W. C. Feldman
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View article: Regularity theory of a gradient degenerate Neumann problem
Regularity theory of a gradient degenerate Neumann problem Open
We study the regularity and comparison principle for a gradient degenerate Neumann problem. The problem is a generalization of the Signorini or thin obstacle problem which appears in the study of certain singular anisotropic free boundary …
View article: Seasonal cycle of carbon dioxide and atmospheric circulation in Mars' southern hemisphere as observed by neutron spectroscopy
Seasonal cycle of carbon dioxide and atmospheric circulation in Mars' southern hemisphere as observed by neutron spectroscopy Open
The south polar seasonal cap consists of CO{sub 2} ice that condenses and sublimes in response to seasonal changes in insolation, advancing equatorward during the fall and winter and receding poleward during spring. Cycling of CO{sub 2} be…
View article: Mid-latitude composition of mars from thermal and epithermal neutrons
Mid-latitude composition of mars from thermal and epithermal neutrons Open
Epithermal neutron data acquired by Mars Odyssey have been analyzed to determine global maps of water-equivalent hydrogen abundance. By assuming that hydrogen was distributed uniformly with depth within the surface, a map of minimum water …
View article: Growth of C02 frost thickness near Chasma Borealis during northern winter and spring.
Growth of C02 frost thickness near Chasma Borealis during northern winter and spring. Open
Epithermal neutron fluxes measured using the Neutron Spectrometer component of the Mars OdysscNGamma-Ray Spectrometer suite of instruments were studied to determ i ne the spatial and temporal dependence of CO2 frost cover of the nor t h po…
View article: Contributions from hydrated states of MgSO[sub 4] to the reservoir of hydrogen at equatorial latitudes on mars
Contributions from hydrated states of MgSO[sub 4] to the reservoir of hydrogen at equatorial latitudes on mars Open
Significant deposits of hydrogen have been observed within large areas near the equator of Mars. The molecular associations of this hydrogen are not known. Several possibilities havc been suggested: (1) buried water ice, (2) water molccule…
View article: Sub-surface deposits of hydrous silicates or hydrated magnesium sulfates as hydrogen reservoirs near the Martian equator : plausible or not?
Sub-surface deposits of hydrous silicates or hydrated magnesium sulfates as hydrogen reservoirs near the Martian equator : plausible or not? Open
Neutron maps obtained using the neutron spectrometer (NS) and the high-energy neutron detector aboard the Mars Odyssey spacecraft reveal variations in the concentration of hydrogen over the martian low to middle latitudes, with up to {appr…
View article: In situ neutron spectroscopy on the martian surface: modeling the hydra instrument for different mission scenarios
In situ neutron spectroscopy on the martian surface: modeling the hydra instrument for different mission scenarios Open
Neutron spectroscopy has proven to be highly successful in remotely detecting and measuring the abundance of water on planetary surfaces such as Mars and the Moon. Because of the central role played by water on Mars and the need to make in…
View article: Regional elemental abundances within South Pole-Aitken basin as measured with lunar prospector gamma-ray spectrometer data.
Regional elemental abundances within South Pole-Aitken basin as measured with lunar prospector gamma-ray spectrometer data. Open
South Pole-Aitken (SPA) basin has been a target of intense study since it is one of the largest impact basins in the solar system. It is thought that SPA basin excavated deep into the lunar crust and possibly even the mantle. Such conclusi…
View article: COMBINED ANALYSIS OF THORIUM AND FAST NEUTRON DATA AT THE LUNAR SURFACE
COMBINED ANALYSIS OF THORIUM AND FAST NEUTRON DATA AT THE LUNAR SURFACE Open
The global distribution of the radioactive elements (U, K, Th) at the lunar surface is an important parameter for an understanding of lunar evolution, because they have provided continuous heat over the lifetime of the Moon. Today, only th…
View article: Continuous time-of-flight ion mass spectrometer
Continuous time-of-flight ion mass spectrometer Open
A continuous time-of-flight mass spectrometer having an evacuated enclosure with means for generating an electric field located in the evacuated enclosure and means for injecting a sample material into the electric field. A source of conti…
View article: Nuclear Spectroscopy for the Exploration of Mars and Beyond
Nuclear Spectroscopy for the Exploration of Mars and Beyond Open
Nuclear spectroscopy will continue to play a critical role in planetary exploration in the next decade, including searching for habitable environments and biosignatures, identifying ideal targets for in-situ resource utilization, and conti…
View article: Nuclear Spectroscopy for the Exploration of Mars and Beyond
Nuclear Spectroscopy for the Exploration of Mars and Beyond Open
Nuclear spectroscopy is the only instrumentation that provides bulk geochemical constraints at depth (up to one meter in the surface). These instruments identify and quantify water and other key elements relevant to planetary exploration, …
View article: Development of a Low-Resource Combined Gamma-Ray and Neutron Spectrometer for Planetary Science
Development of a Low-Resource Combined Gamma-Ray and Neutron Spectrometer for Planetary Science Open
Planetary neutron and gamma-ray spectroscopy (NGRS) has become a standard technique to measure distinctive geochemical composition and volatile abundance signatures for key elements relevant to planetary structure and evolution. Previous N…
View article: Mars Odyssey Neutron Spectrometer Time Series of Corrected Cateogry 1 Counting Rates, 2002-2017
Mars Odyssey Neutron Spectrometer Time Series of Corrected Cateogry 1 Counting Rates, 2002-2017 Open
Ubinned time series of derived neutron data from the Mars Odyssey Neutron Spectrometer (MONS) Category 1 data, from 200 - 2017.
View article: MESSENGER Gamma Ray Spectrometer and Epithermal Neutron Hydrogen Data Reveal Compositional Differences Between Mercury's Hot and Cold Poles
MESSENGER Gamma Ray Spectrometer and Epithermal Neutron Hydrogen Data Reveal Compositional Differences Between Mercury's Hot and Cold Poles Open
The presence of hydrogen, most likely in the form of water ice, is well established in Mercury's permanently shaded polar craters. But lower concentrations that may exist away from the poles have not previously been well constrained. In th…
View article: Elpasolite Planetary Ice and Composition Spectrometer (EPICS): A Low-Resource Combined Gamma-Ray and Neutron Spectrometer for Planetary Science
Elpasolite Planetary Ice and Composition Spectrometer (EPICS): A Low-Resource Combined Gamma-Ray and Neutron Spectrometer for Planetary Science Open
Neutron and gamma-ray spectroscopy (NGRS) is a well established technique for studying the geochemical composition and volatile abundance relevant to planetary structure and evolution of planetary bodies. Previous NGRS instruments have use…
View article: Hydrothermal dynamics in a <scp>CM</scp>‐based model of Ceres
Hydrothermal dynamics in a <span>CM</span>‐based model of Ceres Open
A 2‐D numerical study of the evolution of Ceres from a “frozen mudball” to the present era emphasizes the importance of hydrothermal processes. Particulates released as the “frozen mudball” thaws settle to form a roughly 290 km radius core…
View article: Compositional variability on the surface of 1 Ceres revealed through GRaND measurements of high‐energy gamma rays
Compositional variability on the surface of 1 Ceres revealed through GRaND measurements of high‐energy gamma rays Open
High‐energy gamma rays (HEGRs) from Ceres’s surface were measured using Dawn's Gamma Ray and Neutron Detector (GRaND). Models of cosmic‐ray‐initiated gamma ray production predict that the HEGR flux will inversely vary with single‐layer hyd…
View article: Benchmarking Geant4 for Simulating Galactic Cosmic Ray Interactions Within Planetary Bodies
Benchmarking Geant4 for Simulating Galactic Cosmic Ray Interactions Within Planetary Bodies Open
Galactic cosmic rays undergo complex nuclear interactions with nuclei within planetary bodies that have little to no atmosphere. Radiation transport simulations are a key tool used in understanding the neutron and gamma ray albedo coming f…
View article: Compositional terranes on Mercury: Information from fast neutrons
Compositional terranes on Mercury: Information from fast neutrons Open
We report measurements of the flux of fast neutrons at Mercury from 20ºS to the north pole. On the basis of neutron transport simulations and remotely sensed elemental compositions, cosmic-ray-induced fast neutrons are shown to provide a m…
View article: Galactic cosmic ray variations in the inner heliosphere from solar distances less than 0.5 AU: Measurements from the MESSENGER Neutron Spectrometer
Galactic cosmic ray variations in the inner heliosphere from solar distances less than 0.5 AU: Measurements from the MESSENGER Neutron Spectrometer Open
The Neutron Spectrometer (NS) on board NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft is sensitive to galactic cosmic ray (GCR) protons greater than 125 MeV. During the MESSENGER orbital mission…