844 research outputs found
Evidences Against Temperature Chaos in Mean Field and Realistic Spin Glasses
We discuss temperature chaos in mean field and realistic 3D spin glasses. Our
numerical simulations show no trace of a temperature chaotic behavior for the
system sizes considered. We discuss the experimental and theoretical
implications of these findings.Comment: 4 pages in aps format. 6 .ps figures. It is better to print the paper
in colou
Finding long cycles in graphs
We analyze the problem of discovering long cycles inside a graph. We propose
and test two algorithms for this task. The first one is based on recent
advances in statistical mechanics and relies on a message passing procedure.
The second follows a more standard Monte Carlo Markov Chain strategy. Special
attention is devoted to Hamiltonian cycles of (non-regular) random graphs of
minimal connectivity equal to three
4D Spin Glasses in Magnetic Field Have a Mean Field like Phase
By using numerical simulations we show that the 4D Edwards Anderson
spin glass in magnetic field undergoes a mean field like phase transition. We
use a dynamical approach: we simulate large lattices (of volume ) and work
out the behavior of the system in limit where both and go to infinity,
but where the limit is taken first. By showing that the dynamic
overlap converges to a value smaller than the static one we exhibit replica
symmetry breaking. The critical exponents are compatible with the ones obtained
by mean field computations.Comment: Physrev format, 5 ps figures include
Numerical Evidence for Spontaneously Broken Replica Symmetry in 3D Spin Glasses
By numerical simulations of the Ising spin glass we find evidence that
spontaneous replica symmetry breaking theory and not the droplet model
describes with good accuracy the equilibrium behavior of the system.Comment: PHYSREV format, 2 .ps figures added with figure command in uufiles
forma
An algorithm for counting circuits: application to real-world and random graphs
We introduce an algorithm which estimates the number of circuits in a graph
as a function of their length. This approach provides analytical results for
the typical entropy of circuits in sparse random graphs. When applied to
real-world networks, it allows to estimate exponentially large numbers of
circuits in polynomial time. We illustrate the method by studying a graph of
the Internet structure.Comment: 7 pages, 3 figures, minor corrections, accepted versio
Cryptographical Properties of Ising Spin Systems
The relation between Ising spin systems and public-key cryptography is
investigated using methods of statistical physics. The insight gained from the
analysis is used for devising a matrix-based cryptosystem whereby the
ciphertext comprises products of the original message bits; these are selected
by employing two predetermined randomly-constructed sparse matrices. The
ciphertext is decrypted using methods of belief-propagation. The analyzed
properties of the suggested cryptosystem show robustness against various
attacks and competitive performance to modern cyptographical methods.Comment: 4 pages, 2 figure
Zero-temperature responses of a 3D spin glass in a field
We probe the energy landscape of the 3D Edwards-Anderson spin glass in a
magnetic field to test for a spin glass ordering. We find that the spin glass
susceptibility is anomalously large on the lattice sizes we can reach. Our data
suggest that a transition from the spin glass to the paramagnetic phase takes
place at B_c=0.65, though the possibility B_c=0 cannot be excluded. We also
discuss the question of the nature of the putative frozen phase.Comment: RevTex, 4 pages, 4 figures, clarifications and added reference
Glassiness in a model without energy barriers
We propose a microscopic model without energy barriers in order to explain
some generic features observed in structural glasses. The statics can be
exactly solved while the dynamics has been clarified using Monte Carlo
calculations. Although the model has no thermodynamic transition it captures
some of the essential features of real glasses, i.e., extremely slow
relaxation, time dependent hysteresis effects, anomalous increase of the
relaxation time and aging. This suggests that the effect of entropy barriers
can be an important ingredient to account for the behavior observed in real
glasses.Comment: 11 Pages + 3 Figures, Revtex, uufiles have been replaced since figure
2 was corrupted in the previous submissio
Brassica spp cover crop affects soil microbial activity, carbon and nitrogen nutrient dynamics
A general positive effect of Brassica on soil microbial biomass and its activity was observed at all European sites in no tilled soil at both sampling date. Conversely, Brassica under tillage may produce a negative effect on biochemical properties after CC suppression. The effect of Brassica on C and N dynamics differed among the european sites when soil was tilled. These preliminary results establish the bases for the evaluation of the interaction between the pedoclimatic conditions and Brassica spp effect on soil properties
Sudden emergence of q-regular subgraphs in random graphs
We investigate the computationally hard problem whether a random graph of
finite average vertex degree has an extensively large -regular subgraph,
i.e., a subgraph with all vertices having degree equal to . We reformulate
this problem as a constraint-satisfaction problem, and solve it using the
cavity method of statistical physics at zero temperature. For , we find
that the first large -regular subgraphs appear discontinuously at an average
vertex degree c_\reg{3} \simeq 3.3546 and contain immediately about 24% of
all vertices in the graph. This transition is extremely close to (but different
from) the well-known 3-core percolation point c_\cor{3} \simeq 3.3509. For
, the -regular subgraph percolation threshold is found to coincide with
that of the -core.Comment: 7 pages, 5 figure
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