950 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
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
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
Chaos and plasticity in superconductor vortices: a low-dimensional dynamics
We present new results of numerical simulations for driven vortex lattices in
presence of random disorder at zero temperature. We show that the plastic
dynamics of vortices display dissipative chaos. Intermittency "routes to chaos"
have been clearly identified below the differential resistance peak. The peak
region is characterized by positive Lyapunov exponents characteristic of chaos,
and low frequency broad-band noise. Furthermore we find a low fractal dimension
of the strange attractor, which suggests that only a few dynamical variables
are sufficient to model the complex plastic dynamics of vortices.Comment: 8 pages, 6 figures, accepted for publication in The Physical Review
Regression analysis with missing data and unknown colored noise: application to the MICROSCOPE space mission
The analysis of physical measurements often copes with highly correlated
noises and interruptions caused by outliers, saturation events or transmission
losses. We assess the impact of missing data on the performance of linear
regression analysis involving the fit of modeled or measured time series. We
show that data gaps can significantly alter the precision of the regression
parameter estimation in the presence of colored noise, due to the frequency
leakage of the noise power. We present a regression method which cancels this
effect and estimates the parameters of interest with a precision comparable to
the complete data case, even if the noise power spectral density (PSD) is not
known a priori. The method is based on an autoregressive (AR) fit of the noise,
which allows us to build an approximate generalized least squares estimator
approaching the minimal variance bound. The method, which can be applied to any
similar data processing, is tested on simulated measurements of the MICROSCOPE
space mission, whose goal is to test the Weak Equivalence Principle (WEP) with
a precision of . In this particular context the signal of interest is
the WEP violation signal expected to be found around a well defined frequency.
We test our method with different gap patterns and noise of known PSD and find
that the results agree with the mission requirements, decreasing the
uncertainty by a factor 60 with respect to ordinary least squares methods. We
show that it also provides a test of significance to assess the uncertainty of
the measurement.Comment: 12 pages, 4 figures, to be published in Phys. Rev.
Multidimensional solitons in a low-dimensional periodic potential
Using the variational approximation(VA) and direct simulations, we find
stable 2D and 3D solitons in the self-attractive Gross-Pitaevskii equation
(GPE) with a potential which is uniform in one direction () and periodic in
the others (but the quasi-1D potentials cannot stabilize 3D solitons). The
family of solitons includes single- and multi-peaked ones. The results apply to
Bose-Einstein condensates (BECs) in optical lattices (OLs), and to spatial or
spatiotemporal solitons in layered optical media. This is the first prediction
of {\em mobile} 2D and 3D solitons in BECs, as they keep mobility along .
Head-on collisions of in-phase solitons lead to their fusion into a collapsing
pulse. Solitons colliding in adjacent OL-induced channels may form a bound
state (BS), which then relaxes to a stable asymmetric form. An initially
unstable soliton splits into a three-soliton BS. Localized states in the
self-repulsive GPE with the low-dimensional OL are found too.Comment: 4 pages, 5 figure
The fundamental solution of the unidirectional pulse propagation equation
The fundamental solution of a variant of the three-dimensional wave equation
known as "unidirectional pulse propagation equation" (UPPE) and its paraxial
approximation is obtained. It is shown that the fundamental solution can be
presented as a projection of a fundamental solution of the wave equation to
some functional subspace. We discuss the degree of equivalence of the UPPE and
the wave equation in this respect. In particular, we show that the UPPE, in
contrast to the common belief, describes wave propagation in both longitudinal
and temporal directions, and, thereby, its fundamental solution possesses a
non-causal character.Comment: accepted to J. Math. Phy
Subcritical transition to turbulence in plane Couette flow
International audienceThe transition to turbulence in plane Couette flow was studied experimentally. The subcritical aspect of this transition is revealed by the stable coexistence of laminar and turbulent domains. By perturbing the flow, a critical Reynolds number has been determined, above which an artificially triggered turbulent spot can persist. The study of the spatiotemporal evolution of these spots shows, among other things, the existence of waves traveling away from the turbulent regions
Dynamic Modes of Microcapsules in Steady Shear Flow: Effects of Bending and Shear Elasticities
The dynamics of microcapsules in steady shear flow was studied using a
theoretical approach based on three variables: The Taylor deformation parameter
, the inclination angle , and the phase angle of
the membrane rotation. It is found that the dynamic phase diagram shows a
remarkable change with an increase in the ratio of the membrane shear and
bending elasticities. A fluid vesicle (no shear elasticity) exhibits three
dynamic modes: (i) Tank-treading (TT) at low viscosity of
internal fluid ( and relaxes to constant values), (ii)
Tumbling (TB) at high ( rotates), and (iii) Swinging
(SW) at middle and high shear rate (
oscillates). All of three modes are accompanied by a membrane ()
rotation. For microcapsules with low shear elasticity, the TB phase with no
rotation and the coexistence phase of SW and TB motions are induced by
the energy barrier of rotation. Synchronization of rotation with
TB rotation or SW oscillation occurs with integer ratios of rotational
frequencies. At high shear elasticity, where a saddle point in the energy
potential disappears, intermediate phases vanish, and either or
rotation occurs. This phase behavior agrees with recent simulation results of
microcapsules with low bending elasticity.Comment: 11 pages, 14 figure
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