30,395 research outputs found
Fully-coupled analysis of jet mixing problems. Three-dimensional PNS model, SCIP3D
Numerical procedures formulated for the analysis of 3D jet mixing problems, as incorporated in the computer model, SCIP3D, are described. The overall methodology closely parallels that developed in the earlier 2D axisymmetric jet mixing model, SCIPVIS. SCIP3D integrates the 3D parabolized Navier-Stokes (PNS) jet mixing equations, cast in mapped cartesian or cylindrical coordinates, employing the explicit MacCormack Algorithm. A pressure split variant of this algorithm is employed in subsonic regions with a sublayer approximation utilized for treating the streamwise pressure component. SCIP3D contains both the ks and kW turbulence models, and employs a two component mixture approach to treat jet exhausts of arbitrary composition. Specialized grid procedures are used to adjust the grid growth in accordance with the growth of the jet, including a hybrid cartesian/cylindrical grid procedure for rectangular jets which moves the hybrid coordinate origin towards the flow origin as the jet transitions from a rectangular to circular shape. Numerous calculations are presented for rectangular mixing problems, as well as for a variety of basic unit problems exhibiting overall capabilities of SCIP3D
Gaps, Rings, and Non-Axisymmetric Structures in Protoplanetary Disks - From Simulations to ALMA Observations
Recent observations by the Atacama Large Millimeter/submillimeter Array
(ALMA) of disks around young stars revealed distinct asymmetries in the dust
continuum emission. In this work we want to study axisymmetric and
non-axisymmetric structures, evocated by the magneto-rotational instability in
the outer regions of protoplanetary disks. We combine the results of
state-of-the-art numerical simulations with post-processing radiative transfer
(RT) to generate synthetic maps and predictions for ALMA. We performed
non-ideal global 3D MHD stratified simulations of the dead-zone outer edge
using the FARGO MHD code PLUTO. The stellar and disk parameters are taken from
a parameterized disk model applied for fitting high-angular resolution
multi-wavelength observations of circumstellar disks. The 2D temperature and
density profiles are calculated consistently from a given surface density
profile and Monte-Carlo radiative transfer. The 2D Ohmic resistivity profile is
calculated using a dust chemistry model. The magnetic field is a vertical net
flux field. The resulting dust reemission provides the basis for the simulation
of observations with ALMA. The fiducial model develops a large gap followed by
a jump in surface density located at the dead-zone outer edge. The jump in
density and pressure is strong enough to stop the radial drift of particles. In
addition, we observe the generation of vortices by the Rossby wave instability
(RWI) at the jumps location close to 60 AU. The vortices are steadily generated
and destroyed at a cycle of 40 local orbits. The RT results and simulated ALMA
observations predict the feasibility to observe such large scale structures
appearing in magnetized disks without having a planet.Comment: Language update, added comments, added citations, in press. (A&A
The spectroscopic evolution of the symbiotic star AG Draconis. I.The O VI Raman, Balmer, and helium emission line variations during the outburst of 2006-2008
AG Dra is one of a small group of low metallicity S-type symbiotic binaries
with K-type giants that undergoes occasional short-term outbursts of unknown
origin. Our aim is to study the behavior of the white dwarf during an outburst
using the optical Raman lines and other emission features in the red giant
wind. The goal is to determine changes in the envelope and the wind of the
gainer in this system during a major outburst event and to study the coupling
between the UV and optical during a major outburst. Using medium and high
resolution groundbased optical spectra and comparisons with archival and
spectra, we study the evolution of the Raman O VI features and the
Balmer, He I, and He II lines during the outburst from 2006 Sept. through 2007
May and include more recent observations (2009) to study the subsequent
evolution of the source. The O VI Raman features disappeared completely at the
peak of the major outburst and the subsequent variation differs substantially
from that reported during the previous decade. The He I and He II lines, and
the Balmer lines, vary in phase with the Raman features but there is a
double-valuedness to the He I 6678, 7065 relative to the O VI Raman 6825\AA\
variations in the period between 2006-2008 that has not been previously
reported. The variations in the Raman feature ratio through the outburst
interval are consistent with the disappearance of the O VI FUV resonance wind
lines from the white dwarf and of the surrounding O ionized region
within the red giant wind provoked by the expansion and cooling of the white
dwarf photosphere.Comment: 10 pages, 15 figs. A&A (in press, accepted for publication
23/11/2009
Gravitational lens magnification by Abell 1689: Distortion of the background galaxy luminosity function
Gravitational lensing magnifies the luminosity of galaxies behind the lens.
We use this effect to constrain the total mass in the cluster Abell 1689 by
comparing the lensed luminosities of background galaxies with the luminosity
function of an undistorted field. Since galaxies are assumed to be a random
sampling of luminosity space, this method is not limited by clustering noise.
We use photometric redshift information to estimate galaxy distance and
intrinsic luminosity. Knowing the redshift distribution of the background
population allows us to lift the mass/background degeneracy common to lensing
analysis. In this paper we use 9 filters observed over 12 hours with the Calar
Alto 3.5m telescope to determine the redshifts of 1000 galaxies in the field of
Abell 1689. Using a complete sample of 151 background galaxies we measure the
cluster mass profile. We find that the total projected mass interior to
0.25h^(-1)Mpc is (0.48 +/- 0.16) * 10^(15)h^(-1) solar masses, where our error
budget includes uncertainties from the photometric redshift determination, the
uncertainty in the off-set calibration and finite sampling. This result is in
good agreement with that found by number count and shear-based methods and
provides a new and independent method to determine cluster masses.Comment: 13 pages, 10 figures. Submitted to MNRAS (10/99); Replacement with 1
page extra text inc. new section, accepted by MNRA
Propagation of Exchange Bias in CoFe/FeMn/CoFe Trilayers
CoFe/FeMn, FeMn/CoFe bilayers and CoFe/FeMn/CoFe trilayers were grown in
magnetic field and at room temperature. The exchange bias field
depends strongly on the order of depositions and is much higher at CoFe/FeMn
than at FeMn/CoFe interfaces. By combining the two bilayer structures into
symmetric CoFe/FeMn()/CoFe trilayers, and
of the top and bottom CoFe layers, respectively, are both enhanced.
Reducing of the trilayers also results in enhancements of
both and . These results evidence the propagation of
exchange bias between the two CoFe/FeMn and FeMn/CoFe interfaces mediated by
the FeMn antiferromagnetic order
Real-time 3D Tracking of Articulated Tools for Robotic Surgery
In robotic surgery, tool tracking is important for providing safe tool-tissue
interaction and facilitating surgical skills assessment. Despite recent
advances in tool tracking, existing approaches are faced with major
difficulties in real-time tracking of articulated tools. Most algorithms are
tailored for offline processing with pre-recorded videos. In this paper, we
propose a real-time 3D tracking method for articulated tools in robotic
surgery. The proposed method is based on the CAD model of the tools as well as
robot kinematics to generate online part-based templates for efficient 2D
matching and 3D pose estimation. A robust verification approach is incorporated
to reject outliers in 2D detections, which is then followed by fusing inliers
with robot kinematic readings for 3D pose estimation of the tool. The proposed
method has been validated with phantom data, as well as ex vivo and in vivo
experiments. The results derived clearly demonstrate the performance advantage
of the proposed method when compared to the state-of-the-art.Comment: This paper was presented in MICCAI 2016 conference, and a DOI was
linked to the publisher's versio
Propulsion in a viscoelastic fluid
Flagella beating in complex fluids are significantly influenced by
viscoelastic stresses. Relevant examples include the ciliary transport of
respiratory airway mucus and the motion of spermatozoa in the mucus-filled
female reproductive tract. We consider the simplest model of such propulsion
and transport in a complex fluid, a waving sheet of small amplitude free to
move in a polymeric fluid with a single relaxation time. We show that, compared
to self-propulsion in a Newtonian fluid occurring at a velocity U_N, the sheet
swims (or transports fluid) with velocity U / U_N = [1+De^2 (eta_s)/(eta)
]/[1+De^2], where eta_s is the viscosity of the Newtonian solvent, eta is the
zero-shear-rate viscosity of the polymeric fluid, and De is the Deborah number
for the wave motion, product of the wave frequency by the fluid relaxation
time. Similar expressions are derived for the rate of work of the sheet and the
mechanical efficiency of the motion. These results are shown to be independent
of the particular nonlinear constitutive equations chosen for the fluid, and
are valid for both waves of tangential and normal motion. The generalization to
more than one relaxation time is also provided. In stark contrast with the
Newtonian case, these calculations suggest that transport and locomotion in a
non-Newtonian fluid can be conveniently tuned without having to modify the
waving gait of the sheet but instead by passively modulating the material
properties of the liquid.Comment: 21 pages, 1 figur
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