Search

Attitude control subjected to pointing constraints is a requirement for most spacecraft missions carrying sensitive on-board equipment. Pointing constraints can be divided into two categories: exclusion zones that are defined for sensitive equipment such as telescopes or cameras that can be damaged from celestial objects, and inclusion zones that are defined for communication hardware and solar arrays. This work derives common frame dynamics that are fully derived for Modified Rodrigues Parameters and introduced to an existing novel technique for constrained spacecraft attitude control, which uses a kinematic steering law and servo sub-system. Lyapunov methods are used to redevelop the steering law and servo sub-system in the common frame for the tracking problem for both static and dynamic conic constraints. A numerical example and comparison between the original frame and the common frame for the static constrained tracking problem are presented under both unbounded and limited torque capabilities. Monte Carlo simulations are performed to validate the convergence of the constrained tracking problem for static conic constraints under small perturbations of the initial conditions. The performance of dynamic conic constraints in the tracking problem is addressed and a numerical example is presented. The result of using common frame dynamics in the constrained problem shows decreased control effort required to rotate the spacecraft.

Understanding the consequences of tuning TCR signaling on selection, peripheral T cell function, and tolerance in the context of native TCR repertoires may provide insight into the physiological control of tolerance. In this study, we show that genetic ablation of a natural tuner of TCR signaling, mir-181a-1/b-1, in double-positive thymocytes dampened TCR and Erk signaling and increased the threshold of positive selection. Whereas mir-181a-1/b-1 deletion in mice resulted in an increase in the intrinsic reactivity of naive T cells to self-antigens, it did not cause spontaneous autoimmunity. Loss of mir-181a-1/b-1 dampened the induction of experimental autoimmune encephalomyelitis and reduced basal TCR signaling in peripheral T cells and their migration from lymph nodes to pathogenic sites. Taken together, these results demonstrate that tolerance can be modulated by microRNA gene products through the control of opposing activities in T cell selection and peripheral T cell function.

Facebook pages have been promoted as a cost-effective way of communicating with department alumni, students, faculty, and friends. We analyzed Facebook engagement metrics across a 2-year span for the page for one department of psychology. In addition, we surveyed followers of the page to determine whether different constituency groups appreciated different types of Facebook posts. In general, posts related to current faculty accomplishments were most engaging as judged by Facebook metrics and self-report survey data. The survey data also showed that different constituencies enjoyed posts related to their particular group. These results demonstrate that a department Facebook page can be an effective tool for reaching a wide range of constituent groups. We also discuss some tips for generating and managing a department page as well as challenges.

Differential coordination of growth and patterning across metazoans gives rise to a diversity of sizes and shapes at tissue, organ and organismal levels. Although tissue size and tissue function can be interdependent.sup.1-5, mechanisms that coordinate size and function remain poorly understood. Planarians are regenerative flatworms that bidirectionally scale their adult body size.sup.6,7 and reproduce asexually, via transverse fission, in a size-dependent manner.sup.8-10. This model offers a robust context to address the gap in knowledge that underlies the link between size and function. Here, by generating an optimized planarian fission protocol in Schmidtea mediterranea, we show that progeny number and the frequency of fission initiation are correlated with parent size. Fission progeny size is fixed by previously unidentified mechanically vulnerable planes spaced at an absolute distance along the anterior-posterior axis. An RNA interference screen of genes for anterior-posterior patterning uncovered components of the TGF[beta] and Wnt signalling pathways as regulators of the frequency of fission initiation rather than the position of fission planes. Finally, inhibition of Wnt and TGF[beta] signalling during growth altered the patterning of mechanosensory neurons--a neural subpopulation that is distributed in accordance with worm size and modulates fission behaviour. Our study identifies a role for TGF[beta] and Wnt in regulating size-dependent behaviour, and uncovers an interdependence between patterning, growth and neurological function. A planarian fission protocol shows that the number of progeny and the frequency of fission initiation correlate with parent size, and TGF[beta] and Wnt signalling components are identified as regulators of fission behaviour., Author(s): Christopher P. Arnold [sup.1] [sup.2] , Blair W. Benham-Pyle [sup.1] , Jeffrey J. Lange [sup.1] , Christopher J. Wood [sup.1] , Alejandro Sánchez Alvarado [sup.1] [sup.2] Author Affiliations: (1) [...]

A large scale observational study by educational psychologists of 141 UK primary classrooms used a partial interval time-sampling observational schedule to record the frequency and type of verbal behaviour of teachers and whether students were "on-task" (following the teacher's directions) or "off-task" (not following the teacher's directions). Results were analysed and comparisons made between lessons that followed National Literacy Strategy or Numeracy guidelines and those that did not; between schools from different geographical contexts, e.g. rural or inner-city; between classes where there was one, or more than one, adult present; between schools with different percentages of free school meals; and between a.m. and p.m. lessons. A range of findings included higher rates of students being on-task than found by previous studies, and correlations between high on-task rates and teachers who used high levels of verbal behaviour including positive academic feedback. Teachers used three times more verbal approval for desired social behaviour in the classroom than has been reported in previous studies. It was found that teachers verbally interacted more with students during National Literacy and Numeracy Strategy lessons but that this did not lead to statistically significantly higher on-task rate. Similarly, teachers in inner-city schools interacted more with students, but on-task rates in inner-city schools were not significantly higher. Reasons for this effect are discussed. (Contains 8 tables and 11 figures.)