70 research outputs found
Semi-supervised Learning of Pushforwards For Domain Translation & Adaptation
Given two probability densities on related data spaces, we seek a map pushing
one density to the other while satisfying application-dependent constraints.
For maps to have utility in a broad application space (including domain
translation, domain adaptation, and generative modeling), the map must be
available to apply on out-of-sample data points and should correspond to a
probabilistic model over the two spaces. Unfortunately, existing approaches,
which are primarily based on optimal transport, do not address these needs. In
this paper, we introduce a novel pushforward map learning algorithm that
utilizes normalizing flows to parameterize the map. We first re-formulate the
classical optimal transport problem to be map-focused and propose a learning
algorithm to select from all possible maps under the constraint that the map
minimizes a probability distance and application-specific regularizers; thus,
our method can be seen as solving a modified optimal transport problem. Once
the map is learned, it can be used to map samples from a source domain to a
target domain. In addition, because the map is parameterized as a composition
of normalizing flows, it models the empirical distributions over the two data
spaces and allows both sampling and likelihood evaluation for both data sets.
We compare our method (parOT) to related optimal transport approaches in the
context of domain adaptation and domain translation on benchmark data sets.
Finally, to illustrate the impact of our work on applied problems, we apply
parOT to a real scientific application: spectral calibration for
high-dimensional measurements from two vastly different environmentsComment: 19 pages, 7 figure
Using ChemCam derived geochemistry to identify the paleonet sediment transport direction and source region characteristics of the Stimson formation in Gale crater, Mars.
The NASA Curiosity rover has encountered both ancient and modern dune deposits within Gale crater. The modern dunes are actively migrating across the surface within the Bagnold Dune field of which Curiosity conducted analysis campaigns at two different localities. Variations in mafic-felsic mineral abundances between these two sites have been related to the aeolian mineral sorting regime for basaltic environments identified on the Earth which become preferentially enriched in olivine relative to plagioclase feldspar with increasing distance from the source. This aeolian mineral sorting regime for basaltic minerals has also been inferred for Mars from orbital data. The aim of this study is to investigate whether this aeolian mafic-felsic mineral sorting trend has left a geochemical signature in the ancient dune deposits preserved within the Stimson formation. The Stimson formation unconformably overlies the Murray formation and consists of thickly laminated, cross-bedded sandstone. Stimson outcrops have a variable thickness up to 5 meters covering a total area of 17 square kilometers. A dry, aeolian origin was determined for this sandstone due to the high sphericity and roundness of the grains, uniform bimodal grain size distribution (250-710 microns), and 1-meter-thick cross-beds. Identifying the geochemical signature of mineral sorting can provide insights about the paleo-net sediment transport direction of the dunes and prevailing wind direction at the time of deposition
In situ detection of boron by ChemCam on Mars
We report the first in situ detection of boron on Mars. Boron has been detected in Gale crater at levels Curiosity rover ChemCam instrument in calcium-sulfate-filled fractures, which formed in a late-stage groundwater circulating mainly in phyllosilicate-rich bedrock interpreted as lacustrine in origin. We consider two main groundwater-driven hypotheses to explain the presence of boron in the veins: leaching of borates out of bedrock or the redistribution of borate by dissolution of borate-bearing evaporite deposits. Our results suggest that an evaporation mechanism is most likely, implying that Gale groundwaters were mildly alkaline. On Earth, boron may be a necessary component for the origin of life; on Mars, its presence suggests that subsurface groundwater conditions could have supported prebiotic chemical reactions if organics were also present and provides additional support for the past habitability of Gale crater
An insight into ancient aeolian processes and postâNoachian aqueous alteration in Gale crater, Mars, using ChemCam geochemical data from the Greenheugh capping unit
Aeolian processes have shaped and contributed to the geological record in Gale crater, Mars, long after the fluviolacustrine system existed âŒ3 Ga ago. Understanding these aeolian deposits, particularly those which have been lithified and show evidence for aqueous alteration, can help to constrain the environment at their time of deposition and the role of liquid water later in Marsâ history. The NASA Curiosity rover investigated a prominent outcrop of aeolian sandstone within the Stimson formation at the Greenheugh pediment as part of its investigation of the Glen Torridon area. In this study, we use geochemical data from ChemCam to constrain the effects of aeolian sedimentary processes, sediment provenance, and diagenesis of the sandstone at the Greenheugh pediment, comparing the Greenheugh data to the results from previous Stimson localities situated 2.5 km north and >200 m lower in elevation. Our results, supported by mineralogical data from CheMin, show that the Stimson formation at the Greenheugh pediment was likely sourced from an olivine-rich unit that may be present farther up the slopes of Gale craterâs central mound. Our results also suggest that the Greenheugh pediment Stimson formation was cemented by surface water runoff such as that which may have formed Gediz Vallis. The lack of alteration features in the Stimson formation at the Greenheugh pediment relative to those of the Emerson and Naukluft plateaus suggests that groundwater was not as available at this locality compared to the others. However, all sites share diagenesis at the unconformity
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Overview of the Morphology and Chemistry of Diagenetic Features in the ClayâRich Glen Torridon Unit of Gale Crater, Mars
The clay-rich Glen Torridon region of Gale crater, Mars, was explored between sols 2300 and 3007. Here, we analyzed the diagenetic features observed by Curiosity, including veins, cements, nodules, and nodular bedrock, using the ChemCam, Mastcam, and Mars Hand Lens Imager instruments. We discovered many diagenetic features in Glen Torridon, including dark-toned iron- and manganese-rich veins, magnesium- and fluorine-rich linear features, Ca-sulfate cemented bedrock, manganese-rich nodules, and iron-rich strata. We have characterized the chemistry and morphology of these features, which are most widespread in the higher stratigraphic members in Glen Torridon, and exhibit a wide range of chemistries. These discoveries are strong evidence for multiple generations of fluids from multiple chemical endmembers that likely underwent redox reactions to form some of these features. In a few cases, we may be able to use mineralogy and chemistry to constrain formation conditions of the diagenetic features. For example, the dark-toned veins likely formed in warmer, highly alkaline, and highly reducing conditions, while manganese-rich nodules likely formed in oxidizing and circumneutral conditions. We also hypothesize that an initial enrichment of soluble elements, including fluorine, occurred during hydrothermal alteration early in Gale crater history to account for elemental enrichment in nodules and veins. The presence of redox-active elements, including Fe and Mn, and elements required for life, including P and S, in these fluids is strong evidence for habitability of Gale crater groundwater. Hydrothermal alteration also has interesting implications for prebiotic chemistry during the earliest stages of the craterâs evolution and early Mars
Manganese-Iron Phosphate Nodules at the Groken Site, Gale Crater, Mars
The MSL Curiosity rover investigated dark, Mn-P-enriched nodules in shallow lacustrine/fluvial sediments at the Groken site in Glen Torridon, Gale Crater, Mars. Applying all relevant information from the rover, the nodules are interpreted as pseudomorphs after original crystals of vivianite, (Fe2+,Mn2+)3(PO4)2·8H2O, that cemented the sediment soon after deposition. The nodules appear to have flat faces and linear boundaries and stand above the surrounding siltstone. ChemCam LIBS (laser-induced breakdown spectrometry) shows that the nodules have MnO abundances approximately twenty times those of the surrounding siltstone matrix, contain little CaO, and have SiO2 and Al2O3 abundances similar to those of the siltstone. A deconvolution of APXS analyses of nodule-bearing targets, interpreted here as representing the nodulesâ non-silicate components, shows high concentrations of MnO, P2O5, and FeO and a molar ratio P/Mn = 2. Visible to near-infrared reflectance of the nodules (by ChemCam passive and Mastcam multispectral) is dark and relatively flat, consistent with a mixture of host siltstone, hematite, and a dark spectrally bland material (like pyrolusite, MnO2). A drill sample at the site is shown to contain minimal nodule material, implying that analyses by the CheMin and SAM instruments do not constrain the nodulesâ mineralogy or composition. The fact that the nodules contain P and Mn in a small molar integer ratio, P/Mn = 2, suggests that the nodules contained a stoichiometric Mn-phosphate mineral, in which Fe did (i.e., could) not substitute for Mn. The most likely such minerals are laueite and strunzite, (Fe2+,Mn2+)3(PO4)2·8H2O and â6H2O, respectively, which occur on Earth as alteration products of other Mn-bearing phosphates including vivianite. Vivianite is a common primary and diagenetic precipitate from low-oxygen, P-enriched waters. Calculated phase equilibria show Mn-bearing vivianite could be replaced by laueite or strunzite and then by hematite plus pyrolusite as the system became more oxidizing and acidic. These data suggest that the nodules originated as vivianite, forming as euhedral crystals in the sediment, enclosing sediment grains as they grew. After formation, the nodules were oxidizedâfirst to laueite/strunzite yielding the diagnostic P/Mn ratio, and then to hematite plus an undefined Mn oxy-hydroxide (like pyrolusite). The limited occurrence of these Mn-Fe-P nodules, both in space and time (i.e., stratigraphic position), suggests a local control on their origin. By terrestrial analogies, it is possible that the nodules precipitated near a spring or seep of Mn-rich water, generated during alteration of olivine in the underlying sediments
The aqueous alteration of carbon-bearing phases in CR carbonaceous chondrites
Ph.D. University of Hawaii at Manoa 2014.Includes bibliographical references.By studying carbonaceous chondrites, we can understand the processes that occurred in the protoplanetary disk, constrain the conditions in the solar nebula, and determine the composition and evolution of organic chemicals that led up to the origin of life on Earth. The CR chondrites contain ~ 5 wt% carbon, mainly in the form of macromolecular carbon (MMC). There are examples of petrologic type 3 (primitive) and type 1 (extensively aqueously altered) CR chondrites, which makes the CRs particularly interesting for studying the stages of aqueous alteration. The MMC has been studied using in situ electron probe micro analysis (EPMA), Raman spectroscopy, and secondary ion mass spectrometry (SIMS). EPMA mapping of the carbon Kα X-rays reveals that there are three types of carbon materials in these chondrites: high carbon phases (HCPs), matrix carbon (MC), and calcite. By Raman spectroscopy, we determine that the MC is MMC, but its spectra are unchanged by aqueous alteration. EPMA X-ray mapping suggests that the morphology of the HCPs and the spatial distribution of the MMC changes with extent of aqueous alteration. SIMS measurements have revealed that there is an isotopic difference between the HCPs and the MC in the GRO 95577 and QUE 99177 samples. HCPs have ÎŽ13C â â25 â° and ÎŽ15N â 40 â°, and the MC have ÎŽ13C â â35 â° and ÎŽ15N â 160 â°, relative to standard terrestrial isotope ratios. In order to produce the MC isotopic values, there must be a mix of the +ÎŽ15N and +ÎŽ13C soluble organic molecules and MMC (both present in the matrix). Therefore, the 'true' values for the MMC must be more enriched in 12C and 15N than the MC values. Results from the calcite measurements show that the production of calcite fractionates the carbon due to a combination of calcite crystallization and outgassing of CO2 on the CR parent body
Empirical Raman calibration of trioctahedral ferromagnesium chlorite minerals
Chlorite is a common hydratedâaluminous phyllosilicate mineral group that forms in most geological environments (e.g., hydrothermal, igneous, sedimentary, and metamorphic). The chemical composition of chlorite depends on several factors including temperature, pressure, fluid, and bulk rock composition. Raman spectroscopy is proposed as a quick and costâeffective alternative to scanning electron microscopy and electron probe microâanalysis, which involve complex sample preparation. In this paper, we demonstrate that Raman spectroscopy is a viable technique to determine the chemical composition of chlorite. Our results show that chlorite's Raman spectra changes quantitatively as a function of its chemical composition. Iron (Fe) and magnesium (Mg) content (APFU) is linearly correlated with the peak positions of three bands: Band 1 (99â104âcm â1 ), Band 8 (546â553âcm â1 ), and Band D (3,570â3,580âcm â1 ). In contrast, silicon (Si) and tetrahedral aluminum (Al IV ) are correlated with a single band's position, Band 9b (663â679âcm â1 ). We derived 18 empirical rules from these correlations, aiding geoscientists in accurately identifying and determining chlorite composition using Raman spectroscopy. Moreover, this technique holds potential for determining chlorite's chemical composition during planetary exploration, leveraging existing Raman spectrometers deployed on Mars and for future space missions
Detection of Copper by the ChemCam Instrument Along Curiosity's Traverse in Gale Crater, Mars: Elevated Abundances in Glen Torridon
International audienceLaserâinduced breakdown spectroscopy, as utilized by the ChemCam instrument onboard the Curiosity rover, detected enhanced abundances of the element copper. Since landing in Gale crater (6 August 2012), 10 enhancements in copper abundance were observed during 3007 Martian days (sols) of rover operations and 24Â km of driving (as of 20 January 2021). The most prominent ones were found in the Kimberley area on the crater floor (Aeolis Palus) and in Glen Torridon (GT) on the lower flanks of Aeolis Mons (Mt. Sharp). Enhancements in copper record the former existence of modestly acidic and oxidizing fluids, which were more oxidizing in Kimberley than in GT. Of the two main types of bedrock in the lowest part of GT, Mgârich âcoherentâ and Kârich ârubblyâ (named based on their outcrop expression), copper was detected only in coherent, not in rubbly bedrock. The difference between these two types of bedrock may be due to difference in provenance. Alternatively, based on a recently developed lacustrineâgroundwater mixing model, we suggest that rubbly bedrock was altered by modestly acidic, shallowâsubsurface lake water that leached out both copper and manganese, while coherent bedrock was affected by dominantly alkaline fluids which would be consistent with its mineralogical composition (including siderite) as returned by the CheMin instrument onboard the rover. Higher up in GT, ChemCam data indicated significant gradients in the copper concentration in coherent bedrock on a local scale of only a few meters, which suggests a different alteration style and possibly different types of diagenetic fluids
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