4,945 research outputs found
Impact of Imaging and Distance Perception in VR Immersive Visual Experience
Virtual reality (VR) headsets have evolved to include unprecedented viewing quality. Meanwhile, they have become lightweight, wireless, and low-cost, which has opened to new applications and a much wider audience. VR headsets can now provide users with greater understanding of events and accuracy of observation, making decision-making faster and more effective. However, the spread of immersive technologies has shown a slow take-up, with the adoption of virtual reality limited to a few applications, typically related to entertainment. This reluctance appears to be due to the often-necessary change of operating paradigm and some scepticism towards the "VR advantage". The need therefore arises to evaluate the contribution that a VR system can make to user performance, for example to monitoring and decision-making. This will help system designers understand when immersive technologies can be proposed to replace or complement standard display systems such as a desktop monitor.
In parallel to the VR headsets evolution there has been that of 360 cameras, which are now capable to instantly acquire photographs and videos in stereoscopic 3D (S3D) modality, with very high resolutions. 360° images are innately suited to VR headsets, where the captured view can be observed and explored through the natural rotation of the head. Acquired views can even be experienced and navigated from the inside as they are captured.
The combination of omnidirectional images and VR headsets has opened to a new way of creating immersive visual representations. We call it: photo-based VR. This represents a new methodology that combines traditional model-based rendering with high-quality omnidirectional texture-mapping. Photo-based VR is particularly suitable for applications related to remote visits and realistic scene reconstruction, useful for monitoring and surveillance systems, control panels and operator training.
The presented PhD study investigates the potential of photo-based VR representations. It starts by evaluating the role of immersion and user’s performance in today's graphical visual experience, to then use it as a reference to develop and evaluate new photo-based VR solutions. With the current literature on photo-based VR experience and associated user performance being very limited, this study builds new knowledge from the proposed assessments.
We conduct five user studies on a few representative applications examining how visual representations can be affected by system factors (camera and display related) and how it can influence human factors (such as realism, presence, and emotions). Particular attention is paid to realistic depth perception, to support which we develop target solutions for photo-based VR. They are intended to provide users with a correct perception of space dimension and objects size. We call it: true-dimensional visualization.
The presented work contributes to unexplored fields including photo-based VR and true-dimensional visualization, offering immersive system designers a thorough comprehension of the benefits, potential, and type of applications in which these new methods can make the difference.
This thesis manuscript and its findings have been partly presented in scientific publications. In particular, five conference papers on Springer and the IEEE symposia, [1], [2], [3], [4], [5], and one journal article in an IEEE periodical [6], have been published
Steigerung der thermischen Stabilität von warm- und kaltgewalztem Wolfram durch Kalium-Dotierung für die Fusionsenergietechnik
Fusionskraftwerke der Zukunft stellen enorme Materialanforderungen, beispielsweise in Bezug auf Hitzeresistenz an Plasmakontaktzonen der inneren Reaktorwand und des Divertors. Als abschirmendes Material stellt Wolfram nach aktueller Konzeption die mit Abstand beste Alternative dar. Nachteilig ist dabei jedoch dessen hohe Spröd-duktil-Übergangstemperatur (BDTT), welche aufgrund thermischer und mechanischer Belastungszyklen zu katastrophalem Risswachstum führen kann. Zwar kann die BDTT durch starkes Kaltwalzen drastisch abgesenkt werden, das dabei entstehende, feinkörnige Gefüge ist jedoch thermisch instabil, wodurch es bei relativ niedrigen Temperaturen wiederum zu einer Erhöhung der BDTT kommt.
Neben einer Untersuchung der zu einer solchen Versprödung führenden mikrostrukturellen Restaurationsprozesse, wurde daher in der vorliegenden Arbeit das Potential zur Stabilisierung der Mikrostruktur durch eine Dotierung mit Kalium (K) umfassend analysiert, durch welche die Migration von Korngrenzen und Versetzungen mittels fein verteilter K-Blasen unterdrückt wird. Zwar wird K-Dotierung bereits seit mehr als 100 Jahren bei der industriellen Herstellung von Glühlampendrähten angewendet, die Kombination des Verfahrens mit hochgradiger Walzumformung von Wolfram stellt jedoch einen neuartigen Ansatz dar.
Grundlage der Studie war zunächst die erfolgreiche Herstellung zweier äquivalent gewalzter Blechserien von technisch reinem Wolfram (Referenz) und K-dotiertem Wolfram mit bis zu sehr hohen logarithmischen Umformgraden von 4,7 bzw. 4,6 durch Warm- und Kaltwalzen. Anhand beider Materialserien wurde eine detaillierte Analyse der verformungsbedingten Evolution von Mikrostruktur (durch REM und EBSD), mechanischer Eigenschaften (durch Härteprüfung, Zugversuche und Untersuchungen der Risszähigkeit) und Verteilung von K-Blasen (durch REM) nach den Walzschritten erstellt. Als weiteres Kernstück der Arbeit wurde die Mikrostruktur nach isochronen, isothermen und aufheizratenkontrollierten Wärmebehandlungsreihen zwischen 600 °C und 2400 °C mittels Härteprüfung und REM-Analysen hinsichtlich aufgetretener Restaurationsprozesse in unterschiedlichen Temperaturregimen systematisch untersucht.
Es ist herauszustellen, dass nach höchstem Umformgrad sowohl bei reinem als auch K-dotiertem Wolfram eine nochmals niedrigere BDTT unterhalb von −80 °C im Vergleich zu bisherigen Studien an reinen Wolframblechen vorgefunden wurde. Die Analyse ergab weiterhin, dass die verformungsbedingte Evolution der Mikrostruktur zwischen beiden Blechserien annähernd gleich verlief. Allerdings traten in den K dotierten Blechen mit geringerem Umformgrad mikrometerdicke Lagen auf, die jeweils einzelnen Texturkomponenten zuzuordnen sind und nahezu ausschließlich Kleinwinkelgrenzen enthalten. Da sich dieses Phänomen mit einer hohen BDTT der besagten Bleche in Verbindung bringen ließ, könnte dessen Vermeidung ein wichtiges Qualitätskriterium bei zukünftigen Materialproduktionen darstellen. Weitere mechanische Eigenschaften, wie Mikrohärte, Zugfestigkeit und Dehngrenze, ließen sich in Anlehnung an die Hall-Petch-Beziehung mit der Korngröße korrelieren, wobei in den kaltgewalzten Blechen ein signifikanter Einfluss durch Kleinwinkel-grenzen festgestellt wurde, welche oftmals in einer Hall-Petch-Beziehung nicht berücksichtigt werden.
Die Mechanismen, welche die Dispersion der K-Blasen und damit die Zener-Kräfte gegenüber Erholung, Rekristallisation und Kornwachstum beeinflussen, wurden tiefgreifend analysiert. Maßgeblich ist dabei der Umformgrad der Bleche, der zu einer Streckung der Blasen führt, sowie die Parameter einer darauffolgenden Wärmebehandlung, die den Aufbruch der gestreckten Blasen ähnlich einer Plateau-Rayleigh-Instabilität bewirkt. Die theoretischen Grundlagen dieser Aufbruchskinetik wurden mit den experimentellen Ergebnissen in Einklang gebracht und das Modell für den Grenzfall von Blasen mit geringem Streckungsverhältnis weiterentwickelt. Eine nanoskalige Analyse der chemischen Zusammensetzung zeigte erstmals in-situ eine heterogene Elementverteilung innerhalb des Volumens von K-Blasen aus einer aluminiumreichen und einer volatilen, kaliumreichen Phase sowie erhöhte Gehalte von Silizium und Sauerstoff. Es konnte zudem eine Instabilität dieser chemischen Zusammensetzung nach einer Wärmebehandlung im Bereich von ca. 2400 °C nachgewiesen werden, welche bei Hochtemperaturanwendungen von Relevanz sein kann.
Die Analyse wärmebehandelter Proben ergab, dass Bleche mit geringem Umformgrad in einem niedrigen Temperaturregime nur schwache mikrostrukturelle Änderungen durch Erholung zeigten. Bleche mit hohem Umformgrad offenbarten jedoch drastische Änderungen durch sogenannte erweiterte Erholung (auch als kontinuierliche Rekristallisation bezeichnet), welche einen maßgeblichen Grund für die Versprödung dieser Bleche darstellt. Durch K-Dotierung konnte eine nur geringfügig retardierende Wirkung gegenüber erweiterter Erholung nachgewiesen werden. Erst in einem mittleren Temperaturregime bewiesen K-dotierte Bleche eine deutlich retardierende Wirkung gegenüber der dabei stattfindenden Rekristallisation in Blechen mit geringem Umformgrad bzw. in Blechen mit hohem Umformgrad gegenüber der fortschreitenden erweiterten Erholung mit direktem Übergang zu Kornwachstum. Zudem ergaben sich durch die Dotierung deutliche Unterschiede in der Texturentwicklung, welche den weiteren Verlauf der Restauration durch Kornwachstum beeinflusst. In einem hohen Temperaturregime bewirkte die Dotierung eine nahezu vollständige Stabilisierung gegenüber normalem und abnormalem Kornwachstum bei geringem Umformgrad, bei hohem Umformgrad jedoch besonders starkes abnormales Kornwachstum. Auch etwaige Einflüsse durch unterschiedliche Aufheizraten von 1 K/s und 200 K/s unter Berücksichtigung einer thermischen Aktivierungsäquivalenz wurden an den dicksten Blechen untersucht, jedoch kein aufheizratenbedingter Effekt festgestellt. Dieses Ergebnis steht im Widerspruch zu bisherigen Studien, in denen eine thermische Aktivierungsäquivalenz nicht berücksichtigt wurde.
Die komplexen Zusammenhänge von thermomechanischer Behandlung reiner und K-dotierter Wolframmaterialien und der daraus resultierenden mikrostrukturellen Evolution wurden abschließend einander gegenübergestellt. Aufgrund der gewonnenen Erkenntnisse scheint K-dotiertes Material mit geringem Umformgrad die meisten Vorteile für die Anwendung in Fusionsreaktorkomponenten aufzuweisen, insbesondere durch die enormen Auswirkungen der K-Dotierung auf Kornwachstum sowie der deutlichen Retardierung von Rekristallisation, aber auch durch einen geringeren Herstellungsaufwand im Vergleich zu hochgradig umgeformtem Wolfram
LIPIcs, Volume 251, ITCS 2023, Complete Volume
LIPIcs, Volume 251, ITCS 2023, Complete Volum
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
Ureilite meteorites and the unknown proto-planet: using EBSD to construct a geological history
The ureilites are a group of ultramafic achondrite meteorites composed primarily of olivine and pigeonite, with accessory minerals and a high abundance of carbon in the form of graphite and diamond. There are many hypotheses as to how the ureilite group formed, but the majority of authors are now in agreement that they represent a mantle restite of a now destroyed planetesimal that may have been as large as Mercury (Nabiei et al., 2018). This planetesimal was large enough for the ureilites to form through igneous processing, but not large enough to become a full planet. At some point, possibly within the first 10 million years (Rai et al., 2020) of its life the ureilite parent body (UPB) was subjected to a catastrophic impact which destroyed the planetesimal and created daughter asteroids which are the current parent bodies of the ureilites (Goodrich et al., 2015). This study aims to construct a comprehensive geological history of the samples using Electron Backscatter Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS), Raman spectroscopy and geochemical data. Here we show using Raman peak Full Width Half Maximum (FWHM) data that the majority of diamonds present in the ureilite suite are formed through shock related processes. This is combined with the EBSD data and optical microscopy data to discuss a range of shock features present within the ureilites such as mosaicism. Various slip systems are shown to be activated across the samples indicating deformation occurred during a variety of temperature and pressure conditions throughout ureilite formation. Evidence of shear processes affecting the majority of the samples studied is also presented using the EBSD datasets. A proposed geological history is presented to tie shock and shear features together. Our results agree with recent studies about diamond formation (Nestola et al., 2020) on the UPB which goes some way to negating the need for a large planetesimal to be required in order to explain ureilite formation
Towards an integrated vulnerability-based approach for evaluating, managing and mitigating earthquake risk in urban areas
Tese de doutoramento em Civil EngineeringSismos de grande intensidade, como aqueles que ocorreram na Turquía-Síria (2023) ou México (2017)
deviam chamar a atenção para o projeto e implementação de ações proativas que conduzam à identificação
de bens vulneráveis. A presente tese propõe um fluxo de trabalho relativamente simples para
efetuar avaliações da vulnerabilidade sísmica à escala urbana mediante ferramentas digitais. Um modelo
de vulnerabilidade baseado em parâmetros é adotado devido à afinidade que possui com o Catálogo Nacional
de Monumentos Históricos mexicano. Uma primeira implementação do método (a grande escala)
foi efetuada na cidade histórica de Atlixco (Puebla, México), demonstrando a sua aplicabilidade e algumas
limitações, o que permitiu o desenvolvimento de uma estratégia para quantificar e considerar as incertezas
epistémicas encontradas nos processos de aquisição de dados. Devido ao volume de dados tratado, foi
preciso desenvolver meios robustos para obter, armazenar e gerir informações. O uso de Sistemas de
Informação Geográfica, com programas à medida baseados em linguagem Python e a distribuição de
ficheiros na ”nuvem”, facilitou a criação de bases de dados de escala urbana para facilitar a aquisição de
dados em campo, os cálculos de vulnerabilidade e dano e, finalmente, a representação dos resultados.
Este desenvolvimento foi a base para um segundo conjunto de trabalhos em municípios do estado de
Morelos (México). A caracterização da vulnerabilidade sísmica de mais de 160 construções permitiu a
avaliação da representatividade do método paramétrico pela comparação entre os níveis de dano teórico
e os danos observados depois do terramoto de Puebla-Morelos (2017). Esta comparação foi a base para
efetuar processos de calibração e ajuste assistidos por algoritmos de aprendizagem de máquina (Machine
Learning), fornecendo bases para o desenvolvimento de modelos de vulnerabilidade à medida (mediante
o uso de Inteligência Artificial), apoiados nas evidências de eventos sísmicos prévios.Strong seismic events like the ones of Türkiye-Syria (2023) or Mexico (2017) should guide our attention
to the design and implementation of proactive actions aimed to identify vulnerable assets. This work is
aimed to propose a suitable and easy-to-implement workflow for performing large-scale seismic vulnerability
assessments in historic environments by means of digital tools. A vulnerability-oriented model based
on parameters is adopted given its affinity with the Mexican Catalogue of Historical Monuments. A first
large-scale implementation of this method in the historical city of Atlixco (Puebla, Mexico) demonstrated its
suitability and some limitations, which lead to develop a strategy for quantifying and involving the epistemic
uncertainties found during the data acquisition process. Given the volume of data that these analyses involve,
it was necessary to develop robust data acquisition, storing and management strategies. The use
of Geographical Information System environments together with customised Python-based programs and
cloud-based distribution permitted to assemble urban databases for facilitating field data acquisition, performing
vulnerability and damage calculations, and representing outcomes. This development was the
base for performing a second large-scale assessment in selected municipalities of the state of Morelos
(Mexico). The characterisation of the seismic vulnerability of more than 160 buildings permitted to assess
the representativeness of the parametric vulnerability approach by comparing the theoretical damage estimations against the damages observed after the Puebla-Morelos 2017 Earthquakes. Such comparison is
the base for performing a Machine Learning assisted process of calibration and adjustment, representing
a feasible strategy for calibrating these vulnerability models by using Machine-Learning algorithms and the
empirical evidence of damage in post-seismic scenarios.This work was partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit
Institute for Sustainability and Innovation in Structural Engineering (ISISE), reference UIDB/04029/2020.
This research had financial support provided by the Portuguese Foundation of Science and Technology
(FCT) through the Analysis and Mitigation of Risks in Infrastructures (InfraRisk) program under the PhD
grant PD/BD/150385/2019
Spatially Resolved Chiroptical Spectroscopies Emphasizing Recent Applications to Thin Films of Chiral Organic Dyes
Instrumental techniques able to identify and structurally characterize the aggregation states in thin films of chiral organic π-conjugated materials, from the first-order supramolecular arrangement up to the microscopic and meso-scopic scale, are very helpful for clarifying structure-property relationships. Chiroptical imaging is currently gaining a central role, for its ability of mapping local supramolecular structures in thin films. The present review gives an overview of electronic circular dichroism imaging (ECDi), circularly polarized luminescence imaging (CPLi), and vibrational circular dichroism imaging (VCDi), with a focus on their applications on thin films of chiral organic dyes as case studies
Active SLAM: A Review On Last Decade
This article presents a comprehensive review of the Active Simultaneous
Localization and Mapping (A-SLAM) research conducted over the past decade. It
explores the formulation, applications, and methodologies employed in A-SLAM,
particularly in trajectory generation and control-action selection, drawing on
concepts from Information Theory (IT) and the Theory of Optimal Experimental
Design (TOED). This review includes both qualitative and quantitative analyses
of various approaches, deployment scenarios, configurations, path-planning
methods, and utility functions within A-SLAM research. Furthermore, this
article introduces a novel analysis of Active Collaborative SLAM (AC-SLAM),
focusing on collaborative aspects within SLAM systems. It includes a thorough
examination of collaborative parameters and approaches, supported by both
qualitative and statistical assessments. This study also identifies limitations
in the existing literature and suggests potential avenues for future research.
This survey serves as a valuable resource for researchers seeking insights into
A-SLAM methods and techniques, offering a current overview of A-SLAM
formulation.Comment: 34 pages, 8 figures, 6 table
Polymeric semiconductor and transition-metal dichalcogenide nanocomposites for inkjet-printed thin-film transistor devices
Patterned using subtractive processes, conventional thin-film deposition techniques inevitably require high-vacuum deposition and photolithography to define functional layers to create a device structure. Inkjet printing technology has received considerable attention to realize low-cost and potential mass production of large-area electronics at low temperatures using an additive process approach. However, the materials used in the printing process are based on solution-based electronic inks formulated with organic electronic materials. Among them, conjugated polymers are widely used as a semiconductor for thin-film transistor (TFT) applications, but they possess poor charge transport properties compared to other single or polycrystalline inorganic semiconductors. Moreover, the inkjet printing method has a weakness for depositing polymeric solution that form thin films having a highly ordered molecular structure.
To overcome this limitation when using printed polymers, a hybrid organic/inorganic semiconductor ink was explored. The hybrid semiconductor ink was prepared by mixing two different materials, molybdenum disulfide (MoS₂) nanosheets and solution-based poly(3-hexylthiopene-2,5-diyl) (P3HT), the former is a two-dimensional semiconductor and the latter a conjugated polymer. To enhance the level of exfoliation and stability of MoS₂ nanosheets in P3HT, the surfactant trichloro(dodecyl)silane (DDTS), was used to functionalize the MoS₂ surface. Printed TFTs using the nanosheet suspension were found to enhance the field-effect mobility by approximately 3× compared to TFTs without the suspension. The introduced single-crystalline MoS₂ nanosheets in the P3HT matrix improved the electrical and structural properties of the inkjet-printed thin-film polymer.
Based on these findings and insights, the observed effects can be extended to second-generation polymeric semiconductors, specifically the donor-acceptor (D-A) co-polymers. These materials are renowned for exhibiting the highest mobilities among printable polymers while maintaining ambipolarity, a desirable trait for configuring complementary metal-oxide-semiconductor (CMOS) circuits. In light of this, novel nanocomposite semiconductor inks were developed to demonstrate the influence of 2D nanoparticles on the electronic properties of D-A copolymers, diketopyrrolopyrrole-thieno[3,2-b]thiophene (DPPT-TT). Printed TFTs using this new hybrid semiconductor showed that the field-effect mobility of the devices increased by 33 % and 140 % in both hole (p-type) and electron (n-type) transports, respectively. Atomic force microscopy (AFM) results of the printed hybrid thin film revealed that strongly aggregated polymer domains were observed in films containing the MoS₂ nanosheets. In ultraviolet–visible–near infrared spectroscopy (UV-vis-NIR) measurement, increased intensity of 0-0 and 0-1 peaks from hybrid film indicates improved charge transport was due to enhanced intermolecular charge transfer in the microstructure of the polymer film. Furthermore, the incorporation of hybrid nanocomposites proved particularly beneficial for inkjet-printed TFTs utilizing metal electrodes, as the latter had a tendency to augment contact resistance and thereby compromise device performance. However, the introduction of hybrid nanocomposites effectively counteracted the performance degradation arising from the printed metal electrodes by enhancing the crystallinity of the polymeric film. Moreover, these findings also highlight the feasibility of employing lower sintering temperatures for inkjet-printed metal electrodes. This is attributed to the fact that the result of increased contact resistance associated with lower sintering temperatures can be effectively mitigated by the nanocomposite semiconductor. Consequently, an overall enhancement in device performance was achieved by applying the hybrid nanocomposite ink. This study elucidated the advantageous influence of solution-processed MoS₂ nanosheets on the crystallinity and electrical properties of polymeric thin films, consequently leading to significant improvements in the performance parameters of inkjet-printed TFTs
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