1,542 research outputs found
Scaling Relations of Compressible MHD Turbulence
We study scaling relations of compressible strongly magnetized turbulence. We
find a good correspondence of our results with the Fleck (1996) model of
compressible hydrodynamic turbulence. In particular, we find that the
density-weighted velocity, i.e. , proposed in Kritsuk et
al. (2007) obeys the Kolmogorov scaling, i.e. for the
high Mach number turbulence. Similarly, we find that the exponents of the third
order structure functions for stay equal to unity for the all the Mach
numbers studied. The scaling of higher order correlations obeys the She-Leveque
(1994) scalings corresponding to the two-dimensional dissipative structures,
and this result does not change with the Mach number either. In contrast to
which exhibits different scaling parallel and perpendicular to the local
magnetic field, the scaling of is similar in both directions. In addition,
we find that the peaks of density create a hierarchy in which both physical and
column densities decrease with the scale in accordance to the Fleck (1996)
predictions. This hierarchy can be related ubiquitous small ionized and neutral
structures (SINS) in the interstellar gas. We believe that studies of
statistics of the column density peaks can provide both consistency check for
the turbulence velocity studies and insight into supersonic turbulence, when
the velocity information is not available.Comment: 4 pages, 5 figure
The role of pressure anisotropy in the turbulent intracluster medium
In low-density plasma environments, such as the intracluster medium (ICM),
the Larmour frequency is much larger than the ion-ion collision frequency. In
such a case, the thermal pressure becomes anisotropic with respect to the
magnetic field orientation and the evolution of the turbulent gas is more
correctly described by a kinetic approach. A possible description of these
collisionless scenarios is given by the so-called kinetic magnetohydrodynamic
(KMHD) formalism, in which particles freely stream along the field lines, while
moving with the field lines in the perpendicular direction. In this way a
fluid-like behavior in the perpendicular plane is restored. In this work, we
study fast growing magnetic fluctuations in the smallest scales which operate
in the collisionless plasma that fills the ICM. In particular, we focus on the
impact of a particular evolution of the pressure anisotropy and its
implications for the turbulent dynamics of observables under the conditions
prevailing in the ICM. We present results from numerical simulations and
compare the results which those obtained using an MHD formalism.Comment: 7 pages, 14 figures, Journal of Physics: Conference Serie
Two-Stage Convolutional Neural Network for Breast Cancer Histology Image Classification
This paper explores the problem of breast tissue classification of microscopy
images. Based on the predominant cancer type the goal is to classify images
into four categories of normal, benign, in situ carcinoma, and invasive
carcinoma. Given a suitable training dataset, we utilize deep learning
techniques to address the classification problem. Due to the large size of each
image in the training dataset, we propose a patch-based technique which
consists of two consecutive convolutional neural networks. The first
"patch-wise" network acts as an auto-encoder that extracts the most salient
features of image patches while the second "image-wise" network performs
classification of the whole image. The first network is pre-trained and aimed
at extracting local information while the second network obtains global
information of an input image. We trained the networks using the ICIAR 2018
grand challenge on BreAst Cancer Histology (BACH) dataset. The proposed method
yields 95 % accuracy on the validation set compared to previously reported 77 %
accuracy rates in the literature. Our code is publicly available at
https://github.com/ImagingLab/ICIAR2018Comment: 10 pages, 5 figures, ICIAR 2018 conferenc
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Surface activation for low temperature wafer fusion bonding by radicals produced in an oxygen discharge
A new method of exposing silicon/semiconductor wafers to a mixture of radicals is described, in which these species are generated in an oxygen-rich gas discharge confined between a concentric pair of annular mesh electrodes surrounding the wafers. This approach allows the wafer surfaces to be treated without damage from the energetic ions, strong electric fields, and high UV fluxes associated with direct treatment by exposure to gas discharge plasmas. The process is compared with direct oxygen plasma activation for its latitude with respect to treatment duration, effect on wafer surface roughness and bond strength. Wider process latitude and reduced surface roughening are obtained for treatment by radicals compared with direct plasma exposure. Comparative analysis of treated and untreated silicon surfaces by X-ray photoelectron spectroscopy indicate that traces of fluorine present on the wafer surface before treatment are removed with great efficiency by the process
Discussion of the Electromotive Force Terms in the Model of Parker-unstable Galactic Disks with Cosmic Rays and Shear
We analyze the electromotive force (EMF) terms and basic assumptions of the
linear and nonlinear dynamo theories in our three-dimensional (3D) numerical
model of the Parker instability with cosmic rays and shear in a galactic disk.
We also apply the well known prescriptions of the EMF obtained by the nonlinear
dynamo theory (Blackman & Field 2002 and Kleeorin et al. 2003) to check if the
EMF reconstructed from their prescriptions corresponds to the EMF obtained
directly from our numerical models. We show that our modeled EMF is fully
nonlinear and it is not possible to apply any of the considered nonlinear
dynamo approximations due to the fact that the conditions for the scale
separation are not fulfilled.Comment: 15 pages, 12 figure
Asteroids in the Inner Solar System II - Observable Properties
This paper presents synthetic observations of long-lived, coorbiting
asteroids of Mercury, Venus, the Earth and Mars. Our sample is constructed by
taking the limiting semimajor axes, differential longitudes and inclinations
for long-lived stability provided by simulations. The intervals are randomly
populated with values to create initial conditions. These orbits are
re-simulated to check that they are stable and then re-sampled every 2.5 years
for 1 million years. The Mercurian sample contains only horseshoe orbits, the
Martian sample only tadpoles. For both Venus and the Earth, the greatest
concentration of objects on the sky occurs close to the classical Lagrange
points at heliocentric ecliptic longitudes of 60 and 300 degrees. The
distributions are broad especially if horseshoes are present in the sample. The
full-width half maximum (FWHM) in heliocentric longitude for Venus is 325
degrees and for the Earth is 328 degrees. The mean and most common velocity of
these coorbiting satellites coincides with the mean motion of the parent
planet, but again the spread is wide with a FWHM for Venus of 27.8 arcsec/hr
and for the Earth of 21.0 arcsec/hr. For Mars, the greatest concentration on
the sky occurs at heliocentric ecliptic latitudes of 12 degrees. The peak of
the velocity distribution occurs at 65 arcsec/hr, significantly less than the
Martian mean motion, while its FWHM is 32.3 arcsec/hr. The case of Mercury is
the hardest of all, as the greatest concentration occurs at heliocentric
longitudes close to the Sun.Comment: 16 pages, 11 figures, Monthly Notices (in press). Higher quality
figures available at
http://www-thphys.physics.ox.ac.uk/users/WynEvans/home.htm
The formation of grounding zone wedges: theory and experiments
We present a fluid-mechanical explanation of the formation of sedimentary wedges deposited at ice-stream grounding zones. We model both ice and till as layers of viscous fluid spreading under gravity into an inviscid ocean. To test the fundamentals of our theory, we perform a series of laboratory experiments in which we find that a similar wedge of underlying, less viscous fluid accumulates spontaneously around the grounding line. We formulate a simple local condition relating wedge slopes, which determines wedge geometry. It expresses a balance of fluxes of till either side of the grounding line and involves upstream and downstream gradients of till thicknesses as well as the upper surface gradient of the ice. It shows that a wedge will form, that is the upstream till thickness gradients are positive, when the flux of till driven by the glaciostatic pressure gradient of the overlying ice is greater than the flux of till ahead of the grounding zone. This is related to the unloading of the till as the ice sheet crosses the grounding line
Multi-step particle emission probabilities in superheavy nuclei at moderate excitation energies
The probabilities of -, -, and -evaporation channels in
excited superheavy nuclei were evaluated using the Monte Carlo method. The
calculations utilized microscopically determined nuclear level densities and
were compared with results obtained from the phenomenological Jackson formula.
Effective temperatures derived from the microscopic approach were incorporated
into the Jackson formula for different evaporation channels at low and moderate
excitation energies. Additionally, an analytical formula was introduced to
estimate the average kinetic energy of emitted particles in multi-step
processes.Comment: 10 pages, 3 figure
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