40,487 research outputs found
Magnetic fields in circumstellar disks: The potential of Zeeman observations
Context. Recent high angular resolution polarimetric continuum observations
of circumstellar disks provide new insights into their magnetic field. However,
direct constraints are limited to the plane of sky component of the magnetic
field. Observations of Zeeman split spectral lines are a potential approach to
enhance these insights by providing complementary information.
Aims. We investigate which constraints for magnetic fields in circumstellar
disks can be obtained from Zeeman observations of the CN
lines. Furthermore, we analyze the requirements to perform these observations
and their dependence on selected quantities.
Methods. We simulate the Zeeman splitting with the radiative transfer (RT)
code POLARIS (Reissl et al. 2016) extended by our Zeeman splitting RT extension
ZRAD (Brauer et al. 2017), which is based on the line RT code Mol3D (Ober et
al. 2015).
Results. We find that Zeeman observations of the CN lines
provide significant insights into the magnetic field of circumstellar disks.
However, with the capabilities of recent and upcoming instrument/observatories,
even spatially unresolved observations would be challenging. Nevertheless,
these observations are feasible for the most massive disks with a strong
magnetic field and high abundance of CN/H. The most restrictive quantity is the
magnetic field strength, which should be at least in the order of
. In addition, the inclination of the disk should be around
to preserve the ability to derive the line-of-sight (LOS) magnetic
field strength and to obtain a sufficiently high circularly polarized flux.Comment: 15 pages, 14 figure
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
Maps of zeroes of the grand canonical partition function in a statistical model of high energy collisions
Theorems on zeroes of the truncated generating function in the complex plane
are reviewed. When examined in the framework of a statistical model of high
energy collisions based on the negative binomial (Pascal) multiplicity
distribution, these results lead to maps of zeroes of the grand canonical
partition function which allow to interpret in a novel way different classes of
events in pp collisions at LHC c.m. energies.Comment: 17 pages, figures (ps included); added references, some figures
enlarged. To appear in J. Phys.
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
Squeezing the limit: Quantum benchmarks for the teleportation and storage of squeezed states
We derive fidelity benchmarks for the quantum storage and teleportation of
squeezed states of continuous variable systems, for input ensembles where the
degree of squeezing is fixed, no information about its orientation in phase
space is given, and the distribution of phase space displacements is a
Gaussian. In the limit where the latter becomes flat, we prove analytically
that the maximal classical achievable fidelity (which is 1/2 without squeezing,
for ) is given by , vanishing when the degree of squeezing
diverges. For mixed states, as well as for general distributions of
displacements, we reduce the determination of the benchmarks to the solution of
a finite-dimensional semidefinite program, which yields accurate, certifiable
bounds thanks to a rigorous analysis of the truncation error. This approach may
be easily adapted to more general ensembles of input states.Comment: 19 pages, 4figure
Spin-Lattice Coupling in K0.8Fe1.6Se2 and KFe2Se2: Inelastic Neutron Scattering and ab-initio Phonon Calculations
We report measurements of the temperature dependence of phonon densities of
states in K0.8Fe1.6Se2 using inelastic neutron scattering technique. While
cooling down to 150 K, a phonon peak splitting around 25 meV is observed and a
new peak appears at 31 meV. The measurements support the recent Raman and
infra-red measurements indicating a lowering of symmetry of K0.8Fe1.6Se2 upon
cooling below 250 K. Ab-initio phonon calculations have been carried out for
K0.8Fe1.6Se2 and KFe2Se2. The comparison of the phonon spectra as obtained from
the magnetic as well as non magnetic calculations show pronounced differences.
We show that in the two calculations the energy range of the vibrational
contribution from both Fe and Se are quite different. We conclude that Fe
magnetism is correlated to the phonon dynamics and it plays an important role
in stabilizing the structure of K0.8Fe1.6Se2 as well as that of KFe2Se2. The
calculations highlight the presence of low energy librational modes in
K0.8Fe1.6Se2 as compared to KFe2Se2.Comment: 22 pages, 3 Tables, 7 Figure
Momentum dependent ultrafast electron dynamics in antiferromagnetic EuFe2As2
Employing the momentum-sensitivity of time- and angle-resolved photoemission
spectroscopy we demonstrate the analysis of ultrafast single- and many-particle
dynamics in antiferromagnetic EuFe2As2. Their separation is based on a
temperature-dependent difference of photo-excited hole and electron relaxation
times probing the single particle band and the spin density wave gap,
respectively. Reformation of the magnetic order occurs at 800 fs, which is four
times slower compared to electron-phonon equilibration due to a smaller
spin-dependent relaxation phase space
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