457 research outputs found
Long-Lived Double-Barred Galaxies From Pseudo-Bulges
A large fraction of barred galaxies host secondary bars that are embedded in
their large-scale primary counterparts. These are common also in gas poor
early-type barred galaxies. The evolution of such double-barred galaxies is
still not well understood, partly because of a lack of realistic -body
models with which to study them. Here we report a new mechanism for generating
such systems, namely the presence of rotating pseudo-bulges. We demonstate with
high mass and force resolution collisionless -body simulations that
long-lived secondary bars can form spontaneously without requiring gas,
contrary to previous claims. We find that secondary bars rotate faster than
primary ones. The rotation is not, however, rigid: the secondary bars pulsate,
with their amplitude and pattern speed oscillating as they rotate through the
primary bars. This self-consistent study supports previous work based on
orbital analysis in the potential of two rigidly rotating bars. The pulsating
nature of secondary bars may have important implications for understanding the
central region of double-barred galaxies.Comment: Paper submitted to ApJ
Continuum models of focused electron beam induced processing
© 2015 Toth et al. Focused electron beam induced processing (FEBIP) is a suite of direct-write, high resolution techniques that enable fabrication and editing of nanostructured materials inside scanning electron microscopes and other focused electron beam (FEB) systems. Here we detail continuum techniques that are used to model FEBIP, and release software that can be used to simulate a wide range of processes reported in the FEBIP literature. These include: (i) etching and deposition performed using precursors that interact with a surface through physisorption and activated chemisorption, (ii) gas mixtures used to perform simultaneous focused electron beam induced etching and deposition (FEBIE and FEBID), and (iii) etch processes that proceed through multiple reaction pathways and generate a number of reaction products at the substrate surface. We also review and release software for Monte Carlo modeling of the precursor gas flux which is needed as an input parameter for continuum FEBIP models
Natalizumab induced blood eosinophilia: A retrospective pharmacovigilance cohort study and review of the literature.
OBJECTIVE
To describe frequency of natalizumab related eosinophilia and clinical symptoms of eosinophilic disease in our monocentric cohort.
METHODS
Comparison of clinical characteristics of 115 natalizumab treated and 116 untreated RRMS patients and review of literature.
RESULTS
38% of natalizumab treated patients had eosinophilia, which occurred significantly more frequently compared to untreated MS patients (3%, p-value<0.001). In symptomatic patients, mean eosinophil counts were significantly higher than in asymptomatic patients and symptoms developed within one year.
DISCUSSION
Eosinophilia is a side effect of natalizumab and mostly asymptomatic. However, few patients develop within one year after start of natalizumab an eosinophilic disease as severe side effect
A Kinematic Link between Boxy Bulges, Stellar Bars, and Nuclear Activity in NGC 3079 & NGC 4388
We present direct kinematic evidence for bar streaming motions in two active
galaxies with boxy stellar bulges. The Hawaii Imaging Fabry-Perot
Interferometer was used on the Canada-France-Hawaii 3.6-m telescope and the
University of Hawaii 2.2-m telescope to derive the two-dimensional velocity
field of the line-emitting gas in the disks of the Sc galaxy NGC 3079 and the
Sb galaxy NGC 4388. In contrast to previous work based on long-slit data, the
detection of the bar potential from the Fabry-Perot data does not rely on the
existence of inner Lindblad resonances or strong bar-induced shocks. Simple
kinematic models which approximate the intrinsic gas orbits as nonintersecting,
inclined elliptical annuli that conserve angular momentum characterize the
observed velocity fields. Box-shaped bulges in both NGC 3079 and NGC 4388 are
confirmed using new near-infrared images to reduce dust obscuration.
Morphological analysis of starlight in these galaxies is combined with the gas
kinematics derived from the Fabry-Perot spectra to test evolutionary models of
stellar bars that involve transitory boxy bulges, and to quantify the
importance of such bars in fueling active nuclei. Our data support the
evolutionary bar models, but fail to prove convincingly that the stellar bars
in NGC 3079 and NGC 4388 directly trigger or sustain the nuclear activity.
(abridged)Comment: 31 pages, 18 figures, Latex, requires aaspp4.sty. Accepted for the
Astronomical Journal (November issue
SPH Simulations of Galactic Gaseous Disk with Bar: Distribution and Kinematic Structure of Molecular Clouds toward the Galactic Center
We have performed Smoothed Particle Hydrodynamic (SPH) simulations to study
the response of molecular clouds in the Galactic disk to a rotating bar and
their subsequent evolution in the Galactic Center (GC) region. The Galactic
potential in our models is contributed by three axisymmetric components
(massive halo, exponential disk, compact bulge) and a non-axisymmetric bar.
These components are assumed to be invariant in time in the frame corotating
with the bar. Some noticeable features such as an elliptical outer ring, spiral
arms, a gas-depletion region, and a central concentration have been developed
due to the influence of the bar. The rotating bar induces non-circular motions
of the SPH particles, but hydrodynamic collisions tend to suppress the random
components of the velocity. The velocity field of the SPH particles is
consistent with the kinematics of molecular clouds observed in HCN (1-0)
transition; these clouds are thought to be very dense clouds. However, the l-v
diagram of the clouds traced by CO is quite different from that of our SPH
simulation, being more similar to that obtained from simulations using
collisionless particles. The diagram of a mixture of collisional and
collisionless particles gives better reproduction of the kinematic structures
of the GC clouds observed in the CO line. The fact that the kinematics of HCN
clouds can be reproduced by the SPH particles suggests that the dense clouds in
the GC are formed via cloud collisions induced by rotating bar.Comment: 31 pages, 10 pigures, accepted for publication in Ap
Bar Diagnostics in Edge-On Spiral Galaxies. III. N-Body Simulations of Disks
Present in over 45% of local spirals, boxy and peanut-shaped bulges are
generally interpreted as edge-on bars and may represent a key phase in the
evolution of bulges. Aiming to test such claims, the kinematic properties of
self-consistent 3D N-body simulations of bar-unstable disks are studied. Using
Gauss-Hermite polynomials to describe the stellar kinematics, a number of
characteristic bar signatures are identified in edge-on disks: 1) a major-axis
light profile with a quasi-exponential central peak and a plateau at moderate
radii (Freeman Type II profile); 2) a ``double-hump'' rotation curve; 3) a
sometime flat central velocity dispersion peak with a plateau at moderate radii
and occasional local central minimum and secondary peak; 4) an h3-V correlation
over the projected bar length. All those kinematic features are spatially
correlated and can easily be understood from the orbital structure of barred
disks. They thus provide a reliable and easy-to-use tool to identify edge-on
bars. Interestingly, they are all produced without dissipation and are
increasingly realized to be common in spirals, lending support to bar-driven
evolution scenarios for bulge formation. So called ``figure-of-eight''
position-velocity diagrams are never observed, as expected for realistic
orbital configurations. Although not uniquely related to triaxiality,
line-of-sight velocity distributions with a high velocity tail (i.e. an h3-V
correlation) appear as particularly promising tracers of bars. The stellar
kinematic features identified grow in strength as the bar evolves and vary
little for small inclination variations. Many can be used to trace the bar
length. Comparisons with observations are encouraging and support the view that
boxy and peanut-shaped bulges are simply thick bars viewed edge-on.Comment: 32 pages, 4 figures, AASTeX preprint. Revised following referees'
comments. Now accepted for publication in The Astrophysical Journal. We
strongly suggest you download the version with full resolution figures at
http://www.astro.columbia.edu/~bureau/Publications/Nbody_ApJ04.ps.g
Coarctation of the aorta: pre and postoperative evaluation with MRI and MR angiography; correlation with echocardiography and surgery
Aims: To compare MRI and MRA with Doppler-echocardiography (DE) in native and postoperative aortic coarctation, define the best MR protocol for its evaluation, compare MR with surgical findings in native coarctation. Materials and methods: 136 MR studies were performed in 121 patients divided in two groups: Group I, 55 preoperative; group II, 81 postoperative. In group I, all had DE and surgery was performed in 35 cases. In group II, DE was available for comparison in 71 cases. MR study comprised: spin-echo, cine, velocity-encoded cine (VEC) sequences and 3D contrast-enhanced MRA. Results: In group I, diagnosis of coarctation was made by DE in 33 cases and suspicion of coarctation and/or aortic arch hypoplasia in 18 cases. Aortic arch was not well demonstrated in 3 cases and DE missed one case. There was a close correlation between VEC MRI and Doppler gradient estimates across the coarctation, between MRI aortic arch diameters and surgery but a poor correlation in isthmic measurements. In group II, DE detected a normal isthmic region in 31 out of 35 cases. Postoperative anomalies (recoarctation, aortic arch hypoplasia, kinking, pseudoaneurysm) were not demonstrated with DE in 50% of cases. Conclusions: MRI is superior to DE for pre and post-treatment evaluation of aortic coarctation. An optimal MR protocol is proposed. Internal measurement of the narrowing does not correspond to the external aspect of the surgical narrowin
Discovery of a Boxy Peanut Shaped Bulge in the Near Infrared
We report on the discovery of a boxy/peanut shaped bulge in the highly
inclined barred Seyfert 2 galaxy NGC~7582. The peanut shape is clearly evident
in near infrared images but obscured by extinction from dust in visible
images. This suggests that near infrared imaging surveys will discover a
larger number of boxy/peanut morphologies than visible surveys, particularly in
galaxies with heavy extinction such as NGC~7582. The bulge in NGC~7582 exhibits
strong boxiness compared to other boxy/peanut shaped bulges. If the starburst
was mediated by the bar, then it is likely that the bar formed in less than a
few bar rotation periods or a few years ago. If the bar also
caused the peanut, then the peanut would have formed quickly; on a timescale of
a few bar rotation periods.Comment: AAS Latex and Postcript Figures, accepted for publication in Ap
Forming Young Bulges within Existing Disks: Statistical Evidence for External Drivers
Contrary to traditional models of galaxy formation, recent observations
suggest that some bulges form within preexisting disk galaxies. Such late-epoch
bulge formation within disks seems to be linked to disk gas inflow and central
star formation, caused by either internal secular processes or galaxy mergers
and interactions. We identify a population of galaxies likely to be
experiencing active bulge growth within disks, using the criterion that the
color within the half-light radius is bluer than the outer disk color. Such
blue-centered galaxies make up >10% of star-forming disk galaxies within the
Nearby Field Galaxy Survey, a broad survey designed to represent the natural
diversity of the low-z galaxy population over a wide range of luminosities and
environments. Blue-centered galaxies correlate at 99% confidence with
morphological peculiarities suggestive of minor mergers and interactions. From
this and other evidence, we argue that external drivers rather than internal
secular processes probably account for the majority of blue-centered galaxies.
We go on to discuss quantitative plausibility arguments indicating that
blue-centered evolutionary phases may represent an important mode of bulge
growth for most disk galaxies, leading to significant changes in bulge-to-disk
ratio without destroying disks. If this view is correct, bulge growth within
disks may be a natural consequence of the repeated galaxy mergers and
interactions inherent in hierarchical galaxy formation.Comment: 18 pages including 12 figures, AJ, accepte
Turbulent dissipation in the ISM: the coexistence of forced and decaying regimes and implications for galaxy formation and evolution
We discuss the dissipation of turbulent kinetic energy Ek in the global ISM
by means of 2-D, MHD, non-isothermal simulations in the presence of model
radiative heating and cooling. We argue that dissipation in 2D is
representative of that in three dimensions as long as it is dominated by shocks
rather than by a turbulent cascade. Energy is injected at a few isolated sites
in space, over relatively small scales, and over short time periods. This leads
to the coexistence of forced and decaying regimes in the same flow. We find
that the ISM-like flow dissipates its turbulent energy rapidly. In simulations
with forcing, the input parameters are the radius l_f of the forcing region,
the total kinetic energy e_k each source deposits into the flow, and the rate
of formation of those regions, sfr_OB. The global dissipation time t_d depends
mainly on l_f. In terms of measurable properties of the ISM, t_d >= Sigma_g
u_rms^2/(e_k sfr_OB), where Sigma_g is the average gas surface density and
u_rms is the rms velocity dispersion. For the solar neighborhood, t_d >=
1.5x10^7 yr. The global dissipation time is consistently smaller than the
crossing time of the largest energy-containing scales. In decaying simulations,
Ek decreases with time as t^-n, where n~0.8-0.9. This suggests a decay with
distance d as Ek\propto d^{-2n/(2-n)} in the mixed forced+decaying case. If
applicable to the vertical direction, our results support models of galaxy
evolution in which stellar energy injection provides significant support for
the gas disk thickness, but not models of galaxy formation in which this energy
injection is supposed to reheat an intra-halo medium at distances of up to
10-20 times the optical galaxy size, as the dissipation occurs on distances
comparable to the disk height.Comment: 23 pages, including figures. To appear in ApJ. Abstract abridge
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