757 research outputs found
Self-duality and the Supersymmetric KdV Hierarchy
We show how the supersymmetric KdV equation can be obtained from the
self-duality condition on Yang-Mills fields in four dimension associated with
the graded Lie algebra OSp(2/1). We also obtain the hierarchy of Susy KdV
equations from such a condition. We formulate the Susy KdV hierarchy as a
vanishing curvature condition associated with the U(1) group and show how an
Abelian self-duality condition in four dimension can also lead to these
equations.Comment: 10 page
Self-Duality and the KdV Hierarchy
We derive the entire KdV hierarchy as well as the recursion relations from
the self-duality condition on gauge fields in four dimensions.Comment: 7 page
Mechanical Properties and Fracture Dynamics of Silicene Membranes
As graphene became one of the most important materials today, there is a
renewed interest on others similar structures. One example is silicene, the
silicon analogue of graphene. It share some the remarkable graphene properties,
such as the Dirac cone, but presents some distinct ones, such as a pronounced
structural buckling. We have investigated, through density functional based
tight-binding (DFTB), as well as reactive molecular dynamics (using ReaxFF),
the mechanical properties of suspended single-layer silicene. We calculated the
elastic constants, analyzed the fracture patterns and edge reconstructions. We
also addressed the stress distributions, unbuckling mechanisms and the fracture
dependence on the temperature. We analysed the differences due to distinct edge
morphologies, namely zigzag and armchair
Importância da atividade florestal no Brasil.
A floresta natural e plantada é um importante patrimônio do Brasil,que proporciona significativo benefÃcio social,ambiental e econômico ao PaÃs.Os fatos e números apresentados a seguir demonstram essa afirmativa.Eles são baseados principalmente na SociedadeBrasileirade Silvicultura- SBS(1998)
Potencial de la region semi-arida del Brasil para reforestacion.
La región semiárida en el noreste del Brasil tiene una extensión de 1 100 000 hectáreas y abarcan e1 13 por ciento de1 área total de1 paÃs. Los sue l o s son general mente poco profundos sobre una capa rocosa cristal ina, con limitada capac idad de acumu 1ac ión de agua; cont ienen poco humus y 1a fert i 1 idad natural es baja. E1 cl ima se caracteriza por una precipitación anual promedio de 250 a 1000 mm. Las sequias son frecuentes y a menudo severas. La vegetación tÃpica está formada por un bosque caducifolio de arbustos espinosos y cactus, conocida como "caatinga". Su extensiva explotación ha ocasionado escasez de madera en muchas áreas de 1a región semiárida. Por 10 tanto, es muy importante producir madera para 1ena, postes y estacas en un tiempo corto
Multi-Hamiltonian structure of Plebanski's second heavenly equation
We show that Plebanski's second heavenly equation, when written as a
first-order nonlinear evolutionary system, admits multi-Hamiltonian structure.
Therefore by Magri's theorem it is a completely integrable system. Thus it is
an example of a completely integrable system in four dimensions
Solutions of Podolsky's Electrodynamics Equation in the First-Order Formalism
The Podolsky generalized electrodynamics with higher derivatives is
formulated in the first-order formalism. The first-order relativistic wave
equation in the 20-dimensional matrix form is derived. We prove that the
matrices of the equation obey the Petiau-Duffin-Kemmer algebra. The
Hermitianizing matrix and Lagrangian in the first-order formalism are given.
The projection operators extracting solutions of field equations for states
with definite energy-momentum and spin projections are obtained, and we find
the density matrix for the massive state. The -matrix Schrodinger
form of the equation is derived, and the Hamiltonian is obtained. Projection
operators extracting the physical eigenvalues of the Hamiltonian are found.Comment: 17 pages, minor corrections, published versio
General rules for bosonic bunching in multimode interferometers
We perform a comprehensive set of experiments that characterize bosonic
bunching of up to 3 photons in interferometers of up to 16 modes. Our
experiments verify two rules that govern bosonic bunching. The first rule,
obtained recently in [1,2], predicts the average behavior of the bunching
probability and is known as the bosonic birthday paradox. The second rule is
new, and establishes a n!-factor quantum enhancement for the probability that
all n bosons bunch in a single output mode, with respect to the case of
distinguishable bosons. Besides its fundamental importance in phenomena such as
Bose-Einstein condensation, bosonic bunching can be exploited in applications
such as linear optical quantum computing and quantum-enhanced metrology.Comment: 6 pages, 4 figures, and supplementary material (4 pages, 1 figure
Questioning the validity of non-extensive thermodynamics for classical Hamiltonian systems
We examine the non-extensive approach to the statistical mechanics of
Hamiltonian systems with where is the classical kinetic energy. Our
analysis starts from the basics of the formalism by applying the standard
variational method for maximizing the entropy subject to the average energy and
normalization constraints. The analytical results show (i) that the
non-extensive thermodynamics formalism should be called into question to
explain experimental results described by extended exponential distributions
exhibiting long tails, i.e. -exponentials with , and (ii) that in the
thermodynamic limit the theory is only consistent in the range
where the distribution has finite support, thus implying that configurations
with e.g. energy above some limit have zero probability, which is at variance
with the physics of systems in contact with a heat reservoir. We also discuss
the (-dependent) thermodynamic temperature and the generalized specific
heat.Comment: To appear in EuroPhysics Letter
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