Micro-Brillouin spectroscopy mapping of the residual density field induced by Vickers indentation in a soda-lime silicate glass

High-resolution Brillouin scattering is used to achieve 3-dimensional maps of the longitudinal acoustic mode frequency shift in soda-lime silicate glasses subject to Vickers indentations. Assuming that residual stress-induced effects are simply proportional to density changes, residual densification fields are obtained. The density gradient is nearly isotropic, confirming earlier optical observations made on a similar glass. The results show that Brillouin micro-spectroscopy opens the way to a fully quantitative comparison of experimental data with predictions of mechanical models for the identification of a constitutive law.Comment: 4 pages, 3 figures, revised version, to appear in Appl. Phys. Let

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

Anharmonic vs. relaxational sound damping in glasses: I. Brillouin scattering from densified silica

This series discusses the origin of sound damping and dispersion in glasses. In particular, we address the relative importance of anharmonicity versus thermally activated relaxation. In this first article, Brillouin-scattering measurements of permanently densified silica glass are presented. It is found that in this case the results are compatible with a model in which damping and dispersion are only produced by the anharmonic coupling of the sound waves with thermally excited modes. The thermal relaxation time and the unrelaxed velocity are estimated.Comment: 9 pages with 7 figures, added reference

Synthesis, antitubercular activity and mechanism of resistance of highly effective thiacetazone analogues

Defining the pharmacological target(s) of currently used drugs and developing new analogues with greater potency are both important aspects of the search for agents that are effective against drug-sensitive and drug-resistant Mycobacterium tuberculosis. Thiacetazone (TAC) is an anti-tubercular drug that was formerly used in conjunction with isoniazid, but removed from the antitubercular chemotherapeutic arsenal due to toxic side effects. However, several recent studies have linked the mechanisms of action of TAC to mycolic acid metabolism and TAC-derived analogues have shown increased potency against M. tuberculosis. To obtain new insights into the molecular mechanisms of TAC resistance, we isolated and analyzed 10 mutants of M. tuberculosis that were highly resistant to TAC. One strain was found to be mutated in the methyltransferase MmaA4 at Gly101, consistent with its lack of oxygenated mycolic acids. All remaining strains harbored missense mutations in either HadA (at Cys61) or HadC (at Val85, Lys157 or Thr123), which are components of the bhydroxyacyl-ACP dehydratase complex that participates in the mycolic acid elongation step. Separately, a library of 31 new TAC analogues was synthesized and evaluated against M. tuberculosis. Two of these compounds, 15 and 16, exhibited minimal inhibitory concentrations 10-fold lower than the parental molecule, and inhibited mycolic acid biosynthesis in a dose-dependent manner. Moreover, overexpression of HadAB HadBC or HadABC in M. tuberculosis led to high level resistance to these compounds, demonstrating that their mode of action is similar to that of TAC. In summary, this study uncovered new mutations associated with TAC resistance and also demonstrated that simple structural optimization of the TAC scaffold was possible and may lead to a new generation of TAC-derived drug candidates for the potential treatment of tuberculosis as mycolic acid inhibitors

Spectromètre de haute résolution, fort contraste, haute précision

Nous présentons la réalisation d'un spectromètre de haute résolution, de fort contraste, haute précision adapté à la mesure de raies Brillouin dans les solides. Il s'agit d'un spectromètre optique constitué de l'association d'un interféromètre de Fabry-Perot plan (FPP) et d'un interféromètre de Fabry-Perot sphérique (FPS). Un signal de référence annexe garantit la précision en fréquence de l'instrument

Elastic moduli of XAlSiO4 aluminosilicate glasses: effects of charge-balancing cations

International audienceBrillouin spectroscopy is used to investigate the elastic properties of XAlSiO4 aluminosilicate glasses where X =Li, Na, K, Mg0.5, Ca0.5, Sr0.5, Ba0.5, and Zn0.5. The Brillouin frequency shifts obtained in two different scattering geometries allow the calculation of the refractive index, the two sound velocities and Poisson's ratio.Measurements of the mass density give in turn the elastic moduli and the Debye temperature.We find that the elastic properties scale with the atomic density of the glassy network or the charge-balancing cation field strengthwhile they negatively correlate with the glass transition temperature. Further, Poisson's ratio depends on the nature of the non-framework cations in this glass series

Electron and Lattice Heating Contributions to the Transient Optical Response of a Single Plasmonic Nano-Object

The sudden absorption of light by a metal nanoparticle launches a series of relaxation processes (internal thermalization, acoustic vibrations, and cooling) which induce a transient modification of its optical response. In this work, the transient optical response associated with the internal thermalization of a single gold nanodisk (occurring on a few picoseconds time scale) was quantitatively investigated by time-resolved spectroscopy experiments, and the measured signals were compared with a model accounting for the effects of both electron and ionic lattice heating. We show that experimental time-resolved signals at delays posterior to nanodisk excitation and electron gas thermalization can be simply interpreted as a combination of electron and lattice temperature evolutions, with probe wavelength-dependent weights. This demonstrates the possibility to selectively probe the electronic or lattice dynamics, through the choice of specific probe wavelengths. Additionally, the time-dependent spectral shape of transient extinction cross-section changes is shown to be successively dominated by the effects of electron and lattice heating, which present distinct spectral signatures

Onset of optical-phonon cooling in multilayer graphene revealed by RF noise and black-body radiation thermometries

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