446 research outputs found
Comparison of dynamic of autonomic control indices in cardiovascular system under the treatment by ACE inhibitor (Enalapril) and beta-blocker (Metoprolol) in patients with hypertension
The objective of the present research was to compare the influence of Enalapril and Metoprolol on synchronization of 0.1 Hz-regulation of heart and blood microcirculation. 42 patients aged 49Β±9 years old with hypertension I, II were included in the study. 0.1 Hz-oscillations in heart rate variability (HRV) and blood microcirculation were registered during the passive orthostatic sign while breathing spontaneously. The duration of each test was 10 minutes. Synchronization was estimated as a phase difference between 0.1 Hz-rhythms in heart rate and in filling of blood microcirculation. Quantitative measures of synchronization were also estimated. In addition frequency values of HRV spectrum in LF- and HF-ranges were assessed. Enalapril and Metoprolol had comparable effect on blood pressure reduction. Treatment with both Enalapril and Metoprolol in patients with significant vegetative dysfunction resulted in repair of functional interaction between 0.1 Hz-regulation of heart and blood microcirculation. Enalapril was preferred in hypertensive patients with prevalence of disorders of vegetative regulation of blood microcirculation. Metoprolol influenced positively on 0,1 Hz-rhythm synchronization in patients with predominance of heart vegetative regulation dysfunction and in patients with sympathicotonia. In patients with hypertension and initially normal level of synchronization of 0.1 Hz-mechanisms treatment with Enalapril or Metoprolol caused functional dissociation. Differentiated approach to the choice of hypertensive therapy should consider individual peculiarities of system vegetative dysfunction. The level of synchronization of 0.1 Hz-rhythms in cardiovascular system should especially be evaluated initially and during the treatmen
Piezoelectric Characteristics of LiNbO3 Thin-film Heterostructures via Piezoresponse Force Microscopy
Electro-optic LiNbO3 thin films were deposited on Si(100) and Si(111) substrates using a radio-frequency magnetron sputtering process. The piezoelectric properties of the LiNbO3 films were investigated using the scanning probe microscopy in the piezoresponse mode. The obtained results show the high degree of grains orientation in polycrystalline structure. The piezoelectric modulus (dzz) was estimated to be 16 pm/V (for LiNbO3 / Si(100)) and 22 pm/V (for LiNbO3 / Si(111)) and the polarization about of 0.37 CΒ·m β 2. These values are larger than those reported previously for LiNbO3 films.
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Formation of the Electric Field Distribution in Thin Electro-Optic Layers for Precision Correction their Optical Characteristics
A method of making given field distribution within thin electro-optical layers by using narrow band electrodes placed at the same electric potential. A formula for electric field intensity produced by a single band electrode is obtained. Electric field modeling for different band electrode configurations is undertaken. It was shown, by applying piezoresponse force microscopy, that in case of highly inhomogeneous field the polarization of lithium niobate electro-optical film persisted only in the area above
the band electrode.
Lithium niobate, electro-optical structures, piezoresponse force microscopy, Computer
simulation
Synthesis and Nanoscale Characterization of LiNbO3 Thin Films Deposited on Al2O3 Substrate by RF Magnetron Sputtering under Electric Field
LiNbO3 thin films were deposited on Al2O3 substrates by RF-magnetron sputtering with in-situ electric
field to study the self-polarization effect. The films have been characterized crystallographically by x-ray
diffraction, and morphologically by atomic force microscopy. The films contain crystallites of LiNbO3 with
preferable orientation [012] along the normal to the Al2O3 substrate surface (012). Piezoresponse force
microscopy was used to study vertical and lateral polarization direction in LiNbO3 thin films. The analysis
of the histograms of vertical piezoresponse images allowed to reveal self-polarization effect in films. The
local piezoelectric hysteresis performed on the nanometer scale indicates switching behavior of polarization
for LiNbO3 thin film
Theory of Current-Induced Magnetization Precession
We solve appropriate drift-diffusion and Landau-Lifshitz-Gilbert equations to
demonstrate that unpolarized current flow from a non-magnet into a ferromagnet
can produce a precession-type instability of the magnetization. The fundamental
origin of the instability is the difference in conductivity between majority
spins and minority spins in the ferromagnet. This leads to spin accumulation
and spin currents that carry angular momentum across the interface. The
component of this angular momentum perpendicular to the magnetization drives
precessional motion that is opposed by Gilbert damping. Neglecting magnetic
anisotropy and magnetostatics, our approximate analytic and exact numerical
solutions using realistic values for the material parameters show (for both
semi-infinite and thin film geometries) that a linear instability occurs when
both the current density and the excitation wave vector parallel to the
interface are neither too small nor too large. For many aspects of the problem,
the variation of the magnetization in the direction of the current flows makes
an important contribution.Comment: Submitted to Physical Review
Current-Driven Magnetization Dynamics in Magnetic Multilayers
We develop a quantum analog of the classical spin-torque model for
current-driven magnetic dynamics. The current-driven magnetic excitation at
finite field becomes significantly incoherent. This excitation is described by
an effective magnetic temperature rather than a coherent precession as in the
spin-torque model. However, both the spin-torque and effective temperature
approximations give qualitatively similar switching diagrams in the
current-field coordinates, showing the need for detailed experiments to
establish the proper physical model for current-driven dynamics.Comment: 5 pages, 2 figure
Nonlinear Modulation of Multi-Dimensional Lattice Waves
The equations governing weakly nonlinear modulations of -dimensional
lattices are considered using a quasi-discrete multiple-scale approach. It is
found that the evolution of a short wave packet for a lattice system with cubic
and quartic interatomic potentials is governed by generalized Davey-Stewartson
(GDS) equations, which include mean motion induced by the oscillatory wave
packet through cubic interatomic interaction. The GDS equations derived here
are more general than those known in the theory of water waves because of the
anisotropy inherent in lattices. Generalized Kadomtsev-Petviashvili equations
describing the evolution of long wavelength acoustic modes in two and three
dimensional lattices are also presented. Then the modulational instability of a
-dimensional Stokes lattice wave is discussed based on the -dimensional
GDS equations obtained. Finally, the one- and two-soliton solutions of
two-dimensional GDS equations are provided by means of Hirota's bilinear
transformation method.Comment: Submitted to PR
Cosmological Models with Fractional Derivatives and Fractional Action Functional
Cosmological models of a scalar field with dynamical equations containing
fractional derivatives or derived from the Einstein-Hilbert action of
fractional order, are constructed. A number of exact solutions to those
equations of fractional cosmological models in both cases is given.Comment: 14 page
Formation of the Electric Field Distribution in Thin Electro-Optic Layers for Precision Correction their Optical Characteristics
A method of making given field distribution within thin electro-optical layers by using narrow band electrodes placed at the same electric potential. A formula for electric field intensity produced by a single band electrode is obtained. Electric field modeling for different band electrode configurations is undertaken. It was shown, by applying piezoresponse force microscopy, that in case of highly inhomogeneous field the polarization of lithium niobate electro-optical film persisted only in the area above
the band electrode.
Lithium niobate, electro-optical structures, piezoresponse force microscopy, Computer
simulation
Formation of the Microcrystalline Structure in LiNbO3 Thin Films by Pulsed Light Annealing
LiNbO3 thin films with a thickness of 200 nm were deposited onto Al2O3 substrate by RF-magnetron
sputtering technique without intentional substrate heating. The results demonstrate that post-growth
infrared pulsed light annealing of the amorphous LiNbO3 films leads to the formation of two phases,
LiNbO3 and LiNb3O8. After annealing at temperatures of 700 to 800 Β°C, the percentage of the nonferroelectric
phase LiNb3O8 was minimal. The surface composition of the films annealed at different
temperatures was examined by X-ray photoelectron spectroscopy. Piezoresponse force microscopy was used
to study both the vertical and the lateral polarization and to visualize the piezoelectric inactivity of
LiNb3O8 grains. A comparison of the results of PFM and XPS measurements revealed that there is a
correlation between the fraction of the piezoelectric phase and the film composition: At an annealing
temperature higher than 850 Β°C, the atomic ratio of lithium to niobium decreases compared to the initial
value along with a decrease of the fraction of the piezoelectric phase
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