969 research outputs found

    The hydrodynamic approach for plasmonics in graphene

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    Dissertação de mestrado em PhysicsThe hydrodynamic model approach to plasmonics is based on the simultaneous solution of Euler’s equa tion, Poisson’s equation, and the continuity equation. The quantum mechanical effects enter the model via the statistical pressure induced by the gas of electrons. It is also a form of including the effect of nonlocality. The aim of this thesis is to study the dispersion relation of the surface plasmon-polaritons and the plasmonic wakes created by an external potential, when a graphene sheet is in the vicinity of a metal. It is known they disperse linearly with the wave vector, therefore are of acoustic nature. This problem has been studied for normal plasmons, but the study for acoustic plasmons is missing. In the first part of this thesis, the hydrodynamic model will be used to solve some electrostatic boundary-value problems in planar geometry, that will give the linear dispersion of the SPPs in graphene near a semi-infinite and finite nonlocal metal. The study for the metals, gold and titanium, showed that the nonlocal effects are more visible in titanium, due to its intrinsic proprieties, such as plasmon frequency and background permittivity. The dielectric separation between graphene and metal also enhances the nonlocal effects. The decrease of the dielectric thickness increases the nonlocality. Regarding the finite metal, the results show that the increase of the metal thickness results in a higher energy of the surface plasmon-polaritons in graphene. In this case, the dispersion is also linear in the wavenumber . The second part encompasses the study of the induced potential in graphene, due to an external charge moving parallel to graphene in the y-direction at an height 0. When graphene is in the vicinity of a dielectric an oscillatory V-shaped pattern was per ceived, and the dependence of the angle on the Froude number (or dependence on the velocity of the external charge) provided two different regions, a constant angle region for low Froude numbers where the wake angle takes the value of 21◦ . This is similar to the Kelvin region, where the angle takes the constant value of 19.47◦ . A transition for a Mach region occurs for a plasmonic Froude number of 2.2, where the decrease of the angle happens for higher velocities following the law 1/. When a local metal is added to the system, the oscillatory behavior vanishes and a more continuous V-shaped wake appears in graphene. In this case, the angles follow a quadratic polynomial law, where these decrease with the increasing Froude number. Studying the phase velocity and the dispersion for the classical water wakes and the plasmonic wakes it is possible to see two limiting cases for = −1 and = 0, which correspond to pure gravity waves in deep water and gravity waves in shallow water, respectively. In such manner, it is possible to make an analogy between gravity waves and the plasmonic waves in graphene.A abordagem do modelo hidrodinâmico à plasmônica é baseada na solução simultânea da equação de Euler, da equação de Poisson e da equação de continuidade. Os efeitos da mecânica quântica entram no modelo através da pressão estatística induzida pelo gás de eletrões. É também uma forma de incluir o efeito da não-localidade. O objetivo desta tese é estudar a relação de dispersão e as perturbações plasmô nicas criadas por um potencial externo, quando o grafeno está nas proximidades de um metal. É sabido que os plasmões dispersam linearmente com o vetor de onda, portanto possuem uma natureza acústica. Este problema foi estudado para plasmões normais, no entanto falta o estudo para plasmões acústicos. Na primeira parte desta tese, o modelo hidrodinâmico será usado para resolver alguns problemas eletros táticos de valor de fronteira, que darão a dispersão linear dos SPPs quando o grafeno está próximo a um metal não local semi-finito e finito. O estudo para os metais ouro e titânio mostraram que os efeitos não locais são mais visíveis no titânio, devido às suas propriedades intrínsecas, como frequência plasmônica e permissividade de fundo. A separação dielétrica entre o grafeno e o metal, também potencializa os efeitos não locais. A diminuição da espessura do dielétrico, aumenta a não-localidade. Em relação ao metal finito, os resultados mostram que o aumento da espessura do metal leva ao aumento da energia dos plasmões-polaritões de superfície no grafeno. Neste caso, a dispersão também é linear no vetor de onda . A segunda parte abrange o estudo do potencial induzido no grafeno, devido a uma carga externa movendo-se paralelamente ao grafeno na direção dos y’s, a uma altura 0. Quando o grafeno está na vizinhança de um dielétrico, foi visto um padrão oscilatório em forma de ”V”, e a dependência do ângulo no número de Froude (ou dependência da velocidade da carga externa) mostra duas regiões diferentes, a primeira de ângulo constante para números de Froude baixos onde o ângulo do cone é constante e de valor 21◦ . Sendo semelhante à região de Kelvin, onde o ângulo constante toma o valor de 19.47◦ . Observa-se uma transição para a região de Mach ocorre para um número de Froude plasmónico de 2.2, onde a diminuição do ângulo ocorre para velocidades mais altas seguindo a lei 1/. Quando um me tal local é adicionado ao sistema, o comportamento oscilatório é quebrado e uma onda em forma de ”V”contínua aparece no grafeno. Neste caso, os ângulos seguem uma lei polinomial quadrática, onde os ângulos diminuem com o aumento do número de Froude. Estudando a velocidade de fase e a dispersão para as ondas clássicas na água e as ondas plasmônicas é possível ver dois casos limites para = −1 e = 0, que correspondem a ondas gravíticas puras em águas profundas e ondas gravíticas em águas rasas, respectivamente. Desta forma, é possível fazer uma analogia entre as ondas gravitacionais e as ondas plasmônicas no grafeno

    Leveraging Manifold Theory for Trajectory Design - A Focus on Futuristic Cislunar Missions

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    Optimal control methods for designing trajectories have been studied extensively by astro-dynamicists. Direct and indirect methods provide separate approaches to arrive at the optimal solution, each having their associated advantages and challenges. Among the realm of optimized transfer trajectories, fuel-optimal trajectories are typically most sought and characterized by se-quential thrust and coast arcs. On the other hand, it is well known that a simplified dynamical model like the CR3BP analyzed in a rotating coordinate system, reveal fixed points known as Lagrange points. These spatial points can be orbited, with researchers categorizing periodic orbits around them starting from the simple planar Lyapunov orbits and continuing to the more enigmatic butterfly orbits. Studying linearized dynamics using eigenanalysis in the vicinity of a point on these periodic orbits lead to interesting departures spatially manifesting into the invariant manifolds. This thesis delves into the novel idea of merging aspects of invariant manifold theory and indirect optimal control methods to provide efficient computation of feasible transfer trajectories. The marriage of these ideas provide the possibility of alleviating the challenges of an end-to end optimization using indirect methods for a long mission by utilizing the pre-computed and analyzed manifolds for insertion points of a long terminal coast arc. In addition to this, realistic and accurate mission scenarios require consideration of a high-fidelity dynamical model as well as shadow constraints. A methodology to use the “manifold analogues” in such cases has been discussed and utilized in this thesis along with modelling of eclipses during optimization, providing mission designers a basis for efficient and accurate/mission-ready trajectory design. This overcomes the shortcomings in state of the art software packages such as MYSTIC and COPERNICUS

    LIPIcs, Volume 261, ICALP 2023, Complete Volume

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    LIPIcs, Volume 261, ICALP 2023, Complete Volum

    Centres of goldworking in ancient Egypt: Egyptological questions and sources

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    The archaeological record for goldworking in Egypt comprises uneven information across the stages of procurement, production, and use, including recycling and reworking. East desert mines yield traces of working, including expedition inscriptions. Nile Valley excavations have identified no ancient Egyptian gold workshop, though gold is present within a chariot assembly workshop at the 19th Dynasty royal city Per-Ramses (Qantir). In writings and depictions, named and anonymous goldsmiths appear individually and in groups, adding some detail to our knowledge of their techniques, organization of work, and social setting. Within that part of the record, goldworking time and space seems flexible and project-based

    The High Wasteland, Scar, Form, and Monstrosity in the English Landscape: What Is the Function of the Monster in Representations of the English Landscape?

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    In this thesis, I explore themes and concerns that have arisen in my art practice, namely the relationship between landscape, monstrosity, and subjectivity. The tropes scar and form refer to features analogous in the subject and in the land which take on different specific meanings throughout the project, but in general terms, I relate them to trauma as a defining force. I suggest that monsters can be understood as embodying attitudes to time (a cause of trauma): those being fixity, which is resistant to temporality; and flux, which embraces temporality. Consequently, I define these categories and their opposition, presenting arguments for both monsters of fixity and flux monsters. I examine the construction of false universals of ‘England’ (categories of fixity) in representations of landscape and how they come to dominate the picturing of Britain more generally, alongside a mode I refer to as dynamic-fatalism, which examines the polemics and aesthetics of Wyndham Lewis (1882-1957). In this regard, I look at Lewis’s monstrous Tyro and its role in eliciting dehumanisation as a defining value in conceptions of a stratified society. Emphasis on creative practices and representations related to England serve to dissolve ‘proto-fascistic’ fantasies of a heroic, mono-cultural, and pure base for nation, dependent on categories of fixity. I suggest these values are instead understood as patrician, sexist, class-based, and racially biased. Given that landscape constructions are constitutive of our engagement with landscape, I conclude with a proposal for better ‘analogues’ of nature in the form of virescent space (a category of flux). I argue that virescent space is a phenomenon that sees the monster take on a specific role concerning the subject, one I define in relation to a wilderness destination in the poem Sir Gawain and the Green Knight (c.1370)

    Articulate Furnishings: German Cabinetmakers and the Construction of Elite Experience and Intellectual Culture, 1550-1650

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    This dissertation extends beyond the art historical canon and traditional methodologies to redirectscholarly attention back to a crucial aspect of early modern life: bodily experience and knowledgecreation. Framing the early modern collector’s cabinet as a display technology specific to the Kunst- undWunderkammer, or art and curiosity collection, I illuminate the crucial role of the German cabinetmakerin constructing the interactive furnishings that mediated the cognitive and bodily perception of objects ofknowledge of elite collectors in the sixteenth century. Joining the static functions of object preservationand organization with the dynamic performativity of concealment and revelation, collector’s cabinetsstaged novel and short-lived patterns of interactions between early modern persons and objects. Theconstruction, decoration, and contents of the most spectacular of collector’s cabinets not only impelledbut also actively invited the physical handling of objects. Four chapters contextualize the iconographic,representational, material, organizational, and interactive properties of collector’s cabinets alongsidecontemporary inventories, devotional literature and practices, and treatises on collecting and naturalhistory that document early modern approaches to knowledge acquisition. Grafting previously unmappedforms of early modern experience onto masterworks of artisanal skill and ingenuity, this study illuminatesthe ingenuity of sixteenth-century German cabinetmakers who revolutionized early modern persons’perceptions of and interactions with (art) objectsDoctor of Philosoph

    PhD students´day FMST 2023

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    The authors gave oral presentations of their work online as part of a Doctoral Students’ Day held on 15 June 2023, and they reflect the challenging work done by the students and their supervisors in the fields of metallurgy, materials engineering and management. There are 82 contributions in total, covering a range of areas – metallurgical technology, thermal engineering and fuels in industry, chemical metallurgy, nanotechnology, materials science and engineering, and industrial systems management. This represents a cross-section of the diverse topics investigated by doctoral students at the faculty, and it will provide a guide for Master’s graduates in these or similar disciplines who are interested in pursuing their scientific careers further, whether they are from the faculty here in Ostrava or engineering faculties elsewhere in the Czech Republic. The quality of the contributions varies: some are of average quality, but many reach a standard comparable with research articles published in established journals focusing on disciplines of materials technology. The diversity of topics, and in some cases the excellence of the contributions, with logical structure and clearly formulated conclusions, reflect the high standard of the doctoral programme at the faculty.Ostrav
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