2,530 research outputs found
N-body + Magnetohydrodynamical Simulations of Merging Clusters of Galaxies: Characteristic Magnetic Field Structures Generated by Bulk Flow Motion
We present results from N-body + magnetohydrodynamical simulations of merging
clusters of galaxies. We find that cluster mergers cause various characteristic
magnetic field structures because of the strong bulk flows in the intracluster
medium. The moving substructures result in cool regions surrounded by the
magnetic field. These will be recognized as magnetized cold fronts in the
observational point of view. A relatively ordered magnetic field structure is
generated just behind the moving substructure. Eddy-like field configurations
are also formed by Kelvin-Helmholtz instabilities. These features are similarly
seen even in off-center mergers though the detailed structures change slightly.
The above-mentioned characteristic magnetic field structures are partly
recognized in Faraday rotation measure maps. The higher absolute values of the
rotation measure are expected when observed along the collision axis, because
of the elongated density distribution and relatively ordered field structure
along the axis. The rotation measure maps on the cosmic microwave background
radiation, which covers clusters entirely, could be useful probes of not only
the magnetic field structures but also the internal dynamics of the
intracluster medium.Comment: Accepted for publication in Ap
Topological susceptibility at zero and finite temperature in the Nambu-Jona-Lasinio model
We consider the three flavor Nambu-Jona-Lasinio model with the 't Hooft
interaction incorporating the U(1)_A anomaly. In order to set the coupling
strength of the 't Hooft term, we employ the topological susceptibility
instead of the eta' meson mass. The value for is taken from lattice
simulations. We also calculate at finite temperature within the model.
Comparing it with the lattice data, we extract information about the behavior
of the U(1)_A anomaly at finite temperature. We conclude that within the
present framework, the effective restoration of the U(1)_A symmetry does not
necessarily take place even at high temperature where the chiral symmetry is
restored.Comment: 9 pages, 14 figures, to be published in Phys.Rev.
The dead ringer/retained transcriptional regulatory gene is required for positioning of the longitudinal glia in the Drosophila embryonic CNS
The Drosophila dead ringer (dri, also known as retained, retn) gene encodes a nuclear protein with a conserved DNA-binding domain termed the ARID (AT-rich interaction domain). We show here that dri is expressed in a subset of longitudinal glia in the Drosophila embryonic central nervous system and that dri forms part of the transcriptional regulatory cascade required for normal development of these cells. Analysis of mutant embryos revealed a role for dri in formation of the normal embryonic CNS. Longitudinal glia arise normally in dri mutant embryos, but they fail to migrate to their final destinations. Disruption of the spatial organization of the dri-expressing longitudinal glia accounts for the mild defects in axon fasciculation observed in the mutant embryos. Consistent with the late phenotypes observed, expression of the glial cells missing (gcm) and reversed polarity (repo) genes was found to be normal in dri mutant embryos. However, from stage 15 of embryogenesis, expression of locomotion defects (loco) and prospero (pros) was found to be missing in a subset of LG. This suggests that loco and pros are targets of DRI transcriptional activation in some LG. We conclude that dri is an important regulator of the late development of longitudinal glia
Magnetic helicity transported by flux emergence and shuffling motions in Solar Active Region NOAA 10930
We present a new methodology which can determine magnetic helicity transport
by the passage of helical magnetic field lines from sub-photosphere and the
shuffling motions of foot-points of preexisting coronal field lines separately.
It is well known that only the velocity component which is perpendicular to the
magnetic field () has contribution to the helicity
accumulation. Here, we demonstrate that can be deduced
from horizontal motion and vector magnetograms, under a simple relation of
as suggested by
Dmoulin & Berger (2003). Then after dividing
into two components, as one is tangential and the other is normal to the solar
surface, we can determine both terms of helicity transport. Active region (AR)
NOAA 10930 is analyzed as an example during its solar disk center passage by
using data obtained by the Spectro-Polarimeter and the Narrowband Filter Imager
of Solar Optical Telescope on board Hinode. We find that in our calculation,
the helicity injection by flux emergence and shuffling motions have the same
sign. During the period we studied, the main contribution of helicity
accumulation comes from the flux emergence effect, while the dynamic transient
evolution comes from the shuffling motions effect. Our observational results
further indicate that for this AR, the apparent rotational motion in the
following sunspot is the real shuffling motions on solar surface
Coronary arterial dynamics computation with medical-image-based time-dependent anatomical models and element-based zero-stress state estimates
We propose a method for coronary arterial dynamics computation with medical-image-based time-dependent anatomical models. The objective is to improve the computational analysis of coronary arteries for better understanding of the links between the atherosclerosis development and mechanical stimuli such as endothelial wall shear stress and structural stress in the arterial wall. The method has two components. The first one is element-based zero-stress (ZS) state estimation, which is an alternative to prestress calculation. The second one is a "mixed ZS state" approach, where the ZS states for different elements in the structural mechanics mesh are estimated with reference configurations based on medical images coming from different instants within the cardiac cycle. We demonstrate the robustness of the method in a patient-specific coronary arterial dynamics computation where the motion of a thin strip along the arterial surface and two cut surfaces at the arterial ends is specified to match the motion extracted from the medical images. © 2014 The Author(s)
Comparative patient-specific fsi modeling of cerebral aneurysms
We consider a total of ten cases, at three different locations, half of which
ruptured sometime after the images were taken. We use the stabilized space–time FSI
technique developed by the Team for Advanced Flow Simulation and Modeling, together
with a number of special techniques targeting arterial FSI modeling. We compare the ten
cases based on the wall shear stress, oscillatory shear index, and the arterial-wall stress.
We also investigate how simpler approaches to computer modeling of cerebral aneurysms
perform compared to FSI modeling
Using double radio relics to constrain galaxy cluster mergers: A model of double radio relics in CIZA J2242.8+5301
Galaxy clusters grow by mergers with other clusters and galaxy groups. These
mergers create shock waves within the intracluster medium (ICM) that can
accelerate particles to extreme energies. In the presence of magnetic fields,
relativistic electrons form large regions emitting synchrotron radiation,
so-called radio relics. Behind the shock front, synchrotron and inverse Compton
(IC) losses cause the radio spectral index to steepen away from the shock
front. An example of such a cluster is CIZA J2242.8+5301, where very clear
spectral steepening in the downstream region is observed. Here we present
hydrodynamical simulations of idealized binary cluster mergers with the aim of
constraining the merger scenario for this cluster. From our simulations, we
find that CIZA J2242.8+5301 is probably undergoing a merger in the plane of the
sky (less then 10 deg from edge-on) with a mass ratio of about 2:1, and an
impact parameter < 400 kpc. We find that the core passage of the clusters
happened about 1 Gyr ago. We conclude that double relics relics can set
constraints on the mass ratios, impact parameters, timescales, and viewing
geometry of binary cluster mergers, which is particularly useful when detailed
X-ray observations are not available. In addition, the presence of large radio
relics can be used to constrain the degree of clumping in the outskirts of the
ICM, which is important to constrain the baryon fraction, density and entropy
profiles, around the virial radius and beyond. We find that the amplitude of
density fluctuations, with sizes of < 200 kpc, in the relic in CIZA
J2242.8+5301 is not larger than 30%. [abridged]Comment: 14 pages, 8 figures, accepted for publication in MNRAS on July 20,
201
Imaging Simulations of the Sunyaev-Zel'dovich Effect for ALMA
We present imaging simulations of the Sunyaev-Zel'dovich effect of galaxy
clusters for the Atacama Large Millimeter/submillimeter Array (ALMA) including
the Atacama Compact Array (ACA). In its most compact configuration at 90GHz,
ALMA will resolve the intracluster medium with an effective angular resolution
of 5 arcsec. It will provide a unique probe of shock fronts and relativistic
electrons produced during cluster mergers at high redshifts, that are hard to
spatially resolve by current and near-future X-ray detectors. Quality of image
reconstruction is poor with the 12m array alone but improved significantly by
adding ACA; expected sensitivity of the 12m array based on the thermal noise is
not valid for the Sunyaev-Zel'dovich effect mapping unless accompanied by an
ACA observation of at least equal duration. The observations above 100 GHz will
become excessively time-consuming owing to the narrower beam size and the
higher system temperature. On the other hand, significant improvement of the
observing efficiency is expected once Band 1 is implemented in the future.Comment: 16 pages, 12 figures. Accepted for publication in PASJ. Note added in
proof is include
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