Onset of Superfluidity in 4He Films Adsorbed on Disordered Substrates

We have studied 4He films adsorbed in two porous glasses, aerogel and Vycor, using high precision torsional oscillator and DC calorimetry techniques. Our investigation focused on the onset of superfluidity at low temperatures as the 4He coverage is increased. Torsional oscillator measurements of the 4He-aerogel system were used to determine the superfluid density of films with transition temperatures as low as 20 mK. Heat capacity measurements of the 4He-Vycor system probed the excitation spectrum of both non-superfluid and superfluid films for temperatures down to 10 mK. Both sets of measurements suggest that the critical coverage for the onset of superfluidity corresponds to a mobility edge in the chemical potential, so that the onset transition is the bosonic analog of a superconductor-insulator transition. The superfluid density measurements, however, are not in agreement with the scaling theory of an onset transition from a gapless, Bose glass phase to a superfluid. The heat capacity measurements show that the non-superfluid phase is better characterized as an insulator with a gap.Comment: 15 pages (RevTex), 21 figures (postscript

Origins of the Ambient Solar Wind: Implications for Space Weather

The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue connected with a 2016 ISSI workshop on "The Scientific Foundations of Space Weather." 44 pages, 9 figure

Suplementação da Silagem de Sorgo com Diferentes Fontes de Proteína para Bovinos de Corte Supplementation of Sorghum Silage with Different Sources of Protein for Beef Cattle

Farelo de soja (FS), farinha de penas (FPH) e farelo de soja tratado (FST) com 0,17% de formaldeído foram utilizados como suplementos à silagem de sorgo para avaliar os seus efeitos sobre o consumo, o desempenho e a digestibilidade aparente dos nutrientes em bovinos machos. O tratamento do farelo de soja com formaldeído não diferiu do farelo de soja não tratado para todos os ítens estudados. Por outro lado, a farinha de penas apresentou menores coeficientes de digestibilidade para a MS, MO, PB, FDN e FDA (63,0; 64,9; 61,80; 56,4; e 50,9% versus 65,1; 67,0; 66,8; 58,5; e 53,6% do FS e 66,7; 68,7; 67,2; 61,9; e 57,5% do FST, respectivamente), além de propiciar menor consumo de energia metabolizável por unidade de tamanho metabólico (214 kcal/UTM para a FPH, 234 kcal/UTM para o FS e de 240 kcal/UTM para o FST). Mesmo com estas diferenças nos parâmetros acima mencionados, não foi possível detectar diferenças para o ganho de peso dos animais, de 1,5; 1,6 e 1,7 kg/dia para FPH, FS e FST, respectivamente.<br>Soybean meal (SBM), feather meal (FTM) and treated soybean meal (TSBM) with 0.17% of formaldehyde were used as supplement of sorghum silage to evaluate the effect on intake, performance and nutrient digestibilities with young bulls. Treatment of soybean meal with formaldehyde did not differ from soybean not treated, for all studied parameters. Feather meal supplement presented lower digestibility coefficients for DM, OM, CP, NDF and ADF (63.0, 65.5, 61.8, 56.4, and 50.9%, versus 65.1, 67.0, 66.8, 58.5, and 53.6% for soybean meal and 66.7, 68.7, 67.2, 61.9 and 57.5% for treated soybean meal, respectively). It also showed lower metabolizable energy intake by unit of metabolic weight (214 kcal/MW for FTM, 234 kcal/MW for SBM and 240 kcal/MW for TSBM). Even if differences were observed for all parameters, it was not possible to detect differences in live weight gain (1.5, 1.6 and 1.7 kg/d for FTM, SBM and TSBM)