1,345 research outputs found
Probing Fuzzballs with Particles, Waves and Strings
We probe D1D5 micro-state geometries with massless particles, waves and
strings. To this end, we study geodetic motion, Klein-Gordon equation and
string scattering in the resulting gravitational background. Due to the reduced
rotational symmetry, even in the simple case of a circular fuzzball, the system
cannot be integrated elementarily. Yet, for motion in the plane of the string
profile or in the orthogonal plane to it, one can compute the deflection angle
or the phase shift and identify the critical impact parameter, at which even a
massless probe is captured by the fuzzball if its internal momentum is properly
tuned. We find agreement among the three approaches, thus giving further
support to the fuzzball proposal at the dynamical level.Comment: 35 pages. Extended and improved discussions on the integrability of
the geodetic equations and on the critical impact parameter
Breakdown of a conservation law in incommensurate systems
We show that invariance properties of the Lagrangian of an incommensurate
system, as described by the Frenkel Kontorova model, imply the existence of a
generalized angular momentum which is an integral of motion if the system
remains floating. The behavior of this quantity can therefore monitor the
character of the system as floating (when it is conserved) or locked (when it
is not). We find that, during the dynamics, the non-linear couplings of our
model cause parametric phonon excitations which lead to the appearance of
Umklapp terms and to a sudden deviation of the generalized momentum from a
constant value, signalling a dynamical transition from a floating to a pinned
state. We point out that this transition is related but does not coincide with
the onset of sliding friction which can take place when the system is still
floating.Comment: 7 pages, 6 figures, typed with RevTex, submitted to Phys. Rev. E
Replaced 27-03-2001: changes to text, minor revision of figure
A Fast Quasi-Conformal Mapping Preconditioner for Electromagnetic Integral Equations
Boundary Element Methods (BEMs) are efficient strategies to numerically solve electromagnetic radiation and scattering problems. Unfortunately, however, classical BEM formulations suffer from ill-conditioning when the frequency is low, or the discretization density is high. In the past, several remedies have been presented for these ill-conditioning problems including preconditioners based on CalderĂłn identities, hierarchical bases, and current decompositions. While effective, these strategies however require ad-hoc procedures including mesh-refinements, new basis function definitions, and adapted fast methods that, if not implemented properly, can become computationally cumbersome
Experimental determination of impedance and delay time of the 100 meander transmission line for the SPIRAL2 Single Bunch Selector
International audienceThe Spiral2 driver requires a Single Bunch Selector to reduce the bunch repetition rate at the experimental targets. A 100 ⊠meander line is used in the beta 0.04 medium energy line of the Spiral2 driver. The non standard characteristic impedance figure helps to reduce the pulsed power but introduces the problem of calibrated measurements. The paper describes the results of the different methods used to measure the impedance and the delay of the electrodes
Fish diversity associated with gas platforms: Evaluation of two underwater visual census techniques
Fish assemblages associated with offshore platforms were surveyed using two underwater visual census techniques: strip
transects and mobile point counts. Data were collected from four depth ranges at three platforms off Crotone, Italy (Ionian Sea).
A total of 25 fish species belonging to 12 families were recorded for the three platforms. Significant differences between
sampling methods and depth were observed in the fish assemblage structure, species richness and fish abundance. The mean
number of species recorded with the strip transect method was always greater than that obtained with mobile point counts, whilst
the opposite pattern was observed for mean abundances. Gregarious species such as Boops boops, Chromis chromis, Anthias
anthias and Oblada melanura were responsible for most of the differences in the assemblage structure. According to our results,
both methods allowed us to observe species that are not usually caught by means of fishing gear. When both census techniques
are used, they provide complementary information about the fish assemblages strictly associated with the platform structures
Kinematics and strain analyses of the eastern segment of the Pernicana Fault (Mt. Etna, Italy) derived from geodetic techniques (1997-2005)
This paper analyses the ground deformations occurring on the eastern part of the Pernicana Fault from 1997 to 2005. This segment of the fault was monitored with three local networks based on GPS and EDM techniques. More than seventy GPS and EDM surveys were carried out during the considered period, in order to achieve a higher temporal detail of ground deformation affecting the structure. We report the comparisons among GPS and EDM surveys in terms of absolute horizontal displacements of each GPS benchmark and in terms of strain parameters for each GPS and EDM network. Ground deformation measurements detected a continuous left-lateral movement of the Pernicana Fault. We conclude that, on the easternmost part of the Pernicana Fault, where it branches out into two segments, the deformation is transferred entirely SE-wards by a splay fault
L'evoluzione delle relazioni industriali nel posto di lavoro in un contesto di globalizzazione: una survey internazionale nel settore elettronico ed elettromeccanico
Rivista Sociologia del Lavor
Cancellation of Sudakov Logarithms in Radiative Decays of Quarkonia
We study infrared QCD effects in radiative quarkonia decays. We examine the
endpoint region z -> 1 of the photon spectrum. We point out a cancellation
mechanism for the corrections in , , in
the short-distance coefficient for the color-singlet Fock state in the
quarkonium. The cancellation is due to the coherence of the color radiation,
and applies even though logarithmic contributions are present in the jet
distributions associated with the decay. We comment on the implications of our
results for the modeling of hadronization in the endpoint region and for the
role of color-octet states in the quarkonium.Comment: 15 pages, 1 figur
Global positioning system survey data for active seismic and volcanic areas of eastern Sicily, 1994 to 2013
This work presents and describes a 20-year long database of GPS data collected by geodetic surveys over the seismically and volcanically active eastern Sicily, for a total of more than 6300 measurements. Raw data were initially collected from the various archives at the Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania-Osservatorio Etneo and organized in a single repository. Here, quality and completeness checks were performed, while all necessary supplementary information were searched, collected, validated and organized together with the relevant data. Once all data and information collections were completed, raw binary data were converted into the universal ASCII RINEX format; all data are provided in this format with the necessary information for precise processing. In order to make the data archive readily consultable, we developed software allowing the user to easily search and obtain the needed data by simple alphanumeric and geographic queries.The work of S. Fagone and C. Giardina was supported by the
Servizio Civile Nazionale âTerra in movimento: monitoraggio geodetico delle aree a rischio vulcanico e
sismico della Siciliaâ 2012/2013 Project.PublishedID 1600621IT. Reti di monitoraggio e OsservazioniJCR Journalope
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