341 research outputs found
Interplane charge dynamics in a valence-bond dynamical mean-field theory of cuprate superconductors
We present calculations of the interplane charge dynamics in the normal state
of cuprate superconductors within the valence-bond dynamical mean-field theory.
We show that by varying the hole doping, the c-axis optical conductivity and
resistivity dramatically change character, going from metallic-like at large
doping to insulating-like at low-doping. We establish a clear connection
between the behavior of the c-axis optical and transport properties and the
destruction of coherent quasiparticles as the pseudogap opens in the antinodal
region of the Brillouin zone at low doping. We show that our results are in
good agreement with spectroscopic and optical experiments.Comment: 5 pages, 3 figure
Method of induction control of iron weight fraction in magnetite ore
This paper analyzes the peculiarities of existing methods and means of induction control of magnetic susceptibility of the medium are analyzed. It is concluded that these means have a common drawback due to the low measurement accuracy caused by the wave-like dependence of the instrument sensitivity on the gap between the probe and the medium surface. The ways of increasing the instrument sensitivity and measurement accuracy of controlled parameters by means of inductive measuring transducers are revealed. A method for induction resonance control of iron weight fraction in magnetite ore has been developed, and its effectiveness has been estimated using simulation modeling. Practical recommendations for the development of quality control instruments for magnetite ores have been developed. A variant of the quality control unit layout for working with magnetite ores is proposed
MODEL OF PROVIDING WITH DEVELOPMENT STRATEGY FOR INFORMATION TECHNOLOGIES IN AN ORGANIZATION
Subject of research. The paper presents research and instructional tools for assessment of providing with the development strategy for information technologies in an organization.
Method. The corresponding assessment model is developed which takes into consideration IT-processes equilibrium according to selected efficiency factors of information technologies application.
Basic results. The model peculiarity resides in applying neuro-fuzzy approximators where the conclusion is drawn upon fuzzy logic, and membership functions are adjusted through the use of neural networks. For the adequacy testing of the suggested model, due diligence result analysis has been carried out for the IT-strategy executed in the “Navigator” group of companies at the stage of implementation and support of new technologies and production methods. Data visualization with a circle diagram is applied for the comparative evaluation of the analysis results. The chosen model adequacy is proved by the agreement between predictive assessments for IT-strategy performance targets derived by means of the fuzzy cognitive model over 12 months planning horizon and the real values of these targets upon the expiry of the given planning term.
Practical significance. The developed model application gives the possibility to solve the problem of sustainability assessment for the process of providing the required IT-strategy realization level based upon the fuzzy cognitive map analysis and to reveal IT-objectives changing tendencies for an organization over the stated planning interval
Universal scaling relation in high-temperature superconductors
Scaling laws express a systematic and universal simplicity among complex
systems in nature. For example, such laws are of enormous significance in
biology. Scaling relations are also important in the physical sciences. The
seminal 1986 discovery of high transition-temperature (high-T_c)
superconductivity in cuprate materials has sparked an intensive investigation
of these and related complex oxides, yet the mechanism for superconductivity is
still not agreed upon. In addition, no universal scaling law involving such
fundamental properties as T_c and the superfluid density \rho_s, a quantity
indicative of the number of charge carriers in the superconducting state, has
been discovered. Here we demonstrate that the scaling relation \rho_s \propto
\sigma_{dc} T_c, where the conductivity \sigma_{dc} characterizes the
unidirectional, constant flow of electric charge carriers just above T_c,
universally holds for a wide variety of materials and doping levels. This
surprising unifying observation is likely to have important consequences for
theories of high-T_c superconductivity.Comment: 11 pages, 2 figures, 2 table
Steep anomalous dispersion in coherently prepared Rb vapor
Steep dispersion of opposite signs in driven degenerate two-level atomic
transitions have been predicted and observed on the D2 line of 87Rb in an
optically thin vapor cell. The intensity dependence of the anomalous dispersion
has been studied. The maximum observed value of anomalous dispersion [dn/dnu ~=
-6x10^{-11}Hz^{-1}] corresponds to anegative group velocity V_g ~= -c/23000.Comment: 4 pages, 4 figure
Band-structure trend in hole-doped cuprates and correlation with Tcmax
By calculation and analysis of the bare conduction bands in a large number of
hole-doped high-temperature superconductors, we have identified the energy of
the so-called axial-orbital as the essential, material-dependent parameter. It
is uniquely related to the range of the intra-layer hopping. It controls the Cu
4s-character, influences the perpendicular hopping, and correlates with the
observed Tc at optimal doping. We explain its dependence on chemical
composition and structure, and present a generic tight-binding model.Comment: 5 pages, Latex, 5 eps figure
Nonlinear interaction of light with Bose-Einstein condensate: new methods to generate subpoissonian light
We consider -type model of the Bose-Einstein condensate of sodium
atoms interacting with the light. Coefficients of the Kerr-nonlinearity in the
condensate can achieve large and negative values providing the possibility for
effective control of group velocity and dispersion of the probe pulse. We find
a regime when the observation of the "slow" and "fast" light propagating
without absorption becomes achievable due to strong nonlinearity. An effective
two-level quantum model of the system is derived and studied based on the su(2)
polynomial deformation approach. We propose an efficient way for generation of
subpoissonian fields in the Bose-Einstein condensate at time-scales much
shorter than the characteristic decay time in the system. We show that the
quantum properties of the probe pulse can be controlled in BEC by the classical
coupling field.Comment: 13 pages, 6 figures, 1 tabl
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