92 research outputs found

    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

    From Capture to Display: A Survey on Volumetric Video

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    Volumetric video, which offers immersive viewing experiences, is gaining increasing prominence. With its six degrees of freedom, it provides viewers with greater immersion and interactivity compared to traditional videos. Despite their potential, volumetric video services poses significant challenges. This survey conducts a comprehensive review of the existing literature on volumetric video. We firstly provide a general framework of volumetric video services, followed by a discussion on prerequisites for volumetric video, encompassing representations, open datasets, and quality assessment metrics. Then we delve into the current methodologies for each stage of the volumetric video service pipeline, detailing capturing, compression, transmission, rendering, and display techniques. Lastly, we explore various applications enabled by this pioneering technology and we present an array of research challenges and opportunities in the domain of volumetric video services. This survey aspires to provide a holistic understanding of this burgeoning field and shed light on potential future research trajectories, aiming to bring the vision of volumetric video to fruition.Comment: Submitte

    LIPIcs, Volume 277, GIScience 2023, Complete Volume

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    LIPIcs, Volume 277, GIScience 2023, Complete Volum

    12th International Conference on Geographic Information Science: GIScience 2023, September 12–15, 2023, Leeds, UK

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    Evolución química, textural y microestructural de carbonatos y sulfatos cálcicos durante la diagénesis : un estudio experimental

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    Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Geológicas, leída el 20-01-2023Minerals have a chemical composition and crystal structure that reflect the pressure and temperature conditions of the environment in which they formed. When the conditions change, minerals usually undergo transformations to adapt themselves to these new conditions. When these transformations take place in subsurface conditions, where pressure and temperature are usually low, they are commonly driven by the action of a fluid and involve the replacement of the primary minerals by secondary phases. The presence of a fluid triggers the replacement reaction to take place through an interface coupled dissolution-precipitation (ICDP) mechanism. This mechanism makes the kinetics of the transformation to be much faster than if the transformation were developed by diffusion in solid state. Due to the ubiquity and relevance of mineral replacement reactions in subsurface geological environments, numerous experimental studies on the development of these processes in different systems have been carried out over the last two decades. However, many of the parameters controlling these fluid-driven mineral replacement processes are still poorly understood. This PhD thesis seeks to advance in this understanding. With this aim, experiments have been designed to experimentally study the replacement of calcium carbonate and sulphate phases through dissolution-crystallisation reactions that take place in the temperature range between 25°C and 200°C. The thesis is divided into 5 result chapters, which are presented as scientific article and address two major problems...Los minerales tienen una composición química y una estructura cristalina que reflejan las condiciones de presión y temperatura del entorno en el que se formaron. Cuando las condiciones cambian, los minerales sufren transformaciones para adaptarse a las nuevas condiciones del entorno. Cuando estas transformaciones tienen lugar en condiciones subsuperficiales, donde la presión y la temperatura son bajas, es común que estén catalizadas por la acción de un fluido que conduzca al reemplazamiento de los minerales primarios por fases secundarias. La presencia de un fluido hace que la reacción de reemplazamiento tenga lugar a través un mecanismo acoplado de disolución-cristalización. Este mecanismo facilita que la cinética de la transformación sea mucho más rápida que si se desarrollara por difusión en estado sólido. Debido a la ubicuidad y relevancia de las reacciones de reemplazamiento mineral en los entornos geológicos subsuperficiales, a lo largo de las últimas dos décadas se han realizado numerosos estudios experimentales acerca del desarrollo de estos procesos en distintos sistemas. Sin embargo, todavía no se comprenden bien muchos de los parámetros que controlan los procesos de reemplazamiento mineral mediados por fluidos. Esta tesis doctoral busca avanzar en esta comprensión. Para ello, se han diseñado experimentos orientados a estudiar experimentalmente el reemplazamiento de carbonatos y sulfatos cálcicos a través de reacciones de disolución-cristalización que se desarrollan en el rango de temperaturas entre 25°C y 200°C. La tesis está dividida en 5 capítulos de resultados, que se presentan en forma de artículo científico y que abordan dos grandes problemas...Fac. de Ciencias GeológicasTRUEunpu

    International benchmarking of terrestrial laser scanning approaches for forest inventories

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    The last two decades have witnessed increasing awareness of the potential of terrestrial laser scanning (TLS) in forest applications in both public and commercial sectors, along with tremendous research efforts and progress. It is time to inspect the achievements of and the remaining barriers to TLS-based forest investigations, so further research and application are clearly orientated in operational uses of TLS. In such context, the international TLS benchmarking project was launched in 2014 by the European Spatial Data Research Organization and coordinated by the Finnish Geospatial Research Institute. The main objectives of this benchmarking study are to evaluate the potential of applying TLS in characterizing forests, to clarify the strengths and the weaknesses of TLS as a measure of forest digitization, and to reveal the capability of recent algorithms for tree-attribute extraction. The project is designed to benchmark the TLS algorithms by processing identical TLS datasets for a standardized set of forest attribute criteria and by evaluating the results through a common procedure respecting reliable references. Benchmarking results reflect large variances in estimating accuracies, which were unveiled through the 18 compared algorithms and through the evaluation framework, i.e., forest complexity categories, TLS data acquisition approaches, tree attributes and evaluation procedures. The evaluation framework includes three new criteria proposed in this benchmarking and the algorithm performances are investigated through combining two or more criteria (e.g., the accuracy of the individual tree attributes are inspected in conjunction with plot-level completeness) in order to reveal algorithms’ overall performance. The results also reveal some best available forest attribute estimates at this time, which clarify the status quo of TLS-based forest investigations. Some results are well expected, while some are new, e.g., the variances of estimating accuracies between single-/multi-scan, the principle of the algorithm designs and the possibility of a computer outperforming human operation. With single-scan data, i.e., one hemispherical scan per plot, most of the recent algorithms are capable of achieving stem detection with approximately 75% completeness and 90% correctness in the easy forest stands (easy plots: 600 stems/ha, 20 cm mean DBH). The detection rate decreases when the stem density increases and the average DBH decreases, i.e., 60% completeness with 90% correctness (medium plots: 1000 stem/ha, 15 cm mean DBH) and 30% completeness with 90% correctness (difficult plots: 2000 stems/ha, 10 cm mean DBH). The application of the multi-scan approach, i.e., five scans per plot at the center and four quadrant angles, is more effective in complex stands, increasing the completeness to approximately 90% for medium plots and to approximately 70% for difficult plots, with almost 100% correctness. The results of this benchmarking also show that the TLS-based approaches can provide the estimates of the DBH and the stem curve at a 1–2 cm accuracy that are close to what is required in practical applications, e.g., national forest inventories (NFIs). In terms of algorithm development, a high level of automation is a commonly shared standard, but a bottleneck occurs at stem detection and tree height estimation, especially in multilayer and dense forest stands. The greatest challenge is that even with the multi-scan approach, it is still hard to completely and accurately record stems of all trees in a plot due to the occlusion effects of the trees and bushes in forests. Future development must address the redundant yet incomplete point clouds of forest sample plots and recognize trees more accurately and efficiently. It is worth noting that TLS currently provides the best quality terrestrial point clouds in comparison with all other technologies, meaning that all the benchmarks labeled in this paper can also serve as a reference for other terrestrial point clouds sources.</p

    Wildfire Hazard and Risk Assessment

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    Wildfire risk can be perceived as the combination of wildfire hazards (often described by likelihood and intensity) with the susceptibility of people, property, or other valued resources to that hazard. Reflecting the seriousness of wildfire risk to communities around the world, substantial resources are devoted to assessing wildfire hazards and risks. Wildfire hazard and risk assessments are conducted at a wide range of scales, from localized to nationwide, and are often intended to communicate and support decision making about risks, including the prioritization of scarce resources. Improvements in the underlying science of wildfire hazard and risk assessment and in the development, communication, and application of these assessments support effective decisions made on all aspects of societal adaptations to wildfire, including decisions about the prevention, mitigation, and suppression of wildfire risks. To support such efforts, this Special Issue of the journal Fire compiles articles on the understanding, modeling, and addressing of wildfire risks to homes, water resources, firefighters, and landscapes

    Carbon-Based Materials

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    New carbon materials with improved mechanical, electrical, chemical, and optical properties are predicted and considered to be very promising for practical application. Carbon-based materials in the form of films, fabrics, aerogels, or microstructural materials are known for their large surface areas and pore volumes, light weight, and a great variety of structural morphology. Such unique structures can then be employed for a variety of purposes, for example, the production of new electronic devices, energy storage, and the fabrication of new materials. Nowadays, clear understanding of carbon materials via several examples of synthesis/processing methodologies and properties characterization is required. This Special Issue, “Carbon-Based Materials”, addresses the current state regarding the production and investigation of carbon-based materials. It consists of 13 peer-reviewed papers that cover both theoretical and experimental works in a wide a range of subjects on carbon structures

    Urban morphometrics + earth observation : an integrated approach to rich/extra-large scale taxonomies of urban form

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    Homogeneous fine-grained patterns of urban form represent identifiable areas in cities and allow their classification. Urban morphology uses the concepts of "morphological period," "urban tissue," or "character areas" to link fine-grained homogeneity of form to historical origins and the social and economic characters associated with them. However, identifying such fine-grained spatial patterns is a labor-intensive, specialist operation, thus limiting replicability and scalability. Therefore, comprehensive urban form classification has rarely been conducted at a very large scale, hindering our understanding of how form contributes to social, economic, and environmental urban dynamics. With expanding capacity in geo-computation, urban analytics, and Earth Observation (EO) technology, new numerical approaches to the large-scale and detailed description of urban form have recently emerged. However, limitations due to availability, quality, and consistency of data still apply. We present an integrated approach to extra-large-scale urban form analysis that combines a novel Urban MorphoMetrics (UMM) method for the generation of rich and unsupervised urban form taxonomies with advanced EO feature-extraction techniques. UMM utilizes extremely parsimonious input information to generate a comprehensive set of urban form characters for three morphometric elements (buildings, streets, and plots), over six categories (dimension, shape, spatial distribution, intensity, connectivity, and diversity) and three scales (small, medium, and large). All characters are measured at the building level and clustered into distinct homogeneous urban types, thus creating a comprehensive taxonomy of urban form. UMM is applicable across cases, allowing individual type profiling and cross-case comparison. We illustrate UMM outputs across a range of case studies covering formal and informal urban areas in sharply different geographical and cultural contexts worldwide. The results demonstrate an encouraging ability to map urban form in cities in ways that relate to historical origins, land uses, and other validating geographies.The method also shows a pathway to address varying degrees of availability, quality, and consistency of input data, which is commonly poor, for example, in informal settlements. Explorations of ways to resolve this issue include integrating UMM with EO. The latter offers a way to generate globally consistent input data from freely accessible repositories, hence ensuring full control of quality and consistency. Thus, we show that our first efforts to combine UMM and EO data into an integrated UMM+EO process are suitable for use at a global scale

    Lattice-Preferred Orientation and Microstructures of Minerals and Their Implications for Seismic Anisotropy

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    The lattice-preferred orientation (LPO) of minerals is important for interpreting seismic anisotropy, which occurs in the Earth’s crust and mantle, and for understanding the internal structure of the deep interior of the Earth. The characterization of microstructures, including LPO, grain size, grain shape, and misorientation, is important to determine the deformation conditions, deformation histories, kinematics, and seismic anisotropies in the crust and mantle The articles in this Special Issue prove that studies of LPO and microstructures of minerals and rocks are a major research area and provide a foundation for interpreting seismic anisotropy in the crust, mantle, and subduction zones. Therefore, the authors hope that this Special Issue encompassing recent advances in the measurement of LPOs of different minerals under various tectonic settings will be a fundamental and valuable resource for the readers and researchers interested in exploring the deformation conditions of minerals and rocks, as well as the interpretation of seismic anisotropy in the crust, mantle, and subduction zones
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