5,359 research outputs found
Baryon Structure
A review of the theoretical activity in Italy in the research field of
Hadronic Physics is given. Specific focus is put on phenomenological models
based on the effective degrees of freedom of constituent quarks, on parton
distributions in hard processes in the Bjorken limit and on the possibility of
linking the two concepts via evolution equations. A brief introduction is given
also about the socalled generalized parton distributions.Comment: 20 pages, no figures, invited general report at the "IX Convegno su
Problemi di Fisica Nucleare e Teorica", Cortona, Oct. 9-12, 2002 (Italy), to
appear in World Scientific Proceeding
3D Tracking Using Multi-view Based Particle Filters
Visual surveillance and monitoring of indoor environments using multiple cameras has become a field of great activity in computer vision. Usual 3D tracking and positioning systems rely on several independent 2D tracking modules applied over individual camera streams, fused using geometrical relationships across cameras. As 2D tracking systems suffer inherent difficulties due to point of view limitations (perceptually similar foreground and background regions causing fragmentation of moving objects, occlusions), 3D tracking based on partially erroneous 2D tracks are likely to fail when handling multiple-people interaction. To overcome this problem, this paper proposes a Bayesian framework for combining 2D low-level cues from multiple cameras directly into the 3D world through 3D Particle Filters. This method allows to estimate the probability of a certain volume being occupied by a moving object, and thus to segment and track multiple people across the monitored area. The proposed method is developed on the basis of simple, binary 2D moving region segmentation on each camera, considered as different state observations. In addition, the method is proved well suited for integrating additional 2D low-level cues to increase system robustness to occlusions: in this line, a naĂŻve color-based (HSI) appearance model has been integrated, resulting in clear performance improvements when dealing with complex scenarios
Two-fluid model for VLBI jets. I. Homogeneous and stationary synchrotron emission simulations
In this series of papers, we develop a two-fluid model for VLBI jets. The
idea is that the jet itself is non- or mildly-relativistic (electrons and
protons), while the radiating blobs are relativistic electron-positron `clouds'
moving on helical paths wrapped around the jet. In this work, the emphasis is
on the physical description of the clouds, and not on the structure or origin
of the trajectory. In the simple case where the magnetic field is uniform and
homogeneous accross the cloud, and the properties of the cloud are constant,
the present paper shows synthetic maps of VLBI jets in different
configurations, as well as the variation of different observational parameters
along the trajectory.Comment: to appear in A&A, 8 pages and 10 figure
A first study of the galaxy HRG 2304 and its companion AM 1646-795 (NED01)
Aims. We report the first study of the peculiar ring-like galaxy HRG 2304
(NED02),which was previously classified as a ring galaxy with an elliptical
smooth ring. This object was selected to prove that it is a candidate for the
Solitaire-type ring galaxies in an early stage of ring formation. The main goal
of this work is to provide the spectral characteristics of the current object
and its companion AM 1646-795 (NED01). Methods. The study is based on
spectroscopic observations in the optical band to highlight the characteristics
of this interacting galaxy. To investigate the star formation history of HRG
2304 we used the stellar population synthesis code STARLIGHT. The direct V and
B broad band images were used to enhance some fine structures. Results. Along
the entire long-slit signal, the spectra of HRG 2304 and its companion resemble
that of an early-type galaxy. We estimated a heliocentric systemic redshift of
z = 0.0415, corresponding to heliocentric velocities of 12449 km s-1 for HRG
2304 (NED02) and 12430 km s-1 for AM1646-795 (NED01). The spatial variation in
the contribution of the stellar population components for both objects are
dominated by an old stellar population 2x10^9 < t < 13x10^9 yr. The observed
radial-velocity distribution and the fine structures around HRG 2304 suggest an
ongoing tidal interaction of both galaxies. Conclusions.The spectroscopic
results and the morphological peculiarities of HRG 2304 can be adequately
interpreted as an ongoing interaction with the companion galaxy. Both galaxies
are early-type, the companion is elliptical, and the smooth distribution of the
material around HRG 2304 and its off-center nucleus in the direction of
AM1646-795 (NED01) characterize HRG 2304 as a Solitaire-type galaxy candidate
in an early stage of ring formation.Comment: Accepted for publication in Astronomy and Astrophysics, 9 pages, 10
figures and 3 table
The Efficiency of Gravitational Bremsstrahlung Production in the Collision of Two Schwarzschild Black Holes
We examine the efficiency of gravitational bremsstrahlung production in the
process of head-on collision of two boosted Schwarzschild black holes. We
constructed initial data for the characteristic initial value problem in
Robinson-Trautman spacetimes, that represent two instantaneously stationary
Schwarzschild black holes in motion towards each other with the same velocity.
The Robinson-Trautman equation was integrated for these initial data using a
numerical code based on the Galerkin method. The final resulting configuration
is a boosted black hole with Bondi mass greater than the sum of the individual
mass of each initial black hole. Two relevant aspects of the process are
presented. The first relates the efficiency of the energy extraction
by gravitational wave emission to the mass of the final black hole. This
relation is fitted by a distribution function of non-extensive thermostatistics
with entropic parameter ; the result extends and validates
analysis based on the linearized theory of gravitational wave emission. The
second is a typical bremsstrahlung angular pattern in the early period of
emission at the wave zone, a consequence of the deceleration of the black holes
as they coalesce; this pattern evolves to a quadrupole form for later times.Comment: 16 pages, 4 figures, to appear in Int. J. Modern Phys. D (2008
Testing the black hole "no-hair" hypothesis
Black holes in General Relativity are very simple objects. This property,
that goes under the name of "no-hair," has been refined in the last few decades
and admits several versions. The simplicity of black holes makes them ideal
testbeds of fundamental physics and of General Relativity itself. Here we
discuss the no-hair property of black holes, how it can be measured in the
electromagnetic or gravitational window, and what it can possibly tell us about
our universe.Comment: Commissioned by Classical and Quantum Gravit
Moving Defects in AdS/CFT
We study defects of various dimensions moving through Anti-de Sitter space.
Using the AdS/CFT correspondence this allows us to probe aspects of the dual
quantum field theory. We focus on the energy loss experienced by these defects
as they move through the CFT plasma. We find that the behavior of these
physical quantities is governed by induced world-volume horizons. We identify
world-volume analogs for several gravitational phenomena including black holes,
the Hawking-Page phase transition and expanding cosmological horizons.Comment: 24 pages, 7 figures. Version 2 contains two added reference
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