Acoustic Nature of the Boson Peak in Vitreous Silica

New temperature dependent inelastic x-ray (IXS) and Raman (RS) scattering data are compared to each other and with existing inelastic neutron scattering data in vitreous silica (v-SiO_2), in the 300 - 1775 K region. The IXS data show collective propagating excitations up to Q=3.5 nm^-1. The temperature behaviour of the excitations at Q=1.6 nm^-1 matches that of the boson peak found in INS and RS. This supports the acoustic origin of the excess of vibrational states giving rise to the boson peak in this glass.Comment: 10 pages and 4 figure

Functional Limit Theorems for Multiparameter Fractional Brownian Motion

We prove a general functional limit theorem for multiparameter fractional Brownian motion. The functional law of the iterated logarithm, functional L\'{e}vy's modulus of continuity and many other results are its particular cases. Applications to approximation theory are discussed.Comment: AMS-LaTeX, 23 page

The Raman coupling function in amorphous silica and the nature of the long wavelength excitations in disordered systems

New Raman and incoherent neutron scattering data at various temperatures and molecular dynamic simulations in amorphous silica, are compared to obtain the Raman coupling coefficient $C(\omega)$ and, in particular, its low frequency limit. This study indicates that in the $\omega \to 0$ limit $C(\omega)$ extrapolates to a non vanishing value, giving important indications on the characteristics of the vibrational modes in disordered materials; in particular our results indicate that even in the limit of very long wavelength the local disorder implies non-regular local atomic displacements.Comment: Revtex, 4 ps figure

The nature of the short wavelength excitations in vitreous silica: X-Rays Brillouin scattering study

The dynamical structure factor (S(Q,E)) of vitreous silica has been measured by Inelastic X-ray Scattering varying the exchanged wavevector (Q) at fixed exchanged energy (E) - an experimental procedure that, contrary to the usual one at constant Q, provides spectra with much better identified inelastic features. This allows the first direct evidence of Brillouin peaks in the S(Q,E) of SiO_2 at energies above the Boson Peak (BP) energy, a finding that excludes the possibility that the BP marks the transition from propagating to localised dynamics in glasses.Comment: 4 pages, 3 Postscript figures. To appear in Physical Review Letter

Tipificação do café conilon produzido no Estado do Espírito Santo - safra 98/99.

O Espírito Santo cultiva as espécies de café arábica e conilon, sendo a altitude de 450m o seu divisor. O conilon é utilizado, além da exportação como café verde, para a indústria do solúvel e para o mercado interno. Visando monitorar a qualidade do café conilon no estado, foram amostrados 13 municípios, em março/2000, sendo as amostras referentes à safra 98/99, realizadas no café em estoque na propriedade rural. Quantificou-se o número de grãos sadios, pretos, verdes, ardidos, brocados e quebrados, calculando-se o tipo e a freqüência de ocorrência dos defeitos, por região. Observou-se que os maiores índices de defeitos foram observados na região Centro-Serrana, seguida de Cachoeiro de Itapemirim, Vitória e Colatina. Os defeitos mais freqüentes foram grãos ardidos, brocados, quebrados, verdes e pretos, em ordem decrescente. 17% das amostras apresentaram tipo 6 e superiores. A maior incidência foi de amostras tipo 7 e 7/8