473 research outputs found
Disordered graphene and boron nitride in a microwave tight-binding analog
Experiments on hexagonal graphene-like structures using microwave measuring
techniques are presented. The lowest transverse-electric resonance of coupled
dielectric disks sandwiched between two metallic plates establishes a
tight-binding configuration. The nearest-neighbor coupling approximation is
investigated in systems with few disks. Taking advantage of the high
flexibility of the disks positions, consequences of the disorder introduced in
the graphene lattice on the Dirac points are investigated. Using two different
types of disks, a boron-nitride-like structure (a hexagonal lattice with a
two-atom basis) is implemented, showing the appearance of a band gap.Comment: 12 pages, 14 figure
Domain wall structure in magnetic bilayers with perpendicular anisotropy
We study the magnetic domain wall structure in magnetic bilayers (two
ultrathin ferromagnetic layers separated by a non magnetic spacer) with
perpendicular magnetization. Combining magnetic force and ballistic electron
emission microscopies, we are able to reveal the details of the magnetic
structure of the wall with a high spatial accuracy. In these layers, we show
that the classical Bloch wall observed in single layers transforms into
superposed N\'eel walls due to the magnetic coupling between the ferromagnetic
layers. Quantitative agreement with micromagnetic calculations is achieved.Comment: Author adresses AB, SR, JM and AT: Laboratoire de Physique des
Solides, CNRS, Universit\'e Paris Sud, UMR 8502, 91405 Orsay Cedex, France ML
: Laboratoire PMTM, Institut Galil\'ee, CNRS, Universit\'e Paris-13, UPR
9001, 93430 Villetaneuse, Franc
The essential role of surface pinning in the dynamics of charge density waves submitted to external dc fields
A Charge Density Wave (CDW) submitted to an electric field displays a strong
shear deformation because of pinning at the lateral surfaces of the sample.
This CDW transverse pinning was recently observed but has received little
attention from a theoretical point of view until now despite important
consequences on electrical conductivity properties. Here, we provide a
description of this phenomenon by considering a CDW submitted to an external dc
electric field and constrained by boundary conditions including both
longitudinal pinning due to electrical contacts and transverse surface pinning.
A simple formula for the CDW phase is obtained in 3D by using the Green
function and image charges method. In addition, an analytical expression of the
threshold field dependence on both length and sample cross section is obtained
by considering the phase slip process. We show that the experimental data are
well reproduced with this model and that bulk pinning can be neglected. This
study shows that the dynamical properties of CDW systems could be mainly driven
by boundary effects, despite the comparatively huge sample volumes.Comment: 7 pages of main text, 7 pages of appendices 15 figure
Accurate Anisotropic Fast Marching for Diffusion-Based Geodesic Tractography
Using geodesics for inferring white matter fibre tracts from diffusion-weighted MR data is an attractive method for at least two reasons: (i) the method optimises a global criterion, and hence is less sensitive to local perturbations such as noise or partial volume effects, and (ii) the method is fast, allowing to infer on a large number of connexions in a reasonable computational time. Here, we propose an improved fast marching algorithm to infer on geodesic paths. Specifically, this procedure is designed to achieve accurate front propagation in an anisotropic elliptic medium, such as DTI data. We evaluate the numerical performance of this approach on simulated datasets, as well as its robustness to local perturbation induced by fiber crossing. On real data, we demonstrate the feasibility of extracting geodesics to connect an extended set of brain regions
First isolation of a rhabdovirus from perch Perca fluviatilis in Switzerland
Perca fluviatilis is a fish species of increasing interest to the Swiss fish farming industry. In recent years, recirculation systems have been specifically set up to increase production. In one of these farms, abnormal spiral swimming associated with elevated mortalities occurred in repeated batches of imported perch shortly after stocking on several occasions. No bacterial or
parasitic etiology was detected, but a virus grown in bluegill fry (BF-2) cells was identified as perch rhabdovirus. Subsequent investigations of other samples suggested a viral tropism for the central nervous system (CNS). Phylogenetic analysis of the partial N and entire G gene sequences positioned this isolate in genogroup C of the species Perch rhabdovirus, with high nucleotide and amino acid (aa) sequence identities with the DK5533 strain isolated in Denmark in 1989. Comparative studies using other closely related isolates allowed the distinction of 2 serological Patterns among perch rhabdoviruses and the identification of a proline substitution by a serine in Position 147 of the glycoprotein potentially involved in antigenic differentiation. Even if perch imported onto the farm tested negative by virus isolation prior to transport, they may have been the origin of this outbreak since CNS tissue was not included in the samples that were analyzed. Another possibility might be a sub-clinical infection with a viral load in resident fish too low to be detected.
This study reports the first isolation of a perch rhabdovirus in Switzerland, and emphasizes the necessity of optimizing diagnostic tools that facilitate better control of the risks associated with fish translocation
Component-based programming for higher-order attribute grammars
This paper presents techniques for a component-based style of programming in the context of higher-oder attribute grammars (HAG). Attribute grammar components are "plugged in" into larger attribute grammar systems through higher-order attribute grammars. Higher-order attributes are used as (intermediate) "gluing" data structures.This paper also presents two attribute grammar components that can be re-used across different language-based tool specifications: a visualizer and animator of programs and a graphical user interface AG component. Both components are reused in the definition of a simple language processor. The techniques presented in this paper are implemented in LRC: a purely functional, higher-order attribute grammar-based system that generates language-based tools.(undefined
A numerical variability approach to results stability tests and its application to neuroimaging
Ensuring the long-term reproducibility of data analyses requires results
stability tests to verify that analysis results remain within acceptable
variation bounds despite inevitable software updates and hardware evolutions.
This paper introduces a numerical variability approach for results stability
tests, which determines acceptable variation bounds using random rounding of
floating-point calculations. By applying the resulting stability test to
\fmriprep, a widely-used neuroimaging tool, we show that the test is sensitive
enough to detect subtle updates in image processing methods while remaining
specific enough to accept numerical variations within a reference version of
the application. This result contributes to enhancing the reliability and
reproducibility of data analyses by providing a robust and flexible method for
stability testing
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