75 research outputs found
Fully dynamic clustering and diversity maximization in doubling metrics
We present approximation algorithms for some variants of center-based
clustering and related problems in the fully dynamic setting, where the
pointset evolves through an arbitrary sequence of insertions and deletions.
Specifically, we target the following problems: -center (with and without
outliers), matroid-center, and diversity maximization. All algorithms employ a
coreset-based strategy and rely on the use of the cover tree data structure,
which we crucially augment to maintain, at any time, some additional
information enabling the efficient extraction of the solution for the specific
problem. For all of the aforementioned problems our algorithms yield
-approximations, where is the best known
approximation attainable in polynomial time in the standard off-line setting
(except for -center with outliers where but we get a
-approximation) and is a user-provided
accuracy parameter. The analysis of the algorithms is performed in terms of the
doubling dimension of the underlying metric. Remarkably, and unlike previous
works, the data structure and the running times of the insertion and deletion
procedures do not depend in any way on the accuracy parameter
and, for the two -center variants, on the parameter . For spaces of
bounded doubling dimension, the running times are dramatically smaller than
those that would be required to compute solutions on the entire pointset from
scratch. To the best of our knowledge, ours are the first solutions for the
matroid-center and diversity maximization problems in the fully dynamic
setting
Administration of Aloe arborescens homogenate to cattle: interaction with rumen fermentation and gut absorption of aloin
Aloe has long been used as a traditional medicine for its numerous beneficial properties, which are mainly ascribed to β-polysaccharides and phenolic compounds including anthraquinones, anthrones and chromones. However, few studies on large animals are currently available. The effect of whole leaf Aloe arborescens homogenate on the in vitro rumen fermentative processes was tested using alfalfa hay and barley meal as substrates. The Aloe homogeneate was added at three different concentrations (0.4, 2.0 and 10.0 g L−1 of fermentation liquid). The same homogenate was dosed (200 g) orally and through the rumen cannula to three rumen cannulated heifers and orally to six lactating dairy cows to measure the rumen degradation of aloin and the transfer of aloin from the gut into the blood, respectively. The Aloe homogenate did not affect in vitro rumen fermentations and feed digestibility. The administration of Aloe homogenate did not negatively affect animal feed intake and health neither on the cannulated heifers nor on the dairy cows. Aloin underwent a rapid degradation in the rumen milieu, and became undetectable 2 h after oral dosage. However, when Aloe homogenate was administered to dairy cows, aloin appeared in blood as early as 2 h after administration, reached a maximum after 4 h (6.2 ± 5.8 μg L−1) and progressively decreased thereafter. These results suggest that Aloe compounds can be absorbed into the blood and encourage the study of Aloe as a potential nutraceutical in ruminants. Further studies should determine the most effective in vivo dosage
A Python approach for solar data analysis: SUNDARA (SUNDish Active Region Analyser), preliminary development
This technical note describes the Python package SUNDARA (SUNDish Active Region Analyser), a sophisticated code - fully self-consistent - aimed at the data analysis of solar images.
This analysis is crucial for the INAF Proposal "SunDish Project" (PI: A. Pellizzoni), active since 2018 and devoted to imaging and monitoring the solar atmosphere at high radio frequencies (at present 18 - 26 GHz) through single-dish observations with INAF radio telescopes (SRT and Medicina).
SUNDARA, characterised by a very user-friendly widget, allows to automatically unearth Active Regions (ARs) across the solar disk (or on its edge) through several algorithms; these ARs are modelled through an elliptical 2D-Gaussian kernel.
In little more than 5 minutes, SUNDARA produces a complete analysis of a solar map, saving a directory containing images, plots and several tables with physical information of the solar disk and ARs (brightness temperatures, fluxes and spectral indices, with respective errors).
A deeper analysis (that can be completed in a few hours) is possible thanks to a Bayesian approach based on Markov Chain MonteCarlo (MCMC) simulations.
Moreover, these identified ARs are automatically associate in position with the detected ARs at other observing frequencies, reported in the Heliophysics Event Knowledgebase (HEK) used by the astrophysics and solar physics communities.
SUNDARA has been successfully tested on a large amount of data from solar maps implemented with the radio telescopes of the INAF Network.
For the purposes of this technical note, we report only two cases (one for Medicina, and one for SRT).
This Python package constitutes a crucial tool for the INAF Network to analyse solar images (the Space Weather monitoring network and forecast along the solar cycle will be soon available), and to provide a complete overview of the astrophysical phenomena
On the evolution of the Gamma- and X-ray luminosities of Pulsar Wind Nebulae
Pulsar wind nebulae are a prominent class of very high energy (E > 0.1 TeV)
Galactic sources. Their Gamma-ray spectra are interpreted as due to inverse
Compton scattering of ultrarelativistic electrons on the ambient photons,
whereas the X-ray spectra are due to synchrotron emission. We investigate the
relation between the Gamma- and-X-ray emission and the pulsars' spin-down
luminosity and characteristic age. We find that the distance-independent Gamma-
to X-ray flux ratio of the nebulae is inversely proportional to the spin-down
luminosity, (\propto \dot{E}^-1.9), while it appears proportional to the
characteristic age, (\propto tau_c^2.2), of the parent pulsar. We interpret
these results as due to the evolution of the electron energy distribution and
the nebular dynamics, supporting the idea of so-called relic pulsar wind
nebulae. These empirical relations provide a new tool to classify unidentified
diffuse Gamma-ray sources and to estimate the spin-down luminosity and
characteristic age of rotation powered pulsars with no detected pulsation from
the X- and Gamma-ray properties of the associated pulsar wind nebulae. We apply
these relations to predict the spin-down luminosity and characteristic age of
four (so far unpulsing) candidate pulsars associated to wind nebulae.Comment: Accepted for publication in ApJ (6 pages, 2 figures
SGR 0418+5729: a low-magnetic-field magnetar
Soft gamma-ray repeaters and anomalous X-ray pulsars are a small (but
growing) group of X-ray sources characterized by the emission of short bursts
and by a large variability in their persistent flux. They are believed to be
magnetars, i.e. neutron stars powered by extreme magnetic fields 1E14-1E15 G).
We found evidence for a magnetar with a low magnetic field, SGR 0418+5729,
recently detected after it emitted bursts similar to those of soft gamma-ray
repeaters. New X-ray observations show that its dipolar magnetic field cannot
be greater than 8E12 G, well in the range of ordinary radio pulsars, implying
that a high surface dipolar magnetic field is not necessarily required for
magnetar-like activity. The magnetar population may thus include objects with a
wider range of magnetic-field strengths, ages and evolutionary stages than
observed so far.Comment: 4 pages, 2 figures; to appear in the Proceedings of the Pulsar
Conference 2010, Chia, Sardinia (Italy), 10-15 October 201
Spotting local environments in self-assembled monolayer-protected gold nanoparticles
Organic-inorganic (O-I) nanomaterials are versatile platforms for an incredible high number of applications, ranging from heterogeneous catalysis, molecular sensing, cell targeting, imaging, cancer diagnosis and therapy, just to name a few. Much of their potential stems from the unique control of organic environments around inorganic sites within a single O-I nanomaterial, which allows for new properties inaccessible using purely organic or inorganic materials. Structural and mechanistic characterization plays a key role in understanding and rationally designing such hybrid nanoconstructs. Here, we introduce a general methodology to identify and classify local (supra)molecular environments in an archetypal class of O-I nanomaterials, i.e. self-assembled monolayer-protected gold nanoparticles (SAM-AuNPs). By using an atomistic machine-learning guided workflow based on the Smooth Overlap of Atomic Positions (SOAP) descriptor, we analyze a collection of chemically different SAM-AuNPs, and detect and compare local environments in a way that is agnostic and automated, i.e. with no need of a-priori information and minimal user intervention. In addition, the computational results coupled with experimental electron spin resonance measurements prove that is possible to have more than one local environment inside SAMs, being thickness of the organic shell and solvation primary factors in determining number and nature of multiple co-existing environments. These indications are extended to complex mixed hydrophilic-hydrophobic SAMs. This work demonstrates that it is possible to spot out and compare local molecular environments in SAM-AuNPs exploiting atomistic machine-learning approaches, establishes ground rules to control them, and holds the potential for rational design of O-I nanomaterials instructed from data
A multi-wavelength pipeline for pulsar observations
The Astronomical Observatory in Cagliari (OAC) is a growing facility with a group devoted to pulsar studies across the electromagnetic spectrum. Taking advantage of this expertise we have worked to provide a suite of multi-wavelength software and databases for the observations of pulsars and compact Galactic objects at the Sardinia Radio Telescope (SRT, Bolli et al. 2015, Prandoni et al. 2017)
A dedicated pipeline to analyse solar data with INAF radio telescopes: SUNPIT (SUNdish PIpeline Tool)
This technical note describes SUNPIT (SUNdish PIpeline Tool) - the pipeline aimed at the imaging procedure and the data analysis of the radio solar data - and guides the user to properly reduce and analyse the solar data.
SUNPIT is designed for radio data acquired with some radio telescopes of the INAF Network: the Sardinia Radio Telescope (SRT), and the Medicina Radio Telescope.
The present user manual follows the development of software for solar imaging and data analysis of Active Regions (ARs), performed in the framework of the INAF Proposal "SunDish Project" (PI: A. Pellizzoni).
This project has been active since 2018 with the goal of monitoring the solar atmosphere at high radio frequencies (at present 18 - 26 GHz) through single-dish observations.
These solar observations will be enhanced through the upgrading of SRT with the new cryogenically cooled receivers, including a 19-feed in Q-band (33 - 50 GHz) and a 16-feed in W-band (75 - 116 GHz), in the context of the National Operative Programme (Programma Operativo Nazionale-PON); this project will provide in the near future an upgrading with the new receivers up to 116 GHz also for the Medicina and Noto Radio Telescopes, to provide the scientific community with the instrumentation suited to the study of the Universe at high radio frequencies.
SUNPIT will be suitable for the data of these new forthcoming receivers, when available for the scientific community.
SUNPIT produces a complete analysis of a solar map in about one hour, saving a directory which contains images, plots and several tables with the physical information of the solar disk and ARs (brightness temperatures, fluxes and spectral indices, with the respective errors).
This pipeline – successfully tested – represents a crucial tool (1) to analyse solar images observed with the radio telescopes of the INAF Network, and (2) for the Space Weather monitoring network and forecast (soon available) along the solar cycle
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