11,885 research outputs found
The B-ring's surface mass density from hidden density waves: Less than meets the eye?
Saturn's B ring is the most opaque ring in our solar system, but many of its
fundamental parameters, including its total mass, are not well constrained.
Spiral density waves generated by mean-motion resonances with Saturn's moons
provide some of the best constraints on the rings' mass density, but detecting
and quantifying such waves in the B ring has been challenging because of this
ring's high opacity and abundant fine-scale structure. Using a wavelet-based
analyses of 17 occultations of the star gamma Crucis observed by the Visual and
Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft, we are
able to examine five density waves in the B ring. Two of these waves are
generated by the Janus 2:1 and Mimas 5:2 Inner Lindblad Resonances at 96,427 km
and 101,311 km from Saturn's center, respectively. Both of these waves can be
detected in individual occultation profiles, but the multi-profile wavelet
analysis reveals unexpected variations in the pattern speed of the Janus 2:1
wave that might arise from the periodic changes in Janus' orbit. The other
three wave signatures are associated with the Janus 3:2, Enceladus 3:1 and
Pandora 3:2 Inner Lindblad Resonances at 115,959 km, 115,207 km and 108,546 km.
These waves are not visible in individual profiles, but structures with the
correct pattern speeds can be detected in appropriately phase-corrected average
wavelets. Estimates of the ring's surface mass density derived from these five
waves fall between 40 and 140 g/cm^2, even though the ring's optical depth in
these regions ranges from 1.5 to almost 5. This suggests that the total mass of
the B ring is most likely between one-third and two-thirds the mass of Saturn's
moon Mimas.Comment: 40 Pages, 21 Figures, Accepted for publication in Icarus, a few typos
fixe
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Linking metacognition and mindreading: Evidence from autism and dual-task investigations
Questions of how we know our own and other minds, and whether metacognition and mindreading rely on the same processes, are longstanding in psychology and philosophy. In Experiment 1, children/adolescents with autism (who tend to show attenuated mindreading) showed significantly lower accuracy on an explicit metacognition task than neurotypical children/adolescents, but not on an allegedly metacognitive implicit one. In Experiment 2, neurotypical adults completed these tasks in a single-task condition, or a dual-task condition that required concurrent completion of a secondary task that tapped mindreading. Metacognitive accuracy was significantly diminished by the dual-mindreading-task on the explicit task, but not the implicit task. In Experiment 3, we included additional dual-tasks to rule out the possibility that any secondary task (regardless of whether it required mindreading) would diminish metacognitive accuracy. Finally, in both experiments 1 and 2, metacognitive accuracy on the explicit task, but not the implicit task, was associated significantly with performance on a measure of mindreading ability. These results suggest that explicit metacognitive tasks (used frequently to measure metacognition in humans) share metarepresentational processing resources with mindreading, whereas implicit tasks (which are claimed by some comparative psychologists to measure metacognition in non-human animals) do not
A Tidally-Disrupted Asteroid Around the White Dwarf G29-38
The infrared excess around the white dwarf G29-38 can be explained by
emission from an opaque flat ring of dust with an inner radius 0.14 of the
radius of the Sun and an outer radius approximately equal to the Sun's. This
ring lies within the Roche region of the white dwarf where an asteroid could
have been tidally destroyed, producing a system reminiscent of Saturn's rings.
Accretion onto the white dwarf from this circumstellar dust can explain the
observed calcium abundance in the atmosphere of G29-38. Either as a bombardment
by a series of asteroids or because of one large disruption, the total amount
of matter accreted onto the white dwarf may have been comparable to the total
mass of asteroids in the Solar System, or, equivalently, about 1% of the mass
in the asteroid belt around the main sequence star zeta Lep.Comment: ApJ Letters, in pres
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Behaviour change at work: Empowering energy efficiency in the workplace through user-centred design
Copyright @ 2011 University of California eScholarship RepositoryCO2 emissions from non-domestic buildings - primarily workplaces - make up 18 percent of the UK's carbon footprint. A combination of technology advances and behavioural changes have the potential to make significant impact, but interventions have often been planned in ways which do not take into account the needs, levels of understanding and everyday behavioural contexts of building users - and hence do not achieve the hoped-for success.This paper provides a brief introduction to the Empower project, a current industrial-academic collaboration in the UK which is applying methods from user-centred design practice to understand diverse users' needs, priorities, mental models of energy and decision-making heuristics - as well as the affordances available to them - in a number of office buildings. We are developing and trialling a set of low-cost, simple software interventions tailored to multiple user groups with different degrees of agency over their energy use, which seek to influence more energy efficient behaviour at work in areas such as HVAC, lighting and equipment use. The project comprises an ethnographic research phase, a participatory design programme involving building users in the design of interventions, and iterative trials in a large office building in central London
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