104 research outputs found
Convexification Numerical Method for a Coefficient Inverse Problem for the Riemannian Radiative Transfer Equation
The first globally convergent numerical method for a Coefficient Inverse
Problem (CIP) for the Riemannian Radiative Transfer Equation (RRTE) is
constructed. This is a version of the so-called \textquotedblleft
convexification" principle, which has been pursued by this research group for a
number of years for some other CIPs for PDEs. Those PDEs are significantly
different from RRTE. The presence of the Carleman Weight Function (CWF) in the
numerical scheme is the key element of the convexification. CWF is the
function, which is involved as the weight function in the Carleman estimate for
the corresponding PDE operator. Convergence analysis is presented along with
the results of numerical experiments, which confirm the theory. RRTE governs
the propagation of photons in the diffuse medium in the case when they
propagate along geodesic lines between their collisions. Geodesic lines are
generated by the spatially variable dielectric constant of the medium
Superconductivity in silicon nanostructures
We present the findings of the superconductivity observed in the silicon
nanostructures prepared by short time diffusion of boron on the n-type Si(100)
surface. These Si-based nanostructures represent the p-type ultra-narrow
self-assembled silicon quantum wells, 2nm, confined by the delta - barriers
heavily doped with boron, 3nm. The EPR and the thermo-emf studies show that the
delta - barriers appear to consist of the trigonal dipole centres, which are
caused by the negative-U reconstruction of the shallow boron acceptors. Using
the CV and thermo-emf techniques, the transport of two-dimensional holes inside
SQW is demonstrated to be accompanied by single-hole tunneling through these
negative-U centres that results in the superconductivity of the delta -
barriers. The values of the correlation gaps obtained from these measurements
are in a good agreement with the data derived from the temperature and magnetic
field dependencies of the magnetic susceptibility, which reveal a strong
diamagnetism and additionally identify the superconductor gap value.Comment: 4 pages, 6 figures, presented at the 4th International Conference on
Vortex Matter in Superconductors, Crete, Greece, September 3-9, 200
QCD partition function in the external field in the covariant gauge
The QCD partition function in the external stationary gluomagnetic field is
computed in the third order in external field invariants in arbitrary dimension
and arbitrary covariant gauge. The contributions proportional to third order
invariants in gluon field strength are shown to be dependent on covariant
quantum gauge fixing parameter \alph
Polar optical phonons in wurtzite spheroidal quantum dots: Theory and application to ZnO and ZnO/MgZnO nanostructures
Polar optical-phonon modes are derived analytically for spheroidal quantum
dots with wurtzite crystal structure. The developed theory is applied to a
freestanding spheroidal ZnO quantum dot and to a spheroidal ZnO quantum dot
embedded into a MgZnO crystal. The wurtzite (anisotropic) quantum dots are
shown to have strongly different polar optical-phonon modes in comparison with
zincblende (isotropic) quantum dots. The obtained results allow one to explain
and accurately predict phonon peaks in the Raman spectra of wurtzite
nanocrystals, nanorods (prolate spheroids), and epitaxial quantum dots (oblate
spheroids).Comment: 11 page
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