A fast empirical method for galaxy shape measurements in weak lensing surveys

We describe a simple and fast method to correct ellipticity measurements of galaxies from the distortion by the instrumental and atmospheric point spread function (PSF), in view of weak lensing shear measurements. The method performs a classification of galaxies and associated PSFs according to measured shape parameters, and corrects the measured galaxy ellipticites by querying a large lookup table (LUT), built by supervised learning. We have applied this new method to the GREAT10 image analysis challenge, and present in this paper a refined solution that obtains the competitive quality factor of Q = 104, without any shear power spectrum denoising or training. Of particular interest is the efficiency of the method, with a processing time below 3 ms per galaxy on an ordinary CPU.Comment: 8 pages, 6 figures. Metric values updated according to the final GREAT10 analysis software (Kitching et al. 2012, MNRAS 423, 3163-3208), no qualitative changes. Associated code available at http://lastro.epfl.ch/megalu

Short-range force detection using optically-cooled levitated microspheres

We propose an experiment using optically trapped and cooled dielectric microspheres for the detection of short-range forces. The center-of-mass motion of a microsphere trapped in vacuum can experience extremely low dissipation and quality factors of $10^{12}$, leading to yoctonewton force sensitivity. Trapping the sphere in an optical field enables positioning at less than 1 $\mu$m from a surface, a regime where exotic new forces may exist. We expect that the proposed system could advance the search for non-Newtonian gravity forces via an enhanced sensitivity of $10^5-10^7$ over current experiments at the 1 $\mu$m length scale. Moreover, our system may be useful for characterizing other short-range physics such as Casimir forces.Comment: 4 pages, 3 figures, minor changes, Figs. 1 and 2 replace

Sparse Bayesian mass-mapping with uncertainties: hypothesis testing of structure

A crucial aspect of mass-mapping, via weak lensing, is quantification of the uncertainty introduced during the reconstruction process. Properly accounting for these errors has been largely ignored to date. We present results from a new method that reconstructs maximum a posteriori (MAP) convergence maps by formulating an unconstrained Bayesian inference problem with Laplace-type $\ell_1$-norm sparsity-promoting priors, which we solve via convex optimization. Approaching mass-mapping in this manner allows us to exploit recent developments in probability concentration theory to infer theoretically conservative uncertainties for our MAP reconstructions, without relying on assumptions of Gaussianity. For the first time these methods allow us to perform hypothesis testing of structure, from which it is possible to distinguish between physical objects and artifacts of the reconstruction. Here we present this new formalism, demonstrate the method on illustrative examples, before applying the developed formalism to two observational datasets of the Abel-520 cluster. In our Bayesian framework it is found that neither Abel-520 dataset can conclusively determine the physicality of individual local massive substructure at significant confidence. However, in both cases the recovered MAP estimators are consistent with both sets of data

Weak lensing analysis in three dimensions

We present a comprehensive full-sky 3-dimensional analysis of the weak-lensing fields and their corresponding power spectra. Using the formalism of spin-weight spherical harmonics and spherical Bessel functions, we relate the two-point statistics of the harmonic expansion coefficients of the weak lensing shear and convergence to the power spectrum of the matter density perturbations, and derive small-angle limits. Such a study is relevant in view of the next generation of large-scale weak lensing surveys which will provide distance information about the sources through photometric redshifts. This opens up the possibility of accurate cosmological parameter estimation via weak lensing, with an emphasis on the equation of state of dark energy.Comment: 23 pages, 4 figures, accepted by Phys.Rev.D; replaced with revised version, minor corrections, all figures done with better samplin

Optimal strategies : theoretical approaches to the parametrization of the dark energy equation of state

The absence of compelling theoretical model requires the parameterizing the dark energy to probe its properties. The parametrization of the equation of state of the dark energy is a common method. We explore the theoretical optimization of the parametrization based on the Fisher information matrix. As a suitable parametrization, it should be stable at high redshift and should produce the determinant of the Fisher matrix as large as possible. For the illustration, we propose one parametrization which can satisfy both criteria. By using the proper parametrization, we can improve the constraints on the dark energy even for the same data. We also show the weakness of the so-called principal component analysis method.Comment: 7pages, 11 figures, 2 tables, To match the version accepted by AS

Sparse Bayesian mass-mapping using trans-dimensional MCMC

Uncertainty quantification is a crucial step of cosmological mass-mapping that is often ignored. Suggested methods are typically only approximate or make strong assumptions of Gaussianity of the shear field. Probabilistic sampling methods, such as Markov chain Monte Carlo (MCMC), draw samples form a probability distribution, allowing for full and flexible uncertainty quantification, however these methods are notoriously slow and struggle in the high-dimensional parameter spaces of imaging problems. In this work we use, for the first time, a trans-dimensional MCMC sampler for mass-mapping, promoting sparsity in a wavelet basis. This sampler gradually grows the parameter space as required by the data, exploiting the extremely sparse nature of mass maps in wavelet space. The wavelet coefficients are arranged in a tree-like structure, which adds finer scale detail as the parameter space grows. We demonstrate the trans-dimensional sampler on galaxy cluster-scale images where the planar modelling approximation is valid. In high-resolution experiments, this method produces naturally parsimonious solutions, requiring less than 1% of the potential maximum number of wavelet coefficients and still producing a good fit to the observed data. In the presence of noisy data, trans-dimensional MCMC produces a better reconstruction of mass-maps than the standard smoothed Kaiser-Squires method, with the addition that uncertainties are fully quantified. This opens up the possibility for new mass maps and inferences about the nature of dark matter using the new high-resolution data from upcoming weak lensing surveys such as Euclid

Dinosaur tracks in Triassic Molteno sediments: the earliest evidence of dinosaurs in South Africa?

A fossil tracksite containing well-preserved tridactyl footprints of bipedal theropod dinosaurs is reported from fluvial overbank deposits of Molteno age (Stormberg Group: Triassic) in the northeastern Cape Province, South Africa. They occur stratigraphically below the mudrocks of the Elliot Formation, in which dinosaur remains are comparatively common, and are taken to represent the earliest evidence for dinosaurs in South Africa. They also represent the earliest unequivocal evidence of tetrapods in Molteno deposits.Foundation for Research Development; Trustees of the Port Elizabeth Museu

Fibrin independent proinflammatory effects of tissuefactor in experimental crescentic glomerulonephritis

Fibrin independent proinflammatory effects of tissue factor in experimental crescentic glomerulonephritis.BackgroundTissue factor initiated glomerular fibrin deposition is an important mediator of injury in crescentic glomerulonephritis. Recent data have suggested noncoagulant roles for tissue factor in inflammation.MethodsTo test the hypothesis that in addition to its effects in initiating coagulation, tissue factor has proinflammatory effects in glomerulonephritis, rabbits given crescentic anti-glomerular basement membrane (GBM) antibody–induced glomerulonephritis were defibrinogenated with ancrod. One group of defibrinogenated rabbits was also given anti-tissue factor antibodies. Comparisons were made between these groups, as well as a third group that was neither defibrinogenated with ancrod nor given anti-tissue factor antibodies.ResultsDefibrinogenation alone abolished glomerular fibrin deposition, reduced crescent formation, and limited renal impairment (ancrod-treated, serum creatinine 274 ± 37 μmol/L; untreated 415 ± 51 μmol/L; P < 0.01). Tissue factor inhibition in defibrinogenated rabbits resulted in further protection of renal function (creatinine 140 ± 19 μmol/L, P < 0.01) and reduced proteinuria (0.4 ± 0.2g/day, untreated 2.6 ± 0.4 g/day, P <0.01), which was significantly increased by defibrinogenation alone (ancrod-treated, 5.6 ± 1.2 g/day). Anti-tissue factor antibodies (but not defibrinogenation alone) attenuated glomerular T-cell and macrophage recruitment, and major histocompatibility complex (MHC) class II expression.ConclusionThese results demonstrate important proinflammatory effects of tissue factor in crescentic glomerulonephritis that are fibrin independent and provide in vivo evidence for tissue factor's proinflammatory effects on MHC class II expression and leukocyte accumulation