98 research outputs found
Continuous quantum measurement of a Bose-Einstein condensate: a stochastic Gross-Pitaevskii equation
We analyze the dynamics of a Bose-Einstein condensate undergoing a continuous
dispersive imaging by using a Lindblad operator formalism. Continuous strong
measurements drive the condensate out of the coherent state description assumed
within the Gross-Pitaevskii mean-field approach. Continuous weak measurements
allow instead to replace, for timescales short enough, the exact problem with
its mean-field approximation through a stochastic analogue of the
Gross-Pitaevskii equation. The latter is used to show the unwinding of a dark
soliton undergoing a continuous imaging.Comment: 13 pages, 10 figure
Non-decoupling Effects of Heavy Particles in Triple Gauge Boson Vertices
Non-decoupling effects of heavy particles present in beyond-the-standard
models are studied for the triple gauge boson vertices and
. We show from a general argument that the non-decoupling effects
are described by four independent parameters, in comparison with the three
parameters , and in the oblique corrections. These four parameters
of the effective triple gauge boson vertices are computed in two
beyond-the-standard models. We also study the relation of the four parameters
to the , , parameters, relying on an operator analysis.Comment: 13 pages, plain tex using PHYZZX macropackag
Immersed boundary-finite element model of fluid-structure interaction in the aortic root
It has long been recognized that aortic root elasticity helps to ensure
efficient aortic valve closure, but our understanding of the functional
importance of the elasticity and geometry of the aortic root continues to
evolve as increasingly detailed in vivo imaging data become available. Herein,
we describe fluid-structure interaction models of the aortic root, including
the aortic valve leaflets, the sinuses of Valsalva, the aortic annulus, and the
sinotubular junction, that employ a version of Peskin's immersed boundary (IB)
method with a finite element (FE) description of the structural elasticity. We
develop both an idealized model of the root with three-fold symmetry of the
aortic sinuses and valve leaflets, and a more realistic model that accounts for
the differences in the sizes of the left, right, and noncoronary sinuses and
corresponding valve cusps. As in earlier work, we use fiber-based models of the
valve leaflets, but this study extends earlier IB models of the aortic root by
employing incompressible hyperelastic models of the mechanics of the sinuses
and ascending aorta using a constitutive law fit to experimental data from
human aortic root tissue. In vivo pressure loading is accounted for by a
backwards displacement method that determines the unloaded configurations of
the root models. Our models yield realistic cardiac output at physiological
pressures, with low transvalvular pressure differences during forward flow,
minimal regurgitation during valve closure, and realistic pressure loads when
the valve is closed during diastole. Further, results from high-resolution
computations demonstrate that IB models of the aortic valve are able to produce
essentially grid-converged dynamics at practical grid spacings for the
high-Reynolds number flows of the aortic root
A Finite-Volume Method for Convection Problems with Embedded Moving-Boundaries
htmlabstractAn accurate method, using a novel immersed-boundary approach, is presented for numerically solving linear, scalar convection problems. Moving interior boundary conditions are embedded in the fixed-grid fluxes in the direct neighborhood of the moving boundaries. Tailor-made limiters are derived such that the resulting scheme is monotone. The results obtained are very accurate, without requiring much computational overhead. It is anticipated that the method can readily be extended to real fluid-flow equations
Parallel, Adaptive Grid Computing of Multiphase Flows in Spacecraft Fuel Tanks
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97138/1/AIAA2012-761.pd
From Euclidean to Minkowski space with the Cauchy-Riemann equations
We present an elementary method to obtain Green's functions in
non-perturbative quantum field theory in Minkowski space from calculated
Green's functions in Euclidean space. Since in non-perturbative field theory
the analytical structure of amplitudes is many times unknown, especially in the
presence of confined fields, dispersive representations suffer from systematic
uncertainties. Therefore we suggest to use the Cauchy-Riemann equations, that
perform the analytical continuation without assuming global information on the
function in the entire complex plane, only in the region through which the
equations are solved. We use as example the quark propagator in Landau gauge
Quantum Chromodynamics, that is known from lattice and Dyson-Schwinger studies
in Euclidean space. The drawback of the method is the instability of the
Cauchy-Riemann equations to high-frequency noise, that makes difficult to
achieve good accuracy. We also point out a few curiosities related to the Wick
rotation.Comment: 12 pages in EPJ double-column format, 16 figures. This version: added
paragraph, two reference
Constraints on Masses of Charged PGBs in Technicolor Model from Decay
In this paper we calculate the contributions to the branching ratio of from the charged Pseudo-Goldstone bosons appeared in one generation
Technicolor model. The current experimental results can eliminate large
part of the parameter space in the plane, and
specifically, one can put a strong lower bound on the masses of color octet
charged PGBs : at for free
.Comment: 9 pages, 3 figures(uuencoded), Minor changes(Type error), to appear
in Phys. Rev.
Pattern selection in a lattice of pulse-coupled oscillators
We study spatio-temporal pattern formation in a ring of N oscillators with
inhibitory unidirectional pulselike interactions. The attractors of the
dynamics are limit cycles where each oscillator fires once and only once. Since
some of these limit cycles lead to the same pattern, we introduce the concept
of pattern degeneracy to take it into account. Moreover, we give a qualitative
estimation of the volume of the basin of attraction of each pattern by means of
some probabilistic arguments and pattern degeneracy, and show how are they
modified as we change the value of the coupling strength. In the limit of small
coupling, our estimative formula gives a perfect agreement with numerical
simulations.Comment: 7 pages, 8 figures. To be published in Physical Review
Brane fluctuation and the electroweak chiral Lagrangian
We use the external field method to study the electroweak chiral Lagrangian
of the extra dimension model with brane fluctuation. Under the assumption that
the contact terms between the matters of the standard model and KK excitations
are heavily suppressed, we use the standard procedure to integrate out the
quantum fields of KK excitations and the equation of motion to eliminate the
classic fields of KK excitations. At one-loop level, we find that up to the
order , due to the momentum conservation of the fifth dimension and the
gauge symmetry of the zero modes, there is no constraint on the size of extra
dimension. This result is consistent with the decoupling theorem. However,
meaningful constraints can come from those operators in , which can
contribute considerably to some anomalous vector couplings and can be
accessible in the LC and LHC.Comment: Revised version, 20 pages in ReVTeX, to appear in PR
Force and Motion Generation of Molecular Motors: A Generic Description
We review the properties of biological motor proteins which move along linear
filaments that are polar and periodic. The physics of the operation of such
motors can be described by simple stochastic models which are coupled to a
chemical reaction. We analyze the essential features of force and motion
generation and discuss the general properties of single motors in the framework
of two-state models. Systems which contain large numbers of motors such as
muscles and flagella motivate the study of many interacting motors within the
framework of simple models. In this case, collective effects can lead to new
types of behaviors such as dynamic instabilities of the steady states and
oscillatory motion.Comment: 29 pages, 9 figure
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