Ba(Mg1/3Ta2/3)O3 Thermal Barrier Coating Deposited by Liquid Precursor Plasma Spray: Phases and Microstructure Control

This study explores a new route to deposit complex oxide thermal barrier coatings (TBCs) Ba(Mg1/3Ta2/3)O3 (BMT) from liquid precursors, using a radio frequency (RF) induction plasma spray (IPS), which differs from the most frequently used technique, direct current (DC) air plasma spray (APS). Among the known oxide materials, BMT has the highest melting point (2900-3100 °C). Accordingly, it is envisioned as one of the most promising TBC candidate materials for the aeronautic field. Due to the limits imposed by BMT feedstock decomposition mainly caused by Mg evaporation during the APS process, and to the low service lifespan of dense lamellar coatings, liquid precursors were chosen as feedstock in this work. Indeed, they can attenuate feedstock decomposition by adding an excess of Mg into the initial precursor mixture. Furthermore, liquid precursors, normally prepared by solution and/or nanoscale solid particles suspensions, facilitate the formation of columnar structures. Therefore, the process adopted in this work is named hybrid suspension plasma spray (SPS)/ solution precursor plasma spray (SPPS). X-ray photoelectron spectroscopy (XPS) was used to evaluate quantitatively the element evaporation during plasma spraying. Thermogravimetric / differential thermal analysis (TG/DTA) was applied to investigate the BMT formation. The phase and microstructure were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Plasma diagnostic was performed by optical emission spectroscopy (OES). This project first proved that complex oxide synthesis and coating deposition can occur simultaneously in the Hybrid SPS/SPPS or SPPS processes. The formation mechanism and the correlation between the main BMT phase and four other secondary phases (BaTa2O6, Ba3Ta5O15, Ba4Ta2O9, Mg4Ta2O9) were discussed clearly. The key parameters (plasma power, spraying distance, substrate pre-heating, precursor chemistry and particle size of suspended particles), were explored in order to optimize phase structure and deposition rate of as-sprayed coatings. In addition, this research demonstrated the feasibility of applying RF SPPS to deposit BMT coating with an adjustable microstructure. Lamellar, columnar and dense vertically-cracked structures of BMT can be tuned by adjusting the spraying parameters. This result represents an opportunity to apply RF plasma spray in the TBCs field, in addition to that of DC plasma spray and EB-PVD. Short spray distance and bimodal atomized droplet size distribution were identified as key prerequisites for column formation. Parameters such as substrate roughness, precursor concentration and feed rate were studied with regards to the columnar morphology. A distinctive TBC microstructure, namely vertical grains, was presented in the as-sprayed BMT coatings. The novel material and microstructure differentiate themselves from any commonly-seen TBCs. The phase structure of vertical grains was analyzed with the assistance of elemental mapping and BaO-MgO-Ta2O5 ternary phase diagrams. The formation mechanism of vertical grains was discussed in terms of temperature gradient. Finally, based on the microstructure optimized in this work and other physical property of thermal expansion coefficient, BMT presents the potential for acting as a thermal protection coating on niobium alloy in the foreseeable future.Cette étude explore une nouvelle voie pour déposer des revêtements d’oxydes complexes pour les barrières thermiques (TBC) Ba(Mg1/3Ta2/3)O3 (BMT) à partir de précurseurs liquides. Les dépôts sont faits en utilisant la projection par plasma radiofréquence (RF) à couplage inductif, qui diffère de la technique la plus fréquemment utilisée dans le domaine, à savoir la projection plasma à air (APS) en courant continu (DC). Parmi les matériaux oxydes connus, le BMT a le point de fusion le plus élevé (2900-3100 °C). En conséquence, il est considéré comme l'un des matériaux candidats TBC les plus prometteurs pour le domaine aéronautique. En raison des limites imposées par la décomposition des matières premières du BMT, principalement causée par l'évaporation du Mg pendant le processus APS, et à la faible durée de vie des revêtements lamellaires denses, des précurseurs liquides ont été choisis comme matière première dans ce travail. En effet, ils peuvent atténuer la décomposition des matières premières en ajoutant un excès de Mg dans le mélange initial de précurseurs. En outre, les précurseurs liquides, normalement préparés par des solutions et/ou des suspensions de particules solides à l’échelle nanométrique, facilitent la formation d'une structure colonnaire. Par conséquent, le procédé adopté dans ce travail est nommé projection plasma hybride de suspension (SPS) / précurseur liquide (SPPS). La spectroscopie photoélectronique X (XPS) a été utilisée pour évaluer quantitativement l'évaporation des éléments pendant la projection par plasma. L’analyse thermique thermogravimétrique / différentielle (TG / DTA) a été réalisée pour étudier la formation de BMT. La phase et la microstructure ont été analysées par diffraction des rayons X (XRD) et par microscopie électronique à balayage (SEM), respectivement. Le diagnostic du plasma a été effectué par spectroscopie d'émission optique (OES). Ce projet a d'abord prouvé que la synthèse d'oxydes complexes et le dépôt de revêtement peuvent se produire simultanément dans les processus hybrides SPS/SPPS ou SPPS. Le mécanisme de formation et la corrélation entre la phase principale du BMT et quatre autres phases secondaires (BaTa2O6, Ba3Ta5O15, Ba4Ta2O9, Mg4Ta2O9) ont été clairement discutés. Les paramètres clés (puissance du plasma, distance de projection, préchauffage du substrat, chimie des précurseurs et taille des particules en suspension) ont été étudiés afin d'optimiser la structure des phases et le taux de dépôt des revêtements projetés. En outre, cette recherche a démontré la faisabilité de l’application de RF SPPS pour déposer un revêtement de BMT ayant une microstructure contrôlable. Les structures lamellaires, colonnaires et à fissures verticales denses du BMT peuvent toutes les trois être obtenues en ajustant les paramètres de projection. Ce résultat représente une opportunité d'appliquer la projection plasma RF dans le domaine des TBC, en plus de celle de la projection plasma DC et du dépôt physique en phase vapeur par faisceau d'électrons (EB-PVD). Une courte distance de projection et une distribution bimodale de la taille des gouttelettes atomisées ont été identifiées comme des conditions préalables clés à la formation de colonnes. Des paramètres tels que la rugosité du substrat, la concentration en précurseur et le taux d'alimentation ont été étudiés pour connaître leur influence sur la morphologie en colonne. Une microstructure TBC distinctive, à savoir avec des grains verticaux, a été trouvée dans les revêtements BMT projetés. Le nouveau matériau et la microstructure se distinguent de tous les autres TBC courants. La structure de phase des grains verticaux a été analysée à l'aide d'une cartographie élémentaire et de diagrammes de phases ternaires BaO-MgO-Ta2O5. Le mécanisme de formation des grains verticaux a été discuté en termes de gradient de température. Enfin, sur la base de la microstructure optimisée dans ce travail et d'autres propriétés physiques du coefficient de dilatation thermique, le BMT présente le potentiel d'agir comme un revêtement de protection thermique sur un alliage de niobium dans un avenir prévisible

FedFTN: Personalized Federated Learning with Deep Feature Transformation Network for Multi-institutional Low-count PET Denoising

Low-count PET is an efficient way to reduce radiation exposure and acquisition time, but the reconstructed images often suffer from low signal-to-noise ratio (SNR), thus affecting diagnosis and other downstream tasks. Recent advances in deep learning have shown great potential in improving low-count PET image quality, but acquiring a large, centralized, and diverse dataset from multiple institutions for training a robust model is difficult due to privacy and security concerns of patient data. Moreover, low-count PET data at different institutions may have different data distribution, thus requiring personalized models. While previous federated learning (FL) algorithms enable multi-institution collaborative training without the need of aggregating local data, addressing the large domain shift in the application of multi-institutional low-count PET denoising remains a challenge and is still highly under-explored. In this work, we propose FedFTN, a personalized federated learning strategy that addresses these challenges. FedFTN uses a local deep feature transformation network (FTN) to modulate the feature outputs of a globally shared denoising network, enabling personalized low-count PET denoising for each institution. During the federated learning process, only the denoising network's weights are communicated and aggregated, while the FTN remains at the local institutions for feature transformation. We evaluated our method using a large-scale dataset of multi-institutional low-count PET imaging data from three medical centers located across three continents, and showed that FedFTN provides high-quality low-count PET images, outperforming previous baseline FL reconstruction methods across all low-count levels at all three institutions.Comment: 13 pages, 6 figures, Accepted at Medical Image Analysis Journal (MedIA

Extreme fire weather is the major driver of severe bushfires in southeast Australia

In Australia, the proportion of forest area that burns in a typical fire season is less than for other vegetation types. However, the 2019–2020 austral spring-summer was an exception, with over four times the previous maximum area burnt in southeast Australian temperate forests. Temperate forest fires have extensive socio-economic, human health, greenhouse gas emissions, and biodiversity impacts due to high fire intensities. A robust model that identifies driving factors of forest fires and relates impact thresholds to fire activity at regional scales would help land managers and fire-fighting agencies prepare for potentially hazardous fire in Australia. Here, we developed a machine-learning diagnostic model to quantify nonlinear relationships between monthly burnt area and biophysical factors in southeast Australian forests for 2001–2020 on a 0.25° grid based on several biophysical parameters, notably fire weather and vegetation productivity. Our model explained over 80% of the variation in the burnt area. We identified that burnt area dynamics in southeast Australian forest were primarily controlled by extreme fire weather, which mainly linked to fluctuations in the Southern Annular Mode (SAM) and Indian Ocean Dipole (IOD), with a relatively smaller contribution from the central Pacific El Nino Southern Oscillation (ENSO). Our fire diagnostic model and the non-linear relationships between burnt area and environmental covariates can provide useful guidance to decision-makers who manage preparations for an upcoming fire season, and model developers working on improved early warning systems for forest fires

Hybrid suspension/solution precursor plasma spraying of a complex Ba(Mg1/3Ta2/3)O3 perovskite: Effects of processing parameters and precursor chemistry on phase formation and decomposition

Abstract: Ba(Mg1/3Ta2/3)O3 (BMT) has a high melting point and is envisioned as a thermal barrier coating material. In this study, a hybrid suspension/solution precursor plasma spray process with a radio frequency thermal plasma torch is designed to deposit BMT nanostructured coatings. Six combinations of chemical reagents are investigated as coating precursors: one BMT powder suspension and five Ta2O5 suspensions in nitrate- or acetate-based solutions. X-ray photoelectron spectroscopy is used to evaluate the element evaporation during plasma spraying, while a thermogravimetric/differential thermal analysis is applied to investigate the BMT formation. Parameters such as precursor chemistry, plasma power, spraying distance and substrate preheating are studied with regard to the coating phase structure. Twice the Mg stoichiometric amount with a power of 50 kW shows the best results when using nanocrystallized Ta2O5 as a tantalum precursor. When choosing nitrates as Ba and Mg precursors, crystallized BMT is obtained at lower plasma power (45 kW) when compared to acetates (50 kW). BaTa2O6, Ba3Ta5O15, Ba4Ta2O9, Mg4Ta2O9 are the main secondary phases observed during the BMT coatings deposition. Because of the complicated acetate decomposition process, the coating deposition rate from nitrate precursors is 1.56 times higher than that from acetate precursors

Study of the microstructural control of Ba(Mg1/3Ta2/3)O3 perovskite thermal barrier coating deposited by solution precursor plasma spray

Abstract: Inductively-coupled plasma spraying was used to deposit Ba(Mg1/3Ta2/3)O3 (BMT) on a titanium alloy substrate. By selecting the appropriate spraying parameter, it was possible to tune the BMT coating microstructure from dense splat-like layers to columns and segmented vertical cracks. Of those parameters, a short spraying distance of 34 mm was the most crucial parameter to form a columnar microstructure. An atomization probe that fed a bimodal droplet size distribution was considered as an important prerequisite to obtain a high-quality columnar structure. Small atomized droplet sizes contribute to the formation of columns, while the large ones ensure a high deposition rate. This is further discussed as part of the column formation mechanism. The effects of substrate surface roughness, precursor concentration and feed rate were studied separately. The surface roughness should be controlled between Ra = 1.3 μm and Ra = 2.7 μm to reduce the intercolumnar gaps. The columnar structure evolves into a segmented vertical cracked one when spraying concentrated precursors (30 wt. %). High feed rate (> 6 ml/min) can satisfy a series of requirements such as high deposition rate, low intercolumnar gaps and high intracolumnar porosity. Finally, a desired columnar structure with an intracolumnar porosity of 4.3 % and an intercolumnar porosity of 9.9 % was obtained by spraying a 10 wt. % concentration precursor on a finely sand-blasted substrate (Ra = 1.3 μm) at a feed rate of 8 ml/min

Vertical grain and columnar structured Ba(Mg1/3Ta2/3)O3 thermal barrier coating deposited by solution precursor plasma spray

Abstract: Thermal barrier coatings (TBC) with a lamellar structure are more susceptible to erosion than fully dense ceramics and electron beam physical vapor deposited (EB-PVD) coatings. This paper presents a distinctive structure of Ba(Mg1/3Ta2/3)O3 (BMT) with a columnar-oriented appearance and vertical grain nature, which was deposited by plasma spray rather than EB-PVD. Indeed, a radio frequency solution precursor plasma spray (RF SPPS) process was adopted for the coating deposition. The morphology and elemental composition of the vertical grains are analysed first. With the assistance of optical emission spectroscopy (OES), the formation mechanism of the vertical grains is discussed in detail. In addition, a new TBC system designed for niobium alloy is proposed in this paper. Owing to its high thermal expansion coefficient and unique vertical grain structure, BMT has been considered as the most promising insulation material candidate in this TBC system

Radar-Jamming Classification in the Event of Insufficient Samples Using Transfer Learning

Radar has played an irreplaceable role in modern warfare. A variety of radar-jamming methods have been applied in recent years, which makes the electromagnetic environment more complex. The classification of radar jamming is critical for electronic counter-countermeasures (ECCM). In the field of signal classification, machine learning-based methods take great effort to find proper features as well as classifiers, and deep learning-based methods depend on large training datasets. For the above reasons, an efficient transfer learning-based method is proposed in this paper. Firstly, one-dimensional radar signals were transformed into time–frequency images (TFIs) using linear and bilinear time–frequency analysis, which is inspired by symmetry theory. Secondly, pretrained AlexNet and SqueezeNet networks were modified to classify the processed TFIs. Finally, performance of this method was evaluated and compared using a simulated data set with nine types of radar-jamming signals. The results demonstrate that our proposed classification method performs well in accuracy and efficiency at a 1% training ratio, which is practical for anti-jamming

Radar-Jamming Classification in the Event of Insufficient Samples Using Transfer Learning

Radar has played an irreplaceable role in modern warfare. A variety of radar-jamming methods have been applied in recent years, which makes the electromagnetic environment more complex. The classification of radar jamming is critical for electronic counter-countermeasures (ECCM). In the field of signal classification, machine learning-based methods take great effort to find proper features as well as classifiers, and deep learning-based methods depend on large training datasets. For the above reasons, an efficient transfer learning-based method is proposed in this paper. Firstly, one-dimensional radar signals were transformed into time–frequency images (TFIs) using linear and bilinear time–frequency analysis, which is inspired by symmetry theory. Secondly, pretrained AlexNet and SqueezeNet networks were modified to classify the processed TFIs. Finally, performance of this method was evaluated and compared using a simulated data set with nine types of radar-jamming signals. The results demonstrate that our proposed classification method performs well in accuracy and efficiency at a 1% training ratio, which is practical for anti-jamming

Molecular Principle of Topotecan Resistance by Topoisomerase I Mutations through Molecular Modeling Approaches

Originally isolated from natural products, camptothecin (CPT) has provided extensive playing fields for the development of antitumor drugs. Two of the most successful analogs of CPT, topotecan and irinotecan, have been approved by the FDA for the treatment of colon cancer and ovarian cancer, as well as other cancers. However, the emergence of drug resistance mutations in topoisomerase I is a big challenge for the effective therapy of these drugs. Therefore, in this study, a series of computational approaches from molecular dynamics (MD) simulations to steered molecular dynamics (SMD) simulations and Molecular Mechanics/Generalized Born Surface Area (MM/GBSA) binding free energy calculations were employed to uncover the molecular principle of the topotecan resistance induced by three mutations in DNA topoisomerase I, including E418K, G503S, and D533G. Our results demonstrate a remarkable correlation between the binding free energies predicted by MM/GBSA and the rupture forces computed by SMD, and moreover, the theoretical results given by MM/GBSA and SMD are in excellent agreement with the experimental data for ranking the inhibitory activities: WT > E418K > G503S > D533G. In order to explore the drug resistance mechanism that underlies the loss of the binding affinity of topotecan, the binding modes of topotecan bound to the WT and mutated receptors were presented, and comparisons of the binding geometries and energy contributions on a per residue basis of topotecan between the WT complex and each mutant were also discussed. The results illustrate that the mutations of E418K, G503S, and D533G have great influence on the binding of topotecan to topoisomerase I bound with DNA, and the variations of the polar interactions play critical roles in the development of drug resistance. The information obtained from this study provides useful clues for designing improved topoisomerase I inhibitors for combating drug resistance

In Silico Exploration for Novel Type-I Inhibitors of Tie-2/TEK: The Performance of Different Selection Strategy in Selecting Virtual Screening Candidates

Orientador: Prof. Dr. Rodrigo Vasconcelos MachadoDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Humanas, Programa de Pós-Graduação em Letras. Defesa : Curitiba, 14/02/2020Inclui referências: p. 120-130Área de concentração: Estudos literáriosResumo: Os chamados paratextos editoriais teorizados por Gérard Genette surgem como uma espécie de vestíbulo para o texto e representam escolhas do autor ou do editor da obra, carregando sempre uma intenção que justifica sua existência. Nessa perspectiva, este estudo buscou apresentar como prefácios - autorais e alógrafos, presentes no conjunto de obras da escritora mineira Conceição Evaristo podem indicar caminhos editoriais seguidos pela autora, bem como a construção de sua imagem ao longo de diferentes edições, inclusive as de uma mesma obra publicadas em períodos distintos. Ao mesmo tempo, esta pesquisa buscou verificar como esses mesmos paratextos são utilizados para colocar em evidência junto ao leitor questões centrais da obra da escritora - o sujeito-mulher-negra, a violência contra corpos negros e o expediente da memória e ancestralidade. Fazem parte dessa análise os textos introdutórios de Ponciá Vicêncio, Becos da Memória, Insubmissas Lágrimas de Mulheres, Olhos d'água e Histórias de Leves Enganos e Parecenças. Os resultados apontam para uma nova utilidade para o prefácio, considerando Evaristo como uma voz social da coletividade e detentora de um fazer literário ancorado no que ela mesma definiu como escrevivência. Palavras-chave: Conceição Evaristo. Literatura Negra. História do Livro. Paratextos editoriais. Prefácios.Abstract: The paratexts theorized by Gérard Genette appear as a sort of vestibule for the text and represent the author's or publisher's choices, always carrying an intention that justifies its existence. From this perspective, this study aims to present as prefaces - own and allographs, in the works of writer Conceição Evaristo can indicate editorial paths followed by the writer, as well as the construction of her image along different editions, including the same one published in different years. At the same time, this research aims to verify how these same paratexts highlight the central issues of the writer's work - the black woman, the violence against blacks and the expedient of memory and ancestry. It is part of this analysis the prefaces of Poncia Vicêncio, Becos da Memória, Insubmissas Lágrimas de Mulheres, Olhos d'água, e Histórias de Leves Enganos e Parecenças. The results point to a different use for the preface, considering Evaristo as a social voice of the collectivity and holder of a self-anchored writing, as she defined as escrevivência. Palavras-chave: Conceição Evaristo. Black Literature. Book History. Paratexts. Prefaces