139 research outputs found
An efficient iterative solution method for the Chebyshev collocation of advection-dominated transport problems
A new Chebyshev collocation algorithm is proposed for the iterative solution of advection-diffusion problems. The main features of the method lie in the original way in which a finite-difference preconditioner is built and in the fact that the solution is collocated on a set of nodes matching the standard Gauss-Lobatto-Chebyshev set only in the case of pure diffusion problems. The key point of the algorithm is the capability of the preconditioner to represent the high-frequency modes when dealing with advection-dominated problems. The basic idea is developed for a one-dimensional case and is extended to two-dimensional problems. A series of numerical experiments is carried out to demonstrate the efficiency of the algorithm. The proposed algorithm can also be used in the context of the incompressible Navier-Stokes equations
Numerical simulations on laser absorption enhancement in hybrid metallo-dielectric nanostructured targets for future nuclear astrophysics experiments
The linear electromagnetic interaction between innovative hybrid metallo-dielectric nanostructured targets and laser in visible and IR range is investigated through numerical simulations. The obtained results rely on the optimization of a target based on metallic nanowires (NWs) to enhance light absorption in the visible range of the electromagnetic spectrum. The NWs are grown within the ordered nanoholes of an alumina substrate, thus, forming a plasmonic lattice with triangular symmetry. The remaining volume of the nanoholes on top of the NWs is sealed with a transparent layer of aluminum oxide that is suitable to be chemically modified for containing about 25% of deuterium atoms. The study presented here is carried out within the framework of a scientific program named PLANETA (Plasmonic Laser Absorption on Nano-Engineered Targets) aiming at investigating new laser–matter interaction schemes in the ns domain and for nuclear fusion purposes, involving especially the D–D reaction
Multi-GeV Electron Spectrometer
The advance in laser plasma acceleration techniques pushes the regime of the
resulting accelerated particles to higher energies and intensities. In
particular the upcoming experiments with the FLAME laser at LNF will enter the
GeV regime with almost 1pC of electrons. From the current status of
understanding of the acceleration mechanism, relatively large angular and
energy spreads are expected. There is therefore the need to develop a device
capable to measure the energy of electrons over three orders of magnitude (few
MeV to few GeV) under still unknown angular divergences. Within the PlasmonX
experiment at LNF a spectrometer is being constructed to perform these
measurements. It is made of an electro-magnet and a screen made of
scintillating fibers for the measurement of the trajectories of the particles.
The large range of operation, the huge number of particles and the need to
focus the divergence present unprecedented challenges in the design and
construction of such a device. We will present the design considerations for
this spectrometer and the first results from a prototype.Comment: 7 pages, 6 figures, submitted to NIM
Experimental determination of the energy dependence of the rate of the muon transfer reaction from muonic hydrogen to oxygen for collision energies up to 0.1 eV
We report the first experimental determination of the collision-energy
dependence of the muon transfer rate from the ground state of muonic hydrogen
to oxygen at near-thermal energies. A sharp increase by nearly an order of
magnitude in the energy range 0 - 70 meV was found that is not observed in
other gases. The results set a reliable reference for quantum-mechanical
calculations of low-energy processes with exotic atoms, and provide firm ground
for the measurement of the hyperfine splitting in muonic hydrogen and the
determination of the Zemach radius of the proton by the FAMU collaboration.Comment: 30 pages, 10 figure
Experimental determination of the energy dependence of the rate of the muon transfer reaction from muonic hydrogen to oxygen for collision energies up to 0.1 eV
Design and implementation of the new scintillation light detection system of ICARUS T600
ICARUS T600 is the far detector of the Short Baseline Neutrino program at
Fermilab(USA), which foresees three Liquid Argon Time Projection Chambers along
the Booster Neutrino Beam line to search for LSND-like sterile neutrino signal.
The T600 detector underwent a significant overhauling process at CERN,
introducing new technological developments while maintaining the already
achieved performances. The realization of a new liquid argon scintillation
light detection system is a primary task of the detector overhaul. As the
detector will be subject to a huge flux of cosmic rays, the light detection
system should allow the 3D reconstruction of events contributing to the
identification of neutrino interactions in the beam spill gate. The design and
implementationof the new scintillation light detection system of ICARUS T600 is
described
Threatened and extinct amphibians and reptiles in Italian natural history collections are useful conservation tools
Natural history museums are irreplaceable tools to study and preserve the biological diversity around the globe and among the primary actors in the recognition of species and the logical repositories for their type specimens. In this paper we surveyed the consistency of the preserved specimens of amphibians and reptiles housed in the major Italian scientific collections, and verified the presence of threatened species according to the IUCN Red List, includ-ing the Extinct (EX), Extinct in the Wild (EW), Critically Endangered (CR), Endangered (EN), and Vulnerable (VU) categories. Altogether, we analyzed 39 Italian zoological collections. We confirmed the presence of one extinct reptile (Chioninia coctei) and five extinct or extinct in the wild amphibian species (Atelopus longirostris, Nectophrynoides asperginis, Pseudophilautus leucorhinus, P. nasutus, and P. variabilis). Seven CR amphibians, fourteen CR reptile species and the extinct skink C. coctei are shared by more than one institution. Museums which host the highest number of threatened and extinct amphibian species are respectively Turin (17 CR and 1 EX), Florence (13 CR and 1 EX), and Trento (15 CR and 1 EW), while for reptiles the richest museums are those from Genoa (15 CR and 1 EX), Florence (11 CR and 1 EX), and Pisa (7 CR). Finally, we discussed the utility of natural history museums and the strategies to follow for the implementation of their functionality. © Firenze University Press
First measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen
We report the first measurement of the temperature dependence of muon transfer rate from muonic hydrogen atoms to oxygen between 100 and 300 K. Data were obtained from the X-ray spectra of delayed events in a gaseous target, made of a H2/O2 mixture, exposed to a muon beam. This work sets constraints on theoretical models of muon transfer and is of fundamental importance for the measurement of the hyperfine splitting of muonic hydrogen ground state as proposed by the FAMU collaboration
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