9,227 research outputs found
Machine learning the deuteron
We use machine learning techniques to solve the nuclear two-body bound state
problem, the deuteron. We use a minimal one-layer, feed-forward neural network
to represent the deuteron S- and D-state wavefunction in momentum space, and
solve the problem variationally using ready-made machine learning tools. We
benchmark our results with exact diagonalisation solutions. We find that a
network with 6 hidden nodes (or 24 parameters) can provide a faithful
representation of the ground state wavefunction, with a binding energy that is
within 0.1% of exact results. This exploratory proof-of-principle simulation
may provide insight for future potential solutions of the nuclear many-body
problem using variational artificial neural network techniques.Comment: 8 pages, 7 figures - Final published version including extended
analysis and appendice
Association of fall risk in older adults between gender, fear of falling and autonomy
Aging is a natural process of the individual and is associated with a decline in physical and mental function. Given the high prevalence of older adults worldwide, it becomes ppropriated to identify the consequences of this reduction. The falls appear as a consequence more common in this specific population, which triggers the need to identify the different risk factors, in order to prevent them and create intervention programs in that way.info:eu-repo/semantics/publishedVersio
Universality and Crossover of Directed Polymers and Growing Surfaces
We study KPZ surfaces on Euclidean lattices and directed polymers on
hierarchical lattices subject to different distributions of disorder, showing
that universality holds, at odds with recent results on Euclidean lattices.
Moreover, we find the presence of a slow (power-law) crossover toward the
universal values of the exponents and verify that the exponent governing such
crossover is universal too. In the limit of a 1+epsilon dimensional system we
obtain both numerically and analytically that the crossover exponent is 1/2.Comment: LateX file + 5 .eps figures; to appear on Phys. Rev. Let
Correlations in Hot Asymmetric Nuclear Matter
The single-particle spectral functions in asymmetric nuclear matter are
computed using the ladder approximation within the theory of finite temperature
Green's functions. The internal energy and the momentum distributions of
protons and neutrons are studied as a function of the density and the asymmetry
of the system. The proton states are more strongly depleted when the asymmetry
increases while the occupation of the neutron states is enhanced as compared to
the symmetric case. The self-consistent Green's function approach leads to
slightly smaller energies as compared to the Brueckner Hartree Fock approach.
This effect increases with density and thereby modifies the saturation density
and leads to smaller symmetry energies.Comment: 7 pages, 7 figure
Historias de vida e historias lingüísticas : una aproximación a las identidades
Este texto se presentó como comunicación al II Congreso Internacional de Etnografía y Educación: Migraciones y Ciudadanías. Universidad Autónoma de Barcelona, Barcelona, 5-8 Septiembre 2008Desde una perspectiva etnográfica, a través de las historias de vida e historias lingüísticas de niños inmigrados, realizamos una aproximación a sus identidades, como parte constitutiva de la realidad escolar actual. Pretendemos conocer las situaciones de multiculturalidad y plurilingüismo, para formar identidades y contribuir al desarrollo de la convivencia en las escuelas, mediante una metodología interdisciplinar que combina las aportaciones de las Ciencias Sociales, Educativas y Lingüísticas. La aplicación de este estudio es principalmente de tipo educativo, para mejorar la formación inicial de los maestros. Esta comunicación forma parte de una investigación que se realiza en nuestro Departamento en la que, con un enfoque interdisciplinar, participan las áreas de conocimiento de Didáctica y Organización Escolar, Didáctica de la Lengua y Didáctica de las Ciencias Sociales. Adoptamos unas estrategias comunes para construir conocimiento, a fin de integrar las aportaciones procedentes de diversos ámbitos científicos, de manera globalizada y relacional (ALTAVA et al.,1999). Puesto que la realidad es compleja (MORIN, 1994) y que también lo es su conocimiento, asumimos que su aprendizaje requiere la convergencia de distintos clases de saberes procedentes de diferentes ámbitos científicos. En nuestro caso, realizamos aportaciones desde los campos disciplinares de la Lingüística, la Pedagogía y la Didáctica, y desde el conjunto de las Ciencias Sociales (Historia, Antropología, etc.). Nuestro objeto de estudio general es la situación escolar de los niños inmigrantes en la provincia de Castellón, las estrategias didácticas y organizativas que existen en la escuela respecto a la educación intercultural y al multilingüismo.Para lograrlo, en una perspectiva de indagación y acción, dicha investigación pretende dar respuesta a las situaciones de multiculturalidad y plurilingüismo en las escuelas actuales, dentro de la formación (inicial y permanente) de los maestros; todo ello bajo un planteamiento didáctico y académico de una mayor adaptación a la realidad y al proceso de armonización europeas en los programas y metodología docentes
Levy-Nearest-Neighbors Bak-Sneppen Model
We study a random neighbor version of the Bak-Sneppen model, where "nearest
neighbors" are chosen according to a probability distribution decaying as a
power-law of the distance from the active site, P(x) \sim |x-x_{ac
}|^{-\omega}. All the exponents characterizing the self-organized critical
state of this model depend on the exponent \omega. As \omega tends to 1 we
recover the usual random nearest neighbor version of the model. The pattern of
results obtained for a range of values of \omega is also compatible with the
results of simulations of the original BS model in high dimensions. Moreover,
our results suggest a critical dimension d_c=6 for the Bak-Sneppen model, in
contrast with previous claims.Comment: To appear on Phys. Rev. E, Rapid Communication
The Fractal Properties of Internet
In this paper we show that the Internet web, from a user's perspective,
manifests robust scaling properties of the type where n
is the size of the basin connected to a given point, represents the density
of probability of finding n points downhill and s a
characteristic universal exponent. This scale-free structure is a result of the
spontaneous growth of the web, but is not necessarily the optimal one for
efficient transport. We introduce an appropriate figure of merit and suggest
that a planning of few big links, acting as information highways, may
noticeably increase the efficiency of the net without affecting its robustness.Comment: 6 pages,2 figures, epl style, to be published on Europhysics Letter
The Arabidopsis MAP kinase kinase MKK1 participates in defence responses to the bacterial elicitor flagellin
Semiclassical Evolution of Dissipative Markovian Systems
A semiclassical approximation for an evolving density operator, driven by a
"closed" hamiltonian operator and "open" markovian Lindblad operators, is
obtained. The theory is based on the chord function, i.e. the Fourier transform
of the Wigner function. It reduces to an exact solution of the Lindblad master
equation if the hamiltonian operator is a quadratic function and the Lindblad
operators are linear functions of positions and momenta.
Initially, the semiclassical formulae for the case of hermitian Lindblad
operators are reinterpreted in terms of a (real) double phase space, generated
by an appropriate classical double Hamiltonian. An extra "open" term is added
to the double Hamiltonian by the non-hermitian part of the Lindblad operators
in the general case of dissipative markovian evolution. The particular case of
generic hamiltonian operators, but linear dissipative Lindblad operators, is
studied in more detail. A Liouville-type equivariance still holds for the
corresponding classical evolution in double phase, but the centre subspace,
which supports the Wigner function, is compressed, along with expansion of its
conjugate subspace, which supports the chord function.
Decoherence narrows the relevant region of double phase space to the
neighborhood of a caustic for both the Wigner function and the chord function.
This difficulty is avoided by a propagator in a mixed representation, so that a
further "small-chord" approximation leads to a simple generalization of the
quadratic theory for evolving Wigner functions.Comment: 33 pages - accepted to J. Phys.
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