741 |
Development of a semi-automatic approach to estimate pre-event soil moisture for Flash Flood Guidance in low mountain ranges (Saxony)Luong, Thanh Thi 12 August 2022 (has links)
This thesis is written as a cumulative dissertation based on peer-reviewed papers and supplemented by yet unpublished results. It presents methods and results that contribute to a novel approach for estimating water storage within the soil-water-plant system at a single site or in a small catchment (< 100 km2). The focus is on estimating the current/pre-event condition of a study area using simulated soil moisture and applying it as an indicator for flash flood forecasting. These two steps were combined in a semi-automatic framework that was used as a tool for flash flood monitoring after the Flash Flood Guidance (FFG) concept. This includes catchments for which Hydro-meteorological data and reliable site characteristics are not available. The overall objective was to demonstrate the capabilities and limitations of the regionally applicable modeling framework based on a lumped-physical model and open-source input data. The questions to be answered are: How reliable are the model outputs estimated by an uncalibrated-lumped model based on regional parameterization and forcing data? What are the potential uncertainties and limitations of such a framework? What are the potential applications of water storage in flood monitoring? The data were derived from freely available datasets. Meteorological input data can come from various sensor networks integrated in an open sensor web, mainly from the German Meteorological Service (DWD) and e.g., the forest climate stations of Sachsenforst. The model description required datasets for elevation (10 m, State Office for Environment, Agriculture and Geology-LfULG), land cover (Copernicus: Land Cover 100m), soil characteristics (BK50, LfULG) and soil profiles from the German National Forest Inventory (NFI). In addition, satellite-based soil moisture product (SMAP-L4-GPH from the National Aeronautics and Space Administration-NASA), water gauges data (LfULG) and eddy covariance flux cluster sites of the chair Meteorology at TU Dresden were used for validation.
The first publication provides the framework and elaborates on the integration of a model into the open-data platform. The BROOK90 model (R version) was embedded in an open sensor web to estimate daily water balance components for more than 6,000 (sub-) catchments in Saxony. The model performance was validated with stream gauge observations in ten selected head catchments for discharge and with SMAP-L4-GPH for evapotranspiration and soil moisture. The results indicate that the framework is able to provide reliable soil retention estimates in high resolution.
The second publication addresses the potential use of radar precipitation in this framework. Here the focus is on examining long-term radar-derived precipitation to improve water balance estimates due to its advantages in spatial coverage. The DWD’s re-analysis radar product, RADKLIM, was applied and aggregated for daily model input. A comparison between radar and rain gauge precipitation was performed to evaluate the quality of the product at the study sites, including the compensation for the catch loss in precipitation using the Richter correction. The results show the satisfactory performance of the framework with radar precipitation.
The third publication demonstrates the application of model output to flood warnings. FFG was modified and applied to estimate rainfall thresholds considering the effects of antecedent soil moisture. Once rainfall threshold curves are calculated, only information on rainfall and soil moisture information is needed to issue a warning of a potential flash flood. The method was applied in the Wernersbach catchment in the Tharandt Forest and validated with historical events. The results of the contingency table show the potential of this tool for flash flood warning, but it should be tested with other rainfall runoff models and more catchments prone to flash floods.:Abstract/Zusammenfassung/Tóm tắt
1. Introduction
1.1 Motivation and scope
1.2 Problem formulation
1.3 Target setting
1.4 Structure of the thesis
2. Adjusted Flash Flood Guidance (FFG) framework
2.2 Terminology and definitions
2.2.1 Flash flood
2.2.2 Small catchment
2.3 FFG concept
2.4 Adjusted FFG framework
3. Core publications of the PhD thesis
4. Major findings
5. Conclusions and outlook
References
List of Abbreviations
List of figures
List of the author’s publication
Appendixes including the core publications
Erklärung / Die vorliegende Arbeit ist eine kumulative Dissertation, die auf begutachteten Arbeiten basiert und durch bisher unveröffentlichte Ergebnisse ergänzt wird. Sie stellt Methoden und Ergebnisse vor, die zu einem neuartigen Ansatz zur Abschätzung der Wasserspeicherung im System Boden-Wasser-Pflanze an einem einzelnen Standort oder in einem kleinen Einzugsgebiet (< 100 km2) beitragen. Der Schwerpunkt liegt auf der Abschätzung des aktuellen/vor einem Ereignis herrschenden Zustands eines Untersuchungsgebiets unter Verwendung simulierter Bodenfeuchte und deren Anwendung als Indikator für die Vorhersage von Sturzfluten. Diese beiden Schritte wurden in einem halbautomatischen Modell zusammengefasst, das als Werkzeug für die Überwachung von Sturzfluten nach dem Konzept des Flash Flood Guidance (FFG) verwendet wird. Dies schließt Standorte/Einzugsgebiete ein, für die keine hydrometeorologischen Daten und/oder zuverlässige Standortmerkmale verfügbar sind. Das Gesamtziel bestand darin, die Fähigkeiten und Grenzen des regional anwendbaren Modells auf der Grundlage eines pauschalen physikalischen Modells und von Open-Source-Eingangsdaten zu demonstrieren. Die zu beantwortenden Fragen lauten: Wie zuverlässig sind die von einem unkalibrierten eindimensionalen Modell auf der Grundlage regionaler Parametrisierungs- und Antriebsdaten geschätzten Modellergebnisse? Was sind die potenziellen Unsicherheiten und Grenzen eines solchen Modells? Welches sind die möglichen Anwendungen der simulierten Komponenten des Wasserhaushalts bei der Überwachung von Hochwasser? Die Daten werden aus frei verfügbaren Datensätzen abgeleitet. Die meteorologischen Eingangsdaten stammen aus verschiedenen Sensornetzwerken, die in einem Open Sensor Web integriert sind, hauptsächlich vom Deutschen Wetterdienst (DWD) und z.B. den Waldklimastationen von Sachsenforst. Für die Modellbeschreibung wurden Datensätze für Geländehöhe (10 m, Landesamt für Umwelt, Landwirtschaft und Geologie - LfULG), Landbedeckung (Copernicus: Land Cover 100m), Bodeneigenschaften (BK50, LfULG) und Bodenprofile aus der Bundeswaldinventur (BWI) benötigt. Darüber hinaus werden satellitengestützte Bodenfeuchteprodukte (SMAP-L4-GPH der National Aeronautics and Space Administration-NASA), Pegeldaten (LfULG) und Eddy-Kovarianz-Flusscluster-Standorte des Lehrstuhls für Meteorologie der TU Dresden zur Validierung verwendet.
Die erste Veröffentlichung liefert den Rahmen und erläutert die Integration eines Modells in die offene Datenplattform. Das Modell BROOK90 (R-Version) wurde in ein offenes Sensornetz eingebettet, um tägliche Wasserhaushaltskomponenten für mehr als 6,000 (Teil-)Einzugsgebiete in Sachsen zu schätzen. Die Leistung des Modells wurde anhand von Pegelbeobachtungen in zehn ausgewählten Einzugsgebieten für den Abfluss und mit SMAP-L4-GPH für die Evapotranspiration und Bodenfeuchte validiert. Die Ergebnisse zeigen, dass das System in der Lage ist, zuverlässige Schätzungen der Bodenretention in hoher Auflösung zu liefern.
Die zweite Veröffentlichung befasst sich mit der möglichen Nutzung von Radarniederschlägen in diesem Rahmen. Hier liegt der Schwerpunkt auf der Untersuchung des langfristigen, vom Radar abgeleiteten Niederschlags zur Verbesserung der Wasserbilanzschätzungen aufgrund seiner Vorteile bei der räumlichen Abdeckung. Das Reanalyse-Radarprodukt des DWD, RADKLIM, wurde verwendet und für tägliche Modelleingaben aggregiert. Es wurde ein Vergleich zwischen Radar- und Regenmesser-Niederschlag durchgeführt, um die Qualität des Produkts an den Untersuchungsstandorten zu bewerten, einschließlich der Kompensation des Niederschlagsverlusts durch die Richter-Korrektur. Die Ergebnisse zeigen die zufriedenstellende Leistung des Rahmens mit Radarniederschlag.
Die dritte Veröffentlichung demonstriert die Anwendung der Modelldaten auf Hochwasserwarnungen. Der Leitfaden für Sturzflutwarnungen wurde modifiziert und zur Schätzung der Niederschlagsschwellen unter Berücksichtigung der Auswirkungen der vorherrschenden Bodenfeuchte angewandt. Sobald die Niederschlagsschwellenkurven berechnet sind, werden nur noch Informationen über Niederschlag und Bodenfeuchte benötigt, um eine Warnung vor einer möglichen Sturzflut auszusprechen. Die Methode wurde im Einzugsgebiet des Wernersbachs und im Tharandter Wald angewandt und mit historischen Ereignissen validiert. Die Ergebnisse der Kontingenztabelle zeigen das Potenzial dieses Werkzeugs für die Sturzflutwarnung, es sollte jedoch mit anderen Niederschlagsabflussmodellen und weiteren Einzugsgebieten, die für Sturzfluten anfällig sind, getestet werden.:Abstract/Zusammenfassung/Tóm tắt
1. Introduction
1.1 Motivation and scope
1.2 Problem formulation
1.3 Target setting
1.4 Structure of the thesis
2. Adjusted Flash Flood Guidance (FFG) framework
2.2 Terminology and definitions
2.2.1 Flash flood
2.2.2 Small catchment
2.3 FFG concept
2.4 Adjusted FFG framework
3. Core publications of the PhD thesis
4. Major findings
5. Conclusions and outlook
References
List of Abbreviations
List of figures
List of the author’s publication
Appendixes including the core publications
Erklärung / Luận án tiến sĩ này được viết như một luận án tích lũy dựa trên các bài báo đã được bình duyệt và được bổ sung bởi các kết quả chưa được công bố. Nó trình bày các phương pháp và kết quả góp phần vào một cách tiếp cận mới để ước tính trữ lượng nước trong hệ thống đất-nước- thực vật tại một địa điểm hoặc trong một lưu vực nhỏ (<100 km2). Trọng tâm là ước tính tình trạng hiện tại / trước sự kiện của khu vực nghiên cứu bằng cách sử dụng độ ẩm đất mô phỏng và áp dụng nó như một chỉ báo để dự báo lũ quét. Hai bước này được kết hợp trong một khuôn khổ bán tự động được sử dụng như một công cụ để giám sát lũ quét dựa theo khái niệm Hướng dẫn về lũ quét (FFG). Điều này bao gồm các địa điểm / lưu vực không có sẵn dữ liệu khí tượng thủy văn và / hoặc các đặc điểm thiếu thông tin mô tả chia tiết đáng tin cậy. Mục tiêu tổng thể là chứng minh các khả năng và hạn chế của khung mô hình áp dụng trong khu vực dựa trên một mô hình vật lý tổng hợp và dữ liệu đầu vào nguồn mở. Các câu hỏi cần được trả lời là: Các kết quả đầu ra của mô hình được ước tính bằng một mô hình gộp chưa hiệu chỉnh dựa trên tham số vùng và dữ liệu đáng tin cậy đến mức nào? Những điểm không chắc chắn và hạn chế tiềm ẩn của một khuôn khổ như vậy là gì? Các ứng dụng tiềm năng của thành phần cân bằng nước mô phỏng trong giám sát lũ lụt là gì? Dữ liệu được lấy từ các bộ dữ liệu miễn phí và có sẵn. Dữ liệu đầu vào về khí tượng đến từ các mạng cảm biến khác nhau được tích hợp trong một Open Sensor Web, chủ yếu từ Cơ quan Khí tượng Đức (DWD) và các trạm khí hậu rừng của Sachsenforst. Mô tả mô hình yêu cầu bộ dữ liệu về độ cao (10 m, Văn phòng bang về Môi trường, Nông nghiệp và Địa chất-LfULG), lớp phủ đất (Copernicus: Land Cover 100m), đặc điểm của đất (BK50, LfULG) và cấu hình đất từ Kiểm kê Rừng Quốc gia Đức (NFI). Ngoài ra, sản phẩm độ ẩm của đất dựa trên vệ tinh (SMAP-L4-GPH từ Cơ quan Hàng không và Vũ trụ Quốc gia-NASA), dữ liệu các trạm thủy văn (LfULG) và các cụm địa điểm eddy covariance được giám sát bởi khoa Khí tượng học tại TU Dresden được sử dụng để xác nhận kết quả mô hình đầu ra.
Ấn phẩm đầu tiên cung cấp khuôn khổ và trình bày chi tiết về việc tích hợp một mô hình vào nền tảng dữ liệu mở. Mô hình BROOK90 (phiên bản R) được nhúng vào một trang web cảm biến mở để ước tính các thành phần cân bằng nước hàng ngày cho hơn 6000 lưu vực (phụ) ở Sachsen. Hiệu suất của mô hình đã được xác nhận với các quan sát bằng dữ liệu dòng chảy ở mười lưu vực đầu nguồn được chọn và với SMAP-L4-GPH cho thành phần thoát hơi nước và độ ẩm của đất. Kết quả chỉ ra rằng khung có thể cung cấp các ước tính đáng tin cậy về khả năng giữ nước của đất ở độ phân giải cao.
Ấn phẩm thứ hai đề cập đến khả năng sử dụng lượng mưa radar trong khuôn khổ này. Ở đây, trọng tâm là kiểm tra lượng mưa dài hạn có nguồn gốc từ radar để cải thiện ước tính cân bằng nước do lợi thế của nó trong phạm vi bao phủ không gian. Sản phẩm radar phân tích lại của DWD, RADKLIM, đã được áp dụng và tổng hợp để nhập mô hình hàng ngày. So sánh giữa lượng mưa bằng radar và máy đo mưa đã được thực hiện để đánh giá chất lượng của sản phẩm tại các điểm nghiên cứu, bao gồm cả việc bù đắp cho lượng mưa thất thoát bằng cách sử dụng hiệu chỉnh độ Richter. Kết quả cho thấy hiệu suất khả quan của khung với lượng mưa radar.
Ấn phẩm thứ ba trình bày việc áp dụng đầu ra mô hình để cảnh báo lũ lụt. Hướng dẫn về lũ quét đã được sửa đổi và áp dụng để ước tính ngưỡng lượng mưa xem xét ảnh hưởng của độ ẩm đất trước đây. Khi đường cong ngưỡng mưa được tính toán, chỉ cần thông tin về lượng mưa và thông tin về độ ẩm của đất để đưa ra cảnh báo về khả năng xảy ra lũ quét. Phương pháp này đã được áp dụng ở lưu vực Wernersbach, trong Rừng Tharandt và được xác nhận với các sự kiện lịch sử. Kết quả của bảng dự phòng cho thấy tiềm năng của công cụ này để cảnh báo lũ quét, nhưng nó nên được thử nghiệm với các mô hình dòng chảy lượng mưa khác và các lưu vực dễ xảy ra lũ quét hơn.:Abstract/Zusammenfassung/Tóm tắt
1. Introduction
1.1 Motivation and scope
1.2 Problem formulation
1.3 Target setting
1.4 Structure of the thesis
2. Adjusted Flash Flood Guidance (FFG) framework
2.2 Terminology and definitions
2.2.1 Flash flood
2.2.2 Small catchment
2.3 FFG concept
2.4 Adjusted FFG framework
3. Core publications of the PhD thesis
4. Major findings
5. Conclusions and outlook
References
List of Abbreviations
List of figures
List of the author’s publication
Appendixes including the core publications
Erklärung
|
742 |
Flash Pulse Thermography Measurements of Coat ThicknessHäggkvist, Alexander January 2023 (has links)
The application of varnish, metal coats, and paint is a common practice for modifying or enhancing material properties. Metal coats are frequently used as protective layers against corrosion, heat, and wear, while also influencing characteristics like conductivity, weight, and production costs. Achieving the optimal thickness of the coating is critical, as a too-thin layer may not offer sufficient protection, while an overly thick layer adds unnecessary weight and increases expenses. Therefore, it is crucial to accurately measure the coating thickness without causing any damage. This project focuses on utilising flash pulse thermography, a non-invasive and non-destructive measuring technique, with three algorithms — Dynamical Thermal Tomography, Power Function, and Pulse Phase Thermography — to measure and differentiate between plates with known variations in the number of coating layers. The study also aims to identify the limiting factors associated with the experimental equipment and the characteristics of the thermography algorithms. The thickness calculations were performed both individually for each plate and simultaneously for multiple plates. The results demonstrate that Dynamical Thermal Tomography exhibits superior precision and strong linear correlation when measuring individual plates. On the other hand, the Power Function algorithm outperforms in effectively distinguishing between two plates simultaneously, while providing decent precision for individual plates. It is worth noting that the framerate of the camera significantly affects the performance and serves as the primary limiting factor in this specific experimental setup.Further investigations are necessary to obtain more conclusive results and determine the limitations of accuracy when measuring coating thickness.
|
743 |
Impact of operating conditions on thermal hydrolysis pre-treated digestion return liquorAhuja, Nandita 23 September 2015 (has links)
Return liquor from thermal hydrolysis process (THP) can significantly add to the nitrogen load of a wastewater treatment plant (WWTP) and introduce UV quenching substances to the wastewater stream when recycled. While there are mature technologies in place to handle the inorganic nitrogen produced due to the thermal pretreatment, organic nitrogen remains a parameter of concern for utilities employing THP pretreatment. The impact of operating conditions of the THP on dissolved organic nitrogen (DON) and UV absorbance in return liquor was investigated. Operating conditions studied were (1) operating temperature (2) solids retention time (SRT) in the anaerobic digester (3) THP flash pressure (4) the effect of co-digestion of sewage sludge with food waste and, (5) polymer conditioning. Operating temperature and polymer dose had the most significant impact on DON and UV quenching. It was found that an increase in operating temperature resulted in an increase in DON, which was primarily contributed by the hydrophilic fraction. An increase in temperature also resulted in increased UV254 absorbance. However, this trend was not linear and the increase was more pronounced when the temperature was increased from 150 C to 170 C. Increasing flash pressure from 25 psi to 45 psi did not have a significant impact on the return liquor. However, increasing the flash pressure to 75 psi increased the DON and UV254 absorbing compounds. Co-digesting the sludge with food waste resulted in a slight increase in DON and a decrease in dissolved organic carbon (DOC) and UV quenching compounds. Increasing the SRT from 10 days to 15 days resulted in a slight decrease in DON but did not have any impact on UV254 absorbance. Overall, it can be concluded that optimizing operating conditions of thermal hydrolysis process can result in decreased DON and UV quenching compounds in the recycle stream. / Master of Science
|
744 |
Effets de la variation de la zone optique de lentilles cornéennes multifocales à addition élevée sur le flash global mfERGBoily, Laurence 12 1900 (has links)
La myopie est désormais considérée un problème de santé publique par l’Organisation Mondiale de la Santé et de multiples méthodes ont été mises en place afin de contrôler sa progression chez les jeunes en croissance. Parmi celles-ci, les lentilles cornéennes multifocales sont utilisées, permettant une focalisation au niveau de la rétine centrale et un défocus myopique en périphérie. Ce défocus rétinien aurait comme effet de diminuer la progression de la myopie et l’élongation du globe oculaire. Comme plusieurs études ont montré que la rétine est apte à percevoir le défocus et à différencier son sens, l’utilisation d’outils tels que l’électrorétinographie permet d’étudier ce phénomène plus en profondeur. Cette étude vise donc à mesurer la réponse rétinienne, à 5 différentes excentricités, avec l’électrorétinographie lorsqu’on soumet la rétine à un défocus myopique en utilisant des lentilles cornéennes multifocales à addition élevée et à comparer cet effet lorsque le diamètre de leurs zones optiques varie. Le flash global mfERG a été effectué sur 27 participants à trois reprises, soit avec une lentille cornéenne ne causant pas de défocus et avec deux lentilles multifocales ayant des zones optiques de différents diamètres (4mm et 7mm), permettant ainsi de varier l’aire du défocus. Les résultats montrent que l’amplitude de l’onde directe, causée principalement par les photorécepteurs et les cellules bipolaires, n’est pas influencée par le design des lentilles. L’amplitude de l’onde induite est toutefois diminuée de façon significative avec la LC ayant une zone optique plus petite et causant un défocus sur une plus grande surface rétinienne. Cette différence est présente au niveau de l’anneau 5, qui correspond à une excentricité rétinienne de 15,7o à 24,0o. Ceci précise l’endroit qui semblerait le plus sensible au défocus myopique. Ces données peuvent influencer le design des lentilles souples multifocales utilisées pour le contrôle de la myopie. / Myopia is now considered a public health issue by the World Health Organization and
multiple methods have been developed to control its progression. Among these methods,
soft multifocal contact lenses are used, which allow a focused image on the central retina
and a myopic defocus peripherally. This retinal defocus impacts the progression of myopia
and axial length. Since several studies have shown that the retina is sensitive to the type
of defocus, the use of tools such as electroretinography allow the study of the retinal
response in greater depth. The purpose of this study was to evaluate the retinal response,
at 5 different eccentricities, with electroretinography when the retina is subjected to
myopic defocus using different high addition soft multifocal contact lenses and to
compare this effect when the diameter of their optical zones varies. 27 participants
performed a global flash mfERG three times, either with a single vision contact lens or
with two multifocal lenses carrying different optical zone diameters (4mm and 7mm),
allowing for the variation in defocus area. The results show that the amplitude of the
direct wave, caused mainly by photoreceptors and bipolar cells, is not influenced by the
design of the lenses. The amplitude of the induced wave, however, is significantly
decreased when the optical zone is smaller and the lenses cause a defocus over a larger
retinal area. This difference is present at ring 5, which corresponds to a retinal eccentricity
of 15.7o to 24.0o. This specifies the location that would appear to be most sensitive to
myopic defocus. This data may influence the design of multifocal soft lenses used for
myopia control.
|
745 |
Embedded System Design for Pill Boxes with The Low Power Electronic Paper DisplayKamran, Ali January 2017 (has links)
The rapid development of technology in the health-care sector has led to the discovery of many new illnesses and improved treatments that were not possible earlier. However, many treatments and medicines for a specific disease often come with several side effects. The accuracy in treatments with an optimal result on specified targets is therefore desired with minimum side effects. This requires that the production and the usage processes should be precise. The scope of this study is not about the medicine production phase but rather on managing a medicine schedule. How many times a medicine should be taken in a day is strongly related to its dosage and following a precise timing plays a crucial role in the individual’s health. As a solution, a pill box based on a low power display (Electronic Paper Display, EPD) together with an embedded system has been introduced by the project owner (Victrix AB, Stockholm) .The pill box should have some different functions like alarms, data logging and wireless reporting. Different types of alarms including ringtone, vibration and voice recording/playing are required as well. To be able to trace the already planned timing for taking medicines, system will be able to save and report history of the past 100 days. Since every single idea for solving different parts of the problem should be tested in real system, a Quantitative Research based on experiments be used and the best possible solution be selected and implemented in the project. Studying technical material and also related works besides analyzing generated data after each experiment were a useful tool for the system integration in this work. As the result, a pill box based on an embedded system was designed and integrated successfully. A hardware platform, in form of a prototype system based on an ARM microcontroller and a compatible embedded software have been designed, improved and tested successfully and are available. At the end of this work, the low power E-paper display works properly, alarms can be set and activated, data can be saved and also sent wirelessly. Basically, the result of this project shows how an embedded system can be specialized and programmed to be able to interact with patients and e.g. nurses in order to make a stable and continuous connection between them. Most of determined goals have been achieved and some of them be changed and modified during the work. Also a few additional functions and improvements be suggested as future work.
|
746 |
Flash sintering of tungsten carbideMazo, Isacco 14 July 2023 (has links)
Binderless tungsten carbide (BTC) ceramics are inherently difficult to process and very brittle. Most consolidation techniques for processing pure WC powder require long sintering times and intense energy consumption. High-T pressureless and pressure-assisted sintering processes often lead to low-quality and coarsened microstructures, thus limiting the use of WC ceramics to few niche applications. Field-assisted sintering techniques (FAST), like spark plasma sintering (SPS), significantly improve the densification of fine and ultrafine WC powders. However, SPS requires high current outputs and expensive apparatus. SPS ceramics still lack adequate toughness to extend the use of BTC components in heavy-duty applications requiring reliable load-bearing capability and/or resistance against rapid and unexpected impacts or temperature drops. This research work explored a new consolidation route capable of boosting the mass transport phenomena (accelerated sintering) and, simultaneously, introducing new microstructural features. The process called flash sintering (FS) offers great potential in accelerating diffusion phenomena and altering the crystallographic and/or the defect chemistry of the sintered ceramics. Many scientific studies reported structural alterations, enhanced plastic flow and material softening by introducing “out-of-equilibrium” characteristics. Currently, FS technology requires, for its activation, a negative dependence of the electrical resistivity with temperature (NTC) of the material to be sintered. This is a universal requirement for the flash event to occur thus theoretically inhibiting the flash sintering of conductive materials with a positive temperature coefficient for resistivity (PTC), like metals or WC.
In the present work, we reported how during electrical resistance sintering (ERS) experiments conducted on pure WC nanopowders, a flash event was triggered during the first seconds of the process. This was demonstrated to occur thanks to the different evolution of the electrical properties of a granular compact with temperature. WC powders possess an initial NTC behaviour which can activate a transitory thermal runaway phenomenon which makes the activation of a flash event in these materials possible, intense enough to allow ultrafast densification in less than 10 s. This breakthrough allows to verify whether and how the flash event modifies the final sintered material. FS and SPS sintered ceramics were compared in their microstructural, physical and mechanical properties, thus pointing out how some peculiar modifications are exclusively present in the flash-sintered material. FS can stabilize the WC1-x metastable phase after cooling to room temperature, and this was demonstrated to alter the high-temperature deformation of WC micropillars during compression. In addition, FS BTC are inherently softer with respect to SPS ones, resulting in higher fracture toughness and slightly lower hardness. Even if not final, the results indicate how the flash sintering of WC can be explored further to process engineered BTC ceramics with an optimized hardness/toughness ratio and an enhanced deformability.
|
747 |
Synthesis and Study of Higher Poly(Acene)s: Hexacene, Heptacene, and DerivativesMondal, Rajib 02 October 2007 (has links)
No description available.
|
748 |
The Preservation of Objects Lost at SeaVogtman, Jacqueline 23 March 2010 (has links)
No description available.
|
749 |
Investigating Transmediation in the Revision Process of Seventh Grade WritersBatchelor, Katherine Elizabeth 07 August 2014 (has links)
No description available.
|
750 |
The Evolution of Alexina Louie’s Piano Music: Reflections of a Soul Searching JourneyKim, Yoomi J. 14 July 2009 (has links)
No description available.
|
Page generated in 0.1034 seconds