472 research outputs found
Understanding local neuromuscular mechanisms that explain the efficacy of interventions for patellofemoral pain
Patellofemoral pain (PFP) is a common and persistent knee pain complaint among all age ranges, especially highly active people. Multiple approaches have been used to understand symptom persistence, including identifying a mechanism explaining intervention benefits (i.e. changes in specific deficits in groups that show symptoms’ improvement). Research has been conducted to identify the characteristics associated with PFP, but uncertainty regarding local neuromuscular characteristics remain evident. The thesis aimed to a) identify the local neuromuscular characteristics associated with PFP, b) develop an evidence informed laboratory protocol to detect those characteristics, c) establish protocol reliability and feasibility, and d) identify interventions that can target these neuromuscular characteristics. A systematic review with meta-analysis was completed to identify the neuromuscular characteristics of all muscles that cross the knee in people with PFP compared to uninjured groups. Ten deficits within three neuromuscular domains were found. Within the electromyography (EMG) domain, a delay in Vastus medialis (VM) relative to Vastus lateralis (VL) excitation onset, a high Biceps femoris (BF) mean excitation amplitude, and a lower Hoffman-reflex amplitude of VM were identified. Within the muscle performance domain, lower isometric, concentric, and eccentric extensors peak torque and total work, lower concentric flexors peak torque, and lower rate of torque development (RTD) to reach 30%, 60% and 90% of extensors peak torque were identified. Hamstring tightness was identified within muscle flexibility domain. The systematic review was published and the results used to inform testing protocol development. A second systematic review with meta-analysis was conducted to identify interventions that can target the local deficits associated with PFP. The results indicate that currently an intervention that effectively modifies EMG characteristics cannot be identified. Predominantly, exercise interventions have effects on strength and flexibility in PFP. Specifically, hip and knee targeted exercises are found to have a potential mechanism of benefit through both characteristics categories. A unique approach was introduced within the thesis to develop a deficit-detection protocol based on systematic review results. This approach provided a comprehensive analysis of the protocols from the studies that were included in the meta-analysis. A battery of tests was developed and included; a) VM-VL excitation onset timing in step-up task, b) BF mean excitation amplitude in single-leg triple-hop test, c) isometric, d) concentric and e) eccentric extensors peak torque, f) RTD to 30%, 60% and 90% of isometric peak torque, and hamstrings flexibility. Reliability testing of the deficit-detection protocol was conducted with both uninjured and participants with PFP over two phases. Phase one evaluated the original protocols adapted from the review. Phase two was performed on the EMG and RTD domains to explore the effects of signal processing parameters on reliability, such as; onset detection thresholds modification, unnormalised signals, and the addition of absolute RTD. For the PFP group: reliable results were demonstrated for concentric and eccentric extensors peak torque; RTD of the quadriceps at 25ms, 50ms and 90% of peak torque; and hamstrings flexibility. The uninjured group showed reliable results in: unnormalised BF mean excitation amplitude; all three peak torque tests; RTD to 30% of peak torque and at 150 and 175 milliseconds; and hamstrings flexibility. To establish participant recruitment rate and retention, in addition to the acceptability of the test protocol, a preliminary feasibility study of the deficit-detection protocol was conducted. A sample of 14 participants with PFP were recruited and tested at the Mile-end campus of QMUL before and after a six weeks period. Feasibility results indicate that 25.5% were willing to participate following an online screening process (n=17/55) and 82% met the eligibility criteria following face-to-face assessment (n=14/17). Recruitment rate was 0.5 participants per week and drop-out rate was 35.2% (n=11/17). The results indicate that the protocol did not meet all a-priori feasibility criteria, but the results can inform future research planning. The thesis has successfully identified local deficits associated with PFP, developed a test protocol that demonstrates reliability in evaluating these deficits and assessed the feasibility of the protocol in individuals with PFP. Interventions to cause change within these local deficits have been identified, with gap maps demonstrating where further research is required to better align the mechanisms of treatment effects with specific deficits associated with PFP
Towards a Peaceful Development of Cyberspace - Challenges and Technical Measures for the De-escalation of State-led Cyberconflicts and Arms Control of Cyberweapons
Cyberspace, already a few decades old, has become a matter of course for most of us, part of our everyday life. At the same time, this space and the global infrastructure behind it are essential for our civilizations, the economy and administration, and thus an essential expression and lifeline of a globalized world. However, these developments also create vulnerabilities and thus, cyberspace is increasingly developing into an intelligence and military operational area – for the defense and security of states but also as a component of offensive military planning, visible in the creation of military cyber-departments and the integration of cyberspace into states' security and defense strategies. In order to contain and regulate the conflict and escalation potential of technology used by military forces, over the last decades, a complex tool set of transparency, de-escalation and arms control measures has been developed and proof-tested. Unfortunately, many of these established measures do not work for cyberspace due to its specific technical characteristics. Even more, the concept of what constitutes a weapon – an essential requirement for regulation – starts to blur for this domain. Against this background, this thesis aims to answer how measures for the de-escalation of state-led conflicts in cyberspace and arms control of cyberweapons can be developed. In order to answer this question, the dissertation takes a specifically technical perspective on these problems and the underlying political challenges of state behavior and international humanitarian law in cyberspace to identify starting points for technical measures of transparency, arms control and verification. Based on this approach of adopting already existing technical measures from other fields of computer science, the thesis will provide proof of concepts approaches for some mentioned challenges like a classification system for cyberweapons that is based on technical measurable features, an approach for the mutual reduction of vulnerability stockpiles and an approach to plausibly assure the non-involvement in a cyberconflict as a measure for de-escalation. All these initial approaches and the questions of how and by which measures arms control and conflict reduction can work for cyberspace are still quite new and subject to not too many debates. Indeed, the approach of deliberately self-restricting the capabilities of technology in order to serve a bigger goal, like the reduction of its destructive usage, is yet not very common for the engineering thinking of computer science. Therefore, this dissertation also aims to provide some impulses regarding the responsibility and creative options of computer science with a view to the peaceful development and use of cyberspace
An automatic ANN-based procedure for detecting optimal image sequences supporting LS-PIV applications for rivers monitoring
River flow monitoring has recently experienced rapid development due to advancements in optical methods, which are non-intrusive and enhance safety conditions for operators. Surface velocity fields are obtained recording and analyzing displacements of floating tracer materials, artificially introduced or already present on the water surface. River discharge can be assessed coupling the surface velocity fields with geometric data of a cross section. The accuracy of optical techniques is strongly affected by different environmental and hydraulic factors, and software parameterization, with tracer features that often play a prominent role. An adequate density and spatial distribution of tracer is required to ensure a complete characterization of surface velocity fields. In practical applications such conditions might occur only for a limited portion of the entire acquired images sequence. This work proposes an automatic procedure for identifying and extracting the best portion of a recorded video in terms of seeding characteristics and demonstrates how LS-PIV software performances can be enhanced through this approach. The procedure is implemented through a data-driven empirical approach based on an Artificial Neural Network, trained using data collected during an extensive measurement campaign across different rivers in Sicily (Italy). Performances are evaluated in terms of error in reproducing surface velocity profiles along specific transects, where benchmark profiles derived using an Acoustic Doppler Current Profiler are available. The procedure, also tested via numerical simulations on synthetic image sequences, outperformed an approach based on an existing metric for seeding characterization and represents a simple and useful tool for LS-PIV based applications
Making Presentation Math Computable
This Open-Access-book addresses the issue of translating mathematical expressions from LaTeX to the syntax of Computer Algebra Systems (CAS). Over the past decades, especially in the domain of Sciences, Technology, Engineering, and Mathematics (STEM), LaTeX has become the de-facto standard to typeset mathematical formulae in publications. Since scientists are generally required to publish their work, LaTeX has become an integral part of today's publishing workflow. On the other hand, modern research increasingly relies on CAS to simplify, manipulate, compute, and visualize mathematics. However, existing LaTeX import functions in CAS are limited to simple arithmetic expressions and are, therefore, insufficient for most use cases. Consequently, the workflow of experimenting and publishing in the Sciences often includes time-consuming and error-prone manual conversions between presentational LaTeX and computational CAS formats. To address the lack of a reliable and comprehensive translation tool between LaTeX and CAS, this thesis makes the following three contributions. First, it provides an approach to semantically enhance LaTeX expressions with sufficient semantic information for translations into CAS syntaxes. Second, it demonstrates the first context-aware LaTeX to CAS translation framework LaCASt. Third, the thesis provides a novel approach to evaluate the performance for LaTeX to CAS translations on large-scaled datasets with an automatic verification of equations in digital mathematical libraries. This is an open access book
Brain Computations and Connectivity [2nd edition]
This is an open access title available under the terms of a CC BY-NC-ND 4.0 International licence. It is free to read on the Oxford Academic platform and offered as a free PDF download from OUP and selected open access locations.
Brain Computations and Connectivity is about how the brain works. In order to understand this, it is essential to know what is computed by different brain systems; and how the computations are performed.
The aim of this book is to elucidate what is computed in different brain systems; and to describe current biologically plausible computational approaches and models of how each of these brain systems computes.
Understanding the brain in this way has enormous potential for understanding ourselves better in health and in disease. Potential applications of this understanding are to the treatment of the brain in disease; and to artificial intelligence which will benefit from knowledge of how the brain performs many of its extraordinarily impressive functions.
This book is pioneering in taking this approach to brain function: to consider what is computed by many of our brain systems; and how it is computed, and updates by much new evidence including the connectivity of the human brain the earlier book: Rolls (2021) Brain Computations: What and How, Oxford University Press.
Brain Computations and Connectivity will be of interest to all scientists interested in brain function and how the brain works, whether they are from neuroscience, or from medical sciences including neurology and psychiatry, or from the area of computational science including machine learning and artificial intelligence, or from areas such as theoretical physics
Nonlinear electronic conductivity in lithium niobate domain walls
Applying ferroelectric materials for nanoelectronic circuits opens, next to exploiting completely new functionalities, the possibility of improving resource efficiency in electronic circuits. Due to its defined and easy-to-manipulate domain structure, lithium niobate (LiNbO3, LNO) is a promising candidate to realize such circuits. As a prerequisite, a detailed understanding of the underlying conduction mechanisms is required for a future large scale application.
The main field of attention of this thesis is the domain wall conductivity in lithium niobate, investigated with temperature-dependent dc conductivity measurements as well as higher-harmonic current analysis under alternating-voltage excitation. Thereby the parameters of the electric field are of special interest, comprising the static dc field and both the amplitude and the frequency of the ac excitation voltage. Prior to the analysis of the experimental results, the setups are characterized in depth and a theoretical framework to calculate higher-harmonic current contributions generated by non-ohmic conduction models is derived. In case of high static offset voltages, an ohmic-like conductance is observed, which is ascribed to the intrinsic conductivity of the domain wall. For lower static offset fields, a diode-like current-voltage characteristic is found, originating from the junction of the domain wall and the metallic contact electrode. The results are compared to measurements at an industrial Schottky diode taken under the same conditions. Based on the theory of metal-semiconductor junctions, the effective donor density within the conducting domain wall is estimated to be of the order of 1019/cm3, which agrees well with theoretical calculations in the literature.
An equivalent circuit based on two diodes and two resistors is proposed to model the observed nonohmic conductance. For all experimental techniques, a good agreement between this model and the experimental data is observed, proving especially the non-ohmic conductivity to be of Schottky-type
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 devices’ 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 für 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 für Zuverlässigkeit, welcher in anzuwendenden Standards und publizierten Lebensdauermodellen dokumentiert ist.
Messmethoden für relevante physikalische Parameter in Lastwechseltests sind in Kapitel 3. erläutert. Zunächst werden dynamische und statische Messgenauigkeit für Spannung, Strom und Temperaturen diskutiert. Die tatsächlich erreichbare Messverzögerung tMD der maximalen Sperrschichttemperatur Tjmax und deren Auswirkung auf die Messgenauigkeit der Lastwechselfestigkeit wird dargelegt. Danach werden Methoden zur Rückextrapolation zum Zeitpunkt des Abschaltvorgangs des Laststroms diskutiert. Schließlich wird die Charakterisierung des Wärmepfads vom Bauelement zur Wärmesenke mittels Messung der thermischen Impedanz Zth behandelt.
In Kapitel 4 werden Teststandstopologien beginnend mit standardmäßig genutzten ein- und mehrsträngigen DC-Testständen vorgestellt. Drei vom Autor umgesetzte anwendungsnahe Topologien werden erklärt. Für Tests mit Thyristoren wird ein Testkonzept mit angeschnittenem sinusförmigem Strom und in situ Messung der Sperrschichttemperatur eingeführt. Eine umrichterähnliche Topologie mit aktiv schaltenden IGBTs wird vorgestellt. Zuletzt wird eine Topologie mit hoch frequent schaltenden Prüflingen an niedriger Gleichspannung bei der Schaltverluste signifikant zur Erwärmung der Prüflinge beitragen vorgestellt. Dies ermöglicht 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. Für alle untersuchten Bauelementtypen in Silizium und Siliziumkarbid werden Charakteristiken, empfohlene Methoden für Lastwechseltests und Einflüsse auf Testergebnisse erklärt.
Die Arbeit wird in Kapitel 6 zusammengefasst und Vorschläge zu künftigen 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
Polymères organométalliques de type dicétopyrrolopyrrole trans-bis(phosphine)éthynylplatine(II) pour les cellules solaires organiques
Dans le cadre de cette thèse, il sera question de la conversion de l’énergie solaire en électricité par l’utilisation de cellules solaires organiques (OSCs), plus précisément, sur l’utilisation de polymères et d’oligomères organométalliques de type dicétopyrrolopyrrole trans-bis(phosphine)éthynyl platine(II) (P) comme colorants dans les OSCs. Cette approche a permis d’atteindre des records d’efficacité pour cette catégorie, avec des efficacités allant jusqu’à 13,26%, malgré les faibles rendements rapportés dans le passé pour les motifs [Pt].
Le premier chapitre fait une introduction des concepts généraux retrouvés dans la thèse. Le deuxième chapitre est un article publié en janvier 2020 dans « Journal of Materials Chemistry C ». Ce dernier montre l’utilisation de deux motifs [Pt], l’un comprenant une seule unité dicétopyrrolopyrrole (DPP) par monomère et l’autre en comprenant deux DPPs, comme colorant donneur d’électrons dans des OSCs. Les résultats rapportés comprennent des calculs computationnels sur la nature et le positionnement des orbitales HOMO et LUMO des unités [Pt], des analyses photophysiques sur les polymères à base de [Pt], en absence et en présence d’accepteur d’électrons, et des mesures d’efficacité de conversion énergétique (PCE) lorsqu’ils sont utilisés dans des OSCs. Le troisième chapitre est un article publié en janvier 2021 dans « ACS Applied Polymer Materials ». Ce dernier est la suite directe de l’article présenté au chapitre précédent mais fait cette fois intervenir des groupements agrégants ajoutés aux unités DPPs. Cet ajout permet d’atteindre un PCE record de 13,26%, pour les polymères donneurs d’électrons comprenant du platine. Le quatrième chapitre est un troisième article, publié en janvier 2022 dans « Journal of Inorganic and Organometallic Polymers and Materials ». Cette fois, l’article explore l’utilisation de différents accepteurs d’électrons utilisés conjointement avec un motif [Pt] et décrit la possibilité de transfert d’électrons photo-réducteurs parallèlement aux transferts d’électrons photo-oxydants qui sont généralement mis de l’avant
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