29,550 research outputs found
Hopf solitons and area preserving diffeomorphisms of the sphere
We consider a (3+1)-dimensional local field theory defined on the sphere. The
model possesses exact soliton solutions with non trivial Hopf topological
charges, and infinite number of local conserved currents. We show that the
Poisson bracket algebra of the corresponding charges is isomorphic to that of
the area preserving diffeomorphisms of the sphere. We also show that the
conserved currents under consideration are the Noether currents associated to
the invariance of the Lagrangian under that infinite group of diffeomorphisms.
We indicate possible generalizations of the model.Comment: 6 pages, LaTe
Riccati-type equations, generalised WZNW equations, and multidimensional Toda systems
We associate to an arbitrary -gradation of the Lie algebra of a
Lie group a system of Riccati-type first order differential equations. The
particular cases under consideration are the ordinary Riccati and the matrix
Riccati equations. The multidimensional extension of these equations is given.
The generalisation of the associated Redheffer--Reid differential systems
appears in a natural way. The connection between the Toda systems and the
Riccati-type equations in lower and higher dimensions is established. Within
this context the integrability problem for those equations is studied. As an
illustration, some examples of the integrable multidimensional Riccati-type
equations related to the maximally nonabelian Toda systems are given.Comment: LaTeX2e, 18 page
Development of liquid xenon detectors for medical imaging
In the present paper, we report on our developments of liquid xenon detectors
for medical imaging, positron emission tomography and single photon imaging, in
particular. The results of the studies of several photon detectors
(photomultiplier tubes and large area avalanche photodiode) suitable for
detection of xenon scintillation are also briefly described.Comment: 13 pages, 5 figures, presented on the International Workshop on
Techniques and Applications of Xenon Detectors (Xenon01), ICRR, Univ. of
Tokyo, Kashiwa, Japan, December 3-4, 2001 (submitted to proceedings
Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue
Here we report on a novel chemical route to synthesize homogenous cobalt
doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The
influence of the synthesis temperature, autoclave dwell time and metal doping
on the structural and microstructural as well as on the optical properties of
the synthesized titanate nanotubes is studied and discussed. The optical band
gaps of the CoTNT samples are red shifted in comparison with the values
determined for the undoped samples, such red shifts bringing the absorption
edge of the CoTNT samples into the visible region. CoTNT materials also
demonstrate particular high adsorption ability for methylene blue, the amount
of the adsorbed dye being higher than the one predictable for a monolayer
formation. This suggests the possibility of intercalation of the dye molecule
between the TiO6 layers of the TNT structure. It is also shown that the
methylene blue sensitized Co-doped nanostructures are highly stable under UV
radiation and present a strong and broad absorption in the visible region.Comment: 31 pages, 3 tables, 7 figure
On Z-graded loop Lie algebras, loop groups, and Toda equations
Toda equations associated with twisted loop groups are considered. Such
equations are specified by Z-gradations of the corresponding twisted loop Lie
algebras. The classification of Toda equations related to twisted loop Lie
algebras with integrable Z-gradations is discussed.Comment: 24 pages, talk given at the Workshop "Classical and Quantum
Integrable Systems" (Dubna, January, 2007
Integrable theories and loop spaces: fundamentals, applications and new developments
We review our proposal to generalize the standard two-dimensional flatness
construction of Lax-Zakharov-Shabat to relativistic field theories in d+1
dimensions. The fundamentals from the theory of connections on loop spaces are
presented and clarified. These ideas are exposed using mathematical tools
familiar to physicists. We exhibit recent and new results that relate the
locality of the loop space curvature to the diffeomorphism invariance of the
loop space holonomy. These result are used to show that the holonomy is abelian
if the holonomy is diffeomorphism invariant.
These results justify in part and set the limitations of the local
implementations of the approach which has been worked out in the last decade.
We highlight very interesting applications like the construction and the
solution of an integrable four dimensional field theory with Hopf solitons, and
new integrability conditions which generalize BPS equations to systems such as
Skyrme theories. Applications of these ideas leading to new constructions are
implemented in theories that admit volume preserving diffeomorphisms of the
target space as symmetries. Applications to physically relevant systems like
Yang Mills theories are summarized. We also discuss other possibilities that
have not yet been explored.Comment: 64 pages, 8 figure
Two-component mixture of charged particles confined in a channel: melting
The melting of a binary system of charged particles confined in a {\it
quasi}-one-dimensional parabolic channel is studied through Monte Carlo
simulations. At zero temperature the particles are ordered in parallel chains.
The melting is anisotropic and different melting temperatures are obtained
according to the spatial direction, and the different types of particles
present in the system. Melting is very different for the single-, two- and
four-chain configurations. A temperature induced structural phase transition is
found between two different four chain ordered states which is absent in the
mono-disperse system. In the mixed regime, where the two types of particles are
only slightly different, melting is almost isotropic and a thermally induced
homogeneous distribution of the distinct types of charges is observed.Comment: To appear in Journal of Physics: condensed matter ; (13 pages, 12
figures
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