24,323 research outputs found
A System of n=3 Coupled Oscillators with Magnetic Terms: Symmetries and Integrals of Motion
The properties of a system of n = 3 coupled oscillators with linear terms in
the velocities (magnetic terms) depending in two parameters are studied. We
proved the existence of a bi-Hamiltonian structure arising from a
non-symplectic symmetry, as well the existence of master symmetries and
additional integrals of motion (weak superintegrability) for certain particular
values of the parameters.Comment: Published in SIGMA (Symmetry, Integrability and Geometry: Methods and
Applications) at http://www.emis.de/journals/SIGMA
The Tremblay-Turbiner-Winternitz system on spherical and hyperbolic spaces : Superintegrability, curvature-dependent formalism and complex factorization
The higher-order superintegrability of the Tremblay-Turbiner-Winternitz
system (related to the harmonic oscillator) is studied on the two-dimensional
spherical and hiperbolic spaces, S_\k^2 (\k>0), and H_{\k}^2 (\k<0).
The curvature is considered as a parameter and all the results are
formulated in explicit dependence of . The idea is that the additional
constant of motion can be factorized as the product of powers of two particular
rather simple complex functions (here denoted by and ). This
technique leads to a proof of the superintegrability of the
Tremblay-Turbiner-Winternitz system on S_\k^2 (\k>0) and H_{\k}^2
(\k<0), and to the explicit expression of the constants of motion.Comment: one figur
Description and Optimization of Abstract Machines in a Dialect of Prolog
In order to achieve competitive performance, abstract machines for Prolog and
related languages end up being large and intricate, and incorporate
sophisticated optimizations, both at the design and at the implementation
levels. At the same time, efficiency considerations make it necessary to use
low-level languages in their implementation. This makes them laborious to code,
optimize, and, especially, maintain and extend. Writing the abstract machine
(and ancillary code) in a higher-level language can help tame this inherent
complexity. We show how the semantics of most basic components of an efficient
virtual machine for Prolog can be described using (a variant of) Prolog. These
descriptions are then compiled to C and assembled to build a complete bytecode
emulator. Thanks to the high level of the language used and its closeness to
Prolog, the abstract machine description can be manipulated using standard
Prolog compilation and optimization techniques with relative ease. We also show
how, by applying program transformations selectively, we obtain abstract
machine implementations whose performance can match and even exceed that of
state-of-the-art, highly-tuned, hand-crafted emulators.Comment: 56 pages, 46 figures, 5 tables, To appear in Theory and Practice of
Logic Programming (TPLP
Modelling Free Response of a Solar Plant for Predictive Control
IFAC System Identification, Kitakyushu, Fukuoka,Japan,1997This paper deals with the identification of a nonlinear plant by means of a neural network (NN) modelling approximation. The problem of neural identification is tackled using a static NN in a NARX configuration. A method is proposed to obtain the number of past values needed to feed the network. The on-line adaptation of the model and other issues are discussed. In order to show the benefits that can be achieved with the proposed methods, the NN model is used within a Model Predictive Control (MPC) framework. The MPC scheme uses the prediction of the output of the system calculated as the sum of the free response (obtained using the nonlinear NN model) and the forced response (obtained linearizing around the current operating point) to optimize a performance index. The control scheme has been applied and tested in a solar power plant
Effective Transport Equations for non-Abelian Plasmas
Starting from classical transport theory, we derive a set of covariant
equations describing the dynamics of mean fields and their statistical
fluctuations in a non-Abelian plasma in or out of equilibrium. A general
procedure is detailed for integrating-out the fluctuations as to obtain the
effective transport equations for the mean fields. In this manner, collision
integrals for Boltzmann equations are obtained as correlators of fluctuations.
The formalism is applied to a hot non-Abelian plasma close to equilibrium. We
integrate-out explicitly the fluctuations with typical momenta of the Debye
mass, and obtain the collision integral in a leading logarithmic approximation.
We also identify a source for stochastic noise. The resulting dynamical
equations are of the Boltzmann-Langevin type. While our approach is based on
classical physics, we also give the necessary generalizations to study the
quantum plasmas. Ultimately, the dynamical equations for soft and ultra-soft
fields change only in the value for the Debye mass.Comment: 37 pages, revtex, no figures, section VII G modified, typos remove
Photon Self-Energy in a Color Superconductor
In a color superconductor the diquark condensates break spontaneously both
the color and ordinary electromagnetism, leaving a remanining rotated U(1)
symmetry unbroken. The gauge interactions associated to this rotated symmetry
may be considered as the in-medium electromagnetism. We compute the in-medium
photon self-energy in the presence of diquark condensates at high baryonic
density and weak coupling. This is done to one-loop order for the cases of two
and three quark flavors. For vanishing temperature, a detailed discussion is
given of the low momentum behavior of the photon polarization tensor. A simple
physical picture for the propagation of light in color superconducting media is
obtained. The main new effect is due to the diquark condensates, which lead to
a strong dielectric constant of the medium. The magnetic permeability remains
unchanged, because the primary condensates have vanishing spin and angular
momentum. In the two flavor case, an additional contribution arises due to
gapless quarks and electrons, which is responsible for Debye screening effects.
We also discuss the low energy effective theory for the three flavor case in
the presence of electromagnetic interactions.Comment: 26 pages, 4 postscript figures, appendix added, to appear in PR
Deriving effective transport equations for non-Abelian plasmas
Within classical transport theory, an approach is presented to derive
systematically effective collision terms and noise sources for effective
kinetic equations of non-Abelian plasmas. This procedure amounts to the
`integrating-out' of fluctuations, and is applicable for in- and
out-of-equilibrium situations. When applied to a hot non-Abelian plasma close
to equilibrium we recover the collision integral and the noise source first
obtained by B\"odeker. It is also shown that our approach, and hence
B\"odeker's effective theory, is consistent with the fluctuation-dissipation
theorem.Comment: 7 pages, needs sprocl.sty, invited talk given by DFL at 5th workshop
on QCD (QCD2000), Villefranche-sur-Mer, France, 3-7 Jan 200
Review of Structural Adjustment in the Philippines
This article has been delivered during the Central Bank Diamond Jubilee celebration on November 21,1988. It reviews the issues of Philippine structural adjustments with a focus on the identification of elements in the past Philippine efforts that appear to be critical in the future adjustment endeavor. It also discusses the problems and the potentials of policy-based lending in support of future structural adjustment efforts in the Philippines.tax structure, agrarian reform, liberalization, structural adjustment, balance of payments, structural reforms, policy adjustment, industrialization
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