827 research outputs found
Lunar surface engineering properties experiment definition. Volume 2: Mechanics of rolling sphere-soil slope interaction
The soil deformation mode under the action of a rolling sphere (boulder) was determined, and a theory based on actual soil failure mechanism was developed which provides a remote reconnaissance technique for study of soil conditions using boulder track observations. The failure mechanism was investigated by using models and by testing an instrumented spherical wheel. The wheel was specifically designed to measure contact pressure, but it also provided information on the failure mechanism. Further tests included rolling some 200 spheres down sand slopes. Films were taken of the rolling spheres, and the tracks were measured. Implications of the results and reevaluation of the lunar boulder tracks are discussed
Heat Transfer in Unfrozen and Frozen Porous Media: Experimental Measurement and Pore‐Scale Modelling
Myasthenia gravis: do not forget the patient perspective
Neurological Motor Disorder
Increased fluid flow activity in shallow sediments at the 3 km Long Hugin Fracture in the central North Sea
The North Sea hosts a wide variety of seafloor seeps that may be important for transfer of chemical species, such as methane, from the Earth's interior to its exterior. Here we provide geochemical and geophysical evidence for fluid flow within shallow sediments at the recently discovered, 3-km long Hugin Fracture in the Central North Sea. Although venting of gas bubbles was not observed, concentrations of dissolved methane were significantly elevated (up to six-times background values) in the water column at various locations above the fracture, and microbial mats that form in the presence of methane were observed at the seafloor. Seismic amplitude anomalies revealed a bright spot at a fault bend that may be the source of the water column methane. Sediment porewaters recovered in close proximity to the Hugin Fracture indicate the presence of fluids from two different shallow (<500m) sources: (i) a reduced fluid characterized by elevated methane concentrations and/or high levels of dissolved sulfide (up to 6 mmol L−1), and (ii) a low-chlorinity fluid (Cl ∼305 mmol L−1) that has low levels of dissolved methane and/or sulfide. The area of the seafloor affected by the presence of methane-enriched fluids is similar to the footprint of seepage from other morphological features in the North Sea
Cyber security fear appeals:unexpectedly complicated
Cyber security researchers are starting to experiment with fear appeals, with a wide variety of designs and reported efficaciousness. This makes it hard to derive recommendations for designing and deploying these interventions. We thus reviewed the wider fear appeal literature to arrive at a set of guidelines to assist cyber security researchers. Our review revealed a degree of dissent about whether or not fear appeals are indeed helpful and advisable. Our review also revealed a wide range of fear appeal experimental designs, in both cyber and other domains, which confirms the need for some standardized guidelines to inform practice in this respect. We propose a protocol for carrying out fear appeal experiments, and we review a sample of cyber security fear appeal studies, via this lens, to provide a snapshot of the current state of play. We hope the proposed experimental protocol will prove helpful to those who wish to engage in future cyber security fear appeal research
Milliarcsecond N-Band Observations of the Nova RS Ophiuchi: First Science with the Keck Interferometer Nuller
We report observations of the nova RS Ophiuchi (RS Oph) using the Keck
Interferometer Nuller (KIN), approximately 3.8 days following the most recent
outburst that occurred on 2006 February 12. These observations represent the
first scientific results from the KIN, which operates in N-band from 8 to 12.5
microns in a nulling mode. By fitting the unique KIN data, we have obtained an
angular size of the mid-infrared continuum of 6.2, 4.0, or 5.4 mas for a disk
profile, gaussian profile (FWHM), and shell profile respectively. The data show
evidence of enhanced neutral atomic hydrogen emission and atomic metals
including silicon located in the inner spatial regime near the white dwarf (WD)
relative to the outer regime. There are also nebular emission lines and
evidence of hot silicate dust in the outer spatial region, centered at ! 17 AU
from the WD, that are not found in the inner regime. Our evidence suggests that
these features have been excited by the nova flash in the outer spatial regime
before the blast wave reached these regions. These identifications support a
model in which the dust appears to be present between outbursts and is not
created during the outburst event. We further discuss the present results in
terms of a unifying model of the system that includes an increase in density in
the plane of the orbit of the two stars created by a spiral shock wave caused
by the motion of the stars through the cool wind of the red giant star. These
data show the power and potential of the nulling technique which has been
developed for the detection of Earth-like planets around nearby stars for the
Terrestrial Planet Finder Mission and Darwin missions.Comment: 41 pages, 10 figure
The dusty AGB star RS CrB: first mid-infrared interferometric observations with the Keck Telescopes
We report interferometric observations of the semi-regular variable star RS
CrB, a red giant with strong silicate emission features. The data were among
the first long baseline mid-infrared stellar fringes obtained between the Keck
telescopes, using parts of the new nulling beam combiner. The light was
dispersed by a low-resolution spectrometer, allowing simultaneous measurement
of the source visibility and intensity spectra from 8 to 12 microns. The
interferometric observations allow a non-ambiguous determination of the dust
shell spatial scale and relative flux contribution. Using a simple
spherically-symmetric model, in which a geometrically thin shell surrounds the
stellar photosphere, we find that ~30% to ~70% of the overall mid-infrared flux
- depending on the wavelength - originates from 7-8 stellar radii. The derived
shell opacity profile shows a broad peak around 11 microns (tau ~ 0.06),
characteristic of Mg-rich silicate dust particles.Comment: Accepted for publication in ApJ Letter
More than a century of bathymetric observations and present-day shallow sediment characterization in Belfast Bay, Maine, USA: implications for pockmark field longevity
This paper is not subject to U.S. copyright. The definitive version was published in Geo-Marine Letters 31 (2011): 237-248, doi:10.1007/s00367-011-0228-0.Mechanisms and timescales responsible for
pockmark formation and maintenance remain uncertain,
especially in areas lacking extensive thermogenic fluid
deposits (e.g., previously glaciated estuaries). This study
characterizes seafloor activity in the Belfast Bay, Maine
nearshore pockmark field using (1) three swath bathymetry
datasets collected between 1999 and 2008, complemented
by analyses of shallow box-core samples for radionuclide
activity and undrained shear strength, and (2) historical
bathymetric data (report and smooth sheets from 1872,
1947, 1948). In addition, because repeat swath bathymetry
surveys are an emerging data source, we present a selected
literature review of recent studies using such datasets for
seafloor change analysis. This study is the first to apply the
method to a pockmark field, and characterizes macro-scale
(>5 m) evolution of tens of square kilometers of highly
irregular seafloor. Presence/absence analysis yielded no
change in pockmark frequency or distribution over a 9-year
period (1999–2008). In that time pockmarks did not
detectably enlarge, truncate, elongate, or combine. Historical
data indicate that pockmark chains already existed in
the 19th century. Despite the lack of macroscopic changes
in the field, near-bed undrained shear-strength values of
less than 7 kPa and scattered downcore 137Cs signatures
indicate a highly disturbed setting. Integrating these
findings with independent geophysical and geochemical
observations made in the pockmark field, it can be
concluded that (1) large-scale sediment resuspension and
dispersion related to pockmark formation and failure do not
occur frequently within this field, and (2) pockmarks can
persevere in a dynamic estuarine setting that exhibits
minimal modern fluid venting. Although pockmarks are
conventionally thought to be long-lived features maintained
by a combination of fluid venting and minimal sediment
accumulation, this suggests that other mechanisms may be
equally active in maintaining such irregular seafloor
morphology. One such mechanism could be upwelling
within pockmarks induced by near-bed currents.Graduate support for Brothers came from a
Maine Economic Improvement Fund Dissertation Fellowship
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