Alignment and preliminary outcomes of an ELT-size instrument to a very large telescope: LINC-NIRVANA at LBT

LINC-NIRVANA (LN) is a high resolution, near infrared imager that uses a multiple field-of-view, layer-oriented, multi-conjugate AO system, consisting of four multi-pyramid wavefront sensors (two for each arm of the Large Binocular Telescope, each conjugated to a different altitude). The system employs up to 40 star probes, looking at up to 20 natural guide stars simultaneously. Its final goal is to perform Fizeau interferometric imaging, thereby achieving ELT-like spatial resolution (22.8 m baseline resolution). For this reason, LN is also equipped with a fringe tracker, a beam combiner and a NIR science camera, for a total of more than 250 optical components and an overall size of approximately 6x4x4.5 meters. This paper describes the tradeoffs evaluated in order to achieve the alignment of the system to the telescope. We note that LN is comparable in size to planned ELT instrumentation. The impact of such alignment strategies will be compared and the selected procedure, where the LBT telescope is, in fact, aligned to the instrument, will be described. Furthermore, results coming from early night-time commissioning of the system will be presented.Comment: 8 pages, 6 pages, AO4ELT5 Proceedings, 201

Coactivation of leg reflexes in the stick insect

Cruse H, Dautenhahn K, Schreiner H. Coactivation of leg reflexes in the stick insect. Biological cybernetics. 1992;67(4):369-375.Each leg of a standing stick insect acts as a height controller. The leg contains several joints. Most of these joints are known to be controlled by feedback loops which are the basis of resistance reflexes (review Bässler 1983). This leads to the question of whether the resistance reflex of the whole leg can be understood as a simple, vectorial sum of the individual reflexes provided by the different joints, or whether additional properties emerge by simultaneous stimulation of several joints. Force measurements were performed while passively moving the middle leg tarsus of a fixed stick insect (Carausius morosus) stepwise to different positions. From the dynamic and static forces the torques developed by each joint were calculated. They were compared with the torques developed when only a single joint was moved by the same amount. The comparison shows that for a large range of positions there are no differences between both situations. Differences occur in two cases. First, the muscle system controlling the coxa-trochanter joint seems to be more strongly excited when the entire leg is moved than when only the one joint is moved. This change increases the linearity of the whole system for small deviations from the zero position. Second, the torque developed by the extensor tibiae system for negative steps (corresponding to increased body height), and the levator of coxa and trochanter for positive steps, decreases rather than increases when the whole leg is moved to extreme positions. This contributes to a decrease in the slope of the force-height characteristic and thus to a more non-linear behaviour of the whole system for the extreme positions. It is well known that the amplification factors of resistance reflexes in the leg show a large variation (Bässler 1972a; Kittmann 1991). Our results indicate that any change of the amplification factor influences the reflexes in all leg joints in the same way