2,290 research outputs found
Limit theorems for some adaptive MCMC algorithms with subgeometric kernels: Part II
We prove a central limit theorem for a general class of adaptive Markov Chain
Monte Carlo algorithms driven by sub-geometrically ergodic Markov kernels. We
discuss in detail the special case of stochastic approximation. We use the
result to analyze the asymptotic behavior of an adaptive version of the
Metropolis Adjusted Langevin algorithm with a heavy tailed target density.Comment: 34 page
Accuracy of Tilt Rotor Hover Performance Predictions
The accuracy of various methods used to predict tilt rotor hover performance was established by comparing predictions with large-scale experimental data. A wide range of analytical approaches were examined. Blade lift was predicted with a lifting line analysis, two lifting surface analyses, and by a finite-difference solution of the full potential equation. Blade profile drag was predicted with two different types of airfoil tables and an integral boundary layer analysis. The inflow at the rotor was predicted using momentum theory, two types of prescribed wakes, and two free wake analyses. All of the analyses were accurate at moderate thrust coefficients. The accuracy of the analyses at high thrust coefficients was dependent upon their treatment of high sectional angles of attack on the inboard sections of the rotor blade. The analyses which allowed sectional lift coefficients on the inboard stations of the blade to exceed the maximum observed in two-dimensional wind tunnel tests provided better accuracy at high thrust coefficients than those which limited lift to the maximum two-dimensional value. These results provide tilt rotor aircraft designers guidance on which analytical approaches provide the best results, and the level of accuracy which can be expected from the best analyses
Collective excitations of a trapped Bose-Einstein condensate in the presence of a 1D optical lattice
We study low-lying collective modes of a horizontally elongated 87Rb
condensate produced in a 3D magnetic harmonic trap with the addition of a 1D
periodic potential which is provided by a laser standing-wave along the
horizontal axis. While the transverse breathing mode results unperturbed,
quadrupole and dipole oscillations along the optical lattice are strongly
modified. Precise measurements of the collective mode frequencies at different
height of the optical barriers provide a stringent test of the theoretical
model recently introduced [M.Kraemer et al. Phys. Rev. Lett. 88 180404 (2002)].Comment: 4 pages, 4 figure
Damping and frequency shift in the oscillations of two colliding Bose-Einstein condensates
We have investigated the center-of-mass oscillations of a Rb87 Bose-Einstein
condensate in an elongated magneto-static trap. We start from a trapped
condensate and we transfer part of the atoms to another trapped level, by
applying a radio-frequency pulse. The new condensate is produced far from its
equilibrium position in the magnetic potential, and periodically collides with
the parent condensate. We discuss how both the damping and the frequency shift
of the oscillations are affected by the mutual interaction between the two
condensates, in a wide range of trapping frequencies. The experimental data are
compared with the prediction of a mean-field model.Comment: 5 RevTex pages, 7 eps figure
Automatic detection of arcs and arclets formed by gravitational lensing
We present an algorithm developed particularly to detect gravitationally
lensed arcs in clusters of galaxies. This algorithm is suited for automated
surveys as well as individual arc detections. New methods are used for image
smoothing and source detection. The smoothing is performed by so-called
anisotropic diffusion, which maintains the shape of the arcs and does not
disperse them. The algorithm is much more efficient in detecting arcs than
other source finding algorithms and the detection by eye.Comment: A&A in press, 12 pages, 16 figure
MOND and Cosmology
I review various ideas on MOND cosmology and structure formation beginning
with non-relativistic models in analogy with Newtonian cosmology. I discuss
relativistic MOND cosmology in the context of Bekenstein's theory and propose
an alternative biscalar effective theory of MOND in which the acceleration
parameter is identified with the cosmic time derivative of a matter coupling
scalar field. Cosmic CDM appears in this theory as scalar field oscillations of
the auxiliary "coupling strength" field.Comment: 8 pages, LaTeX, 2 figures, to appear in proceedings of IAP05 in
Paris: Mass Profiles and Shapes of Cosmological Structures, G. Mamon, F.
Combes, C. Deffayet and B. Fort (eds), (EDP-Sciences 2005
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