Presentation, Analysis, and Simulation of Active Alignment Strategies for the James Webb Space Telescope

This paper presents three characteristics in the simulated active alignment strategy of the James Webb Space Telescope. The first includes the analysis and comparison of a baseline active alignment strategy with a damped least squares strategy. This baseline utilizes prior knowledge by means of direct human operator interaction to engage sets of telescope compensators to target specific aberration signatures. The baseline is compared to a damped least-squares strategy that utilizes simultaneous engagement of all telescope compensators without explicit human operator inter<actiori to achieve a least-squares telescope compensation. Second, we discuss how the active alignment of the JWST is encapsulated in a linear optical model developed at the Space Telescope Science Institute. This linear optical model provides a framework for an efficient and robust description of the optical control properties of the JWST and clearly articulates the necessity for having a multi-instrument multi-field wavefront sensing strategy to overcome control system non independence and the effects of non-common path errors in the main wavefront sensing camera. Finally. we present analytical results that explicitly map the telescope wavefront responses to the telescope control modes, and we present Monte-Carlo optical performance simulation results that demonstrate the efficacy of the damped least-squares active alignment and the prior-knowledge active alignment schemes

Magnetic Flux Transport at the Solar Surface

After emerging to the solar surface, the Sun's magnetic field displays a complex and intricate evolution. The evolution of the surface field is important for several reasons. One is that the surface field, and its dynamics, sets the boundary condition for the coronal and heliospheric magnetic fields. Another is that the surface evolution gives us insight into the dynamo process. In particular, it plays an essential role in the Babcock-Leighton model of the solar dynamo. Describing this evolution is the aim of the surface flux transport model. The model starts from the emergence of magnetic bipoles. Thereafter, the model is based on the induction equation and the fact that after emergence the magnetic field is observed to evolve as if it were purely radial. The induction equation then describes how the surface flows -- differential rotation, meridional circulation, granular, supergranular flows, and active region inflows -- determine the evolution of the field (now taken to be purely radial). In this paper, we review the modeling of the various processes that determine the evolution of the surface field. We restrict our attention to their role in the surface flux transport model. We also discuss the success of the model and some of the results that have been obtained using this model.Comment: 39 pages, 15 figures, accepted for publication in Space Sci. Re

Term admissions to neonatal units in England: a role for transitional care? A retrospective cohort study

Objective To identify the primary reasons for term admissions to neonatal units in England, to determine risk factors for admissions for jaundice and to estimate the proportion who can be cared for in a transitional setting without separation of mother and baby. Design Retrospective observational study using neonatal unit admission data from the National Neonatal Research Database and data of live births in England from the Office for National Statistics. Setting All 163 neonatal units in England 2011–2013. Participants 133 691 term babies born ≥37 weeks gestational age and admitted to neonatal units in England. Primary and secondary outcomes Primary reasons for admission, term babies admitted for the primary reason of jaundice, patient characteristics, postnatal age at admission, total length of stay, phototherapy, intravenous fluids, exchange transfusion and kernicterus. Results Respiratory disease was the most common reason for admission overall, although jaundice was the most common reason for admission from home (22% home vs 5% hospital). Risk factors for admission for jaundice include male, born at 37 weeks gestation, Asian ethnicity and multiple birth. The majority of babies received only a brief period of phototherapy, and only a third received intravenous fluids, suggesting that some may be appropriately managed without separation of mother and baby. Admission from home was significantly later (3.9 days) compared with those admitted from elsewhere in the hospital (1.7 days) (p<0.001). Conclusion Around two-thirds of term admissions for jaundice may be appropriately managed in a transitional care setting, avoiding separation of mother and baby. Babies with risk factors may benefit from a community midwife postnatal visit around the third day of life to enable early referral if necessary. We recommend further work at the national level to examine provision and barriers to transitional care, referral pathways between primary and secondary care, and community postnatal care