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 $j,m$ indices. Employing simulations of channel flows with Re$_\lambda\approx 70$ we demonstrate that different components characterized by different $j$ display different scaling exponents, but for a given $j$ these remain the same at different distances from the wall. The $j=0$ 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.