20,453 research outputs found
Renormalized field theory and particle density profile in driven diffusive systems with open boundaries
We investigate the density profile in a driven diffusive system caused by a
plane particle source perpendicular to the driving force. Focussing on the case
of critical bulk density we use a field theoretic renormalization
group approach to calculate the density as a function of the distance
from the particle source at first order in (: spatial
dimension). For we find reasonable agreement with the exact solution
recently obtained for the asymmetric exclusion model. Logarithmic corrections
to the mean field profile are computed for with the result for .Comment: 32 pages, RevTex, 4 Postscript figures, to appear in Phys. Rev.
Strongly anisotropic roughness in surfaces driven by an oblique particle flux
Using field theoretic renormalization, an MBE-type growth process with an
obliquely incident influx of atoms is examined. The projection of the beam on
the substrate plane selects a "parallel" direction, with rotational invariance
restricted to the transverse directions. Depending on the behavior of an
effective anisotropic surface tension, a line of second order transitions is
identified, as well as a line of potentially first order transitions, joined by
a multicritical point. Near the second order transitions and the multicritical
point, the surface roughness is strongly anisotropic. Four different roughness
exponents are introduced and computed, describing the surface in different
directions, in real or momentum space. The results presented challenge an
earlier study of the multicritical point.Comment: 11 pages, 2 figures, REVTeX
Locally Adaptive Frames in the Roto-Translation Group and their Applications in Medical Imaging
Locally adaptive differential frames (gauge frames) are a well-known
effective tool in image analysis, used in differential invariants and
PDE-flows. However, at complex structures such as crossings or junctions, these
frames are not well-defined. Therefore, we generalize the notion of gauge
frames on images to gauge frames on data representations defined on the extended space of positions and
orientations, which we relate to data on the roto-translation group ,
. This allows to define multiple frames per position, one per
orientation. We compute these frames via exponential curve fits in the extended
data representations in . These curve fits minimize first or second
order variational problems which are solved by spectral decomposition of,
respectively, a structure tensor or Hessian of data on . We include
these gauge frames in differential invariants and crossing preserving PDE-flows
acting on extended data representation and we show their advantage compared
to the standard left-invariant frame on . Applications include
crossing-preserving filtering and improved segmentations of the vascular tree
in retinal images, and new 3D extensions of coherence-enhancing diffusion via
invertible orientation scores
Pulmonary giant cells and their significance for the diagnosis of asphyxiation
This study was performed to prove whether the detection of polynuclear giant cells in lungs is useful for the diagnosis of asphyxiation due to throttling or strangulation. Therefore, lung specimens of 54 individuals with different natural and unnatural causes of death were investigated. In most lungs examined numerous alveolar macrophages with 1-2 nuclei were found. Polynuclear giant cells, which were arbitrarily defined as alveolar macrophages containing 3 or more nuclei, were observed in all groups investigated except in the cases of hypoxia due to covering the head with plastic bags. Apparent differences between the other groups in particular an increased number in cases of throttling or strangulation, could not be observed. Immunohistochemical investigations confirmed the hypothesis that the observed polynuclear giant cells were derived from alveolar macrophages. The immunohistochemical analysis of the proliferation marker antigen Ki 67 revealed no positive reaction in the nuclei of polynuclear giant cells indicating that these cells had not developed shortly before death by endomitosis as an adaptative change following reduction in oxygen supply. The results provide evidence that the detection of pulmonary polynuclear giant cells cannot be used as a practical indicator for death by asphyxiation due to throttling or strangulation
On Critical Exponents and the Renormalization of the Coupling Constant in Growth Models with Surface Diffusion
It is shown by the method of renormalized field theory that in contrast to a
statement based on a mathematically ill-defined invariance transformation and
found in most of the recent publications on growth models with surface
diffusion, the coupling constant of these models renormalizes nontrivially.
This implies that the widely accepted supposedly exact scaling exponents are to
be corrected. A two-loop calculation shows that the corrections are small and
these exponents seem to be very good approximations.Comment: 4 pages, revtex, 2 postscript figures, to appear in Phys.Rev.Let
Correlation of eigenstates in the critical regime of quantum Hall systems
We extend the multifractal analysis of the statistics of critical wave
functions in quantum Hall systems by calculating numerically the correlations
of local amplitudes corresponding to eigenstates at two different energies. Our
results confirm multifractal scaling relations which are different from those
occurring in conventional critical phenomena. The critical exponent
corresponding to the typical amplitude, , gives an almost
complete characterization of the critical behavior of eigenstates, including
correlations. Our results support the interpretation of the local density of
states being an order parameter of the Anderson transition.Comment: 17 pages, 9 Postscript figure
Mean-field scaling function of the universality class of absorbing phase transitions with a conserved field
We consider two mean-field like models which belong to the universality class
of absorbing phase transitions with a conserved field. In both cases we derive
analytically the order parameter as function of the control parameter and of an
external field conjugated to the order parameter. This allows us to calculate
the universal scaling function of the mean-field behavior. The obtained
universal function is in perfect agreement with recently obtained numerical
data of the corresponding five and six dimensional models, showing that four is
the upper critical dimension of this particular universality class.Comment: 8 pages, 2 figures, accepted for publication in J. Phys.
AgroDataCube and AGINFRA+: Operationalising Big Data for Agricultural Informatics
Big Data methods and tools are becoming widely adopted by the ICT industry and create new opportunities for data intensive science in the agro-environmental domain. However, Big Data adoption is still in its infancy for Agricultural Information Systems, and many barriers still exist for wider use of big data analysis ..
Surface critical behavior of driven diffusive systems with open boundaries
Using field theoretic renormalization group methods we study the critical
behavior of a driven diffusive system near a boundary perpendicular to the
driving force. The boundary acts as a particle reservoir which is necessary to
maintain the critical particle density in the bulk. The scaling behavior of
correlation and response functions is governed by a new exponent eta_1 which is
related to the anomalous scaling dimension of the chemical potential of the
boundary. The new exponent and a universal amplitude ratio for the density
profile are calculated at first order in epsilon = 5-d. Some of our results are
checked by computer simulations.Comment: 10 pages ReVTeX, 6 figures include
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