22,442 research outputs found
Noise-Activated Escape from a Sloshing Potential Well
We treat the noise-activated escape from a one-dimensional potential well of
an overdamped particle, to which a periodic force of fixed frequency is
applied. We determine the boundary layer behavior, and the physically relevant
length scales, near the oscillating well top. We show how stochastic behavior
near the well top generalizes the behavior first determined by Kramers, in the
case without forcing. Both the case when the forcing dies away in the weak
noise limit, and the case when it does not, are examined. We also discuss the
relevance of various scaling regimes to recent optical trap experiments.Comment: 9 pages, no figures, REVTeX, expanded versio
Anisotropy of nickel-base superalloy single crystals
The influence of orientation on the tensile and stress rupture behavior of 52 Mar-M247 single crystals was studied. Tensile tests were performed at temperatures between 23 and 1093 C; stress rupture behavior was examined between 760 and 1038 C. The mechanical behavior of the single crystals was rationalized on the basis of the Schmid factor contours for the operative slip systems and the lattice rotations which the crystals underwent during deformation. The tensile properties correlated well with the appropriate Schmid factor contours. The stress rupture lives at lower testing temperatures were greatly influenced by the lattice rotations required to produce cross slip. A unified analysis was attained for the stress rupture life data generated for the Mar-M247 single crystals at 760 and 774 C under a stress of 724 MPa and the data reported for Mar-M200 single crystals tested at 760 C under a stress of 689 MPa. Based on this analysis, the stereographic triangle was divided into several regions which were rank ordered according to stress rupture life for this temperature regime
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Calibration and comparison of chlorine decay models for a test water distribution system
This paper investigates the kinetics of monochloramine as disinfectant in a 1.3 km water pipe. A novel procedure for the correction of chlorine meter errors is introduced and applied. Parameter estimation using nonlinear optimisation procedures is used to identify decay coefficients for monochloramine models with a single coefficient or two coefficients as used in EPANET. Important difficulties in fitting these parameters which come about because of the model structure are highlighted. Finally, results of
decay coefficients are presented and investigated for flow, inlet chlorine concentration and temperature dependence
Effect of strain on hyperfine-induced hole-spin decoherence in quantum dots
We theoretically consider the effect of strain on the spin dynamics of a
single heavy-hole (HH) confined to a self-assembled quantum dot and interacting
with the surrounding nuclei via hyperfine interaction. Confinement and strain
hybridize the HH states, which show an exponential decay for a narrowed nuclear
spin bath. For different strain configurations within the dot, the dependence
of the spin decoherence time on external parameters is shifted and the
non-monotonic dependence of the peak is altered. Application of external strain
yields considerable shifts in the dependence of on external parameters.
We find that external strain affects mostly the effective hyperfine coupling
strength of the conduction band (CB), indicating that the CB admixture of the
hybridized HH states plays a crucial role in the sensitivity of on
strain
Real-space Hopfield diagonalization of inhomogeneous dispersive media
We introduce a real-space technique able to extend the standard Hopfield
approach commonly used in quantum polaritonics to the case of inhomogeneous
lossless materials interacting with the electromagnetic field. We derive the
creation and annihilation polaritonic operators for the system normal modes as
linear, space-dependent superpositions of the microscopic light and matter
fields, and we invert the Hopfield transformation expressing the microscopic
fields as functions of the polaritonic operators. As an example, we apply our
approach to the case of a planar interface between vacuum and a polar
dielectric, showing how we can consistently treat both propagative and surface
modes, and express their nonlinear interactions, arising from phonon
anharmonicity, as polaritonic scattering terms. We also show that our theory
can be naturally extended to the case of dissipative materials
Theoretical Investigation of Phonon Polaritons in SiC Micropillar Resonators
Of late there has been a surge of interest in localised phonon polariton
resonators which allow for sub-diffraction confinement of light in the
mid-infrared spectral region by coupling to optical phonons at the surface of
polar dielectrics. Resonators are generally etched on deep substrates which
support propagative surface phonon polariton resonances. Recent experimental
work has shown that understanding the coupling between localised and
propagative surface phonon polaritons in these systems is vital to correctly
describe the system resonances. In this paper we comprehensively investigate
resonators composed of arrays of cylindrical SiC resonators on SiC substrates.
Our bottom-up approach, starting from the resonances of single, free standing
cylinders and isolated substrates, and exploiting both numerical and analytical
techniques, allows us to develop a consistent understanding of the parameter
space of those resonators, putting on firmer ground this blossoming technology.Comment: 10 Pages, 8 Figure
Variations of the Lifshitz-van der Waals force between metals immersed in liquids
We present a theoretical calculation of the Lifshitz-van der Waals force
between two metallic slabs embedded in a fluid, taking into account the change
of the Drude parameters of the metals when in contact with liquids of different
index of refraction. For the three liquids considered in this work, water,
and the change in the Drude parameters of the metal imply a
difference of up to 15% in the determination of the force at short separations.
These variations in the force is bigger for liquids with a higher index of
refraction.Comment: 2 figures, 1 tabl
Superconductivity in striped and multi-Fermi-surface Hubbard models: From the cuprates to the pnictides
Single- and multi-band Hubbard models have been found to describe many of the
complex phenomena that are observed in the cuprate and iron-based
high-temperature superconductors. Simulations of these models therefore provide
an ideal framework to study and understand the superconducting properties of
these systems and the mechanisms responsible for them. Here we review recent
dynamic cluster quantum Monte Carlo simulations of these models, which provide
an unbiased view of the leading correlations in the system. In particular, we
discuss what these simulations tell us about superconductivity in the
homogeneous 2D single-orbital Hubbard model, and how charge stripes affect this
behavior. We then describe recent simulations of a bilayer Hubbard model, which
provides a simple model to study the type and nature of pairing in systems with
multiple Fermi surfaces such as the iron-based superconductors.Comment: Published as part of Superstripes 2011 (Rome) conference proceeding
Radiofrequency spectroscopy of Li p-wave molecules: towards photoemission spectroscopy of a p-wave superfluid
Understanding superfluidity with higher order partial waves is crucial for
the understanding of high- superconductivity. For the realization of a
superfluid with anisotropic order parameter, spin-polarized fermionic lithium
atoms with strong p-wave interaction are the most promising candidates to date.
We apply rf-spectroscopy techniques that do not suffer from severe final-state
effects \cite{Perali08} with the goal to perform photoemission spectroscopy on
a strongly interacting p-wave Fermi gas similar to that recently applied for
s-wave interactions \cite{Stewart08}. Radiofrequency spectra of both quasibound
p-wave molecules and free atoms in the vicinity of the p-wave Feshbach
resonance located at 159.15\,G \cite{Schunck05} are presented. The observed
relative tunings of the molecular and atomic signals in the spectra with
magnetic field confirm earlier measurements realized with direct rf-association
\cite{Fuchs08}. Furthermore, evidence of bound molecule production using
adiabatic ramps is shown. A scheme to observe anisotropic superfluid gaps, the
most direct proof of p-wave superfluidity, with 1d-optical lattices is
proposed.Comment: 5 pages, 3 figure
Signatures of the term in ultrastrongly-coupled oscillators
We study a bosonic matter excitation coupled to a single-mode cavity field
via electric dipole. Counter-rotating and terms are included in the
interaction model, being the vector potential of the cavity
field. In the ultrastrong coupling regime the vacuum of the bare modes is no
longer the ground state of the Hamiltonian and contains a nonzero population of
polaritons, the true normal modes of the system. If the parameters of the model
satisfy the Thomas-Reiche-Kuhn sum rule, we find that the two polaritons are
always equally populated. We show how this prediction could be tested in a
quenching experiment, by rapidly switching on the coupling and analyzing the
radiation emitted by the cavity. A refinement of the model based on a
microscopic minimal coupling Hamiltonian is also provided, and its consequences
on our results are characterized analytically.Comment: 11 pages, 5 figure
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