7,876 research outputs found
On the Usability of Probably Approximately Correct Implication Bases
We revisit the notion of probably approximately correct implication bases
from the literature and present a first formulation in the language of formal
concept analysis, with the goal to investigate whether such bases represent a
suitable substitute for exact implication bases in practical use-cases. To this
end, we quantitatively examine the behavior of probably approximately correct
implication bases on artificial and real-world data sets and compare their
precision and recall with respect to their corresponding exact implication
bases. Using a small example, we also provide qualitative insight that
implications from probably approximately correct bases can still represent
meaningful knowledge from a given data set.Comment: 17 pages, 8 figures; typos added, corrected x-label on graph
Kaplan-Narayanan-Neuberger lattice fermions pass a perturbative test
We test perturbatively a recent scheme for implementing chiral fermions on
the lattice, proposed by Kaplan and modified by Narayanan and Neuberger, using
as our testing ground the chiral Schwinger model. The scheme is found to
reproduce the desired form of the effective action, whose real part is gauge
invariant and whose imaginary part gives the correct anomaly in the continuum
limit, once technical problems relating to the necessary infinite extent of the
extra dimension are properly addressed. The indications from this study are
that the Kaplan--Narayanan--Neuberger (KNN) scheme has a good chance at being a
correct lattice regularization of chiral gauge theories.Comment: LaTeX 18 pages, 3 figure
Nonequilibrium-induced metal-superconductor quantum phase transition in graphene
We study the effects of dissipation and time-independent nonequilibrium drive
on an open superconducting graphene. In particular, we investigate how
dissipation and nonequilibrium effects modify the semi-metal-BCS quantum phase
transition that occurs at half-filling in equilibrium graphene with attractive
interactions. Our system consists of a graphene sheet sandwiched by two
semi-infinite three-dimensional Fermi liquid reservoirs, which act both as a
particle pump/sink and a source of decoherence. A steady-state charge current
is established in the system by equilibrating the two reservoirs at different,
but constant, chemical potentials. The nonequilibrium BCS superconductivity in
graphene is formulated using the Keldysh path integral formalism, and we obtain
generalized gap and number density equations valid for both zero and finite
voltages. The behaviour of the gap is discussed as a function of both
attractive interaction strength and electron densities for various
graphene-reservoir couplings and voltages. We discuss how tracing out the
dissipative environment (with or without voltage) leads to decoherence of
Cooper pairs in the graphene sheet, hence to a general suppression of the gap
order parameter at all densities. For weak enough attractive interactions we
show that the gap vanishes even for electron densities away from half-filling,
and illustrate the possibility of a dissipation-induced metal-superconductor
quantum phase transition. We find that the application of small voltages does
not alter the essential features of the gap as compared to the case when the
system is subject to dissipation alone (i.e. zero voltage).Comment: 13 pages, 8 figure
A multi-dimensional and integrative approach to examining the high-risk and ultra-high-risk stages of bipolar disorder
published_or_final_versio
Magnetoresistance of a 2-dimensional electron gas in a random magnetic field
We report magnetoresistance measurements on a two-dimensional electron gas
(2DEG) made from a high mobility GaAs/AlGaAs heterostructure, where the
externally applied magnetic field was expelled from regions of the
semiconductor by means of superconducting lead grains randomly distributed on
the surface of the sample. A theoretical explanation in excellent agreement
with the experiment is given within the framework of the semiclassical
Boltzmann equation.Comment: REVTEX 3.0, 11 pages, 3 Postscript figures appended. The manuscript
can also be obtained from our World Wide Web server:
http://roemer.fys.ku.dk/randmag.ht
Factors affecting the chemical efficacy of 2% sodium hypochlorite against oral steady-state dual-species biofilms:Exposure time and volume application
Aim To study the influence of time and volume of 2% sodium hypochlorite (NaOCl) on biofilm removal and to investigate the changes induced on the biofilm architecture. Steady-state, dual-species biofilms of standardized thickness and a realistic contact surface area between biofilms and NaOCl were used. Methodology Streptococcus oralis J22 and Actinomyces naeslundii T14V-J1 biofilms were grown on saliva-coated hydroxyapatite discs within sample holders in the Constant Depth Film Fermenter (CDFF) for 96 h. Two per cent NaOCl was statically applied for three different time intervals (60, 120 and 300 s) and in two different volumes (20 and 40 mu L) over the biofilm samples. The diffusion-driven effects of time and volume on biofilm disruption and dissolution were assessed with Optical Coherence Tomography (OCT). Structural changes of the biofilms treated with 2% NaOCl were studied with Confocal Laser Scanning Microscopy (CLSM) and Low Load Compression Testing (LLCT). A two-way analysis of variance (2-way anova) was performed, enabling the effect of each independent variable as well as their interaction on the outcome measures. Results Optical coherence tomography revealed that by increasing the exposure time and volume of 2% NaOCl, both biofilm disruption and dissolution significantly increased. Analysis of the interaction between the two independent variables revealed that by increasing the volume of 2% NaOCl, significant biofilm dissolution could be achieved in less time. Examination of the architecture of the remaining biofilms corroborated the EPS-lytic action of 2% NaOCl, especially when greater volumes were applied. The viscoelastic analysis of the 2% NaOCl-treated biofilms revealed that the preceding application of higher volumes could impact their subsequent removal. Conclusions Time and volume of 2% NaOCl application should be taken into account for maximizing the anti-biofilm efficiency of the irrigant and devising targeted disinfecting regimes against remaining biofilms
Excitation of spin-isospin giant resonance states in 12c(gamma,pi+)12b using tagged photons
The angular distribution of positive pions from the reaction, 12C(gamma,pi+)12B* were measured at five angles (theta= 35°, 55°, 90°, 125°, 145°) using the tagged photons in the
range 176 < Egamma < 182 MeV. The pi+ spectra were measured with a system of DeltaE-E plastic scintillator telescopes. The separation of pi+ from other particles was achieved by
measuring the DeltaE vs. E scatter plot and also by observing the delayed decay muons from the stopped pi+ in the E-detector
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