10,165 research outputs found
Structure preserving schemes for mean-field equations of collective behavior
In this paper we consider the development of numerical schemes for mean-field
equations describing the collective behavior of a large group of interacting
agents. The schemes are based on a generalization of the classical Chang-Cooper
approach and are capable to preserve the main structural properties of the
systems, namely nonnegativity of the solution, physical conservation laws,
entropy dissipation and stationary solutions. In particular, the methods here
derived are second order accurate in transient regimes whereas they can reach
arbitrary accuracy asymptotically for large times. Several examples are
reported to show the generality of the approach.Comment: Proceedings of the XVI International Conference on Hyperbolic
Problem
Rotating Hele-Shaw cells with ferrofluids
We investigate the flow of two immiscible, viscous fluids in a rotating
Hele-Shaw cell, when one of the fluids is a ferrofluid and an external magnetic
field is applied. The interplay between centrifugal and magnetic forces in
determining the instability of the fluid-fluid interface is analyzed. The
linear stability analysis of the problem shows that a non-uniform, azimuthal
magnetic field, applied tangential to the cell, tends to stabilize the
interface. We verify that maximum growth rate selection of initial patterns is
influenced by the applied field, which tends to decrease the number of
interface ripples. We contrast these results with the situation in which a
uniform magnetic field is applied normally to the plane defined by the rotating
Hele-Shaw cell.Comment: 12 pages, 3 ps figures, RevTe
Uncertainty quantification for kinetic models in socio-economic and life sciences
Kinetic equations play a major rule in modeling large systems of interacting
particles. Recently the legacy of classical kinetic theory found novel
applications in socio-economic and life sciences, where processes characterized
by large groups of agents exhibit spontaneous emergence of social structures.
Well-known examples are the formation of clusters in opinion dynamics, the
appearance of inequalities in wealth distributions, flocking and milling
behaviors in swarming models, synchronization phenomena in biological systems
and lane formation in pedestrian traffic. The construction of kinetic models
describing the above processes, however, has to face the difficulty of the lack
of fundamental principles since physical forces are replaced by empirical
social forces. These empirical forces are typically constructed with the aim to
reproduce qualitatively the observed system behaviors, like the emergence of
social structures, and are at best known in terms of statistical information of
the modeling parameters. For this reason the presence of random inputs
characterizing the parameters uncertainty should be considered as an essential
feature in the modeling process. In this survey we introduce several examples
of such kinetic models, that are mathematically described by nonlinear Vlasov
and Fokker--Planck equations, and present different numerical approaches for
uncertainty quantification which preserve the main features of the kinetic
solution.Comment: To appear in "Uncertainty Quantification for Hyperbolic and Kinetic
Equations
A new approach to quantitative propagation of chaos for drift, diffusion and jump processes
This paper is devoted the the study of the mean field limit for many-particle
systems undergoing jump, drift or diffusion processes, as well as combinations
of them. The main results are quantitative estimates on the decay of
fluctuations around the deterministic limit and of correlations between
particles, as the number of particles goes to infinity. To this end we
introduce a general functional framework which reduces this question to the one
of proving a purely functional estimate on some abstract generator operators
(consistency estimate) together with fine stability estimates on the flow of
the limiting nonlinear equation (stability estimates). Then we apply this
method to a Boltzmann collision jump process (for Maxwell molecules), to a
McKean-Vlasov drift-diffusion process and to an inelastic Boltzmann collision
jump process with (stochastic) thermal bath. To our knowledge, our approach
yields the first such quantitative results for a combination of jump and
diffusion processes.Comment: v2 (55 pages): many improvements on the presentation, v3: correction
of a few typos, to appear In Probability Theory and Related Field
Performance of the Gas Gain Monitoring system of the CMS RPC muon detector and effective working point fine tuning
The Gas Gain Monitoring (GGM) system of the Resistive Plate Chamber (RPC)
muon detector in the Compact Muon Solenoid (CMS) experiment provides fast and
accurate determination of the stability in the working point conditions due to
gas mixture changes in the closed loop recirculation system. In 2011 the GGM
began to operate using a feedback algorithm to control the applied voltage, in
order to keep the GGM response insensitive to environmental temperature and
atmospheric pressure variations. Recent results are presented on the feedback
method used and on alternative algorithms
Tanaka Theorem for Inelastic Maxwell Models
We show that the Euclidean Wasserstein distance is contractive for inelastic
homogeneous Boltzmann kinetic equations in the Maxwellian approximation and its
associated Kac-like caricature. This property is as a generalization of the
Tanaka theorem to inelastic interactions. Consequences are drawn on the
asymptotic behavior of solutions in terms only of the Euclidean Wasserstein
distance
Vanishing magnetization relaxation in the high field quantum limit in YBa_2Cu_3O_(7-δ)
We have investigated the magnetic response of untwinned single crystals of YBa_2Cu_3O_(7-δ) at millikelvin temperatures using a Bi thin film magnetometer of micron dimensions. Below T=0.8 K, the magnetization relaxation rate S crosses over from thermally activated to quantum behavior. Above a sharply defined and strongly temperature-dependent threshold field, S disappears altogether. In concert with the vanishing magnetization relaxation, discrete steps appear in the magnetic hysteresis B(H), each of which corresponds to the `'stick-slip'' motion of 10^3 vortices under the magnetometer
Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18
Combining the precise parallaxes and optical photometry delivered by Gaia's
second data release (Gaia DR2) with the photometric catalogues of PanSTARRS-1,
2MASS, and AllWISE, we derive Bayesian stellar parameters, distances, and
extinctions for 265 million stars brighter than G=18. Because of the wide
wavelength range used, our results substantially improve the accuracy and
precision of previous extinction and effective temperature estimates. After
cleaning our results for both unreliable input and output data, we retain 137
million stars, for which we achieve a median precision of 5% in distance, 0.20
mag in V-band extinction, and 245 K in effective temperature for G<14,
degrading towards fainter magnitudes (12%, 0.20 mag, and 245 K at G=16; 16%,
0.23 mag, and 260 K at G=17, respectively). We find a very good agreement with
the asteroseismic surface gravities and distances of 7000 stars in the Kepler,
the K2-C3, and the K2-C6 fields, with stellar parameters from the APOGEE
survey, as well as with distances to star clusters. Our results are available
through the ADQL query interface of the Gaia mirror at the Leibniz-Institut
f\"{u}r Astrophysik Potsdam (gaia.aip.de) and as binary tables at data.aip.de.
As a first application, in this paper we provide distance- and
extinction-corrected colour-magnitude diagrams, extinction maps as a function
of distance, and extensive density maps, demonstrating the potential of our
value-added dataset for mapping the three-dimensional structure of our Galaxy.
In particular, we see a clear manifestation of the Galactic bar in the stellar
density distributions, an observation that can almost be considered a direct
imaging of the Galactic bar.Comment: 25 pages, 23 figures + appendix, accepted for publication in A&A.
Data (doi:10.17876/gaia/dr.2/51) are available through ADQL queries at
gaia.aip.d
CMS endcap RPC gas gap production for upgrade
The CMS experiment will install a RE4 layer of 144 new Resistive Plate Chambers (RPCs) on the existing york YE3 at both endcap regions to trigger high momentum muons from the proton-proton interaction. In this paper, we present the detailed procedures used in the production of new RPC gas gaps adopted in the CMS upgrade. Quality assurance is enforced as ways to maintain the same quality of RPC gas gaps as the existing 432 endcap RPC chambers that have been operational since the beginning of the LHC operation
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