Search results for "methods"
showing 10 items of 4526 documents
A partially reflecting random walk on spheres algorithm for electrical impedance tomography
2015
In this work, we develop a probabilistic estimator for the voltage-to-current map arising in electrical impedance tomography. This novel so-called partially reflecting random walk on spheres estimator enables Monte Carlo methods to compute the voltage-to-current map in an embarrassingly parallel manner, which is an important issue with regard to the corresponding inverse problem. Our method uses the well-known random walk on spheres algorithm inside subdomains where the diffusion coefficient is constant and employs replacement techniques motivated by finite difference discretization to deal with both mixed boundary conditions and interface transmission conditions. We analyze the global bias…
'School adopts an experiment': the magnetic levitation of superconductors
2010
The event 'School adopts an experiment' is an event targeted at high schools and secondary schools. It is based on a tight and direct collaboration between researchers and school students and teachers. Several schools were involved in the event by 'adopting' an experiment in physics research laboratories. Groups of selected students were first trained by university researchers, then they demonstrated the experiments to other students and teachers during the event. Students who adopted an experiment acquired knowledge of the subjects connected with the experiment in a most impressive way compared with the usual didactics at school. Further positive points were: (i) to establish a close and d…
'School adopts an experiment': the photoluminescence in extra-virgin olive oil and in tonic water
2011
We report a laboratory activity, carried out along with high- and secondary-school students, that can be done to increase the interest of the young in scientific studies. Groups of selected students ‘adopted’ experiments at physics research laboratories, under the guidance of university researchers. Subsequently, the students demonstrated the experiments to the public at large during the annual science festival organized in Palermo by the association PalermoScienza, in collaboration with the University of Palermo. Experiments on the magnetic levitation of superconductors and on the photoluminescence of several substances were proposed. We discuss the experiment on photoluminescence as a cas…
Energy and radiative properties of the (3)Π1 and (5)Σ+1 states of RbCs: Experiment and theory
2017
We combined high-resolution Fourier-transform spectroscopy and large-scale electronic structure calculation to study energy and radiative properties of the high-lying $(3)^{1}\mathrm{\ensuremath{\Pi}}$ and $(5)^{1}\mathrm{\ensuremath{\Sigma}}^{+}$ states of the RbCs molecule. The laser-induced $(5)^{1}\mathrm{\ensuremath{\Sigma}}^{+},(4)^{1}\mathrm{\ensuremath{\Sigma}}^{+},(3)^{1}\mathrm{\ensuremath{\Pi}}\ensuremath{\rightarrow}A(2)^{1}\mathrm{\ensuremath{\Sigma}}^{+}\ensuremath{\sim} b(1)^{3}\mathrm{\ensuremath{\Pi}}$ fluorescence (LIF) spectra were recorded by the Bruker IFS-125(HR) spectrometer in the frequency range $\ensuremath{\nu}\ensuremath{\in}[5500,10\phantom{\rule{0.16em}{0ex}}00…
Electronic structure of Rf+ (Z=104) from ab initio calculations
2021
We report calculation of the energy spectrum and the spectroscopic properties of the superheavy element ion: ${\mathrm{Rf}}^{+}$. We use the four-component relativistic Dirac-Coulomb Hamiltonian and the multireference configuration interaction model to tackle the complex electronic structure problem that combines strong relativistic effects and electron correlation. We determine the energies of the ground and the low-lying excited states of ${\mathrm{Rf}}^{+}$, which originate from the $7{s}^{2}6{d}^{1},\phantom{\rule{0.28em}{0ex}}7{s}^{1}6{d}^{2},\phantom{\rule{0.28em}{0ex}}7{s}^{2}7{p}^{1}$, and $7{s}^{1}6{d}^{1}7{p}^{1}$ configurations. The results are discussed vis-\`a-vis the lighter h…
Tailored pump-probe transient spectroscopy with time-dependent density-functional theory: controlling absorption spectra
2016
Recent advances in laser technology allow us to follow electronic motion at its natural time-scale with ultra-fast time resolution, leading the way towards attosecond physics experiments of extreme precision. In this work, we assess the use of tailored pumps in order to enhance (or reduce) some given features of the probe absorption (for example, absorption in the visible range of otherwise transparent samples). This type of manipulation of the system response could be helpful for its full characterization, since it would allow us to visualize transitions that are dark when using unshaped pulses. In order to investigate these possibilities, we perform first a theoretical analysis of the non…
Systematic analysis of the peripherality of the Be10(d,p)Be11 transfer reaction and extraction of the asymptotic normalization coefficient of Be11 bo…
2018
We reanalyze the experiment of Schmitt et al. on the $^{10}\mathrm{Be}(d,p)^{11}\mathrm{Be}$ transfer reaction [Phys. Rev. Lett. 108, 192701 (2012)] by exploring the beam-energy and angular ranges at which the reaction is strictly peripheral. We consider the adiabatic distorted wave approximation (ADWA) to model the reaction and use a Halo-EFT description of $^{11}\mathrm{Be}$ to systematically explore the sensitivity of our calculations to the short-range physics of the $^{10}\mathrm{Be}\ensuremath{-}n$ wave function. We find that by selecting the data at low beam energy and forward scattering angle the calculated cross sections scale nearly perfectly with the asymptotic normalization coef…
ARGO-YBJ constraints on very high energy emission from GRBs
2009
The ARGO-YBJ (Astrophysical Radiation Ground-based Observatory at YangBaJing) experiment is designed for very high energy $\gamma$-astronomy and cosmic ray researches. Due to the full coverage of a large area ($5600 m^2$) with resistive plate chambers at a very high altitude (4300 m a.s.l.), the ARGO-YBJ detector is used to search for transient phenomena, such as Gamma-ray bursts (GRBs). Because the ARGO-YBJ detector has a large field of view ($\sim$2 sr) and is operated with a high duty cycle ($>$90%), it is well suited for GRB surveying and can be operated in searches for high energy GRBs following alarms set by satellite-borne observations at lower energies. In this paper, the sensitivit…
Application of dictionary learning to denoise LIGO’s blip noise transients
2020
Data streams of gravitational-wave detectors are polluted by transient noise features, or ``glitches,'' of instrumental and environmental origin. In this work we investigate the use of total variation methods and learned dictionaries to mitigate the effect of those transients in the data. We focus on a specific type of transient, ``blip" glitches, as this is the most common type of glitch present in the LIGO detectors and their waveforms are easy to identify. We randomly select 100 blip glitches scattered in the data from advanced LIGO's O1 run, as provided by the citizen-science project Gravity Spy. Our results show that dictionary-learning methods are a valid approach to model and subtrac…
Penning-trap-assisted study of excitations in Br88 populated in β decay of Se88
2017
Excited levels of $^{88}\mathrm{Br}$ populated in the $\ensuremath{\beta}$ decay of $^{88}\mathrm{Se}$ have been studied by means of $\ensuremath{\beta}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ spectroscopy methods. Neutron-rich parent $^{88}\mathrm{Se}$ nuclei were produced with proton-induced fission of $^{238}\mathrm{U}$ using the Ion Guide Isotope Separator On-Line (IGISOL) method and separated from contaminants using a dipole magnet and the coupled JYFLTRAP Penning trap at the Accelerator Laboratory of the University of Jyv\"askyl\"a. The level scheme of $^{88}\mathrm{Br}$ has been constructed and $logft$ values of levels were determined. The ground-state spin o…