2,994 research outputs found
Richness-mass relation self-calibration for galaxy clusters
This work attains a threefold objective: first, we derived the richness-mass
scaling in the local Universe from data of 53 clusters with individual
measurements of mass. We found a 0.46+-0.12 slope and a 0.25+-0.03 dex scatter
measuring richness with a previously developed method. Second, we showed on a
real sample of 250 0.06<z<0.9 clusters, most of which are at z<0.3, with
spectroscopic redshift that the colour of the red sequence allows us to measure
the clusters' redshift to better than Delta z=0.02. Third, we computed the
predicted prior of the richness-mass scaling to forecast the capabilities of
future wide-field-area surveys of galaxy clusters to constrain cosmological
parameters. We computed the uncertainty and the covariance matrix of the
(evolving) richness-mass scaling of a PanStarrs 1+Euclid-like survey accounting
for a large suite of sources of errors. We find that the richness-mass scaling
parameters, which are the input ingredients of cosmological forecasts using
cluster counts, can be determined 10^5 times better than estimated in previous
works that did not use weak-lensing mass estimates. The better knowledge of the
scaling parameters likely has a strong impact on the relative importance of the
different probes used to constrain cosmological parameters. Richness-mass
scaling parameters were recovered, but only if the cluster mass function and
the weak-lensing redshift-dependent selection function were accounted for in
the fitting of the mass-richness scaling. This emphasizes the limitations of
often adopted simplifying assumptions, such as having a mass-complete
redshift-independent sample. The fitting code used for computing the predicted
prior, including the treatment of the mass function and of the weak-lensing
selection function, is provided in the appendix. [Abridged]Comment: A&A, in pres
Collapsing dynamics of attractive Bose-Einstein condensates
The self-similar collapse of 3D and quasi-2D atom condensates with negative
scattering length is examined. 3D condensates are shown to blow up following
the scenario of {\it weak collapse}: The inner core of the condensate diverges
with an almost zero particle number, while its tail distribution spreads out to
large distances with a constant density profile. For this case, the 3-body
recombination arrests the collapse, but it weakly dissipates the atoms. The
confining trap then reforms the condensate at later times. In contrast, 2D
condensates undergo a {\it strong collapse}: The atoms stay mainly located at
center and recombination sequentially absorbs a significant amount of
particles.Comment: 4 pages, submitted for publicatio
Chaotic dynamics of superconductor vortices in the plastic phase
We present numerical simulation results of driven vortex lattices in presence
of random disorder at zero temperature. We show that the plastic dynamics is
readily understood in the framework of chaos theory. Intermittency "routes to
chaos" have been clearly identified, and positive Lyapunov exponents and
broad-band noise, both characteristic of chaos, are found to coincide with the
differential resistance peak. Furthermore, the fractal dimension of the strange
attractor reveals that the chaotic dynamics of vortices is low-dimensional.Comment: 5 pages, 3 figures Accepted for publication in Physical Review
Letter
Fusion, collapse, and stationary bound states of incoherently coupled waves in bulk cubic media
We study the interaction between two localized waves that propagate in a bulk (two transverse dimensions) Kerr medium, while being incoherently coupled through cross-phase modulation. The different types of stationary solitary wave solutions are found and their stability is discussed. The results of numerical simulations suggest that the solitary waves are unstable. We derive sufficient conditions for when the wave function is bound to collapse or spread out, and we develop a theory to describe the regions of different dynamical behavior. For localized waves with the same center we confirm these sufficient conditions numerically and show that only when the equations and the initial conditions are symmetric are they also close to being necessary conditions. Using Gaussian initial conditions we predict and confirm numerically the power-dependent characteristic initial separations that divide the phase space into collapsing and diffracting solutions, and further divide each of these regions into subregions of coupled (fusion) and uncoupled dynamics. Finally we illustrate how, close to the threshold of collapse, the waves can cross several times before eventually collapsing or diffracting
An Ultra Fast Image Generator (UFig) for wide-field astronomy
Simulated wide-field images are becoming an important part of observational
astronomy, either to prepare for new surveys or to test measurement methods. In
order to efficiently explore vast parameter spaces, the computational speed of
simulation codes is a central requirement to their implementation. We introduce
the Ultra Fast Image Generator (UFig) which aims to bring wide-field imaging
simulations to the current limits of computational capabilities. We achieve
this goal through: (1) models of galaxies, stars and observational conditions,
which, while simple, capture the key features necessary for realistic
simulations, and (2) state-of-the-art computational and implementation
optimizations. We present the performances of UFig and show that it is faster
than existing public simulation codes by several orders of magnitude. It allows
us to produce images more quickly than SExtractor needs to analyze them. For
instance, it can simulate a typical 0.25 deg^2 Subaru SuprimeCam image (10k x
8k pixels) with a 5-sigma limiting magnitude of R=26 in 30 seconds on a laptop,
yielding an average simulation time for a galaxy of 30 microseconds. This code
is complementary to end-to-end simulation codes and can be used as a fast,
central component of observational methods relying on simulations.Comment: Submitted to Astronomy and Computing. 13 pages, 9 figure
Spatiotemporal perspective on the decay of turbulence in wall-bounded flows
Using a reduced model focusing on the in-plane dependence of plane Couette
flow, it is shown that the turbulent-to-laminar relaxation process can be
understood as a nucleation problem similar to that occurring at a thermodynamic
first-order phase transition. The approach, apt to deal with the large
extension of the system considered, challenges the current interpretation in
terms of chaotic transients typical of temporal chaos. The study of the
distribution of the sizes of laminar domains embedded in turbulent flow proves
that an abrupt transition from sustained spatiotemporal chaos to laminar flow
can take place at some given value of the Reynolds number R_{low}, whether or
not the local chaos lifetime, as envisioned within low-dimensional dynamical
systems theory, diverges at finite R beyond R_{low}.Comment: 9 pages, 3 figures, published in 2009 as a Rapid Communication in
Phys. Rev. E, vol. 79, article 025301, corrected to include erratum Phys.
Rev. E 79, 039904. References to now published material have been updated. A
note has been added pointing to recent related work by D. Barkley
(arXiv:1101.4125v1
Sessile Legionella pneumophila is able to grow on surfaces and generate structured monospecies biofilms
Currently, models for studying Legionella pneumophila biofilm formation rely on multi-species biofilms with low reproducibility or on growth in rich medium, where planktonic growth is unavoidable. The present study describes a new medium adapted to the growth of L. pneumophila monospecies biofilms in vitro. A microplate model was used to test several media. After incubation for 6 days in a specific biofilm broth not supporting planktonic growth, biofilms consisted of 5.36 ± 0.40 log (cfu cm−2) or 5.34 ± 0.33 log (gu cm−2). The adhered population remained stable for up to 3 weeks after initial inoculation. In situ confocal microscope observations revealed a typical biofilm structure, comprising cell clusters ranging up to 300 μm in height. This model is adapted to growing monospecies L. pneumophila biofilms that are structurally different from biofilms formed in a rich medium. High reproducibility and the absence of other microbial species make this model useful for studying genes involved in biofilm formation
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