406 research outputs found
IRC préterminale : il n'est jamais trop tôt pour référer au spécialiste : Revue cochrane pour le praticien
Cette rubrique présente les résultats d'une revue systématique récente telle que publiée dans la Cochrane Library (www.thecochranelibrary.com). Volontairement limité à un champ de recherche circonscrit, cet article reflète l'état actuel des connaissances de ce domaine. Il ne s'agit donc pas de recommandations pour guider la prise en charge d'une problématique clinique considérée dans sa globalité (guidelines). Les auteurs de ce résumé se basent sur la revue systématique et ne remettent pas en question le choix des articles inclus dans la revue.
Scénario: Vous suivez un patient de 71 ans connu pour un diabète et une hypertension bien contrôlés, ainsi qu'une insuffisance rénale chronique de longue date, progressive, actuellement sévère (créatinine à 267 mmol/l, taux de filtration glomérulaire estimé (TFGe) à 21 ml/min/1,73 m2). Son état général est bon, son poids est stable et il ne présente pas de symptômes urémiques.
Question: Faut-il adresser ce patient à un néphrologue
Nonlinear electron-phonon coupling in doped manganites
We employ time-resolved resonant x-ray diffraction to study the melting of
charge order and the associated insulator-metal transition in the doped
manganite PrCaMnO after resonant excitation of a
high-frequency infrared-active lattice mode. We find that the charge order
reduces promptly and highly nonlinearly as function of excitation fluence.
Density functional theory calculations suggest that direct anharmonic coupling
between the excited lattice mode and the electronic structure drive these
dynamics, highlighting a new avenue of nonlinear phonon control
The photoinduced transition in magnetoresistive manganites: a comprehensive view
We use femtosecond x-ray diffraction to study the structural response of
charge and orbitally ordered PrCaMnO thin films across a phase
transition induced by 800 nm laser pulses. By investigating the dynamics of
both superlattice reflections and regular Bragg peaks, we disentangle the
different structural contributions and analyze their relevant time-scales. The
dynamics of the structural and charge order response are qualitatively
different when excited above and below a critical fluence . For
excitations below the charge order and the superlattice is only partially
suppressed and the ground state recovers within a few tens of nanosecond via
diffusive cooling. When exciting above the critical fluence the superlattice
vanishes within approximately half a picosecond followed by a change of the
unit cell parameters on a 10 picoseconds time-scale. At this point all memory
from the symmetry breaking is lost and the recovery time increases by many
order of magnitudes due to the first order character of the structural phase
transition
Domain size effects on the dynamics of a charge density wave in 1T-TaS2
Recent experiments have shown that the high temperature incommensurate (I)
charge density wave (CDW) phase of 1T-TaS2 can be photoinduced from the lower
temperature, nearly commensurate (NC) CDW state. Here we report a time-resolved
x-ray diffraction study of the growth process of the photoinduced I-CDW
domains. The layered nature of the material results in a marked anisotropy in
the size of the photoinduced domains of the I-phase. These are found to grow
self-similarly, their shape remaining unchanged throughout the growth process.
The photoinduced dynamics of the newly formed I-CDW phase was probed at various
stages of the growth process using a double pump scheme, where a first pump
creates I-CDW domains and a second pump excites the newly formed I-CDW state.
We observe larger magnitudes of the coherently excited I-CDW amplitude mode in
smaller domains, which suggests that the incommensurate lattice distortion is
less stable for smaller domain sizes.Comment: 8 pages, 8 figure
Prediction of cognitive outcome based on the progression of auditory discrimination during coma.
To date, no clinical test is able to predict cognitive and functional outcome of cardiac arrest survivors. Improvement of auditory discrimination in acute coma indicates survival with high specificity. Whether the degree of this improvement is indicative of recovery remains unknown. Here we investigated if progression of auditory discrimination can predict cognitive and functional outcome.
We prospectively recorded electroencephalography responses to auditory stimuli of post-anoxic comatose patients on the first and second day after admission. For each recording, auditory discrimination was quantified and its evolution over the two recordings was used to classify survivors as "predicted" when it increased vs. "other" if not. Cognitive functions were tested on awakening and functional outcome was assessed at 3 months using the Cerebral Performance Categories (CPC) scale.
Thirty-two patients were included, 14 "predicted survivors" and 18 "other survivors". "Predicted survivors" were more likely to recover basic cognitive functions shortly after awakening (ability to follow a standardized neuropsychological battery: 86% vs. 44%; p=0.03 (Fisher)) and to show a very good functional outcome at 3 months (CPC 1: 86% vs. 33%; p=0.004 (Fisher)). Moreover, progression of auditory discrimination during coma was strongly correlated with cognitive performance on awakening (phonemic verbal fluency: rs=0.48; p=0.009 (Spearman)).
Progression of auditory discrimination during coma provides early indication of future recovery of cognitive functions. The degree of improvement is informative of the degree of functional impairment. If confirmed in a larger cohort, this test would be the first to predict detailed outcome at the single-patient level
Coherent Acoustic Perturbation of Second-Harmonic-Generation in NiO
We investigate the structural and magnetic origins of the unusual ultrafast
second-harmonicgeneration (SHG) response of femtosecond-laser-excited nickel
oxide (NiO) previously attributed to oscillatory reorientation dynamics of the
magnetic structure induced by d-d excitations. Using time-resolved x-ray
diffraction from the (3/2 3/2 3/2) magnetic planes, we show that changes in the
magnitude of the magnetic structure factor following ultrafast optical
excitation are limited to = 1.5% in the first 30 ps. An
extended investigation of the ultrafast SHG response reveals a strong
dependence on wavelength as well as characteristic echoes, both of which give
evidence for an acoustic origin of the dynamics. We therefore propose an
alternative mechanism for the SHG response based on perturbations of the
nonlinear susceptibility via optically induced strain in a spatially confined
medium. In this model, the two observed oscillation periods can be understood
as the times required for an acoustic strain wave to traverse one coherence
length of the SHG process in either the collinear or anti-collinear geometries.Comment: 26 pages, 7 figure
Ultrafast relaxation dynamics of the antiferrodistortive phase in Ca doped SrTiO3
The ultrafast dynamics of the octahedral rotation in Ca:SrTiO3 is studied by
time resolved x-ray diffraction after photo excitation over the band gap. By
monitoring the diffraction intensity of a superlattice reflection that is
directly related to the structural order parameter of the soft-mode driven
antiferrodistortive phase in Ca:SrTiO3, we observe a ultrafast relaxation on a
0.2 ps timescale of the rotation of the oxygen octahedron, which is found to be
independent of the initial temperaure despite large changes in the
corresponding soft-mode frequency. A further, much smaller reduction on a
slower picosecond timescale is attributed to thermal effects. Time-dependent
density-functional-theory calculations show that the fast response can be
ascribed to an ultrafast displacive modification of the soft-mode potential
towards the normal state, induced by holes created in the oxygen 2p states
Structural and magnetic dynamics of a laser induced phase transition in FeRh
We use time-resolved x-ray diffraction and magnetic optical Kerr effect to
study the laser induced antiferromagnetic to ferromagnetic phase transition in
FeRh. The structural response is given by the nucleation of independent
ferromagnetic domains (\tau_1 ~ 30ps). This is significantly faster than the
magnetic response (\tau_2 ~ 60ps) given by the subsequent domain realignment.
X-ray diffraction shows that the two phases co-exist on short time-scales and
that the phase transition is limited by the speed of sound. A nucleation model
describing both the structural and magnetic dynamics is presented.Comment: 5 pages, 3 figures - changed to reflect version accepted for PR
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