Search

This paper presents a generalized, multibody dynamics model for a tracked vehicle equipped with a towing winch and control strategies that enhance vehicle mobility by regulating track slip based on real-time terrain characterization and automating winch use. The vehicle model is validated under conditions where no action is taken by the winch. Thereafter, two mobility enhancing control strategies are outlined. The first strategy regulates track slip to a real-time estimated value that generates maximum net traction. This is done by computing state-force estimates from a Kalman filter that are compared to terrain traction models using a Bayesian hypothesis selection approach. If the vehicle is traction limited and the first strategy fails, a second strategy that automates winch use is activated. Simulation results are shown for both scenarios. [ABSTRACT FROM AUTHOR]

This paper provides a methodology for the estimation of resistance, thrust, and resistive torques on each wheel of a rigid-wheeled vehicle generated at the vehicle-terrain interface, and from these forces and moments, a methodology to estimate terrain parameters is presented. Terrain force estimation, which is independent of a terrain model, can infer the ability to accelerate, climb, or tow a load independent of the underlying terrain properties. When a terrain model is available, parameters of that model, such as soil cohesion, friction angle, maximum normal stress, and stress distribution parameters, are determined from estimated vehicle-terrain forces using a multiple-model estimation approach, providing parameters that relate to accepted mobility metrics. The methodology requires a standard proprioceptive sensor suite-accelerometers, rate gyros, wheel speeds, motor torques, and ground speed. Sinkage sensors are not required. Simulation results demonstrate efficacy of the method on three terrains spanning a range of soil cohesions reported in the literature. [ABSTRACT FROM AUTHOR]

Eddy current sensors provide an inexpensive means of detecting surface and embedded flaws in metallic structures due to fatigue, corrosion, and manufacturing defects. However, use of eddy current sensors for imaging flaws to determine their geometry is limited by sensitivity and mathematical uniqueness issues, as the magnetic flux distribution sensed at the boundary of a structure can be similar for dissimilar flaw geometries or flaw depths. This paper investigates the use of feedback control based on measured magnetic flux at a point on the boundary of the structure in order to address sensitivity and uniqueness issues for eddy current sensors and thus to enhance the ability to use these simple inexpensive sensors to determine flaw geometry. Using a parametrized two-dimensional flaw in which width and depth of the flaw are to be determined, scalar metrics are developed to relate the forward solution of the electromagnetic dynamics to the inverse problem of damage geometry reconstruction. Geometry is determined by interpolating metrics on a mesh and employing a systematic ranking process that is robust to weakly unique inverse problems. Finally, the concept of sensitivity enhancing feedback control (SEC) is applied to enrich the data set in order to improve damage geometry reconstruction. SEC feeds back measured magnetic flux at a single point along a scan line to affect the current density. Closed-loop compensation of eddy current dynamics is shown to improve uniqueness of scalar damage metrics to damage geometry parameters. Performance is demonstrated by simulation of geometry construction using finite-element models of two-dimensional flaws embedded in a material, both with and without feedback control and for noisy and noiseless simulated magnetic flux density measurement. For noiseless data, flaw depth and width are reconstructed within the resolution of the mesh (0.01 mm) using feedback control, while the relative accuracy of damage geometry identification for open-loop data is on the order of 0.1 mm in each dimension. Simulation of damage geometry identification with noisy data demonstrates lower relative error using closed-loop data, as measured by the mean and standard deviation in identified depth and width. [ABSTRACT FROM AUTHOR]

Creativity represents the pinnacle of higher-level cognition, but exactly how it is achieved remains poorly understood, especially when simultaneously facing the opposing challenge of intractable complexity. The aims of the current study were (a) to examine how the brain may achieve the dual goals of creativity and complexity reduction, and (b) to begin developing higher-level cognition and creativity in robots. We address these aims by (a) modeling an example of insight problem solving and comparing it to empirical data, and (b) testing the model on a robot platform. Unlike other models, we propose a single mechanism for both creative problem solving and complexity reduction. Focusing on creativity, the computational mechanism leads to insightful problem solving by restructuring an internal belief representation based on evidence collected during an incubation period. Because insightful problem solving has been examined closely in nonhuman primates, providing detailed quantitative datasets lacking in humans, we tested the model by comparing simulations to insightful problem solving by rhesus monkeys. Results show that the proposed model accounts for both the discontinuous three stage problem-solving patterns and the spontaneous generalization to novel cases observed with the monkeys. To test the model in a physical environment, we implemented it in a vision-equipped robot, and the model solved the same insight problem from camera percepts. Our model shows how the creative brain may address the dual challenges of complex environments–finding unprecedented opportunity hidden within potentially intractable complexity–and suggests that both challenges may be met by a single underlying computational mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Pichia pastoris is a methylotrophic yeast that has been genetically engineered to express over one thousand heterologous proteins valued for industrial, pharmaceutical and basic research purposes. In most cases, the 5′ untranslated region (UTR) of the alcohol oxidase 1 (AOX1) gene is fused to the coding sequence of the recombinant gene for protein expression in this yeast. Because the effect of the AOX1 5′UTR on protein expression is not known, site-directed mutagenesis was performed in order to decrease or increase the length of this region. Both of these types of changes were shown to affect translational efficiency, not transcript stability. While increasing the length of the 5′UTR clearly decreased expression of a β-galactosidase reporter in a proportional manner, a deletion analysis demonstrated that the AOX1 5′UTR contains a complex mixture of both positive and negative cis-acting elements, suggesting that the construction of a synthetic 5′UTR optimized for a higher level of expression may be challenging. [Copyright &y& Elsevier]