4,273 research outputs found
Radiative transitions in mesons in a non relativistic quark model
In the framework of the non relativistic quark model, an exhaustive study of
radiative transitions in mesons is performed. The emphasis is put on several
points. Some traditional approximations (long wave length limit, non
relativistic phase space, dipole approximation for E1 transitions, gaussian
wave functions) are analyzed in detail and their effects commented. A complete
treatment using three different types of realistic quark-antiquark potential is
made. The overall agreement with experimental data is quite good, but some
improvements are suggested.Comment: 42 pages, 2 figure
Auxiliary field method and analytical solutions of the Schr\"{o}dinger equation with exponential potentials
The auxiliary field method is a new and efficient way to compute approximate
analytical eigenenergies and eigenvectors of the Schr\"{o}dinger equation. This
method has already been successfully applied to the case of central potentials
of power-law and logarithmic forms. In the present work, we show that the
Schr\"{o}dinger equation with exponential potentials of the form can also be analytically solved by using the
auxiliary field method. Formulae giving the critical heights and the energy
levels of these potentials are presented. Special attention is drawn on the
Yukawa potential and the pure exponential one
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
Wetting of cholesteric liquid crystals
We investigate theoretically the wetting properties of cholesteric liquid
crystals at a planar substrate. If the properties of substrate and of the
interface are such that the cholesteric layers are not distorted the wetting
properties are similar to those of a nematic liquid crystal. If, on the other
hand, the anchoring conditions force the distortion of the liquid crystal
layers the wetting properties are altered, the free cholesteric-isotropic
interface is non-planar and there is a layer of topological defects close to
the substrate. These deformations can either promote or hinder the wetting of
the substrate by a cholesteric, depending on the properties of the cholesteric
liquid crystal
Synthesis of sub-5 nm Co-doped SnO nanoparticles and their structural, microstructural, optical and photocatalytic properties
A swift chemical route to synthesize Co-doped SnO nanopowders is
described. Pure and highly stable SnCoO (0 x
0.15) crystalline nanoparticles were synthesized, with mean grain sizes <
5 nm and the dopant element homogeneously distributed in substitutional sites
of the SnO matrix. The UV-visible diffuse reflectance spectra of the
SnCoO samples reveal red shifts, the optical bandgap
energies decreasing with increasing Co concentration. The Urbach energies of
the samples were calculated and correlated with their bandgap energies. The
photocatalytic activity of the SnCoO samples was
investigated for the 4-hydroxylbenzoic acid (4-HBA) degradation process. A
complete photodegradation of a 10 ppm 4-HBA solution was achieved using 0.02%
(w/w) of SnCoO nanoparticles in 60 min of
irradiation.Comment: 29 pages, 2 tables, 10 figure
Regularity estimates for the solution and the free boundary to the obstacle problem for the fractional Laplacian
We use a characterization of the fractional Laplacian as a Dirichlet to
Neumann operator for an appropriate differential equation to study its obstacle
problem. We write an equivalent characterization as a thin obstacle problem. In
this way we are able to apply local type arguments to obtain sharp regularity
estimates for the solution and study the regularity of the free boundary
SU(2) Ă SU(2) Ă U(1) basis for symmetric SO(6) representations : matrix elements of the generators
Matrix elements of the group generators for the symmetric irreducible representations of SO(6) are explicitly calculated in a closed form employing the decomposition chain SO(6) â SU(2) x SU(2) x U(1) (which is different from the well known Wigner supermultiplet scheme). The relation to the Gel'fand Tsetlin method using SO(6) â SO(5) â ... â SO(2) is indicated. An example of a physical application is given
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