Seasonally Frozen Soil Effects on the Seismic Performance of Highway Bridges

INE/AUTC 12.0

Recognising the Clothing Categories from Free-Configuration Using Gaussian-Process-Based Interactive Perception

In this paper, we propose a Gaussian Process- based interactive perception approach for recognising highly- wrinkled clothes. We have integrated this recognition method within a clothes sorting pipeline for the pre-washing stage of an autonomous laundering process. Our approach differs from reported clothing manipulation approaches by allowing the robot to update its perception confidence via numerous interactions with the garments. The classifiers predominantly reported in clothing perception (e.g. SVM, Random Forest) studies do not provide true classification probabilities, due to their inherent structure. In contrast, probabilistic classifiers (of which the Gaussian Process is a popular example) are able to provide predictive probabilities. In our approach, we employ a multi-class Gaussian Process classification using the Laplace approximation for posterior inference and optimising hyper-parameters via marginal likelihood maximisation. Our experimental results show that our approach is able to recognise unknown garments from highly-occluded and wrinkled con- figurations and demonstrates a substantial improvement over non-interactive perception approaches

Experimental evidence of ageing and slow restoration of the weak-contact configuration in tilted 3D granular packings

Granular packings slowly driven towards their instability threshold are studied using a digital imaging technique as well as a nonlinear acoustic method. The former method allows us to study grain rearrangements on the surface during the tilting and the latter enables to selectively probe the modifications of the weak-contact fraction in the material bulk. Gradual ageing of both the surface activity and the weak-contact reconfigurations is observed as a result of repeated tilt cycles up to a given angle smaller than the angle of avalanche. For an aged configuration reached after several consecutive tilt cycles, abrupt resumption of the on-surface activity and of the weak-contact rearrangements occurs when the packing is subsequently inclined beyond the previous maximal tilting angle. This behavior is compared with literature results from numerical simulations of inclined 2D packings. It is also found that the aged weak-contact configurations exhibit spontaneous restoration towards the initial state if the packing remains at rest for tens of minutes. When the packing is titled forth and back between zero and near-critical angles, instead of ageing, the weak-contact configuration exhibits "internal weak-contact avalanches" in the vicinity of both the near-critical and zero angles. By contrast, the stronger-contact skeleton remains stable

Dead Time Compensation for High-Flux Ranging

Dead time effects have been considered a major limitation for fast data acquisition in various time-correlated single photon counting applications, since a commonly adopted approach for dead time mitigation is to operate in the low-flux regime where dead time effects can be ignored. Through the application of lidar ranging, this work explores the empirical distribution of detection times in the presence of dead time and demonstrates that an accurate statistical model can result in reduced ranging error with shorter data acquisition time when operating in the high-flux regime. Specifically, we show that the empirical distribution of detection times converges to the stationary distribution of a Markov chain. Depth estimation can then be performed by passing the empirical distribution through a filter matched to the stationary distribution. Moreover, based on the Markov chain model, we formulate the recovery of arrival distribution from detection distribution as a nonlinear inverse problem and solve it via provably convergent mathematical optimization. By comparing per-detection Fisher information for depth estimation from high- and low-flux detection time distributions, we provide an analytical basis for possible improvement of ranging performance resulting from the presence of dead time. Finally, we demonstrate the effectiveness of our formulation and algorithm via simulations of lidar ranging.Comment: Revision with added estimation results, references, and figures, and modified appendice

Experimental Studies of Squat Gravity Caissons and Monopiles for Offshore Applications

This dissertation presents initial results from geotechnical centrifuge experiments on squat gravity caissons and monopiles under cyclic eccentric loading in soft clay under undrained conditions. These experiments were conducted in the 1-g laboratory at Texas A&M University and the 150g-ton centrifuge at Rensselaer Polytechnic Institute. All tested caissons had a length to diameter aspect ratios of two with four tested in the 1-g laboratory and four caissons tested in the centrifuge. Though this aspect ratio is a bit atypical, it could be a reasonable option for offshore renewable hydrokinetic systems or a component in tripod or tetrapod wind tower foundation systems. 1-g experimental results focus of the effect of caisson interior venting on capacity. Centrifuge experimental results focus on behavior arising from an unrestricted vertical coordinate, allowing self-weight to contribute to combined loading, the impact of depth of rotation on caisson resistance, and the global stiffness and damping ratio of the caissons. With the advent of high accuracy sensors and increased interest in geotechnical centrifuge testing simulating loading within serviceability limits a stronger understanding the strength and orientation of centrifuge gravity relative to the scale model is necessary. This dissertation presents a methodology for determining the 2-Dimensional centrifuge gravity within a model independent of centrifuge type or geometry. This can be used to recompose the gravity field from the direct measurement of single gravity vector, given angular velocity. Finally, the methodology is compared to the mechanics of drum and beam centrifuges to provide physical meaning to coordinate rotation variables. Microelectromechanical systems (MEMS) accelerometers are becoming more prevalent in geotechnical engineering and geotechnical centrifuge modeling. In geotechnical centrifuge experiments these sensors have shown much promise, but still exhibit some limitations. This dissertation proposes a new methodology for the use of single-axis low g, high accuracy, MEMS accelerometers to measure orientation of on object in a geotechnical centrifuge. The inclusion of the measured component of cross-axis in orientation calculations significantly improves measurements of absolute orientation, a 3.8º improvement in this study, and reduces errors in orientation measurement by allowing high accuracy low-g accelerometers to be used in the centrifuge

Collisional Formation and Modeling of Asteroid Families

In the last decade, thanks to the development of sophisticated numerical codes, major breakthroughs have been achieved in our understanding of the formation of asteroid families by catastrophic disruption of large parent bodies. In this review, we describe numerical simulations of asteroid collisions that reproduced the main properties of families, accounting for both the fragmentation of an asteroid at the time of impact and the subsequent gravitational interactions of the generated fragments. The simulations demonstrate that the catastrophic disruption of bodies larger than a few hundred meters in diameter leads to the formation of large aggregates due to gravitational reaccumulation of smaller fragments, which helps explain the presence of large members within asteroid families. Thus, for the first time, numerical simulations successfully reproduced the sizes and ejection velocities of members of representative families. Moreover, the simulations provide constraints on the family dynamical histories and on the possible internal structure of family members and their parent bodies.Comment: Chapter to appear in the (University of Arizona Press) Space Science Series Book: Asteroids I

Research on Hydraulics and River Dynamics

This Special Issue includes nine original contributions focused on river hydraulics. Four of these resulted from cooperation between universities from different countries: (a) Russia and Poland , (b) Taiwan and the USA , (c) Iran and Italy, and (d) India and Italy . The other contributions resulted from research carried out in universities from South Korea [5], Greece [6], China , and Japan