A critique on previous work in vision aided navigation

This paper presents a critique on previous work in the field of vision aided navigation, particularly in the fusion of visual and inertial sensors for navigation. Several improvements and updates are proposed for the existent systems. GPS receivers have allowed for accurate navigation for many vehicles and robotic platforms. GPS based navigation can, however, prove to be impractical in applications where there is no GPS reception such as underground, indoors or in some urban areas. This pertains, in particular, to many robotic applications where position must be known in global coordinates or relative to a reference point. An inertial navigation system (INS) can be used to calculate one’s relative navigation state via dead-reckoning calculations. The downfall of a low-cost INS is the errors associated with the system. While these errors are initially small, integration causes large drift errors over time. To combat this problem, cameras can be used to estimate the errors present in the INS readings. These results can then be used to correct the navigation state output from the INS. While the motion estimations from the cameras are not error-free, this method is made highly effective because of the complementary nature of the errors from the cameras and INS. Several improvements are proposed for this method; algorithmically, in updates to its hardware, and with the introduction of graphics processors to improve computational performance. The overall system performance, individual steps, algorithms, and results are compared to results from similar works to those of the proposed improvements. It is shown that the accuracy, responsiveness and overall performance of the system can potentially be greatly improved

Dynamic Analysis of Vascular Morphogenesis Using Transgenic Quail Embryos

Background: One of the least understood and most central questions confronting biologists is how initially simple clusters or sheet-like cell collectives can assemble into highly complex three-dimensional functional tissues and organs. Due to the limits of oxygen diffusion, blood vessels are an essential and ubiquitous presence in all amniote tissues and organs. Vasculogenesis, the de novo self-assembly of endothelial cell (EC) precursors into endothelial tubes, is the first step in blood vessel formation [1]. Static imaging and in vitro models are wholly inadequate to capture many aspects of vascular pattern formation in vivo, because vasculogenesis involves dynamic changes of the endothelial cells and of the forming blood vessels, in an embryo that is changing size and shape. Methodology/Principal Findings: We have generated Tie1 transgenic quail lines Tg(tie1:H2B-eYFP) that express H2B-eYFP in all of their endothelial cells which permit investigations into early embryonic vascular morphogenesis with unprecedented clarity and insight. By combining the power of molecular genetics with the elegance of dynamic imaging, we follow the precise patterning of endothelial cells in space and time. We show that during vasculogenesis within the vascular plexus, ECs move independently to form the rudiments of blood vessels, all while collectively moving with gastrulating tissues that flow toward the embryo midline. The aortae are a composite of somatic derived ECs forming its dorsal regions and the splanchnic derived ECs forming its ventral region. The ECs in the dorsal regions of the forming aortae exhibit variable mediolateral motions as they move rostrally; those in more ventral regions show significant lateral-to-medial movement as they course rostrally. Conclusions/Significance: The present results offer a powerful approach to the major challenge of studying the relative role(s) of the mechanical, molecular, and cellular mechanisms of vascular development. In past studies, the advantages of the molecular genetic tools available in mouse were counterbalanced by the limited experimental accessibility needed for imaging and perturbation studies. Avian embryos provide the needed accessibility, but few genetic resources. The creation of transgenic quail with labeled endothelia builds upon the important roles that avian embryos have played in previous studies of vascular development

Order Matters: A Distributed Sampling Method for Multi-Object Tracking

Multi-Object tracking (MOT) is an important problem in a number of vision applications. For particle filter (PF) tracking, as the number of objects tracked increases, the search space for random sampling explodes in dimension. Partitioned sampling (PS) solves this problem by partitioning the search space, then searching each partition sequentially. However, sequential weighted resampling steps cause an impoverishment effect that increases with the number of objects. This effect depends on the specific order in which the partitions are explored, creating an erratic and undesirable performance. We propose a method to search the state space that fairly distributes these impoverishment effects between the objects by defining a set of mixture components and performing PS in each of these components using one of a small set of representative object orderings. Using synthetic and real data, we show that our method retains the overall performance and reduced computational cost of PS, while improving performance in scenes where the impoverishment effect is significant

Low cost sonar based on echolocation: an embedded system approach

Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do ParanáOne of the greatest challenges of mobile robot applications is obstacle detection and its localization. Most systems applied to address this problem can be branched into two segments: vision-based and non-vision based. In the former, camera detection and image processing are sensitive to variations in environmental conditions as well as their high cost. For this reason, this option is not interesting. In the second segment, on the other hand, ultrasonic sensors stand out for their attractive features at an affordable cost and, unlike other systems, are capable of operating in a variety of environments. The main problem using these devices is the difficulty of correctly handling the data acquired, limiting their efficiency. The present work focuses on the improvement and employment of a low cost location system based on ultrasonic sensors, combining trigonometric and signal processing techniques. The work is divided into two parts: processed version in MATLAB and application of embedded system. For the version in MATLAB, two optimal techniques — envelope detection and cross-correlation — were evaluated. For the embedded system approach, the technique with the best performance was implemented. In both parts, the validation of results obtained occurred through a set of measurements with various objects in assorted configurations.Um dos maiores desafios das aplicações de robôs móveis é a detecção de obstáculos e sua localização. A maioria dos sistemas aplicados para solucionar esse problema pode ser ramificada em dois segmentos: baseado em visão e em não visão. No primeiro, a detecção por câmera e o processamento de imagens são sensíveis as variações nas condições ambientais, além de possuírem alto custo. No segundo segmento, por outro lado, os sensores ultrassônicos se destacam por seus recursos atraentes a um custo acessível e, ao contrário de outros sistemas, são capazes de operar em uma variedade de ambientes. O principal problema do uso desses dispositivos é a dificuldade de manipular corretamente os dados adquiridos, limitando sua eficiência. O presente trabalho enfoca na melhoria e no emprego de um sistema de localização de baixo custo, baseado em sensores ultrassônicos, combinando técnicas trigonométricas e de processamento de sinais. O trabalho está dividido em duas partes: versão processada em MATLAB e aplicação do sistema embarcado. Para a versão em MATLAB, duas técnicas ótimas — detecção de envelope e correlação cruzada — foram avaliadas. Para a abordagem de sistema embarcado, foi implementada a técnica com o melhor desempenho. Em ambas as partes, a validação dos resultados obtidos ocorreu através de um conjunto de medidas com vários objetos em configurações variadas

UNDERSTANDING THE ROLE OF CHARGE ON PARTICLE TRANSPORT WITHIN SEMIDILUTE AND CONCENTRATED BIOPOLYMER SOLUTIONS AND TAU PROTEIN CONDENSATES

Biological polymer networks such as mucus, extracellular matrix, nuclear pore complex, and bacterial biofilms, play a critical role in governing the transport of nutrients, biomolecules and particles within cells and tissues. The interactions between particle and polymer chains are responsible for effective selective filtering of particles within these macromolecular networks. This selective filtering is not dictated by steric alone but must use additional interactions such electrostatics, hydrophobic and hydrodynamic effects to control particle transport within biogels. Depending on chemical composition and desired function, biogels use selective filtering to allow some particles to permeate while preventing others from penetrating the biogel. The mechanisms underlying selective filtering are still not well understood yet have important ramifications for a variety of biomedical applications. Controlling these non-steric interactions are critical to understanding molecular transport in vivo as well as for engineering optimized gel penetrating therapeutics. Fluorescence correlation spectroscopy (FCS) is an ideal tool to study particle transport properties within uncharged and charged polymer solutions. In this dissertation, our research focuses primarily on the role of electrostatics on the particle diffusion behavior within polymer solutions in the semi-dilute and concentrated regimes. Using a series of charged dye molecules, with similar size and core chemistry but varying net molecular charge, we systematically investigated their diffusion behavior in polymer solutions and networks made up of polysaccharide and proteins. Specifically, we studied in Chapter 3 the probe diffusion in semidilute and concentrated dextran solutions. The hindered diffusion observed in attractive gels is dependent on the probe net charge and shows a dependence on the solution ionic strength. Using a biotinylated probe, we also show evidence of an additional non-electrostatic interaction between the biotin molecule and the dextran polymer chains. In contrast, comparisons to a highly charged, water soluble polyvinylamine (PVAm) semidilute solution shows that all probes, regardless of charge, were highly hindered and a weaker dependence on solution ionic strength was observed. In Chapter 4, we characterized the transport properties of our probe molecules within pure and mixed charge solutions of amino(+)-dextran and carboxymethyl(-)-dextran. We show that these mixed charge polymer solutions still have the potential to be efficient filters for interacting particles even with comparably few attractive interaction sites. By chemical modification of the amino dextran, we also compare these results to those obtained in polyampholytic solutions. Lastly, we investigate the transport properties of both probes and a much larger bovine serum albumin (BSA) protein molecule within liquid-liquid phase separated (LLPS) tau protein in chapter 5. Tau is an intrinsically disordered protein with both positive and negatively charged amino acids. We show that despite having a high local protein concentration, tau droplets are relatively low density and comparable to semidilute polymer solutions. Both probe molecules and BSA are observed by FCS to be recruited within the liquid droplet resulting in ~10x fold increase in particle concentration inside the tau droplet compared to outside. Probe transport within the phase separated tau is sensitive to probe net charge and solution ionic strength. Lastly, we show that BSA transport inside the tau droplet can be fairly well described by using Stokes-Einstein adjusted for the experimentally determined microviscosity within the tau droplet

La percepción como muestreo estocástico en grafos dinámicos

Esta tesis estudia y desarrolla técnicas novedosas que permiten a los robots percibir apropiadamente el entorno de forma autónoma. Para conseguir esto es posible y conveniente usar la información del entorno de la que se disponga. Generalmente, dicha información queda plasmada en el código del robot como construcciones if-then-else difíciles de entender cuando el mundo del robot es considerablemente complejo. Se propone el uso de “Active Grammar-based Modeling” (AGM), una técnica desarrollada dentro de la tesis, que usa descripciones de muy alto nivel que permiten al desarrollador obtener más flexibilidad y escalabilidad, así como reducir el tiempo de desarrollo y la cantidad de errores que se cometen al programar los robots. La solución propuesta pasa por describir la gramática del entorno en un lenguaje específico de dominio que posteriormente se traduce a PDDL, permitiendo usar así planificadores de Inteligencia Artificial clásicos para decidir qué ha de hacer el robot para cumplir sus objetivos y comprobar que las modificaciones que el robot hace al modelo del entorno son válidas de acuerdo a la gramática. Además, AGM permite coordinar fácilmente diferentes filtros de partículas para su ejecución simultánea, pudiendo además elegir distintos filtros de partículas dependiendo del contexto en el que el robot se encuentre, optimizando así el sistema perceptivo de los robots. Además de dicha técnica la tesis presenta diferentes algoritmos usados dentro de AGM, así como varios experimentos relacionados con el modelado activo de entornos de interior usando cámaras RGBD.This thesis develops and studies novel techniques that allow robots to properly model their environments autonomously. For this purpose it is possible and feasible to use all the available information that robots can use. Generally this information results in if-then-else constructs that are hard to understand then the environments of the robots are considerably complex. It is proposed to use “Active Grammar-based Modeling” (AGM), a new technique developed within this thesis. It uses very high-level descriptions that allow developers to achieve higher flexibility and scalability, as well as reducing the development time and the amount of programming errors. The solution consists on describing the grammar of the environment using a domain-specific language that is compiled into PDDL, allowing AGM-based systems to use classic AI planners to decide what robots should do to achieve their goales and incrementally verify that the model generated is valid according to the grammar described. Moreover, AGM can coordinate different particle filters so they can work simultaneously, allowing to choose the most appropriate filters depending on the context. This enhances the accuracy and effectivenes of the perceptual systems of the robots Along AGM, this thesis also presents the different algorithms used by AGM, as well as different experiment related to active indoor modeling using RGBD cameras

In-situ monitoring of the mechanical properties during the photopolymerization of acrylate resins using particle tracking microrheology

The fundamentals of the photopolymerization process are not well understood. As a result, issues affecting the cure speed and overall quality of the final product (shape, size, and surface finish) of photopolymerization impose significant limitations on applications that require fast processing and high spatial resolution. To address this issue, microrheology was employed to perform in-situ monitoring of the liquid-to-gel transition during free-radical photopolymerization. Photosensitive acrylate and hydrogel resins were exposed to ultraviolet light, while the Brownian motion of micrometer sized, inert fluorescent tracer particles was tracked via optical videomicroscopy. Statistical analysis of particle motion yielded the rheological properties of the embedding medium as a function of time and location, thereby relating UV exposure to the progress of polymerization and gelation. The microrheological setup enabled a detailed study of three-dimensional gelation profiles; other experimental parameters that were initially varied include photoinitiator concentration, monomer composition, and light intensity. Significant changes in gelation time were observed with varying UV intensity and UV penetration depth into the sample. In addition, oxygen inhibition was found to significantly impact the cure speed of monomeric resins. The preliminary results were used to test the accuracy of the energy threshold model, which is often used to empirically predict the outcome of photopolymerization reactions. By using lithographic masks to generate well-defined UV illumination patterns with characteristic dimensions of tens of micrometers, it could be shown unambiguously that the diffusion of oxygen, an inhibitor, plays a critical role in the polymerization reaction. The experiments are in excellent agreement with a simple two-step model of oxygen consumption followed by polymerization. The use of high-speed electronic shutters in the UV light path enabled us to control the illumination time of the samples with high precision. Microrheological analysis could be used to reconstruct three-dimensional profiles of partially polymerized samples. Traditional photorheometry is not capable of resolving the evolution of sample rheology with such spatial resolution. In addition, experiments with pulsed illumination were used to quantify the role of dark reactions due to residual free radicals after termination of UV illumination.Ph.D.Committee Chair: Dr. Victor Breedveld; Committee Member: Dr. Clifford Henderson; Committee Member: Dr. David Rosen; Committee Member: Dr. Peter Ludovice; Committee Member: Dr. Sai Kuma