2,532 research outputs found
Close-circuit domain quadruplets in BaTiO nanorods embedded in SrTiO film
Cylindrical BaTiO3 nanorods embedded in (100)-oriented SrTiO3 epitaxial film
in a brush-like configuration are investigated in the framework of the
Ginzburg-Landau-Devonshire model. It is shown that strain compatibility at
BaTiO3/SrTiO3 interfaces keeps BaTiO3 nanorods in the rhombohedral phase even
at room temperature. Depolarization field at the BaTiO3/SrTiO3 interfaces is
reduced by an emission of the 109-degree or 71-degree domain boundaries. In
case of nanorods of about 10-80 nm diameter, the ferroelectric domains are
found to form a quadruplet with a robust flux-closure arrangement of the
in-plane components of the spontaneous polarization. The out-of-plane
components of the polarization are either balanced or oriented up or down along
the nanorod axis. Switching of the out-of-plane polarization with coercive
field of about V/m occurs as a collapse of a 71-degree cylindrical
domain boundary formed at the curved circumference surface of the nanorod. The
remnant domain quadruplet configuration is chiral, with the macroscopic
symmetry. More complex stable domain configurations with coexisting clockwise
and anticlockwise quadruplets contain interesting arrangement of strongly
curved 71-degree boundaries.Comment: Erratta - corrected error in Fig.
Concentration inequalities for random fields via coupling
We present a new and simple approach to concentration inequalities for
functions around their expectation with respect to non-product measures, i.e.,
for dependent random variables. Our method is based on coupling ideas and does
not use information inequalities. When one has a uniform control on the
coupling, this leads to exponential concentration inequalities. When such a
uniform control is no more possible, this leads to polynomial or
stretched-exponential concentration inequalities. Our abstract results apply to
Gibbs random fields, in particular to the low-temperature Ising model which is
a concrete example of non-uniformity of the coupling.Comment: New corrected version; 22 pages; 1 figure; New result added:
stretched-exponential inequalit
Domain walls of ferroelectric BaTiO3 within the Ginzburg-Landau-Devonshire phenomenological model
Mechanically compatible and electrically neutral domain walls in tetragonal,
orthorhombic and rhombohedral ferroelectric phases of BaTiO3 are systematically
investigated in the framework of the phenomenological
Ginzburg-Landau-Devonshire (GLD) model with parameters of Ref. [Hlinka and
Marton, Phys. Rev. 74, 104104 (2006)]. Polarization and strain profiles within
domain walls are calculated numerically and within an approximation leading to
the quasi-one-dimensional analytic solutions applied previously to the
ferroelectric walls of the tetragonal phase [W. Cao and L.E. Cross, Phys. Rev.
44, 5 (1991)]. Domain wall thicknesses and energy densities are estimated for
all mechanically compatible and electrically neutral domain wall species in the
entire temperature range of ferroelectric phases. The model suggests that the
lowest energy walls in the orthorhombic phase of BaTiO3 are the 90-degree and
60-degree walls. In the rhombohedral phase, the lowest energy walls are the
71-degree and 109-degree walls. All these ferroelastic walls have thickness
below 1 nm except for the 90-degree wall in the tetragonal phase and the
60-degree S-wall in the orthorhombic phase, for which the larger thickness of
the order of 5 nm was found. The antiparallel walls of the rhombohedral phase
have largest energy and thus they are unlikely to occur. The calculation
indicates that the lowest energy structure of the 109-degree wall and few other
domain walls in the orthorhombic and rhombohedral phases resemble Bloch-like
walls known from magnetism.Comment: 12 pages, 9 figure
Study of timing performance of Silicon Photomultiplier and application for a Cherenkov detector
Silicon photomultipliers are very versatile photo detectors due to their high
photon detection efficiency, fast response, single photon counting capability,
high amplification, and their insensitivity to magnetic fields. At our
institute we are studying the performance of these photo detectors at various
operating conditions. On the basis of the experience in the laboratory we built
a prototype of a timing Cherenkov detector consisting of a quartz radiator with
two mm MPPCs S10362-33-100C from Hamamatsu Photonics as
photodetectors. The MPPC sensors were operated with Peltier cooling to minimize
thermal noise and to avoid gain drifts. The test measurements at the DANE
Beam-Test Facility (BTF) at the Laboratori Nazionali di Frascati (LNF) with
pulsed 490 MeV electrons and the results on timing performance with Cherenkov
photons are presented.Comment: Conference proceedings of 12th Vienna Conference on Instrumentation
201
Studies on the maize cold tolerance tests in the MartonvĂĄsĂĄr phytotron
The climatic conditions in Hungary and in the countries to which seed is exported
makes the study of maize cold tolerance and constant improvements in the cold tolerance
of MartonvĂĄsĂĄr hybrids especially important. An improvement in the early spring cold
tolerance of maize would allow it to be grown in more northern areas with a cooler
climate, while on traditional maize-growing areas the profitability of maize production
could be improved by earlier sowing, leading to a reduction in transportation and drying
costs and in diseases caused by Fusarium sp. The recognition of this fact led MartonvĂĄsĂĄr
researchers to start investigating this subject nearly four decades ago. The phytotron has
proved an excellent tool for studying and improving the cold tolerance of maize. The
review will give a brief summary of the results achieved in the field of maize cold
tolerance in the MartonvĂĄsĂĄr institute in recent decades
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