1,621 research outputs found
Propagating and evanescent waves in absorbing media
We compare the behavior of propagating and evanescent light waves in
absorbing media with that of electrons in the presence of inelastic scattering.
The imaginary part of the dielectric constant results primarily in an
exponential decay of a propagating wave, but a phase shift for an evanescent
wave. We then describe how the scattering of quantum particles out of a
particular coherent channel can be modeled by introducing an imaginary part to
the potential in analogy with the optical case. The imaginary part of the
potential causes additional scattering which can dominate and actually prevent
absorption of the wave for large enough values of the imaginary part. We also
discuss the problem of maximizing the absorption of a wave and point out that
the existence of a bound state greatly aids absorption. We illustrate this
point by considering the absorption of light at the surface of a metal.Comment: Brief Review, to appear in the American Journal of Physics,
http://www.kzoo.edu/ajp
Shuttle TPS thermal performance and analysis methodology
Thermal performance of the thermal protection system was approximately as predicted. The only extensive anomalies were filler bar scorching and over-predictions in the high Delta p gap heating regions of the orbiter. A technique to predict filler bar scorching has been developed that can aid in defining a solution. Improvement in high Delta p gap heating methodology is still under study. Minor anomalies were also examined for improvements in modeling techniques and prediction capabilities. These include improved definition of low Delta p gap heating, an analytical model for inner mode line convection heat transfer, better modeling of structure, and inclusion of sneak heating. The limited number of problems related to penetration items that presented themselves during orbital flight tests were resolved expeditiously, and designs were changed and proved successful within the time frame of that program
Universal quantum fluctuations of a cavity mode driven by a Josephson junction
We analyze the quantum dynamics of a superconducting cavity coupled to a
voltage biased Josephson junction. The cavity is strongly excited at resonances
where the voltage energy lost by a Cooper pair traversing the circuit is a
multiple of the cavity photon energy. We find that the resonances are
accompanied by substantial squeezing of the quantum fluctuations of the cavity
over a broad range of parameters and are able to identify regimes where the
fluctuations in the system take on universal values.Comment: 5 pages, 4 figure
Charge noise at Cooper-pair resonances
We analyze the charge dynamics of a superconducting single-electron
transistor (SSET) in the regime where charge transport occurs via Cooper-pair
resonances. Using an approximate description of the system Hamiltonian, in
terms of a series of resonant doublets, we derive a Born-Markov master equation
describing the dynamics of the SSET. The average current displays sharp peaks
at the Cooper-pair resonances and we find that the charge noise spectrum has a
characteristic structure which consists of a series of asymmetric triplets of
peaks. The strongest feature in the charge noise spectrum is the triplet of
peaks centered at zero frequency which has a peak spacing equal to the level
separation within the doublets and is similar to the triplet in the spectrum of
a driven, damped, two-level system. We also explore the back-action that the
SSET charge noise would have on an oscillator coupled to the island charge,
measurement of which provides a way of probing the charge noise spectrum.Comment: 14 pages, 7 figure
Noise properties of two single electron transistors coupled by a nanomechanical resonator
We analyze the noise properties of two single electron transistors (SETs)
coupled via a shared voltage gate consisting of a nanomechanical resonator.
Working in the regime where the resonator can be treated as a classical system,
we find that the SETs act on the resonator like two independent heat baths. The
coupling to the resonator generates positive correlations in the currents
flowing through each of the SETs as well as between the two currents. In the
regime where the dynamics of the resonator is dominated by the back-action of
the SETs, these positive correlations can lead to parametrically large
enhancements of the low frequency current noise. These noise properties can be
understood in terms of the effects on the SET currents of fluctuations in the
state of a resonator in thermal equilibrium which persist for times of order
the resonator damping time.Comment: Accepted for publication in Phys. Rev.
Chiral and Continuum Extrapolation of Partially-Quenched Lattice Results
The vector meson mass is extracted from a large sample of partially quenched,
two-flavor lattice QCD simulations. For the first time, discretisation,
finite-volume and partial quenching artefacts are treated in a unified
framework which is consistent with the low-energy behaviour of QCD. This
analysis incorporates the leading infrared behaviour dictated by chiral
effective field theory. As the two-pion decay channel cannot be described by a
low-energy expansion alone, a highly-constrained model for the decay channel of
the rho-meson is introduced. The latter is essential for extrapolating lattice
results from the quark-mass regime where the rho is observed to be a physical
bound state.Comment: 9 pages, 3 figures; revised version appearing in PL
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