14 research outputs found

    Morphing and Sampling Network for Dense Point Cloud Completion

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    3D point cloud completion, the task of inferring the complete geometric shape from a partial point cloud, has been attracting attention in the community. For acquiring high-fidelity dense point clouds and avoiding uneven distribution, blurred details, or structural loss of existing methods' results, we propose a novel approach to complete the partial point cloud in two stages. Specifically, in the first stage, the approach predicts a complete but coarse-grained point cloud with a collection of parametric surface elements. Then, in the second stage, it merges the coarse-grained prediction with the input point cloud by a novel sampling algorithm. Our method utilizes a joint loss function to guide the distribution of the points. Extensive experiments verify the effectiveness of our method and demonstrate that it outperforms the existing methods in both the Earth Mover's Distance (EMD) and the Chamfer Distance (CD).Comment: 8pages, 7 figures, AAAI202

    Digital Multispectral Map Reconstruction Using Aerial Imagery

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    Advances made in the computer vision field allowed for the establishment of faster and more accurate photogrammetry techniques. Structure from Motion(SfM) is a photogrammetric technique focused on the digital spatial reconstruction of objects based on a sequence of images. The benefit of Unmanned Aerial Vehicle (UAV) platforms allowed the ability to acquire high fidelity imagery intended for environmental mapping. This way, UAV platforms became a heavily adopted method of survey. The combination of SfM and the recent improvements of Unmanned Aerial Vehicle (UAV) platforms granted greater flexibility and applicability, opening a new path for a new remote sensing technique aimed to replace more traditional and laborious approaches often associated with high monetary costs. The continued development of digital reconstruction software and advances in the field of computer processing allowed for a more affordable and higher resolution solution when compared to the traditional methods. The present work proposed a digital reconstruction algorithm based on images taken by a UAV platform inspired by the work made available by the open-source project OpenDroneMap. The aerial images are inserted in the computer vision program and several operations are applied to them, including detection and matching of features, point cloud reconstruction, meshing, and texturing, which results in a final product that represents the surveyed site. Additionally, from the study, it was concluded that an implementation which addresses the processing of thermal images was not integrated in the works of OpenDroneMap. By this point, their work was altered to allow for the reconstruction of thermal maps without sacrificing the resolution of the final model. Standard methods to process thermal images required a larger image footprint (or area of ground capture in a frame), the reason for this is that these types of images lack the presence of invariable features and by increasing the image’s footprint, the number of features present in each frame also rises. However, this method of image capture results in a lower resolution of the final product. The algorithm was developed using open-source libraries. In order to validate the obtained results, this model was compared to data obtained from commercial products, like Pix4D. Furthermore, due to circumstances brought about by the current pandemic, it was not possible to conduct a field study for the comparison and assessment of our results, as such the validation of the models was performed by verifying if the geographic location of the model was performed correctly and by visually assessing the generated maps.Avanços no campo da visão computacional permitiu o desenvolvimento de algoritmos mais eficientes de fotogrametria. Structure from Motion (SfM) é uma técnica de fotogrametria que tem como objetivo a reconstrução digital de objectos no espaço derivados de uma sequência de imagens. A característica importante que os Veículos Aérios não-tripulados (UAV) conseguem fornecer, a nível de mapeamento, é a sua capacidade de obter um conjunto de imagens de alta resolução. Devido a isto, UAV tornaram-se num dos métodos adotados no estudo de topografia. A combinação entre SfM e recentes avanços nos UAV permitiram uma melhor flexibilidade e aplicabilidade, permitindo deste modo desenvolver um novo método de Remote Sensing. Este método pretende substituir técnicas tradicionais, as quais estão associadas a mão-de-obra intensiva e a custos monetários elevados. Avanços contínuos feitos em softwares de reconstrução digital e no poder de processamento resultou em modelos de maior resolução e menos dispendiosos comparando a métodos tradicionais. O presente estudo propõe um algoritmo de reconstrução digital baseado em imagens obtidas através de UAV inspiradas no estudo disponibilizado pela OpenDroneMap. Estas imagens são inseridas no programa de visão computacional, onde várias operações são realizadas, incluindo: deteção e correspondência de caracteristicas, geração da point cloud, meshing e texturação dos quais resulta o produto final que representa o local em estudo. De forma complementar, concluiu-se que o trabalho da OpenDroneMap não incluia um processo de tratamento de imagens térmicas. Desta forma, alterações foram efetuadas que permitissem a criação de mapas térmicos sem sacrificar resolução do produto final, pois métodos típicos para processamento de imagens térmicas requerem uma área de captura maior, devido à falta de características invariantes neste tipo de imagens, o que leva a uma redução de resolução. Desta forma, o programa proposto foi desenvolvido através de bibliotecas open-source e os resultados foram comparados com modelos gerados através de software comerciais. Além do mais, devido à situação pandémica atual, não foi possível efetuar um estudo de campo para validar os modelos obtidos, como tal esta verificação foi feita através da correta localização geográfica do modelo, bem como avaliação visual dos modelos criados

    New Directions for Contact Integrators

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    Contact integrators are a family of geometric numerical schemes which guarantee the conservation of the contact structure. In this work we review the construction of both the variational and Hamiltonian versions of these methods. We illustrate some of the advantages of geometric integration in the dissipative setting by focusing on models inspired by recent studies in celestial mechanics and cosmology.Comment: To appear as Chapter 24 in GSI 2021, Springer LNCS 1282

    Detached eddy simulation of unsteady turbulent flows in the draft tube of a bulb turbine

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    Les aspirateurs de turbines hydrauliques jouent un rôle crucial dans l’extraction de l’énergie disponible. Dans ce projet, les écoulements dans l’aspirateur d’une turbine de basse chute ont été simulés à l'aide de différents modèles de turbulence dont le modèle DDES, un hybride LES/RANS, qui permet de résoudre une partie du spectre turbulent. Déterminer des conditions aux limites pour ce modèle à l’entrée de l’aspirateur est un défi. Des profils d’entrée 1D axisymétriques et 2D instationnaires tenant compte des sillages et vortex induits par les aubes de la roue ont notamment été testés. Une fluctuation artificielle a également été imposée, afin d’imiter la turbulence qui existe juste après la roue. Les simulations ont été effectuées pour deux configurations d’aspirateur du projet BulbT. Pour la deuxième, plusieurs comparaisons avec des données expérimentales ont été faites pour deux conditions d'opération, à charge partielle et dans la zone de baisse rapide du rendement après le point de meilleur rendement. Cela a permis d’évaluer l'efficacité et les lacunes de la modélisation turbulente et des conditions limites à travers leurs effets sur les quantités globales et locales. Les résultats ont montrés que les structures tourbillonnaires et sillages sortant de la roue sont adéquatement résolus par les simulations DDES de l’aspirateur, en appliquant les profils instationnaires bidimensionnels et un schéma de faible dissipation pour le terme convectif. En outre, les effets de la turbulence artificielle à l'entrée de l’aspirateur ont été explorés à l'aide de l’estimation de l’intermittence du décollement, de corrélations en deux points, du spectre d'énergie et du concept de structures cohérentes lagrangiennes. Ces analyses ont montré que les détails de la dynamique de l'écoulement et de la séparation sont modifiés, ainsi que les patrons des lignes de transport à divers endroits de l’aspirateur. Cependant, les quantités globales comme le coefficient de récupération de l’aspirateur ne sont pas influencées par ces spécificités locales.Draft tubes play a crucial role in elevating the available energy extraction of hydroturbines. In this project, turbulent flows in the draft tube of a low-head bulb turbine were simulated using, among others, an advance hybrid LES/RANS turbulent model, called DDES, which can resolve portions of the turbulent spectrum. Providing appropriate inflow boundary conditions for such models is a challenging issue. In this regard, different inflow boundary conditions were tested, including axisymmetric 1D profiles, and unsteady 2D inflow profiles that take runner blade wakes and vortices into account. Artificial fluctuation at the inlet section of the draft tube was also included to mimic the turbulence existing after the runner. Simulations were conducted for two draft tube configurations of the BulbT project. For one of them, intensive comparisons with experimental data were done for two operating conditions, one at part load and another in the sharp drop-off portion of the efficiency hill after the best efficiency point. This allowed to assess the effectiveness and shortcomings of the adopted turbulence modeling and boundary conditions through their effects on the global and local quantities. The results showed that the runner-related vortical structures and wakes are appropriately resolved using stand-alone DDES simulation of the draft tube flows. This is achieved by applying unsteady 2D inflow profiles along with adopting low dissipation scheme for the convective term. Furthermore, the effects of applying artificial turbulence at inlet were explored using separation intermittency, two-point correlation, energy spectrum and Lagrangian coherent structure concepts. These analyses revealed that the type of inflow boundary conditions modifies the details of the flow and separation dynamics as well as patterns of the transport barriers in different regions of the draft tube. However, the global quantities such as recovery coefficient are not influenced by these local features

    Advances in Quantum Theory

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    The quantum theory is the first theoretical approach that helps one to successfully understand the atomic and sub-atomic worlds which are too far from the cognition based on the common intuition or the experience of the daily-life. This is a very coherent theory in which a good system of hypotheses and appropriate mathematical methods allow one to describe exactly the dynamics of the quantum systems whose measurements are systematically affected by objective uncertainties. Thanks to the quantum theory we are able now to use and control new quantum devices and technologies in quantum optics and lasers, quantum electronics and quantum computing or in the modern field of nano-technologies

    Rastertunneluntersuchungen auf strukturierten Edelmetall-(111)-Oberflächen

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    This thesis comprises low temperature UHV STM and STS experiments. Firstly, the electronic structure of decorated Ag(111) surfaces is explored, with focus on quasielectron lifetimes in Shockley surface states, made accessible by constructing monatomically deep hexagonal and triangular surface vacancies, by argon ion bombardment and tip-substrate impact. Within the resonators, the surface electrons are confined to broadened standing wave states, described well by a particle-in-a-box model. The linewidths show an approximately linear increase with binding energy. The two main contributions identified are the intrinsic lifetime, due to electron-electron and electron-phonon interaction, and lossy scattering at the boundary. An estimate of the relative strength shows that the latter is the limiting factor for lifetime. Comparison of various previously published lifetime data yields a consistent picture. Supplemental experiments on one-dimensional atomic chains and vacancy rows yield the surface state dispersion, and a transmission resonance peak at 1.7 V on the chain. Comparison to adsorbed Ag oligomers shows a decrease in energy with cluster size. Fowler-Nordheim spectroscopy finds a reduced sample work function on the nanostructures. The second part explores the adsorption characteristics of submonolayers of the perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA) molecule on the vicinal Au(111) surfaces Au(788), Au(433), and Au(877). Substrate areas with a high step density prefer formation of molecular chains along the steps, with a strong preference for {111} type steps. Otherwise island formation in the known herringbone and square phases is seen. With increasing sample bias, the molecules undergo a contrast transition in STM, at an energy shifted by 0.35 V between the two phases. A DFT calculation suggests that the transition correlates to the LUMO, and the shift is due to a variation in intermolecular hydrogen bond strength.Die Arbeit beinhaltet Tieftemperatur-UHV-STM- und STS-Experimente. Die elektronische Struktur von dekorierten Ag(111)-Oberflächen wird untersucht, insbesondere Quasielektronen-Lebensdauern von Shockley-Oberflächenzuständen, die zugänglich gemacht werden durch Erzeugung einatomar tiefer sechs- und dreieckiger Fehlstellen, mittels Argonionen-Beschuss und Spitze-Probe-Kontakten. In den Resonatoren werden die Elektronen in energetisch verbreiterten Stehende-Welle-Zuständen gebunden, die gut durch ein Potentialtopfmodell beschrieben werden. Die Linienbreiten steigen etwa linear mit der Bindungsenergie. Die Hauptbeiträge sind die intrinsische Lebensdauer, aufgrund von Elektron-Elektron- und Elektron-Phonon-Wechselwirkungen, und verlustbehaftete Streuung an den Rändern. Eine Abschätzung der relativen Stärken zeigt, dass letztere den begrenzenden Faktor für die Lebensdauer darstellt. Vergleich mit Daten aus der Literatur ergibt somit ein konsistentes Bild. Experimente auf eindimensionalen Atom- und Fehlstellenketten ergeben die Dispersion des Oberflächenzustands, und auf den Atomketten eine Resonanz bei 1.7 V. Vergleich mit adsorbierten Ag-Oligomeren ergibt eine mit der Clustergröße sinkende Energie. Fowler-Nordheim-Spektroskopie zeigt eine Senkung der Austrittsarbeit auf den Ketten. Der zweite Teil behandelt die Adsorption von Submonolagen von Perylen-3,4,9,10-tetracarboxyl-dianhydrid (PTCDA) auf den Au(111)-vizinalen Oberflächen Au(788), Au(433) und Au(877). Substrate mit hoher Stufendichte begünstigen die Bildung von Molekülketten entlang der Stufen, vornehmlich des {111}-Typs. Andere Substrate zeigen Inselwachstum in den von Au(111) bekannten Quadrat- und Fischgrätenphasen. Ansteigende Probenspannung ergibt in STM einen Kontrastübergang, dessen Energie phasenabhängig um 0.35 V verschoben ist. Eine DFT-Rechnung identifiziert den Übergang mit dem LUMO und erklärt die Verschiebung durch geänderte Bindungsstärke der Wasserstoffbrücken
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