Efficiency of the Wang-Landau algorithm: a simple test case

We analyze the efficiency of the Wang-Landau algorithm to sample a multimodal distribution on a prototypical simple test case. We show that the exit time from a metastable state is much smaller for the Wang Landau dynamics than for the original standard Metropolis-Hastings algorithm, in some asymptotic regime. Our results are confirmed by numerical experiments on a more realistic test case

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

Preprototype nitrogen supply subsystem development

The design and development of a test stand for the Nitrogen Generation Module (NGM) and a series of tests which verified its operation and performance capability are described. Over 900 hours of parametric testing were achieved. The results from this testing were then used to design an advanced NGM and a self contained, preprototype Nitrogen Supply Subsystem. The NGM consists of three major components: nitrogen generation module, pressure controller and hydrazine storage tank and ancillary components. The most important improvement is the elimination of all sealing surfaces, achieved with a total welded or brazed construction. Additionally, performance was improved by increasing hydrogen separating capability by 20% with no increase in overall packaging size

Cross-correlation Tomography: Measuring Dark Energy Evolution with Weak Lensing

A cross-correlation technique of lensing tomography is presented to measure the evolution of dark energy in the universe. The variation of the weak lensing shear with redshift around massive foreground objects like bright galaxies and clusters depends solely on ratios of angular diameter distances. Use of the massive foreground halos allow us to compare relatively high, linear shear values in the same part of the sky, thus largely eliminating the dominant source of systematic error in cosmological weak lensing measurements. The statistic we use does not rely on knowledge of the foreground mass distribution and is only shot-noise limited. We estimate the constraints that deep lensing surveys with photometric redshifts can provide on the dark energy density Omega, the equation of state parameter w and its redshift derivative w'. The accuracies on w and w' are: sigma(w) ~ 0.02 fsky^{-1/2} and sigma(w') ~ 0.05 fsky^{-1/2}, where fsky is the fraction of sky covered by the survey and sigma(Omega)=0.03 is assumed in the marginalization. Combining our cross-correlation method with standard lensing tomography, which has complementary degeneracies, will allow measurement of the dark energy parameters with significantly better accuracy.Comment: 5 pages, 2 figures, submitted to PRL. Error in shear signal corrected - parameter constraints about a factor of 2 wors