49 research outputs found
High frequency sound waves in vitreous silica
We report a molecular dynamics simulation study of the sound waves in
vitreous silica in the mesoscopic exchanged momentum range. The calculated
dynamical structure factors are in quantitative agreement with recent
experimental inelastic neutron and x-ray scattering data. The analysis of the
longitudinal and transverse current spectra allows to discriminate between
opposite interpretations of the existing experimental data in favour of the
propagating nature of the high frequency sound waves.Comment: 4 pages, Revtex, 4 ps figures; to be published in Phys. Rev. Lett.,
February 198
Spectral Shape of Relaxations in Silica Glass
Precise low-frequency light scattering experiments on silica glass are
presented, covering a broad temperature and frequency range (9 GHz < \nu < 2
THz). For the first time the spectral shape of relaxations is observed over
more than one decade in frequency. The spectra show a power-law low-frequency
wing of the relaxational part of the spectrum with an exponent
proportional to temperature in the range 30 K < T < 200 K. A comparison of our
results with those from acoustic attenuation experiments performed at different
frequencies shows that this power-law behaviour rather well describes
relaxations in silica over 9 orders of magnitude in frequency. These findings
can be explained by a model of thermally activated transitions in double well
potentials.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Frequency behavior of Raman coupling coefficient in glasses
Low-frequency Raman coupling coefficient of 11 different glasses is
evaluated. It is found that the coupling coefficient demonstrates a universal
linear frequency behavior near the boson peak maximum and a superlinear
behavior at very low frequencies. The last observation suggests vanishing of
the coupling coefficient when frequency tends to zero. The results are
discussed in terms of the vibration wavefunction that combines features of
localized and extended modes.Comment: 8 pages, 9 figure
Herkules â Held zwischen Tugend und Hybris. Ein europĂ€ischer Erinnerungsort der FrĂŒhen Neuzeit?
This essay traces some of the contexts and media in which "Heracles-Hercules" - as a hero between virtue and hubris - was visible in European societies from the end of the middle ages onwards. It discusses whether this example of the reception, appropriation and transformation of classical myths in the early modern period can be understood as a European "lieu de mémoire", and to what extent the concept of "lieux de mémoire" (or sites of memory) can foster our understanding of a particular object of study (here the Heracles/Hercules myth). Against this backdrop, we conclude with some general questions about the more ambitious project* of a comprehensive register of European "lieux de mémoire".
* * Published as: Boer, Pim den / Duchhardt, Heinz / Kreis, Georg / Schmale, Wolfgang (eds.): EuropĂ€ische Erinnerungsorte, 3 vols., Munich 2011â201