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The Topology of Foliations Formed by the Generic K-Orbits of a Subclass of the Indecomposable MD5-Groups
The present paper is a continuation of [13], [14] of the authors.
Specifically, the paper considers the MD5-foliations associated to connected
and simply connected MD5-groups such that their Lie algebras have 4-dimensional
commutative derived ideal. In the paper, we give the topological classification
of all considered MD5-foliations. A description of these foliations by certain
fibrations or suitable actions of and the Connes' C*-algebras
of the foliations which come from fibrations are also given in the paper.Comment: 20 pages, no figur
Triangular de Rham Cohomology of Compact Kahler Manifolds
We study the de Rham 1-cohomology H^1_{DR}(M,G) of a smooth manifold M with
values in a Lie group G. By definition, this is the quotient of the set of flat
connections in the trivial principle bundle by the so-called gauge
equivalence. We consider the case when M is a compact K\"ahler manifold and G
is a solvable complex linear algebraic group of a special class which contains
the Borel subgroups of all complex classical groups and, in particular, the
group of all triangular matrices. In this case, we get a
description of the set H^1_{DR}(M,G) in terms of the 1-cohomology of M with
values in the (abelian) sheaves of flat sections of certain flat Lie algebra
bundles with fibre (the Lie algebra of G) or, equivalently, in terms
of the harmonic forms on M representing this cohomology
Spectral Properties of the Generalized Spin-Fermion Models
In order to account for competition and interplay of localized and itinerant
magnetic behaviour in correlated many body systems with complex spectra the
various types of spin-fermion models have been considered in the context of the
Irreducible Green's Functions (IGF) approach. Examples are generalized d-f
model and Kondo-Heisenberg model. The calculations of the quasiparticle
excitation spectra with damping for these models has been performed in the
framework of the equation- of-motion method for two-time temperature Green's
Functions within a non-perturbative approach. A unified scheme for the
construction of Generalized Mean Fields (elastic scattering corrections) and
self-energy (inelastic scattering) in terms of the Dyson equation has been
generalized in order to include the presence of the two interacting subsystems
of localized spins and itinerant electrons. A general procedure is given to
obtain the quasiparticle damping in a self-consistent way. This approach gives
the complete and compact description of quasiparticles and show the flexibility
and richness of the generalized spin-fermion model concept.Comment: 37 pages, Late
Modelling variability of solar activity cycles
Context. Solar activity cycles vary in amplitude and duration. The variations
can be at least partly explained by fluctuations in dynamo parameters. Aims. We
want to restrict uncertainty in fluctuating dynamo parameters and find out
which properties of the fluctuations control the amplitudes of the magnetic
field and energy in variable dynamo cycles. Methods. A flux-transport model for
the solar dynamo with fluctuations of the Babcock-Leighton type -effect
was applied to generate statistics of magnetic cycles for our purposes. The
statistics were compared with data on solar cycle periods to restrict the
correlation time of dynamo fluctuations. Results. A characteristic time of
fluctuations in the -effect is estimated to be close to the solar
rotation period. The fluctuations produce asymmetry between the times of rise
and descent of dynamo cycles, the rise time being on average shorter. The
affect of the fluctuations on cycle amplitudes depends on the phase of the
cycle in which the fluctuations occur. Negative fluctuations (decrease in
) in the rise phase delay decay of poloidal field and increase the
cycle amplitude in toroidal field and magnetic energy. Negative fluctuation in
the decline phase reduces the polar field at the end of a cycle and the
amplitude of the next cycle. The low amplitude of the 24th solar cycle compared
to the preceding 23rd cycle can be explained by this effect. Positive
fluctuations in the descent phase enhance the magnetic energy of the next cycle
by increasing the seed poloidal field for the next cycle. The statistics of the
computed energies of the cycles suggest that superflares of erg
are not possible on the Sun.Comment: 8 pages, 11 figures, A&A (accepted
Comment on "Influence of Pair Breaking and Phase Fluctuations on Disordered High Tc Cuprate Superconductors"
It is shown that an account for combined effect of both nonmagnetic and
magnetic scatterers on Tc and/or an assumption about a non-pure d-wave order
parameter allows for a quantitative explanation of the experimental data on the
electron irradiation-induced suppression of superconductivity in Y-123 single
crystals within the AG-like pair breaking theory, without resorting to phase
fluctuations effects.Comment: Comment on the paper by F. Rullier-Albenque et al., Phys. Rev. Lett.
91, 047001 (2003
Resonant-pulse operations on the buried donor charge qubits in semiconductors
A new scheme is proposed for rotations of a double-donor charge qubit whose
logical states are defined by the two lowest energy states of a single electron
localized around one or another donor. It is shown that making use of the
microwave pulses tuned to the resonance with an auxiliary excited molecular
level allows for implementation of various one-qubit operations in very short
times. Decoherence effects are analyzed by the example of the P:Si system
and shown to be weak enough for experimental realization of this scheme being
possible.Comment: 4 pages, 1 figure, to appear in PR
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