3,408 research outputs found
Cosmic Ray Physics with ACORDE at LHC
The use of large underground high-energy physics experiments, for comic ray
studies, have been used, in the past, at CERN, in order to measure, precisely,
the inclusive cosmic ray flux in the energy range from 2x10^10 - 2x10^12 eV.
ACORDE, ALICE Cosmic Rays DEtector, will act as Level 0 cosmic ray trigger and,
together with other ALICE apparatus, will provide precise information on cosmic
rays with primary energies around 10^15 - 10^17 eV. This paper reviews the main
detector features, the present status, commissioning and integration with other
apparatus. Finally, we discuss the ACORDE-ALICE cosmic ray physics program.Comment: Contribution to the 2007 Europhysics Conference on High Energy
Physics - Manchester, England 19-25 July 2007; 3 pages, 3 figure
Optimal Control Realizations of Lagrangian Systems with Symmetry
A new relation among a class of optimal control systems and Lagrangian
systems with symmetry is discussed. It will be shown that a family of solutions
of optimal control systems whose control equation are obtained by means of a
group action are in correspondence with the solutions of a mechanical
Lagrangian system with symmetry. This result also explains the equivalence of
the class of Lagrangian systems with symmetry and optimal control problems
discussed in \cite{Bl98}, \cite{Bl00}.
The explicit realization of this correspondence is obtained by a judicious
use of Clebsch variables and Lin constraints, a technique originally developed
to provide simple realizations of Lagrangian systems with symmetry. It is
noteworthy to point out that this correspondence exchanges the role of state
and control variables for control systems with the configuration and Clebsch
variables for the corresponding Lagrangian system.
These results are illustrated with various simple applications
Integrated Approach to Free Space Optical Communications in Strong Turbulence
The propagation of a free space optical communication signal through atmospheric turbulence experiences random fluctuations in intensity, including signal fades which negatively impact the communications link performance. This research develops an analytical probability density function (PDF) to model the best case scenario of using multiple independent beams to reduce the intensity fluctuations. The PDF was further developed to account for partially correlated beams, such as would be experienced by beams having finite separation. The PDF was validated with results obtained from digital simulations as well as lab experiments. The research showed that as the number of transmitted beams increases the probability of fade decreases. While fade probability is reduced by adding more beams, using more than four transmitters does little to improve the overall performance. Additionally, the use of pulse position modulation (PPM) provided significant improvement over traditional fixed threshold on/off keying with the impact of signal fading reduced. Combining PPM with multiple transmitters produced the best overall bit error rate results
High Energy Laser Pointing through Extended Turbulence
The airborne laser (ABL) uses adaptive optics to compensate the atmospheric turbulence between the ABL and the target. The primary purpose of this compensation is to increase the energy density of the energy laser at the target. However, the specifics of the engagement scenario require the tracking point of reference and the adaptive optics point of reference to be located at different points on the target. This research considers the effects of tracking a target in one direction while compensating for atmospheric turbulence in a different directions. The target references used are a point source and a rectangle, while a point source alone is used for the adaptive optics reference. It will be shown that compensating for atmospheric turbulence in a different direction than tracking results in a bias in the mean tracking error while having no appreciable effect on track jitter
SL(2,R)-geometric phase space and (2+2)-dimensions
We propose an alternative geometric mathematical structure for arbitrary
phase space. The main guide in our approach is the hidden SL(2,R)-symmetry
which acts on the phase space changing coordinates by momenta and vice versa.
We show that the SL(2,R)-symmetry is implicit in any symplectic structure. We
also prove that in any sensible physical theory based on the SL(2,R)-symmetry
the signature of the flat target "spacetime" must be associated with either
one-time and one-space or at least two-time and two-space coordinates. We
discuss the consequences as well as possible applications of our approach on
different physical scenarios.Comment: 17 pages, no figure
Cosmological parameter inference with Bayesian statistics
Bayesian statistics and Markov Chain Monte Carlo (MCMC) algorithms have found
their place in the field of Cosmology. They have become important mathematical
and numerical tools, especially in parameter estimation and model comparison.
In this paper, we review some fundamental concepts to understand Bayesian
statistics and then introduce MCMC algorithms and samplers that allow us to
perform the parameter inference procedure. We also introduce a general
description of the standard cosmological model, known as the CDM
model, along with several alternatives, and current datasets coming from
astrophysical and cosmological observations. Finally, with the tools acquired,
we use an MCMC algorithm implemented in python to test several cosmological
models and find out the combination of parameters that best describes the
Universe.Comment: 30 pages, 17 figures, 5 tables; accepted for publication in Universe;
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