1,087 research outputs found
Motel user manual
MOTEL is a logic-based knowledge representation languages of the KL-ONE family. It contains as a kernel the KRIS language which is a decidable sublanguage of first-order predicate logic. Whereas KRIS is a single-agent knowledge representation system, i.e. KRIS is only able to represent general world knowledge or the knowledge of one agent about the world, MOTEL is a multi-agent knowledge representation system. The MOTEL language allows modal contexts and modal concept forming operators which allow to represent and reason about the believes and wishes of multiple agents. Furthermore it is possible to represent defaults and stereotypes. Beside the basic resoning facilities for consistency checking, classification, and realization, MOTEL provides an abductive inference mechanism. Furthermore it is able to give explanations for its inferences
Reliability of Intra-Retinal Layer Thickness Estimates
Purpose Measurement of intra-retinal layer thickness using optical coherence
tomography (OCT) has become increasingly prominent in multiple sclerosis (MS)
research. Nevertheless, the approaches used for determining the mean layer
thicknesses vary greatly. Insufficient data exist on the reliability of
different thickness estimates, which is crucial for their application in
clinical studies. This study addresses this lack by evaluating the
repeatability of different thickness estimates. Methods Studies that used
intra-retinal layer segmentation of macular OCT scans in patients with MS were
retrieved from PubMed. To investigate the repeatability of previously applied
layer estimation approaches, we generated datasets of repeating measurements
of 15 healthy subjects and 13 multiple sclerosis patients using two OCT
devices (Cirrus HD-OCT and Spectralis SD-OCT). We calculated each thickness
estimate in each repeated session and analyzed repeatability using intra-class
correlation coefficients and coefficients of repeatability. Results We
identified 27 articles, eleven of them used the Spectralis SD-OCT, nine Cirrus
HD-OCT, two studies used both devices and two studies applied RTVue-100.
Topcon OCT-1000, Stratus OCT and a research device were used in one study
each. In the studies that used the Spectralis, ten different thickness
estimates were identified, while thickness estimates of the Cirrus OCT were
based on two different scan settings. In the simulation dataset, thickness
estimates averaging larger areas showed an excellent repeatability for all
retinal layers except the outer plexiform layer (OPL). Conclusions Given the
good reliability, the thickness estimate of the 6mm-diameter area around the
fovea should be favored when OCT is used in clinical research. Assessment of
the OPL was weak in general and needs further investigation before OPL
thickness can be used as a reliable parameter
The structure of a polyketide synthase bimodule core
Polyketide synthases (PKSs) are predominantly microbial biosynthetic enzymes. They assemble highly potent bioactive natural products from simple carboxylic acid precursors. The most versatile families of PKSs are organized as assembly lines of functional modules. Each module performs one round of precursor extension and optional modification, followed by directed transfer of the intermediate to the next module. While enzymatic domains and even modules of PKSs are well understood, the higher-order modular architecture of PKS assembly lines remains elusive. Here, we visualize a PKS bimodule core using cryo-electron microscopy and resolve a two-dimensional meshwork of the bimodule core formed by homotypic interactions between modules. The sheet-like organization provides the framework for efficient substrate transfer and for sequestration of trans-acting enzymes required for polyketide production
Optical properties of metallic (III,Mn)V ferromagnetic semiconductors in the infrared to visible range
We report on a study of the ac conductivity and magneto-optical properties of
metallic ferromagnetic (III,Mn)V semiconductors in the infrared to visible
spectrum. Our analysis is based on the successful kinetic exchange model for
(III,Mn)V ferromagnetic semiconductors. We perform the calculations within the
Kubo formalism and treat the disorder effects pertubatively within the Born
approximation, valid for the metallic regime. We consider an eight-band
Kohn-Luttinger model (six valence bands plus two conduction bands) as well as a
ten-band model with additional dispersionless bands simulating
phenomenologically the upper-mid-gap states induced by antisite and
interstitial impurities. These models qualitatively account for
optical-absorption experiments and predict new features in the mid-infrared
Kerr angle and magnetic-circular-dichroism properties as a function of Mn
concentration and free carrier density.Comment: 10 pages, 7 figures, some typos correcte
Collective effects in spin-crossover chains with exchange interaction
The collective properties of spin-crossover chains are studied.
Spin-crossover compounds contain ions with a low-spin ground state and low
lying high-spin excited states and are of interest for molecular memory
applications. Some of them naturally form one-dimensional chains. Elastic
interaction and Ising exchange interaction are taken into account. The
transfer-matrix approach is used to calculate the partition function, the
fraction of ions in the high-spin state, the magnetization, susceptibility,
etc., exactly. The high-spin-low-spin degree of freedom leads to collective
effects not present in simple spin chains. The ground-state phase diagram is
mapped out and compared to the case with Heisenberg exchange interaction. The
various phases give rise to characteristic behavior at nonzero temperatures,
including sharp crossovers between low- and high-temperature regimes. A
Curie-Weiss law for the susceptibility is derived and the paramagnetic Curie
temperature is calculated. Possible experiments to determine the exchange
coupling are discussed.Comment: 9 pages, 13 color figures, published versio
Criteria for Blood Vessel Discrimination
Introduction The diagnostic potential of optical coherence tomography (OCT) in
neurological diseases is intensively discussed. Besides the sectional view of
the retina, modern OCT scanners produce a simultaneous top-view confocal
scanning laser ophthalmoscopy (cSLO) image including the option to evaluate
retinal vessels. A correct discrimination between arteries and veins
(labeling) is vital for detecting vascular differences between healthy
subjects and patients. Up to now, criteria for labeling (cSLO) images
generated by OCT scanners do not exist. Objective This study reviewed labeling
criteria originally developed for color fundus photography (CFP) images.
Methods The criteria were modified to reflect the cSLO technique, followed by
development of a protocol for labeling blood vessels. These criteria were
based on main aspects such as central light reflex, brightness, and vessel
thickness, as well as on some additional criteria such as vascular crossing
patterns and the context of the vessel tree. Results and Conclusion They
demonstrated excellent inter-rater agreement and validity, which seems to
indicate that labeling of images might no longer require more than one rater.
This algorithm extends the diagnostic possibilities offered by OCT
investigations
Comparação de Diferentes Parametrizações da Turbulência numa Atmosfera Neutra
Comparação de diferentes parametrizações da turbulêncianuma atmosfera neutr
'Theory for the enhanced induced magnetization in coupled magnetic trilayers in the presence of spin fluctuations'
Motivated by recent experiments, the effect of the interlayer exchange
interaction on the magnetic properties of coupled Co/Cu/Ni
trilayers is studied theoretically. Here the Ni film has a lower Curie
temperature than the Co film in case of decoupled layers. We
show that by taking into account magnetic fluctuations the interlayer coupling
induces a strong magnetization for T\gtsim T_{C,\rm Ni} in the Ni film. For
an increasing the resonance-like peak of the longitudinal Ni
susceptibility is shifted to larger temperatures, whereas its maximum value
decreases strongly. A decreasing Ni film thickness enhances the induced Ni
magnetization for T\gtsim T_{C,\rm Ni}. The measurements cannot be explained
properly by a mean field estimate, which yields a ten times smaller effect.
Thus, the observed magnetic properties indicate the strong effect of 2D
magnetic fluctuations in these layered magnetic systems. The calculations are
performed with the help of a Heisenberg Hamiltonian and a Green's function
approach.Comment: 4 pages, 3 figure
Estudo da Difusão Empregando´Parâmetros Turbulentos que Descrevem a Capacidade de Mistura da Camada Limite Planetária
Estudo da difusão empregando parâmetros turbulentos quedescrevem a capacidade de mistura daCamada Limite Planetári
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