The dissertation investigates the issues of analyzing a digital Sigma-Delta digital-to-analog converter (DAC) for audio power amplifiers. The main objects of research include a digital Sigma-Delta audio power DAC, improvement of its structure and an experimental research. The primary purpose of the dissertation is to suggest methods for improvement the structure of digital Sigma-Delta audio power DAC interpolator and the converter analysis. / Disertacijoje nagrinėjami Sigma-Delta skaitmeniniai-analoginiai (skaičiaus-analogo, SA) keitikliai garso galios stiprintuvams. Pagrindinis tyrimų objektas – skaitmeninis Sigma-Delta garso galios SA keitiklis, jo sandaros tobulinamas bei eksperimentinis tyrimas. Disertacijos tikslas – pasiūlyti skaitmeninio Sigma-Delta garso galios SA keitiklio interpoliatoriaus struktūros tobulinimo bei keitiklio tyrimo metodus.

Com as evoluções tecnológicas nas áreas de hardware, microeletrônica, sistemas de informação e computação, o conceito de sistemas ciberfísicos (do inglês Cyber-Physical Systems) vem ganhando importância. Este sistemas se referem à junção entre sistemas computacionais distribuídos e processos físicos da natureza e, são base fundamental para a nova revolução industrial que esta sendo introduzida. Esta revolução industrial é marcada pela completa descentralização do controle dos processos produtivos e uma proliferação de dispositivos inteligentes interconectados, ao longo de toda a cadeia de produção e logística. Sistemas de automação, e particularmente os sistemas de automação industrial, nos quais elementos computacionais controlam e automatizam a execução de processos físicos em plantas industriais, são um exemplo de sistemas ciber-físicos. Com isso, percebe-se que é necessário relacionar objetos físicos a informações associadas a este objeto no mundo cibernético. Para isso, destaca-se o conceito e o uso do Digital Twin, que é uma representação virtual de objetos físicos. O Digital Twin possibilita a virtualização e centralização do controle no produto. Este estudo irá explorar uma metodologia de modelagem genérica e flexível para o Digital Twin usando a ferramenta AutomationML e propor uma arquitetura de comunicação para a troca de dados sob a ótica de Cyber Physical Systems. Com a implementação dessa metodologia, pretende-se validar o conceito proposto e oferecer um método de modelagem e configuração para obter dados, extrair conhecimento e proporcionar sistemas de visualização para os usuários. / With technological advances in the fields of hardware, microelectronics and computer systems, Cyber Physical Systems is a new concept that is gaining importance. This systems are integrations of computation, networking, and physical processes. Cyber Physical Systems are one of the pillars for the new industrial revolution, and it is marked by the complete decentralization of the control of production processes and, marked by a proliferation of interconnected intelligent devices throughout the production and logistics chain. Embedded computers and networks monitor and control the physical processes, with feedback loops where physical processes affect computations and vice versa. A industrial automation system, is an example of cyber physical systems where computational elements control and automate the execution of physical processes in industrial plants. Thus, it is clear the need to relate physical objects to information associated with this object in the cyber world. For this, this work pretends to use the concept of Digital Twin, that is a virtual representation of physical objects. Digital Twin enables the virtualization of physical components and descentralization of control. This study will explore a generic and flexible modeling methodology for Digital Twin using the AutomationML tool. Also this work proposes a communication architecture for the exchange of data from the perspective of Cyber Physical Systems. With the implementation of this methodology, we intend to validate the proposed concept and offer a modeling and configuration method to obtain data, extract knowledge and provide visualization systems for users.

Com as evoluções tecnológicas nas áreas de hardware, microeletrônica, sistemas de informação e computação, o conceito de sistemas ciberfísicos (do inglês Cyber-Physical Systems) vem ganhando importância. Este sistemas se referem à junção entre sistemas computacionais distribuídos e processos físicos da natureza e, são base fundamental para a nova revolução industrial que esta sendo introduzida. Esta revolução industrial é marcada pela completa descentralização do controle dos processos produtivos e uma proliferação de dispositivos inteligentes interconectados, ao longo de toda a cadeia de produção e logística. Sistemas de automação, e particularmente os sistemas de automação industrial, nos quais elementos computacionais controlam e automatizam a execução de processos físicos em plantas industriais, são um exemplo de sistemas ciber-físicos. Com isso, percebe-se que é necessário relacionar objetos físicos a informações associadas a este objeto no mundo cibernético. Para isso, destaca-se o conceito e o uso do Digital Twin, que é uma representação virtual de objetos físicos. O Digital Twin possibilita a virtualização e centralização do controle no produto. Este estudo irá explorar uma metodologia de modelagem genérica e flexível para o Digital Twin usando a ferramenta AutomationML e propor uma arquitetura de comunicação para a troca de dados sob a ótica de Cyber Physical Systems. Com a implementação dessa metodologia, pretende-se validar o conceito proposto e oferecer um método de modelagem e configuração para obter dados, extrair conhecimento e proporcionar sistemas de visualização para os usuários. / With technological advances in the fields of hardware, microelectronics and computer systems, Cyber Physical Systems is a new concept that is gaining importance. This systems are integrations of computation, networking, and physical processes. Cyber Physical Systems are one of the pillars for the new industrial revolution, and it is marked by the complete decentralization of the control of production processes and, marked by a proliferation of interconnected intelligent devices throughout the production and logistics chain. Embedded computers and networks monitor and control the physical processes, with feedback loops where physical processes affect computations and vice versa. A industrial automation system, is an example of cyber physical systems where computational elements control and automate the execution of physical processes in industrial plants. Thus, it is clear the need to relate physical objects to information associated with this object in the cyber world. For this, this work pretends to use the concept of Digital Twin, that is a virtual representation of physical objects. Digital Twin enables the virtualization of physical components and descentralization of control. This study will explore a generic and flexible modeling methodology for Digital Twin using the AutomationML tool. Also this work proposes a communication architecture for the exchange of data from the perspective of Cyber Physical Systems. With the implementation of this methodology, we intend to validate the proposed concept and offer a modeling and configuration method to obtain data, extract knowledge and provide visualization systems for users.

Users and providers benefit considerably from public Wi-Fi hotspots. Users receive wireless Internet access and providers draw new prospective customers. While users are able to enjoy the ease of Wi-Fi Internet hotspot networks in public more conveniently, they are more susceptible to a particular type of fraud and identify theft, referred to as evil twin attack (ETA). Through setting up an ETA, an attacker can intercept sensitive data such as passwords or credit card information by snooping into the communication links. Since the objective of free open (unencrypted) public Wi-Fi hotspots is to provide ease of accessibility and to entice customers, no security mechanisms are in place. The public’s lack of awareness of the security threat posed by free open public Wi-Fi hotspots makes this problem even more heinous. Client-side systems to help wireless users detect and protect themselves from evil twin attacks in public Wi-Fi hotspots are in great need. In this dissertation report, the author explored the problem of the need for client-side detection systems that will allow wireless users to help protect their data from evil twin attacks while using free open public Wi-Fi. The client-side evil twin attack detection system constructed as part of this dissertation linked the gap between the need for wireless security in free open public Wi-Fi hotspots and limitations in existing client-side evil twin attack detection solutions. Based on design science research (DSR) literature, Hevner’s seven guidelines of DSR, Peffer’s design science research methodology (DSRM), Gregor’s IS design theory, and Hossen & Wenyuan’s (2014) study evaluation methodology, the author developed design principles, procedures and specifications to guide the construction, implementation, and evaluation of a prototype client-side evil twin attack detection artifact. The client-side evil twin attack detection system was evaluated in a hotel public Wi-Fi environment. The goal of this research was to develop a more effective, efficient, and practical client-side detection system for wireless users to independently detect and protect themselves from mobile evil twin attacks while using free open public Wi-Fi hotspots. The experimental results showed that client-side evil twin attack detection system can effectively detect and protect users from mobile evil twin AP attacks in public Wi-Fi hotspots in various real-world scenarios despite time delay caused by many factors.

This is a study exploring how robust one feature descriptors, scale invariant feature transform (SIFT), and one feature detector, feature accelerated segmentation test (FAST), are in terms of handling fetoscopic acquired data when mosaicing. Today’s treatment of severe Twin-to-Twin Transfusion Syndrome at Karolinska University Hospital is fetoscopic guided laser occlusion of chorioangiopagous vessels (FLOC) where intersecting blood vessels causing a transfusion (Anastomoses) in between the fetuses are occluded. These blood vessels are located somewhere on the placenta. The fetoscopy includes navigation of a relatively large area where the field of view (FOV) is limited. The limited FOV during the fetoscopy makes it cumbersome to navigate and identify intersected blood vessels. The motivation of this study is to explore ways of dealing with the complications during FLOC by mosaicing an overview of the placenta that can be used as an assisting map to make the procedure safer by improving navigation of the fetoscope and identification of blood vessels during FLOC. In this study, the steps of mosaicing are defined based on mosaicing frameworks to explore how these methods perform in terms of being able to mosaic a map of the placenta. The methods have been tested on non-fetoscopic acquired data as well as fetoscopic acquired data to create a relative measure in between the two. Three tests on non- fetoscopic data were performed to explore how well the methods handled mosaicing of data with distinctive characteristics. The same methods were then tested on unprocessed fetoscopic data before being tested on preprocessed fetoscopic data to see if the results were affected by external preprocessing. The results showed that there were differences in between the methods. SIFT and FAST showed that they have potential of mosaicing non-fetoscopic data of varying extent. SIFT gave an impression of being more robust during all of the tests. SIFT especially performed better during the tests on data with few potential keypoints which is an advantage when speaking of fetoscopic acquired data. SIFT also managed to mosaic a larger area than FAST when mosaicing preprocessed fetoscopic data. Preprocessing the data improved the mosaicing when using SIFT but further improvements are needed. / Denna studie utforskar hur robust en intressepunktsbeskrivare, scale invariant feature transform (SIFT), och enintressepunktsdetektor, feature accelerated segmentation test (FAST), hanterar digitala bilder insamlade av ett fetoskop med syfte att sy ihop dessa till en översiktskarta. Dagens behandling av tvillingtransfusionsyndrom vid Karolinska Universitetssjukhuset är fetoscopic guided laser occlusion of chorioangiopagous vessels (FLOC). Under denna fetoskopi bränner man och därmed blockerar korsande blodkärl som orsakar en transfusion (anastomoses) och obalans i blodomloppet mellan två tvillingfoster. Dessa blodkärl är lokaliserade på placentan. Fetoskopin omfattar navigering av en relativt stor area med ett begränsat synfält. Det begränsade synfältet under FLOC gör det svårt att orientera fetoskopet och identifiera korsande blodkärl som orsakar transfusionen. Syftet med studien är att utforska ett sätt att hantera komplikationerna med FLOC igenom att utforska sätt att skapa en översiktskarta av placentan under FLOC. Denna översiktskarta kan nyttjas under FLOC och därmed göra proceduren säkrare igenom att kartan underlättar orienteringen av fetoskopet och identifiering av orsakande blodkärl. I denna studie är stegen för att skapa en översiktskarta baserade på olika datorseende ramverk för att se hur dessa tillvägagångssätt presterar när det gäller att skapa en översiktskarta. Metoderna för att skapa en översiktskarta har testats på data insamlad med webkamera och data insamlad med fetoskop för att skapa en relativ uppfattning om hur de står sig beroende på indata. Tre tester på data insamlad med webkamera genomfördes för att utforska hur väl metoderna hanterade data med många potentiella intressepunkter, rörelse orsakad av handhållen enhet/kamera, repetitiva mönster, översiktskartor som resulterande i större upplösning, och liten möjlighet att hitta intressepunkter. Samma metoder testades sedan på icke behandlad data insamlad med fetoskop innan den testades på förbehandlad data insamlad med fetoskop för att se förbehandlingensnödvändighet och prestation. Resultaten visar att det är skillnader mellan de två metoderna använda i denna studie, både när det gäller data insamlad med fetoskop och webkamera. SIFT och FAST visar potential av olika grad när det gäller att skapa en översiktskarta med data insamlad av webkamera. SIFT visade sig vara mer robust under alla tester inklusive data insamlad med fetoskop. SIFT presterade speciellt bättre under testen som omfattade få antal möjliga intressepunkter vilket är en fördel när det gäller data insamlad med fetoskop. SIFT lyckades också skapa översiktskartor med större area än FAST när förbehandlad fetoskopisk data testades. När det gäller SIFT så visade resultaten en förbättring när data insamlad med fetoskop förbehandlades men att ytterligare förbättringar är nödvändiga.

Cyber-physical systems (CPSs) are used in several industries, such as healthcare, automotive, manufacturing, and more. The fact that CPSs often contain components integrated via communication networks means that malicious actors can exploit vulnerabilities in these components through cyber attacks. CRYSTAL Framework has been shown in previous research to be able to detect cyber attacks on CPSs. However, this has only been proven in simulation. Our research builds upon these previous research as we aim to prove that CRYSTAL Framework is a viable method for monitoring real systems to detect abnormal behaviours.  The Tiny Twin is an abstract behavioral model that defines normal running behaviour of a system, which can then be used by to compare the current state of a monitored system to detect possible attacks and abnormal behaviours. We built a monitor that integrates such a Tiny Twin, working by passively listening on input and output of components in a monitored system. We designed and implemented two different scenarios, a security alarm system and a temperature control system (TCS), to test the CRYSTAL Framework. In testing both implemented scenarios our monitor successfully detected all but one attacks during runtime by comparing the system's current state with the expected state as defined in the Tiny Twin.

Humans are social by nature, and the physical distancing due to COVID has converted many of our daily interactions into virtual ones. Among the negative consequences of this, we find the lack of an element that is essential to humans' well-being, which is the physical touch. With more interactions shifting towards the digital world of the metaverse, we want to provide individuals with the means to include the physical touch in their interactions. We explore the Digital Twin technology's prospect to support in reducing the impact of this on humans. We provide a definition of the concept of Robo Twin and explain its role in mediating human interactions. Besides, we survey research works related to Digital Twin's physical representation with a focus on under-actuated Digital Twin's robotic arms. In this thesis, we first provide findings from the literature, to support researchers' decisions in the adoption and use of designs and implementations of Digital Twin's robotic arms, and to inform future research on current challenges and gaps in existing research works. Subsequently, we design and implement two right-handed under-actuated Digital Twin's robotic arms to mediate the physical interaction between two individuals by allowing them to perform a handshake while they are physically distanced. This experiment served as a proof of concept for our proposed idea of Robo Twin. The findings are very promising as our evaluation shows that the participants are highly interested in using our system to make a handshake with their loved ones when they are physically separated. With this Robo Twin Arm system, we also find a correlation between the handshake characteristics and gender and/or personality traits of the participants from the quantitative handshake data collected during the experiment. Moreover, it is a step towards the design and development of Digital Twin's under-actuated robotic arms and ways to enhance the overall user experience with such a system.

<p>The modern world of manufacturing is in the middle of an industrial revolution with the digital and physical worlds integrating through cyber-physical systems.  Through a virtual model that is able to communicate with its physical system known as the Digital Twin, catered decisions can be made based on the current state of the system.  The digital twin presents immense opportunities and challenges as there is a greater need to understand how these new technologies work together. </p> <p><br></p> <p>This thesis is an experimental investigation of the characteristics of the essential components of the Digital Twin.  A Digital Twin Framework is developed to explore the impacts of model accuracy and update frequency on the system’s performance measure. A simple inventory management system and a more complex manufacturing plant is modeled through the framework providing a method to study the interactions of the physical and digital systems with empirical data.</p> <p><br></p> <p><br></p> <p>As the decision policies are affected by the state changes in the system, designing the Digital Twin must account for the direct and indirect impact of its components. </p> <p>Furthermore, we show the importance of communication and information exchange between the Digital Twin and its physical system.  A key characteristic for developing and applying a digital twin is to monitor the update frequency and its impact on performance.  Through the study there are implications of optimal combinations of the digital twin components and how the physical system responds.  There are also limits to how effective the Digital Twin can be in certain instances and is an area of research that needs further investigation.  </p> <p><br></p> <p>The goal of this work is to help practitioners and researchers implement and use the Digital Twin more effectively.  Better understanding the interactions of the model components will help guide designing Digital Twins to be more effective as they become an integral part of the future of manufacturing.</p>

The Digital Twin (DT), a tool dedicated for decision-making and management, has recently started making its way into today’s digitalized world. It is described as a digital representation of a physical object, system, or process, mimicking its physical counterpart using real-time data and monitoring which can be used for decision-making, optimization, and designing (Singh et al., 2021). Not only can DTs be used for a single object, but can also be implemented on whole cities generating valuable insights improving a city’s management, operability, and realization. However, due to the infancy of the concept, further research is required to presuppose accurate city DTs. This can be done by exploring the implementation of DTs in the different sectors of a city (Shahat et al., 2021). Therefore, this report aims to identify areas in which an university in Sweden could benefit from the implementation of a DT, contributing to the knowledge gap regarding DT implementation in the education sector and furthermore the city DT development as a whole. To identify areas in which the university could benefit from a DT, semi-structured interviews were held with chief positions at the university. The aim of the interviews was to identify the university’s main challenges, and then map the challenges to DT solutions in literature and previous research. The identified challenges at the university were Decision-making processes, Recruitment procedures and forecasting, Quality assurance, and Unclear action plan on becoming a sustainable campus. The challenges Decision-making processes and Recruitment procedures and forecasting were mapped to the Digital Twin of an Organization (DTO). This kind of DT can help organizations with, for instance, responding to changes and delivering value for customers (van der Aalst et al., 2021). The last challenge, Unclear action plan on becoming a sustainable campus, was connected to a DT that can help the university in enhancing its energy management.

Zhan Siyan. / "November 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (p. 133-152) / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.