Articoli di riviste: "Matériaux à gradient de composition"

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Tudurí, Adriana, Leandro Bergamino, Roberto Violante, José Luis Cavallotto e Felipe García-Rodríguez. "SPATIAL AND TEMPORAL VARIATION IN THE PRESENT AND HISTORICAL SEDIMENTARY ORGANIC MATTER WITHIN THE RÍO DE LA PLATA ESTUARY (SOUTH AMERICA) IN RELATION TO THE SALINITY/TURBIDITY GRADIENT / VARIAÇÃO ESPACIAL E TEMPORAL PRESENTE E HISTÓRICA DA MATÉRIA ORGÂNICA SEDIMENTAR NO ESTUÁRIO DO RÍO DE LA PLATA (AMÉRICA DO SUL) EM RELAÇÃO AO GRADIENTE DE SALINIDADE / TURBIDEZ". Journal of Sedimentary Environments 3, n. 4 (23 dicembre 2018): 265–79. http://dx.doi.org/10.12957/jse.2018.39152.

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The aim of this study is to examine sedimentary organic matter sources, spatial distribution and temporal variability in a large estuarine system, the Río de la Plata estuary (South America). For this purpose, this work integrates recent and historical carbon and nitrogen isotopes (δ13C, δ15N), total organic carbon, total nitrogen, C/N ratios and sediment grain size analyses along the Río de la Plata estuary. Principal component analysis based on biogeochemical variables and salinity revealed two main biogeochemical contrasting zones, corresponding to the upper and the lower estuary. Such zones are derived from the density gradient observed at the maximum turbidity zone acting as a physical barrier by trapping fine sediments and controlling primary productivity. As a consequence, sedimentary total organic carbon and total nitrogen increase from upper reaches towards lower reaches to attain maximum values under the turbidity gradient due to the presence of fine sediments. On the other hand, C/N ratios display an opposite trend, with higher values in the upper reaches due to a higher influence of continental organic matter. Moreover, Stable Isotope Analysis in R (SIAR) based on δ13C and δ15N reveals that the main organic matter source to the sediment appears to be the continental particulate organic matter and the estimated percentages of terrestrial allochthonous contribution (C3 plants) indicated a decreased contribution towards the lower reaches. The paleoenvironmental analysis shows a change in the sedimentary organic matter composition since 1970 associated to an increased influence of terrestrial organic matter. This trend is related to an increase in the Paraná River flow, which in turn is related to climatic variability (i.e., the polarity change of the Pacific Decadal Oscillation). ResumoO objetivo deste estudo é estimar fontes de matéria orgânica sedimentar, distribuição espacial e variabilidade temporal num grande sistema estuarino, o estuário do Río de la Plata (América do Sul). Este trabalho integra dados atuais e históricos de isótopos de carbono e nitrogênio (δ13C, δ15N), carbono orgânico total, nitrogênio total, relação C/N e granulometria do sedimento ao longo do estuário do Río de la Plata. A análise de componentes principais baseada em variáveis biogeoquímicas e salinidade revelou duas zonas biogeoquímicas contrastantes, correspondentes ao estuário superior e inferior. Tais zonas são definidas por diferenças no gradiente de densidade na zona de turbidez máxima, o qual atua como uma barreira física, causando o aprisionamento de sedimentos finos e influenciando a produtividade primária. Como conseqüência, o carbono orgânico total sedimentar e o nitrogênio total aumentam dos trechos superiores para os trechos inferiores atingindo valores máximos sob o gradiente de turbidez devido à presença de sedimentos finos. Por outro lado, a razão C/N exibe uma tendência oposta, atingindo valores mais elevados no estuário superior devido a uma maior influência da matéria orgânica continental. Os resultados isotópicos de δ13C e δ15N sugerem que a principal fonte de matéria orgânica para o sedimento é a matéria orgânica particulada continental. A contribuição alóctone terrestre (plantas C3) diminui no estuário inferior. A análise paleoambiental mostra uma mudança na composição da matéria orgânica sedimentar a partir de 1970, causada pelo aumento do fornecimento da matéria orgânica terrestre. Essa tendência está relacionada a um aumento no fluxo do Rio Paraná, na sequência de alterações climáticas relacionadas com a mudança de polaridade da Oscilação Decadal do Pacífico.

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Hermann, Jörg, Chao Shen, Antonio Hermann, Olivier Aleixo da Luz, Aya Taleb e Frédéric Pelascini. "Analyse élémentaire : Des matériaux sans étalonnage". Photoniques, n. 103 (luglio 2020): 46–49. http://dx.doi.org/10.1051/photon/202010346.

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La mesure de la composition élémentaire d’un matériau nécessite habituellement un étalonnage à l’aide de références de composition proche du matériau à analyser. Cela implique de connaître la composition du matériau et d’avoir à disposition des étalons adéquats. La spectroscopie du plasma induit par laser permet de s’affranchir de cette étape d’étalonnage et de réaliser une analyse basée sur la comparaison d’un spectre mesuré avec le spectre calculé à l’aide d’un modèle : c’est l’approche « calibration-free ».

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Calligaro, Thomas, e Claire Pacheco. "Un accélérateur de particules fait parler les œuvres d’art et les objets archéologiques". Reflets de la physique, n. 63 (ottobre 2019): 14–20. http://dx.doi.org/10.1051/refdp/201963014.

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Depuis sa création jusqu’à son altération, la vie d’une œuvre d’art ou d’un objet archéologique s’inscrit au cœur de sa matière. L’enjeu des sciences du patrimoine est d’interroger cette matière sur l’activité des hommes, tout en préservant ces témoins de notre histoire. Retrouver les savoir-faire du passé, comprendre le choix des matériaux employés et déterminer l’origine des matières premières en sont les principales motivations. En révélant directement et sans dommages la composition élémentaire des matériaux anciens, l’analyse par faisceau d’ions réalisée à AGLAÉ (Accélérateur Grand Louvre pour l’Analyse Élémentaire) est parfaitement adaptée aux problématiques des sciences du patrimoine.

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Wei Zhang e Wai-Kuen Cham. "Gradient-Directed Multiexposure Composition". IEEE Transactions on Image Processing 21, n. 4 (aprile 2012): 2318–23. http://dx.doi.org/10.1109/tip.2011.2170079.

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Abbaoui, M., Z. Koalaga e A. Lefort. "Composition et coefficients de transport des plasmas de matériaux plastiques (polymères)". Canadian Journal of Physics 70, n. 12 (1 dicembre 1992): 1291–308. http://dx.doi.org/10.1139/p92-210.

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Composition at equilibrium, electrical and thermal conductivities, and dynamic viscosity coefficient are calculated for plasmas produced by vaporization of plastic materials (polymers) containing some percentage of carbon, hydrogen, oxygen, and nitrogen. Temperature and pressure ranges are 5000 – 30 000 K and 0.1–1 MPA. By indicating the role played by some particles on the characteristics of the discharge, this study has shown the influence of the nature of the material.[Journal translation]

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Li, Qiang, e Ming Qing Wu. "Based on the Gradient Source Representation of Functionally Gradient Materials". Applied Mechanics and Materials 496-500 (gennaio 2014): 80–83. http://dx.doi.org/10.4028/www.scientific.net/amm.496-500.80.

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In the process of functionally gradient material entity modeling, in order to meet the design requirements, one needs to constantly change coefficient of material composition equation. In order to facilitate visual design of functionally graded material entities within the distribution, the method based on gradient material source be adopted to directly change the coefficient of material composition functions, and according to the coefficient of material composition equation function image to choose material composition functions. Homogenous approaching gradient is used, the feasibility of change of gradient direction transformatio is proved.

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Garnett, D. R., e G. A. Shields. "The composition gradient across M81". Astrophysical Journal 317 (giugno 1987): 82. http://dx.doi.org/10.1086/165257.

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Cherradi, N., D. Delfosse, B. Ilschner e A. Kawasaki. "Matériaux à gradient : exploitation du concept et techniques de production par métallurgie des poudres". Revue de Métallurgie 93, n. 2 (febbraio 1996): 185–96. http://dx.doi.org/10.1051/metal/199693020185.

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Boudon, Pierre. "L’entrelacs architectural". Protée 33, n. 2 (31 agosto 2006): 9–18. http://dx.doi.org/10.7202/012288ar.

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Résumé Le rapport entre enveloppement et cheminement définit une articulation fondamentale dans la composition architecturale contemporaine. Partant de cette considération, nous développons un art de la composition dont les principes sont au-delà de la manifestation sensible, sous forme de volumes habitables ; de par la continuité des parcours, cet art n’est pas sans faire penser aux « jeux de ficelle » des enfants dont la signification n’est pas seulement ludique mais cosmique. Les figures souples que ceux-ci dessinent peuvent être comparées à des espaces architecturaux en évolution, traduits en termes de matériaux abstraits.

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Manaila, R., A. Devenyi, D. Biro, L. David, P. B. Barna e A. Kovacs. "Multilayer TiAlN coatings with composition gradient". Surface and Coatings Technology 151-152 (marzo 2002): 21–25. http://dx.doi.org/10.1016/s0257-8972(01)01633-4.

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Huang, Jianguo, Izumi Ichinose, Toyoki Kunitake e Aiko Nakao. "Zirconia−Titania Nanofilm with Composition Gradient". Nano Letters 2, n. 6 (giugno 2002): 669–72. http://dx.doi.org/10.1021/nl0255653.

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Tao Chen, Jun-Yan Zhu, A. Shamir e Shi-Min Hu. "Motion-Aware Gradient Domain Video Composition". IEEE Transactions on Image Processing 22, n. 7 (luglio 2013): 2532–44. http://dx.doi.org/10.1109/tip.2013.2251642.

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Meilliez, Francis, e Jean-Jacques Belin. "Territoire et matériaux, géologie et histoire : visite en pays de Pévèle". Annales de la Société géologique du Nord - (2e Série), Tome 29, n. 29 (1 dicembre 2022): 121–32. http://dx.doi.org/10.54563/asgn.1932.

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Un territoire, en surface, est déterminé par sa composition et sa structure : la Pévèle rassemble des roches tendres (argiles, sables) au cœur d’une synforme largement ouverte, esquissée par les niveaux crayeux du Crétacé supérieur, discordants sur un socle paléozoïque, structuré par l’orogenèse varisque. L’observation d’églises de plusieurs villages conduit à s’interroger sur la provenance des pierres dures qui ont été nécessaires, et sur leurs conditions d’acheminement il y a environ 1 000 ans.

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Fréchette, Charles-Antoine. "L’Écomimétisme ou les reflets des manifestations sonores de l’environnement". Circuit 25, n. 2 (9 settembre 2015): 19–37. http://dx.doi.org/10.7202/1032933ar.

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Le compositeur Charles-Antoine Fréchette présente les enjeux reliés à sa méthode de composition dite écomimétique. Avec cette méthode, il est question d’analyser des prélèvements sonores de l’environnement au sonagramme pour en tirer des contenus fréquentiels, dynamiques et rythmiques. Ces données récoltées et classées à travers des axes typologiques multiples, différenciés et superposés, concourent à l’élaboration de processus formels qui permettent de relier progressivement les composantes des matériaux entre eux. Ainsi, toutes les structures et les procédés structurels découlent de la manipulation des informations provenant des sources environnementales. Cette approche rigoureuse distingue l’écomimétisme des naturalismes traditionnels anecdotiques. Les résultats des analyses permettent aussi d’explorer les instruments afin de découvrir des techniques instrumentales mimétiques pour révéler métaphoriquement des sons de l’environnement. L’idée de la métamorphose se retrouve donc dans le transfert des sources sonores aux instruments, et dans la transformation progressive des matériaux, continuellement déduits les uns des autres. Formellement, il s’agit d’envisager des situations musicales immersives comme des territoires plus ou moins concrets, virtuels ou abstraits.

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Vílchez, J. M., B. E. J. Pagel, Angeles I. Díaz, Elena Terlevich e M. G. Edmunds. "The chemical composition gradient across M 33". Monthly Notices of the Royal Astronomical Society 235, n. 3 (dicembre 1988): 633–53. http://dx.doi.org/10.1093/mnras/235.3.633.

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Smither, R., K. Abu Saleem, M. Beno, C. Kurtz, A. Khounsary e N. Abrosimov. "Diffraction efficiency and diffraction bandwidth of thermal-gradient and composition-gradient crystals". Review of Scientific Instruments 76, n. 12 (dicembre 2005): 123107. http://dx.doi.org/10.1063/1.2130928.

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Bouscant, Liouba, Michel Gonneville e Ofer Pelz. "Matériaux anciens dans la musique contemporaine actuelle. Postmodernisme et modernisme en questions". Revue musicale OICRM 2, n. 2 (6 giugno 2019): 1–43. http://dx.doi.org/10.7202/1060129ar.

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Cet article vise à contribuer à la réflexion sur le procédé de l’emprunt thématique dans la composition au XXIe siècle, en étudiant plus particulièrement le cas de deux compositeurs actuels reconnus, établis au Canada : Michel Gonneville né en 1950 et Ofer Pelz né en 1978. Il s’agit de comprendre, après des décennies de structuralisme et de postmodernisme, le sens et l’apport de l’alliance entre le langage contemporain du début des années 2000 et des matériaux thématiques passés issus de la musique savante. Peut-on analyser celle-ci encore comme postmoderne et, si tel n’est pas le cas, quelle alternative apparaît ?

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Maulet, M., Zh B. Sagdoldina, B. K. Rakhadilov, D. N. Kakimzhanov e N. M. Magazov. "Influence of the content of aluminum on the structure of gradient detonation coatings based on NiCr-Al". Bulletin of the Karaganda University. "Physics" Series 107, n. 3 (30 settembre 2022): 18–24. http://dx.doi.org/10.31489/2022ph3/18-24.

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This paper studies the effects of aluminium content in the composite powder on the structure of detonation gradient coatings based on NiCr-Al. Gradient coatings were obtained by detonation spraying with a gradual stepwise decrease in the barrel filling volume with an acetylene-oxygen gas mixture from 50% to 25%. The elemental and phase composition, microstructure and surface roughness of coatings based on NiCr-Al with different aluminium content of 15%, 20%, and 30% were investigated. By varying the aluminium content in the powder composition, coatings with a gradient structure were obtained. The study results showed that the phase composition of the gradient coating strongly depends on the mass fraction of Al. In the case of an aluminium content of 30% in the composition of the composite powder, the formation of aluminium oxide was detected. It is established that under the same detonation deposition modes, the formation of the gradient structure of coatings will strongly depend on the aluminium content in the NiCr-Al composition. The study results showed that the optimal composition of the powder is NiCr – 80% and Al – 20% to obtain NiCr-Al coatings with a gradient structure.

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Bresnahan, Brady L., e David L. Poerschke. "High-Throughput Multi-Principal Element Alloy Exploration Using a Novel Composition Gradient Sintering Technique". Metals 14, n. 5 (9 maggio 2024): 558. http://dx.doi.org/10.3390/met14050558.

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This work demonstrates the capabilities and advantages of a novel sintering technique to fabricate bulk composition gradient materials. Pressure distribution calculations were used to compare several tooling geometries for use with current-activated, pressure-assisted densification or spark plasma sintering to densify a gradient along the long dimension of the specimen. The selected rectangular tooling design retains a low aspect ratio to ensure a uniform pressure distribution during consolidation by using a side loading configuration to form the gradient along the longest dimension. Composition gradients of NixCu1−x, MoxNb1−x, and MoNbTaWHfx (x from 0 to 1) were fabricated with the tooling. The microstructure, composition, and crystal structure were characterized along the gradient in the as-sintered condition and after annealing to partially homogenize the layers. The successful fabrication of a composition gradient in a difficult-to-process material like the refractory multi-principal element alloy system MoNbTaWHfx shows the utility of this approach for high-throughput screening of large material composition spaces.

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Jeon, Yong Min, Si Hong Ryu, Min Jun Kim e Seong Eui Lee. "Study on Ag-Ti Thin Film Structure with Compositional Gradient Fabricated by Sputtering Process". Korean Journal of Metals and Materials 61, n. 12 (5 dicembre 2023): 909–14. http://dx.doi.org/10.3365/kjmm.2023.61.12.909.

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In this study, a composition-gradient thin film was applied for the formation of intermediate layer of Ti seed layer for an stable electrode stack Ag metal layer. Various composition of Ag-Ti hetero metal layer were simultaneously deposited by using the sputtering process with Ti and Ag target, respectively. An intermediate layer was deposited at a gradient composition ratio such as 5:5 and 7:3. In addition, the optimal deposition conditions were evaluated by confirming the plasma codition such as density of plasma ion, plasma potential with the Langmuir Probe (Hiden ESPion). Flow rate, power, and composition ratio were optimized as variables for thin film structures of compositional gradient thin films. In addition, thin film samples were heat treated at 200 ℃, 300 ℃, and 400 ℃ to relieve the residual stress between the interface of laminated thin films. Under these conditions, a composition-gradient thin film was evaluated by XRD (X-Ray Diffraction, SmartLab Rigaku 9kW), SEM (Scanning Electron Microscope, Nova NanoSEM 450), and EDS (energy dispersive X-ray spectroscopy). As a result of the measurement, it was confirmed that interfacial diffusion occurred due to the composition gradient thin film. When the composition gradient intermediate layer was applied to thin film stack, the residual stress increased more than that of single thin film stack. However, after stress relief annealing, residual stress was dramatically decreased compared to single stack.

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Vazan, Allona, Ravit Helled e Tristan Guillot. "Jupiter’s evolution with primordial composition gradients". Astronomy & Astrophysics 610 (febbraio 2018): L14. http://dx.doi.org/10.1051/0004-6361/201732522.

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Recent formation and structure models of Jupiter suggest that the planet can have composition gradients and not be fully convective (adiabatic). This possibility directly affects our understanding of Jupiter’s bulk composition and origin. In this Letter we present Jupiter’s evolution with a primordial structure consisting of a relatively steep heavy-element gradient of 40 M⊕. We show that for a primordial structure with composition gradients, most of the mixing occurs in the outer part of the gradient during the early evolution (several 107 yr), leading to an adiabatic outer envelope (60% of Jupiter’s mass). We find that the composition gradient in the deep interior persists, suggesting that ~40% of Jupiter’s mass can be non-adiabatic with a higher temperature than the one derived from Jupiter’s atmospheric properties. The region that can potentially develop layered convection in Jupiter today is estimated to be limited to ~10% of the mass.

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HE, GANG, CHAO PENG, MINGZHONG HE, JIANHE HONG, HAIFENG LI e YANSHENG GONG. "COMBINATORIAL PREPARATION AND FERROELECTRIC PROPERTIES OF COMPOSITIONALLY GRADIENT PZT THIN FILMS". Functional Materials Letters 06, n. 03 (28 maggio 2013): 1350036. http://dx.doi.org/10.1142/s1793604713500367.

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Using a combinatorial synthesis process, compositionally gradient PZT thin films were conveniently prepared by a chemical solution decomposition (CSD) method. The thin films showed a perovskite structure with (111)-preferred orientation and a thickness of around 450 nm. The surface morphology and ferroelectric properties were significantly different, depending on the direction of compositional gradient. The detailed composition and gradient of the composition was seen to affect the property of compositionally gradient PZT thin films. The gradient thin film PZT654, with a Zr:Ti ratio of 6:4 at the bottom of the film nearest to the substrate, and with an total composition around the morphotropic phase boundary (MPB, x = 0.52) showed favorable ferroelectric properties. However, no typical offset of the hysteresis loops was observed in our work.

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Barkan, Nezahat Pınar, Mathieu Chevalier, Jean-Nicolas Pradervand e Antoine Guisan. "Alteration of Bumblebee Venom Composition toward Higher Elevation". Toxins 12, n. 1 (19 dicembre 2019): 4. http://dx.doi.org/10.3390/toxins12010004.

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Venomous animals use venom, a complex biofluid composed of unique mixtures of proteins and peptides, for either predation or defense. Bumblebees, which occur in various habitats due to their unique thermoregulatory properties, mainly use venom for defense. Herein, we conducted an exploratory analysis of the venom composition of a bumblebee species (Bombus pascuorum) along an elevation gradient in the western Swiss Alps using shot-gun proteomic approaches to assess whether their defense mechanism varies along the gradient. The gradient was characterized by high temperatures and low humidity at low elevations and low temperatures and high humidity at high elevations. Venom composition is changing along the elevation gradient, with proteomic variation in the abundances of pain-inducing and allergenic proteins. In particular, the abundance of phospholipase A2-like, the main component of bumblebee venom, gradually decreases toward higher elevation (lower temperature), suggesting venom alteration and thus a decrease in bumblebee defense towards harsher environments. Larger datasets may complement this study to validate the observed novel trends.

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Jalouli, Alireza, Muhammed Kilinc, Austin Marga, Mengying Bian, Tim Thomay, Athos Petrou e Hao Zeng. "Transition metal dichalcogenide graded alloy monolayers by chemical vapor deposition and comparison to 2D Ising model". Journal of Chemical Physics 156, n. 13 (7 aprile 2022): 134704. http://dx.doi.org/10.1063/5.0081929.

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In this work, a chemical vapor deposition (CVD) method was developed for the synthesis of transition metal dichalcogenide alloy monolayers, with a composition gradient in the radial direction. The composition gradient was achieved by controlling the substrate cooling rate during the CVD growth. The two types of alloys, namely, WS2(1−x)Se2x and MoS2(1−x)Se2x, were found to exhibit an opposite composition gradient. This is attributed to their different cohesive energies. A two-dimensional Ising model is used to explain the growth mechanism, where two ends of the composition were modeled as a magnetically ordered phase and a paramagnetic phase. The composition as a function of substrate temperature is then represented by the thermal magnetization curve.

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Lin, Qiyuan, e Giovanni Zangari. "(Digital Presentation) The Evolution of Composition and Morphology during the Initial Growth of Electrodeposited Ni-Fe Films". ECS Meeting Abstracts MA2022-01, n. 23 (7 luglio 2022): 1206. http://dx.doi.org/10.1149/ma2022-01231206mtgabs.

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The anomalous codeposition of Ni-Fe tends to develop a composition gradient zone along the growth direction within the near-substrate region. Although it has been shown that such a composition gradient can be mitigated by the pulsed deposition method, a fundamental understanding of this behavior based on the anomalous codeposition mechanism has not been achieved yet. In this work, the evolution of the composition and the morphology during the (pulsed) electrodeposition of Ni-Fe films was reported. A theory based on the Fe deposition mechanism originally described by Bockris, Drazic, and Despic [1] was proposed and described in detail, which was used to rationalize not only the occurrence and the decline of the composition gradient, but also the opposite signs of the composition gradient observed under the potentiostatic mode and the pulse-reverse potential mode. [1] O’M. Bockris, D. Drazic, A. R. Despic, The Electrode Kinetics of the Deposition and Dissolution of Iron, Electrochimica Acta 4, no. 2 (1961) 325–361.

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Wang, Jingye, Bin Sheng, Ping Li, Yuxi Jin e David Dagan Feng. "Illumination-Guided Video Composition via Gradient Consistency Optimization". IEEE Transactions on Image Processing 28, n. 10 (ottobre 2019): 5077–90. http://dx.doi.org/10.1109/tip.2019.2916769.

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Leoni, Matteo, Paolo Scardi, Renato Pelosato, Isabella Natali Sora, Giovanni Dotelli, Paola Gallo Stampino e Arianna Lo Presti. "Phase composition gradient in leached polluted cement monoliths". Cement and Concrete Research 37, n. 11 (novembre 2007): 1483–95. http://dx.doi.org/10.1016/j.cemconres.2007.08.013.

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Tokuyama, Hideaki, Masahiro Sasaki e Shuji Sakohara. "Preparation of a novel composition-gradient thermosensitive gel". Colloids and Surfaces A: Physicochemical and Engineering Aspects 273, n. 1-3 (febbraio 2006): 70–74. http://dx.doi.org/10.1016/j.colsurfa.2005.08.006.

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Yang, Shuoguang, Mengdi Wang e Ethan X. Fang. "Multilevel Stochastic Gradient Methods for Nested Composition Optimization". SIAM Journal on Optimization 29, n. 1 (gennaio 2019): 616–59. http://dx.doi.org/10.1137/18m1164846.

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Wu, Hui, ZhaoHui Su, Yuki Terayama e Atsushi Takahara. "Polystyrene-based blend nanorods with gradient composition distribution". Science China Chemistry 55, n. 5 (16 febbraio 2012): 726–34. http://dx.doi.org/10.1007/s11426-012-4501-5.

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MOULOUNGUI, Z., E. LACROUX, C. VACA-GARCIA e J. PEYDECASTAING. "Destruction des farines animales : valorisation des fractions lipidiques en biolubrifiants et additifs biocarburants, et du résidu protéique (ou de l’ensemble)". INRAE Productions Animales 17, HS (20 dicembre 2004): 117–22. http://dx.doi.org/10.20870/productions-animales.2004.17.hs.3637.

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L’objectif des travaux est d’étudier la faisabilité de nouvelles voies d’élimination et de valorisation des farines animales. Nous abordons ici l’étude de deux voies de valorisation complémentaires et indépendantes: d’une part, la valorisation de la fraction lipidique en «biocarburant» et «biolubrifiant» et, d’autre part, celle du résidu délipidé ou de l’ensemble de la matrice dans la fabrication de matériaux polymères. Dans un premier temps, les études développées se proposent de mettre en oeuvre un suivi qualité selon les recommandations de la Direction Générale de l’Alimentation. Ensuite, l’étude de la mise en oeuvre d’outils d’extraction à haut débit et de méthodes rapides de caractérisation des constituants majeurs et mineurs a pour but de caractériser la matrice «farines animales». La connaissance de la composition de la matrice a gouverné l’orientation de la stratégie de transformation de la fraction lipidique axée sur les études de transfert d’acyles. Elle permet d’obtenir des acides gras à partir des lipides extraits, puis de les utiliser pour synthétiser des esters gras simples. En perspective, nous proposons d’associer cette méthodologie à des technologies spécifiques qui permettront d’envisager la décontamination des farines animales lors de leur transformation. La deuxième partie des travaux consiste à utiliser les farines animales ainsi que les farines obtenues après extraction des lipides comme matières premières dans le cadre d’une étude de faisabilité concernant de nouveaux matériaux polymères. Il s’agit de procéder à la déstructuration thermochimique des macromolécules animales (susceptible de dégrader l’agent pathogène) dans le but de les réduire à l’état de monomères destinés à participer à la synthèse d’un nouveau polymère. Les essais de liquéfaction de cette matrice en présence de phénol ont donné des résultats encourageants. La fabrication de matériaux polymères constituerait une voie de valorisation permettant d’écouler de grandes quantités de farines animales.

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Zeghichi, Leila, e Saliha Benalia. "Les géopolymères : matières premières et influence des paramètres de composition: a review". Journal of Engineering and Exact Sciences 9, n. 11 (31 dicembre 2023): 18838. http://dx.doi.org/10.18540/jcecvl9iss11pp18838.

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La recherche des liants alternatifs aux ciments classiques polluants est devenue une nécessité vu leur impact sur l’environnement, Une des solutions réside dans le remplacement des ciments Portlands par une nouvelle génération de liants minéraux, connus sous le nom de géopolymères, qui ont des propriétés similaires à celles du ciment Portland. Ces liants sont obtenus par activation alcaline de matériaux siliceux ou aluminosilicates. Ce papier résume les articles publiés récemment qui mettent en évidence les différents ingrédients entrant dans la composition des liants géopolymères : matières minérales servant de source alumino -silicates et activeurs chimiques utilisés pour la synthèse des géopolymères. Les Paramètres influençant les propriétés des géopolymères tels que la concentration de la solution alcaline, Rapport Si/Al de précurseur et le Mode de cure (régime de durcissement) ainsi que les géopolymères hybrides, synthétisés à base d’un mélange de deux précurseurs aluminosilicates laitier/métakaolin sont détaillés dans la deuxième partie. Au total 78 études ont été examinées et discutées.

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Liu, N., Y. L. Liu, Z. L. Zhao, H. O. Yang e W. X. Xu. "The preparation of gradient titanium alloy through laser deposition". IOP Conference Series: Materials Science and Engineering 1270, n. 1 (1 dicembre 2022): 012118. http://dx.doi.org/10.1088/1757-899x/1270/1/012118.

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Functionally gradient materials (FGMs) with continuous variation in composition or microstructure can realize gradient properties in different positions of the same component. The layer-by-layer laser deposition additive manufacturing is one of the most promising technologies that prepare FGMs with gradient properties. The present study is focused on the preparation of gradient titanium alloy by laser depositing Ti2AlNb powders on the substrate of a near-α high temperature titanium alloy. The microstructure, composition, and micro-hardness of prepared gradient titanium alloy with and without transition layer were compared and analyzed. Results show that an obvious bonding interface with variant microstructure morphology and element contents formed during directly deposited Ti2AlNb powders on near-α titanium alloy substrate and the bonding interface exhibits higher micro-hardness than the substrate and the deposited zone. However, the microstructure and the element exhibit gradient distribution characteristics along the deposition direction after adding the mixed powders of both two alloys as intermediate transition layers between the near-α titanium alloy and the Ti2AlNb alloy. The gradient distributed micro-hardness from the substrate to the top deposited zone sufficiently demonstrates the feasibility of obtaining gradient properties of gradient titanium alloy with composition transition layer during laser depositing.

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Johnson, Christopher L., e Alison C. Dunn. "Composition controls soft hydrogel surface layer dimensions and contact mechanics". Biointerphases 17, n. 6 (novembre 2022): 061002. http://dx.doi.org/10.1116/6.0002047.

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Hydrogels are soft hydrated polymer networks that are widely used in research and industry due to their favorable properties and similarity to biological tissues. However, it has long been difficult to create a hydrogel emulating the heterogeneous structure of special tissues, such as cartilage. One potential avenue to develop a structural variation in a hydrogel is the “mold effect,” which has only recently been discovered to be caused by absorbed oxygen within the mold surface interfering with the polymerization. This induces a dilute gradient-density surface layer with altered properties. However, the precise structure of the gradient-surface layer and its contact response have not yet been characterized. Such knowledge would prove useful for designs of composite hydrogels with altered surface characteristics. To fully characterize the hydrogel gradient-surface layer, we created five hydrogel compositions of varying monomer and cross-linker content to encompass variations in the layer. Then, we used particle exclusion microscopy during indentation and creep experiments to probe the contact response of the gradient layer of each composition. These experiments showed that the dilute structure of the gradient layer follows evolving contact behavior allowing poroelastic squeeze-out at miniscule pressures. Stiffer compositions had thinner gradient layers. This knowledge can potentially be used to create hydrogels with a stiff load-bearing bulk with altered surface characteristics tailored for specific tribological applications.

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Pero, Edgardo J. I., Paola A. Rueda Martín e María C. Reynaga. "Species and genus richness and assemblage composition of stream caddisflies (Insecta: Trichoptera) vary with latitude in mountain rainforest of Argentina". Marine and Freshwater Research 70, n. 5 (2019): 687. http://dx.doi.org/10.1071/mf18209.

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Evidence found in results of studies of latitudinal gradients of benthic macroinvertebrate diversity is variable. This study analysed how species and genus richness and the composition of caddisfly assemblages (Insecta: Trichoptera) vary in Argentinean mountain forest through a latitudinal gradient from 22 to 28°S. Qualitative and quantitative data from 20 stream sites were compared. Assemblage richness and composition were analysed by comparing linear regressions, rank–abundance (RA) curves and non-metric multidimensional scaling (nMDS). Taxonomic richness increased from high to low latitude. RA curves showed changes in assemblage composition and structure across the latitudinal gradient. The nMDS revealed that the composition of the assemblages also changed along the latitudinal gradient. The patterns are similar to those observed in plants and vertebrates from the study region. The results are of particular note because a latitudinal gradient of aquatic insect diversity has rarely been observed in a narrow range.

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Chang, Shiun Wei, Chun Ming Chen e Ju Liang He. "Power Modulated Plasma-Polymerized Gradient Anti-Fingerprint Transparent Protective Coating with a Gradient Composition". Advanced Materials Research 509 (aprile 2012): 135–37. http://dx.doi.org/10.4028/www.scientific.net/amr.509.135.

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Polymeric materials have been widely used as flexible substrates and housing parts of modern electronic wares. However, their low hardness and scratch resistance must be improved by additional protective surface coatings, which require not only mechanical durability but also additional functions such as surface hydrophobicity, oleophobicity as well as anti-fingerprint performance. To satisfy these, a power modulated plasma polymerization technique was designed to synthesize a transparent compositional gradient coating on polycarbonate (PC) substrate. Firstly, a constant flow rate of tetramethyldisiloxane (TMDSO) precursor was introduced where higher plasma power was employed to deposit a hard H-C-Si-O bottom layer. The plasma power was then decreased meanwhile admitting increased fluoromethane (CF4) gas flow as the second precursor to obtain a top layer with low surface energy. The hard bottom layer acts as a strong mechanical support and the top layer gives additional hydrophobicity and oleophobicity. Ultimately, the coating shows that a pencil hardness of 3H and Scotch-tape adhesion of 5B improves its protective function. A water contact angle of 105° and oil contact angle of 31.7° can be obtained. The coated specimen remains an optical transparency of 90% close to bare PC material. Comparing with commercialized screen protectors, the developed coating shows superior protective and anti-fingerprint performance.

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Makarov, A. M., T. I. Bobkova, A. F. Vasiliev, D. A. Geraschenkov, I. S. Prudnikov e B. V. Farmakovsky. "Effect of gas phase composition on functional-gradient coatings formation by supersonic cold gas dynamic spraying". Voprosy Materialovedeniya, n. 1(93) (6 gennaio 2019): 65–69. http://dx.doi.org/10.22349/1994-6716-2018-93-1-65-69.

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The paper develops method for manufacturing wear and corrosion-resistant gradient coating. A special feature of the proposed method is the creation of chemical composition gradient due to controlled variation of the gas phase composition when applying supersonic cold gas-dynamic spraying. This ensures high adhesive strength of the composite coatings of the metal-non-metal system in combination with high micro-hardness of the peripheral layers. Such functional gradient coatings have wide practical applications.

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Prata, Eduardo Magalhães Borges, Aloysio De Pádua Teixeira, Carlos Alfredo Joly e Marco Antonio Assis. "The role of climate on floristic composition in a latitudinal gradient in the Brazilian Atlantic Forest". Plant Ecology and Evolution 151, n. 3 (28 novembre 2018): 303–13. http://dx.doi.org/10.5091/plecevo.2018.1407.

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Background and aims – Latitudinal gradients have an important influence on species distribution reflecting the effects of environmental factors such as temperature, rainfall, soil, and geographical distance. In the southeastern Brazilian Atlantic Forest, the role of climatic variables in the floristic composition is better known for altitudinal gradients of the Serra do Mar Mountains rather than for the latitudinal gradient. Here, we investigated the effects of mean annual temperature and rainfall on tree species distribution and composition in a latitudinal gradient in the Atlantic forest.Methods – We calculated each species frequency of occurrence and the latitudinal range. We used multivariate analyses (direct ordination, Hierarchical Clustering followed by Indicator Species analysis and NMDS) to investigate variation in floristic composition, and regression analyses to evaluate mean annual temperatures and rainfall effects on tree species composition along the latitudinal gradient (21°S to 28°S).Key results – A total of 789 species were registered, of which a majority (646 species) were present in less than 20% of the sampled areas, and only four species (0.5%) were present in more than 80% of the sampled areas. Only ten species (1.3%) reached the maximum latitudinal range (~6°). We found a strong correlation between variation in floristic composition and the spatial position in the latitudinal gradient. The cluster analyses detected two main floristic groups, one composed by the forests from Rio de Janeiro (21°S to 23°S) and the second by the forests from São Paulo, Paraná and Santa Catarina States (23°S to 28°S). The multiple regression analysis revealed a strong effect of the climatic variables on the variation of the floristic composition along the latitudinal gradient (r2 = 0.81, P < 0.001), where 62.82% of the variation were explained by mean annual temperature, 8.27% by annual rainfall and 10.45% by both variables together.Conclusions – The restricted distribution of most species may be explained by variations in mean annual temperature and annual rainfall along the latitudinal gradient. For instance, the decreasing mean annual temperature along the coast and the occurrence of frosts at higher latitudes may limit the southward distribution of some species while the lower annual rainfall (with marked seasonality) in the north of the gradient may limit the northward distribution of other species. Although mean annual temperature explained most of the variation in species composition along the latitudinal gradient, the abrupt variation in annual rainfall may explain the high floristic dissimilarity detected in the north of the gradient.

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Levasseur, Denis. "Les eskers : essai de synthèse bibliographique". Géographie physique et Quaternaire 49, n. 3 (30 novembre 2007): 459–79. http://dx.doi.org/10.7202/033066ar.

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RÉSUMÉ L'essai propose une revue de la littérature sur les eskers. On y expose les informations de base (définition, terminologie, dimensions, distribution et caractères sédimentologiques généraux, incluant granulomere, fabriques, paléocourants, déformations et composition pétrographique) avant de présenter un historique des théories sur l'origine de ces constructions (hypothèses sous-glaciaire, supra- et intraglaciaire, de marge glaciaire et autres). De plus, on examine les différents modèles de sédimentation des eskers (chenal subaérien, canalisation forcée, deltaïque) et quelques généralités sur leur formation (écoulement des eaux de fonte, stabilité des conduits sous-glaciaires, source des matériaux, diachronisme des constructions et longueur des tunnels). On discute enfin du développement des eskers associés aux glaciers d'aujourd'hui.

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Kessler, D. A., V. N. Gamezo e E. S. Oran. "Gas-phase detonation propagation in mixture composition gradients". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 370, n. 1960 (13 febbraio 2012): 567–96. http://dx.doi.org/10.1098/rsta.2011.0342.

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The propagation of detonations through several fuel–air mixtures with spatially varying fuel concentrations is examined numerically. The detonations propagate through two-dimensional channels, inside of which the gradient of mixture composition is oriented normal to the direction of propagation. The simulations are performed using a two-component, single-step reaction model calibrated so that one-dimensional detonation properties of model low- and high-activation-energy mixtures are similar to those observed in a typical hydrocarbon–air mixture. In the low-activation-energy mixture, the reaction zone structure is complex, consisting of curved fuel-lean and fuel-rich detonations near the line of stoichiometry that transition to decoupled shocks and turbulent deflagrations near the channel walls where the mixture is extremely fuel-lean or fuel-rich. Reactants that are not consumed by the leading detonation combine downstream and burn in a diffusion flame. Detonation cells produced by the unstable reaction front vary in size across the channel, growing larger away from the line of stoichiometry. As the size of the channel decreases relative to the size of a detonation cell, the effect of the mixture composition gradient is lessened and cells of similar sizes form. In the high-activation-energy mixture, detonations propagate more slowly as the magnitude of the mixture composition gradient is increased and can be quenched in a large enough gradient.

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Sotov, Anton, Artem Kantyukov, Anatoliy Popovich e Vadim Sufiiarov. "A Review on Additive Manufacturing of Functional Gradient Piezoceramic". Micromachines 13, n. 7 (17 luglio 2022): 1129. http://dx.doi.org/10.3390/mi13071129.

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Functionally graded piezoceramics are a new generation of engineering materials whose final properties are determined by a chemical composition gradient (volume distribution), material microstructure, or design characteristics. This review analyzes possible ways to create a functionally graded piezoceramic material (gradient chemical composition, gradient porosity—controlled and disordered porosity) by additive manufacturing methods, to control such materials’ functional characteristics. An analysis of the creation of gradient piezoceramics using binder jetting technology is presented in more detail. The review shows that today, the creation of functional gradient piezoceramics by additive manufacturing is a poorly-studied but promising research area, due to the rapid development of the additive manufacturing market and their unique features in shaping parts.

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Zubar, Tatiana I., Tatsiana I. Usovich, Daria I. Tishkevich, Oleg D. Kanafyev, Vladimir A. Fedkin, Anna N. Kotelnikova, Maria I. Panasyuk et al. "Features of Galvanostatic Electrodeposition of NiFe Films with Composition Gradient: Influence of Substrate Characteristics". Nanomaterials 12, n. 17 (25 agosto 2022): 2926. http://dx.doi.org/10.3390/nano12172926.

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NiFe films with a composition gradient are of particular interest from the point of view of fundamental science and practical applications. Such gradient magnetic structures may exhibit unique functional properties useful for sensory applications and beyond. The issue surrounds the anomaly concerning the compositional gradient formed near the substrate in electrolytically deposited binary and ternary iron-containing alloys, which has not previously been clearly explained. In this work, light is shed on this issue, and a clear relationship is found between the structure and surface properties of the substrate, the initially formed NiFe layers and the film composition gradient.

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Guevara-Araya, María José, Víctor M. Escobedo, Valeria Palma-Onetto e Marcia González-Teuber. "Changes in Diversity and Community Composition of Root Endophytic Fungi Associated with Aristolochia chilensis along an Aridity Gradient in the Atacama Desert". Plants 11, n. 11 (5 giugno 2022): 1511. http://dx.doi.org/10.3390/plants11111511.

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Despite the widespread occurrence of fungal endophytes (FE) in plants inhabiting arid ecosystems, the environmental and soil factors that modulate changes in FE diversity and community composition along an aridity gradient have been little explored. We studied three locations along the coast of the Atacama Desert in Chile, in which the plant Aristolochia chilensis naturally grows, and that differ in their aridity gradient from hyper-arid to semi-arid. We evaluated if root-associated FE diversity (frequency, richness and diversity indexes) and community composition vary as a function of aridity. Additionally, we assessed whether edaphic factors co-varying with aridity (soil water potential, soil moisture, pH and nutrients) may structure FE communities. We expected that FE diversity would gradually increase towards the aridity gradient declines, and that those locations that had the most contrasting environments would show more dissimilar FE communities. We found that richness indexes were inversely related to aridity, although this pattern was only partially observed for FE frequency and diversity. FE community composition was dissimilar among contrasting locations, and soil water availability significantly influenced FE community composition across the gradient. The results indicate that FE diversity and community composition associated with A. chilensis relate to differences in the aridity level across the gradient. Overall, our findings reveal the importance of climate-related factors in shaping changes in diversity, structure and distribution of FE in desert ecosystems.

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Li, Qiang, Jing Yuan Yu e Xu Dong Sun. "Study on Preparation and Anodic Oxidation of Gradient Porous NiTi Alloy". Advanced Materials Research 430-432 (gennaio 2012): 1373–77. http://dx.doi.org/10.4028/www.scientific.net/amr.430-432.1373.

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Gradient porous NiTi alloys were prepared by powder metallurgy method using NH4HCO3 as space-holder and modified by direct current-pulse anodic oxidation technology in low temperature. Pore characteristic and phase composition of gradient porous NiTi alloys were studied. Microstructure, composition, anti-corrosion and Ni ion release behavior of surface film were observed. The results show the porosity of porous NiTi alloys decreases from 53.2% to 42.8%, when the content of NH4HCO3 varying from uniformity to gradient distribution. The sintered gradient porous NiTi alloys composes with TiNi, Ti2Ni and TiNi3 phases. After anodic oxidation, Ti oxidation film with the thick of 240nm was formed on the gradient porous NiTi alloy. The corrosion resistance of gradient porous NiTi alloy was obviously improved and the rate of Ni release was significantly reduced.

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Chen, Jing, Xinmin Song, Baozhu Li, Xiaoli Luo, Youjing Wang e Jinfang Wang. "Influence of Compositional Gradient Effect on Tight Condensate Gas Reservoir Development". Geofluids 2022 (15 giugno 2022): 1–9. http://dx.doi.org/10.1155/2022/5237534.

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Condensate gas is a transition fluid between oil and gas, which is sensitive to the reservoir temperature and pressure. In condensate gas reservoir, especially in the moderate-giant one, fluid composition often varies with depth. This phenomenon has important influences on development. Anisothermal compositional gradient theory is used to analyze the main factors influencing the compositional gradient distribution to understand the basic regularities of the compositional variation with depth. Geothermal gradient, fluid composition, reservoir temperature, and reservoir pressure will affect the compositional gradient, of which geothermal gradient has the most direct and obvious influence. Furthermore, fluid model with compositional gradient was built in a tight condensate gas reservoir of the Middle East, and the influence of compositional gradient on dynamic performance is evaluated. The results show that the compositional gradient has a significant influence on the original gas in place, development strategy, central processing facilities, and so on. Therefore, compositional gradient requires more attention while exploiting moderate-giant condensate gas reservoirs in order to achieve more economical benefits.

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Wang, Pengfei, Risheng Liu, Nenggan Zheng e Zhefeng Gong. "Asynchronous Proximal Stochastic Gradient Algorithm for Composition Optimization Problems". Proceedings of the AAAI Conference on Artificial Intelligence 33 (17 luglio 2019): 1633–40. http://dx.doi.org/10.1609/aaai.v33i01.33011633.

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In machine learning research, many emerging applications can be (re)formulated as the composition optimization problem with nonsmooth regularization penalty. To solve this problem, traditional stochastic gradient descent (SGD) algorithm and its variants either have low convergence rate or are computationally expensive. Recently, several stochastic composition gradient algorithms have been proposed, however, these methods are still inefficient and not scalable to large-scale composition optimization problem instances. To address these challenges, we propose an asynchronous parallel algorithm, named Async-ProxSCVR, which effectively combines asynchronous parallel implementation and variance reduction method. We prove that the algorithm admits the fastest convergence rate for both strongly convex and general nonconvex cases. Furthermore, we analyze the query complexity of the proposed algorithm and prove that linear speedup is accessible when we increase the number of processors. Finally, we evaluate our algorithm Async-ProxSCVR on two representative composition optimization problems including value function evaluation in reinforcement learning and sparse mean-variance optimization problem. Experimental results show that the algorithm achieves significant speedups and is much faster than existing compared methods.

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Ilschner, B., e D. Delfosse. "Synthesis of Multiphase Powder Systems with a Composition Gradient". Solid State Phenomena 8-9 (gennaio 1991): 61–70. http://dx.doi.org/10.4028/www.scientific.net/ssp.8-9.61.

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Poulin, R., e T. L. F. Leung. "Latitudinal gradient in the taxonomic composition of parasite communities". Journal of Helminthology 85, n. 3 (12 novembre 2010): 228–33. http://dx.doi.org/10.1017/s0022149x10000696.

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AbstractAlthough latitudinal gradients in diversity have been well studied, latitudinal variation in the taxonomic composition of communities has received less attention. Here, we use a large dataset including 950 surveys of helminth endoparasite communities in 650 species of vertebrate hosts to test for latitudinal changes in the relative contributions of trematodes, cestodes, nematodes and acanthocephalans to parasite assemblages. Although the species richness of helminth communities showed no consistent latitudinal variation, their taxonomic composition varied as a function of both host type and latitude. First, trematodes and acanthocephalans accounted for a higher proportion of species in helminth communities of fish, whereas nematodes achieved a higher proportion of the species in communities of bird and especially mammal hosts. Second, the proportion of trematodes in helminth communities of birds and mammals increased toward higher latitudes. Finally, the proportion of nematodes per community increased toward lower latitudes regardless of the type of host. We present tentative explanations for these patterns, and argue that new insights in parasite community ecology can be gained by searching for latitudinal gradients not only in parasite species richness, but also in the taxonomic composition of parasite assemblages.

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Li, Yong, Kai Zhang e Bailin Zheng. "Interaction between diffusion and stresses in composition-gradient electrodes". Solid State Ionics 283 (dicembre 2015): 103–8. http://dx.doi.org/10.1016/j.ssi.2015.10.011.

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Prakash, Aditya, Tawqeer Nasir Tak, Arijit Lodh, Niraj Nayan, S. V. S. Narayana Murty, P. J. Guruprasad e Indradev Samajdar. "Composition Gradient and Particle Deformed Zone: An Emerging Correlation". Metallurgical and Materials Transactions A 50, n. 3 (3 gennaio 2019): 1250–60. http://dx.doi.org/10.1007/s11661-018-5076-3.

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