1,407 research outputs found
On the embedding of spacetime in five-dimensional Weyl spaces
We revisit Weyl geometry in the context of recent higher-dimensional theories
of spacetime. After introducing the Weyl theory in a modern geometrical
language we present some results that represent extensions of Riemannian
theorems. We consider the theory of local embeddings and submanifolds in the
context of Weyl geometries and show how a Riemannian spacetime may be locally
and isometrically embedded in a Weyl bulk. We discuss the problem of classical
confinement and the stability of motion of particles and photons in the
neighbourhood of branes for the case when the Weyl bulk has the geometry of a
warped product space. We show how the confinement and stability properties of
geodesics near the brane may be affected by the Weyl field. We construct a
classical analogue of quantum confinement inspired in theoretical-field models
by considering a Weyl scalar field which depends only on the extra coordinate.Comment: 16 pages, new title and references adde
Programmed buckling by controlled lateral swelling in a thin elastic sheet
Recent experiments have imposed controlled swelling patterns on thin polymer
films, which subsequently buckle into three-dimensional shapes. We develop a
solution to the design problem suggested by such systems, namely, if and how
one can generate particular three-dimensional shapes from thin elastic sheets
by mere imposition of a two-dimensional pattern of locally isotropic growth.
Not every shape is possible. Several types of obstruction can arise, some of
which depend on the sheet thickness. We provide some examples using the
axisymmetric form of the problem, which is analytically tractable.Comment: 11 pages, 9 figure
Complexity Characterization in a Probabilistic Approach to Dynamical Systems Through Information Geometry and Inductive Inference
Information geometric techniques and inductive inference methods hold great
promise for solving computational problems of interest in classical and quantum
physics, especially with regard to complexity characterization of dynamical
systems in terms of their probabilistic description on curved statistical
manifolds. In this article, we investigate the possibility of describing the
macroscopic behavior of complex systems in terms of the underlying statistical
structure of their microscopic degrees of freedom by use of statistical
inductive inference and information geometry. We review the Maximum Relative
Entropy (MrE) formalism and the theoretical structure of the information
geometrodynamical approach to chaos (IGAC) on statistical manifolds. Special
focus is devoted to the description of the roles played by the sectional
curvature, the Jacobi field intensity and the information geometrodynamical
entropy (IGE). These quantities serve as powerful information geometric
complexity measures of information-constrained dynamics associated with
arbitrary chaotic and regular systems defined on the statistical manifold.
Finally, the application of such information geometric techniques to several
theoretical models are presented.Comment: 29 page
Volume Fractions of the Kinematic "Near-Critical" Sets of the Quantum Ensemble Control Landscape
An estimate is derived for the volume fraction of a subset in the neighborhood
of the critical set
of the kinematic quantum ensemble control landscape J(U) = Tr(U\rho U' O),
where represents the unitary time evolution operator, {\rho} is the initial
density matrix of the ensemble, and O is an observable operator. This estimate
is based on the Hilbert-Schmidt geometry for the unitary group and a
first-order approximation of . An upper bound on these
near-critical volumes is conjectured and supported by numerical simulation,
leading to an asymptotic analysis as the dimension of the quantum system
rises in which the volume fractions of these "near-critical" sets decrease to
zero as increases. This result helps explain the apparent lack of influence
exerted by the many saddles of over the gradient flow.Comment: 27 pages, 1 figur
Up conversion from visible to ultraviolet in bulk ZnO implanted with Tm ions
We report on the up-converted ultraviolet near-band edge emission of bulk ZnO generated by visible and ultraviolet photons with energies below the band gap. This up-converted photoluminescence was observed in samples intentionally doped with Tm ions, suggesting that the energy levels introduced by the rare earth ion in the ZnO band gap are responsible for this process.FCT/FEDER - POCTI/CTM/45236/02FCT/FEDER - POCTI/FAT/4882
Surface modification of Co-doped ZnO nanocrystals and its effects on the magnetic properties
A series of chemically prepared Co2+-doped ZnO colloids has been surface modified either by
growing shells of ZnSe or by the in situ encapsulation in poly styrene . The surface modification
effects using these two distinct chemical strategies on the magnetic properties of the nanocrystals
were probed by electron paramagnetic resonance EPR . Structural characterization by means of
x-ray diffraction and transmission electron microscopy gave no evidence of second phase formation
within the detection limits of the used equipment. The EPR analysis was carried out by simulations
of the powderlike EPR spectra. The results confirm that in the core of these nanocrystals Co was
incorporated as Co2+, occupying the Zn2+ sites in the wurtzite structure of ZnO. Additionally we
identify two Co signals stemming from the nanocrystals’ shell. The performed surface modifications
clearly change the relative intensity of the EPR spectrum components, revealing the core and shell
signals
Symbolic dynamics for the -centre problem at negative energies
We consider the planar -centre problem, with homogeneous potentials of
degree -\a<0, \a \in [1,2). We prove the existence of infinitely many
collisions-free periodic solutions with negative and small energy, for any
distribution of the centres inside a compact set. The proof is based upon
topological, variational and geometric arguments. The existence result allows
to characterize the associated dynamical system with a symbolic dynamics, where
the symbols are the partitions of the centres in two non-empty sets
Influência da época de semeadura e de espécies de plantas de cobertura sobre os números de vagens e de grãos por vagens de Feijão-caupi em Roraima.
Otimização de método para prospecção tecnológica de myrciaria dubia (kunt.) Mcvaugh na Amazônia setentrional.
Surfaces immersed in Lie algebras associated with elliptic integrals
The main aim of this paper is to study soliton surfaces immersed in Lie
algebras associated with ordinary differential equations (ODE's) for elliptic
functions. That is, given a linear spectral problem for such an ODE in matrix
Lax representation, we search for the most general solution of the wave
function which satisfies the linear spectral problem. These solutions allow for
the explicit construction of soliton surfaces by the Fokas-Gel'fand formula for
immersion, as formulated in (Grundland and Post 2011) which is based on the
formalism of generalized vector fields and their prolongation structures. The
problem has been reduced to examining three types of symmetries, namely, a
conformal symmetry in the spectral parameter (known as the Sym-Tafel formula),
gauge transformations of the wave function and generalized symmetries of the
associated integrable ODE. The paper contains a detailed explanation of the
immersion theory of surfaces in Lie algebras in connection with ODE's as well
as an exposition of the main tools used to study their geometric
characteristics. Several examples of the Jacobian and P-Weierstrass elliptic
functions are included as illustrations of the theoretical results.Comment: 22 pages, 3 sets of figures. Keywords: Generalized symmetries,
integrable models, surfaces immersed in Lie algebra
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