Refining Weakly-Supervised Free Space Estimation Through Data Augmentation and Recursive Training

Free space estimation is an important problem for autonomous robot navigation. Traditional camera-based approaches rely on pixel-wise ground truth annotations to train a segmentation model. To cover the wide variety of environments and lighting conditions encountered on roads, training supervised models requires large datasets. This makes the annotation cost prohibitively high. In this work, we propose a novel approach for obtaining free space estimates from images taken with a single road-facing camera. We rely on a technique that generates weak free space labels without any supervision, which are then used as ground truth to train a segmentation model for free space estimation. We study the impact of different data augmentation techniques on the performances of free space predictions, and propose to use a recursive training strategy. Our results are benchmarked using the Cityscapes dataset and improve over comparable published work across all evaluation metrics. Our best model reaches 83.64% IoU (+2.3%), 91.75 Precision (+2.4%) and 91.29% Recall (+0.4%). These results correspond to 88.8% of the IoU, 94.3% of the Precision and 93.1% of the Recall obtained by an equivalent fully-supervised baseline, while using no ground truth annotation. Our code and models are freely available online

Visual Perception For Robotic Spatial Understanding

Humans understand the world through vision without much effort. We perceive the structure, objects, and people in the environment and pay little direct attention to most of it, until it becomes useful. Intelligent systems, especially mobile robots, have no such biologically engineered vision mechanism to take for granted. In contrast, we must devise algorithmic methods of taking raw sensor data and converting it to something useful very quickly. Vision is such a necessary part of building a robot or any intelligent system that is meant to interact with the world that it is somewhat surprising we don\u27t have off-the-shelf libraries for this capability. Why is this? The simple answer is that the problem is extremely difficult. There has been progress, but the current state of the art is impressive and depressing at the same time. We now have neural networks that can recognize many objects in 2D images, in some cases performing better than a human. Some algorithms can also provide bounding boxes or pixel-level masks to localize the object. We have visual odometry and mapping algorithms that can build reasonably detailed maps over long distances with the right hardware and conditions. On the other hand, we have robots with many sensors and no efficient way to compute their relative extrinsic poses for integrating the data in a single frame. The same networks that produce good object segmentations and labels in a controlled benchmark still miss obvious objects in the real world and have no mechanism for learning on the fly while the robot is exploring. Finally, while we can detect pose for very specific objects, we don\u27t yet have a mechanism that detects pose that generalizes well over categories or that can describe new objects efficiently. We contribute algorithms in four of the areas mentioned above. First, we describe a practical and effective system for calibrating many sensors on a robot with up to 3 different modalities. Second, we present our approach to visual odometry and mapping that exploits the unique capabilities of RGB-D sensors to efficiently build detailed representations of an environment. Third, we describe a 3-D over-segmentation technique that utilizes the models and ego-motion output in the previous step to generate temporally consistent segmentations with camera motion. Finally, we develop a synthesized dataset of chair objects with part labels and investigate the influence of parts on RGB-D based object pose recognition using a novel network architecture we call PartNet

Assessing coupled mechanical behavior and environmental degradation at submicron scales

Mechanical and electromechanical properties, deformation and fracture mechanisms, and environmental resistance of materials at submicron scales have been investigated through the combination of nanomechanical testing, high resolution microscopy, diffraction, and electrochemical testing. Nanomechanical techniques were used to isolate environmental, orientation, and size effects. Material evaluation focuses on metals, both model and engineering alloys, in bulk and thin-film form as well as oxide-substrate systems. Yield behavior of Ni 200, a model material, depends on sampled volume size, orientation, and surface preparation. Exposure to high-pressure hydrogen gas is also found to impact incipient plasticity and mechanical properties of commercially pure Ni 201. Nanomechanical testing of oxide-substrate systems can be used to study coupling of environment and size effects. Investigation of films grown on 304L stainless steel and commercially pure grade II Ti via nanosecond pulsed laser irradiation has enabled isolation of film fracture behavior and the effect of processing on mechanical and electromechanical properties. Additionally, laser processing causes substrate composition gradients that limit environmental stability. Combining techniques provides a unique approach for understanding and improving materials reliability in harsh environments

Satellite microwave sensing of oceanic cloud liquid water: application to the earth radiation budget and climate

March 1995.Sponsored by NASA Graduate Student Fellowship in Global Change Research NGT-30046.Sponsored by NASA Research NAG-8-981.Sponsored by NOAA NA37RJ0202

The Diffractive Dissociation Process at π^-p → π^- (π^-π^+p) 14 GeV/c

We describe an experiment in which a 14 GeV/c π- beam was incident on a hydrogen bubble chamber. Fast forward scattered pions traversed a wire spark chamber spectrometer downstream of the bubble chamber. Events identified as inelastic by the spectrometer induced a trigger of the bubble chamber camera. The film produced contained a heavy enrichment of events of proton diffractive dissociation. We have studied a sample from this exposure of 4400 events of the reaction π-p → π-N* → π-π-π+p. In the two body mass spectra the only noteworthy feature is the Δ++(1230). In the N* mass spectrum we observe enhancements at 1.49 GeV, 1.72 GeV, and 2.0 GeV. For the prominent 1.72 GeV feature we give estimates of the width and cross section as well as evidence favoring a substantial branching fraction to πΔ(1230). We looked for production of N*(1470) followed by decay to πΔ(1230) with negative result. An examination of the Δ++(1230) decay distribution suggests that the Deck mechanism is the major contributor to the πΔ subchannel. We tested the s-channel and t-channel helicity conservation rules. We observed violent conflict with sCHC and mild conflict with tCHC. We also tested for simultaneous validity of tCHC and the Gribov- Morrison rule and found no significant contradiction with this dual hypothesis.</p

Characterization of High Power Impulse Magnetron Sputtering Discharges

La tendance actuelle dans le domaine du dépôt physique en phase vapeur porte en partie sur le développement de processus permettant une ionisation élevée du matériau pulvérisé. Cette forte ionisation permet d'obtenir des conditions favorables à la fabrication de couches minces très denses. C'est le cas de la pulvérisation magnétron pulsée de grande puissance (HiPIMS), une technique de dépôt récemment introduite dans les milieux académiques et industriels. Ainsi, une forte dissipation de puissance au niveau de la cible durant chaque impulsion HiPIMS mène à la génération d'un plasma de haute densité et à une ionisation considérable du matériau pulvérisé. Pour cette raison principale, la concetration en ions métalliques d'un plasma HiPIMS peut être élevée, ce qui peut mener à une auto-pulvérisation de la cible. Malgré les importants progrès tant dans la compréhension que dans l'application de cette nouvelle technique de dépôt, une multitude de questions reliées à la dynamique complexe des décharges HiPIMS restent ouvertes. Ces questions concernent nottement les décharges opérées dans des mélanges gazeux réactifs employés dans la préparation de revêtements protecteurs et optiques. Ainsi, à titre d'exemple, il existe très peu d'information concernant la propagation entre la cible et le substrat d'un plasma riche en métal lors de chaque impulsion HiPIMS. Ceci est pourtant un critère important facilitant l'optimisation des conditions de dépôt. Ajoutons qu'il existe plusieurs types de sources de puissance offrant des formes d'impulsion en courant et en tension très différentes, mais qu'aucune analyse rigoureuse de leur décharge respective menant à l'identiffication des avantages et des inconvénients sur le processus de dépôt n'est disponible en ce moment. Le but de la présente thèse consiste ainsi à répondre aux problématiques et aux besoins déffinis plus-haut. En premier lieu nous menons une étude approfondie des processus en phase gazeuse durant des impulsions HiPIMS opérées avec une cible de Cr dans des milieux de Ar, de O2/Ar, de N2 et un mélange de N2 et Ar (N2/Ar) en utilisant primordialement l'émission optique émanant des différentes espèces excitées par le plasma. Nous nous concentrons ensuite sur l'évaluation critique des deux types de décharges pulsées à grande puissance générées par----------abstract Recent development in the field of physical vapor deposition has shown a great interest in processes that provide high level ionization of the sputtered material, enabling thus the fabrication of dense coatings exhibiting superior material and functional characteristics. This is particularly the case of high power pulsed magnetron sputtering (HiPIMS), recently introduced to both academia and industry, that combines magnetron sputtering and pulsed power technology. The high power dissipated on the target during each HiPIMS pulse leads to the generation of high-density plasma and to a significant ionization of the sputtered target material. Hence, the HiPIMS plasma can be rich in metal ions which, in turn, contribute to target self-sputtering. Despite great advances in the understanding as well as in the application of this novel deposition technique, there remain numerous open questions related to the complex dynamics of the pulsed HiPIMS discharges, particularly if operated in the reactive gas mixtures employed in the preparation of functional protective and optical lms. For instance, there is still little information available about the propagation of the metal-rich plasma in between the target and the substrate during individual HiPIMS pulses, an important criterion for facilitating the optimization of the deposition conditions. Furthermore, there exists a variety of commercial HiPIMS power supplies exhibiting very dierent pulse shape-, voltage- and current characteristics. However, a rigorous analysis of the respective discharges { that could identify their particular benets and drawbacks with respect to the deposition process { is missing. This work addresses the issues and needs dened above. First, we perform an in-depth investigation of the gas-phase processes during the HiPIMS pulses operated above a Cr target in Ar, O2, N2 and in N2/Ar mixtures, mostly using optical emission emanating from different plasma-excited species. Afterwards, we focus on the critical assessment of the two principal types of high power pulsed discharges generated by the commercially available power supplies

Towards patient-speci�fic modelling of cerebral blood flow using lattice-Boltzmann methods

Patient-specifi�c Computational fluid dynamics (CFD) studies of cerebral blood flow have the potential to help plan neurosurgery, but developing realistic simulation methods that deliver results quickly enough presents a major challenge. The majority of CFD studies assume that the arterial walls are rigid. Since the lattice-Boltzmann method (LBM) is computationally efficient on multicore machines, some methods for carrying out lattice-Boltzmann simulations of time-dependent fluid flow in elastic vessels are developed. They involve integrating the equations of motion for a number of points on the wall. The calculations at every lattice site and point on the wall depend only on information from neighbouring lattice sites or wall points, so they are suitable for efficient computation on multicore machines. The �first method is suitable for three-dimensional axisymmetric vessels. The steady-state solutions for the wall displacement and flow �fields in a cylinder at realistic parameters for cerebral blood ow agree closely with the analytical solutions. Compared to simulations with rigid walls, simulations with elastic walls require 13% more computational e�ffort at the parameters chosen in this study. A scheme is then developed for a more complex geometry in two dimensions, which applies the full theory of linear elasticity. The steady-state wall pro�files obtained from simulations of a Starling resistor agree closely with those from existing computational studies. I �find that it is essential to change the lattice sites from solid to fluid and vice versa if the wall crosses any of them during the simulation. Simple tests of the dynamics show that when the mass of the wall is much greater than that of the fluid, the period of oscillation of the wall agrees within 7% of the expected period. This method could be extended to three dimensions for use in cerebral blood ow simulations