60 research outputs found
Inverse kinetic theory for incompressible thermofluids
An interesting issue in fluid dynamics is represented by the possible
existence of inverse kinetic theories (IKT) which are able to deliver, in a
suitable sense, the complete set of fluid equations which are associated to a
prescribed fluid. From the mathematical viewpoint this involves the formal
description of a fluid by means of a classical dynamical system which advances
in time the relevant fluid fields. The possibility of defining an IKT for the
3D incompressible Navier-Stokes equations (INSE), recently investigated (Ellero
\textit{et al}, 2004-2007) raises the interesting question whether the theory
can be applied also to thermofluids, in such a way to satisfy also the second
principle of thermodynamics. The goal of this paper is to prove that such a
generalization is actually possible, by means of a suitable \textit{extended
phase-space formulation}. We consider, as a reference test, the case of
non-isentropic incompressible thermofluids, whose dynamics is described by the
Fourier and the incompressible Navier-Stokes equations, the latter subject to
the conditions of validity of the Boussinesq approximation.Comment: Contributed paper at RGD26 (Kyoto, Japan, July 2008
Generalized covariant gyrokinetic dynamics of magnetoplasmas
A basic prerequisite for the investigation of relativistic astrophysical
magnetoplasmas, occurring typically in the vicinity of massive stellar objects
(black holes, neutron stars, active galactic nuclei, etc.), is the accurate
description of single-particle covariant dynamics, based on gyrokinetic theory
(Beklemishev et al.,1999-2005). Provided radiation-reaction effects are
negligible, this is usually based on the assumption that both the space-time
metric and the EM fields (in particular the magnetic field) are suitably
prescribed and are considered independent of single-particle dynamics, while
allowing for the possible presence of gravitational/EM perturbations driven by
plasma collective interactions which may naturally arise in such systems. The
purpose of this work is the formulation of a generalized gyrokinetic theory
based on the synchronous variational principle recently pointed out (Tessarotto
et al., 2007) which permits to satisfy exactly the physical realizability
condition for the four-velocity. The theory here developed includes the
treatment of nonlinear perturbations (gravitational and/or EM) characterized
locally, i.e., in the rest frame of a test particle, by short wavelength and
high frequency. Basic feature of the approach is to ensure the validity of the
theory both for large and vanishing parallel electric field. It is shown that
the correct treatment of EM perturbations occurring in the presence of an
intense background magnetic field generally implies the appearance of
appropriate four-velocity corrections, which are essential for the description
of single-particle gyrokinetic dynamics.Comment: Contributed paper at RGD26 (Kyoto, Japan, July 2008
The exact radiation-reaction equation for a classical charged particle
An unsolved problem of classical mechanics and classical electrodynamics is
the search of the exact relativistic equations of motion for a classical
charged point-particle subject to the force produced by the action of its EM
self-field. The problem is related to the conjecture that for a classical
charged point-particle there should exist a relativistic equation of motion (RR
equation) which results both non-perturbative, in the sense that it does not
rely on a perturbative expansion on the electromagnetic field generated by the
charged particle and non-asymptotic, i.e., it does not depend on any
infinitesimal parameter. In this paper we intend to propose a novel solution to
this well known problem, and in particular to point out that the RR equation is
necessarily variational. The approach is based on two key elements: 1) the
adoption of the relativistic hybrid synchronous Hamilton variational principle
recently pointed out (Tessarotto et al, 2006). Its basic feature is that it can
be expressed in principle in terms of arbitrary "hybrid" variables (i.e.,
generally non-Lagrangian and non-Hamiltonian variables); 2) the variational
treatment of the EM self-field, taking into account the exact particle
dynamics.Comment: Contributed paper at RGD26 (Kyoto, Japan, July 2008
SPATIO TEMPORAL DATA CUBE APPLIED TO AIS CONTAINERSHIPS TREND ANALYSIS IN THE EARLY YEARS OF THE BELT AND ROAD INITIATIVE – FROM GLOBAL TO LOCAL SCALE
Maritime trade represents a significant part of all global import-export trade. The traffic of containerships can be monitored through Automatic Identification System (AIS), due to the fact that the International Maritime Organization (IMO) regulation requires AIS to be fitted aboard all ships of 300 gross tonnage and upwards engaged on international voyages. The approach proposed by the authors aimed to extract value added information from an AIS dataset, with a focus on maritime economy. Using an AIS dataset of global position of containerships from 01/01/2012 to 31/12/2016, the paper focuses on space-time data cube creation and analysis for a better understanding of maritime trades trends. Data cube creation has been tested at different spatio-temporal bins dimension and on different specific topics (TEU classes, alliances, chokepoints and port areas), analysing the sensitivity on trend results, and highlighting how appropriate spatio-temporal bins dimensions are important to effectively highlight relevant trends. Results of the trend analysis are discussed and validated with the main data and information found over the period 2012–2016. The aim of this paper is to demonstrate the suitability of this approach applied to AIS data and to highlight its limitations. The authors can conclude that the approach used has proved to be adequate in describing the evolution of the global import-export trade
Generalized Grad-Shafranov equation for gravitational Hall-MHD equilibria
The consistent theoretical description of gravitational Hall-MHD (G-Hall-MHD)
equilibria is of fundamental importance for understanding the phenomenology of
accretion disks (AD) around compact objects (black holes, neutron stars, etc.).
The very existence of these equilibria is actually suggested by observations,
which show evidence of quiescent, and essentially non-relativistic, AD plasmas
close to compact stars, thus indicating that accretion disks may be
characterized by slowly varying EM and fluid fields. These (EM) fields, in
particular the electric field, may locally be extremely intense, so that AD
plasmas are likely to be locally non-neutral and therefore characterized by the
presence of Hall currents. This suggests therefore that such equilibria should
be described in the framework of the Hall-MHD theory. Extending previous
approaches, holding for non-rotating plasmas or based on specialized
single-species model equilibria which ignore the effect of space-time
curvature, the purpose of this work is the formulation of a generalized
Grad-Shafranov (GGS) equation suitable for the investigation of G-Hall-MHD
equilibria in AD's where non-relativistic plasmas are present. For this purpose
the equilibria are assumed to be generated by a strong axisymmetric stellar
magnetic field and by the gravitating plasma characterizing the AD
Axisymmetric gravitational MHD equilibria in the presence of plasma rotation
In this paper, extending the investigation developed in an earlier paper
(Cremaschini et al., 2008), we pose the problem of the kinetic description of
gravitational Hall-MHD equilibria which may arise in accretion disks (AD)
plasmas close to compact objects. When intense EM and gravitational fields,
generated by the central object, are present, a convenient approach can be
achieved in the context of the Vlasov-Maxwell description. In this paper the
investigation is focused primarily on the following two aspects:
1) the formulation of the kinetic treatment of G-Hall-MHD equilibria. Based
on the identification of the relevant first integrals of motion, we show that
an explicit representation can be given for the equilibrium kinetic
distribution function. For each species this is represented as a superposition
of suitable generalized Maxwellian distributions;
2) the determination of the constraints to be placed on the fluid fields for
the existence of the kinetic equilibria. In particular, this permits a unique
determination of the functional form of the species number densities and of the
fluid partial pressures, in terms of suitably prescribed flux functions.Comment: Contributed paper at RGD26 (Kyoto, Japan, July 2008
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