3,311 research outputs found
Antiproton annihilation on light nuclei at very low energies
The recent experimental data obtained by the OBELIX group on D and
He total annihilation cross sections are analyzed. The combined
analysis of these data with existing antiprotonic atom data allows, for the
first time, the imaginary parts of the S-wave scattering lengths for the two
nuclei to be extracted. The obtained values are: for D and for He. This
analysis indicates an unexpected behaviour of the imaginary part of the
-nucleus S-wave scattering length as a function of the atomic weight
A: (p) > (D) > (He).Comment: 13 pages, 5 figure
Inversion of electrical conductivity data with Tikhonov regularization approach: some considerations
Electromagnetic induction measurements, which are generally used to determine lateral variations of apparent
electrical conductivity, can provide quantitative estimates of the subsurface conductivity at different depths.
Quantitative inference about the Earth’s interior from experimental data is, however, an ill-posed problem. Using
the generalised McNeill’s theory for the EM38 ground conductivity meter, we generated synthetic apparent
conductivity curves (input data vector) simulating measurements at different heights above the soil surface. The
electrical conductivity profile (the Earth model) was then estimated solving a least squares problem with Tikhonov
regularization optimised with a projected conjugate gradient algorithm. Although the Tikhonov approach improves
the conditioning of the resulting linear system, profile reconstruction can be surprisingly far from the desired true
one. On the contrary, the projected conjugate gradient provided the best solution without any explicit regularization
(a = 0) of the objective function of the least squares problem. Also, if the initial guess belongs to the image of the
system matrix, Im(A), we found that it provides a unique solution in the same subspace Im(A)
Inversion of electrical conductivity data with Tikhonov regularization approach: some considerations
Electromagnetic induction measurements, which are generally used to determine lateral variations of apparent
electrical conductivity, can provide quantitative estimates of the subsurface conductivity at different depths.
Quantitative inference about the Earth's interior from experimental data is, however, an ill-posed problem. Using
the generalised McNeill's theory for the EM38 ground conductivity meter, we generated synthetic apparent
conductivity curves (input data vector) simulating measurements at different heights above the soil surface. The
electrical conductivity profile (the Earth model) was then estimated solving a least squares problem with Tikhonov
regularization optimised with a projected conjugate gradient algorithm. Although the Tikhonov approach improves
the conditioning of the resulting linear system, profile reconstruction can be surprisingly far from the desired true
one. On the contrary, the projected conjugate gradient provided the best solution without any explicit regularization
( a= 0) of the objective function of the least squares problem. Also, if the initial guess belongs to the image of the
system matrix, Im(A), we found that it provides a unique solution in the same subspace Im(A)
Limits on the low energy antinucleon-nucleus annihilations from the Heisenberg principle
We show that the quantum uncertainty principle puts some limits on the
effectiveness of the antinucleon-nucleus annihilation at very low energies.
This is caused by the fact that the realization a very effective short-distance
reaction process implies information on the relative distance of the reacting
particles. Some quantitative predictions are possible on this ground, including
the approximate A-independence of antinucleon-nucleus annihilation rates.Comment: 10 pages, no figure
Synchronous byzantine lattice agreement in O(log(f)) rounds
In the Lattice Agreement (LA) problem, originally proposed by Attiya et al. [1], a set of processes has to decide on a chain of a lattice. More precisely, each correct process proposes an element e of a certain join-semi lattice L and it has to decide on a value that contains e. Moreover, any pair pi, pj of correct processes has to decide two values deci and decj that are comparable (e.g., deci = decj or decj < deci). In this paper we present new contributions for the synchronous case. We investigate the problem in the usual message passing model for a system of n processes with distinct unique IDs. We first prove that, when only authenticated channels are available, the problem cannot be solved if f = n/3 or more processes are Byzantine. We then propose a novel algorithm that works in a synchronous system model with signatures (i.e., the authenticated message model), tolerates up to f byzantine failures (where f < n/3) and that terminates in O(log f) rounds. We discuss how to remove authenticated messages at the price of algorithm resiliency (f < n/4). Finally, we present a transformer that converts any synchronous LA algorithm to an algorithm for synchronous Generalised Lattice Agreement
La librettologia, crocevia interdisciplinare : problemi e prospettive
Gli studi sulla librettistica hanno conosciuto negli ultimi decenni un significativo sviluppo, pi\uf9 rilevante dalla prospettiva musicologica che non da quelle storico-letteraria e storico-linguistica; la prospettiva filologica, relativa anche al testo verbale oltre che a quello musicale, \ue8 stata seguita e sviluppata a sua volta pi\uf9 dai musicologi che dai filologi e dagli storici della letteratura. Anche dalla documentazione lessicografica del termine librettologia, solo in parte sinonimo di librettistica, la prospettiva musicologica risulta prevalente. Questo volume, che riporta gli atti del convegno dallo stesso titolo svoltosi all\u2019Universit\ue0 degli Studi di Milano nel giugno del 2018, con la partecipazione di musicologi, storici della letteratura, storici della lingua e studiosi di teatro, intende offrire un contributo nella direzione di una necessaria interazione, finora poco sviluppata, tra le discipline coinvolte nel campo della librettistica. I temi riguardano principalmente il rapporto dei libretti e delle opere con le fonti, quello tra parole e musica, la filologia dei libretti.This book contains the studies presented at a conference dedicated to librettology, a field of research that is still recent and that involves many disciplines. In fact, contributions from historians of the language, musicologists, literary historians and theater scholars are collected; the topics covered range from philology, to the relationship between words and music, to staging, to teaching and to the cultural tradition of opera
Coulomb corrections to low energy antiproton annihilation cross sections on protons and nuclei
We calculate, in a systematic way, the enhancement effect on
antiproton-proton and antiproton-nucleus annihilation cross sections at low
energy due to the initial state electrostatic interaction between the
projectile and the target nucleus. This calculation is aimed at future
comparisons between antineutron and antiproton annihilation rates on different
targets, for the extraction of pure isospin channels.Comment: 18 pages, 4 figures (latex format
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