10,344 research outputs found

    The evolutionary state of young protoplanetary disks

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    Observations of protoplanetary disks have been focused on low-mass, classical T-Tauri stars and on intermediate mass Herbig Ae/Be stars. The observations of the Herbig stars have introduced a bias in the intermediate mass range since they exclude the earlier stages of disk evolution. The heaviest T-Tauri stars, the intermediate mass T-Tauri stars (IMTT stars), with spectral type from F to early K and with masses ≥1.5 M☉, are the younger precursors of the Herbig stars. To get a complete picture of the evolution of protoplanetary disks IMTT stars needs to be studied. Many IMTT stars have already been included in samples of classical T-Tauri stars where they are the most massive stars in the samples. This thesis seeks to remove some of this bias by focusing on the IMTT stars and observations of the disks around them. This thesis presents the research of a sample of 49 identified IMTT stars with infrared access. Their disks are compared with those of the known Herbig Ae/Be stars to examine their evolutionary status. The thesis also presents spatially resolved near-infrared scattered light observations of the IMTT star RY Tau. Using radiative transfer modelling the observations are recreated and features reminiscent of a dusty disk wind is assessed.Finally, it presents near-infrared spatially resolved scattered light observations of 23 optically bright stars in the Orion high mass star forming region. The observations are analysed in context of the stellar parameters, stellar multiplicity and the environment of a high star forming region

    In vivo strain measurements in the human buttock during sitting using MR-based digital volume correlation

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    Advancements in systems for prevention and management of pressure ulcers require a more detailed understanding of the complex response of soft tissues to compressive loads. This study aimed at quantifying the progressive deformation of the buttock based on 3D measurements of soft tissue displacements from MR scans of 10 healthy subjects in a semi-recumbent position. Measurements were obtained using digital volume correlation (DVC) and released as a public dataset. A first parametric optimisation of the global registration step aimed at aligning skeletal elements showed acceptable values of Dice coefficient (around 80%). A second parametric optimisation on the deformable registration method showed errors of and against two simulated fields with magnitude and , respectively, generated with a finite element model of the buttock under sitting loads. Measurements allowed the quantification of the slide of the gluteus maximus away from the ischial tuberosity (IT, average 13.74 mm) that was only qualitatively identified in the literature, highlighting the importance of the ischial bursa in allowing sliding. Spatial evolution of the maximus shear strain on a path from the IT to the seating interface showed a peak of compression in the fat, close to the interface with the muscle. Obtained peak values were above the proposed damage threshold in the literature. Results in the study showed the complexity of the deformation of the soft tissues in the buttock and the need for further investigations aimed at isolating factors such as tissue geometry, duration and extent of load, sitting posture and tissue properties

    Impulse Response Interpolation via Optimal Transport

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    Interpolation between multiple room impulse responses is often necessary for dynamic auralization of virtual acoustic environments, in which a listener can move with six degrees-of-freedom. The spatial room impulse response (SRIR) represents the combined effects of the surround room as sound propagates from a source to the listener and varies as the source or listener positions change. The early portion of the SRIR contains sparse reflections, considered to be distinct sound events, that tend to be impaired with interpolation methods based on simple linear combinations. With parametric processing of SRIRs, corresponding sound events are able to be mapped to one another and produce a more physically accurate spatiotemporal interpolation of the early portion of the SRIR. In this thesis, a novel method for parametric SRIR interpolation is proposed based on the principle of optimal transportation. First, SRIRs are represented as point clouds of sound pressure in a 3D virtual source space. Mappings between two point clouds are obtained by defining a partial optimal transport problem problem, solvable with familiar linear programming techniques. The partial relaxation is implemented by permitting both point-to-point mappings and dummy mappings. The obtained optimal transport plan is used to compute the interpolated point cloud which is converted back to an SRIR. Testing of the proposed method against three baseline comparison methods was done with SRIRs generated by geometrical acoustical modeling. An error metric based on the difference in energy between low-passed rendering of the omnidirectional room impulse response was used. Statistical results indicate that the proposed method consistently outperforms the baseline methods of interpolation. Qualitative examination of the mapping methods confirms that partial transport produces more physically accurate spatiotemporal mappings. For future work, it is suggested to consider different cost functions, interpolate between measured SRIRs, and to render the responses to allow perceptual tests

    Teaching the actuality of revolution: Aesthetics, unlearning, and the sensations of struggle

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    Exploring the nexus between aesthetics, pedagogy, and politics illustrates the central role education plays in reproducing injustice and inhibiting confidence in revolutionary struggle. Demonstrating how capitalism and its attendant forms of oppression are not merely cognitive but perceptual, Derek R. Ford proposes that revolutionary education demands the production of aesthetic experiences through which we sense the possibility and actuality of alternative worlds. To create such encounters, Ford develops a praxis of teaching and a pedagogy of unlearning that, in our current conjuncture, creates conditions for encountering what Jennifer Ponce de León calls “an other aesthetics.” Mapping contemporary capital as a perceptual ecology of structures, social relations, beliefs, and feelings, Teaching the Actuality of Revolution: Aesthetics, Unlearning, and the Sensations of Struggle provides an extensive new set of concepts, practices, and readings for revolutionaries to better plan, enact, reflect on, and refine our organizing efforts

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    Existence and stability of shrinkers for the harmonic map heat flow in higher dimensions

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    We study singularity formation for the heat flow of harmonic maps from Rd\R^d. For each d4d \geq 4, we construct a compact, dd-dimensional, rotationally symmetric target manifold that allows for the existence of a corotational self-similar shrinking solution (shortly \emph{shrinker}) that represents a stable blowup mechanism for the corresponding Cauchy problem.Comment: 31 page

    Fluidic Nozzles for Automotive Washer Systems: Computational Fluid Dynamics and Experimental Analysis

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    One of the main goals of this project was to cultivate an understanding of fluidic nozzle geometries and characteristic flow. Through this knowledge, three new fluidic nozzle concepts were developed to be used as components in several windscreen washer systems for an automotive part supplier, Kautex Textron CVS Ltd.Accurate and conclusive visualisation of flow through fluidic nozzles was vital in understanding how they can be best utilised for different applications. Over the past century, the specific needs of automotive cleaning systems have greatly developed with new technological discoveries, these advances allow the driver further knowledge of their surroundings. These specialised systems each require a different type of maintenance and cleaning system depending on their usage and the different size and shape of the vehicle. By completing this project, it is hoped to allow manufacturers to accurately identify what sort of fluidic nozzles are best for windscreen cleaning systems for a vehicle and how to design a nozzle to suit their specification. Fluidic nozzles have been researched experimentally and computationally to ensure an accurate comparison of results. By guaranteeing a precise comparison it will negate the need for high volume testing of nozzles in experimental situations, greatly reducing time and resources required to analyse a fluidic nozzle.The fluidic nozzles that are investigated and developed in this project were modelled and examined both experimentally and computationally, this ensured valid and accurate results were achieved by both the computational modelling and experimental testing. The development of the nozzles within this project was conducted using several experimental and computational setups to analyse the spray distribution, angle and oscillatory frequency amongst other parameters significant to the nozzle usage on a vehicle. Through this it was possible to tailor nozzle dimensions to allow for a streamlined design approach, this increased efficiency in fluidic nozzle development for any specification given by a vehicle manufacturing company customer. In addition to this the water flow emitted from the outlet was experimentally tested and modelled with both stationary and high surrounding velocities to examine how external variables affect the flow of the water from the nozzle.iiiThis project has been useful in the design manufacturing process of fluidic nozzles, by utilising computational modelling it has allowed a faster and cheaper method of analysing the effect of design alterations to fluidic nozzles. There is a greatly reduced frequency required for rapid prototyping of an array of fluidic chips with minimal dimensional differences to be used in the experimental stages of design, as once the inlet boundary conditions are established the nozzle can be redesigned completely within reason without the need for additional material wastage. This ensures a more easy and precise method of testing the manufacturing tolerances of a fluidic nozzle with a target of reaching customer specifications are always achieved.Three nozzles were aimed developed to satisfy conditions set by the customers, the vehicle manufacturers at which the new nozzle designs are aimed at are Honda, Nissan and Toyota. The nozzles to be established were designed for use on windscreen washer systems with a varying number of nozzles and with diverse windscreen sizes for different vehicles, resulting in a wide variety of specifications that must be met for each vehicle manufacturer. This meant that a single nozzle could not be utilised for all vehicles, instead a base model of fluidic chip was developed for the Nissan vehicle which was then dimensionally changed to suit the other vehicles.Throughout this project there were design specifications changes and ambiguities from the automotive company customers, leading to redesigns of the fluidic chips designed in this project. This means that although only two of the three fluidic nozzle designs are successfully in production, a much greater understanding of the mechanics of the fluid flow within the fluidic nozzle was achieved

    Adaptive Robotic Information Gathering via Non-Stationary Gaussian Processes

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    Robotic Information Gathering (RIG) is a foundational research topic that answers how a robot (team) collects informative data to efficiently build an accurate model of an unknown target function under robot embodiment constraints. RIG has many applications, including but not limited to autonomous exploration and mapping, 3D reconstruction or inspection, search and rescue, and environmental monitoring. A RIG system relies on a probabilistic model's prediction uncertainty to identify critical areas for informative data collection. Gaussian Processes (GPs) with stationary kernels have been widely adopted for spatial modeling. However, real-world spatial data is typically non-stationary -- different locations do not have the same degree of variability. As a result, the prediction uncertainty does not accurately reveal prediction error, limiting the success of RIG algorithms. We propose a family of non-stationary kernels named Attentive Kernel (AK), which is simple, robust, and can extend any existing kernel to a non-stationary one. We evaluate the new kernel in elevation mapping tasks, where AK provides better accuracy and uncertainty quantification over the commonly used stationary kernels and the leading non-stationary kernels. The improved uncertainty quantification guides the downstream informative planner to collect more valuable data around the high-error area, further increasing prediction accuracy. A field experiment demonstrates that the proposed method can guide an Autonomous Surface Vehicle (ASV) to prioritize data collection in locations with significant spatial variations, enabling the model to characterize salient environmental features.Comment: International Journal of Robotics Research (IJRR). arXiv admin note: text overlap with arXiv:2205.0642

    Evaluating the anticipated outcomes of MRI seizure image from open-source tool- Prototype approach

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    Epileptic Seizure is an abnormal neuronal exertion in the brain, affecting nearly 70 million of the world's population (Ngugi et al., 2010). So many open-source neuroimaging tools are used for metabolism checkups and analysis purposes. The scope of open-source tools like MATLAB, Slicer 3D, Brain Suite21a, SPM, and MedCalc are explained in this paper. MATLAB was used by 60% of the researchers for their image processing and 10% of them use their proprietary software. More than 30% of the researchers use other open-source software tools with their processing techniques for the study of magnetic resonance seizure image
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