An investigation of lucky imaging techniques Smith, Andrew; Bailey, Jeremy; Hough, J. H. ...
Monthly notices of the Royal Astronomical Society,
October 2009, Volume:
398, Issue:
4
Journal Article
Peer reviewed
We present an empirical analysis of the effectiveness of frame selection (also known as lucky imaging) techniques for high-resolution imaging. A high-speed image recording system has been used to ...observe a number of bright stars. The observations were made over a wide range of values of D/r0 and exposure time. The improvement in Strehl ratio of the stellar images due to aligning frames and selecting the best frames was evaluated as a function of these parameters. We find that improvement in Strehl ratio by factors of 4–6 can be achieved over a range of D/r0 from 3 to 12, with a slight peak at D/r0∼ 7. The best Strehl improvement is achieved with exposure times of 10 ms or less, but significant improvement is still obtained at exposure times as long as 640 ms. Our results are consistent with previous investigations but cover a much wider range of parameter space. We show that Strehl ratios of >0.7 can be achieved in appropriate conditions whereas previous studies have generally shown maximum Strehl ratios of ∼0.3. The results are in reasonable agreement with the simulations of Baldwin, Warner & Mackay.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Optical polarimetry observations on La Palma, Canary Islands, during a Saharan dust episode show dichroic extinction indicating the presence of vertically aligned particles in the atmosphere. ...Modelling of the extinction together with particle orientation indicates that the alignment could have been due to an electric field of the order of 2 kV/m. Two alternative mechanisms for the origin of the field are examined: the effect of reduced atmospheric conductivity and charging of the dust layer, the latter effect being a more likely candidate. It is concluded that partial alignment may be a common feature of Saharan dust layers. The modelling indicates that the alignment can significantly alter dust optical depth. This "Venetian blind effect" may have decreased optical thickness in the vertical direction by as much as 10% for the case reported here. It is also possible that the alignment and the electric field modify dust transport.
PlanetPol: A Very High Sensitivity Polarimeter Hough, J. H.; Lucas, P. W.; Bailey, J. A. ...
Publications of the Astronomical Society of the Pacific,
09/2006, Volume:
118, Issue:
847
Journal Article
Peer reviewed
Open access
We have built and used on several occasions an optical broadband stellar polarimeter, PlanetPol, which employs photoelastic modulators and avalanche photodiodes and achieves a photon‐noise–limited ...sensitivity of at least 1 in 106in fractional polarization. Observations of a number of polarized standards taken from the literature show that the accuracy of polarization measurements is ∼1%. We have developed a method for accurately measuring the polarization of altitude‐azimuth mounted telescopes by observing bright nearby stars at different parallactic angles, and we find that the on‐axis polarization of the William Herschel Telescope is typically ∼15 × 10−6, measured with an accuracy of a few parts in 107. The nearby stars (distance less than 32 pc) are found to have very low polarizations, typically a few ×10−6, indicating that very little interstellar polarization is produced close to the Sun and that their intrinsic polarization is also low. Although the polarimeter can be used for a wide range of astronomy, the very high sensitivity was set by the goal of detecting the polarization signature of unresolved extrasolar planets.
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BFBNIB, NMLJ, NUK, PNG, UL, UM, UPUK
Introduction This study sought to determine the effect of a 2-year, multicomponent health intervention (Spirited Life) targeting metabolic syndrome and stress simultaneously. Design An RCT using a ...three-cohort multiple baseline design was conducted in 2010–2014. Setting/participants Participants were United Methodist clergy in North Carolina, U.S., in 2010, invited based on occupational status. Of invited 1,745 clergy, 1,114 consented, provided baseline data, and were randomly assigned to immediate intervention ( n =395), 1-year waitlist ( n =283), or 2-year waitlist ( n =436) cohorts for a 48-month trial duration. Intervention The 2-year intervention consisted of personal goal setting and encouragement to engage in monthly health coaching, an online weight loss intervention, a small grant, and three workshops delivering stress management and theological content supporting healthy behaviors. Participants were not blinded to intervention. Main outcome measures Trial outcomes were metabolic syndrome (primary) and self-reported stress and depressive symptoms (secondary). Intervention effects were estimated in 2016 in an intention-to-treat framework using generalized estimating equations with adjustment for baseline level of the outcome and follow-up time points. Log-link Poisson generalized estimating equations with robust SEs was used to estimate prevalence ratios (PRs) for binary outcomes; mean differences were used for continuous/score outcomes. Results Baseline prevalence of metabolic syndrome was 50.9% and depression was 11.4%. The 12-month intervention effect showed a benefit for metabolic syndrome (PR=0.86, 95% CI=0.79, 0.94, p <0.001). This benefit was sustained at 24 months of intervention (PR=0.88; 95% CI=0.78, 1.00, p =0.04). There was no significant effect on depression or stress scores. Conclusions The Spirited Life intervention improved metabolic syndrome prevalence in a population of U.S. Christian clergy and sustained improvements during 24 months of intervention. These findings offer support for long-duration behavior change interventions and population-level interventions that allow participants to set their own health goals. Trial registration This study is registered at www.clinicaltrials.gov NCT01564719.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Hydroxide catalysis bonds are used in the aLIGO gravitational wave detectors and are an essential technology within the mirror suspensions that allowed detector sensitivities to be reached, which ...enabled the first direct detections of gravitational waves. Methods aimed at further improving hydroxide catalysis bonds for future upgrades to these detectors, in order to increase detection rates and the number of detectable sources, are explored. Also, the effect on the bonds of an aLIGO suspension construction procedure involving heat, the fiber welding process, is investigated. Here we show that thermal treatments can be beneficial to improving some of the bond properties important to the mirror suspensions in interferometric gravitational wave detectors. It was found that heat treating bonds at 150 °C increases bond strength by a factor of approximately 1.5 and a combination of bond aging and heat treatment of the optics at 150 °C reduces the mechanical loss of a bond from 0.10 to 0.05. It is also shown that current construction procedures do not reduce bond strength.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Purpose
There is a growing consensus in education that schools can and should attend to students’ social-emotional development. Emerging research and popular texts indicate that students’ mindsets, ...beliefs, dispositions, emotions and behaviors can advance outcomes, such as college readiness, career success, mental health and relationships. Despite this growing awareness, many districts and schools are still struggling to implement strategies that develop students’ social-emotional skills. The purpose of this paper is to fill this gap by examining the social-emotional learning (SEL) practices in ten middle schools with strong student-reported data on SEL outcomes, particularly for African American and Latinx students.
Design/methodology/approach
Case study methods, including interviews, observations and document analysis, were employed.
Findings
The authors identify six categories of common SEL practices: strategies that promote positive school climate and relationships, supporting positive behavior, use of elective courses and extracurricular activities, SEL-specific classroom practices and curricula, personnel strategies and measurement and data use. Absence of a common definition of SEL and lack of alignment among SEL practices were two challenges cited by respondents.
Originality/value
This is the first study to analyze SEL practices in outlier schools, with a focus on successful practices with schools that have a majority of African American and/or Latinx students.
The search for gravitational wave signals from astrophysical sources has led to the current work to upgrade the two largest of the long-baseline laser interferometers, the LIGO detectors. The first ...fused silica mirror suspensions for the Advanced LIGO gravitational wave detectors have been installed at the LIGO Hanford and Livingston sites. These quadruple pendulums use synthetic fused silica fibers produced using a CO2 laser pulling machine to reduce thermal noise in the final suspension stage. The suspension thermal noise in Advanced LIGO is predicted to be limited by internal damping in the surface layer of the fibers, damping in the weld regions, and the strength of the fibers. We present here a new method for increasing the fracture strength of fused silica fibers by laser polishing of the stock material from which they are produced. We also show measurements of mechanical loss in laser polished fibers, showing a reduction of 30% in internal damping in the surface layer.
One of the most significant limits to the sensitivity of current, and future, long-baseline interferometric gravitational wave detectors is thermal displacement noise of the test masses and their ...suspensions. This paper reports results of analytical and experimental studies of the limits to thermal noise performance of cryogenic silicon test mass suspensions set by two constraints on suspension fibre dimensions: the minimum dimensions required to allow conductive cooling for extracting incident laser beam heat deposited in the mirrors; and the minimum dimensions of fibres (set by their tensile strength) which can support test masses of the size envisaged for use in future detectors. We report experimental studies of breaking strength of silicon ribbons, and resulting design implications for the feasibility of suspension designs for future gravitational wave detectors using silicon suspension fibres. We analyse the implication of this study for thermal noise performance of cryogenically cooled silicon suspensions.
To evaluate the efficacy of behavioral counseling combined with technology-based self-monitoring for sodium restriction in hemodialysis (HD) patients.
Randomized clinical trial.
English literate ...adults undergoing outpatient, in-center intermittent HD for at least 3 months.
Over a 16-week period, both the intervention and the attention control groups were shown 6 educational modules on the HD diet. The intervention group also received social cognitive theory-based behavioral counseling and monitored their diets daily using handheld computers.
Average daily interdialytic weight gain (IDWGA) was calculated for every week of HD treatment over the observation period by subtracting the post-dialysis weight at the previous treatment time (t-1) from the pre-dialysis weight at the current treatment time (t), dividing by the number of days between treatments. Three 24-hour dietary recalls were obtained at baseline, 8 weeks, and 16 weeks and evaluated using the Nutrient Data System for Research.
A total of 179 participants were randomized, and 160 (89.4%) completed final measurements. IDWGA did not differ significantly by treatment group at any time point considered (P > .79 for each). A significant differential change in dietary sodium intake observed at 8 weeks (-372 mg/day; P = .05) was not sustained at 16 weeks (-191 mg/day; P = .32).
The BalanceWise Study intervention appeared to be feasible and acceptable to HD patients although IDWGA was unchanged and the desired behavioral changes observed at 8 weeks were not sustained. Unmeasured factors may have contributed to the mixed findings, and further research is needed to identify the appropriate patients for such interventions.
Further improvements in the low frequency sensitivity of gravitational wave detectors are important for increasing the observable population of astrophysical sources, such as intermediate mass ...compact black hole binary systems. Improvements in the lower stage mirror and suspension systems will set challenging targets for the required thermal noise performance of the cantilever blade springs, which provide vertical softness and, thus, isolation to the mirror suspension stack. This is required due to the coupling between the vertical and horizontal axes due to the curvature of the Earth. This can be achieved through use of high mechanical Q materials, which are compatible with cryogenic cooling, such as crystalline silicon. However, such materials are brittle, posing further challenges for assembly/jointing and, more generally, for long-term robustness. Here, we report on experimental studies of the breaking strength of silicon at room temperature, via both tensile and 4-point flexural testing; and on the effects of various surface treatments and coatings on durability and strength. Single- and multi-layer DLC (diamond-like carbon) coatings, together with magnetron-sputtered silica and thermally-grown silica, are investigated, as are the effects of substrate preparation and argon plasma pre-treatment. Application of single- or multi-layer DLC coatings can significantly improve the failure stress of silicon flexures, in addition to improved robustness for handling (assessed through abrasion tests). Improvements of up to 80% in tensile strength, a twofold increase in flexural strength, in addition to a 6.4 times reduction in the vertical thermal noise contribution of the suspension stack at 10 Hz are reported (compared to current Advanced LIGO design). The use of silicon blade springs would also significantly reduce potential 'crackling noise' associated with the underlying discrete events associated with plastic deformation in loaded flexures.
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