Glass-specific behavior in the damping of acoustic-like vibrations

High frequency sound is observed in lithium diborate glass, Li$_2$O--2B$_2$O$_3$, using Brillouin scattering of light and x-rays. The sound attenuation exhibits a non-trivial dependence on the wavevector, with a remarkably rapid increase towards a Ioffe-Regel crossover as the frequency approaches the boson peak from below. An analysis of literature results reveals the near coincidence of the boson-peak frequency with a Ioffe-Regel limit for sound in {\em all} sufficiently strong glasses. We conjecture that this behavior, specific to glassy materials, must be quite universal among them.Comment: 4 pages, 4 figures, revised versio

Eliminating the broadening by finite aperture in Brillouin spectroscopy

We present a new optical arrangement which allows to avoid the broadening by finite aperture in Brillouin spectroscopy. In this system, all the rays scattered at the same angle by the whole scattering volume are collected on a single pixel of the area detector. This allows to use large collection angles, increasing the luminosity without lowering the accuracy of the frequency-shift and linewidth measurements. Several results of experimental checks are provided, showing the efficiency of the device.Comment: 14 pages, 8 figure

Acoustic damping in Li2_2O-2B2_2O3_3 glass observed by inelastic x-ray and optical Brillouin scattering

The dynamic structure factor of lithium-diborate glass has been measured at several values of the momentum transfer $Q$ using high resolution inelastic x-ray scattering. Much attention has been devoted to the low $Q$-range, below the observed Ioffe-Regel crossover \qco{}$\simeq$ 2.1 nm$^{-1}$. We find that below \qco{}, the linewidth of longitudinal acoustic waves increases with a high power of either $Q$, or of the frequency $\Omega$, up to the crossover frequency \OMco{} $\simeq$ 9 meV that nearly coincides with the center of the boson peak. This new finding strongly supports the view that resonance and hybridization of acoustic waves with a distribution of rather local low frequency modes forming the boson peak is responsible for the end of acoustic branches in strong glasses. Further, we present high resolution Brillouin light-scattering data obtained at much lower frequencies on the same sample. These clearly rule out a simple $\Omega^2$-dependence of the acoustic damping over the entire frequency range.Comment: 5 pages, 5 figures, submitted to the proceedings of IDMRCS 2005, Lille, Franc

Création d’un réseau métier drones sensu-lato : pertinence, contours, intérêt ?

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Determination of crystallite size in polished graphitized carbon by Raman spectroscopy

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On a reliable structural characterization of polished carbons in meteorites by Raman microspectroscopy

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A prospective observational trial of fusion imaging in infrarenal aneurysms

Objective Use of three-dimensional fusion has been shown to significantly reduce radiation exposure and contrast material use in complex (fenestrated and branched) endovascular aneurysm repair (EVAR). Cydar software (CYDAR Medical, Cambridge, United Kingdom) is a cloud-based technology that can provide imaging guidance by overlaying preoperative three-dimensional vessel anatomy from computed tomography scans onto live fluoroscopy images both in hybrid operating rooms and on mobile C-arms. The aim of this study was to determine whether radiation dose reduction would occur with the addition of fusion imaging to infrarenal repair in all imaging environments. Methods All patients who consented to involvement in the trial and who were treated with EVAR in our center from March 2016 until April 2017 were included. A teaching session about radiation protection and Cydar fusion software use was provided to all operators before the start of the fusion group enrollment. This group was compared with a retrospective cohort of patients treated in the same center from March 2015 to March 2016, after a dedicated program of radiation awareness and reduction was introduced. Ruptured aneurysms and complex EVAR were excluded. Preoperative and perioperative characteristics were recorded, including parameters of radiation dose, such as air kerma and dose-area product. Results were expressed in median and interquartile range. Results Forty-four patients were prospectively enrolled and compared with 21 retrospective control patients. No significant differences were found in comparing sex, body mass index, and age at repair. The median operation time (wire to wire) and fluoroscopy time were 90 (75-105) minutes and 30 (22-34) minutes, respectively, without significant differences between groups (P = .56 and P = .36). Dose-area product was nonsignificantly higher in the control group, 21.7 (8.9-85.9) Gy cm2, compared with the fusion group, 12.4 (7.5-23.4) Gy cm2 (P = .10). Air kerma product was significantly higher in the control group, 142 (61-541) mGy, compared with 82 (51-115) mGy in the fusion group (P = .03). The number of digital subtraction angiography runs was significantly lower in the fusion group (8 [6-11]) compared with the control group (10 [9-14]); (P = .03). There were no significant differences in the frequency of adverse events, endoleaks, or additional procedures required. Conclusions When it is used in simple procedures such as infrarenal aneurysm repair, image-based fusion technology is feasible both in hybrid operating rooms and on mobile systems and leads to an overall 50% reduction in radiation dose. Fusion technology should become standard of care for centers attempting to maximize radiation dose reduction, even if capital investment of a hybrid operating room is not feasible

Igneous rock powder identification using colour cameras: A powerful method for space exploration

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