Theory of High-Tc Superconducting Cuprates Based on Experimental Evidence

A model of superconductivity in layered high-temperature superconducting cuprates is proposed, based on the extended saddle point singularities in the electron spectrum, weak screening of the Coulomb interaction and phonon-mediated interaction between electrons plus a small short -range repulsion of Hund's, or spin-fluctuation, origin. This permits to explain the large values of $Tc$, features of the isotope effect on oxygen and copper, the existence of two types of the order parameter, the peak in the inelastic neutron scattering, the positive curvature of the upper critical field, as function of temperature etc.Comment: RevTeX 3.x, 11 Postscript figures (included); send comments to [email protected]

Generation of tunable entanglement and violation of a Bell-like inequality between different degrees of freedom of a single photon

We demonstrate a scheme to generate noncoherent and coherent correlations, i.e., a tunable degree of entanglement, between degrees of freedom of a single photon. Its nature is analogous to the tuning of the purity (first-order coherence) of a single photon forming part of a two-photon state by tailoring the correlations between the paired photons. Therefore, well-known tools such as the Clauser-Horne-Shimony-Holt (CHSH) Bell-like inequality can also be used to characterize entanglement between degrees of freedom. More specifically, CHSH inequality tests are performed, making use of the polarization and the spatial shape of a single photon. The four modes required are two polarization modes and two spatial modes with different orbital angular momentum.Comment: 7 pages, 5 figures. Updated to be consistent with published versio

Distributed fluorescent optical fiber proximity sensor: Towards a proof of concept

Fluorescent fibers are optical fibers which emit light as a response to an incident phenomenon, usually an incident light. Operation depends on the doping dyes, which determine specific fluorescence and optical characteristics useful in the development of optical sensors. In this work we propose a low-cost distributed proximity sensor implemented using a red fluorescent fiber, to provide a security option for a surface plasmon resonance system. Operation of the proposed sensor relies on having the incident illumination intensity varied by the presence or absence of an obstacle in the vicinity of the sensing element. This will influence the radiated fluorescence accordingly. The proposed setup for the implementation of the optical proximity sensor assumes having a high brightness LED deployed for axial fiber illumination and a blue LED for side illumination. Electronic processing then accounts for gain and digitization. Measurement results of the prototype validate the proposed concept

Dual regimes of ion migration in high repetition rate femtosecond laser inscribed waveguides

Ion migration in high repetition rate femtosecond laser inscribed waveguides is currently being reported in different optical glasses. For the first time we discuss and experimentally demonstrate the presence of two regimes of ion migration found in laser written waveguides. Regime-I, corresponds to the initial waveguide formation mainly via light element migration (in our case atomic weight < 31u), whereas regime-II majorly corresponds to the movement of heavy elements. This behavior brings attention to a problem which has never been analyzed before and that affects laser written active waveguides in which active ions migrate changing their local spectroscopic properties. The migration of active ions may in fact detune the pre-designed optimal values of active photonic devices. This paper experimentally evidences this problem and provides solutions to avert it.Comment: 4 pages, 5 figure

Characterization by Electron Diffraction of Two Thermodynamical Phases of Precipitation in Nb-Microalloyed Steels

Excellent mechanical properties (high strength and toughness) of microalloyed steels are mainly caused by induced precipitation during thermomechanical treatment (TMT) and grain refinement. It has been recently found that TMT of Nb-microalloyed steels can give rise to two different kinds of precipitates, manifested by the double plateau in the statically recrystallised fraction (Xa) against time curves. This work presents an electron diffraction study performed in a transmission electron microscope, equipped with an EDS analytical system. Lattice parameters of a great deal of particles, smaller than 200 nm and with face cubic centred structure, have been measured. Frequency distribution of the values of lattice parameters shows that these are grouped in two sets whose mean values are close. Comparison of these values with those found in the literature for carbides, nitrides and carbonitrides usually present in microalloyed steels demonstrates that they are Nb carbonitrides with slight stoichiometric differences (NbCxNy).Peer reviewe

The Upper Critical Field in Disordered Two-Dimensional Superconductors

We present calculations of the upper critical field in superconducting films as a function of increasing disorder (as measured by the normal state resistance per square). In contradiction to previous work, we find that there is no anomalous low-temperature positive curvature in the upper critical field as disorder is increased. We show that the previous prediction of this effect is due to an unjustified analytical approximation of sums occuring in the perturbative calculation. Our treatment includes both a careful analysis of first-order perturbation theory, and a non-perturbative resummation technique. No anomalous curvature is found in either case. We present our results in graphical form.Comment: 11 pages, 8 figure

Practical dermatology

DERMATOLOGYSKIN DISEASESКОЖНЫЕ БОЛЕЗНИМЕТОДИЧЕСКИЕ РЕКОМЕНДАЦИИПРАКТИЧЕСКАЯ ДЕРМАТОЛОГИЯRecommendations include tests, clinical tasks and practical skills in dermatology that are used as during practical classes as at the examination

MICROSTRUCTURAL STUDIES FOR OPTIMIZATION OF HEAT TREATMENT IN COMPONENTS OF STEEL X38CrMoV5-1 SUBJECTED TO HIGH STRESSES

This material X38CrMoV5-1 is an alloyed steel used for hot working, with good toughness and high resistance to thermal shock. The presence of Cr, Mo and V gives this steel a high resistance to wear, keeping its hardness properties at high temperature. Cr and Mo delay softening annealing and inhibit the grain growth. The great resistance to high temperatures of this type of steels is related with an easy martensitic transformation. This transformation happens even at low cooling speeds. The properties of these types of martensitic steels result as a consequence of their complex microstructure that is obtained by an extremely controlled thermal treatment. Dilatometric testing was performed on continuous cooling from austenization temperature (1050ºC). This testing shows the high hardenability of this type of steels. ATD studies have been done to complement the dilatometric testing. After the previous results, it has been considered that the optimal treatment to get tough and tenacious structure, consists in submitting material to an annealing processing at 780ºC/1hour, followed by a quenching treatment at 1020ºC/1hour and finally cooling in oil with a double tempering at 580ºC/2 hours. This treatment provides the best properties that guarantee service with safety parts.Peer Reviewe

Energy Gap Induced by Impurity Scattering: New Phase Transition in Anisotropic Superconductors

It is shown that layered superconductors are subjected to a phase transition at zero temperature provided the order parameter (OP) reverses its sign on the Fermi-surface but its angular average is finite. The transition is regulated by an elastic impurity scattering rate $1/\tau$. The excitation energy spectrum, being gapless at the low level of scattering, develops a gap as soon as the scattering rate exceeds some critical value of $1/\tau_\star$.Comment: Revtex, 11 page

Universal transport in 2D granular superconductors

The transport properties of quench condensed granular superconductors are presented and analyzed. These systems exhibit transitions from insulating to superconducting behavior as a function of inter-grain spacing. Superconductivity is characterized by broad transitions in which the resistance drops exponentially with reducing temperature. The slope of the log R versus T curves turns out to be universaly dependent on the normal state film resistance for all measured granular systems. It does not depend on the material, critical temperature, geometry, or experimental set-up. We discuss possible physical scenarios to explain these findings.Comment: 4 pages, 3 figure