10,519 research outputs found
Relaxation dynamics of multi-level tunneling systems
A quantum mechanical treatment of an asymmetric double-well potential (DWP)
interacting with a heat bath is presented for circumstances where the
contribution of higher vibrational levels to the relaxation dynamics cannot be
excluded from consideration. The deep quantum limit characterized by a discrete
energy spectrum near the barrier top is considered. The investigation is
motivated by simulations on a computer glass which show that the considered
parameter regime is ``typical'' for DWPs being responsible for the relaxation
peak of sound absorption in glasses. Relaxation dynamics resembling the
spatial- and energy-diffusion-controlled limit of the classical Kramers'
problem, and Arrhenius-like behavior is found under specific conditions.Comment: 23 pages, RevTex, 2 figures can be received from the Authors upon
reques
Random matrix theory for CPA: Generalization of Wegner's --orbital model
We introduce a generalization of Wegner's -orbital model for the
description of randomly disordered systems by replacing his ensemble of
Gaussian random matrices by an ensemble of randomly rotated matrices. We
calculate the one- and two-particle Green's functions and the conductivity
exactly in the limit . Our solution solves the CPA-equation of the
-Anderson model for arbitrarily distributed disorder. We show how the
Lloyd model is included in our model.Comment: 3 pages, Rev-Te
Resolved sidebands in a strain-coupled hybrid spin-oscillator system
We report on single electronic spins coupled to the motion of mechanical
resonators by a novel mechanism based on crystal strain. Our device consists of
single-crystalline diamond cantilevers with embedded Nitrogen-Vacancy center
spins. Using optically detected electron spin resonance, we determine the
unknown spin-strain coupling constants and demonstrate that our system resides
well within the resolved sideband regime. We realize coupling strengths
exceeding ten MHz under mechanical driving and show that our system has the
potential to reach strong coupling. Our novel hybrid system forms a resource
for future experiments on spin-based cantilever cooling and coherent
spin-oscillator coupling.Comment: 4 pages, 4 figures and supplementary information. Comments welcome.
Further information under http://www.quantum-sensing.physik.unibas.ch
Rigorous mean field model for CPA: Anderson model with free random variables
A model of a randomly disordered system with site-diagonal random energy
fluctuations is introduced. It is an extension of Wegner's -orbital model to
arbitrary eigenvalue distribution in the electronic level space. The new
feature is that the random energy values are not assumed to be independent at
different sites but free. Freeness of random variables is an analogue of the
concept of independence for non-commuting random operators. A possible
realization is the ensemble of at different lattice-sites randomly rotated
matrices. The one- and two-particle Green functions of the proposed hamiltonian
are calculated exactly. The eigenstates are extended and the conductivity is
nonvanishing everywhere inside the band. The long-range behaviour and the
zero-frequency limit of the two-particle Green function are universal with
respect to the eigenvalue distribution in the electronic level space. The
solutions solve the CPA-equation for the one- and two-particle Green function
of the corresponding Anderson model. Thus our (multi-site) model is a rigorous
mean field model for the (single-site) CPA. We show how the Llyod model is
included in our model and treat various kinds of noises.Comment: 24 pages, 2 diagrams, Rev-Tex. Diagrams are available from the
authors upon reques
Evaluation of the effects of space environment exposure on index of refraction and extinction coefficients of Apollo window materials
Temperature and radiation effects on index of refraction and extinction coefficients of Apollo window material
SPARC CCMVal (2010), SPARC Report on the Evaluation of Chemistry-Climate Models: Chapter 5: Transport
A low-loss, broadband antenna for efficient photon collection from a coherent spin in diamond
We report the creation of a low-loss, broadband optical antenna giving highly
directed output from a coherent single spin in the solid-state. The device, the
first solid-state realization of a dielectric antenna, is engineered for
individual nitrogen vacancy (NV) electronic spins in diamond. We demonstrate a
directionality close to 10. The photonic structure preserves the high spin
coherence of single crystal diamond (T2>100us). The single photon count rate
approaches a MHz facilitating efficient spin readout. We thus demonstrate a key
enabling technology for quantum applications such as high-sensitivity
magnetometry and long-distance spin entanglement.Comment: 5 pages, 4 figures and supplementary information (5 pages, 8
figures). Comments welcome. Further information under
http://www.quantum-sensing.physik.unibas.c
Properties of synchronization in the systems of non-identical coupled van der Pol and van der Pol - Duffing oscillators. Broadband synchronization
The particular properties of dynamics are discussed for the dissipatively
coupled van der Pol oscillators, non-identical in values of parameters
controlling the Hopf bifurcation. Possibility of a special synchronization
regime in an infinitively long band between oscillation death and quasiperiodic
areas is shown for such system. Features of the bifurcation picture are
discussed for different values of the control parameters and for the case of
additional Duffing-type nonlinearity. Analysis of the abridged equations is
presented.Comment: 19 pages, 9 figure
Modelling the effect of gap junctions on tissue-level cardiac electrophysiology
When modelling tissue-level cardiac electrophysiology, continuum
approximations to the discrete cell-level equations are used to maintain
computational tractability. One of the most commonly used models is represented
by the bidomain equations, the derivation of which relies on a homogenisation
technique to construct a suitable approximation to the discrete model. This
derivation does not explicitly account for the presence of gap junctions
connecting one cell to another. It has been seen experimentally [Rohr,
Cardiovasc. Res. 2004] that these gap junctions have a marked effect on the
propagation of the action potential, specifically as the upstroke of the wave
passes through the gap junction.
In this paper we explicitly include gap junctions in a both a 2D discrete
model of cardiac electrophysiology, and the corresponding continuum model, on a
simplified cell geometry. Using these models we compare the results of
simulations using both continuum and discrete systems. We see that the form of
the action potential as it passes through gap junctions cannot be replicated
using a continuum model, and that the underlying propagation speed of the
action potential ceases to match up between models when gap junctions are
introduced. In addition, the results of the discrete simulations match the
characteristics of those shown in Rohr 2004. From this, we suggest that a
hybrid model -- a discrete system following the upstroke of the action
potential, and a continuum system elsewhere -- may give a more accurate
description of cardiac electrophysiology.Comment: In Proceedings HSB 2012, arXiv:1208.315
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