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News Article | October 19, 2015
Site: http://www.techtimes.com/rss/sections/space.xml

Pluto continues to puzzle and intrigue scientists as data and images flow back to Earth from NASA's New Horizons spacecraft, and the latest images have astronomer saying "it's the pits." That's their response to images of the dwarf planet that show hundreds of deep pits scattered across the Sputnik Planum, the heart-shaped region scientist think is a huge depression on the surface filled with frozen gases, mostly nitrogen. The images, gathered by the spacecraft's Long Range Reconnaissance Imager (LORRI) instrument and posted to a public website, show a pattern of clusters of small pits and troughs. The researchers suggest the pits and troughs, some hundreds of meters across and probably tens of meters deep, may be the result of the sublimation or evaporation of the volatile ices on the surface that then reveals darker materials in the surface beneath. Those ices covering much of Pluto's surface are likely only a "surface veneer" covering a widespread water-ice based bedrock veneer, they say. As evidence they cite mountains on the dwarf planet that rise almost 2 miles above their surroundings. If those mountains were made of frozen ices of nitrogen, carbon dioxide or methane -- instead of bedrock -- they would collapse rapidly, the researchers explain. "Pluto is weird, in a good way," says Hal Weaver, New Horizons project scientist with Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. "The pits, and the way they're aligned, provide clues about the ice flow and the exchange of volatiles between the surface and atmosphere, and the science team is working hard to understand what physical processes are at play here." The pits are just one of the discoveries about Pluto presented in a study by the New Horizons team published [pdf] in the journal Science. Astronomers think the surface at the Sputnik Planum is around 100 million years old, which makes the region much younger than other geological features seen in other regions of Pluto. It is surprisingly free of any craters, compared to other areas of the dwarf planet's surface, suggesting that in at least some areas activity including ice flows, sublimation, internal convection and winds have all likely shaped Pluto. "What's striking to me is that, yes, there is activity, but it's not everywhere and that's an interesting part of the puzzle," says astronomer Will Grundy at the Lowell Observatory, who leads the New Horizon surface composition team and co-authored the study. "It's obviously a special place that doesn't fit into the pattern you see across the rest of the surface," says Grundy of the Sputnik Planum and its puzzling pits.

Giacalone J.,University of Arizona | Decker R.,Johns Hopkins Applied Physics Laboratory
Astrophysical Journal | Year: 2010

We address the origin of the enhancement of ∼ 40keV to 5 MeV ions at the solar wind termination shock. Using self-consistent two-dimensional hybrid simulations (kinetic proton, fluid electron) of a shock moving through a plasma similar to that observed in the outer heliosphere, we conclude that the observed ion enhancements are consistent with accelerated "core" interstellar pickup ions (those that have not previously undergone any significant energization) by the termination shock via a combination of shock drift acceleration and particle scattering in meandering magnetic fields in the vicinity of the shock. In addition to the consequences for our understanding of anomalous cosmic rays, this work is also relevant to the more-general long-standing problem of accelerating low-energy particles by shocks that move nearly normal to a mean magnetic field. © 2010. The American Astronomical Society. All rights reserved. Source

Lucas B.C.,Johns Hopkins Applied Physics Laboratory
Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention | Year: 2012

An emerging topic is to build image segmentation systems that can segment hundreds to thousands of objects (i.e. cell segmentation\tracking, full brain parcellation, full body segmentation, etc.). Multi-object Level Set Methods (MLSM) perform this task with the benefit of sub-pixel precision. However, current implementations of MLSM are not as computationally or memory efficient as their region growing and graph cut counterparts which lack sub-pixel precision. To address this performance gap, we present a novel parallel implementation of MLSM that leverages the sparse properties of the algorithm to minimize its memory footprint for multiple objects. The new method, Multi-Object Geodesic Active Contours (MOGAC), can represent N objects with just two functions: a label mask image and unsigned distance field. The time complexity of the algorithm is shown to be O((M (power)d)/P) for M (power)d pixels and P processing units in dimension d = {2,3}, independent of the number of objects. Results are presented for 2D and 3D image segmentation problems. Source

Mason G.M.,Johns Hopkins Applied Physics Laboratory | Gloeckler G.,University of Michigan
Space Science Reviews | Year: 2012

At energies above the bulk solar wind and pick-up ion cutoff, observations reveal an interplanetary suprathermal ion population extending to ∼1 MeV/nucleon and even higher energies. These suprathermal ions are found under a wide variety of conditions including periods when there are no obvious nearby accelerating shocks. We review the observational properties of these ions in quiet solar wind periods near 1 AU, including transient Corotating Interaction Region (CIR) events, and other, quieter periods in between transient enhancements. The particle energy spectra are power laws close to E -1.5 in the range above the solar wind, rolling over at energies of a few hundred keV/nucleon to a few MeV/nucleon. Although the C/O and Fe/O ratios of the tails is close to that of the solar wind, pickup ions and 3He found in the tails indicate sources distinct from the solar wind. We briefly review several mechanisms that have been proposed to explain these ions. © 2011 Springer Science+Business Media B.V. Source

Hu Y.,University of Maryland Baltimore County | Marks B.S.,Johns Hopkins Applied Physics Laboratory | Menyuk C.R.,U.S. Navy | Urick V.J.,University of Maryland Baltimore County | Williams K.J.,University of Maryland Baltimore County
Journal of Lightwave Technology | Year: 2014

Nonlinearity in p-i-n photodetectors leads to power generation at harmonics of the input frequency, limiting the performance of RF-photonic systems. We use one-dimensional and two-dimensional simulations of the drift-diffusion equations to determine the physical origin of the saturation in a simple heterojunction p-i-n photodetector at room temperature. Incomplete ionization, external loading, impact ionization, and the Franz-Keldysh effect are all included in the model. Impact ionization is the main source of nonlinearity at large reverse bias ( >10 V in the device that we simulated). The electron and hole current contributions to the second harmonic power were calculated. We find that impact ionization has a greater effect on the electrons than it does on the holes. We also find that the hole velocity saturates slowly with increasing reverse bias, and the hole current makes a large contribution to the harmonic power at 10 V. This result implies that decreasing the hole injection will decrease the harmonic power. © 1983-2012 IEEE. Source

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