1,092 research outputs found
The rheological behavior of CO2 ice: application to glacial flow on Mars
Vast amounts of solid CO2 reside in topographic basins of the south polar layered deposits (SPLD) on Mars and exhibit morphological features indicative of glacial flow. Previous experimental studies showed that coarse-grained CO2 ice is 1â2 orders of magnitude weaker than water ice under Martian polar conditions. Here we present data from a series of deformation experiments on high-purity, fine-grained CO2 ice over a broader range of temperatures than previously explored (158â213 K). The experiments confirm previous observations of highly non-linear power-law creep at larger stresses, but also show a transition to a previously-unseen linear-viscous creep regime at lower stresses. We examine the viscosity of CO2 within the SPLD and predict that the CO2-rich layers may be stronger than previously thought. We also predict that CO2 ice flows much more readily than H2O ice on steep flanks of SPLD topographic basins, allowing the CO2 to pond as observed.National Aeronautics and Space Administration (NASA) NNH16ZDA001N-SS
The rheological behavior of CO2 ice: application to glacial flow on Mars
Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 47(22), (2020): e2020GL090431, doi:10.1029/2020GL090431.Vast quantities of solid CO2 reside in topographic basins of the south polar layered deposits (SPLD) on Mars and exhibit morphological features indicative of glacial flow. Previous experimental studies showed that CO2 ice is 1â2 orders of magnitude weaker than water ice under Martian polar conditions. Here we present data from deformation experiments on pure, fineâgrained CO2 ice, over a broader range of temperatures than previously explored (158â213 K). The experiments confirm previous observations of highly nonlinear power law creep at larger stresses, but also show a transition to a previously unseen linearâviscous creep regime at lower stresses. We examine the viscosity of CO2 within the SPLD and predict that the CO2ârich deposits are modestly stronger than previously thought. Nevertheless, CO2 ice flows much more readily than H2O ice, particularly on the steep flanks of SPLD topographic basins, allowing the CO2 to pond as observed.This work was funded by NASA grant NNH16ZDA001NâSSW awarded to Smith and Goldsby. Additional salary support for Cross was provided by the WHOI Investment in Science Fund.2021-04-2
Opticks
A treatise of the reflexions, refractions, inflexions and colours of light. Also two treatises of the species and magnitude of curvilinear figures
Searches for Stable Strangelets in Ordinary Matter: Overview and a Recent Example
Our knowledge on the possible existence in nature of stable exotic particles
depends solely upon experimental observation. Guided by this general principle
and motivated by theoretical hypotheses on the existence of stable particles of
strange quark matter, a variety of experimental searches have been performed.
We provide an introduction to the theoretical hypotheses, an overview of the
past searches, and a more detailed description of a recent search for
helium-like strangelets in the Earth's atmosphere using a sensitive laser
spectroscopy method
A comparison of the development of audiovisual integration in children with autism spectrum disorders and typically developing children
This study aimed to investigate the development of audiovisual integration in children with Autism Spectrum Disorder (ASD). Audiovisual integration was measured using the McGurk effect in children with ASD aged 7â16 years and typically developing children (control group) matched approximately for age, sex, nonverbal ability and verbal ability. Results showed that the children with ASD were delayed in visual accuracy and audiovisual integration compared to the control group. However, in the audiovisual integration measure, children with ASD appeared to âcatch-upâ with their typically developing peers at the older age ranges. The suggestion that children with ASD show a deficit in audiovisual integration which diminishes with age has clinical implications for those assessing and treating these children
Science results from sixteen years of MRO SHARAD operations
In operation for >16 years to date, the Mars Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD) sounder
has acquired data at its nominal 300â450 m along-track and 3-km cross-track resolution covering >55% of the
Martian surface, with nearly 100% overlap in coverage at that scale in the polar regions and in a number of
smaller mid-latitude areas. While SHARAD data have opened a new window into understanding the interior
structures and properties of Martian ices, volcanics, and sedimentary deposits up to a few kilometers in depth,
they have also led to new revelations about the deeper interior and the behavior of the planetâs ionosphere. Here
we summarize the data collected by SHARAD over this time period, the methods used in the analysis of that data,
and the resulting scientific findings. The polar data are especially rich, revealing complex structures that
comprise up to several dozen reflecting interfaces that extend to depths of 3 km, which inform the evolution of
Martian climate in the late Amazonian period. SHARAD observations of mid-latitude lobate debris aprons and
other glacier-like landforms detect strong basal reflections and low dielectric loss, confirming that they are icerich
debris-covered glaciers. In other mid-latitude terrains, SHARAD data demonstrate the presence of widespread
ground ices, likely at lower concentrations. SHARAD signals also probe non-icy materials, mapping out
stacked lava flows, probing low-density materials thought to be ash-fall deposits, and occasionally penetrating
sedimentary deposits, all of which reveal the structures and interior properties diagnostic of emplacement
processes. SHARAD signals are impacted by their passage through the Martian ionosphere, revealing variations
in time and space of the total electron content linked with the remanent magnetic field. Advanced techniques
developed over the course of the mission, which include subband and super-resolution processing, coherent and
incoherent summing, and three-dimensional (3D) radar imaging, are enabling new discoveries and extending the
utility of the data. For 3D imaging, a cross-track spacing at the nominal 3-km resolution is more than sufficient to
achieve good results, but finer spacing of 0.5 km or less significantly improves the spatially interpolated radar
images. Recent electromagnetic modeling and a flight test show that SHARADâs signal-to-noise ratio can be
greatly improved with a large (~120âŠ) roll of the spacecraft to reduce interference with the spacecraft body. Both
MRO and SHARAD are in remarkably fine working order, and the teams look forward to many more years in
which to pursue improvements in coverage density, temporal variability in the ionosphere, and data quality that
promise exciting new discoveries at Mars
Gridmapping the northern plains of Mars: Geomorphological, Radar and Water-Equivalent Hydrogen results from Arcadia Plantia
A project of mapping ice-related landforms was undertaken to understand the role of sub-surface ice in the northern plains. This work is the first continuous regional mapping from CTX (âConTeXt Cameraâ, 6 m/pixel; Malin et al., 2007) imagery in Arcadia Planitia along a strip 300 km across stretching from 30°N to 80°N centred on the 170° West line of longitude. The distribution and morphotypes of these landforms were used to understand the permafrost cryolithology. The mantled and textured signatures occur almost ubiquitously between 35° N and 78° N and have a positive spatial correlation with inferred ice stability based on thermal modelling, neutron spectroscopy and radar data. The degradational features into the LDM (Latitude Dependent Mantle) include pits, scallops and 100 m polygons and provide supporting evidence for sub-surface ice and volatile loss between 35-70° N in Arcadia with the mantle between 70-78° N appearing much more intact. Pitted terrain appears to be much more pervasive in Arcadia than in Acidalia and Utopia suggesting that the Arcadia study area had more wide-spread near-surface sub-surface ice, and thus was more susceptible to pitting, or that the ice was less well-buried by sediments. Correlations with ice stability models suggest that lack of pits north of 65-70° N could indicate a relatively young age (~1Ma), however this could also be explained through regional variations in degradation rates. The deposition of the LDM is consistent with an airfall hypothesis however there appears to be substantial evidence for fluvial processes in southern Arcadia with older, underlying processes being equally dominant with the LDM and degradation thereof in shaping the landscape
A role for steroid 5 alpha-reductase 1 in vascular remodeling during endometrial decidualization
University of Kentucky Measurements of Wind, Temperature, Pressure and Humidity in Support of LAPSE-RATE Using Multisite Fixed-Wing and Rotorcraft Unmanned Aerial Systems
In July 2018, unmanned aerial systems (UASs) were deployed to measure the properties of the lower atmosphere within the San Luis Valley, an elevated valley in Colorado, USA, as part of the Lower Atmospheric Profiling Studies at Elevation â a Remotely-piloted Aircraft Team Experiment (LAPSE-RATE). Measurement objectives included detailing boundary layer transition, canyon cold-air drainage and convection initiation within the valley. Details of the contribution to LAPSE-RATE made by the University of Kentucky are provided here, which include measurements by seven different fixed-wing and rotorcraft UASs totaling over 178 flights with validated data. The data from these coordinated UAS flights consist of thermodynamic and kinematic variables (air temperature, humidity, pressure, wind speed and direction) and include vertical profiles up to 900âm above the ground level and horizontal transects up to 1500âm in length. These measurements have been quality controlled and are openly available in the Zenodo LAPSE-RATE community data repository (https://zenodo.org/communities/lapse-rate/, last access: 23 July 2020), with the University of Kentucky data available at https://doi.org/10.5281/zenodo.3701845 (Bailey et al., 2020)
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