756 research outputs found
Spectral and stratigraphic mapping of hydrated sulfate and phyllosilicate-bearing deposits in northern Sinus Meridiani, Mars
We present detailed stratigraphic and spectral analyses that focus on a region in
northern Sinus Meridiani located between 1°N to 5°N latitude and 3°W to 1°E longitude.
Several stratigraphically distinct units are defined and mapped using morphologic
expression, spectral properties, and superposition relationships. Previously unreported
exposures of hydrated sulfates and Fe/Mg smectites are identified using MRO CRISM and
MEX OMEGA nearâinfrared (1.0 to 2.5 ”m) spectral reflectance observations. Layered
deposits with monohydrated and polyhydrated sulfate spectral signatures that occur in
association with a northeastâsouthwest trending valley are reexamined using highresolution
CRISM, HiRISE, and CTX images. Layers that are spectrally dominated by
monohydrated and polyhydrated sulfates are intercalated. The observed compositional
layering implies that multiple wetting events, brine recharge, or fluctuations in evaporation
rate occurred. We infer that these hydrated sulfateâbearing layers were unconformably
deposited following the extensive erosion of preexisting layered sedimentary rocks and
may postdate the formation of the sulfateâ and hematiteâbearing unit analyzed by the MER
Opportunity rover. Therefore, at least two episodes of deposition separated by an
unconformity occurred. Fe/Mg phyllosilicates are detected in units that predate the sulfateand
hematiteâbearing unit. The presence of Fe/Mg smectite in older units indicates that the
relatively low pH formation conditions inferred for the younger sulfateâ and hematitebearing
unit are not representative of the aqueous geochemical environment that prevailed
during the formation and alteration of earlier materials. Sedimentary deposits indicative of
a complex aqueous history that evolved over time are preserved in Sinus Meridiani, Mars
Differential electrophysiological response during rest, self-referential, and non-self-referential tasks in human posteromedial cortex
The electrophysiological basis for higher brain activity during rest and internally directed cognition within the human default mode network
(DMN) remains largely unknown. Here we use intracranial recordings in
the human posteromedial cortex (PMC), a core node within the DMN,
during conditions of cued rest, autobiographical judgments, and
arithmetic processing. We found a heterogeneous profile of PMC
responses in functional, spatial, and temporal domains. Although the
majority of PMC sites showed increased broad gamma band activity
(30-180 Hz) during rest, some PMC sites, proximal to the retrosplenial
cortex, responded selectively to autobiographical stimuli. However, no
site responded to both conditions, even though they were located within
the boundaries of the DMN identified with resting-state functional
imaging and similarly deactivated during arithmetic processing. These
findings, which provide electrophysiological evidence for heterogeneity
within the core of the DMN, will have important implications for
neuroimaging studies of the DMN
Phyllosilicate and Hydrated Sulfate Deposits in Meridiani
Several phyllosilicate and hydrated sulfate deposits in Meridiani have been mapped in detail with high resolution MRO CRISM [1] data. Previous studies have documented extensive exposures of outcrop in Meridiani (fig 1), or etched terrain (ET), that has been interpreted to be sedimentary in origin [e.g., 2,3]. These deposits have been mapped at a regional scale with OMEGA data and show enhanced hydration (1.9 m absorption) in several areas [4]. However, hydrated sulfate detections were restricted to valley exposures in northern Meridiani ET [5]. New high resolution CRISM images show that hydrated sulfates are present in several spatially isolated exposures throughout the ET (fig 1). The hydrated sulfate deposits in the valley are vertically heterogeneous with layers of mono and polyhydrated sulfates and are morphologically distinct from other areas of the ET. We are currently mapping the detailed spatial distribution of sulfates and searching for distinct geochemical horizons that may be traced back to differential ground water recharge and/or evaporative loss rates. The high resolution CRISM data has allowed us to map out several phyllosilicate deposits within the fluvially dissected Noachian cratered terrain (DCT) to the south and west of the hematite-bearing plains (Ph) and ET (fig 1). In Miyamoto crater, phyllosilicates are located within ~30km of the edge of Ph, which is presumably underlain by acid sulfate deposits similar to those explored by Opportunity. The deposits within this crater may record the transition from fluvial conditions which produced and/or preserved phyllosilicates deposits to a progressively acid sulfate dominated groundwater system in which large accumulations of sulfate-rich evaporites were deposited
Cold sintering of bioglass and bioglass/polymer composites
Bioactive glasses are widely utilized to regenerate bone tissue and aid bonding of orthopedic implants. Forming composites of bioglass with bioactive polymers allow the mechanical properties and biological response to be tailored. Although several methods for creating bioglassâpolymer composites exist, they require dissolution of the polymer, controlled phase separation, and appear to have an upper limit of âŒ30 vol.% bioglass. Cold sintering is a novel technique for the densification of ceramics and glasses which utilizes a liquid phase and pressure to allow the production of components at reduced temperatures. We demonstrate that cold sintering (100°C) of Bioglass 45S5 powder produced via flame spray pyrolysis and the fabrication of Bioglass 45S5âpolymer composites. Assessment of the in vitro response revealed that composites were not cytotoxic. Solid-state 31P and 29Si MAS NMR studies of the silicon and phosphorus speciation in the glass powder, as-received, wetted, and sintered samples show similarities to reactions expected when bioglass is implanted in the body which along with Raman spectroscopy data gave insight into the cold sintering densification mechanism
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Identification of buried lunar impact craters from GRAIL data and implications for the nearside maria
Gravity observations from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have revealed more than 100 quasiâcircular mass anomalies, 26â300âkm in diameter, on the lunar nearside. These anomalies are interpreted to be impact craters filled primarily by mare deposits, and their characteristics are consistent with those of impact structures that formed prior to, and during, intervals of flooding of feldspathic terrane by mare basalt lavas. We determine that mare deposits have an average density contrast of 850âșÂłâ°â°ââââ kg mâ»Âł relative to the surrounding crust. The presence of a large population of volcanically buried craters with minimal topographic expression and diameters up to 300âkm requires an average nearside mare thickness of at least 1.5âkm and local lenses of mare basalt as thick as ~7âkm
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