38 research outputs found
Trapped Modes in Linear Quantum Stochastic Networks with Delays
Networks of open quantum systems with feedback have become an active area of
research for applications such as quantum control, quantum communication and
coherent information processing. A canonical formalism for the interconnection
of open quantum systems using quantum stochastic differential equations (QSDEs)
has been developed by Gough, James and co-workers and has been used to develop
practical modeling approaches for complex quantum optical, microwave and
optomechanical circuits/networks. In this paper we fill a significant gap in
existing methodology by showing how trapped modes resulting from feedback via
coupled channels with finite propagation delays can be identified
systematically in a given passive linear network. Our method is based on the
Blaschke-Potapov multiplicative factorization theorem for inner matrix-valued
functions, which has been applied in the past to analog electronic networks.
Our results provide a basis for extending the Quantum Hardware Description
Language (QHDL) framework for automated quantum network model construction
(Tezak \textit{et al.} in Philos. Trans. R. Soc. A, Math. Phys. Eng. Sci.
370(1979):5270-5290, to efficiently treat scenarios in which each
interconnection of components has an associated signal propagation time delay
Systematic Stochastic Reduction of Inertial Fluid-Structure Interactions subject to Thermal Fluctuations
We present analysis for the reduction of an inertial description of
fluid-structure interactions subject to thermal fluctuations. We show how the
viscous coupling between the immersed structures and the fluid can be
simplified in the regime where this coupling becomes increasingly strong. Many
descriptions in fluid mechanics and in the formulation of computational methods
account for fluid-structure interactions through viscous drag terms to transfer
momentum from the fluid to immersed structures. In the inertial regime, this
coupling often introduces a prohibitively small time-scale into the temporal
dynamics of the fluid-structure system. This is further exacerbated in the
presence of thermal fluctuations. We discuss here a systematic reduction
technique for the full inertial equations to obtain a simplified description
where this coupling term is eliminated. This approach also accounts for the
effective stochastic equations for the fluid-structure dynamics. The analysis
is based on use of the Infinitesmal Generator of the SPDEs and a singular
perturbation analysis of the Backward Kolomogorov PDEs. We also discuss the
physical motivations and interpretation of the obtained reduced description of
the fluid-structure system. Working paper currently under revision. Please
report any comments or issues to [email protected]: 19 pages, 1 figure. arXiv admin note: substantial text overlap with
arXiv:1009.564
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Stochastic Reductions for Inertial Fluid-Structure Interactions Subject to Thermal Fluctuations
We present analysis for the reduction of an inertial description of
fluid-structure interactions subject to thermal fluctuations. We show how the
viscous coupling between the immersed structures and the fluid can be
simplified in the regime where this coupling becomes increasingly strong. Many
descriptions in fluid mechanics and in the formulation of computational methods
account for fluid-structure interactions through viscous drag terms to transfer
momentum from the fluid to immersed structures. In the inertial regime, this
coupling often introduces a prohibitively small time-scale into the temporal
dynamics of the fluid-structure system. This is further exacerbated in the
presence of thermal fluctuations. We discuss here a systematic reduction
technique for the full inertial equations to obtain a simplified description
where this coupling term is eliminated. This approach also accounts for the
effective stochastic equations for the fluid-structure dynamics. The analysis
is based on use of the Infinitesmal Generator of the SPDEs and a singular
perturbation analysis of the Backward Kolomogorov PDEs. We also discuss the
physical motivations and interpretation of the obtained reduced description of
the fluid-structure system. Working paper currently under revision. Please
report any comments or issues to [email protected]
The First Three Rungs of the Cosmological Distance Ladder
It is straightforward to determine the size of the Earth and the distance to
the Moon without making use of a telescope. The methods have been known since
the 3rd century BC. However, few amateur or professional astronomers have
worked this out from data they themselves have taken. Here we use a gnomon to
determine the latitude and longitude of South Bend, Indiana, and College
Station, Texas, and determine a value of the radius of the Earth of 6290 km,
only 1.4 percent smaller than the true value. We use the method of Aristarchus
and the size of the Earth's shadow during the lunar eclipse of 2011 June 15 to
derive an estimate of the distance to the Moon (62.3 R_Earth), some 3.3 percent
greater than the true mean value. We use measurements of the angular motion of
the Moon against the background stars over the course of two nights, using a
simple cross staff device, to estimate the Moon's distance at perigee and
apogee. Finally, we use simultaneous CCD observations of asteroid 1996 HW1
obtained with small telescopes in Socorro, New Mexico, and Ojai, California, to
derive a value of the Astronomical Unit of (1.59 +/- 0.19) X 10^8 km, about 6
percent too large. The data and methods presented here can easily become part
of a beginning astronomy lab class.Comment: 34 pages, 11 figures, accepted for publication in American Journal of
Physic
WSES guidelines for management of Clostridium difficile infection in surgical patients
In the last two decades there have been dramatic changes in the epidemiology of Clostridium difficile infection (CDI), with increases in incidence and severity of disease in many countries worldwide. The incidence of CDI has also increased in surgical patients. Optimization of management of C difficile, has therefore become increasingly urgent. An international multidisciplinary panel of experts prepared evidenced-based World Society of Emergency Surgery (WSES) guidelines for management of CDI in surgical patients.Peer reviewe
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Stochastic Reductions for Inertial Fluid-Structure Interactions Subject to Thermal Fluctuations
We present analysis for the reduction of an inertial description of
fluid-structure interactions subject to thermal fluctuations. We show how the
viscous coupling between the immersed structures and the fluid can be
simplified in the regime where this coupling becomes increasingly strong. Many
descriptions in fluid mechanics and in the formulation of computational methods
account for fluid-structure interactions through viscous drag terms to transfer
momentum from the fluid to immersed structures. In the inertial regime, this
coupling often introduces a prohibitively small time-scale into the temporal
dynamics of the fluid-structure system. This is further exacerbated in the
presence of thermal fluctuations. We discuss here a systematic reduction
technique for the full inertial equations to obtain a simplified description
where this coupling term is eliminated. This approach also accounts for the
effective stochastic equations for the fluid-structure dynamics. The analysis
is based on use of the Infinitesmal Generator of the SPDEs and a singular
perturbation analysis of the Backward Kolomogorov PDEs. We also discuss the
physical motivations and interpretation of the obtained reduced description of
the fluid-structure system. Working paper currently under revision. Please
report any comments or issues to [email protected]