200 research outputs found
Recrystallization and investigation of bismuth thin films by means of electron beam in transmission electron microscope
Thin bismuth films obtained by vacuum deposition were recrystallized under electron beam of scanning electron microscope at 5 kV and examined in a transmission electron microscope at 200 kV. In recrystallized films, various microstructures were detected: single-crystal, polycrystalline and amorphous regions, more or less faceted grains, single crystals and untransparent drop-shaped particles. In the crystallized film, a strong internal bending of the crystal lattice is detected, up to 110 deg/μm. © Published under licence by IOP Publishing Ltd.Partial support of project 3.6121.2017/8.9 (The Ministry of Education and Science of the Russian Federation) and Agreement No 02.A03.21.0006 (Act 211 Government of the Russian Federation) is acknowledged
Transitions between "" and "0" states in superconductor -- ferromagnet -- superconductor junctions
Experimental and theoretical study of superconductor (S) -- ferromagnet (F)
-- superconductor junctions showed that in certain range of parameters (e.g.,
the length of the ferromagnet , the exchange field, ) the
ground state of a SFS junction corresponds to superconducting phase difference
or 0. The phase diagram of a SFS junction with the respect to and 0
states is investigated in this letter in space. It is
shown that the phase diagram is very sensitive to the geometry of the system,
in particular, to the amount of disorder.Comment: Minor changes. References adde
Derivative pricing under the possibility of long memory in the supOU stochastic volatility model
We consider the supOU stochastic volatility model which is able to exhibit
long-range dependence. For this model we give conditions for the discounted
stock price to be a martingale, calculate the characteristic function, give a
strip where it is analytic and discuss the use of Fourier pricing techniques.
Finally, we present a concrete specification with polynomially decaying
autocorrelations and calibrate it to observed market prices of plain vanilla
options
On Robustness of Discrete Time Optimal Filters
A new result on stability of an optimal nonlinear filter for a Markov chain with respect to small perturbations on every step is established. An exponential recurrence of the signal is assumed
Domain wall effects in ferromagnet-superconductor structures
We investigate how domain structure of the ferromagnet in
superconductor-ferromagnet heterostructures may change their transport
properties. We calculate the distribution of current in the superconductor
induced by magnetic field of Bloch domain walls, find the ``lower critical''
magnetization of the ferromagnet that provides vortices in the superconductor
Centers of crystallization in antimony thin films studied by transnission electron microscopy
We performed TEM studies of 7 crystallization centers using specially evaporated Sb thin films in finite areas. Strong internal lattice bending is revealed by use of the bend contour method.Partial support of project 3.6121.2017/8.9 (RF Ministry of Education and Science) and agreement № 02.A03.21.0006 (Act 211 Government of the RF) is acknowledged
Stability of junction configurations in ferromagnet-superconductor heterostructures
We investigate the stability of possible order parameter configurations in
clean layered heterostructures of the type, where is a
superconductor and a ferromagnet. We find that for most reasonable values
of the geometric parameters (layer thicknesses and number) and of the material
parameters (such as magnetic polarization, wavevector mismatch, and oxide
barrier strength) several solutions of the {\it self consistent} microscopic
equations can coexist, which differ in the arrangement of the sequence of ``0''
and ``'' junction types (that is, with either same or opposite sign of the
pair potential in adjacent layers). The number of such coexisting self
consistent solutions increases with the number of layers. Studying the relative
stability of these configurations requires an accurate computation of the small
difference in the condensation free energies of these inhomogeneous systems. We
perform these calculations, starting with numerical self consistent solutions
of the Bogoliubov-de Gennes equations. We present extensive results for the
condensation free energies of the different possible configurations, obtained
by using efficient and accurate numerical methods, and discuss their relative
stabilities. Results for the experimentally measurable density of states are
also given for different configurations and clear differences in the spectra
are revealed. Comprehensive and systematic results as a function of the
relevant parameters for systems consisting of three and seven layers (one or
three junctions) are given, and the generalization to larger number of layers
is discussed.Comment: 17 pages, including 14 Figures. Higher resolution figures available
from the author
Dynamics of gravity driven three-dimensional thin films on hydrophilic-hydrophobic patterned substrates
We investigate numerically the dynamics of unstable gravity driven
three-dimensional thin liquid films on hydrophilic-hydrophobic patterned
substrates of longitudinal stripes and checkerboard arrangements. The thin film
can be guided preferentially on hydrophilic longitudinal stripes, while fingers
develop on adjacent hydrophobic stripes if their width is large enough. On
checkerboard patterns, the film fingering occurs on hydrophobic domains, while
lateral spreading is favoured on hydrophilic domains, providing a mechanism to
tune the growth rate of the film. By means of kinematical arguments, we
quantitatively predict the growth rate of the contact line on checkerboard
arrangements, providing a first step towards potential techniques that control
thin film growth in experimental setups.Comment: 30 pages, 12 figure
Air entrainment through free-surface cusps
In many industrial processes, such as pouring a liquid or coating a rotating
cylinder, air bubbles are entrapped inside the liquid. We propose a novel
mechanism for this phenomenon, based on the instability of cusp singularities
that generically form on free surfaces. The air being drawn into the narrow
space inside the cusp destroys its stationary shape when the walls of the cusp
come too close. Instead, a sheet emanates from the cusp's tip, through which
air is entrained. Our analytical theory of this instability is confirmed by
experimental observation and quantitative comparison with numerical simulations
of the flow equations
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