Search results for "methods [Diffusion Tensor Imaging]"
showing 10 items of 992 documents
Deep learning for multimessenger core-collapse supernova detection
2020
The detection of gravitational waves from core-collapse supernova (CCSN) explosions is a challenging task, yet to be achieved, in which it is key the connection between multiple messengers, including neutrinos and electromagnetic signals. In this work, we present a method for detecting these kind of signals based on machine learning techniques. We tested its robustness by injecting signals in the real noise data taken by the Advanced LIGO-Virgo network during the second observation run, O2. We trained a newly developed Mini-Inception Resnet neural network using time-frequency images corresponding to injections of simulated phenomenological signals, which mimic the waveforms obtained in 3D n…
Using the transit of Venus to probe the upper planetary atmosphere
2015
The atmosphere of a transiting planet shields the stellar radiation providing us with a powerful method to estimate its size and density. In particular, because of their high ionization energy, atoms with high atomic number (Z) absorb short-wavelength radiation in the upper atmosphere, undetectable with observations in visible light. One implication is that the planet should appear larger during a primary transit observed in high energy bands than in the optical band. The last Venus transit in 2012 offered a unique opportunity to study this effect. The transit has been monitored by solar space observations from Hinode and Solar Dynamics Observatory (SDO). We measure the radius of Venus duri…
Relativistic Positioning Systems: current status
2009
A {\em relativistic positioning system} consists in a set of four clocks broadcasting their respective proper time by means of light signals. Among them, the more important ones are the {\em auto-located positioning systems,} in which every clock broadcasts not only its proper time but also the proper times that it receives from the other three. At this level, no reference to any exterior system (the Earth surface, for example) and no synchronization are needed. The current status of the theory of relativistic positioning systems is sketched.
Non-linear cosmological collapse of quintessence
2015
We present a study of the fully relativistic spherical collapse in presence of quintessence using on Numerical Relativity, following the method proposed by the authors in a previous article [arXiv:1409.3476]. We ascertain the validity of the method by studying the evolution of a spherically symmetric quintessence inhomogeneity on a de Sitter background and we find that it has an impact on the local expansion around the centre of coordinates. We then proceed to compare the results of our method to those of the more largely adopted top-hat model. We find that quintessence inhomogeneities do build up under the effect that matter inhomogeneities have on the local space-time yet remain very smal…
Denoising of gravitational-wave signal GW150914 via total-variation methods
2016
We apply a regularized Rudin-Osher-Fatemi total variation (TV) method to denoise the transient gravitational wave signal GW150914. We have previously applied TV techniques to denoise numerically generated grav- itational waves embedded in additive Gaussian noise, obtaining satisfactory results irrespective of the signal morphology or astrophysical origin. We find that the non-Gaussian, non-stationary noise from the gravitational wave event GW150914 can also be successfully removed with TV-denoising methods. The quality of the de- noised waveform is comparable to that obtained with the Bayesian approach used in the discovery paper [1]. TV-denoising techniques may thus offer an additional via…
The thermal neutron capture cross section of the radioactive isotope $^{60}$Fe
2015
50% of the heavy element abundances are produced via slow neutron capture reactions in different stellar scenarios. The underlying nucleosynthesis models need the input of neutron capture cross sections. One of the fundamental signatures for active nucleosynthesis in our galaxy is the observation of long-lived radioactive isotopes, such as $^{60}$Fe with a half-life of $2.60\times10^6$ yr. To reproduce this $\gamma$-activity in the universe, the nucleosynthesis of $^{60}$Fe has to be understood reliably. A $^{60}$Fe sample produced at the Paul-Scherrer-Institut was activated with thermal and epithermal neutrons at the research reactor at the Johannes Gutenberg-Universit\"at Mainz. The therm…
Testing the X-IFU calibration requirements: an example for quantum efficiency and energy resolution
2018
With its array of 3840 Transition Edge Sensors (TESs) operated at 90 mK, the X-Ray Integral Field Unit (X-IFU) on board the ESA L2 mission Athena will provide spatially resolved high-resolution spectroscopy (2.5 eV FWHM up to 7 keV) over the 0.2 to 12 keV bandpass. The in-flight performance of the X-IFU will be strongly affected by the calibration of the instrument. Uncertainties in the knowledge of the overall system, from the filter transmission to the energy scale, may introduce systematic errors in the data, which could potentially compromise science objectives - notably those involving line characterisation e.g. turbulence velocity measurements - if not properly accounted for. Defining…
Autonomous on-board data processing and instrument calibration software for the SO/PHI
2018
The extension of on-board data processing capabilities is an attractive option to reduce telemetry for scientific instruments on deep space missions. The challenges that this presents, however, require a comprehensive software system, which operates on the limited resources a data processing unit in space allows. We implemented such a system for the Polarimetric and Helioseismic Imager (PHI) on-board the Solar Orbiter (SO) spacecraft. It ensures autonomous operation to handle long command-response times, easy changing of the processes after new lessons have been learned and meticulous book-keeping of all operations to ensure scientific accuracy. This contribution presents the requirements a…
An experiment to study the structure of the focal volume in apertured focusing systems
2001
We present a simple experiment, specifically designed for students of undergraduate optics courses, where the influence of an aperture stop position on the three-dimensional structure of the focal volume of focusing systems is studied. The experiment, which involves only simple optical elements, permits an undergraduate student to generate different focal structures by simply axially displacing the aperture stop.
Dense matter with eXTP
2019
In this White Paper we present the potential of the Enhanced X-ray Timing and Polarimetry (eXTP) mission for determining the nature of dense matter; neutron star cores host an extreme density regime which cannot be replicated in a terrestrial laboratory. The tightest statistical constraints on the dense matter equation of state will come from pulse profile modelling of accretion-powered pulsars, burst oscillation sources, and rotation-powered pulsars. Additional constraints will derive from spin measurements, burst spectra, and properties of the accretion flows in the vicinity of the neutron star. Under development by an international Consortium led by the Institute of High Energy Physics o…