38,406 research outputs found
Constructive spherical codes on layers of flat tori
A new class of spherical codes is constructed by selecting a finite subset of
flat tori from a foliation of the unit sphere S^{2L-1} of R^{2L} and designing
a structured codebook on each torus layer. The resulting spherical code can be
the image of a lattice restricted to a specific hyperbox in R^L in each layer.
Group structure and homogeneity, useful for efficient storage and decoding, are
inherited from the underlying lattice codebook. A systematic method for
constructing such codes are presented and, as an example, the Leech lattice is
used to construct a spherical code in R^{48}. Upper and lower bounds on the
performance, the asymptotic packing density and a method for decoding are
derived.Comment: 9 pages, 5 figures, submitted to IEEE Transactions on Information
Theor
A model for vortex formation in magnetic nanodots
We use Monte Carlo simulation to study the vortex nucleation on magnetic
nanodots at low temperature. In our simulations, we have considered a simple
microscopic two-dimensional anisotropic Heisenberg model with term to describe
the anisotropy due to the presence of the nanodot edge. We have considered the
thickness of the edge, which was not considered in previous works, introducing
a term that controls the energy associated to the edge. Our results clearly
show that the thickness of the edge has a considerable influence in the vortex
nucleation on magnetic nanodots. We have obtained the hysteresis curve for
several values of the surface anisotropy and skin depth parameter (). The
results are in excellent agreement with experimental data
Knowledge and attitude towards the gradual reduction of salt in bread – an online survey
Aim: Assess knowledge and attitude towards the gradual reduction of salt
in bread and the potential impact on eating habits of children (6-18 years)
and their families, as part as a Health Impact Assessment pilot study.N/
Entropy, non-ergodicity and non-Gaussian behaviour in ballistic transport
Ballistic transportation introduces new challenges in the thermodynamic
properties of a gas of particles. For example, violation of mixing, ergodicity
and of the fluctuation-dissipation theorem may occur, since all these processes
are connected. In this work, we obtain results for all ranges of diffusion,
i.e., both for subdiffusion and superdiffusion, where the bath is such that it
gives origin to a colored noise. In this way we obtain the skewness and the
non-Gaussian factor for the probability distribution function of the dynamical
variable. We put particular emphasis on ballistic diffusion, and we demonstrate
that in this case, although the second law of thermodynamics is preserved, the
entropy does not reach a maximum and a non-Gaussian behavior occurs. This
implies the non-applicability of the central limit theorem.Comment: 9 pages, 2 figure
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