2,320 research outputs found

    Measuring and Correcting the Effects of Scintillation in Astronomy

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    High-precision ground-based time-resolved photometry is significantly limited by the effects of the Earth's atmosphere. Optical atmospheric turbulence, produced by the mixing of layers of air of different temperatures, results in layers of spatially and temporally varying refractive indices. These result in phase aberrations of the star light which have two effects: firstly the point spread function is broadened, thus limiting the resolution, and secondly the propagation of these aberrations results in spatio-temporal intensity fluctuations in the pupil-plane of the telescope known as scintillation. The first effect can be corrected with adaptive optics, however the scintillation noise remains. In this thesis, the results from testing a scintillation correction technique that uses tomographic wavefront sensing are presented. The technique was explored extensively in simulation before being tested on-sky on the Isaac Newton Telescope in La Palma, Spain. Scintillation noise also limits the signal-to-noise ratio that can be achieved for standard differential photometry as the random noise fluctuations in the comparison star and the target star light curves add in quadrature. A differential photometry technique that uses optimised temporal binning of the comparison star to minimise the addition of random noise fluctuations is presented and tested both in simulation and with on-sky data. Finally, an investigation into the use of sparse arrays of small telescopes to reduce scintillation noise in photometry is presented. The impact of several parameters on the correlation of scintillation noise measured between sub-apertures in the array is explored

    Posthuman Creative Styling can a creative writer’s style of writing be described as procedural?

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    This thesis is about creative styling — the styling a creative writer might use to make their writing unique. It addresses the question as to whether such styling can be described as procedural. Creative styling is part of the technique a creative writer uses when writing. It is how they make the text more ‘lively’ by use of tips and tricks they have either learned or discovered. In essence these are rules, ones the writer accrues over time by their practice. The thesis argues that the use and invention of these rules can be set as procedures. and so describe creative styling as procedural. The thesis follows from questioning why it is that machines or algorithms have, so far, been incapable of producing creative writing which has value. Machine-written novels do not abound on the bookshelves and writing styled by computers is, on the whole, dull in comparison to human-crafted literature. It came about by thinking how it would be possible to reach a point where writing by people and procedural writing are considered to have equal value. For this reason the thesis is set in a posthuman context, where the differences between machines and people are erased. The thesis uses practice to inform an original conceptual space model, based on quality dimensions and dynamic-inter operation of spaces. This model gives an example of the procedures which a posthuman creative writer uses when engaged in creative styling. It suggests an original formulation for the conceptual blending of conceptual spaces, based on the casting of qualities from one space to another. In support of and informing its arguments are ninety-nine examples of creative writing practice which show the procedures by which style has been applied, created and assessed. It provides a route forward for further joint research into both computational and human-coded creative writing

    Machine learning in solar physics

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    The application of machine learning in solar physics has the potential to greatly enhance our understanding of the complex processes that take place in the atmosphere of the Sun. By using techniques such as deep learning, we are now in the position to analyze large amounts of data from solar observations and identify patterns and trends that may not have been apparent using traditional methods. This can help us improve our understanding of explosive events like solar flares, which can have a strong effect on the Earth environment. Predicting hazardous events on Earth becomes crucial for our technological society. Machine learning can also improve our understanding of the inner workings of the sun itself by allowing us to go deeper into the data and to propose more complex models to explain them. Additionally, the use of machine learning can help to automate the analysis of solar data, reducing the need for manual labor and increasing the efficiency of research in this field.Comment: 100 pages, 13 figures, 286 references, accepted for publication as a Living Review in Solar Physics (LRSP

    Slitless spectrophotometry with forward modelling: principles and application to atmospheric transmission measurement

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    In the next decade, many optical surveys will aim to tackle the question of dark energy nature, measuring its equation of state parameter at the permil level. This requires trusting the photometric calibration of the survey with a precision never reached so far, controlling many sources of systematic uncertainties. The measurement of the on-site atmospheric transmission for each exposure, or on average for each season or for the full survey, can help reach the permil precision for magnitudes. This work aims at proving the ability to use slitless spectroscopy for standard star spectrophotometry and its use to monitor on-site atmospheric transmission as needed, for example, by the Vera C. Rubin Observatory Legacy Survey of Space and Time supernova cosmology program. We fully deal with the case of a disperser in the filter wheel, which is the configuration chosen in the Rubin Auxiliary Telescope. The theoretical basis of slitless spectrophotometry is at the heart of our forward model approach to extract spectroscopic information from slitless data. We developed a publicly available software called Spectractor (https://github.com/LSSTDESC/Spectractor) that implements each ingredient of the model and finally performs a fit of a spectrogram model directly on image data to get the spectrum. We show on simulations that our model allows us to understand the structure of spectrophotometric exposures. We also demonstrate its use on real data, solving specific issues and illustrating how our procedure allows the improvement of the model describing the data. Finally, we discuss how this approach can be used to directly extract atmospheric transmission parameters from data and thus provide the base for on-site atmosphere monitoring. We show the efficiency of the procedure on simulations and test it on the limited data set available.Comment: 30 pages, 36 figures, submitted to Astronomy and Astrophysic

    Design and implementation of a prototype infrared video bolometer (IRVB) in MAST Upgrade

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    A prototype infrared video bolometer (IRVB) was successfully deployed in the Mega Ampere Spherical Tokamak Upgrade (MAST Upgrade or MAST-U), the first deployment of such a diagnostic in a spherical tokamak. The IRVB was designed to study the radiation around the lower x-point, another first in tokamaks, and has the potential to estimate emissivity profiles with spatial resolution beyond what is achievable with resistive bolometry. The system was fully characterized prior to installation on MAST-U, and the results are summarized here. After installation, it was verified that the actual measurement geometry in the tokamak qualitatively matches the design; this is a particularly difficult process for bolometers and was done using specific features of the plasma itself. The installed IRVB measurements are consistent both with observations from other diagnostics, including magnetic reconstruction, visible light cameras, and resistive bolometry, as well as with the IRVB-designed view. Early results show that with conventional divertor geometry and only intrinsic impurities (for example, C and He), the progression of radiative detachment follows a similar path to that observed for large aspect ratio tokamaks: The peak of the radiation moves along the separatrix from the targets to the x-point and high-field side midplane with a toroidally symmetric structure that can eventually lead to strong effects on the core plasma inside the separatrix

    Radiation Response, Mechanical Property Changes, and Corrosion Behavior of Molten Salt Reactor Materials

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    Corrosion related failures pose risk to the integrity of routinely cycled and permanent reactor components long before radiation damage alone adversely impact reactor performance. Compared to Light Water Reactors (LWRs), Molten Salt Reactors (MSRs) have not enjoyed a history of continuous engineering development and refinement. Hastelloy N, a nickel superalloy developed at ORNL explicitly for molten fluoride salt conditions, and 316SS, a widely used austenitic alloy, are among the leading candidates for immediate deployment in MSR systems. Data collected during initial development of Hastelloy N suffered from limitations in available microscopy and spectroscopy techniques, obfuscating the role of radiation damage and mechanical stress in the microstructural evolution of the alloy. 316SS, considered a more economical alternative to the nickel superalloy, is restricted by lower corrosion resistance and strength at high temperature. The present work bridges some of the nuanced gaps in knowledge related to Hastelloy N microstructural evolution, as well as evaluating the feasibility of coating systems for enhanced corrosion resistance for 316SS. Hastelloy N was exposed to light ion irradiation, micromechanical testing, and immersion corrosion using FLiNaK molten salt after either irradiation or static strain mounting using the three-point bending technique. 316SS, either coated using a modified cathodic cage plasma nitriding technique or mounted under static strain, was exposed to heavy ion irradiation. Several evaluation techniques were used including scanning electron microscopy (SEM), electron dispersive x-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and micromechanical pillar compression testing. The results show that, low-dose irradiation and subsequent elemental segregation and embrittlement, as well as tensile mechanical stress loading, have a deleterious effect on the corrosion resistance of Hastelloy N. Nickel coating on 316SS is demonstrated as highly radiation tolerant. Combination of irradiation and the three-point bending technique demonstrates a feasible pathway for further evaluation of alloys and coating systems for MSR applications

    Quantification of phase transformation in metastable stainless steels after laser surface modification

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    Aquest estudi investiga els efectes de la modificació de la superfície per làser en la microestructura i les propietats de l'acer inoxidable austenític metestable. La superfície de les mostres d'acer inoxidable 301LN va ser modificada utilitzant un làser de pulso nanosegon. Es van variar dos paràmetres principals del làser, com la intensitat (I) i la velocitat de varrido (S), per evaluar la seva influència en les propietats de la superfície modificada. Es van utilitzar tècniques de caracterització com la difracció de raigs X (XRD), microscòpia electrònica de varrido (SEM) i la prova de duresa Vickers per evaluar la microestructura i les propietats de la zona tractada. Els resultats indicuen que la modificació de la superfície per làser pot millorar significativament la duresa de la superfície de l'acer inoxidable. Aquest estudi destaca el potencial de la modificació de la superfície per làser com un mètode viable per millorar les propietats de duresa de l'acer inoxidable i proporciona una guia per identificar els paràmetres òptims del làser per a aplicacions específiques.Este estudio investiga los efectos de la modificación superficial con láser sobre la microestructura y las propiedades del acero inoxidable austenítico metaestable. Se modificó la superficie de muestras de acero inoxidable 301LN utilizando un láser pulsado de nanosegundos. Se variaron dos parámetros principales del láser, como la intensidad (I) y la velocidad de barrido (S), para evaluar su influencia en las propiedades de la superficie modificada. Se utilizaron técnicas de caracterización como la difracción de rayos X (DRX), la microscopía electrónica de barrido (MEB) y el ensayo de dureza Vickers para evaluar la microestructura y las propiedades de la zona tratada. Los resultados indican que la modificación superficial con láser puede mejorar significativamente la dureza superficial del acero inoxidable. Este estudio pone de relieve el potencial de la modificación superficial con láser como método viable para mejorar las propiedades de dureza del acero inoxidable y proporciona orientación para identificar los parámetros óptimos del láser para aplicaciones específicas.This study investigates the effects of laser surface modification on the microstructure and properties of metastable austenitic stainless steel. The surface of 301LN stainless steel samples was modified using a nanosecond pulsed laser. Two main laser parameters such as intensity (I) and scanning speed (S) were varied to evaluate their influence on the modified surface properties. Characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and Vickers hardness testing were utilized to evaluate the microstructure and properties of the treated zone. Results indicate that laser surface modification can significantly enhance the surface hardness of stainless steel. This study highlights the potential of laser surface modification as a viable method for improving the hardness properties of stainless steel and provides guidance for identifying the optimal laser parameters for specific applications

    Simply red: A Late Bronze Age glass ingot from Amarna

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    Chemical analysis of a visually opaque, turquoise-blue ingot from the Late Bronze Age royal capital at Amarna, housed in the Garstang Museum, University of Liverpool, shows an excess of copper colourant which indicates that the intended colour was opaque red. Trace element analysis places the location of manufacture in Egypt, and the date, finds location, dimensions and analysis suggest that the glass was made at Amarna. This, coupled with other recent finds of ingots/part ingots at the site, suggests that Amarna was producing not only blue glass, but a variety of different colours in this early period of Egyptian glassmaking. Other royal locations, such as the later site at Qantir where red glass predominates, appear to specialise in specific colours. These findings suggest that the political and economic focus of different ruling elites during the New Kingdom (1550–1069 BCE) influenced the volume and range of colours of the glasses manufactured

    Thermo-osmotic slip flows around a thermophoretic microparticle characterized by optical trapping of tracers

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    熱が誘起するすべり流れを検出 --光ピンセットを援用した可視化手法により熱泳動のメカニズム解明へ--. 京都大学プレスリリース. 2023-12-05.Thermo-osmotic flow around a microparticle in a liquid is characterized by observing and analyzing the distribution of tiny particles, i.e., tracers, near the surface of the microparticle. First, an optical-trapping laser is used to localize the tracer motion along a circular path near the circumference of the microparticle. Then, upon creating an overall temperature gradient in the liquid, the tracers on the circular path, originally uniformly distributed, gather toward the hotter side of the microparticle, indicating a flow along the particle toward the heat. Analyzing the tracer distribution further, it is found that (i) the flow magnitude decreases with the distance from the surface and (ii) changing the surface property of the microparticle results in a change in the flow magnitude. These results show that the observed flow is a thermally induced slip flow along the surface of the microparticle. Then, assuming a simple slip boundary condition for a fluid equation, we evaluate the magnitude of the slip coefficient based on two kinds of experimental data: (i) the thermophoretic velocity of the microparticle and (ii) the thermo-osmotic flow around the microparticle. The results of the two approaches are in quantitative agreement. They are also compared with those of theoretical models for a slip flow in existing studies

    Graphonomics and your Brain on Art, Creativity and Innovation : Proceedings of the 19th International Graphonomics Conference (IGS 2019 – Your Brain on Art)

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    [Italiano]: “Grafonomia e cervello su arte, creatività e innovazione”. Un forum internazionale per discutere sui recenti progressi nell'interazione tra arti creative, neuroscienze, ingegneria, comunicazione, tecnologia, industria, istruzione, design, applicazioni forensi e mediche. I contributi hanno esaminato lo stato dell'arte, identificando sfide e opportunità, e hanno delineato le possibili linee di sviluppo di questo settore di ricerca. I temi affrontati includono: strategie integrate per la comprensione dei sistemi neurali, affettivi e cognitivi in ambienti realistici e complessi; individualità e differenziazione dal punto di vista neurale e comportamentale; neuroaesthetics (uso delle neuroscienze per spiegare e comprendere le esperienze estetiche a livello neurologico); creatività e innovazione; neuro-ingegneria e arte ispirata dal cervello, creatività e uso di dispositivi di mobile brain-body imaging (MoBI) indossabili; terapia basata su arte creativa; apprendimento informale; formazione; applicazioni forensi. / [English]: “Graphonomics and your brain on art, creativity and innovation”. A single track, international forum for discussion on recent advances at the intersection of the creative arts, neuroscience, engineering, media, technology, industry, education, design, forensics, and medicine. The contributions reviewed the state of the art, identified challenges and opportunities and created a roadmap for the field of graphonomics and your brain on art. The topics addressed include: integrative strategies for understanding neural, affective and cognitive systems in realistic, complex environments; neural and behavioral individuality and variation; neuroaesthetics (the use of neuroscience to explain and understand the aesthetic experiences at the neurological level); creativity and innovation; neuroengineering and brain-inspired art, creative concepts and wearable mobile brain-body imaging (MoBI) designs; creative art therapy; informal learning; education; forensics
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