35,923 research outputs found
DC Spin Current Generation in a Rashba-type Quantum Channel
We propose and demonstrate theoretically that resonant inelastic scattering
(RIS) can play an important role in dc spin current generation. The RIS makes
it possible to generate dc spin current via a simple gate configuration: a
single finger-gate that locates atop and orients transversely to a quantum
channel in the presence of Rashba spin-orbit interaction. The ac biased
finger-gate gives rise to a time-variation in the Rashba coupling parameter,
which causes spin-resolved RIS, and subsequently contributes to the dc spin
current. The spin current depends on both the static and the dynamic parts in
the Rashba coupling parameter, and , respectively, and is
proportional to . The proposed gate configuration has the
added advantage that no dc charge current is generated. Our study also shows
that the spin current generation can be enhanced significantly in a double
finger-gate configuration.Comment: 4 pages,4 figure
All-optical switching in a two-channel waveguide with cubic-quintic nonlinearity
We consider dynamics of spatial beams in a dual-channel waveguide with
competing cubic and quintic (CQ) nonlinearities. Gradually increasing the power
in the input channel, we identify four different regimes of the pulses coupling
into the cross channel, which alternate three times between full pass and full
stop, thus suggesting three realizations of switching between the channels. As
in the case of the Kerr (solely cubic) nonlinearity, the first two regimes are
the linear one, and one dominated by the self-focusing nonlinearity, with the
beam which, respectively, periodically couples between the channels, or stays
in the input channel. Further increase of the power reveals two novel
transmission regimes, one characterized by balance between the competing
nonlinearities, which again allows full coupling between the channels, and a
final regime dominated by the self-defocusing quintic nonlinearity. In the
latter case, the situation resembles that known for a self-repulsive
Bose-Einstein condensate trapped in a double-well potential, which is
characterized by strong symmetry breaking; accordingly, the beam again abides
in the input channel, contrary to an intuitive expectation that the
self-defocusing nonlinearity would push it into the cross channel. The
numerical results are qualitatively explained by a simple analytical model
based on the variational approximation.Comment: Journal of Physics B (in press
Inter- and Intra-Chain Attractions in Solutions of Flexible Polyelectrolytes at Nonzero Concentration
Constant temperature molecular dynamics simulations were used to study
solutions of flexible polyelectrolyte chains at nonzero concentrations with
explicit counterions and unscreened coulombic interactions. Counterion
condensation, measured via the self-diffusion coefficient of the counterions,
is found to increase with polymer concentration, but contrary to the prediction
of Manning theory, the renormalized charge fraction on the chains decreases
with increasing Bjerrum length without showing any saturation. Scaling analysis
of the radius of gyration shows that the chains are extended at low polymer
concentrations and small Bjerrum lengths, while at sufficiently large Bjerrum
lengths, the chains shrink to produce compact structures with exponents smaller
than a gaussian chain, suggesting the presence of attractive intrachain
interactions. A careful study of the radial distribution function of the
center-of-mass of the polyelectrolyte chains shows clear evidence that
effective interchain attractive interactions also exist in solutions of
flexible polyelectrolytes, similar to what has been found for rodlike
polyelectrolytes. Our results suggest that the broad maximum observed in
scattering experiments is due to clustering of chains.Comment: 12 pages, REVTeX, 15 eps figure
Scalable Parallel Numerical CSP Solver
We present a parallel solver for numerical constraint satisfaction problems
(NCSPs) that can scale on a number of cores. Our proposed method runs worker
solvers on the available cores and simultaneously the workers cooperate for the
search space distribution and balancing. In the experiments, we attained up to
119-fold speedup using 256 cores of a parallel computer.Comment: The final publication is available at Springe
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