9,878 research outputs found
Surface networks
© Copyright CASA, UCL. The desire to understand and exploit the structure of continuous surfaces is common to researchers in a range of disciplines. Few examples of the varied surfaces forming an integral part of modern subjects include terrain, population density, surface atmospheric pressure, physico-chemical surfaces, computer graphics, and metrological surfaces. The focus of the work here is a group of data structures called Surface Networks, which abstract 2-dimensional surfaces by storing only the most important (also called fundamental, critical or surface-specific) points and lines in the surfaces. Surface networks are intelligent and ânatural â data structures because they store a surface as a framework of âsurface â elements unlike the DEM or TIN data structures. This report presents an overview of the previous works and the ideas being developed by the authors of this report. The research on surface networks has fou
Conceptual studies on the integration of a nuclear reactor system to a manned rover for Mars missions
Multiyear civilian manned missions to explore the surface of Mars are thought by NASA to be possible early in the next century. Expeditions to Mars, as well as permanent bases, are envisioned to require enhanced piloted vehicles to conduct science and exploration activities. Piloted rovers, with 30 kWe user net power (for drilling, sampling and sample analysis, onboard computer and computer instrumentation, vehicle thermal management, and astronaut life support systems) in addition to mobility are being considered. The rover design, for this study, included a four car train type vehicle complete with a hybrid solar photovoltaic/regenerative fuel cell auxiliary power system (APS). This system was designed to power the primary control vehicle. The APS supplies life support power for four astronauts and a limited degree of mobility allowing the primary control vehicle to limp back to either a permanent base or an accent vehicle. The results showed that the APS described above, with a mass of 667 kg, was sufficient to provide live support power and a top speed of five km/h for 6 hours per day. It was also seen that the factors that had the largest effect on the APS mass were the life support power, the number of astronauts, and the PV cell efficiency. The topics covered include: (1) power system options; (2) rover layout and design; (3) parametric analysis of total mass and power requirements for a manned Mars rover; (4) radiation shield design; and (5) energy conversion systems
Quantitative assessment of Earthâs radiation belt modeling
The âQuantitative Assessment of Radiation Belt Modelingâ focus group was in place at Geospace Environment Modeling from 2014 to 2018. The overarching goals of this focus group were to bring together the current stateâofâtheâart models for the acceleration, transport, and loss processes in Earth's radiation belts; develop eventâspecific and global inputs of wave, plasma, and magnetic field to drive these models; and combine all these components to achieve a quantitative assessment of radiation belt modeling by validating against contemporary radiation belt measurements. This article briefly reviews the current understanding of radiation belt dynamics and related modeling efforts, summarizes the activities and accomplishments of the focus group, and discusses future directions.Accepted manuscrip
Quantitative assessment of radiation belt modeling
The âQuantitative Assessment of Radiation Belt Modelingâ focus group was in place at Geospace Environment Modeling from 2014 to 2018. The overarching goals of this focus group were to bring together the current stateâofâtheâart models for the acceleration, transport, and loss processes in Earth's radiation belts; develop eventâspecific and global inputs of wave, plasma, and magnetic field to drive these models; and combine all these components to achieve a quantitative assessment of radiation belt modeling by validating against contemporary radiation belt measurements. This article briefly reviews the current understanding of radiation belt dynamics and related modeling efforts, summarizes the activities and accomplishments of the focus group, and discusses future directions.Accepted manuscrip
Spectral Variability from the Patchy Atmospheres of T and Y Dwarfs
Brown dwarfs of a variety of spectral types have been observed to be
photometrically variable. Previous studies have focused on objects at the L/T
transition, where the iron and silicate clouds in L dwarfs break up or
dissipate. However, objects outside of this transitional effective temperature
regime also exhibit variability. Here, we present models for mid-late T dwarfs
and Y dwarfs. We present models that include patchy salt and sulfide clouds as
well as water clouds for the Y dwarfs. We find that for objects over 375 K,
patchy cloud opacity would generate the largest amplitude variability within
near-infrared spectral windows. For objects under 375 K, water clouds also
become important and generate larger amplitude variability in the mid-infrared.
We also present models in which we perturb the temperature structure at
different pressure levels of the atmosphere to simulate hot spots. These models
show the most variability in the absorption features between spectral windows.
The variability is strongest at wavelengths that probe pressure levels at which
the heating is the strongest. The most illustrative types of observations for
understanding the physical processes underlying brown dwarf variability are
simultaneous, multi-wavelength observations that probe both inside and outside
of molecular absorption features.Comment: 6 pages, 5 figures, Accepted for publication in ApJ Letter
Photolytic Hazes in the Atmosphere of 51 Eri b
We use a 1D model to address photochemistry and possible haze formation in
the irradiated warm Jupiter, 51 Eridani b. The intended focus was to be carbon,
but sulfur photochemistry turns out to be important. The case for organic
photochemical hazes is intriguing but falls short of being compelling. If
organic hazes form, they are likeliest to do so if vertical mixing in 51 Eri b
is weaker than in Jupiter, and they would be found below the altitudes where
methane and water are photolyzed. The more novel result is that photochemistry
turns HS into elemental sulfur, here treated as S. In the cooler
models, S is predicted to condense in optically thick clouds of solid
sulfur particles, whilst in the warmer models S remains a vapor along with
several other sulfur allotropes that are both visually striking and potentially
observable. For 51 Eri b, the division between models with and without
condensed sulfur is at an effective temperature of 700 K, which is within error
its actual effective temperature; the local temperature where sulfur condenses
is between 280 and 320 K. The sulfur photochemistry we have discussed is quite
general and ought to be found in a wide variety of worlds over a broad
temperature range, both colder and hotter than the 650-750 K range studied
here, and we show that products of sulfur photochemistry will be nearly as
abundant on planets where the UV irradiation is orders of magnitude weaker than
it is on 51 Eri b.Comment: 24 pages including 11 figures and a tabl
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