2,260 research outputs found
Evolving rules for document classification
We describe a novel method for using Genetic Programming to create compact classification rules based on combinations of N-Grams (character strings). Genetic programs acquire fitness by producing rules that are effective classifiers in terms of precision and recall when evaluated against a set of training documents. We describe a set of functions and terminals and provide results from a classification task using the Reuters 21578 dataset. We also suggest that because the induced rules are meaningful to a human analyst they may have a number of other uses beyond classification and provide a basis for text mining applications
Observing Long Cosmic Strings Through Gravitational Lensing
We consider the gravitational lensing produced by long cosmic strings formed
in a GUT scale phase transition. We derive a formula for the deflection of
photons which pass near the strings that reduces to an integral over the light
cone projection of the string configuration plus constant terms which are not
important for lensing. Our strings are produced by performing numerical
simulations of cosmic string networks in flat, Minkowski space ignoring the
effects of cosmological expansion. These strings have more small scale
structure than those from an expanding universe simulation - fractal dimension
1.3 for Minkowski versus 1.1 for expanding - but share the same qualitative
features. Lensing simulations show that for both point-like and extended
objects, strings produce patterns unlike more traditional lenses, and, in
particluar, the kinks in strings tend to generate demagnified images which
reside close to the string. Thus lensing acts as a probe of the small scale
structure of a string. Estimates of lensing probablity suggest that for string
energy densities consistant with string seeded structure formation, on the
order of tens of string lenses should be observed in the Sloan Digital Sky
Survey quasar catalog. We propose a search strategy in which string lenses
would be identified in the SDSS quasar survey, and the string nature of the
lens can be confirmed by the observation of nearby high redshift galaxies which
are also be lensed by the string.Comment: 24 pages revtex with 12 postscript firgure
Autonomous three-dimensional formation flight for a swarm of unmanned aerial vehicles
This paper investigates the development of a new guidance algorithm for a formation of unmanned aerial vehicles. Using the new approach of bifurcating potential fields, it is shown that a formation of unmanned aerial vehicles can be successfully controlled such that verifiable autonomous patterns are achieved, with a simple parameter switch allowing for transitions between patterns. The key contribution that this paper presents is in the development of a new bounded bifurcating potential field that avoids saturating the vehicle actuators, which is essential for real or safety-critical applications. To demonstrate this, a guidance and control method is developed, based on a six-degreeof-freedom linearized aircraft model, showing that, in simulation, three-dimensional formation flight for a swarm of unmanned aerial vehicles can be achieved
Entanglement of electrons in interacting molecules
Quantum entanglement is a concept commonly used with reference to the
existence of certain correlations in quantum systems that have no classical
interpretation. It is a useful resource to enhance the mutual information of
memory channels or to accelerate some quantum processes as, for example, the
factorization in Shor's Algorithm. Moreover, entanglement is a physical
observable directly measured by the von Neumann entropy of the system. We have
used this concept in order to give a physical meaning to the electron
correlation energy in systems of interacting electrons. The electronic
correlation is not directly observable, since it is defined as the difference
between the exact ground state energy of the many--electrons Schroedinger
equation and the Hartree--Fock energy. We have calculated the correlation
energy and compared with the entanglement, as functions of the nucleus--nucleus
separation using, for the hydrogen molecule, the Configuration Interaction
method. Then, in the same spirit, we have analyzed a dimer of ethylene, which
represents the simplest organic conjugate system, changing the relative
orientation and distance of the molecules, in order to obtain the configuration
corresponding to maximum entanglement.Comment: 15 pages, 7 figures, standard late
Entanglement and the SU(2) phase states in atomic systems
We show that a system of 2n identical two-level atoms interacting with n
cavity photons manifests entanglement and that the set of entangled states
coincides with the so-called SU(2) phase states. In particular, violation of
classical realism in terms of the GHZ and GHSH conditions is proved. We discuss
a new property of entanglement expressed in terms of local measurements. We
also show that generation of entangled states in the atom-photon systems under
consideration strongly depends on the choice of initial conditions and that the
parasitic influence of cavity detuning can be compensated through the use of
Kerr medium.Comment: 10 pages, 1 figur
Gravitational-Wave Stochastic Background Detection with Resonant-Mass Detectors
In this paper we discuss how the standard optimal Wiener filter theory can be
applied, within a linear approximation, to the detection of an isotropic
stochastic gravitational-wave background with two or more detectors. We apply
then the method to the AURIGA-NAUTILUS pair of ultra low temperature bar
detectors, near to operate in coincidence in Italy, obtaining an estimate for
the sensitivity to the background spectral density of $\simeq 10^{-49}\
Hz^{-1}\simeq 8\times10^{-5}\times\rho_c\rho_c\simeq1.9 \times 10^{-26}\
kg/m^3\simeq 6
\times10^{-5}\times\rho_c\simeq 2\times10^{-5}\times
\rho_c\simeq 2 \times10^{-6}\rho_c$.Comment: 32 pages, postscript file, also available at
http://axln01.lnl.infn.it/reports/stoch.htm
Test of Bell's Inequality using the Spin Filter Effect in Ferromagnetic Semiconductor Micro-structures
A theoretical proposal for testing Bell's inequality in mesoscopic systems is
presented. We show that the entanglement of two electron spins can be detected
in the spin filter effect in the mesoscopic semiconductor / ferromagnetic
semiconductor / semiconductor junction. The current-current correlation
function is calculated by use of the quantum scattering theory and we compare
it with the local hidden variable theory. We also discuss the influence of an
imperfect spin filter and derive the condition to see the violation of Bell's
inequality experimentally.Comment: 6 pages, 4 figures, submitted to J. Phys. Soc. Jp
Contribution of Long Wavelength Gravitational Waves to the CMB Anisotropy
We present an in depth discussion of the production of gravitational waves
from an inflationary phase that could have occurred in the early universe,
giving derivations for the resulting spectrum and energy density. We also
consider the large-scale anisotropy in the cosmic microwave background
radiation coming from these waves. Assuming that the observed quadrupole
anisotropy comes mostly from gravitational waves (consistent with the
predictions of a flat spectrum of scalar density perturbations and the measured
dipole anisotropy) we describe in detail how to derive a value for the scale of
inflation of GeV, which is at a particularly interesting
scale for particle physics. This upper limit corresponds to a 95\% confidence
level upper limit on the scale of inflation assuming only that the quadrupole
anisotropy from gravitational waves is not cancelled by another source. Direct
detection of gravitational waves produced by inflation near this scale will
have to wait for the next generation of detectors.Comment: (LaTeX 16 pages), 2 figures not included, YCTP-P16-9
Self-Reported Occupational Exposure to HIV and Factors Influencing its Management Practice: A Study of Healthcare Workers in Tumbi and Dodoma Hospitals, Tanzania.
Blood borne infectious agents such as hepatitis B virus (HBV), hepatitis C virus (HCV) and human immune deficiency virus (HIV) constitute a major occupational hazard for healthcare workers (HCWs). To some degree it is inevitable that HCWs sustain injuries from sharp objects such as needles, scalpels and splintered bone during execution of their duties. However, in Tanzania, there is little or no information on factors that influence the practice of managing occupational exposure to HIV by HCWs. This study was conducted to determine the prevalence of self-reported occupational exposure to HIV among HCWs and explore factors that influence the practice of managing occupational exposure to HIV by HCWs in Tanzania. Self-administered questionnaire was designed to gather information of healthcare workers' occupational exposures in the past 12 months and circumstances in which these injuries occurred. Practice of managing occupational exposure was assessed by the following questions: Nearly half of the HCWs had experienced at least one occupational injury in the past 12 months. Though most of the occupational exposures to HIV were experienced by female nurses, non-medical hospital staff received PEP more frequently than nurses and doctors. Doctors and nurses frequently encountered occupational injuries in surgery room and labor room respectively. HCWs with knowledge on the possibility of HIV transmission and those who knew whom to contact in event of occupational exposure to HIV were less likely to have poor practice of managing occupational exposure. Needle stick injuries and splashes are common among HCWs at Tumbi and Dodoma hospitals. Knowledge of the risk of HIV transmission due to occupational exposure and knowing whom to contact in event of exposure predicted practice of managing the exposure. Thus provision of health education on occupational exposure may strengthen healthcare workers' practices to manage occupational exposure
Scaling Property of the global string in the radiation dominated universe
We investigate the evolution of the global string network in the radiation
dominated universe by use of numerical simulations in 3+1 dimensions. We find
that the global string network settles down to the scaling regime where the
energy density of global strings, , is given by with the string tension per unit length and the scaling parameter,
, irrespective of the cosmic time. We also find that the
loop distribution function can be fitted with that predicted by the so-called
one scale model. Concretely, the number density, , of the loop with
the length, , is given by
where and is related with the Nambu-Goldstone(NG)
boson radiation power from global strings, , as with
. Therefore, the loop production function also scales and
the typical scale of produced loops is nearly the horizon distance. Thus, the
evolution of the global string network in the radiation dominated universe can
be well described by the one scale model in contrast with that of the local
string network.Comment: 18 pages, 9 figures, to appear in Phys. Rev.
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