This work shows how to use a differential geometry tool to design a novel nonlinear active fault tolerant flight control system for aircraft. The proposed control scheme consists of two main ...subsystems: a controller, which is designed for the nominal plant, and a fault detection and diagnosis module, which provides fault estimation. A further feedback loop exploits the fault estimation to accommodate faults affecting the system. The estimate convergence and the stability of the active fault tolerant flight controller are theoretically proved. Finally, high fidelity simulations show the effectiveness of the scheme.
•Extension of nonlinear geometric approach to active fault tolerant control system.•Proofs of convergence of fault estimation for active fault tolerant control system.•New results in estimation of actuators fault decoupled from wind gusts.•New nominal controller design procedure with assured stability properties.•Proof of stability of active fault tolerant control system.
Summary
This paper presents a novel scheme for diagnosis of faults affecting sensors that measure the satellite attitude, body angular velocity, flywheel spin rates, and defects in control torques ...from reaction wheel motors. The proposed methodology uses adaptive observers to provide fault estimates that aid detection, isolation, and estimation of possible actuator and sensor faults. The adaptive observers do not need a priori information about fault internal models. A nonlinear geometric approach is used to avoid that aerodynamic disturbance torques have unwanted influence on the fault estimates. An augmented high‐fidelity spacecraft model is exploited during design and validation to replicate faults. This simulation model includes disturbance torques as experienced in low Earth orbits. This paper includes an analysis to assess robustness properties of the method with respect to parameter uncertainties and disturbances. The results document the efficacy of the suggested methodology.
14‐3‐3 proteins are positive regulators of the tumor suppressor p53, the mutation of which is implicated in many human cancers. Current strategies for targeting of p53 involve restoration of ...wild‐type function or inhibition of the interaction with MDM2, its key negative regulator. Despite the efficacy of these strategies, the alternate approach of stabilizing the interaction of p53 with positive regulators and, thus, enhancing tumor suppressor activity, has not been explored. Here, we report the first example of small‐molecule stabilization of the 14‐3‐3 – p53 protein‐protein interaction (PPI) and demonstrate the potential of this approach as a therapeutic modality. We also observed a disconnect between biophysical and crystallographic data in the presence of a stabilizing molecule, which is unusual in 14‐3‐3 PPIs.
The aim of this paper was to systematically review published data about the comparison of radiolabelled metaiodobenzylguanidine (MIBG) scintigraphy and positron emission tomography (PET) with ...different radiopharmaceuticals in patients with pheochromocytoma and paraganglioma (Pheo/PGL).
A comprehensive literature search of studies published in PubMed/MEDLINE and Embase databases through September 2012 and regarding MIBG scintigraphy and PET imaging with different radiopharmaceuticals in patients with Pheo/PGL was carried out.
Twenty-eight studies comprising 852 patients who underwent both MIBG scintigraphy and PET or PET/CT with different radiopharmaceuticals were included and discussed. Three studies evaluated carbon-11-hydroxyephedrine (11CHED) as PET radiopharmaceutical, nine studies fluorine-18-dopamine (18FDA), eight studies fluorine-18-dihydroxyphenylalanine (18FDOPA), twelve studies fluorine-18-fluorodeoxyglucose (18FFDG) and five studies gallium-68-somatostatin analogues.
Despite the heterogeneity of the studies included in the analysis, it can be concluded that the diagnostic performance of PET with various agents is clearly superior to that of MIBG scintigraphy in patients with Pheo/PGL, mainly for familial, extra-adrenal and metastatic diseases; however, MIBG maintains a unique role in selecting patients suitable for 131I-MBG therapy. Further larger prospective studies comparing MIBG and different PET tracers in patients with Pheo/PGL as well as a cost-effectiveness analysis of the two techniques are needed.
The identification of gene-by-environment interactions is important for understanding the genetic basis of chronic obstructive pulmonary disease (COPD). Many COPD genetic association analyses assume ...a linear relationship between pack-years of smoking exposure and forced expiratory volume in 1 s (FEV(1)); however, this assumption has not been evaluated empirically in cohorts with a wide spectrum of COPD severity.
The relationship between FEV(1) and pack-years of smoking exposure was examined in four large cohorts assembled for the purpose of identifying genetic associations with COPD. Using data from the Alpha-1 Antitrypsin Genetic Modifiers Study, the accuracy and power of two different approaches to model smoking were compared by performing a simulation study of a genetic variant with a range of gene-by-smoking interaction effects.
Non-linear relationships between smoking and FEV(1) were identified in the four cohorts. It was found that, in most situations where the relationship between pack-years and FEV(1) is non-linear, a piecewise linear approach to model smoking and gene-by-smoking interactions is preferable to the commonly used total pack-years approach. The piecewise linear approach was applied to a genetic association analysis of the PI*Z allele in the Norway Case-Control cohort and a potential PI*Z-by-smoking interaction was identified (p=0.03 for FEV(1) analysis, p=0.01 for COPD susceptibility analysis).
In study samples of subjects with a wide range of COPD severity, a non-linear relationship between pack-years of smoking and FEV(1) is likely. In this setting, approaches that account for this non-linearity can be more powerful and less biased than the more common approach of using total pack-years to model the smoking effect.
The main contribution of this paper is the description and application of a comprehensive set of methodologies for fault detection and isolation (FDI) of aircraft sensors. In particular, a new ...nonlinear geometric approach (NLGA) and an efficient linear polynomial method (PM) are presented and compared, together with simulation results obtained from a commercial aircraft model. Adaptive filters with disturbance decoupling for fault identification are designed via the developed NLGA-based method. On the other hand, the FDI scheme based on linear PM exploits a disturbance decoupling technique in connection with a linear dynamic filter design procedure. The FDI strategies are applied to the aircraft simulator data in a flight condition characterised by tight–coupled longitudinal and lateral dynamics. Moreover, in order to analyse robustness and reliability properties of the two FDI schemes, extensive simulations are performed in the presence of turbulence, measurement noise and modelling errors.
Summary
Iron oxy‐hydroxides in soil are known to have a large affinity for arsenate (As(V)) inorganic species. At the soil–root interface such mineral components are embedded by mucilaginous material ...that is secreted from continuously growing root cap cells. In order to determine the role of plant mucilages in As(V) sorption by iron oxy‐hydroxides, we layered a calcium (Ca)‐polygalacturonate network (CaPGA) on to amorphous iron (Fe) (III) hydroxide (ferrihydrite, Fh) particles. The scanning electron micrographs of the CaPGA network coating the ferrihydrite (Fh–CaPGA) show a regular structure with a honeycomb‐like pattern where interlacing fibrils form a porous system. The FT‐IR spectra of Fh–CaPGA suggest that CaPGA fibrils are retained by the surface Fe(III) nuclei of Fh through electrostatic interactions. The sorption experiments carried out at pH 4.3 and 5.8 indicated a smaller amount of As(V) sorbed by Fh–CaPGA than by Fh alone, being less after 3 and 24 hours of reaction by about 70 and 30%, respectively. The sorption of As(V) by Fh was also studied in the presence of caffeic acid (CAF), an important root exudate. Simultaneous sorption kinetics show that As(V) sorption by Fh is almost independent of CAF concentration, indicating a greater affinity of arsenate ions towards the Fh surfaces. However, the amount of As(V) sorbed by the Fh coated by CaPGA, in the presence of 0.25, 0.5 and 1.0 mm CAF, is markedly smaller by about 20, 27 and 40%, respectively, than that found in the As(V)–CAF‐Fh ternary systems. This is caused mainly by redox reactions involving CAF and the surface Fe(III) nuclei of Fh leading to the formation of CAF oxidation products which prevent As(V) sorption.
The paper presents a new method for the estimation of the electric parameters of induction motors (IMs). During the identification process the rotor flux is also estimated. The procedure relies on ...standstill tests performed with a standard drive architecture, hence, it is suitable for self-commissioning drives. The identification scheme is based on the model reference adaptive system (MRAS) approach. A novel parallel adaptive observer (PAO) has been designed, starting from the series-parallel Kreisselmeier observer. The most interesting features of the proposed method are the following: 1) rapidity and accuracy of the identification process; 2) low-computational burden; 3)excellent noise rejection, thanks to the adopted parallel structure; 4) avoidance of incorrect parameter estimation due to magnetic saturation phenomena, thanks to recursive rotor flux monitoring. The performances of the new scheme are shown by means of simulation and experimental tests. The estimation results are validated by comparison with a powerful batch nonlinear least square (NLS) method and by evaluating the steady-state mechanical curve of the IM used in the tests.
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