Tracking granules on the Sun's surface and reconstructing horizontal velocity fields: I. the CST algorithm

Determination of horizontal velocity fields on the solar surface is crucial for understanding the dynamics of structures like mesogranulation or supergranulation or simply the distribution of magnetic fields. We pursue here the development of a method called CST for coherent structure tracking, which determines the horizontal motion of granules in the field of view. We first devise a generalization of Strous method for the segmentation of images and show that when segmentation follows the shape of granules more closely, granule tracking is less effective for large granules because of increased sensitivity to granule fragmentation. We then introduce the multi-resolution analysis on the velocity field, based on Daubechies wavelets, which provides a view of this field on different scales. An algorithm for computing the field derivatives, like the horizontal divergence and the vertical vorticity, is also devised. The effects from the lack of data or from terrestrial atmospheric distortion of the images are also briefly discussed.Comment: in press in Astronomy and Astrophysics, 9 page

Silicon material task. Part 3: Low-cost silicon solar array project

The feasibility of a process for carbon reduction of low impurity silica in a plasma heat source was investigated to produce low-cost solar-grade silicon. Theoretical aspects of the reaction chemistry were studied with the aid of a computer program using iterative free energy minimization. These calculations indicate a threshold temperature exists at 2400 K below which no silicon is formed. The computer simulation technique of molecular dynamics was used to study the quenching of product species

LSA silicon material task closed-cycle process development

The initial effort on feasibility of the closed cycle process was begun with the design of the two major items of untested equipment, the silicon tetrachloride by product converter and the rotary drum reactor for deposition of silicon from trichlorosilane. The design criteria of the initial laboratory equipment included consideration of the reaction chemistry, thermodynamics, and other technical factors. Design and construction of the laboratory equipment was completed. Preliminary silicon tetrachloride conversion experiments confirmed the expected high yield of trichlorosilane, up to 98 percent of theoretical conversion. A preliminary solar-grade polysilicon cost estimate, including capital costs considered extremely conservative, of $6.91/kg supports the potential of this approach to achieve the cost goal. The closed cycle process appears to have a very likely potential to achieve LSA goals

A single sub-km Kuiper Belt object from a stellar Occultation in archival data

The Kuiper belt is a remnant of the primordial Solar System. Measurements of its size distribution constrain its accretion and collisional history, and the importance of material strength of Kuiper belt objects (KBOs). Small, sub-km sized, KBOs elude direct detection, but the signature of their occultations of background stars should be detectable. Observations at both optical and X-ray wavelengths claim to have detected such occultations, but their implied KBO abundances are inconsistent with each other and far exceed theoretical expectations. Here, we report an analysis of archival data that reveals an occultation by a body with a 500 m radius at a distance of 45 AU. The probability of this event to occur due to random statistical fluctuations within our data set is about 2%. Our survey yields a surface density of KBOs with radii larger than 250 m of 2.1^{+4.8}_{-1.7} x 10^7 deg^{-2}, ruling out inferred surface densities from previous claimed detections by more than 5 sigma. The fact that we detected only one event, firmly shows a deficit of sub-km sized KBOs compared to a population extrapolated from objects with r>50 km. This implies that sub-km sized KBOs are undergoing collisional erosion, just like debris disks observed around other stars.Comment: To appear in Nature on December 17, 2009. Under press embargo until 1800 hours London time on 16 December. 19 pages; 7 figure

Nuclear Power: a Hedge against Uncertain Gas and Carbon Prices?

High fossil fuel prices have rekindled interest in nuclear power. This paper identifies specific nuclear characteristics making it unattractive to merchant generators in liberalised electricity markets, and argues that non-fossil fuel technologies have an overlooked à ¢à  à  option valueà ¢à  à  given fuel and carbon price uncertainty. Stochastic optimisation estimates the company option value of keeping open the choice between nuclear and gas technologies. This option value decreases sharply as the correlation between electricity, gas, and carbon prices rises, casting doubt on whether private investorsà ¢à  à  fuel-mix diversification incentives in electricity markets are aligned with the social value of a diverse fuel-mix

Wetting to Non-wetting Transition in Sodium-Coated C_60

Based on ab initi and density-functional theory calculations, an empirical potential is proposed to model the interaction between a fullerene molecule and many sodium atoms. This model predicts homogeneous coverage of C_60 below 8 Na atoms, and a progressive droplet formation above this size. The effects of ionization, temperature, and external electric field indicate that the various, and apparently contradictory, experimental results can indeed be put into agreement.Comment: 4 pages, 4 postscript figure

Changes in Grape Maturity Induced by Spraying Ethanol

Three different ethanol solutions were sprayed onto Cabernet Sauvignon (Vitis vinifera L.) clusters during the ripening period: 2.5, 5 and 10% by volume in water. Controls were sprayed with water alone. Three different times of spraying were also tested: 8, 10 and 13 weeks post-flowering. One of the observed changes was a lower titratable acidity in grape samples at harvest, when the clusters were sprayed with ethanol at 10 weeks, in comparison with controls. The wines made with grapes treated with ethanol after mid-veraison, had higher ODs at 520 nm than did the controls. This may due to a combined effect of red pigment levels and acidity. In addition, following malolactic fermentation, the acidity levels of wines made with ethanoltreated grapes were slightly higher than those made with the control grapes. Spraying ethanol at 13 weeks post-flowering increased the berry weight by 10% at harvest without decreasing the °Brix value. The corresponding wines had similar degrees of alcohol. This observation was made for the first time in 2001