83 research outputs found
The Quantum Galilei Group
The quantum Galilei group is defined. The bicrossproduct
structure of and the corresponding Lie algebra is revealed. The
projective representations for the two-dimensional quantum Galilei group are
constructed.Comment: AMSTe
Superintegrable models of Winternitz type
A general procedure is outlined which allows one to construct superintegrable
models of Winternitz type. Some examples are presented.Comment: 6 pages, LaTeX; To appear in Phys. Lett.
Global Symmetries of Noncommutative Space-time
The global counterpart of infinitesimal symmetries of noncommutative
space-time is discussed.Comment: 7 pages, no figures; minor changes in the bibliography; final version
accepted for publication in Phys. Rev.
Performance Evaluation of Road Traffic Control Using a Fuzzy Cellular Model
In this paper a method is proposed for performance evaluation of road traffic
control systems. The method is designed to be implemented in an on-line
simulation environment, which enables optimisation of adaptive traffic control
strategies. Performance measures are computed using a fuzzy cellular traffic
model, formulated as a hybrid system combining cellular automata and fuzzy
calculus. Experimental results show that the introduced method allows the
performance to be evaluated using imprecise traffic measurements. Moreover, the
fuzzy definitions of performance measures are convenient for uncertainty
determination in traffic control decisions.Comment: The final publication is available at http://www.springerlink.co
Proper holomorphic mappings between symmetrized ellipsoids
We characterize the existence of proper holomorphic mappings in the special
class of bounded -balanced domains in , called the
symmetrized ellipsoids. Using this result we conclude that there are no
non-trivial proper holomorphic self-mappings in the class of symmetrized
ellipsoids. We also describe the automorphism groupof these domains.Comment: 10 pages, some modification
Noncommutative Parameters of Quantum Symmetries and Star Products
The star product technique translates the framework of local fields on
noncommutative space-time into nonlocal fields on standard space-time. We
consider the example of fields on - deformed Minkowski space,
transforming under -deformed Poincar\'{e} group with noncommutative
parameters. By extending the star product to the tensor product of functions on
-deformed Minkowski space and -deformed Poincar\'{e} group we
represent the algebra of noncommutative parameters of deformed relativistic
symmetries by functions on classical Poincar\'{e} group.Comment: LaTeX2e, 10 pages. To appear in the Proceedings of XXIII
International Colloquium on Group-Theoretical Methods in Physics, July 31-
August 5, Dubna, Russia". The names of the authors correcte
Notes about the Caratheodory number
In this paper we give sufficient conditions for a compactum in
to have Carath\'{e}odory number less than , generalizing an old result of
Fenchel. Then we prove the corresponding versions of the colorful
Carath\'{e}odory theorem and give a Tverberg type theorem for families of
convex compacta
Noncommutative Differential Forms on the kappa-deformed Space
We construct a differential algebra of forms on the kappa-deformed space. For
a given realization of the noncommutative coordinates as formal power series in
the Weyl algebra we find an infinite family of one-forms and nilpotent exterior
derivatives. We derive explicit expressions for the exterior derivative and
one-forms in covariant and noncovariant realizations. We also introduce
higher-order forms and show that the exterior derivative satisfies the graded
Leibniz rule. The differential forms are generally not graded-commutative, but
they satisfy the graded Jacobi identity. We also consider the star-product of
classical differential forms. The star-product is well-defined if the
commutator between the noncommutative coordinates and one-forms is closed in
the space of one-forms alone. In addition, we show that in certain realizations
the exterior derivative acting on the star-product satisfies the undeformed
Leibniz rule.Comment: to appear in J. Phys. A: Math. Theo
Magnetic fields and the dynamics of spiral galaxies
We investigate the dynamics of magnetic fields in spiral galaxies by
performing 3D MHD simulations of galactic discs subject to a spiral potential.
Recent hydrodynamic simulations have demonstrated the formation of inter-arm
spurs as well as spiral arm molecular clouds provided the ISM model includes a
cold HI phase. We find that the main effect of adding a magnetic field to these
calculations is to inhibit the formation of structure in the disc. However,
provided a cold phase is included, spurs and spiral arm clumps are still
present if in the cold gas. A caveat to two phase
calculations though is that by assuming a uniform initial distribution, in the warm gas, emphasizing that models with more consistent
initial conditions and thermodynamics are required. Our simulations with only
warm gas do not show such structure, irrespective of the magnetic field
strength. Furthermore, we find that the introduction of a cold HI phase
naturally produces the observed degree of disorder in the magnetic field, which
is again absent from simulations using only warm gas. Whilst the global
magnetic field follows the large scale gas flow, the magnetic field also
contains a substantial random component that is produced by the velocity
dispersion induced in the cold gas during the passage through a spiral shock.
Without any cold gas, the magnetic field in the warm phase remains relatively
well ordered apart from becoming compressed in the spiral shocks. Our results
provide a natural explanation for the observed high proportions of disordered
magnetic field in spiral galaxies and we thus predict that the relative
strengths of the random and ordered components of the magnetic field observed
in spiral galaxies will depend on the dynamics of spiral shocks.Comment: 17 pages, 14 figures, accepted by MNRA
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