14,197 research outputs found
Magnetically Stimulated Diffusion of Rydberg Gases
The specific kind of diffusion stimulated (rather than suppressed) by the
external magnetic field, which was predicted for the first time by Schmelcher
and Cederbaum in 1992, is considered here for the case of high-angular-momentum
(i.e., approximately "circular") Rydberg atoms. The coefficient of such
diffusion was calculated by a purely analytical approach and was found to be
well relevant to the experiments on antihydrogen formation.Comment: REVTeX4, 4 pages, 1 EPS figure; v2: additional numerical estimates
and extended discussion in the end of pape
Local magnetic divertor for control of the plasma-limiter interaction in a tokamak
An experiment is described in which plasma flow to a tokamak limiter is controlled through the
use of a local toroidal divertor coil mounted inside the limiter itself. This coil produces a local
perturbed field B_C approximately equal to the local unperturbed toroidal field B_T ≃ 3 kG, such
that when B_C adds to B_T the field lines move into the limiter and the local plasma flow to it
increases by a factor as great as 1.6, and when B_C subtracts from B_T the field lines move away
from the limiter and the local plasma flow to it decreases by as much as a factor of 4. A simple
theoretical model is used to interpret these results. Since these changes occur without significantly
affecting global plasma confinement, such a control scheme may be useful for optimizing the
performance of pumped limiters
The Addition Spectrum of a Lateral Dot from Coulomb and Spin Blockade Spectroscopy
Transport measurements are presented on a class of electrostatically defined
lateral dots within a high mobility two dimensional electron gas (2DEG). The
new design allows Coulomb Blockade(CB) measurements to be performed on a single
lateral dot containing 0, 1 to over 50 electrons. The CB measurements are
enhanced by the spin polarized injection from and into 2DEG magnetic edge
states. This combines the measurement of charge with the measurement of spin
through spin blockade spectroscopy. The results of Coulomb and spin blockade
spectroscopy for first 45 electrons enable us to construct the addition
spectrum of a lateral device. We also demonstrate that a lateral dot containing
a single electron is an effective local probe of a 2DEG edge.Comment: 4 pages, 4 figures submitted to Physical Review
Superluminal Caustics of Close, Rapidly-Rotating Binary Microlenses
The two outer triangular caustics (regions of infinite magnification) of a
close binary microlens move much faster than the components of the binary
themselves, and can even exceed the speed of light. When , where
is the caustic speed, the usual formalism for calculating the lens
magnification breaks down. We develop a new formalism that makes use of the
gravitational analog of the Li\'enard-Wiechert potential. We find that as the
binary speeds up, the caustics undergo several related changes: First, their
position in space drifts. Second, they rotate about their own axes so that they
no longer have a cusp facing the binary center of mass. Third, they grow larger
and dramatically so for . Fourth, they grow weaker roughly in
proportion to their increasing size. Superluminal caustic-crossing events are
probably not uncommon, but they are difficult to observe.Comment: 12 pages, 7 ps figures, submitted to Ap
Detection Rates for Close Binaries Via Microlensing
Microlensing is one of the most promising methods of reconstructing the
stellar mass function down to masses even below the hydrogen-burning limit. The
fundamental limit to this technique is the presence of unresolved binaries,
which can in principle significantly alter the inferred mass function. Here we
quantify the fraction of binaries that can be detected using microlensing,
considering specifically the mass ratio and separation of the binary. We find
that almost all binary systems with separations greater than of
their combined Einstein ring radius are detectable assuming a detection
threshold of . For two M dwarfs, this corresponds to a limiting separation
of \gsim 1 \au. Since very few observed M dwarfs have companions at
separations \lsim 1 \au, we conclude that close binaries will probably not
corrupt the measurements of the mass function. We find that the detectability
depends only weakly on the mass ratio. For those events for which individual
masses can be determined, we find that binaries can be detected down to .Comment: 19 pages including 6 figures. Uses phyyzx format. Send requests for
higher quality figures to [email protected]
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