Suboptimal Stabilization of Unknown Nonlinear Systems via Extended State Observers

This paper introduces a locally optimal stabilizer for multi-input muti-output autonomous nonlinear systems of any order with totally unknown dynamics. The control scheme proposed in this paper lies at the intersection of the active disturbance rejection control (ADRC) and the state-dependent Riccati equation (SDRE) technique. It is shown that using an extended state observer (ESO), a state-dependent coefficient matrix for the nonlinear system is obtainable which is used by the SDRE technique to construct a SDRE+ESO controller. As the SDRE technique is not guaranteed to be globally asymptotically stable, for systems with known linearization at the equilibrium, an algorithmic method is proposed for an approximated estimation of its region of attraction (ROA). Then, it is shown that the global asymptotic stability is achievable using a switching controller constructed by the SDRE+ESO method and ADRC for inside and outside the estimated ROA, respectively.Comment: 6 pages, 1 figur

Synthesis and Study of Verdazyl Stable Free Radical Substituted Oligothiophenes for Magnetoresistive and Spintronic Properties

Interest in spin polarizing materials and their application in electronic devices in the field of spintronics has been steadily growing in recent years. The development of wholly organic spin polarizing materials has been of particular interest due to the material flexibility, solution processing, synthetic modifiability, and longer spin lifetimes of organics compared to inorganic analogs. One class of organic compounds with significant room for exploration is polyconjugated π systems coupled with stable radicals. We have explored the synthesis of oligothiophenes substituted with verdazyl stable free radicals with differing thiophene chain lengths, through a series of halogenation, borylation, and palladium catalyzed Suzuki-Miyarua coupling reactions. The characterization methods employed include IR, NMR, UV-Vis, ESR, GC/LC-MS, and X-ray crystallography. We have successfully synthesized two novel bisverdazyls with conjugated oligomer spacers and analyzed the magnetism, electrochemical redox potentials, crystal structure, and molecular packing of the aforementioned diradicals. We hope to build on this work by analyzing the bisverdazyls for their magnetoresistance, conductivity, and spin polarization properties. Furthermore, we also plan to synthesize more efficient bisverdazyl conjugated spacers utilizing EDOT units, which promise improved conductivity and spin propagation

Orbit Estimation Using a Horizon Detector in the Presence of Uncertain Celestial Body Rotation and Geometry

This paper presents an orbit estimation using non-simultaneous horizon detector measurements in the presence of uncertainties in the celestial body rotational velocity and its geometrical characteristics. The celestial body is modelled as a tri-axial ellipsoid with a three-dimensional force field. The non-simultaneous modelling provides the possibility to consider the time gap between horizon measurements. An unscented Kalman filter is used to estimate the spacecraft motion states and estimate the geometric characteristics as well as the rotational velocity of the celestial body. A Monte-Carlo simulation is implemented to verify the results. Simulations showed that using non-simultaneous horizon vector measurements, the spacecraft state errors converge to zero even in the presence of an uncertain geometry and rotational velocity of the celestial body.Comment: 17 pages, 7 figures, accepted for publication in Acta Astronautic