1,043 research outputs found
Quantum shape effects on Zeeman splittings in semiconductor nanostructures
We develop a general method to calculate Zeeman splittings of electrons and
holes in semiconductor nanostructures within the tight-binding framework. The
calculation is carried out in the electron-hole picture and is extensible to
the excitonic calculation by including the electron-hole Coulomb interaction.
The method is suitable for the investigation of quantum shape effects and the
anisotropy of the g-factors. Numerical results for CdSe and CdTe nanostructures
are presented
On possible violation of the CHSH Bell inequality in a classical context
It has been shown that there is a small possibility to experimentally violate
the CHSH Bell inequality in a 'classical' context. The probability of such a
violation has been estimated in the framework of a classical probabilistic
model in the language of a random-walk representation.Comment: 9 pages, 1 figur
On the Floquet Theory of Delay Differential Equations
We present an analytical approach to deal with nonlinear delay differential
equations close to instabilities of time periodic reference states. To this end
we start with approximately determining such reference states by extending the
Poincar'e Lindstedt and the Shohat expansions which were originally developed
for ordinary differential equations. Then we systematically elaborate a linear
stability analysis around a time periodic reference state. This allows to
approximately calculate the Floquet eigenvalues and their corresponding
eigensolutions by using matrix valued continued fractions
Pattern Competition in the Photorefractive Semiconductors
We analytically study the photorefractive Gunn effect in n-GaAs subjected to
two external laser beams which form a moving interference pattern (MIP) in the
semiconductor. When the intensity of the spatially independent part of the MIP,
denoted by , is small, the system has a periodic domain train (PDT),
consistent with the results of linear stability analysis. When is large,
the space-charge field induced by the MIP will compete with the PDT and result
in complex dynamics, including driven chaos via quasiperiodic route
Inclusion of organ deformation in dose calculations
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135079/1/mp9039.pd
Adiabatic reduction near a bifurcation in stochastically modulated systems
We re-examine the procedure of adiabatic elimination of fast relaxing
variables near a bifurcation point when some of the parameters of the system
are stochastically modulated. Approximate stationary solutions of the
Fokker-Planck equation are obtained near threshold for the pitchfork and
transcritical bifurcations. Stochastic resonance between fast variables and
random modulation may shift the effective bifurcation point by an amount
proportional to the intensity of the fluctuations. We also find that
fluctuations of the fast variables above threshold are not always Gaussian and
centered around the (deterministic) center manifold as was previously believed.
Numerical solutions obtained for a few illustrative examples support these
conclusions.Comment: RevTeX, 19 pages and 16 figure
Extension of Lorenz Unpredictability
It is found that Lorenz systems can be unidirectionally coupled such that the
chaos expands from the drive system. This is true if the response system is not
chaotic, but admits a global attractor, an equilibrium or a cycle. The
extension of sensitivity and period-doubling cascade are theoretically proved,
and the appearance of cyclic chaos as well as intermittency in interconnected
Lorenz systems are demonstrated. A possible connection of our results with the
global weather unpredictability is provided.Comment: 32 pages, 13 figure
A general scaling relation for the critical current density in Nb3Sn
We review the scaling relations for the critical current density (Jc) in
Nb3Sn wires and include recent findings on the variation of the upper critical
field (Hc2) with temperature (T) and A15 composition. We highlight deficiencies
in the Summers/Ekin relations, which are not able to account for the correct
Jc(T) dependence. Available Jc(H) results indicate that the magnetic field
dependence for all wires can be described with Kramer's flux shear model, if
non-linearities in Kramer plots are attributed to A15 inhomogeneities. The
strain (eps) dependence is introduced through a temperature and strain
dependent Hc2*(T,eps) and Ginzburg- Landau parameter kappa1(T,eps) and a strain
dependent critical temperature Tc(eps). This is more consistent than the usual
Ekin unification, which uses two separate and different dependencies on Hc2*(T)
and Hc2*(eps). Using a correct temperature dependence and accounting for the
A15 inhomogeneities leads to a remarkable simple relation for Jc(H,T,eps).
Finally, a new relation for s(eps) is proposed, based on the first, second and
third strain invariants.Comment: Accepted Topical Review for Superconductor, Science and Technolog
Dissipation and spontaneous symmetry breaking in brain dynamics
We compare the predictions of the dissipative quantum model of brain with
neurophysiological data collected from electroencephalograms resulting from
high-density arrays fixed on the surfaces of primary sensory and limbic areas
of trained rabbits and cats. Functional brain imaging in relation to behavior
reveals the formation of coherent domains of synchronized neuronal oscillatory
activity and phase transitions predicted by the dissipative model.Comment: Restyled, slight changes in title and abstract, updated bibliography,
J. Phys. A: Math. Theor. Vol. 41 (2008) in prin
Strong exciton-plasmon coupling in semiconducting carbon nanotubes
We study theoretically the interactions of excitonic states with surface
electromagnetic modes of small-diameter (~1 nm) semiconducting single-walled
carbon nanotubes. We show that these interactions can result in strong
exciton-surface-plasmon coupling. The exciton absorption line shape exhibits
Rabi splitting ~0.1 eV as the exciton energy is tuned to the nearest interband
surface plasmon resonance of the nanotube. We also show that the quantum
confined Stark effect may be used as a tool to control the exciton binding
energy and the nanotube band gap in carbon nanotubes in order, e.g., to bring
the exciton total energy in resonance with the nearest interband plasmon mode.
The exciton-plasmon Rabi splitting we predict here for an individual carbon
nanotube is close in its magnitude to that previously reported for hybrid
plasmonic nanostructures artificially fabricated of organic semiconductors on
metallic films. We expect this effect to open up paths to new tunable
optoelectronic device applications of semiconducting carbon nanotubes.Comment: 22 pages, 8 figures, accepted for PR
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