404 research outputs found
Electrical Noise From Phase Separation In Pr2/3Ca1/3MnO3 Single Crystal
Low frequency electrical noise measurements have been used to probe the
electronic state of the perovskite-type manganese oxide Pr2/3Ca1/3MnO3 versus
temperature and in the vicinity of the field-induced transition from the
insulating, charge-ordered state (I-CO) to the metallic, ferromagnetic state
(M-F). At high temperature we have observed a high level of the excess noise
with mainly a gaussian distribution of the resistance fluctuations, and the
associated power spectral density has a standard 1/f dependence. However, in
the hysteretic region, where the electrical resistance depends dramatically on
the sample history, we have observed a huge non-gaussian noise characterized by
two level fluctuator-like switching (TLS) in the time domain. We discuss the
origin of the noise in terms of percolative behavior of the conductivity. We
speculate that the dominant fluctuators are manganese clusters switching
between the M-F and the I-CO phases.Comment: RevTeX, 6 pages with 3 figure
Influence of site and stand factors on Hymenoscyphus fraxineus-induced basal lesions
Hymenoscyphus fraxineus is an invasive fungus in Europe and causes a severe decline affecting ash, which began in the late 1990s. One of the symptoms associated with the disease is lesions in the outer bark of the collar area. However, the aetiology of these basal lesions, and in particular the relative roles of H.fraxineus and Armillaria species, is still controversial; moreover, little is known about the influence of environmental factors on the disease epidemiology.This study therefore surveyed 42 plots located in northeastern France, in an area affected by ash decline since 2008, in order to determine which environmental factors condition the severity of lesions associated with H.fraxineus on ash collar. The spatial pattern that is a consequence of the invasive spread of the disease was taken into account in the analysis, using a spatial hierarchical Bayesian model fitted by integrated nested laplace approximation (INLA).Results show that while basal lesions are tightly associated with H.fraxineus, their severity is influenced by the Armillaria species present in the plot. Sites with vegetation indicating moist conditions, or more humid topographical positions, were associated with more developed basal lesions
Apsidal motion in the massive binary HD152218
Massive binary systems are important laboratories in which to probe the
properties of massive stars and stellar physics in general. In this context, we
analysed optical spectroscopy and photometry of the eccentric short-period
early-type binary HD 152218 in the young open cluster NGC 6231. We
reconstructed the spectra of the individual stars using a separating code. The
individual spectra were then compared with synthetic spectra obtained with the
CMFGEN model atmosphere code. We furthermore analysed the light curve of the
binary and used it to constrain the orbital inclination and to derive absolute
masses of 19.8 +/- 1.5 and 15.0 +/- 1.1 solar masses. Combining radial velocity
measurements from over 60 years, we show that the system displays apsidal
motion at a rate of (2.04^{+.23}_{-.24}) degree/year. Solving the
Clairaut-Radau equation, we used stellar evolution models, obtained with the
CLES code, to compute the internal structure constants and to evaluate the
theoretically predicted rate of apsidal motion as a function of stellar age and
primary mass. In this way, we determine an age of 5.8 +/- 0.6 Myr for HD
152218, which is towards the higher end of, but compatible with, the range of
ages of the massive star population of NGC 6231 as determined from isochrone
fitting.Comment: Accepted for publication in Astronomy & Astrophysic
Improved 1000-m running performance and pacing strategy with caffeine and placebo effect: a balanced placebo design study
Purpose: To investigate the placebo effect of caffeine on pacing strategy and performance over 1000-m running time-trials using a balanced placebo design.
Methods: Eleven well-trained male middle-distance athletes performed seven 1000-m time-trials (one familiarisation, two baseline and four experimental). Experimental trials consisted of the administration of four treatments: informed caffeine/received caffeine (CC), informed caffeine/received placebo (CP), informed placebo/received caffeine (PC), and informed placebo/received placebo (PP). Treatments were randomized. Split times were recorded at 200-, 400-, 600-, 800- and 1000-m and peak heart rate (HRpeak) and rating of perceived exertion (RPE) were recorded at the completion of the trial.
Results: Relative to baseline, participants ran faster during CC (d = 0.42) and CP (d = 0.43). These changes were associated with an increased pace during the first half of the trial. No differences were shown in pacing or performance between baseline and the PC (d = 0.21) and open administration of placebo (d = 0.10). No differences were reported between treatments for HRpeak (η2 = 0.084) and RPE (η2 = 0.009).
Conclusions: Our results indicate that the effect of believing to have ingested caffeine improved performance to the same magnitude as actually receiving caffeine. These improvements were associated with an increase in pace during the first half of the time-trial
Lattice and spin excitations in multiferroic h-YMnO3
We used Raman and terahertz spectroscopies to investigate lattice and
magnetic excitations and their cross-coupling in the hexagonal YMnO3
multiferroic. Two phonon modes are strongly affected by the magnetic order.
Magnon excitations have been identified thanks to comparison with neutron
measurements and spin wave calculations but no electromagnon has been observed.
In addition, we evidenced two additional Raman active peaks. We have compared
this observation with the anti-crossing between magnon and acoustic phonon
branches measured by neutron. These optical measurements underly the unusual
strong spin-phonon coupling
Elastic Tensor of YNi_2B_2C
The complete elastic tensor of YNi_2B_2C was determined by application of the
resonant ultrasound spectroscopy technique to a single-crystal sample. Elastic
constants were found to be in good agreement with partial results obtained from
`time-of-flight' measurements performed on samples cut from the same ingot.
From the measured constants, the bulk modulus and Debye temperature are
calculated.Comment: 5 pages, 3 figure
Easy clip to treat anal fistula tracts: a word of caution
International audienceBackground and aims: Closing the internal opening by a clip ovesco has been recently proposed for healing the fistula tract, but, to date, data on benefit are poorly analyzed. The aim was to report a preliminary multicenter experience. Materials and methods Retrospective study was undertaken in six different French centers: surgical procedure, immediate complications, and follow-up have been collected. Results Nineteen clips were inserted in 17 patients (M/F, 4/13; median age, 42 years [29–54]) who had an anal fistula: 12 (71 %) high fistulas (including 4 rectovaginal fistulas), 5 (29 %) lower fistulas (with 3 rectovaginal fistulas), and 6 (35 %) Crohn’s fistulas. Out of 17 patients, 15 had a seton drainage beforehand. The procedure was easy in 8 (47 %) patients and the median operative time was 27.5 min (20–36.5). Postoperative period was painful for 11 (65 %) patients. A clip migration was noted in 11 patients (65 %) after a median follow-up of 10 days (5.5–49.8). Eleven patients (65 %) who failed had reoperation including 10 new drainages within the first month (0.5–5). After a mean follow-up of 4 months (2–7),, closing the tract was observed in 2 patients (12 %) following the first insertion of the clip and in another one after a second insertion. Conclusion: Treatment of anal fistula by placing a clip on the internal opening is disappointing and deleterious for some patients. A better assessment before dissemination is recommended
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