310 research outputs found
Simulations of spectral lines from an eccentric precessing accretion disc
Two dimensional SPH simulations of a precessing accretion disc in a q=0.1
binary system (such as XTE J1118+480) reveal complex and continuously varying
shape, kinematics, and dissipation. The stream-disc impact region and disc
spiral density waves are prominent sources of energy dissipation.The dissipated
energy is modulated on the period P_{sh} = ({P_{orb}}^{-1}-{P_{prec}}^{-1}^{-1}
with which the orientation of the disc relative to the mass donor repeats. This
superhump modulation in dissipation energy has a variation in amplitude of ~10%
relative to the total dissipation energy and evolves, repeating exactly only
after a full disc precession cycle. A sharp component in the light curve is
associated with centrifugally expelled material falling back and impacting the
disc. Synthetic trailed spectrograms reveal two distinct "S-wave" features,
produced respectively by the stream gas and the disc gas at the stream-disc
impact shock. These S-waves are non-sinusoidal, and evolve with disc precession
phase. We identify the spiral density wave emission in the trailed spectrogram.
Instantaneous Doppler maps show how the stream impact moves in velocity space
during an orbit. In our maximum entropy Doppler tomogram the stream impact
region emission is distorted, and the spiral density wave emission is
uppressed. A significant radial velocity modulation of the whole line profile
occurs on the disc precession period. We compare our SPH simulation with a
simple 3D model: the former is appropriate for comparison with emission lines
while the latter is preferable for skewed absorption lines from precessing
discs.Comment: See http://physics.open.ac.uk/FHMR/ for associated movie (avi) files.
The full paper is in MNRAS press. Limited disk space limit of 650k, hence low
resolution figure file
When is forgetting not forgetting? A discursive analysis of differences in forgetting talk between adults with cystic fibrosis with different levels of adherence to nebulizer treatments
Forgetting is often cited as a reason why people struggle to adhere to treatments for chronic conditions. Interventions have tried to improve forgetting behavior using reminders. We used a discursive psychological approach to explore differences in how high and low adherers constructed forgetting their nebulizer treatments for cystic fibrosis. Interviews were conducted with 18 adults from a cystic fibrosis center in the United Kingdom. High adherers constructed forgetting treatments as occasional lapses in automaticity and temporary lapses in memory that they found easy to repair. Low adherers utilized forgetting to normalize more consistent nonadherence to treatments. However, it is important to contextualize forgetting as a discursive resource that helped these participants to negotiate moral discourses around adherence to treatment that reminder interventions cannot address; we therefore recommend a more behavioral, patient-focused, theory-driven approach to intervention development
Attribute abstraction, feature-dimensionality, and the scaling of product similarities
This paper examines the attributes that consumers use when making product similarity judgments and their effect on similarity scaling. Previous research suggests that concrete brands are judged using dichotomous features while more abstract product categories are judged using continuous dimensions. This, in turn, suggests that the appropriateness of spatial scaling increases relative to tree scaling as one moves from brands to product categories. The results of two studies support an increase in the fit of spaces relative to trees from brands to categories. However, the abstractness of the judgments appears to be driving the effect, not the use of features or dimensions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30067/1/0000437.pd
The Sloan Digital Sky Survey Reverberation Mapping Project: Ensemble Spectroscopic Variability of Quasar Broad Emission Lines
We explore the variability of quasars in the MgII and Hbeta broad emission
lines and UV/optical continuum emission using the Sloan Digital Sky Survey
Reverberation Mapping project (SDSS-RM). This is the largest spectroscopic
study of quasar variability to date: our study includes 29 spectroscopic epochs
from SDSS-RM over months, containing 357 quasars with MgII and 41 quasars
with Hbeta . On longer timescales, the study is also supplemented with
two-epoch data from SDSS-I/II. The SDSS-I/II data include an additional
quasars with MgII and 572 quasars with Hbeta. The MgII emission line is
significantly variable ( 10% on 100-day timescales), a necessary
prerequisite for its use for reverberation mapping studies. The data also
confirm that continuum variability increases with timescale and decreases with
luminosity, and the continuum light curves are consistent with a damped
random-walk model on rest-frame timescales of days. We compare the
emission-line and continuum variability to investigate the structure of the
broad-line region. Broad-line variability shows a shallower increase with
timescale compared to the continuum emission, demonstrating that the broad-line
transfer function is not a -function. Hbeta is more variable than MgII
(roughly by a factor of ), suggesting different excitation mechanisms,
optical depths and/or geometrical configuration for each emission line. The
ensemble spectroscopic variability measurements enabled by the SDSS-RM project
have important consequences for future studies of reverberation mapping and
black hole mass estimation of quasars.Comment: 20 pages, 25 figures. ApJ accepted: minor revisions following referee
repor
Associations of sperm telomere length with semen parameters, clinical outcomes and lifestyle factors in human normozoospermic samples
Background
Many studies have demonstrated that lifestyle factors can affect sperm quality and fertility. Sperm telomere length (STL) has been reported as potential biomarker or sperm quality. However, no studies have investigated how lifestyle factors can affect STL and associated clinical outcomes.
Objectives
The purpose of this manuscript is to investigate any association between STL with lifestyle factors, semen parameters and clinical outcomes.
Materials and methods
Sperm telomere length was measured using real‐time PCR in normozoospermic male partners (n = 66) of couples undergoing ART treatment. Each participant also completed a detailed questionnaire about general lifestyle. Linear regression univariate analysis and ANCOVA were performed to respectively determine correlations between STL and study parameters or identify statistically significant differences in STL while controlling for age, BMI and other factors.
Results
Using a linear regression model, STL is positively correlated with in vitro fertilization success (n = 65, r = 0.37, P = .004) but not with embryo cleavage rates and post‐implantation clinical outcomes including gestational age‐adjusted birth weight. No associations were observed between STL and sperm count, concentration or progressive motility. We further found that STL did not associate age, BMI, health or lifestyle factors.
Discussion
In somatic cells, the rate of telomere shortening is influenced by a number of lifestyle factors such as smoking, diet and occupation. However, little is known about how lifestyle factors affect STL and subsequently reproductive outcome. Out data suggest that STL might have an important role mechanistically for fertilization rate regardless of sperm parameters and lifestyle factors.
Conclusion
The results of this study demonstrate that STL is associated with in vitro fertilization rates, but not with semen parameters nor lifestyle factors. Further investigations are warranted to identify the potential variation of STL overtime to clarify its significance as a potential biomarker in ART
Deployable Optical Receiver Array Cubesat
Small satellites and cubesats often have low data transmission rates due to the use of low-gain radio links in UHF and S bands. These links typically provide up to only 1 Mbps for communication between the ground and LEO, limiting the applications and mission operations of small satellites. Optical communication technology can enable much higher data rates and is rapidly gaining hold for larger satellites, including for crosslinks within SpaceX’s Starlink constellation and upcoming NASA deep space missions. However, it has been difficult to implement on small satellites and cubesats due to the need for precision pointing on the order of arcseconds to align the narrow optical laser beam between terminals--a laser transmitter in LEO may yield a footprint less than 100 meters wide at its receiving ground station. We report the development of a 3U cubesat to demonstrate new optical communication technology that eliminates precision pointing accuracy requirements on the host spacecraft. The deployable optical receiver aperture (DORA) aims to demonstrate 1 Gbps data rates over distances of thousands of kilometers. DORA requires an easily accommodated host pointing accuracy of only 10 degrees with minimal stability, allowing the primary mission to continue without reorienting to communicate and/or enabling small satellite missions using low-cost off-the-shelf ADCS systems. To achieve this performance, DORA replaces the traditional receiving telescope on the spacecraft with a collection of wide-angle photodiodes that can identify the angle of arrival for incoming communication lasers and steer the onboard transmitting laser in the corresponding direction. This work is motivated by NASA’s plans for a lunar communications and navigation network and supported by NASA’s Space Technology Program (STP). It is ideally suited for crosslink communications among small spacecraft, especially for those forming a swarm and/or a constellation, and for surface to orbit communications. We will implement the deployable optical receiver aperture and miniature transmission telescope as a 1U payload in the 3U cubesat and conduct the demonstration flight in LEO. Future implementations of the DORA technology are expected to further enable omnidirectional receiving of multiple optical communications simultaneously and accommodate multiple transmitting modules on a single cubesat
Solar Cell Degradation due to Proton Belt Enhancements During Electric Orbit Raising to GEO
The recent introduction of all‐electric propulsion on geosynchronous satellites enables lower‐cost access to space by replacing chemical propellant. However, the time period required to initially raise the satellite to geostationary orbit (GEO) is around 200 days. During this time the satellite can be exposed to dynamic increases in trapped flux which are challenging to model. To understand the potential penalty of this new technique in terms of radiation exposure, the influence of several key parameters on solar cell degradation during the electric orbit raising period has been investigated. This is achieved by calculating the accumulation of non‐ionising dose through time for a range of approaches. We demonstrate the changes in degradation caused by launching during a long‐lived (100s of days) enhancement in MeV trapped proton flux for three different electric orbit raising scenarios and three different thicknesses of coverglass. Results show that launching in an active environment can increase solar cell degradation due to trapped protons by ~5% before start of service compared with a quiet environment. The crucial energy range for such enhancements in proton flux is 3‐10MeV (depending on shielding). Further changes of a few percent can occur between different trajectories, or when a 50μm change in coverglass thickness is applied
The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview
The Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM) is a
dedicated multi-object RM experiment that has spectroscopically monitored a
sample of 849 broad-line quasars in a single 7 deg field with the SDSS-III
BOSS spectrograph. The RM quasar sample is flux-limited to i_psf=21.7 mag, and
covers a redshift range of 0.1<z<4.5. Optical spectroscopy was performed during
2014 Jan-Jul dark/grey time, with an average cadence of ~4 days, totaling more
than 30 epochs. Supporting photometric monitoring in the g and i bands was
conducted at multiple facilities including the CFHT and the Steward Observatory
Bok telescopes in 2014, with a cadence of ~2 days and covering all lunar
phases. The RM field (RA, DEC=14:14:49.00, +53:05:00.0) lies within the CFHT-LS
W3 field, and coincides with the Pan-STARRS 1 (PS1) Medium Deep Field MD07,
with three prior years of multi-band PS1 light curves. The SDSS-RM 6-month
baseline program aims to detect time lags between the quasar continuum and
broad line region (BLR) variability on timescales of up to several months (in
the observed frame) for ~10% of the sample, and to anchor the time baseline for
continued monitoring in the future to detect lags on longer timescales and at
higher redshift. SDSS-RM is the first major program to systematically explore
the potential of RM for broad-line quasars at z>0.3, and will investigate the
prospects of RM with all major broad lines covered in optical spectroscopy.
SDSS-RM will provide guidance on future multi-object RM campaigns on larger
scales, and is aiming to deliver more than tens of BLR lag detections for a
homogeneous sample of quasars. We describe the motivation, design and
implementation of this program, and outline the science impact expected from
the resulting data for RM and general quasar science.Comment: 25 pages, submitted to ApJS; project website at http://www.sdssrm.or
The Sloan Digital Sky Survey Reverberation Mapping project : composite lags at z ≤ 1
Funding: STFC grant ST/M001296/1 (KH).We present composite broad-line region (BLR) reverberation mapping lag measurements for Hα, Hβ, He II λ4686, and Mg II for a sample of 144, z ≲ 1 quasars from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project. Using only the 32-epoch spectroscopic light curves in the first six-month season of SDSS-RM observations, we compile correlation function measurements for individual objects and then coadd them to allow the measurement of the average lags for our sample at mean redshifts of 0.4 (for Hα) and ∼0.65 (for the other lines). At similar quasar luminosities and redshifts, the sample-averaged lag decreases in the order of Mg II, Hα, Hβ, and He II. This decrease in lags is accompanied by an increase in the mean line width of the four lines, and is roughly consistent with the virialized motion for BLR gas in photoionization equilibrium. These are among the first RM measurements of stratified BLR structure at z > 0.3. Dividing our sample by luminosity, Hα shows clear evidence of increasing lags with luminosity, consistent with the expectation from the measured BLR size-luminosity relation based on Hβ. The other three lines do not show a clear luminosity trend in their average lags due to the limited dynamic range of luminosity probed and the poor average correlation signals in the divided samples, a situation that will be improved with the incorporation of additional photometric and spectroscopic data from SDSS-RM. We discuss the utility and caveats of composite lag measurements for large statistical quasar samples with reverberation mapping dataPostprintPeer reviewe
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