Dynamic sound attenuation at hypersonic frequencies in silica glass

In order to clarify the origin of the dominant processes responsible for the acoustic attenuation of phonons, which is a much debatted topic, we present Bril louin scattering experiments in various silica glasses of different OH impurities content. A large temperature range, from 5 to 1500 K is investigated, up to the glass transition temperature. Comparison of the hypersonic wave attenuation in various samples allows to identify two different processes. The first one induce s a low temperature peak related to relaxational processes; it is strongly sensitive to the extrinsic defects. The second, dominant in the hig h temperature range, is weakly dependent on the impurities and can be ascribed to anharmonic interactions

In situ measurements of density fluctuations and compressibility in silica glass as a function of temperature and thermal history

In this paper, small-angle X-ray scattering measurements are used to determine the different compressibility contributions, as well as the isothermal compressibility, in thermal equilibrium in silica glasses having different thermal histories. Using two different methods of analysis, in the supercooled liquid and in the glassy state, we obtain respectively the temperature and fictive temperature dependences of the isotheraml compressibility. The values obtained in the glass and supercooled liquid states are very close to each other. They agree with previous determinations of the literature. The compressibility in the glass state slightly decreases with increasing fictive temperature. The relaxational part of the compressibility is also calculated and compared to previous determinations. We discussed the small differences between the different determinations

Quantum statistical effects in nano-oscillator arrays

We have theoretically predicted the density of states(DOS), the low temperature specific heat, and Brillouin scattering spectra of a large, free standing array of coupled nano-oscillators. We have found significant gaps in the DOS of 2D elastic systems, and predict the average DOS to be nearly independent of frequency over a broad band f < 50GHz. At low temperatures, the measurements probe the quantum statistics obeyed by rigid body modes of the array and, thus, could be used to verify the quantization of the associated energy levels. These states, in turn, involve center-of mass motion of large numbers of atoms, N > 1.e14, and therefore such observations would extend the domain in which quantum mechanics has been experimentally tested. We have found the required measurement capability to carry out this investigation to be within reach of current technology.Comment: 1 tex file, 3 figures, 1 bbl fil

A multidimensional global migration model for use in cohort-component population projections

Background: International migration is influenced by economic and social factors that change over time. However, given the complexity of these relationships, global population scenarios to date include only stylized migration assumptions that do not account for changes in the drivers of migration. On the other hand, existing projection models of international migration do not resolve all demographic dimensions necessary to interact with the cohort-component models typically used for population projections. Objective: Here we present a global model of bilateral migration that resolves these dimensions while also accounting for important external, economic, and social factors. Methods: We include age, education, and gender dependencies into a recently developed model of migration by origin, destination, and country of birth. We calibrate the model on bilateral flow data, couple it to a widely used cohort-component population model, and project migration until 2050 under three alternative socioeconomic scenarios. Conclusions: The extended model fits data better than the original migration model and is more sensitive to the choice of socioeconomic scenario, thus yielding a wider range of projections. Regional net migration flows projected by the model are substantially larger than in the stylized assumptions. The largest flows are projected in the most economically unequal scenario, while previously, the same scenario was assumed to have the smallest flows. Contribution: The results offer an opportunity to reconcile stylized migration assumptions with quantitative estimates of the roles of important migration drivers. The coupled migration-population modeling framework means that interactions between migration and other demographic processes can be captured, and the migration component can be evaluated in more detail than before

Voltage-programmable liquid optical interface

Recently, there has been intense interest in photonic devices based on microfluidics, including displays and refractive tunable microlenses and optical beamsteerers, that work using the principle of electrowetting. Here, we report a novel approach to optical devices in which static wrinkles are produced at the surface of a thin film of oil as a result of dielectrophoretic forces. We have demonstrated this voltage-programmable surface wrinkling effect in periodic devices with pitch lengths of between 20 and 240 µm and with response times of less than 40 µs. By a careful choice of oils, it is possible to optimize either for high-amplitude sinusoidal wrinkles at micrometre-scale pitches or more complex non-sinusoidal profiles with higher Fourier components at longer pitches. This opens up the possibility of developing rapidly responsive voltage-programmable, polarization-insensitive transmission and reflection diffraction devices and arbitrary surface profile optical devices

Water Dynamics at Protein Interfaces: Ultrafast Optical Kerr Effect Study

The behavior of water molecules surrounding a protein can have an important bearing on its structure and function. Consequently, a great deal of attention has been focused on changes in the relaxation dynamics of water when it is located at the protein surface. Here we use the ultrafast optical Kerr effect to study the H-bond structure and dynamics of aqueous solutions of proteins. Measurements are made for three proteins as a function of concentration. We find that the water dynamics in the first solvation layer of the proteins are slowed by up to a factor of 8 in comparison to those in bulk water. The most marked slowdown was observed for the most hydrophilic protein studied, bovine serum albumin, whereas the most hydrophobic protein, trypsin, had a slightly smaller effect. The terahertz Raman spectra of these protein solutions resemble those of pure water up to 5 wt % of protein, above which a new feature appears at 80 cm–1, which is assigned to a bending of the protein amide chain

Umidade e congelamento de grãos de amaranto e sua capacidade de expansão térmica

O objetivo deste trabalho foi avaliar a influência do teor de umidade, da temperatura de armazenamento e do momento da hidratação de grãos de amaranto (Amaranthus cruentus L. ) sobre sua capacidade de expansão térmica, bem como comparar as composições químicas de grãos crus e pipocados. Os atributos diâmetro médio ponderado, volume de expansão, densidade, rendimento, quantidade descartada e tempo de residência de grãos da variedade BRS Alegria foram avaliados de acordo com três teores de umidade (9,5, 11,5 e 13,5%), duas formas de armazenamento, temperatura ambiente de ±28ºC e congelado a -18ºC, e dois momentos de hidratação, antes e após congelamento. Utilizou-se chapa metálica aquecida a 215ºC para pipocar os grãos. Grãos congelados com umidade de 13,5% tiveram maior diâmetro médio ponderado e volume de expansão, e menor densidade e tempo de residência. A umidade de 13,5% proporcionou os maiores rendimentos e expansão dos grãos. O armazenamento a -18ºC produziu pipocas maiores e mais leves do que em condições ambientais. As pipocas apresentaram redução nos teores de proteínas e fibras insolúveis e aumento nos de lipídeos e fibras solúveis, em relação ao grão cru. O congelamento dos grãos a -18ºC e sua hidratação a 13,5% de umidade favorecem o pipocamento de grãos de amaranto, com produção de pipocas de melhor qualidade

RAYLEIGH SCATTERING: COLLISIONAL MOTIONS IN LIQUIDS∗LIQUIDS^{*}

$^{*}$This research was supported by the Atomic Energy Commission. $^{\dagger}$Present address: Naval Research Laboratory, Washington, D.C.""Author Institution: Department of Physics, The Catholic University of AmericaMeasurements of light scattered in the Rayleigh wing were made over the range from 5 to $500 cm^{-1}$ in $CCI_{4}$, $C_{6}H_{12}$, $C_{5}H_{12}$, $CH_{3}OH$, $C_{2}H_{5}OH$, $H_{2}O$, $NH_{3}$ and $CHCl_{3}$. These data when compared with earlier data on Ar, Xe, and SnBr, indicate that in all of these liquids there is present the essentially exponential frequency dependence typical of collision induced effects. A calculation of the spectrum for large frequency shifts based on a binary interaction picture employing a Lennard-Jones potential and a short range electronic overlap distortion model agrees well with the experimental results in liquid argon. Further, assuming that molecular frame distortion is proportional to the interaction force, a similar calculation yields excellent agreement for the molecular systems. It is concluded that isolated binary interactions are mainly responsible for the spectral density in the wings of the Rayleigh Spectrum