21,503 research outputs found
Far Infrared Slab Lensing and Subwavelength Imaging in Crystal Quartz
We examine the possibility of using negative refraction stemming from the
phonon response in an anisotropic crystal to create a simple slab lens with
plane parallel sides, and show that imaging from such a lens should be possible
at room temperature despite the effects of absorption that are inevitably
present due to phonon damping. In particular, we consider the case of crystal
quartz, a system for which experimental measurements consistent with all-angle
negative refraction have already been demonstrated. Furthermore, we investigate
the possibility of subwavelength imaging from such materials, and show that it
should be possible for certain configurations.Comment: 12 pages, 10 figure
Avoided crossings in mesoscopic systems: electron propagation on a non-uniform magnetic cylinder
We consider an electron constrained to move on a surface with revolution
symmetry in the presence of a constant magnetic field parallel to the
surface axis. Depending on and the surface geometry the transverse part of
the spectrum typically exhibits many crossings which change to avoided
crossings if a weak symmetry breaking interaction is introduced. We study the
effect of such perturbations on the quantum propagation. This problem admits a
natural reformulation to which tools from molecular dynamics can be applied. In
turn, this leads to the study of a perturbation theory for the time dependent
Born-Oppenheimer approximation
The Outer Envelopes of Globular Clusters. II. NGC 1851, NGC 5824 and NGC 1261
We present a second set of results from a wide-field photometric survey of
the environs of Milky Way globular clusters. The clusters studied are NGC 1261,
NGC 1851 and NGC 5824: all have data from DECam on the Blanco 4m telescope. NGC
5824 also has data from the Magellan Clay telescope with MegaCam. We confirm
the existence of a large diffuse stellar envelope surrounding NGC 1851 of size
at least 240 pc in radius. The radial density profile of the envelope follows a
power-law decline with index and the projected shape is
slightly elliptical. For NGC 5824 there is no strong detection of a diffuse
stellar envelope, but we find the cluster is remarkably extended and is similar
in size (at least 230 pc in radius) to the envelope of NGC 1851. A stellar
envelope is also revealed around NGC 1261. However, it is notably smaller in
size with radius 105 pc. The radial density profile of the envelope is
also much steeper with . We discuss the possible nature
of the diffuse stellar envelopes, but are unable to draw definitive conclusions
based on the current data. NGC 1851, and potentially NGC 5824, could be
stripped dwarf galaxy nuclei, akin to the cases of Cen, M54 and M2. On
the other hand, the different characteristics of the NGC 1261 envelope suggest
that it may be the product of dynamical evolution of the cluster.Comment: 18 pages, 11 figures, accepted to MNRA
Recomendação do tratamento químico de sementes de soja (Glycine max (L.) Merrill.
bitstream/item/54004/1/12.pd
Geometric Phase, Curvature, and Extrapotentials in Constrained Quantum Systems
We derive an effective Hamiltonian for a quantum system constrained to a
submanifold (the constraint manifold) of configuration space (the ambient
space) by an infinite restoring force. We pay special attention to how this
Hamiltonian depends on quantities which are external to the constraint
manifold, such as the external curvature of the constraint manifold, the
(Riemannian) curvature of the ambient space, and the constraining potential. In
particular, we find the remarkable fact that the twisting of the constraining
potential appears as a gauge potential in the constrained Hamiltonian. This
gauge potential is an example of geometric phase, closely related to that
originally discussed by Berry. The constrained Hamiltonian also contains an
effective potential depending on the external curvature of the constraint
manifold, the curvature of the ambient space, and the twisting of the
constraining potential. The general nature of our analysis allows applications
to a wide variety of problems, such as rigid molecules, the evolution of
molecular systems along reaction paths, and quantum strip waveguides.Comment: 27 pages with 1 figure, submitted to Phys. Rev.
Broca-do-café: Previsão de Infestação e Recomendações de Controle para Safra 2001/2002 no Estado de Rondônia.
Trabalho reúne informações sobre a broca-do-café, em plantações de café conilon, em Rondônia. Tópicos trabalhados: Infestação da broca na safra 2001; Previsão de infestação na safra 2001/2002; Amostragem para avaliação da infestação; Recomendações para o controle da broca-do-café.bitstream/item/100456/1/CT55-brocadocafe.pd
Surviving opinions in Sznajd models on complex networks
The Sznajd model has been largely applied to simulate many sociophysical
phenomena. In this paper we applied the Sznajd model with more than two
opinions on three different network topologies and observed the evolution of
surviving opinions after many interactions among the nodes. As result, we
obtained a scaling law which depends of the network size and the number of
possible opinions. We also observed that this scaling law is not the same for
all network topologies, being quite similar between scale-free networks and
Sznajd networks but different for random networks.Comment: 9 pages, 3 figure
Efeito de subdoses do herbicida S-metolachlor nas características fisiológicas de nabo forrageiro.
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