32,608 research outputs found
Barium release system
A chemical system is described for releasing a good yield of free barium neutral atoms and barium ions in the upper atmosphere and interplanetary space for the study of the geophysical properties of the medium. The barium is released in the vapor phase so that it can be ionized by solar radiation and also be excited to emit resonance radiation in the visible range. The ionized luminous cloud of barium becomes a visible indication of magnetic and electrical characteristics in space and allows determination of these properties over relatively large areas at a given time
Rocket having barium release system to create ion clouds in the upper atmosphere
A chemical system for releasing a good yield of free barium atoms and barium ions to create ion clouds in the upper atmosphere and interplanetary space for the study of the geophysical properties of the medium is presented
A piezo-bar pressure probe
Piezo-bar pressure type probe measures the impact velocity or pressure of a moving debris cloud. It measures pressures up to 200,000 psi and peak pressures may be recorded with a total pulse duration between 5 and 65 musec
Dimensional Dependence of the Hydrodynamics of Core-Collapse Supernovae
The multidimensional character of the hydrodynamics in core-collapse
supernova (CCSN) cores is a key facilitator of explosions. Unfortunately, much
of this work has necessarily been performed assuming axisymmetry and it remains
unclear whether or not this compromises those results. In this work, we present
analyses of simplified two- and three-dimensional CCSN models with the goal of
comparing the multidimensional hydrodynamics in setups that differ only in
dimension. Not surprisingly, we find many differences between 2D and 3D models.
While some differences are subtle and perhaps not crucial to understanding the
explosion mechanism, others are quite dramatic and make interpreting 2D CCSN
models problematic. In particular, we find that imposing axisymmetry
artificially produces excess power at the largest spatial scales, power that
has been deemed critical in the success of previous explosion models and has
been attributed solely to the standing accretion shock instability.
Nevertheless, our 3D models, which have an order of magnitude less power on
large scales compared to 2D models, explode earlier. Since we see explosions
earlier in 3D than in 2D, the vigorous sloshing associated with the large scale
power in 2D models is either not critical in any dimension or the explosion
mechanism operates differently in 2D and 3D. Possibly related to the earlier
explosions in 3D, we find that about 25% of the accreted material spends more
time in the gain region in 3D than in 2D, being exposed to more integrated
heating and reaching higher peak entropies, an effect we associate with the
differing characters of turbulence in 2D and 3D. Finally, we discuss a simple
model for the runaway growth of buoyant bubbles that is able to quantitatively
account for the growth of the shock radius and predicts a critical luminosity
relation.Comment: Submitted to the Astrophysical Journa
Teacher and student perceptions of the development of learner autonomy : a case study in the biological sciences
Biology teachers in a UK university expressed a majority view that student learning autonomy increases with progression through university. A minority suggested that pre-existing diversity in learning autonomy was more important and that individuals not cohorts differ in their learning autonomy. They suggested that personal experience prior to university and age were important and that mature students are more autonomous than 18-20 year olds. Our application of an autonomous learning scale (ALS) to four year-groups of biology students confirmed that the learning autonomy of students increases through their time at university but not that mature students are necessarily more autonomous than their younger peers. It was evident however that year of study explained relatively little
On the calculation of supersonic, separating, and reattaching flows
A method is developed for solving the laminar and turbulent compressible boundary-layer equations for separating and reattaching flows. Results of this method are compared with experimental data for two laminar and three turbulent boundary-layer, shock-wave interactions. Several Navier-Stokes solutions were obtained for each of the laminar boundary-layer, shock-wave interactions considered. Comparison of these solutions indicates a first-order sensitivity in C sub f to the computational mesh selected in both the viscous and inviscid portions of the flow
Review of meteoroid-bumper interaction studies at McGill University
Experimental investigation of meteoroid-bumper impact, debris cloud expansion, and second surface pressure loadin
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