362 research outputs found
Possible quantum kinematics. II. Non-minimal case
The quantum analogs of the N-dimensional Cayley-Klein spaces with different
combinations of quantum and Cayley-Klein structures are described for
non-minimal multipliers, which include the first and the second powers of
contraction parameters in the transformation of deformation parameter. The
noncommutative analogs of (N-1)-dimensional constant curvature spaces are
introduced. Part of these spaces for N=5 are interpreted as the noncommutative
analogs of (1+3) space-time models. As a result the wide variety of the quantum
deformations of realistic kinematics are suggested.Comment: 13 pages, no figure
The R.I. Pimenov unified gravitation and electromagnetism field theory as semi-Riemannian geometry
More then forty years ago R.I. Pimenov introduced a new geometry --
semi-Riemannian one -- as a set of geometrical objects consistent with a
fibering He suggested the heuristic principle according to
which the physically different quantities (meter, second, coulomb etc.) are
geometrically modelled as space coordinates that are not superposed by
automorphisms. As there is only one type of coordinates in Riemannian geometry
and only three types of coordinates in pseudo-Riemannian one, a multiple
fibered semi-Riemannian geometry is the most appropriate one for the treatment
of more then three different physical quantities as unified geometrical field
theory.
Semi-Euclidean geometry with 1-dimensional fiber and
4-dimensional Minkowski space-time as a base is naturally interpreted as
classical electrodynamics. Semi-Riemannian geometry with the
general relativity pseudo-Riemannian space-time and 1-dimensional
fiber responsible for the electromagnetism, provides the unified field
theory of gravitation and electromagnetism. Unlike Kaluza-Klein theories, where
the 5-th coordinate appears in nondegenerate Riemannian or pseudo-Riemannian
geometry, the theory based on semi-Riemannian geometry is free from defects of
the former. In particular, scalar field does not arise.
PACS: 04.50.Cd, 02.40.-k, 11.10.KkComment: 16 pages, 2 figures. Submited to Physics of Atomic Nucle
Optical conductivity and penetration depth in MgB2
The complex conductivity of a MgB2 film has been investigated in the
frequency range 4 cm^{-1}< nu < 30 cm^{-1} and for temperatures 2.7 K < T <300
K. The overall temperature dependence of both components of the complex
conductivity is reminiscent of BCS-type behavior, although a detailed analysis
reveals a number of discrepancies. No characteristic feature of the isotropic
BCS gap temperature evolution is observed in the conductivity spectra in the
superconducting state. A peak in the temperature dependence of the real part of
the conductivity is detected for frequencies below 9 cm^{-1}. The
superconducting penetration depth follows a T^2 behavior at low temperatures.Comment: 4 pages, 4 figure
Organic Derivatives of Mercury and Tin as Promoters of Membrane Lipid Peroxidation
The toxicity mechanisms of mercury and tin organic derivatives are still under debate. Generally the
presence of organic moieties in their molecules makes these compounds lipophilic and membrane active
species. The recent results suggest that Hg and Sn compounds deplete HS-groups in proteins, glutathione and
glutathione-dependent enzymatic systems; this process also results in the production of reactive oxygen
species (ROS), the enhancement of membrane lipids peroxidation and damage of the antioxidative defence
system. The goal of this review is to present recent results in the studies oriented towards the role of
organomercury and organotin compounds in the xenobiotic-mediated enhancement of radical production and
hence in the promotion of cell damage as a result of enhanced lipids peroxidation. Moreover the conception
of the carbon to metal bond cleavage that leads to the generation of reactive organic radicals is discussed as
one of the mechanisms of mercury and tin organic derivatives toxicity. The possible use of natural and
synthetic antioxidants as detoxification agents is described. The data collected recently and presented here
are fundamentally important to recognizing the difference between the role of metal center and of organic
fragments in the biochemical behavior of organomercury and organotin compounds in their interaction with
primary biological targets when entering a living organism
Universal relationship between the penetration depth and the normal-state conductivity in YBaCuO
The absolute values of the conductivity in the normal state sigma_n and of
the low temperature penetration depths lambda(0) were measured for a number of
different samples of the YBaCuO family. We found a striking correlation between
sigma_n and 1/lambda^2, regardless of doping, oxygen reduction or defects, thus
providing a simple method to predict the superconducting penetration depth and
to have an estimate of the sample quality by measuring the normal-state
conductivity.Comment: 7 pages, 1 figure, Europhys. Lett., accepte
Charge ordering and magneto-polarons in NaCoO
Using spectral ellipsometry, we have measured the dielectric function of a
NaCoO crystal that exhibits bulk antiferromagnetism with
T=19.8 K. We identify two prominent transitions as a function of
temperature. The first one at 280 K involves marked changes of the electronic
and the lattice response that are indicative of charge ordering in the
CoO layers. The second transition coincides with T=19.8 K and
reveals a sizeable spin-charge coupling. The data are discussed in terms of
charge ordering and formation of magneto-polarons due to a charge-induced
spin-state transition of adjacent Co ions
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