9,513 research outputs found

    Spectral Sequences and Khovanov Homology

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    In this thesis, we will focus on two main topics; the common thread between both will be the existence of spectral sequences relating Khovanov homology to other knot invariants. Our first topic is an invariant MKh(L) for links in thickened disks with multiple punctures. This invariant is different from but inspired by both the Asaeda-Pryzytycki-Sikora (APS) homology and its specialization to links in the solid torus. Our theory will be constructed from a Z^n-filtration on the Khovanov complex, and as a result we will get various spectral sequences relating MKh(L) to Kh(L), AKh(L), and APS(L). Our second topic is the Dowlin spectral sequence, which has E_2-page isomorphic to the reduced Khovanov homology Kh(L), and which converges to the knot Floer homology HFK(L) on the E_infinity-page. While it was previously known that these two pages are link invariants, we prove that every page is an invariant by defining weak maps on the underlying filtered complex which correspond to Reidemeister moves. This result is based on joint work with Samuel Tripp

    Soliton Gas: Theory, Numerics and Experiments

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    The concept of soliton gas was introduced in 1971 by V. Zakharov as an infinite collection of weakly interacting solitons in the framework of Korteweg-de Vries (KdV) equation. In this theoretical construction of a diluted soliton gas, solitons with random parameters are almost non-overlapping. More recently, the concept has been extended to dense gases in which solitons strongly and continuously interact. The notion of soliton gas is inherently associated with integrable wave systems described by nonlinear partial differential equations like the KdV equation or the one-dimensional nonlinear Schr\"odinger equation that can be solved using the inverse scattering transform. Over the last few years, the field of soliton gases has received a rapidly growing interest from both the theoretical and experimental points of view. In particular, it has been realized that the soliton gas dynamics underlies some fundamental nonlinear wave phenomena such as spontaneous modulation instability and the formation of rogue waves. The recently discovered deep connections of soliton gas theory with generalized hydrodynamics have broadened the field and opened new fundamental questions related to the soliton gas statistics and thermodynamics. We review the main recent theoretical and experimental results in the field of soliton gas. The key conceptual tools of the field, such as the inverse scattering transform, the thermodynamic limit of finite-gap potentials and the Generalized Gibbs Ensembles are introduced and various open questions and future challenges are discussed.Comment: 35 pages, 8 figure

    Quantum dots based superluminescent diodes and photonic crystal surface emitting lasers

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    This thesis reports the design, fabrication, and electrical and optical characterisations of GaAs-based quantum dot (QD) photonic devices, specifically focusing on superluminescent diodes (SLDs) and photonic crystal surface-emitting lasers (PCSELs). The integration of QD active regions in these devices is advantageous due to their characteristics such as temperature insensitivity, feedback insensitivity, and ability to utilise the ground state (GS) and excited state (ES) of the dots. In an initial study concerning the fabrication of QD-SLDs, the influence of ridge waveguide etch depth on the electrical and optical properties of the devices are investigated. It is shown that the output power and modal gain from shallow etched ridge waveguide is higher than those of deep etched waveguides. Subsequently, the thermal performance of the devices is analysed. With increased temperature over 170 ºC, the spectral bandwidth is dramatically increased by thermally excited carrier transition in excited states of the dots. Following this, an investigation of a high dot density hybrid quantum well/ quantum dot (QW/QD) active structure for broadband, high-modal gain SLDs is presented. The influence of the number of QD layers on the modal gain of hybrid QW/QD structures is analysed. It is shown that higher number of dot layer provides higher modal gain value, however, there is lack of emission from QW due to the requirement of large number of carriers to saturate the QD. Additionally, a comparison is made between “unchirped QD” and “ chirped QD” of hybrid QW/QD structure in terms of modal gain and spectral bandwidth. It is showed that “chirped” of the QD can improve the “flatness” of the spectral bandwidth. Lastly, the use of self-assembled InAs QD as the active material in epitaxially regrown GaAs-based PCSELs is explored for the first time. Initially, it is shown that both GS and ES lasing can be achieved for QD-PCSELs by changing the grating period of the photonic crystal (PC). The careful design of these grating periods allows lasing from neighbouring devices at GS ( ~1230 nm) and ES (~1140 nm), 90 nm apart in wavelength. Following this, the effect of device area, PC etch depth, PC atom shape (circle or triangle or orientation) on lasing performance is presented. It is shown that lower threshold current density and higher slope efficiencies is achieved with increasing the device size. The deeper PC height device has higher output power due to more suitable height and minimal distance to active region. The triangular atom shape has slightly higher slope efficiency compared to triangular atom shape which is attributed to breaking in-plane symmetry and increase out-of-plane emission

    Reinterpreting English Chinoiserie From A Postcolonial And Personal/Taiwanese Perspective: Creating New Narratives Through Art Practice

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    This PhD investigates how to reinterpret English chinoiserie from a postcolonial and personal/Taiwanese perspective through art practice. I explore aspects of history to scrutinise British/European receptions of China and Chineseness as a visual language in eighteenth-century English chinoiserie. This leads me to investigate eighteenth-century Sino-British/East-Europe historiographies to interrogate how to review relevant pre-colonial Sino-British contact. I also review Chineseness as an identity in relation to Taiwanese history, diaspora and my art practice. My findings reject a uniform insider Chineseness and instead point to plurality and subjectivity. That is multiple and personal perspectives from which to revisit history – which informs my approach in which to respond to chinoiserie. I create notional interlocution, a new postcolonial strategy of fictional (auto)ethnography, through contextualising concepts of constructivism, poststructualism, art-based research, and aspects of postcolonial theory. Via this new methodological framework, I make three artist films regarding the chinoiserie collections at the three chosen cultural heritage sites: This is China… explores the chinoiserie interior at the Royal Pavilion Brighton; Another beautiful dream investigates the Chinese wallpaper at Harewood House; and A note on Delftware interrogates the Delftware vases at Chatsworth House. My films are open-ended, yet critical and philosophical, and create new spaces in which to revisit chinoiserie. The films form a trilogy for their shared exploration of English chinoiserie but can be considered independently and seen as independent works

    Critical terrorism studies and the far-right: Beyond problems and solutions?

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    Recent years have witnessed increasing academic, media, and political attention to the threat of far-right terrorism. In this article, I argue that scholarship on this threat has suffered from two limitations, each with antecedents in terrorism research more broadly. First, is an essentialist approach to this phenomenon as an extra-discursive object of knowledge to be defined, explained, catalogued, risk assessed, and (ultimately) resolved. Second, is a temptation to emphasise, even accentuate, the scale of this threat. These limitations are evident, I argue, within scholarship motivated by a problem-solving aspiration for policy relevance. They are evident too, though, within critical interventions in which a focus on far-right terrorism is seen as an important corrective to established biases and blind spots within (counter-)terrorism research and practice. In response, I argue for an approach rooted in the problematisation and desecuritisation of the far-right threat. This, I suggest, facilitates important new reflection on the far-right’s production within and beyond terrorism research, as well as on the purposes and politics of critique therein

    The Characterisation and Treatment of Resistant Hypertension

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    Hypertension is a highly prevalent condition and, as a risk factor for vascular disease in particular, a leading contributory cause of death worldwide. Recent consensus guidelines suggest that moderate and severe (grade II and III) hypertension should be treated rapidly to achieve targets though, prior to the inception of this thesis, the evidence for the safety and efficacy of this approach, together with the physiological consequences of rapid hypertension treatment in moderate and severe disease, was limited. This thesis explores the clinical consequences of an 18-week treatment programme for individuals with grade II and III hypertension, using guideline- recommended pharmacological treatment, delivered over an accelerated timeframe. The blood pressure response to treatment is reported, together with the tolerance and safety of the protocol, as defined by the protocol completion rate, frequency of medication side effects and clinically significant adverse events. The programme also provided an opportunity to study health-rated quality of life in patients with moderate and severe hypertension and the effect of rapid treatment on health-related quality of life. This allowed for the first validation (according to modern standards) of an English language disease-specific instrument for measuring health-related quality of life in hypertension, following translation of the original MINICHAL disease-specific instrument from the original Spanish. In addition, the clinical treatment programme provided an opportunity to study the microvascular response to rapid treatment of moderate and severe hypertension, particularly with relevance to the rarefaction of hypertension and its reversal with treatment. Moreover, the morphological and functional myocardial consequences of treatment were determined, using cardiac MR imaging. Accordingly, this thesis presents evidence supporting the rapid treatment of moderate and severe hypertension, providing an opportunity for this to be studied in future investigations, with the aim of exploring whether this approach is prognostically advantageous for patients

    Modern Folk Devils

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    The devilish has long been integral to myths, legends, and folklore, firmly located in the relationships between good and evil, and selves and others. But how are ideas of evil constructed in current times and framed by contemporary social discourses? Modern Folk Devils builds on and works with Stanley Cohen’s theory on folk devils and moral panics to discuss the constructions of evil. The authors present an array of case-studies that illustrate how the notion of folk devils nowadays comes into play and animates ideas of otherness and evil throughout the world. Examining current fears and perceived threats, this volume investigates and analyzes how and why these devils are constructed. The chapters discuss how the devilish may take on many different forms: sometimes they exist only as a potential threat, other times they are a single individual or phenomenon or a visible group, such as refugees, technocrats, Roma, hipsters, LGBT groups, and rightwing politicians. Folk devils themselves are also given a voice to offer an essential complementary perspective on how panics become exaggerated, facts distorted, and problems acutely angled.;Bringing together researchers from anthropology, sociology, political studies, ethnology, and criminology, the contributions examine cases from across the world spanning from Europe to Asia and Oceania

    Differential Models, Numerical Simulations and Applications

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    This Special Issue includes 12 high-quality articles containing original research findings in the fields of differential and integro-differential models, numerical methods and efficient algorithms for parameter estimation in inverse problems, with applications to biology, biomedicine, land degradation, traffic flows problems, and manufacturing systems

    Recent Advances in Single-Particle Tracking: Experiment and Analysis

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    This Special Issue of Entropy, titled “Recent Advances in Single-Particle Tracking: Experiment and Analysis”, contains a collection of 13 papers concerning different aspects of single-particle tracking, a popular experimental technique that has deeply penetrated molecular biology and statistical and chemical physics. Presenting original research, yet written in an accessible style, this collection will be useful for both newcomers to the field and more experienced researchers looking for some reference. Several papers are written by authorities in the field, and the topics cover aspects of experimental setups, analytical methods of tracking data analysis, a machine learning approach to data and, finally, some more general issues related to diffusion
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