222 research outputs found
Digital analysis of the volume of the human foetal suprarenal arteries
Vascularisation of an organ is an index of its metabolic activity. The suprarenal
glands are of crucial importance in the development of pregnancy. No data
were found by the authors to describe the volume of the human foetal suprarenal
arteries throughout pregnancy. The study was designed to form a database
of human foetal suprarenal arterial volume in relation to foetal age and sex.
Digital images were obtained at 4-week intervals of the suprarenal arteries of
30 foetuses aged between 12–40 Hbd. The arteries were primarily filled with LBS
latex. A unique form of software was designed to assist in incorporating vector
graphics, spliced functions of Bezier, into the analysis. The arteries contoured by
the geometric curves were calculated for their initial, average and terminal diameter,
length and volume. The measurements were compared in relation to
foetal age and sex at 4-week intervals. Foetal age was assessed by means of
calculation from the last menstrual period, manual measurement of foot length
and ultrasonagraphic measurement of femoral length.
The suprarenal arteries in human foetuses are of strongly individual variation
both in their origin and quantity. The volume of the arteries appears constant in
the group analysed
Growth dynamics of the renal and suprarenal arteries in human foetuses
The kidneys and suprarenal cortex are of common embryonic origin. The suprarenal
gland and kidney have a common pathway in angiogenesis. Each of the
organs is of key importance for intrauterine and individual development, yet
they vary greatly in growth dynamics throughout pregnancy. The authors compared
the arterial supply of these organs quantitatively in respect to foetal age
and sex
Solitons in coupled atomic-molecular Bose-Einstein condensates in a trap
We consider coupled atomic-molecular Bose-Einstein condensate system in a
quasi-one-dimensional trap. In the vicinity of a Feshbach resonance the system
can reveal soliton-like behavior. We analyze bright soliton solutions for the
system in the trap and in the presence of the interactions between particles.
We show that with increasing number of particles in the system two bright
soliton solutions start resembling dark soliton profiles known in an atomic
Bose-Einstein condensate with repulsive interactions between atoms. We analyze
also methods for experimental preparation and detection of the soliton states.Comment: 7 pages, 7 figures, published versio
Modification of emission properties of ZnO layers due to plasmonic near-field coupling to Ag nanoislands
A simple fabrication method of Ag nanoislands on ZnO films is presented.
Continuous wave and time-resolved photoluminescence and transmission are
employed to investigate modifications of visible and UV emissions of ZnO
brought about by coupling to localized surface plasmons residing on Ag
nanoislands. The size of the nanoislands, determining their absorption and
scattering efficiencies, is found to be an important factor governing plasmonic
modification of optical response of ZnO films. The presence of the Ag
nanoislands of appropriate dimensions causes a strong (threefold) increase in
emission intensity and up to 1.5 times faster recombination. The experimental
results are successfully described by model calculations within the Mie theory.Comment: 14 pages, 5 figure
Wannier-Bloch approach to localization in high harmonics generation in solids
Emission of high-order harmonics from solids provides a new avenue in
attosecond science. On one hand, it allows to investigate fundamental processes
of the non-linear response of electrons driven by a strong laser pulse in a
periodic crystal lattice. On the other hand, it opens new paths toward
efficient attosecond pulse generation, novel imaging of electronic wave
functions, and enhancement of high-order harmonic generation (HHG) intensity. A
key feature of HHG in a solid (as compared to the well-understood phenomena of
HHG in an atomic gas) is the delocalization of the process, whereby an electron
ionized from one site in the periodic lattice may recombine with any other.
Here, we develop an analytic model, based on the localized Wannier wave
functions in the valence band and delocalized Bloch functions in the conduction
band. This Wannier-Bloch approach assesses the contributions of individual
lattice sites to the HHG process, and hence addresses precisely the question of
localization of harmonic emission in solids. We apply this model to investigate
HHG in a ZnO crystal for two different orientations, corresponding to wider and
narrower valence and conduction bands, respectively. Interestingly, for
narrower bands, the HHG process shows significant localization, similar to
harmonic generation in atoms. For all cases, the delocalized contributions to
HHG emission are highest near the band-gap energy. Our results pave the way to
controlling localized contributions to HHG in a solid crystal, with hard to
overestimate implications for the emerging area of atto-nanoscience
Bimodality and hysteresis in systems driven by confined L\'evy flights
We demonstrate occurrence of bimodality and dynamical hysteresis in a system
describing an overdamped quartic oscillator perturbed by additive white and
asymmetric L\'evy noise. Investigated estimators of the stationary probability
density profiles display not only a turnover from unimodal to bimodal character
but also a change in a relative stability of stationary states that depends on
the asymmetry parameter of the underlying noise term. When varying the
asymmetry parameter cyclically, the system exhibits a hysteresis in the
occupation of a chosen stationary state.Comment: 4 pages, 5 figures, 30 reference
Stationary states for underdamped anharmonic oscillators driven by Cauchy noise
Using methods of stochastic dynamics, we have studied stationary states in
the underdamped anharmonic stochastic oscillators driven by Cauchy noise. Shape
of stationary states depend both on the potential type and the damping. If the
damping is strong enough, for potential wells which in the overdamped regime
produce multimodal stationary states, stationary states in the underdamped
regime can be multimodal with the same number of modes like in the overdamped
regime. For the parabolic potential, the stationary density is always unimodal
and it is given by the two dimensional -stable density. For the mixture
of quartic and parabolic single-well potentials the stationary density can be
bimodal. Nevertheless, the parabolic addition, which is strong enough, can
destroy bimodlity of the stationary state.Comment: 9 page
Polarizing Bubble Collisions
We predict the polarization of cosmic microwave background (CMB) photons that
results from a cosmic bubble collision. The polarization is purely E-mode,
symmetric around the axis pointing towards the collision bubble, and has
several salient features in its radial dependence that can help distinguish it
from a more conventional explanation for unusually cold or hot features in the
CMB sky. The anomalous "cold spot" detected by the Wilkinson Microwave
Anisotropy Probe (WMAP) satellite is a candidate for a feature produced by such
a collision, and the Planck satellite and other proposed surveys will measure
the polarization on it in the near future. The detection of such a collision
would provide compelling evidence for the string theory landscape.Comment: Published version. 15 pages, 8 figure
The Gravity Dual of a Density Matrix
For a state in a quantum field theory on some spacetime, we can associate a
density matrix to any subset of a given spacelike slice by tracing out the
remaining degrees of freedom. In the context of the AdS/CFT correspondence, if
the original state has a dual bulk spacetime with a good classical description,
it is natural to ask how much information about the bulk spacetime is carried
by the density matrix for such a subset of field theory degrees of freedom. In
this note, we provide several constraints on the largest region that can be
fully reconstructed, and discuss specific proposals for the geometric
construction of this dual region.Comment: 19 pages, LaTeX, 8 figures, v2: footnote and reference adde
Levy stable noise induced transitions: stochastic resonance, resonant activation and dynamic hysteresis
A standard approach to analysis of noise-induced effects in stochastic
dynamics assumes a Gaussian character of the noise term describing interaction
of the analyzed system with its complex surroundings. An additional assumption
about the existence of timescale separation between the dynamics of the
measured observable and the typical timescale of the noise allows external
fluctuations to be modeled as temporally uncorrelated and therefore white.
However, in many natural phenomena the assumptions concerning the
abovementioned properties of "Gaussianity" and "whiteness" of the noise can be
violated. In this context, in contrast to the spatiotemporal coupling
characterizing general forms of non-Markovian or semi-Markovian L\'evy walks,
so called L\'evy flights correspond to the class of Markov processes which
still can be interpreted as white, but distributed according to a more general,
infinitely divisible, stable and non-Gaussian law. L\'evy noise-driven
non-equilibrium systems are known to manifest interesting physical properties
and have been addressed in various scenarios of physical transport exhibiting a
superdiffusive behavior. Here we present a brief overview of our recent
investigations aimed to understand features of stochastic dynamics under the
influence of L\'evy white noise perturbations. We find that the archetypal
phenomena of noise-induced ordering are robust and can be detected also in
systems driven by non-Gaussian, heavy-tailed fluctuations with infinite
variance.Comment: 7 pages, 8 figure
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