ABSTRACT
We present a scenario for the formation and the morphology of the arrow-shaped dwarf irregular galaxy NGC 1427A in the Fornax Cluster. This galaxy shows intriguing stellar and gaseous tails ...pointing in different directions for which alternative but not conclusive formation scenarios have been proposed in the literature. We performed N-body/SPH simulations of dwarf galaxies falling into a model of the Fornax cluster, exhibiting a jellyfish-like appearance while undergoing ram-pressure stripping. We noted that some of our models show interesting tail morphologies similar to that of NGC 1427A. In this way, the peculiar NGC 1427A structure can be studied using models whose stellar and neutral gas photometry and kinematics are in good agreement with the observed ones, without the need of invoking an interaction with a nearby galaxy. Thanks to the tails, we can identify the requirements for a galaxy to expose such a structure and assess the possible position and velocity of the galaxy in the cluster. This puts constraints on the orbit of the galaxy, its position in the cluster and the time since its pericentre passage. From the statistics of identified snapshots following our modelling, we found that the most likely position of the galaxy is around 200 kpc in front of the cluster centre, travelling towards the cluster with a velocity angle with respect to the line-of-sight direction of around 50 deg. This analysis can be useful in future observations of similar galaxies in clusters to characterize their position and velocity in the cluster and their formation.
The intrinsic nature of noisy and complex data sets is often concealed in low-dimensional structures embedded in a higher dimensional space. Number of methodologies have been developed to extract and ...represent such structures in the form of manifolds (i.e. geometric structures that locally resemble continuously deformable intervals of Rj1). Usually a-priori knowledge of the manifold's intrinsic dimensionality is required. Additionally, their performance can often be hampered by the presence of a significant high-dimensional noise aligned along the low-dimensional core manifold. In real-world applications, the data can contain several low-dimensional structures of different dimensionalities. We propose a framework for dimensionality estimation and reconstruction of multiple noisy manifolds embedded in a noisy environment. To the best of our knowledge, this work represents the first attempt at detection and modelling of a set of coexisting general noisy manifolds by uniting two aspects of multi-manifold learning: the recovery and approximation of core noiseless manifolds and the construction of their probabilistic models. The easy-to-understand hyper-parameters can be manipulated to obtain an emerging picture of the multi-manifold structure of the data. We demonstrate the workings of the framework on two synthetic data sets, presenting challenging features for state-of-the-art techniques in Multi-Manifold learning. The first data set consists of multiple sampled noisy manifolds of different intrinsic dimensionalities, such as Möbius strip, toroid and spiral arm. The second one is a topologically complex set of three interlocked toroids. Given the absence of such unified methodologies in the literature, the comparison with existing techniques is organized along the two separate aspects of our approach mentioned above, namely manifold approximation and probabilistic modelling. The framework is then applied to a complex data set containing simulated gas volume particles from a particle simulation of a dwarf galaxy interacting with its host galaxy cluster. Detailed analysis of the recovered 1D and 2D manifolds can help us to understand the nature of Star Formation in such complex systems.
SuperAGILE: The hard X-ray imager for the AGILE space mission Feroci, M.; Costa, E.; Soffitta, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2007, Letnik:
581, Številka:
3
Journal Article
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Odprti dostop
SuperAGILE is a coded mask experiment based on silicon microstrip detectors. It operates in the 15–45
keV nominal energy range, providing crossed one-dimensional images of the X-ray sky with an ...on-axis angular resolution of 6
arcmin, over a field of view in excess of 1
sr. It was designed as the hard X-ray monitor of the AGILE space mission, a small satellite of the Italian Space Agency devoted to image the gamma-ray sky in the 30
MeV–50
GeV energy band. The AGILE mission was launched in a low-earth orbit on 23rd April 2007. In this paper we describe the SuperAGILE experiment, its construction and test processes, and its performance before flight, based on the on-ground test and calibrations.
Abstract Objective To increase fruit and vegetable (FV) consumption of youth in Body Quest: Food of the Warrior (BQ), a childhood obesity prevention program. Design Quasi-experimental. Setting ...Supplemental Nutrition Assistance Program–Education eligible schools (n = 60). Participants Third-grade students (n = 2,477). Intervention Treatment groups (n = 1,674) self-reported foods consumed through the School Lunch Program for 17 weekly assessments; they participated in BQ curriculum, iPad app education, and weekly FV tastings. Control groups (n = 803) completed only pre- and post-assessments. Main Outcome Measure Weekly FV consumed through School Lunch Program. Analysis ANCOVA and growth modeling. Results From before to after the program, the treatment group demonstrated significant, moderate increases in fruit ( P < .01) and vegetable ( P < .001) consumptions, increasing from 7 to 8 weekly FV servings. After the program, the treatment group consumed significantly ( P < .001) more FV than the control group. Fruit and vegetable consumption increased to class 10 and then stabilized. From before to after the program, all FV predictors were significantly higher and included gender (vegetables), race (FV), and free/reduced lunch (fruit). Conclusions and Implications Nutrition programs can increase FV intake. Even moderate increases in FV intake can be an initial step for the prevention of chronic disease.
Silicon drift detectors (SDD) of small dimensions (up to 1
cm
2) have been successfully employed in X-ray spectroscopy due to their small anode geometry, which allows to minimize the electronic noise ...due to the readout device. Many applications, however, require large sensitive areas to be covered (e.g. X-ray astronomy), so that these detectors are effectively impractical. We present the spectroscopic performance of a 53
cm
2 sensitive area, multi-anode SDD, measured at room temperature using an eight-channel readout setup. The measurements, taken using
55Fe and
241Am sources, and X-ray tubes generating energies down to 2
keV, show energy resolutions in the range 290–570
eV FWHM, at 20
°C, depending on the number of anodes collecting the signal. Further developments we are carrying out could improve the detector characteristics and allow to approach the performance of small area SDDs.
Abstract We analyzed the inactive nucleus of the main-belt comet 2010 LH15 at a true anomaly of 262°. Observations using the Gemini North Telescope in 2023 July yielded an absolute R -band magnitude ...of (18.4 ± 0.2) mag. Assuming a C-type geometric albedo and phase function, we estimated the nucleus radius to be (0.5 ± 0.1) km. The examination of the lightcurve profile did not yield clear evidence for a rotational period shorter than 2 hr.
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The Oxia Planum region has been chosen as the landing site for the future ESA ExoMars 2022 rover for both scientific value and engineering safety (Ivanov et al., 2020). The main goal of this work ...is the identification and measurement of boulders located over different areas of the Oxia Planum landing region to understand the generation/degradation processes that occurred over the studied area. For the boulders manual identification and counting, we use different HiRISE images and we calculate their size-frequency distribution and spatial density. The data are well-fitted with power-law and exponential curves with shallower indices in the Amazonian units, ranging from –4.03 to –4.74 for the power-law fit and from –1.43 to –1.80 for the exponential fit, while steeper indices in the three exhumed Noachian units studied (from –5.20 to ‒5.57 for the power-law fit and from –1.77 to –2.13 for the exponential fit). As previously studied in the former Oxia Planum landing centre (Pajola et al., 2017), the formation of boulders in this area is related to impact processes: the Amazonian unit is between 2.4 to 48.2 times richer of boulders than the exhumed Noachian units. By comparing these results with other boulder distributions, identified on other Oxia exhumed Noachian locations, we obtain a smaller boulder spatial density. We also compare our results with those derived from other Martian landing sites, finding that, for instance, the new centre location of the ExoMars ellipse is 4.5 times less dangerous than the Pathfinder landing site. The boulder analysis is of fundamental importance from an engineering perspective, returning the safest areas where the ExoMars 2022 rover might land and traverse.
Super-massive black holes in active galaxies can accelerate particles to relativistic energies, producing jets with associated -ray emission. Galactic 'microquasars', which are binary systems ...consisting of a neutron star or stellar-mass black hole accreting gas from a companion star, also produce relativistic jets, generally together with radio flares. Apart from an isolated event detected in Cygnus X-1, there has hitherto been no systematic evidence for the acceleration of particles to gigaelectronvolt or higher energies in a microquasar, with the consequence that we are as yet unsure about the mechanism of jet energization. Here we report four -ray flares with energies above 100 MeV from the microquasar Cygnus X-3 (an exceptional X-ray binary that sporadically produces radio jets). There is a clear pattern of temporal correlations between the -ray flares and transitional spectral states of the radio-frequency and X-ray emission. Particle acceleration occurred a few days before radio-jet ejections for two of the four flares, meaning that the process of jet formation implies the production of very energetic particles. In Cygnus X-3, particle energies during the flares can be thousands of times higher than during quiescent states.
Filamentary structures (one-dimensional manifolds) are ubiquitous in astronomical data sets. Be it in particle simulations or observations, filaments are always tracers of a perturbation in the ...equilibrium of the studied system and hold essential information on its history and future evolution. However, the recovery of such structures is often complicated by the presence of a large amount of background and transverse noise in the observation space. While the former is generally considered detrimental to the analysis, the latter can be attributed to measurement errors and it can hold essential information about the structure. To further complicate the scenario, one-dimensional manifolds (filaments) are generally non-linear and their geometry difficult to extract and model. Thus, in order to study hidden manifolds within the dataset, particular care has to be devoted to background noise removal and transverse noise modeling, while still maintaining accuracy in the recovery of their geometrical structure. We propose 1-DREAM: a toolbox composed of five main Machine Learning methodologies whose aim is to facilitate manifold extraction in such cases. Each methodology has been designed to address particular issues when dealing with complicated low-dimensional structures convoluted with noise and it has been extensively tested in previously published works. However, for the first time, in this work all methodologies are presented in detail, joint within a cohesive framework and demonstrated for three particularly interesting astronomical cases: a simulated jellyfish galaxy, a filament extracted from a simulated cosmic web and the stellar stream of Omega-Centauri as observed with the GAIA DR2. Two newly developed visualization techniques are also proposed, that take full advantage of the results obtained with 1-DREAM. This contribution presents the toolbox in all its details and the code is made publicly available to benefit the community. The controlled experiments on a purposefully built data set prove the accuracy of the pipeline in recovering the real underlying structures.
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•Toolbox with five semi-automated methods for manifold extraction and modeling.•Background noise removal;•Transverse noise attenuation;•Point-dimensionality estimation;•Manifold’s mean curve extraction and corresponding transverse noise modeling.•Two visualization approaches to represent information on extracted manifolds.•Global: Bi-dimensional profile. Information shown along main manifold’s directions;•Local: coherent orthonormal coordinate frames. Orthogonal plane shifted along length.•Demonstration of the toolbox to three interesting astronomical cases.•Simulated dwarf galaxy with elongated arms.•Extracted simulated cosmic web filament.•Omega-Centauri stream as observed via the GAIA DR2.
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