DEGRADED MODE VEHICLE LATERAL CONTROL UNDER FAULT IN REAR SENSORS

ABSTRACT This paper is concerned with vehicle lateral control for Automated Highway Systems (AHS) studied as a part of the California PATH 1 Program. In the PATH lateral control system, magnetometers are installed under both the front and the rear bumpers of the vehicle; these magnetometers measure the lateral deviation of the vehicle relative to the magnets buried along the centerline of each automated lane. Lateral controllers have been designed and tested successfully provided that there is no fault in magnetometers. It has been argued that these controllers are NOT tolerant to the fault in magnetometers. The focus of this paper is the degraded mode lateral control under fault in rear magnetometers. The aim of the controller design is to accomplish adequate performance with the remaining set of magnetometers: the front magnetometers. The effects of the fault are examined, and the significance of the linear time varying (LTV) property of the front magnetometer based vehicle lateral dynamics is recognized. Popular control methods for LTV systems generally involve gain scheduling by switching between several LTI controllers. Such controllers are complicated and it is difficult to prove the stability of the switching mechanism. To derive a simple, effective LTV controller, feedback linearization is applied to approximately cancel out the time varying terms in the plant and to function as a gain scheduler. However, due to the weakly damped zeros of the plant, feedback linearization with state feedbac

Spectral analysis of winter wheat leaves for detection and differentiation of diseases and insects

Yellow rust (Puccinia striiformis f. sp. Tritici), powdery mildew (Blumeria graminis) and wheat aphid (Sitobion avenae F.) infestation are three serious conditions that have a severe impact on yield and grain quality of winter wheat worldwide. Discrimination among these three stressors is of practical importance, given that specific procedures (i.e. adoption of fungicide and insecticide) are needed to treat different diseases and insects. This study examines the potential of hyperspectral sensor systems in discriminating these three stressors at leaf level. Reflectance spectra of leaves infected with yellow rust, powdery mildew and aphids were measured at the early grain filling stage. Normalization was performed prior to spectral analysis on all three groups of samples for removing differences in the spectral baseline among different cultivars. To obtain appropriate bands and spectral features (SFs) for stressor discrimination and damage intensity estimation, a correlation analysis and an independent t-test were used jointly. Based on the most efficient bands/SFs, models for discriminating stressors and estimating stressor intensity were established by Fisher’s linear discriminant analysis (FLDA) and partial least square regression (PLSR), respectively. The results showed that the performance of the discrimination model was satisfactory in general, with an overall accuracy of 0.75. However, the discrimination model produced varied classification accuracies among different types of diseases and insects. The regression model produced reasonable estimates of stress intensity, with an R2 of 0.73 and a RMSE of 0.148. This study illustrates the potential use of hyperspectral information in discriminating yellow rust, powdery mildew and wheat aphid infestation in winter wheat. In practice, it is important to extend the discriminative analysis from leaf level to canopy level

Lateral Control of an Articulated Bus for Lane Guidance and Curbside Precision Docking

Abstract-This paper presents the design, implementation, and field testing of a lane assist system that provides lane guidance and curbside precision docking functions for a 60 ft articulated bus. The challenges in this lateral control design include the extra lightly-damped mode from the articulated section, the relatively large disturbance due to the sharp Scurves for precision docking, and the uncertainties introduced by public roads and live traffic. To tackle these challenges, the control problem is formulated as a mixed / synthesis problem and solved by LMI optimization. Extensive field tests were conducted in live traffic and the results show adequate and consistent performances

Abundant phosphorus expected for possible life in Enceladus’s ocean

Saturn’s moon Enceladus has a potentially habitable subsurface water ocean that contains canonical building blocks of life (organic and inorganic carbon, ammonia, possibly hydrogen sulfide) and chemical energy (disequilibria for methanogenesis). However, its habitability could be strongly affected by the unknown availability of phosphorus (P). Here, we perform thermodynamic and kinetic modeling that simulates P geochemistry based on recent insights into the geochemistry of the ocean–seafloor system on Enceladus. We find that aqueous P should predominantly exist as orthophosphate (e.g., HPO42−), and total dissolved inorganic P could reach 10−7 to 10−2 mol/kg H2O, generally increasing with lower pH and higher dissolved CO2, but also depending upon dissolved ammonia and silica. Levels are much higher than <10−10 mol/kg H2O from previous estimates and close to or higher than ∼10−6 mol/kg H2O in modern Earth seawater. The high P concentration is primarily ascribed to a high (bi)carbonate concentration, which decreases the concentrations of multivalent cations via carbonate mineral formation, allowing phosphate to accumulate. Kinetic modeling of phosphate mineral dissolution suggests that geologically rapid release of P from seafloor weathering of a chondritic rocky core could supply millimoles of total dissolved P per kilogram of H2O within 105 y, much less than the likely age of Enceladus’s ocean (108 to 109 y). These results provide further evidence of habitable ocean conditions and show that any oceanic life would not be inhibited by low P availability