7,405 research outputs found
A System for Induction of Oblique Decision Trees
This article describes a new system for induction of oblique decision trees.
This system, OC1, combines deterministic hill-climbing with two forms of
randomization to find a good oblique split (in the form of a hyperplane) at
each node of a decision tree. Oblique decision tree methods are tuned
especially for domains in which the attributes are numeric, although they can
be adapted to symbolic or mixed symbolic/numeric attributes. We present
extensive empirical studies, using both real and artificial data, that analyze
OC1's ability to construct oblique trees that are smaller and more accurate
than their axis-parallel counterparts. We also examine the benefits of
randomization for the construction of oblique decision trees.Comment: See http://www.jair.org/ for an online appendix and other files
accompanying this articl
Nematic - Isotropic Transition in Porous Media - a Monte Carlo Study
We propose a lattice model to simulate the influence of porous medium on the
Nematic - Isotropic transition of liquid crystal confined to the pores. The
effects of pore size and pore connectivity are modelled through a disorder
parameter. Monte Carlo calculations based on the model leads to results that
compare well with experiments.Comment: 11 pages; 4 figure
Complex free energy landscapes in biaxial nematics and role of repulsive interactions : A Wang - Landau study
General quadratic Hamiltonian models, describing interaction between crystal
molecules (typically with symmetry) take into account couplings
between their uniaxial and biaxial tensors. While the attractive contributions
arising from interactions between similar tensors of the participating
molecules provide for eventual condensation of the respective orders at
suitably low temperatures, the role of cross-coupling between unlike tensors is
not fully appreciated. Our recent study with an advanced Monte Carlo technique
(entropic sampling) showed clearly the increasing relevance of this cross term
in determining the phase diagram, contravening in some regions of model
parameter space, the predictions of mean field theory and standard Monte Carlo
simulation results. In this context, we investigated the phase diagrams and the
nature of the phases therein, on two trajectories in the parameter space: one
is a line in the interior region of biaxial stability believed to be
representative of the real systems, and the second is the extensively
investigated parabolic path resulting from the London dispersion approximation.
In both the cases, we find the destabilizing effect of increased cross-coupling
interactions, which invariably result in the formation of local biaxial
organizations inhomogeneously distributed. This manifests as a small, but
unmistakable, contribution of biaxial order in the uniaxial phase.The free
energy profiles computed in the present study as a function of the two dominant
order parameters indicate complex landscapes, reflecting the difficulties in
the ready realization of the biaxial phase in the laboratory.Comment: 23 pages, 12 figure
Haldane Exclusion Statistics and the Boltzmann Equation
We generalize the collision term in the one-dimensional Boltzmann-Nordheim
transport equation for quasiparticles that obey the Haldane exclusion
statistics. For the equilibrium situation, this leads to the ``golden rule''
factor for quantum transitions. As an application of this, we calculate the
density response function of a one-dimensional electron gas in a periodic
potential, assuming that the particle-hole excitations are quasiparticles
obeying the new statistics. We also calculate the relaxation time of a nuclear
spin in a metal using the modified golden rule.Comment: version accepted for publication in J. of Stat. Phy
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