1,576 research outputs found
Unified interpretation of superluminal behaviors in wave propagation
No full textBy using two approaches, we demonstrate that superluminal behaviors in wave propagation can be attributed to mechanisms acting in the nearfield
limit. One approach is based on complex waves, while the other relies on a path-integral treatment of stochastic motion. The results of the
two approaches are comparable, and suitable for interpreting the data obtained in microwave experiments; these experiments, over a wide range
of distances, show a time advance which, in any case, is limited to nanoseconds
Sound attenuation in a unexplored frequency region: Brillouin ultraviolet light scattering measurements in v-SiO2
No full textWe report ultraviolet Brillouin light-scattering experimental data on v-SiO2 in an unexplored frequency
region, performed with a newly available spectrometer, up to exchanged wave vector q values of 0.075 nm−1,
at different temperatures. The measured attenuation follows a q2 law and is temperature dependent. Such
temperature dependence is found to be in good agreement with that measured at lower q, suggesting that the
broadening of the Brillouin peak is mainly due to a dynamic attenuation mechanism. The comparison of the
present data with those obtained by inelastic x-ray and visible scattering indicates the existence of a crossover
among different attenuation mechanisms, whose nature is briefly discussed
Sound attenuation in a unexplored frequency region: Brillouin ultraviolet light scattering measurements in v-Si O2
No full textWe report ultraviolet Brillouin light-scattering experimental data on v-Si O2 in an unexplored frequency region, performed with a newly available spectrometer, up to exchanged wave vector q values of 0.075 nm-1, at different temperatures. The measured attenuation follows a q2 law and is temperature dependent. Such temperature dependence is found to be in good agreement with that measured at lower q, suggesting that the broadening of the Brillouin peak is mainly due to a dynamic attenuation mechanism. The comparison of the present data with those obtained by inelastic x-ray and visible scattering indicates the existence of a crossover among different attenuation mechanisms, whose nature is briefly discussed
Vibrational analysis as a powerful tool in structure elucidation of polyarsenicals : a DFT-based investigation of arsenicin A
No full textA detailed experimental and theoretical vibrational analysis of arsenicin A, the first polyarsenicals isolated from Nature, is here reported. By exploiting the different and complementary selection rules of the Infrared (IR) absorption and of the Raman scattering transitions and by carrying out Density Functional Theory (DFT) calculations on several candidate structures we arrive to a substantiation of the structure of arsenicin A. We demonstrate that vibrational spectroscopy can be a very useful tool in structure elucidation in cases where Mass Spectroscopy (MS) measurements lead to shifty information and Nuclear Magnetic Resonance investigations are hindered by the presence in the molecule of silent nuclei and/or elements of symmetry. From one side, our approach allows to establish a reliable top-down methodology based on molecular vibrational parameters for the structural elucidation of any unknown organic compounds of medium-small size on which, today, accurate theoretical calculations can be carried out in reasonable times without recourse to great computing resources. From the other side, our investigation points out i) the great potential of Raman scattering spectroscopy, when coupled to a good level of theoretical analysis, to establish the skeleton of structurally undetermined molecules and ii) the better capability of IR absorption spectroscopy to distinguish different atom connectivities inside a given molecular skeleton
Raman Spectroscopy of Thallium Chloride in the Melting Region
No full textWe have followed the temperature dependence of the second order Raman spectra of b.c.c. thalliumchloride crystals and polycrystalline powders with particular regard to the region immediately preceding and following melting. Our results, concerning mainly the behavior of the LA(X)-TA(X) peak, imply the appearance of a new damping mechanism for the TA(X) phonon approximately 10°C below the melting temperature. Furthermore, this conjecture seems to be supported by calorimetric measurements near melting
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