35,481 research outputs found
Indirect Dissociative Recombination of LiH Molecules Fueled by Complex Resonance Manifolds
The LiH molecule is prototypical of the indirect dissociative
recombination (DR) process, in which a colliding electron destroys the molecule
through Rydberg capture pathways. This Letter develops the first quantitative
test of the Siegert state multichannel quantum defect theory description of
indirect DR for a diatomic molecular ion. The R-matrix approach is adopted to
calculate ab-initio quantum defects, functions of the internuclear distance
that characterize both Rydberg states and the zero-energy collisions of
electrons with LiH ions. The calculated DR rate coefficient agrees
accurately with recent experimental data (S. Krohn et al, Phys. Rev. Lett. 86,
4005). We identify the doorways to fast indirect DR as complex resonance
manifolds, which couple closed channels having both high and low principal
quantum numbers. This sheds new light on the competition between direct and
indirect DR pathways, and suggests the reason why previous theory
underestimated the DR rate by an order of magnitude.Comment: Submitted to PR
Information Storage in Black Holes
The information loss paradox for Schwarzschild black holes is examined, using
the ADS/CFT correspondence extended to the bulk. It is found that
the only option compatible with the preservation of the quantum unitarity is
when a regular remnant region of the black hole survives to the black hole
evaporation process, where information can be stored and eventually retrieved.Comment: 5 pages Latex file, no figures. A honourable mention in the 2005 GRF
essay competitio
D-Brane Topology Changing Transitions
We study D-branes on three-dimensional orbifold backgrounds that admit
topologically distinct resolutions differing by flop transitions. We show that
these distinct phases are part of the vacuum moduli space of the super
Yang-Mills gauge theory describing the D-brane dynamics. In this way we
establish that D-branes --- like fundamental strings --- allow for physically
smooth topology changing transitions.Comment: 16 pages, 3 figures, Harvma
Observation of wave-packet propagation in the ion cyclotron range of frequencies in a tokamak plasma
Experimental observation of wave-packet propagation in the ion cyclotron range of frequencies in a tokamak plasma is reported. Studies were carried out in the Caltech Research Tokamak [Phys. Fluids 23, 614 (1980)] in a pure hydrogen plasma and in a regime where fast-wave damping was sufficiently small to permit multiple toroidal transits of the wave packet. Waves were launched by exciting a small loop antenna with a short burst of radio-frequency current and were detected with shielded magnetic probes. Probe scans revealed a large increase in wave-packet amplitude at smaller minor radii, and the packet velocity was found to be independent of radial position. Measurement of the packet transit time yielded direct information about the wave group velocity. Packet velocity was investigated as a function of the fundamental excitation frequency, plasma density, and toroidal magnetic field. Results are compared with the predictions of a cold plasma model that includes a vacuum layer at the edge
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