8,336 research outputs found
The connection between mass, environment and slow rotation in simulated galaxies
Recent observations from integral field spectroscopy (IFS) indicate that the
fraction of galaxies that are slow rotators, , depends primarily on
stellar mass, with no significant dependence on environment. We investigate
these trends and the formation paths of slow rotators (SRs) using the EAGLE and
Hydrangea hydro-dynamical simulations. EAGLE consists of several cosmological
boxes of volumes up to , while Hydrangea consists of
cosmological simulations of galaxy clusters and their environment. Together
they provide a statistically significant sample in the stellar mass range
, of galaxies. We
construct IFS-like cubes and measure stellar spin parameters, , and ellipticities, allowing us to classify galaxies into slow/fast
rotators as in observations. The simulations display a primary dependence of
on stellar mass, with a weak dependence on environment. At fixed
stellar mass, satellite galaxies are more likely to be SRs than centrals.
shows a dependence on halo mass at fixed stellar mass for central
galaxies, while no such trend is seen for satellites. We find that % of SRs at have experienced at least one merger with mass ratio , with dry mergers being at least twice more common than wet mergers.
Individual dry mergers tend to decrease , while wet mergers
mostly increase it. However, % of SRs at have not experienced
mergers, and those inhabit halos with median spins twice smaller than the halos
hosting the rest of the SRs. Thus, although the formation paths of SRs can be
varied, dry mergers and/or halos with small spins dominate.Comment: Accepted for publications in MNRAS (20 pages, 17 main body, 1.5
appendix). Changes include analysis of the orbital angular momentum effect on
lambdaR and slightly different ellipticity calculatio
The kinematic component of the cosmological redshift
It is widely believed that the cosmological redshift is not a Doppler shift.
However, Bunn & Hogg have recently pointed out that to settle properly this
problem, one has to transport parallelly the velocity four-vector of a distant
galaxy to the observer's position. Performing such a transport along the null
geodesic of photons arriving from the galaxy, they found that the cosmological
redshift is purely kinematic. Here we argue that one should rather transport
the velocity four-vector along the geodesic connecting the points of
intersection of the world-lines of the galaxy and the observer with the
hypersurface of constant cosmic time. We find that the resulting relation
between the transported velocity and the redshift of arriving photons is not
given by a relativistic Doppler formula. Instead, for small redshifts it
coincides with the well known non-relativistic decomposition of the redshift
into a Doppler (kinematic) component and a gravitational one. We perform such a
decomposition for arbitrary large redshifts and derive a formula for the
kinematic component of the cosmological redshift, valid for any FLRW cosmology.
In particular, in a universe with Omega_m = 0.24 and Omega_Lambda = 0.76, a
quasar at a redshift 6, at the time of emission of photons reaching us today
had the recession velocity v = 0.997c. This can be contrasted with v = 0.96c,
had the redshift been entirely kinematic. Thus, for recession velocities of
such high-redshift sources, the effect of deceleration of the early Universe
clearly prevails over the effect of its relatively recent acceleration. Last
but not least, we show that the so-called proper recession velocities of
galaxies, commonly used in cosmology, are in fact radial components of the
galaxies' four-velocity vectors. As such, they can indeed attain superluminal
values, but should not be regarded as real velocities.Comment: 10 pages, 1 figure; matches the version published in MNRA
Determining the influence and effects of manufacturing variables on sulfur dioxide cells
A survey of the Li/SO2 manufacturing community was conducted to determine where variability exists in processing. The upper and lower limits of these processing variables might, by themselves or by interacting with other variables, influence safety, performance, and reliability. A number of important variables were identified and a comprehensive design experiment is being proposed to make the proper determinations
Resolving Subhaloes' Lives with the Hierarchical Bound-Tracing Algorithm
We develop a new code, the Hierarchical Bound-Tracing (HBT for short) code,
to find and trace dark matter subhaloes in simulations based on the merger
hierarchy of dark matter haloes. Application of this code to a recent benchmark
test of finding subhaloes demonstrates that HBT stands as one of the best codes
to trace the evolutionary history of subhaloes. The success of the code lies in
its careful treatment of the complex physical processes associated with the
evolution of subhaloes and in its robust unbinding algorithm with an adaptive
source subhalo management. We keep a full record of the merger hierarchy of
haloes and subhaloes, and allow growth of satellite subhaloes through accretion
from its "satellite-of-satellites", hence allowing mergers among satellites.
Local accretion of background mass is omitted, while rebinding of stripped mass
is allowed. The justification of these treatments is provided by case studies
of the lives of individual subhaloes and by the success in finding the complete
subhalo catalogue. We compare our result to other popular subhalo finders and
show that HBT is able to well resolve subhaloes in high density environment and
keep strict physical track of subhaloes' merger history. This code is fully
parallelized and freely available upon request to the authors.Comment: 15 pages; accepted for publication by MNRA
Optical control of photon tunneling through an array of nanometer scale cylindrical channels
We report first observation of photon tunneling gated by light at a different
wavelength in an artificially created array of nanometer scale cylindrical
channels in a thick gold film. Polarization properties of gated light provide
strong proof of the enhanced nonlinear optical mixing in nanometric channels
involved in the process. This suggests the possibility of building a new class
of "gated" photon tunneling devices for massive parallel all-optical signal and
image processing.Comment: 4 pages, 4 figure
Protocol for the Delirium and Cognitive Impact in Dementia (DECIDE) study: A nested prospective longitudinal cohort study
BACKGROUND:
Delirium is common, affecting at least 20% of older hospital inpatients. It is widely accepted that delirium is associated with dementia but the degree of causation within this relationship is unclear. Previous studies have been limited by incomplete ascertainment of baseline cognition or a lack of prospective delirium assessments. There is an urgent need for an improved understanding of the relationship between delirium and dementia given that delirium prevention may plausibly impact upon dementia prevention. A well-designed, observational study could also answer fundamental questions of major importance to patients and their families regarding outcomes after delirium.
The Delirium and Cognitive Impact in Dementia (DECIDE) study aims to explore the association between delirium and cognitive function over time in older participants. In an existing population based cohort aged 65 years and older, the effect on cognition of an episode of delirium will be measured, independent of baseline cognition and illness severity. The predictive value of clinical parameters including delirium severity, baseline cognition and delirium subtype on cognitive outcomes following an episode of delirium will also be explored.
METHODS:
Over a 12 month period, surviving participants from the Cognitive Function and Ageing Study II-Newcastle will be screened for delirium on admission to hospital. At the point of presentation, baseline characteristics along with a number of disease relevant clinical parameters will be recorded. The progression/resolution of delirium will be monitored. In those with and without delirium, cognitive decline and dementia will be assessed at one year follow-up. We will evaluate the effect of delirium on cognitive function over time along with the predictive value of clinical parameters.
DISCUSSION:
This study will be the first to prospectively elucidate the size of the effect of delirium upon cognitive decline and incident dementia. The results will be used to inform future dementia prevention trials that focus on delirium intervention
Patients’ Survival Expectations Before Localized Prostate Cancer Treatment by Treatment Status
Influence of baryons on the orbital structure of dark matter haloes
We explore the dynamical signatures imprinted by baryons on dark matter
haloes during the formation process using the OverWhelmingly Large Simulations
(OWLS), a set of state-of-the-art high-resolution cosmological hydrodynamical
simulations. We present a detailed study of the effects of the implemented
feedback prescriptions on the orbits of dark matter particles, stellar
particles and subhaloes, analysing runs with no feedback, with stellar feedback
and with feedback from supermassive black holes. We focus on the central
regions (0.25 r_{200}) of haloes with virial masses ~ 6 x 10^{13} (~ 7 x
10^{11}) Msun/h at z = 0(2). We also investigate how the orbital content
(relative fractions of the different orbital types) of these haloes depends on
several key parameters such as their mass, redshift and dynamical state. The
results of spectral analyses of the orbital content of these simulations are
compared, and the change in fraction of box, tube and irregular orbits is
quantified. Box orbits are found to dominate the orbital structure of dark
matter haloes in cosmological simulations. There is a strong anticorrelation
between the fraction of box orbits and the central baryon fraction. While
radiative cooling acts to reduce the fraction of box orbits, strong feedback
implementations result in a similar orbital distribution to that of the dark
matter only case. The orbital content described by the stellar particles is
found to be remarkably similar to that drawn from the orbits of dark matter
particles, suggesting that either they have forgotten their dynamical history,
or that subhaloes bringing in stars are not biased significantly with respect
to the main distribution. The orbital content of the subhaloes is in broad
agreement with that seen in the outer regions of the particle distributions.Comment: 18 pages, 13 figures, 3 tables. Accepted for publication in MNRA
HI content in galaxies in loose groups
Gas deficiency in cluster spirals is well known and ram-pressure stripping is
considered the main gas removal mechanism. In some compact groups too gas
deficiency is reported. However, gas deficiency in loose groups is not yet well
established. Lower dispersion of the member velocities and the lower density of
the intra-group medium in small loose groups favour tidal stripping as the main
gas removal process in them. Recent releases of data from HI Parkes all sky
survey (HIPASS) and catalogues of nearby loose groups with associated diffuse
X-ray emission have allowed us to test this notion. In this paper, we address
the following questions: (a) do galaxies in groups with diffuse X-ray emission
statistically have lower gas content compared to the ones in groups without
diffuse X-ray emission? (b) does HI deficiency vary with the X-ray luminosity
of the loose group in a systematic way? We find that (a) galaxies in groups
with diffuse X-ray emission, on average, are HI deficient, and have lost more
gas compared to those in groups without X-ray emission; the later are found not
to have significant HI deficiency; (b) no systematic dependence of the HI
deficiency with X-ray luminosity is found. Ram pressure assisted tidal
stripping and evaporation by thermal conduction are the two possible mechanisms
to account for this excess gas loss.Comment: 9 pages, 4 figures, accepted in MNRA
Development of a Coherent Doppler Lidar for Precision Maneuvering and Landing of Space Vehicles
A coherent Doppler lidar has been developed to address NASAs need for a high-performance, compact, and cost-effective velocity and altitude sensor onboard its landing vehicles. Future robotic and manned missions to planetary bodies require precise ground-relative velocity vector and altitude data to execute complex descent maneuvers and safe, soft landing at a pre-designated site. This lidar sensor, referred to as a Navigation Doppler Lidar, meets the required performance of landing missions while complying with vehicle size, mass, and power constraints. Operating from over five kilometers altitude, the lidar obtains velocity and range precision measurements with 2 cm/sec and 2 meters, respectively, dominated by the vehicle motion. After a series of flight tests onboard helicopters and rocket-powered free-flyer vehicles, the Navigation Doppler Lidar is now being ruggedized for future missions to various destinations in the solar system
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