69 research outputs found
Bogomol’nyi equations on constant curvature spaces
This thesis is concerned with the anti-self-dual Yang-Mills equations and their reductions to Bogomol’nyi equations on constant curvature spaces. Chapters 1 and 2 contain introductory material. Chapter 1 discusses the origin of the equations in particle physics and their role in integrable systems. Chapter 2 describes the equations and the reduction process and outlines the construction of solutions via the twistor transform. In Chapter 3 we consider Bogomol’nyi equations on (2 + 1)-dimensional manifolds and show that for constant curvature space-times the equations are integrable and consider solutions in the negative scalar curvature case. In Chapter 4 we cover the negative scalar curvature case in more detail, constructing a number of soliton solutions including non-trivial scattering and consider the zero-curvature limit. In Chapter 5 we consider Bogomornyi equations in 3- diniensional hyperbolic space, derive an ansatz for solutions of the equation and use it to construct a number of new solutions. Chapter 6 contains concluding remarks
The EPICS Software Framework Moves from Controls to Physics
The Experimental Physics and Industrial Control System (EPICS), is an open-source software framework for high-performance distributed control, and is at the heart of many of the world’s large accelerators and telescopes. Recently, EPICS has undergone a major revision, with the aim of better computing supporting for the next generation of machines and analytical tools. Many new data types, such as matrices, tables, images, and statistical descriptions, plus users’ own data types, now supplement the simple scalar and waveform types of the former EPICS. New computational architectures for scientific computing have been added for high-performance data processing services and pipelining. Python and Java bindings have enabled powerful new user interfaces. The result has been that controls are now being integrated with modelling and simulation, machine learning, enterprise databases, and experiment DAQs. We introduce this new EPICS (version 7) from the perspective of accelerator physics and review early adoption cases in accelerators around the world
Effects of syntactic cueing therapy on picture naming and connected speech in acquired aphasia
Language therapy for word-finding difficulties in aphasia usually involves picture naming of single words with the support of cues. Most studies have addressed nouns in isolation, even though in connected speech nouns are more frequently produced with determiners. We hypothesised that improved word finding in connected speech would be most likely if intervention treated nouns in usual syntactic contexts. Six speakers with aphasia underwent language therapy using a software program developed for the purpose, which provided lexical and syntactic (determiner) cues. Exposure to determiners with nouns would potentially lead to improved picture naming of both treated and untreated nouns, and increased production of determiner plus noun combinations in connected speech. After intervention, picture naming of treated words improved for five of the six speakers, but naming of untreated words was unchanged. The number of determiner plus noun combinations in connected speech increased for four speakers. These findings attest to the close relationship between frequently co-occurring content and function words, and indicate that intervention for word-finding deficits can profitably proceed beyond single word naming, to retrieval in appropriate syntactic contexts. We also examined the relationship between effects of therapy, and amount and intensity of therapy. We found no relationship between immediate effects and amount or intensity of therapy. However, those participants whose naming maintained at follow-up completed the therapy regime in fewer sessions, of relatively longer duration. We explore the relationship between therapy regime and outcomes, and propose future considerations for research
The interplay of local electron correlations and ultrafast spin dynamics in fcc Ni
The complex electronic structure of metallic ferromagnets is determined by a balance between exchange interaction, electron hopping leading to band formation, and local Coulomb repulsion. The interplay between the respective terms of the Hamiltonian is of fundamental interest, since it produces most, if not all, of the exotic phenomena observed in the solid state. By combining high energy and temporal resolution in femtosecond time-resolved X-ray absorption spectroscopy with ab initio time-dependent density functional theory we analyze the electronic structure in fcc Ni on the time scale of these interactions in a pump-probe experiment. We distinguish transient broadening and energy shifts in the absorption spectra, which we demonstrate to be caused by electron repopulation and correlation-induced modifications of the electronic structure, respectively. Importantly, the theoretical description of this experimental result hence requires to take the local Coulomb interaction into account, revealing a temporal interplay between band formation, exchange interaction, and Coulomb repulsion
Photon shot-noise limited transient absorption soft X-ray spectroscopy at the European XFEL
Femtosecond transient soft X-ray Absorption Spectroscopy (XAS) is a very promising technique that can be employed at X-ray Free Electron Lasers (FELs) to investigate out-of-equilibrium dynamics for material and energy research. Here we present a dedicated setup for soft X-rays available at the Spectroscopy & Coherent Scattering (SCS) instrument at the European X-ray Free Electron Laser (EuXFEL). It consists of a beam-splitting off-axis zone plate (BOZ) used in transmission to create three copies of the incoming beam, which are used to measure the transmitted intensity through the excited and unexcited sample, as well as to monitor the incoming intensity. Since these three intensity signals are detected shot-by-shot and simultaneously, this setup allows normalized shot-by-shot analysis of the transmission. For photon detection, the DSSC imaging detector, which is capable of recording up to 800 images at 4.5 MHz frame rate during the FEL burst, is employed and allows approaching the photon shot-noise limit. We review the setup and its capabilities, as well as the online and offline analysis tools provided to users
Megahertz-rate ultrafast X-ray scattering and holographic imaging at the European XFEL
The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence and pulse duration. All XFEL facilities built until recently provided X-ray pulses at a relatively low repetition rate, with limited data statistics. Here, results from the first megahertz-repetition-rate X-ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL are presented. The experimental capabilities that the SCS instrument offers, resulting from the operation at megahertz repetition rates and the availability of the novel DSSC 2D imaging detector, are illustrated. Time-resolved magnetic X-ray scattering and holographic imaging experiments in solid state samples were chosen as representative, providing an ideal test-bed for operation at megahertz rates. Our results are relevant and applicable to any other non-destructive XFEL experiments in the soft X-ray range
Biotic interactions enhance survival and fitness in the caddisfly Micropterna sequax (Trichoptera: Limnephilidae)
Observation of fluctuation-mediated picosecond nucleation of a topological phase
peer reviewedTopological states of matter exhibit fascinating physics combined with an intrinsic stability. A key challenge is the fast creation of topological phases, which requires massive reorientation of charge or spin degrees of freedom. Here we report the picosecond emergence of an extended topological phase that comprises many magnetic skyrmions. The nucleation of this phase, followed in real time via single-shot soft X-ray scattering after infrared laser excitation, is mediated by a transient topological fluctuation state. This state is enabled by the presence of a time-reversal symmetry-breaking perpendicular magnetic field and exists for less than 300 ps. Atomistic simulations indicate that the fluctuation state largely reduces the topological energy barrier and thereby enables the observed rapid and homogeneous nucleation of the skyrmion phase. These observations provide fundamental insights into the nature of topological phase transitions, and suggest a path towards ultrafast topological switching in a wide variety of materials through intermediate fluctuating states. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.Leibniz Association Grant no. K162/2018 (OptiSPIN
The effectiveness of psychological interventions for loneliness: A systematic review and meta-analysis
Chronic loneliness is associated with a range of mental health difficulties. Previous theory and research indicate that psychological interventions show promise for reducing loneliness, however, there have been no systematic reviews or meta-analyses to ascertain the efficacy of these interventions across the lifespan. The aim of this study was to synthesise, meta-analyse and explore the heterogeneity in RCTs of psychological interventions for loneliness in order to establish their efficacy.
Five databases (Ovid Embase, Ovid Medline, PsycINFO, Web of Science and CINAHL) were systematically searched in order to identify relevant studies. Included studies were required to be peer-reviewed RCTs examining psychological interventions for loneliness. Two independent coders examined the abstracts of the 3973 studies and 103 full texts, finding 31 studies that met inclusion criteria, 28 of which contained sufficient statistical information to be included in the meta-analysis. The quality of included studies was assessed using the Cochrane Risk of Bias Tool.
The 31 studies (N = 3959) that were included in the systematic review were conducted with participants from a diverse range of cultures, age groups and populations. The interventions were of mixed quality and were mostly face to face, group-based and delivered weekly. The most common type of intervention was Cognitive Behavioural Therapy (CBT).
28 studies (N = 3039) were included in a meta-analysis which found that psychological interventions significantly reduced loneliness compared to control groups, yielding a small to medium effect size (g = 0.43). Subgroup analysis and meta-regressions were conducted in order to explore heterogeneity and found that type of psychological intervention was approaching significance as a moderator of the effectiveness of psychological interventions for loneliness.
In conclusion, psychological interventions for loneliness across the lifespan are effective. This finding should inform policy makers, researchers and clinicians going forward, especially in the context of increased loneliness due to the COVID-19 pandemic. There was considerable heterogeneity in the effectiveness of the interventions, suggesting that future research should also explore what works for whom and consider personalising psychological treatment
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