590 research outputs found
The weathering of micrometeorites from the Transantarctic Mountains
Micrometeorites are cosmic dust particles recovered from the
Earth's surface that dominate the influx of extraterrestrial material
accreting to our planet. This paper provides the first in-depth study of
the weathering of micrometeorites within the Antarctic environment that
will allow primary and secondary features to be distinguished. It is
based on the analysis of 366 particles from Larkman Nunatak and 25 from
the Transantarctic Mountain collection. Several important morphological
categories of weathering effects were identified: (1) irregular and
faceted cavities, (2) surface etch pits, (3) infilled cavities, (4)
replaced silicate phases, and (5) hydrated and replaced metal. These
features indicate that congruent dissolution of silicate phases, in
particular olivine, is important in generating new pore space within
particles. Comparison of the preservation of glass and olivine also
indicates preferential dissolution of olivine by acidic solutions during
low temperature aqueous alteration. Precipitation of new hydrous phases
within cavities, in particular ferrihydrite and jarosite, results in
pseudomorph textures within heavily altered particles. Glass, in
contrast, is altered to palagonite gels and shows a sequential
replacement indicative of varying water to rock ratios. Metal is variably
replaced by Fe-oxyhydroxides and results in decreases in Ni/Fe ratio. In
contrast, sulphides within metal are largely preserved. Magnetite, an
essential component of micrometeorites formed during atmospheric entry,
is least altered by interaction with the terrestrial environment. The
extent of weathering in the studied micrometeorites is sensitive to
differences in their primary mineralogy and varies significantly with
particle type. Despite these differences, we propose a weathering scale
for micrometeorites based on both their degree of terrestrial alteration
and the level of encrustation by secondary phases. The compositions and
textures of weathering products, however, suggest open system behaviour
and variable water to rock ratios that imply climatic variation over the
lifetime of the micrometeorite deposits
Efficient Active Learning for Image Classification and Segmentation using a Sample Selection and Conditional Generative Adversarial Network
Training robust deep learning (DL) systems for medical image classification
or segmentation is challenging due to limited images covering different disease
types and severity. We propose an active learning (AL) framework to select most
informative samples and add to the training data. We use conditional generative
adversarial networks (cGANs) to generate realistic chest xray images with
different disease characteristics by conditioning its generation on a real
image sample. Informative samples to add to the training set are identified
using a Bayesian neural network. Experiments show our proposed AL framework is
able to achieve state of the art performance by using about 35% of the full
dataset, thus saving significant time and effort over conventional methods
Power and Purchasing: Why Strategic Purchasing Fails
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/162754/2/milq12471.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162754/1/milq12471_am.pd
Individual and environmental contributors to psychological distress during imprisonment
Criminal Justice: Legitimacy, accountability, and effectivit
The parent body of the ca. 480 kyr-old Tunguska-like impact over Antarctica.
第2回極域科学シンポジウム/第34回南極隕石シンポジウム 11月17日(木) 国立国語研究所 2階講
Nederlandse ingenieurs over opleiding voor niet-technische taakaspekten : verslag van een enquête bij 2000 Nederlandse ingenieurs
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