3,774 research outputs found
Study of crack-initiation phenomena associated with stress corrosion of aluminum alloys Annual report, 6 Jun. 1967 - 6 Jun. 1968
Electron microscopic, fractographic, and microprobe observations of crack initiation and propagation phenomena associated with stress corrosion of aluminum alloy
Morphology and thermal conductivity of model organic aerogels
The intersection volume of two independent 2-level cut Gaussian random fields
is proposed to model the open-cell microstructure of organic aerogels. The
experimentally measured X-ray scattering intensity, surface area and solid
thermal conductivity of both polymeric and colloidal organic aerogels can be
accounted for by the model.Comment: 5 pages. RevTex with 4 encapsulated figures. Higher resolution
figures have been submitted for publication. To be published in Phys. Rev. E
(Rapid Comm.). email, [email protected]
Results of magnetospheric barium ion cloud experiment of 1971
The barium ion cloud experiment involved the release of about 2 kg of barium at an altitude of 31 482 km, a latitude of 6.926 N., and a longitude of 74.395 W. Significant erosion of plasma from the main ion core occurred during the initial phase of the ion cloud expansion. From the motion of the outermost striational filaments, the electric field components were determined to be 0.19 mV/m in the westerly direction and 0.68 mV/m in the inward direction. The differences between these components and those measured from balloons flown in the proximity of the extremity of the field line through the release point implied the existence of potential gradients along the magnetic field lines. The deceleration of the main core was greater than theoretically predicted. This was attributed to the formation of a polarization wake, resulting in an increase of the area of interaction and resistive dissipation at ionospheric levels. The actual orientation of the magnetic field line through the release point differed by about 10.5 deg from that predicted by magnetic field models that did not include the effect of ring current
Local Axisymmetric Diffusive Stability of Weakly-Magnetized, Differentially-Rotating, Stratified Fluids
We study the local stability of stratified, differentially-rotating fluids to
axisymmetric perturbations in the presence of a weak magnetic field and of
finite resistivity, viscosity and heat conductivity. This is a generalization
of the Goldreich-Schubert-Fricke (GSF) double-diffusive analysis to the
magnetized and resistive, triple-diffusive case. Our fifth-order dispersion
relation admits a novel branch which describes a magnetized version of
multi-diffusive modes. We derive necessary conditions for axisymmetric
stability in the inviscid and perfect-conductor (double-diffusive) limits. In
each case, rotation must be constant on cylinders and angular velocity must not
decrease with distance from the rotation axis for stability, irrespective of
the relative strength of viscous, resistive and heat diffusion. Therefore, in
both double-diffusive limits, solid body rotation marginally satisfies our
stability criteria. The role of weak magnetic fields is essential to reach
these conclusions. The triple-diffusive situation is more complex, and its
stability criteria are not easily stated. Numerical analysis of our general
dispersion relation confirms our analytic double-diffusive criteria, but also
shows that an unstable double-diffusive situation can be significantly
stabilized by the addition of a third, ostensibly weaker, diffusion process. We
describe a numerical application to the Sun's upper radiative zone and
establish that it would be subject to unstable multi-diffusive modes if
moderate or strong radial gradients of angular velocity were present.Comment: 29 pages, 1 table, accepted for publication in Ap
Elliptic aspects of statistical mechanics on spheres
Our earlier results on the temperature inversion properties and the
ellipticisation of the finite temperature internal energy on odd spheres are
extended to orbifold factors of odd spheres and then to other thermodynamic
quantities, in particular to the specific heat. The behaviour under modular
transformations is facilitated by the introduction of a modular covariant
derivative and it is shown that the specific heat on any odd sphere can be
expressed in terms of just three functions. It is also shown that the free
energy on the circle can be written elliptically.Comment: 22 pages. JyTe
Neutron capture cross sections of tungsten and rhenium Annual summary report
Neutron capture cross sections for natural tungsten and rheniu
Evaluation of an explicit vocabulary teaching intervention for children learning English as an additional language in primary school
Many children learning English as an Additional Language (EAL) possess lower levels of English vocabulary knowledge relative to their non-EAL English-speaking peers. Longitudinal work suggests that this group discrepancy does not decrease markedly over time as a result of regular classroom teaching. Twelve EAL learners with English vocabulary weaknesses took part in a low-intensity, 10-week vocabulary intervention. Working one-to-one with speech and language therapy students, children took part in weekly activities designed to promote receptive and productive knowledge of 20 target words within the Tier-2 vocabulary category. When assessed on a bespoke word knowledge assessment, children made statistically significant gains between pretest and posttest in both receptive and productive knowledge of taught words, and maintained this knowledge six months later. Multi-component explicit vocabulary instruction offering opportunities for active engagement and discussion is thus presented as one potentially effective means of promoting the Tier-2 vocabulary knowledge of EAL learners in primary school in England
A 40th deg and order gravitational field model for Mars
Understanding the origin and evolution of major photographic features on Mars, such as the hemispheric dichotomy and Tharsis rise, will require improved resolution of that planet's gravitational and topographic fields. The highest resolution gravity model for Mars published to date was derived from Doppler tracking data from the Mariner 9 and Viking 1 and 2 spacecraft, and is of 18th degree and order. That field has a maximum spatial resolution of approx. 600 km, which is comparable to that of the best topographic model. The resolution of previous gravity models was limited not by data density, but rather by the computational resources available at the time. Because this restriction is no longer a limitation, the Viking and Mariner data sets were reanalyzed and a gravitational field was derived complete to the 40th degree and order with a corresponding maximum spatial resolution of 300 km where the data permit
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