19,946 research outputs found
Discovering Regression Rules with Ant Colony Optimization
The majority of Ant Colony Optimization (ACO) algorithms for data mining have dealt with classification or clustering problems. Regression remains an unexplored research area to the best of our knowledge. This paper proposes a new ACO algorithm that generates regression rules for data mining applications. The new algorithm combines components from an existing deterministic (greedy) separate and conquer algorithm—employing the same quality metrics and continuous attribute processing techniques—allowing a comparison of the two. The new algorithm has been shown to decrease the relative root mean square error when compared to the greedy algorithm. Additionally a different approach to handling continuous attributes was investigated showing further improvements were possible
Fresh look at randomly branched polymers
We develop a new, dynamical field theory of isotropic randomly branched
polymers, and we use this model in conjunction with the renormalization group
(RG) to study several prominent problems in the physics of these polymers. Our
model provides an alternative vantage point to understand the swollen phase via
dimensional reduction. We reveal a hidden Becchi-Rouet-Stora (BRS) symmetry of
the model that describes the collapse (-)transition to compact
polymer-conformations, and calculate the critical exponents to 2-loop order. It
turns out that the long-standing 1-loop results for these exponents are not
entirely correct. A runaway of the RG flow indicates that the so-called
-transition could be a fluctuation induced first order
transition.Comment: 4 page
Levy-flight spreading of epidemic processes leading to percolating clusters
We consider two stochastic processes, the Gribov process and the general
epidemic process, that describe the spreading of an infectious disease. In
contrast to the usually assumed case of short-range infections that lead, at
the critical point, to directed and isotropic percolation respectively, we
consider long-range infections with a probability distribution decaying in d
dimensions with the distance as 1/R^{d+\sigma}. By means of Wilson's momentum
shell renormalization-group recursion relations, the critical exponents
characterizing the growing fractal clusters are calculated to first order in an
\epsilon-expansion. It is shown that the long-range critical behavior changes
continuously to its short-range counterpart for a decay exponent of the
infection \sigma =\sigma_c>2.Comment: 9 pages ReVTeX, 2 postscript figures included, submitted to Eur.
Phys. J.
Mean-field scaling function of the universality class of absorbing phase transitions with a conserved field
We consider two mean-field like models which belong to the universality class
of absorbing phase transitions with a conserved field. In both cases we derive
analytically the order parameter as function of the control parameter and of an
external field conjugated to the order parameter. This allows us to calculate
the universal scaling function of the mean-field behavior. The obtained
universal function is in perfect agreement with recently obtained numerical
data of the corresponding five and six dimensional models, showing that four is
the upper critical dimension of this particular universality class.Comment: 8 pages, 2 figures, accepted for publication in J. Phys.
Drived diffusion of vector fields
A model for the diffusion of vector fields driven by external forces is
proposed. Using the renormalization group and the -expansion, the
dynamical critical properties of the model with gaussian noise for dimensions
below the critical dimension are investigated and new transport universality
classes are obtained.Comment: 11 pages, title changed, anisotropic diffusion further discussed and
emphasize
Compaction dynamics in ductile granular media
Ductile compaction is common in many natural systems, but the temporal
evolution of such systems is rarely studied. We observe surprising oscillations
in the weight measured at the bottom of a self-compacting ensemble of ductile
grains. The oscillations develop during the first ten hours of the experiment,
and usually persist through the length of an experiment (one week). The weight
oscillations are connected to the grain--wall contacts, and are directly
correlated with the observed strain evolution and the dynamics of grain--wall
contacts during the compaction. Here, we present the experimental results and
characteristic time constants of the system, and discuss possible reasons for
the measured weight oscillations.Comment: 11 pages, 14 figure
Influence of humidity on granular packings with moving walls
A significant dependence on the relative humidity H for the apparent mass
(Mapp) measured at the bottom of a granular packing inside a vertical tube in
relative motion is demonstrated experimentally. While the predictions of
Janssen's model are verified for all values of H investigated (25%< H <80%),
Mapp increases with time towards a limiting value at high relative humidities
(H>60%) but remains constant at lower ones (H=25%). The corresponding Janssen
length is nearly independent of the tube velocity for H>60% but decreases
markedly for H=25%. Other differences are observed on the motion of individual
beads in the packing. For H=25%, they are almost motionless while the mean
particle fraction of the packing remains constant; for H>60% the bead motion is
much more significant and the mean particle fraction decreases. The dependence
of these results on the bead diameter and their interpretation in terms of the
influence of capillary forces are discussed.Comment: 6 pages, 6 figure
Out-of-equilibrium critical dynamics at surfaces: Cluster dissolution and non-algebraic correlations
We study nonequilibrium dynamical properties at a free surface after the
system is quenched from the high-temperature phase into the critical point. We
show that if the spatial surface correlations decay sufficiently rapidly the
surface magnetization and/or the surface manifold autocorrelations has a
qualitatively different universal short time behavior than the same quantities
in the bulk. At a free surface cluster dissolution may take place instead of
domain growth yielding stationary dynamical correlations that decay in a
stretched exponential form. This phenomenon takes place in the
three-dimensional Ising model and should be observable in real ferromagnets.Comment: 4 pages, 4 figure
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