4,553 research outputs found
The modifcation by diffuse radiation of "cometary tail" formation behind globules
We study the evolution of a globule of neutral material immersed in the more tenuous hotter plasma of an H II region surrounding newly born OB stars. The neutral globule is illuminated by the direct ionizing radiation of OB stars, and by diffuse radiation emitted by recombination in the surrounding ionized gas. We perform 2D, time dependent axisymmetric hydrodynamic simulations, and find that, for values of the diffuse field of the order of 10% of the direct field, the evolution of the globule is completely different to its evolution when the diffuse field is neglected
158µJ pulses from a single transverse mode, large mode-area EDFA
We report the amplification of 10pJ-100pJ, semiconductor diode pulses up to an energy of 158µJ and peak powers >100kW in a multi-stage fibre amplifier chain based on a single-mode, large mode-area erbium doped amplifier design. These results represent the highest single-mode pulse energy ever extracted from any doped fibre system
Nonequilibrium charge density wave ordering from anomalous velocity in itinerant helical magnets
The Karplus-Luttinger anomalous velocity is shown to lead to
electric-field-induced charge accumulation in nearly ferromagnetic noncollinear
magnets with itinerant electrons, like . For helical magnetic ordering,
the balance between this accumulation and the Coulomb interaction leads to a
nonequilibrium charge density wave state with the period of the helix, even
when such accumulation is forbidden by an approximate gauge-like symmetry in
the absence of electric field. We compute the strength of such charge
accumulation as an example of how unexpected many-electron physics is induced
by the inclusion of the one-electron Karplus-Luttinger term whenever the local
exchange field felt by conduction electrons does not satisfy the current-free
Maxwell equations.Comment: 5 pages and 1 figur
Finite temperature theory of the scissors mode in a Bose gas using the moment method
We use a generalized Gross-Pitaevskii equation for the condensate and a
semi-classical kinetic equation for the noncondensate atoms to discuss the
scissors mode in a trapped Bose-condensed gas at finite temperatures. Both
equations include the effect of collisions between the condensate and
noncondensate atoms. We solve the coupled moment equations describing
oscillations of the quadrupole moments of the condensate and noncondensate
components to find the collective mode frequencies and collisional damping
rates as a function of temperature. Our calculations extend those of
Gu\'ery-Odelin and Stringari at T=0 and in the normal phase. They complement
the numerical results of Jackson and Zaremba, although Landau damping is left
out of our approach. Our results are also used to calculate the quadrupole
response function, which is related to the moment of inertia. It is shown
explicitly that the moment of inertia of a trapped Bose gas at finite
temperatures involves a sum of an irrotational component from the condensate
and a rotational component from the thermal cloud atoms.Comment: 18 pages, 8 figure
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