2,530 research outputs found
NNACS software package for education and research of neural networks in control systems
A need of educational software development for neural networks application in control systems is posed. Specific requirements for such software are highlighted. Original open source software package for educational and research tasks is introduced. Its capabilities and examples of use are presentedСформулирована потребность в разработке программного пакета для обучения нейросетевым подходам в системах автоматического управления. Отмечены специфические требования к подобным программам. Представлен оригинальный программный пакет для учебных и научно-исследовательских целей, доступный в исходных текстах. Перечислены его возможности и приведены примеры использовани
Materials Contrast in Piezoresponse Force Microscopy
Piezoresponse Force Microscopy contrast in transversally isotropic material
corresponding to the case of c+ - c- domains in tetragonal ferroelectrics is
analyzed using Green's function theory by Felten et al. [J. Appl. Phys. 96, 563
(2004)]. A simplified expression for PFM signal as a linear combination of
relevant piezoelectric constant are obtained. This analysis is extended to
piezoelectric material of arbitrary symmetry with weak elastic and dielectric
anisotropies. This result provides a framework for interpretation of PFM
signals for systems with unknown or poorly known local elastic and dielectric
properties, including nanocrystalline materials, ferroelectric polymers, and
biopolymers.Comment: 20 pages, 3 figures, 1 table, accepted to Appl. Phys. Lett. (without
Appendices), algebraic errors were correcte
Experimental verification of minima in excited long-range Rydberg states of Rb_2
Recent theoretical studies with alkali atoms A excited to high
Rydberg states predicted the existence of ultra long-range molecular bound
states. Such excited dimers have large electric dipole moments which, in
combination with their long radiative lifetimes, make them excellent candidates
for manipulation in applications. This letter reports on experimental
investigations of the self-broadening of Rb principal series lines, which
revealed multiple satellites in the line wings. The positions of the satellites
agree quantitatively with theoretically-predicted minima in the excited
long-range Rydberg states of Rb.Comment: 3 figures, 5 pages in two-column forma
On the keV sterile neutrino search in electron capture
A joint effort of cryogenic microcalorimetry (CM) and high-precision
Penning-trap mass spectrometry (PT-MS) in investigating atomic orbital electron
capture (EC) can shed light on the possible existence of heavy sterile
neutrinos with masses from 0.5 to 100 keV. Sterile neutrinos are expected to
perturb the shape of the atomic de-excitation spectrum measured by CM after a
capture of the atomic orbital electrons by a nucleus. This effect should be
observable in the ratios of the capture probabilities from different orbits.
The sensitivity of the ratio values to the contribution of sterile neutrinos
strongly depends on how accurately the mass difference between the parent and
the daughter nuclides of EC-transitions can be measured by, e.g., PT-MS. A
comparison of such probability ratios in different isotopes of a certain
chemical element allows one to exclude many systematic uncertainties and thus
could make feasible a determination of the contribution of sterile neutrinos on
a level below 1%. Several electron capture transitions suitable for such
measurements are discussed.Comment: 16 pages, 9 figures, 2 table
Bichiral structure of feroelectric domain wall driven by flexoelectricity
The influence of flexoelectric coupling on the internal structure of neutral
domain walls in tetragonal phase of perovskite ferroelectrics is studied. The
effect is shown to lower the symmetry of 180-degree walls which are oblique
with respect to the cubic crystallographic axes, while {100} and {110} walls
stay "untouched". Being of the Ising type in the absence of the flexoelectric
interaction, the oblique domain walls acquire a new polarization component with
a structure qualitatively different from the classical Bloch-wall structure. In
contrast to the Bloch-type walls, where the polarization vector draws a helix
on passing from one domain to the other, in the flexoeffect-affected wall, the
polarization rotates in opposite directions on the two sides of the wall and
passes through zero in its center. Since the resulting polarization profile is
invariant upon inversion with respect to the wall center it does not brake the
wall symmetry in contrast to the classical Bloch-type walls. The flexoelectric
coupling lower the domain wall energy and gives rise to its additional
anisotropy that is comparable to that conditioned by the elastic anisotropy.
The atomic orderof- magnitude estimates shows that the new polarization
component P2 may be comparable with spontaneous polarization Ps, thus
suggesting that, in general, the flexoelectric coupling should be mandatory
included in domain wall simulations in ferroelectrics. Calculations performed
for barium titanate yields the maximal value of the P2, which is much smaller
than that of the spontaneous polarization. This smallness is attributed to an
anomalously small value of a component of the "strain-polarization"
elecrostictive tensor in this material
Fixed Volume Effect on Polar Properties and Phase Diagrams of Ferroelectric Semi-ellipsoidal Nanoparticles
For advanced applications in modern industry it is very important to reduce
the volume of ferroelectric nanoparticles without serious deterioration of
their polar properties. In many practically important cases fixed volume
(rather than fixed size) corresponds to realistic technological conditions of
nanoparticles fabrication. The letter is focused on the theoretical study of
the behavior of ferroelectric polarization, paramagnetoelectric coefficient and
phase diagrams of semi-ellipsoidal nanoparticles with fixed volume V. Our
approach combines the Landau-Ginzburg-Devonshire phenomenology, classical
electrostatics and elasticity theory. Our results show that the size effects of
the phase diagrams and polarization of semi-ellipsoidal BiFeO3 nanoparticles
nontrivially depends on V. These findings provide a path to optimize the polar
properties of nanoparticles by controlling their phase diagrams at a fixed
volume.Comment: 15 pages, 5 figures, we added the section IV. Paramagnetoelectric
(PME) coefficient at fixed volume in this version and changed title and
abstract accordingl
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