30,103 research outputs found
Tricriticality and Reentrance in a Naive Spin-Glass Model
In this paper a spin-1 spin-glass model under the presence of a uniform
crystal field is investigated. It is shown that the model presents both
continuous and first-order phase transition separated by a tricritical point.
The phase diagram is obtained within the replica-symmetric solution and
exhibits reentrance phenomena at low temperatures. Possibly it is the simplest
model which can describe inverse freezing phenomena.Comment: 12 pages, 1 figur
Hierarchical Features of Large-Scale Cortical Connectivity
The analysis of complex networks has revealed patterns of organization in a
variety of natural and artificial systems, including neuronal networks of the
brain at multiple scales. In this paper, we describe a novel analysis of the
large-scale connectivity between regions of the mammalian cerebral cortex,
utilizing a set of hierarchical measurements proposed recently. We examine
previously identified functional clusters of brain regions in macaque visual
cortex and cat cortex and find significant differences between such clusters in
terms of several hierarchical measures, revealing differences in how these
clusters are embedded in the overall cortical architecture. For example, the
ventral cluster of visual cortex maintains structurally more segregated, less
divergent connections than the dorsal cluster, which may point to functionally
different roles of their constituent brain regions.Comment: 17 pages, 6 figure
Broad distribution effects in sums of lognormal random variables
The lognormal distribution describing, e.g., exponentials of Gaussian random
variables is one of the most common statistical distributions in physics. It
can exhibit features of broad distributions that imply qualitative departure
from the usual statistical scaling associated to narrow distributions.
Approximate formulae are derived for the typical sums of lognormal random
variables. The validity of these formulae is numerically checked and the
physical consequences, e.g., for the current flowing through small tunnel
junctions, are pointed out.Comment: 14 pages, 9 figures. Minor changes + Gini coefficient and 4 refs.
adde
- …