2,076 research outputs found
Network-wide assessment of 4D trajectory adjustments using an agent-based model
This paper presents results from the SESAR ER3 Domino project. It focuses on an ECAC-wide assessment of two 4D-adjustment mechanisms, implemented separately and conjointly. These reflect flight behaviour en-route and at-gate, optimising given (cost) objective functions. New metrics designed to capture network effects are used to analyse the results of a microscopic, agent based model. The results show that some implementations of the mechanisms allow the protection of the network from ‘domino’ effects. Airlines focusing on costs may trigger additional side-effects on passengers, displaying, in some instances, clear trade-offs between passenger- and flight-centric metrics
Inverse cascade in Charney-Hasegawa-Mima turbulence
The inverse energy cascade in Charney-Hasegawa-Mima turbulence is
investigated. Kolmogorov law for the third order velocity structure function is
shown to be independent on the Rossby number, at variance with the energy
spectrum, as shown by high resolution direct numerical simulations. In the
asymptotic limit of strong rotation, coherent vortices are observed to form at
a dynamical scale which slowly grows with time. These vortices form an almost
quenched pattern and induce strong deviation form Gaussianity in the velocity
field.Comment: 4 pages, 5 figure
Peripheral mixing of passive scalar at small Reynolds number
Mixing of a passive scalar in the peripheral region close to a wall is
investigated by means of accurate direct numerical simulations of both a
three-dimensional Couette channel flow at low Reynolds numbers and a
two-dimensional synthetic flow. In both cases, the resulting phenomenology can
be understood in terms of the theory recently developed by Lebedev and Turitsyn
[Phys. Rev. E 69, 036301, 2004]. Our results prove the robustness of the
identified mechanisms responsible for the persistency of scalar concentration
close to the wall with important consequences in completely different fields
ranging from microfluidic applications to environmental dispersion modeling.Comment: 4 pages, 5 figure
Strategic allocation of flight plans in air traffic management: an evolutionary point of view
We present a simplified model of the strategic allocation of trajectories in a generic airspace for commercial flights.
In this model, two types of companies, characterised by different cost functions and different strategies, compete for the allocation of trajectories in the airspace. With an analytical model and numerical simulations, we show that the relative advantage of the two populations -- companies -- depends on external factors like traffic demand as well as on the composition of the population. We show that there exists a stable equilibrium state which depends on the traffic demand. We also show that the equilibrium solution is not the optimal at the global level, but rather that it tends to favour one of the two business models -- the archetype for low-cost companies.
Finally, linking the cost of allocated flights with the fitness of a company, we study the evolutionary dynamics of the system, investigating the fluctuations of population composition around the equilibrium and the speed of convergence towards it. We prove that in the presence of noise due to finite populations, the equilibrium point is shifted and is reached more slowly
Large-scale confinement and small-scale clustering of floating particles in stratified turbulence
We study the motion of small inertial particles in stratified turbulence. We
derive a simplified model, valid within the Boussinesq approximation, for the
dynamics of small particles in presence of a mean linear density profile. By
means of extensive direct numerical simulations, we investigate the statistical
distribution of particles as a function of the two dimensionless parameters of
the problem. We find that vertical confinement of particles is mainly ruled by
the degree of stratification, with a weak dependency on the particle
properties. Conversely, small scale fractal clustering, typical of inertial
particles in turbulence, depends on the particle relaxation time and is almost
independent on the flow stratification. The implications of our findings for
the formation of thin phytoplankton layers are discussed.Comment: 5 pages, 6 figure
Networks of equities in financial markets
We review the recent approach of correlation based networks of financial
equities. We investigate portfolio of stocks at different time horizons,
financial indices and volatility time series and we show that meaningful
economic information can be extracted from noise dressed correlation matrices.
We show that the method can be used to falsify widespread market models by
directly comparing the topological properties of networks of real and
artificial markets.Comment: 9 pages, 8 figures. Accepted for publication in EPJ
Nonlinear diffusion model for Rayleigh-Taylor mixing
The complex evolution of turbulent mixing in Rayleigh-Taylor convection is
studied in terms of eddy diffusiviy models for the mean temperature profile. It
is found that a non-linear model, derived within the general framework of
Prandtl mixing theory, reproduces accurately the evolution of turbulent
profiles obtained from numerical simulations. Our model allows to give very
precise predictions for the turbulent heat flux and for the Nusselt number in
the ultimate state regime of thermal convection.Comment: 4 pages, 4 figure, PRL in pres
Point-particle method to compute diffusion-limited cellular uptake
We present an efficient point-particle approach to simulate
reaction-diffusion processes of spherical absorbing particles in the
diffusion-limited regime, as simple models of cellular uptake. The exact
solution for a single absorber is used to calibrate the method, linking the
numerical parameters to the physical particle radius and uptake rate. We study
configurations of multiple absorbers of increasing complexity to examine the
performance of the method, by comparing our simulations with available exact
analytical or numerical results. We demonstrate the potentiality of the method
in resolving the complex diffusive interactions, here quantified by the
Sherwood number, measuring the uptake rate in terms of that of isolated
absorbers. We implement the method in a pseudo-spectral solver that can be
generalized to include fluid motion and fluid-particle interactions. As a test
case of the presence of a flow, we consider the uptake rate by a particle in a
linear shear flow. Overall, our method represents a powerful and flexible
computational tool that can be employed to investigate many complex situations
in biology, chemistry and related sciences.Comment: 13 pages, 13 figure
Multifractal clustering of passive tracers on a surface flow
We study the anomalous scaling of the mass density measure of Lagrangian
tracers in a compressible flow realized on the free surface on top of a three
dimensional flow. The full two dimensional probability distribution of local
stretching rates is measured. The intermittency exponents which quantify the
fluctuations of the mass measure of tracers at small scales are calculated from
the large deviation form of stretching rate fluctuations. The results indicate
the existence of a critical exponent above which exponents
saturate, in agreement with what has been predicted by an analytically solvable
model. Direct evaluation of the multi-fractal dimensions by reconstructing the
coarse-grained particle density supports the results for low order moments.Comment: 7 pages, 4 figures, submitted to EP
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