27,282 research outputs found
Generation of spin current and polarization under dynamic gate control of spin-orbit interaction in low-dimensional semiconductor systems
Based on the Keldysh formalism, the Boltzmann kinetic equation and the drift
diffusion equation have been derived for studying spin polarization flow and
spin accumulation under effect of the time dependent Rashba spin-orbit
interaction in a semiconductor quantum well. The time dependent Rashba
interaction is provided by time dependent electric gates of appropriate shapes.
Several examples of spin manipulation by gates have been considered. Mechanisms
and conditions for obtaining the stationary spin density and the induced
rectified DC spin current are studied.Comment: 10 pages, 3 figures, RevTeX
Kondo and charge fluctuation resistivity due to Anderson impurities in graphene
Motivated by experiments on ion irradiated graphene, we compute the
resistivity of graphene with dilute impurities. In the local moment regime we
employ the perturbation theory up to third order in the exchange coupling to
determine the behavior at high temperatures within the Kondo model. Resistivity
due to charge fluctuations is obtained within the mean field approach on the
Anderson impurity model. Due to the linear spectrum of the graphene the Kondo
behavior is shown to depend on the gate voltage applied. The location of the
impurity on the graphene sheet is an important variable determining its effect
on the Kondo scale and resistivity. Our results show that for chemical
potential nearby the node the charge fluctuations is responsible for the
observed temperature dependence of resistivity while away from the node the
spin fluctuations take over. Quantitative agreement with experimental data is
achieved if the energy of the impurity level varies linearly with the chemical
potential.Comment: 17 pages, 15 figures, published versio
Strain-Induced Coupling of Spin Current to Nanomechanical Oscillations
We propose a setup which allows to couple the electron spin degree of freedom
to the mechanical motions of a nanomechanical system not involving any of the
ferromagnetic components. The proposed method employs the strain induced
spin-orbit interaction of electrons in narrow gap semiconductors. We have shown
how this method can be used for detection and manipulation of the spin flow
through a suspended rod in a nanomechanical device.Comment: 4 pages, 1 figur
Hadronic production of the -wave excited -states ()
Adopting the complete approach of the perturbative QCD (pQCD)
and updated parton distribution functions, we have estimated the hadronic
production of -wave excited -states (). In the estimate,
special care on the relation of the production amplitude to the derivative of
wave function at origin of the potential model is payed. For experimental
references, main uncertainties are discussed, and the total cross sections and
the distributions of the production with reasonable cuts at the energies of
Tevatron and LHC are computed and presented. The results show that -wave
production may contribute to the -meson production indirectly by a factor
about 0.5 of the direct production, and with such a big cross section, it is
worth further to study the possibility to observe the -wave production
itself experimentally.Comment: 23 pages, 9 figures, to replace for revising the misprints ec
Studying resist stochastics with the multivariate poisson propagation model
Progress in the ultimate performance of extreme ultraviolet resist has arguably decelerated in recent years suggesting an approach to stochastic limits both in photon counts and material parameters. Here we report on the performance of a variety of leading extreme ultraviolet resist both with and without chemical amplification. The measured performance is compared to stochastic modeling results using the Multivariate Poisson Propagation Model. The results show that the best materials are indeed nearing modeled performance limits
Bubble drag reduction requires large bubbles
In the maritime industry, the injection of air bubbles into the turbulent
boundary layer under the ship hull is seen as one of the most promising
techniques to reduce the overall fuel consumption. However, the exact mechanism
behind bubble drag reduction is unknown. Here we show that bubble drag
reduction in turbulent flow dramatically depends on the bubble size. By adding
minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise
completely unchanged strongly turbulent Taylor-Couette flow containing bubbles,
we dramatically reduce the drag reduction from more than 40% to about 4%,
corresponding to the trivial effect of the bubbles on the density and viscosity
of the liquid. The reason for this striking behavior is that the addition of
surfactants prevents bubble coalescence, leading to much smaller bubbles. Our
result demonstrates that bubble deformability is crucial for bubble drag
reduction in turbulent flow and opens the door for an optimization of the
process.Comment: 4 pages, 2 figure
Self-similar decay of high Reynolds number Taylor-Couette turbulence
We study the decay of high-Reynolds number Taylor-Couette turbulence, i.e.
the turbulent flow between two coaxial rotating cylinders. To do so, the
rotation of the inner cylinder (Re, the outer cylinder is at
rest) is stopped within 12 s, thus fully removing the energy input to the
system. Using a combination of laser Doppler anemometry and particle image
velocimetry measurements, six decay decades of the kinetic energy could be
captured. First, in the absence of cylinder rotation, the flow-velocity during
the decay does not develop any height dependence in contrast to the well-known
Taylor vortex state. Second, the radial profile of the azimuthal velocity is
found to be self-similar. Nonetheless, the decay of this wall-bounded
inhomogeneous turbulent flow does not follow a strict power law as for decaying
turbulent homogeneous isotropic flows, but it is faster, due to the strong
viscous drag applied by the bounding walls. We theoretically describe the decay
in a quantitative way by taking the effects of additional friction at the walls
into account.Comment: 7 pages, 6 figure
Analytical three-dimensional bright solitons and soliton-pairs in Bose-Einstein condensates with time-space modulation
We provide analytical three-dimensional bright multi-soliton solutions to the
(3+1)-dimensional Gross-Pitaevskii (GP) equation with time and space-dependent
potential, time-dependent nonlinearity, and gain/loss. The zigzag propagation
trace and the breathing behavior of solitons are observed. Different shapes of
bright solitons and fascinating interactions between two solitons can be
achieved with different parameters. The obtained results may raise the
possibility of relative experiments and potential applications.Comment: 5 pages, 4 figure
The meson annihilation to leptons and inclusive light hadrons
The annihilation of the meson to leptons and inclusive light hadrons is
analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find
that the decay mode, which escapes from the helicity suppression, contributes a
sizable fraction width. According to the analysis, the branching ratio due to
the contribution from the color-singlet component of the meson can be of
order (10^{-2}). We also estimate the contributions from the color-octet
components. With the velocity scaling rule of NRQCD, we find that the
color-octet contributions are sizable too, especially, in certain phase space
of the annihilation they are greater than (or comparative to) the color-singlet
component. A few observables relevant to the spectrum of charged lepton are
suggested, that may be used as measurements on the color-octet and
color-singlet components in the future experiments. A typical long
distance contribution in the annihilation is estimated too.Comment: 26 pages, 5 figures (6 eps-files), submitted to Phys. Rev.
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