Improved Modeling in a Matlab-Based Navigation System

An innovative approach to autonomous navigation is available for low earth orbit satellites. The system is developed in Matlab and utilizes an Extended Kalman Filter (EKF) to estimate the attitude and trajectory based on spacecraft magnetometer and gyro data. Preliminary tests of the system with real spacecraft data from the Rossi X-Ray Timing Explorer Satellite (RXTE) indicate the existence of unmodeled errors in the magnetometer data. Incorporating into the EKF a statistical model that describes the colored component of the effective measurement of the magnetic field vector could improve the accuracy of the trajectory and attitude estimates and also improve the convergence time. This model is identified as a first order Markov process. With the addition of the model, the EKF attempts to identify the non-white components of the noise allowing for more accurate estimation of the original state vector, i.e. the orbital elements and the attitude. Working in Matlab allows for easy incorporation of new models into the EKF and the resulting navigation system is generic and can easily be applied to future missions resulting in an alternative in onboard or ground-based navigation

Remodelling of the respiratory network in a mouse model of Rett syndrome depends on brain-derived neurotrophic factor regulated slow calcium buffering

Rett syndrome caused by MeCP2 mutations is a devastating neurodevelopmental disorder accompanied by severe breathing irregularities. Using transduction of organotypic slices from model MeCP2–/y mice with neuron-specific calcium sensor protein D3cpv, we examined the slow calcium buffering in neurons in pre-Bötzinger complex (preBötC), a component of the complex respiratory network. Examination of wild-type (WT) and MeCP2 null mice showed clear differences in the spatial organisations of neurons in preBötC and also in the disturbances in calcium homeostasis in mutant mice during early postnatal development. Deregulated calcium buffering in MeCP2–/y neurons was indicated by increased amplitude and kinetics of depolarisation-induced calcium transients. Both effects were related to an insufficient calcium uptake into the endoplasmic reticulum that was restored after pretreatment with brain-derived neurotrophic factor (BNDF). Conversely, the inhibition of BDNF signalling in WT neurons produced disturbances similar to those observed in MeCP2–/y mice. Brief hypoxia and calcium release from internal stores induced global calcium increases, after which the processes of many MeCP2–/y neurons were retracted, an effect that was also corrected by pretreatment with BDNF. The data obtained point to a tight connection between calcium homeostasis and long-term changes in neuronal connectivity. We therefore propose that calcium-dependent retraction of neurites in preBötC neurons can cause remodelling of the neuronal network during development and set up the conditions for appearance of breathing irregularities in Rett model mice