1,627 research outputs found
Interpretation of the unpolarized azimuthal asymmetries in SIDIS
The measurement of azimuthal modulations in hadron leptoproduction on
unpolarized nucleons allows to get information on the intrinsic transverse
momentum of quarks in a nucleon through both the Cahn
effect and the Boer-Mulders function. We have compared the azimuthal
asymmetries in the cross section of muons scattered off an
unpolarised deuteron target as measured by COMPASS with a Monte Carlo program,
based on the model of quark anti-quark pair production at string
breaking, which accounts for the Cahn effect. Large differences have been
observed between data and Monte Carlo, in particular at large values of the
fraction of the longitudinal momentum of the fragmenting quark carried by the
produced hadron. We found out that most of these differences are due to pions
from exclusive vector mesons contaminating the SIDIS sample, which also exhibit
large azimuthal modulations. Using the measurements of the exclusive reaction
we had done in 2006, we can reproduce
reasonably well the observed differences. Subtracting the contribution of
hadrons produced in the decay of exclusive vector mesons from the SIDIS
unpolarised azimuthal asymmetries is therefore a prerequisite condition for
extracting and the Boer-Mulders function.Comment: to be published in the 23rd International Spin Physics Symposium
(SPIN2018) proceedings, 11 pages, 7 figure
Binary interaction algorithms for the simulation of flocking and swarming dynamics
Microscopic models of flocking and swarming takes in account large numbers of
interacting individ- uals. Numerical resolution of large flocks implies huge
computational costs. Typically for interacting individuals we have a cost
of . We tackle the problem numerically by considering approximated
binary interaction dynamics described by kinetic equations and simulating such
equations by suitable stochastic methods. This approach permits to compute
approximate solutions as functions of a small scaling parameter
at a reduced complexity of O(N) operations. Several numerical results show the
efficiency of the algorithms proposed
Boltzmann type control of opinion consensus through leaders
The study of formations and dynamics of opinions leading to the so called
opinion consensus is one of the most important areas in mathematical modeling
of social sciences. Following the Boltzmann type control recently introduced in
[G. Albi, M. Herty, L. Pareschi arXiv:1401.7798], we consider a group of
opinion leaders which modify their strategy accordingly to an objective
functional with the aim to achieve opinion consensus. The main feature of the
Boltzmann type control is that, thanks to an instantaneous binary control
formulation, it permits to embed the minimization of the cost functional into
the microscopic leaders interactions of the corresponding Boltzmann equation.
The related Fokker-Planck asymptotic limits are also derived which allow to
give explicit expressions of stationary solutions. The results demonstrate the
validity of the Boltzmann type control approach and the capability of the
leaders control to strategically lead the followers opinion
Kinetic description of optimal control problems and applications to opinion consensus
In this paper an optimal control problem for a large system of interacting
agents is considered using a kinetic perspective. As a prototype model we
analyze a microscopic model of opinion formation under constraints. For this
problem a Boltzmann-type equation based on a model predictive control
formulation is introduced and discussed. In particular, the receding horizon
strategy permits to embed the minimization of suitable cost functional into
binary particle interactions. The corresponding Fokker-Planck asymptotic limit
is also derived and explicit expressions of stationary solutions are given.
Several numerical results showing the robustness of the present approach are
finally reported.Comment: 25 pages, 18 figure
Linear multistep methods for optimal control problems and applications to hyperbolic relaxation systems
We are interested in high-order linear multistep schemes for time
discretization of adjoint equations arising within optimal control problems.
First we consider optimal control problems for ordinary differential equations
and show loss of accuracy for Adams-Moulton and Adams-Bashford methods, whereas
BDF methods preserve high--order accuracy. Subsequently we extend these results
to semi--lagrangian discretizations of hyperbolic relaxation systems.
Computational results illustrate theoretical findings
- …