The layered transition metal oxide composition series of Li1+xV1-xO2 was synthesized using the solid state synthesis technique. X-ray diffraction was used to determine the dependence of structure on composition and clearly indicated a structural anomaly at x = 0 caused by the unusual magnetic ordering on the triangular lattice of the V3+ layer. To prevent magnetic frustration V3+ cations undergo orbital ordering and subsequent periodic displacent to form “trimers”. The periodicity of this phenomena results in a superlattice structure that can be observed as a faint peak in XRD spectra. The relationship between composition, superlattice peak intensity and lattice parameters was clearly documented for the first time. Li/Li1+xV1-xO2 cells were made and tested. Recent literature has shown that the transformation to 1T Li2VO2 upon lithiation is dependant on a nonzero x (ideally x = 0.07 for maximum capacity) to make a small number of tetrahedrally coordinated Li sites accessible. These sites then act as a trigger for shearing into the 1T phase. The cells described within this work intercalated significant amounts of lithium at a higher potential than the to 1T transition, possibly signifying occupation of a large number of the tetrahedral sites. LiVO2 is known to undergo delithiation even in ambient conditons and this can lead to cationic disorder. Cationic disorder is an inhibitor of anion sheet shearing and this suggests that sample handling could be a cause of the observed electrochemical behaviour. The effects of air and water exposure were investigated.

Neutron and x-ray diffraction has been used to study charge, orbital and magnetic ordering in some transition metal oxides. The long standing controversy regarding the nature of the ground state (Verwey structure) of the canonical charge ordered material magnetite (Fe3O4) has been resolved by x-ray single crystal diffraction studies on an almost single domain sample at 90 K. The Verwey structure is confirmed to have Cc symmetry with 56 unique sites in the asymmetric unit. Charge ordering is shown to be a useful first approximation to describe the nature of the ground state, and the conjecture that Verwey made in 1939 has finally been confirmed. However, three-site distortions which couple to the orbital ordering of the Fe2+ ordered states (trimerons) are shown to provide a more complete description of the low temperature structure. Trimerons explain the rather continuous distribution of the valence states observed in magnetite below Tv, anomalous shortening of Fe-Fe distances and the off-centre distortions resulting in ferroelectricity. DFT+U electronic structure calculations on the experimental coordinates support the conclusion of this crystallographic study, with the highest electron densities calculated for those Fe-Fe distances predicated to participate in the trimeron bonds. The 6H-perovskites of the type Ba3ARu2O9 have been reinvestigated by high resolution neutron and x-ray power diffraction. The charge ordered state of Ba3NaRu2O9 has been characterised at 110 K (P2/c, a =5.84001(2) Å, b = 10.22197(4) Å, c = 14.48497(6) Å, β = 90.2627(3) °) and shown to consist of a structure with near integer charge ordering of Ru5+ 2O9 / Ru6+ 2O9 dimers. The ground state has been shown to be very sensitive to external perturbations, with a novel melting of charge ordering observed under x-ray irradiation below 40 K (C2/c, a =5.84470(2) Å, b = 10.17706(3) Å, c = 14.45866(5) Å, β = 90.2151(3)-° at 10 K). High pressure studies reveal that the Ru-Ru intra-dimer distance may dictate the response of the system to pressure. Empirical trends in the Ba3ARu2O9 series of compounds have shown that change in ‘chemical pressure’ in these systems may be rationalised in terms of Coulomb’s law. In A = La and Y the magnetic ordering is shown to be FM within the Ru2O9 dimers (1.4(2) μB and 0.5(1) μB, respectively per Ru), representing the first case of intra dimer FM coupling reported in a system containing face-sharing RuO6 octahedra . The overall AFM coupling of the dimers implies an as yet unobserved breaking of the parent symmetry. In A = Nd, a complex competition between the crystal field effect of Nd3+ and the magnetic ordering of the Ru2O9 FM moments has been observed, leading first vi to FM order of Nd at 25 K (1.56(7) μB) followed by ordering of Ru moments (0.5(1) μB) and a spin reorientation transition of Nd moments at 18 K. In A = Ca, the formation of a singlet ground state is observed in Ru2O9 rather than the expected AFM coupling and below 100 K Ba3CaRu2O9 is diamagnetic. All five systems indicate that the Ru2O9 dimer is the physically significant unit in these systems when considering structural trends and the ordering of charge, spin and orbital degrees of freedom.

No description available.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1991. / Includes bibliographical references (leaves 152-154) / Microfiche. / xvi,154 leaves, bound ill. 29 cm

Recent advances in spaceborne GPS technology have shown significant advantages in many aspects over conventional technologies. For instance, spaceborne GPS can realize autonomous orbit determination with significant savings in spacecraft life cycle, in power, and in mass. At present, the onboard orbit determination in real time or near-real time can typically achieve 3D orbital accuracy of metres to tens metres with Kalman filtering process, but 21st century space engineering requires onboard orbit accuracy of better than 5 metres, and even sub-metre for some space applications. The research focuses on the development of GPS-based autonomous orbit determination techniques for spacecraft. Contributions are made to the field of GPS-based orbit determination in the following five areas: Techniques to simplify the orbital dynamical models for onboard processing have been developed in order to reduce the computional burden while retaining full model accuracy. The Earth gravity acceleration approximation method was established to replace the traditional recursive acceleration computations. Results have demonstrated that with the computation burden for a 55× spherical harmonic gravity model, we achieve the accuracy of a 7070× model. Efforts were made for the simplification of solar & lunar ephemerides, atmosphere density model and orbit integration. All these techniques together enable a more accurate orbit integrator to operate onboard. Efficient algorithms for onboard GPS measurement outlier detection and measurement improvement have been developed. In addition, a closed-form single point position method was implemented to provide an initial orbit solution without any a priori information. The third important contribution was made to the development of sliding-window short-arc orbit filtering techniques for onboard processing. With respect to the existing Kalman recursive filtering, the short-arc method is more stable because more measurements are used. On the other hand, the short-arc method requires less accurate orbit dynamical model information compared to the long-arc method, thus it is suitable for onboard processing. Our results have demonstrated that by using the 1 ~ 2 revolutions of LEO code GPS data we can achieve an orbit accuracy of 1 ~ 2 metres. Sliding-window techniques provide sub-metre level orbit determination solutions with 5~20 minutes delay. A software platform for the GPS orbit determination studies has been established. Methods of orbit determination in near-real time have been developed and tested. The software system includes orbit dynamical modelling, GPS data processing, orbit filtering and result analysis modules, providing an effective technical basis for further studies. Furthermore a ground-based near-real time orbit determination system has been established for FedSat, Australia's first satellite in 30 years. The system generates 10-metre level orbit solution with half-day latency on an operational basis. This system has supported the scientific missions of FedSat such as Ka-band tracking and GPS atmosphere studies within the Cooperative Research Centre for Satellite System (CRCSS) community. Though it is different from the onboard orbit determination, it provides important test-bed for the techniques described in previous section. This thesis focuses on the onboard orbit determination techniques that were discussed in Chapter 2 through Chapter 6. The proposed onboard orbit determination algorithms were successfully validated using real onboard GPS data collected from Topex/Poseidon, CHAMP and SAC-C satellites.

Techn. Universiẗat, Diss., 2007--Darmstadt.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Generating and stabilizing periodic motions in nonlinear systems is a challenging task. In the control system community this topic is also known as limit cycle control. In recent years a framework known as Virtual Holonomic Constraints (VHC) has been developed as one of the solutions to this problem. The aim of this thesis is to give an insight into this approach and its practical application. The contribution of this work is primarily the experimental validation of the theory. A step by step procedure of this methodology is given for motion planning, as well as for controller design. Three particular setups were chosen for experiments: the inertia wheel pendulum, the Furuta pendulum and the two-link planar pendulum. These under-actuated mechanical systems are well known benchmarking setups for testing advanced control design methods. Further application is intended for cases such as biped robot walking/running, human and animal locomotion analysis, etc.

Made available in DSpace on 2014-06-11T19:22:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2002Bitstream added on 2014-06-13T18:06:46Z : No. of bitstreams: 1 santos_ea_me_prud.pdf: 5551398 bytes, checksum: 44d7038addc722ceeedb8176aa4648fe (MD5) / Este trabalho apresenta um modelo matemático alternativo aos filtros passa-baixas convencionais no Processamento Digital de Imagens. O modelo de Equação Diferencial Parcial (EDP) foi aplicado em imagens orbitais para extração das feições de interesse e os resultados obtidos foram comparados com os resultados do operador de Sobel e o Gradiente Morfológico. O modelo matemático utilizado no trabalho foi baseado na teoria de EDPs e surge como uma proposta metodológica alternativa para a área de Cartografia. O modelo de EDP consiste em aplicar seletivamente a equação, suavizando adequadamente uma imagem sem perder as bordas e outros detalhes contidos na imagem, principalmente pistas de aeroportos e estradas pavimentadas. / This work presents an alternative mathematical model for conventional low-pass filters in Digital Image Processing. The model of Partial Differential Equation (PDE) was applied to orbital image to extract features of interest and the obtained results were compared to over obtained for Sobel operator and Morphological Gradient. The mathematical model used in this work was based on PDE theory and was intented to be on alternative methodology for Cartography area. This model consists in selectivels applying the model of PDE, in order adequatels smooth an image without losing edges and other details on the image, mainls airports tracks and paved roads.

Dissertação (mestrado) - Pontifícia Universidade Católica do Paraná, Curitiba, 2004 / Inclui bibliografia / O objetivo deste estudo foi avaliar e comparar, em dois momentos, a atividade eletromiográfica (EMG) da poção inferior do músculo orbicular da boca (OI) e do músculo mentual (MT), em indivíduos respiradores predominantemente nasais (RPN) ou bucais (RPB).