1,810 research outputs found
Fiber Bragg grating as an optical filter tuned by a magnetic field
We describe a novel tunable optical filter for use in optical-frequency-domain multiplexed communication
systems. The shift in the Bragg condition of a fiber Bragg grating as a result of magnetically induced circular
birefringence is calculated with coupled-mode theory on the basis of circular states of polarization, and the
values obtained for silica and terbium-doped optical fibers are compared
Overview of progress in European medium sized tokamaks towards an integrated plasma-edge/wall solution
Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads
to tolerable heat and particle loads on the wall is a major challenge. The new European
medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade
(AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide
parameter range, is instrumental to progress in the field, as ITER and DEMO core/pedestal
and SOL parameters are not achievable simultaneously in present day devices. A two prong
approach is adopted. On the one hand, scenarios with tolerable transient heat and particle
loads, including active edge localised mode (ELM) control are developed. On the other hand,
divertor solutions including advanced magnetic configurations are studied. Considerable
progress has been made on both approaches, in particular in the fields of: ELM control with
resonant magnetic perturbations (RMP), small ELM regimes, detachment onset and control,
as well as filamentary scrape-off-layer transport. For example full ELM suppression has now
been achieved on AUG at low collisionality with n = 2 RMP maintaining good confinement
HH(98,y2) 0.95. Advances have been made with respect to detachment onset and control.
Studies in advanced divertor configurations (Snowflake, Super-X and X-point target divertor)
shed new light on SOL physics. Cross field filamentary transport has been characterised in a
wide parameter regime on AUG, MAST and TCV progressing the theoretical and experimental
understanding crucial for predicting first wall loads in ITER and DEMO. Conditions in the
SOL also play a crucial role for ELM stability and access to small ELM regimes.European Commission (EUROfusion 633053
Toward a Clean Sample of Ultra-Luminous X-ray Sources
CONTEXT. Observational follow-up programmes for the characterization of
ultra-luminous X-ray sources (ULXs) require the construction of clean samples
of such sources in which the contamination by foreground/background sources is
minimum.
AIMS. In this article we calculate the degree of foreground/background
contaminants among the ULX sample candidates in the Colbert & Ptak (2002)
catalogue and compare these computations with available spectroscopical
identifications.
METHODS. We use statistics based on known densities of X-ray sources and
AGN/QSOs selected in the optical. The analysis is done individually for each
parent galaxy. The existing identifications of the optical counterparts are
compiled from the literature.
RESULTS. More than a half of the ULXs, within twice the distance of the major
axis of the 25 mag/arcsec isophote from RC3 nearby galaxies and with X-ray
luminosities [2-10 keV] erg/s, are expected to be high
redshift background QSOs. A list of 25 objects (clean sample) confirmed to be
real ULXs or to have a low probability of being contaminant
foreground/background objects is provided.Comment: 9 pages, accepted in A&
Vacancy induced zero energy modes in graphene stacks: The case of ABC trilayer
The zero energy modes induced by vacancies in ABC stacked trilayer graphene
are investigated. Depending on the position of the vacancy, a new zero energy
solution is realised, different from those obtained in multilayer compounds
with Bernal stacking. The electronic modification induced in the sample by the
new vacancy states is characterised by computing the local density of states
and their localisation properties are studied by the inverse participation
ratio. We also analyse the situation in the presence of a gap in the spectrum
due to a perpendicular electric field.Comment: 6 pages, 4 figures Published in special issue: Exploring Graphene,
Recent Research Advance
Two emission line objects with z>0.2 in the optical filament apparently connecting the Seyfert galaxy NGC 7603 to its companion
We present new spectroscopic observations of an old case of anomalous
redshift--NGC 7603 and its companion. The redshifts of the two galaxies which
are apparently connected by a luminous filament are z=0.029 and z=0.057
respectively. We show that in the luminous filament there are two compact
emission line objects with z=0.243 and z=0.391. They lie exactly on the line
traced by the filament connecting the galaxies. As far as we are aware, this is
the most impressive case of a system of anomalous redshifts discovered so far.Comment: 4 pages, 4 figures, accepted to be published in A&A-Letter
Isolation of chick retina cones and study of their diversity based on oil droplet colour and nucleus position
The chick retina has four morphological cone types that differ not only in shape, but also in the visual pigment in the outer segment, in the colour of the oil droplet in the inner segment and in synaptic connectivity. Neither the type of droplet nor the visual pigment has been definitively established for the four cone types. The main aim of the present work has been the isolation of entire live photoreceptors in order to study the oil droplet colour in each cone type and to quantify each type. We have improved an earlier retinal cell isolation method and obtained large numbers of entire cones. Principal cones (27% of the cones) possess a yellow or colourless droplet. Accessory cones (27% of the cones) all contain a small pale green droplet. Straight cones (44% of the cones) have a red, orange, yellow, or colourless droplet. Oblique cones (1.66% of the cones) all have a colourless droplet. We have found that straight cones with a red, orange, or yellow droplet differ in terms of the position of the nucleus and their percentage and conclude that they are distributed in three rows in the outer nuclear layer (ONL) of the central retina. Our study of 4,6-diamidino-2-phenylindole-stained retinal sections has revealed three rows of nuclei instead of the two currently thought to form the ONL. Together, our results show a larger cone diversity than previously known, suggest a larger functional diversity and provide an efficient method for isolating entire chick photoreceptors
Vibrational Properties of Nanoscale Materials: From Nanoparticles to Nanocrystalline Materials
The vibrational density of states (VDOS) of nanoclusters and nanocrystalline
materials are derived from molecular-dynamics simulations using empirical
tight-binding potentials. The results show that the VDOS inside nanoclusters
can be understood as that of the corresponding bulk system compressed by the
capillary pressure. At the surface of the nanoparticles the VDOS exhibits a
strong enhancement at low energies and shows structures similar to that found
near flat crystalline surfaces. For the nanocrystalline materials an increased
VDOS is found at high and low phonon energies, in agreement with experimental
findings. The individual VDOS contributions from the grain centers, grain
boundaries, and internal surfaces show that, in the nanocrystalline materials,
the VDOS enhancements are mainly caused by the grain-boundary contributions and
that surface atoms play only a minor role. Although capillary pressures are
also present inside the grains of nanocrystalline materials, their effect on
the VDOS is different than in the cluster case which is probably due to the
inter-grain coupling of the modes via the grain-boundaries.Comment: 10 pages, 7 figures, accepted for publication in Phys. Rev.
Liver segmentation in MRI: a fully automatic method based on stochastic partitions
There are few fully automated methods for liver segmentation in magnetic resonance images (MRI) despite the benefits of this type of acquisition in comparison to other radiology techniques such as computed tomography (CT). Motivated by medical requirements, liver segmentation in MRI has been carried out. For this purpose, we present a new method for liver segmentation based on the watershed transform and stochastic partitions. The classical watershed over-segmentation is reduced using a marker-controlled algorithm. To improve accuracy of selected contours, the gradient of the original image is successfully enhanced by applying a new variant of stochastic watershed. Moreover, a final classifier is performed in order to obtain the final liver mask. Optimal parameters of the method are tuned using a training dataset and then they are applied to the rest of studies (17 datasets). The obtained results (a Jaccard coefficient of 0.91 +/- 0.02) in comparison to other methods demonstrate that the new variant of stochastic watershed is a robust tool for automatic segmentation of the liver in MRI. (C) 2014 Elsevier Ireland Ltd. All rights reserved.This work has been supported by the MITYC under the project NaRALap (ref. TSI-020100-2009-189), partially by the CDTI under the project ONCOTIC (IDI-20101153), by Ministerio de Educacion y Ciencia Spain, Project Game Teen (TIN2010-20187) projects Consolider-C (SEJ2006-14301/PSIC), "CIBER of Physiopathology of Obesity and Nutrition, an initiative of ISCIII" and Excellence Research Program PROMETEO (Generalitat Valenciana. Conselleria de Educacion, 2008-157). We would like to express our gratitude to the Hospital Clinica Benidorm, for providing the MR datasets and to the radiologist team of Inscanner for the manual segmentation of the MR images.López-Mir, F.; Naranjo Ornedo, V.; Angulo, J.; Alcañiz Raya, ML.; Luna, L. (2014). Liver segmentation in MRI: a fully automatic method based on stochastic partitions. Computer Methods and Programs in Biomedicine. 114(1):11-28. https://doi.org/10.1016/j.cmpb.2013.12.022S1128114
Polarization Diagnostics for Cool Core Cluster Emission Lines
The nature of the interaction between low-excitation gas filaments at ~104 K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ~107 K in the centers of galaxy clusters remains a puzzle. The presence of a strong, empirical correlation between the two gas phases is indicative of a fundamental relationship between them, though as yet of undetermined cause. The cooler filaments, originally thought to have condensed from the hot gas, could also arise from a merger or the disturbance of cool circumnuclear gas by nuclear activity. Here, we have searched for intrinsic line emission polarization in cool core galaxy clusters as a diagnostic of fundamental transport processes. Drawing on developments in solar astrophysics, direct energetic particle impact induced polarization holds the promise to definitively determine the role of collisional processes such as thermal conduction in the ISM physics of galaxy clusters, while providing insight into other highly anisotropic excitation mechanisms such as shocks, intense radiation fields, and suprathermal particles. Under certain physical conditions, theoretical calculations predict of the order of 10% polarization. Our observations of the filaments in four nearby cool core clusters place stringent upper limits ( 0.1%) on the presence of emission line polarization, requiring that if thermal conduction is operative, the thermal gradients are not in the saturated regime. This limit is consistent with theoretical models of the thermal structure of filament interfacesPeer reviewe
Dynamical model for Pion - Nucleon Bremsstrahlung
A dynamical model based on effective Lagrangians is proposed to describe the
bremsstrahlung reaction at low energies. The
degrees of freedom are incorporated in a way consistent with
both, electromagnetic gauge invariance and invariance under contact
transformations. The model also includes the initial and final state
rescattering of hadrons via a T-matrix with off-shell effects. The differential cross sections are calculated using three different
T-matrix models and the results are compared with the soft photon
approximation, and with experimental data. The aim of this analysis is to test
the off-shell behavior of the different T-matrices under consideration.Comment: 16 pages, latex, 6 eps figures. Accepted for publication in Physical
Review
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