22,857 research outputs found
Effects of Random Biquadratic Couplings in a Spin-1 Spin-Glass Model
A spin-1 model, appropriated to study the competition between bilinear
(J_{ij}S_{i}S_{j}) and biquadratic (K_{ij}S_{i}^{2}S_{j}^{2}) random
interactions, both of them with zero mean, is investigated. The interactions
are infinite-ranged and the replica method is employed. Within the
replica-symmetric assumption, the system presents two phases, namely,
paramagnetic and spin-glass, separated by a continuous transition line. The
stability analysis of the replica-symmetric solution yields, besides the usual
instability associated with the spin-glass ordering, a new phase due to the
random biquadratic couplings between the spins.Comment: 16 pages plus 2 ps figure
Statistical Mechanics Characterization of Neuronal Mosaics
The spatial distribution of neuronal cells is an important requirement for
achieving proper neuronal function in several parts of the nervous system of
most animals. For instance, specific distribution of photoreceptors and related
neuronal cells, particularly the ganglion cells, in mammal's retina is required
in order to properly sample the projected scene. This work presents how two
concepts from the areas of statistical mechanics and complex systems, namely
the \emph{lacunarity} and the \emph{multiscale entropy} (i.e. the entropy
calculated over progressively diffused representations of the cell mosaic),
have allowed effective characterization of the spatial distribution of retinal
cells.Comment: 3 pages, 1 figure, The following article has been submitted to
Applied Physics Letters. If it is published, it will be found online at
http://apl.aip.org
Long-Time Behaviour and Self-Similarity in a Coagulation Equation with Input of Monomers
For a coagulation equation with Becker-Doring type interactions and
time-independent monomer input we study the detailed long-time behaviour of
nonnegative solutions and prove the convergence to a self-similar function.Comment: 30 pages, 5 Figures, now published in Markov Processes and Related
Fields 12, 367-398, (2006
On quasi-Jacobi and Jacobi-quasi bialgebroids
We study quasi-Jacobi and Jacobi-quasi bialgebroids and their relationships
with twisted Jacobi and quasi Jacobi manifolds. We show that we can construct
quasi-Lie bialgebroids from quasi-Jacobi bialgebroids, and conversely, and also
that the structures induced on their base manifolds are related via a quasi
Poissonization
HST Observations of the Central-Cusp Globular Cluster NGC 6752. The Effect of Binary Stars on the Luminosity Function in the Core
We consider the effect of binary stars on the main-sequence luminosity
functions observed in the core of globular clusters, with specific reference to
NGC 6752. We find that mass segregation results in an increased binary fraction
at fainter magnitudes along the main-sequence. If this effect is not taken into
account when analyzing luminosity functions, erroneous conclusions can be drawn
regarding the distribution of single stars, and the dynamical state of the
cluster. In the core of NGC 6752, our HST data reveal a flat luminosity
function, in agreement with previous results. However, when we correct for the
increasing binary fraction at faint magnitudes, the LF begins to fall
immediately below the turn-off. This effect appears to be confined to the inner
core radius of the cluster.Comment: 10 pages, 3 figures Accepted to ApJ Lett Vol 513 Number
The complex channel networks of bone structure
Bone structure in mammals involves a complex network of channels (Havers and
Volkmann channels) required to nourish the bone marrow cells. This work
describes how three-dimensional reconstructions of such systems can be obtained
and represented in terms of complex networks. Three important findings are
reported: (i) the fact that the channel branching density resembles a power law
implies the existence of distribution hubs; (ii) the conditional node degree
density indicates a clear tendency of connection between nodes with degrees 2
and 4; and (iii) the application of the recently introduced concept of
hierarchical clustering coefficient allows the identification of typical scales
of channel redistribution. A series of important biological insights is drawn
and discussedComment: 3 pages, 1 figure, The following article has been submitted to
Applied Physics Letters. If it is published, it will be found online at
http://apl.aip.org
Wavepacket scattering on graphene edges in the presence of a (pseudo) magnetic field
The scattering of a Gaussian wavepacket in armchair and zigzag graphene edges
is theoretically investigated by numerically solving the time dependent
Schr\"odinger equation for the tight-binding model Hamiltonian. Our theory
allows to investigate scattering in reciprocal space, and depending on the type
of graphene edge we observe scattering within the same valley, or between
different valleys. In the presence of an external magnetic field, the well know
skipping orbits are observed. However, our results demonstrate that in the case
of a pseudo-magnetic field, induced by non-uniform strain, the scattering by an
armchair edge results in a non-propagating edge state.Comment: 8 pages, 7 figure
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