11,592 research outputs found
Universal Features of the Time Evolution of Evanescent Modes in a Left-Handed Perfect Lens
The time evolution of evanescent modes in Pendry's perfect lens proposal for
ideally lossless and homogeneous, left-handed materials is analyzed. We show
that time development of sub-wavelength resolution exhibits universal features,
independent of model details. This is due to the unavoidable near-degeneracy of
surface electromagnetic modes in the deep sub-wavelength region. By means of a
mechanical analog, it is shown that an intrinsic time scale (missed in
stationary studies) has to be associated with any desired lateral resolution. A
time-dependent cut-off length emerges, removing the problem of divergences
claimed to invalidate Pendry's proposal.Comment: 4 pages, 3 figures, title slightly changed, reference added, minor
correction
The Inverse Amplitude Method and Adler Zeros
The Inverse Amplitude Method is a powerful unitarization technique to enlarge
the energy applicability region of Effective Lagrangians. It has been widely
used to describe resonances from Chiral Perturbation Theory as well as for the
Strongly Interacting Symmetry Breaking Sector. In this work we show how it can
be slightly modified to account also for the sub-threshold region,
incorporating correctly the Adler zeros required by chiral symmetry and
eliminating spurious poles. These improvements produce negligible effects on
the physical region.Comment: 17 pages, 4 figure
Contrastive grammar : a theory and practice handbook
En consonancia con los lineamientos del programa vigente de Gramática Contrastiva, materia incluida en el programa de estudios del Traductorado de Inglés de la Facultad de Lenguas, Universidad Nacional de Córdoba, el objetivo principal de Contrastive Grammar: A Theory and Practice Handbook es brindar a los estudiantes un manual que combine las gramáticas descriptivas del inglés y del español. No pretende ser una revisión completa de todas las diferencias lingüísticas existentes entre ambas lenguas: por el contrario, el objetivo del presente manual es combinar información teórica clave con prácticas variadas respecto de estructuras dispares que representan la fuente más frecuente de interferencia entre los dos sistemas.Fil: Gómez Calvillo, M. Natalia. Universidad Nacional de Córdoba. Facultad de Lenguas; Argentina.Fil: Meehan, Patricia. Universidad Nacional de Córdoba. Facultad de Lenguas; Argentina.Fil: Díaz, M. Josefina. Universidad Nacional de Córdoba. Facultad de Lenguas; Argentina.Fil: Rolfi, Laura. Universidad Nacional de Córdoba. Facultad de Lenguas; Argentina
A Motivating Exploration on Lunar Craters and Low-Energy Dynamics in the Earth -- Moon System
It is known that most of the craters on the surface of the Moon were created
by the collision of minor bodies of the Solar System. Main Belt Asteroids,
which can approach the terrestrial planets as a consequence of different types
of resonance, are actually the main responsible for this phenomenon. Our aim is
to investigate the impact distributions on the lunar surface that low-energy
dynamics can provide. As a first approximation, we exploit the hyberbolic
invariant manifolds associated with the central invariant manifold around the
equilibrium point L_2 of the Earth - Moon system within the framework of the
Circular Restricted Three - Body Problem. Taking transit trajectories at
several energy levels, we look for orbits intersecting the surface of the Moon
and we attempt to define a relationship between longitude and latitude of
arrival and lunar craters density. Then, we add the gravitational effect of the
Sun by considering the Bicircular Restricted Four - Body Problem. As further
exploration, we assume an uniform density of impact on the lunar surface,
looking for the regions in the Earth - Moon neighbourhood these colliding
trajectories have to come from. It turns out that low-energy ejecta originated
from high-energy impacts are also responsible of the phenomenon we are
considering.Comment: The paper is being published in Celestial Mechanics and Dynamical
Astronomy, vol. 107 (2010
Double neutral pion photoproduction at threshold
We consider the chiral expansion of the threshold amplitude for the reaction
to order . We substantiate a
claim that this photoproduction channel is significantly enhanced close to
threshold due to pion loops. A precise measurement of the corresponding cross
sections is called for which allows to test chiral perturbation theory.Comment: 8 pp, LaTe
Exceptional orthogonal polynomials and the Darboux transformation
We adapt the notion of the Darboux transformation to the context of
polynomial Sturm-Liouville problems. As an application, we characterize the
recently described Laguerre polynomials in terms of an isospectral
Darboux transformation. We also show that the shape-invariance of these new
polynomial families is a direct consequence of the permutability property of
the Darboux-Crum transformation.Comment: corrected abstract, added references, minor correction
Quasi-exact solvability beyond the SL(2) algebraization
We present evidence to suggest that the study of one dimensional
quasi-exactly solvable (QES) models in quantum mechanics should be extended
beyond the usual \sla(2) approach. The motivation is twofold: We first show
that certain quasi-exactly solvable potentials constructed with the \sla(2)
Lie algebraic method allow for a new larger portion of the spectrum to be
obtained algebraically. This is done via another algebraization in which the
algebraic hamiltonian cannot be expressed as a polynomial in the generators of
\sla(2). We then show an example of a new quasi-exactly solvable potential
which cannot be obtained within the Lie-algebraic approach.Comment: Submitted to the proceedings of the 2005 Dubna workshop on
superintegrabilit
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