429 research outputs found
Disentangling Scaling Properties in Anisotropic and Inhomogeneous Turbulence
We address scaling in inhomogeneous and anisotropic turbulent flows by
decomposing structure functions into their irreducible representation of the
SO(3) symmetry group which are designated by indices. Employing
simulations of channel flows with Re we demonstrate that
different components characterized by different display different scaling
exponents, but for a given these remain the same at different distances
from the wall. The exponent agrees extremely well with high Re
measurements of the scaling exponents, demonstrating the vitality of the SO(3)
decomposition.Comment: 4 page
Turbulent Bubbly Flow
Turbulent bubbly flow is investigated by calculating and quantifying the motion and the action of microbubbles in homogeneous, isotropic and stationary turbulence. Direct numerical simulation is employed for the flow Navier-Stokes equations and Lagrangian tracking is used for computing the bubble trajectories. The forces acting on bubbles are fluid acceleration plus added mass effects, drag, lift and buoyancy. They are taken into account by a point-force model, which is reasonable for bubble Reynolds numbers of order 1, that correspond to microbubbles of diameter ~ 200µm in water (¿ ~ 10¿2cm2/s and g = 981cm/s2)
Modeling lithium rich carbon stars in the Large Magellanic Cloud: an independent distance indicator ?
We present the first quantitative results explaining the presence in the
Large Magellanic Cloud of some asymptotic giant branch stars that share the
properties of lithium rich carbon stars. A self-consistent description of
time-dependent mixing, overshooting, and nuclear burning was required. We
identify a narrow range of masses and luminosities for this peculiar stars.
Comparison of these models with the luminosities of the few Li-rich C stars in
the Large Magellanic Cloud provides an independent distance indicator for the
LMCComment: 7 pages, 2 figure
Using boundary methods to compute the Casimir energy
We discuss new approaches to compute numerically the Casimir interaction
energy for waveguides of arbitrary section, based on the boundary methods
traditionally used to compute eigenvalues of the 2D Helmholtz equation. These
methods are combined with the Cauchy's theorem in order to perform the sum over
modes. As an illustration, we describe a point-matching technique to compute
the vacuum energy for waveguides containing media with different
permittivities. We present explicit numerical evaluations for perfect
conducting surfaces in the case of concentric corrugated cylinders and a
circular cylinder inside an elliptic one.Comment: To be published in the Proceedings of QFEXT09, Norman, OK
Dynamical Casimir effect in superconducting circuits: a numerical approach
We present a numerical analysis of the particle creation for a quantum field
in the presence of time dependent boundary conditions. Having in mind recent
experiments involving superconducting circuits, we consider their description
in terms of a scalar field in a one dimensional cavity satisfying generalized
boundary conditions that involve a time-dependent linear combination of the
field and its spatial and time derivatives. We evaluate numerically the
Bogoliubov transformation between {\it in} and {\it out}-states and find that
the rate of particle production strongly depends on whether the spectrum of the
unperturbed cavity is equidistant or not, and also on the amplitude of the
temporal oscillations of the boundary conditions. We provide analytic
justifications for the different regimes found numerically.Comment: 20 pages. 11 figure
Decoherence induced by a fluctuating Aharonov-Casher phase
Dipoles interference is studied when atomic systems are coupled to classical
electromagnetic fields. The interaction between the dipoles and the classical
fields induces a time-varying Aharonov-Casher phase. Averaging over the phase
generates a suppression of fringe visibility in the interference pattern. We
show that, for suitable experimental conditions, the loss of contrast for
dipoles can be observable and almost as large as the corresponding one for
coherent electrons. We analyze different trajectories in order to show the
dependence of the decoherence factor with the velocity of the particles.Comment: 13 pages, 3 figures. To appear in Phys. Rev.
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