1,827 research outputs found
Classification of public administration complaints
Complaint management is a problem faced by many organizations that is both vital to customer image and highly dependent on human resources. This work attempts to tackle a part of the problem, by classifying summaries of complaints using machine learning models in order to better redirect these to the appropriate responders. The main challenges of this task is that training datasets are often small and highly imbalanced. This can can have a big impact on the performance of classification models. The dataset analyzed in this work suffers from both of these problems, being relatively small and having labels in different proportions. In this work, two different techniques are analyzed: combining classes together to increase the number of elements of the new class; and, providing new artificial examples for some classes via translation into other languages. The classification models explored were the following: k-NN, SVM, Naïve Bayes, boosting, and Deep Learning approaches, including transformers. The paper concludes that although, as expected, the classes with little representation are hard to classify, the techniques explored helped to boost the performance, especially in the classes with a low number of elements. SVM and BERT-based models outperformed their peers.info:eu-repo/semantics/publishedVersio
Photoluminescence spectrum of an interacting two-dimensional electron gas at \nu=1
We report on the theoretical photoluminescence spectrum of the interacting
two-dimensional electron gas at filling factor one (\nu=1). We considered a
model similar to the one adopted to study the X-ray spectra of metals and
solved it analytically using the bosonization method previously developed for
the two-dimensional electron gas at \nu=1. We calculated the emission spectra
of the right and the left circularly polarized radiations for the situations
where the distance between the two-dimensional electron gas and the valence
band hole are smaller and greater than the magnetic length. For the former, we
showed that the polarized photoluminescence spectra can be understood as the
recombination of the so-called excitonic state with the valence band hole
whereas, for the latter, the observed emission spectra can be related to the
recombination of a state formed by a spin down electron bound to n spin waves.
This state seems to be a good description for the quantum Hall skyrmion.Comment: Revised version, 10 pages, 5 figures, accepted to Phys. Rev.
Studies in a Random Noise Model of Decoherence
We study the effects of noise and decoherence for a double-potential well
system, suitable for the fabrication of qubits and quantum logic elements. A
random noise term is added to the hamiltonian, the resulting wavefunction found
numerically and the density matrix obtained by averaging over noise signals.
Analytic solutions using the two-state model are obtained and found to be
generally in agreement.
In particular, a simple formula for the decoherence rate in terms of the
noise parameters in the two-state model is reviewed and verified for the full
simulation with the multi-level system. The formalism is extended to describe
multiple sources of noise or different "dephasing" axes at the same time.
Furthermore, the old formula for the "Turing-Watched Pot" effect is generalized
to the case where the environmental interactions do not conserve the "quality"
in question.
Various forms for the noise signal are investigated. An interesting result is
the importance of the noise power at low frequency. If it vanishes there is, in
leading order, no decoherence. This is verified in a numerical simulation where
two apparently similar noise signals, but differing in the power at zero
frequency, give strikingly different decoherence effects. A short discussion of
situations dominated by low frequency noise is given.Comment: 27 pages, 10 figures. New section added on Very Low Frequency Noise,
with two additional figures. Conclusions, Abstract modified accordingly.
Various other small editorial changes and clarification
Quantum effect in the diffusion along a potential barrier: Comments on the synthesis of superheavy elements
We discuss a quantum effect in the diffusion process by developing a theory,
which takes the finite curvature of the potential field into account. The
transport coefficients of our theory satisfy the well-known
fluctuation-dissipation theorem in the limit of Markovian approximation in the
cases of diffusion in a flat potential and in a potential well. For the
diffusion along a potential barrier, the diffusion coefficient can be related
to the friction coefficient by an analytic continuation of the
fluctuation-dissipation theorem for the case of diffusion along a potential
well in the asymptotic time, but contains strong non-Markovian effects at short
times. By applying our theory to the case of realistic values of the
temperature, the barrier curvature, and the friction coefficient, we show that
the quantum effects will play significant roles in describing the synthesis of
superheavy elements, i.e., the evolution from the fusion barrier to the
conditional saddle, in terms of a diffusion process. We especially point out
the importance of the memory effect, which increases at lower temperatures. It
makes the net quantum effects enhance the probability of crossing the
conditional saddle.Comment: 12 pages, 3 figures, accepted for publication in Phys. Rev.
NMR linewidth and Skyrmion localization in quantum Hall ferromagnets
The non-monotonic behavior of the NMR signal linewidth in the 2D quantum Hall
system is explained in terms of the interplay between skyrmions localization,
due to the influence of disorder, and the non-trivial temperature dependent
skyrmion dynamics.Comment: 5 pages, 2 figure
Models for local ohmic quantum dissipation
We construct model master equations for local quantum dissipation. The master
equations are in the form of Lindblad generators, with imposed constraints that
the dissipations be strictly linear (i.e. ohmic), isotropic and translationally
invariant. A particular form for is chosen to satisfy the constraints. The
resulting master equations are given in both the Schr\"odinger and Heisenberg
forms. We obtain fluctuation-dissipation relations, and discuss the relaxation
of average kinetic energy to effective thermal equilibrium values. We compare
our results to the Dekker and the Caldeira-Leggett master equations. These
master equations allow a more general approach to quantum dissipation and the
dynamics of quantum coherence to account for the nontrivial system-environment
coupling in a local environment.Comment: 19 pages, REVTEX, PSU/TH/12
Finite-momentum condensate of magnetic excitons in a bilayer quantum Hall system
We study the bilayer quantum Hall system at total filling factor \nu_T = 1
within a bosonization formalism which allows us to approximately treat the
magnetic exciton as a boson. We show that in the region where the distance
between the two layers is comparable to the magnetic length, the ground state
of the system can be seen as a finite-momentum condensate of magnetic excitons
provided that the excitation spectrum is gapped. We analyze the stability of
such a phase within the Bogoliubov approximation firstly assuming that only one
momentum Q0 is macroscopically occupied and later we consider the same
situation for two modes \pm Q0. We find strong evidences that a first-order
quantum phase transition at small interlayer separation takes place from a
zero-momentum condensate phase, which corresponds to Halperin 111 state, to a
finite-momentum condensate of magnetic excitons.Comment: 18 pages, 11 figures, final versio
Fluctuation-dissipation theorem and quantum tunneling with dissipation at finite temperature
A reformulation of the fluctuation-dissipation theorem of Callen and Welton
is presented in such a manner that the basic idea of Feynman-Vernon and
Caldeira -Leggett of using an infinite number of oscillators to simulate the
dissipative medium is realized manifestly without actually introducing
oscillators. If one assumes the existence of a well defined dissipative
coefficient which little depends on the temperature in the energy
region we are interested in, the spontanous and induced emissions as well as
induced absorption of these effective oscillators with correct Bose
distribution automatically appears.
Combined with a dispersion relation, we reproduce the tunneling formula in
the presence of dissipation at finite temperature without referring to an
explicit model Lagrangian. The fluctuation-dissipation theorem of Callen-Welton
is also generalized to the fermionic dissipation (or fluctuation) which allows
a transparent physical interpretation in terms of second quantized fermionic
oscillators. This fermionic version of fluctuation-dissipation theorem may
become relevant in the analyses of, for example, fermion radiation from a black
hole and also supersymmetry at the early universe.Comment: 19 pages. Phys. Rev. E (in press
Effective theory of fluctuating circulating currents in high-Tc cuprates
We derive an effective dissipative quantum field theory for fluctuating
orbital currents in clean sheets of high- cuprates, based on a
three-band model. The Coulomb repulsion term between - and -sites is
decoupled in terms of current operators representing horizontal and vertical
parts of circulating currents within each unit cell of the lattice. The
model has ordering of currents at finite temperatures. The dissipative kernel
in the model is of the form , indicating Landau damping.
Applications of the effective theory to other models are also discussed.Comment: 5 pages, 1 figure, 16 references. To be published in Physical Review
Quasiclassical Equations of Motion for Nonlinear Brownian Systems
Following the formalism of Gell-Mann and Hartle, phenomenological equations
of motion are derived from the decoherence functional formalism of quantum
mechanics, using a path-integral description. This is done explicitly for the
case of a system interacting with a ``bath'' of harmonic oscillators whose
individual motions are neglected. The results are compared to the equations
derived from the purely classical theory. The case of linear interactions is
treated exactly, and nonlinear interactions are compared using classical and
quantum perturbation theory.Comment: 24 pages, CALT-68-1848 (RevTeX 2.0 macros
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