2,498 research outputs found
Partial data inverse problems for the Hodge Laplacian
We prove uniqueness results for a Calderon type inverse problem for the Hodge
Laplacian acting on graded forms on certain manifolds in three dimensions. In
particular, we show that partial measurements of the relative-to-absolute or
absolute-to-relative boundary value maps uniquely determine a zeroth order
potential. The method is based on Carleman estimates for the Hodge Laplacian
with relative or absolute boundary conditions, and on the construction of
complex geometric optics solutions which reduce the Calderon type problem to a
tensor tomography problem for 2-tensors. The arguments in this paper allow to
establish partial data results for elliptic systems that generalize the scalar
results due to Kenig-Sjostrand-Uhlmann.Comment: 54 pages, updated versio
Resolvent estimates for the magnetic Schr\"odinger operator in dimension
It is well known that the resolvent of the free Schr\"odinger operator on
weighted spaces has norm decaying like at energy
. There are several works proving analogous high-frequency estimates
for magnetic Schr\"odinger operators, with large long or short range
potentials, in dimensions . We prove that the same estimates remain
valid in all dimensions .Comment: 21 page
A monolithic collapse origin for the thin/thick disc structure of ESO 243-49
ESO 243-49 is a high-mass (circular velocity ) edge-on S0 galaxy in the Abell 2877 cluster at a distance of
. To elucidate the origin of its thick disc, we use MUSE
science verification data to study its kinematics and stellar populations. The
thick disc emits of the light at heights in excess of
(). The rotation velocities of its stars
lag by compared to those in the thin disc, which is
compatible with the asymmetric drift. The thick disc is found to be more
metal-poor than the thin disc, but both discs have old ages. We suggest an
internal origin for the thick disc stars in high-mass galaxies. We propose that
the thick disc formed either first in a turbulent phase with a high
star formation rate and that a thin disc formed shortly afterwards, or because of the dynamical heating of a thin pre-existing component. Either
way, the star formation in ESO 243-49 was quenched just a few Gyrs after the
galaxy was born and the formation of a thin and a thick disc must have occurred
before the galaxy stopped forming stars. The formation of the discs was so fast
that it could be described as a monolithic collapse where several generations
of stars formed in a rapid succession.Comment: Accepted for publication in A&A. The reduced data-cube as well as the
data necessary to build the kinematic and stellar population maps are
available at
https://etsin.avointiede.fi/dataset/urn-nbn-fi-csc-kata2016092414291163237
THE USE OF MOTION ANALYSIS AS A COACHING AID TO IMPROVE THE INDIVIDUAL TECHNIQUE IN SPRINT HURDLES
Biomechanical data are oflen presented as a group average, which may not always help individual athletes to improve their own performance. The purpose of this study was to analyse techniques in sprint hurdles within the athlete and find critical individual aspects, which influence performance. The hurdle clearance of three athletes (eight trials each) were videotaped with four video camera recorders and analysed three-dimensionally. There were several statistically significant correlations between the critical overall horizontal velocity and other variables, especially for one athlete. Such trends in individual performance presented ideas to coaches, athletes and also to researchers, regarding what happened in less successful runs and which technical points were worth individual attention in training
Exponential instability in the fractional Calder\'on problem
In this note we prove the exponential instability of the fractional
Calder\'on problem and thus prove the optimality of the logarithmic stability
estimate from \cite{RS17}. In order to infer this result, we follow the
strategy introduced by Mandache in \cite{M01} for the standard Calder\'on
problem. Here we exploit a close relation between the fractional Calder\'on
problem and the classical Poisson operator. Moreover, using the construction of
a suitable orthonormal basis, we also prove (almost) optimality of the Runge
approximation result for the fractional Laplacian, which was derived in
\cite{RS17}. Finally, in one dimension, we show a close relation between the
fractional Calder\'on problem and the truncated Hilbert transform.Comment: 17 page
Microgravity experiments on the collisional behavior of Saturnian ring particles
In this paper we present results of two novel experimental methods to
investigate the collisional behavior of individual macroscopic icy bodies. The
experiments reported here were conducted in the microgravity environments of
parabolic flights and the Bremen drop tower facility. Using a cryogenic
parabolic-flight setup, we were able to capture 41 near-central collisions of
1.5-cm-sized ice spheres at relative velocities between 6 and . The analysis of the image sequences provides a uniform distribution
of coefficients of restitution with a mean value of and values ranging from to 0.84. Additionally, we
designed a prototype drop tower experiment for collisions within an ensemble of
up to one hundred cm-sized projectiles and performed the first experiments with
solid glass beads. We were able to statistically analyze the development of the
kinetic energy of the entire system, which can be well explained by assuming a
granular `fluid' following Haff's law with a constant coefficient of
restitution of . We could also show that the setup is
suitable for studying collisions at velocities of
appropriate for collisions between particles in Saturn's dense main rings.Comment: Accepted for publication in the Icarus Special Issue "Cassini at
Saturn
Spatial Structure and Coherent Motion in Dense Planetary Rings Induced by Self-Gravitational Instability
We investigate the formation of spatial structure in dense, self-gravitating
particle systems such as Saturn's B-ring through local -body simulations to
clarify the intrinsic physics based on individual particle motion. In such a
system, Salo (1995) showed that the formation of spatial structure such as
wake-like structure and particle grouping (clump) arises spontaneously due to
gravitational instability and the radial velocity dispersion increases as the
formation of the wake structure. However, intrinsic physics of the phenomena
has not been clarified. We performed local -body simulations including
mutual gravitational forces between ring particles as well as direct
(inelastic) collisions with identical (up to ) particles. In the
wake structure particles no longer move randomly but coherently. We found that
particle motion was similar to Keplerian motion even in the wake structure and
that the coherent motion was produced since the particles in a clump had
similar eccentricity and longitude of perihelion. This coherent motion causes
the increase and oscillation in the radial velocity dispersion. The mean
velocity dispersion is rather larger in a more dissipative case with a smaller
restitution coefficient and/or a larger surface density since the coherence is
stronger in the more dissipative case. Our simulations showed that the
wavelength of the wake structure was approximately given by the longest
wavelength \hs{\lambda}{cr} = 4\pi^2 G\Sigma/\kappa^2 in the linear theory of
axisymmetric gravitational instability in a thin disk, where , , and
are the gravitational constant, surface density, and a epicyclic
frequency.Comment: Accepted by Earth, Planets, and Space. 39 pages, 20 figures.
PostScript files also available from
http://www.geo.titech.ac.jp/nakazawalab/hdaisaka/works
- …