3,817 research outputs found
Codice per il calcolo della pericolositĂ sismica da dati di sito: SASHA (Site Approach to Seismic Hazard Assessment)
Viene presentato il codice di calcolo SASHA che implementa l’approccio probabilistico proposto da Albarello e Mucciarelli (2002) alla stima della pericolosità sismica in termini di intensità macrosismica. Elemento chiave della metodologia è la storia sismica locale, ovvero i risentimenti documentati al sito dei terremoti passati eventualmente integrati da risentimenti “virtuali” dedotti a partire da dati epicentrali. La procedura (approccio “di sito”), appositamente sviluppata per l’analisi di dati di intensità , consente di utilizzare in modo formalmente corretto la grande quantità di informazioni macrosismiche disponibili in paesi come l’Italia.
Oltre al presente testo, nel quale è descritto in dettaglio l’utilizzo del programma (metodologia, opzioni di calcolo, formato dei file di input/output), vengono allegati l’eseguibile di SASHA e un esempio dei file di input (catalogo epicentrale e dei risentimenti macrosismici, elenco di località ) e output
Spin-based quantum gating with semiconductor quantum dots by bichromatic radiation method
A potential scheme is proposed for realizing a two-qubit quantum gate in
semiconductor quantum dots. Information is encoded in the spin degrees of
freedom of one excess conduction electron of each quantum dot. We propose to
use two lasers, radiation two neighboring QDs, and tuned to blue detuning with
respect to the resonant frequencies of individual excitons. The two-qubit phase
gate can be achieved by means of both Pauli-blocking effect and dipole-dipole
coupling between intermediate excitonic states.Comment: Europhysics Letters 66 (2004) 1
Timing the millisecond pulsars in 47 Tucanae
In the last 10 years 20 millisecond pulsars have been discovered in the
globular cluster 47 Tucanae. Hitherto, only 3 of these had published timing
solutions. Here we improve upon these 3 and present 12 new solutions. These
measurements can be used to determine a variety of physical properties of the
pulsars and of the cluster. The 15 pulsars have positions determined with
typical uncertianties of only a few milliarcsec and they are all located within
1.2 arcmin of the cluster centre. We have also measured the proper motions of 5
of the pulsars, which are consistent with the proper motion of 47 Tuc based on
Hipparcos data. The period derivatives measured for many of the pulsars are
dominated by the dynamical effects of the cluster gravitational field, and are
used to constrain the surface mass density of the cluster. All pulsars have
characteristic ages T > 170 Myr and magnetic fields B < 2.4e9 Gauss, and the
average T > 1 Gyr. We have measured the rate of advance of periastron for the
binary pulsar J0024-7204H, implying a total system mass 1.4+-0.8 solar masses.Comment: 17 pages, 11 included figures, accepted for publication in MNRA
Confronto fra stime di pericolositĂ sismica in Italia
Allo scopo di valutare l’attendibilità delle stime di pericolosità sismica recentemente proposte per l’Italia sulla base
di un approccio standard basato sull’impiego di informazioni geologiche (zone sismogenetiche) e sismologiche
(catalogo sismico epicentrale), viene proposto un confronto con stime di pericolosità effettuate a partire dall’analisi
statistica delle storie sismiche di sito relative alle 1401 localitĂ per le quali esistono informazioni circa glie effetti
macrosismici osservati in occasione di almeno dieci terremoti del passato. In particolare, sono stati messi a
confronto i valori dell’accelerazione massima orizzontale del moto del suolo corrispondente ad una probabilità di
eccedenza del 10% in 50 anni dedotti con l’approccio standard, con i valori dell’intensità macrosismica
corrispondente alle stesse probabilitĂ di eccedenza per un tempo di ritorno di 50 anni. Il confronto, effettuato con
una procedura non parametrica che non richiede l’impiego relazioni di conversione empiriche, indica che le
differenze osservate sono fortemente correlate con la geometria delle zone sismotettoniche utilizzate nell’approccio
standard. In particolare, la zonazione sembra incompleta (sembrano esistere zone “nascoste”) e a tratti troppo
grossolana (a causa della scarsitĂ dei dati disponibili) per rappresentare adeguatamente i processi sismogenici attivi
nell’area italiana
Non-linear matter power spectrum from Time Renormalisation Group: efficient computation and comparison with one-loop
We address the issue of computing the non-linear matter power spectrum on
mildly non-linear scales with efficient semi-analytic methods. We implemented
M. Pietroni's Time Renormalization Group (TRG) method and its Dynamical 1-Loop
(D1L) limit in a numerical module for the new Boltzmann code CLASS. Our
publicly released module is valid for LCDM models, and optimized in such a way
to run in less than a minute for D1L, or in one hour (divided by number of
nodes) for TRG. A careful comparison of the D1L, TRG and Standard 1-Loop
approaches reveals that results depend crucially on the assumed initial
bispectrum at high redshift. When starting from a common assumption, the three
methods give roughly the same results, showing that the partial resumation of
diagrams beyond one loop in the TRG method improves one-loop results by a
negligible amount. A comparison with highly accurate simulations by M. Sato &
T. Matsubara shows that all three methods tend to over-predict non-linear
corrections by the same amount on small wavelengths. Percent precision is
achieved until k~0.2 h/Mpc for z>2, or until k~0.14 h/Mpc at z=1.Comment: 24 pages, 7 figures, revised title and conclusions, version accepted
in JCAP, code available at http://class-code.ne
Observation of spin Coulomb drag in a two-dimensional electron gas
An electron propagating through a solid carries spin angular momentum in
addition to its mass and charge. Of late there has been considerable interest
in developing electronic devices based on the transport of spin, which offer
potential advantages in dissipation, size, and speed over charge-based devices.
However, these advantages bring with them additional complexity. Because each
electron carries a single, fixed value (-e) of charge, the electrical current
carried by a gas of electrons is simply proportional to its total momentum. A
fundamental consequence is that the charge current is not affected by
interactions that conserve total momentum, notably collisions among the
electrons themselves. In contrast, the electron's spin along a given spatial
direction can take on two values, "up" and "down", so that the spin current and
momentum need not be proportional. Although the transport of spin polarization
is not protected by momentum conservation, it has been widely assumed that,
like the charge current, spin current is unaffected by electron-electron (e-e)
interactions. Here we demonstrate experimentally not only that this assumption
is invalid, but that over a broad range of temperature and electron density,
the flow of spin polarization in a two-dimensional gas of electrons is
controlled by the rate of e-e collisions
Présence de chimiorécepteurs sur l'aile des tsé-tsé (Diptera : Glossinidae)
Cette note signale pour la première fois l'existence de chimiorécepteurs sur les ailes des mouches tsé-tsé. Ceux-ci sont principalement localisés sur le milieu de la nervure costale. Leur morphologie est comparable à celle des chimiorécepteurs observés sur les pattes. Leur nombre ne différe pas entre les sexes comme pour les pattes, mais entre les espèces. Ceci suggère un rôle dans la perception chimique proche de l'environnement, par rapport aux chimiorécepteurs des pattes qui semblent impliqués dans le comportement sexuel. L'étude a été conduite sur six espèces ou sous-espèces de glossines. (Résumé d'auteur
- …