2,019 research outputs found
Regularized extremal shift in problems of stable control
We discuss a technical approach, based on the method of regularized extremal shift (RES), intended to help solve problems of stable control of uncertain dynamical systems. Our goal is to demonstrate the essence and abilities of the RES technique; for this purpose we construct feedback controller for approximate tracking a prescribed trajectory of an inaccurately observed system described by a parabolic equation. The controller is "resource-saving" in a sense that control resource spent for approximate tracking do not exceed those needed for tracking in an "ideal" situation where the current values of the input disturbance are fully observable. © 2013 IFIP International Federation for Information Processing.German Sci. Found. (DFG) Eur. Sci. Found. (ESF);Natl. Inst. Res. Comput. Sci. Control France (INRIA);DFG Research Center MATHEON;Weierstrass Institute for Applied Analysis and Stochastics (WIAS);European Patent Offic
Bosonic Spectral Function and The Electron-Phonon Interaction in HTSC Cuprates
In Part I we discuss accumulating experimental evidence related to the
structure and origin of the bosonic spectral function in high-temperature
superconducting (HTSC) cuprates at and near optimal doping. Some global
properties of the spectral function, such as number and positions of peaks, are
extracted by combining optics, neutron scattering, ARPES and tunnelling
measurements. These methods give convincing evidence for strong electron-phonon
interaction (EPI) with the coupling constant between 1-3 in cuprates near
optimal doping. Here we clarify how these results are in favor of the
Eliashberg-like theory for HTSC cuprates near optimal doping. In Part II we
discuss some theoretical ingredients - such as strong EPI, strong correlations
- which are necessary to explain the experimental results related to the
mechanism of d-wave pairing in optimally doped cuprates. These comprise the
Migdal-Eliashberg theory for EPI in strongly correlated systems which give rise
to the forward scattering peak. The latter is further supported by the weakly
screened Madelung interaction in the ionic-metallic structure of layered
cuprates. In this approach EPI is responsible for the strength of pairing while
the residual Coulomb interaction (by including spin fluctuations) triggers the
d-wave pairing.Comment: 59 pages, 38 figures, review articl
Ab initio calculations of the physical properties of transition metal carbides and nitrides and possible routes to high-Tc
Ab initio linear-response calculations are reported of the phonon spectra and
the electron-phonon interaction for several transition metal carbides and
nitrides in a NaCl-type structure. For NbC, the kinetic, optical, and
superconducting properties are calculated in detail at various pressures and
the normal-pressure results are found to well agree with the experiment.
Factors accounting for the relatively low critical temperatures Tc in
transition metal compounds with light elements are considered and the possible
ways of increasing Tc are discussed.Comment: 19 pages, 7 figure
On the theory of magnetic field dependence of heat conductivity in dielectric in isotropic model
Phonon polarization in a magnetic field is analyzed in isotropic model. It is
shown, that at presence of spin-phonon interaction phonon possess circular
polari-zation which causes the appearance of heat flux component perpendicular
both to temperature gradient and magnetic field.Comment: 5 pages, 0 figure
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