18,224 research outputs found
Observation of thermally-induced magnetic relaxation in a magnetite grain using off-axis electron holography
A synthetic basalt comprising magnetic Fe3O4 grains (~ 50 nm to ~ 500 nm in diameter) is
investigated using a range of complementary nano-characterisation techniques. Off-axis electron
holography combined with in situ heating allowed for the visualisation of the thermally-induced
magnetic relaxation of an Fe3O4 grain (~ 300 nm) from an irregular domain state into a vortex state at
550˚C, just below its Curie temperature, with the magnetic intensity of the vortex increasing on cooling
Regular string-like braneworlds
In this work, we propose a new class of smooth thick string-like braneworld
in six dimensions. The brane exhibits a varying brane-tension and an
asymptotic behavior. The brane-core geometry is parametrized by the Bulk
cosmological constant, the brane width and by a geometrical deformation
parameter. The source satisfies the dominant energy condition for the
undeformed solution and has an exotic asymptotic regime for the deformed
solution. This scenario provides a normalized massless Kaluza-Klein mode for
the scalar, gravitational and gauge sectors. The near-brane geometry allows
massive resonant modes at the brane for the state and nearby the brane for
.Comment: 14 pages, 12 figures. Some modifications to match the published
version in EPJ
Análise da competitividade potencial de uma cadeia de exportação de feijão.
A presente pesquisa, em andamento, apresenta como problema central de pesquisa: a cadeia de feijão para exportação é competitiva para transformar potencialidades em verdadeiras oportunidades de mercado, e o grau de competitividade indica que vale a pena direcionar esforços em organizar a cadeia produtiva de feijão para exportação
Análise de uma potencial cadeia de exportação de feijões sob a ótica da nova economia institucional.
Tem como objetivo fazer uso da Nova Economia Institucional (NEI) com ferramenta de análise das possíveis interações da cadeia produtiva do feijão para exportação.CONAFE
Spin-glass behaviour on random lattices
The ground-state phase diagram of an Ising spin-glass model on a random graph
with an arbitrary fraction of ferromagnetic interactions is analysed in the
presence of an external field. Using the replica method, and performing an
analysis of stability of the replica-symmetric solution, it is shown that
, correponding to an unbiased spin glass, is a singular point in the
phase diagram, separating a region with a spin-glass phase () from a
region with spin-glass, ferromagnetic, mixed, and paramagnetic phases
()
Semiclassical theory for small displacements
Characteristic functions contain complete information about all the moments
of a classical distribution and the same holds for the Fourier transform of the
Wigner function: a quantum characteristic function, or the chord function.
However, knowledge of a finite number of moments does not allow for accurate
determination of the chord function. For pure states this provides the overlap
of the state with all its possible rigid translations (or displacements). We
here present a semiclassical approximation of the chord function for large
Bohr-quantized states, which is accurate right up to a caustic, beyond which
the chord function becomes evanescent. It is verified to pick out blind spots,
which are displacements for zero overlaps. These occur even for translations
within a Planck area of the origin. We derive a simple approximation for the
closest blind spots, depending on the Schroedinger covariance matrix, which is
verified for Bohr-quantized states.Comment: 16 pages, 4 figures
One-step replica symmetry breaking solution of the quadrupolar glass model
We consider the quadrupolar glass model with infinite-range random
interaction. Introducing a simple one-step replica symmetry breaking ansatz we
investigate the para-glass continuous (discontinuous) transition which occurs
below (above) a critical value of the quadrupole dimension m*. By using a
mean-field approximation we study the stability of the one-step replica
symmetry breaking solution and show that for m>m* there are two transitions.
The thermodynamic transition is discontinuous but there is no latent heat. At a
higher temperature we find the dynamical or glass transition temperature and
the corresponding discontinuous jump of the order parameter.Comment: 10 pages, 3 figure
Random replicators with high-order interactions
We use tools of the equilibrium statistical mechanics of disordered systems
to study analytically the statistical properties of an ecosystem composed of N
species interacting via random, Gaussian interactions of order p >= 2, and
deterministic self-interactions u <= 0. We show that for nonzero u the effect
of increasing the order of the interactions is to make the system more
cooperative, in the sense that the fraction of extinct species is greatly
reduced. Furthermore, we find that for p > 2 there is a threshold value which
gives a lower bound to the concentration of the surviving species, preventing
then the existence of rare species and, consequently, increasing the robustness
of the ecosystem to external perturbations.Comment: 7 pages, 4 Postscript figure
Non-Chern-Simons Topological Mass Generation in (2+1) Dimensions
By dimensional reduction of a massive BF theory, a new topological field
theory is constructed in (2+1) dimensions. Two different topological terms, one
involving a scalar and a Kalb-Ramond fields and another one equivalent to the
four-dimensional BF term, are present. We constructed two actions with these
topological terms and show that a topological mass generation mechanism can be
implemented. Using the non-Chern-Simons topological term, an action is proposed
leading to a classical duality relation between Klein-Gordon and Maxwell
actions. We also have shown that an action in (2+1) dimensions with the
Kalb-Ramond field is related by Buscher's duality transformation to a massive
gauge-invariant Stuckelberg-type theory.Comment: 8 pages, no figures, RevTE
Uniform approximation for the overlap caustic of a quantum state with its translations
The semiclassical Wigner function for a Bohr-quantized energy eigenstate is
known to have a caustic along the corresponding classical closed phase space
curve in the case of a single degree of freedom. Its Fourier transform, the
semiclassical chord function, also has a caustic along the conjugate curve
defined as the locus of diameters, i.e. the maximal chords of the original
curve. If the latter is convex, so is its conjugate, resulting in a simple fold
caustic. The uniform approximation through this caustic, that is here derived,
describes the transition undergone by the overlap of the state with its
translation, from an oscillatory regime for small chords, to evanescent
overlaps, rising to a maximum near the caustic. The diameter-caustic for the
Wigner function is also treated.Comment: 14 pages, 9 figure
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