1,848 research outputs found
Deposition And Drying Dynamics Of Liquid Crystal Droplets
Drop drying and deposition phenomena reveal a rich interplay of fundamental science and engineering, give rise to fascinating everyday effects (coffee rings), and influence technologies ranging from printing to genotyping. Here we investigate evaporation dynamics, morphology, and deposition patterns of drying lyotropic chromonic liquid crystal droplets. These drops differ from typical evaporating colloidal drops primarily due to their concentration-dependent isotropic, nematic, and columnar phases. Phase separation occurs during evaporation, and in the process creates surface tension gradients and significant density and viscosity variation within the droplet. As a result, the drying multiphase drops exhibit different convective currents, drop morphologies, and deposition patterns (coffee-rings)
FUSE Observations of a Full Orbit of Hercules X-1: Signatures of Disk, Star, and Wind
We observed an entire 1.7 day orbit of the X-ray binary Hercules X-1 with the
Far Ultraviolet Spectroscopic Explorer (FUSE). Changes in the O VI 1032,1037
line profiles through eclipse ingress and egress indicate a Keplerian accretion
disk spinning prograde with the orbit. These observations may show the first
double-peaked accretion disk line profile to be seen in the Hercules X-1
system. Doppler tomograms of the emission lines show a bright spot offset from
the Roche lobe of the companion star HZ Her, but no obvious signs of the
accretion disk. Simulations show that the bright spot is too far offset from
the Roche lobe to result from uneven X-ray heating of its surface. The absence
of disk signatures in the tomogram can be reproduced in simulations which
include absorption from a stellar wind. We attempt to diagnose the state of the
emitting gas from the C III 977, C III 1175, and N III 991 emission lines. The
latter may be enhanced through Bowen fluorescence.Comment: Accepted for publication in The Astrophysical Journa
The Origin of Soft X-rays in DQ Herculis
DQ Herculis (Nova Herculis 1934) is a deeply eclipsing cataclysmic variable
containing a magnetic white dwarf primary. The accretion disk is thought to
block our line of sight to the white dwarf at all orbital phases due to its
extreme inclination angle. Nevertheless, soft X-rays were detected from DQ Her
with ROSAT PSPC. To probe the origin of these soft X-rays, we have performed
Chandra ACIS observations. We confirm that DQ Her is an X-ray source. The bulk
of the X-rays are from a point-like source and exhibit a shallow partial
eclipse. We interpret this as due to scattering of the unseen central X-ray
source, probably in an accretion disk wind. At the same time, we observe what
appear to be weak extended X-ray features around DQ Her, which we interpret as
an X-ray emitting knot in the nova shell.Comment: 18 pages including 4 figures, accepted for publication in
Astrphyisical Journa
Measurements of the effect of collisions on transverse beam halo diffusion in the Tevatron and in the LHC
Beam-beam forces and collision optics can strongly affect beam lifetime,
dynamic aperture, and halo formation in particle colliders. Extensive
analytical and numerical simulations are carried out in the design and
operational stage of a machine to quantify these effects, but experimental data
is scarce. The technique of small-step collimator scans was applied to the
Fermilab Tevatron collider and to the CERN Large Hadron Collider to study the
effect of collisions on transverse beam halo dynamics. We describe the
technique and present a summary of the first results on the dependence of the
halo diffusion coefficient on betatron amplitude in the Tevatron and in the
LHC.Comment: 4 pages, 2 figures. Submitted to the Proceedings of the ICFA
Mini-Workshop on Beam-beam Effects in Hadron Colliders (BB2013), Geneva,
Switzerland, 18-22 March 201
M-Dwarf Fast Rotators and the Detection of Relatively Young Multiple M-Star Systems
We have searched the Kepler light curves of ~3900 M-star targets for evidence
of periodicities that indicate, by means of the effects of starspots, rapid
stellar rotation. Several analysis techniques, including Fourier transforms,
inspection of folded light curves, 'sonograms', and phase tracking of
individual modulation cycles, were applied in order to distinguish the
periodicities due to rapid rotation from those due to stellar pulsations,
eclipsing binaries, or transiting planets. We find 178 Kepler M-star targets
with rotation periods, P_rot, of < 2 days, and 110 with P_rot < 1 day. Some 30
of the 178 systems exhibit two or more independent short periods within the
same Kepler photometric aperture, while several have three or more short
periods. Adaptive optics imaging and modeling of the Kepler pixel response
function for a subset of our sample support the conclusion that the targets
with multiple periods are highly likely to be relatively young physical binary,
triple, and even quadruple M star systems. We explore in detail the one object
with four incommensurate periods all less than 1.2 days, and show that two of
the periods arise from one of a close pair of stars, while the other two arise
from the second star, which itself is probably a visual binary. If most of
these M-star systems with multiple periods turn out to be bound M stars, this
could prove a valuable way of discovering young hierarchical M-star systems;
the same approach may also be applicable to G and K stars. The ~5% occurrence
rate of rapid rotation among the ~3900 M star targets is consistent with spin
evolution models that include an initial contraction phase followed by magnetic
braking, wherein a typical M star can spend several hundred Myr before spinning
down to periods longer than 2 days.Comment: 17 pages, 12 figures, 2 tables; accepted for publication in The
Astrophysical Journa
Beam halo dynamics and control with hollow electron beams
Experimental measurements of beam halo diffusion dynamics with collimator
scans are reviewed. The concept of halo control with a hollow electron beam
collimator, its demonstration at the Tevatron, and its possible applications at
the LHC are discussed.Comment: 5 pages, 4 figures, in Proceedings of the 52nd ICFA Advanced Beam
Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams
(HB2012), Beijing, China, 17-21 September 201
Evolutionary influences on the structure of red-giant acoustic oscillation spectra from 600d of Kepler observations
Context: The Kepler space mission is reaching continuous observing times long
enough to start studying the fine structure of the observed p-mode spectra.
Aims: In this paper, we aim to study the signature of stellar evolution on the
radial and p-dominated l=2 modes in an ensemble of red giants that show
solar-type oscillations. Results: We find that the phase shift of the central
radial mode (eps_c) is significantly different for red giants at a given large
frequency separation (Dnu_c) but which burn only H in a shell (RGB) than those
that have already ignited core He burning. Even though not directly probing the
stellar core the pair of local seismic observables (Dnu_c, eps_c) can be used
as an evolutionary stage discriminator that turned out to be as reliable as the
period spacing of the mixed dipole modes. We find a tight correlation between
eps_c and Dnu_c for RGB stars and no indication that eps_c depends on other
properties of these stars. It appears that the difference in eps_c between the
two populations becomes if we use an average of several radial orders, instead
of a local, i.e. only around the central radial mode, Dnu to determine the
phase shift. This indicates that the information on the evolutionary stage is
encoded locally, in the shape of the radial mode sequence. This shape turns out
to be approximately symmetric around the central radial mode for RGB stars but
asymmetric for core He burning stars. We computed radial modes for a sequence
of RG models and find them to qualitatively confirm our findings. We also find
that, at least in our models, the local Dnu is an at least as good and mostly
better proxy for both the asymptotic spacing and the large separation scaled
from the model density than the average Dnu. Finally, we investigate the
signature of the evolutionary stage on the small frequency separation and
quantify the mass dependency of this seismic parameter.Comment: 12 pages, 9 figures, accepted for publication in A&
Use of tranexamic acid in major trauma: a sex-disaggragated analysis of the Clinical Randomisation of an Antifibrinolytic in Significant Haemorrhage (CRASH-2 and CRASH-3) trials and UK trauma registry (Trauma and Audit Research Network) data.
Women are less likely than men to receive some emergency treatments. This study examines whether the effect of tranexamic acid (TXA) on mortality in trauma patients varies by sex and whether the receipt of TXA by trauma patients varies by sex.
First, we conducted a sex-disaggregated analysis of data from the Clinical Randomisation of an Antifibrinolytic in Significant Haemorrhage (CRASH)-2 and CRASH-3 trials. We used interaction tests to determine whether the treatment effect varied by sex. Second, we examined data from the Trauma and Audit Research Network (TARN) to explore sex differences in the receipt of TXA. We used logistic regression models to estimate the odds ratio for receipt of TXA in females compared with males. Results are reported as n (%), risk ratios (RR), and odds ratios (OR) with 95% confidence intervals.
Overall, 20 211 polytrauma patients (CRASH-2) and 12 737 patients with traumatic brain injuries (CRASH-3) were included in our analysis. TXA reduced the risk of death in females (RR=0.69 [0.52-0.91]) and in males (RR=0.80 [0.71-0.90]) with no significant heterogeneity by sex (P=0.34). We examined TARN data for 216 364 patients aged ≥16 yr with an Injury Severity Score ≥9 with 98 879 (46%) females and 117 485 (54%) males. TXA was received by 7198 (7.3% [7.1-7.4%]) of the females and 19 697 (16.8% [16.6-17.0%]) of the males (OR=0.39 [0.38-0.40]). The sex difference in the receipt of TXA increased with increasing age.
Administration of TXA to patients with bleeding trauma reduces mortality to a similar extent in women and men, but women are substantially less likely to be treated with TXA
- …