279 research outputs found
Cool DZ white dwarfs II: Compositions and evolution of old remnant planetary systems
In a previous study, we analysed the spectra of 230 cool ( <
9000 K) white dwarfs exhibiting strong metal contamination, measuring
abundances for Ca, Mg, Fe and in some cases Na, Cr, Ti, or Ni. Here we
interpret these abundances in terms of the accretion of debris from extrasolar
planetesimals, and infer parent body compositions ranging from crust-like (rich
in Ca and Ti) to core-like (rich in Fe and Ni). In particular, two white
dwarfs, SDSSJ0823+0546 and SDSSJ0741+3146, which show log[Fe/Ca] > 1.9 dex, and
Fe to Ni ratios similar to the bulk Earth, have accreted by far the most
core-like exoplanetesimals discovered to date. With cooling ages in the range
1-8 Gyr, these white dwarfs are among the oldest stellar remnants in the Milky
Way, making it possible to probe the long-term evolution of their ancient
planetary systems. From the decrease in maximum abundances as a function of
cooling age, we find evidence that the arrival rate of material on to the white
dwarfs decreases by 3 orders of magnitude over a 6.5 Gyr span in white
dwarf cooling ages, indicating that the mass-reservoirs of post-main sequence
planetary systems are depleted on a 1 Gyr e-folding time-scale.
Finally, we find that two white dwarfs in our sample are members of wide
binaries, and both exhibit atypically high abundances, thus providing strong
evidence that distant binary companions can dynamically perturb white dwarf
planetary systems.Comment: 21 pages, 10 figures, 1 table, accepted for publication in MNRA
Can We Accurately Measure Axial Segment Coordination during Turning Using Inertial Measurement Units (IMUs)?
Camera-based 3D motion analysis systems are considered to be the gold standard for
movement analysis. However, using such equipment in a clinical setting is prohibitive due to the
expense and time-consuming nature of data collection and analysis. Therefore, Inertial
Measurement Units (IMUs) have been suggested as an alternative to measure movement in clinical
settings. One area which is both important and challenging is the assessment of turning kinematics
in individuals with movement disorders. This study aimed to validate the use of IMUs in the
measurement of turning kinematics in healthy adults compared to a camera-based 3D motion
analysis system. Data were collected from twelve participants using a Vicon motion analysis system
which were compared with data from 4 IMUs placed on the; forehead, middle thorax, and feet in
order to determine accuracy and reliability. The results demonstrated that IMUs sensors produced
reliable kinematic measures and showed excellent reliability (ICCs 0.80–0.98) and no significant
differences were seen in paired t-tests in all parameters when comparing the two systems. This
suggests that IMU sensors provide a viable alternative to camera-based motion capture that could
be used in isolation to gather data from individuals with movement disorders in clinical settings
and real-life situations
Measuring the Initial-Final Mass-Relation using wide double white dwarf binaries from Gaia DR3
The Initial-Final Mass-Relation (IFMR) maps the masses of main sequence stars
to their white dwarf descendants. The most common approach to measure the IFMR
has been to use white dwarfs in clusters. However, it has been shown that wide
double white dwarfs can also be used to measure the IFMR using a Bayesian
approach. We have observed a large sample of 90 Gaia double white dwarfs using
FORS2 on the VLT. Considering 52 DA+DA, DA+DC, and DC+DC pairs, we applied our
extended Bayesian framework to probe the IFMR in exquisite detail. Our
monotonic IFMR is well constrained by our observations for initial masses of
1-5 Msun, with the range 1-4 Msun mostly constrained to a precision of 0.03
Msun or better. We add an important extension to the framework, using a
Bayesian mixture-model to determine the IFMR robustly in the presence of
systems departing from single star evolution. We find a large but uncertain
outlier fraction of 5921 percent, with outlier systems requiring an
additional Gyr uncertainty in their cooling age
differences. However, we find that this fraction is dominated by a few systems
with massive components near 0.9 Msun, where we are most sensitive to outliers,
but are also able to establish four systems as merger candidatesComment: Accepted for publication in MNRA
The properties of cool DZ white dwarfs.
Over the last few decades it has become clear that metals present within the atmospheres of more than one quarter of white dwarfs signify recent accretion of minor bodies from their planetary systems. Spectral analysis of these metal-polluted white dwarfs allows determination of the accreted body composition, providing the most direct method for measuring the makeup of exoplanetary material. So far, most detailed abundance analyses have mostly been limited to a few systems at a time.
In this thesis, I present a sample of 231 cool DZ white dwarfs identified from SDSS spectroscopy. These stars exhibit strong metal lines from multiple elements, permitting detailed abundance analyses of each. Furthermore their low effective temperatures of 9000{4400 K imply corresponding cooling ages of 1{8 Gyr, allowing me to examine some of the oldest planetary systems in orbit of stellar remnants.
Across the sample, I found a huge diversity in the metal abundance ratios, with Fe/Ca varying by a factor 100. I developed a simple method for interpreting the rocky geology of the accreted parent bodies, indicating that some were composed of > 80 % crust material, and with > 80 % core material for others. Using the calculated white dwarf ages, I identified a downwards trend of the highest levels of metal pollution for the oldest systems, suggesting their mass reservoirs of exoplanetesimals
become depleted on a ' 1 Gyr time scale.
Finally, Zeeman split metal lines are found in the spectra of 33 of these systems, with surface magnetic fields in the range 0:25{30 MG. Investigation of this rare combination of metals and magnetism has consequences for the formation of white dwarf magnetic fields, and motivates new research in atomic physics
Children With Developmental Coordination Disorder Exhibit Greater Stepping Error Despite Similar Gaze Patterns and State Anxiety Levels to Their Typically Developing Peers
This study examined stepping accuracy, gaze behavior, and state-anxiety in children with (N = 21, age M = 10.81, SD = 1.89) and without (N = 18, age M = 11.39, SD = 2.06) developmental coordination disorder (DCD) during an adaptive locomotion task. Participants walked at a self-selected pace along a pathway, placing their foot into a raised rectangular floor-based target box followed by either no obstacles, one obstacle, or two obstacles. Stepping kinematics and accuracy were determined using three-dimensional motion capture, whilst gaze was determined using mobile eye-tracking equipment. The children with DCD displayed greater foot placement error and variability when placing their foot within the target box and were more likely to make contact with its edges than their typically developing (TD) peers. The DCD group also displayed greater variability in the length and width of their steps in the approach to the target box. No differences were observed between groups in any of the gaze variables measured, in mediolateral velocity of the center of mass during the swing phase into the target box, or in the levels of self-reported state-anxiety experienced prior to facing each task. We therefore provide the first quantifiable evidence that deficits to foot placement accuracy and precision may be partially responsible for the increased incidence of trips and falls in DCD, and that these deficits are likely to occur independently from gaze behavior and state-anxiety
A comparison of turning kinematics at different amplitudes during standing turns between older and younger adults
It is well-established that processes involving changing direction or turning in which either or both standing and walking turns are utilized involve coordination of the whole-body and stepping characteristics. However, the turn context and whole-body coordination have not been fully explored during different turning amplitudes. For these reasons, this present study aimed to determine the effects of turning amplitude on whole-body coordination. The findings from this study can be utilized to inform the rationale behind fall prevention factors and to help design an exercise strategy to address issues related to amplitude of turning in older adults. Twenty healthy older and twenty healthy younger adults were asked to complete standing turns on level ground using three randomly selected amplitudes, 90°, 135° and 180°, at their self-selected turn speed. Turning kinematics and stepping variables were recorded using Inertial Measurement Units. Analysis of the data was carried out using Mixed Model Analysis of Variance with two factors (2 groups × 3 turning amplitudes) and further post hoc pairwise analysis to examine differences between factors. There were significant interaction effects (p < 0.05) between the groups and turning amplitudes for step duration and turn speed. Further analysis using Repeated Measure Analysis of Variance tests determined a main effect of amplitude on step duration and turn speed within each group. Furthermore, post hoc pairwise comparisons revealed that the step duration and turn speed increased significantly (p < 0.001) with all increases in turning amplitude in both groups. In addition, significant main effects for group and amplitudes were seen for onset latency of movement for the head, thorax, pelvis, and feet, and for peak head–thorax and peak head–pelvis angular separations and stepping characteristics, which all increased with turn amplitude and showed differences between groups. These results suggest that large amplitude turns result in a change in turning and stepping kinematics. Therefore, when assessing the turning characteristics of older adults or those in frail populations, the turning amplitude should be taken into account during turning, and could be gradually increased to challenge motor control as part of exercise falls prevention strategies
The Effect of Different Turn Speeds on Whole-Body Coordination in Younger and Older Healthy Adults
Difficulty in turning is prevalent in older adults and results in postural instability and risk of falling. Despite this, the mechanisms of turning problems have yet to be fully determined, and it is unclear if different speeds directly result in altered posture and turning characteristics. The aim of this study was to identify the effects of turning speeds on whole-body coordination and to explore if these can be used to help inform fall prevention programs in older adults. Forty-two participants (21 healthy older adults and 21 younger adults) completed standing turns on level ground. Inertial Measurement Units (XSENS) were used to measure turning kinematics and stepping characteristics. Participants were randomly tasked to turn 180° at one of three speeds; fast, moderate, or slow to the left and right. Two factors mixed model analysis of variance (MM ANOVA) with post hoc pairwise comparisons were performed to assess the two groups and three turning speeds. Significant interaction effects (p 0.05) were seen in; reorientation onset latency of head, pelvis, and feet, peak segmental angular separation, and stepping characteristics (step frequency and step size), which all changed with increasing turn speed. Repeated measures ANOVA revealed the main effects of speeds within the older adults group on those variables as well as the younger adults group. Our results suggest that turning speeds result in altered whole-body coordination and stepping behavior in older adults, which use the same temporospatial sequence as younger adults. However, some characteristics differ significantly, e.g., onset latency of segments, peak head velocity, step frequency, and step size. Therefore, the assessment of turning speeds elucidates the exact temporospatial differences between older and younger healthy adults and may help to determine some of the issues that the older population face during turning, and ultimately the altered whole-body coordination, which lead to falls
Recommended from our members
Wine glass size and wine sales: four replication studies in one restaurant and two bars
Funder: National Institute for Health Research; doi: http://dx.doi.org/10.13039/501100000272Abstract: Objective: Previous research suggests that wine glass size affects sales of wine in bars, with more wine purchased when served in larger glasses. The current four studies, conducted in one restaurant (Studies 1 and 2) and two bars (Studies 3 and 4) in Cambridge, England, aim to establish the reproducibility of this effect of glass size on sales. A multiple treatment reversal design was used, involving wine being served in sequential fortnightly periods in different sized glasses of the same design (290 ml, 350 ml, and 450 ml). The primary outcome was daily wine volume (ml) sold. Results: Restaurant: Daily wine volume sold was 13% (95% CI 2%, 24%) higher when served with 350 ml vs. 290 ml glasses in Study 1. A similar direction of effect was seen in Study 2 (6%; 95% CI − 1%, 15%). Bars: Daily wine volume sold was 21% (95% CI 9%, 35%) higher when served with 450 ml vs. 350 ml glasses in Study 3. This effect was not observed in Study 4 (− 7%, 95% CI − 16%, 3%). Meaningful differences were not demonstrated with any other glass comparison. These results partially replicate previous studies showing that larger glasses increase wine sales. Considerable uncertainty remains about the magnitude of any effect and the contexts in which it might occur. Trial registration Study 1: ISRCTN17958895 (21/07/2017), Study 2: ISRCTN17097810 (29/03/2018), Study 3 and 4: ISRCTN39401124 (10/05/2018
- …