Elektronenstrukturtheorie von magnetoresistiven Effekten in atomaren Kontakten induziert durch Spin-Bahn-Kopplung und Spin-Nichtkollinearität

In this thesis magnetoresistive effects caused by spin-orbit coupling (SOC) and spin non-collinearity are studied on the atomic scale based on electronic structure theory. The full-potential linearized augmented plane wave method is applied, which relies on density functional theory (DFT). The electronic structure is projected on Wannier functions from which a tight-binding (TB) like Hamiltonian is constructed. This Hamiltonian is used in a Green's function formalism to obtain the transmission function within the Landauer approach. The anisotropic magnetoresistance (AMR) of symmetric Ni monowire junctions terminated by Co, Rh, and Ir apex atoms is investigated as a function of the distance between the apex atoms. A non-trivial distance dependence is found, which is due to the interplay of the magnetization-direction-dependent SOC-induced orbital mixing and the decay of the transition-matrix element across the gap between the apex atoms, which both depend on the orbital symmetry. These findings allow to explain scanning tunneling microscopy (STM) experiments of the distance dependence of the AMR in Co and Ir adatoms on W(110). Furthermore, single-molecule junctions consisting of metal-benzene complexes contacted by Ni and Co monowires are studied. The hybridization of the molecular orbitals with the orbitals of the adjacent metal atom results in an orbital-symmetry-filtered transmission function, which leads to a giant molecular AMR. Going beyond the monowire geometry, the AMR is investigated in Pt break junctions, in which Pt is expected to become magnetic. Pt trimers contacted by bulk-like bcc-(001) electrodes are studied finding an AMR of up to 20% in agreement with recent experimental results. Finally, it is shown based on TB and DFT that spin mixing caused by non-collinear spin structures leads to a tunneling non-collinear magnetoresistance, which has been discovered in STM experiments probing magnetic skyrmions in PdFe/Ir(111) with non-magnetic tips.In dieser Arbeit werden magnetoresistive Effekte durch Spin-Bahn-Kopplung (SBK) und nicht-kollineare (NK) Spinstrukturen auf der atomaren Skala mittels der Elektronenstrukturtheorie untersucht. Die “Full potential linearized augmented plane wave” Methode, die auf der Dichtefunktionaltheorie (DFT) beruht, wird angewendet. Die elektronische Struktur wird auf Wannier-Funktionen projiziert, mit denen eine “Tight-Binding” (TB) ähnliche Hamiltonmatrix konstruiert wird. Dieser Hamilitonian wird in einem Greensche-Funktionen-Formalismus verwendet, um die Transmissionsfunktion innerhalb der Landauer-Methode zu gewinnen. Der anisotrope magnetoresistive Effekt (AMR) von symmetrischen, einatomigen Ni-Ketten mit Co-, Rh- und Ir-Endatomen wird als Funktion des Abstandes zwischen den Endatomen untersucht. Die Abstandsabhängigkeit entsteht durch das Zusammenspiel des magnetisierungsrichtungsabhängigen, SBK-induzierten Mischens der Orbitale und dem Abfallen der Übergangsmatrixelemente zwischen den Endatomen entsteht, die beide von der Orbitalsymmetrie abhängen. Diese Erkenntnisse erlauben es Rastertunnelmikroskopie (RTM) Experimente des abstandsabhängigen AMR von Co und Ir Adatomen auf W(110) zu erklären. Weiterhin werden Einzelmolekülkontakte bestehend aus Metall-Benzol-Komplexen, die von einatomigen Ni- und Co-Ketten kontaktiert werden, studiert. Die resultierende, orbitalsymmetriegefilterte Transmissionsfunktion führt zu einem gigantischen molekularen AMR. Anschließend wird der AMR in Pt-Bruchkontakten, in denen Pt magnetisch werden soll, untersucht. Von bcc-(001)-Elektroden kontaktierte Pt-Trimere werden studiert und ein AMR von bis zu 20% in Übereinstimmung mit jüngsten, experimentellen Daten wird gefunden. Schließlich wird basierend auf TB und DFT gezeigt, dass das Mischen der Spinkanäle durch NK Spinstrukturen zum NK magnetischen Tunnelwiderstand führt. Dieser wurde in RTM-Experimenten, in denen Skyrmionen in PdFe/Ir(111) mit nicht-magnetischen Spitzen sondiert wurden, entdeckt

Effect of local chemistry and structure on thermal transport in doped GaAs

Using a first-principles approach, we analyze the impact of \textit{DX} centers formed by S, Se, and Te dopant atoms on the thermal conductivity of GaAs. Our results are in good agreement with experiments and unveil the physics behind the drastically different effect of each kind of defect. We establish a causal chain linking the electronic structure of the dopants to the thermal conductivity of the bulk solid, a macroscopic transport coefficient. Specifically, the presence of lone pairs leads to the formation of structurally asymmetric \textit{DX} centers that cause resonant scattering of incident phonons. The effect of such resonances is magnified when they affect the part of the spectrum most relevant for thermal transport. We show that these resonances are associated with localized vibrational modes in the perturbed phonon spectrum. Finally, we illustrate the connection between flat adjacent minima in the energy landscape and resonant phonon scattering through detailed analyses of the energy landscape of the defective structures.Comment: 7 pages, 7 figure

Adopting an ecological perspective on skill performance and learning in sport

The sub-discipline of motor learning frames understanding of skill performance and practice in sports, relevant for developing talent and enhancing expertise of athletes (Ribeiro et al., 2021). Research in this area has important implications for the professional support work of practitioners such as coaches, trainers and sport scientists (Woods et al., 2020). Ecological dynamics is a contemporary, transdisciplinary theory of motor learning, expertise and talent development in sport, which investigates dynamic person-environment interactions as the relevant scale of analysis for understanding human performance. Influenced and shaped by key ideas in biological, physical, social and anthropological sciences, an ecological perspective conceptualises athletes and sports teams as complex adaptive systems. An ecological perspective helps sport scientists to characterize the functional relationship that emerges from the continuous interactions of the individual athlete, task and environment, which is vital for understanding skill adaptation and talent development

Hardware-in-the-Loop Co-Simulation Based Validation of Power System Control Applications

Renewables are key enablers for the realization of a sustainable energy supply but grid operators and energy utilities have to mange their intermittent behavior and limited storage capabilities by ensuring the security of supply and power quality. Advanced control approaches, automation concepts, and communication technologies have the potential to address these challenges by providing new intelligent solutions and products. However, the validation of certain aspects of such smart grid systems, especially advanced control and automation concepts is still a challenge. The main aim of this work therefore is to introduce a hardware-in-the-loop co-simulation-based validation framework which allows the simulation of large-scale power networks and control solutions together with real-world components. The application of this concept to a selected voltage control example shows its applicability.Comment: 2018 IEEE 27th International Symposium on Industrial Electronics (ISIE

‘Embracing turbulent waters’: Enhancing athlete self-regulation using the ‘PoST’ framework for performance preparation at the 2020 Tokyo Olympic Games

Sport science has increasingly witnessed use of contemporary ecological approaches to athlete development, preparation, and skill acquisition, providing alternatives to traditional pedagogical approaches. Here we examine an ecological perspective on transferring theory into coaching practice for athlete self-regulation and performance preparation, by presenting the case example of one lead coach and three athletes representing Team GB in the sport of Canoe Slalom at the 2020 Olympics in Tokyo. The aims of this case exemplar are: 1) to offer insights into how an ecological dynamics rationale supported integration of nonlinear pedagogy and (skill) training periodisation, underpinning athlete preparation for world class Canoe Slalom competition; and 2), to provide a first-hand perspective on transfer of theory to support self-regulation, skill learning, and performance preparation in high-performance sport. In the case example, the ‘Periodisation of Skill Training’ framework (i.e., termed ‘PoST’ framework) for venue specific preparation at the Tokyo Olympics was applied and adapted. Principles of co-design, the Constraints-Led Approach, perception-action coupling and representative learning design were embedded within collaborative application of the framework across a support team including athlete, coach and psychologist. To conclude, facilitating athlete self-regulation is highlighted in practical exemplars to support paddlers to cope with the dynamic environments in canoe slalom

Principles for technology use in athlete support across the skill level continuum

A major challenge to sport practitioners working across all levels of sport is ensuring that technological platforms are integrated effectively to assist learning along the development pathway. Under the framework of ecological dynamics, we introduce technology as a support opportunity for athletes to learn to become better attuned to, and utilise, key sources of information to self-regulate their actions. Importantly, technology not only supports learning, but also serves as a tool to encourage active engagement in learning from early childhood to late adulthood. Coaches also need to be wary of the potential perils of the mismanagement of technology use and how it can act as a learning rate limiter. Misuse of technological tools may inhibit the learning process by inhibiting an athlete’s ability or willingness to explore and exploit available information in the performance environment, as well as stimulate possible feelings of control and surveillance. By illustrating how technology may complement athlete learning under the guidance of the theoretical framework of ecological dynamics, it is intended that coaches may gain a better understanding of how technological tools can be used more strategically to enhance learning. </jats:p

Specialist Coaching Integrated into a Department of Methodology in Team Sports Organisations

Abstract: With increasing resources in sports organisations being allocated to the development and preparation of individual athletes and sub-groups with specialist performance roles, the work of coaches, specialist (role) coaches and support staff needs to be functionally and coherently integrated. This integration of sport science support and coaching can be administered by staff in a Department of Methodology (DoM). Particularly, in this paper, we propose how specialist coaching can be situated in a DoM, presenting a model advocating effective functioning in high-performance team sports organisations. Using principles of ecological dynamics, we provide a rationale for a functional methodology for the design of practice tasks in a DoM that views learners as wayfinders, self-regulating their way through competitive performance environments. This rationale for athlete self-regulation in practice could improve athlete performance by enhancing problem solving, engagement with constraints of learning designs and supporting better attunement to contextual information abundant in a competitive environment. Finally, by introducing this unified and multidisciplinary DoM, specialist coaches, team coaches and sport science support staff, within the organisational structure, can collaboratively debate and co-design individualised athlete training programmes to enrich skill adaptability and performance functionality. To underline these contentions, three high-performance sport case studies from Australian Football: goalkeeping in Association Football and Rugby League are presented

Specialist role coaching and skill training periodisation: A football goalkeeping case study

© The Author(s) 2020. In sports like association football, professional teams are increasingly devoting resources to the role-based development of individual athletes and sub-groups. By employing ‘specialist coaches’ into athlete-support structures, clubs aim to facilitate individualised athlete training programs to enhance performance preparation as well as skill learning and talent development. Here, we discuss how contemporary pedagogical training approaches, like Nonlinear Pedagogy and the Constraints-Led approach, can enhance effectiveness of specialist role-based athlete development programs to facilitate performance functionality. We argue the need for a model of specialist role-based coaching practice in high performance sports organisations, based on a unified theoretical rationale, such as ecological dynamics. To exemplify the nature of specialist role-based coaching, a case study addresses how Nonlinear Pedagogy and Constraints-Led approach are being used for training professional football goalkeepers in an U23 years age group. Integrating key concepts from ecological dynamics, allied to principles of Nonlinear Pedagogy and the Constraints-Led approach, common skill training principles for specialist role coaches are highlighted. These illustrate the use of the recently introduced ‘Periodization of Skill Training’ framework for specialist role coaching, practically exemplifying a way to harness opportunities for performance enhancement and individualised talent development in the football goalkeeping context

Coach to learn and learn to coach: synergising performance and development in the athlete-coach-environment learning system

While high-performance sport traditionally highlights a dualist perspective on distinct pathways of development and performance coaching, an ecological dynamics rationale recognises the deeply entwined relations between development and performance. Acknowledging an athlete-environment-centred approach, an increasingly relevant topic concerns “coach learning”, supporting the idea that theories of athlete development present useful insights for understanding coach development. In this position paper, it is argued that athlete and coach learning are not independent from one another, thus forming part of an athlete-coach-environment learning system. This first of two insights papers discusses the contiguity between athlete development and performance and coach learning. It seeks to highlight a dual coach learning pathway towards “coaching to learn” (infused by knowledge of the environment) and “learning to coach” (supported by knowledge about the environment). To underline the interconnectedness of athlete/coach learning, two examples are discussed from: I) the 2021 Wheelchair Rugby League World Cup; and II), high-performance workshops for Olympic sport coaches

Principles to guide talent development practices in sport: the exemplar case of British Rugby League Football

The value of talent development programmes, aimed at nurturing children and adolescents into high performance sport, has been widely questioned. However, there seems to be some agreement that the general concept of talent development is not the issue, rather, the problems exist in the design, implementation, and management of these systems. These challenges were exemplified in 2021 across British Rugby League Football, where the academy system came under scrutiny from the National Governing Body and many commentators from within the sport. In this paper, we argue that without a theoretical framework to guide learning in development, further operational guidance will continue to foster many of the practices that lead to criticism within the academic literature and from key stakeholders. Situated within the theoretical framework of ecological dynamics, we propose six principles to guide talent development practices of youth athletes; 1) athlete development is non-linear; 2) academies should be development focused, not performance driven; 3) the importance of generality and specificity of practice in athlete development; 4) the implementation of contemporary pedagogical models; 5) skilled intentionality, and; 6) an ethos of amateurism in a professional academy. We encourage practitioners to consider implementing these principles to realign talent development programmes, thereby supporting fun, collaboration, inclusion, and a long-term enjoyment of movement and sports participation