4,971 research outputs found
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
Novel 129Xe Magnetic Resonance Imaging and Spectroscopy Measurements of Pulmonary Gas-Exchange
Gas-exchange is the primary function of the lungs and involves removing carbon dioxide from the body and exchanging it within the alveoli for inhaled oxygen. Several different pulmonary, cardiac and cardiovascular abnormalities have negative effects on pulmonary gas-exchange. Unfortunately, clinical tests do not always pinpoint the problem; sensitive and specific measurements are needed to probe the individual components participating in gas-exchange for a better understanding of pathophysiology, disease progression and response to therapy.
In vivo Xenon-129 gas-exchange magnetic resonance imaging (129Xe gas-exchange MRI) has the potential to overcome these challenges. When participants inhale hyperpolarized 129Xe gas, it has different MR spectral properties as a gas, as it diffuses through the alveolar membrane and as it binds to red-blood-cells. 129Xe MR spectroscopy and imaging provides a way to tease out the different anatomic components of gas-exchange simultaneously and provides spatial information about where abnormalities may occur.
In this thesis, I developed and applied 129Xe MR spectroscopy and imaging to measure gas-exchange in the lungs alongside other clinical and imaging measurements. I measured 129Xe gas-exchange in asymptomatic congenital heart disease and in prospective, controlled studies of long-COVID. I also developed mathematical tools to model 129Xe MR signals during acquisition and reconstruction. The insights gained from my work underscore the potential for 129Xe gas-exchange MRI biomarkers towards a better understanding of cardiopulmonary disease. My work also provides a way to generate a deeper imaging and physiologic understanding of gas-exchange in vivo in healthy participants and patients with chronic lung and heart disease
Methods and Results of Power Cycling Tests for Semiconductor Power Devices
This work intends to enhance the state of the research in power cycling tests with statements on achievable measurement accuracy, proposed test bench topologies and recommendations on improved test strategies for various types of semiconductor power devices.
Chapters 1 and 2 describe the current state of the power cycling tests in the context of design for reliability comprising applicable standards and lifetime models.
Measurement methods in power cycling tests for the essential physical parameters are explained in chapter 3. The dynamic and static measurement accuracy of voltage, current and temperature are discussed. The feasibly achievable measurement delay tmd of the maximal junction temperature Tjmax, its consequences on accuracy and methods to extrapolate to the time point of the turn-off event are explained. A method to characterize the thermal path of devices to the heatsink via measurements of the thermal impedance Zth is explained.
Test bench topologies starting from standard setups, single to multi leg DC benches are discussed in chapter 4. Three application-closer setups implemented by the author are explained. For tests on thyristors a test concept with truncated sinusoidal current waveforms and online temperature measurement is introduced. An inverter-like topology with actively switching IGBTs is presented. In contrast to standard setups, there the devices under test prove switching capability until reaching the end-of-life criteria. Finally, a high frequency switching topology with low DC-link voltage and switching losses contributing significantly to the overall power losses is presented providing new degrees of freedom for setting test conditions.
The particularities of semiconductor power devices in power cycling tests are thematized in chapter 5. The first part describes standard packages and addressed failure mechanisms in power cycling. For all relevant power electronic devices in silicon and silicon carbide, the devicesâ characteristics, methods for power cycling and their consequences for test results are explained.
The work is concluded and suggestions for future work are given in chapter 6.:Abstract 1
Kurzfassung 3
Acknowledgements 5
Nomenclature 10
Abbreviations 10
Symbols 12
1 Introduction 19
2 Applicable Standards and Lifetime Models 25
3 Measurement parameters in power cycling tests 53
4 Test Bench Topologies 121
5 Semiconductor Power Devices in Power Cycling 158
6 Conclusion and Outlook 229
References 235
List of Publications 253
Theses 257Diese Arbeit bereichert den Stand der Wissenschaft auf dem Gebiet von Lastwechseltests mit Beiträgen zu verbesserter Messgenauigkeit, vorgeschlagenen Teststandstopologien und verbesserten Teststrategien fßr verschiedene Arten von leistungselektronischen Bauelementen. Kurzgefasst der Methodik von Lastwechseltests.
Das erste Themengebiet in Kapitel 1 und Kapitel 2 beschreibt den aktuellen Stand zu Lastwechseltests im Kontext von Design fßr Zuverlässigkeit, welcher in anzuwendenden Standards und publizierten Lebensdauermodellen dokumentiert ist.
Messmethoden fĂźr relevante physikalische Parameter in Lastwechseltests sind in Kapitel 3. erläutert. Zunächst werden dynamische und statische Messgenauigkeit fĂźr Spannung, Strom und Temperaturen diskutiert. Die tatsächlich erreichbare MessverzĂśgerung tMD der maximalen Sperrschichttemperatur Tjmax und deren Auswirkung auf die Messgenauigkeit der Lastwechselfestigkeit wird dargelegt. Danach werden Methoden zur RĂźckextrapolation zum Zeitpunkt des Abschaltvorgangs des Laststroms diskutiert. SchlieĂlich wird die Charakterisierung des Wärmepfads vom Bauelement zur Wärmesenke mittels Messung der thermischen Impedanz Zth behandelt.
In Kapitel 4 werden Teststandstopologien beginnend mit standardmäĂig genutzten ein- und mehrsträngigen DC-Testständen vorgestellt. Drei vom Autor umgesetzte anwendungsnahe Topologien werden erklärt. FĂźr Tests mit Thyristoren wird ein Testkonzept mit angeschnittenem sinusfĂśrmigem Strom und in situ Messung der Sperrschichttemperatur eingefĂźhrt. Eine umrichterähnliche Topologie mit aktiv schaltenden IGBTs wird vorgestellt. Zuletzt wird eine Topologie mit hoch frequent schaltenden PrĂźflingen an niedriger Gleichspannung bei der Schaltverluste signifikant zur Erwärmung der PrĂźflinge beitragen vorgestellt. Dies ermĂśglicht neue Freiheitsgrade um Testbedingungen zu wählen.
Die Besonderheiten von leistungselektronischen Bauelementen werden in Kapitel 5 thematisiert. Der erste Teil beschreibt Gehäusetypen und adressierte Fehlermechanismen in Lastwechseltests. Fßr alle untersuchten Bauelementtypen in Silizium und Siliziumkarbid werden Charakteristiken, empfohlene Methoden fßr Lastwechseltests und Einflßsse auf Testergebnisse erklärt.
Die Arbeit wird in Kapitel 6 zusammengefasst und Vorschläge zu kßnftigen Arbeiten werden unterbreitet.:Abstract 1
Kurzfassung 3
Acknowledgements 5
Nomenclature 10
Abbreviations 10
Symbols 12
1 Introduction 19
2 Applicable Standards and Lifetime Models 25
3 Measurement parameters in power cycling tests 53
4 Test Bench Topologies 121
5 Semiconductor Power Devices in Power Cycling 158
6 Conclusion and Outlook 229
References 235
List of Publications 253
Theses 25
A Design Science Research Approach to Smart and Collaborative Urban Supply Networks
Urban supply networks are facing increasing demands and challenges and thus constitute a relevant field for research and practical development. Supply chain management holds enormous potential and relevance for society and everyday life as the flow of goods and information are important economic functions. Being a heterogeneous field, the literature base of supply chain management research is difficult to manage and navigate. Disruptive digital technologies and the implementation of cross-network information analysis and sharing drive the need for new organisational and technological approaches. Practical issues are manifold and include mega trends such as digital transformation, urbanisation, and environmental awareness.
A promising approach to solving these problems is the realisation of smart and collaborative supply networks. The growth of artificial intelligence applications in recent years has led to a wide range of applications in a variety of domains. However, the potential of artificial intelligence utilisation in supply chain management has not yet been fully exploited. Similarly, value creation increasingly takes place in networked value creation cycles that have become continuously more collaborative, complex, and dynamic as interactions in business processes involving information technologies have become more intense.
Following a design science research approach this cumulative thesis comprises the development and discussion of four artefacts for the analysis and advancement of smart and collaborative urban supply networks. This thesis aims to highlight the potential of artificial intelligence-based supply networks, to advance data-driven inter-organisational collaboration, and to improve last mile supply network sustainability. Based on thorough machine learning and systematic literature reviews, reference and system dynamics modelling, simulation, and qualitative empirical research, the artefacts provide a valuable contribution to research and practice
Corporate Social Responsibility: the institutionalization of ESG
Understanding the impact of Corporate Social Responsibility (CSR) on firm performance as it relates to industries reliant on technological innovation is a complex and perpetually evolving challenge. To thoroughly investigate this topic, this dissertation will adopt an economics-based structure to address three primary hypotheses. This structure allows for each hypothesis to essentially be a standalone empirical paper, unified by an overall analysis of the nature of impact that ESG has on firm performance. The first hypothesis explores the evolution of CSR to the modern quantified iteration of ESG has led to the institutionalization and standardization of the CSR concept. The second hypothesis fills gaps in existing literature testing the relationship between firm performance and ESG by finding that the relationship is significantly positive in long-term, strategic metrics (ROA and ROIC) and that there is no correlation in short-term metrics (ROE and ROS). Finally, the third hypothesis states that if a firm has a long-term strategic ESG plan, as proxied by the publication of CSR reports, then it is more resilience to damage from controversies. This is supported by the finding that pro-ESG firms consistently fared better than their counterparts in both financial and ESG performance, even in the event of a controversy. However, firms with consistent reporting are also held to a higher standard than their nonreporting peers, suggesting a higher risk and higher reward dynamic. These findings support the theory of good management, in that long-term strategic planning is both immediately economically beneficial and serves as a means of risk management and social impact mitigation. Overall, this contributes to the literature by fillings gaps in the nature of impact that ESG has on firm performance, particularly from a management perspective
Strategies for Early Learners
Welcome to learning about how to effectively plan curriculum for young children. This textbook will address: ⢠Developing curriculum through the planning cycle ⢠Theories that inform what we know about how children learn and the best ways for teachers to support learning ⢠The three components of developmentally appropriate practice ⢠Importance and value of play and intentional teaching ⢠Different models of curriculum ⢠Process of lesson planning (documenting planned experiences for children) ⢠Physical, temporal, and social environments that set the stage for childrenâs learning ⢠Appropriate guidance techniques to support childrenâs behaviors as the self-regulation abilities mature. ⢠Planning for preschool-aged children in specific domains including o Physical development o Language and literacy o Math o Science o Creative (the visual and performing arts) o Diversity (social science and history) o Health and safety ⢠Making childrenâs learning visible through documentation and assessmenthttps://scholar.utc.edu/open-textbooks/1001/thumbnail.jp
Transformation of the business model to establish sustainable value in the consumer durables super store industry of Sri Lanka
The business model of an organization, operates as the fundamental blue print of the planning process, which shapes the nature of the strategies executed during the course of operation. These strategies in turn are responsible for the value creation or value erosion that takes place during the operation of the organization determining its sustainability, and in a broader context the sustainability of the industry. The research is done for the Consumer Durables Super Store (CDSS) industry of Sri Lanka concerning the existing business model, the value erosion occurring as a result of it and the risk it carries to the sustainability of the industry. The theoretical aspect of the research to develop a relationship based business model was anchored on the understanding of existing frameworks relating to sustainable value and extracting relevant areas of each of these frameworks (alignment of value, transforming current strategies and service offerings to create sustainable value) to develop a suitable hybrid framework with modifications to the literature to suite the research context.Ten in-depth interviews with CDSS organizational representatives holding leadership, sales and marketing management positions, and two focus group sessions with fifty selected customers were conducted in a virtual environment due to the prevailing pandemic situation. The data collected were analyzed with NVIVO 12, with themes relevant to the research utilized as codes, giving a clear understanding over the buyer and seller purview on the themes of the research. The findings surfaced the value erosion caused due to the financially driven strategies originated from the transactional orientation of the existing business model. The theories adopted to construct the relationship oriented business model to rectify the value erosion taking place, based on sustainable value, value alignment and service offerings, were modified to incorporate âquality of tradeâ to bridge the gap, leading towards the creation and delivery of sustainable value to the buyer-seller eco system of the industry
Early Neanderthal social and behavioural complexity during the Purfleet Interglacial: handaxes in the latest Lower Palaeolithic.
Only a handful of âflagshipâ sites from the Purfleet Interglacial (Marine Isotope Stage 9, c. 350-290,000 years ago) have been properly examined, but the archaeological succession at the proposed type-site at Purfleet suggests a period of complexity and transition, with three techno-cultural groups represented in Britain. The first was a simple toolkit lacking handaxes (the Clactonian), and
the last a more sophisticated technology presaging the coming Middle Palaeolithic (simple prepared core or proto-Levallois technology). Sandwiched between were Acheulean groups, whose handaxes comprise the great majority of the extant archaeological record of the period â these are the focus of this study. It has previously been suggested that some features of the Acheulean in the Purfleet Interglacial were chronologically restricted, particularly the co-occurrence of ficrons and cleavers. These distinctive forms may have exceeded pure functionality and were perhaps imbued with a deeper social and cultural meaning. This study supports both the previously suggested preference for narrow, pointed morphologies, and the chronologically restricted pairing of ficrons and cleavers. By drawing on a wide spatial and temporal range of sites these patterns could be identified beyond the handful of âflagshipâ sites
previously studied. Hypertrophic âgiantsâ have now also been identified as a chronologically restricted form. Greater metrical variability was found than had been anticipated, leading to the creation of two new sub-groups (IA and IB) which are tentatively suggested to represent spatial and
perhaps temporal patterning. The picture in the far west of Britain remains unclear, but the possibility of different Acheulean groups operating in the Solent area, and a late survival of the Acheulean, are both suggested. Handaxes with backing and macroscopic asymmetry may represent prehensile or ergonomic considerations not commonly found on handaxes from earlier interglacial periods. It is argued that these forms anticipate similar developments in the Late Middle Palaeolithic in an example of convergent evolution
World Development Report 2022
This new World Development Report focuses on the interrelated economic risks that households, businesses, financial institutions, and governments worldwide are facing as a consequence of the COVID-19 crisis. The Report offers new insights from research on the
interconnectedness of balance sheets and the potential spillover effects across sectors. It
also offers policy recommendations based on these insights. Specifically, it addresses the
question of how to reduce the financial risks stemming from the extraordinary policies
adopted in response to the COVID-19 crisis while supporting an equitable recovery.
The unfolding COVID-19 pandemic has already led to millions of deaths, job losses,
business failures, and school closings, triggering the most encompassing economic crisis
in almost a century. Poverty rates have soared and inequality has widened both across
and within countries. Disadvantaged groups that had limited financial resilience to begin
with and workers with lower levels of educationâespecially younger ones and womenâ
have been disproportionately affected.
The response by governments has included a combination of cash transfers to households,
credit guarantees for firms, easier liquidity conditions, repayment grace periods for much of
the private sector, and accounting and regulatory forbearance for many financial institutions. Although these actions have helped to partially mitigate the economic and social consequences of the pandemic, they have also resulted in elevated risks, including public overindebtedness, increased financial fragility, and a general erosion in transparency. Emerging
economies have been left with very limited fiscal space, and they will be made even more
vulnerable by the impending normalization of monetary policy in advanced economies.
This Report highlights several priority areas for action.
First is the need for early detection of significant financial risks. Because the balance
sheets of households, firms, financial sector institutions, and governments are tightly
interrelated, risks may be hidden. The share of nonperforming loans has generally
remained below what was feared at the beginning of the crisis. But this could be due to
forbearance policies that delayed debt repayments and relaxed accounting standards.
Firm surveys in emerging economies reveal that many businesses expect to be in payment
arrears in the coming months, and so private debt could suddenly become public debt, as
in many past crises.
The interdependence of economic policies across countries matters as well. Public debt
has reached unprecedented levels. As monetary policy tightens in advanced economies,
interest rates will need to increase in emerging economies as well, and their currencies
will likely depreciate. Higher interest rates make debt service more expensive, reinforcing the trend of recent years, and weaker currencies make debt service more burdensome
relative to the size of the economy. Liquidity problems could suddenly morph into solvency
problems
Towards creating multi-matrix continuous fibre polymer composites using an out-of-vacuum bag process
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