913 research outputs found
Asymmetric Drift and the Stellar Velocity Ellipsoid
We present the decomposition of the stellar velocity ellipsoid using stellar
velocity dispersions within a 40 deg wedge about the major-axis (sigma_maj),
the epicycle approximation, and the asymmetric drift equation. Thus, we employ
no fitted forms for sigma_maj and escape interpolation errors resulting from
comparisons of the major and minor axes. We apply the theoretical construction
of the method to integral field data taken for NGC 3949 and NGC 3982. We derive
the vertical-to-radial velocity dispersion ratio (sigma_z / sigma_R) and find
(1) our decomposition method is accurate and reasonable, (2) NGC 3982 appears
to be rather typical of an Sb type galaxy with sigma_z / sigma_R = 0.73
(+0.13/-0.11) despite its high surface brightness and small size, and (3) NGC
3949 has a hot disk with sigma_z / sigma_R = 1.18 (+0.36/-0.28).Comment: 4 pages including 3 figures, to appear in "Island Universes:
Structure and Evolution of Disk Galaxies", Terschelling, Netherlands, July
3-8, 200
Twinning superlattices in indium phosphide nanowires
Here, we show that we control the crystal structure of indium phosphide (InP)
nanowires by impurity dopants. We have found that zinc decreases the activation
barrier for 2D nucleation growth of zinc-blende InP and therefore promotes the
InP nanowires to crystallise in the zinc blende, instead of the commonly found
wurtzite crystal structure. More importantly, we demonstrate that we can, by
controlling the crystal structure, induce twinning superlattices with
long-range order in InP nanowires. We can tune the spacing of the superlattices
by the wire diameter and the zinc concentration and present a model based on
the cross-sectional shape of the zinc-blende InP nanowires to quantitatively
explain the formation of the periodic twinning.Comment: 18 pages, 4 figure
The Link between the Baryonic Mass Distribution and the Rotation Curve Shape
The observed rotation curves of disc galaxies, ranging from late-type dwarf
galaxies to early-type spirals, can be fit remarkably well simply by scaling up
the contributions of the stellar and HI discs. This `baryonic scaling model'
can explain the full breadth of observed rotation curves with only two free
parameters. For a small fraction of galaxies, in particular early-type spiral
galaxies, HI scaling appears to fail in the outer parts, possibly due to
observational effects or ionization of the HI. The overall success of the
baryonic scaling model suggests that the well-known global coupling between the
baryonic mass of a galaxy and its rotation velocity (known as the baryonic
Tully-Fisher relation), applies at a more local level as well, and it seems to
imply a link between the baryonic mass distribution and the distribution of
total mass (including dark matter).Comment: 10 pages, accepted for publication in MNRA
A near-infrared study of the obscured 3C129 galaxy cluster
We present a catalogue of 261 new infrared selected members of the 3C129
galaxy cluster. The cluster, located at 0.02, forms part of the
Perseus-Pisces filament and is obscured at optical wavelengths due to its
location in the zone of avoidance. We identified these galaxies using the
and band imaging data provided by the UKIDSS Galactic Plane Survey within
an area with a radius of centred on the X-ray emission of the
cluster at . A total of 26 of the
identified galaxy members have known redshifts 24 of which are from our 2016
Westerbork HI survey and two are from optical spectroscopy. An analysis of the
galaxy density at the core of the 3C129 cluster shows it to be less dense than
the Coma and Norma clusters, but comparable to the galaxy density in the core
of the Perseus cluster. From an assessment of the spatial and velocity
distributions of the 3C129 cluster galaxies that have redshifts, we derived a
velocity of km/s and km/s for the
main cluster, with a substructure in the cluster outskirts at km/s with km/s. The presence of this substructure is
consistent with previous claims based on the X-ray analysis that the cluster is
not yet virialised and may have undergone a recent merger.Comment: 33 pages, 16 figures, includes an appendix, accepted for publication
in A&
Geometry-dependent electrostatics near contact lines
Long-ranged electrostatic interactions in electrolytes modify their contact
angles on charged substrates in a scale and geometry dependent manner. For
angles measured at scales smaller than the typical Debye screening length, the
wetting geometry near the contact line must be explicitly considered. Using
variational and asymptotic methods, we derive new transcendental equations for
the contact angle that depend on the electrostatic potential only at the three
phase contact line. Analytic expressions are found in certain limits and
compared with predictions for contact angles measured with lower resolution. An
estimate for electrostatic contributions to {\it line} tension is also given.Comment: 3 .eps figures, 5p
Intestinal motility distal of a deviating ileostomy after rectal resection with the construction of a primary anastomosis:results of the prospective COLO-MOVE study
Purpose No consensus exists regarding the use of preoperative bowel preparation for patients undergoing a low anterior resection (LAR). Several comparative studies show similar outcomes when a single time enema (STE) is compared with mechanical bowel preparation (MBP). It is hypothesized that STE is comparable with MBP due to a decrease in intestinal motility distal of a newly constructed diverting ileostomy (DI). Methods In this prospective single-centre cohort study, patients undergoing a LAR with primary anastomosis and DI construction were given a STE 2 h pre-operatively. Radio-opaque markers were inserted in the efferent loop of the DI during surgery, and plain abdominal X-rays were made during the first, third, fifth and seventh postoperative day to visualize intestinal motility. Results Thirty-nine patients were included. Radio-opaque markers were situated in the ileum or right colon in 100%, 100% and 97.1% of the patients during respectively the first, third and fifth postoperative day. One patient had its most distal marker situated in the left colon during day five. In none of the patients, the markers were seen distal of the anastomosis. Conclusion Intestinal motility distally of the DI is decreased in patients who undergo a LAR resection with the construction of an anastomosis and DI, while preoperatively receiving a STE
- …