37 research outputs found
Smart random walkers: the cost of knowing the path
In this work we study the problem of targeting signals in networks using
entropy information measurements to quantify the cost of targeting. We
introduce a penalization rule that imposes a restriction to the long paths and
therefore focus the signal to the target. By this scheme we go continuously
from fully random walkers to walkers biased to the target. We found that the
optimal degree of penalization is mainly determined by the topology of the
network. By analyzing several examples, we have found that a small amount of
penalization reduces considerably the typical walk length, and from this we
conclude that a network can be efficiently navigated with restricted
information.Comment: 9 pages, 11 figure
A study of memory effects in a chess database
A series of recent works studying a database of chronologically sorted chess
games --containing 1.4 million games played by humans between 1998 and 2007--
have shown that the popularity distribution of chess game-lines follows a
Zipf's law, and that time series inferred from the sequences of those
game-lines exhibit long-range memory effects. The presence of Zipf's law
together with long-range memory effects was observed in several systems,
however, the simultaneous emergence of these two phenomena were always studied
separately up to now. In this work, by making use of a variant of the
Yule-Simon preferential growth model, introduced by Cattuto et al., we provide
an explanation for the simultaneous emergence of Zipf's law and long-range
correlations memory effects in a chess database. We find that Cattuto's Model
(CM) is able to reproduce both, Zipf's law and the long-range correlations,
including size-dependent scaling of the Hurst exponent for the corresponding
time series. CM allows an explanation for the simultaneous emergence of these
two phenomena via a preferential growth dynamics, including a memory kernel, in
the popularity distribution of chess game-lines. This mechanism results in an
aging process in the chess game-line choice as the database grows. Moreover, we
find burstiness in the activity of subsets of the most active players, although
the aggregated activity of the pool of players displays inter-event times
without burstiness. We show that CM is not able to produce time series with
bursty behavior providing evidence that burstiness is not required for the
explanation of the long-range correlation effects in the chess database.Comment: 18 pages, 7 figure
Memory and long-range correlations in chess games
In this paper we report the existence of long-range memory in the opening
moves of a chronologically ordered set of chess games using an extensive chess
database. We used two mapping rules to build discrete time series and analyzed
them using two methods for detecting long-range correlations; rescaled range
analysis and detrented fluctuation analysis. We found that long-range memory is
related to the level of the players. When the database is filtered according to
player levels we found differences in the persistence of the different subsets.
For high level players, correlations are stronger at long time scales; whereas
in intermediate and low level players they reach the maximum value at shorter
time scales. This can be interpreted as a signature of the different strategies
used by players with different levels of expertise. These results are robust
against the assignation rules and the method employed in the analysis of the
time series.Comment: 12 pages, 5 figures. Published in Physica
Disorder-induced mechanism for positive exchange bias fields
We propose a mechanism to explain the phenomenon of positive exchange bias on
magnetic bilayered systems. The mechanism is based on the formation of a domain
wall at a disordered interface during field cooling (FC) which induces a
symmetry breaking of the antiferromagnet, without relying on any ad hoc
assumption about the coupling between the ferromagnetic (FM) and
antiferromagnetic (AFM) layers. The domain wall is a result of the disorder at
the interface between FM and AFM, which reduces the effective anisotropy in the
region. We show that the proposed mechanism explains several known experimental
facts within a single theoretical framework. This result is supported by Monte
Carlo simulations on a microscopic Heisenberg model, by micromagnetic
calculations at zero temperature and by mean field analysis of an effective
Ising like phenomenological model.Comment: 5 pages, 4 figure
Inverse transition in the two dimensional dipolar frustrated ferromagnet
We show that the mean field phase diagram of the dipolar frustrated
ferromagnet in an external field presents an inverse transition in the
field-temperature plane. The presence of this type of transition has recently
been observed experimentally in ultrathin films of Fe/Cu(001). We study a
coarse-grained model Hamiltonian in two dimensions. The model supports stripe
and bubble equilibrium phases, as well as the paramagnetic phase. At variance
with common expectations, already in a single mode approximation, the model
shows a sequence of paramagnetic-bubbles-stripes-paramagnetic phase transitions
upon lowering the temperature at fixed external field. Going beyond the single
mode approximation leads to the shrinking of the bubbles phase, which is
restricted to a small region near the zero field critical temperature. Monte
Carlo simulations results with a Heisenberg model are consistent with the mean
field results.Comment: 8 pages, 6 figure
Innovation and Nested Preferential Growth in Chess Playing Behavior
Complexity develops via the incorporation of innovative properties. Chess is
one of the most complex strategy games, where expert contenders exercise
decision making by imitating old games or introducing innovations. In this
work, we study innovation in chess by analyzing how different move sequences
are played at the population level. It is found that the probability of
exploring a new or innovative move decreases as a power law with the frequency
of the preceding move sequence. Chess players also exploit already known move
sequences according to their frequencies, following a preferential growth
mechanism. Furthermore, innovation in chess exhibits Heaps' law suggesting
similarities with the process of vocabulary growth. We propose a robust
generative mechanism based on nested Yule-Simon preferential growth processes
that reproduces the empirical observations. These results, supporting the
self-similar nature of innovations in chess are important in the context of
decision making in a competitive scenario, and extend the scope of relevant
findings recently discovered regarding the emergence of Zipf's law in chess.Comment: 8 pages, 4 figures, accepted for publication in Europhysics Letters
(EPL