3,524 research outputs found
Apollo 17 EVA-1 and EVA-2 Task Decomposition: Planning for Artemis and Future Mars Missions
A decomposition of the Apollo 17 mission extravehicular activities (EVA) tasks can be used to prepare for Artemis and future Mars missions. A categorized minute by minute breakdown of the astronauts activites could be used to plan future EVAs and determine which scientific tasks or equipment may be prioritized. This is especially relevant in this critical stage for the upcoming Atemis missions and science activity planning. The infographics generated from the decomposition provide a higher level view of actual EVAs and could aid in making future EVAs more efficient and successful
Magnitude bias of microlensed sources towards the Large Magellanic Cloud
There are lines of evidence suggesting that some of the observed microlensing
events in the direction of the Large Magellanic Cloud (LMC) are caused by
ordinary star lenses as opposed to dark Machos in the Galactic halo. Efficient
lensing by ordinary stars generally requires the presence of one or more
additional concentrations of stars along the line of sight to the LMC disk. If
such a population behind the LMC disk exists, then the source stars (for
lensing by LMC disk objects) will be drawn preferentially from the background
population and will show systematic differences from LMC field stars. One such
difference is that the (lensed) source stars will be farther away than the
average LMC field stars, and this should be reflected in their apparent
baseline magnitudes. We focus on red clump stars: these should appear in the
color-magnitude diagram at a few tenths of a magnitude fainter than the field
red clump. Suggestively, one of the two near-clump confirmed events,
MACHO-LMC-1, is a few tenths of magnitude fainter than the clump.Comment: To appear in ApJ Letters. Shortened to match the accepted version, 8
pages plus 1 ps figur
Coherent phonon scattering effects on thermal transport in thin semiconductor nanowires
The thermal conductance by phonons of a quasi-one-dimensional solid with
isotope or defect scattering is studied using the Landauer formalism for
thermal transport. The conductance shows a crossover from localized to Ohmic
behavior, just as for electrons, but the nature of this crossover is modified
by delocalization of phonons at low frequency. A scalable numerical
transfer-matrix technique is developed and applied to model
quasi-one-dimensional systems in order to confirm simple analytic predictions.
We argue that existing thermal conductivity data on semiconductor nanowires,
showing an unexpected linear dependence, can be understood through a model that
combines incoherent surface scattering for short-wavelength phonons with nearly
ballistic long-wavelength phonons. It is also found that even when strong
phonon localization effects would be observed if defects are distributed
throughout the wire, localization effects are much weaker when defects are
localized at the boundary, as in current experiments.Comment: 13 page
Self-similar impulsive capillary waves on a ligament
We study the short-time dynamics of a liquid ligament, held between two solid
cylinders, when one is impulsively accelerated along its axis. A set of
one-dimensional equations in the slender-slope approximation is used to
describe the dynamics, including surface tension and viscous effects. An exact
self-similar solution to the linearized equations is successfully compared to
experiments made with millimetric ligaments. Another non-linear self-similar
solution of the full set of equations is found numerically. Both the linear and
non-linear solutions show that the axial depth at which the liquid is affected
by the motion of the cylinder scales like . The non-linear solution
presents the peculiar feature that there exists a maximum driving velocity
above which the solution disappears, a phenomenon probably related to
the de-pinning of the contact line observed in experiments for large pulling
velocities
The Diffusion of Scientific Knowledge across Time and Space
This chapter discusses the consequences of academic mobility and the extent to which the movement of high-achieving faculty members affects both scientific and commercialization activities at their old and new schools. It looks at articles published by, and patents granted to, the mobile scientist before they departed for the new school, comparing these to similar outputs by scientists who did not move. The heterogeneity that can distort simpler comparisons can be limited. The analysis suggests that the citations to a departing scientist's articles from the university where he or she departs are barely affected by the move. However, citations to the departing scientist's patents (whether made in articles or patents) decline sharply at the originating school. This suggests that the physical proximity of the researcher is important to ensuring knowledge flows to industry. Citations to the scientist's work at his or her new location increase dramatically once the move is complete. Barriers to scientific mobility may actually be socially detrimental, as they prevent the kind of knowledge gains from the mixing of ideas. Keywords: diffusion; scientific knowledge; professional transitions; academic mobility; physical proximity; researche
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