23,915 research outputs found
Evolutionary approach to overcome initialization parameters in classification problems
Proceeding of: 7th International Work-Conference on Artificial and Natural Neural Networks, IWANN 2003 Maó, Menorca, Spain, June 3–6, 2003.The design of nearest neighbour classifiers is very dependent from some crucial parameters involved in learning, like the number of prototypes to use, the initial localization of these prototypes, and a smoothing parameter. These parameters have to be found by a trial and error process or by some automatic methods. In this work, an evolutionary approach based on Nearest Neighbour Classifier (ENNC), is described. Main property of this algorithm is that it does not require any of the above mentioned parameters. The algorithm is based on the evolution of a set of prototypes that can execute several operators in order to increase their quality in a local sense, and emerging a high classification accuracy for the whole classifier
Quantum Algorithm to Solve Satisfiability Problems
A new quantum algorithm is proposed to solve Satisfiability(SAT) problems by
taking advantage of non-unitary transformation in ground state quantum
computer. The energy gap scale of the ground state quantum computer is analyzed
for 3-bit Exact Cover problems. The time cost of this algorithm on general SAT
problems is discussed.Comment: 5 pages, 3 figure
Imprinted Networks as Chiral Pumps
We investigate the interaction between a chirally imprinted network and a
solvent of chiral molecules. We find, a liquid crystalline polymer network is
preferentially swollen by one component of a racemic solvent. This ability to
separate is linked to the chiral order parameter of the network, and can be
reversibly controlled via temperature or a mechanical deformation. It is
maximal near the point at which the network loses its imprinted structure. One
possible practical application of this effect would be a mechanical device for
sorting mixed chiral molecules.Comment: 4 pages, 5 figure
Neutron star matter in the quark-meson coupling model in strong magnetic fields
The effects of strong magnetic fields on neutron star matter are investigated
in the quark-meson coupling (QMC) model. The QMC model describes a nuclear
many-body system as nonoverlapping MIT bags in which quarks interact through
self-consistent exchange of scalar and vector mesons in the mean-field
approximation. The results of the QMC model are compared with those obtained in
a relativistic mean-field (RMF) model. It is found that quantitative
differences exist between the QMC and RMF models, while qualitative trends of
the magnetic field effects on the equation of state and composition of neutron
star matter are very similar.Comment: 16 pages, 4 figure
Quasi-classical determination of the in-plane magnetic field phase diagram of superconducting Sr_2RuO_4
We have carried out a determination of the magnetic-field-temperature (H-T)
phase diagram for realistic models of the high field superconducting state of
tetragonal Sr_2RuO_4 with fields oriented in the basal plane. This is done by a
variational solution of the Eilenberger equations.This has been carried for
spin-triplet gap functions with a {\bf d}-vector along the c-axis (the chiral
p-wave state) and with a {\bf d}-vector that can rotate easily in the basal
plane. We find that, using gap functions that arise from a combination of
nearest and next nearest neighbor interactions, the upper critical field can be
approximately isotropic as the field is rotated in the basal plane. For the
chiral {\bf d}-vector, we find that this theory generically predicts an
additional phase transition in the vortex state. For a narrow range of
parameters, the chiral {\bf d}-vector gives rise to a tetracritical point in
the H-T phase diagram. When this tetracritical point exists, the resulting
phase diagram closely resembles the experimentally measured phase diagram for
which two transitions are only observed in the high field regime. For the
freely rotating in-plane {\bf d}-vector, we also find that additional phase
transition exists in the vortex phase. However, this phase transition
disappears as the in-plane {\bf d}-vector becomes weakly pinned along certain
directions in the basal plane.Comment: 12 pages, 8 figure
Spin-spin correlators in Majorana representation
In the Majorana representation of a spin 1/2 we find an identity which
relates spin-spin correlators to one-particle fermionic correlators. This
should be contrasted with the straightforward approach in which two-particle
(four-fermion) correlators need to be calculated. We discuss applications to
the analysis of the dynamics of a spin coupled to a dissipative environment and
of a quantum detector performing a continuous measurement of a qubit's state
Lattice dynamics and electron-phonon coupling in Sr2RuO4
The lattice dynamics in SrRuO has been studied by inelastic neutron
scattering combined with shell-model calculations. The in-plane bond-stretching
modes in SrRuO exhibit a normal dispersion in contrast to all
electronically doped perovskites studied so far. Evidence for strong electron
phonon coupling is found for c-polarized phonons suggesting a close connection
with the anomalous c-axis charge transport in SrRuO.Comment: 11 pages, 8 figures 2 table
Spin dynamics from Majorana fermions
Using the Majorana fermion representation of spin-1/2 local moments, we show
how it is possible to directly read off the dynamic spin correlation and
susceptibility from the one-particle propagator of the Majorana fermion. We
illustrate our method by applying it to the spin dynamics of a non-equilibrium
quantum dot, computing the voltage-dependent spin relaxation rate and showing
that, at weak coupling, the fluctuation-dissipation relation for the spin of a
quantum dot is voltage-dependent. We confirm the voltage-dependent Curie
susceptibility recently found by Parcollet and Hooley [Phys. Rev. B {\bf 66},
085315 (2002)].Comment: Small modifications added to figure and tex
Emergence of intrinsic superconductivity below 1.178 K in the topologically non-trivial semimetal state of CaSn3
Topological materials which are also superconducting are of great current
interest, since they may exhibit a non-trivial topologically-mediated
superconducting phase. Although there have been many reports of pressure-tuned
or chemical-doping-induced superconductivity in a variety of topological
materials, there have been few examples of intrinsic, ambient pressure
superconductivity in a topological system having a stoichiometric composition.
Here, we report that the pure intermetallic CaSn3 not only exhibits topological
fermion properties but also has a superconducting phase at 1.178 K under
ambient pressure. The topological fermion properties, including the nearly zero
quasi-particle mass and the non-trivial Berry phase accumulated in cyclotron
motions, were revealed from the de Haas-van Alphen (dHvA) quantum oscillation
studies of this material. Although CaSn3 was previously reported to be
superconducting at 4.2K, our studies show that the superconductivity at 4.2K is
extrinsic and caused by Sn on the degraded surface, whereas its intrinsic bulk
superconducting transition occurs at 1.178 K. These findings make CaSn3 a
promising candidate for exploring new exotic states arising from the interplay
between non-trivial band topology and superconductivity, e.g. topological
superconductivityComment: 20 pages,4 figure
- …