83 research outputs found
Real Time Relativity: exploration learning of special relativity
Real Time Relativity is a computer program that lets students fly at
relativistic speeds though a simulated world populated with planets, clocks,
and buildings. The counterintuitive and spectacular optical effects of
relativity are prominent, while systematic exploration of the simulation allows
the user to discover relativistic effects such as length contraction and the
relativity of simultaneity. We report on the physics and technology
underpinning the simulation, and our experience using it for teaching special
relativity to first year university students
Effect of temperature anisotropy on various modes and instabilities for a magnetized non-relativistic bi-Maxwellian plasma
Using kinetic theory for homogeneous collisionless magnetized plasmas, we
present an extended review of the plasma waves and instabilities and discuss
the anisotropic response of generalized relativistic dielectric tensor and
Onsager symmetry properties for arbitrary distribution functions. In general,
we observe that for such plasmas only those electromagnetic modes whose
magnetic field perturbations are perpendicular to the ambient magneticeld,
i.e.,B1 \perp B0, are effected by the anisotropy. However, in oblique
propagation all modes do show such anisotropic effects. Considering the
non-relativistic bi-Maxwellian distribution and studying the relevant
components of the general dielectric tensor under appropriate conditions, we
derive the dispersion relations for various modes and instabilities. We show
that only the electromagnetic R- and L- waves, those derived from them and the
O-mode are affected by thermal anisotropies, since they satisfy the required
condition B1\perpB0. By contrast, the perpendicularly propagating X-mode and
the modes derived from it (the pure transverse X-mode and Bernstein mode) show
no such effect. In general, we note that the thermal anisotropy modifies the
parallel propagating modes via the parallel acoustic effect, while it modifies
the perpendicular propagating modes via the Larmor-radius effect. In oblique
propagation for kinetic Alfven waves, the thermal anisotropy affects the
kinetic regime more than it affects the inertial regime. The generalized fast
mode exhibits two distinct acoustic effects, one in the direction parallel to
the ambient magnetic field and the other in the direction perpendicular to it.
In the fast-mode instability, the magneto-sonic wave causes suppression of the
firehose instability. We discuss all these propagation characteristics and
present graphic illustrations
Electromagnetic Fluctuations during Fast Reconnection in a Laboratory Plasma
Clear evidence for a positive correlation is established between the
magnitude of magnetic fluctuations in the lower-hybrid frequency range and
enhancement of reconnection rates in a well-controlled laboratory plasma. The
fluctuations belong to the right-hand polarized whistler wave branch,
propagating obliquely to the reconnecting magnetic field, with a phase velocity
comparable to the relative drift velocity between electrons and ions. The short
coherence length and large variation along the propagation direction indicate
their strongly nonlinear nature in three dimensions.Comment: 4 pages, 6 figures, submitted to Phys. Rev. Let
Ion acoustic wave experiments in a high school plasma physics laboratory
We describe a successful alliance between a university and several high schools. The alliance is centered on a laboratory experiment constructed by students and faculty. The experiment involves sophisticated concepts and equipment not readily available in high schools. Much of the experiment is directly related to the science and mathematics learned in high school, with opportunities to extend their understanding by applying it to a research experience. The experiment is in plasma physics, but a similar alliance can be implemented in any area of science. Although the number of high school students affected by any one alliance is small, the impact is potentially large in the scientific life of a participating student or teacher
Wind anisotropies and GRB progenitors
We study the effect of wind anisotropies on the stellar evolution leading to
collapsars. Rotating models of a 60 M star with on the ZAMS, accounting for shellular rotation and a magnetic
field, with and without wind anisotropies, are computed at =0.002 until the
end of the core He-burning phase. Only the models accounting for the effects of
the wind anisotropies retain enough angular momentum in their core to produce a
Gamma Ray Burst (GRB). The chemical composition is such that a type Ic
supernova event occurs. Wind anisotropies appear to be a key physical
ingredient in the scenario leading to long GRBs.Comment: 5 pages, 4 figures, accepted for publication in A&A Lette
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