1,505 research outputs found
Generalized Pearson distributions for charged particles interacting with an electric and/or a magnetic field
The linear Boltzmann equation for elastic and/or inelastic scattering is
applied to derive the distribution function of a spatially homogeneous system
of charged particles spreading in a host medium of two-level atoms and
subjected to external electric and/or magnetic fields. We construct a
Fokker-Planck approximation to the kinetic equations and derive the most
general class of distributions for the given problem by discussing in detail
some physically meaningful cases. The equivalence with the transport theory of
electrons in a phonon background is also discussed.Comment: 24 pages, version accepted on Physica
Inert states of spin-S systems
We present a simple but efficient geometrical method for determining the
inert states of spin-S systems. It can be used if the system is described by a
spin vector of a spin-S particle and its energy is invariant in spin rotations
and phase changes. Our method is applicable to an arbitrary S and it is based
on the representation of a pure spin state of a spin-S particle in terms of 2S
points on the surface of a sphere. We use this method to find candidates for
some of the ground states of spinor Bose-Einstein condensates.Comment: 4 pages, 2 figures, minor changes, references added, typos correcte
A simple test for hidden variables in spin-1 system
We resolve an old problem about the existence of hidden parameters in a
three-dimensional quantum system by constructing an appropriate Bell's type
inequality. This reveals a nonclassical nature of most spin- states. We
shortly discuss some physical implications and an underlying cause of this
nonclassical behavior, as well as a perspective of its experimental
verification.Comment: 4 pages, 1 figur
Nonadiabatic effects in the dynamics of atoms confined in a cylindric time-orbiting-potential magnetic trap
In a time-orbiting-potential magnetic trap the neutral atoms are confined by
means of an inhomogeneous magnetic field superimposed to an uniform rotating
one. We perform an analytic study of the atomic motion by taking into account
the nonadiabatic effects arising from the spin dynamics about the local
magnetic field. Geometric-like magnetic-fields determined by the Berry's phase
appear within the quantum description. The application of a variational
procedure on the original quantum equation leads to a set of dynamical
evolution equations for the quantum average value of the position operator and
of the spin variables. Within this approximation we derive the
quantum-mechanical ground state configuration matching the classical adiabatic
solution and perform some numerical simulations.Comment: 12 pages, 4 figure
Numerical modelling of ellipsoidal inclusions
Within the framework of numerical algorithms for the threedimensional
random packing of granular materials this work presents an
innovative formulation for polydispersed ellipsoidal particles, including
an overlapping detection algorithm for an optimized simulation of the
mesostructure of geomaterials, particularly concrete.
Granular composite cement-based materials can be so reconstructed with
adequate precision in terms of grain size distribution. Specifically, the
algorithm performance towards the assumed inclusion shape (ellipsoidal or
spheric) and degree of regularity (round or irregular) is here discussed.
Examples on real grading curves prove that this approach is effective.
The advantages of the proposed method for computational mechanics
purposes are also disclosed when properly interfaced with visualization
CAD (Computer Aided Design) tools
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