Implications of regolith thickness in the Apollo 16 landing site

Determining thickness of regolith in Apollo 16 landing site by Monte Carlo metho

Martian doublet craters

Monte Carlo cratering simulation model to show nonrandomness of formation of Mars tangential meteorite crater

Intelligent ranking for photo galleries using sharing intent

Users often share digital photographs over communication links, e.g., via SMS, chat, URLs, etc. This disclosure describes techniques to determine and present ranked candidate images for sharing to other users and user devices. The ranking is based on a variety of characteristics of the images, including time of capture of the images, as well as other user-permitted factors that can indicate user intent, such as history of previous sharing of images by the user, the current or recent device context of the user (chat or conversation, application being used, data on the user’s screen, and so on), etc. By intelligently ranking images in sharing galleries, the user\u27s time spent searching for and sharing images can be reduced, which can improve user satisfaction and sharing frequency

Comparative studies of lunar, Martian, and Mercurian craters and plains

The spatial distribution of lunar smooth plains is not consistent with experimental simulations of melt rock emplacement during cratering in layered materials. Nor is it consistent with the location of melt rocks (suevite) near the Ries basin. Lunar smooth plains surrounding Imbrium are most extensive in areas where pre-existing craters are most degraded. This observation suggests that plains form by impact of basin and local primary crater ejecta, together with deposition of debris excavated by the resultant secondary cratering events. Craters within the belt of smooth plains surrounding the Caloris basin on Mercury are most degraded nearest the basin; this suggests that Mercurian smooth plains must, at least in part, be emplaced in a manner similar to plains surrounding the Imbrium basin. Mercurian uplands have a primary crater population deficient in small crater diameters (less than approximately 30 km). Lunar uplands far from major basins also have a crater population deficient in small crater sizes. Martian cratered terrain exhibits a similar crater deficiency, which was previously interpreted as due to obliteration of small craters (less than approximately 30 km) by some surface process. A crater size distribution deficient in small sizes (less than approximately 30 km) on the Mercurian, lunar, and Martian uplands has implications for the origin of debris bombarding the inner solar system during the period recorded by these surfaces. It is proposed that during late heavy bombardment, the inner solar system was inundated with bodies that broke up under tidal fission as they approached the planets. Such a mechanism would lend to production of a crater population deficient in small crater sizes, and it would also explain the large degree of spatial clustering of primary craters on Mercury, the moon, and Mars

Measurement of phosphorus segregation in silicon at the atomic-scale using STM

In order to fabricate precise atomic-scale devices in silicon using a combination of scanning tunnelling microscopy (STM) and molecular beam epitaxy it is necessary to minimize the segregation/diffusion of dopant atoms during silicon encapsulation. We characterize the surface segregation/diffusion of phosphorus atoms from a $\delta$-doped layer in silicon after encapsulation at 250$^{\circ}$C and room temperature using secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES), and STM. We show that the surface phosphorus density can be reduced to a few percent of the initial $\delta$-doped density if the phosphorus atoms are encapsulated with 5 or 10 monolayers of epitaxial silicon at room temperature. We highlight the limitations of SIMS and AES to determine phosphorus segregation at the atomic-scale and the advantage of using STM directly

Local energy balance, specific heats and the Oberbeck-Boussinesq approximation

A thermodynamic argument is proposed in order to discuss the most appropriate form of the local energy balance equation within the Oberbeck-Boussinesq approximation. The study is devoted to establish the correct thermodynamic property to be used in order to express the relationship between the change of internal energy and the temperature change. It is noted that, if the fluid is a perfect gas, this property must be identified with the specific heat at constant volume. If the fluid is a liquid, a definitely reliable approximation identifies this thermodynamic property with the specific heat at constant pressure. No explicit pressure work term must be present in the energy balance. The reasoning is extended to the case of fluid saturated porous media.Comment: 14 pages, 2 figures, 1 table, submitted for publicatio

Simulation study of GaAsP/Si tandem solar cells

A model, adapted from the Shockley-Queisser detailed balance model to tandem solar cells with a monolithically grown GaAsxP1-x top junction on a Si bottom junction, has been developed. Updated data have been used for the absorption spectrums. Two surface geometries, flat and ideally textured, have been investigated. As an important improvement over existing models, the effects of threading-dislocations related Shockley-Read-Hall recombinations in the GaAsxP1-x cell, due to the lattice mismatch between the GaAsxP1-x epilayers and the Si substrate, have been taken into consideration. Auger recombinations in the Si bottom cell and luminescent coupling between the cells have also been considered. For a dislocation free 2-μm thick top cell, maximal theoretical efficiencies of 41.6% and 39.1% have been calculated for a textured and a flat surface, respectively. For threading dislocation (TD) densities below 10^4 cm^-2, the impact of TDs in the GaAsxP1-x layers on the solar cell performances is very limited. With TD densities over 10^5 cm^-2, the top cell open circuit voltage is reduced, hence the overall efficiency. For TD densities over 4×10^6 cm^-2, as the diffusion length of minority carriers in the base gets smaller than the base thickness, the short circuit current in the top GaAsxP1-x cell is also reduced, resulting in a decrease in the optimal top cell bandgap. Using non ideal EQEs and surface recombination rates from published experimental data, the long-term efficiency potential of the investigated technology has been estimated to be ~35.1% for an ideally textured GaAsxP1 x/Si tandem cell with a TD density of 10^5 cm^-2 (~33.0% with a flat surface)