterize in terms of a photo-z probability density function (PDF), due to the fact that the analytical relation mapping the photometric parameters on to the redshift space is virtually unknown. We present METAPHOR (Machine-learning Estimation Tool for Accurate PHOtometric Redshifts), a method designed to provide a reliable PDF of the error distribution for empirical techniques. The method is implemented as a modular workflow, whose internal engine for photo-z estimation makes use of the MLPQNA neural network (Multi Layer Perceptron with Quasi Newton learning rule), with the possibility to easily replace the specific machine-learning model chosen to predict photo-z. We present a summary of results on SDSS-DR9 galaxy data, used also to perform a direct comparison with PDFs obtained by the LE PHARE spectral energy distribution template fitting. We show that METAPHOR is capable to estimate the precision and reliability of photometric redshifts obtained with three different self-adaptive techniques, I.e. MLPQNA, Random Forest and the standard K-Nearest Neighbors models
Oxycodone/Acetaminophen: The Tailoring Combination Treatment for Specific Clinical Profile of Opioid Well-Responsive Cancer Pain
Background: International guidelines recommend moderate-to-severe cancer pain to be treated with strong opioids. However, pain management remains an unsolved matter, at least in the demanding oncology and palliative care setting. Although cancer pain consists of multiple components, which interact in complex ways where combination therapy can better intercept multiple pain characteristics, few studies have used a non-opioid/opioid association to exploit possible synergistic actions. Even the efforts of a recent approach emphasizing appropriate pain assessment and accurate classification to obtain personalized pain management have not produced a satisfactory analgesic strategy.
Objective: This analysis was intended to evaluate the effectiveness of the immediate release fixed combination of oxycodone/acetaminophen (OxyIR/Par) for the treatment of moderate-to-severe intensity background pain used alone or in combination with other strong opioids in cancer patients with breakthrough cancer pain (BTcP). This is a secondary analysis of a wider observational, prospective, multicenter study [Italian Oncologic Pain multiSetting Multicentric Survey (IOPS-MS)] performed on 179 patients treated with opioids for cancer pain who received the fixed combination of oxycodone/acetaminophen (OxyIR/Par) for the treatment of background pain (BGP).
Results: Cancer patients with breakthrough cancer pain and controlled BGP (Background Pain) were classified according to the presence of analgesic therapy with tablets of fixed combination OxyIR/Par alone (group A, n=120) or tablets of fixed combination OxyIR/Par combined with other strong opioids (group B, n=59). Clinical features of group A were different to group B: higher mean Karnofsky Performance Status Index 70.3% (95% CI=67.2-73.5; median=70, CI=60-80) vs 58.3 (95% CI=53.4-63.2; median=50, CI=45-70) (P<0.001), and mainly group A patients were treated in an ambulatory setting (55.0% group A vs 33.9% group B) (p<0.001). Both groups had managed BGP with similar mean dosages (group A: 12.0, CI=10.5-13.4; group B: 13.1, CI=11.0-15.1) and frequencies of OxyIR/Par alone for group A and in association to other opioids for group B, but Breakthrough cancer Pain (BTcP) exhibited different characteristics in the two groups, showing a lower mean intensity numerical rating scale (NRS) of 7.5 (95% CI=7.2-7.7; median=7, CI=7-8 group A) vs 7.9 (95% CI=7.6, 8.2; median= 8, CI=7-9 group B) (P=0.04) and a higher percentage of patients had a faster onset, defined as the maximum intensity reached in less than 10 minutes, 81.7% (N=98) in group A vs 59.3% (n=35) in group B (P=0.002).
Conclusion: This is the first analysis about the efficacy of an immediate-release fixed combination of OxyIR/Par in the real world for moderate-to-severe background cancer pain and breakthrough cancer pain. The oral fixed combination OxyIR/Par provided an adequate level of analgesia for moderate-severe background cancer pain, in a different cohort of cancer patients with different performance status, both in ambulatory and palliative settings. The low dosage of fixed combination OxyIR/Par was effective alone or in association with other opioids
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