569 research outputs found
Shifting of the magnetic resonance peak to lower energy in the superconducting state of underdoped YBa_2Cu_3O_{6.8}
Inelastic neutron scattering has been used to determine the dynamic spin
fluctuations in an underdoped high temperature superconductor YBCO_{6.8} single
crystal. The magnetic resonance, that occurs around 40 meV in overdoped
samples, is shifted to a lower energy, E_r= 34 meV. A constant ratio, , almost independent of the doping level, is found. According
to numerous theoretical approaches, this finding supports the idea that the
resonance energy is proportional (approximately twice) to the superconducting
gap.Comment: 8 pages, 3 figures, accepted in Europhysics Lette
Observation of Macroscopic Structural Fluctuations in bcc Solid 4He
We report neutron diffraction studies of low density bcc and hcp solid 4He.
In the bcc phase, we observed a continuous dynamical behaviour involving
macroscopic structural changes of the solid. The dynamical behaviour takes
place in a cell full of solid, and therefore represents a solidsolid
transformation. The structural changes are consistent with a gradual rotation
of macroscopic grains separated by low angle grain boundaries. We suggest that
these changes are triggered by random momentary vibrations of the experimental
system. An analysis of Laue diffraction patterns indicates that in some cases
these structural changes, once initiated by a momentary impulse, seem to
proceed at a constant rate over times approaching an hour. The energy
associated with these macroscopic changes appears to be on the order of kT.
Under similar conditions (temperature and pressure), these effects were absent
in the hcp phase.Comment: 14 pages, 6 figure, accepted for PR
New excitations in bcc He - an inelastic neutron scattering study
We report neutron scattering measurements on bcc solid % He. We studied
the phonon branches and the recently discovered ''optic-like'' branch along the
main crystalline directions. In addition, we discovered another, dispersionless
"optic-like'' branch at an energy around 1 meV (~11K). The properties of
the two "optic-like" branches seem different. Since one expects only 3 acoustic
phonon branches in a monoatomic cubic crystal, these new branches must
represent different type of excitations. One possible interpretation involves
localized excitations unique to a quantum solid.Comment: 4 pages, 3 figures, accepted by PRB, Rapid Communication
Super-resolution photoacoustic and ultrasound imaging with sparse arrays
It has previously been demonstrated that model-based reconstruction methods
relying on a priori knowledge of the imaging point spread function (PSF)
coupled to sparsity priors on the object to image can provide super-resolution
in photoacoustic (PA) or in ultrasound (US) imaging. Here, we experimentally
show that such reconstruction also leads to super-resolution in both PA and US
imaging with arrays having much less elements than used conventionally (sparse
arrays). As a proof of concept, we obtained super-resolution PA and US
cross-sectional images of microfluidic channels with only 8 elements of a
128-elements linear array using a reconstruction approach based on a linear
propagation forward model and assuming sparsity of the imaged structure.
Although the microchannels appear indistinguishable in the conventional
delay-and-sum images obtained with all the 128 transducer elements, the applied
sparsity-constrained model-based reconstruction provides super-resolution with
down to only 8 elements. We also report simulation results showing that the
minimal number of transducer elements required to obtain a correct
reconstruction is fundamentally limited by the signal-to-noise ratio. The
proposed method can be straigthforwardly applied to any transducer geometry,
including 2D sparse arrays for 3D super-resolution PA and US imaging
Detection of the tagged or untagged photons in acousto-optic imaging of thick highly scattering media by photorefractive adaptive holography
We propose an original adaptive wavefront holographic setup based on the
photorefractive effect (PR), to make real-time measurements of acousto-optic
signals in thick scattering media, with a high flux collection at high rates
for breast tumor detection. We describe here our present state of art and
understanding on the problem of breast imaging with PR detection of the
acousto-optic signal
Theoretical study of Acousto-optical coherence tomography using random phase jumps on US and light
Acousto-Optical Coherence Tomography (AOCT) is variant of Acousto Optic
Imaging (called also ultrasonic modulation imaging) that makes possible to get
z resolution with acoustic and optic Continuous Wave (CW) beams. We describe
here theoretically the AOCT e ect, and we show that the Acousto Optic tagged
photons remains coherent if they are generated within a speci c z region of the
sample. We quantify the z selectivity for both the tagged photon eld, and for
the M. Lesa re et al. photorefractive signal
Mitochondrial dynamicsâfusion, fission, movement, and mitophagyâin neurodegenerative diseases
Neurons are metabolically active cells with high energy demands at locations distant from the cell body. As a result, these cells are particularly dependent on mitochondrial function, as reflected by the observation that diseases of mitochondrial dysfunction often have a neurodegenerative component. Recent discoveries have highlighted that neurons are reliant particularly on the dynamic properties of mitochondria. Mitochondria are dynamic organelles by several criteria. They engage in repeated cycles of fusion and fission, which serve to intermix the lipids and contents of a population of mitochondria. In addition, mitochondria are actively recruited to subcellular sites, such as the axonal and dendritic processes of neurons. Finally, the quality of a mitochondrial population is maintained through mitophagy, a form of autophagy in which defective mitochondria are selectively degraded. We review the general features of mitochondrial dynamics, incorporating recent findings on mitochondrial fusion, fission, transport and mitophagy. Defects in these key features are associated with neurodegenerative disease. Charcot-Marie-Tooth type 2A, a peripheral neuropathy, and dominant optic atrophy, an inherited optic neuropathy, result from a primary deficiency of mitochondrial fusion. Moreover, several major neurodegenerative diseasesâincluding Parkinson's, Alzheimer's and Huntington's diseaseâinvolve disruption of mitochondrial dynamics. Remarkably, in several disease models, the manipulation of mitochondrial fusion or fission can partially rescue disease phenotypes. We review how mitochondrial dynamics is altered in these neurodegenerative diseases and discuss the reciprocal interactions between mitochondrial fusion, fission, transport and mitophagy
Construction d'un graphe de connaissances Ă partir des annotations d'articles scientifiques et de leur contenu en sciences de la vie
National audienceIn this paper, we present an RDF knowledge graph to describe, structure and integrate annotations of named entities automatically extracted by the Alvis NLP tool from scientific publications on wheat genetics and phenotyping. These named entities refer to the names of genes, traits, phenotypes, markers and varieties involved in wheat breeding. However, once extracted, these annotations are stored ina raw format making it difficult for researchers to exploit?them. Hence, our interest in transforming (lifting) them into?a format compatible with linked data publication standardsin order to build a knowledge graph in which knowledge?coming from both genomic knowledge bases and scientific articles has been semantically described and integrated.Based on a set of competency questions formulated by a?domain expert, we validated the relevance of the proposed?model and consequently the generated knowledge graph.Dans ce papier, nous prĂ©sentons un graphe de connaissances RDF permettant de dĂ©crire, structurer et intĂ©grer des annotations d'entitĂ©s nommĂ©es extraites automatiquement par l'outil Alvis NLP Ă partir de publications scientifiques portant sur la gĂ©nĂ©tique et le phĂ©notypage de blĂ©. Ces entitĂ©s nommĂ©es se rĂ©fĂšrent Ă la fois Ă des noms de gĂšnes, traits, phĂ©notypes, marqueurs et variĂ©tĂ©s impliquĂ©s dans la culture du blĂ©. Cependant, une fois extraites, ces annotations sont stockĂ©es dans un format brut rendant difficile leur exploitation par les chercheurs. D'oĂč, notre intĂ©rĂȘt de les transformer (lifter) en un format compatible avec les standards de publication de donnĂ©es liĂ©es afin de construire un graphe de connaissances dans lequel des entitĂ©s provenant Ă la fois de bases de connaissances gĂ©nomiques et d'articles scientifiques ont Ă©tĂ© sĂ©mantiquement dĂ©crites et intĂ©grĂ©es. BasĂ© sur un ensemble de questions de compĂ©tence formulĂ©es par un expert du domaine, nous avons validĂ© la pertinence du modĂšle proposĂ© et par consĂ©quent le graphe de connaissances gĂ©nĂ©rĂ©
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